| The use of therapeutic cell-types, such as stem and progenitor cells, has gained much interest as a potential therapeutic approach for ischemic regeneration, but the mechanisms are not fully understood. Adipose Tissue-derived Stromal/Stem Cells (ASCs) secrete physiologically relevant levels of HGF. The specific contribution of HGF to ASC potency was determined by silencing HGF expression. A dual-cassette lentiviral construct expressing GFP and either a small hairpin RNA (shRNA) specifically targeted to HGF mRNA (shHGF) or an inactive control sequence (shCtrl) were used to stably transduce ASCs. Transduced ASC-shHGF secreted less HGF, which led to a reduced ability to promote survival, proliferation and migration of mature and progenitor endothelial cells in vitro. ASC-shHGF were also significantly impaired, compared to ASC-shCtrl, in their ability to promote reperfusion in a mouse hindlimb ischemia model. The diminished ability of ASC-shHGF to promote reperfusion of ischemic tissues was reflected by reduced densities of capillaries in reperfused tissues. In addition, fewer ASCs were detected at 3 wk in ischemic limbs of mice treated with ASC-shHGF. In a second study, we have used a chronic cardiac ischemia model to assess the mechanisms of ASC-dependent tissue repair. ASCs or carrier alone were injected into the peri-infarct region and heart function was evaluated by serial echocardiography. Whereas, saline treated hearts showed significantly reduced function based on multiple parameters, ASC-treated rats consistently exhibited better cardiac function at 1 month compared to 4 days after LAD occlusion. Histological analysis demonstrated that ASC treated hearts had lower fibrosis and a higher small arteriole density. It was determined through immunofluorescent detection of HLA-ABC-expressing cells that human ASCs where present at one month and were predominantly localized to peri-infarct regions, but did not apparently differentiate into cardiomyocytes in significant numbers. In conclusion, we have demonstrated that ASCs have great potential as a cell therapy for tissue regeneration following ischemic insult. Given the abundant source of autologous ASCs, therapies with these cells have a higher potential for widespread adoption compared to rarer therapeutic cell types. Local factor secretion by donor cells is a key element of cell-based therapies. |
