Effect of cigarette smoking on muscle in vitamin D deficient mice

Rationale: Skeletal muscle weakness is a major complication in COPD patients. Vitamin D (vitD), which is essential for maintaining skeletal muscle strength and performance, is low in COPD. We examined whether vitD deficiency would enhance muscle susceptibility to smoking has been examined in a smoking mouse model. Methods: VitD deficient (normal calcium and phosphorus levels) and sufficient mice were daily exposed to room air or cigarette smoke (CS) for 6, 12 and 18 weeks. Afterwards, muscle function was measured in vitro . Results: VitD serum levels were 66% lower in VitD deficient mice. Smoking lowered body weight gain at each time point (no effect of vitD deficiency). In deficient mice, soleus mass was lower after smoking at each time point. Deficiency caused decreased muscle force of the EDL after 18 weeks (no extra effect of smoking) while soleus force was unchanged at each time point. Deficiency was found to enhance fatigability of the EDL at each time point. Smoking solely enhanced muscle fatigue in smoking mice with sufficient serum levels after 18 weeks. Muscle fiber proportions were unchanged in soleus and EDL at 12 weeks. Conclusions: VitD deficiency decreased EDL force and enhanced fatigability over time, without an additional effect of smoking.