316-OR: Genetic Deletion of Beta-Cell Pkm1, Pkm2, and Pck2 Identifies PEP as an Essential Signal for Compartmentalized KATP Closure and Cycling of the Insulin Secretory Pathway

Abstract

β-cells use pyruvate kinase to sense nutrients and respond with appropriate insulin secretion. Here, we used β-cell deletion to identify the functions of constitutively active PKm1 and allosterically recruitable PKm2, and assess their regulation by mitochondrial PEP from PCK2. We demonstrate that both PKm isoforms are present in the KATP channel microcompartment. Compartmentation nullifies the disparities in PK isoform expression and activity, allowing the minor but recruitable PKm2 isoform to fully participate in KATP regulation. However, this shared control does not extend to β-cell response to amino acids, which requires PKm1 for the initiation of Ca2+ influx and insulin secretion and PKm2 for their termination. Mitochondrial PEP is required for this cycling between “on” and “off” states, as demonstrated by β-cell-specific deletion of PCK2. PCK2 was revealed to be an essential mechanism of β-cell cataplerosis, possessing metabolic control over cytosolic ATP/ADP generation in response to anaplerotic fuels. Further, PCK2 is required for amino acid-stimulated Ca2+ influx (via PKm1) and efflux (via PKm2) . These data provide strong genetic evidence for a revised oscillatory model of β-cell metabolism in which PKM1- and PKM2-driven PEP cycles play unique roles in the initiation and termination of nutrient-stimulated insulin secretion. Disclosure H.R.Foster: None. T.Ho: None. E.Potapenko: None. R.L.Cardone: n/a. R.Kibbey: Consultant; Agios, Inc. M.J.Merrins: None. Funding NIH/NIDDK (R01DK113103) HRSA (T32HP10010) NIH/NIA (T32AG000213)