Logan Steele
Skeletal muscle, the largest organ in the body, is known for its role in posture and locomotion. However, recent studies have identified it as an endocrine organ, producing and releasing hundreds of myokines, which are cytokines or peptides. These myokines have endocrine, autocrine, and paracrine effects, mediating the health benefits of exercise and acting as signalling molecules to communicate with other organs, including the brain, liver, and adipose tissue. Understanding the mechanisms of myokine production and their effects on organ crosstalk may lead to new pharmacological approaches for treating various clinical disorders.
| Characteristics | Values |
|---|---|
| Type of organ | Skeletal muscle |
| Function | Physical force, posture, locomotion |
| Secretes | Myokines, proteins, peptides, metabolites, lipids, RNA molecules |
| Role of secretions | Regulate intramuscular cross talk, act as endocrine signalling mediators, improve functionality of working muscle |
| Effects of secretions | Anti-inflammatory, protective effects of muscular exercise, multiple health benefits |
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What You'll Learn
Skeletal muscle is the largest organ in the body
However, skeletal muscle is not just a component of our locomotor system. Recent evidence has identified skeletal muscle as a secretory organ, producing and releasing several hundred peptides, known as myokines. These myokines are cytokines or other peptides that are produced, expressed, and released by muscle fibres. They exert autocrine, paracrine, or endocrine effects, and play a role in muscle-liver and muscle-adipose tissue crosstalk. The muscle secretome, which consists of these secreted peptides, provides a new understanding of how muscles communicate with other organs, such as adipose tissue, the liver, the pancreas, bones, and the brain.
Furthermore, skeletal muscle has been shown to synthesise and secrete multiple factors that have beneficial effects on peripheral and remote organs, including the skeletal muscle itself. This has led to the recognition of skeletal muscle as one of the endocrine organs in the body. The identification of these myokines and their functions may lead to new pharmacological approaches for the treatment of clinical disorders.
In addition to their role in communication between organs, myokines may also contribute to the health benefits of exercise. For example, fibroblast growth factor 21 (FGF-21) is a myokine that is increased in expression following acute exercise. Other myokines, such as muscle-derived interleukin-6, may also have protective effects on the body, particularly in relation to diseases associated with a physically inactive lifestyle.
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Exercise increases the production of myokines
Skeletal muscle has long been known to play a key role in locomotion and posture retention. However, in the past decade, it has also been identified as a secretory organ, producing, expressing, and releasing several hundred peptides, known as myokines. These myokines are cytokines or other peptides that are produced, expressed, and released by muscle fibres and exert either autocrine, paracrine, or endocrine effects.
The secretion of myokines during exercise can also have therapeutic effects. For instance, oncostatin M, which is released from muscles during exercise, has been found to restrain mammary cancer cell growth in vitro. Additionally, SPARC, which is induced in the plasma of trained individuals, has been found to suppress colon tumorigenesis via regular exercise in mice.
The discovery of myokines and their role in exercise adaptations has provided a new paradigm for understanding how muscles communicate with other organs and the health benefits of exercise. Further research in this area may lead to the development of new pharmacological approaches for the treatment of clinical disorders.
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Myokines have a positive impact on multiple organs
Skeletal muscle has been identified as an endocrine organ, capable of producing and secreting hundreds of myokines. Myokines are cytokines or peptides produced, expressed, and released by muscle fibres. They can have autocrine, paracrine, or endocrine effects. Myokines have been shown to have a positive impact on multiple organs, including the brain, liver, and pancreas.
Myokines have been found to positively influence brain health and cognitive function. For example, physical exercise triggers histone modifications and protein synthesis, ultimately improving mood and cognitive abilities. Aerobic exercise in humans leads to structural alterations in the brain, while wheel-running in rodents promotes neurogenesis and enhances synaptic transmission in the hippocampus. Cathepsin B and irisin are myokines that cross the blood-brain barrier and stimulate BDNF production and hippocampal neurogenesis. Additionally, physical activity and exercise training are associated with a decreased risk of dementia and improved brain health.
The liver is another organ positively impacted by myokines. Exercise induces the expression of myokines in the liver, such as ANGPTL4. While the contribution of skeletal muscle to systemic ANGPTL4 levels following exercise requires further investigation, it highlights the complex interplay between organs and myokines. Fibroblast growth factor 21 (FGF-21) is another myokine with a connection to the liver. Serum levels of FGF-21 increase after acute exercise, although the liver is the primary contributor to exercise-induced increases in FGF-21.
Myokines also play a role in pancreatic health. Specifically, IL-6 positively regulates β-cell mass by stimulating β-cell proliferation and preventing apoptosis induced by metabolic stress. Exercise-induced increases in IL-6 production may help protect pancreatic β-cell mass and function. Additionally, myokines such as angiogenin and osteoprotegerin, which are triceps-specific, can mediate anti-inflammatory actions and protect β-cell survival.
In summary, myokines have a positive impact on multiple organs, including the brain, liver, and pancreas. They contribute to improved cognitive function, neurogenesis, and β-cell health. Further research is ongoing to fully understand the complex interactions between myokines and various organs, but the current evidence highlights the beneficial effects of myokines released by skeletal muscle as an endocrine organ.
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Myokines are produced in response to exercise
Skeletal muscle is an endocrine organ that can produce and secrete hundreds of myokines, which are cytokines or other peptides produced, expressed, and released by muscle fibres. Myokines exert autocrine, paracrine, or endocrine effects, and are involved in the control of muscle size and may be important to be restored to normal levels to alleviate muscle wasting in various conditions.
The secretion of myokines in response to exercise has been shown to have beneficial effects on metabolic diseases, and a combined therapeutic regimen of regular exercise and pharmaceutical treatment is often recommended for their clinical management. For example, myokines can act in an endocrine manner to facilitate crosstalk between muscle and adipose tissue, thus working together to improve overall metabolic health.
Furthermore, myokines induced by exercise may mediate protective effects of muscular exercise with regard to diseases associated with a physically inactive lifestyle. For instance, myokines can decrease the risk of a network of diseases, and exercise may be prescribed as medicine for lifestyle-related disorders such as type 2 diabetes, dementia, cardiovascular diseases, and cancer.
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Myokines are involved in muscle-organ crosstalk
Skeletal muscle has been identified as an endocrine organ, with the ability to produce, express and release several hundred secreted peptides, known as myokines. These myokines are cytokines or other peptides that are produced, expressed, and released by muscle fibres and exert either autocrine, paracrine, or endocrine effects.
Myokines are also involved in muscle proliferation, differentiation, and regeneration independent of exercise. During exercise, myokines are produced in response to energy demands, which mediate muscle-organ crosstalk. Myokines with anticancer effects have also been recognized, including Oncostatin M, irisin, and SPARC, which have been shown to suppress breast and colon cancer growth.
The identification of muscle as a secretory organ began with the finding of muscle-derived IL-6 in 2000 and the subsequent definition of myokines in 2003. Since then, hundreds of myokines have been identified, providing a new paradigm for understanding how muscles communicate with other organs.
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Frequently asked questions
Yes, skeletal muscle has been identified as an endocrine organ.
Skeletal muscle has the capacity to produce, express and release several hundred secreted peptides, known as myokines. These myokines can have autocrine, paracrine, or endocrine effects.
Some identified myokines include myostatin, LIF, IL-6, IL-7, BDNF, IGF-1, FGF-2, FSTL-1, and irisin.
Understanding the endocrine functions of skeletal muscle can lead to new pharmacological approaches for the treatment of clinical disorders. Additionally, it highlights the importance of physical activity in maintaining and improving human health.
