Vitamin D prevents lipid accumulation in murine muscle through regulation of PPARγ and perilipin-2 expression

Vitamin D plays an important role in regulation of skeletal muscle tone and contraction. Serum vitamin D status is linked to muscle power and force in adolescent girls, and vitamin D deficiency is associated with myopathies in children and poorer physical performance in the elderly. We previously reported that vitamin D deficiency is linked to a significant increase in muscle fatty infiltration in healthy young women, and studies in patients with neuromuscular disorders also associate muscle weakening and lipid content. In order to better understand the link between vitamin D status and skeletal muscle lipid metabolism, we compared the effect of a low (25 IU/kg) or normal (1000 IU/kg) vitamin D-3 diet on muscle fat in female FVB mice maintained in a room without UVB lighting to minimize endogenous vitamin D production. Animals on low vitamin D diet displayed lower circulating 25(OH)D levels and a dramatic increase (287 +/- 52% compared to normal diet, p < 0.0001) in lipid deposition in skeletal muscle accompanied by muscle fiber disorganization. Lipid droplet staining increased by 242 +/- 23% (p < 0.0001) in low vitamin D diet, and lipid droplet coat protein perilipin-2 and nuclear receptor transcription factor PPAR gamma expression levels were increased compared to mice fed the normal vitamin D diet: average staining for PLIN2: 0.22 +/- 0.08 (25 IU/kg diet) vs 0.10 +/- 0.02 (1000 IU/kg). Average staining for PPARy: 0.24 +/- 0.06 (25 IU/kg diet) vs 0.07 +/- 0.04 (1000 IU/kg) p < 0.0001. Tissue mass spectrometry imaging revealed major differences in muscle phospholipids profile depending on diet. In vitro, 1,25(OH)(2)D-3 treatment of 3T3-L1 pre-adipocytes inhibited appearance of lipid droplets by 79 +/- 9.3%, and caused a 80 10% and 25 +/- 8% (p = 0.001) reduction in PPAR gamma and perilipin-2 mRNA levels (by qPCR) compared to control cells. In summary, we report here the first in vivo model illustrating the important structural muscle fiber disorganization and fat accumulation inside and outside muscle fibers that accompany vitamin D deficiency. Furthermore, we show that the underlying mechanisms involve PPAR gamma and perilipin-2.