Topical Application of Nitrate Ameliorates Skin Fibrosis by Regulating ST2CD4 T Cells in Systemic Sclerosis Mouse Model.

Systemic sclerosis (SSc) is characterized by intractable multiorgan fibrosis caused by vascular and immune dysfunction. Currently, effective therapeutic options for patients with SSc are limited. Nitrate, an abundant nutrient in the diet, has been demonstrated to be preventative and therapeutic for several diseases. To determine whether nitrate can slow or reverse SSc progression, topical application of nitrate delivered by dissolving microneedles was used to treat a bleomycin-induced dermal fibrosis mouse model. In this study, nitrate considerably attenuated dermal thickness, stiffness, and collagen deposition. Bulk RNA sequencing of skin revealed that Cd4 was a key hub gene in SSc nitrate therapy. In addition, bleomycin-induced cytokines and chemokines were inhibited by nitrate, and CD4 T cells infiltration markedly declined. Il4, Il6, Il13, and Tgfb expressions in CD4 T cells isolated from skin biopsies also significantly decreased. Mechanistically, Il1rl1, a type 2 immune response inducer, was markedly repressed in isolated CD4 T cells and dermal tissues after nitrate treatment. Remarkably, compared with wild-type mice, mice lacking Il1rl1 showed impaired transcriptional profiles after intradermal bleomycin injection. Adoptive transfer of ST2CD4 T cells promoted bleomycin-induced Rag2 mice dermal fibrosis. Collectively, these findings demonstrate that nitrate targeting ST2CD4 T cells is an effective therapeutic option for SSc.