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The activins-follistatins-inhibins (AFI) hormonal system affects bone metabolism. Treatments that alter bone metabolism may also alter the AFI molecules. In this non-randomized, open-label, head-to-head comparative study, circulating levels of the AFI system were evaluated in postmenopausal women with osteoporosis treated for 12 mo with either teriparatide (n = 23) or denosumab (n = 22). Τeriparatide treatment increased activin B (P=.01) and activin AB (P=.004) and the ratios activin A/follistatin (P=.006), activin B/follistatin (P=.007), activin AB/follistatin (P<.001), and activin AB/ follistatin-like 3 (FSTL3) (P=.034). The significant P for trend in group × time interactions of activins B and AB and of the ratio activin AB/FSTL3 remained robust after adjustment for BMI and LS BMD but it was lost for activin B after adjustment for previous antiresorptive treatment. The effect of teriparatide on BMD was attenuated when it was adjusted for baseline activins levels or their 12-mo changes. No changes were observed after denosumab treatment. In conclusion, activins B and AB, as well as the ratios of all activins to follistatin and of activin AB to FSTL3 increased with teriparatide treatment, possibly in a compensatory manner. Future studies are needed to study the potentially important role activins may play in bone biology and any associations with the effect of teriparatide on BMD. Clinical Trials identifier: NCT04206618. ClinicalTrials.gov  https://clinicaltrials.gov/search?term=NCT04206618., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society for Bone and Mineral Research. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Objective: The TGF-β superfamily member activin, a dimer of the gene products of INHBA and/or INHBB, has been implicated in immune cell maturation and recruitment, but its immune impact within epithelial ovarian cancer (EOC) is not well characterized. We sought to explore differences in activin (INHBA/ Inhibin-βA and INHBB/ Inhibin-βB) between malignant and ovarian tissues at the RNA and protein level and assess the relationship between activin and immune cells in EOC., Methods: Publicly available RNA sequencing data were accessed from GEO (#GSE143897) with normalization and quantification performed via DESeq2. Immune gene expression profile was further explored within the TCGA-OV cohort derived from The Cancer Genome Atlas (TCGA). Immunohistochemical analysis was performed to evaluate activin A and T-cell markers CD8 and FoxP3 at the protein level. ELISA to activin-A was used to assess levels in the ascites of advanced EOC patients. Kaplan-Meier curves were generated to visualize survival outcomes., Results: Gene expression levels of components of the activin signaling pathway were elevated within EOC when compared to a benign cohort, with differences in activin type I/II receptor gene profiles identified. Additionally, INHBA gene expression was linked to lymphocytic immune markers in EOC samples. Immunohistochemistry analysis revealed a positive correlation of CD8 and FOXP3 staining with activin A at the protein level in both primary and metastatic epithelial ovarian cancer samples. Furthermore, Activin-A (inhibin-βA) is significantly elevated in EOC patient ascites., Conclusion: INHBA expression is elevated within EOC, correlating with worse survival, with activin protein levels correlating with specific immune infiltration. Our findings suggest that activin-A may play a role in suppressing anti-tumor immunity in EOC, highlighting its potential as a therapeutic target., (© 2024 The Author(s). Cancer Medicine published by John Wiley & Sons Ltd.)

The discovery of the Spemann-Mangold organizer strongly influenced subsequent research on embryonic induction, with research aiming to elucidate the molecular characteristics of organizer activity being currently underway. Herein, we review the history of research on embryonic induction, and describe how the mechanisms of induction phenomena and developmental processes have been investigated. Classical experiments investigating the differentiation capacity and inductive activity of various embryonic regions were conducted by many researchers, and important theories of region-specific induction and the concept for chain of induction were proposed. The transition from experimental embryology to developmental biology has enabled us to understand the mechanisms of embryonic induction at the molecular level. Consequently, many inducing substances and molecules such as transcriptional factors and peptide growth factors involved in the organizer formation were identified. One of peptide growth factors, activin, acts as a mesoderm- and endoderm-inducing substance. Activin induces several tissues and organs from the undifferentiated cell mass of amphibian embryos in a concentration-dependent manner. We review the extent to which we can control in vitro organogenesis from undifferentiated cells, and discuss the application to stem cell-based regenerative medicine based on insights gained from animal experiments, such as in amphibians., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The transforming growth factor-β (TGF-β) family member activin A (hereafter Activin-A) is overexpressed in many cancer types, often correlating with cancer-associated cachexia and poor prognosis. Activin-A secretion by melanoma cells indirectly impedes CD8 + T cell-mediated anti-tumor immunity and promotes resistance to immunotherapies, even though Activin-A can be proinflammatory in other contexts. To identify underlying mechanisms, we here analyzed the effect of Activin-A on syngeneic grafts of Braf mutant YUMM3.3 mouse melanoma cells and on their microenvironment using single-cell RNA sequencing. We found that the Activin-A-induced immune evasion was accompanied by a proinflammatory interferon signature across multiple cell types, and that the associated increase in tumor growth depended at least in part on pernicious STING activity within the melanoma cells. Besides corroborating a role for proinflammatory signals in facilitating immune evasion, our results suggest that STING holds considerable potential as a therapeutic target to mitigate tumor-promoting Activin-A signaling at least in melanoma., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Pinjusic, Ambrosini, Lourenco, Fournier, Iseli, Guex, Egorova, Nassiri and Constam.)

Background/aim: Activin, a member of the TGF-β super family of cytokines, is involved in head and neck squamous cell carcinoma (HNSCC). This study examined the constituents of the activin axis in order to further elucidate the role of activin A in HNSCC progression., Materials and Methods: Immunohistochemistry (IHC), reverse transcription polymerase chain reaction (RT-PCR), MTT, and matrigel invasion assays, in addition to analysis of the tumor cancer genome atlas (TCGA), were employed., Results: IHC in HNSCC and oral leukoplakia (OPL) lesions demonstrated increased expression of the inhibin subunit βA (INHBA) (p<0.0001), as well as activin receptor type IB (ACVR1B) (p<0.0032) compared to normal mucosa. TCGA analysis revealed increased INHBA expression was associated with lymph node positive tumors (p=0.024), decreased overall survival (p=0.0167), and decreased promoter methylation (p<0.0001). Concomitant up-regulated expression of gene pathways strongly correlated with INHBA expression demonstrated further deleterious effects on survival (p<0.0148)., Conclusion: Activin may be an important component of early carcinogenesis in OPL and HNSCC with unfavorable effects on clinical end-points such as survival., (Copyright © 2023 International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

The functional and neurophysiological distinction between the dorsal and ventral hippocampus affects also GABAergic inhibition. In line with this notion, ventral CA1 pyramidal cells displayed a more dynamic and effective response to inhibitory input compared to their dorsal counterparts. We posit that this difference is effected by the dorsal-ventral gradient of activin A, a member of the transforming growth factor-β family, which is increasingly recognized for its modulatory role in brain regions involved in cognitive functions and affective behavior. Lending credence to this hypothesis, we found that in slices from transgenic mice expressing a dominant-negative mutant of activin receptor IB (dnActRIB), inhibitory transmission was enhanced only in CA1 neurons of the dorsal hippocampus, where the basal activin A level is much higher than in the ventral hippocampus. We next asked how a rise in endogenous activin A would affect GABAergic inhibition along the longitudinal axis of the hippocampus. We performed ex vivo recordings in wild-type and dnActRIB mice after overnight exposure to an enriched environment (EE), which engenders a robust increase in activin A levels in both dorsal and ventral hippocampi. Compared to control mice from standard cages, the behaviorally induced surge in activin A produced a decline in ventral inhibition, an effect that was absent in slices from dnActRIB mice. Underscoring the essential role of activin in the EE-associated modulation of ventral inhibition, this effect was mimicked by acute application of recombinant activin A in control slices. In summary, both genetic and behavioral manipulations of activin receptor signaling affected the dorsal-ventral difference in synaptic inhibition, suggesting that activin A regulates the strength of GABAergic inhibition in a region-specific fashion.

Although originally characterised as proteins involved in the control of reproductive function, activins, and to a lesser degree inhibins, are also important regulators of homeostasis in extragonadal tissues. Accordingly, disrupted inhibin/activin expression can have detrimental effects not only on fertility and fecundity but also on the regulation of muscle, fat and bone mass. Indeed, only recently, two complementary mouse models of inhibin designed to lack bioactivity/responsiveness revealed that inhibin A/B deficiency during pregnancy restricts embryo and fetal survival. Conversely, hyper-elevated levels of activin A/B, as are frequently observed in patients with advanced cancers, can not only promote gonadal tumour growth but also cancer cachexia. As such, it is not surprising that inhibin/activin genetic variations or altered circulating levels have been linked to reproductive disorders and cancer. Whilst some of the detrimental health effects associated with disrupted inhibin/activin levels can be attributed to accompanied changes in circulating follicle-stimulating hormone (FSH) levels, there is now abundant evidence that activins, in particular, have fundamental FSH-independent tissue homeostatic roles. Increased understanding of inhibin/activin activity, garnered over several decades, has enabled the development of targeted therapies with applications for both reproductive and extra-gonadal tissues. Inhibin- or activin-targeted technologies have been shown not just to enhance fertility and fecundity but also to reduce disease severity in models of cancer cachexia. Excitingly, these technologies are likely to benefit human medicine and be highly valuable to animal breeding and veterinary programmes.

Purpose: Adenocarcinomas of the esophagus (AEG) and stomach (AS) are among the most common cancers worldwide. Novel markers for risk stratification and guiding treatment are strongly needed. Activin is a multi-functional cytokine with context specific pro- and anti-tumorigenic effects. We aimed to investigate the prognostic role of activin tumor protein expression in AEG/ASs., Methods: Tissue from a retrospective cohort of 277 patients with AEG/AS treated primarily by surgery at the Charité - Universitätsmedizin Berlin was collected and analyzed by immunohistochemistry using a specific antibody to the activin homodimer inhibin beta A. Additionally, we evaluated T-cell infiltration and PD1 expression as well as expression of PD-L1 by immunohistochemistry as possible confounding factors. Clinico-pathologic data were collected and correlated with activin protein expression., Results: Out of 277 tumor samples, 72 (26.0%) exhibited high activin subunit inhibin beta A protein expression. Higher expression was correlated with lower Union for International Cancer Control (UICC) stage and longer overall survival. Interestingly, activin subunit expression correlated with CD4 + T-cell infiltration, and the correlation with higher overall survival was exclusively seen in tumors with high CD4 + T-cell infiltration, pointing towards a role of activin in the tumor immune response in AEG/ASs., Conclusion: In our cohort of AEG/AS, higher activin subunit levels were correlated with longer overall survival, an effect exclusively seen in tumors with high CD4 + cell infiltration. Further mechanistic research is warranted discerning the exact effect of this context specific cytokine., (© 2022. The Author(s).)

Background: Cachexia is frequent, deadly, and untreatable for patients with pancreatic ductal adenocarcinoma (PDAC). The reproductive hormone and cytokine Activin is a mediator of PDAC cachexia, and Activin receptor targeting was clinically tested for cancer cachexia therapy. However, sex-specific manifestations and mechanisms are poorly understood, constraining development of effective treatments., Methods: Cachexia phenotypes, muscle gene/protein expression, and effects of the Activin blocker ACVR2B/Fc were assessed in LSL-Kras G12D/+ , LSL-Trp53 R172H/+ , and Pdx-1-Cre (KPC) mice with autochthonic PDAC. Effects of PDAC and sex hormones were modelled by treating C2C12 myotubes with KPC-cell conditioned medium (CM) and estradiol. Muscle gene expression by RNAseq and change in muscle from serial CT scans were measured in patients with PDAC., Results: Despite equivalent tumour latency (median 17 weeks) and mortality (24.5 weeks), male KPC mice showed earlier and more severe cachexia than females. In early PDAC, male gastrocnemius, quadriceps, and tibialis anterior muscles were reduced (-21.7%, -18.9%, and -20.8%, respectively, all P < 0.001), with only gastrocnemius reduced in females (-16%, P < 0.01). Sex differences disappeared in late PDAC. Plasma Activin A was similarly elevated between sexes throughout, while oestrogen and testosterone levels suggested a virilizing effect of PDAC in females. Estradiol partially protected myotubes from KPC-CM induced atrophy and promoted expression of the potential Activin inhibitor Fstl1. Early-stage female mice showed greater muscle expression of Activin inhibitors Fst, Fstl1, and Fstl3; this sex difference disappeared by late-stage PDAC. ACVR2B/Fc initiated in early PDAC preserved muscle and fat only in male KPC mice, with increases of 41.2%, 52.6%, 39.3%, and 348.8%, respectively, in gastrocnemius, quadriceps, tibialis, and fat pad weights vs. vehicle controls, without effect on tumour. No protection was observed in females. At protein and RNA levels, pro-atrophy pathways were induced more strongly in early-stage males, with sex differences less evident in late-stage disease. As with mass, ACVR2B/Fc blunted atrophy-associated pathways only in males. In patients with resectable PDAC, muscle expression of Activin inhibitors FSTL1, FSLT3, and WFIKKN2/GASP2 were higher in women than men. Overall, among 124 patients on first-line gemcitabine/nab-paclitaxel for PDAC, only men displayed muscle loss (P < 0.001); average muscle wasting in men was greater (-6.63 ± 10.70% vs. -1.62 ± 12.00% mean ± SD, P = 0.038) and more rapid (-0.0098 ± 0.0742%/day vs. -0.0466 ± 0.1066%/day, P = 0.017) than in women., Conclusions: Pancreatic ductal adenocarcinoma cachexia displays sex-specific phenotypes in mice and humans, with Activin a preferential driver of muscle wasting in males. Sex is a major modulator of cachexia mechanisms. Consideration of sexual dimorphism is essential for discovery and development of effective treatments., (© 2022 The Authors. Journal of Cachexia, Sarcopenia and Muscle published by John Wiley & Sons Ltd on behalf of Society on Sarcopenia, Cachexia and Wasting Disorders.)

Activin ligands are formed from two disulfide-linked inhibin β (Inhβ) subunit chains. They exist as homodimeric proteins, as in the case of activin A (ActA; InhβA/InhβA) or activin C (ActC; InhβC/InhβC), or as heterodimers, as with activin AC (ActAC; InhβA:InhβC). While the biological functions of ActA and activin B (ActB) have been well characterized, little is known about the biological functions of ActC or ActAC. One thought is that the InhβC chain functions to interfere with ActA production by forming less active ActAC heterodimers. Here, we assessed and characterized the signaling capacity of ligands containing the InhβC chain. ActC and ActAC activated SMAD2/3-dependent signaling via the type I receptor, activin receptor-like kinase 7 (ALK7). Relative to ActA and ActB, ActC exhibited lower affinity for the cognate activin type II receptors and was resistant to neutralization by the extracellular antagonist, follistatin. In mature murine adipocytes, which exhibit high ALK7 expression, ActC elicited a SMAD2/3 response similar to ActB, which can also signal via ALK7. Collectively, these results establish that ActC and ActAC are active ligands that exhibit a distinct signaling receptor and antagonist profile compared to other activins., Competing Interests: EG, LO, EK, KV, DB, TT No competing interests declared, EB, RC, RK Past employee of Acceleron Pharma and is now an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc, (© 2022, Goebel et al.)

SMAD2, an effector of the NODAL/Activin signalling pathway, regulates developmental processes by sensing distinct chromatin states and interacting with different transcriptional partners. However, the network of factors that controls SMAD2 chromatin binding and shapes its transcriptional programme over time is poorly characterised. Here, we combine ATAC-seq with computational footprinting to identify temporal changes in chromatin accessibility and transcription factor activity upon NODAL/Activin signalling. We show that SMAD2 binding induces chromatin opening genome wide. We discover footprints for FOXI3, FOXO3 and ZIC3 at the SMAD2-bound enhancers of the early response genes, Pmepa1 and Wnt3, respectively, and demonstrate their functionality. Finally, we determine a mechanism by which NODAL/Activin signalling induces delayed gene expression, by uncovering a self-enabling transcriptional cascade whereby activated SMADs, together with ZIC3, induce the expression of Wnt3. The resultant activated WNT pathway then acts together with the NODAL/Activin pathway to regulate expression of delayed target genes in prolonged NODAL/Activin signalling conditions. This article has an associated First Person interview with the first author of the paper., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2022. Published by The Company of Biologists Ltd.)

Background: Activins and bone morphogenetic proteins (BMPs) play critical, sometimes opposing roles, in multiple physiological and pathological processes and diseases. They signal to distinct Smad branches; activins signal mainly to Smad2/3, while BMPs activate mainly Smad1/5/8. This gives rise to the possibility that competition between the different type I receptors through which activin and BMP signal for common type II receptors can provide a mechanism for fine-tuning the cellular response to activin/BMP stimuli. Among the transforming growth factor-β superfamily type II receptors, ACVR2A/B are highly promiscuous, due to their ability to interact with different type I receptors (e.g., ALK4 vs. ALK2/3/6) and with their respective ligands [activin A (ActA) vs. BMP9/2]. However, studies on complex formation between these full-length receptors situated at the plasma membrane, and especially on the potential competition between the different activin and BMP type I receptors for a common activin type II receptor, were lacking., Results: We employed a combination of IgG-mediated patching-immobilization of several type I receptors in the absence or presence of ligands with fluorescence recovery after photobleaching (FRAP) measurements on the lateral diffusion of an activin type II receptor, ACVR2A, to demonstrate the principle of competition between type I receptors for ACVR2. Our results show that ACVR2A can form stable heteromeric complexes with ALK4 (an activin type I receptor), as well as with several BMP type I receptors (ALK2/3/6). Of note, ALK4 and the BMP type I receptors competed for binding ACVR2A. To assess the implications of this competition for signaling output, we first validated that in our cell model system (U2OS cells), ACVR2/ALK4 transduce ActA signaling to Smad2/3, while BMP9 signaling to Smad1/5/8 employ ACVR2/ALK2 or ACVR2/ALK3. By combining ligand stimulation with overexpression of a competing type I receptor, we showed that differential complex formation of distinct type I receptors with a common type II receptor balances the signaling to the two Smad branches., Conclusions: Different type I receptors that signal to distinct Smad pathways (Smad2/3 vs. Smad1/5/8) compete for binding to common activin type II receptors. This provides a novel mechanism to balance signaling between Smad2/3 and Smad1/5/8., (© 2022. The Author(s).)

Background: Immunoregulatory genes encoding activin A (Inhba) and B (Inhbb), and indolamine 2,3-dioxygenase-1 (Ido1) are highly expressed in the murine caput epididymidis, which also has a network of intraepithelial mononuclear phagocytes. This environment is postulated to promote immunological tolerance to epididymal sperm. The factors regulating the immunoregulatory agents in the epididymal caput are poorly understood., Objectives: This study aimed to investigate the potential role of testicular lumicrine factors in regulating activin and other immune-related genes in the caput epididymidis., Materials and Methods: The efferent ducts in adult C57/Bl6 mice were exposed and ligated bilaterally. Serum and tissues were collected seven days later. Animals with bilateral sham ligation and animals with no ligations (collectively referred to as the "intact" group) were used as controls., Results: Pressure-induced seminiferous epithelial damage due to intratubular fluid accumulation was observed in all ligated testes. Testicular inhibin was significantly increased and testosterone was elevated in some animals following bilateral ligation, but serum testosterone, serum LH, and serum inhibin were normal. Ligation caused epithelial regression in the initial segment, with similar but less severe effects in other caput segments. Activin A staining by immunohistochemistry in the epithelium was reduced in bilateral ligation, particularly in the initial segment, with moderately reduced staining intensity in the rest of the caput. Inhba expression within the caput was not significantly affected by bilateral ligation, but Inhbb was reduced by more than 60%. Transcripts encoding the macrophage-specific receptor Cx3cr1 were significantly reduced following bilateral ligation, but other immune cell markers, Ido1, and inflammatory genes were unaffected., Conclusion: These data indicate that testicular lumicrine secretion regulates several genes that are preferentially expressed in the initial segment, but has marginal effects on genes such as those encoding activin A and IDO1, which are expressed more widely in the caput., (© 2021 American Society of Andrology and European Academy of Andrology.)

Bovine embryonic stem cells (ESC) have features associated with the primed pluripotent state including low expression of one of the core pluripotency transcription factors, NANOG. It has been reported that NANOG expression can be upregulated in porcine ESC by treatment with activin A and the WNT agonist CHIR99021. Accordingly, it was tested whether expression of NANOG and another pluripotency factor SOX2 could be stimulated by activin A and the WNT agonist CHIR99021. Immunoreactive NANOG and SOX2 were analyzed for bovine ESC lines derived under conditions in which activin A and CHIR99021 were added singly or in combination. Activin A enhanced NANOG expression but also reduced SOX2 expression. CHIR99021 depressed expression of both NANOG and SOX2. In a second experiment, activin A enhanced blastocyst development while CHIR99021 treatment impaired blastocyst formation and reduced number of blastomeres. Activin A treatment decreased blastomeres in the blastocyst that were positive for either NANOG or SOX2 but increased those that were CDX2+ and that were GATA6+ outside the inner cell mass. CHIR99021 reduced SOX2+ and NANOG+ blastomeres without affecting the number or percent of blastomeres that were CDX2+ and GATA6+. Results indicate activation of activin A signaling stimulates NANOG expression during self-renewal of bovine ESC but suppresses cells expressing pluripotency markers in the blastocyst and increases cells expressing CDX2. Actions of activin A to promote blastocyst development may involve its role in promoting trophectoderm formation. Furthermore, results demonstrate the negative role of canonical WNT signaling in cattle for pluripotency marker expression in ESC and in formation of the inner cell mass and epiblast during embryonic development. This article has an associated First Person interview with the first author of the paper., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Ovarian granulosa cells (GC) play an essential role in the development and atresia of follicles. Emerging studies suggest that non-coding RNAs are involved in the regulation of GC apoptosis. Here, we aimed to analyze the function of ssc-circINHA-001, coded by the first exon of the inhibin subunit α gene ( INHA ), in resisting GC apoptosis and follicular atresia by enhancing the expression of the inhibin subunit β A ( INHBA ) through a cluster of miRNAs. A higher expression of ssc-circINHA-001 in healthy follicles compared to early atretic follicles was detected by qRT-PCR. Its circular structure was confirmed by RNase R treatment and reversed PCR. The function of ssc-circINHA-001 in GC resistance to apoptosis was detected by in vitro transfection of its si-RNA. Furthermore, the dual-luciferase reporter assay suggested that ssc-circINHA-001 adsorbed three miRNAs, termed miR-214-5p, miR-7144-3p, and miR-9830-5p, which share the common target INHBA . A low expression of ssc-circINHA-001 increased the levels of the free miRNAs, inhibited INHBA expression, and thus raised GCs apoptosis through a shift from the secretion of activin to that of inhibin. Our study demonstrated the existence of a circRNA-microRNAs- INHBA regulatory axis in follicular GC apoptosis and provides insight into the relationship between circRNA function and its coding gene in inhibin/activin balance and ovarian physiological functions.

FSH is critical for fertility. Transcription of FSHB, the gene encoding the beta subunit, is rate-limiting in FSH production and is regulated by both GnRH and activin. Activin signals through SMAD transcription factors. Although the mechanisms and importance of activin signaling in mouse Fshb transcription are well-established, activin regulation of human FSHB is less well understood. We previously reported a novel enhancer of FSHB that contains a fertility-associated single nucleotide polymorphism (rs10031006) and requires a region resembling a full (8 base-pair) SMAD binding element (SBE). Here, we investigated the role of the putative SBE within the enhancer in activin and GnRH regulation of FSHB. In mouse gonadotrope-derived LβT2 cells, the upstream enhancer potentiated activin induction of both the human and mouse FSHB proximal promoters and conferred activin responsiveness to a minimal promoter. Activin induction of the enhancer required the SBE and was blocked by the inhibitory SMAD7, confirming involvement of the classical SMAD signaling pathway. GnRH induction of FSHB was also potentiated by the enhancer and dependent on the SBE, consistent with known activin/GnRH synergy regulating FSHB transcription. In DNA pull-down, the enhancer SBE bound SMAD4, and chromatin immunoprecipitation demonstrated SMAD4 enrichment at the enhancer in native chromatin. Combined activin/GnRH treatment elevated levels of the active transcriptional histone marker, histone 3 lysine 27 acetylation, at the enhancer. Overall, this study indicates that the enhancer is directly targeted by activin signaling and identifies a novel, evolutionarily conserved mechanism by which activin and GnRH can regulate FSHB transcription., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Activins are members of the transforming growth factor-β superfamily implicated in the pathogenesis of several immunoinflammatory disorders. Based on our previous studies demonstrating that overexpression of activin-A in murine lung causes pathology sharing key features of coronavirus disease 2019 (COVID-19), we hypothesized that activins and their natural inhibitor follistatin might be particularly relevant to COVID-19 pathophysiology., Methods: Activin-A, activin-B, and follistatin were retrospectively analyzed in 574 serum samples from 263 COVID-19 patients hospitalized in 3 independent centers, and compared with demographic, clinical, and laboratory parameters. Optimal scaling with ridge regression was used to screen variables and establish a prediction model., Result: The activin/follistatin axis was significantly deregulated during the course of COVID-19, correlated with severity and independently associated with mortality. FACT-CLINYCoD, a scoring system incorporating follistatin, activin-A, activin-B, C-reactive protein, lactate dehydrogenase, intensive care unit admission, neutrophil/lymphocyte ratio, age, comorbidities, and D-dimers, efficiently predicted fatal outcome (area under the curve [AUC], 0.951; 95% confidence interval, .919-.983; P <10-6). Two validation cohorts indicated similar AUC values., Conclusions: This study demonstrates a link between activin/follistatin axis and COVID-19 mortality and introduces FACT-CLINYCoD, a novel pathophysiology-based tool that allows dynamic prediction of disease outcome, supporting clinical decision making., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Functional interactions between the levels of clock gene expression and adrenal steroidogenesis were studied in human adrenocortical H295R cells. Fluctuations of Bmal1, Clock, Per2 and Cry1 mRNA levels were found in H295R cells treated with forskolin (FSK) in a serum-free condition. The changes of clock gene expression levels were diverged, with Clock mRNA level being significantly higher than Cry1 and Per2 mRNA levels after 12-h stimulation with FSK. After FSK induction, mRNA levels of StAR and CYP11B2 were highest at 12 hours and CYP17 mRNA level reached a peak at 6 hours, but HSD3B1 mRNA level was transiently decreased at 3 hours. The expression levels of Clock mRNA showed a significant positive correlation with StAR among the interrelationships between mRNA levels of key steroidogenic factors and clock genes. Knockdown of Clock gene by siRNA led to a significant reduction of FSK-induced expression of StAR and CYP17 after 12-h treatment with FSK. BMP-6 and activin, which modulate adrenal steroidogenesis, had inhibitory effects on Clock mRNA expression, whereas treatment with follistatin, a binding protein of activin, increased Clock mRNA levels in the presence of FSK, suggesting an endogenous function of activin in regulation of Clock mRNA expression. Collectively, the results indicated that changes of Clock mRNA expression, being upregulated by FSK and suppressed by BMP-6 and activin, were tightly linked to StAR expression by human adrenocortical cells.

Accumulating evidence suggests that the adiponectin (APN) paradox might be involved in promoting aging-associated chronic diseases such as Alzheimer's disease (AD). In human brain, APN regulation of the evolvability of amyloidogenic proteins (APs), including amyloid-β (Aβ) and tau, in developmental/reproductive stages, might be paradoxically manifest as APN stimulation of AD through antagonistic pleiotropy in aging. The unique mechanisms underlying APN activity remain unclear, a better understanding of which might provide clues for AD therapy. In this paper, we discuss the possible relevance of activin, a member of transforming growth factor β (TGFβ) superfamily of peptides, to antagonistic pleiotropy effects of APN. Notably, activin, a multiple regulator of cell proliferation and differentiation, as well as an endocrine modulator in reproduction and an organizer in early development, might promote aging-associated disorders, such as inflammation and cancer. Indeed, serum activin, but not serum TGFβ increases during aging. Also, activin/TGFβ signal through type II and type I receptors, both of which are transmembrane serine/threonine kinases, and the serine/threonine phosphorylation of APs, including Aβ42 serine 8 and αS serine 129, may confer pathological significance in neurodegenerative diseases. Moreover, activin expression is induced by APN in monocytes and hepatocytes, suggesting that activin might be situated downstream of the APN paradox. Finally, a meta-analysis of genome-wide association studies demonstrated that two SNPs relevant to the activin/TGFβ receptor signaling pathways conferred risk for major aging-associated disease. Collectively, activin might be involved in the APN paradox of AD and could be a significant therapeutic target.

Rheumatic heart disease (RHD) is an autoimmune disease caused by rheumatic fever following group A hemolytic streptococcal infection and primarily affects the mitral valve. RHD is currently a major global health problem. However, the exact pathological mechanisms associated with RHD‑induced cardiac valve damage remain to be elucidated. The endothelial‑mesenchymal transition (EndMT) serves a key role in a number of diseases with an important role in cardiac fibrosis and the activin/Smad2 and 3 signaling pathway is involved in regulating the EndMT. Nevertheless, there are no studies to date, to the best of the authors' knowledge, investigating the association between RHD and EndMT. Thus, the aim of the current study was to investigate the potential role of EndMT in cardiac valve damage and assess whether activin/Smad2 and 3 signaling was activated during RHD‑induced valvular injury in a rat model of RHD induced by inactivated Group A streptococci and complete Freund's adjuvant. Inflammation and fibrosis were assessed by hematoxylin and eosin and Sirius red staining. Serum cytokine and rheumatoid factor levels were measured using ELISA kits. Expression levels of activin/Smad2 and 3 signaling pathway‑related factors [activin A, Smad2, Smad3, phosphorylated (p‑)Smad2 and p‑Smad3], EndMT‑related factors [lymphoid enhancer factor‑1 (LEF‑1), Snail1, TWIST, zinc finger E‑box‑binding homeobox (ZEB)1, ZEB2, α smooth muscle actin (α‑SMA) and type I collagen α 1 (COL1A1)], apoptosis‑related markers (BAX and cleaved caspase‑3) and valvular inflammation markers (NF‑κB and p‑NF‑κB) were detected using reverse transcription‑quantitative PCR and western blot analyses. Compared with the control group, the degree of valvular inflammation and fibrosis, serum levels of IL‑6, IL‑17, TNF‑α and expression of apoptosis‑related markers (BAX and cleaved caspase‑3) and valvular inflammation marker (p‑NF‑κB), activin/Smad2 and 3 signaling pathway‑related factors (activin A, p‑Smad2 and p‑Smad3), EndMT‑related factors (LEF‑1, Snail1, TWIST, ZEB 1, ZEB2, α‑SMA and COL1A1) were significantly increased in the RHD group. These results suggested that the activin/Smad2 and 3 signaling pathway was activated during the development of valvular damage caused by RHD and that the EndMT is involved in RHD‑induced cardiac valve damage.

Myostatin (MSTN) is a transforming growth factor-β (TGF-β) family member that normally acts to limit muscle growth. The function of MSTN is partially redundant with that of another TGF-β family member, activin A. MSTN and activin A are capable of signaling through a complex of type II and type I receptors. Here, we investigated the roles of two type II receptors (ACVR2 and ACVR2B) and two type I receptors (ALK4 and ALK5) in the regulation of muscle mass by these ligands by genetically targeting these receptors either alone or in combination specifically in myofibers in mice. We show that targeting signaling in myofibers is sufficient to cause significant increases in muscle mass, showing that myofibers are the direct target for signaling by these ligands in the regulation of muscle growth. Moreover, we show that there is functional redundancy between the two type II receptors as well as between the two type I receptors and that all four type II/type I receptor combinations are utilized in vivo. Targeting signaling specifically in myofibers also led to reductions in overall body fat content and improved glucose metabolism in mice fed either regular chow or a high-fat diet, demonstrating that these metabolic effects are the result of enhanced muscling. We observed no effect, however, on either bone density or muscle regeneration in mice in which signaling was targeted in myofibers. The latter finding implies that MSTN likely signals to other cells, such as satellite cells, in addition to myofibers to regulate muscle homeostasis., (Copyright © 2020 the Author(s). Published by PNAS.)

Introduction: Activin A is involved in the regulation of a surprisingly broad number of processes that are relevant for cancer development and treatment; it is implicated in cell autonomous functions and multiple regulatory functions in the tumor microenvironment., Areas Covered: This article summarizes the current knowledge about activin A in cell growth and death, migration and metastasis, angiogenesis, stemness and drug resistance, regulation of antitumor immunity, and cancer cachexia. We explore the role of activin A as a biomarker and discuss strategies for using it as target for cancer therapy. Literature retrieved from Medline until 25 June 2020 was considered., Expert Opinion: While many functions of activin A were investigated in preclinical models, there is currently limited experience from clinical trials. Activin A has growth- and migration-promoting effects, contributes to immune evasion and cachexia and is associated with shorter survival in several cancer types. Targeting activin A could offer the chance to simultaneously limit tumor growth and spreading, improve drug response, boost antitumor immune responses and improve cancer-associated or treatment-associated cachexia, bone loss, and anemia. Nevertheless, defining which patients have the highest likelihood of benefiting from these effects is challenging and will require further work.

Among the physiological consequences of extended spaceflight are loss of skeletal muscle and bone mass. One signaling pathway that plays an important role in maintaining muscle and bone homeostasis is that regulated by the secreted signaling proteins, myostatin (MSTN) and activin A. Here, we used both genetic and pharmacological approaches to investigate the effect of targeting MSTN/activin A signaling in mice that were sent to the International Space Station. Wild type mice lost significant muscle and bone mass during the 33 d spent in microgravity. Muscle weights of Mstn -/- mice, were largely maintained during spaceflight. Systemic inhibition of MSTN/activin A signaling using a soluble form of the activin type IIB receptor (ACVR2B), which can bind each of these ligands, led to dramatic increases in both muscle and bone mass, with effects being comparable in ground and flight mice. Exposure to microgravity and treatment with the soluble receptor each led to alterations in numerous signaling pathways, which were reflected in changes in levels of key signaling components in the blood as well as their RNA expression levels in muscle and bone. These findings have implications for therapeutic strategies to combat the concomitant muscle and bone loss occurring in people afflicted with disuse atrophy on Earth as well as in astronauts in space, especially during prolonged missions.wild type mice, were largely maintained during spaceflight. Systemic inhibition of MSTN/activin A signaling using a soluble form of the activin type IIB receptor (ACVR2B), which can bind each of these ligands, led to dramatic increases in both muscle and bone mass, with effects being comparable in ground and flight mice. Exposure to microgravity and treatment with the soluble receptor each led to alterations in numerous signaling pathways, which were reflected in changes in levels of key signaling components in the blood as well as their RNA expression levels in muscle and bone. These findings have implications for therapeutic strategies to combat the concomitant muscle and bone loss occurring in people afflicted with disuse atrophy on Earth as well as in astronauts in space, especially during prolonged missions., Competing Interests: The authors declare no competing interest., (Copyright © 2020 the Author(s). Published by PNAS.)

Activins and inhibins - comprising activin A, B, AB, C and E, and inhibin A and B isoforms - belong to the transforming growth factor beta (TGFβ) superfamily. They regulate several biological processes, including cellular proliferation, differentiation and invasiveness, to enhance the formation and functioning of many human tissues and organs. In this review, we have discussed the role of activin and inhibin signaling in the physiological and female-specific pathological events that occur in the female reproductive system. The up-to-date evidence indicates that these cytokines regulate germ cell development, follicular development, ovulation, uterine receptivity, decidualization and placentation through the activation of several signaling pathways; and that their dysregulated expression is involved in the pathogenesis and pathophysiology of the numerous diseases, including pregnancy complications, that disturb reproduction. Hence, some of the isoforms have been suggested as potential biomarkers and therapeutic targets for the management of some of these diseases. Tackling the research directions highlighted in this review will enhance a detailed comprehension and the clinical utility of these cytokines., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Activin (ACV) A induces various cellular functions via activin receptor type 2 (ACVR2A/2B)-activin receptor-like kinase (ALK) 4 -Smad 2/3 pathway. Although the production of ACVA is indicated in bovine oviducts, its role on the oviduct is unclear. Oviductal isthmus needs to change its function rapidly at peri-fertilization, however, the mechanism is unknown. This study was aimed to clarify the role of ACVA in the morphological changes of oviductal isthmus in cows. First, mRNA expressions of INHBA (ACVA component) and its receptors (ALK4, ACVR2A and ACVR2B) in the isthmic tissues were examined throughout the estrous cycle. INHBA was the highest, however, ACVR2A was the lowest on the day of ovulation, suggesting reduced ACV signal transduction in the isthmus just after ovulation. Proteins of ACVRs and Smad2/3 were clearly detected in the cultured epithelial cells. It is known that ACVA regulates cellular apoptosis. Our data showed that the number of cleaved caspase-3-positive epithelial cells was largest at 2-3 days after ovulation in the isthmus. Interestingly, our study demonstrated that follistatin (ACV/TGFB/BMP inhibitor) significantly decreased the BCL2/BAX ratio in the cultured isthmic epithelial cells. To clarify which ALK pathway is involved in the regulation of BCL2/BAX ratio, the effects of SB431542 (ACV signaling (ALK4) and TGFB signaling (ALK5) inhibitor), SB525334 (ALK5 inhibitor) and LDN193189 (BMP signaling (ALK2/3) inhibitor) were investigated in the next study. The results showed that only SB431542 significantly decreased BCL2/BAX and the others had no effects. These results suggest that decreased ACVA-ACVR2A-ALK4 signal at the post-ovulation induces cyclic apoptosis of isthmic epithelial cells in bovine oviducts., Competing Interests: Declaration of competing interest The authors have no conflicts of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Temporal patterning of neural progenitors leads to the sequential production of diverse neurons. To understand how extrinsic cues influence intrinsic temporal programs, we studied Drosophila mushroom body progenitors (neuroblasts) that sequentially produce only three neuronal types: γ, then α'β', followed by αβ. Opposing gradients of two RNA-binding proteins Imp and Syp comprise the intrinsic temporal program. Extrinsic activin signaling regulates the production of α'β' neurons but whether it affects the intrinsic temporal program was not known. We show that the activin ligand Myoglianin from glia regulates the temporal factor Imp in mushroom body neuroblasts. Neuroblasts missing the activin receptor Baboon have a delayed intrinsic program as Imp is higher than normal during the α'β' temporal window, causing the loss of α'β' neurons, a decrease in αβ neurons, and a likely increase in γ neurons, without affecting the overall number of neurons produced. Our results illustrate that an extrinsic cue modifies an intrinsic temporal program to increase neuronal diversity., Competing Interests: AR No competing interests declared, CD Reviewing editor, eLife, (© 2020, Rossi and Desplan.)

Cancer-associated fibroblasts (CAFs) are key regulators of tumorigenesis and promising targets for next-generation therapies. We discovered that cancer cell-derived activin A reprograms fibroblasts into pro-tumorigenic CAFs. Mechanistically, this occurs via Smad2-mediated transcriptional regulation of the formin mDia2, which directly promotes filopodia formation and cell migration. mDia2 also induces expression of CAF marker genes through prevention of p53 nuclear accumulation, resulting in the production of a pro-tumorigenic matrisome and secretome. The translational relevance of this finding is reflected by activin A overexpression in tumor cells and of mDia2 in the stroma of skin cancer and other malignancies and the correlation of high activin A/mDia2 levels with poor patient survival. Blockade of this signaling axis using inhibitors of activin, activin receptors, or mDia2 suppressed cancer cell malignancy and squamous carcinogenesis in 3D organotypic cultures, ex vivo, and in vivo, providing a rationale for pharmacological inhibition of activin A-mDia2 signaling in stratified cancer patients., (© 2020 The Authors. Published under the terms of the CC BY 4.0 license.)

Activins belong to the transforming growth factor (TGF)-β family of multifunctional cytokines and signal via the activin receptors ALK4 or ALK7 to activate the SMAD2/3 pathway. In some cases, activins also signal via the bone morphogenetic protein (BMP) receptor ALK2, causing activation of the SMAD1/5/8 pathway. In this study, we aimed to dissect how activin A and activin B homodimers, and activin AB and AC heterodimers activate the two main SMAD branches. We compared the activin-induced signaling dynamics of ALK4/7-SMAD2/3 and ALK2-SMAD1/5 in a multiple myeloma cell line. Signaling via the ALK2-SMAD1/5 pathway exhibited greater differences between ligands than signaling via ALK4/ALK7-SMAD2/3. Interestingly, activin B and activin AB very potently activated SMAD1/5, resembling the activation commonly seen with BMPs. As SMAD1/5 was also activated by activins in other cell types, we propose that dual specificity is a general mechanism for activin ligands. In addition, we found that the antagonist follistatin inhibited signaling by all the tested activins, whereas the antagonist cerberus specifically inhibited activin B. Taken together, we propose that activins may be considered dual specificity TGF-β family members, critically affecting how activins may be considered and targeted clinically.

The transforming growth factor-β (TGF-β) family controls embryogenesis, stem cell differentiation, and tissue homeostasis. However, how post-translation modifications contribute to fine-tuning of TGF-β family signaling responses is not well understood. Inhibitory (I)-Smads can antagonize TGF-β/Smad signaling by recruiting Smurf E3 ubiquitin ligases to target the active TGF-β receptor for proteasomal degradation. A proteomic interaction screen identified Vpr binding protein (VprBP) as novel binding partner of Smad7. Mis-expression studies revealed that VprBP negatively controls Smad2 phosphorylation, Smad2-Smad4 interaction, as well as TGF-β target gene expression. VprBP was found to promote Smad7-Smurf1-TβRI complex formation and induce proteasomal degradation of TGF-β type I receptor (TβRI). Moreover, VprBP appears to stabilize Smurf1 by suppressing Smurf1 poly-ubiquitination. In multiple adult and mouse embryonic stem cells, depletion of VprBP promotes TGF-β or Activin-induced responses. In the mouse embryo VprBP expression negatively correlates with mesoderm marker expression, and VprBP attenuated mesoderm induction during zebrafish embryogenesis. Our findings thereby uncover a novel regulatory mechanism by which Smurf1 controls the TGF-β and Activin cascade and identify VprBP as a critical determinant of embryonic mesoderm induction., (© The Author(s) (2019). Published by Oxford University Press on behalf of Journal of Molecular Cell Biology, IBCB, SIBS, CAS.)

Background: The majority of patients with advanced cancer develop cachexia, a weight loss syndrome that severely reduces quality of life and limits survival. Our understanding of the underlying mechanisms that cause the condition is limited, and there are currently no treatment options that can completely reverse cachexia. Several tumour-derived factors and inflammatory mediators have been suggested to contribute to weight loss in cachectic patients. However, inconsistencies between studies are recurrent. Activin A and interleukin 6 (IL-6) are among the best studied factors that seem to be important, and several studies support their individual role in cachexia development., Methods: We investigated the interplay between activin A and IL-6 in the cachexia-inducing TOV21G cell line, both in culture and in tumours in mice. We previously found that the human TOV21G cells secrete IL-6 that induces autophagy in reporter cells and cachexia in mice. Using this established cachexia cell model, we targeted autocrine activin A by genetic, chemical, and biological approaches. The secretion of IL-6 from the cancer cells was determined in both culture and tumour-bearing mice by a species-specific ELISA. Autophagy reporter cells were used to monitor the culture medium for autophagy-inducing activities, and muscle mass changes were evaluated in tumour-bearing mice., Results: We show that activin A acts in an autocrine manner to promote the synthesis and secretion of IL-6 from cancer cells. By inhibiting activin A signalling, the production of IL-6 from the cancer cells is reduced by 40-50% (up to 42% reduction on protein level, P = 0.0048, and 48% reduction on mRNA level, P = 0.0308). Significantly reduced IL-6 secretion (P < 0.05) from the cancer cells is consistently observed when using biological, chemical, and genetic approaches to interfere with the autocrine activin A loop. Inhibiting activin signalling also reduces the ability of the cancer cells to accelerate autophagy in non-cancerous cells (up to 43% reduced autophagy flux, P = 0.0006). Coherent to the in vitro data, the use of an anti-activin receptor 2 antibody in cachectic tumour-bearing mice reduces serum levels of cancer cell-derived IL-6 by 62% (from 417 to 159 pg/mL, P = 0.03), and, importantly, it reverses cachexia and counteracts loss of all measured muscle groups (P < 0.0005)., Conclusions: Our data support a functional link between activin A and IL-6 signalling pathways and indicate that interference with activin A-induced IL-6 secretion from the tumour has therapeutic potential for cancer-induced cachexia., (© 2019 The Authors. Journal of Cachexia, Sarcopenia and Muscle published by John Wiley & Sons Ltd on behalf of Society on Sarcopenia, Cachexia and Wasting Disorders.)

Background: The interface between the epididymis and the immune system is implicated in many male reproductive pathologies. The resident immune cell populations and immune-environment within the epididymis are significantly different from the testis, which is an immune-privileged site. Moreover, the immune cell subsets and immunological responses between different regions of the epididymis vary considerably. The cauda epididymis is more susceptible to autoimmune responses than the caput in rodent models of active immunization or suppressed immune tolerance, and in men with congenital or physical damage to the reproductive tract. Activins are members of the transforming growth factor-β family of cytokines that are crucial for testis and epididymal development; however, they also have complex immunoregulatory properties and may play an essential role in the regulation of immunity in the reproductive tract., Materials and Methods: Our recent research and relevant publications by other researchers identified following a PubMed search are reviewed., Results: The caput epididymis displays elevated endogenous expression of activins A and B and the immunoregulatory gene, indoleamine-2,3-dioxygenase, co-existing with an extensive population of intra-epithelial and interstitial macrophages and dendritic cells, which appear to be involved in regulating tolerance against sperm antigens. The caput is also relatively resistant to inflammatory damage caused by autoimmunity or bacterial infection, but the cauda, which exhibits low activin expression and high levels of the activin-binding protein, follistatin, is highly susceptible to inflammatory damage. Paradoxically, inflammation in the cauda induces increased activin production, and inhibition of activin activity reduces inflammatory responses. Studies using mouse models with altered levels of activins and follistatin indicate a relationship between the activins and genes involved in inflammation and immunoregulation., Conclusion: The existing data indicate that activins play a complex role in controlling inflammation and immunity in the epididymis and vas deferens., (© 2019 American Society of Andrology and European Academy of Andrology.)

Kisspeptin (encoded by the Kiss-1 gene) in the arcuate nucleus (ARC) of the hypothalamus governs the hypothalamic-pituitary-gonadal (HPG) axis by regulating pulsatile release of gonadotropin-releasing hormone (GnRH). Meanwhile, kisspeptin in the anteroventral periventricular nucleus (AVPV) region has been implicated in estradiol (E2)-induced GnRH surges. Kiss-1-expressing cell model mHypoA-55 exhibits characteristics of Kiss-1 neurons in the ARC region. On the other hand, Kiss-1 expressing mHypoA-50 cells originate from the AVPV region. In the mHypoA-55 ARC cells, activin significantly increased Kiss-1 gene expression. Follistatin alone reduced Kiss-1 expression within these cells. Interestingly, activin-induced Kiss-1 gene expression was completely abolished by follistatin. Inhibin A, but not inhibin B reduced Kiss-1 expression. Activin-increased Kiss-1 expression was also abolished by inhibin A. Pretreatment of the cells with follistatin or inhibin A significantly inhibited kisspeptin- or GnRH-induced Kiss-1 gene expression in mHypoA-55 cells. In contrast, in the mHypoA-50 AVPV cell model, activin, follistatin, and inhibin A did not modulate Kiss-1 gene expression. The subunits that compose activin and inhibin, as well as follistatin were expressed in both mHypoA-55 and mHypoA-50 cells. Expression of inhibin βA and βB subunits and follistatin was much higher in mHypoA-55 ARC cells. Furthermore, we found that expression of the inhibin α subunit and follistatin genes was modulated in the presence of E2 in mHypoA-55 ARC cells. The results of this study suggest that activin, follistatin, and inhibin A within the ARC region participate in the regulation of the HPG axis under the influence of E2., (© The Author(s) 2019. Published by Oxford University Press on behalf of Society for the Study of Reproduction.)

TGFβ family ligands, which include the TGFβs, BMPs, and activins, signal by forming a ternary complex with type I and type II receptors. For TGFβs and BMPs, structures of ternary complexes have revealed differences in receptor assembly. However, structural information for how activins assemble a ternary receptor complex is lacking. We report the structure of an activin class member, GDF11, in complex with the type II receptor ActRIIB and the type I receptor Alk5. The structure reveals that receptor positioning is similar to the BMP class, with no interreceptor contacts; however, the type I receptor interactions are shifted toward the ligand fingertips and away from the dimer interface. Mutational analysis shows that ligand type I specificity is derived from differences in the fingertips of the ligands that interact with an extended loop specific to Alk4 and Alk5. The study also reveals differences for how TGFβ and GDF11 bind to the same type I receptor, Alk5. For GDF11, additional contacts at the fingertip region substitute for the interreceptor interactions that are seen for TGFβ, indicating that Alk5 binding to GDF11 is more dependent on direct contacts. In support, we show that a single residue of Alk5 (Phe 84 ), when mutated, abolishes GDF11 signaling, but has little impact on TGFβ signaling. The structure of GDF11/ActRIIB/Alk5 shows that, across the TGFβ family, different mechanisms regulate type I receptor binding and specificity, providing a molecular explanation for how the activin class accommodates low-affinity type I interactions without the requirement of cooperative receptor interactions., Competing Interests: Conflict of interest statement: T.B.T. is a consultant for Acceleron Pharma and Scientific Founder for Eclode. R.C. and R.K. are current employees of Acceleron Pharma with ownership interest in the company. A.N.E. and V.J.I. are current employees of Regeneron Pharmaceuticals with ownership interest in the company. The other authors report no competing interests.

Background/aim: Perinatal diethylstilbestrol (DES) treatment induces the polyovular follicle containing two or more oocytes in a follicle of mouse ovary through estrogen receptor (ER) β. The aim of the study was to investigate the direct effects of DES on the neonatal mouse ovary and the gene expression of activins., Materials and Methods: Ovaries from neonatal wild-type (WT) or ERβ- knockout (ERβKO) mice were organ-cultured in a serum-free medium with or without DES, and polyovular follicle induction and expression of activin signaling related genes were examined., Results: The polyovular follicle and cyst incidence in DES-treated organ-cultured ovaries from WT mice, but not from ERβKO mice, was significantly higher than that of control non-treated cultures. DES altered inhibin (Inh) a, Inhba and Inhbb expression in organ-cultured ovaries from C57BL/6J mice, while no change in Inha and an increase of Inhbb were observed by DES, in both WT and ERβKO mice., Conclusion: Alterations in activin signaling are involved in the polyovular follicle induction by DES., (Copyright© 2019, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Despite the advances in the management of hemoglobinopathies, further insight into disease pathophysiology is necessary to improve our therapeutic approach. Activin-A has emerged as a regulator of erythropoiesis and bone turnover in malignant disorders; however, clinical data in hemoglobinopathies are currently scarce. Thus, we aimed to investigate the role of activin-A among hemoglobinopathy patients and evaluate the rationale of its targeting. Circulating levels of activin-A were measured in patients (n = 227) with beta-thalassemia major (TM) (n = 58), beta-thalassemia intermedia (TI) (n = 43), double heterozygous sickle cell/beta-thalassemia (HbS/beta-thal) (n = 109), or homozygous sickle cell disease (n = 17), and we explored possible correlations with clinical and laboratory data. Seventeen age- and gender-matched, healthy individuals served as controls. Bone marrow density (BMD) was determined using dual-energy X-ray absorptiometry. TM and HbS/beta-thal patients had elevated activin-A compared to controls (p = 0.041 and p = 0.038, respectively). In TM patients, high circulating activin-A showed strong correlations with hemolysis markers, namely reticulocyte count (p = 0.011) and high lactate dehydrogenase (LDH; p = 0.024). Similarly, in HbS/beta-thal patients, activin-A showed positive correlations with indirect bilirubin (p < 0.001), ferritin (p = 0.005), and LDH (p = 0.044). High activin-A correlated with low Z-score of both lumbar spine BMD in TI patients (p < 0.01) and femoral neck BMD in TM patients (p < 0.01). Serum activin-A is elevated in patients with TM and HbS/beta-thal and correlates with markers of hemolysis and low BMD. These data support a role of activin-A in the biology of these disorders and provide further rationale for the broader clinical development of activin-A inhibitors in this setting.

Understanding regulators of folliculogenesis remains limited in the domestic dog (Canis familiaris), which challenges our ability to develop in vitro follicle culture systems for canid genome rescue efforts. Here, we investigated the influence of activin on dog follicle development and survival, oocyte quality, and FSH receptor expression in culture. Preantral (150 - ≤230 μm diameter), early antral (231 - ≤330 μm), and antral (>330-550 μm) stage follicles were encapsulated in a fibrin-alginate hydrogel with 0, 100, or 200 ng/ml rhActivin plus 0, 0.1, 1, or 10 μg/ml FSH for 12 or 21 d of in vitro culture. All follicle groups increased in diameter (P < 0.05) with activin acting synergistically with FSH to improve (P < 0.05) growth and antral cavity expansion (to >630 μm) in early antral and antral cohorts. This complementary effect was not linked to changes in FSHR mRNA expression (P > 0.05). Although not influencing (P > 0.05) follicle survival or transzonal projection (TZP) density in shorter term 12 d culture, activin in the presence of 1 ng/ml FSH maintained TZP density from the 12-21 d interval. Activin also increased oocyte diameter and improved nuclear integrity compared to un-supplemented controls. These results indicate that activin acts synergistically with FSH to promote growth and antral cavity expansion of the dog follicle in vitro, information useful to formulating an effective culture microenvironment for this species., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Activins and their receptors play important roles in the control of hair follicle morphogenesis, but their role in vibrissae follicle growth remains unclear. To investigate the effect of Activin B on vibrissae follicles, the anagen induction assay and an in vitro vibrissae culture system were constructed. Hematoxylin and eosin staining were performed to determine the hair cycle stages. The 5-ethynyl-2'-deoxyuridine (EdU) and Cell Counting Kit-8 (CCK-8) assays were used to examine the cell proliferation. Flow cytometry was used to detect the cell cycle phase. Inhibitors and Western blot analysis were used to investigate the signaling pathway induced by Activin B. As a result, we found that the vibrissae follicle growth was accelerated by 10 ng/mL Activin B in the anagen induction assay and in an organ culture model. 10 ng/mL Activin B promoted hair matrix cell proliferation in vivo and in vitro. Moreover, Activin B modulates hair matrix cell growth through the ERK⁻Elk1 signaling pathway, and Activin B accelerates hair matrix cell transition from the G1/G0 phase to the S phase through the ERK⁻Cyclin D1 signaling pathway. Taken together, these results demonstrated that Activin B may promote mouse vibrissae growth by stimulating hair matrix cell proliferation and cell cycle progression through ERK signaling.

Cyclin-dependent kinase (CDK) 4 and CDK6 inhibitors are effective therapeutic options for hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer. Although CDK4/6 inhibitors mainly target the cyclin D-CDK4/6-retinoblastoma tumor suppressor protein (RB) axis, little is known about the clinical impact of inhibiting phosphorylation of other CDK4/6 target proteins. Here, we focused on other CDK4/6 targets, SMAD proteins. We showed that a CDK4/6 inhibitor palbociclib and activin-SMAD2 signaling cooperatively inhibited cell cycle progression of a luminal-type breast cancer cell line T47D. Palbociclib enhanced SMAD2 binding to the genome by inhibiting CDK4/6-mediated linker phosphorylation of the SMAD2 protein. We also showed that cyclin G2 plays essential roles in SMAD2-dependent cytostatic response. Moreover, comparison of the SMAD2 ChIP-seq data of T47D cells with those of Hs578T (triple-negative breast cancer cells) indicated that palbociclib augmented different SMAD2-mediated functions based on cell type, and enhanced SMAD2 binding to the target regions on the genome without affecting its binding pattern. In summary, palbociclib enhances the cytostatic effects of the activin-SMAD2 signaling pathway, whereas it possibly strengthens the tumor-promoting aspect in aggressive breast cancer., (© 2018 The Authors. Cancer Science published by John Wiley & Sons Australia, Ltd on behalf of Japanese Cancer Association.)

As the follicular environment transits from being activin dominant to inhibin dominant during folliculogenesis, it is assumed that activin plays an important role in the early stage of follicular growth. We examined the effects of activin on morphological, biochemical and molecular changes in isolated preantral follicles. Preantral follicles were mechanically isolated from 14-day old female C57BL/6 mice. Each follicle was cultured and observed for 14 days usingan in vitro follicle culture system containing FSH, FSH + activin A and FSH + inhibin in the culture medium. We subsequently examined FSH receptor (FSH-R) mRNA expression in isolated follicle cultures with or without activin on days 0 and 2. Activin was observed to significantly stimulate follicle enlargement on days 2, 4, 6 and 8, accelerate morphological changes and increase estradiollevels in culture medium on days 4, 12 and 14. In contrast, inhibin did not alter follicular growth. Additionally, activin stimulated the expression of FSH-R mRNA in isolated granulosa cells. It was demonstrated that activin stimulated the growth of preantral follicles, mainly during the early stage of folliculogenesis, by inducing FSH-R expression, in an isolated follicle culture system. J. Med. Invest. 66 : 165-171, February, 2019.

Activin and Wnt signaling are necessary and sufficient for mesendoderm (ME) differentiation of human embryonic stem cells (ESCs). In this study, we report that during ME differentiation induced by Activin and Wnt, Activin/Smad2 induces a decrease of the repressive histone modification of H3K27me3 by promoting the proteasome-dependent degradation of enhancer of zeste 2 polycomb (EZH2)-repressive complex 2 subunit. As a result, recruitment of the forkhead protein FOXH1 on open chromatin regions integrates the signals of Activin/Smad2 and Wnt/β-catenin to activate the expression of the ME genes including HAS2 and ALDH3A2 Consistently, H3K27me3 decrease is enriched on open chromatin around regulatory regions. Furthermore, knockdown of HAS2 or ALDH3A2 greatly attenuates ME differentiation. These findings unveil a pathway from extracellular signals to epigenetic modification-mediated gene activation during ME commitment., (© 2018 Xu et al.)

Regionalised interaction of the activins, follistatin and inhibin was investigated in the male reproductive tract of mice lacking the inhibin α-subunit (Inha -/- ). Serum and intratesticular activin B, although not activin A and follistatin, were increased in Inha -/- mice at 25 days of age, but all three proteins were elevated at 56 days. None of these proteins were altered within the epididymis and vas deferens at either age. At 25 days, histology of the epididymis and vas deferens was similar to wild-type. At 56 days, the testis contained extensive somatic cell tumours, leading to Leydig cell regression and testosterone deficiency. The epididymis and vas deferens showed epithelial regression and increased prominence of the interstitial stroma. Immunoregulatory and fibrotic gene expression in the epididymis and vas deferens were unchanged. Thus, absence of the inhibin α-subunit has marginal effects on activins in the epididymis and vas deferens, and regression of these tissues is associated with androgen deficiency., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Women with hypertensive disorders of pregnancy have an increased risk of subsequent heart failure and cardiovascular disease when compared with women with normotensive pregnancies. Although the mechanisms underlying these findings are unclear, elevated levels of the biomarker activin A are associated with myocardial dysfunction and may have predictive value. We hypothesized that elevated levels of antepartum activin A levels would correlate with postpartum cardiac dysfunction in women with hypertensive disorders of pregnancy. We prospectively studied 85 women to determine whether increased antepartum activin A levels were associated with cardiac dysfunction at 1 year postpartum as measured by global longitudinal strain. Thirty-two patients were diagnosed with preeclampsia, 28 were diagnosed with gestational or chronic hypertension, and the remainder were nonhypertensive controls. Activin A levels were measured with ELISA both in the third antepartum trimester and at 1 year postpartum. Comprehensive echocardiograms including measurement of global longitudinal strain were also performed at enrollment and at 1 year postpartum. Antepartum activin A levels correlated with worsening antepartum global longitudinal strain ( r =0.70; P =0.0001). Across the entire cohort, elevated antepartum activin A levels were associated with the development of abnormal global longitudinal strain at 1 year (C statistic 0.74; P =0.004). This association remained significant after multivariable adjustment for clinically relevant confounders (C statistic 0.93; P =0.01). Postpartum activin A levels also correlated with increasing left ventricular mass index ( P =0.02), increasing mean arterial pressures ( P =0.02), and decreasing E' values ( P =0.01). Activin A may be a useful tool for identifying and monitoring patients at risk for postpartum development of cardiovascular disease., (© 2018 American Heart Association, Inc.)

TGF-β/BMP superfamily ligands require heteromeric complexes of type 1 and 2 receptors for ligand-dependent downstream signaling. Activin A, a TGF-β superfamily member, inhibits growth of multiple myeloma cells, but the mechanism for this is unknown. We therefore aimed to clarify how activins affect myeloma cell survival. Activin A activates the transcription factors SMAD2/3 through the ALK4 type 1 receptor, but may also activate SMAD1/5/8 through mutated variants of the type 1 receptor ALK2 (also known as ACVR1). We demonstrate that activin A and B activate SMAD1/5/8 in myeloma cells through endogenous wild-type ALK2. Knockdown of the type 2 receptor BMPR2 strongly potentiated activin A- and activin B-induced activation of SMAD1/5/8 and subsequent cell death. Furthermore, activity of BMP6, BMP7 or BMP9, which may also signal via ALK2, was potentiated by knockdown of BMPR2. Similar results were seen in HepG2 liver carcinoma cells. We propose that BMPR2 inhibits ALK2-mediated signaling by preventing ALK2 from oligomerizing with the type 2 receptors ACVR2A and ACVR2B, which are necessary for activation of ALK2 by activins and several BMPs. In conclusion, BMPR2 could be explored as a possible target for therapy in patients with multiple myeloma.This article has an associated First Person interview with the first author of the paper., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

Background: Bacterial meningitis is associated with high mortality and long-term neurological sequelae. Increasing the phagocytic activity of microglia could improve the resistance of the CNS against infections. We studied the influence of activin A, a member of the TGF-β family with known immunoregulatory and neuroprotective effects, on the functions of microglial cells in vitro., Methods: Primary murine microglial cells were treated with activin A (0.13 ng/ml-13 μg/ml) alone or in combination with agonists of TLR2, 4, and 9. Phagocytosis of Escherichia coli K1 as well as release of TNF-α, IL-6, CXCL1, and NO was assessed., Results: Activin A dose-dependently enhanced the phagocytosis of Escherichia coli K1 by microglial cells activated by agonists of TLR2, 4, and 9 without further increasing NO and proinflammatory cytokine release. Cell viability of microglial cells was not affected by activin A., Conclusions: Priming of microglial cells with activin A could increase the elimination of bacteria in bacterial CNS infections. This preventive strategy could improve the resistance of the brain to infections, particularly in elderly and immunocompromised patients.

Clinical findings and a variety of experimental models indicate that Leydig cell dysfunction accompanies damage to the seminiferous tubules with increasing severity. Most studies support the idea that intratesticular signaling from the seminiferous tubules to Leydig cells regulates steroidogenesis, which is disrupted when hypospermatogenesis occurs. Sertoli cells seem to play a pivotal role in this process. In this review, we summarize relevant clinical and experimental observations and present evidence to support the hypothesis that testicular activin signaling and its regulation by testicular inhibin may link seminiferous tubular dysfunction to reduced testosterone biosynthesis., (© 2018 American Society of Andrology and European Academy of Andrology.)

Background: Sheng-ji Hua-yu(SJHY) formula is one of the most useful Traditional Chinese medicine (TCM) in the treatment of the delayed diabetic wound. However, elucidating the related molecular biological mechanism of how the SJHY Formula affects excessive inflammation in the process of re-epithelialization of diabetic wound healing is a task urgently needed to be fulfilled. The objectives of this study is to evaluate the effect of antagonisic expression of pro-/anti-inflammatory factors on transforming growth factor-β(TGF-β) superfamily (activin and follistatin) in the process of re-epithelialization of diabetic wound healing in vivo, and to characterize the involvement of the activin/follistatin protein expression regulation, phospho-Smad (pSmad2), and Nuclear factor kappa B p50 (NF-kB) p50 in the diabetic wound healing effects of SJHY formula., Methods: SJHY Formula was prepared by pharmaceutical preparation room of Yueyang Hospital of Integrated Traditional Chinese and Western Medicine. Diabetic wound healing activity was evaluated by circular excision wound models. Wound healing activity was examined by macroscopic evaluation. Activin/follistatin expression regulation, protein expression of pSmad2 and NF-kB p50 in skin tissue of wounds were analyzed by Real Time PCR, Western blot, immunohistochemistry and hematoxylin and eosin (H&E) staining., Results: Macroscopic evaluation analysis showed that wound healing of diabetic mice was delayed, and SJHY Formula accelerated wound healing time of diabetic mice. Real Time PCR analysis showed higher mRNA expression of activin/follistatin in diabetic delayed wound versus the wound in normal mice. Western Blot immunoassay analysis showed reduction of activin/follistatin proteins levels by SJHY Formula treatment 15 days after injury. Immunohistochemistry investigated the reduction of pSmad2 and NF-kB p50 nuclear staining in the epidermis of diabetic SJHY versus diabetic control mice on day 15 after wounding. H&E staining revealed that SJHY Formula accelerated re-epithelialization of diabetic wound healing., Conclusion: The present study found that diabetic delayed wound healing time is closely related to the high expression level of activin/follistatin, which leads to excessive inflammation in the process of re-epithelization. SJHY Formula accelerates re-epithelialization and healing time of diabetic wounds through decreasing the high expression of activin/follistatin.

Transforming growth factor-β (TGF-β) family members, which include TGF-βs, activins and bone morphogenetic proteins, are pleiotropic cytokines that elicit cell type-specific effects in a highly context-dependent manner in many different tissues. These secreted protein ligands signal via single-transmembrane Type I and Type II serine/threonine kinase receptors and intracellular SMAD transcription factors. Deregulation in signaling has been implicated in a broad array of diseases, and implicate the need for intricate fine tuning in cellular signaling responses. One important emerging mechanism by which TGF-β family receptor signaling intensity, duration, specificity and diversity are regulated and/or mediated is through cell surface co-receptors. Here, we provide an overview of the co-receptors that have been identified for TGF-β family members. While some appear to be specific to TGF-β family members, others are shared with other pathways and provide possible ways for signal integration. This review focuses on novel functions of TGF-β family co-receptors, which continue to be discovered., (© The Author(s) 2017. Published by Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Drosophila color vision is achieved by comparing outputs from two types of color-sensitive photoreceptors, R7 and R8. Ommatidia (unit eyes) are classified into two subtypes, known as 'pale' or 'yellow', depending on Rhodopsin expression in R7 and R8. Subtype specification is controlled by a stochastic decision in R7 and instructed to the underlying R8. We find that the Activin receptor Baboon is required in R8 to receive non-redundant signaling from the three Activin ligands, activating the transcription factor dSmad2. Concomitantly, two BMP ligands activate their receptor, Thickveins, and the transcriptional effector, Mad. The Amon TGFβ processing factor appears to regulate components of the TGFβ pathway specifically in pale R7. Mad and dSmad2 cooperate to modulate the Hippo pathway kinase Warts and the growth regulator Melted; two opposing factors of a bi-stable loop regulating R8 Rhodopsin expression. Therefore, TGFβ and growth pathways interact in postmitotic cells to precisely coordinate cell-specific output.

Background: Several myokines are produced by cardiac muscle. We investigated changes in myokine levels at the time of acute myocardial infarction (MI) and following reperfusion in relation to controls., Methods: Patients with MI (MI Group, n=31) treated with percutaneous coronary intervention (PCI) were compared to patients with stable coronary artery disease (CAD) subjected to scheduled PCI (CAD Group, n=40) and controls with symptoms mimicking CAD without stenosis in angiography (Control Group, n=43). The number and degree of stenosis were recorded. Irisin, follistatin, follistatin-like 3, activin A and B, ALT, AST, CK and CK-MB were measured at baseline and 6 or 24h after the intervention., Results: MI and CAD patients had lower irisin than controls (p<0.001). MI patients had higher follistatin, activin A, CK, CK-MB and AST than CAD patients and controls (all p≤0.001). None of the myokines changed following reperfusion. Circulating irisin was associated with the degree of stenosis in all patients (p=0.05). Irisin was not inferior to CK-MB in predicting MI while folistatin and activin A could discriminate MI from CAD patients with similar to CK-MB accuracy. None of these myokines was altered following PCI in contrast to CK-MB., Conclusions: Irisin levels are lower in MI and CAD implying that their production may depend on myocadial blood supply. Follistatin and activin A are higher in MI than in CAD suggesting increased release due to myocardial necrosis. They can predict MI with accuracy similar to CK-MB and their role in the diagnosis of MI remains to be confirmed by prospective large clinical studies., (Copyright © 2017 Elsevier Inc. All rights reserved.)