Satellite cells are multipotent stem cells found in skeletal muscle tissue and play a key role in the growth, maintenance and repair of muscles.

These self-renewing cells are located between the sarcolemma and the basement membrane of the muscle fibers and are at rest in most healthy, adult muscle tissue. Satellite cells are activated in response to muscle injury, causing them to multiply and differentiate into myoblasts. The myoblasts then become myocytes, which fuse together to form new, healthy muscle tissue.

Satellite cells are skeletal muscle stem cells
Satellite cells are multipotent stem cells found in skeletal muscle tissue

What are satellite cells?

Satellite cells (SCs) are skeletal muscle stem cells that grow, maintain, and repair muscle tissue. They make up between 3% and 11% of skeletal muscle tissue and are located between the sarcolemma and the basement membrane of the muscle fibers.

SCs renew themselves and multipotentThis means they can lead to several other cell types, including Myocytes (Cardiac and skeletal muscle cells), Adipocytes (Fat cells) and Osteocytes (a type of bone cell). you are calm in most healthy adult muscle tissue and are activated in response to muscle injuries.

Satellite cells are located in muscle fibers
Satellite cells are located between the sarcolemma and the basement membrane of the muscle fibers

Activation of satellite cells

SCs in adult muscle tissues tend to be calm, which means that they are not actively dividing cells. They are activated by an injury to the muscle and multiply at a rate determined by the extent of the trauma. In the case of minor muscle injuries, only a small number of satellite cells multiply. If the trauma is severe, a greater number of SCs are activated.

Function of satellite cells

Muscle repair

SCs play a central role in maintaining and repairing muscles and are responsible for regenerating muscle tissue in the event of an injury. This process is known as Myogenesis and occurs in response to both minor injuries (such as microscopic cracks caused by exercise) and more serious trauma.

Injuries to muscle tissue stimulate the proliferation of SCs, which then differentiate into formation Myoblasts. The myoblasts then become Myocytes; long, tubular cells that fuse into skeletal muscle fibers (called Myofibers).

These myofibers are the functional units of skeletal muscle and can be used to repair and regenerate muscle tissue in the event of injury.

New muscle fibers are formed from satellite cells
Satellite cells differentiate and fuse to form new muscle fibers

Muscle growth

SCs can also contribute to long-term muscle growth, although their role in the process is still hotly debated.

Studies have shown that SCs are activated through intense exercise. This is often a reaction to localized injuries in the muscle tissue. However, exercise can also induce widespread activation of satellite cells, which cannot be explained by local muscle injuries. Hence, there is likely another mechanism by which SCs are activated to multiply and fuse during exercise, and this may contribute to the gradual accumulation of muscle tissue.

Satellite cells can play a role in muscle hypertrophy
Satellite cells can contribute to muscle growth

Production of adipocytes and osteocytes

The main function of SCs is to repair muscle tissue and most develop into myocytes

However, satellite cells are multipotent and can also lead to adipocytes and osteocytes. Adipocytes are the body’s fat cells and are used for long-term storage of energy in the form of lipids. Together they make that Adipose tissue (or fatty tissue) that is either under the skin throughout the body (subcutaneous Fat) or around the internal organs (visceral Fat).

Osteocytes are the most common types of bone cells and make up 90-95% of bone tissue. Their key function is to maintain the mineral composition of bone tissue through deposition and reabsorption of bone and by signaling other osteocytes in the event of bone damage. Osteocytes also regulate the activity of other bone cells (the Osteoblasts and Osteoclasts).

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