Effects of continuous light exposure on muscle fiber remodeling and lipid metabolism in mice / 中华内分泌代谢杂志

ABSTRACT

Objective:To observe the effects of continuous light exposure on skeletal muscle fiber type transformation and lipid metabolism, and to explore its internal relationship.Methods:Mice were randomly divided into normal light group and 24-hour continuous light group by random number table. The serum and skeletal muscle lipid content and urine 6-sulfatoxymelatonin(6-SML)level were detected by ELISA. The expression of circadian clock and lipid metabolism related genes mRNA were observed by realtime PCR. The muscle fiber type and lipid deposition were evaluated by tissue immunofluorescence as well as oil red O staining.Results:Compared with the normal light group, the level of 6-SML in urine at night decreased( P<0.05), and the expression level and rhythm of brain and muscle ARNT-like protein 1(Bmal1), circadian locomotor output cycles protein kaput(Clock), and period 2(Per2)mRNA in the skeletal muscle changed in continuous light group. In addition, the body weight, blood lipid, free fatty acid, and triglyceride contents of skeletal muscle in continuous light group increased significantly( P<0.05 or P<0.01), the expression of carnitine palmitoyltransferase 1b (Cpt1b)mRNA, the key enzyme of fatty acid oxidation, decreased significantly( P<0.05), while the expression of stearoyl-CoA desaturase(Scd1)mRNA, a lipid synthesis related gene, increased significantly( P<0.01). Further immunofluorescence analysis showed that the proportion of slow muscle fibers decreased and that of fast muscle fibers increased in continuous light group(both P<0.05). Conclusion:The process of ectopic deposition of lipid in skeletal muscle in mice induced by continuous light exposure may be related to the remodeling of skeletal muscle fibers.