Background/Purpose:  Scleroderma is a multisystem connective tissue disease characterized by extensive tissue fibrosis and its three prominent cardinal features are vasculopathy, excessive collagen deposition and immunological abnormalities. Metformin (MET) has anti-inflammatory and anti-fibrotic effects. Therefore, we investigated the potential effect of metformin on fibrosis in a murine model bleomycin (BLM) of scleroderma.

Methods: A total of 50 mice were randomly divided into 5 group: MET treatment groups (200mg/kg, 100mg/kg, 50mg/kg), model group and control group. Scleroderma was induced in C57BL mice by subcutaneous injections of BLM daily, after 2 hours interval, different dose MET was intraperitoneally injected, while control group received with normal saline at corresponding time point. At the end of the fourth week, all mice were sacrificed and spleen tissues were collected for flow cytometry analysis. The skin samples were harvested for immunohistochemistry and quantify biological parameters (hydroxyproline content and RT-PCR).

Results: MET treatments markedly alleviated histopathological changes (dermal thickness and collagen deposition) and hydroxyproline contents compared with model group (P<0.05). The abnormal differentiation of Th17 cells, Th1 cells, Th2 cells and follicular helper T (Tfh) cells was significantly inhibited by MET (P<0.05), while the proliferation of Treg cells were upregulated (P<0.05). Moreover, the expression levels of specific cytokines and transcriptions factors related to Th17 cells changed: interleukin-17A (IL-17A) and retinoic-acid-receptor related orphan receptors gamma t (RORγt) were decreased whereas forkhead box protein 3 (Foxp3) was increased partly in a dose-depend manner. In addition, MET treatment inhibited spleen germinal center B cells formation (P<0.01).

Conclusion: Our results indicate that MET can effectively alleviate the fibrotic disorders by modulating the balance between Treg cells and effector T cells and germinal center B cells formation.