Role of prolyl hydroxylase domain proteins in the regulation of insulin secretion

Type 2 diabetes is associated with impaired nutrient‐regulated anaplerosis and insulin secretion in pancreatic β ‐cells. One key anaplerotic substrate that may be involved in regulating insulin release is α ‐ketoglutarate ( α KG). Since prolyl hydroxylase domain proteins ( PHD s) can metabolize cytosolic α KG, we sought to explore the role of this enzyme in the regulation of β ‐cell function. The oxygen‐sensing PHD s regulate the stability of hypoxia‐inducible factor 1 α (HIF1 α ) as well as other proline‐containing proteins by catalyzing the hydroxylation of proline residues. This reaction is dependent on sufficient levels of oxygen, iron, and α KG. In the present study, we utilized both pharmacological and genetic approaches to assess the impact of inhibiting PHD activity on β ‐cell function. We demonstrate that ethyl‐3,4‐dihydroxybenzoate ( EDHB ), a PHD inhibitor, significantly blunted glucose‐stimulated insulin secretion ( GSIS ) from 832/13 clonal cells, rat, and human islets. EDHB reduced glucose utilization, ATP / ADP ratio, and key TCA cycle intermediates such as pyruvate, citrate, fumarate, and malate. si RNA ‐mediated knockdown of PHD 1 and PHD 3 inhibited GSIS , whereas si RNA ‐mediated knockdown of PHD 2 had no effect on GSIS . Taken together, the current results demonstrate an important role for PHD s as mediators of islet insulin secretion.