Peripheral artery disease is a major health problem in the United States that effects 8.5 million people and can lead to limb pain, decreased mobility, and in severe cases amputation. The ability to form a robust collateral network to restore blood flow and prevent ischemia leads to a better prognosis and restoration of function. The growth of collaterals is a complex process that involves recruitment of various cell types including smooth muscle cells, endothelial cells, and macrophages. Migration and proliferation of these cells are processes regulated by numerous cytokine and paracrine signals. We hypothesize that an important and novel source of these signals is satellite cells. Satellite cells are myogenic progenitor cells that lie below the basal lamina of muscle fibers. In healthy muscle, the cells are quiescent but in response to injury, such as ischemia, they become activated and proliferate. We hypothesized that activated satellite cells produce factors that will influence critical cells for vessel formation in addition to differentiating to repair muscle. To study the paracrine effects of satellite cells on vascular smooth muscle cells, we used a co-culture system with freshly isolated satellite cells from the ischemic leg as the stimulus. We found that satellite cells significantly increased smooth muscle migration 2.5 fold compared to media alone using a modified Boyden chamber assay. BrdU staining to assess proliferation showed modest increases in smooth muscle proliferation (1.3 fold change, p<0.01). Finally, to investigate these paracrine effects in vivo, we delivered alginate encapsulated satellite cells to mice following the hind limb ischemia procedure, which is a model of collateral growth. We found that mice that received the encapsulated satellite cells had significantly improved perfusion as measured by Laser Doppler imaging at day 14 post surgery when compared to empty capsules (perfusion ratio of 0.87 ± 0.04 (cells) vs 0.68 ± 0.07 (empty capsules), p<0.05). This result demonstrates that satellite cells can positively influence collateral growth in vivo. We believe that satellite cells play a critical role in collateral vessel formation and may potentially be a therapeutic strategy for the treatment of peripheral artery disease.
Predictive Value of the Mouse Model of Critical Limb Ischemia: Methodological Differences May Dictate the Outcome of Preclinical Efficacy