Gr43a in macrophage-like hemocytes modulates insulin-like peptide secretion in Drosophila larvae

Abstract

Gustatory receptor (Gr) 43a is an established fructose-sensing chemoreceptor which modifies behavioral outputs in Drosophila, highlighting Gr43a as solely functional in neuronal contexts. However, we discovered Gr43a is expressed in Drosophila hemocytes which hints at a potential functional role for a sweet taste receptor in a non-neuronal context. Further investigations reveal that Hemolectin-positive hemocytes, which share resemblance to mammalian macrophages, are Gr43a-positive. We verified that hemocytes sense fructose and induce calcium release. Though the exact mechanism remains under investigation, we also observed that knocking down Gr43a in the macrophage-like hemocytes of Drosophila late third-instar larva significantly prevents retention of Drosophila insulin-like peptide 2 (Dilp2). Altogether, this discovery uncovers a non-neuronal role for Drosophila Gr43a and reaffirms the metabolic function of hemocytes. Findings here elucidate how macrophages contribute to internal energy balance via insulin modulation and will benefit our understanding of macrophage-dependent immunometabolism mechanisms.