Absence of CD34 on Murine Skeletal Muscle Satellite Cells Marks a Reversible State of Activation during Acute Injury

Background: Skeletal muscle satellite cells are myogenic progenitors that reside on myofiber surface beneath the basal lamina. In recent years satellite cells have been identified and isolated based on their expression of CD34, a sialomucin surface receptor traditionally used as a marker of hematopoietic stem cells. Interestingly, a minority of satellite cells lacking CD34 has been described. Methodology/Principal Findings: In order to elucidate the relationship between CD34+ and CD34- satellite cells we utilized fluorescence-activated cell sorting (FACS) to isolate each population for molecular analysis, culture and transplantation studies. Here we show that unless used in combination with a7 integrin, CD34 alone is inadequate for purifying satellite cells. Furthermore, the absence of CD34 marks a reversible state of activation dependent on muscle injury. Conclusions/Significance: Following acute injury CD34- cells become the major myogenic population whereas the percentage of CD34+ cells remains constant. In turn activated CD34- cells can reverse their activation to maintain the pool of CD34+ reserve cells. Such activation switching and maintenance of reserve pool suggests the satellite cell compartment is tightly regulated during muscle regeneration

Current evidence that exercise can increase the number of adult stem cells

The number of adult stem cells (ASCs) is very small, limiting the regenerative potential of tissues. One of the most studied ASCs in humans is the satellite cell (SC), which proliferates and increases pool size under exercise stress and muscle damage. This review examines the growth factor response to specific types of exercise to show the potential of exercise to stimulate not only SC self-renewal, but also other ASCs. We postulate that the same factors that stimulate a high proliferation of SCs in skeletal muscle after physical exercise should also stimulate the proliferation of ASCs in the tissue in which they reside, such as heart, bone, liver and etc. Regular exercise should be promoted, not only for disease prevention, but to maintain a high ASCs reserve and progenitor cell potential for rapid activation in response to future stressors and damage. © 2012 Springer Science+Business Media B.V