Transcriptional Regulation Of Brown Adipocyte Functions By Mitochondrial Oxidative Phosphorylation Deficiency

AimsObesity is characterized by adipose tissue hypertrophy and hyperplasia.Adipose tissue is composed of white and brown adipose tissue.White adipose tissue is an energy storage organ with endocrine function.While brown adipose tissue is important in the regulation of whole body energy balance and insulin sensitivity due to its non-shivering thermogenesis.As a result,it has become a new target in the treatment of obesity and related metabolic diseases.Mitochondrial respiratory deficiency was often found in the adipose tissue in people with obesity and type 2 diabetes.A growing body of evidences also suggest that the mitochondrial regulatory capacity is essential in the regulation of brown adipocytes function,but the mechanism remains elusive.We have established pharmacological and genetic models of mitochondrial oxidative phosphorylation system(OXPHOS)deficiency in brown adipocytes.We investigated how respiratory capacity impact on brown adipocyte thermogenic function and explored the underlying mechanism.MethodsPharmacology model and genetic model of brown adipocyte OXPHOS deficiency were established by either treating cells with 100 nM rotenone or stably expressing shRNA against complex I assembly factor Ndufaf5.The gene expression levels were analyzed by Q-PCR.Glucose and lipid metabolism were analyzed using Gas Chromatography-Mass Spectrometry(GC-MS)and Liquid Chromatography-Mass Spectrometry(LC-MS).The underlying mechanism leads to alternations in lipid metabolism and thermogenic capacity was studied by investigating changes in PPARy protein levels or its post-translational modifications.ResultsMitochondrial oxidative phosphorylation deficiency significantly reduced expression of thermogenic genes and peroxisome genes in brown adipocytes.In addition,oxidative phosphorylation defects inhibit the metabolic function of mitochondria,resulting in a significant decrease in content of TCA cycle intermediate fumaric acid,succinic acid,and malic acid?In contrast,the content of total fatty acids,free fatty acids,lyso-phosphatidylcholines,ceramides,lactic acid and amino acids increased.Respiratory deficiency also increased endoplasmic reticulum(ER)stress evidently by increased phosphatidylcholine/phosphatidylethanolamine ratio and protein levels of ER stress markers.Alternations in brown adipocyte thermogenic capacity may caused by reduced PPARy2 protein level.Additionally,increased PPARy2 acetylation also reduced its promoter occupancy of PPARy that leads to reduced thermogenic gene expression.ConclusionMitochondrial OXPHOS deficiency leads to reduced PPAR?2 protein level and increased PPARy2 acetylation which result in reduced thermogenenic genes and peroxisomal gene expression.Further studies are warranted to elucidate the exact signals that leads to the changes in transcriptional program.