These results are the first to demonstrate a key role for sCD13 in SSc skin fibrosis and suggest that targeting the sCD13-B1R signaling axis is a promising novel therapeutic approach for SSc.

The expression of CD13, B1R, and MMP14 was examined in SSc skin and explanted dermal fibroblasts. The efficacy of B1R antagonists in the inhibition on fibrosis was determined in vitro and in vivo.

Systemic sclerosis (SSc) is an autoimmune multisystem disease with poorly understood pathogenesis and ineffective treatment options. Soluble CD13 (sCD13), generated by the cleavage of cell surface CD13 via matrix metalloproteinase 14 (MMP14), signals through the bradykinin receptor B1 (B1R) to elicit pro-inflammatory, pro-arthritic, and pro-angiogenic responses. In this study, we explored the antifibrotic potential of targeting the sCD13-B1R axis in SSc.

Expression of the genes for CD13, B1R, and MMP14 was elevated in skin biopsies from patients with diffuse cutaneous (dc) SSc. Notably, single-cell analysis of SSc skin biopsies revealed the highest BDKRB1 expression in COL8A1-positive myofibroblasts, a population exclusively seen in SSc. Transforming growth factor beta (TGFβ) induced the expression of BDKRB1 and production of sCD13 by dcSSc skin fibroblasts. Treatment of dcSSc fibroblasts with sCD13 promoted fibrotic gene expression, signaling, cell proliferation, migration, and gel contraction. The pro-fibrotic responses of sCD13 or TGFβ were prevented by a B1R antagonist. Mice lacking Cd13 or Bdkrb1 were resistant to bleomycin-induced skin fibrosis and inflammation. Pharmacological B1R inhibition had a comparable antifibrotic effect.