The Effect And Mechanism Of PPARγ On NKT Cell Function In Obesity

Background: Living habits and dietary structure are constantly changing,resulting in a rapid increase in the incidence of obesity.Nowadays obesity has become a global epidemic and threatens people’s health.There are many factors involved in the induction and deterioration of obesity,not only diet and lifestyle,but also the immune system and gut bacteria.Lymphocytes are the immune cells that play the core role in the immune system.As the unique subtype of immune cell,natural killer T cell(NKT)plays an important role in both congenital and adaptive immune lines,and is well known for its role in regulating inflammatory response caused by a variety of reasons.While its role in obesity has been studied before,it’s not at all clear on a deeper level.It has been reported that Peroxisome proliferator activated receptor γ(PPARγ)can regulate the expression of a variety of nuclear target genes and thus affect the metabolism of fat.It will cause abnormal lipid metabolism in adipocytes and promote the occurrence of obesity.PPARγ has long been a star molecule in the study of obesity.It is mainly expressed in metabolic tissues and the immune system,and is an important participant in adipocyte differentiation.It is also closely related to the body’s immunity and insulin resistance,and plays an important role in the connection between the immune system and the metabolic system.Therefore,signal molecules regulating PPARγ expression are the core factors related to fat metabolism in obesity regardless of environmental or genetic factors.However,the molecular mechanism by which PPARγ molecules affect the function of NKT cells under different conditions of obesity is still unclear.Aims: The aim of this study was to explore the molecular mechanism by which PPARγ molecules affect the function of NKT cells in the condition of two different obesity backgrounds: high fat diet and leptin receptor gene deficiency.Methods: In this study,12-week-old OB/OB mice were used as the background of genetic factors for obesity.Flow microsphere technology was used to detect changes in the levels of different cytokines in the supernatant of NKT cells in OB/OB mice and wild-type(WT)mice after induction and stimulation in vitro.In vivo experiments,α-Gal Cer antigen was injected into mice by intraperitoneal injection technology,and cytokine expression levels of NKT cells in fat and liver tissues of two groups of mice were detected.In addition,flow cytometry was used to detect the expression of lipid metabolism-related molecules such as PPARγ and SREBP1 in NKT cells of liver and adipose tissue,as well as the cholesterol level on the cell membrane.Moreover,PPARγ specific agonist was added into mouse liver and adipose NKT cells in vitro to observe the downstream molecular expression of PPARγ after the addition of agonist.In addition,in order to simulate the background of obesity caused by environmental factors,4-week-old mice were fed with high fat for 5 months to complete the modeling.Similarly,flow cytometry was used to detect the expression of lipid metabolism-related molecules in NKT cells in mice.In vitro experiments,a variety of exogenous free fatty acids were added into the amplified NKT cells to detect the effects of lipid accumulation on molecules related to lipid metabolism in NKT cells.To further explore,mitochondrial staining test was selected to detect the changes of cellular reactive oxygen species ROS and mitochondrial membrane potential after free fatty acids.Results: In OB/OB mice,NKT cells in adipose and liver tissues functioned abnormally and polarized toward Th2 type.In addition,it was found that the expression level of lipid metabolism-related molecules in NKT cells was significantly reduced,as was the cholesterol level in the cell membrane.In addition,the downstream molecular level of PPARγ was recovered to a certain extent after the addition of PPARγ specific agonist.The expression level of PPARγ in liver and adipose NKT cells of mice fed high fat diet was also significantly reduced compared with normal diet.Further investigation of the mechanism found that accumulation of exogenous free fatty acids down-regulated the expression levels of lipid metabolism-related molecules in a dosedependent manner in NKT cells.Mitochondrial dye staining experiments showed that free fatty acids decreased cellular reactive oxygen species(ROS)and mitochondrial membrane potential under lipid accumulation condition.Conclusion: In the context of inherited obesity and high-fat diet-induced obesity,reduced expression of lipid-metabolism-related molecules such as PPARγ in NKT cells was observed in mouse adipose tissue and liver tissue.In terms of mechanism,the downregulated expression of lipid-metabolism-related molecules such as PPARγ in mouse NKT cells is dose-dependent and accompanied by mitochondrial dysfunction.