Transcription factor c-Maf drives macrophages to promote hypertrophic scar formation

Background: Hypertrophic scar (HS) is caused by the abnormal proliferation of fibroblasts and excessive deposition of extracellular matrix (ECM). Emerging evidence demonstrates that c-Maf positive M2 macrophages were mainly located in the hypertrophic scar tissues of proliferative phase. But whether c-Maf positive M2 macrophages can promote hypertrophic scar formation through modulating hypertrophic scar fibroblasts remains elusive.

Aims: The aim of this study is to investigate the effects of c-Maf positive M2 macrophages on the biological behaviors and functions of hypertrophic scar fibroblasts and the potential mechanism.

Methods: HE and Masson trichrome staining were used to examine the histological features of human hypertrophic scar. Immunofluorescence staining was employed to label and quantify the c-Maf⁺ /CD68⁺ M2 macrophages. CCK8, wound healing, and transwell assays were utilized to test the effects of c-Maf overexpressed M2 macrophages or the cell culture supernatants on the proliferation and migration of hypertrophic scar derived fibroblasts (HFBs) and normal skin derived fibroblasts (NFBs). Western blot and qPCR were harnessed to test the expressions of COL1, COL3, and α-SMA in the co-cultivated fibroblasts and TGF-β1 in the c-Maf overexpressed M2 macrophages.

Results: Increased number of c-Maf⁺ /CD68⁺ M2 macrophages were found in HS in contrast to the normal skin (NS). Elevated proliferation and migration were observed in the HFBs or NFBs co-cultured with c-Maf overexpressed macrophages or the cell culture supernatants. A higher mRNA and protein expressions of COL1, COL3, and α-SMA were recorded in the HFBs co-cultured with c-Maf overexpressed macrophages or treated with its culture supernatants. In addition, augmented mRNA and protein expressions of TGF-β1 were also investigated in the c-Maf overexpressed macrophages.

Conclusion: c-Maf positive macrophages promote hypertrophic scar formation through regulating HFBs proliferation, migration, and ECM deposition via the secreted TGF-β1.