The polyol pathway is a crucial glucose sensor in Drosophila
A major nutrient source for animals is glucose, which induces transcriptional responses that shift metabolism. Such metabolic adaptation should be appropriately scaled to the ingested glucose levels, and decoupling causes human metabolic diseases. However, the identity of the crucial sensor metabolite(s) that transmit circulating glucose levels to the transcriptional machinery remains elusive. Here we show that the polyol pathway, which converts glucose to fructose via sorbitol, is required for activation of the master metabolic regulator Mondo, the Drosophila homologue of MondoA/ChREBP. We demonstrate that under normal nutritional conditions polyol pathway metabolites promote Mondos nuclear localization and cause global changes in metabolic gene expression. Polyol pathway mutants block nuclear localization of Mondo and Mondo-mediated gene expression despite intact glycolytic and pentose phosphate pathways. Our results uncover the normal physiological function of this pathway and cast a new light on the adverse effects of high fructose diets in human health.