Botulinum neurotoxin type A1 alleviates bleomycin-induced skin fibrosis by inhibiting phosphatidylinositol 3-kinase-protein kinase B (PI3K-Akt) pathway and associated cell cycle and proliferation.

Localized scleroderma (LoS) is a chronic dermal disease with fibrotic skin and subcutaneous tissues. Owing to the largely undefined pathogenesis, there is no specific medical treatment for LoS. Recent investigator-initiated tests have revealed the clinical efficacy of botulinum neurotoxin type A1 (BoNT/A1) on treating LoS. However, the mechanism of action of BoNT/A1-based LoS intervention has not been fully illustrated. In this study, we used a bleomycin-induced skin fibrosis mouse model for evaluating the therapeutic effects and mechanism of actions of BoNT/A1 relevant to LoS. It was found that BoNT/A1 treatment could alleviate the pathological changes in mice in a dose-dependent manner. Further analysis showed that BoNT/A1 could suppress the proliferation of primary human dermal fibroblasts by arresting the cell cycle at G0/G1 phase. RNA sequencing and subsequent western blotting analysis of human dermal fibroblasts revealed phosphatidylinositol 3-kinase-protein kinase B signaling as one of the most affected pathways in BoNT/A1 treatment groups. Experiments with phosphatidylinositol 3-kinase-protein kinase B agonist 740Y-P showed that BoNT/A1 suppressed skin fibrosis by inhibiting phosphatidylinositol 3-kinase-protein kinase B signaling. Collectively, our study provides experimental evidence at the animal, cellular, and molecular levels for the clinical use of BoNT/A1 for treating LoS.