FoxO Transcription Factors Promote Autophagy in Cardiomyocytes.

In the heart, autophagy is required for normal cardiac function and also has been implicated in cardiovascular disease. FoxO transcription factors promote autophagy in skeletal muscle and have additional roles in regulation of cell size, proliferation, and metabolism. Here we investigate the role of FoxO transcription factors in regulating autophagy and cell size in cardiomyocytes. In cultured rat neonatal cardiomyocytes, glucose deprivation leads to decreased cell size and induction of autophagy pathway genes LC3, Gabarapil, and Atg12, Likewise, overexpression of either FoxOl or FoxO3 reduces cardiomyocyte cell size and induces expression of autophagy pathway genes. Moreover, inhibition of FoxO activity by dominant negative FoxOl (~256) blocks cardiomyocyte cell size reduction upon starvation, suggesting the necessity of FoxO function in cardiomyocyte cell size regulation. Under starvation conditions, endogenous FoxOl and FoxO3 are localized to the nucleus and bind to promoter sequences of Gabarapil and Atg12. In vivo studies show that cellular stress, such as starvation or ischemia/ reperfusion in mice, results in induction of autophagy in the heart with concomitant dephosphorylation of FoxO, consistent with'increased activity of nuclear FoxO transcription factors. Together these results provide evidence for an important role for FoxOl and FoxO3 in regulating autophagy and cell size in cardiomyocytes. [ABSTRACT FROM AUTHOR]