An LKB1-mitochondria axis controls Th17 effector function [RNA-Seq 2]

T helper 17 (Th17) cells are a distinct subset of CD4+ T cells necessary for maintaining gut homeostasis and have prominent roles in autoimmunity and inflammation1. Th17 cells have unique metabolic features, including a stem cell-like signature2,3 and reliance on mitochondrial respiratory chain function and tricarboxylic acid (TCA) cycle to coordinate metabolic and epigenetic remodeling4,5. Dynamic changes in mitochondrial membrane morphology are key to sustain organelle function6. However, it remains unclear whether mitochondrial membrane remodeling orchestrates metabolic and differentiation events in Th17 cells. Here we demonstrate that mitochondrial membrane fusion and tight cristae organization are required for Th17 cell function (i.e. cytokine expression) but dispensable in other T cell subsets. We find that Th17 cells rely on mitochondrial fusion as a result of their low metabolic activity. Thus, lowering metabolic activity in other T cell subsets by nutrient restriction was sufficient to increase reliance on mitochondrial fusion for effector function. Transcriptional, proteomic, and metabolomic profiling identified the serine/threonine kinase liver associated kinase B1 (LKB1) as an essential node coupling mitochondrial function to cytokine expression in T cells. By genetic and metabolomic approaches, we demonstrate that LKB1 regulates IL-17A expression by controlling TCA cycle metabolites and transcriptional remodeling. Th-17 cell-specific deletion of optic atrophy 1 (OPA1), a protein involved in mitochondrial inner membrane fusion and cristae organization, reduced autoimmune pathogenesis in a mouse model of multiple sclerosis, while additional deletion of LKB1 restored disease. Our findings highlight distinct mitochondrial requirements in CD4+ T cells, identify mitochondrial membrane fusion as a major determinant of Th17 responses, and reveal LKB1 as a sensor of mitochondrial integrity that links mitochondrial cues to effector programs in Th17 cells. CD4+ T cells were isolated from cell suspensions from spleen and peripheral lymph nodes (LN) from wild type and Opa1 conditional floxed mice crossed with CD4Cre to generate Opa1 deficient CD4 T cells. CRISPR-Cas9 deletion of LKB1 was performed with Alt-R™ CRISPR-Cas9 System (IDT) and 4D-Nucleofector™ technology (Lonza) in freshly isolated CD4+ T cells. Isolated CD4s were then polarized to Th17 using TGF-β (5 ng ml-1), IL-6 (10 ng ml-1), IL-1β (10 ng ml-1), anti-mouse IFN-γ (10 μg ml-1) and anti-mouse IL-4 (10 μg ml-1). RNA was extracted from polarized cells and then sequenced. 3 biological replicates were isolated, processed and analyzed.