Skeletal atrophy is the wasting away or decrease in the size of skeletal muscles. This results in weakening, shrinking, and a reduction in muscle mass and fiber cross-sectional area. It leads to reduced force production, increased fatigue, decreased exercise capacity, and a lower quality of life. Importantly, skeletal muscle atrophy occurs when the rate of protein degradation exceeds protein synthesis.
Types and Causes of Skeletal Atrophy
Several factors can contribute to skeletal atrophy. One prominent example is spinal muscular atrophy (SMA), a group of inherited diseases affecting motor neurons—the specialized nerve cells that control muscle movement. This results in muscle weakness and wasting. Various types of SMA exist, ranging in severity from infantile-onset to later-onset forms.
Another major cause is disuse atrophy. This occurs when muscles aren't used regularly, such as during prolonged bed rest or immobilization after injury. Other causes include:
- Aging: Age-related muscle loss (sarcopenia) is a common form of atrophy.
- Malnutrition: Lack of sufficient protein and other essential nutrients can impair muscle growth and maintenance.
- Certain diseases: Various illnesses, including cancer, AIDS, and chronic kidney disease, can contribute to skeletal muscle atrophy.
- Denervation: Damage to the nerves supplying a muscle can lead to atrophy.
Understanding the Mechanisms
Skeletal muscle atrophy involves complex cellular mechanisms. These include changes in protein degradation pathways, such as:
- The ubiquitin-proteasome system
- Autophagy
- Caspase activation
These pathways are responsible for breaking down muscle proteins, exceeding the rate of protein synthesis, leading to muscle loss. Signal transduction pathways also play a crucial role in regulating these processes.
Impact and Management
Skeletal atrophy significantly affects an individual's physical function and quality of life. Managing atrophy depends on the underlying cause. Treatment strategies may include:
- Physical therapy: Exercise programs to stimulate muscle growth and function.
- Nutritional interventions: Dietary adjustments to increase protein intake and other essential nutrients.
- Medications: Specific drugs, depending on the cause of atrophy. For SMA, there are now therapies that target the underlying genetic defect.
