Author + information
Diabetic cardiomyopathy (DCM) is associated with suppressed autophagy and augmented apoptosis in the heart although the interplay between the two remains elusive. The ability of Mst1 to regulate both autophagy and apoptosis makes it a possible candidate in the progression of DCM.
Wild-type, Mst1 transgenic and Mst1 knockout mice were challenged with streptozotocin to induce experimental diabetes. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) to assess cardiac glucose metabolism. Cardiac function, cardiomyocyte apoptosis and autophagosomes (evaluated using Transmission electron microscopy) in mice were compared between groups. In addition, cultured neonatal mice cardiomyocytes were subjected to simulated diabetes to probe mechanism. For induction of simulated diabetes injury, cells were cultured in high glucose medium (30mM). The adenoviruses harboring GFP-LC3 (GFP-LC3) was purchased from GeneChem technology Ltd (Shanghai, China). The adenoviruses harboring Mst1 (Ad-Mst1), Mst1 shRNA (Ad-sh-Mst1) were purchased from hanbio technology Ltd (Shanghai, China) and were transduced 24h after transduction of GFP-LC3. After 36h, the cardiomyocytes were treated either in the regular glucose medium (5.5mM) or high glucose medium (30mM) for 48h. Fluorescence microscopic detection of GFP-LC3, aggresomes and p62 were conducted according to the manufacturer's instructions. The related proteins of autophagy and apoptosis were examined by western blot analysis.
Mst1 knockout alleviated, while Mst1 overexpression aggravated cardiac dysfunction under diabetes. Diabetes led to a defective 18F-FDG uptake in the heart, the effect of which was significantly improved by Mst1 knockout. Diabeteic Mst1 transgenic mice exhibited decreased LC3 expression and enhanced protein aggregation. In contrast, typical autophagosome were observed in diabetic Mst1 knockout mice with increased LC3 expression and reduced protein aggregation. Mst1 down-regulation promoted autophagic flux as evidenced by increased LC3-II and decreased p62 expression in the presence of bafilomycin A1. Furthermore, Mst1 overexpression increased, while Mst1 knockout decreased cardiomyocyte apoptosis both in vivo and in vitro. Co-immunoprecipitation assays showed that Mst1 overexpression promoted Beclin1 binding to Bcl-2, induced dissociation of Bcl-2 from Bax in diabetic mice. Conversely, Mst1 knockout disrupted the Beclin1-Bcl-2 complex, enhanced the interaction between Bcl-2 and Bax.
We demonstrate here that Mst1, a proapoptotic signaling kinase, may facilitate the progression of DCM by inhibiting autophagy. Mst1 induces interdependent modulation of Beclin1, Bcl-2 and Bax, thereby regulating autophagy and apoptosis simultaneously. Mst1 knockout restores autophagy and protects against apoptosis in cardiomyocytes, en route to the rescue against DCM. Mst1 may represent a novel target for the treatment of heart failure in diabetic patients.