To understand the role of mitochondrial uncoupling protein (UCP) in regulating insulin signaling and glucose homeostasis, we created transgenicDrosophila lines with targeted UCP expression in insulin producing cells (IPCs). Increased UCP activity in IPCs results in decreased steady state Ca(2+) levels in IPCs as well as decreased PI3K activity and increased FoxO nuclear localization in periphery. This reduced systemic insulin signaling is accompanied by a mild hyperglycemia and extended life span. To test the hypothesis that ATP-sensitive potassium (K(ATP)) channels may link changes in metabolic activity (e.g., glucose mediated ATP production or UCP-mediated ATP reduction) with insulin secretion, we characterized the effects of glucose and a specific K(ATP) channel blocker, glibenclamide on membrane potential in adult IPCs. Exposure to glucose depolarizes membrane potential of IPCs and this effect is mimicked with glibenclamide, suggesting that K(ATP) channels contribute to the mechanism whereby IPCs sense changes in circulating sugar. Further, as demonstrated in mammalian beta-pancreatic cells, high glucose initiates a robust Ca(2+) influx in adult IPCs. The presence of functional K(ATP) channels in adult IPCs is further substantiated by in situ hybridization detecting the transcript for the sulfonylurea receptor (Sur) subunit of the K(ATP) channel in those cells. Quantitative expression analysis demon-strates a reduction in transcripts for both Sur and the inward rectifying potassium channel (Kir) subunits when IPCs are partially ablated. In summary, we have demonstrated a role for UCP in adult Drosophila IPCs in influencing systemic insulin signaling and longevity by a mechanism that may involve K(ATP) channels.
Keywords: DILPs; Drosophila IIS pathway; IPCs; KATP channels; UCP; glucose homeostasis.