Elevated Fibronectin Levels in Profibrotic CD14 Monocytes and CD14 Macrophages in Systemic Sclerosis

Background: Systemic sclerosis (SSc) is an autoimmune disease characterized by overproduction of extracellular matrix (ECM) and multiorgan fibrosis. Animal studies pointed to bone marrow-derived cells as a potential source of pathological ECM-producing cells in immunofibrotic disorders. So far, involvement of monocytes and macrophages in the fibrogenesis of SSc remains poorly understood.

Methods And Results: Immunohistochemistry analysis showed accumulation of CD14 monocytes in the collagen-rich areas, as well as increased amount of alpha smooth muscle actin (αSMA)-positive fibroblasts, CD68 and mannose-R macrophages in the heart and lungs of SSc patients. The full genome transcriptomics analyses of CD14 blood monocytes revealed dysregulation in cytoskeleton rearrangement, ECM remodeling, including elevated (gene encoding fibronectin) expression and TGF-β signalling pathway in SSc patients. In addition, single cell RNA sequencing analysis of tissue-resident CD14 pulmonary macrophages demonstrated activated profibrotic signature with the elevated expression in SSc patients with interstitial lung disease. Peripheral blood CD14 monocytes obtained from either healthy subjects or SSc patients exposed to profibrotic treatment with profibrotic cytokines TGF-β, IL-4, IL-10, and IL-13 increased production of type I collagen, fibronectin, and αSMA. In addition, CD14 monocytes co-cultured with dermal fibroblasts obtained from SSc patients or healthy individuals acquired a spindle shape and further enhanced production of profibrotic markers. Pharmacological blockade of the TGF-β signalling pathway with SD208 (TGF-β receptor type I inhibitor), SIS3 (Smad3 inhibitor) or (5Z)-7-oxozeaenol (TGF-β-activated kinase 1 inhibitor) ameliorated fibronectin levels and type I collagen secretion.

Conclusions: Our findings identified activated profibrotic signature with elevated production of profibrotic fibronectin in CD14 monocytes and CD14 pulmonary macrophages in SSc and highlighted the capability of CD14 monocytes to acquire a profibrotic phenotype. Taking together, tissue-infiltrating CD14 monocytes/macrophages can be considered as ECM producers in SSc pathogenesis.