Nuclear Receptor DHR96 Acts as a Sentinel for Low Cholesterol Concentrations in Drosophila melanogaster

Abstract

All eukaryotic cells have to maintain cholesterol concentrations within defined margins in order to function normally. Perturbing cholesterol homeostasis can result in a wide range of cellular and systemic defects, including cardiovascular diseases, as well as Niemann-Pick and Tangier diseases. Here, we show that DHR96 is indispensable for mediating the transcriptional response to dietary cholesterol and that it acts as a key regulator of the Niemann-Pick type C gene family, as well as of other genes involved in cholesterol uptake, metabolism, and transport. DHR96 mutants are viable and phenotypically normal on a standard medium but fail to survive on diets that are low in cholesterol. DHR96 mutants have aberrant cholesterol levels, demonstrating a defect in maintaining cholesterol homeostasis. Remarkably, we found that a high-cholesterol diet phenocopied the genomic profile of the DHR96 mutation, indicating that DHR96 resides at the top of a genetic hierarchy controlling cholesterol homeostasis in insects. We propose a model whereby DHR96 is activated when cellular cholesterol concentrations drop below a critical threshold in order to protect cells from severe cholesterol deprivation.