A mutation in the mitochondrial fission gene Dnm1l leads to cardiomyopathy

Cardiac dysfunction due to mitochondrial impairment assessed by human iPS cells caused by DNM1L mutations

BACKGROUND

DNM1L encodes dynamin-related protein 1, which plays an important role in mitochondrial and peroxisomal division. The DNM1L mutation leads to cardiac dysfunction in patients and animal models. However, the mechanism of cardiac dysfunction caused by DNM1L mutation has not been elucidated clearly at least in the studies of human cardiomyocytes.

METHODS

We established human induced pluripotent stem cells (hiPSCs) from two pediatric patients with DNM1L mutation. The hiPSCs were differentiated into hiPSC-derived cardiomyocytes (hiPS-CMs). Mitochondrial morphology and function, cardiomyocyte Ca2+ dynamics, and contractile and diastolic function of hiPS-CMs were analyzed.

RESULTS

The morphology of the mitochondria was abnormally elongated in patient-derived hiPS-CMs. The mitochondrial membrane potential and oxygen consumption rate were significantly decreased, resulting in reduced ATP production. In the analysis of Ca2+ dynamics, the 50% time to decay was significantly longer in patient-derived hiPS-CMs than in healthy control. High-precision live-imaging system analysis revealed that contractile and diastolic function was significantly impaired under isoproterenol stimulation.

CONCLUSION

DNM1L mutations cause mitochondrial impairment with less production of ATP in cardiomyocytes. This leads to abnormal intracellular Ca2+ dynamics, resulting in contractile and diastolic dysfunction.

IMPACT

DNM1L mutations was identified in two pediatric patients who developed cardiac dysfunction and human induced pluripotent stem cells (hiPSCs) were established from these two patients and differentiated into hiPSC-derived cardiomyocytes (hiPS-CMs). DNM1L mutations induced abnormal mitochondrial morphology, mitochondrial dysfunction, and insufficient ATP production in hiPS-CMs. In addition, hiPS-CMs with DNM1L mutation showed abnormal Ca2+ kinetics and impaired contractile and diastolic function. This is the first study that elucidate the mechanism of cardiac dysfunction caused by DNM1L mutations by using hiPSCs.

Mitochondria associated membranes in dilated cardiomyopathy: connecting pathogenesis and cellular dysfunction

Dilated cardiomyopathy (DCM) is a leading cause of heart failure, yet therapeutic options remain limited. While traditional research has focused on mechanisms such as energy deficits and calcium dysregulation, increasing evidence suggests that mitochondria-associated membranes (MAMs) could provide new insights into understanding and treating DCM. In this narrative review, we summarize the key role of MAMs, crucial endoplasmic reticulum (ER)-mitochondria interfaces, in regulating cellular processes such as calcium homeostasis, lipid metabolism, and mitochondrial dynamics. Disruption of MAMs function may initiate pathological cascades, including ER stress, inflammation, and cell death. These disruptions in MAM function lead to further destabilization of cellular homeostasis. Identifying MAMs as key modulators of cardiac health may provide novel insights for early diagnosis and targeted therapies in DCM.

Mitochondrial Dysfunction in Neurodegenerative Diseases: Mechanisms and Corresponding Therapeutic Strategies

Neurodegenerative disease (ND) refers to the progressive loss and morphological abnormalities of neurons in the central nervous system (CNS) or peripheral nervous system (PNS). Examples of neurodegenerative diseases include Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Recent studies have shown that mitochondria play a broad role in cell signaling, immune response, and metabolic regulation. For example, mitochondrial dysfunction is closely associated with the onset and progression of a variety of diseases, including ND, cardiovascular diseases, diabetes, and cancer. The dysfunction of energy metabolism, imbalance of mitochondrial dynamics, or abnormal mitophagy can lead to the imbalance of mitochondrial homeostasis, which can induce pathological reactions such as oxidative stress, apoptosis, and inflammation, damage the nervous system, and participate in the occurrence and development of degenerative nervous system diseases such as AD, PD, and ALS. In this paper, the latest research progress of this subject is detailed. The mechanisms of oxidative stress, mitochondrial homeostasis, and mitophagy-mediated ND are reviewed from the perspectives of β-amyloid (Aβ) accumulation, dopamine neuron damage, and superoxide dismutase 1 (SOD1) mutation. Based on the mechanism research, new ideas and methods for the treatment and prevention of ND are proposed.

De Novo DNM1L Pathogenic Variant Associated with Lethal Encephalocardiomyopathy-Case Report and Literature Review

Pathogenic variants in DNM1L, encoding dynamin-like protein-1 (DRP1), cause a lethal encephalopathy. DRP1 defective function results in altered mitochondrial networks, characterized by elongated/spaghetti-like, highly interconnected mitochondria. We validated in yeast the pathogenicity of a de novo DNM1L variant identified by whole exome sequencing performed more than 10 years after the patient's death. Meanwhile, we reviewed the broadness and specificities of DNM1L-related phenotype. The patient, who exhibited developmental delay in her third year, developed a therapy-refractory myoclonic status epilepticus, followed by neurological deterioration with brain atrophy and refractory epilepsy. She died of heart failure due to hypertrophic cardiomyopathy. She was found to be heterozygous for the DNM1L variant (NM_ 012062.5):c.1201G>A, p.(Gly401Ser). We demonstrated its deleterious impact and dominant negative effect by assessing haploid and diploid mutant yeast strains, oxidative growth, oxygen consumption, frequency of petite, and architecture of the mitochondrial network. Structural modeling of p.(Gly401Ser) predicted the interference of the mutant protein in the self-oligomerization of the DRP1 active complex. DNM1L-related phenotypes include static or (early) lethal encephalopathy and neurodevelopmental disorders. In addition, there may be ophthalmological impairment, peripheral neuropathy, ataxia, dystonia, spasticity, myoclonus, and myopathy. The clinical presentations vary depending on mutations in different DRP1 domains. Few pathogenic variants, the p.(Gly401Ser) included, cause an encephalocardiomyopathy with refractory status epilepticus.

Is mitochondrial morphology important for cellular physiology?

Mitochondria are double membrane-bound organelles the network morphology of which in cells is shaped by opposing events of fusion and fission executed by dynamin-like GTPases. Mutations in these genes can perturb the form and functions of mitochondria in cell and animal models of mitochondrial diseases. An expanding array of chemical, mechanical, and genetic stressors can converge on mitochondrial-shaping proteins and disrupt mitochondrial morphology. In recent years, studies aimed at disentangling the multiple roles of mitochondrial-shaping proteins beyond fission or fusion have provided insights into the homeostatic relevance of mitochondrial morphology. Here, I review the pleiotropy of mitochondrial fusion and fission proteins with the aim of understanding whether mitochondrial morphology is important for cell and tissue physiology.

Cardiac remodeling: novel pathophysiological mechanisms and therapeutic strategies

Morphological and structural remodeling of the heart, including cardiac hypertrophy and fibrosis, has been considered as a therapeutic target for heart failure for approximately three decades. Groundbreaking heart failure medications demonstrating reverse remodeling effects have contributed significantly to medical advancements. However, nearly 50% of heart failure patients still exhibit drug resistance, posing a challenge to the healthcare system. Recently, characteristics of heart failure resistant to ARBs and β-blockers have been defined, highlighting preserved systolic function despite impaired diastolic function, leading to the classification of heart failure with preserved ejection fraction (HFpEF). The pathogenesis and aetiology of HFpEF may be related to metabolic abnormalities, as evidenced by its mimicry through endothelial dysfunction and excessive intake of high-fat diets. Our recent findings indicate a significant involvement of mitochondrial hyper-fission in the progression of heart failure. This mitochondrial pathological remodeling is associated with redox imbalance, especially hydrogen sulphide accumulation due to abnormal electron leak in myocardium. In this review, we also introduce a novel therapeutic strategy for heart failure from the current perspective of mitochondrial redox-metabolic remodeling.

The Abl1 tyrosine kinase is a key player in doxorubicin-induced cardiomyopathy and its p53/p73 cell death mediated signaling differs in atrial and ventricular cardiomyocytes

BACKGROUND

Doxorubicin is an important anticancer drug, however, elicits dose-dependently cardiomyopathy. Given its mode of action, i.e. topoisomerase inhibition and DNA damage, we investigated genetic events associated with cardiomyopathy and searched for mechanism-based possibilities to alleviate cardiotoxicity. We treated rats at clinically relevant doses of doxorubicin. Histopathology and transmission electron microscopy (TEM) defined cardiac lesions, and transcriptomics unveiled cardiomyopathy-associated gene regulations. Genomic-footprints revealed critical components of Abl1-p53-signaling, and EMSA-assays evidenced Abl1 DNA-binding activity. Gene reporter assays confirmed Abl1 activity on p53-targets while immunohistochemistry/immunofluorescence microscopy demonstrated Abl1, p53&p73 signaling.

RESULTS

Doxorubicin treatment caused dose-dependently toxic cardiomyopathy, and TEM evidenced damaged mitochondria and myofibrillar disarray. Surviving cardiomyocytes repressed Parkin-1 and Bnip3-mediated mitophagy, stimulated dynamin-1-like dependent mitochondrial fission and induced anti-apoptotic Bag1 signaling. Thus, we observed induced mitochondrial biogenesis. Transcriptomics discovered heterogeneity in cellular responses with minimal overlap between treatments, and the data are highly suggestive for distinct cardiomyocyte (sub)populations which differed in their resilience and reparative capacity. Genome-wide footprints revealed Abl1 and p53 enriched binding sites in doxorubicin-regulated genes, and we confirmed Abl1 DNA-binding activity in EMSA-assays. Extraordinarily, Abl1 signaling differed in the heart with highly significant regulations of Abl1, p53 and p73 in atrial cardiomyocytes. Conversely, in ventricular cardiomyocytes, Abl1 solely-modulated p53-signaling that was BAX transcription-independent. Gene reporter assays established Abl1 cofactor activity for the p53-reporter PG13-luc, and ectopic Abl1 expression stimulated p53-mediated apoptosis.

CONCLUSIONS

The tyrosine kinase Abl1 is of critical importance in doxorubicin induced cardiomyopathy, and we propose its inhibition as means to diminish risk of cardiotoxicity.

De Novo DNM1L Mutation in a Patient with Encephalopathy, Cardiomyopathy and Fatal Non-Epileptic Paroxysmal Refractory Vomiting

Mitochondrial fission and fusion are vital dynamic processes for mitochondrial quality control and for the maintenance of cellular respiration; they also play an important role in the formation and maintenance of cells with high energy demand including cardiomyocytes and neurons. The DNM1L (dynamin-1 like) gene encodes for the DRP1 protein, an evolutionary conserved member of the dynamin family that is responsible for the fission of mitochondria; it is ubiquitous but highly expressed in the developing neonatal heart. De novo heterozygous pathogenic variants in the DNM1L gene have been previously reported to be associated with neonatal or infantile-onset encephalopathy characterized by hypotonia, developmental delay and refractory epilepsy. However, cardiac involvement has been previously reported only in one case. Next-Generation Sequencing (NGS) was used to genetically assess a baby girl characterized by developmental delay with spastic-dystonic, tetraparesis and hypertrophic cardiomyopathy of the left ventricle. Histochemical analysis and spectrophotometric determination of electron transport chain were performed to characterize the muscle biopsy; moreover, the morphology of mitochondria and peroxisomes was evaluated in cultured fibroblasts as well. Herein, we expand the phenotype of DNM1L-related disorder, describing the case of a girl with a heterozygous mutation in DNM1L and affected by progressive infantile encephalopathy, with cardiomyopathy and fatal paroxysmal vomiting correlated with bulbar transitory abnormal T2 hyperintensities and diffusion-weighted imaging (DWI) restriction areas, but without epilepsy. In patients with DNM1L mutations, careful evaluation for cardiac involvement is recommended.

Sulfur metabolism as a new therapeutic target of heart failure

Sulfur-based redox signaling has long attracted attention as critical mechanisms underlying the development of cardiac diseases and resultant heart failure. Especially, post-translational modifications of cysteine (Cys) thiols in proteins mediate oxidative stress-dependent cardiac remodeling including myocardial hypertrophy, senescence, and interstitial fibrosis. However, we recently revealed the existence of Cys persulfides and Cys polysulfides in cells and tissues, which show higher redox activities than Cys and substantially contribute to redox signaling and energy metabolism. We have established simple evaluation methods that can detect polysulfides in proteins and inorganic polysulfides in cells and revealed that polysulfides abundantly expressed in normal hearts are dramatically catabolized by exposure to ischemic/hypoxic and environmental electrophilic stress, which causes vulnerability of the heart to mechanical load. Accumulation of hydrogen sulfide, a nucleophilic catabolite of persulfides/polysulfides, may lead to reductive stress in ischemic hearts, and perturbation of polysulfide catabolism can improve chronic heart failure after myocardial infarction in mice. This review focuses on the (patho)physiological role of sulfur metabolism in hearts, and proposes that sulfur catabolism during ischemic/hypoxic stress has great potential as a new therapeutic strategy for the treatment of ischemic heart failure.

Regulation of PM2.5 on mitochondrial damage in H9c2 cells through miR-421/SIRT3 pathway and protective effect of miR-421 inhibitor and resveratrol

Fine particulate matter (PM2.5) exposure is associated with cardiovascular disease (CVD) morbidity and mortality. Mitochondria are sensitive targets of PM2.5, and mitochondrial dysfunction is closely related to the occurrence of CVD. The epigenetic mechanism of PM2.5-triggered mitochondrial injury of cardiomyocytes is unclear. This study focused on the miR-421/SIRT3 signaling pathway to investigate the regulatory mechanism in cardiac mitochondrial dynamics imbalance in rat H9c2 cells induced by PM2.5. Results illustrated that PM2.5 impaired mitochondrial function and caused dynamics homeostasis imbalance. Besides, PM2.5 up-regulated miR-421 and down-regulated SIRT3 gene expression, along with decreasing p-FOXO3a (SIRT3 downstream target gene) and p-Parkin expression and triggering abnormal expression of fusion gene OPA1 and fission gene Drp1. Further, miR-421 inhibitor (miR-421i) and resveratrol significantly elevated the SIRT3 levels in H9c2 cells after PM2.5 exposure and mediated the expression of SOD2, OPA1 and Drp1, restoring the mitochondrial morphology and function. It suggests that miR-421/SIRT3 pathway plays an epigenetic regulatory role in mitochondrial damage induced by PM2.5 and that miR-421i and resveratrol exert protective effects against PM2.5-incurred cardiotoxicity.

Gene-expression profiling of endomyocardial biopsies from dogs with dilated cardiomyopathy phenotype

INTRODUCTION

The employment of advanced molecular biology technologies has expanded the diagnostic investigation of cardiomyopathies in dogs; these technologies have predominantly been performed on postmortem samples, although the recent use of endomyocardial biopsy in living dogs has enabled a better premortem diagnostic approach to study the myocardial injury.

ANIMALS, MATERIALS, AND METHODS

Endomyocardial biopsies were collected in nine dogs with a dilated cardiomyopathy phenotype (DCM-p) and congestive heart failure and submitted to histologic examination, next-generation sequencing (NGS), and polymerase chain reaction analysis. Data from three healthy dogs (Fastq files) were retrieved from a previously approved study and used as a control group for ribonucleic acid sequencing.

RESULTS

Histologic examination revealed endocardial fibrosis in 6 of 9 dogs, whereas lymphocytic interstitial infiltrates were detected in 2 of 9 dogs, and lymphoplasmacytic and macrophage infiltrates were detected in 1 of 9 dogs. On polymerase chain reaction analysis, two dogs tested positive for canine parvovirus 2 and one dog for canine distemper virus. Gene-expression pathways involved in cellular energy metabolism (especially carbohydrates-insulin) and cardiac structural proteins were different in all DCM-p dogs compared to those in the control group. When dogs with lymphocytic interstitial infiltrates were compared to those in the control group, NGS analysis revealed the predominant role of genes related to inflammation and pathogen infection.

CONCLUSIONS

NGS technology performed on in vivo endomyocardial biopsies has identified different molecular and genetic factors that could play a role in the development and/or progression of DCM-p in dogs.

Mtfp1 ablation enhances mitochondrial respiration and protects against hepatic steatosis

Hepatic steatosis is the result of imbalanced nutrient delivery and metabolism in the liver and is the first hallmark of Metabolic dysfunction-associated steatotic liver disease (MASLD). MASLD is the most common chronic liver disease and involves the accumulation of excess lipids in hepatocytes, inflammation, and cancer. Mitochondria play central roles in liver metabolism yet the specific mitochondrial functions causally linked to MASLD remain unclear. Here, we identify Mitochondrial Fission Process 1 protein (MTFP1) as a key regulator of mitochondrial and metabolic activity in the liver. Deletion of Mtfp1 in hepatocytes is physiologically benign in mice yet leads to the upregulation of oxidative phosphorylation (OXPHOS) activity and mitochondrial respiration, independently of mitochondrial biogenesis. Consequently, liver-specific knockout mice are protected against high fat diet-induced steatosis and metabolic dysregulation. Additionally, Mtfp1 deletion inhibits mitochondrial permeability transition pore opening in hepatocytes, conferring protection against apoptotic liver damage in vivo and ex vivo. Our work uncovers additional functions of MTFP1 in the liver, positioning this gene as an unexpected regulator of OXPHOS and a therapeutic candidate for MASLD.

Mitochondrial Dysfunction in Arrhythmia and Cardiac Hypertrophy

Arrhythmia and cardiac hypertrophy are two very common cardiovascular diseases that can lead to heart failure and even sudden death, thus presenting a serious threat to human life and health. According to global statistics, nearly one million people per year die from arrhythmia, cardiac hypertrophy and other associated cardiovascular diseases. Hence, there is an urgent need to find new treatment targets and to develop new intervention measures. Recently, mitochondrial dysfunction has been examined in relation to heart disease with a view to lowering the incidence of arrhythmia and cardiac hypertrophy. The heart is the body's largest energy consuming organ, turning over about 20 kg of adenosine triphosphate (ATP) per day in the mitochondria. Mitochondrial oxidative phosphorylation (OXPHOS) produces up to 90% of the ATP needed by cardiac muscle cells for contraction and relaxation. Dysfunction of heart mitochondria can therefore induce arrhythmia, cardiac hypertrophy and other cardiovascular diseases. Mitochondrial DNA (mtDNA) mutations cause disorders in OXPHOS and defects in the synthesis of muscle contraction proteins. These lead to insufficient production of secondary ATP, increased metabolic requirements for ATP by the myocardium, and the accumulation of reactive oxygen species (ROS). The resulting damage to myocardial cells eventually induces arrhythmia and cardiac hypertrophy. Mitochondrial damage decreases the efficiency of energy production, which further increases the production of ROS. The accumulation of ROS causes mitochondrial damage and eventually leads to a vicious cycle of mitochondrial damage and low efficiency of mitochondrial energy production. In this review, the mechanism underlying the development of arrhythmia and cardiac hypertrophy is described in relation to mitochondrial energy supply, oxidative stress, mtDNA mutation and Mitochondrial dynamics. Targeted therapy for arrhythmia and cardiac hypertrophy induced by mitochondrial dysfunction is also discussed in terms of its potential clinical value. These strategies should improve our understanding of mitochondrial biology and the pathogenesis of arrhythmia and cardiac hypertrophy. They may also identify novel strategies for targeting mitochondria in the treatment of these diseases.

Disease-associated mutations in Drp1 have fundamentally different effects on the mitochondrial fission machinery

Patient mutations have been identified throughout dynamin-related protein 1 (Drp1), the key protein mediator of mitochondrial fission. These changes generally impact young children and often result in severe neurological defects and, in some instances, death. Until now, the underlying functional defect leading to patient phenotypes has been largely speculative. We therefore analyzed six disease-associated mutations throughout the GTPase and middle domains (MD) of Drp1. The MD plays a role in Drp1 oligomerization, and three mutations in this region were predictably impaired in self-assembly. However, another mutant in this region (F370C) retained oligomerization capability on pre-curved membranes despite being assembly-limited in solution. Instead, this mutation impaired membrane remodeling of liposomes, which highlights the importance of Drp1 in generating local membrane curvature before fission. Two GTPase domain mutations were also observed in different patients. The G32A mutation was impaired in GTP hydrolysis both in solution and in the presence of lipid but remains capable of self-assembly on these lipid templates. The G223V mutation also exhibited decreased GTPase activity and was able to assemble on pre-curved lipid templates; however, this change impaired membrane remodeling of unilamellar liposomes similar to F370C. This demonstrates that the Drp1 GTPase domain also contributes to self-assembly interactions that drive membrane curvature. Overall, the functional defects caused by mutations in Drp1 are highly variable even for mutations that reside within the same functional domain. This study provides a framework for characterizing additional Drp1 mutations to provide a comprehensive understanding of functional sites within this essential protein.

FTY720-P, a Biased S1PR Ligand, Increases Mitochondrial Function through STAT3 Activation in Cardiac Cells

FTY720 is an FDA-approved sphingosine derivative drug for the treatment of multiple sclerosis. This compound blocks lymphocyte egress from lymphoid organs and autoimmunity through sphingosine 1-phosphate (S1P) receptor blockage. Drug repurposing of FTY720 has revealed improvements in glucose metabolism and metabolic diseases. Studies also demonstrate that preconditioning with this compound preserves the ATP levels during cardiac ischemia in rats. The molecular mechanisms by which FTY720 promotes metabolism are not well understood. Here, we demonstrate that nanomolar concentrations of the phosphorylated form of FTY720 (FTY720-P), the active ligand of S1P receptor (S1PR), activates mitochondrial respiration and the mitochondrial ATP production rate in AC16 human cardiomyocyte cells. Additionally, FTY720-P increases the number of mitochondrial nucleoids, promotes mitochondrial morphology alterations, and induces activation of STAT3, a transcription factor that promotes mitochondrial function. Notably, the effect of FTY720-P on mitochondrial function was suppressed in the presence of a STAT3 inhibitor. In summary, our results suggest that FTY720 promotes the activation of mitochondrial function, in part, through a STAT3 action.

Comprehensive Analysis of Mitochondrial Dynamics Alterations in Heart Diseases

The most common alterations affecting mitochondria, and associated with cardiac pathological conditions, implicate a long list of defects. They include impairments of the mitochondrial electron transport chain activity, which is a crucial element for energy formation, and that determines the depletion of ATP generation and supply to metabolic switches, enhanced ROS generation, inflammation, as well as the dysregulation of the intracellular calcium homeostasis. All these signatures significantly concur in the impairment of cardiac electrical characteristics, loss of myocyte contractility and cardiomyocyte damage found in cardiac diseases. Mitochondrial dynamics, one of the quality control mechanisms at the basis of mitochondrial fitness, also result in being dysregulated, but the use of this knowledge for translational and therapeutic purposes is still in its infancy. In this review we tried to understand why this is, by summarizing methods, current opinions and molecular details underlying mitochondrial dynamics in cardiac diseases.

Sericin-mediated improvement of dysmorphic cardiac mitochondria from hypercholesterolaemia is associated with maintaining mitochondrial dynamics, energy production, and mitochondrial structure

CONTEXT

Sericin is a component protein in the silkworm cocoon [Bombyx mori Linnaeus (Bombycidae)] that improves dysmorphic cardiac mitochondria under hypercholesterolemic conditions. This is the first study to explore cardiac mitochondrial proteins associated with sericin treatment.

OBJECTIVE

To investigate the mechanism of action of sericin in cardiac mitochondria under hypercholesterolaemia.

MATERIALS AND METHODS

Hypercholesterolaemia was induced in Wistar rats by feeding them 6% cholesterol-containing chow for 6 weeks. The hypercholesterolemic rats were separated into 2 groups (n = 6 for each): the sericin-treated (1,000 mg/kg daily) and nontreated groups. The treatment conditions were maintained for 4 weeks prior to cardiac mitochondria isolation. The mitochondrial structure was evaluated by immunolabeling electron microscopy, and differential mitochondrial protein expression was determined and quantitated by two-dimensional gel electrophoresis coupled with mass spectrometry.

RESULTS

A 32.22 ± 2.9% increase in the percent striated area of cardiac muscle was observed in sericin-treated hypercholesterolemic rats compared to the nontreatment group (4.18 ± 1.11%). Alterations in mitochondrial proteins, including upregulation of optic atrophy 1 (OPA1) and reduction of NADH-ubiquinone oxidoreductase 75 kDa subunit (NDUFS1) expression, are correlated with a reduction in mitochondrial apoptosis under sericin treatment. Differential proteomic observation also revealed that sericin may improve mitochondrial energy production by upregulating acetyl-CoA acetyltransferase (ACAT1) and NADH dehydrogenase 1α subcomplex subunit 10 (NDUFA10) expression.

DISCUSSION AND CONCLUSIONS

Sericin treatment could improve the dysmorphic mitochondrial structure, metabolism, and energy production of cardiac mitochondria under hypercholesterolaemia. These results suggest that sericin may be an alternative treatment molecule that is related to cardiac mitochondrial abnormalities.

Mitochondrial Fission Process 1 controls inner membrane integrity and protects against heart failure

Mitochondria are paramount to the metabolism and survival of cardiomyocytes. Here we show that Mitochondrial Fission Process 1 (MTFP1) is an inner mitochondrial membrane (IMM) protein that is dispensable for mitochondrial division yet essential for cardiac structure and function. Constitutive knockout of cardiomyocyte MTFP1 in mice resulted in a fatal, adult-onset dilated cardiomyopathy accompanied by extensive mitochondrial and cardiac remodeling during the transition to heart failure. Prior to the onset of disease, knockout cardiac mitochondria displayed specific IMM defects: futile proton leak dependent upon the adenine nucleotide translocase and an increased sensitivity to the opening of the mitochondrial permeability transition pore, with which MTFP1 physically and genetically interacts. Collectively, our data reveal new functions of MTFP1 in the control of bioenergetic efficiency and cell death sensitivity and define its importance in preventing pathogenic cardiac remodeling.

Mitochondrial dynamics involves molecular and mechanical events in motility, fusion and fission

Mitochondria are cell organelles that play pivotal roles in maintaining cell survival, cellular metabolic homeostasis, and cell death. Mitochondria are highly dynamic entities which undergo fusion and fission, and have been shown to be very motile in vivo in neurons and in vitro in multiple cell lines. Fusion and fission are essential for maintaining mitochondrial homeostasis through control of morphology, content exchange, inheritance of mitochondria, maintenance of mitochondrial DNA, and removal of damaged mitochondria by autophagy. Mitochondrial motility occurs through mechanical and molecular mechanisms which translocate mitochondria to sites of high energy demand. Motility also plays an important role in intracellular signaling. Here, we review key features that mediate mitochondrial dynamics and explore methods to advance the study of mitochondrial motility as well as mitochondrial dynamics-related diseases and mitochondrial-targeted therapeutics.

Novel DNM1L variants impair mitochondrial dynamics through divergent mechanisms

Imbalances in mitochondrial and peroxisomal dynamics are associated with a spectrum of human neurological disorders. Mitochondrial and peroxisomal fission both involve dynamin-related protein 1 (DRP1) oligomerisation and membrane constriction, although the precise biophysical mechanisms by which distinct DRP1 variants affect the assembly and activity of different DRP1 domains remains largely unexplored. We analysed four unreported de novo heterozygous variants in the dynamin-1-like gene DNM1L affecting different highly conserved DRP1 domains, leading to developmental delay, seizures, hypotonia, and/or rare cardiac complications in infancy. Single-nucleotide DRP1 stalk domain variants were found to correlate with more severe clinical phenotypes, with in vitro recombinant human DRP1 mutants demonstrating greater impairments in protein oligomerisation, DRP1-peroxisomal recruitment, and both mitochondrial and peroxisomal hyperfusion compared to GTPase or GTPase-effector domain variants. Importantly, we identified a novel mechanism of pathogenesis, where a p.Arg710Gly variant uncouples DRP1 assembly from assembly-stimulated GTP hydrolysis, providing mechanistic insight into how assembly-state information is transmitted to the GTPase domain. Together, these data reveal that discrete, pathological DNM1L variants impair mitochondrial network maintenance by divergent mechanisms.

Mitochondrial Quality Control in the Heart: The Balance between Physiological and Pathological Stress

Alterations in mitochondrial function and morphology are critical adaptations to cardiovascular stress, working in concert in an attempt to restore organelle-level and cellular-level homeostasis. Processes that alter mitochondrial morphology include fission, fusion, mitophagy, and biogenesis, and these interact to maintain mitochondrial quality control. Not all cardiovascular stress is pathologic (e.g., ischemia, pressure overload, cardiotoxins), despite a wealth of studies to this effect. Physiological stress, such as that induced by aerobic exercise, can induce morphologic adaptations that share many common pathways with pathological stress, but in this case result in improved mitochondrial health. Developing a better understanding of the mechanisms underlying alterations in mitochondrial quality control under diverse cardiovascular stressors will aid in the development of pharmacologic interventions aimed at restoring cellular homeostasis.

Mitochondrial homeostasis and redox status in cardiovascular diseases: Protective role of the vagal system

Mitochondria participate in essential cellular functions, including energy production, metabolism, redox homeostasis regulation, intracellular Ca²⁺ handling, apoptosis, and cell fate determination. Disruption of mitochondrial homeostasis under pathological conditions results in mitochondrial reactive oxygen species (ROS) generation and energy insufficiency, which further disturb mitochondrial and cellular homeostasis in a deleterious loop. Mitochondrial redox status has therefore become a potential target for therapy against cardiovascular diseases. In this review, we highlight recent progress in determining the roles of mitochondrial processes in regulating mitochondrial redox status, including mitochondrial dynamics (fusion-fission pathways), mitochondrial cristae remodeling, mitophagy, biogenesis, and mitochondrion-organelle interactions (endoplasmic reticulum-mitochondrion interactions, nucleus-mitochondrion communication, and lipid droplet-mitochondrion interactions). The strategies that activate vagal system include direct vagal activation (electrical vagal stimulation and administration of vagal neurotransmitter acetylcholine) and pharmacological modulation (choline and cholinesterase inhibitors). The vagal system plays an important role in maintaining mitochondrial homeostasis and suppressing mitochondrial oxidative stress by promoting mitochondrial biogenesis and mitophagy, moderating mitochondrial fusion and fission, strengthening mitochondrial cristae stabilization, regulating mitochondrion-organelle interactions, and inhibiting mitochondrial Ca²⁺ overload. Therefore, enhancement of vagal activity can maintain mitochondrial homeostasis and represents a promising therapeutic strategy for cardiovascular diseases.

Inhibition of DRP1 Impedes Zygotic Genome Activation and Preimplantation Development in Mice

Mitochondrion plays an indispensable role during preimplantation embryo development. Dynamic-related protein 1 (DRP1) is critical for mitochondrial fission and controls oocyte maturation. However, its role in preimplantation embryo development is still lacking. In this study, we demonstrate that inhibition of DRP1 activity by mitochondrial division inhibitor-1, a small molecule reported to specifically inhibit DRP1 activity, can cause severe developmental arrest of preimplantation embryos in a dose-dependent manner in mice. Meanwhile, DRP1 inhibition resulted in mitochondrial dysfunction including decreased mitochondrial activity, loss of mitochondrial membrane potential, reduced mitochondrial copy number and inadequate ATP by disrupting both expression and activity of DRP1 and mitochondrial complex assembly, leading to excessive ROS production, severe DNA damage and cell cycle arrest at 2-cell embryo stage. Furthermore, reduced transcriptional and translational activity and altered histone modifications in DRP1-inhibited embryos contributed to impeded zygotic genome activation, which prevented early embryos from efficient development beyond 2-cell embryo stage. These results show that DRP1 inhibition has potential cytotoxic effects on mammalian reproduction, and DRP1 inhibitor should be used with caution when it is applied to treat diseases. Additionally, this study improves our understanding of the crosstalk between mitochondrial metabolism and zygotic genome activation.

MITOL-mediated DRP1 ubiquitylation and degradation promotes mitochondrial hyperfusion in CMT2A-linked MFN2 mutant

Mutations in Mitofusin2 (MFN2), associated with the pathology of the debilitating neuropathy, Charcot-Marie-Tooth type 2A (CMT2A) are known to alter mitochondrial morphology. One such abundant MFN2 mutant, R364W results in the generation of elongated, interconnected mitochondria. However, the mechanism leading to this mitochondrial aberration remains poorly understood. Here we show that mitochondrial hyperfusion in the presence of R364W-MFN2 is due to increased degradation of DRP1. The Ubiquitin E3 ligase MITOL is known to ubiquitylate both MFN2 and DRP1. Interaction with and its subsequent ubiquitylation by MITOL is stronger in presence of WT-MFN2 than R364W-MFN2. This differential interaction of MITOL with MFN2 in the presence of R364W-MFN2 renders the ligase more available for DRP1 ubiquitylation. Multimonoubiquitylation and proteasomal degradation of DRP1 in R364W-MFN2 cells in the presence of MITOL eventually leads to mitochondrial hyperfusion. Here we provide a mechanistic insight into mitochondrial hyperfusion, while also reporting that MFN2 can indirectly modulate DRP1 - an effect not shown before.

Role of GTPase-Dependent Mitochondrial Dynamins in Heart Diseases

Heart function maintenance requires a large amount of energy, which is supplied by the mitochondria. In addition to providing energy to cardiomyocytes, mitochondria also play an important role in maintaining cell function and homeostasis. Although adult cardiomyocyte mitochondria appear as independent, low-static organelles, morphological changes have been observed in cardiomyocyte mitochondria under stress or pathological conditions. Indeed, cardiac mitochondrial fission and fusion are involved in the occurrence and development of heart diseases. As mitochondrial fission and fusion are primarily regulated by mitochondrial dynamins in a GTPase-dependent manner, GTPase-dependent mitochondrial fusion (MFN1, MFN2, and OPA1) and fission (DRP1) proteins, which are abundant in the adult heart, can also be regulated in heart diseases. In fact, these dynamic proteins have been shown to play important roles in specific diseases, including ischemia-reperfusion injury, heart failure, and metabolic cardiomyopathy. This article reviews the role of GTPase-dependent mitochondrial fusion and fission protein-mediated mitochondrial dynamics in the occurrence and development of heart diseases.

Therapeutic potential and recent advances on targeting mitochondrial dynamics in cardiac hypertrophy: A concise review

Pathological cardiac hypertrophy begins as an adaptive response to increased workload; however, sustained hemodynamic stress will lead it to maladaptation and eventually cardiac failure. Mitochondria, being the powerhouse of the cells, can regulate cardiac hypertrophy in both adaptive and maladaptive phases; they are dynamic organelles that can adjust their number, size, and shape through a process called mitochondrial dynamics. Recently, several studies indicate that promoting mitochondrial fusion along with preventing mitochondrial fission could improve cardiac function during cardiac hypertrophy and avert its progression toward heart failure. However, some studies also indicate that either hyperfusion or hypo-fission could induce apoptosis and cardiac dysfunction. In this review, we summarize the recent knowledge regarding the effects of mitochondrial dynamics on the development and progression of cardiac hypertrophy with particular emphasis on the regulatory role of mitochondrial dynamics proteins through the genetic, epigenetic, and post-translational mechanisms, followed by discussing the novel therapeutic strategies targeting mitochondrial dynamic pathways.

All-Trans Retinoic Acid Increases DRP1 Levels and Promotes Mitochondrial Fission

In the heart, mitochondrial homeostasis is critical for sustaining normal function and optimal responses to metabolic and environmental stressors. Mitochondrial fusion and fission are thought to be necessary for maintaining a robust population of mitochondria, and disruptions in mitochondrial fission and/or fusion can lead to cellular dysfunction. The dynamin-related protein (DRP1) is an important mediator of mitochondrial fission. In this study, we investigated the direct effects of the micronutrient retinoid all-trans retinoic acid (ATRA) on the mitochondrial structure in vivo and in vitro using Western blot, confocal, and transmission electron microscopy, as well as mitochondrial network quantification using stochastic modeling. Our results showed that ATRA increases DRP1 protein levels, increases the localization of DRP1 to mitochondria in isolated mitochondrial preparations. Our results also suggested that ATRA remodels the mitochondrial ultrastructure where the mitochondrial area and perimeter were decreased and the circularity was increased. Microscopically, mitochondrial network remodeling is driven by an increased rate of fission over fusion events in ATRA, as suggested by our numerical modeling. In conclusion, ATRA results in a pharmacologically mediated increase in the DRP1 protein. It also results in the modulation of cardiac mitochondria by promoting fission events, altering the mitochondrial network, and modifying the ultrastructure of mitochondria in the heart.

Genetic Neuropathy Due to Impairments in Mitochondrial Dynamics

Mitochondria are dynamic organelles capable of fusing, dividing, and moving about the cell. These properties are especially important in neurons, which in addition to high energy demand, have unique morphological properties with long axons. Notably, mitochondrial dysfunction causes a variety of neurological disorders including peripheral neuropathy, which is linked to impaired mitochondrial dynamics. Nonetheless, exactly why peripheral neurons are especially sensitive to impaired mitochondrial dynamics remains somewhat enigmatic. Although the prevailing view is that longer peripheral nerves are more sensitive to the loss of mitochondrial motility, this explanation is insufficient. Here, we review pathogenic variants in proteins mediating mitochondrial fusion, fission and transport that cause peripheral neuropathy. In addition to highlighting other dynamic processes that are impacted in peripheral neuropathies, we focus on impaired mitochondrial quality control as a potential unifying theme for why mitochondrial dysfunction and impairments in mitochondrial dynamics in particular cause peripheral neuropathy.

The Power of Yeast in Modelling Human Nuclear Mutations Associated with Mitochondrial Diseases

The increasing application of next generation sequencing approaches to the analysis of human exome and whole genome data has enabled the identification of novel variants and new genes involved in mitochondrial diseases. The ability of surviving in the absence of oxidative phosphorylation (OXPHOS) and mitochondrial genome makes the yeast Saccharomyces cerevisiae an excellent model system for investigating the role of these new variants in mitochondrial-related conditions and dissecting the molecular mechanisms associated with these diseases. The aim of this review was to highlight the main advantages offered by this model for the study of mitochondrial diseases, from the validation and characterisation of novel mutations to the dissection of the role played by genes in mitochondrial functionality and the discovery of potential therapeutic molecules. The review also provides a summary of the main contributions to the understanding of mitochondrial diseases emerged from the study of this simple eukaryotic organism.

dnm1 deletion blocks mitochondrial fragmentation in Δfzo1 cells

Mitochondrial division and fusion play critical roles in maintaining functional mitochondria. Fzo1 is an outer mitochondrial membrane GTPase that played an essential role in mitochondrial fusion in budding yeast Saccharomyces cerevisiae. Here, we report the characterization of the Schizosaccharomyces pombe homologue of S. cerevisiae Fzo1p, Fzo1. Disruption of the fzo1 gene in S. pombe results in a fragmented mitochondrial morphology and a dramatically reduced growth on glycerol medium phenotype, indicating that deletion of fzo1 compromises respiratory function. Fluorescence microscopy shows that Fzo1p is located in the mitochondria. Overexpressing Fzo1 from a heterologous promoter induces mitochondrial aggregation. We also find that dnm1 mutations could both block mitochondrial fragmentation and rescue respiration growth defect in Δfzo1 single mutant cells. Our results proposed that a genetic interaction between fzo1 and a balance between division- and fusion-controlled mitochondrial shape and function in S. pombe. This study represents the first report of Fzo1 mediator of mitochondrial fusion in S. pombe.

Mitochondrial Fission and Mitophagy Coordinately Restrict High Glucose Toxicity in Cardiomyocytes

Hyperglycemia-induced mitochondrial dysfunction plays a key role in the pathogenesis of diabetic cardiomyopathy. Injured mitochondrial segments are separated by mitochondrial fission and eliminated by autophagic sequestration and subsequent degradation in the lysosome, a process termed mitophagy. However, it remains poorly understood how high glucose affects the activities of, and the relationship between, mitochondrial fission and mitophagy in cardiomyocytes. In this study, we determined the functional roles of mitochondrial fission and mitophagy in hyperglycemia-induced cardiomyocyte injury. High glucose (30 mM, HG) reduced mitochondrial connectivity and particle size and increased mitochondrial number in neonatal rat ventricular cardiomyocytes, suggesting an enhanced mitochondrial fragmentation. SiRNA knockdown of the pro-fission factor dynamin-related protein 1 (DRP1) restored mitochondrial size but did not affect HG toxicity, and Mdivi-1, a DRP1 inhibitor, even increased HG-induced cardiomyocyte injury, as shown by superoxide production, mitochondrial membrane potential and cell death. However, DRP1 overexpression triggered mitochondrial fragmentation and mitigated HG-induced cardiomyocyte injury, suggesting that the increased mitochondrial fission is beneficial, rather than detrimental, to cardiomyocytes cultured under HG conditions. This is in contrast to the prevailing hypothesis that mitochondrial fragmentation mediates or contributes to HG cardiotoxicity. Meanwhile, HG reduced mitophagy flux as determined by the difference in the levels of mitochondria-associated LC3-II or the numbers of mitophagy foci indicated by the novel dual fluorescent reporter mt-Rosella in the absence and presence of the lysosomal inhibitors. The ability of HG to induce mitochondrial fragmentation and inhibit mitophagy was reproduced in adult mouse cardiomyocytes. Overexpression of Parkin, a positive regulator of mitophagy, or treatment with CCCP, a mitochondrial uncoupler, induced mitophagy and attenuated HG-induced cardiomyocyte death, while Parkin knockdown had opposite effects, suggesting an essential role of mitophagy in cardiomyocyte survival under HG conditions. Strikingly, Parkin overexpression increased mitochondrial fragmentation, while DRP1 overexpression accelerated mitophagy flux, demonstrating a reciprocal activation loop that controls mitochondrial fission and mitophagy. Thus, strategies that promote the mutual positive interaction between mitochondrial fission and mitophagy while simultaneously maintain their levels within the physiological range would be expected to improve mitochondrial health, alleviating hyperglycemic cardiotoxicity.

Angiotensin-(1-9) prevents cardiomyocyte hypertrophy by controlling mitochondrial dynamics via miR-129-3p/PKIA pathway

Angiotensin-(1-9) is a peptide from the noncanonical renin-angiotensin system with anti-hypertrophic effects in cardiomyocytes via an unknown mechanism. In the present study we aimed to elucidate it, basing us initially on previous work from our group and colleagues who proved a relationship between disturbances in mitochondrial morphology and calcium handling, associated with the setting of cardiac hypertrophy. Our first finding was that angiotensin-(1-9) can induce mitochondrial fusion through DRP1 phosphorylation. Secondly, angiotensin-(1-9) blocked mitochondrial fission and intracellular calcium dysregulation in a model of norepinephrine-induced cardiomyocyte hypertrophy, preventing the activation of the calcineurin/NFAT signaling pathway. To further investigate angiotensin-(1-9) anti-hypertrophic mechanism, we performed RNA-seq studies, identifying the upregulation of miR-129 under angiotensin-(1-9) treatment. miR-129 decreased the transcript levels of the protein kinase A inhibitor (PKIA), resulting in the activation of the protein kinase A (PKA) signaling pathway. Finally, we showed that PKA activity is necessary for the effects of angiotensin-(1-9) over mitochondrial dynamics, calcium handling and its anti-hypertrophic effects.

New perspectives on the role of Drp1 isoforms in regulating mitochondrial pathophysiology

Mitochondria are dynamic organelles constantly undergoing fusion and fission. A concerted balance between the process of mitochondrial fusion and fission is required to maintain cellular health under different physiological conditions. Mutation and dysregulation of Drp1, the major driver of mitochondrial fission, has been associated with various neurological, oncological and cardiovascular disorders. Moreover, when subjected to pathological insults, mitochondria often undergo excessive fission, generating fragmented and dysfunctional mitochondria leading to cell death. Therefore, manipulating mitochondrial fission by targeting Drp1 has been an appealing therapeutic approach for cytoprotection. However, studies have been inconsistent. Studies employing Drp1 constructs representing alternate Drp1 isoforms, have demonstrated differing impacts of these isoforms on mitochondrial fission and cell death. Furthermore, there are distinct expression patterns of Drp1 isoforms in different tissues, suggesting idiosyncratic engagement in specific cellular functions. In this review, we will discuss these inherent variations among human Drp1 isoforms and how they could affect Drp1-mediated mitochondrial fission and cell death.

Role of Mitophagy in Cardiovascular Disease

Cardiovascular disease is the leading cause of mortality worldwide, and mitochondrial dysfunction is the primary contributor to these disorders. Recent studies have elaborated on selective autophagy-mitophagy, which eliminates damaged and dysfunctional mitochondria, stabilizes mitochondrial structure and function, and maintains cell survival and growth. Numerous recent studies have reported that mitophagy plays an important role in the pathogenesis of various cardiovascular diseases. This review summarizes the mechanisms underlying mitophagy and advancements in studies on the role of mitophagy in cardiovascular disease.

C-Phycocyanin Ameliorates Mitochondrial Fission and Fusion Dynamics in Ischemic Cardiomyocyte Damage

Mitochondrial dysfunction is a predominant risk factor in ischemic heart disease, in which the imbalance of mitochondrial fusion and fission deteriorates mitochondrial function and might lead to cardiomyocyte death. C-phycocyanin (C-pc), an active component from blue-green algae, such as Spirulina platensis, has been reported to have anti-apoptosis and anti-oxidation functions. In this study, the effects of C-pc on mitochondrial dynamics of cardiomyocytes was examined using an oxygen–glucose deprivation/reoxygenation (OGD/R) model in H9c2 cells, an in vitro model to study the ischemia in the heart. Cell viability assay showed that C-pc dose-dependently reduced OGD/R-induced cell death. Intracellular reactive oxygen species production induced by OGD/R was decreased in C-pc-treated groups in a dose-dependent manner as well. H9c2 cells subjected to OGD/R showed excessive mitochondrial fission and diminished mitochondrial fusion. C-pc treatment significantly ameliorated unbalanced mitochondrial dynamics induced by OGD/R and regulated mitochondrial remodeling through inhibiting mitochondrial fission while promoting fusion. The enhanced expressions of dynamin 1-like protein and mitochondrial fission 1 protein induced by OGD/R were suppressed by C-pc, while the subdued expressions of mitochondrial fusion proteins mitofusins 1 and 2 and optic atrophy 1 induced by OGD/R increased in C-pc-treated groups. Triple immunofluorescence staining revealed that C-pc treatment reduced the recruitment of dynamin 1-like protein from cytoplasm to mitochondrial membranes. Furthermore, C-pc protected H9c2 cells against OGD/R-induced cytochrome c/apoptotic protease activating factor-1 intrinsic apoptosis and suppressed the phosphorylations of extracellular signal-regulated kinase and c-Jun N-terminal kinase. These results suggest that C-pc protects cardiomyocytes from ischemic damage by affecting mitochondrial fission and fusion dynamics and reducing apoptosis and, thus, may be of potential as a prophylactic or therapeutic agent for ischemic heart disease.

Mitochondrial dynamics and their potential as a therapeutic target

Mitochondrial dynamics shape the mitochondrial network and contribute to mitochondrial function and quality control. Mitochondrial fusion and division are integrated into diverse cellular functions and respond to changes in cell physiology. Imbalanced mitochondrial dynamics are associated with a range of diseases that are broadly characterized by impaired mitochondrial function and increased cell death. In various disease models, modulating mitochondrial fusion and division with either small molecules or genetic approaches has improved function. Although additional mechanistic understanding of mitochondrial fusion and division will be critical to inform further therapeutic approaches, mitochondrial dynamics represent a powerful therapeutic target in a wide range of human diseases.

Association of mitochondria with microtubules inhibits mitochondrial fission by precluding assembly of the fission protein Dnm1

Mitochondria are organized as tubular networks in the cell and undergo fission and fusion. Although several of the molecular players involved in mediating mitochondrial dynamics have been identified, the precise cellular cues that initiate mitochondrial fission or fusion remain largely unknown. In fission yeast (Schizosaccharomyces pombe), mitochondria are organized along microtubule bundles. Here, we employed deletions of kinesin-like proteins to perturb microtubule dynamics and used high-resolution and time-lapse fluorescence microscopy, revealing that mitochondrial lengths mimic microtubule lengths. Furthermore, we determined that compared with WT cells, mutant cells with long microtubules exhibit fewer mitochondria, and mutant cells with short microtubules have an increased number of mitochondria because of reduced mitochondrial fission in the former and elevated fission in the latter. Correspondingly, upon onset of closed mitosis in fission yeast, wherein interphase microtubules assemble to form the spindle within the nucleus, we observed increased mitochondrial fission. We found that the consequent rise in the mitochondrial copy number is necessary to reduce partitioning errors during independent segregation of mitochondria between daughter cells. We also discovered that the association of mitochondria with microtubules physically impedes the assembly of the fission protein Dnm1 around mitochondria, resulting in inhibition of mitochondrial fission. Taken together, we demonstrate a mechanism for the regulation of mitochondrial fission that is dictated by the interaction between mitochondria and the microtubule cytoskeleton.

Adrenergic Regulation of Drp1-Driven Mitochondrial Fission in Cardiac Physio-Pathology

Abnormal mitochondrial morphology, especially fragmented mitochondria, and mitochondrial dysfunction are hallmarks of a variety of human diseases including heart failure (HF). Although emerging evidence suggests a link between mitochondrial fragmentation and cardiac dysfunction, it is still not well described which cardiac signaling pathway regulates mitochondrial morphology and function under pathophysiological conditions such as HF. Mitochondria change their shape and location via the activity of mitochondrial fission and fusion proteins. This mechanism is suggested as an important modulator for mitochondrial and cellular functions including bioenergetics, reactive oxygen species (ROS) generation, spatiotemporal dynamics of Ca²⁺ signaling, cell growth, and death in the mammalian cell- and tissue-specific manners. Recent reports show that a mitochondrial fission protein, dynamin-like/related protein 1 (DLP1/Drp1), is post-translationally modified via cell signaling pathways, which control its subcellular localization, stability, and activity in cardiomyocytes/heart. In this review, we summarize the possible molecular mechanisms for causing post-translational modifications (PTMs) of DLP1/Drp1 in cardiomyocytes, and further discuss how these PTMs of DLP1/Drp1 mediate abnormal mitochondrial morphology and mitochondrial dysfunction under adrenergic signaling activation that contributes to the development and progression of HF.

Leptin-induced cardiomyocyte hypertrophy is associated with enhanced mitochondrial fission

Cardiac pathology including hypertrophy has been associated with an imbalance between mitochondrial fission and fusion. Generally, well-balanced mitochondrial fission and fusion are essential for proper functions of mitochondria. Leptin is a 16-kDa appetite-suppressing protein which has been shown to induce cardiomyocyte hypertrophy. In the present study, we determined whether leptin can influence mitochondrial fission or fusion and whether this can be related to its hypertrophic effect. Cardiomyocytes treated for 24 h with 3.1 nM leptin (50 ng/ml), a concentration representing plasma levels in obese individuals, demonstrated an increase in surface area and a significant 1.6-fold increase in the expression of the β-myosin heavy chain. Mitochondrial staining with MitoTracker Green dye showed elongated structures in control cells with an average length of 4.5 µm. Leptin produced a time-dependent increase in mitochondrial fragmentation with decreasing mitochondrial length. The hypertrophic response to leptin was also associated with increased protein levels of the mitochondrial fission protein dynamin-related protein1 (Drp1) although gene expression of Drp1 was unaffected possibly suggesting post-translational modifications of Drp1. Indeed, leptin treatment was associated with decreased levels of phosphorylated Drp1 and increased translocation of Drp1 to the mitochondria thereby demonstrating a pro-fission effect of leptin. As calcineurin may dephosphorylate Drp1, we determined the effect of a calcineurin inhibitor, FK506, which prevented leptin-induced hypertrophy as well as mitochondrial fission and mitochondrial dysfunction. In conclusion, our data show that leptin-induced cardiomyocyte hypertrophy is associated with enhanced mitochondrial fission via a calcineurin-mediated pathway. The ability of leptin to stimulate mitochondrial fission may be important in understanding the role of this protein in cardiac pathology especially that related to mitochondrial dysfunction.

Amplification of Glyceronephosphate O-Acyltransferase and Recruitment of USP30 Stabilize DRP1 to Promote Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and the underlying pathophysiology of HCC is highly complex. In this study, we report that, in a bioinformatic screen of 2,783 genes encoding metabolic enzymes, GNPAT, which encodes the enzyme glyceronephosphate O-acyltransferase, is amplified, upregulated, and highly correlated with poor clinical outcome in human patients with HCC. High GNPAT expression in HCC was due to its amplification and transcriptional activation by the c-Myc/KDM1A complex. GNPAT compensated the oncogenic phenotypes in c-Myc-depleted HCC cells. Mechanistically, GNPAT recruited the enzyme USP30, which deubiquitylated and stabilized dynamin-related protein 1 (DRP1), thereby facilitating regulation of mitochondrial morphology, lipid metabolism, and hepatocarcinogenesis. Inhibition of GNPAT and DRP1 dramatically attenuated lipid metabolism and hepatocarcinogenesis. Furthermore, DRP1 mediated the oncogenic phenotypes driven by GNPAT. Taken together, these results indicate that GNPAT and USP30-mediated stabilization of DRP1 play a critical role in the development of HCC.Significance: This study identifies and establishes the role of the enzyme GNPAT in liver cancer progression, which may serve as a potential therapeutic target for liver cancer. Cancer Res; 78(20); 5808-19. ©2018 AACR.

Osteopontin deficiency ameliorates Alport pathology by preventing tubular metabolic deficits

Alport syndrome is a rare hereditary renal disorder with no etiologic therapy. We found that osteopontin (OPN) is highly expressed in the renal tubules of the Alport mouse and plays a causative pathological role. OPN genetic deletion ameliorated albuminuria, hypertension, tubulointerstitial proliferation, renal apoptosis, and hearing and visual deficits in the Alport mouse. In Alport renal tubules we found extensive cholesterol accumulation and increased protein expression of dynamin-3 (DNM3) and LDL receptor (LDLR) in addition to dysmorphic mitochondria with defective bioenergetics. Increased pathological cholesterol influx was confirmed by a remarkably increased uptake of injected DiI-LDL cholesterol by Alport renal tubules, and by the improved lifespan of the Alport mice when crossed with the Ldlr-/- mice with defective cholesterol influx. Moreover, OPN-deficient Alport mice demonstrated significant reduction of DNM3 and LDLR expression. In human renal epithelial cells, overexpressing DNM3 resulted in elevated LDLR protein expression and defective mitochondrial respiration. Our results suggest a potentially new pathway in Alport pathology where tubular OPN causes DNM3- and LDLR-mediated enhanced cholesterol influx and impaired mitochondrial respiration.

Novel insights into the role of mitochondrial fusion and fission in cardiomyocyte apoptosis induced by ischemia/reperfusion

As the main source of energy in the body, mitochondria are highly dynamic organelles, which are constantly going through fusion and fission. The fine balance of mitochondrial fusion and fission plays an important role in maintaining the stability of cardiomyocyte homeostasis. The processes of mitochondrial fusion and fission are very complex, which is mediated by fusion and fission proteins. Disruptions in these processes through controlling fusion and fission proteins affect mitochondrial functions and cardiomyocyte survival. Ischemia/reperfusion (I/R) can regulate the expression and post-translational modifications of fusion and fission proteins thereby inducing the abnormality of mitochondrial fusion and fission and cardiomyocyte apoptosis. Furthermore, intervention with the expression and function of fusion and fission proteins influences on cardiomyocyte apoptosis under I/R conditions. In this review, we focus on the current developments in the effects of mitochondrial fusion and fission on cardiomyocyte functions, the implications for cardiomyocyte apoptosis in response to I/R, and possible mechanisms. And we review their roles as a potential therapeutic target for treating I/R-induced cardiomyocyte injury.

Anilinopyrimidine Resistance in Botrytis cinerea Is Linked to Mitochondrial Function

Crop protection anilinopyrimidine (AP) fungicides were introduced more than 20 years ago for the control of a range of diseases caused by ascomycete plant pathogens, and in particular for the control of gray mold caused by Botrytis cinerea. Although early mode of action studies suggested an inhibition of methionine biosynthesis, the molecular target of this class of fungicides was never fully clarified. Despite AP-specific resistance having been described in B. cinerea field isolates and in multiple other targeted species, the underlying resistance mechanisms were unknown. It was therefore expected that the genetic characterization of resistance mechanisms would permit the identification of the molecular target of these fungicides. In order to explore the widest range of possible resistance mechanisms, AP-resistant B. cinerea UV laboratory mutants were generated and the mutations conferring resistance were determined by combining whole-genome sequencing and reverse genetics. Genetic mapping from a cross between a resistant field isolate and a sensitive reference isolate was used in parallel and led to the identification of an additional molecular determinant not found from the characterized UV mutant collection. Together, these two approaches enabled the characterization of an unrivaled diversity of resistance mechanisms. In total, we report the elucidation of resistance-conferring mutations within nine individual genes, two of which are responsible for almost all instances of AP resistance in the field. All identified resistance-conferring genes encode proteins that are involved in mitochondrial processes, suggesting that APs primarily target the mitochondria. The functions of these genes and their possible interactions are discussed in the context of the potential mode of action for this important class of fungicides.

Dilated Cardiomyopathy: Genetic Determinants and Mechanisms

Nonischemic dilated cardiomyopathy (DCM) often has a genetic pathogenesis. Because of the large number of genes and alleles attributed to DCM, comprehensive genetic testing encompasses ever-increasing gene panels. Genetic diagnosis can help predict prognosis, especially with regard to arrhythmia risk for certain subtypes. Moreover, cascade genetic testing in family members can identify those who are at risk or with early stage disease, offering the opportunity for early intervention. This review will address diagnosis and management of DCM, including the role of genetic evaluation. We will also overview distinct genetic pathways linked to DCM and their pathogenetic mechanisms. Historically, cardiac morphology has been used to classify cardiomyopathy subtypes. Determining genetic variants is emerging as an additional adjunct to help further refine subtypes of DCM, especially where arrhythmia risk is increased, and ultimately contribute to clinical management.

Role of Mitochondrial Dysfunction in Hypertension and Obesity

Mitochondria are essential for the maintenance of normal physiological function of tissue cells. Mitochondria are subject to dynamic processes in order to establish a control system related to survival or cell death and adaptation to changes in the metabolic environment of cells. Mitochondrial dynamics includes fusion and fission processes, biogenesis, and mitophagy. Modifications of mitochondrial dynamics in organs involved in energy metabolism such as the pancreas, liver, skeletal muscle, and white adipose tissue could be of relevance for the development of insulin resistance, obesity, and type 2 diabetes. Mitochondrial dynamics and the factors involved in its regulation are also critical for neuronal development, survival, and function. Modifications in mitochondrial dynamics in either agouti-related peptide (AgRP) or pro-opiomelanocortin (POMC), circuits which regulates feeding behavior, are related to changes of food intake, energy balance, and obesity development. Activation of the sympathetic nervous system has been considered as a crucial point in the pathogenesis of hypertension among obese individuals and it also plays a key role in cardiac remodeling. Hypertension-related cardiac hypertrophy is associated with changes in metabolic substrate utilization, dysfunction of the electron transport chain, and ATP synthesis. Alterations in both mitochondrial dynamics and ROS production have been associated with endothelial dysfunction, development of hypertension, and cardiac hypertrophy. Finally, it might be postulated that alterations of mitochondrial dynamics in white adipose tissue could contribute to the development and maintenance of hypertension in obesity situations through leptin overproduction. Leptin, together with insulin, will induce activation of sympathetic nervous system with consequences at renal, vascular, and cardiac levels, driving to sodium retention, hypertension, and left ventricular hypertrophy. Moreover, both leptin and insulin will induce mitochondrial alterations into arcuate nucleus leading to signals driving to increased food intake and reduced energy expenditure. This, in turn would perpetuate white adipose tissue excess and its well-known metabolic and cardiovascular consequences.

Experimental and Human Evidence for Lipocalin-2 (Neutrophil Gelatinase-Associated Lipocalin [NGAL]) in the Development of Cardiac Hypertrophy and heart failure

BACKGROUND

Cardiac hypertrophy increases the risk of developing heart failure and cardiovascular death. The neutrophil inflammatory protein, lipocalin-2 (LCN2/NGAL), is elevated in certain forms of cardiac hypertrophy and acute heart failure. However, a specific role for LCN2 in predisposition and etiology of hypertrophy and the relevant genetic determinants are unclear. Here, we defined the role of LCN2 in concentric cardiac hypertrophy in terms of pathophysiology, inflammatory expression networks, and genomic determinants.

METHODS AND RESULTS

We used 3 experimental models: a polygenic model of cardiac hypertrophy and heart failure, a model of intrauterine growth restriction and Lcn2-knockout mouse; cultured cardiomyocytes; and 2 human cohorts: 114 type 2 diabetes mellitus patients and 2064 healthy subjects of the YFS (Young Finns Study). In hypertrophic heart rats, cardiac and circulating Lcn2 was significantly overexpressed before, during, and after development of cardiac hypertrophy and heart failure. Lcn2 expression was increased in hypertrophic hearts in a model of intrauterine growth restriction, whereas Lcn2-knockout mice had smaller hearts. In cultured cardiomyocytes, Lcn2 activated molecular hypertrophic pathways and increased cell size, but reduced proliferation and cell numbers. Increased LCN2 was associated with cardiac hypertrophy and diastolic dysfunction in diabetes mellitus. In the YFS, LCN2 expression was associated with body mass index and cardiac mass and with levels of inflammatory markers. The single-nucleotide polymorphism, rs13297295, located near LCN2 defined a significant cis-eQTL for LCN2 expression.

CONCLUSIONS

Direct effects of LCN2 on cardiomyocyte size and number and the consistent associations in experimental and human analyses reveal a central role for LCN2 in the ontogeny of cardiac hypertrophy and heart failure.