Metabolic Functions of Pyruvate Kinase M2 in Pancreatic Beta-cells

ABSTRACT Over 450 million people suffer from type 2 diabetes (T2D), a disease defined by the failure of pancreatic β-cells. In the first period of support, we showed that pharmacologic activators of pyruvate kinase (PK) potentiate insulin secretion from mouse, rat, and human islets, as well as diabetic rats in vivo, identifying PK as a potential therapeutic target for T2D. We further demonstrated that PK plays an important role in β-cell nutrient sensing. We discovered a novel paradigm in which plasma-membrane associated PK closes KATP channels to initiate insulin secretion, and that the PKm1 and PKm2 isoforms tune the amino acid sensitivity of KATP closure via the mitochondrial phosphoenolpyruvate (PEP) cycle. The purpose of renewing this R01 is to ascertain the mechanism by which PK amplifies insulin secretion. Our preliminary studies revealed that PK activators amplify the insulinotropic actions of the incretin hormone glucagon-like peptide 1 (GLP1) but not glucose-dependent insulinotropic peptide (GIP), indicating receptor-specific signaling through pyruvate kinase. Further observations suggest a major unexplored contribution of PK to the kinetics of β-cell cAMP generation during nutrient stimulation. Based on our preliminary studies, our central hypothesis is that pyruvate kinase and GLP1 receptor (GLP1R) signaling converge on cAMP production to amplify insulin release. We will: 1) Determine which PK isoforms control β-cell cAMP levels, and whether the PEP cycle is required, 2) Define the mechanisms by which β-cell GLP1R signaling recruits pyruvate kinase, and 3) Determine, under metabolic stress conditions, whether PK contributes to the mechanism of existing and novel anti-diabetic drugs that target GLP1R and GIPR. Completion of these aims will define the interplay between PK and β-cell GPCR signaling, and shed light on the mechanisms underlying the efficacy of widely used incretin-based therapies for T2D, thus guiding the development of next-generation incretin mimetics biased toward the compartmentalized signaling pathways identified to be most effective for treating β-cell dysfunction at each stage of T2D progression.