MFAP4 Promotes Scar Formation by Regulating Macrophage-Myofibroblast Transformation Through Activation of the TGF-β/Smad3 Signalling Pathway.

Hypertrophic scar is a pathological consequence of abnormal wound healing, marked by excessive fibroblast proliferation and extracellular matrix (ECM) accumulation. Macrophage-to-myofibroblast transformation (MMT) plays a key role in this process, but its regulatory mechanisms remain under investigation. This study found that microfibril-associated protein 4 (MFAP4) is significantly upregulated in mice scar tissue and is closely associated with the MMT process. In a mouse excision injury model, knockdown of MFAP4 in vivo macrophages using adeno-associated virus (AAV)-mediated RNA interference significantly reduced dermal thickening and disorganized collagen fibre deposition in mice scar tissues. Macrophage infiltration, expression of the myofibroblast marker α-SMA, and the proportion of MMT cells (F4/80+α-SMA+) were shown to be remarkably reduced. In vitro, TGF-β1 induces elevated MFAP4 expression within mouse-derived bone marrow-derived macrophages (BMDMs) and promotes MMT. MFAP4 knockdown inhibits TGF-β1-induced myofibroblast transformation and expression of ECM synthesis-related molecules (α-SMA, Col-I and Vimentin), while MFAP4 overexpression enhances these effects. Mechanistic studies suggest that MFAP4 regulates this process via the TGF-β/Smad3 signalling activation. MFAP4 promotes Smad3 phosphorylation (p-Smad3), and overexpression of Smad3 in MFAP4-knockdown mouse-derived BMDMs reverses the inhibitory effects of MFAP4 deficiency on MMT and ECM synthesis. These results reveal a key role for the MFAP4-TGF-β/Smad3 axis in regulating MMT-driven scar formation, providing novel insights into the mechanisms of hypertrophic scarring in mice and underlying therapeutic targets for clinical intervention.