123-OR: Deletion of Both Pcsk1 And Pcsk2 in Beta Cells: Lack of Mature Insulin Drives Beta-Cell Expansion and Dysfunction, but Not Severe Diabetes in Mice

Proinsulin (PI) is processed to mature insulin by prohormone convertases 1/3 (Pcsk1) and 2 (Pcsk2). In individuals with T1D and T2D, there is an increase in the circulating PI:insulin ratio. We hypothesized that β-cell Pcsk1 and Pcsk2 deletion would result in β-cell dysfunction, loss of insulin production, and marked hyperglycemia. Single Pcsk1flox/flox Ins1cre/+ (Pcsk1βKO), Pcsk2flox/flox Ins1cre/+ (Pcsk2βKO), and double Pcsk1flox/flox Pcsk2flox/flox Ins1cre/+ (DPCβKO) β-cell prohormone convertase knockout mice were generated (with respective Pcsk1+/+ Pcsk2+/+ Ins1cre/+ controls) and monitored until 30 weeks old. Pcsk2βKO mice displayed no glycemic phenotype, while Pcsk1βKO mice displayed mild hyperglycemia and impaired glucose tolerance by 26 weeks of age. DPCβKO mice displayed mild hyperglycemia (10.1±1.6 vs. 12.3±2.1 mM; p=0.006) and marked glucose intolerance by 10 weeks of age (AUC: 418±135 vs. 1485±360; p<0.0001). No animals displayed obesity relative to controls. Insulin+ pancreas area was doubled in DPCβKO male mice (p=0.0004) and DPCβKO islets showed early glucose-induced Ca2+ influx and loss of oscillatory Ca2+ flux. Pcsk2βKO islets had unaltered mature insulin, while Pcsk1βKO islets had reduced mature insulin. DPCβKO islets contained no detectable mature insulin by western blot. In contrast, Pcsk2βKO islets had markedly reduced mature islet amyloid polypeptide (IAPP), while Pcsk1βKO islets contained normal mature IAPP levels. Our results suggest that complete loss of β-cell prohormone processing, including PI processing, can drive β-cell dysfunction and expansion, but only mild diabetes and glucose intolerance. Although Pcsk2 deletion in β cells does not impact glycemia or PI processing, it is required for normal proIAPP processing. In total, our data support the idea that altered β-cell prohormone processing does not impact obesity but can contribute to the pathogenesis of diabetes via β-cell dysfunction. Disclosure A. Taylor: None. Y. Chen: None. D. Pasula: None. D. S. Luciani: None. B. Verchere: Advisory Panel; Self; Integrated Nanotherapeutics Inc., Sirona Biochem, Stock/Shareholder; Self; Integrated Nanotherapeutics Inc. Funding Canadian Institutes of Health Research

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