SREBP governs a triglyceride:glycogen metabolic switch in Drosophila

Tissues store nutrients as triglyceride (TG) or glycogen at specific ratios, but how these reserves are sensed and balanced remains poorly understood. Here we show that blockage of de novo lipogenesis (DNL) in the Drosophila fat body (FB) triggers a cell autonomous metabolic switch characterized by severe fat depletion and profound glycogen accumulation that supports animal development. Despite lipid loss, Drosophila develop normally but exhibit shortened lifespans and impaired female fecundity. Mechanistically, we identify SREBP-dependent metabolic rewiring that facilitates a switch from TG to glycogen storage, triggered by fatty acid deficiency when DNL is inhibited, and which is rescued by dietary fatty acids. Fat depleted FBs require glycolysis but exhibit blunted mitochondrial metabolism, and no dependence on lactate utilization. Finally, we identify histone acetyltransferases (HATs) Nej and Tip60, which support SREBP activity, as essential for this metabolic switch. Collectively, we propose that in response to DNL deficiency, the fat-depleted FB undergoes a SREBP-mediated TG-to-glycogen metabolic switch preserving organismal development at the cost of reproductive success.

Fat body-specific FASN1 loss leads to fat-depleted but viable Drosophila that complete their developmental lifecycle by rewiring energy metabolism to store glycogen instead of fat FASN1-deficient larvae functionally rely on glycogen synthesis and glycolysis, but not lactate metabolism, and display blunted TCA metabolismMetabolic screening reveals a SREBP-dependent TG:glycogen metabolic switch in response to blockage of DNL fatty acid biosynthesisHistone acetyltransferases (HATs) Nej and Tip60, and acetyl-CoA synthase, are required for the TG:glycogen metabolic switch.