Vitamin D deficiency impairs skeletal muscle function in a smoking mouse model

Area of Science:

• Pulmonary Medicine
• Nutritional Science
• Skeletal Muscle Physiology

Background:

• Chronic obstructive pulmonary disease (COPD) is linked to skeletal muscle dysfunction.
• Vitamin D is crucial for muscle strength, and deficiency is common in COPD patients, yet its specific impact on muscle dysfunction is unclear.
• Understanding this relationship is vital for managing COPD-related muscle impairments.

Purpose of the Study:

• To investigate the time-course effects of vitamin D deficiency on limb muscle function in mice exposed to cigarette smoke.
• To differentiate the independent and combined effects of smoking and vitamin D deficiency on lung and muscle parameters.

Main Methods:

• Mice with normal or deficient vitamin D levels were exposed to air or cigarette smoke for 6, 12, or 18 weeks.
• Evaluated lung inflammation, compliance, emphysema scores, body mass, and skeletal muscle (soleus and EDL) function, including mass, contractility, and fiber characteristics.
• Assessed vitamin D receptor expression and markers of oxidative stress in muscles.

Main Results:

• Synergistic effects of smoking and vitamin D deficiency exacerbated lung inflammation and emphysema.
• Smoking reduced body and muscle mass and caused type II fiber atrophy but did not affect muscle contractility.
• Vitamin D deficiency alone decreased muscle force over time, downregulated vitamin D receptor, and increased lipid peroxidation, without altering muscle dimensions or contractility parameters.
• Combined exposure worsened soleus mass loss and EDL fiber atrophy at 18 weeks but did not further impair muscle function compared to individual factors.

Conclusions:

• In a mild COPD mouse model, smoking and vitamin D deficiency exert independent detrimental effects on skeletal muscle.
• Vitamin D deficiency impairs muscle force generation and increases oxidative stress, while smoking primarily affects muscle mass and fiber type.
• The combined impact on lung disease is synergistic, but on skeletal muscle, their noxious effects are distinct and additive, highlighting the importance of addressing vitamin D status in COPD management.