Sympathetic Neurotransmitters Control Energy Metabolism And Its Mechanism

BackgroundObesity is a global epidemic disease,leading to metabolic diseases such as type 2 diabetes,hypertension,coronary heart diseases and neurodegenerative diseases.Brown adipose tissue(BAT)is a heat-producing organ in the body and can be used to improve obesity-related metabolic diseases by its function of heat-producing and energy-consuming.The thermogenic effect of BAT is regulated by sympathetic nerves(SN),and common sympathetic neurotransmitters include Norepinephrine(NE),Adenine Triphosphate Nucleotide(ATP),etc.Our previous study found that ATP can enhance the thermogenesis of NE-induced brown adipocytes.At present,there are few methods for measuring cell heat production directly,and metabolic indexes such as Oxygen consumption rate(OCR),reactive Oxygen species(ROS)and Reduction-oxidation reaction(Redox)cannot directly reflect heat production of cells.Therefore,a super sensitive method that directly measures cell heat production is further developed in this study.Objective1.To establish a super-sensitive mito-temperature measurement based on Rhodamine dyes to study the relationship between thermogenesis and the metabolic indexes such as OCR and ROS in BAs;2.To monitor the effects of sympathetic neurotransmitters on thermogenesis,ROS and Redox of brown adipocytes;3.To investigate the regulation effects of ATP on energy metabolism by knocking out the vesicular nucleotide transporter(VNUT)in C57BL/6J mice.Methods1.Establishing a novel mito-thermometer based on tetra-methyl rhodamine methyl ester(TMRM)and rhodamine 800(Rh800)to monitor the thermogenic effect of BAs treated with NE and NE+ATP;2.Using the Mito-SOX to detect the ROS levels in BAs before and after the treatment of NE and NE+ATP;3.Using the autofluorescence of FAD and FAD+NADH to monitor the Redox in BAs before and after NE and NE+ATP stimulation;4.Feeding wild type and VNUT-KO mice with high-fat diet to monitor the changes of body weight and fat,blood glucose and lipid,glucose and insulin tolerance.Results1.The novel mitochondrial temperature measurement method based on TMRM is more sensitive than that based on RhB-ME;2.Thermogenesis of brown adipocytes treated with succinate was not coupled with OCR,ROS and Redox,the mechanism of which was a futile cycle formed between mitochondrial complex V and UCP1;3.ATP enhanced the heat production,ROS level and Redox of NE induced brown adipocytes;4.High-fat diet is more likely to induce obesity in VNUT-KO mice,which is characterized by increased body weight,high body fat percentage and decreased insulin sensitivity.Conclusion1.The novel mito-thermometer based on TMRM is more sensitive and convenient;2.The thermogenesis and metabolic level are not coupled and the mechanism is the futile cycle formed between mitochondrial complex V and UCP1;3.The sympathetic neurotransmitter ATP enhances the metabolism of NEinduced brown adipocytes.VNUT-KO mice have lower metabolic rates and more prone to obesity induced by high-fat diet.