CD109 Attenuates Bleomycin-induced Pulmonary Fibrosis by Inhibiting TGF-b Signaling

Pulmonary fibrosis is a fatal condition characterized by fibroblast and myofibroblast proliferation and collagen deposition. TGF-b plays a pivotal role in the development of pulmonary fibrosis. Therefore, modulation of TGF-b signaling is a promising therapeutic strategy for treating pulmonary fibrosis. To date, however, interventions targeting TGF-b have not shown consistent efficacy. CD109 is a GPI-anchored glycoprotein that binds to TGF-b receptor I and negatively regulates TGF-b signaling. However, no studies have examined the role and therapeutic potential of CD109 in pulmonary fibrosis. The purpose of this study was to determine the role and therapeutic value of CD109 in bleomycin-induced pulmonary fibrosis. CD109-transgenic mice overexpressing CD109 exhibited significantly attenuated pulmonary fibrosis, preserved lung function, and reduced lung fibroblasts and myofibroblasts compared with wild-type (WT) mice. CD109^−/− mice exhibited pulmonary fibrosis comparable to WT mice. CD109 expression was induced in variety types of cells, including lung fibroblasts and macrophages, upon bleomycin exposure. Recombinant CD109 protein inhibited TGF-b signaling and significantly decreased ACTA2 expression in human fetal lung fibroblast cells in vitro. Administration of recombinant CD109 protein markedly reduced pulmonary fibrosis in bleomycin-treated WT mice in vivo. Our results suggest that CD109 is not essential for the development of pulmonary fibrosis, but excess CD109 protein can inhibit pulmonary fibrosis development, possibly through suppression of TGF-b signaling. CD109 is a novel therapeutic candidate for treating pulmonary fibrosis. The Journal of Immunology, 2024, 212: 1221–1231.