Study Of Dietary Lactate Supplementation On Obesity And Adipose Browning In Mice

The medical regimen of obesity has always been an urgent clinical problem,and promoting adipose browning represents a new direction.Prospective studies have suggested that yogurt may contribute to anti-obesity effects,but its molecular mechanism remains unclear.The lactate is known as a major ingredient of yogurt,while its cognate receptor G protein-coupled receptor 81(GPR81)is highly expressed in adipose tissues in mammals.Lactate and GPR81 have been recently reported to regulate pathophysiological processes,but it is not clear whether lactate and GPR81 mediate obesity and adipose browning.Hence,we aimed to study the anti-obesity effect of lactate in vivo through obese mouse models,and then explored the mechanism underlying this process in vitro.The main research contents are as follows:First,we explored the biological function of lactate receptor GPR81 by breeding GPR81knockout mice and constructing a browning mouse model.The results showed that the deficiency of GPR81 weakened thermoregulation and thermogenesis ability.According to histopathology and the expression of browning markers,the deficiency of GPR81 greatly attenuated experimental adipose browning induced by the?₃-adrenergic receptor agonist CL316243.Moreover,the expression of GPR81 was regulated by multiple factors such as obesity and adipose browning through Western Blot.Then,we investigated the effects of lactate on obesity and adipose browning by constructing an obesity mouse model induced by 60%high fat diet.We demonstrated that oral administration of lactate effectively alleviated body weight gain,lowered white adipose tissue(WAT)accumulation,improved dyslipidemia and glycometabolism disorder and induced adipose browning to a certain extent.The details are as follows:(1)low dose and high dose of lactate declined the body weight of obese mice by 12.2%(p<0.001)and 11.6%(p<0.001);(2)high dose of lactate reduced the ratio of epididymal white adipose tissue(e WAT)and inguinal subcutaneous adipose tissue(i WAT)normalized to body weight by 31.2%(p<0.05)and 54.7%(p<0.05);(3)lactate was effective in recovering the high fat diet-induced increase in levels of plasma triglycerides,cholesterol,low-density lipoprotein cholesterol,non-esterified fatty acid and fasting blood glucose,and improved glucose tolerance;(4)histological analysis revealed smaller adipocyte sizes and richer cytoplasmic staining in WAT of lactate-treated mice compared with controls;(5)lactate upregulated the m RNA levels of uncoupling protein 1(UCP1)and other browning markers;(6)lactate enhanced thermogenesis and improved basic metabolism and exercise.More importantly,lactate was well tolerated in obese mice as indicated by food intake,liver function test as well as kidney function test.We further examined the influence of lactate treatment on?₃-adrenergic receptor agonist stimulation in obesity and inducing adipose browning.Data clearly indicated that the combination of lactate and CL316243 treatment resulted in a synergistic effect in alleviating body weight gain,lowering WAT accumulation and improving dyslipidemia.Notably,CL316243-associated enhanced expression of browning markers as well as histopathology could be strengthened by high dose of lactate treatment.Meanwhile,the co-treatment greatly strengthened thermogenesis and basic metabolism.Finally,we explored the possible mechanism through the obese mouse model and3T3-L1 adipocytes experiments.Our study found that lactate might activate GPR81 and trigger p38-UCP1 activation,then induce adipose browning and adaptive thermogenesis.The details are as follows:(1)compared with lean mice,plasma lactate levels were elevated in obese mice,while lactate concentration in WAT was markedly lowered in obese mice;(2)lactate upregulated the protein levels of GPR81,UCP1 and p-p38;(3)lactate upregulated the expression of GPR81,UCP1 and p-p38 in 3T3-L1 adipocytes,while such lactate-driven UCP1 induction was abolished by pharmacological p38 blockade;(4)the deficiency of GPR81 weakened the protein levels of UCP1 and p-p38 in WAT.Collectively,our findings revealed a critical role of lactate and GPR81 in obesity and adipose browning,and provided a new explanation as to how yogurt consumption could lower the risk of obesity.