PRMT5 in T helper lymphocytes is essential for cholesterol biosynthesis-mediated Th17 responses and autoimmunity

Protein Arginine Methyltransferase (PRMT) 5 catalyzes symmetric dimethylation of arginine, a post-translational modification involved in cancer and embryonic development. However, the role of PRMT5 in T helper (Th) cell polarization and Th cell-mediated disease has not yet been elucidated. Here we report that PRMT5 is necessary for Th17 differentiation and EAE, via enhancement of cholesterol biosynthesis and activation of ROR-γt. PRMT5 additionally controls thymic and peripheral homeostasis in the CD4 Th cell life cycle, as well as iNK T and CD8 T cell development or maintenance, respectively. Overall, our two conditional PRMT5 KO models that selectively delete PRMT5 in all T cells (T-PRMT5 Δ/Δ ) or Th cells (iCD4-PRMT5 Δ/Δ ) unveil a crucial role for PRMT5 in T cell proliferation, Th17 responses and disease. These results point to Th PRMT5 and its downstream cholesterol biosynthesis pathway as promising therapeutic targets in Th17-mediated diseases.