Abstract
<title>Abstract</title> <p> Deletion of the <italic>Drosophila</italic> -specific gene <italic>Neprilysin-like 15</italic> ( <italic>Nepl15</italic> ) results in significant reductions in glycogen and glycerolipid storage in mutant males and increased glycogen storage in mutant females without affecting food intake. Previous studies also indicated downregulation of insulin/mTOR signaling, the central pathway regulating nutrient homeostasis, growth, fertility, locomotor activity, and lifespan. Consistent with these metabolic alterations, <italic>Nepl15</italic> mutants exhibit several anti-obesity and healthy-aging phenotypes but display markedly reduced survival under starvation, suggesting impaired nutrient reserve utilization. The present study investigated the intracellular mechanisms underlying these phenotypes by examining insulin signaling and the expression of genes involved in carbohydrate and lipid metabolism. Although transcript levels of the insulin-like peptides ( <italic>Dilp2</italic> , <italic>Dilp5</italic> , and <italic>Dilp6</italic> ) and the insulin receptor ( <italic>InR</italic> ) remained unchanged, <italic>Nepl15</italic> mutants exhibited reduced Akt phosphorylation, increased dFoxo abundance, reduced <italic>Glut1</italic> expression, and previously reported suppression of mTOR signaling, indicating attenuation of insulin signaling downstream of the insulin receptor. Consistent with impaired anabolic signaling, male mutants showed reduced expression of glycogen metabolic genes ( <italic>GlyS</italic> and <italic>GlyP</italic> ), whereas genes involved in lipid metabolism exhibited predominantly male-specific reductions, including <italic>Lipin</italic> , <italic>Acc</italic> , <italic>Fasn1</italic> , and <italic>Fasn2</italic> , while <italic>Midway</italic> and <italic>Brummer</italic> remained unchanged. In addition, expression of the metabolic regulator <italic>PGC1α</italic> ( <italic>spargel</italic> ) was significantly reduced in males, consistent with previously reported reductions in <italic>AMPKα</italic> expression. Together, these findings demonstrate that <italic>Nepl15</italic> functions as an upstream regulator of insulin-dependent anabolic signaling and nutrient partitioning, linking intracellular signaling to glycogen and lipid storage independently of nutrient intake. These results identify <italic>Nepl15</italic> as a previously unrecognized regulator of metabolic homeostasis in <italic>Drosophila</italic> and provide new insight into the metabolic functions of the evolutionarily conserved neprilysin family. </p>