RESUMEN
BACKGROUND:Hypoxic exercise can promote the degradation of body fat,and changes in the external environment can affect the circadian rhythm of animals,but the mechanisms by which changes in circadian rhythm regulate adipose tissue browning and fat degradation are unclear. OBJECTIVE:To elucidate the mechanism of clock gene regulation on epididymal adipose tissue Browning in obese rats undergoing hypoxia exercise. METHODS:Forty obese rats were randomly selected and divided into four groups(n=10 per group):normoxic sedentary group,hypoxic sedentary group,normoxic exercise group,and hypoxic exercise group for 4 weeks of intervention.The rats in the sedentary groups were not intervened,while those in the hypoxic groups lived in a hypoxic chamber with an oxygen concentration of 13.6%for the whole day.In the exercise groups,adaptive training was performed in the 1st week,and the speed and length of training remained unchanged for the last 3 weeks.The body mass,body length and perirenal fat mass of obese rats were measured.Serum levels of triacylglycerol,total cholesterol,low-density lipoprotein cholesterol,and high-density lipoprotein cholesterol in obese rats were detected by a biochemical assay kit.Liver fat content was observed by oil red O staining.Hematoxylin-eosin staining was used to evaluate the browning of epididymal adipose tissue of rats in different groups.RNA sequencing combined with bioinformatics analysis was used to analyze transcriptome changes in adipose tissue.The mRNA expressions of PGC-1α,Beclin 1,KLF 2 and Perilipin 1 in epididymal adipose tissue were detected by RT-PCR. RESULTS AND CONCLUSION:Hypoxic exercise intervention significantly decreased body mass,body fat percentage,Lee's index,serum triacylglycerol,total cholesterol,and low-density lipoprotein cholesterol levels(P＜0.01),and significantly increased high-density lipoprotein cholesterol level(P＜0.01).Oil red O staining and hematoxylin-eosin staining results showed that hypoxic exercise was more effective in promoting fat mobilization in liver tissue and promoting the browning of parepididymal adipose tissue compared with normoxic sedentary group,hypoxic sedentary group,and normoxic exercise group.RNA-seq results showed that hypoxic exercise significantly upregulated the expression of clock genes Dbp,Nr1d1,Sik1 and adipose tissue browning gene Ppargc1a(PGC-1α)and downregulated the expression of Arntl(Bmal1),accompanied by the enhanced expression of genes related to substance metabolism.qRT-PCR indicated that hypoxic exercise significantly increased the mRNA expression levels of PGC-1α and Perilipin1(P＜0.01).Therefore,these findings indicate that clock genes play an important role in promoting adipose tissue browning during hypoxic exercise.