Regulation of cAMP accumulation and activity by distinct phosphodiesterase subtypes in INS-1 cells and human pancreatic β-cells

Abstract

Pancreatic {beta}-cells express multiple phosphodiesterase (PDE) subtypes, but the specific roles for each in {beta}-cell function, particularly in humans, is not clear. We evaluated the cellular role of PDE1, PDE3, and PDE4 activity in the rat insulinoma cell line INS-1 and in primary human {beta}-cells using subtype-selective PDE inhibitors. Using a genetically encoded, FRET-based cAMP sensor, we found that the PDE1 inhibitor 8MM-IBMX and the PDE4 inhibitor rolipram elevated cAMP levels above baseline in the absence and presence of 18 mM glucose in INS-1 cells. Inhibition of PDE1 or PDE4 potentiated glucose-stimulated insulin secretion in INS-1 cells. In contrast, the inhibition of PDE3 with cilostamide had little effect on cAMP levels or glucose-stimulated insulin secretion. PDE1 inhibition, but not PDE3 of PDE4 inhibition, reduced palmitate-induced caspase-3/7 activation, and enhanced CREB phosphorylation in INS-1 cells. In human {beta}-cells, only PDE3 or PDE4 inhibition increased cAMP levels in 1.7 mM glucose, but PDE1, PDE3, or PDE4 inhibition potentiated cAMP levels in 16.7 mM glucose. Inhibition of PDE1 or PDE4 increased cAMP levels to a greater extent in 16.7 mM glucose than in 1.7 mM glucose in human {beta}-cells. In contrast, elevation of cAMP levels by PDE3 inhibition was not different at these glucose concentrations. PDE1 inhibition also potentiated insulin secretion from human islets, suggesting that the role of PDE1 may be conserved between INS-1 cells and human pancreatic {beta}-cells. Our results suggest that inhibition of PDE1 may be a useful strategy to potentiate glucose-stimulated insulin secretion, and to protect {beta}-cells from the toxic effects of excess fatty acids.