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Background: The dynamics of mitochondrial respiratory cristae (MRC) and its impact on oxidative phosphorylation (OXPHOS) play a crucial role in driving the progression of high-grade glioma (HGG). However, the underlying mechanism remains unclear. Methods: In the present study, we employed machine learning-based transmission electron microscopy analysis of 7141 mitochondria from 54 resected glioma patients. Additionally, we conducted bioinformatics analysis and multiplex immunohistochemical (mIHC) staining of clinical glioma microarrays to identify key molecules involved in glioma. Subsequently, we modulated the expression levels of mitochondrial dynamic-1-like protein (DNM1L/DRP1), and its two receptors, mitochondrial fission protein 1 (FIS1) and mitochondrial fission factor (MFF), via lentiviral transfection to further investigate the central role of these molecules in the dynamics of glioblastoma (GBM) cells and glioma stem cells (GSCs). We then evaluated the potential impact of DNM1L/DRP1, FIS1, and MFF on the proliferation and progression of GBM cells and GSCs using a combination of CCK-8 assay, Transwell assay, Wound Healing assay, tumor spheroid formation assay and cell derived xenograft assay employing NOD/ShiLtJGpt-Prkdcem26Cd52Il2rgem26Cd22/Gpt (NCG) mouse model. Subsequently, we validated the ability of the DNM1L/DRP1-FIS1 axis to remodel MRC structure through mitophagy by utilizing Seahorse XF analysis technology, mitochondrial function detection, MRC abundance detection and monitoring dynamic changes in mitophagy. Results: Our findings revealed that compared to low-grade glioma (LGG), HGG exhibited more integrated MRC structures. Further research revealed that DNM1L/DRP1, FIS1, and MFF played pivotal roles in governing mitochondrial fission and remodeling MRC in HGG. The subsequent validation demonstrated that DNM1L/DRP1 exerts a positive regulatory effect on FIS1, whereas the interaction between MFF and FIS1 demonstrates a competitive inhibition relationship. The down-regulation of the DNM1L/DRP1-FIS1 axis significantly impaired mitophagy, thereby hindering the remodeling of MRC and inhibiting OXPHOS function in glioma, ultimately leading to the inhibition of its aggressive progression. In contrast, MFF exerts a contrasting effect on MRC integrity, OXPHOS activity, and glioma progression. Conclusions: This study highlights that the DNM1L/DRP1-FIS1 axis stabilizes MRC structures through mitophagy in HGG cells while driving their OXPHOS activity ultimately leading to robust disease progression. The inhibition of the DNM1L/DRP1-FIS1 axis hinders MRC remodeling and suppresses GBM progression. We propose that down-regulation of the DNM1L/DRP1-FIS1 axis could be a potential therapeutic strategy for treating HGG. [ABSTRACT FROM AUTHOR]

Abstract Background The dynamics of mitochondrial respiratory cristae (MRC) and its impact on oxidative phosphorylation (OXPHOS) play a crucial role in driving the progression of high-grade glioma (HGG). However, the underlying mechanism remains unclear. Methods In the present study, we employed machine learning-based transmission electron microscopy analysis of 7141 mitochondria from 54 resected glioma patients. Additionally, we conducted bioinformatics analysis and multiplex immunohistochemical (mIHC) staining of clinical glioma microarrays to identify key molecules involved in glioma. Subsequently, we modulated the expression levels of mitochondrial dynamic-1-like protein (DNM1L/DRP1), and its two receptors, mitochondrial fission protein 1 (FIS1) and mitochondrial fission factor (MFF), via lentiviral transfection to further investigate the central role of these molecules in the dynamics of glioblastoma (GBM) cells and glioma stem cells (GSCs). We then evaluated the potential impact of DNM1L/DRP1, FIS1, and MFF on the proliferation and progression of GBM cells and GSCs using a combination of CCK-8 assay, Transwell assay, Wound Healing assay, tumor spheroid formation assay and cell derived xenograft assay employing NOD/ShiLtJGpt-Prkdc em26Cd52 Il2rg em26Cd22/Gpt (NCG) mouse model. Subsequently, we validated the ability of the DNM1L/DRP1-FIS1 axis to remodel MRC structure through mitophagy by utilizing Seahorse XF analysis technology, mitochondrial function detection, MRC abundance detection and monitoring dynamic changes in mitophagy. Results Our findings revealed that compared to low-grade glioma (LGG), HGG exhibited more integrated MRC structures. Further research revealed that DNM1L/DRP1, FIS1, and MFF played pivotal roles in governing mitochondrial fission and remodeling MRC in HGG. The subsequent validation demonstrated that DNM1L/DRP1 exerts a positive regulatory effect on FIS1, whereas the interaction between MFF and FIS1 demonstrates a competitive inhibition relationship. The down-regulation of the DNM1L/DRP1-FIS1 axis significantly impaired mitophagy, thereby hindering the remodeling of MRC and inhibiting OXPHOS function in glioma, ultimately leading to the inhibition of its aggressive progression. In contrast, MFF exerts a contrasting effect on MRC integrity, OXPHOS activity, and glioma progression. Conclusions This study highlights that the DNM1L/DRP1-FIS1 axis stabilizes MRC structures through mitophagy in HGG cells while driving their OXPHOS activity ultimately leading to robust disease progression. The inhibition of the DNM1L/DRP1-FIS1 axis hinders MRC remodeling and suppresses GBM progression. We propose that down-regulation of the DNM1L/DRP1-FIS1 axis could be a potential therapeutic strategy for treating HGG.

Summary: Progression of acute traumatic brain injury (TBI) into chronic neurodegeneration is a major health problem with no protective treatments. Here, we report that acutely elevated mitochondrial fission after TBI in mice triggers chronic neurodegeneration persisting 17 months later, equivalent to many human decades. We show that increased mitochondrial fission after mouse TBI is related to increased brain levels of mitochondrial fission 1 protein (Fis1) and that brain Fis1 is also elevated in human TBI. Pharmacologically preventing Fis1 from binding its mitochondrial partner, dynamin-related protein 1 (Drp1), for 2 weeks after TBI normalizes the balance of mitochondrial fission/fusion and prevents chronically impaired mitochondrial bioenergetics, oxidative damage, microglial activation and lipid droplet formation, blood-brain barrier deterioration, neurodegeneration, and cognitive impairment. Delaying treatment until 8 months after TBI offers no protection. Thus, time-sensitive inhibition of acutely elevated mitochondrial fission may represent a strategy to protect human TBI patients from chronic neurodegeneration.

Abstract Background Acute kidney injury (AKI) is a common clinical disorder with complex etiology and poor prognosis, and currently lacks specific and effective treatment options. Mitochondrial dynamics dysfunction is a prominent feature in AKI, and modulation of mitochondrial morphology may serve as a potential therapeutic approach for AKI. Methods We induced ischemia–reperfusion injury (IRI) in mice (bilateral) and Bama pigs (unilateral) by occluding the renal arteries. ATP depletion and recovery (ATP-DR) was performed on proximal renal tubular cells to simulate in vitro IRI. Renal function was evaluated using creatinine and urea nitrogen levels, while renal structural damage was assessed through histopathological staining. The role of Drp1 was investigated using immunoblotting, immunohistochemistry, immunofluorescence, and immunoprecipitation techniques. Mitochondrial morphology was evaluated using confocal microscopy. Results Renal IRI induced significant mitochondrial fragmentation, accompanied by Dynamin-related protein 1 (Drp1) translocation to the mitochondria and Drp1 phosphorylation at Ser616 in the early stages (30 min after reperfusion), when there was no apparent structural damage to the kidney. The use of the Drp1 inhibitor P110 significantly improved kidney function and structural damage. P110 reduced Drp1 mitochondrial translocation, disrupted the interaction between Drp1 and Fis1, without affecting the binding of Drp1 to other mitochondrial receptors such as MFF and Mid51. High-dose administration had no apparent toxic side effects. Furthermore, ATP-DR induced mitochondrial fission in renal tubular cells, accompanied by a decrease in mitochondrial membrane potential and an increase in the translocation of the pro-apoptotic protein Bax. This process facilitated the release of dsDNA, triggering the activation of the cGAS-STING pathway and promoting inflammation. P110 attenuated mitochondrial fission, suppressed Bax mitochondrial translocation, prevented dsDNA release, and reduced the activation of the cGAS-STING pathway. Furthermore, these protective effects of P110 were also observed renal IRI model in the Bama pig and folic acid-induced nephropathy in mice. Conclusions Dysfunction of mitochondrial dynamics mediated by Drp1 contributes to renal IRI. The specific inhibitor of Drp1, P110, demonstrated protective effects in both in vivo and in vitro models of AKI.

Myocardial infarction is characterized by cardiomyocyte death, and can be exacerbated by mitochondrial damage and endoplasmic reticulum injury. In the present study, we investigated whether communication between mitochondria and the endoplasmic reticulum contributes to cardiomyocyte death after myocardial infarction. Our data demonstrated that hypoxia treatment (mimicking myocardial infarction) promoted cardiomyocyte death by inducing the c-Jun N-terminal kinase (JNK) pathway. The activation of JNK under hypoxic conditions was dependent on overproduction of mitochondrial reactive oxygen species (mtROS) in cardiomyocytes, and mitochondrial division was identified as the upstream inducer of mtROS overproduction. Silencing mitochondrial division activators, such as B cell receptor associated protein 31 (BAP31) and mitochondrial fission 1 (Fis1), repressed mitochondrial division, thereby inhibiting mtROS overproduction and preventing JNK-induced cardiomyocyte death under hypoxic conditions. These data revealed that a novel death-inducing mechanism involving the BAP31/Fis1/mtROS/JNK axis promotes hypoxia-induced cardiomyocyte damage. Considering that BAP31 is localized within the endoplasmic reticulum and Fis1 is localized in mitochondria, abnormal mitochondria-endoplasmic reticulum communication may be a useful therapeutic target after myocardial infarction. [ABSTRACT FROM AUTHOR]

Background: Acute kidney injury (AKI) is a common clinical disorder with complex etiology and poor prognosis, and currently lacks specific and effective treatment options. Mitochondrial dynamics dysfunction is a prominent feature in AKI, and modulation of mitochondrial morphology may serve as a potential therapeutic approach for AKI. Methods: We induced ischemia–reperfusion injury (IRI) in mice (bilateral) and Bama pigs (unilateral) by occluding the renal arteries. ATP depletion and recovery (ATP-DR) was performed on proximal renal tubular cells to simulate in vitro IRI. Renal function was evaluated using creatinine and urea nitrogen levels, while renal structural damage was assessed through histopathological staining. The role of Drp1 was investigated using immunoblotting, immunohistochemistry, immunofluorescence, and immunoprecipitation techniques. Mitochondrial morphology was evaluated using confocal microscopy. Results: Renal IRI induced significant mitochondrial fragmentation, accompanied by Dynamin-related protein 1 (Drp1) translocation to the mitochondria and Drp1 phosphorylation at Ser616 in the early stages (30 min after reperfusion), when there was no apparent structural damage to the kidney. The use of the Drp1 inhibitor P110 significantly improved kidney function and structural damage. P110 reduced Drp1 mitochondrial translocation, disrupted the interaction between Drp1 and Fis1, without affecting the binding of Drp1 to other mitochondrial receptors such as MFF and Mid51. High-dose administration had no apparent toxic side effects. Furthermore, ATP-DR induced mitochondrial fission in renal tubular cells, accompanied by a decrease in mitochondrial membrane potential and an increase in the translocation of the pro-apoptotic protein Bax. This process facilitated the release of dsDNA, triggering the activation of the cGAS-STING pathway and promoting inflammation. P110 attenuated mitochondrial fission, suppressed Bax mitochondrial translocation, prevented dsDNA release, and reduced the activation of the cGAS-STING pathway. Furthermore, these protective effects of P110 were also observed renal IRI model in the Bama pig and folic acid-induced nephropathy in mice. Conclusions: Dysfunction of mitochondrial dynamics mediated by Drp1 contributes to renal IRI. The specific inhibitor of Drp1, P110, demonstrated protective effects in both in vivo and in vitro models of AKI. [ABSTRACT FROM AUTHOR]

Background: We aimed to elucidate the mechanism of change in mitochondrial fusion- and fission-related mediators for maintaining cell function through the effects of acupuncture treatment and apply findings to a liver disease model. We focused on the optic atrophy-1 (OPA1) and fission protein 1 (Fis1) genes of rat liver cells. Methods: Sprague Dawley rats were divided into a control group (no treatment) and LR2, LR3, LR4 and LR8 groups (acupuncture treatment to those points). Acupuncture was performed on each point for 10 minutes once daily for 4 days. Changes in the mRNA expression of Peroxisome proliferator-activated receptor-gamma coactivator 1-a (PGC-1a) and Fis1 were observed via quantitative real-time polymerase chain reaction (qRT-PCR); changes in OPA1, mitofusin-2 (MFN2), mitofusin-1 (MFN1), dynamin-related protein 1 (DRP1) and adenosine monophosphate-activated protein kinase (AMPK) proteins were observed through western blotting and endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) expressions were observed through immunohistochemistry. Result: OPA1 decreased in the LR3 and LR8 groups and Fis1 increased in the LR2 and LR4 groups. AMPK and PGC-1a decreased significantly in all acupuncture groups. eNOS and nNOS expression reduced in all acupuncture groups. Therefore, acupuncture can regulate mitochondrial fusion/fission by influencing the following mediators: AMPK, PGC-1a, OPA1, Fis1, eNOS and nNOS. [ABSTRACT FROM AUTHOR]

Triptolide (TP) has various pharmacological activities, but its hepatotoxicity limits its therapeutic potential. Licorice has been evaluated to harmonize various medicines, and its active ingredient glycyrrhizic acid (GA) has been identified for its detoxification effect. In this study, we demonstrated that the combination of GA and TP (G&T) could mitigate TP-induced hepatotoxicity. To explore TP toxicity and G&T detoxification mechanisms, transcriptomics and proteomics have been utilized. TP was found to promote the expression of PKCα and FIS1, accompanied by an increase in mitochondrial fission. After pretreatment with GA, improvements were observed in TP-induced mitochondrial fission, as well as the expression of active-caspase3, and cytochrome c release. Silencing PKCα and FIS1 has a similar effect to GA on the regulation of mitochondria-dependent apoptosis and mitochondrial fission. In conclusion, PKCα and FIS1-involved mitochondrial dynamic regulation is associated with TP-induced hepatotoxicity. The G&T combination may be an effective strategy for ameliorating TP-induced toxicity.

Background : A significant amount of research has been conducted to establish the validity of acupuncture, and it has been demonstrated through animal disease model studies that acupuncture influences mitochondrial changes. However, to more accurately examine the mechanisms of acupuncture treatment effectiveness in pathological models, it is crucial to investigate changes in disease-free animals. Among various hypotheses regarding the effects of acupuncture on the body, we focused on the result that acupuncture stimulation is related to mitochondria. Objectives: We examined the effects of acupuncture mitochondrial fission and fusionrelated mediators in disease-free Sprague Dawley (SD) rats' spleen meridian acupoints. Methods : SD rats were divided into control, SP1, SP2, SP3, SP5, and SP9 acupuncture groups. Acupuncture was performed at each point for 10 minutes daily for four days. Peroxisome proliferator-activated receptor-gamma coactivator 1-α (PGC-1α) and fission protein 1 (Fis1) levels were evaluated using quantitative real-time polymerase chain reaction (qRT-PCR), while dynamin-related protein 1 (DRP1), optic atrophy-1 (OPA1), mitofusin-1 (MFN1), and mitofusin-2 (MFN2) levels were assessed via western blotting. Mitochondria protein concentrations and NADH dehydrogenase activity in spleen tissues were measured using enzyme-linked immunosorbent assay (ELISA). Results : PGC-1α expression decreased in the SP1 (p < 0.01), SP5 (p < 0.05), and SP9 (p < 0.05) groups, while Fis1 expression increased in the SP1 (p < 0.01), SP5 (p < 0.01), and SP9 (p < 0.05) groups. DRP1, OPA1, MFN1, and MFN2 levels exhibited no significant changes. Mitochondrial protein concentrations decreased in the SP2 (p < 0.01), SP3 (p < 0.01), SP5 (p < 0.01), and SP9 (p < 0.01) groups, while NADH dehydrogenase activity decreased in the SP2 (p < 0.05) and SP9 (p < 0.05) groups. Conclusion : Acupuncture at the SP9 acupoint influenced the mitochondrial fission pathway by modulating PGC-1α and Fis1 mediators in the rat spleen under non-disease conditions.

Mitochondrial dynamics plays a significant role in shaping the mitochondrial network and maintaining mitochondrial function. Imbalanced mitochondrial dynamics can cause mitochondrial dysfunction leading to a wide range of diseases/disorders. The aim of this study was to investigate the expression of mitochondrial dynamics markers and regulatory molecules in whole adrenal glands, cortices, and medullae obtained from adult male rats exposed to acute and repeated psychophysical stress, the most common stress in human society. The transcriptional profiles of most of the mitochondrial dynamics markers investigated here were altered: 81%-(17/21) in the whole adrenal gland, 76.2%-(16/21) in the adrenal cortex, and 85.7%-(18/21) in the adrenal medulla. Changes were evident in representatives of every process of mitochondrial dynamics. Markers of mitobiogenesis were changed up to 62.5%-(5/8) in the whole adrenal gland, 62.5%-(5/8) in the adrenal cortex, and 87.5%-(7/8) in the adrenal medulla. Markers of mitofusion were changed up to 100%-(3/3) in the whole adrenal gland, 66.7%-(5/8) in the adrenal cortex, and 87.5%-(7/8) in the adrenal medulla, while all markers of mitofission and mitophagy were changed in the adrenal glands. Moreover, almost all markers of mitochondrial functionality were changed: 83.3%-(5/6) in the whole adrenal, 83.3%-(5/6) in the cortex, 66.7%-(4/6) in the medulla. Accordingly, the study highlights the significant impact of acute and repeated stress on mitochondrial dynamics in the adrenal gland. [ABSTRACT FROM AUTHOR]

Cells from glioblastoma multiforme (GBM) feature up-regulation of the mechanistic Target of Rapamycin (mTOR), which brings deleterious effects on malignancy and disease course. At the cellular level, up-regulation of mTOR affects a number of downstream pathways and suppresses autophagy, which is relevant for the neurobiology of GBM. In fact, autophagy acts on several targets, such as protein clearance and mitochondrial status, which are key in promoting the malignancy GBM. A defective protein clearance extends to cellular prion protein (PrPc). Recent evidence indicates that PrPc promotes stemness and alters mitochondrial turnover. Therefore, the present study measures whether in GBM cells abnormal amount of PrPc and mitochondrial alterations are concomitant in baseline conditions and whether they are reverted by mTOR inhibition. Proteins related to mitochondrial turnover were concomitantly assessed. High amounts of PrPc and altered mitochondria were both mitigated dose-dependently by the mTOR inhibitor rapamycin, which produced a persistent activation of the autophagy flux and shifted proliferating cells from S to G1 cell cycle phase. Similarly, mTOR suppression produces a long-lasting increase of proteins promoting mitochondrial turnover, including Pink1/Parkin. These findings provide novel evidence about the role of autophagy in the neurobiology of GBM. [ABSTRACT FROM AUTHOR]

Background: Aging can increase the risks of various liver diseases and act as an unfavorable prognostic factor and increase mortality. Therefore, this study aimed to investigate the effect of 8-week resistance training with liposomal vitamin C on the expression of UCP1 and FIS1 in hepatocytes of elderly rats. Material and Methods: The present study was an experimental study with a control group. Twenty-five male rats (Wistar) aged 24 weeks (280-320 g) were randomly divided into 5 groups; young control group, elderly + resistance training group, elderly + liposomal vitamin C group, elderly + resistance training + liposomal vitamin C group and old age control group. In the groups receiving liposomal vitamin C, liposomal vitamin C was administered daily based on kilograms of body weight. Results: UCP1 expression was significantly reduced in the elderly group compared to the young group (P=0.001). However, the expression of UCP1 in the elderly group + resistance training along with vitamin C consumption increased significantly compared to the elderly group (P=0.001). Also, FIS1 expression was significantly increased in the elderly group compared to the young group (P=0.001). However, the expression of FIS1 in the elderly group + resistance training with vitamin C consumption was significantly reduced compared to the young group (P=0.001). Results: Aging increases FIS1 expression and decreases UCP1 expression in rat liver tissue. However, resistance training with vitamin C decreases FIS1 expression and increases UCP1 expression in elderly rats

ABSTRACTThe diarrheagenic pathogen enteropathogenic Escherichia coli is responsible for significant childhood mortality and morbidity. EPEC and related attaching-and-effacing (A/E) pathogens use a type III secretion system to hierarchically deliver effector proteins into host cells and manipulate epithelial structure and function. Subversion of host mitochondrial biology is a key aspect of A/E pathogen virulence strategy, but the mechanisms remain poorly defined. We demonstrate that the early-secreted effector EspZ and the late-secreted effector EspH have contrasting effects on host mitochondrial structure and function. EspZ interacts with FIS1, a protein that induces mitochondrial fragmentation and mitophagy. Infection of epithelial cells with either wildtype EPEC or an isogenic espZ deletion mutant (ΔespZ) robustly upregulated FIS1 abundance, but a marked increase in mitochondrial fragmentation and mitophagy was seen only in ΔespZ-infected cells. FIS1-depleted cells were protected against ΔespZ-induced fission, and EspZ-expressing transfected epithelial cells were protected against pharmacologically induced mitochondrial fission and membrane potential disruption. Thus, EspZ interacts with FIS1 and blocks mitochondrial fragmentation and mitophagy. In contrast to WT EPEC, ΔespH-infected epithelial cells had minimal FIS1 upregulation and exhibited hyperfused mitochondria. Consistent with the contrasting impacts on organelle shape, mitochondrial membrane potential was preserved in ΔespH-infected cells, but profoundly disrupted in ΔespZ-infected cells. Collectively, our studies reveal hitherto unappreciated roles for two essential EPEC virulence factors in the temporal and dynamic regulation of host mitochondrial biology.

Recent evidence shows that methamphetamine (METH) produces mitochondrial alterations that contribute to neurotoxicity. Nonetheless, most of these studies focus on mitochondrial activity, whereas mitochondrial morphology remains poorly investigated. In fact, morphological evidence about the fine structure of mitochondria during METH toxicity is not available. Thus, in the present study we analyzed dose-dependent mitochondrial structural alterations during METH exposure. Light and transmission electron microscopy were used, along with ultrastructural stoichiometry of catecholamine cells following various doses of METH. In the first part of the study cell death and cell degeneration were assessed and they were correlated with mitochondrial alterations observed using light microscopy. In the second part of the study, ultrastructural evidence of specific mitochondrial alterations of crests, inner and outer membranes and matrix were quantified, along with in situ alterations of mitochondrial proteins. Neurodegeneration induced by METH correlates significantly with specific mitochondrial damage, which allows definition of a scoring system for mitochondrial integrity. In turn, mitochondrial alterations are concomitant with a decrease in fission/mitophagy protein Fis1 and DRP1 and an increase in Pink1 and Parkin in situ, at the mitochondrial level. These findings provide structural evidence that mitochondria represent both direct and indirect targets of METH-induced toxicity. [ABSTRACT FROM AUTHOR]

Peroxisomes are highly dynamic and responsive organelles, which can adjust their morphology, number, intracellular position, and metabolic functions according to cellular needs. Peroxisome multiplication in mammalian cells involves the concerted action of the membrane-shaping protein PEX11β and division proteins, such as the membrane adaptors FIS1 and MFF, which recruit the fission GTPase DRP1 to the peroxisomal membrane. The latter proteins are also involved in mitochondrial division. Patients with loss of DRP1, MFF or PEX11β function have been identified, showing abnormalities in peroxisomal (and, for the shared proteins, mitochondrial) dynamics as well as developmental and neurological defects, whereas the metabolic functions of the organelles are often unaffected. Here, we provide a timely update on peroxisomal membrane dynamics with a particular focus on peroxisome formation by membrane growth and division. We address the function of PEX11β in these processes, as well as the role of peroxisome–ER contacts in lipid transfer for peroxisomal membrane expansion. Furthermore, we summarize the clinical phenotypes and pathophysiology of patients with defects in the key division proteins DRP1, MFF, and PEX11β as well as in the peroxisome–ER tether ACBD5. Potential therapeutic strategies for these rare disorders with limited treatment options are discussed. [ABSTRACT FROM AUTHOR]

Background: Due to poor prognosis and treatment failure, gastric cancer (GC) is still regarded as one of the deadliest malignancies worldwide, demanding new molecular targets for therapeutic and diagnostic approaches. Therefore, the current study was aimed to investigate the expression levels of FIS1 gene involving in mitochondrial fission as a promising target in gastric tumor progression. Material and Methods: A total of eighty clinical tissue samples including 40 gastric primary tumor samples and 40 paired marginal samples were prepared. Total RNA was extracted and reverse transcribed to complementary DNA. Then, FIS1 expression levels were quantified in GC samples compared to normal ones using q-PCR. Furthermore, the correlation between FIS1 expression and clinicopathological features of patients was evaluated. Results: The obtained results illustrated that FIS1 is significantly (p = 0.0013) overexpressed in gastric tumors compared to noncancerous marginal tissues; indicating the possible role of FIS1 through gastric tumorigenesis. Further analysis showed that FIS1 upregulation was significantly (p = 0.0419) correlated with metastasis in patients. Also, ROC curve analysis estimated an area under the curve (AUC) value of 0.7209 for FIS1 to discriminate cancer patients from healthy cases. Conclusion: Taken together, our findings suggested FIS1 as a promising tumor marker where its overexpression predicts tumor metastasis of gastric cancer. [ABSTRACT FROM AUTHOR]

Mitophagy, a form of autophagy, plays a role in cancer development, progression and recurrence. Cancer stem cells (CSCs) also play a key role in these processes, although it not known whether mitophagy can regulate the stemness of CSCs. Here, we employed the A549‐SD human non‐small cell lung adenocarcinoma CSC model that we have developed and characterized to investigate the effect of mitophagy on the stemness of CSCs. We observed a positive relationship between mitophagic activity and the stemness of lung CSCs. At the mechanistic level, our results suggest that augmentation of mitophagy in lung CSCs can be induced by FIS1 through mitochondrial fission. In addition, we assessed the clinical relevance of FIS1 in lung adenocarcinoma using The Cancer Genome Atlas database. An elevation in FIS1, when observed together with other prognostic markers for lung cancer progression, was found to correlate with shorter overall survival.

Mitochondria are unavoidably subject to organellar stress resulting from exposure to a range of reactive molecular species. Consequently, cells operate a poorly understood quality control programme of mitophagy to facilitate elimination of dysfunctional mitochondria. Here, we used a model stressor, deferiprone (DFP), to investigate the molecular basis for stress‐induced mitophagy. We show that mitochondrial fission 1 protein (Fis1) is required for DFP‐induced mitophagy and that Fis1 is SUMOylated at K149, an amino acid residue critical for Fis1 mitochondrial localization. We find that DFP treatment leads to the stabilization of the SUMO protease SENP3, which is mediated by downregulation of the E3 ubiquitin (Ub) ligase CHIP. SENP3 is responsible for Fis1 deSUMOylation and depletion of SENP3 abolishes DFP‐induced mitophagy. Furthermore, preventing Fis1 SUMOylation by conservative K149R mutation enhances Fis1 mitochondrial localization. Critically, expressing a Fis1 K149R mutant restores DFP‐induced mitophagy in SENP3‐depleted cells. Thus, we propose a model in which SENP3‐mediated deSUMOylation facilitates Fis1 mitochondrial localization to underpin stress‐induced mitophagy. Synopsis: SENP3‐mediated deSUMO‐2/3‐ylation of Fis1 promotes mitophagy induced by deferiprone (DFP). SENP3 is stabilized by DFP treatment that downregulates the E3 ubiquitin ligase CHIP, and is required for DFP‐induced mitophagy.Fis1 is essential for DFP‐induced mitophagy and is a target for SUMO‐2/3‐ylation.SENP3 is responsible for Fis1 deSUMO‐2/3‐ylation at K149.SENP3 facilitates DFP‐induced mitophagy via deSUMOylating Fis1. [ABSTRACT FROM AUTHOR]

Selective brain hypothermia is considered an effective treatment for neuronal injury after stroke, and avoids the complications of general hypothermia. However, the mechanisms by which selective brain hypothermia affects mitochondrial fission remain unknown. In this study, we investigated the effect of selective brain hypothermia on the expression of fission 1 (Fis1) protein, a key factor in the mitochondrial fission system, during focal cerebral ischemia/reperfusion injury. Sprague-Dawley rats were divided into four groups. In the sham group, the carotid arteries were exposed only. In the other three groups, middle cerebral artery occlusion was performed using the intraluminal filament technique. After 2 hours of occlusion, the filament was slowly removed to allow blood reperfusion in the ischemia/reperfusion group. Saline, at 4°C and 37°C, were perfused through the carotid artery in the hypothermia and normothermia groups, respectively, followed by restoration of blood flow. Neurological function was assessed with the Zea Longa 5-point scoring method. Cerebral infarct volume was assessed by 2,3,5-triphenyltetrazolium chloride staining, and apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. Fis1 and cytosolic cytochrome c levels were assessed by western blot assay. Fis1 mRNA expression was assessed by quantitative reverse transcription-polymerase chain reaction. Mitochondrial ultrastructure was evaluated by transmission electron microscopy. Compared with the sham group, apoptosis, Fis1 protein and mRNA expression and cytosolic cytochrome c levels in the cortical ischemic penumbra and cerebral infarct volume were increased after reperfusion in the other three groups. These changes caused by cerebral ischemia/reperfusion were inhibited in the hypothermia group compared with the normothermia group. These findings show that selective brain hypothermia inhibits Fis1 expression and reduces apoptosis, thereby ameliorating focal cerebral ischemia/reperfusion injury in rats. Experiments were authorized by the Ethics Committee of Qingdao Municipal Hospital of China (approval No. 2019008).

Cells from glioblastoma multiforme (GBM) feature up-regulation of the mechanistic Target of Rapamycin (mTOR), which brings deleterious effects on malignancy and disease course. At the cellular level, up-regulation of mTOR affects a number of downstream pathways and suppresses autophagy, which is relevant for the neurobiology of GBM. In fact, autophagy acts on several targets, such as protein clearance and mitochondrial status, which are key in promoting the malignancy GBM. A defective protein clearance extends to cellular prion protein (PrPc). Recent evidence indicates that PrPc promotes stemness and alters mitochondrial turnover. Therefore, the present study measures whether in GBM cells abnormal amount of PrPc and mitochondrial alterations are concomitant in baseline conditions and whether they are reverted by mTOR inhibition. Proteins related to mitochondrial turnover were concomitantly assessed. High amounts of PrPc and altered mitochondria were both mitigated dose-dependently by the mTOR inhibitor rapamycin, which produced a persistent activation of the autophagy flux and shifted proliferating cells from S to G1 cell cycle phase. Similarly, mTOR suppression produces a long-lasting increase of proteins promoting mitochondrial turnover, including Pink1/Parkin. These findings provide novel evidence about the role of autophagy in the neurobiology of GBM.

Myocardial infarction is characterized by cardiomyocyte death, and can be exacerbated by mitochondrial damage and endoplasmic reticulum injury. In the present study, we investigated whether communication between mitochondria and the endoplasmic reticulum contributes to cardiomyocyte death after myocardial infarction. Our data demonstrated that hypoxia treatment (mimicking myocardial infarction) promoted cardiomyocyte death by inducing the c-Jun N-terminal kinase (JNK) pathway. The activation of JNK under hypoxic conditions was dependent on overproduction of mitochondrial reactive oxygen species (mtROS) in cardiomyocytes, and mitochondrial division was identified as the upstream inducer of mtROS overproduction. Silencing mitochondrial division activators, such as B cell receptor associated protein 31 (BAP31) and mitochondrial fission 1 (Fis1), repressed mitochondrial division, thereby inhibiting mtROS overproduction and preventing JNK-induced cardiomyocyte death under hypoxic conditions. These data revealed that a novel death-inducing mechanism involving the BAP31/Fis1/mtROS/JNK axis promotes hypoxia-induced cardiomyocyte damage. Considering that BAP31 is localized within the endoplasmic reticulum and Fis1 is localized in mitochondria, abnormal mitochondria-endoplasmic reticulum communication may be a useful therapeutic target after myocardial infarction.

Myocardial infarction is characterized by cardiomyocyte death, and can be exacerbated by mitochondrial damage and endoplasmic reticulum injury. In the present study, we investigated whether communication between mitochondria and the endoplasmic reticulum contributes to cardiomyocyte death after myocardial infarction. Our data demonstrated that hypoxia treatment (mimicking myocardial infarction) promoted cardiomyocyte death by inducing the c-Jun N-terminal kinase (JNK) pathway. The activation of JNK under hypoxic conditions was dependent on overproduction of mitochondrial reactive oxygen species (mtROS) in cardiomyocytes, and mitochondrial division was identified as the upstream inducer of mtROS overproduction. Silencing mitochondrial division activators, such as B cell receptor associated protein 31 (BAP31) and mitochondrial fission 1 (Fis1), repressed mitochondrial division, thereby inhibiting mtROS overproduction and preventing JNK-induced cardiomyocyte death under hypoxic conditions. These data revealed that a novel death-inducing mechanism involving the BAP31/Fis1/mtROS/JNK axis promotes hypoxia-induced cardiomyocyte damage. Considering that BAP31 is localized within the endoplasmic reticulum and Fis1 is localized in mitochondria, abnormal mitochondria-endoplasmic reticulum communication may be a useful therapeutic target after myocardial infarction. [ABSTRACT FROM AUTHOR]

Mitophagy, a form of autophagy, plays a role in cancer development, progression and recurrence. Cancer stem cells (CSCs) also play a key role in these processes, although it not known whether mitophagy can regulate the stemness of CSCs. Here, we employed the A549‐SD human non‐small cell lung adenocarcinoma CSC model that we have developed and characterized to investigate the effect of mitophagy on the stemness of CSCs. We observed a positive relationship between mitophagic activity and the stemness of lung CSCs. At the mechanistic level, our results suggest that augmentation of mitophagy in lung CSCs can be induced by FIS1 through mitochondrial fission. In addition, we assessed the clinical relevance of FIS1 in lung adenocarcinoma using The Cancer Genome Atlas database. An elevation in FIS1, when observed together with other prognostic markers for lung cancer progression, was found to correlate with shorter overall survival. [ABSTRACT FROM AUTHOR]

Increased levels of dysfunctional mitochondria within skeletal muscle are correlated with numerous age‐related physiopathological conditions. Improving our understanding of the links between mitochondrial function and muscle proteostasis, and the role played by individual genes and regulatory networks, is essential to develop treatments for these conditions. One potential player is the mitochondrial outer membrane protein Fis1, a crucial fission factor heavily involved in mitochondrial dynamics in yeast but with an unknown role in higher‐order organisms. By using Drosophila melanogaster as a model, we explored the effect of Fis1 mutations generated by transposon Minos‐mediated integration. Mutants exhibited a higher ratio of damaged mitochondria with age as well as elevated reactive oxygen species levels compared with controls. This caused an increase in oxidative stress, resulting in large accumulations of ubiquitinated proteins, accelerated muscle function decline, and mitochondrial myopathies in young mutant flies. Ectopic expression of Fis1 isoforms was sufficient to suppress this phenotype. Loss of Fis1 led to unbalanced mitochondrial proteostasis within fly muscle, decreasing both flight capabilities and lifespan. Fis1 thus clearly plays a role in fly mitochondrial dynamics. Further investigations into the detailed function of Fis1 are necessary for exploring how mitochondrial function correlates with muscle health during aging. [ABSTRACT FROM AUTHOR]

Mitochondrial fission protein 1 (Fis1) was identified in yeast as being essential for mitochondrial division or fission and subsequently determined to mediate human mitochondrial and peroxisomal fission. Yet, its exact functions in humans, especially in regard to mitochondrial fission, remains an enigma as genetic deletion of Fis1 elongates mitochondria in some cell types, but not others. Fis1 has also been identified as an important component of apoptotic and mitophagic pathways suggesting the protein may have multiple, essential roles. This review presents current perspectives on the emerging functions of Fis1 and their implications in human health and diseases, with an emphasis on Fis1’s role in both endocrine and neurological disorders.

Mitochondrial fission protein 1 (Fis1) was identified in yeast as being essential for mitochondrial division or fission and subsequently determined to mediate human mitochondrial and peroxisomal fission. Yet, its exact functions in humans, especially in regard to mitochondrial fission, remains an enigma as genetic deletion of Fis1 elongates mitochondria in some cell types, but not others. Fis1 has also been identified as an important component of apoptotic and mitophagic pathways suggesting the protein may have multiple, essential roles. This review presents current perspectives on the emerging functions of Fis1 and their implications in human health and diseases, with an emphasis on Fis1's role in both endocrine and neurological disorders. [ABSTRACT FROM AUTHOR]

ABSTRACT Malaria remains a huge global health burden, and control of this disease has run into a severe bottleneck. To defeat malaria and reach the goal of eradication, a deep understanding of the parasite biology is urgently needed. The mitochondrion of the malaria parasite is essential throughout the parasite’s life cycle and has been validated as a clinical drug target. In the asexual development of Plasmodium spp., the single mitochondrion grows from a small tubular structure to a complex branched network. This branched mitochondrion is divided at the end of schizogony when 8 to 32 daughter cells are produced, distributing one mitochondrion to each forming merozoite. In mosquito and liver stages, the giant mitochondrial network is split into thousands of pieces and daughter mitochondria are segregated into individual progeny. Despite the significance of mitochondrial fission in Plasmodium, the underlying mechanism is largely unknown. Studies of mitochondrial fission in model eukaryotes have revealed that several mitochondrial fission adaptor proteins are involved in recruiting dynamin GTPases to physically split mitochondrial membranes. Apicomplexan parasites, however, share no identifiable homologs of mitochondrial fission adaptor proteins with yeast or humans, except for Fis1. Here, we investigated the localization and essentiality of the Fis1 homolog in Plasmodium falciparum, PfFis1 (PF3D7_1325600), during the asexual life cycle. We found that PfFis1 requires an intact C terminus for mitochondrial localization but is not essential for parasite development or mitochondrial fission. The dispensable role of PfFis1 indicates that Plasmodium contains additional fission adaptor proteins on the mitochondrial outer membrane that could be essential for mitochondrial fission. IMPORTANCE Malaria is responsible for over 230 million clinical cases and ∼half a million deaths each year. The single mitochondrion of the malaria parasite functions as a metabolic hub throughout the parasite’s developmental cycle (DC) and also as a source of ATP in certain stages. To pass on its essential functions, the parasite’s mitochondrion needs to be properly divided and segregated into all progeny during cell division via a process termed mitochondrial fission. Due to the divergent nature of Plasmodium spp., the molecular players involved in mitochondrial fission and their mechanisms of action remain largely unknown. Here, we found that the only identifiable mitochondrial fission adaptor protein that is evolutionarily conserved in the Apicomplexan phylum, Fis1, it not essential in P. falciparum asexual stages. Our data suggest that malaria parasites use redundant fission adaptor proteins on the mitochondrial outer membrane to mediate the fission process.

ABSTRACT Toxoplasma gondii’s single mitochondrion is very dynamic and undergoes morphological changes throughout the parasite’s life cycle. During parasite division, the mitochondrion elongates, enters the daughter cells just prior to cytokinesis, and undergoes fission. Extensive morphological changes also occur as the parasite transitions from the intracellular environment to the extracellular environment. We show that treatment with the ionophore monensin causes reversible constriction of the mitochondrial outer membrane and that this effect depends on the function of the fission-related protein Fis1. We also observed that mislocalization of the endogenous Fis1 causes a dominant-negative effect that affects the morphology of the mitochondrion. As this suggests that Fis1 interacts with proteins critical for maintenance of mitochondrial structure, we performed various protein interaction trap screens. In this manner, we identified a novel outer mitochondrial membrane protein, LMF1, which is essential for positioning of the mitochondrion in intracellular parasites. Normally, while inside a host cell, the parasite mitochondrion is maintained in a lasso shape that stretches around the parasite periphery where it has regions of coupling with the parasite pellicle, suggesting the presence of membrane contact sites. In intracellular parasites lacking LMF1, the mitochondrion is retracted away from the pellicle and instead is collapsed, as normally seen only in extracellular parasites. We show that this phenotype is associated with defects in parasite fitness and mitochondrial segregation. Thus, LMF1 is necessary for mitochondrial association with the parasite pellicle during intracellular growth, and proper mitochondrial morphology is a prerequisite for mitochondrial division. IMPORTANCE Toxoplasma gondii is an opportunistic pathogen that can cause devastating tissue damage in the immunocompromised and congenitally infected. Current therapies are not effective against all life stages of the parasite, and many cause toxic effects. The single mitochondrion of this parasite is a validated drug target, and it changes its shape throughout its life cycle. When the parasite is inside a cell, the mitochondrion adopts a lasso shape that lies in close proximity to the pellicle. The functional significance of this morphology is not understood and the proteins involved are currently not known. We have identified a protein that is required for proper mitochondrial positioning at the periphery and that likely plays a role in tethering this organelle. Loss of this protein results in dramatic changes to the mitochondrial morphology and significant parasite division and propagation defects. Our results give important insight into the molecular mechanisms regulating mitochondrial morphology.

Peroxisomes are essential for a number of cellular functions, including reactive oxygen species metabolism, fatty acid β‐oxidation and lipid synthesis. To ensure optimal functionality, peroxisomal size, shape and number must be dynamically maintained; however, many aspects of how this is regulated remain poorly characterised. Here, we show that the localisation of Miro1 and Miro2—outer mitochondrial membrane proteins essential for mitochondrial trafficking—to peroxisomes is not required for basal peroxisomal distribution and long‐range trafficking, but rather for the maintenance of peroxisomal size and morphology through peroxisomal fission. Mechanistically, this is achieved by Miro negatively regulating Drp1‐dependent fission, a function that is shared with the mitochondria. We further find that the peroxisomal localisation of Miro is regulated by its first GTPase domain and is mediated by an interaction through its transmembrane domain with the peroxisomal‐membrane protein chaperone, Pex19. Our work highlights a shared regulatory role of Miro in maintaining the morphology of both peroxisomes and mitochondria, supporting a crosstalk between peroxisomal and mitochondrial biology. Synopsis: Miro1 and Miro2 localise to peroxisomes but do not regulate basal microtubule‐dependent peroxisomal distribution. Instead, they modulate peroxisomal size and abundance. The targeting of Miro to peroxisomes is regulated by its first GTPase domain and binding of Pex19 to Miro's transmembrane domain.Miro is not required for basal long‐range peroxisomal distribution.Miro negatively regulates the recruitment of Drp1 to peroxisomes to modulate fission. [ABSTRACT FROM AUTHOR]

[Display omitted] • TP-induced hepatotoxicity is associated with mitochondrial dynamic. • TP interferes with mitochondrial dynamics through PKCα and FIS1. • The G&T combination can reduce TP-induced hepatotoxicity. • The G&T combination inhibited the up-regulation of FIS1. Triptolide (TP) has various pharmacological activities, but its hepatotoxicity limits its therapeutic potential. Licorice has been evaluated to harmonize various medicines, and its active ingredient glycyrrhizic acid (GA) has been identified for its detoxification effect. In this study, we demonstrated that the combination of GA and TP (G&T) could mitigate TP-induced hepatotoxicity. To explore TP toxicity and G&T detoxification mechanisms, transcriptomics and proteomics have been utilized. TP was found to promote the expression of PKCα and FIS1, accompanied by an increase in mitochondrial fission. After pretreatment with GA, improvements were observed in TP-induced mitochondrial fission, as well as the expression of active-caspase3, and cytochrome c release. Silencing PKCα and FIS1 has a similar effect to GA on the regulation of mitochondria-dependent apoptosis and mitochondrial fission. In conclusion, PKCα and FIS1-involved mitochondrial dynamic regulation is associated with TP-induced hepatotoxicity. The G&T combination may be an effective strategy for ameliorating TP-induced toxicity. [ABSTRACT FROM AUTHOR]

Glioblastoma (GBM) cells feature mitochondrial alterations, which are documented and quantified in the present study, by using ultrastructural morphometry. Mitochondrial impairment, which roughly occurs in half of the organelles, is shown to be related to mTOR overexpression and autophagy suppression. The novelty of the present study consists of detailing an mTOR-dependent mitophagy occlusion, along with suppression of mitochondrial fission. These phenomena contribute to explain the increase in altered mitochondria reported here. Administration of the mTOR inhibitor rapamycin rescues mitochondrial alterations. In detail, rapamycin induces the expression of genes promoting mitophagy (PINK1, PARKIN, ULK1, AMBRA1) and mitochondrial fission (FIS1, DRP1). This occurs along with over-expression of VPS34, an early gene placed upstream in the autophagy pathway. The topographic stoichiometry of proteins coded by these genes within mitochondria indicates that, a remarkable polarization of proteins involved in fission and mitophagy within mitochondria including LC3 takes place. Co-localization of these proteins within mitochondria, persists for weeks following rapamycin, which produces long-lasting mitochondrial plasticity. Thus, rapamycin restores mitochondrial status in GBM cells. These findings add novel evidence about mitochondria and GBM, while fostering a novel therapeutic approach to restore healthy mitochondria through mTOR inhibition.

SS-31 is a kind of mitochondrion-targeted peptide. Recent studies indicated significant neuroprotective effects of SS-31. In this study, we investigated that SS-31 protected the murine cultured microglial cells (BV-2) against lipopolysaccharide (LPS)-induced inflammation and oxidative stress through stabilizing mitochondrial morphology. The morphological study showed that SS-31 preserved LPS-induced mitochondrial ultrastructure by reducing the fission protein 1 (Fis1) expression. Flow cytometry and Western blot verified that SS-31 defended the BV-2 cells against LPS-stimulated inflammation and oxidative stress via suppressing Fis1. To sum up, our study represents that SS-31 preserves BV-2 cells from LPS-stimulated inflammation and oxidative stress by down-regulating the Fis1 expression. • SS-31 effectively protected BV-2 cells from LPS-induced inflammation and oxidative stress. • Fis1 over-expression could increase inflammation and oxidative stress in BV-2 cells, while down-regulation of Fis1 expression got the opposite result. • The protective effect of SS-31 could be associated with its inhibition of Fis1. [ABSTRACT FROM AUTHOR]

Mitochondrial dynamics and mitophagy are important aspects of mitochondrial quality control, and are linked to neurodegenerative diseases and muscular diseases. Fis1, a protein on the mitochondrial outer membrane, is thought to mediate mitochondrial fission. However, Fis1 null worms and mammalian cells only display mild fission defects but show aberrant mitophagy. To assess Fis1 function in vivo , we generated conditional knock-out Fis1 mice to allow for specific Fis1 deletion in adult skeletal muscle. In the absence of Fis1 in Type I muscle, mitochondrial hyperfusion, respiratory chain deficiency, and increased mitophagy were found. Moreover, abnormal mitophagy was aggravated by endurance exhaustive exercise stress (EEE), suggesting that Fis1 is involved in maintaining normal mitophagy in mitochondria-rich Type I muscle during exercise. Additionally, Fis1 loss induced delayed onset muscle ultrastructure change (DOMUC) in Type I muscle and strong inflammation in response to acute exhaustive exercise (EE). Thus, we identify a role for Fis1 in maintaining normal mitochondrial structure and function at rest and under exercise stress. [ABSTRACT FROM AUTHOR]

• The marked heterogeneity of acute myeloid leukemia (AML) renders precisely predicting patient prognosis extremely difficult. • The expression of FSI1, SPI1, PDCD7 and Ang2 was analyzed in 100 CN-AML patients and 100 controls using real-time PCR as well as FLT3/ITD and NPM1 mutational status. • FSI1, SPI1, PDCD7 and Ang2 were significantly overexpressed in the bone marrow of AML patients. FSI1 was independently prognostic CR response after induction therapy while PDCD7 was an independent risk factor for RFS and OS in AML patients The marked heterogeneity of acute myeloid leukemia (AML) renders precisely predicting patient prognosis extremely difficult. Genetic alterations, fusions and mutations, may result in misexpression of key genes in AML. We aimed to investigate the expression patterns of 4 novel genes; FIS1, SPI1, PDCD7 and Ang2 to determine their potential prognostic role in AML patients. Bone marrow mononuclear cells were analyzed for of FIS1, SPI1, PDCD7 and Ang2 expression levels by real-time quantitative PCR as well as of FLT3/ITD and NPM1 mutations in 100 newly diagnosed cytogenetically normal (CN-AML) patients, and 100 non-malignant controls. FIS1, SPI1, PDCD7 and Ang2 were significantly overexpressed in CN-AML patients (p < 0.001). Their high expression levels were significantly associated with lower complete remission (CR) rate, shorter relapse-free survival (RFS) and overall survival (OS). On multivariate analysis, high FIS1 expression showed a significant impact on CR response after induction therapy (OR = 88.777, 95% C.I: 2.85–2765.78, p = 0.011) while high PDCD7 appeared to be an independent risk factor for RFS (HR = 5.107, 95% C.I: 1.731–15.066, p = 0.003) and OS (HR = 7.353, 95% C.I: 1.859–29.079, p = 0.004) in CN-AML patients. FIS1 and PDCD7 expression are considered independent risk factors and should be integrated into the current AML stratification system. [ABSTRACT FROM AUTHOR]

Abstract Huntington's disease (HD) is a fatal hereditary neurodegenerative disorder, best known for its clinical triad of progressive motor impairment, cognitive deficits and psychiatric disturbances, is caused by CAG-repeat expansion in exon 1 of Huntingtin (HTT). However, in addition to the neurological disease, mutant HTT (mHTT), which is ubiquitously expressed in all tissues, impairs other organ systems. Not surprisingly, cardiovascular dysautonomia as well as the deterioration of circadian rhythms are among the earliest detectable pathophysiological changes in individuals with HD. Mitochondrial dysfunction in the brain and skeletal muscle in HD has been well documented, as the disease progresses. However, not much is known about mitochondrial abnormalities in the heart. In this study, we describe a role for Drp1/Fis1-mediated excessive mitochondrial fission and dysfunction, associated with lysosomal dysfunction in H9C2 expressing long polyglutamine repeat (Q73) and in human iPSC-derived cardiomyocytes transfected with Q77. Expression of long polyglutamine repeat led to reduced ATP production and mitochondrial fragmentation. We observed an increased accumulation of damaged mitochondria in the lysosome that was coupled with lysosomal dysfunction. Importantly, reducing Drp1/Fis1-mediated mitochondrial damage significantly improved mitochondrial function and cell survival. Finally, reducing Fis1-mediated Drp1 recruitment to the mitochondria, using the selective inhibitor of this interaction, P110, improved mitochondrial structure in the cardiac tissue of R6/2 mice. We suggest that drugs focusing on the central nervous system will not address mitochondrial function across all organs, and therefore will not be a sufficient strategy to treat or slow down HD disease progression. [ABSTRACT FROM AUTHOR]

Objective: To investigate the effects and underlying mechanisms of mitochondrial fission protein FIS1 on the migration and invasion of hepatocellular carcinoma (HCC) cells. Methods: Immunohistochemistry analysis was used for evaluating the expression levels of FIS1 in 10 cases of primary tissues and paired metastatic lesions of HCC to analyze the correlation of expression of FIS1 with the metastasis of HCC. Transwell assays was used to detect the changes of migration and invasion capability of HCC cells after FIS1 was knocked down by RNA interference. In addition, expressions of Epithelial-Mesenchymal Transition (EMT) markers of E-cadherin, ZO-1, N-cadherin and Vimentin were detected by qPCR and Western blot after FIS1 was knocked down by RNA interference. Results: FIS1 was highly expressed in the primary tissues of HCC compared to the paired metastatic lesions. Knockdown of FIS1 inhibited the migration and invasion of HCC cells. In addition, knockdown of FIS1 repressed the expressions of epithelial markers of E-cadherin and ZO-1, while activated the expressions of mesenchymal markers of N-cadherin and Vimentin in HCC cells. Conclusions: Mitochondrial fission protein FIS1 was highly expressed in the metastatic tissues of HCC and promoted the migration and invasion of HCC cells mainly through inducing the epithelial-mesenchymal transition. [ABSTRACT FROM AUTHOR]

Tetratricopeptide repeat (TPR) domains are ubiquitous protein interaction domains that adopt a modular antiparallel array of α-helices. The TPR fold typically adopts a monomeric state, and consensus TPRs sequences successfully fold into the expected monomeric topology. The versatility of the TPR fold also supports different quaternary structures, which may function as regulatory switches. One example is yeast mitochondrial fission 1 (Fis1) that appears to interconvert between monomer and dimer states in regulating division of peroxisomes and mitochondria. Whether human Fis1 can also interconvert like the yeast molecule is unknown. A TPR consensus proline residue present in human Fis1 is absent in the yeast molecule and, when added, prevents yeast Fis1 dimerization suggesting that the TPR consensus proline might have persisted to prevent TPR oligomerization. Here, we address this question with human Fis1 and the consensus TPR protein CTPR3. We demonstrate that human Fis1 does not form a noncovalent dimer via its TPR domain, despite conditions that favor dimerization of the yeast protein. We also show that the presence of the consensus proline is not sufficient to forbid TPR dimerization. Lastly, an analysis of all available TPR protein structures (22 nonredundant structures, totaling 64 TPRs-42 with the consensus proline and 22 without) revealed that the consensus proline is not necessary for turn formation, but does favor shorter turns. This work suggests the TPR consensus proline is not to prevent oligomerization, but to favor tight turns between repeats. [ABSTRACT FROM AUTHOR]

Pluripotent stem cells are known to display distinct metabolic phenotypes than their somatic counterparts. While accumulating studies are focused on the roles of glucose and amino acid metabolism in facilitating pluripotency, little is known regarding the role of lipid metabolism in regulation of stem cell activities. Here, we show that fatty acid ( FA) synthesis activation is critical for stem cell pluripotency. Our initial observations demonstrated enhanced lipogenesis in pluripotent cells and during cellular reprogramming. Further analysis indicated that de novo FA synthesis controls cellular reprogramming and embryonic stem cell pluripotency through mitochondrial fission. Mechanistically, we found that de novo FA synthesis regulated by the lipogenic enzyme ACC1 leads to the enhanced mitochondrial fission via (i) consumption of AcCoA which affects acetylation-mediated FIS1 ubiquitin-proteasome degradation and (ii) generation of lipid products that drive the mitochondrial dynamic equilibrium toward fission. Moreover, we demonstrated that the effect of Acc1 on cellular reprogramming via mitochondrial fission also exists in human iPSC induction. In summary, our study reveals a critical involvement of the FA synthesis pathway in promoting ESC pluripotency and iPSC formation via regulating mitochondrial fission. [ABSTRACT FROM AUTHOR]

Cumulative evidence suggests the importance of organelle homeostasis in regulating metabolic functions in response to various cellular stresses. Particularly, the dynamism and health of the mitochondria-peroxisome network through fission and fusion are essential for cellular function; dysfunctional dynamism underlies the pathogenesis of several degenerative diseases including Parkinson's disease. Here, we investigated the role of Fis1 in cartilage homeostasis and its relevance to osteoarthritis (OA). We found that Fis1 is significantly suppressed in human OA chondrocytes compared to that in normal chondrocytes. Fis1 depletion through siRNA induced peroxisomal dysfunction. Moreover, Fis1 suppression altered miRNA profiles, especially those implicated in lysosomal regulation. Lysosomal destruction using LAMP-1-specific targeted nanorods or lysosomal dysfunction through chloroquine treatment resulted in enhanced chondrocyte apoptosis and/or suppression of autophagy. Accordingly, lysosomal activity and autophagy were severely decreased in OA chondrocytes despite abundant LAMP-1-positive organelles. Moreover, Fis1 morpholino-injected zebrafish embryos displayed lysosome accumulation, mitochondrial dysfunction, and peroxisome reduction. Collectively, these data suggest interconnected links among Fis1-modulated miRNA, lysosomes, and autophagy, which contributes to chondrocyte survival/apoptosis. This study represents the first functional study of Fis1 with its pathological relevance to OA. Our data suggest a new target for controlling cartilage-degenerative diseases, such as OA. Key message: [ABSTRACT FROM AUTHOR]

Summary Peroxisomal division comprises three steps: elongation, constriction, and fission. Translocation of dynamin-like protein 1 (DLP1), a member of the large GTPase family, from the cytosol to peroxisomes is a prerequisite for membrane fission; however, the molecular machinery for peroxisomal targeting of DLP1 remains unclear. This study investigated whether mitochondrial fission factor (Mff), which targets DLP1 to mitochondria, may also recruit DLP1 to peroxisomes. Results show that endogenous Mff is localized to peroxisomes, especially at the membrane-constricted regions of elongated peroxisomes, in addition to mitochondria. Knockdown of MFF abrogates the fission stage of peroxisomal division and is associated with failure to recruit DLP1 to peroxisomes, while ectopic expression of MFF increases the peroxisomal targeting of DLP1. Co-expression of MFF and PEX11β, the latter being a key player in peroxisomal elongation, increases peroxisome abundance. Overexpression of MFF also increases the interaction between DLP1 and Pex11pβ, which knockdown of MFF, but not Fis1, abolishes. Moreover, results show that Pex11pβ interacts with Mff in a DLP1-dependent manner. In conclusion, Mff contributes to the peroxisomal targeting of DLP1 and plays a key role in the fission of the peroxisomal membrane by acting in concert with Pex11pβ and DLP1.

Separation of metabolic pathways in organelles is critical for eukaryotic life. Accordingly, the number, morphology and function of organelles have to be maintained through processes linked with membrane remodeling events. Despite their acknowledged significance and intense study many questions remain about the molecular mechanisms by which organellar membranes proliferate. Here, using the example of peroxisome proliferation, we give an overview of how proteins elongate membranes. Subsequent membrane fission is achieved by dynamin-related proteins shared with mitochondria. We discuss basic criteria that membranes have to fulfill for these fission factors to complete the scission. Because peroxisome elongation is always associated with unequal distribution of matrix and membrane proteins, we propose peroxisomal division to be non-stochastic and asymmetric. We further show that these organelles need not be functional to carry on membrane elongation and present the most recent findings concerning members of the Pex11 protein family as membrane elongation factors. These factors, beside known proteins such as BAR-domain proteins, represent another family of proteins containing an amphipathic α-helix with membrane bending activity.

Mitochondrial components have been abundantly detected in bone matrix, implying that they are somehow transported extracellularly to regulate osteogenesis. Here, we demonstrate that mitochondria and mitochondrial-derived vesicles (MDVs) are secreted from mature osteoblasts to promote differentiation of osteoprogenitors. We show that osteogenic induction stimulates mitochondrial fragmentation, donut formation, and secretion of mitochondria through CD38/cADPR signaling. Enhancing mitochondrial fission and donut formation through Opa1 knockdown or Fis1 overexpression increases mitochondrial secretion and accelerates osteogenesis. We also show that mitochondrial fusion promoter M1, which induces Opa1 expression, impedes osteogenesis, whereas osteoblast-specific Opa1 deletion increases bone mass. We further demonstrate that secreted mitochondria and MDVs enhance bone regeneration in vivo. Our findings suggest that mitochondrial morphology in mature osteoblasts is adapted for extracellular secretion, and secreted mitochondria and MDVs are critical promoters of osteogenesis. [Display omitted] • Mitochondrial fission and donut formation increase during osteoblast maturation • Fragmented mitochondria and MDVs are secreted extracellularly during osteogenesis • Increasing mitochondrial fission through OPA1 downregulation enhances osteogenesis • Treatment of osteoblast-secreted mitochondria accelerates bone regeneration Suh et al. report that during osteogenesis, mitochondria in osteoblasts form donut shapes, divide into small mitochondria, and are secreted into the extracellular space to promote osteoprogenitor differentiation. Disruption of any of these processes impairs osteogenesis, whereas modulation of mitochondrial morphology toward fission enhances osteoblast maturation. [ABSTRACT FROM AUTHOR]

Acute respiratory distress syndrome (ARDS) is one of the most devastating complications of sepsis lacking of effective therapy. Mitochondrial dynamics undergoing continuous fusion and fission play a crucial role in mitochondrial structure and function. Fis1, as a small protein located on the outer membrane of mitochondria, has been thought to be an important protein mediated mitochondrial fission. During ARDS, alveolar macrophages suffer from increased oxidative stress and apoptosis, and also accompanied by disrupted mitochondrial dynamics. In addition, as one of the products of heme degradation catalyzed by heme oxygenase, carbon monoxide (CO) possesses powerful protective properties in vivo or in vitro models, such as anti-inflammatory, antioxidant and anti-apoptosis function. However, there is little evidence that CO alleviates oxidative stress damage through altering mitochondrial fission in alveolar macrophages. In the present study, our results showed that CO increased cell vitality, improved mitochondrial SOD activity, reduced reactive oxygen species (ROS) production and inhibited cell apoptosis in NR8383 exposed to LPS. Meanwhile, CO decreased the expression of Fis1, increased mitochondrial membrane potential and sustained elongation of mitochondria in LPS-incubated NR8383. Overall, our study underscored a critical role of CO in suppressing the expression of Fis1 and alleviating LPS- induced oxidative stress damage in alveolar macrophages. [ABSTRACT FROM AUTHOR]

Background: Radio-Adaptive Response (RAR) is a biological defense mechanism whereby exposure to low dose ionizing radiation (IR) mitigates the detrimental effects of high dose irradiation. RAR has been widely observed in vivo using as endpoint less induction of apoptosis. However, sex differences associated with RAR and variations between males and females on global gene expression influenced by RAR have not been still investigated. In addition, the response to radiation-induced apoptosis is associated with phosphorylation of TRP53 at both the serine 15 (ser-18 in the mouse) and serine 392 (ser-389 in mice) residues, but the role of these two phosphorylated forms in male and female RAR remains to be elucidated. Results: We analyzed the effect of administering priming low dose radiation (0.075 Gy of X-rays) prior to high dose radiation (1.75 Gy of γ-rays) on the level of caspase-3-mediated apoptosis and on global transcriptional expression in thymocytes of male and female mice. Here, we provide the first evidence of a differential sex effect of RAR on the reduction of thymocyte apoptosis with males showing lesser levels of caspase-3-mediated apoptosis than females. Analysis of transcriptomic profiles of 1944 genes involved in apoptosis signaling in radio-adapted thymocytes identified 17 transcripts exhibiting differential expression between both sexes. Among them, Dlc1 and Fis1 are closely related to the apoptosis mediated by the TRP53 protein. Our data demonstrate that overexpression of Dlc1 and Fis1 occur concomitantly with a highest accumulation of phosphoserine-18-TRP53 and caspase-3 in radio-adapted thymocytes of female mice. In an opposite way, both down-modulation of Fis1 and phosphoserine-389-TRP53 accumulation appear to be associated with protection from thymocyte apoptosis mediated by caspase-3 in males. Conclusions: Transcriptomic analysis performed in this work reveals for the first time sex-specific differences in gene expression influenced by RAR. Our results also suggest a sex-dependent dual role for phosphoserine-18-TRP53 and phosphoserine-389-TRP53 in the regulation of the radio-adaptive response in mouse thymocytes. [ABSTRACT FROM AUTHOR]

In mammals, peroxisomes perform crucial functions in cellular metabolism, signalling and viral defense which are essential to the health and viability of the organism. In order to achieve this functional versatility peroxisomes dynamically respond to molecular cues triggered by changes in the cellular environment. Such changes elicit a corresponding response in peroxisomes, which manifests itself as a change in peroxisome number, altered enzyme levels and adaptations to the peroxisomal structure. In mammals the generation of new peroxisomes is a complex process which has clear analogies to mitochondria, with both sharing the same division machinery and undergoing a similar division process. How the regulation of this division process is integrated into the cell's response to different stimuli, the signalling pathways and factors involved, remains somewhat unclear. Here, we discuss the mechanism of peroxisomal fission, the contributions of the various division factors and examine the potential impact of post-translational modifications, such as phosphorylation, on the proliferation process. We also summarize the signalling process and highlight the most recent data linking signalling pathways with peroxisome proliferation. This article is part of a Special Issue entitled: Peroxisomes edited by Ralf Erdmann. [ABSTRACT FROM AUTHOR]

Damaged mitochondria can be selectively eliminated by mitophagy. Although two gene products mutated in Parkinson’s disease, PINK1, and Parkin have been found to play a central role in triggering mitophagy in mammals, how the pre-autophagosomal isolation membrane selectively and accurately engulfs damaged mitochondria remains unclear. In this study, we demonstrate that TBC1D15, a mitochondrial Rab GTPase-activating protein (Rab-GAP), governs autophagosome biogenesis and morphology downstream of Parkin activation. To constrain autophagosome morphogenesis to that of the cargo, TBC1D15 inhibits Rab7 activity and associates with both the mitochondria through binding Fis1 and the isolation membrane through the interactions with LC3/GABARAP family members. Another TBC family member TBC1D17, also participates in mitophagy and forms homodimers and heterodimers with TBC1D15. These results demonstrate that TBC1D15 and TBC1D17 mediate proper autophagic encapsulation of mitochondria by regulating Rab7 activity at the interface between mitochondria and isolation membranes.

It is well known that resistance exercise increases muscle protein synthesis and muscle strength. However, little is known about the effect of resistance exercise on mitochondrial dynamics, which is coupled with mitochondrial function. In skeletal muscle, mitochondria exist as dynamic networks that are continuously remodeling through fusion and fission. The purpose of this study was to investigate the effect of acute and chronic resistance exercise, which induces muscle hypertrophy, on the expression of proteins related to mitochondrial dynamics in rat skeletal muscle. Resistance exercise consisted of maximum isometric contraction, which was induced by percutaneous electrical stimulation of the gastrocnemius muscle. Our results revealed no change in levels of proteins that regulate mitochondrial fission (Fis1 and Drp1) or fusion (Opa1, Mfn1, and Mfn2) over the 24-h period following acute resistance exercise. Phosphorylation of Drp1 at Ser616 was increased immediately after exercise ( P < 0.01). Four weeks of resistance training (3 times/week) increased Mfn1 ( P < 0.01), Mfn2 ( P < 0.05), and Opa1 ( P < 0.01) protein levels without altering mitochondrial oxidative phosphorylation proteins. These observations suggest that resistance exercise has little effect on mitochondrial biogenesis but alters the expression of proteins involved in mitochondrial fusion and fission, which may contribute to mitochondrial quality control and improved mitochondrial function. [ABSTRACT FROM AUTHOR]

The mitochondrial fission protein Fis1 regulates yeast mitochondrial fission and is required for ethanol-induced mitochondrial fragmentation and apoptosis. To examine the function of Fis1 in a plant pathogenic fungus, we cloned the MoFIS1 gene, a homolog of Saccharomyces cerevisiae FIS1 , from Magnaporthe oryzae and characterized its function by targeted gene deletion and mutant phenotypic analysis. MoFIS1 deletion mutants were unaltered in conidial germination, appressorium formation, and mating tests, but were severely defective in colony growth, conidiation, virulence on rice and barley, growth under nitrogen and glucose deficiency, and growth under osmotic stress. Blast lesions on rice leaves caused by the Δ Mofis1 strain were significantly reduced, were non-proliferating, and were less coalesced as compared to the highly coalesced and proliferating lesions resulting from infection with the wild-type strain. The defects in growth, conidiation, and virulence of the mutant were restored in a complementation strain of Δ Mofis1 . A MoFis1-GFP fusion protein co-localized with Mitotracker red in mitochondria. These results show that MoFIS1 encodes a mitochondrial protein that regulates fungal growth, conidiation, and virulence in M. oryzae . [ABSTRACT FROM AUTHOR]