Loss of IP₃ receptor function in neuropeptide secreting neurons leads to obesity in adult Drosophila

Abstract

Background: Intracellular calcium signaling regulates a variety of cellular and physiological processes. The inositol 1,4,5 trisphosphate receptor (IP₃R) is a ligand gated calcium channel present on the membranes of endoplasmic reticular stores. In previous work we have shown that Drosophila mutants for the IP3R (itpr^ku) become unnaturally obese as adults with excessive storage of lipids on a normal diet. While the phenotype manifests in cells of the fat body, genetic studies suggest dysregulation of a neurohormonal axis. Results: We show that knockdown of the IP₃R, either in all neurons or in peptidergic neurons alone, mimics known itpr mutant phenotypes. The peptidergic neuron domain includes, but is not restricted to, the medial neurosecretory cells as well as the stomatogastric nervous system. Conversely, expression of an itpr⁺ cDNA in the same set of peptidergic neurons rescues metabolic defects of itpr^ku mutants. Transcript levels of a gene encoding a gastric lipase CG5932 (magro), which is known to regulate triacylglyceride storage, can be regulated by itpr knockdown and over-expression in peptidergic neurons. Thus, the focus of observed itpr mutant phenotypes of starvation resistance, increased body weight, elevated lipid storage and hyperphagia derive primarily from peptidergic neurons. Conclusions: The present study shows that itpr function in peptidergic neurons is not only necessary but also sufficient for maintaining normal lipid metabolism in Drosophila. Our results suggest that intracellular calcium signaling in peptidergic neurons affects lipid metabolism by both cell autonomous and non-autonomous mechanisms.