In Vivo Genetic Evidence That the Pyruvate Kinase Isoforms PKM1 and PKM2 Differentially Control Beta Cell Fuel Sensing

Pancreatic β-cells couple nutrient metabolism with appropriate insulin secretion. Here, we examined the requirements of pyruvate kinase (PK) isoforms in fuel sensing through the β-cell specific deletion of consititutively active PKM1 and allosterically recruitable PKM2 (PKM1- βKO, PKM2-βKO). β-cell deletion of PEP carboxykinase (PCK2-βKO) was used to block mitochondrial PEP production, leaving glycolytic PEP production intact. In vivo, only the PKM1-βKO mice showed glucose intolerance, and ex vivo insulin secretion was correspondingly reduced. Glucose-dependent Ca2+ oscillations were comparable in PKM1 βKO and PKM2-βKO islets, while the oscillatory frequency and duty cycle in PCK2-βKO islets increased relative to controls, suggesting redundancy in the PK response to glycolytic but not mitochondrial PEP. Using direct single-channel measurements of KATP in intact β-cells, amino acids were sufficient to stimulate KATP closure in control and PKM2-βKO cells, but failed to do so in the PCK2-βKO and PKM1-βKO models. PK activators (PKa) rescued KATP closure in PKM1- but not PCK2-deficient β-cells, arguing that PKM1 and PCK2 mediate membrane depolarization in response to mitochondrial fuels. The dependence of PKM2 on glucose was confirmed by the ability of PKa to rescue KATP closure in excised membrane patches from PKM1-βKO mice. Consistently, calcium influx stimulated by amino acids at low glucose was deficient in islets from PKM1-βKO and PCK2-βKO mice. PKa was sufficient to rescue the calcium defect in the PKM1-βKO islets but did not fully rescue the PCK2-βKO. Our findings provide strong genetic and electrophysiological evidence that the PCK2-PKM1 pathway is uniquely suited to direct the active (secretory) phase of calcium oscillations through direct effects on KATP, when FBP is low and PKM2 is inactive. While more limited in function, PKM2 can be therapeutically targeted, endowing it with the ability to respond to mitochondrial PEP and boost insulin secretion. Disclosure H. R. Foster: None. T. Ho: None. E. Potapenko: None. S. L. Lewandowski: None. S. Sdao: None. H. R. Vandeusen: None. R. L. Cardone: None. R. Kibbey: Research Support; Self; Agios, Inc. M. J. Merrins: None. Funding Health Resources and Services Administration (T32HP10010); National Institute on Aging (T32AG000213); National Institutes of Health (R01DK113103)