Alternatively activated macrophages derived from THP-1 cells promote the fibrogenic activities of human dermal fibroblasts.

Macrophages play a key role in the wound healing process and can be divided into classically activated macrophages (M1) and alternatively activated macrophages (M2). Fibroblasts maintain the physical integrity of connective tissue, participate in wound closure as well as produce and remodel extracellular matrix. Macrophages have a close relationship with fibroblasts by increasing the production of matrix metalloproteinase-1 (MMP-1) for faster wound closure and remodeling and myofibroblast differentiation from fibroblasts. In this study, resting state (M0), M1 and M2 macrophages differentiated from the human monocytic THP-1 cell line were used to co-culture with human dermal fibroblasts (HDF) for 48, 96 and 144 hours to investigate the effect of macrophages subsets on the fibrogenic activity of fibroblasts. The differentiation and polarization from THP-1 cells to M0, M1 and M2 macrophages were characterized by flow cytometry and cell cycle analysis. Cell sorting was performed to purify M0 and M2 macrophages. Cell proliferation, collagen synthesis, myofibroblast formation, gene expression of anti-fibrotic and pro-fibrotic factors, MMP-1 activity, and cytokine concentration were investigated. Results showed differentiation of M0 and polarization of M1 and M2 macrophages. M2 macrophages promoted the fibrogenic activities of co-cultured HDF by facilitating cell proliferation, increasing the collagen content, alpha-smooth muscle actin expressed cells, expression of the pro-fibrotic genes and concentration of M2 macrophage related factors, as well as decreasing the expression of the anti-fibrotic genes and MMP-1 activity. These findings reinforce the pro-fibrotic role of M2 macrophages, suggesting therapeutic strategies in fibrotic diseases should target M2 macrophages in the future.