Mutual amplification of GLI2/Hedgehog and cJUN/AP1 signaling in fibroblasts in Systemic Sclerosis (SSc) - potential implications for combined therapies

• Published in: Arthritis & rheumatology (Hoboken, N.J.)
• Main Authors: Bergmann, Christina, Chenguiti Fakhouri, Sara, Thuong, Trinh-Minh, Filla, Tim, Rigau, Aleix Rius, 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: Journal Article
• Language: English
• Published: United States 26.08.2024
• ISSN: 2326-5205
• DOI: 10.1002/art.42979

Deregulation of the cJUN/AP1- and hedgehog/GLI2 signaling pathways have been implicated in fibroblast activation in Systemic Sclerosis (SSc). However, the consequences of their concomitant upregulation are unknown. Here, we tested the hypothesis that mutual amplification of both pathways might drive persistent fibroblast activation. Cultured fibroblasts and skin sections of diffuse SSc-patients and healthy volunteers were analyzed. cJUN/AP1- and hedgehog/GLI2-signaling were inhibited using knockdown and pharmacologic approaches. Hedgehog signaling was activated in mice by fibroblast-specific overexpression of constitutively-active Smoothend. cJUN and GLI2 are concomitantly upregulated and colocalize in fibroblasts of SSc patients 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- and GLI2-signaling inhibits fibroblast activation and collagen release: Inhibition of cJUN/AP1-signaling ameliorates hedgehog-induced fibroblast activation and skin fibrosis in Smo -mice with a reduction of skin thickness of 103 % (p=0.0043) in the treatment group compared to the fibrotic control group. Moreover, combined pharmacological inhibition of cJUN/AP1- and hedgehog/GLI2 exerts additive antifibrotic effects in a model of TGFβ-driven experimental fibrosis (TBR mice). The transcription factors cJUN and GLI2 reinforce each other's activity to promote fibroblast activation in SSc. Interruption of this crosstalk by combined inhibition of both pathways exerts additive anti-fibrotic effects at well tolerated doses.