Mesenchymal stem cells (MSC) have been used clinically to treat a range of conditions, and have been shown to enhance skin wound healing in vivo. There is evidence suggesting that the beneficial effects of MSC transplantation may be mediated more through their paracrine activity than through their differentiation into mature cell types.
This thesis has sought to examine the effects of MSC secreted factors on dermal fibroblasts, keratinocytes, and endothelial cells, using an in vitro wound healing model. The results presented demonstrate that mesenchymal stem cell-conditioned culture medium (MSC-CM) enhances wound closure by dermal fibroblasts and keratinocytes through increased skin cell migration. MSC-CM was similarly shown to enhance wound closure by endothelial cells. The contents of MSC-CM were analysed by immunological techniques and mass spectrometry to reveal targets for further investigation. These included cytokines, notably interleukin-6 (IL-6), interleukin-8 (IL-8) and transforming growth factor-beta one (TGF-ß1); and extracellular matrix (ECM) components, notably collagen type I, fibronectin and decorin. Examining these factors individually or in combination with each other or MSC-CM demonstrated differential and interdependent effects. Fibronectin was generally stimulatory to wound closure, whilst decorin was inhibitory. The cytokines studied had variable effects, e.g. TGF-ß1 was stimulatory to fibroblast migration in combination with collagen type I, elicited no effect in combination with fibronectin, and was inhibitory to keratinocyte migration in both conditions.
This study has thereby progressed our understanding of how MSC secreted factors influence skin wound healing and suggests that further investigation of MSC activity is needed in order to inform the eventual clinical use of MSC to treat severe or chronic skin wounds. With further work, MSC-related therapy, using MSC transplantation or the delivery of MSC secreted products, might provide a preferable alternative to current treatment strategies for these wounds, either in terms of patient benefit or clinical cost reduction.