Suppression of TH17 differentiation and autoimmunity by a synthetic ROR ligand

Abstract

The nuclear receptors RORα and RORγt (retinoic acid receptor-related orphan receptors α and γt) are essential for the development of TH17 cells, the T-helper cells that produce interleukin-17. Two groups report the identification of RORγt inhibitors, compounds that could have potential in the treatment of autoimmune diseases. Huh et al. used a chemical screen in an insect-cell-based reporter system to identify the cardiac glycoside digoxin and various derivatives as inhibitors of the transcriptional activity of RORγt. Through this mechanism, these compounds block the differentiation of TH17 cells in mice, and inhibit interleukin-17 production in vitro in human T cells. Solt et al. describe a synthetic ligand, named SR1001, that functions as an inverse agonist for RORα and RORγt, and show that it blocks TH17 development in vitro and inhibits experimental encephalomyelitis in mice. T-helper cells that produce interleukin-17 (TH17 cells) are a recently identified CD4+ T-cell subset with characterized pathological roles in autoimmune diseases1,2,3. The nuclear receptors retinoic-acid-receptor-related orphan receptors α and γt (RORα and RORγt, respectively) have indispensible roles in the development of this cell type4,5,6,7. Here we present SR1001, a high-affinity synthetic ligand—the first in a new class of compound—that is specific to both RORα and RORγt and which inhibits TH17 cell differentiation and function. SR1001 binds specifically to the ligand-binding domains of RORα and RORγt, inducing a conformational change within the ligand-binding domain that encompasses the repositioning of helix 12 and leads to diminished affinity for co-activators and increased affinity for co-repressors, resulting in suppression of the receptors’ transcriptional activity. SR1001 inhibited the development of murine TH17 cells, as demonstrated by inhibition of interleukin-17A gene expression and protein production. Furthermore, SR1001 inhibited the expression of cytokines when added to differentiated murine or human TH17 cells. Finally, SR1001 effectively suppressed the clinical severity of autoimmune disease in mice. Our data demonstrate the feasibility of targeting the orphan receptors RORα and RORγt to inhibit specifically TH17 cell differentiation and function, and indicate that this novel class of compound has potential utility in the treatment of autoimmune diseases.