Endothelial-to-mesenchymal transition (EndMT) mainly exists in cardiovascular development and disease progression, and is well known to contribute to cardiac fibrosis. Recent studies indicated that autophagy also participates in the regulation of cardiac fibrosis. However, the precise role of autophagy in cardiac fibrosis and the underlying molecular mechanism remain unclear. The present study aimed to explore the role of autophagy in EndMT, reveal the underlying molecular mechanism, and seek new therapy for cardiac fibrosis. In the present study, we found that EndMT and autophagy were induced simultaneously by hypoxia in human cardiac microvascular endothelial cells (HCMECs). Rapamycin, an autophagy enhancer, attenuated EndMT with promoting angiogenesis, while 3-methyladenine (3-MA) and chloroquine (CQ), agents that inhibit autophagy, accelerated the progression accompanied by the decrease in counts of tube formation under hypoxia conditions. Interestingly, intervening autophagy by rapamycin, 3-MA, or CQ did not affect hypoxia-induced autocrine TGFβ signaling, but changed the expression of Snail protein without alterations in the expression of Snail mRNA. Furthermore, the colocalization of LC3 and Snail indicated that autophagy might mediate Snail degradation under hypoxia conditions in HCMECs. Interaction of p62, the substrate of autophagy, with Snail by co-immunoprecipitation especially in hypoxia-incubated cells confirmed the hypothesis. In conclusion, autophagy serves as a cytoprotective mechanism against EndMT to promote angiogenesis by degrading Snail under hypoxia conditions, suggesting that autophagy targetted therapeutic strategies may be applicable for cardiac fibrosis by EndMT.
Endothelial-mesenchymal transition (EndMT) is an essential mechanism in the cardiovascular system, for both cardiovascular development and cardiovascular diseases (CVDs). Recent studies indicate that runt-related transcriprunt-related transcription factor 3 (RUNX3) contributes to EndMT and endothelial cell dysfunction. However, the underlying molecular mechanism remains unknown. The present study was designed to investigate the role of RUNX3 in EndMT and endothelial cell function, and to elucidate the underlying molecular mechanism. Human cardiac microvascular endothelial cells (HCMECs) were incubated in strictly controlled hypoxic conditions (1% O2). HCMECs were cultured under normoxic conditions (21% O2), and then moved to a strictly controlled hypoxic environment (1% O2). Under this hypoxic condition, the cells were transfected with the lentiviral vector containing RUNX3 or an empty lentiviral vector for 8 h. After the cells were cultured under hypoxic conditions for 4 days, CD31 and α-smooth muscle actin colocalization were assessed by immunofluorescence microscopy. Transwell migration and tube formation assays were used to examine the migration and angiogenesis ability. RT-qPCR and western blotting were used to determine the expression of molecules involved in EndMT. Hypoxia induced the transition of HCMECs to mesenchymal cells and markedly promoted tube formation and cell migration. Transforming growth factor-β (TGF-β) and Notch signaling were activated during the hypoxia-induced EndMT of HCMECs. RUNX3 knockdown attenuated EndMT of HCMECs, promoted angiogenic phenotype, and reduced endothelial cell migration. In conclusion, our results showed that RUNX3 knockdown attenuated hypoxia-induced EndMT and reversed endothelial cell functions. RUNX3 is a common downstream target of TGF-β and Notch signaling, and may be a novel therapeutic target for treating CVD mediated by EndMT.
Visceral adipose tissue-derived serine protease inhibitor (Vaspin) is an adipocytokine that has been shown to exert anti-inflammatory effects and inhibits apoptosis under diabetic conditions. This study was designed to investigate the impact of vaspin on autophagy in tumor necrosis factor (TNF)-α-induced injury in cardiomyocytes and its cardioprotective effects in the pathogenesis of diabetic cardiomyopathy (DCM). H9C2 cells were treated with TNF-α with or without vaspin in vitro. Tumor necrosis factor-α treatment inhibited autophagy and promoted apoptosis in H9C2 cells after stimulating for 24 hours. Pretreatment with vaspin significantly mitigated apoptosis induced by TNF-α partly because of augment effects of vaspin on autophagy as demonstrated by a higher ratio of LC3-II/LC3-I, higher expression of Beclin-1, and increased autophagosomes formation. Furthermore, the AKT agonist IGF-1 significantly reversed the effect of vaspin on autophagy. In vivo DCM model was also developed by treating rats with streptozotocin followed by intraperitoneal injection with vaspin. In DCM rats, upregulation of vaspin reversed cardiac dysfunction, as identified by increased left ventricular ejection fractions and fractional shortening levels, a higher Em/Am ratio, and lower levels of TNF-α, lactate dehydrogenase, creatine kinase, and creatine kinase-myocardial isoenzyme. In conclusion, vaspin attenuated the TNF-α-induced apoptosis by promoting autophagy probably through inhibiting the PI3K/AKT/mTOR pathway and further ameliorated the cardiac dysfunction in DCM rats.
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