Mfn2 Affects Embryo Development via Mitochondrial Dysfunction and Apoptosis

BackgroundGrowth factors, energy sources, and mitochondrial function strongly affect embryo growth and development in vitro. The biological role and prospective significance of the mitofusin gene Mfn2 in the development of preimplantation embryos remain poorly understood. Our goal is to profile the role of Mfn2 in mouse embryos and determine the underlying mechanism of Mfn2 function in embryo development.MethodsWe transfected Mfn2-siRNA into 2-cell fertilized eggs and then examined the expression of Mfn2, the anti-apoptotic protein Bcl-2, and the apoptosis-promoting protein Bax by Western blot. Additionally, we determined the blastocyst formation rate and measured ATP levels, mtDNA levels, mitochondrial membrane potential (ΔΨm), and apoptosis in all of the embryos.ResultsThe results indicate that the Mfn2 and Bcl-2 levels were markedly decreased, whereas Bax levels were increased in the T group (embryos transfected with Mfn2-siRNA) compared with the C group (embryos transfected with control-siRNA). The blastocyst formation rate was significantly decreased in the T group. The ATP content and the relative amounts of mtDNA and cDNA in the T group were significantly reduced compared with the C group. In the T group, ΔΨm and Ca²⁺ levels were reduced, and the number of apoptotic cells was increased.ConclusionLow in vitro expression of Mfn2 attenuates the blastocyst formation rate and cleavage speed in mouse zygotes and causes mitochondrial dysfunction, as confirmed by the ATP and mtDNA levels and mitochondrial membrane potential. Mfn2 deficiency induced apoptosis through the Bcl-2/Bax and Ca²⁺ pathways. These findings indicate that Mfn2 could affect preimplantation embryo development through mitochondrial function and cellular apoptosis.     

线粒体融合与分裂在中枢神经系统疾病中的研究进展

线粒体是一种高度动态的细胞器,通过不断的融合和分裂维持其动态平衡,参与生理病理功能调节。线粒体融合与分裂主要由融合分裂相关蛋白调控,如Drp1、Fis1、Mfn1、Mfn2、OPA1等,多种诱导因子通过调节线粒体融合分裂相关蛋白表达及活化进而调节线粒体形态和生理功能。现有研究表明线粒体融合分裂的异常可能是许多中枢神经系统疾病的发病机制之一。本文从线粒体融合分裂的分子调控机制及其在缺血性脑中风、帕金森综合征和阿尔兹海默症等中枢神经系统疾病中的研究进展方面进行综述,为相关疾病的防治提供一定参考和线索。     

Mitofusin 2 ameliorates hypoxia-induced apoptosis via mitochondrial function and signaling pathways

Mitochondrial dynamics play a critical role in mitochondrial function and signaling. Although mitochondria play a critical role in hypoxia/ischemia, the further mechanisms between mitochondrial dynamics and ischemia are still unclear. The current study aimed to determine the role of mitofusin 2, a key regulator of mitochondrial fusion, in a hypoxic model and to explore a novel strategy for cerebral ischemia via modulation of mitochondrial dynamics. To the best of our knowledge, this is the first study to investigate both mitochondrial function and molecular pathways to determine the role of mitofusin 2 in hypoxia-induced neuronal apoptosis. In vivo, C57BL/6 mice (male, 19–25 g) underwent a permanent middle cerebral artery occlusion for 12 or 24 h (n = 6 per group). In vitro, cobalt chloride was used to mimic hypoxia in immortalized hippocampal neurons. Down- or up-regulation of Mfn2 was induced to investigate the role of Mfn2 in hypoxia, especially in mitochondrial function and signaling pathways. The findings demonstrated that decreased mitofusin 2 occurred both in vivo and in vitro hypoxic models; second, the anti-apoptotic effect of Mfn2 may work via restoration of mitochondrial function; third, the modulation of the B Cell Leukemia 2/Bcl-2 Associated X protein and extracellular signal-regulated kinase 1/2 signaling pathways highlight the role of Mfn2 in signaling pathways beyond fusion. In summary, depletion of mitofusin 2 would lead to apoptosis both in normal or hypoxic conditions; however, mitofusin 2 overexpression could attenuate hypoxia-induced apoptosis, which represents a potential novel strategy for neuroprotection against ischemic brain damage.     

SIRT2抑制对MPP+诱导的帕金森病细胞模型凋亡和线粒体动态平衡的影响*

探究siRNA敲减沉默信息调节因子2(SIRT2)对1-甲基-4-苯基吡啶离子(MPP⁺)诱导的帕金森病细胞模型细胞损伤的影响和机制。CCK-8法检测不同浓度MPP⁺处理对体外培养小鼠海马神经元HT-22细胞生存率的影响。将细胞分为对照组、MPP⁺最佳浓度处理组(1 mmol/L MPP⁺处理组)、阴性转染组(对照组基础上转染SIRT2阴性序列)、SIRT2 siRNA处理组(损伤组基础上转染SIRT2 siRNA)。观察各组细胞凋亡情况,检测凋亡相关蛋白(Bcl-2、Bax、Caspase-9)、线粒体分裂及融合相关蛋白(Drp1、Fis1、OPA1、Mfn1、Mfn2)。与对照组相比,MPP⁺处理组细胞抑制率均升高,细胞抑制率随MPP⁺浓度增加而逐渐增加(P<0.05)。与SIRT2 siRNA转染组相比,损伤组Bax、Caspase-9、Drp1、Fis1蛋白表达和细胞凋亡率升高,Bcl-2、Mfn1、Mfn2蛋白表达降低(P<0.05)。SIRT2在MPP⁺诱导帕金森病细胞模型中表达升高,抑制SIRT2可减轻MPP⁺诱导帕金森病细胞模型中细胞凋亡并促进线粒体融合,从而对神经元具有一定的保护作用。     

Contribution of neural cell death to depressive phenotypes of streptozotocin-induced diabetic mice

Major depression disorder (MDD) or depression is highly prevalent in individuals with diabetes, and the depressive symptoms are more severe and less responsive to antidepressant therapies in these patients. The underlying mechanism is little understood. We hypothesized that the pathophysiology of comorbid depression was more complex than that proposed for MDD and that neural cell death played a role in the disease severity. To test this hypothesis, we generated streptozotocin (STZ)-induced diabetic mice. These mice had blood glucose levels threefold above controls and exhibited depressive phenotypes as judged by a battery of behavioral tests, thus confirming the comorbidity in mice. Immunohistological studies showed markedly increased TUNEL-positive cells in the frontal cortex and hippocampus of the comorbid mice, indicating apoptosis. This finding was supported by increased caspase-3 and decreased Bcl-2 proteins in these brain regions. In addition, the serum brain-derived neurotrophic factor (BDNF) level of comorbid mice was reduced compared with controls, further supporting the neurodegenerative change. Mechanistic analyses showed an increased expression of mitochondrial fission genes fission protein 1 (Fis1) and dynamin-related protein 1 (Drp1), and a decreased expression of mitochondrial fusion genes mitofusin 1 (Mfn1), mitofusin 2 (Mfn2) and optical atrophy 1 (Opa1). Representative assessment of the proteins Drp1 and Mfn2 mirrored the mRNA changes. The data demonstrated that neural cell death was associated with the depressive phenotype of comorbid mice and that a fission-dominant expression of genes and proteins mediating mitochondrial dynamics played a role in the hyperglycemia-induced cell death. The study provides new insight into the disease mechanism and could aid the development of novel therapeutics aimed at providing neuroprotection by modulating mitochondrial dynamics to treat comorbid depression with diabetes.KEY WORDS: Depression, Diabetes, Comorbidity, Apoptosis, Neurodegeneration, Mitochondria     

Response of mitochondrial fusion and fission protein gene expression to exercise in rat skeletal muscle

The purpose of this study was to investigate the changes in the gene expression of Mitofusion (Mfn) 1 and 2 and Fission 1 (Fis1) and mitochondrial energy metabolism in response to altered energy demand during prolonged exercise in rat skeletal muscle. Male Sprague–Dawley rats were subjected to an acute bout of treadmill running at various durations and killed immediately or during recovery. Mfn1/2 and Fis1 mRNA and protein contents, reactive oxygen species (ROS) generation, state 3 and state 4 respiration rates, trans-innermembrane potential and ATP synthase activity were measured in isolated muscle mitochondria. We found that (1) Mfn1/2 mRNA contents were progressively decreased during 150 min of exercise, along with decreased Mfn 1 protein levels. Fis1 mRNA and protein contents showed significant increases after 120–150 min of exercise. These changes persisted through the recovery period up to 24 h. (2) Mitochondrial ROS generation and state 4 respiration showed progressive increases up to 120 min, but dropped at 150 min of exercise. (3) State 3 respiration rate and respiratory control index were unchanged initially but decreased at 150 and 120 min of exercise, respectively, whereas ATP synthase activity was elevated at 45 min and returned to resting level thereafter. Our data suggested that the gene expression of mitochondrial fusion and fission proteins in skeletal muscle can respond rapidly to increased metabolic demand during prolonged exercise, which could significantly affect the efficiency of oxidative phosphorylation.     

The decreased expression of mitofusin-1 and increased fission-1 together with alterations in mitochondrial morphology in the kidney of rats with chronic fluorosis may involve elevated oxidative stress

This study was designed to characterize changes in the expression of mitofusin-1 (Mfn1) and fission-1 (Fis1), as well as in mitochondrial morphology in the kidney of rats subjected to chronic fluorosis and to elucidate whether any mitochondrial injury observed is associated with increased oxidative stress. Sixty Sprague-Dawley (SD) rats were divided randomly into 3 groups of 20 each, i.e., the untreated control group (natural drinking water containing <0.5 mg fluoride/L), the low-fluoride group (drinking water supplemented with 10 mg fluoride/L, prepared with NaF) and the high-fluoride group (50 mg fluoride/L), and treated for 6 months. Thereafter, renal expression of Mfn1 and Fis1 at both the protein and mRNA levels was determined by immunohistochemistry and real-time PCR, respectively. In addition, the malondiadehyde (MDA) was quantitated by the thiobarbituric acid procedure and the total antioxidative capability (T-AOC) by a colorimetric method. The morphology of renal mitochondria was observed under the transmission electron microscope. In the renal tissues of rats with chronic fluorosis, expression of both Mfn1 protein and mRNA was clearly reduced, whereas that of Fis1 was elevated. The level of MDA was increased and the T-AOC lowered. Swollen or fragmented mitochondria in renal cells were observed under the electronic microscope. These findings indicate that chronic fluorosis can lead to the abnormal mitochondrial dynamics and changed morphology in the rat kidney, which in mechanism might be induced by a high level of oxidative stress in the disease.     

Reduction of endoplasmic reticulum stress attenuates the defects caused by Drosophila mitofusin depletion

Ablation of the mitochondrial fusion and endoplasmic reticulum (ER)–tethering protein Mfn2 causes ER stress, but whether this is just an epiphenomenon of mitochondrial dysfunction or a contributor to the phenotypes in mitofusin (Mfn)-depleted Drosophila melanogaster is unclear. In this paper, we show that reduction of ER dysfunction ameliorates the functional and developmental defects of flies lacking the single Mfn mitochondrial assembly regulatory factor (Marf). Ubiquitous or neuron- and muscle-specific Marf ablation was lethal, altering mitochondrial and ER morphology and triggering ER stress that was conversely absent in flies lacking the fusion protein optic atrophy 1. Expression of Mfn2 and ER stress reduction in flies lacking Marf corrected ER shape, attenuating the developmental and motor defects. Thus, ER stress is a targetable pathogenetic component of the phenotypes caused by Drosophila Mfn ablation.     

Inhibition of the proteasome preserves Mitofusin-2 and mitochondrial integrity,protecting cardiomyocytes during ischemia-reperfusion injury

Cardiomyocyte loss is the main cause of myocardial dysfunction following an ischemia-reperfusion (IR) injury. Mitochondrial dysfunction and altered mitochondrial network dynamics play central roles in cardiomyocyte death. Proteasome inhibition is cardioprotective in the setting of IR; however, the mechanisms underlying this protection are not well-understood. Several proteins that regulate mitochondrial dynamics and energy metabolism, including Mitofusin-2 (Mfn2), are degraded by the proteasome. The aim of this study was to evaluate whether proteasome inhibition can protect cardiomyocytes from IR damage by maintaining Mfn2 levels and preserving mitochondrial network integrity. Using ex vivo Langendorff-perfused rat hearts and in vitro neonatal rat ventricular myocytes, we showed that the proteasome inhibitor MG132 reduced IR-induced cardiomyocyte death. Moreover, MG132 preserved mitochondrial mass, prevented mitochondrial network fragmentation, and abolished IR-induced reductions in Mfn2 levels in heart tissue and cultured cardiomyocytes. Interestingly, Mfn2 overexpression also prevented cardiomyocyte death. This effect was apparently specific to Mfn2, as overexpression of Miro1, another protein implicated in mitochondrial dynamics, did not confer the same protection. Our results suggest that proteasome inhibition protects cardiomyocytes from IR damage. This effect could be partly mediated by preservation of Mfn2 and therefore mitochondrial integrity.     

Dynamin‐related protein 1‐mediated mitochondrial fission contributes to IR‐783‐induced apoptosis in human breast cancer cells

IR‐783 is a kind of heptamethine cyanine dye that exhibits imaging, cancer targeting and anticancer properties. A previous study reported that its imaging and targeting properties were related to mitochondria. However, the molecular mechanism behind the anticancer activity of IR‐783 has not been well demonstrated. In this study, we showed that IR‐783 inhibits cell viability and induces mitochondrial apoptosis in human breast cancer cells. Exposure of MDA‐MB‐231 cells to IR‐783 resulted in the loss of mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) depletion, mitochondrial permeability transition pore (mPTP) opening and cytochrome c (Cyto C) release. Furthermore, we found that IR‐783 induced dynamin‐related protein 1 (Drp1) translocation from the cytosol to the mitochondria, increased the expression of mitochondrial fission proteins mitochondrial fission factor (MFF) and fission‐1 (Fis1), and decreased the expression of mitochondrial fusion proteins mitofusin1 (Mfn1) and optic atrophy 1 (OPA1). Moreover, knockdown of Drp1 markedly blocked IR‐783‐mediated mitochondrial fission, loss of MMP, ATP depletion, mPTP opening and apoptosis. Our in vivo study confirmed that IR‐783 markedly inhibited tumour growth and induced apoptosis in an MDA‐MB‐231 xenograft model in association with the mitochondrial translocation of Drp1. Taken together, these findings suggest that IR‐783 induces apoptosis in human breast cancer cells by increasing Drp1‐mediated mitochondrial fission. Our study uncovered the molecular mechanism of the anti‐breast cancer effects of IR‐783 and provided novel perspectives for the application of IR‐783 in the treatment of breast cancer.     

Involvement of pericardial adipose tissue in cardiac fibrosis of dietary-induced obese minipigs— Role of mitochondrial function

BackgroundHeart is a high energy demand organ and cardiac fat is the main local energy source for heart. Alteration in cardiac fat may affect cardiac energy and contribute to heart dysfunction. We previously observed a link between alteration in pericardial fat (PAT) and local adverse effects on myocardial fibrosis in obese minipigs. This study investigated the role of PAT on cardiac energy and mitochondrial function, and elucidated a potential mechanism for PAT in cardiac fibrosis.Materials and methodsFive-month-old Lee-Sung minipigs were made obese by feeding a high-fat diet (HFD) for 6 months. The conditioned medium from PAT of obese minipigs (PAT-CM) was collected and H9C2 cells were treated with it to study mechanisms.ResultsHFD caused a cardiac energy deficit and fibrosis in the left ventricle. An elevated content of IL6 and malondialdehyde was found in the PAT of obese pigs. Obese pigs exhibited an increased level of oleic acid and a reduced level of saturated fatty acids in PAT compared to control pigs. HFD did not alter the metabolic characteristics of epicardial fat. PAT-CM caused apoptosis of H9C2 cells and inhibited basal mitochondrial respiration and ATP production. Protein expressions for mitochondrial dynamics- (Mfn2, Opa1, Drp1, and Fis1) and a mitophagy-related protein (Parkin) were suppressed by PAT-CM. PAT-CM enhanced the protein expression of LC3II, and the ratio of LC3II/LC3I.To conclude, PAT was involved in cardiac fibrosis of HFD-fed minipigs. The secretomes of PAT impaired mitochondrial functions and caused cardiomyocyte apoptosis in a paracrine manner.     

Vagal nerve stimulation improves mitochondrial dynamics via an M3 receptor/CaMKKβ/AMPK pathway in isoproterenol‐induced myocardial ischaemia

Mitochondrial dynamics—fission and fusion—are associated with ischaemic heart disease (IHD). This study explored the protective effect of vagal nerve stimulation (VNS) against isoproterenol (ISO)‐induced myocardial ischaemia in a rat model and tested whether VNS plays a role in preventing disorders of mitochondrial dynamics and function. Isoproterenol not only caused cardiac injury but also increased the expression of mitochondrial fission proteins [dynamin‐related peptide1 (Drp1) and mitochondrial fission protein1 (Fis‐1)) and decreased the expression of fusion proteins (optic atrophy‐1 (OPA1) and mitofusins1/2 (Mfn1/2)], thereby disrupting mitochondrial dynamics and leading to increase in mitochondrial fragments. Interestingly, VNS restored mitochondrial dynamics through regulation of Drp1, Fis‐1, OPA1 and Mfn1/2; enhanced ATP content and mitochondrial membrane potential; reduced mitochondrial permeability transition pore (MPTP) opening; and improved mitochondrial ultrastructure and size. Furthermore, VNS reduced the size of the myocardial infarction and ameliorated cardiomyocyte apoptosis and cardiac dysfunction induced by ISO. Moreover, VNS activated AMP‐activated protein kinase (AMPK), which was accompanied by phosphorylation of Ca²⁺/calmodulin‐dependent protein kinase kinase β (CaMKKβ) during myocardial ischaemia. Treatment with subtype‐3 of muscarinic acetylcholine receptor (M₃R) antagonist 4‐diphenylacetoxy‐N‐methylpiperidine methiodide or AMPK inhibitor Compound C abolished the protective effects of VNS on mitochondrial dynamics and function, suggesting that M₃R/CaMKKβ/AMPK signalling are involved in mediating beneficial effects of VNS. This study demonstrates that VNS modulates mitochondrial dynamics and improves mitochondrial function, possibly through the M₃R/CaMKKβ/AMPK pathway, to attenuate ISO‐induced cardiac damage in rats. Targeting mitochondrial dynamics may provide a novel therapeutic strategy in IHD.     

有氧运动改善AD模型APP/PS1双转基因小鼠中枢神经元线粒体融合分裂动态平衡

线粒体融合分裂平衡是线粒体动力学的需要。本研究观察12周规律有氧运动对APP/PS1双转基因小鼠中枢神经元线粒体融合分裂动态平衡的影响。本研究采用3月龄雄性APP/PS1小鼠（AD模型）随机分为AD安静组（AS）、AD运动组（AE）,同月龄雄性C57BL/6J小鼠做正常对照组（CS）。AE组进行12周规律跑台运动,5 d/周,60 min/d。前10 min运动速度12 m/min,后50 min运动速度15 m/min,跑台坡度为0°。八臂迷宫实验检测小鼠工作记忆错误频率和参考记忆错误频率;Western印迹检测小鼠皮层、海马组织中线粒体分裂蛋白Drp1和Fis1的含量,以及Drp1的活性（p-Drp1-Ser616）、线粒体融合蛋白Mfn1、Mfn2、Opa1的表达水平;透射电镜观察皮层、海马线粒体形态结构、健康线粒体比率及线粒体平均直径。本研究证实AS组较CS组工作记忆错误频率显著提高（P<0.05）,12周有氧运动显著降低工作记忆错误频率（P<0.05）。AS组小鼠皮层Fis1蛋白和海马脑区Drp1、Fis1蛋白表达水平及皮层、海马脑区Drp1蛋白的活性增加（P<0.05）。而皮层Mfn1和海马Mfn1、Mfn2蛋白表达水平显著降低（P<0.05）。12周有氧运动显著减低Fis1、Drp1蛋白表达及Drp1蛋白的活性,提高Mfn1、Mfn2蛋白表达水平（P<0.05）。AS组小鼠皮层、海马线粒体多呈现球形,部分线粒体膜结构消失,线粒体嵴结构紊乱。且AS组较CS组小鼠健康线粒体比率降低、直径缩短。12周规律有氧运动可明显改善线粒体形态和结构,提高健康线粒体比率及直径。本研究提示,12周规律有氧运动可有效抑制皮层、海马脑区线粒体分裂蛋白Drp1和 Fis1的表达,降低Drp1的活性（p-Drp1-Ser616）,上调线粒体融合蛋白Mfn1、Mfn2的蛋白表达水平,改善线粒体形态和结构以促进线粒体质量控制,是有氧运动改善AD模型空间学习记忆能力的分子机制之一。     

High glucose induces mitochondrial dysfunction and apoptosis in human retinal pigment epithelium cells via promoting SOCS1 and Fas/FasL signaling

Diabetic retinopathy (DR) is one of the most serious complications of diabetes mellitus (DM), however, the contribution of high glucose (HG) or hyperglycemia to DR is far from fully understanding. In the present study, we examined the expression of Fas/FasL signaling and suppressors of cytokine signaling (SOCS)1 and 3 in HG-induced human retinal pigment epithelium cells (ARPE-19 cells). And then we investigated the regulatory role of both Fas and SOCS1 in HG-induced mitochondrial dysfunction and apoptosis. Results demonstrated that HG with more than 40 mM induced mitochondrial dysfunction via reducing mitochondrial membrane potential (MMP) and via inhibiting the Bcl-2 level, which is the upstream signaling of mitochondria in ARPE-19 cells. HG also upreuglated the Fas signaling and SOCS levels probably via promoting JAK/STAT signaling in ARPE-19 cells. Moreover, the exogenous Fas or entogenous overexpressed SOCS1 accentuated the HG-induced mitochondrial dysfunction and apoptosis, whereas the knockdown of either Fas or SOCS1 reduced the HG-induced mitochondria dysfunction and apoptosis. Thus, the present study confirmed that both Fas/FasL signaling and SOCS1 promoted the HG-induced mitochondrial dysfunction and apoptosis. These results implies the key regulatory role of Fas signaling and SOCS in DR.     

Protective Effect of Boerhaavia diffusa L. against Mitochondrial Dysfunction in Angiotensin II Induced Hypertrophy in H9c2 Cardiomyoblast Cells

Mitochondrial dysfunction plays a critical role in the development of cardiac hypertrophy and heart failure. So mitochondria are emerging as one of the important druggable targets in the management of cardiac hypertrophy and other associated complications. In the present study, effects of ethanolic extract of Boerhaavia diffusa (BDE), a green leafy vegetable against mitochondrial dysfunction in angiotensin II (Ang II) induced hypertrophy in H9c2 cardiomyoblasts was evaluated. H9c2 cells challenged with Ang II exhibited pathological hypertrophic responses and mitochondrial dysfunction which was evident from increment in cell volume (49.09±1.13%), protein content (55.17±1.19%), LDH leakage (58.74±1.87%), increased intracellular ROS production (26.25±0.91%), mitochondrial superoxide generation (65.06±2.27%), alteration in mitochondrial transmembrane potential (ΔΨm), opening of mitochondrial permeability transition pore (mPTP) and mitochondrial swelling. In addition, activities of mitochondrial respiratory chain complexes (I-IV), aconitase, NADPH oxidase, thioredoxin reductase, oxygen consumption rate and calcium homeostasis were evaluated. Treatment with BDE significantly prevented the generation of intracellular ROS and mitochondrial superoxide radicals and protected the mitochondria by preventing dissipation of ΔΨm, opening of mPTP, mitochondrial swelling and enhanced the activities of respiratory chain complexes and oxygen consumption rate in H9c2 cells. Activities of aconitase and thioredoxin reductase which was lowered (33.77±0.68% & 45.81±0.71% respectively) due to hypertrophy, were increased in BDE treated cells (P≤0.05). Moreover, BDE also reduced the intracellular calcium overload in Ang II treated cells. Overall results revealed the protective effects of B. diffusa against mitochondrial dysfunction in hypertrophy in H9c2 cells and the present findings may shed new light on the therapeutic potential of B. diffusa in addition to its nutraceutical potentials.     

Doxorubicin-induced cardiomyocyte apoptosis: Role of mitofusin 2

BackgroundDoxorubicin (DOX) is an anti-tumor agent that is widely used in clinical setting for cancer treatment. The application of the DOX, however, is limited by its cardiac toxicity which can induce heart failure through an undefined mechanism. Mitofusin 2 (Mfn2) is a mitochondrial GTPase fusion protein that is located on the outer membrane of mitochondria (OMM). The Mfn2 plays an important role in mitochondrial fusion and fission. The aim of this study is to identify the role of the Mfn2 in DOX-induced cardiomyocyte apoptosis.MethodsCultured neonatal rat cardiomyocytes were used in this study. Mfn2 expression in cardiomyocytes was determined after the cardiomyocytes were challenged with DOX. Cardiomyocyte mitochondrial fission, mitochondrial reactive oxygen species (ROS) production was assessed with mitochondrial fragmentation and MitoSOX fluorescence probe, respectively. Cardiomyocyte apoptosis was determined with caspase3 activity and TUNEL staining.ResultsChallenging of the cardiomyocytes with DOX resulted in increasing in cardiomyocyte oxidative stress and apoptosis. In addition, levels of Mfn2 in cardiomyocytes were decreased after the cells were challenged with DOX which was associated with increased mitochondrial fission (fragmentation) and mitochondrial ROS production. An increase in cardiomyocyte levels of Mfn2 attenuated the DOX-induced increase in mitochondrial fission and prevented cardiomyocyte mitochondrial ROS production. An increase in cardiomyocyte levels of Mfn2 or pretreatment of cardiomyocytes with an anti-oxidant, Mito-tempo, also prevented the DOX-induced cardiomyocyte apoptosis.ConclusionOur results indicate that DOX results in a decreased cardiomyocyte Mfn2 expression which promotes mitochondrial fission and ROS production further leads to cardiomyocyte apoptosis.