Characterization and application of adipose derived stem cells following burn injury
Severe burns induce a prolonged inflammatory response in subcutaneous adipose tissue that modulates signaling in adipose-derived stem cells (ASCs), which hold potential for healing burn wounds or generating skin substitutes. Using a 60% rat scald burn model, we investigated the cellular source of inflammation within adipose tissue and whether inflammation affects ASC fate and function. Endpoints included inflammatory marker expression, expression of ASC-specific cell-surface markers, DNA damage, differentiation potential, and proliferation. Inflammatory marker expression was induced in adipocytes and the SVF at 24 and 48 hours postburn; expression of inflammatory marker mRNA transcripts and protein returned to normal in the SVF isolated 1 week postburn. In enriched ASCs, burns did not alter cell-surface expression of stem cell markers, markers of inflammation, differentiation potential, or proliferative ability. These results suggest that adipocytes and the SVF, not ASCs, are the main source of inflammation after burns and that ASCs are unaffected by burns or culturing procedures. Following characterization of post-burn ASCs, we evaluated whether topical application of ASCs improves burn wound healing in an ovine burn model. Topical application of ASCs significantly increased the size of the implanted graft, blood flow and vascular endothelial growth factor (VEGF) (p< 0.05) and Collagen-1 (p<0.01) protein expression in treated animals compared to the controls. Monocyte chemo-attractant protein-1 (MCP-1) mRNA expression was also greater with ASC treatment (p< 0.05). ASCs secreted a significant amount of MCP-1 compared to the different cell lines when challenged with lipopolysaccharide (LPS) or 2% burn serum. Human umbilical vein endothelial cells (HUVEC), when treated with 100ng/mL of MCP-1 or 2% of ASC, conditioned media (ASC-CM) increased the expression of MCP-1, VEGF-165 and HIF-1α mRNA transcripts compared to the controls. Fibroblast migration was significantly increased in the presence of ASC-CM or with recombinant MCP-1 peptide (p<0.001). ASCs constitutively produce an abundant quantity of MCP-1 and the expression of MCP-1 fluctuates depending upon the microenvironment. This work suggests that post burn ASCs or SVF can be used for cell-based therapy, and that the applied cells stimulate wound healing and angiogenesis pathway potentially via an MCP-1 mediated mechanism.