The Paracrine Effects of Satellite Cells on Collateral Vessel Formation

Abstract

Satellite cells are myogenic cells that play a critical role in skeletal muscle repair. In healthy muscle they are maintained in a quiescent state but upon injury to the muscle they activate resulting in increased proliferation. While many of the activated satellite cells differentiate into myoblasts which fuse to repair the muscle, some return to the quiescent state to serve as a “stem cell” population. However, another key aspect of muscle regeneration is reestablishing vascular supply, yet the role of satellite cells in this process is not well established. Satellite cells have been shown to produce several proteins that have the potential to act as paracrine signals. Thus, we hypothesized that satellite cells promote vascular growth through paracrine signaling induced by activation following muscle injury or ischemic damage from diseases such as peripheral artery disease. The model of collateral growth used in this study was a murine model of hind limb ischemia in which the femoral artery and vein are ligated and excised. Using this model, we showed ischemic muscle damage increased satellite cell numbers 3.4 fold (p<0.01) as measured by isolating cells from the hind limb muscles using magnetic bead sorting. To determine if satellite cells produce paracrine factors, we used a modified Boyden chamber co‐culture system for migration where satellite cells served as the chemoattractant and proliferation where satellite cells were the growth stimuli. We found that satellite cells freshly isolated from the ischemic limb led to a 3.5 fold increase in smooth muscle cell migration (p<0.0001) and a 1.3 fold increase (p<0.01) in smooth muscle cell proliferation. Additionally, cultured satellite cells increased endothelial cell migration 1.9 fold and proliferation 1.3 fold. Both smooth muscle cell and endothelial cell migration and proliferation are required for the development of collateral vessels, and these results demonstrate that satellite cells produce paracrine factors that increase both of these critical processes. To test the potential therapeutic capability of satellite cells in vivo, alginate encapsulated satellite cells were delivered in the hind limb at the time of the ischemia procedure. Alginate encapsulation has been previously shown to increase the cell retention and viability of other cell types, and using a whole animal in vivo imager to track luciferase expression of the cells, we found the encapsulated cells were viable for up to 2 weeks. The satellite cells also improved the recovery with the mice that received satellite cells having significantly increased perfusion over the mice that received empty capsules at 2 weeks post‐surgery as measured by Laser Doppler imaging (perfusion ratio of 0.87 ± 0.04 (cells) vs 0.68 ± 0.07 (empty capsules), p<0.05). In conclusion our studies have shown that satellite cells proliferate in response to ischemia, produce paracrine factors that increase vascular cell migration in vitro, and lead to functional increases in perfusion in vivo. We believe these results demonstrate the critical role satellite cells play in collateral vessel formation and may be a potential new therapeutic approach for treating peripheral artery disease.Support or Funding InformationNIH F32HL124974 (LH)