Enhanced HIF-1α cooperation by a human RORγt mutant potentiates Th17 pathogenicity

T helper 17 (Th17) cells are pivotal in mucosal defense and autoimmune pathology, with their function governed by the transcription factor retinoic acid receptor-related orphan receptor gamma t (RORγt). Although genome-wide association studies link RORC variants to inflammatory diseases, their functional consequences remain poorly understood. We identify a pathogenic RORγt mutation N277D (mouse homolog N275D) that amplifies Th17 pathogenicity through cooperation with hypoxia-inducible factor HIF-1α. This mutation enhances IFN-γ and other Th1-type cytokine production by Th17 cells, exacerbating colitis without disrupting T cell development or homeostasis. Integrated transcriptomic and metabolomic profiling reveals activation of glycolytic and hypoxia-associated pathways, consistent with increased RORγt^N275D recruitment by HIF-1α to the Pdk1 locus. Notably, silencing Pdk1 normalizes the excessive IFN-γ production in RORγt^N275D Th17 cells. Together, these findings define a regulatory axis linking RORγt and HIF-1α that coordinates transcriptional and metabolic programs in pathogenic Th17 cells, providing a framework for dissecting the functional impact of autoimmune risk variants.