Pyruvate kinase modulates the link between β-cell fructose metabolism and insulin secretion

Glucose triggers insulin secretion from pancreatic β-cells through intracellular glucose metabolism, ATP production, and closure of ATP-sensitive K+ channels (KATP channels). Fructose also stimulates insulin secretion, but the underlying mechanisms remain unclear. This study investigated the contribution of phospholipase C (PLC) signaling and fructose metabolism to fructose-stimulated insulin secretion (FSIS) using MIN6-K8 clonal β-cells and mouse islets. Fructose-induced PLC activation, assessed by inositol 1-phosphate accumulation, was reduced in fructose-unresponsive β-cell models, such as diabetic mouse islets and KATP channel-deficient β-cells, suggesting that β-cell fructose responsiveness is primarily determined by PLC signaling. Although FSIS was dependent on KATP channels and Ca2+ influx, the ATP/ADP ratio was unexpectedly lowered by fructose, and suppression of intracellular fructose metabolism hardly affected FSIS. Metabolic flux analysis revealed that the accumulation of fructose 1-phosphate (F1P) suppressed pyruvate kinase (PK) activity, contributing to ATP depletion. Strikingly, a small-molecule PK activator, TEPP-46, antagonized F1P-mediated PK suppression, prevented the drop in the ATP/ADP ratio, and restored FSIS in MIN6-K8 cells, normal mouse islets, and fructose-unresponsive diabetic mouse islets. These findings revealed the metabolic effects of fructose in β-cells and identified PK as a key regulator linking β-cell fructose metabolism and FSIS, thereby providing new insights into the mechanisms of insulin secretion and potential therapeutic targets for fructose-associated metabolic diseases. ### Competing Interest Statement The authors have declared no competing interest.