Diet-enhanced LRG1 expression promotes insulin hypersecretion and ER stress in pancreatic beta cells.

AIMS/HYPOTHESIS: Upregulation of serum leucine-rich α-2-glycoprotein 1 (LRG1) has been implicated in diet-induced obesity and metabolic disorders. However, its specific hormonal actions remain unclear. This study aimed to determine whether diet-enhanced serum LRG1 levels promote hyperinsulinaemia by directly stimulating insulin secretion from pancreatic beta cells. METHODS: Human serum samples were obtained from individuals (both male and female) undergoing plastic surgery. Male C57BL/6 wild-type and Lrg1 whole-body knockout (Lrg1(KO)) mice were fed a 45% high-fat diet, with serum samples collected every 2 weeks to monitor LRG1 and insulin levels throughout diet-induced obesity. MIN6 beta cells were used to investigate the effects of LRG1 on insulin secretion and intracellular Ca(2+) release. Antibodies targeting various LRG1 epitopes were used to neutralise LRG1 stimulation in MIN6 cells, and their effectiveness was tested in vivo to assess their ability to prevent LRG1-induced hyperinsulinaemia. RESULTS: We observed a significant positive association between human serum LRG1 levels and both age and BMI, with elevated levels observed in individuals with vs without type 2 diabetes. In mice fed a high-fat diet, LRG1 upregulation in serum was associated with hyperinsulinaemia. Lrg1 knockout protected mice from diet-induced islet hyperplasia and the loss of beta cell mass. Furthermore, neutralising LRG1 activity prevented the onset of diet-induced hyperinsulinaemia and preserved glucose tolerance. Mechanistically, LRG1 induces inositol triphosphate (IP(3)) production and intracellular Ca(2+) release from the endoplasmic reticulum (ER) in a phospholipase C (PLC)-dependent manner, leading to excessive insulin secretion and ER stress in MIN6 beta cells. CONCLUSIONS/INTERPRETATION: In summary, this study identifies LRG1 as a significant contributor to hyperinsulinaemia and beta cell dysfunction. Targeting LRG1 activity emerges as a promising therapeutic approach for addressing diet-induced beta cell dysfunction and managing type 2 diabetes.