Enhanced THBS2 promotes collagen synthesis and inflammatory secretome of fibroblasts in idiopathic pulmonary fibrosis

Abstract

The pathogenesis of pulmonary fibrosis involves structural remodeling and functional impairment of lung tissue, accompanied by increased secretion of pro-inflammatory mediators and abnormal synthesis of the extracellular matrix (ECM). Thrombospondin-2 (THBS2), an ECM glycoprotein encoding gene, has been extensively studied in liver and heart fibrosis. However, its role in idiopathic pulmonary fibrosis (IPF) in humans remains incompletely understood. Lung fibroblasts were obtained from normal individuals and IPF patients, and THBS2 expression was detected. Then, THBS2 overexpression and knockdown cell models as well as exogenous human THBS2 active protein administration cell models were established to explore the role of THBS2 in cell aggressive phenotype, collagen synthesis and proinflammatory mediator secretion. Furthermore, TGF-β1 inhibitor was used to investigate the underlying mechanism of THBS2 affecting collagen synthesis. Finally, in the bleomycin (BLM) -induced pulmonary fibrosis model, the severity of pulmonary fibrosis in mice was evaluated by administering exogenous mouse THBS2 active protein. THBS2 expression was significantly up-regulated in lung tissues of IPF patients and in IPF lung fibroblasts. THBS2 Overexpression and exogenous human THBS2 active protein markedly enhanced the proliferation and migration of fibroblasts and increased the levels of COL1A1, COL1A2, COL3A1, LOX and LOXL2. These effects were attenuated after knockdown of THBS2 in IPF fibroblasts. Animal models also confirmed that exogenous mouse THBS2 protein could aggravate bleomycin-induced pathological changes and collagen deposition in lung tissues of mice. Using TGF-β1 inhibitor SB525334 reduced the protein expression of downstream molecules (TGFBR1, TGFBR2, P-Smad2/3) and collagen synthesis but did not inhibit the upregulation of post-translational modification enzymes LOX and LOXL2 involved in collagen synthesis. Meanwhile, we observed that THBS2 overexpression significantly promoted inflammatory secretome (IL-1β, IL-6 and IL-8). THBS2 is overexpressed in IPF. Functionally, THBS2 promotes the invasive phenotype (proliferation and migration), collagen synthesis and inflammation secretome in fibroblasts. Mechanistically, THBS2 promotes collagen synthesis through the TGF-β1/Smad2/3 signaling pathway.