Differentiation Potential of CD14+ Monocytes into Myofibroblasts in Patients with Systemic Sclerosis

Background: Circulating monocytes are a highly plastic and functionally heterogeneic cell type with an activated phenotype in patients with systemic sclerosis (SSc). CD14(+) monocytes have the potential to differentiate into extra-cellular matrix (ECM) producing cells, possibly participating in fibrogenesis. Aim: To study the effect of GM-CSF, IL-4 and endothelin -1 (ET-1) alone or in combination on monocyte differentiation into myofibroblasts. Methods: CD14(+) cells were isolated from peripheral blood from 14 SSc patients and healthy controls by positive selection and incubated with different combinations of GM-CSF, IL-4 and ET-1 for 14 days. Type-1 collagen and alpha-SMA were detected by Western blot, qPCR and confocal microscopy. HLA-DR, CD11c and CD14 expression was analysed by flow cytometry. A collagen gel contraction assay was performed for functional myofibroblast assessment. Results: GM-CSF both induced collagen and alpha-SMA expression after 14 days. ET-1 further increased GM-CSF-induced collagen expression in a dose dependent manner up to 30-fold. IL-4/GM-CSF combination leads to a more DC-like phenotype of monocytes associated with reduced collagen and alpha-SMA expression compared to GM-CSF alone. Collagen and alpha-SMA expression was higher in monocytes from SSc patients and monocytes were more prone to obtain a spindle form. In contrast to controls, ET-1 and IL-4 alone were sufficient to induce alpha-SMA expression in monocytes from SSc patients. Despite the induction of alpha-SMA expression, monocyte-derived myofibroblasts only had a moderate capability of contraction in functional analyses. Conclusion: SSc monocytes display increased maturation towards myofibroblasts demonstrated by their phenotype and alpha-SMA expression when compared to monocytes from healthy controls, however only with minor functional contraction properties.