PKD deletion promotes autophagy and inhibits hypertrophy in cardiomyocyte.

Protein kinase D (PKD) plays an important role in the development of cardiac hypertrophy induced by pressure overload. However, the mechanism involved is unclear. This study, using primary cardiomyocyte culture, PKD knockdown and overexpression, and other molecular techniques, tested our hypothesis that PKD pathway mediates cardiac hypertrophy by negatively regulating autophagy in cardiomyocyte. Neonatal cardiomyocytes were isolated from Wistar rats and cell hypertrophy was induced by norepinephrine treatment (PE, 10-4 mol/L), and divided into the following groups: (1) Vehicle; (2) PE; (3) PE + control siRNA; (4) PE + Rapamycin (100 nM); (5) PE + PKD-siRNA (2 × 108 U/0.1 ml); (6) PE + PKD siRNA + 3 MA (10 mM). The results showed that PE treatment induced cardiomyocyte hypertrophy, which were confirmed by cell size and biomarkers of cardiomyocyte hypertrophy including increased ANP and BNP mRNA. PKD knockdown or Rapamycin significantly inhibited PE-induced cardiomyocyte hypertrophy. In addition, PKD siRNA increased autophagy activity determined by electron microscopy, increased biomarkers of autophagy by Western blot, accompanied by down-regulated AKT/mTOR/S6K pathway. All the effects of PKD knockout were inhibited by co-treatment with 3-MA, an autophagy inhibitor. Oppositely, the autophagy in cardiomyocytes was inhibited by PKD overexpression. These results suggest that PKD participates in the development of cardiac hypertrophy by regulating autophagy via AKT/mTOR/S6K pathway.