Effects of glucokinase activators GKA50 and LY2121260 on proliferation and apoptosis in pancreatic INS-1 beta cells

Aims/hypothesis: Glucokinase (GK), an Enzyme that phosphorylates glucose to form glucose 6-phosphate, serves as the glucose sensor that regulates Insulin secretion in beta cells. GK activators (GKAs) activate GK via binding to an allosteric site of the Enzyme. GKAs increase glucose-stimulated Insulin secretion and decrease blood glucose levels. Using the differentiated beta cell line INS-1, we investigated the role of GKAs in promoting beta cell growth and survival and preventing beta cell Apoptosis induced by chronic exposure to high levels of glucose.

Methods: Proliferation was assessed using BrdU incorporation. Apoptosis was measured using Caspase-3 activity. Immunoblot analysis was used to detect protein levels and the degree of phosphorylation.

Results: The GK agonists GKA50 and LY2121260 increased both cell replication and cell numbers when tested at basal levels of glucose (3 mmol/l) in INS-1 cells. GKAs promoted INS-1 cell proliferation via upregulation of Insulin Receptor substrate-2 and subsequent activation of protein kinase B phosphorylation. GKA50 also prevented the INS-1 cell Apoptosis that was induced by chronic high glucose conditions, probably via an increase in GK protein levels and normalisation of the apoptotic protein BCL2-associated agonist of cell death (BAD) and its phosphorylation. As a result of the reduction in cell Apoptosis, GKA50 prevented cell loss and maintained glucose-stimulated Insulin secretion. In addition, the anti-apoptotic activity of GKA50 was significantly abrogated by other GKAs that do not inhibit Apoptosis, suggesting that direct binding of GKA50 to GK is essential for its anti-apoptotic effect.

Conclusion/interpretation: Our results suggest novel roles of GKAs in promoting beta cell growth and preventing chronic-hyperglycaemia-induced beta cell Apoptosis. Thus, GKAs may provide novel therapeutics that increase beta cell mass to maintain euglycaemia in diabetes.