The role of mitochondrial fission in cardiovascular health and disease

Jenner A., Peña‐Blanco A., Salvador‐Gallego R., Ugarte‐Uribe B., Zollo C., Ganief T., Bierlmeier J., Mund M., Lee J.E., Ries J., Schwarzer D., Macek B., Garcia‐Saez A.J.

Ramonett A., Kwak E., Ahmed T., Flores P.C., Ortiz H.R., Lee Y.S., Vanderah T.W., Largent-Milnes T., Kashatus D.F., Langlais P.R., Mythreye K., Lee N.Y.

Proper regulation of mitochondrial dynamics requires dynamin-related protein 1 retrograde movement via GAIP/RGS19-interacting protein-myosin VI transport system.

He W., Tang Y., Li C., Zhang X., Huang S., Tan B., Yang Z.

Background: Despite the development of radiation therapy (RT) techniques, concern regarding the serious and irreversible heart injury induced by RT has grown due to the lack of early intervention measures. Although exercise can act as an effective and economic nonpharmacologic strategy to combat fatigue and improve quality of life for cancer survivors, limited data on its application in radiation-induced heart disease (RIHD) and the underlying molecular mechanism are available.Methods: Fifteen young adult male mice were enrolled in this study and divided into 3 groups (including exercised RIHD group, sedentary RIHD group, and controls; n =5 samples/group). While the mice in the control group were kept in cages without irradiation, those in the exercised RIHD group underwent 3weeks of aerobic exercise on the treadmill after radiotherapy. At the end of the 3rd week following RT, FNDC5/irisin expression, cardiac function, aerobic fitness, cardiomyocyte apoptosis, mitochondrial function, and mitochondrial turnover in the myocardium were assessed to identify the protective role of exercise in RIHD and investigate the potential mechanism.Results: While sedentary RIHD group had impaired cardiac function and aerobic fitness than controls, the exercised RIHD mice had improved cardiac function and aerobic fitness, elevated ATP production and the mitochondrial protein content, decreased mitochondrial length, and increased formation of mitophagosomes compared with sedentary RIHD mice. These changes were accompanied by the elevated expression of FNDC5/irisin, a fission marker (DRP1) and mitophagy markers (PINK1 and LC3B) in exercised RIHD group than that of sedentary RIHD group, but the expression of biogenesis (TFAM) and fusion (MFN2) markers was not significantly changed.Conclusion: Exercise could enhance cardiac function and aerobic fitness in RIHD mice partly through an autocrine mechanism via FNDC5/irisin, in which autophagy was selectively activated, suggesting that FNDC5/irisin may act as an intervening target to prevent the development of RIHD.

Duan C., Kuang L., Hong C., Xiang X., Liu J., Li Q., Peng X., Zhou Y., Wang H., Liu L., Li T.

Mitochondrial mass imbalance is one of the key causes of cardiovascular dysfunction after hypoxia. The activation of dynamin-related protein 1 (Drp1), as well as its mitochondrial translocation, play important roles in the changes of both mitochondrial morphology and mitochondrial functions after hypoxia. However, in addition to mediating mitochondrial fission, whether Drp1 has other regulatory roles in mitochondrial homeostasis after mitochondrial translocation is unknown. In this study, we performed a series of interaction and colocalization assays and found that, after mitochondrial translocation, Drp1 may promote the excessive opening of the mitochondrial permeability transition pore (mPTP) after hypoxia. Firstly, mitochondrial Drp1 maximumly recognizes mPTP channels by binding Bcl-2-associated X protein (BAX) and a phosphate carrier protein (PiC) in the mPTP. Then, leucine-rich repeat serine/threonine-protein kinase 2 (LRRK2) is recruited, whose kinase activity is inhibited by direct binding with mitochondrial Drp1 after hypoxia. Subsequently, the mPTP-related protein hexokinase 2 (HK2) is inactivated at Thr-473 and dissociates from the mitochondrial membrane, ultimately causing structural disruption and overopening of mPTP, which aggravates mitochondrial and cellular dysfunction after hypoxia. Thus, our study interprets the dual direct regulation of mitochondrial Drp1 on mitochondrial morphology and functions after hypoxia and proposes a new mitochondrial fission-independent mechanism for the role of Drp1 after its translocation in hypoxic injury.

Vercellino I., Sazanov L.A.

The mitochondrial oxidative phosphorylation system is central to cellular metabolism. It comprises five enzymatic complexes and two mobile electron carriers that work in a mitochondrial respiratory chain. By coupling the oxidation of reducing equivalents coming into mitochondria to the generation and subsequent dissipation of a proton gradient across the inner mitochondrial membrane, this electron transport chain drives the production of ATP, which is then used as a primary energy carrier in virtually all cellular processes. Minimal perturbations of the respiratory chain activity are linked to diseases; therefore, it is necessary to understand how these complexes are assembled and regulated and how they function. In this Review, we outline the latest assembly models for each individual complex, and we also highlight the recent discoveries indicating that the formation of larger assemblies, known as respiratory supercomplexes, originates from the association of the intermediates of individual complexes. We then discuss how recent cryo-electron microscopy structures have been key to answering open questions on the function of the electron transport chain in mitochondrial respiration and how supercomplexes and other factors, including metabolites, can regulate the activity of the single complexes. When relevant, we discuss how these mechanisms contribute to physiology and outline their deregulation in human diseases. Mitochondrial respiration relies on five enzymatic complexes that couple electron transport with proton pumping, leading to ATP synthesis. Recent studies have shed new light on the organization, assembly and mechanisms of the respiratory complexes, including the formation of their larger assemblies — respiratory supercomplexes — and their roles in physiology.

Boutry M., Kim P.K.

Mitochondrial division is not an autonomous event but involves multiple organelles, including the endoplasmic reticulum (ER) and lysosomes. Whereas the ER drives the constriction of mitochondrial membranes, the role of lysosomes in mitochondrial division is not known. Here, using super-resolution live-cell imaging, we investigate the recruitment of lysosomes to the site of mitochondrial division. We find that the ER recruits lysosomes to the site of division through the interaction of VAMP-associated proteins (VAPs) with the lysosomal lipid transfer protein ORP1L to induce a three-way contact between the ER, lysosome, and the mitochondrion. We also show that ORP1L might transport phosphatidylinositol-4-phosphate (PI(4)P) from lysosomes to mitochondria, as inhibiting its transfer or depleting PI(4)P at the mitochondrial division site impairs fission, demonstrating a direct role for PI(4)P in the division process. Our findings support a model where the ER recruits lysosomes to act in concert at the fission site for the efficient division of mitochondria. Membrane contact sites between organelles have specialized functions that are only beginning to be understood. Here, the authors show that ORP1L mediates lysosome recruitment and PI(4)P signaling at endoplasmic reticulum-lysosome-mitochondria three-way contact sites involved in mitochondrial division.

Valera-Alberni M., Joffraud M., Miro-Blanch J., Capellades J., Junza A., Dayon L., Núñez Galindo A., Sanchez-Garcia J.L., Valsesia A., Cercillieux A., Söllner F., Ladurner A.G., Yanes O., Cantó C.

Summary Mitochondria constantly undergo fusion and fission events, referred as mitochondrial dynamics, which determine mitochondrial architecture and bioenergetics. Cultured cell studies demonstrate that mitochondrial dynamics are acutely regulated by phosphorylation of the mitochondrial fission orchestrator dynamin-related protein 1 (Drp1) at S579 or S600. However, the physiological impact and crosstalk of these phosphorylation sites is poorly understood. Here, we describe the functional interrelation between S579 and S600 phosphorylation sites in vivo and their role on mitochondrial remodeling. Mice carrying a homozygous Drp1 S600A knockin (Drp1 KI) mutation display larger mitochondria and enhanced lipid oxidation and respiratory capacities, granting improved glucose tolerance and thermogenic response upon high-fat feeding. Housing mice at thermoneutrality blunts these differences, suggesting a role for the brown adipose tissue in the protection of Drp1 KI mice against metabolic damage. Overall, we demonstrate crosstalk between Drp1 phosphorylation sites and provide evidence that their modulation could be used in the treatment and prevention of metabolic diseases.

Varuzhanyan G., Ladinsky M.S., Yamashita S., Abe M., Sakimura K., Kanki T., Chan D.C.

ABSTRACT Male germline development involves choreographed changes to mitochondrial number, morphology and organization. Mitochondrial reorganization during spermatogenesis was recently shown to require mitochondrial fusion and fission. Mitophagy, the autophagic degradation of mitochondria, is another mechanism for controlling mitochondrial number and physiology, but its role during spermatogenesis is largely unknown. During post-meiotic spermatid development, restructuring of the mitochondrial network results in packing of mitochondria into a tight array in the sperm midpiece to fuel motility. Here, we show that disruption of mouse Fis1 in the male germline results in early spermatid arrest that is associated with increased mitochondrial content. Mutant spermatids coalesce into multinucleated giant cells that accumulate mitochondria of aberrant ultrastructure and numerous mitophagic and autophagic intermediates, suggesting a defect in mitophagy. We conclude that Fis1 regulates mitochondrial morphology and turnover to promote spermatid maturation.

Pangou E., Bielska O., Guerber L., Schmucker S., Agote-Arán A., Ye T., Liao Y., Puig-Gamez M., Grandgirard E., Kleiss C., Liu Y., Compe E., Zhang Z., Aebersold R., Ricci R., et. al.

Mitochondria are highly dynamic organelles subjected to fission and fusion events. During mitosis, mitochondrial fission ensures equal distribution of mitochondria to daughter cells. If and how this process can actively drive mitotic progression remains largely unknown. Here, we discover a pathway linking mitochondrial fission to mitotic progression in mammalian cells. The mitochondrial fission factor (MFF), the main mitochondrial receptor for the Dynamin-related protein 1 (DRP1), is directly phosphorylated by Protein Kinase D (PKD) specifically during mitosis. PKD-dependent MFF phosphorylation is required and sufficient for mitochondrial fission in mitotic but not in interphasic cells. Phosphorylation of MFF is crucial for chromosome segregation and promotes cell survival by inhibiting adaptation of the mitotic checkpoint. Thus, PKD/MFF-dependent mitochondrial fission is critical for the maintenance of genome integrity during cell division.

Kleele T., Rey T., Winter J., Zaganelli S., Mahecic D., Perreten Lambert H., Ruberto F.P., Nemir M., Wai T., Pedrazzini T., Manley S.

Mitochondrial fission is a highly regulated process that, when disrupted, can alter metabolism, proliferation and apoptosis1–3. Dysregulation has been linked to neurodegeneration3,4, cardiovascular disease3 and cancer5. Key components of the fission machinery include the endoplasmic reticulum6 and actin7, which initiate constriction before dynamin-related protein 1 (DRP1)8 binds to the outer mitochondrial membrane via adaptor proteins9–11, to drive scission12. In the mitochondrial life cycle, fission enables both biogenesis of new mitochondria and clearance of dysfunctional mitochondria through mitophagy1,13. Current models of fission regulation cannot explain how those dual fates are decided. However, uncovering fate determinants is challenging, as fission is unpredictable, and mitochondrial morphology is heterogeneous, with ultrastructural features that are below the diffraction limit. Here, we used live-cell structured illumination microscopy to capture mitochondrial dynamics. By analysing hundreds of fissions in African green monkey Cos-7 cells and mouse cardiomyocytes, we discovered two functionally and mechanistically distinct types of fission. Division at the periphery enables damaged material to be shed into smaller mitochondria destined for mitophagy, whereas division at the midzone leads to the proliferation of mitochondria. Both types are mediated by DRP1, but endoplasmic reticulum- and actin-mediated pre-constriction and the adaptor MFF govern only midzone fission. Peripheral fission is preceded by lysosomal contact and is regulated by the mitochondrial outer membrane protein FIS1. These distinct molecular mechanisms explain how cells independently regulate fission, leading to distinct mitochondrial fates. Mitochondrial fission at the organelle periphery generates small daughter mitochondria that are removed by mitophagy whereas fission at the midzone leads to proliferation.

Bekhite M., González-Delgado A., Hübner S., Haxhikadrija P., Kretzschmar T., Müller T., Wu J.M., Bekfani T., Franz M., Wartenberg M., Gräler M., Greber B., Schulze P.C.

Oversupply of fatty acids (FAs) to cardiomyocytes (CMs) is associated with increased ceramide content and elevated the risk of lipotoxic cardiomyopathy. Here we investigate the role of ceramide accumulation on mitochondrial function and mitophagy in cardiac lipotoxicity using CMs derived from human induced pluripotent stem cell (hiPSC). Mature CMs derived from hiPSC exposed to the diabetic-like environment or transfected with plasmids overexpressing serine-palmitoyltransferase long chain base subunit 1 (S PTLC1 ), a subunit of the serine-palmitoyltransferase (SPT) complex, resulted in increased intracellular ceramide levels. Accumulation of ceramides impaired insulin-dependent phosphorylation of Akt through activating protein phosphatase 2A (PP2A) and disturbed gene and protein levels of key metabolic enzymes including GLUT4, AMPK, PGC-1α, PPARα, CD36, PDK4, and PPARγ compared to controls. Analysis of CMs oxidative metabolism using a Seahorse analyzer showed a significant reduction in ATP synthesis-related O 2 consumption, mitochondrial β-oxidation and respiratory capacity, indicating an impaired mitochondrial function under diabetic-like conditions or SPTLC1 -overexpression. Further, ceramide accumulation increased mitochondrial fission regulators such as dynamin-related protein 1 (DRP1) and mitochondrial fission factor (MFF) as well as auto/mitophagic proteins LC3B and PINK-1 compared to control. Incubation of CMs with the specific SPT inhibitor (myriocin) showed a significant increase in mitochondrial fusion regulators the mitofusin 2 (MFN2) and optic atrophy 1 (OPA1) as well as p-Akt, PGC-1 α, GLUT-4, and ATP production. In addition, a significant decrease in auto/mitophagy and apoptosis was found in CMs treated with myriocin. Our results suggest that ceramide accumulation has important implications in driving insulin resistance, oxidative stress, increased auto/mitophagy, and mitochondrial dysfunction in the setting of lipotoxic cardiomyopathy. Therefore, modulation of the de novo ceramide synthesis pathway may serve as a novel therapeutic target to treat metabolic cardiomyopathy. • Ceramide accumulation has important implications in deriving cardiotoxicity, oxidative stress and insulin resistance. • Ceramide accumulation increased auto/mitophagy and mitochondrial dysfunction in the h-iPSC-derived cardiomyocytes. • Blocking de novo synthesis pathway of ceramide rescued mitochondrial function in SPTLC1 -overexpressed cardiomyocytes. • Modulation of the de novo synthesis pathway may serve as a therapeutic target to treat metabolic cardiomyopathy.

Hsiao Y.T., Shimizu I., Wakasugi T., Yoshida Y., Ikegami R., Hayashi Y., Suda M., Katsuumi G., Nakao M., Ozawa T., Izumi D., Kashimura T., Ozaki K., Soga T., Minamino T.

Prognosis of severe heart failure remains poor. Urgent new therapies are required. Some heart failure patients do not respond to established multidisciplinary treatment and are classified as “non-responders”. The outcome is especially poor for non-responders, and underlying mechanisms are largely unknown. Mitofusin-1 (Mfn1), a mitochondrial fusion protein, is significantly reduced in non-responding patients. This study aimed to elucidate the role of Mfn1 in the failing heart. Twenty-two idiopathic dilated cardiomyopathy (IDCM) patients who underwent endomyocardial biopsy of intraventricular septum were included. Of the 22 patients, 8 were non-responders (left ventricular (LV) ejection fraction (LVEF) of < 10% improvement at late phase follow-up). Electron microscopy (EM), quantitative PCR, and immunofluorescence studies were performed to explore the biological processes and molecules involved in failure to respond. Studies in cardiac specific Mfn1 knockout mice (c-Mfn1 KO), and in vitro studies with neonatal rat ventricular myocytes (NRVMs) were also conducted. A significant reduction in mitochondrial size in cardiomyocytes, and Mfn1, was observed in non-responders. A LV pressure overload with thoracic aortic constriction (TAC) c-Mfn1 KO mouse model was generated. Systolic function was reduced in c-Mfn1 KO mice, while mitochondria alteration in TAC c-Mfn1 KO mice increased. In vitro studies in NRVMs indicated negative regulation of Mfn1 by the β-AR/cAMP/PKA/miR-140-5p pathway resulting in significant reduction in mitochondrial respiration of NRVMs. The level of miR140-5p was increased in cardiac tissues of non-responders. Mfn1 is a biomarker of heart failure in non-responders. Therapies targeting mitochondrial dynamics and homeostasis are next generation therapy for non-responding heart failure patients.

Singh A., Faccenda D., Campanella M.

Mitochondria play a vital role in cellular metabolism and are central mediator of intracellular signalling, cell differentiation, morphogenesis and demise. An increasingly higher number of pathologies is linked with mitochondrial dysfunction, which can arise from either genetic defects affecting core mitochondrial components or malfunctioning pathways impairing mitochondrial homeostasis. As such, mitochondria are considered an important target in several pathologies spanning from neoplastic to neurodegenerative diseases as well as metabolic syndromes. In this review we provide an overview of the state-of-the-art in mitochondrial pharmacology, focusing on the novel compounds that have been generated in the bid to correct mitochondrial aberrations. Our work aims to serve the scientific community working on translational medical science by highlighting the most promising pharmacological approaches to target mitochondrial dysfunction in disease.

Wu Q., Zheng D., Liu P., Yang H., Li L., Kuang S., Lai Y., Rao F., Xue Y., Lin J., Liu S., Chen C., Deng C.

Mitochondrial dysfunction and impaired Ca2+ handling are involved in the development of diabetic cardiomyopathy (DCM). Dynamic relative protein 1 (Drp1) regulates mitochondrial fission by changing its level of phosphorylation, and the Orai1 (Ca2+ release-activated calcium channel protein 1) calcium channel is important for the increase in Ca2+ entry into cardiomyocytes. We aimed to explore the mechanism of Drp1 and Orai1 in cardiomyocyte hypertrophy caused by high glucose (HG). We found that Zucker diabetic fat rats induced by administration of a high-fat diet develop cardiac hypertrophy and impaired cardiac function, accompanied by the activation of mitochondrial dynamics and calcium handling pathway-related proteins. Moreover, HG induces cardiomyocyte hypertrophy, accompanied by abnormal mitochondrial morphology and function, and increased Orai1-mediated Ca2+ influx. Mechanistically, the Drp1 inhibitor mitochondrial division inhibitor 1 (Mdivi-1) prevents cardiomyocyte hypertrophy induced by HG by reducing phosphorylation of Drp1 at serine 616 (S616) and increasing phosphorylation at S637. Inhibition of Orai1 with single guide RNA (sgOrai1) or an inhibitor (BTP2) not only suppressed Drp1 activity and calmodulin-binding catalytic subunit A (CnA) and phosphorylated-extracellular signal-regulated kinase (p-ERK1/2) expression but also alleviated mitochondrial dysfunction and cardiomyocyte hypertrophy caused by HG. In addition, the CnA inhibitor cyclosporin A and p-ERK1/2 inhibitor U0126 improved HG-induced cardiomyocyte hypertrophy by promoting and inhibiting phosphorylation of Drp1 at S637 and S616, respectively. In summary, we identified Drp1 as a downstream target of Orai1-mediated Ca2+ entry, via activation by p-ERK1/2-mediated phosphorylation at S616 or CnA-mediated dephosphorylation at S637 in DCM. Thus, the Orai1–Drp1 axis is a novel target for treating DCM.

Rogers M.A., Hutcheson J.D., Okui T., Goettsch C., Singh S.A., Halu A., Schlotter F., Higashi H., Wang L., Whelan M.C., Mlynarchik A.K., Daugherty A., Nomura M., Aikawa M., Aikawa E.

Abstract Aims Proteostasis maintains protein homeostasis and participates in regulating critical cardiometabolic disease risk factors including proprotein convertase subtilisin/kexin type 9 (PCSK9). Endoplasmic reticulum (ER) remodeling through release and incorporation of trafficking vesicles mediates protein secretion and degradation. We hypothesized that ER remodeling that drives mitochondrial fission participates in cardiometabolic proteostasis. Methods and results We used in vitro and in vivo hepatocyte inhibition of a protein involved in mitochondrial fission, dynamin-related protein 1 (DRP1). Here, we show that DRP1 promotes remodeling of select ER microdomains by tethering vesicles at ER. A DRP1 inhibitor, mitochondrial division inhibitor 1 (mdivi-1) reduced ER localization of a DRP1 receptor, mitochondrial fission factor, suppressing ER remodeling-driven mitochondrial fission, autophagy, and increased mitochondrial calcium buffering and PCSK9 proteasomal degradation. DRP1 inhibition by CRISPR/Cas9 deletion or mdivi-1 alone or in combination with statin incubation in human hepatocytes and hepatocyte-specific Drp1-deficiency in mice reduced PCSK9 secretion (−78.5%). In HepG2 cells, mdivi-1 increased low-density lipoprotein receptor via c-Jun transcription and reduced PCSK9 mRNA levels via suppressed sterol regulatory binding protein-1c. Additionally, mdivi-1 reduced macrophage burden, oxidative stress, and advanced calcified atherosclerotic plaque in aortic roots of diabetic Apoe-deficient mice and inflammatory cytokine production in human macrophages. Conclusions We propose a novel tethering function of DRP1 beyond its established fission function, with DRP1-mediated ER remodeling likely contributing to ER constriction of mitochondria that drives mitochondrial fission. We report that DRP1-driven remodeling of select ER micro-domains may critically regulate hepatic proteostasis and identify mdivi-1 as a novel small molecule PCSK9 inhibitor.

Kulkarni H., Gaikwad A.B.

Yang W., Li Y., Feng R., Liang P., Tian K., Hu L., Wang K., Qiu T., Zhang J., Sun X., Yao X.

Awaji A.A., Alshehri K.M.

Han B., Tian J., Li J., Chen Y., Liu N., Ma Y., Wang C., Guo X., Liu Y., Zhang Z.

Huang W., Wang D., Hu P., Zhu Y., Zhou Y., Chen Y., Yu Z., Zhang T., Hu N., Tian X., Zhang Z.

Chang X., Zhou S., Huang Y., Liu J., Wang Y., Guan X., Wu Q., Liu Z., Liu R.

Ravindran R., Gustafsson Å.B.

Jia G., Song E., Huang Q., Chen M., Liu G.

Mitochondria are essential organelles responsible for cellular energy supply. The maintenance of mitochondrial structure and function relies heavily on quality control systems, including biogenesis, fission, and fusion. Mitochondrial fusion refers to the interconnection of two similar mitochondria, facilitating the exchange of mitochondrial DNA, metabolic substrates, proteins, and other components. This process is crucial for rescuing damaged mitochondria and maintaining their normal function. In mammals, mitochondrial fusion involves two sequential steps: outer membrane fusion, regulated by mitofusin 1 and 2 (MFN1/2), and inner membrane fusion, mediated by optic atrophy 1 (OPA1). Dysfunction in mitochondrial fusion has been implicated in the development of various acute and chronic lung injuries. Regulating mitochondrial fusion, maintaining mitochondrial dynamics, and improving mitochondrial function are effective strategies for mitigating lung tissue and cellular damage. This study reviews the expression and regulatory mechanisms of mitochondrial fusion proteins in lung injuries of different etiologies, explores their relationship with lung injury diseases, and offers a theoretical foundation for developing novel therapeutic approaches targeting mitochondrial fusion proteins in lung injury.

Su S., Wu X., Li B., Zhang F., Zhang K., Wang H., Lin Y., Chen J.

Zhang J., Zhang Y., Lei W., Zhou J., Xu Y., Hao Z., Liao Y., Huang F., Chen M.

Tan Y., Huang Y., Chen W., Lang T., Wang L., Chen X., Yu H., Qiu Z., Cui K., Guo C., Wang Y., Zhou Z.

Wang D., Wu J., Xu Z., Jia J., Lai Y., He Z.

ABSTRACTThe global prevalence of skeletal muscle diseases has progressively escalated in recent years. This study aimed to explore the potential role of matrix stiffness in the repair mechanisms following skeletal muscle injury. We observed an increase in muscle stiffness, a significant rise in the number of type I muscle fibres and a notable elevation in mRNA expression levels of Myh7/2 alongside a decrease in Myh1/4 on day 3 post tibialis anterior muscle injury. To replicate these in vivo changes, C2C12 cells were cultured under high matrix stiffness conditions, and compared to those on low matrix stiffness, the C2C12 cells cultured on high matrix stiffness showed increased expression levels of Myh7/2 mRNA and production levels of MYH7/2, indicating differentiation into slow‐twitch muscle fibre types. Furthermore, up‐regulation of DRP1 phosphorylation along with elevated F‐actin fluorescence intensity and RHOA and ROCK1 production indicates that high matrix stiffness induces cytoskeletal remodelling to regulate mitochondrial fission processes. Our data also revealed up‐regulation in mRNA expression level for Actb, phosphorylation level for DRP1, mitochondrial quantity and MYH7/2 production level. Importantly, these effects were effectively reversed by the application of ROCK inhibitor Y‐27632, highlighting that targeting cytoskeletal dynamics can modulate myogenic differentiation pathways within C2C12 cells. These findings provide valuable insights into how matrix stiffness influences fibre type transformation during skeletal muscle injury repair while suggesting potential therapeutic targets for intervention.

He T., sha J., hu Y., shao C., zhou Y., chen L., yao J., Gao J.

AbstractBackgroundThe heart undergoes growth in response to both pathological and physiological stimuli. Pathological hypertrophy often leads to cardiomyocyte loss and heart failure (HF), whereas physiological hypertrophy paradoxically protects the heart and enhances cardiomyogenesis. The molecular mechanisms that distinguish these two forms of hypertrophy remain unclear.MethodsIn this study, we utilized single-cell transcriptomics from transverse aortic constriction (TAC) models at 2, 5, 8, and 11 weeks (GSE120064), along with bulk RNA sequencing from mice subjected to 12 months of exercise-induced physiological hypertrophy and cardiomyogenesis (CRA007207), to investigate the molecular differences between pathological and physiological hypertrophy.ResultsOur results reveal the following. Mitochondrial-related pathways are the primary drivers of the pathological changes that occur following TAC. The mitochondrial fission and fusion pathways exhibited increased activity at 2 weeks but decreased activity at 5, 8, and 11 weeks post TAC. The expression pattern of exercise-induced physiological hypertrophy was similar to that of 2-week TAC-induced changes, indicating that the early stage of TAC represents an adaptive physiological response or physiological hypertrophy. Notably, during HF, the fission genes Fis1 and Dnm1l increase, in contrast to the expected decrease in fusion genes. These findings were experimentally validated, indicating that the mitochondrial fission genes Fis1 and Dnm1l are key promoters of HF.ConclusionsOur data indicate that the balance between mitochondrial fission and fusion plays a critical role in the transition from physiological to pathological hypertrophy. The fission-related genes Fis1 and Dnm1l have emerged as key drivers of pathological hypertrophy and heart failure. These findings suggest that targeting fission genes, particularly Fis1 and Dnm1l, may represent promising therapeutic strategies for managing heart failure.

Chen G., Gan J., Wu F., Zhou Z., Duan Z., Zhang K., Wang S., Jin H., Li Y., Zhang C., Lin Z.

Abstract Background and Aims Myocardial infarction (MI) is an ischaemic cardiovascular disease associated with increased morbidity and mortality. Previous studies have suggested that serine carboxypeptidase 1 (Scpep1) is involved in vascular diseases; however, its role in cardiac diseases remains unclear. This study aims to explore the role of Scpep1 in regulating cardiac homeostasis during MI. Methods The impact of Scpep1 deficiency or cardiac-specific knock-down and Scpep1 overexpression on heart function was evaluated in mice with MI. Its downstream functional mediators of Scpep1 were elucidated using proteomic analysis and confirmed by employing loss- and gain-of-function strategies. Results Circulating and cardiac Scpep1 levels were up-regulated in mice with MI. Genetic ablation or cardiac-specific knock-down of Scpep1 alleviated MI-induced cardiac dysfunction and damage in mice. In contrast, cardiac-specific Scpep1 overexpression aggravated these adverse effects. Mechanistically, Scpep1 exacerbated MI-induced cardiac dysfunction and damage by impaired mitochondrial bioenergetics via binding to Pex3 to promote its degradation, ultimately contributing to mitochondrial fission and apoptosis. Moreover, the expressional profiles of Scpep1 in plasma samples and heart tissues of patients with MI or ischaemic cardiomyopathy were in line with those observed in the mouse models. In addition, pharmaceutical inhibition of Scpep1 notably improved MI-induced cardiac dysfunction and damage by improving mitochondrial fragmentation and bioenergetics post-MI. Conclusions Scpep1 deficiency mitigates MI by improving Pex3-mediated mitochondrial fission and subsequent cardiomyocyte apoptosis. Scpep1 constitutes a potential therapeutic target for attenuating MI.

Zhang K., Zhu Y., Tang A., Zhou Z., Yang Y., Liu Z., Li Y., Liang X., Feng Z., Wang J., Jiang T., Jiang Q., Wu D.