A3.7 Anti-fibrotic and anti-inflammatory effect of mesenchymal stem cells in murine hypochlorite-induced systemic sclerosis

Background and objectives Systemic sclerosis (SSc) is a rare disease with unmet medical need and fibrosis-related mortality. Absence of efficient treatments has prompted to develop novel therapeutic strategies among which mesenchymal stem cells (MSCs) appear one of the most attractive options. Herein we provide the first preclinical study using MSCs in the relevant hypochlorite (HOCl)-induced murine model of diffuse SSc, recapitulating the main features of the disease: multivisceral fibrosis, vasculopathy, and autoimmunity. Materials and methods Balb/c mice underwent six weeks of daily intradermal injections of HOCl leading to SSc-HOCl phenotype. Different doses of syngenic bone marrow-derived MSCs were infused in the tail vein of the mice, either the day before disease induction, or at day 21. Skin thickness was measured weekly, and samples of skin and lung were taken at euthanasia (d42) to assess by RT-qPCR the expression of collagens I and III, TGFβ1, alpha-smooth actin muscle (α-SMA), MMP-1 and -9, Tissue Inhibitor of MMP (TIMP1), Hepatocyte Growth Factor (HGF), VEGFA, IL-1β, TNF-α, IL-6, IL-10, Superoxide Dismutase (SOD2), and Heme Oxygenase (HMOX1). Anti-scl70 antibodies levels were measured in sera by ELISA. Results We first compared the effects of different doses of MSCs (2.5 × 10 5 ; 5 × 10 5 and 10 6 ) infused the day before disease induction, on clinical and biological parameters. When considering skin thickness in time, we observed a slower progression in MSC-treated mice, with the best results obtained with the lowest dose of 2.5 × 10 5 MSCs. At euthanasia, a lower expression of fibrotic markers (collagens I and III, TGF-β1, α-SMA) was observed in both skin and lung of treated mice, consistent with histological improvement and inversely proportional to the injected dose. Importantly, sera from treated mice exhibited lower levels of anti-scl70 autoantibodies and enhanced antioxidant capacity, confirming the systemic effect of MSCs. Of interest, MSC administration was also efficient when infused at d21 while disease is known to be established. We further provide evidence at a molecular level that in skin and lung tissues, MSCs exerted an anti-fibrotic role by normalising extracellular matrix remodelling parameters (MMP-1 and -9, TIMP-1, HGF, VEGFA), as well as reducing pro-inflammatory cytokines (IL1β, TNF-α, IL-6, IL-10) and increasing antioxidant defenses (SOD2, HMOX1). Conclusion This preclinical study is the first to demonstrate the therapeutic efficacy of MSCs in a model of diffuse SSc, acting through the modulation of inflammation, tissue remodelling and antioxidant defenses. The benefits observed are particularly promising in sight of clinical perspectives.