UVA1 irradiation attenuates collagen production via Ficz/AhR/MAPK signaling activation in scleroderma

Scleroderma is an autoimmune disease mainly characterized by progressive fibrosis of the skin. There are two types of scleroderma, namely localized scleroderma (LS) and systemic sclerosis (SSc); skin lesions in both types of scleroderma are histologically identical. Progressive skin sclerosis induces psychological and ecological burden for scleroderma patients. However, there is no effective treatment for scleroderma due to its unclear etiology. Aryl hydrocarbon receptor (AhR) is recognized as an environmental chemical effector that can respond to ultraviolet radiation, which has been demonstrated to participate in the pathogenesis of SSc in our previous study. In this study, we verify whether the anti-fibrosis effect of ultraviolet A1 (UVA1) phototherapy could be partially induced through Ficz/AhR/MAPK signaling activation for fibrotic lesions in both SSc and LS patients. This is the first study to show the association between the AhR pathway and the anti-fibrotic mechanism of UVA1 phototherapy, which provides additional evidence of the role of AhR in the fibrotic mechanism of systemic scleroderma from different perspectives. Ficz and other AhR agonists may replace UVA1 phototherapy as anti-fibrotic agents in scleroderma.