Abstract
Skeletal muscle has remarkable regenerative abilities regulated by a highly orchestrated process involving the activation of cellular and molecular responses, which are dependent on satellite cells. These cells maintain the stem cell population and provide numerous myogenic cells that proliferate, differentiate, fuse and lead to new myofiber formation for a functional contractile tissue. We have isolated and characterized satellite cells obtained from human biopsies and established an in vitro model of myogenesis, evaluating muscle regeneration, monitoring the dynamic increases of the specific myogenic regulatory factors and the final formation of multinucleated myofibers. As the skeletal muscle is an endocrine tissue able of producing many substances that can act on distant organs, and it can be physiologically modulated by a variety of hormones, we embarked in a project of characterization of muscle cell endocrinology machinery. The expression of a large array of hormone receptors was quantified during the process of myogenesis. The results obtained showed a significant and generalized increase of all the tested hormone receptors along the process of differentiation of human cultured cells from myoblasts to myocytes. Interestingly, also the production of the myokine irisin increased in a parallel manner. These findings point to the human cultured myoblasts as an ideal model to characterize the skeletal muscle endocrine machinery and its hormonal regulation.
Highlights
Skeletal muscle is the most abundant tissue in the human body, accounting for about 40–45% of total body weight
The cell populations derived from human skeletal muscle biopsies (Fig. 1a), obtained by surgical resection, were amplified in Matrigel® coated plates in order to increase cell adherence and maintain cell phenotype
Expanded cells were subsequently characterized by flow cytometry in order to verify their phenotype, analyzing the cluster of differentiation (CD) marker surface proteins (CD44, CD90, CD105, CD56, CD34, CD45) and one of the most reliable markers of the satellite cells (PAX-7)
Summary
Skeletal muscle is the most abundant tissue in the human body, accounting for about 40–45% of total body weight. It plays an important role in controlling physical activity, including voluntary locomotion, postural behavior, and breathing. To regenerate new muscle fibers after damage by injury or intense physical activity [1]. The regeneration and remodeling of skeletal muscles are extremely complex biological processes, in which skeletal muscle stem cells ( known as satellite cells, SCs) are involved. Satellite cells self-renew to maintain their own population, re-establishing their numbers and quiescent state by homing back to highly specialized niches, allowing future rounds of regeneration [4]. Specific temporal factors, called Myogenic Regulatory Factors (MRFs), members of the basic helix-loop-helix (bHLH) family of transcription factors including Myf-5, MyoD1, Myogenin and MRF4, are an essential group of four muscle-specific proteins responsible for acting at multiple points in the muscle lineage to cooperatively establish the skeletal muscle phenotype [4, 5]
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