Prolonged Inorganic Arsenic Exposure Through Drinking Water Impairs The Function Of Brown Adipose Tissues In Female Mice

Object:Arsenic is a metalloid element widely found in nature.Epidemiological studies have shown that arsenic is one of the risk factors for the occurrence of disorders of glucose and lipid metabolism in the body,and the disorders of glucose and lipid metabolism are inseparable from the disorders of adipose tissue function.Different from the excess energy of white fat storage body,brown adipose tissue（BAT）consumes excess energy of the body through uncoupling protein 1（UCP1）-mediated nonshivering thermogenesis（NST）and plays a key role in maintaining the steady state process of glucose and lipid metabolism.Our previous studies found that iAs can inhibit adipogenesis through peroxisome proliferator-activated receptor-γ（PPARγ）and suppress glucose uptake function in 3T3-L1cells.The objective of our study is to investigate the effects of sub-chronic arsenic exposure on BAT function and related mechanisms,and thus may provide an original idea to study the mechanisms linking exposure to iAs to increased risk of metabolic disorder.Methods:1.Exposing C57BL/6 female mice to drinking water containing iAs,including iAs³⁺and iAs⁵⁺,which concentration are close to the actual exposure level of the crowd for 14-17weeks.Control group,5 ppm group and,20 ppm group were set up in the current study;2.Use a small animal body composition analyzer to detect body fat content in mice;3.Using a small animal thermometer to monitor changes in body temperature under cold exposure in mice,evaluate the BST non-trivial heat production（NST）function;4.Glucose tolerance test and insulin tolerance test were used to evaluate glucose metabolism and insulin sensitivity,respectively.5.Calculate and evaluate mouse organ coefficient;6.H&E staining was used to observe the morphological changes and lipid accumulation of Brown adipocyte（BAC）after iAs exposure.7.Using qRT-PCR technique to detect the BAT newborn differentiation,NST and mitochondrial number-related mRNA expression levels after iAs exposure;8.Western Blot technique was used to detect the BAT newborn differentiation,lipolysis,NST,mitochondrial number,and function-related protein expression of mice after exposure to iAs.Results:1.Effects of iAs exposure on glucose and lipid metabolism in mice:The glucose tolerance test showed that the blood glucose level at 5 minutes was significantly higher in the 5 ppm group than that in the control group（p<0.05）;Insulin tolerance experiment showed that the blood glucose of the 5 ppm group at the 120th minute was significantly higher than that of the control group（p<0.05）;2.Organ coefficient analysis:Compared with the control group,BAT weight was significantly increased in the 5 ppm group（p<0.05）;3.H&E staining analysis of pathological sections:compared with the control group,lipid accumulation in BACs of 5 ppm group was excessively accumulated and cell numbers were decreased;4.iAs exposure inhibited BAT differentiation:mRNA and protein levels of BAT differentiation genes,including Pparg,Pparg1,Pparg2,and Prdm16 in the 5 ppm group were significantly lower than those in the control group（p<0.05）;5.iAs exposure to BAT thermogenic function:Compared with the control group,mRNA expression of Ucp1,Dio2,Elovl3,Elovl6,Cox8b,Cox7a1,and Cidea in the 5 ppm group was significantly decreased（p<0.05）,UCP1 protein level was also significant Decreased（p<0.05）;6.Mitochondrial function of BAT after exposure to iAs:Compared with the control group,BAT mitochondria content decreased in the 5 ppm group,and protein expression levels of PGC-1α,COX IV,and NDUFS4 decreased significantly（p<0.05）.Conclusion:iAs-treated mice demonstrated the phenotype of cold intolerance and whitening of BAT.iAs exposure inhibited development of brown adipocytes（BAC）via a mechanism involving suppressing expression of PPARγand PRDM16.Additionally,iAs exposure decreased mitochondrial count and oxidative phosphorylation function in BAT and thus reducing UCP1 expression.Furthermore,expression of adipose triglyceride lipase（ATGL）was decreased in iAs-treated mice,leading to disturbances in glucose and lipid metabolism.