Pharmacologic activation of the mitochondrial phosphoenolpyruvate cycle enhances islet function in vivo

Abstract

Highlights:• Loss of mitochondrial phosphoenolpyruvate (PEP) impairs insulin release in vivo.• Pyruvate kinase (PK) activators stimulate beta-cells in preclinical diabetes models.• PEP cycling in vivo depends on PK and mitochondrial PEPCK (PCK2) for insulin release. • Acute and 3-week oral PK activator amplifies insulin release during hyperglycemia. eTOC Blurb:Abudukadier et al. show that small molecule pyruvate kinase activation in vivo and in vitro increases insulin secretion in rodent and human models of diabetes. The phosphoenolpyruvate (PEP) cycling mechanism and its amplification are dependent on mitochondrial PEPCK (PCK2). SummaryThe mitochondrial GTP (mtGTP)-dependent phosphoenolpyruvate (PEP) cycle is an anaplerotic-cataplerotic mitochondrial shuttle utilizing mitochondrial PEPCK (PCK2) and pyruvate kinase (PK). PEP cycling stimulates insulin secretion via OxPhos-independent lowering of ADP by PK. We assess in vivo whether islet PCK2 is necessary for glucose sensing and if speeding the PEP cycle via pharmacological PK activators amplifies insulin secretion. Pck2 -/mice had severely impaired insulin secretion during islet perifusion, oral glucose tolerance tests and hyperglycemic clamps. Acute and chronic pharmacologic PK activator therapy improved islet insulin secretion from normal, high-fat diet (HFD) fed, or Zucker diabetic fatty (ZDF) rats, and glucolipotoxic or diabetic humans. A similar improvement in insulin secretion was observed in regular chow and HFD rats in vivo.Insulin secretion and cytosolic Ca 2+ during PK activation were dependent on PCK2.These data provide a preclinical rationale for strategies, such as PK activation, that target the PEP cycle to improve glucose homeostasis.

Pyruvate Kinase Controls Signal Strength in the Insulin Secretory Pathway

“…For SAME to be responsive to PKa, it must enhance the supply of PEP. This fits with the observation, shown in the companion paper, that SAME requires PCK2 to increase insulin secretion (Abulizi et al, 2020), and confirms in human islets that, like glycolysis, mitochondrial anaplerosis-cataplerosis can provide a source of PEP to PK that, in turn, is responsive to PK activation.…”

“…Thus, a key finding here is that PK underlies a separate mode of β-cell glucosesensing downstream of GK that may provide a mechanism dependent upon anaplerosis. While targeting OxPhos in β-cells has not been successful therapeutically, preclinical data suggest the anaplerotic mechanism may be of potential benefit (Abulizi et al, 2020).…”

“…A further limitation is the need to evaluate PKa in vivo. This is addressed by the companion paper (Abulizi et al, 2020).…”

ROCK1 regulates insulin secretion from β-cells

“…For example, small molecule activators of PK potently amplify GSIS by switching mitochondria from oxidative phosphorylation to anaplerotic phosphoenolpyruvate biosynthesis [11]. Moreover, PK activation ameliorates GSIS in islets obtained from animals and humans manifesting insulin resistance and type 2 diabetes [12].…”

“…Recent studies demonstrate that activation of PK promotes insulin section during glucose stimulation in INS-1 -cells and human islets [11]. Furthermore, PK activators can enhance insulin secretion from normal, high-fat diet fed, or Zucker diabetic fatty rats, and diabetic humans [12] indicating the significance of PK in regulating -cell secretory function.…”