Delineation of the molecular determinants of the unique allosteric binding site of the orphan nuclear receptor RORγt.

Nuclear receptors (NRs) are high-interest targets in drug discovery because of their involvement in numerous biological processes and diseases. Classically, NRs are targeted via their hydrophobic, orthosteric pocket. Although successful, this approach comes with challenges, including off-target effects due to lack of selectivity. Allosteric modulation of NR activity constitutes a promising pharmacological strategy. The retinoic acid receptor-related orphan receptor-γt (RORγt) is a constitutively active NR that positively regulates the expression of interleukin-17 in T helper 17 cells. Inhibiting this process is an emerging strategy for managing autoimmune diseases. Recently, an allosteric binding pocket in the C-terminal region of the ligand-binding domain (LBD) of RORγt was discovered that is amenable to small-molecule drug discovery. Compounds binding this pocket induce a reorientation of helix 12, thereby preventing coactivator recruitment. Therefore, inverse agonists binding this site with high affinity are actively being pursued. To elucidate the pocket formation mechanism, verify the uniqueness of this pocket, and substantiate the relevance of targeting this site, here we identified the key characteristics of the RORγt allosteric region. We evaluated the effects of substitutions in the LBD on coactivator, orthosteric, and allosteric ligand binding. We found that two molecular elements unique to RORγt, the length of helix 11' and a Gln-487 residue, are crucial for the formation of the allosteric pocket. The unique combination of elements present in RORγt suggests a high potential for subtype-selective targeting of this NR to more effectively treat patients with autoimmune diseases.

Concomitant suppression of TH2 and TH17 cell responses in allergic asthma by targeting retinoic acid receptor-related orphan receptor γt.

BACKGROUND: Allergic asthma is a heterogeneous chronic inflammatory disease of the airways with a massive infiltration of eosinophils or neutrophils mediated by allergen-specific TH2 and TH17 cells, respectively. Therefore successful treatment of allergic asthma will require suppression of both TH2 and TH17 cells. OBJECTIVE: We sought to investigate the role of the TH17 cell pathway in regulating TH2 cell responses in allergic asthma. METHODS: Allergic asthma was induced by intranasal challenge with proteinase allergens in C57BL/6, Il17a-/-Il17f-/-, and retinoic acid receptor-related orphan receptor γt (RORγt)gfp/gfp mice. A pharmacologic RORγt inhibitor was used to evaluate its preventive and therapeutic effects in allergic asthma. Characteristics of allergic airway inflammation were analyzed by using flow cytometry, histology, quantitative real-time PCR, and ELISA. Mixed bone marrow chimeric mice, fate mapping analysis, short hairpin RNA transduction, and in vitro T-cell differentiation were used for mechanistic studies. RESULTS: Mice deficient in IL-17A and IL-17F, as well as RORγt, exhibited a significant reduction not only in TH17 cell responses but also in TH2 cell responses in an animal model of allergic asthma. Similarly, mice treated with an RORγt inhibitor had significantly diminished TH17 and TH2 cell responses, leading to reduced neutrophil and eosinophil numbers in the airway. RORγt-deficient T cells were intrinsically defective in differentiating into TH2 cells and expressed increased levels of B-cell lymphoma 6 (Bcl6). Bcl6 knockdown resulted in a remarkable restoration of TH2 cell differentiation in RORγt-deficient T cells. Blockade of RORγt also significantly hampered the differentiation of human TH2 and TH17 cells from naive CD4+ T cells. CONCLUSION: RORγt in T cells is required for optimal TH2 cell differentiation by suppressing Bcl6 expression; this finding suggests that targeting RORγt might be a promising approach for the treatment of allergic asthma by concomitantly suppressing TH17 and TH2 cell responses in the airway.

Abnormal CD161+ immune cells and retinoic acid receptor-related orphan receptor γt-mediate enhanced IL-17F expression in the setting of genetic hypertension.

BACKGROUND: Hypertension is considered an immunologic disorder. However, the role of the IL-17 family in genetic hypertension in the spontaneously hypertensive rat (SHR) has not been investigated. OBJECTIVE: We tested the hypothesis that enhanced TH17 programming and IL-17 expression in abundant CD161+ immune cells in SHRs represent an abnormal proinflammatory adaptive immune response. Furthermore, we propose that this response is driven by the master regulator retinoic acid receptor-related orphan receptor γt (RORγt) and a nicotinic proinflammatory innate immune response. METHODS: We measured expression of the CD161 surface marker on splenocytes in SHRs and normotensive control Wistar-Kyoto (WKY) rats from birth to adulthood. We compared expression of IL-17A and IL-17F in splenic cells under different conditions. We then determined the functional effect of these cytokines on vascular reactivity. Finally, we tested whether pharmacologic inhibition of RORγt can attenuate hypertension in SHRs. RESULTS: SHRs exhibited an abnormally large population of CD161+ cells at birth that increased with age, reaching more than 30% of the splenocyte population at 38 weeks. The SHR splenocytes constitutively expressed more RORγt than those of WKY rats and produced more IL-17F on induction. Exposure of WKY rat aortas to IL-17F impaired endothelium-dependent vascular relaxation, whereas IL-17A did not. Moreover, in vivo inhibition of RORγt by digoxin decreased systolic blood pressure in SHRs. CONCLUSIONS: SHRs have a markedly enhanced potential for RORγt-driven expression of proinflammatory and prohypertensive IL-17F in response to innate immune activation. Increased RORγt and IL-17F levels contribute to SHR hypertension and might be therapeutic targets.

Discovery of novel N-sulfonamide-tetrahydroquinolines as potent retinoic acid receptor-related orphan receptor γt inverse agonists for the treatment of autoimmune diseases.

Targeting the nuclear receptor RORγt is thought to be effective in autoimmune disorders. Tertiary sulfonamide 1 was found to be a potent RORγt inverse agonist previously. However, the high hepatic clearance value limits its druggability. In this study, we designed and synthesized a series of N-sulfonamide-tetrahydroquinolines by molecular modeling and scaffold hopping strategy, aiming at improving the metabolic stabilities. Detailed SAR exploration led to identification of potent RORγt inverse agonists such as 13 with moderate binding affinity and inhibitory activity of Th17 cell differentiation. Binding mode of 13 with RORγt-LBD was revealed by molecular docking. Moreover, 13 showed lower intrinsic clearance in mouse liver microsomes compared with 1 and potent in vivo efficacy and safety in psoriasis models, which can be used as a good starting point for the further optimization.

RORγt Expression and Lymphoid Neogenesis in the Brain of Patients with Secondary Progressive Multiple Sclerosis.

Ectopic B-cell follicle-like structures (ELS) are found in the meninges of patients with secondary progressive multiple sclerosis (SPMS). Because cells expressing the transcriptional regulator retinoic acid receptor-related orphan receptor-γt (RORγt) and producing interleukin 17 (IL17), e.g. T helper 17 cells and lymphoid tissue inducer (LTi) cells, have been implicated in the formation of ELS, we studied RORγt and IL17 expression in brain tissue from patients with SPMS an assessed their relationships to immune infiltrates and meningeal ELS. By immunohistochemistry, small numbers of RORγt-positive cells were detected in the meninges of 6 of 12 SPMS cases analyzed. RORγt-positive cells were localized in B-cell follicles or aggregates and nearby diffuse meningeal infiltrates, and predominantly co-expressed CD3. Only a few RORγt-positive, CD3-negative cells were observed, suggesting the presence of group 3 innate lymphoid cells, which comprise the LTi cell subset. Some IL17-positive cells, co-expressing in part RORγt and predominantly CD3, were found in meningeal B-cell follicles from 4 SPMS cases. Rare RORγt-positive and IL17-positive cells were detected in white matter. Gene expression analysis of laser dissected meningeal infiltrates and white matter lesions confirmed low frequencies and virtual absence of RORγt and IL17 signals, respectively. Thus, there is selective migration or survival of RORγt-positive cells in MS patient meninges and an association of these cells with ELS.

Increased RUNX1 expression in patients with immune thrombocytopenia.

Immune thrombocytopenia (ITP) is a heterogeneous autoimmune disease, characterized by dysregulation of cellular immunity. Th17 and associated IL-17 were involved in the pathogenesis of ITP. Runt-related transcription factor 1 (RUNX1), a member of the runt domain-containing family of transcription factors, is required for Th17 differentiation. Whether RUNX1 was involved in the pathogenesis of ITP remains poorly understood. In this study, 30 active ITP patients, 20 ITP in remission and 20 age and gender matched healthy controls were included. Peripheral blood mononuclear cells (PBMCs) were isolated to measure mRNA level of RUNX1 and retinoic acid receptor-related orphan receptor-γt (RORγt) by quantitative real-time PCR and Th17 cells by flow cytometry. Meanwhile, plasma was extracted for measurement of IL-17 level by ELISA. Our results showed a significantly higher expression of RUNX1, RORγt, Th17 cells and plasma level of IL-17 in active ITP patients than that in healthy controls. No differences of expression of RUNX1, RORγt and Th17 cells were observed between remission patients and controls. Furthermore, a significantly positive correlation of RUNX1 with RORγt was found in active ITP patients. In conclusion, RUNX1 was associated with the pathogenesis of ITP possibly through regulation of Th17 cell differentiation and therapeutically targeting it might be a novel approach in ITP treatment.