[Role of mitochondrial dynamics in diabetic cardiomyopathy and regulatory mechanisms].

Cardiovascular complications are the leading cause of death in diabetic patients. Among them, diabetic cardiomyopathy (DCM) is a type of specific cardiomyopathy excluding myocardial damage caused by hypertension and coronary heart disease. It is characterized by abnormal metabolism of cardiomyocytes and gradual decline of cardiac function. The clinical manifestations of DCM are impaired diastolic function in early stage and impaired systolic function in late stage. Eventually it developed into heart failure. Mitochondria are the main organelles that provide energy in cardiomyocytes. Mitochondrial dynamics refers to the dynamic process of mitochondrial fusion and fission, which is an important approach for mitochondrial quality control. Mitochondrial dynamics plays a crucial role in maintaining mitochondrial homeostasis and cardiac function. The proteins that regulate mitochondrial fission are mainly Drp1 and its receptors, Fis1, MFF, MiD49 and MiD51. The protein that performs mitochondrial outer membrane fusion is Mfn1/2, and the inner membrane fusion protein is Opa1. This paper reviews recent progress on mitochondrial dynamics in DCM. The main contents are as follows: mitochondrial dynamics imbalance in both type 1 and 2 DCM is manifested as increased fission and inhibited fusion. The molecular mechanism of the former is mainly associated with up-regulated Drp1 and down-regulated Opa1, while the molecular mechanism of the latter is mainly associated with up-regulated Drp1 and down-regulated Mfn1/2. Increased mitochondrial fission and inhibited fusion can lead to mitochondrial dysfunction and promote the development of DCM. The active ingredients of the traditional Chinese medicine such as punicalagin, paeonol and endogenous substance melatonin can improve mitochondrial function and alleviate the symptoms of DCM by inhibiting mitochondrial fission or promoting mitochondrial fusion. This article is helpful to further understand the role and mechanism of mitochondrial dynamics in DCM, and provide new treatment methods and intervention strategies for clinical DCM patients based on mitochondrial dynamics.

IP3R1-mediated MAMs formation contributes to mechanical trauma-induced hepatic injury and the protective effect of melatonin.

INTRODUCTION: There is a high morbidity and mortality rate in mechanical trauma (MT)-induced hepatic injury. Currently, the molecular mechanisms underlying liver MT are largely unclear. Exploring the underlying mechanisms and developing safe and effective medicines to alleviate MT-induced hepatic injury is an urgent requirement. The aim of this study was to reveal the role of mitochondria-associated ER membranes (MAMs) in post-traumatic liver injury, and ascertain whether melatonin protects against MT-induced hepatic injury by regulating MAMs. METHODS: Hepatic mechanical injury was established in Sprague-Dawley rats and primary hepatocytes. A variety of experimental methods were employed to assess the effects of melatonin on hepatic injury, apoptosis, MAMs formation, mitochondrial function and signaling pathways. RESULTS: Significant increase of IP3R1 expression and MAMs formation were observed in MT-induced hepatic injury. Melatonin treatment at the dose of 30 mg/kg inhibited IP3R1-mediated MAMs and attenuated MT-induced liver injury in vivo. In vitro, primary hepatocytes cultured in 20% trauma serum (TS) for 12 h showed upregulated IP3R1 expression, increased MAMs formation and cell injury, which were suppressed by melatonin (100 µmol/L) treatment. Consequently, melatonin suppressed mitochondrial calcium overload, increased mitochondrial membrane potential and improved mitochondrial function under traumatic condition. Melatonin's inhibitory effects on MAMs formation and mitochondrial calcium overload were blunted when IP3R1 was overexpressed. Mechanistically, melatonin bound to its receptor (MR) and increased the expression of phosphorylated ERK1/2, which interacted with FoxO1 and inhibited the activation of FoxO1 that bound to the IP3R1 promoter to inhibit MAMs formation. CONCLUSION: Melatonin prevents the formation of MAMs via the MR-ERK1/2-FoxO1-IP3R1 pathway, thereby alleviating the development of MT-induced liver injury. Melatonin-modulated MAMs may be a promising therapeutic therapy for traumatic hepatic injury.

Ischemia/reperfusion-induced MiD51 upregulation recruits Drp1 to mitochondria and contributes to myocardial injury.

The translocation of Drp1 from the cytosol to mitochondria leads to Drp1 activation and mitochondrial fission in myocardial ischemia/reperfusion (MI/R). However, the molecular mechanism underlying mitochondrial Drp1 translocation remains poorly understood. Mitochondrial Drp1 recruitment relies on 4 binding partners including MiD49, MiD51, Mff and Fis1. This study was to elucidate which one facilitate mitochondrial Drp1 translocation and its role in MI/R injury. MI/R was induced by ligating the left anterior descending coronary artery for 30 min and subsequent reperfusion for 3 h. Primary neonatal cardiomyocytes were subjected to hypoxia for 2 h and reoxygenation for 4 h. SiRNA or Adeno-associated virus (AAV) expressing shRNA was used to knock down the key binding partner in vitro or in vivo respectively. The expression of MiD51 rather than other binding partners (MiD49, Mff or Fis1) was increased after MI/R. MiD51 knockdown inhibited hypoxia/reoxygenation (H/R) or ischemia/reperfusion (I/R)-induced mitochondrial Drp1 translocation. SiRNA-induced knockdown of MiD51 suppressed mitochondrial oxidative stress, improved mitochondrial function and alleviate cellular injury in H/R cardiomyocytes. AAV-mediated knockdown of MiD51 reduced myocardial injury and improved cardiac function in the I/R hearts, while mitochondrial Drp1 translocation and cardiac function were not affected by MiD51 knockdown in the hearts without I/R. MiD51 is identified as the binding partner that promotes mitochondrial Drp1 translocation and contributes to MI/R injury. Inhibition of MiD51 may be a potential therapeutic target to alleviate MI/R injury.

Paeonol protects against doxorubicin-induced cardiotoxicity by promoting Mfn2-mediated mitochondrial fusion through activating the PKCε-Stat3 pathway.

INTRODUCTION: The anti-cancer medication doxorubicin (Dox) is largely restricted in clinical usage due to its significant cardiotoxicity. The only medication approved by the FDA for Dox-induced cardiotoxicity is dexrazoxane, while it may reduce the sensitivity of cancer cells to chemotherapy and is restricted for use. There is an urgent need for the development of safe and effective medicines to alleviate Dox-induced cardiotoxicity. OBJECTIVES: The objective of this study was to determine whether Paeonol (Pae) has the ability to protect against Dox-induced cardiotoxicity and if so, what are the underlying mechanisms involved. METHODS: Sprague-Dawley rats and primary cardiomyocytes were used to create Dox-induced cardiotoxicity models. Pae's effects on myocardial damage, mitochondrial function, mitochondrial dynamics and signaling pathways were studied using a range of experimental methods. RESULTS: Pae enhanced Mfn2-mediated mitochondrial fusion, restored mitochondrial function and cardiac performance both in vivo and in vitro under the Dox conditions. The protective properties of Pae were blunted when Mfn2 was knocked down or knocked out in Dox-induced cardiomyocytes and hearts respectively. Mechanistically, Pae promoted Mfn2-mediated mitochondria fusion by activating the transcription factor Stat3, which bound to the Mfn2 promoter in a direct manner and up-regulated its transcriptional expression. Furthermore, molecular docking, surface plasmon resonance and co-immunoprecipitation studies showed that Pae's direct target was PKCε, which interacted with Stat3 and enabled its phosphorylation and activation. Pae-induced Stat3 phosphorylation and Mfn2-mediated mitochondrial fusion were inhibited when PKCε was knocked down. Furthermore, Pae did not interfere with Dox's antitumor efficacy in several tumor cells. CONCLUSION: Pae protects the heart against Dox-induced damage by stimulating mitochondrial fusion via the PKCε-Stat3-Mfn2 pathway, indicating that Pae might be a promising therapeutic therapy for Dox-induced cardiotoxicity while maintaining Dox's anticancer activity.

Mfn2-mediated mitochondrial fusion alleviates doxorubicin-induced cardiotoxicity with enhancing its anticancer activity through metabolic switch.

Imbalanced mitochondrial dynamics including inhibited mitochondrial fusion is associated with cardiac dysfunction as well as tumorigenesis. This study sought to explore the effects of promoting mitochondrial fusion on doxorubicin(Dox)-induced cardiotoxicity and its antitumor efficacy, with a focus on the underlying metabolic mechanisms. Herein, the inhibition of Mfn2-mediated mitochondrial fusion was identified as a key phenotype in Dox-induced cardiotoxicity. Restoration of Mfn2-mediated mitochondrial fusion enhanced mitochondrial oxidative metabolism, reduced cellular injury/apoptosis and inhibited mitochondria-derived oxidative stress in the Dox-treated cardiomyocytes. Application of lentivirus expressing Drp1 (mitochondrial fusion inhibitor) or Rote/Anti A (mitochondrial complex I/III inhibitors) blunted the above protective effects of Mfn2. Cardiac-specific Mfn2 transgenic mice showed preserved mitochondrial fusion and attenuated myocardial injury upon Dox exposure in vivo. The suppression of Mfn2-mediated mitochondrial fusion was induced by Dox-elicited upregulation of FoxO1, which inhibited the transcription of Mfn2 by binding to its promoter sites. In the B16 melanoma, Mfn2 upregulation not only attenuated tumor growth alone but also further delayed tumor growth in the presence of Dox. Mechanistically, Mfn2 synergized with the inhibitory action of Dox on glycolysis metabolism in the tumor cells. One common feature in both cardiomyocytes and tumor cells was that Mfn2 increased the ratio of oxygen consumption rate to extracellular acidification rate, suggesting Mfn2 triggered a shift from aerobic glycolysis to mitochondrial oxidative metabolism. In conclusion, targeting Mfn2-mediated mitochondrial fusion may provide a dual therapeutic advantage in Dox-based chemotherapy by simultaneously defending against Dox-induced cardiotoxicity and boosting its antitumor potency via metabolic shift.