Statin-Induced Geranylgeranyl Pyrophosphate Depletion Promotes PCSK9–Dependent Adipose Insulin Resistance

Abstract

Statin treatment is accepted to prevent adverse cardiovascular events. However, statin therapy has been reported to be dose-dependently associated with increased risk for new-onset type 2 diabetes mellitus (T2DM). Proprotein convertase subtilisin/kexin type 9 (PCSK9) is expressed in adipose tissue and is positively correlated with lipid metabolism. It is, however, unknown if PCSK9 participates in adipocyte insulin resistance occurring as a result of statin use. Our goal was to use an in vitro adipose tissue explant approach to support the hypothesis that PCSK9 regulates statin-induced new-onset T2DM. Studies were performed using Pcsk−/− and C57Bl/6J control mice. Pcsk9−/− and control mice were fed a high-fat diet to affect a state of chronically altered lipid metabolism and increased PCSK9. Epididymal fat was excised and incubated with atorvastatin (1 µmol/L) in the absence and presence of insulin or geranylgeranyl pyrophosphate (GGPP). PCSK9 mRNA was evaluated using quantitative rtPCR. We further examined the effects of atorvastatin on insulin-mediated AKT signaling in adipose tissue explants by immunoblotting. Atorvastatin was found to upregulate PCSK9 gene expression in adipose tissue. The metabolic intermediate GGPP is required to downregulate PCSK9 expression. PCSK9 deficiency protects against statin-induced impairments in insulin signaling. Moreover, supplementation with GGPP reversed atorvastatin-induced suppression of insulin signaling. Furthermore, the basal and atorvastatin-stimulated release of free fatty acids was observed in adipose tissue from wild-type mice but not PCSK9 deficient mice. Collectively, we describe a novel mechanism for PCSK9 expression in adipose tissue that could mediate statin-impaired adipose insulin resistance.