Polycystin-2-dependent control of cardiomyocyte autophagy

Abstract

Aims: Considerable evidence points to critical roles of intracellular Ca2+ homeostasis in the modulation and control of autophagic activity. Yet, underlying molecular mechanisms remain unknown. Mutations in the gene (pkd2) encoding polycystin-2 (PC2) are associated with autosomal dominant polycystic kidney disease (ADPKD), the most common inherited nephropathy. PC2 has been associated with impaired Ca2+ handling in cardiomyocytes and indirect evidence suggests that this protein may be involved in autophagic control. Here, we investigated the role for PC2 as an essential regulator of Ca2+ homeostasis and autophagy.

Methods and results: Activation of autophagic flux triggered by mTOR inhibition either pharmacologically (rapamycin) or by means of nutrient depletion was suppressed in cells depleted of PC2. Moreover, cardiomyocytespecific PC2 knockout mice (alpha Mhc-cre;Pkd2(FIF) mice) manifested impaired autophagic flux in the setting of nutrient deprivation. Stress-induced autophagy was blunted by intracellular Ca2+ chelation using BAPTA-AM, whereas removal of extracellular Ca2+ had no effect, pointing to a role of intracellular Ca2+ homeostasis in stress-induced cardiomyocyte autophagy. To determine the link between stress-induced autophagy and PC2-induced Ca2+ mobilization, we over-expressed either wild-type PC2 (WT) or a Ca2+-channel deficient PC2 mutant (PC2-D509V). PC2 over-expression increased autophagic flux, whereas PC2-D509V expression did not. Importantly, autophagy induction triggered by PC2 over-expression was attenuated by BAPTA-AM, supporting a model of PC2-dependent control of autophagy through intracellular Ca2+. Furthermore, PC2 ablation was associated with impaired Ca2+ handling in cardiomyocytes marked by partial depletion of sarcoplasmic reticulum Ca2+ stores. Finally, we provide evidence that Ca2+-mediated autophagy elicited by PC2 is a mechanism conserved across multiple cell types.

Conclusion: Together, this study unveils PC2 as a novel regulator of autophagy acting through control of intracellular Ca2+ homeostasis.