Granulocyte-colony stimulating factor reduces cardiomyocyte apoptosis and ameliorate autophagy and endoplasmic reticulum stress in a rat model of diabetic cardiomyopathy

Background: In recent studies, cardiomyocyte apoptosis was shown to play an important role in the development of diabetic cardiomyopathy. Furthermore, inhibition of autophagy and prolonged endoplasmic reticulum (ER) stress contributed to cardiomyocyte apoptosis. Previously, we reported that granulocyte-colony stimulating factor (G-CSF) improved cardiac diastolic dysfunction and attenuated apoptosis in diabetic cardiomyopathy. However, the mechanisms of the anti-apoptotic effects of G-CSF in diabetic cardiomyopathy were not fully understood. In this study, we investigated whether the anti-apoptotic effects of G-CSF was associated with autophagy and ER stress in a rat model of diabetic cardiomyopathy. Methods: We induced the diabetes mellitus in a rat model by high-fat diet and low-dose streptozotocin. Diabetic rats were randomized to treatment with 5 days of G-CSF (DM + G-CSF rats) intraperitoneally or saline (DM + Saline rats). Cardiac function was evaluated by serial echocardiography performed before and 4 weeks after treatment. The extent of fibrosis was examined by Masson???s trichrome (MT) staining. Apoptosis in the myocardium was confirmed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and the expression of Bcl-2, an anti-apoptotic protein, measured by western blotting. To clarify the effect of G-CSF on process of autophagy and ER stress, we examined the expressions of the proteins related with autophagy (Beclin-1, LC3, and P62), and ER stress (GRP78, Caspase-9, and Caspase-12). Furthermore, to explore whether the mechanism of the anti-apoptotic effect of G-CSF was related to autophagy in diabetic condition, we measured the cardiomyocyte apoptosis rate after inhibition of autophagy in diabetic condition using flow cytometry. Results: G-CSF treatment significantly improved cardiac diastolic dysfunction in serial echocardiography assessments and attenuated fibrosis and apoptosis. The expression of anti-apoptotic protein Bcl-2 was reduced in diabetic rats, and its expression was stimulated by G-CSF treatment. Furthermore, the expressions of autophagy related proteins Beclin-1 and LC3 were down-regulated and expression of P62, a marker of degradation of autophagosome, was up-regulated in diabetic rats. Conversely, the expression of Beclin-1 and LC3 were increased and the expression of P62 was reduced by G-CSF treatment. In addition, the expressions of ER stress markers GRP78, Caspase-9, and Caspase-12 were markedly increased in diabetic rats, where as those of ER stress related proteins were reduced by G-CSF. In particular, G-CSF reduced high glucose induced cardiomyocyte apoptosis and this anti-apoptotic effect was abrogated by an autophagy inhibitor. Conclusion: G-CSF reduced cardiomyocyte apoptosis accompanied by activation of autophagy and reduction of ER stress in a rat model of diabetic cardiomyopathy. Notably, the anti-apoptotic effect of G-CSF was abolished by the autophagy inhibitor. Our findings suggest that the anti-apoptotic effect of G-CSF might be associated with the activation of autophagy and reduction of ER stress in a rat model of diabetic cardiomyopathy.Docto