A Study Of T Cell DsbA-L Function In Adipose Tissue Thermogenesis And The Underlying Mechanisms

Objective:Obesity has become a global health problem and a great economic burden to our society.Increasing thermogenesis in adipose tissue has been considered as an effective approach to alleviate obesity.While we know that adipose tissue-resident T cells contribute to obesity-induced inflammation,and certain T cell types have been found to participate in the regulation of adipose tissue thermogenesis.However,the mechanism by which T cells regulate thermogenesis remains unclear.The disulfide bond A oxidoreductase-like protein(DsbA-L)is a critical regulator of mitochondrial function in many non-immune cells such as hepatocytes and adipocytes,and further regulates systemic metabolic homeostasis.The current study aimed at exploring the effects of DsbA-L on T cell mitochondrial functions,as well as whether and how T cell DsbA-L regulates thermogenesis.Approach and Results:First,we analyzed the changes in mitochondrial function of T cells in high fat diet(HFD)-fed mice by flow cytometry.We found that HFD feeding impaired T cell mitochondrial function in brown adipose tissue(BAT)in mice.By using flow cytometry,Seahorse assay,Western blot,and confocal microscopy,we found that T cell-specific knockout of DsbA-L had no significant effect on the proliferation and development of T cells,but significantly impaired T cell mitochondrial functions such as ATP synthesis,mitochondrial respiratory ability,mitochondria mass,and calcium influx.T cell-specific knockout of DsbA-L significantly reduced mouse body weight gain,decreased fat composition,alleviated steatohepatitis,and improved glucose tolerance and insulin sensitivity.To analyze the mechanism behind the altered metabolic phenotypes in the T cell-specific DsbA-L knockout mice,we measured food intake,activity and energy consumption using metabolic cages,and calories in the mouse feces with oxygen bomb calorimeters.In addition,we also detected the expression of UCP-1 and other thermogenic genes by Western blot and RT-PCR.We found that DsbA-L knockout mice had similar food intake,activity,and fecal calories compared to the control mice,but displayed higher energy expenditure and thermogenesis-related gene expression in adipose tissue.T cell-specific knockout of DsbA-L elevated thermogenesis and energy expenditure in mice even in thermoneutral condition,which indicates that T cell DsbA-L mainly regulates diet-induced thermogenesis.The number of most T cell subtypes did not change,but IFN-γ~+T cells were significantly reduced in the T cell-specific DsbA-L knockout mice.Finally,we supplemented IFN-γto the BAT both in vitro and intraperitoneally in vivo to test its effect on thermogenesis.We found IFN-γsupplementation inhibited the accumulation of c AMP,an important signaling molecule downstream of theβ3-adrenergic signaling pathway,by up-regulating the expression of PDE4D,and thereby suppressed the expression of thermogenic genes in brown adipose tissue.Conclusions:T cell-specific knockout of DsbA-L impaired the mitochondrial functions of T cells,enhanced diet-induced thermogenesis in brown adipose tissue,and protected mice from HFD-induced obesity,hepatic steatosis,and insulin resistance.A possible mechanism is that the lack of DsbA-L in T cells reduced the production of IFN-γ,promoted the stimulation of theβ3 adrenergic signaling pathway by reducing the expression of phosphodiesterase-4D,and thereby inhibited diet-induced thermogenesis.Our research revealed T cell mitochondrial function influenced the interaction of T cells and brown adipose tissue and regulated thermogenesis and energy homeostasis.Targeting T cell mitochondria is a potential direction to control obesity and reduce related metabolic disease risks.