Vitamin D Ameliorates Skeletal Muscle Atrophy After Spinal Cord Injury by Upregulating TIGAR and Enhancing Mitochondrial Function.

BACKGROUND

Skeletal muscle atrophy following spinal cord injury (SCI) is a debilitating secondary complication with no effective treatment. This study aimed to investigate the therapeutic efficacy of vitamin D (VD) in SCI-induced muscle atrophy and to elucidate the underlying molecular mechanisms.

METHODS

SCI patients' serum VD levels were measured, and muscle mass was assessed using dual-energy X-ray examination. Adult male C57BL/6 mice underwent a complete T10 spinal cord transection or sham surgery. On Day 3 post-injury, mice received daily oral gavage of either VD (150 IU/kg) or vehicle (coconut oil) for 25 days. Body weight and motor function were assessed, and muscle-specific parameters including hindlimb circumference, muscle mass, fibre cross-sectional area (CSA) and fibre type composition were evaluated. Quantitative proteomics, Western blotting, and transmission electron microscopy (TEM) were further employed to investigate the molecular mechanisms in the gastrocnemius muscle.

RESULTS

Serum VD level showed a significant positive correlation with the muscle index (R2 = 0.6495, p < 0.01). Compared to vehicle-treated SCI mice, VD supplementation significantly attenuated body weight loss and promoted motor recovery (p < 0.05). VD treatment markedly preserved hindlimb muscle mass (p < 0.01) and prevented the reduction in the CSA of gastrocnemius (p < 0.01), extensor digitorum longus (p < 0.05) and soleus muscles (p < 0.05). Furthermore, VD alleviated the SCI-induced pathological shift from oxidative (Type I/IIA) to glycolytic (Type IIB) muscle fibres. Proteomic analysis revealed that VD restored cellular energy metabolism homeostasis. And it was related to the upregulation of the metabolic regulator TIGAR (p < 0.05). This was associated with a significant increase in mitochondrial number (p < 0.001) and an improvement in mitochondrial ultrastructure.

CONCLUSION

VD mitigates skeletal muscle atrophy following SCI by restoring metabolic and mitochondrial homeostasis through the upregulation of TIGAR. Our findings establish a strong preclinical rationale for investigating VD supplementation as a therapeutic strategy to preserve muscle health in SCI patients.