Abstract 15056: Cardiac P62/sqstm1 Deficiency Exacerbates Hypoxic Stress vi a Impaired Hypoxia Inducible Factor 1α Signaling

Abstract

Ischemic heart disease (IHD), a major cause of heart failure, is characterized by metabolic dysfunction and myocardial cell death. Cellular hypoxia activates hypoxia inducible factor 1α (HIF1α) to initiate metabolic, angiogenic, and growth-factor related responses. Under normoxia, HIF1α is degraded by prolyl hydroxylase (PHD) domain-containing proteins via the proteasome. Due to the short half-life of HIF1α (<5mins), PHD inhibitors are utilized to stabilize HIF1α and improve cardiac function in pre-clinical models of ischemia/infarction. However, evidence exists that PHD inhibitors exert off-target effects. Based on prior studies in cancer cells demonstrating that the autophagy adaptor protein p62 prevents HIF1α degradation, we hypothesized that p62 stabilizes cardiac HIF1α and provides cardioprotection from hypoxia. We generated mice with tamoxifen-inducible cardiomyocyte-specific p62 deletion (p62icKO mice; 8 week male and female) and exposed them to 7% O 2 for 6h. Hypoxia increased cardiac mRNA expression of Sqstm1 , Bnip3 , and Hmox1 in wild-type (WT) but not p62icKO mice. Underscoring functional relevance, ejection fraction and fractional shortening were less, oxidative stress was elevated, and apoptosis was greater, in p62icKO vs. WT mice exposed to hypoxia. Mechanisms were evaluated using cultured H9c2 cardiomyoblasts exposed to 21% (normoxia) or 1% (hypoxia) O 2 for 24h. Hypoxia increased both HIF1α and p62 protein expression. To determine the role of p62, H9c2 cells were transfected with p62 or scrambled (ctrl) siRNA for 48h, followed by 24 h hypoxia. Hypoxia-induced HIF1α protein accrual and expression of HIF1α downstream targets Egln1 , Vegfa , Bnip3 and Hmox1 mRNA was attenuated in H9c2 cells transfected with p62 vs. control siRNA. These data indicate p62 stabilizes cardiac HIF1α and regulates its transcriptional activation. Thus, p62 could be a novel therapeutic target for treatment of IHD.