Abstract: Objective To study the effect of bone marrow mesenchymal stem cell-derived exosomes (BMSC-exos) on the proliferation and migration ability of hypertrophic scar-derived fibroblasts (HSFs), and to verify the signaling pathway of BMSC-exos inhibiting collagen synthesis by HSFs. 
Methods Bone marrow mesenchymal stem cells (BMSCs), BMSC-exos and HSFs in SD rats  were isolated and cultured. They were divided into blank control group (PBS group), experimental group (BMSC-exos group), and negative control group (exocrine mesenchymal stem cell concentrated supernatant group). The effect of exosomes on proliferation and migration of HSFs was detected by flow cytometry and cell scratch test. The mRNA expressions of TIMP-1, matrix metalloproteinase 1 (MMP-1), type Ⅰ collagen (Col-Ⅰ) and type Ⅲ collagen (Col-Ⅲ) in cells of the three groups were detected by fluorescence quantitative polymerase chain reaction (FQ-PCR) method. The protein levels of transforming growth factor-β1 (TGF-β1), α-smooth muscle actin (α-SMA) and Col-Ⅰ, and the phosphorylation level of smad2/3 in the three groups were detected by Western blot. 
Results BMSC-exos inhibited the proliferation and migration ability of HSFs. The mRNA expression of TIMP-1, Col-Ⅰ, and Col-Ⅲ in BMSC-exos group were significantly decreased, while the mRNA expression of MMP-1 was significantly increased, showing significant difference (P＜0.05). The protein levels of TGF-β1, α-SMA and Col-Ⅰand the phosphorylation level of smad2/3 in BMSC-exos group were decreased significantly, suggesting significant difference (P＜0.05). 
Conclusion BMSC-exos inhibit the proliferation and migration of HSFs, and inhibit the collagen synthesis of HSFs through TGF-β1/smad2/3 signal pathway, thus playing a role in inhibiting the development of hypertrophic scar.

Key words: mesenchymal stem cells, exosomes, scar, fibroblasts