Background: Retinoic acid-related orphan receptor-α, RORα, is a member of the orphan nuclear receptor family and functions as a transcriptional activator. RORα has been implicated in various pathophysiological processes, including cancer, inflammation, immunological responses, cerebellar development, circadian rhythm regulation and lipid homeostasis. However, its involvement in rheumatologic diseases, particularly fibrotic tissue remodeling, remains unexplored. This study aims to investigate the role of RORα in fibroblast activation and fibrotic tissue remodeling.

Objectives: The objective of this study is to elucidate the role of RORα in fibroblast activation and fibrotic tissue remodeling, particularly in systemic sclerosis and other fibrotic diseases. We aim to assess RORα expression in fibrotic tissues and experimental models, evaluate the impact of RORα modulation on fibroblast function and explore the antifibrotic potential of the selective inverse agonist SR3335. Additionally, we seek to identify RORα-regulated gene networks and elucidate its involvement in key pathways, such as the Hippo signaling pathway, to establish RORα as a potential therapeutic target in fibrosis.

Methods: RORα expression was analyzed in systemic sclerosis (SSc) patients, other fibrotic diseases and experimental fibrosis models using real-time PCR, Western blotting and immunofluorescence. RORα expression was modulated via knockdown and knockout techniques in vitro and in vivo. The pharmaceutical potential of targeting RORα was explored using SR3335, a selective inverse agonist, to assess its antifibrotic efficacy in three mouse models: bleomycin-induced dermal fibrosis, bleomycin-induced pulmonary fibrosis and CCl ₄ -induced liver fibrosis. RNA-Seq identified RORα target genes in fibroblasts.

Results: RORα expression was elevated in fibroblasts from various fibrotic diseases and organs, including hypertrophic scars, fibrotic skin, lungs and liver, compared to non-fibrotic controls. Increased RORα expression was also observed in murine SSc models. Rorα knockdown in murine fibroblasts attenuated TGFβ-induced fibroblast-to-myofibroblast transition and reduced collagen synthesis. Pharmacologic inhibition of RORα with SR3335 significantly decreased TGFβ-induced myofibroblast differentiation and the deposition of type I collagen and fibronectin in human fibroblasts. SR3335 treatment also demonstrated potent antifibrotic effects in murine models of bleomycin-induced dermal and pulmonary fibrosis, as well as CCl ₄ -induced liver fibrosis. RNA-Seq identified RORα as a novel upstream regulator of profibrotic genes, including COL1A1 , ACTA2 , CTGF and PAI-1 . Mechanistically, RORα was found to modulate Hippo signaling, a key pathway in fibroblast activation. TGFβ enhanced Hippo reporter activity, which was inhibited by SR3335. Western blots confirmed that SR3335 diminished the upregulation of Hippo signaling components TAZ and YAP. Immunofluorescence analyses corroborated these findings, showing reduced nuclear and total TAZ and YAP levels following SR3335 treatment.

Conclusion: Our findings position RORα as a pivotal regulator of fibroblast activation in fibrotic tissue remodeling and a novel upstream regulator of Hippo signaling. Targeting of RORα may offer potential as a novel molecular target for the treatment of SSc and other fibrotic diseases.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: Cuong Tran-Manh: None declared, Rosebeth Kagwiria: None declared, Ruifang Liang: None declared, Thuong Trinh-Minh: None declared, Christoph Liebel: None declared, Xiang Zhou: None declared, Jörg Distler CEO of 4D Science and scientific lead of FibroCure, Active Biotech, Anamar, ARXX, AstraZeneca, Bayer Pharma, Boehringer Ingelheim, Callidatas, Celgene, Galapagos, GSK, Inventiva, Janssen, Kyverna, Novartis, Pfizer, Quell Therapeutics and UCB, Anamar, ARXX, BMS, Bayer Pharma, Boehringer Ingelheim, Cantargia, Celgene, CSL Behring, Exo Therapeutics, Galapagos, GSK, Incyte, Inventiva, Kiniksa, Kyverna, Lassen Therapeutics, Mestag, Sanofi-Aventis, RedX, UCB and ZenasBio.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.