Mesenchymal Stem Cells Improve Wound Healing Via Early Activation of the Matrix Metalloproteinase-9 and Vascular Endothelial Growth Factor: Using a 3-Dimensional Collagen Gel Model.

There is great progress on clinical application of stem cells. Stem cells are self-renewing and are potent in differentiating into multiple tissues. It has been reported that mesenchymal stem cells (MSCs) had successfully improved skin-substitute wound healing. We investigate the effects MSCs on wound healing using a 3D collagen gel system in a full thickness large-sized skin defect rat model. Three full thickness skin and tissue defects of 2 x 2 cm in size were excised on the backs of female SD-rats and replaced with 3D collagen gel contains 2 millions of male rat MSCs (rMSCs) on one site. Two different sites were control. One replaced with 3D collagen gel without rMSCs and the other site was empty. Wound size, histology and protein expression were evaluated at 3, 7 and 14 days after injury. Cultured rMSCs were confirmed to be negative for hematopoietic markers by flow cytometry and to be capable of differentiating into osteocytes, chondrocytes, and adipocytes in vitro. The wound size was significantly smaller in the rMSCs-treated sites than control sites (P < 0.01) and the most effect of wound healing was obtained at day 7. A lot of rat Y chromosome positive cells were found in rMSCs treated sites. The expression of matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF) were increased on the rMSCs-treated sites at day 3 but on the other hand those levels on the control sites were increased at day 7. This data suggest that MSCs accelerate wound healing and 3D collagen gel model can stably introduce MSCs to the defected skin area. Early activation of MMP-9 as well as previously known VEGF may play crucial roles in dermal remodeling and accelerate the processes of dermal and epidermal wound healing after MSCs treatment.