The role of pyruvate carboxylase in insulin secretion and proliferation in rat pancreatic beta cells.

AIMS/HYPOTHESIS: Pyruvate carboxylase (PC) or pyruvate dehydrogenase (PDH) is required to transfer carbons from pyruvate into the Krebs cycle. PC activity is preserved in the islets of obese animals, but it is reduced in the islets of animal models of type 2 diabetes, suggesting that PC is important in beta cell adaptation to insulin resistance and that PC reduction may lead to beta cell failure.

METHODS

To confirm the significance of PC, we first lowered activity using Pc (now known as Pcx) small interfering RNA (siRNA) in INS-1 cells and in dispersed rat islet cells. Second, we overexpressed PC in INS-1 cells, and third, we inhibited PDH by overexpressing the gene encoding pyruvate dehydrogenase kinase 4 (Pdk4) in INS-1 cells.

RESULTS

Treatment of INS-1 cells or dispersed rat islet cells with Pc siRNA resulted in a significant reduction in insulin secretion in both cell types and reduced proliferation in INS-1 cells. This treatment also reduced the content of oxaloacetate, malate and ATP, as well as the NADPH:NADP(+) ratio and activity of the pyruvate-malate shuttle. Overexpression of PC in INS-1 cells led to an elevation of insulin secretion and cell proliferation, whereas inhibition of PDH activity by overexpressing Pdk4 in INS-1 cells did not reduce insulin secretion.

CONCLUSIONS/INTERPRETATION: Our findings indicate that the PC pathway in beta cells might play a key role in pyruvate metabolism, insulin secretion and cell proliferation.