Mutual Amplification of GLI2 /Hedgehog and Transcription Factor JUN / AP ‐1 Signaling in Fibroblasts in Systemic Sclerosis: Potential Implications for Combined Therapies

• Published in: Arthritis & rheumatology (Hoboken, N.J.) N.J.), 2024-10
• Main Authors: Bergmann, Christina, Chenguiti Fakhouri, Sara, Trinh‐Minh, Thuong, Filla, Tim, Rius Rigau, Aleix, Ekici, Arif B., Merlevede, Benita, Hallenberger, Ludwig, Zhu, Honglin, Dees, Clara, Matei, Alexandru‐Emil, Auth, Janina, Györfi, Andrea‐Hermina, Zhou, Xiang, Rauber, Simon, Bozec, Aline, Dickel, Nicholas, Liang, Chunguang, Kunz, Meik, Schett, Georg, Distler, Jörg H.W.
• Format: Article
• Language: English
• ISSN: 2326-5191; 2326-5205; 2326-5205
• DOI: 10.1002/art.42979

Deregulation of the cJUN/AP-1 and hedgehog/GLI2 signaling pathways has been implicated in fibroblast activation in systemic sclerosis (SSc). However, the consequences of their concomitant up-regulation are unknown. Here, we tested the hypothesis that mutual amplification of both pathways might drive persistent fibroblast activation.OBJECTIVEDeregulation of the cJUN/AP-1 and hedgehog/GLI2 signaling pathways has been implicated in fibroblast activation in systemic sclerosis (SSc). However, the consequences of their concomitant up-regulation are unknown. Here, we tested the hypothesis that mutual amplification of both pathways might drive persistent fibroblast activation.Cultured fibroblasts and skin sections of patients with diffuse SSc and healthy volunteers were analyzed. cJUN/AP-1 signaling and hedgehog/GLI2 signaling were inhibited using knockdown and pharmacologic approaches. Hedgehog signaling was activated in mice by fibroblast-specific overexpression of constitutively active Smoothened.METHODSCultured fibroblasts and skin sections of patients with diffuse SSc and healthy volunteers were analyzed. cJUN/AP-1 signaling and hedgehog/GLI2 signaling were inhibited using knockdown and pharmacologic approaches. Hedgehog signaling was activated in mice by fibroblast-specific overexpression of constitutively active Smoothened.cJUN and GLI2 are concomitantly up-regulated and colocalize in fibroblasts of patients with SSc compared to healthy controls. Activation of hedgehog/GLI2 signaling induces the expression of cJUN in vitro and in vivo, whereas inactivation of GLI2 inhibits cJUN expression. Likewise, inactivation of cJUN impairs the expression of GLI2. This mutual regulation occurs at the level of transcription with binding of cJUN and GLI2 to specific binding motifs. Interference with this mutual amplification of cJUN signaling and GLI2 signaling inhibits fibroblast activation and collagen release: Inhibition of cJUN/AP-1 signaling ameliorates hedgehog-induced fibroblast activation and skin fibrosis in SmoACT mice with a reduction of skin thickness of 103% (P = 0.0043) in the treatment group compared to the fibrotic control group. Moreover, combined pharmacologic inhibition of cJUN/AP-1 and hedgehog/GLI2 exerts additive antifibrotic effects in a model of TGFβ-driven experimental fibrosis (TBRACT mice).RESULTScJUN and GLI2 are concomitantly up-regulated and colocalize in fibroblasts of patients with SSc compared to healthy controls. Activation of hedgehog/GL