Muscle Damage and Stem Cells

Adult skeletal muscle is different to heart muscle and the smooth muscle of the intestines as it is under somatic nervous system control and is, therefore, able to be controlled voluntarily. The skeletal muscle is made up of muscle fibers which are formed when myoblasts fuse together during early development. Myoblasts are the embryonic stem cells which give rise to muscle cells and the ability to specifically culture these myoblasts has given researchers into muscle repair and regeneration an opportunity to develop possible treatments for muscle trauma using stem cells. The myofibers are long, cylindrical cells with multiple nuclei, and consist of actin and myosin myofibrils which, when repeated, form a sarcomere which gives the muscle its striated appearance. Myosin and actin are the ‘thick’ and ‘thin’ filaments that interact to induce muscle contraction, and the type of myosin is often used to categorize the muscle fibers as either fast or slow twitch muscles. A muscle is a collection of muscle fibers each covered with a sarcoplasmic reticulum which contains calcium ions needed to induce muscle contraction.

Stem Cells or Satellite Cells?

Skeletal muscle tissue also contains stem cells, which are referred to as satellite cells, and these are responsible for repairing the muscle following damage. To ensure rapid tissue repair these stem cells need to be able to migrate to the site of injury or trauma quickly and, until recently, this process has been poorly understood. Skeletal muscle damage activates the stem cells which then proliferate and migrate to the injury site where they either form new multinucleated myofibers or fuse to damaged myofibers. The environment in which the stem cells find themselves is what influences their activity and most muscle stem cells remain quiescent (inactive) in their stem cell niche until needed.

Stem Cell Injections Often Ineffective

Transplanting stem cells into healthy muscle tissue may not, therefore, result in any observable muscle growth or development because these stem cells will respond to the existing chemical environment telling them to remain inactive. Additionally, less than 1% of the cells derived from donor satellite cells introduced into muscle tissue are thought to survive the first few days after transplant, and those that do are restricted in terms of movement making stem cell muscle regeneration extremely difficult to achieve to any significant degree (Ten Broek, et al, 2010). Researchers have begun to look at the potential for other multipotent muscle stem cells and non-muscle-derived stem cells for tissue regeneration as well as investigating those factors which influence the activity and migration of stem cells to injury sites.

Bio-Engineered Muscle Tissue

Skeletal muscle reconstruction using stem cells relies on the ability of the stem cells to give rise to myogenic cells and the use of biocompatible scaffolds to structure the muscle regrowth. Rossi (et al, 2011) designed a technique for bioengineering muscle tissue using satellite cells or muscle progenitor cells implanted on a photo-cross-linkable hyaluronan-based hydrogel, hyaluronic acid-photoinitiator complex. Using mouse models with induced muscular injuries, the researchers observed major improvements in muscle structure and number of new myofibers in those mice receiving satellite cells embedded in hydrogel, compared to those receiving just the hydrogel or the hydrogel plus muscle precursor cells but no muscle satellite cells. The tissue reconstruction included neural and vascular networks and the formation of a functional stem cell niche thereby allowing for future muscle repair even after the initial stem cell transplant.

Continue –> Muscle Stem Cell Migration and Activity
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