3006-LB: CALCOCO2 Deficiency Impairs Beta-Cell Function through Hyperactivation of Autophagy

Introduction and Objective: Pancreatic beta cell loss and/or dysfunction underlies all forms of diabetes. Two independent genetic association signals at the CALCOCO2 locus influence type 2 diabetes (T2D)-risk. We previously identified CALCOCO2 as a novel regulator of insulin content through a pooled genome-wide CRISPR screen. We aimed to define how CALCOCO2 deficiency impairs insulin granule homeostasis in human beta cells and to identify the underlying mechanism. Methods: We mapped the CALCOCO2 interactome by immunoprecipitation-mass-spectrometry and assessed the impact of CALCOCO2 loss on beta cell function, mitochondrial respiration, and autophagy in EndoC-βH1 cells after siRNA-mediated CALCOCO2 knockdown. To test the T2D-associated coding variant (p.Pro389Ala), we generated stable EndoC-βH1 lines and measured insulin content, glucose-stimulated insulin secretion, and autophagy. Autophagic activity was manipulated by co-silencing ATG5 or BECN1, or by pharmacologic inhibition with chloroquine. Results: We identified TBK1 and NBR1 as binding partners in human beta-cells, implicating CALCOCO2 in regulating autophagy/mitophagy pathways. CALCOCO2 knockdown reduced insulin granule number, disrupted mitochondrial cristae and decreased spare respiratory capacity by 23% (p