Critical Limb Ischaemia in Adult Human Skeletal Muscle Increases Satellite Cell Proliferation but Not Differentiation

Abstract

Critical Limb Ischaemia (CLI) is defined as the presence of rest pain, ulcers and/or gangrene in a limb for over 2 weeks. Associated exercise intolerance is caused by muscle fibre atrophy, fibro- fatty infiltration, nerve dysfunction, mitochondrial damage and myofibril disorder. We aimed to determine the behaviour of satellite cells, responsible for the repair and regeneration of damaged muscle, in repairing the damage caused to critically ischaemic adult human skeletal muscle. CD34, pax7 and MyoD are all markers of satellite cells at different stages of the cell cycle and allow for an assessment of their number and activity in ischaemia. Local ethical committee approval and informed consent was obtained. Samples of harvested gastrocnemius muscle of patients undergoing major perigenicular amputation for CLI (n = 10) were analysed and compared to a control group undergoing coronary artery bypass grafting (n = 10). Using immunohistochemistry, the expression of pax7, CD34 and MyoD was assessed in five sequential blinded randomly generated fields. Statistical testing of the data collected was made via the Mann Whitney U test. Protein electrophoresis was used to confirm overall protein expression of the satellite cell markers. There was a significant increase in the number of satellite cells observed in CLI muscle sections as demonstrated by the expression of pax7 (2.4× fold p < 0.0001). CD34 expressing Haematopoietic Stem Cells (HSCs) and satellite cells were also more abundant, with a 2× fold increase observed (p < 0.0001) whilst those cells expressing both CD34 and pax7 and identified as quiescent satellite cells, were significantly greater in number in the CLI samples (2.9× fold p < 0.0001), confirmed via immunohistochemistry and protein electrophoresis. There was a significant decrease in the expression of MyoD positive or activated satellite cells (p < 0.0001). This indicates an increase in the proliferation of the satellite cell population as a response to CLI but less active cells are observed.