Deficiency of the autophagy gene ATG16L1 induces insulin resistance through KLHL9/KLHL13/CUL3-mediated IRS1 degradation

Abstract

Connections between deficient autophagy and insulin resistance have emerged, however, the mechanism through which reduced autophagy impairs insulin-signaling remains unknown. We examined mouse embryonic fibroblasts lacking <i>Atg16l1</i> (ATG16L1 KO mouse embryonic fibroblasts (MEFs)), an essential autophagy gene, and observed deficient insulin and insulin-like growth factor-1 signaling. ATG16L1 KO MEFs displayed reduced protein content of insulin receptor substrate-1 (IRS1), pivotal to insulin signaling, whereas IRS1myc overexpression recovered downstream insulin signaling. Endogenous IRS1 protein content and insulin signaling were restored in ATG16L1 KO mouse embryonic fibroblasts (MEF) upon proteasome inhibition. Through proximity-dependent biotin identification (BioID) and co-immunoprecipitation, we found that Kelch-like proteins KLHL9 and KLHL13, which together form an E3 ubiquitin (Ub) ligase complex with cullin 3 (CUL3), are novel IRS1 interactors. Expression of <i>Klhl9</i> and <i>Klhl13</i> was elevated in ATG16L1 KO MEFs and siRNA-mediated knockdown of <i>Klhl9</i>, <i>Klhl13</i>, or <i>Cul3</i> recovered IRS1 expression. Moreover, <i>Klhl13</i> and <i>Cul3</i> knockdown increased insulin signaling. Notably, adipose tissue of high-fat fed mice displayed lower <i>Atg16l1</i> mRNA expression and IRS1 protein content, and adipose tissue <i>KLHL13</i> and <i>CUL3</i> expression positively correlated to body mass index in humans. We propose that ATG16L1 deficiency evokes insulin resistance through induction of <i>Klhl9</i> and <i>Klhl13</i>, which, in complex with <i>Cul3</i>, promote proteasomal IRS1 degradation.