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

2 ABSTRACT Glucose triggers insulin secretion from pancreatic β-cells through intracellular glucose metabolism, ATP production, and closure of ATP-sensitive K + channels (K ATP 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 K ATP channel-deficient β-cells, suggesting that β-cell fructose responsiveness is primarily determined by PLC signaling. Although FSIS was dependent on K ATP channels and Ca 2+ 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. 1 GRAPHICAL ABSTRACT Left: Fructose-stimulated insulin secretion (FSIS) is driven by sweet taste receptor (STR)-mediated PLC signaling in pancreatic β-cells. Meanwhile, fructose metabolism does not promote FSIS because fructose causes accumulation of fructose 1-phosphate (F1P), which suppresses pyruvate kinase M2 (PKM2), lowering the ATP/ADP ratio. Right: A small-molecule PK activator counteracted F1P-mediated PKM2 inhibition, prevented ATP decrease, and substantially enhanced FSIS in normal and diabetic mouse β-cells. Thus, PK has been identified as a key regulator linking β-cell fructose metabolism and FSIS.