The Role Of Sodium And Low Density Lipoprotein Receptor On Regulation Of White Adipose Tissue Browning

Background and objective:In view of obesity,a variety of metabolic syndrome-related diseases including cardiovascular disease and diabetes are induced,and it is an effective method to deal with obesity by regulating the body's energy consumption.Brown adipose tissue?BAT?and beige fat cells differentiated from white adipose tissue?WAT?has been proven to induce thermogenesis which may improve a variety of metabolic diseases associated with obesity.A variety of factors and pathways involved in the regulation of the biological functions of brown and beige fat cells have been successfully identified,providing promising therapeutic targets for metabolic diseases.Sodium?Na⁺?is usually sensed by the periventricular device adjacent to the third ventricle and has been shown to be closely related to the stimuli of the sympathetic nervous system?SNS?,which is also related to the basal metabolic rate and the activation of BAT or WAT browning.Recent studies have shown that extra Na⁺intake caused decreased body fat in rats,which may imply that Na⁺regulate the activity of adipose tissue,but the evidence was not clear,and the regulatory mechanism need more exploration.Low-density lipoprotein receptor?LDLr?is involved in the uptake and utilization of low-density cholesterol while lipid metabolism is often associated with energy metabolism.Studies have shown that LDLr knockout(LDLr^-/-)mice was resistance to obesity compared with wild-type mice during a high-calorie diet,which may imply that LDLr deficiency leads to metabolic boost,but the specific mechanism is still lack of understanding.This study proposes that high Na⁺diet or LDLr deficiency can activate BAT and promote browning of white fat,which will be verified by a series of animal experiments.The study is divided into two parts:1.LDLr deficiency leads to BAT activation and white fat browning,and probably interferes the efficiency of cold stimulation on adipose tissue.2.Na⁺can activate BAT and cause browning of white fat,and this process may mediated by the neuropeptide Y?NPY?in the arcuate nucleus of the hypothalamus.Research method:1.C57 mice were given gradient saline to observe the effects of different doses of Na⁺on mice.2.Indirect calorimetry was used to measure and calculate the 24-hour energy expenditure of C57 mice after 2%saline feeding.The thermogenesis gene expression of BAT and WATi was detected by q-PCR and Western blotting?WB?.3.The transcriptome sequencing method was used to observe the changes of gene expression profile of hypothalamus in C57 mice after 2%saline feeding.4.Indirect calorimetry was used to measure and calculate the 24-hour energy expenditure of NPY knockout mice(NPY^-/-)after 2%saline feeding,and the expression of thermogenesis genes were detect BAT and WATi by q-PCR and Western blotting.5.The NPY-FLEX-loaded virus was injected into a specific part of the brain of NPY^LSL/LSL mice using a brain stereotactic injection instrument.Cre recombinase was used to specifically restore the expression of NPY in the arcuate nucleus of the hypothalamus.Techniques such as q-PCR and Western Blotting were used to detect the expression of thermogenesis genes in BAT and WATi.6.Indirect calorimetry was used to measure the oxygen consumption and carbon dioxide production of LDLr^-/-mice and C57 mice under cold exposure for 24 hours,and the respiratory exchange rate and energy consumption were calculated by the parameters above.7.Using q-PCR and Western blotting to test the expression of BAT and WATi thermogenesis genes in LDLr^-/-mice and C57 mice under cold exposure.Research result:1.The results of gradient saline feeding experiment showed that the body weight,body fat and blood lipid of C57 mice decreased when the concentration of feeding saline reached1%,and the effect was dose-dependent.2.2%saline feeding could increase the basal metabolic rate and the expression of thermogenesis genes in adipose tissue of C57 mice.3.Transcriptome sequencing analysis showed that the expression of genes related to feeding and energy metabolism in hypothalamus changed greatly,in which the expression of NPY decreased and the expression of tyrosine hydroxylase?TH?increased.4.2%saline had no effect on the basal metabolic rate and the expression of thermogenesis genes in adipose tissue of NPY^-/-mice.5.2%saline feeding could re-increase the expression of thermogenesis genes in adipose tissue after restoring the expression of NPY in hypothalamic arcuate nucleus in NPY knockout mice.6.The basal metabolic rate and the expression of thermogenesis genes in adipose tissue of LDLr^-/-mice were higher than those of C57 mice under normal diet.However,the basal metabolic rate and the expression of thermogenesis genes in adipose tissue of C57 mice were significantly increased after cold exposure,while the LDLr^-/-mice remain less pronounced.Conclusion:1.Extra intake of Na⁺induces increased expression of thermogenesis genes in BAT and WATi,which may be mediated by NPY in hypothalamic arcuate nucleus.2.LDLr deficiency can increase the activity of BAT and induce the browning of WATi in mice,and LDLr interferes with the induction of heat generation by cold exposure.