APOO Knockout Promotes Brown Adipose Tissue Whitening And High-fat Induced Obesity By Inhibiting Peroxisome Fatty Acid Oxidation

Background: Obesity is a major health burden in today’s society and has become a serious global health problem.The imbalance of energy homeostasis in the body is the main cause of obesity.Decreased thermogenic activity of adipose tissue,especially brown adipose tissue,is a key factor in energy imbalance.By promoting brown adipose tissue heat production and improving its metabolic level,it can effectively reduce the occurrence and development of metabolic-related diseases such as obesity,which has been a hotspot in metabolic research in recent years.APOO is a mitochondrial inner membrane protein involved in the composition of the MICOS complex(mitochondrial contact site and cristae composition system).Whether APOO is involved in the regulation of adipose tissue function by affecting mitochondrial structure and function is unclear.Objective: This study aimed to investigate the effect of APOO-specific adipose tissue knockout on adipose tissue,especially brown adipose tissue,function and systemic metabolic phenotype.Methods:1)The m RNA transcript levels of APOO and UCP1 in human adipose tissue were detected by RT-q PCR;2)By constructing an Apoo adipose tissue-specific knockout mouse model and challenging with a normal diet and a high-fat diet,the changes in body weight,glucose tolerance and insulin tolerance of the mice were detected,and the size of lipid droplets and the expression levels of thermogenic marker proteins were detected by HE staining of brown adipose tissue and immunohistochemistry;3)The changesin body temperature of mice were detected by acute cold stimulation at 4°C and the energy metabolism of mice was detected by metabolic cages;4)Detection of mitochondrial morphology and function by transmission electron microscopy and flow cytometry,and detection of metabolic levels in brown adipose primary cells using Seahorse;5)The protein expression levels of fatty acid oxidation-related and PPAR-α in brown adipose tissue of normal and high-fat diet mice were detected by Western Blot,and the size of lipid droplets and the expression levels of thermogenesis marker proteins were detected by PPAR-αagonist intervention in mice.Results:1)The expression of APOO in human adipose tissue was significantly positively correlated with the brown adipose tissue marker UCP1,suggesting that APOO may be involved in brown adipose tissue thermogenesis;2)Apoo adipose tissue knockout promotes age-related brown fat whitening;simultaneously promotes high-fat diet-induced obesity and brown fat whitening without affecting glucose metabolism and insulin sensitivity;3)Apoo adipose tissue knockout caused mice intolerance to cold stimulation and reduced body heat production and energy expenditure;4)Apoo knockout affects the mitochondrial morphology of brown adipocytes,reduces mitochondrial membrane potential,and inhibits cellular oxidative phosphorylation,thereby promoting cellular metabolic reprogramming,manifested as enhanced glycolysis and decreased peroxisomal fatty acid oxidation;5)Apoo knockout reduced the number of peroxisomes by inhibiting the expression of PPAR-α,and decreased the expression of SCP2 and EHHADH involved in fatty acid oxidation in peroxisomes;PPAR-αactivation could reverse the whitening of brown adipose tissue caused by Apoo knockout.Conclusions: APOO plays an important role in the reprogramming of glucose and lipid metabolism in brown fat and the effect of thermogenesis on obesity,suggesting that APOO may be an important potential target for interfering with obesity and the occurrence and development of obesity-related metabolic diseases.