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Background & Aims Activation factor-1 transcription factor family members activating transcription factors 2 and 7 (ATF2 and ATF7) have highly redundant functions owing to highly homologous DNA binding sites. Their role in intestinal epithelial homeostasis and repair is unknown. Here, we assessed the role of these proteins in these conditions in an intestine-specific mouse model. Methods We performed in vivo and ex vivo experiments using Villin-CreERT2Atf2fl/flAtf7ko/ko mice. We investigated the effects of intestinal epithelium-specific deletion of the Atf2 DNA binding region in Atf7-/- mice on cellular proliferation, differentiation, apoptosis, and epithelial barrier function under homeostatic conditions. Subsequently, we exposed mice to 2% dextran sulfate sodium (DSS) for 7 days and 12 Gy whole-body irradiation and assessed the response to epithelial damage. Results Activating phosphorylation of ATF2 and ATF7 was detected mainly in the crypts of the small intestine and the lower crypt region of the colonic epithelium. Under homeostatic conditions, no major phenotypic changes were detectable in the intestine of ATF mutant mice. However, on DSS exposure or whole-body irradiation, the intestinal epithelium showed a clearly impaired regenerative response. Mutant mice developed severe ulceration and inflammation associated with increased epithelial apoptosis on DSS exposure and were less able to regenerate colonic crypts on irradiation. In vitro, organoids derived from double-mutant epithelium had a growth disadvantage compared with wild-type organoids, impaired wound healing capacity in scratch assay, and increased sensitivity to tumor necrosis factor-α–induced damage. Conclusions ATF2 and ATF7 are dispensable for epithelial homeostasis, but are required to maintain epithelial regenerative capacity and protect against cell death during intestinal epithelial damage and repair., Graphical abstract

Significance Preeclampsia endangers the lives and well-being of mother and baby. The syndrome is associated with placental dysfunction. High demand for energy to support active nutrient transport and hormone production increases placental susceptibility to mitochondrial stress. Here, we investigate mitochondrial activity and explore stress-response pathways in preeclamptic placentas. We demonstrate activation of noncanonical mitochondrial unfolded protein response (UPRmt) pathways associated with reduced CLPP, a key protease in UPRmt signalling, that compromises mitochondrial respiration. The changes can be recapitulated in trophoblast cells by hypoxia–reoxygenation. Either activation of UPRmt or knockdown of CLPP can sufficiently reduce mitochondrial respiration. Translation of CLPP is negatively regulated by the endoplasmic reticulum UPR pathway. Understanding mitochondrial stress provides new insights into the pathophysiology of early-onset preeclampsia., Preeclampsia (PE) is a dangerous complication of pregnancy, especially when it presents at

The mitochondrial unfolded protein response (UPRmt) is a cytoprotective signaling pathway triggered by mitochondrial dysfunction. UPRmt activation upregulates chaperones, proteases, antioxidants, and glycolysis at the gene level to restore proteostasis and cell energetics. Activating transcription factor 5 (ATF5) is a proposed mediator of the mammalian UPRmt. Herein, we hypothesized pharmacological UPRmt activation may protect against cardiac ischemia-reperfusion (I/R) injury in an ATF5-dependent manner. Accordingly, in vivo administration of the UPRmt inducers oligomycin or doxycycline 6 h before ex vivo I/R injury (perfused heart) was cardioprotective in wild-type but not global Atf5−/− mice. Acute ex vivo UPRmt activation was not cardioprotective, and loss of ATF5 did not impact baseline I/R injury without UPRmt induction. In vivo UPRmt induction significantly upregulated many known UPRmt-linked genes (cardiac quantitative PCR and Western blot analysis), and RNA-Seq revealed an UPRmt-induced ATF5-dependent gene set, which may contribute to cardioprotection. This is the first in vivo proof of a role for ATF5 in the mammalian UPRmt and the first demonstration that UPRmt is a cardioprotective drug target. NEW & NOTEWORTHY Cardioprotection can be induced by drugs that activate the mitochondrial unfolded protein response (UPRmt). UPRmt protection is dependent on activating transcription factor 5 (ATF5). This is the first in vivo evidence for a role of ATF5 in the mammalian UPRmt.

Cellular senescence plays an important role in aging and is induced by cyclin-dependent kinase (Cdk) inhibitors that accumulate following stresses during aging. However, the underlying mechanism remains elusive. Herein, we demonstrate that activating transcription factor 7 (ATF7), the stress-responsive recruiter of histone H3K9 di- and trimethyltransferases, functions in the accumulation of Cdk inhibitors. Atf7-deficient (Atf7-/- ) mice have a shorter lifespan than wild-type (WT) mice. Levels of p16Ink4a Cdk inhibitor mRNA increased with age more rapidly in Atf7-/- mice than in WT animals. ATF7 binds to the p16Ink4a gene promoter and was released with age. Consistently, histone H3K9me2 levels on the p16Ink4a gene promoter were lower in Atf7-/- mice than in WT animals. Similar results were obtained when Atf7-/- and WT mouse embryonic fibroblasts (MEFs) were cultured under 20% oxygen conditions, which induces cellular senescence via oxidative stress. Phosphorylation of ATF7 by p38 was also increased with the passage of MEFs, consistent with previous observations that ATF7 phosphorylation by p38 induces its release from chromatin. These results indicate that stress-induced and ATF7-dependent epigenetic changes on p16Ink4a genes play an important role in cellular senescence.

The differentiation of sensory neurons involves gene expression changes induced by specific transcription factors. Vomeronasal sensory neurons (VSNs) in the mouse vomeronasal organ (VNO) consist of two major subpopulations of neurons expressing vomeronasal 1 receptor (V1r)/Gαi2 or vomeronasal 2 receptor (V2r)/Gαo, which differentiate from a common neural progenitor. We previously demonstrated that the differentiation and survival of VSNs were inhibited in ATF5 transcription factor-deficient mice (Nakano et al. Cell Tissue Res 363:621-633, 2016). These defects were more prominent in V2r/Gαo-type than in V1r/Gαi2-type VSNs; however, the molecular mechanisms responsible for the differentiation of V2r/Gαo-type VSNs by ATF5 remain unclear. To identify a cofactor involved in ATF5-regulated VSN differentiation, we investigated the expression and function of CCAAT/enhancer-binding protein gamma (C/EBPγ, Cebpg), which is a major C/EBP family member expressed in the mouse VNO and dimerizes with ATF5. The results obtained showed that C/EBPγ mRNAs and proteins were broadly expressed in the postmitotic VSNs of the neonatal VNO, and their expression decreased by the second postnatal week. The C/EBPγ protein was expressed in the nuclei of approximately 70% of VSNs in the neonatal VNO, and 20% of the total VSNs co-expressed C/EBPγ and ATF5 proteins. We examined the trans-acting effects of C/EBPγ and ATF5 on V2r transcription and found that the co-expression of C/EBPγ and ATF5, but not C/EBPγ or ATF5 alone, increased Vmn2r66 promoter reporter activity via the C/EBP:ATF response element (CARE) in Neuro2a cells. These results suggest the role of C/EBPγ on ATF5-regulated VSN differentiation in early postnatal development.

Hepatocellular carcinoma (HCC) is a common cancer with poor prognosis. Hepatitis B virus (HBV) is one of the leading causes of HCC, but the precise mechanisms by which this infection promotes cancer development are not fully understood. Recently, miR-340-5p, a microRNA (miRNA) that has been identified as a cancer suppressor gene, was found to inhibit the migration and invasion of liver cancer cells. However, the effect of miR-340-5p on cell proliferation and apoptosis in HBV-associated HCC remains unknown. In our study, we show that miR-340-5p plays an important role during HBV infection and hepatocellular carcinoma development. Specifically, this miRNA directly binds to the mRNA encoding activating transcription factor 7 (ATF7), a protein that both promotes cell proliferation and suppresses apoptosis through its interaction with heat shock protein A member 1B (HSPA1B). We further found that miR-340-5p is downregulated by HBV, which enhances ATF7 expression, leading to enhanced cell proliferation and inhibition of apoptosis. Notably, ATF7 is upregulated in HCC tissue, suggesting that HBV may target miR-340-5p in vivo to promote ATF7/HSPA1B-mediated proliferation and apoptosis and regulate liver cancer progression. This work helps to elucidate the complex interactions between HBV and host miRNAs and further suggests that miR-340-5p may represent a promising candidate for the development of improved therapeutic strategies for HCC.

Muscleblind-like splicing regulators (MBNLs) are RNA-binding factors that have an important role in developmental processes. Dysfunction of these factors is a key contributor of different neuromuscular degenerative disorders, including Myotonic Dystrophy type 1 (DM1). Since DM1 is a multisystemic disease characterized by symptoms resembling accelerated aging, we asked which cellular processes do MBNLs regulate that make them necessary for normal lifespan. By utilizing the model organism Caenorhabditis elegans, we found that loss of MBL-1 (the sole ortholog of mammalian MBNLs), which is known to be required for normal lifespan, shortens lifespan by decreasing the activity of p38 MAPK/PMK-1 as well as the function of transcription factors ATF-7 and SKN-1. Furthermore, we show that mitochondrial stress caused by the knockdown of mitochondrial electron transport chain components promotes the longevity of mbl-1 mutants in a partially PMK-1-dependent manner. Together, the data establish a mechanism of how DM1-associated loss of muscleblind affects lifespan. Furthermore, this study suggests that mitochondrial stress could alleviate symptoms caused by the dysfunction of muscleblind splicing factor, creating a potential approach to investigate for therapy.

The pathogenesis of Parkinson’s disease (PD) remains elusive, but mitochondrial dysfunction is believed to be one crucial step in its pathogenesis. The mitochondrial unfolded protein response (UPR(mt)) is an important mitochondrial quality control strategy that maintains mitochondrial function in response to disturbances of mitochondrial protein homeostasis. Activation of the UPR(mt) and the beneficial effect of rescuing mitochondrial proteostasis have been reported in several genetic models of PD. However, the pathogenic relevance of the UPR(mt) in idiopathic PD is unknown. The present study examined the link between the UPR(mt) and mitochondrial dysfunction in 1-methyl-4-phenylpyridinium (MPP(+))-treated SH-SY5Y cells. Treatment with MPP(+) induced activation of the UPR(mt), reflected by an increase in the expression of UPR(mt)-related chaperones, proteases, and transcription mediators. UPR(mt) activation that was induced by overexpressing mutant ornithine transcarbamylase significantly reduced the production of mitochondrial reactive oxygen species (ROS) and improved cell survival in SH-SY5Y cells following MPP(+) treatment. Moreover, the overexpression of activating transcription factor 5 (mammalian UPR(mt) transcription factor) conferred protection against MPP(+)-induced ROS production and against cell death in SH-SY5Y cells. Overall, our results demonstrate the beneficial effect of UPR(mt) activation in MPP(+)-treated cells, shedding new light on the mechanism of mitochondrial dysfunction in the pathogenesis of PD.

Background:The benefits of exercise training in the cardiovascular system have been well accepted; however, the underlying mechanism remains to be explored. Here, we report the initial functional characterization of an exercise-induced cardiac physiological hypertrophy–associated novel long noncoding RNA (lncRNA).Methods:Using lncRNA microarray profiling, we identified lncRNAs in contributing the modulation of exercise-induced cardiac growth that we termed cardiac physiological hypertrophy–associated regulator (CPhar). Mice with adeno-associated virus serotype 9 driving CPhar overexpression and knockdown were used in in vivo experiments. Swim training was used to induce physiological cardiac hypertrophy in mice, and ischemia reperfusion injury surgery was conducted to investigate the protective effects of CPhar in mice. To investigate the mechanisms of CPhar’s function, we performed various analyses including quantitative reverse transcription polymerase chain reaction, Western blot, histology, cardiac function (by echocardiography), functional rescue experiments, mass spectrometry, in vitro RNA transcription, RNA pulldown, RNA immunoprecipitation, chromatin immunoprecipitation assay, luciferase reporter assay, and coimmunoprecipitation assays.Results:We screened the lncRNAs in contributing the modulation of exercise-induced cardiac growth through lncRNA microarray profiling and found that CPhar was increased with exercise and was necessary for exercise-induced physiological cardiac growth. The gain and loss of function of CPhar regulated the expression of proliferation markers, hypertrophy, and apoptosis in cultured neonatal mouse cardiomyocytes. Overexpression of CPhar prevented myocardial ischemia reperfusion injury and cardiac dysfunction in vivo. We identified DDX17 (DEAD-Box Helicase 17) as a binding partner of CPhar in regulating CPhar downstream factor ATF7 (activating transcription factor 7) by sequestering C/EBPβ (CCAAT/enhancer binding protein beta).Conclusions:Our study of this lncRNA CPhar provides new insights into the regulation of exercise-induced cardiac physiological growth, demonstrating the cardioprotective role of CPhar in the heart, and expanding our mechanistic understanding of lncRNA function, as well.

N6,2′-O-dimethyladenosine (m6Am), a terminal modification adjacent to the mRNA cap, is a newly discovered reversible RNA modification. Yet, a specific and sensitive tool to directly map transcriptome-wide m6Am is lacking. Here, we report m6Am-seq, based on selective in vitro demethylation and RNA immunoprecipitation. m6Am-seq directly distinguishes m6Am and 5′-UTR N6-methyladenosine (m6A) and enables the identification of m6Am at single-base resolution and 5′-UTR m6A in the human transcriptome. Using m6Am-seq, we also find that m6Am and 5′-UTR m6A respond dynamically to stimuli, and identify key functional methylation sites that may facilitate cellular stress response. Collectively, m6Am-seq reveals the high-confidence m6Am and 5′-UTR m6A methylome and provides a robust tool for functional studies of the two epitranscriptomic marks., m6Am is a dynamic and reversible RNA modification found on the mRNA cap. Here the authors report m6Am-seq to directly distinguish m6Am from m6A and identify functional methylation sites.

Activating transcription factor 5 (ATF5) belongs to the activating transcription factor/cyclic adenosine monophosphate (cAMP) response element-binding protein family of basic region leucine zipper transcription factors. ATF5 plays an important role in cell stress regulation and is involved in cell differentiation and survival, as well as centrosome maintenance and development. Accumulating evidence demonstrates that ATF5 plays an oncogenic role in cancer by regulating gene expressions involved in tumorigenesis and tumor survival. Recent studies have indicated that ATF5 may also modify the gene expressions involved in other diseases. This review explores in detail the regulation of ATF5 expression and signaling pathways and elucidates the role of ATF5 in cancer biology. Furthermore, an overview of putative therapeutic strategies that can be used for restoring aberrant ATF5 activity in different cancer types is provided.

MNRR1 (CHCHD2) is a bi-organellar regulator of mitochondrial function that directly activates cytochrome c oxidase in the mitochondria and functions in the nucleus as a transcriptional activator for hundreds of genes. Since MNRR1 depletion contains features of a mitochondrial disease phenotype, we evaluated the effects of forced expression of MNRR1 on the mitochondrial disease MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes) syndrome. MELAS is a multisystem encephalomyopathy disorder that can result from a heteroplasmic mutation in the mitochondrial DNA (mtDNA; m.3243A > G) at heteroplasmy levels of ∼50 to 90%. Since cybrid cell lines with 73% m.3243A > G heteroplasmy (DW7) display a significant reduction in MNRR1 levels compared to the wild type (0% heteroplasmy) (CL9), we evaluated the effects of MNRR1 levels on mitochondrial functioning. Overexpression of MNRR1 in DW7 cells induces the mitochondrial unfolded protein response (UPR(mt)), autophagy, and mitochondrial biogenesis, thereby rescuing the mitochondrial phenotype. It does so primarily as a transcription activator, revealing this function to be a potential therapeutic target. The role of MNRR1 in stimulating UPR(mt), which is blunted in MELAS cells, was surprising and further investigation uncovered that under conditions of stress the import of MNRR1 into the mitochondria was blocked, allowing the protein to accumulate in the nucleus to enhance its transcription function. In the mammalian system, ATF5, has been identified as a mediator of UPR(mt). MNRR1 knockout cells display an ∼40% reduction in the protein levels of ATF5, suggesting that MNRR1 plays an important role upstream of this known mediator of UPR(mt).

Heparan sulfate proteoglycans (HSPGs) consist of a core protein with side chains of the glycosaminoglycan heparan sulfate (HS). We have previously identified (i) the HSPGs syndecan-1 (SDC1), and collagen type XVIII (COL18) inside mouse and human islet beta cells, and (ii) a critical role for HS in beta cell survival and protection from reactive oxygen species (ROS). The objective of this study was to investigate whether endoplasmic reticulum (ER) stress contributes to oxidative stress and type 2 diabetes (T2D) by depleting beta cell HSPGs/HS. A rapid loss of intra-islet/beta cell HSPGs, HS and heparanase (HPSE, an HS-degrading enzyme) accompanied upregulation of islet ER stress gene expression in both young T2D-prone db/db and Akita Ins2WT/C96Y mice. In MIN6 beta cells, HSPGs, HS and HPSE were reduced following treatment with pharmacological inducers of ER stress (thapsigargin or tunicamycin). Treatment of young db/db mice with Tauroursodeoxycholic acid (TUDCA), a chemical protein folding chaperone that relieves ER stress, improved glycemic control and increased intra-islet HSPG/HS. In vitro, HS replacement with heparin (a highly sulfated HS analogue) significantly increased the survival of wild-type and db/db beta cells and restored their resistance to hydrogen peroxide-induced death. We conclude that ER stress inhibits the synthesis/maturation of HSPG core proteins which are essential for HS assembly, thereby exacerbating oxidative stress and promoting beta cell failure. Diminished intracellular HSPGs/HS represent a previously unrecognized critical link bridging ER stress, oxidative stress and beta cell failure in T2D.

Activating transcription factor 5 (ATF5) is a member of the cAMP response element binding protein (CREB)/ATF family of basic leucine zipper transcription factors. We previously reported that ATF5-deficient (ATF5−/−) mice exhibited behavioural abnormalities, including abnormal social interactions, reduced behavioural flexibility, increased anxiety-like behaviours, and hyperactivity in novel environments. ATF5−/− mice may therefore be a useful animal model for psychiatric disorders. ATF5 is highly expressed in the ventricular zone and subventricular zone during cortical development, but its physiological role in higher-order brain structures remains unknown. To investigate the cause of abnormal behaviours exhibited by ATF5−/− mice, we analysed the embryonic cerebral cortex of ATF5−/− mice. The ATF5−/− embryonic cerebral cortex was slightly thinner and had reduced numbers of radial glial cells and neural progenitor cells, compared to a wild-type cerebral cortex. ATF5 deficiency also affected the basal processes of radial glial cells, which serve as a scaffold for radial migration during cortical development. Further, the radial migration of cortical upper layer neurons was impaired in ATF5−/− mice. These results suggest that ATF5 deficiency affects cortical development and radial migration, which may partly contribute to the observed abnormal behaviours.

mTOR is well known to promote tumor growth but its roles in enhancing chemotherapy and radiotherapy have not been well studied. mTOR inhibition by rapamycin can sensitize cancer cells to radiotherapy. Here we show that Maf1 is required for rapamycin to increase radio-sensitivity in A549 lung cancer cells. In response to ionizing radiation (IR), Maf1 is inhibited by Akt-dependent re-phosphorylation, which activates mitochondrial unfolded protein response (UPRmt) through ATF5. Rapamycin suppresses IR-induced Maf1 re-phosphorylation and UPRmt activation in A549 cells, resulting in increased sensitivity to IR-mediated cytotoxicity. Consistently, Maf1 knockdown activates ATF5-transcription of mtHSP70 and HSP60, enhances mitochondrial membrane potential, reduces intracellular ROS levels and dampens rapamycin's effect on increasing IR-mediated cytotoxicity. In addition, Maf1 overexpression suppresses ethidium bromide-induced UPRmt and enhances IR-mediated cytotoxicity. Supporting our cell-based studies, elevated expression of UPRmt makers (mtHSP70 and HSP60) are associated with poor prognosis in patients with lung adenocarcinoma (LAUD). Together, our study reveals a novel role of Maf1-UPRmt axis in mediating rapamycin's enhancing effect on IR sensitivity in A549 lung cancer cells.

Mitochondrial unfolding protein response (UPRmt) effectively resists the pathological cardiac hypertrophy and improves the mitochondrial function. However, the specific activation mechanism and drugs that can effectively activate UPRmt in the cardiac muscle are yet to be elucidated. The aim of this study was to determine the regulation role of UPRmt on preventing pathological cardiac hypertrophy by tetrahydrocurcumin (THC) and explore its underlying molecular mechanism. Male C57BL/6J wild-type (WT) mice were divided into a control group and subjected to sham treatment for 4 weeks, and a test group which was subjected to transverse aortic constriction (TAC) surgery. Animals in the control and test group were orally administered THC (50 mg/kg) for 4 weeks after TAC procedure; an equivalent amount of saline was orally administered in the control sham-treated group and the TAC group. Subsequently, oxidative stress and UPRmt markers were assessed in these mice, and cardiac hypertrophy, fibrosis, and cardiac function were tested. Small interfering RNA (siRNA) targeting proliferator-activated receptor-gamma coactivator (PGC)-1α and activating transcription factor 5 (ATF5) were used to determine the UPRmt activation mechanism. THC supplement partly upregulated UPRmt effectors and inhibited TAC-induced oxidative stress compared with TAC-operated WT mice, thereby substantially attenuating contractile dysfunction, cardiac hypertrophy, and fibrosis. Furthermore, PGC-1α knockdown blunted the UPRmt activation and the cardioprotective role of THC. The interaction between PGC-1α and ATF5 was tested in neonatal rat cardiac myocytes under normal conditions. The results showed that PGC-1α was an upstream effector of ATF5 and partly activated UPRmt. In vitro, phenylephrine- (PE-) induced cardiomyocyte hypertrophy caused ATF5 upregulating rather than downregulating corresponding to the downregulation of PGC-1α. The PGC-1α/ATF5 axis mediated the UPRmt activation and stress-resistance role of THC in vitro. Collectively, the present study provides the first evidence that PGC-1 and ATF5 can form a signaling axis to partly activate UPRmt that mediates the cardioprotective role of THC in pathological cardiac hypertrophy.

Yoshida etal. (2020) report in this issue of Molecular Cell that a paternal low-protein diet elevates ROS in the testicular germ cells, altering ATF7 activity and H3K9me2 abundance on target genes, including tRNA loci. These changes are maintained in spermatozoa, regulating tsRNA biogenesis, and together transmit intergenerational effects.

Various stresses increase disease susceptibility and accelerate aging, and increasing evidence suggests that these effects can be transmitted over generation. Epidemiological studies suggest that stressors experienced by parents affect the longevity of their offspring, possibly by regulating telomere dynamics. Telomeres are elongated by telomerase and shortened by certain stresses as well as telomere repeat-containing RNA (TERRA), a telomere transcript. However, the mechanism underlying the transgenerational effects is poorly understood. Here, we show that TNF-α, which is induced by various psychological stresses, induces the p38-dependent phosphorylation of ATF7, a stress-responsive chromatin regulator, in mouse testicular germ cells. This caused a release of ATF7 from the TERRA gene promoter in the subtelomeric region, which disrupted heterochromatin and induced TERRA. TERRA was transgenerationally transmitted to zygotes via sperm and caused telomere shortening. These results suggest that ATF7 and TERRA play key roles in paternal stress-induced telomere shortening in the offspring. papers2://publication/uuid/098E3E6E-869C-4DAB-97AF-BDA0E6DF6B90 PMC6326783

Objective Loss of insulin secretion due to failure or death of the insulin secreting β cells is the central cause of diabetes. The cellular response to stress (endoplasmic reticulum (ER), oxidative, inflammatory) is essential to sustain normal β cell function and survival. Pancreatic and duodenal homeobox 1 (PDX1), Activating transcription factor 4 (ATF4), and Activating transcription factor 5 (ATF5) are transcription factors implicated in β cell survival and susceptibility to stress. Our goal was to determine if a PDX1-ATF transcriptional complex or complexes regulate β cell survival in response to stress and to identify direct transcriptional targets. Methods Pdx1, Atf4 and Atf5 were silenced by viral delivery of gRNAs or shRNAs to Min6 insulinoma cells or primary murine islets. Gene expression was assessed by qPCR, RNAseq analysis, and Western blot analysis. Chromatin enrichment was measured in the Min6 β cell line and primary isolated mouse islets by ChIPseq and ChIP PCR. Immunoprecipitation was used to assess interactions among transcription factors in Min6 cells and isolated mouse islets. Activation of caspase 3 by immunoblotting or by irreversible binding to a fluorescent inhibitor was taken as an indication of commitment to an apoptotic fate. Results RNASeq identified a set of PDX1, ATF4 and ATF5 co-regulated genes enriched in stress and apoptosis functions. We further identified stress induced interactions among PDX1, ATF4, and ATF5. PDX1 chromatin occupancy peaks were identified over composite C/EBP-ATF (CARE) motifs of 26 genes; assessment of a subset of these genes revealed co-enrichment for ATF4 and ATF5. PDX1 occupancy over CARE motifs was conserved in the human orthologs of 9 of these genes. Of these, Glutamate Pyruvate Transaminase 2 (Gpt2), Cation transport regulator 1 (Chac1), and Solute Carrier Family 7 Member 1 (Slc7a1) induction by stress was conserved in human islets and abrogated by deficiency of Pdx1, Atf4, and Atf5 in Min6 cells. Deficiency of Gpt2 reduced β cell susceptibility to stress induced apoptosis in both Min6 cells and primary islets. Conclusions Our results identify a novel PDX1 stress inducible complex (es) that regulates expression of stress and apoptosis genes to govern β cell survival., Graphical abstract Image 1, Highlights • PDX1 binds to composite CEBP/ATF (CARE) sites of stress and apoptosis genes. • A novel stress inducible transcriptional complex involving PDX1, ATF4, and ATF5 is discovered. • Novel stress induced targets of the complex involved in fate decisions are identified. • Silencing of one of these targets, Gpt2, protects β cells from apoptosis due to stress.

The mitochondrial unfolded protein response (UPRmt) is a protein quality control mechanism that strives to achieve proteostasis in the face of misfolded proteins. Because of the reliance of mitochondria on both the nuclear and mitochondrial genomes, a perturbation of the coordination of these genomes results in a mitonuclear imbalance in which holoenzymes are unable to assume mature stoichiometry and thereby activates the UPRmt. Thus, we sought to perturb this genomic coordination by using a systemic antisense oligonucleotide (in vivo morpholino) targeted to translocase of the inner membrane channel subunit 23 (Tim23), the major channel of the inner membrane. This resulted in a 40% reduction in Tim23 protein content, a 32% decrease in matrix-destined protein import, and a trend to elevate reactive oxygen species (ROS) emission under maximal respiration conditions. This import defect activated the C/EBP homologous protein (CHOP) branch of the UPRmt, as evident from increases in caseinolytic mitochondrial matrix peptidase proteolytic subunit (ClpP) and chaperonin 10 (cpn10) but not the activating transcription factor 5 (ATF5) arm. Thus, in the face of proteotoxic stress, CHOP and ATF5 could be activated independently to regain proteostasis. Our second aim was to investigate the role of proteolytically derived peptides in mediating retrograde signaling. Peptides released from the mitochondrion following basal proteolysis were isolated and incubated with import reactions. Dose- and time-dependent effect of peptides on protein import was observed. Our data suggest that mitochondrial proteolytic byproducts exert an inhibitory effect on protein import, possibly to reduce excessive protein import as a potential negative feedback mechanism. The inhibition of import into the organelle also serves a retrograde function, possibly via ROS emission, to modify nuclear gene expression and ultimately improve folding capacity.

The inverse association between plasma HDL cholesterol (HDL-C) levels and risk for cardiovascular disease (CVD) has been demonstrated by numerous epidemiological studies. However, efforts to reduce CVD risk by pharmaceutically manipulating HDL-C levels failed and refused the HDL hypothesis. HDL-C levels in the general population are highly heterogeneous and are determined by a combination of genetic and environmental factors. Insights into the causes of HDL-C heterogeneity came from the study of monogenic HDL deficiency syndromes but also from genome wide association and Μendelian randomization studies which revealed the contribution of a large number of loci to low or high HDL-C cases in the general or in restricted ethnic populations. Furthermore, HDL-C levels in the plasma are under the control of transcription factor families acting primarily in the liver including members of the hormone nuclear receptors (PPARs, LXRs, HNF-4) and forkhead box proteins (FOXO1-4) and activating transcription factors (ATFs). The effects of certain lipid lowering drugs used today are based on the modulation of the activity of specific members of these transcription factors. During the past decade, the roles of small or long non-coding RNAs acting post-transcriptionally on the expression of HDL genes have emerged and provided novel insights into HDL regulation and new opportunities for therapeutic interventions. In the present review we summarize recent progress made in the genetics and the regulation (transcriptional and post-transcriptional) of HDL metabolism.

Activating transcription factor 5 (ATF5) is a member of the ATF/cAMP response element–binding protein family of transcription factors. ATF5 regulates stress responses and cell survival, proliferation, and differentiation and also plays a role in viral infections, cancer, diabetes, schizophrenia, and the olfactory system. Moreover, it was found to also have a critical cell cycle–dependent structural function at the centrosome. However, the mechanism that controls the localization of ATF5 at the centrosome is unclear. Here we report that ATF5 is small ubiquitin-like modifier (SUMO) 2/3–modified at a conserved SUMO-targeting consensus site in various types of mammalian cells. We found that SUMOylation of ATF5 is elevated in the G(1) phase of the cell cycle and diminished in the G(2)/M phase. ATF5 SUMOylation disrupted the interaction of ATF5 with several centrosomal proteins and dislodged ATF5 from the centrosome at the end of the M phase. Of note, blockade of ATF5 SUMOylation deregulated the centrosome cycle, impeded ATF5 translocation from the centrosome, and caused genomic instability and G(2)/M arrest in HeLa cells. Our results indicate that ATF5 SUMOylation is an essential mechanism that regulates ATF5 localization and function at the centrosome.

The in vivo function of p38 mitogen-activated protein kinase (MAPK) signaling in regulating the response to simulated microgravity is still largely unclear. Using Caenorhabditis elegans as an assay system, we investigated the in vivo function of p38 MAPK signaling in regulating the response of animals to simulated microgravity and the underlying molecular mechanism. Simulated microgravity treatment significantly increased the transcriptional expressions of genes (pmk-1, sek-1, and nsy-1) encoding core p38 MAPK signaling pathway and the expression of phosphorylated PMK-1/p38 MAPK. The pmk-1, sek-1, or nsy-1 mutant was susceptible to adverse effects of simulated microgravity. The intestine-specific activity of PMK-1 was required for its function in regulating the response to simulated microgravity, and the entire p38 MAPK signaling pathway could act in the intestine to regulate the response to simulated microgravity. In the intestine, SKN-1 and ATF-7, two transcriptional factors, were identified as downstream targets for PMK-1 in regulating the response to simulated microgravity. Therefore, the activation of p38 MAPK signaling may mediate a protection mechanism for nematodes against the adverse effects of simulated microgravity. Additionally, our results highlight the potential crucial role of intestinal cells in response to simulated microgravity in nematodes.

Epigenetic inheritance of heterochromatin requires DNA sequence-independent propagation mechanisms, coupling to RNAi, or input from DNA sequence, but how DNA contributes to inheritance is not understood. Here, we identify a DNA element (termed “maintainer”) that is sufficient for epigenetic inheritance of preexisting histone H3 lysine 9 methylation (H3K9me) and heterochromatin in Schizosaccharomyces pombe, but cannot establish de novo gene silencing in wild-type cells. This maintainer is a composite DNA element with binding sites for the Atf1/Pcr1 and Deb1 transcription factors and the Origin Recognition Complex (ORC), located within a 130-base pair region, and can be converted to a silencer in cells with lower rates of H3K9me turnover, suggesting that it participates in recruiting the H3K9 methyltransferase Clr4/Suv39h. These results suggest that, in the absence of RNAi, histone H3K9me is only heritable when it can collaborate with maintainer-associated DNA-binding proteins that help recruit the enzyme responsible for its epigenetic deposition.

Mitochondria form a cellular network of organelles, or cellular compartments, that efficiently couple nutrients to energy production in the form of ATP. As cancer cells rely heavily on glycolysis, historically mitochondria and the cellular pathways in place to maintain mitochondrial activities were thought to be more relevant to diseases observed in non-dividing cells such as muscles and neurons. However, more recently it has become clear that cancers rely heavily on mitochondrial activities including lipid, nucleotide and amino acid synthesis, suppression of mitochondria-mediated apoptosis as well as oxidative phosphorylation (OXPHOS) for growth and survival. Considering the variety of conditions and stresses that cancer cell mitochondria may incur such as hypoxia, reactive oxygen species and mitochondrial genome mutagenesis, we examine potential roles for a mitochondrial-protective transcriptional response known as the mitochondrial unfolded protein response (UPRmt) in cancer cell biology.

Hyperactivated Ras regulates many oncogenic pathways in several malignant human cancers including glioblastoma and it is an attractive target for cancer therapies. Ras activation in cancer cells drives protein internalization via macropinocytosis as a key nutrient-gaining process. By utilizing this unique endocytosis pathway, here we create a biologically inspired nanostructure that can induce cancer cells to ‘drink drugs' for targeting activating transcription factor-5 (ATF5), an overexpressed anti-apoptotic transcription factor in glioblastoma. Apolipoprotein E3-reconstituted high-density lipoprotein is used to encapsulate the siRNA-loaded calcium phosphate core and facilitate it to penetrate the blood–brain barrier, thus targeting the glioblastoma cells in a macropinocytosis-dependent manner. The nanostructure carrying ATF5 siRNA exerts remarkable RNA-interfering efficiency, increases glioblastoma cell apoptosis and inhibits tumour cell growth both in vitro and in xenograft tumour models. This strategy of targeting the macropinocytosis caused by Ras activation provides a nanoparticle-based approach for precision therapy in glioblastoma and other Ras-activated cancers., Drug delivery in brain tumours is still a significant clinical concern. In this study, the authors develop a biomimetic lipoprotein nanoparticle for the efficient delivery of ATF5 siRNA in Ras-activated brain cancer cells, where the nanoparticle is internalized by macropinocytosis in a Ras-dependent manner.

Obesity increases risk for liver toxicity by the anti-leukemic agent asparaginase, but the mechanism is unknown. Asparaginase activates the integrated stress response (ISR) via sensing amino acid depletion by the eukaryotic initiation factor 2 (eIF2) kinase GCN2. The goal of this work was to discern the impact of obesity, alone versus alongside genetic disruption of the ISR, on mechanisms of liver protection during chronic asparaginase exposure in mice. Following diet-induced obesity, biochemical analysis of livers revealed that asparaginase provoked hepatic steatosis that coincided with activation of another eIF2 kinase PKR-like endoplasmic reticulum kinase (PERK), a major ISR transducer to ER stress. Genetic loss of Gcn2 intensified hepatic PERK activation to asparaginase, yet surprisingly, mRNA levels of key ISR gene targets such as Atf5 and Trib3 failed to increase. Instead, mechanistic target of rapamycin complex 1 (mTORC1) signal transduction was unleashed, and this coincided with liver dysfunction reflected by a failure to maintain hydrogen sulfide production or apolipoprotein B100 (ApoB100) expression. In contrast, obese mice lacking hepatic activating transcription factor 4 (Atf4) showed an exaggerated ISR and greater loss of endogenous hydrogen sulfide but normal inhibition of mTORC1 and maintenance of ApoB100 during asparaginase exposure. In both genetic mouse models, expression and phosphorylation of Sestrin2, an ATF4 gene target, was increased by asparaginase, suggesting mTORC1 inhibition during asparaginase exposure is not driven via eIF2-ATF4-Sestrin2. In conclusion, obesity promotes a maladaptive ISR during asparaginase exposure. GCN2 functions to repress mTORC1 activity and maintain ApoB100 protein levels independently of Atf4 expression, whereas hydrogen sulfide production is promoted via GCN2-ATF4 pathway.

// Ming Hu 1 , Bin Wang 1 , Dongmeng Qian 1 , Mengyuan Wang 2 , Rui Huang 1 , Li Wei 3 , Ling Li 1 , Li Zhang 1 , David X. Liu 4 1 Department of Basic Medical Sciences, Qingdao University, Qingdao, China 2 College of Life Sciences, Qingdao University, Qingdao, China 3 The Hospital of People’s Liberation Army, Weifang, China 4 Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, Spokane, WA, USA Correspondence to: Bin Wang, email: humcnn@gmail.com Keywords: HCMV, IE86, glioma, ATF5, acetylation Received: March 08, 2017 Accepted: April 03, 2017 Published: April 17, 2017 ABSTRACT Human cytomegalovirus (HCMV), a widespread beta-herpes virus, infects a high percentage of gliomas. HCMV is specifically detected in human gliomas at a low level of expression raises the possibility that it may regulate the malignant phenotype in a chronic manner. Although HCMV is not recognized as an oncogenic virus, it might dysregulate signaling pathways involved in initiation and promotion of malignancy. Here, our immunohistochemical staining reveals that nucleus staining of the HCMV 86-kDa immediate-early protein (IE86) is markedly increased in GBM (58.56%) compared with that in nontumorous samples (4.20%) and low-grade glioma(19.56%). IE86 staining positively correlates with the staining of activating transcription factor 5 (ATF5) which is essential for glioma cell viability and proliferation suggesting that HCMV IE86 could have important implications in glioma biology. Moreover, we find that the IE86 overexpression enhances glioma cell’s growth in vitro and in vivo . We demonstrate that IE86 protein physically interacts with, and acetylates ATF5 thereby promoting glioma cell survival. Therefore, our findings illustrate the biological significance of HCMV infection in accelerating glioma progression, and provide novel evidence that HCMV infection may serve as a therapeutic target in human glioma.

Several microRNAs (miRNAs) have been identified to play roles in adipocyte differentiation. However, little is known about their involvement in the differentiation of ovine intramuscular adipocytes. Here, the role of one such miRNA, miR-340-5p, in ovine adipocyte differentiation was investigated. Stromal vascular (SV) cells were isolated from skeletal muscle tissues of 1-month-old lambs and induced to differentiate into mature adipocytes. miRNA mimics and inhibitors were used for miR-340-5p overexpression and knockdown assays. For overexpression and knockdown of activating transcription factor 7 (ATF7), lentivirus infection was performed. Luciferase reporter assay was performed to determine the relationship between miR-340-5p and ATF7. The expression of adipogenesis marker genes, PPARγ, C/EBPα, FABP4, ADIPOQ, and ACC, and formation of lipid droplets were detected after the overexpression and inhibition of miR-340-5p, or upon overexpression or knockdown of ATF7. miR-340-5p inhibited the expression of the marker genes and the formation of lipid droplets. ATF7 positively regulated the expression of the marker genes and the formation of lipids. Thus, ATF7 is the target of miR-340-5p in sheep. Overall, these findings indicate that miR-340-5p acts as an inhibitor of the differentiation of intramuscular adipocytes by targeting ATF7. Our study provides a new theoretical basis for improving sheep meat quality.

Cellular stress response mechanisms normally function to enhance survival and allow for cells to return to homeostasis following an adverse event. Cancer cells often co-opt these same mechanisms as a means to evade apoptosis and mitigate a state of constant cellular stress. Activating transcription factor 5 (ATF5) is upregulated under diverse stress conditions and is overexpressed in a variety of cancers. It was demonstrated ATF5 is a survival factor in transformed, but not normal cells. However, the regulation of ATF5 is not fully understood. The purpose of the present study was to investigate miRNA regulation at the 3' untranslated region (UTR) of ATF5, with the goal of demonstrating a reversal of the upregulation of ATF5 induced under diverse cellular stress in cancer cells. A multifactorial approach using in silico analysis was employed to identify miRNAs 433-3p, 520b-3p, and 129-5p as potential regulators of ATF5, based on their predicted binding sites over the span of the ATF5 3' UTR. Luciferase reporter assay data validated all three miRNA candidates by demonstrating direct binding to the target ATF5 3'. However, functional studies revealed miR-520b-3p as the sole candidate able to reverse the upregulation of ATF5 protein under diverse cellular stress. Additionally, miR-520b-3p levels were inversely related to ATF5 mRNA under endoplasmic reticulum stress and amino acid deprivation. This is the first evidence that regulation at the 3' UTR is involved in modulating ATF5 levels under cellular stress and suggests an important role for miRNA-520b-3p in the regulation of ATF5.

The Activating Transcription Factor 5 (ATF5) is a basic leucine-zipper (bZIP) transcription factor (TF) with proposed stress-protective, anti-apoptotic and oncogenic roles which were all established in cell systems. In whole animals, Atf5 function seems highly context dependent. Atf5 is strongly expressed in the rodent nose and mice knockout (KO) pups have defective olfactory sensory neurons (OSNs), smaller olfactory bulbs (OB), while adults are smell deficient. It was therefore proposed that Atf5 plays an important role in maturation and maintenance of OSNs. Atf5 expression was also described in murine liver and bones where it appears to promote differentiation of progenitor cells. By contrast in the rodent brain, Atf5 was first described as uniquely expressed in neuroprogenitors and thus, proposed to drive their proliferation and inhibit their differentiation. However, it was later also found in mature neurons stressing the need for additional work in whole animals. ATF5 is well conserved with two paralogs, atf5a and atf5b in zebrafish. Here, we present the expression patterns for both from 6 h (hpf) to 5day post-fertilization (dpf). We found early expression for both genes, and from 1dpf onwards overlapping expression patterns in the inner ear and the developing liver. In the brain, at 24hpf both atf5a and atf5b were expressed in the forebrain, midbrain, and hindbrain. However, from 2dpf and onwards we only detected atf5a expression namely in the olfactory bulbs, the mesencephalon, and the metencephalon. We further evidenced additional differential expression for atf5a in the sensory neurons of the olfactory organs, and for atf5b in the neuromasts, that form the superficial sensory organ called the lateral line (LL). Our results establish the basis for future functional analyses in this lower vertebrate.

Survivin (BIRC5, product of the BIRC5 gene) is highly expressed in many tumor types and has been widely identified as a potential target for cancer therapy. However, effective anti-survivin drugs remain to be developed. Here we report that both vector-delivered and cell-penetrating dominant-negative (dn) forms of the transcription factor ATF5 that promote selective death of cancer cells in vitro and in vivo cause survivin depletion in tumor cell lines of varying origins. dn-ATF5 decreases levels of both survivin mRNA and protein. The depletion of survivin protein appears to be driven at least in part by enhanced proteasomal turnover and depletion of the deubiquitinase USP9X. Survivin loss is rapid and precedes the onset of cell death triggered by dn-ATF5. Although survivin downregulation is sufficient to drive tumor cell death, survivin over-expression does not rescue cancer cells from dn-ATF5-promoted apoptosis. This indicates that dn-ATF5 kills malignant cells by multiple mechanisms that include, but are not limited to, survivin depletion. Cell-penetrating forms of dn-ATF5 are currently being developed for potential therapeutic use and the present findings suggest that they may pose an advantage over treatments that target only survivin.

The basic leucine zipper transcription factor ATF5 is overexpressed in many tumor types and interference with its expression or function inhibits cancer cell survival. As a potential therapeutic approach to exploit these findings, we created dominant-negative (DN) ATF5 forms lacking DNA-binding ability that retain the ATF5 leucine zipper, and thus associate with and sequester ATF5's requisite leucine zipper–binding partners. Preclinical studies with DN-ATF5, including a cell-penetrating form, show in vitro and in vivo efficacy in compromising cancer cell survival. However, DN-ATF5's targets, and particularly those required for tumor cell survival, have been unknown. We report that cells lacking ATF5 succumb to DN-ATF5, indicating that ATF5 itself is not DN-ATF5's obligate target. Unbiased pull-down assays coupled with mass spectrometry and immunoblotting revealed that DN-ATF5 associates in cells with the basic leucine zipper proteins CEBPB and CEBPD and coiled-coil protein CCDC6. Consistent with DN-ATF5 affecting tumor cell survival by suppressing CEBPB and CEBPD function, DN-ATF5 interferes with CEBPB and CEBPD transcriptional activity, while CEBPB or CEBPD knockdown promotes apoptotic death of multiple cancer cells lines, but not of normal astrocytes. We propose a two-pronged mechanism by which DN-ATF5 kills tumor cells. One is by inhibiting heterodimer formation between ATF5 and CEBPB and CDBPD, thus suppressing ATF5-dependent transcription. The other is by blocking the formation of transcriptionally active CEBPB and CEBPD homodimers as well as heterodimers with partners in addition to ATF5. Implications: This study indicates that the potential cancer therapeutic DN-ATF5 acts by associating with and blocking the transcriptional activities of CEBPB and CEBPD.

Activating transcription factor 5 (ATF5) is necessary for the development of various tissues, particularly under stress. Dysfunctions of ATF5 have been shown to be involved in many diseases. The exact function of ATF5 is tissue-specific, and its role in erythropoiesis is still unknown. We here employed the loss of function strategy to investigate the role of ATF5 in murine erythropoiesis. We found that knockdown of Atf5 impaired the proliferation of fetal liver erythroid progenitors. Furthermore, erythroid differentiation was inhibited by ATF5 deficiency. Our study suggests that ATF5 may be a potential therapeutic target for treating blood diseases with ineffective erythropoiesis.

Chronic inflammation is a driving force for the development of metabolic disease including diabetes and obesity. However, the functional characteristics of T-cell senescence in the abnormal glucose homeostasis are not fully understood. We studied the patients visiting a hospital for routine health check-ups, who were divided into two groups: normal controls and people with prediabetes. Gene expression profiling of peripheral blood mononuclear cells from normal controls and patients with type 2 diabetes was undertaken using microarray analysis. We also investigated the immunometabolic characteristics of peripheral and hepatic senescent T cells in the normal subjects and patients with prediabetes. Moreover, murine senescent T cells were tested functionally in the liver of normal or mice with metabolic deterioration caused by diet-induced obesity. Human senescent (CD28−CD57+) CD8+ T cells are increased in the development of diabetes and proinflammatory cytokines and cytotoxic molecules are highly expressed in senescent T cells from patients with prediabetes. Moreover, we demonstrate that patients with prediabetes have higher concentrations of reactive oxygen species (ROS) in their senescent CD8+ T cells via enhancing capacity to use glycolysis. These functional properties of senescent CD8+ T cells contribute to the impairment of hepatic insulin sensitivity in humans. Furthermore, we found an increase of hepatic senescent T cells in mouse models of aging and diet-induced obesity. Adoptive transfer of senescent CD8+ T cells also led to a significant deterioration in systemic abnormal glucose homeostasis, which is improved by ROS scavengers in mice. This study defines a new clinically relevant concept of T-cell senescence-mediated inflammatory responses in the pathophysiology of abnormal glucose homeostasis. We also found that T-cell senescence is associated with systemic inflammation and alters hepatic glucose homeostasis. The rational modulation of T-cell senescence would be a promising avenue for the treatment or prevention of diabetes.

Mitochondrial dysfunction elicits stress responses that safeguard cellular homeostasis against metabolic insults. Mitochondrial integrated stress response (ISRmt) is a major response to mitochondrial (mt)DNA expression stress (mtDNA maintenance, translation defects), but the knowledge of dynamics or interdependence of components is lacking. We report that in mitochondrial myopathy, ISRmt progresses in temporal stages and development from early to chronic and is regulated by autocrine and endocrine effects of FGF21, a metabolic hormone with pleiotropic effects. Initial disease signs induce transcriptional ISRmt (ATF5, mitochondrial one-carbon cycle, FGF21, and GDF15). The local progression to 2nd metabolic ISRmt stage (ATF3, ATF4, glucose uptake, serine biosynthesis, and transsulfuration) is FGF21 dependent. Mitochondrial unfolded protein response marks the 3rd ISRmt stage of failing tissue. Systemically, FGF21 drives weight loss and glucose preference, and modifies metabolism and respiratory chain deficiency in a specific hippocampal brain region. Our evidence indicates that FGF21 is a local and systemic messenger of mtDNA stress in mice and humans with mitochondrial disease.

The stress response and cell survival are necessary for normal pancreatic β-cell function, glucose homeostasis, and prevention of diabetes. The homeodomain transcription factor and human diabetes gene pancreas/duodenum homeobox protein 1 (Pdx1) regulates β-cell survival and endoplasmic reticulum stress susceptibility, in part through direct regulation of activating transcription factor 4 (Atf4). Here we show that Atf5, a close but less-studied relative of Atf4, is also a target of Pdx1 and is critical for β-cell survival under stress conditions. Pdx1 deficiency led to decreased Atf5 transcript, and primary islet ChIP-sequencing localized PDX1 to the Atf5 promoter, implicating Atf5 as a PDX1 target. Atf5 expression was stress inducible and enriched in β cells. Importantly, Atf5 deficiency decreased survival under stress conditions. Loss-of-function and chromatin occupancy experiments positioned Atf5 downstream of and parallel to Atf4 in the regulation of eIF4E-binding protein 1 (4ebp1), a mammalian target of rapamycin (mTOR) pathway component that inhibits protein translation. Accordingly, Atf5 deficiency attenuated stress suppression of global translation, likely enhancing the susceptibility of β cells to stress-induced apoptosis. Thus, we identify ATF5 as a member of the transcriptional network governing pancreatic β-cell survival during stress.

Fibroblast growth factor 21 (FGF21) is the first known endocrine signal activated by protein restriction. Although FGF21 is robustly elevated in low-protein environments, increased FGF21 is also seen in various other contexts such as fasting, overfeeding, ketogenic diets, and high-carbohydrate diets, leaving its nutritional context and physiological role unresolved and controversial. Here, we use the Geometric Framework, a nutritional modeling platform, to help reconcile these apparently conflicting findings in mice confined to one of 25 diets that varied in protein, carbohydrate, and fat content. We show that FGF21 was elevated under low protein intakes and maximally when low protein was coupled with high carbohydrate intakes. Our results explain how elevation of FGF21 occurs both under starvation and hyperphagia, and show that the metabolic outcomes associated with elevated FGF21 depend on the nutritional context, differing according to whether the animal is in a state of under- or overfeeding.

The activating transcription factor (ATF)2 family of transcription factors regulates a variety of metabolic processes, including adipogenesis and adaptive thermogenesis. ATF7 is a member of the ATF2 family, and mediates epigenetic changes induced by environmental stresses, such as social isolation and pathogen infection. However, the metabolic role of ATF7 remains unknown. The aim of the present study is to examine the role of ATF7 in metabolism using ATF7-dificeint mice. Atf7(-/-) mice exhibited lower body weight and resisted diet-induced obesity. Serum triglycerides, resistin, and adipose tissue mass were all significantly lower in ATF7-deficient mice. Fasting glucose levels and glucose tolerance were unaltered, but systemic insulin sensitivity was increased, by ablation of ATF7. Indirect calorimetry revealed that oxygen consumption by Atf7(-/-) mice was comparable to that of wild-type littermates on a standard chow diet, but increased energy expenditure was observed in Atf7(-/-) mice on a high-fat diet. Hence, ATF7 ablation may impair the development and function of adipose tissue and result in elevated energy expenditure in response to high-fat-feeding obesity and insulin resistance, indicating that ATF7 is a potential therapeutic target for diet-induced obesity and insulin resistance.