Abstract 14111: Polycystin 2 is Required for Stress-induced Activation of Autophagy in Heart
Background: Autophagy is a ubiquitous process of intracellular protein and organelle recycling, critical to numerous forms of stress responsiveness. Polycystins are integral membrane proteins localized to the cytoplasmic membrane, primary cilia, and endoplasmic reticulum (ER). Polycystin 1 (PC1) and polycystin 2 (PC2) form a complex in which the activity of PC2, a calcium channel, is regulated by PC1. Mutations in the genes encoding PC1 or PC2 (pkd1, pkd2) are implicated in a number of human diseases, including polycystic kidney disease. Importantly, the activities of mTOR and AMPK, two major regulators of autophagy, are dysregulated in these diseases. Given this, we hypothesized that PC2 participates in the regulation of cardiomyocyte autophagy.
Methods and Results: The gene coding for PKD2 was selectively silenced exclusively in cardiomyocytes by crossing mice expressing Cre recombinase driven by the αMHC promoter with mice harboring a “floxed” pkd2 allele (PKD2F/F). Short-term nutrient deprivation induced robust accumulation of autophagic vacuoles and LC3 lipidation in both wild-type and PKD2F/F mice. However, this phenomenon was attenuated in animals lacking PKD2. Studies in vitro using neonatal rat cardiac myocytes and isolated cardiac fibroblasts revealed that knock down of PKD2 using two sequence-independent siRNA constructs inhibited autophagic induction elicited by starvation or mTOR inhibition (rapamycin). Interestingly, whereas nutrient deprivation induced strong inactivation of mTOR and activation of AMPK, PKD2 knockdown under these conditions did not affect AKT or AMPK activity. As the ER participates in the formation of autophagic vacuoles, we evaluated the intracellular distribution of PC2 and its possible interaction with proteins involved in the autophagic machinery. We found that PC2 co-localized with ER markers in cardiomyocytes and co-immunoprecipitated with Beclin 1 protein.
Conclusions: These results demonstrate that PC2 is required for induction of autophagy in vitro and in vivo in a manner independent of both mTOR and AMPK signaling. PC2 is localized to the myocyte ER, where it interacts with Beclin 1. Together, these data suggest that PC2 is a novel regulator of autophagy in cardiomyocytes.
- © 2013 by American Heart Association, Inc.