Mechanism Of Lymphocytes Immunosuppression Caused By High-fat Diet Induced Oxidative Stress

With growth in the living standard, the great changes in dietary patterns occur in urban and rural residents. High energy intake leads to situations of obesity, which may influence immune function. High fat diet (HFD) has long been linked to immune dysfunction and developed oxidative stress. ROS generation elevation induced by HFD may be the main reason of changing the gene expression profiles and functional status. Whereas the molecular mechanistic events associated with immune deficiency remain to be fully determined. In this study, we explored the molecular mechanism of HFD-induced oxidative stress on lymphocytes function and energy status, and the improvement effects of lipoic acid (LA) on redox status and lymphocytes immunosuppression.1. HFD-indcued oxidative stress inhibits lymphocytes functionThe objective of this investigation was to study whether HFD could influence immune system redox status. Male C57BL/6 mice were randomly assigned to three groups. The control group were administrated with an ordinary diet.The two experimental groups were fed with a high-fat diet,high fat plus 0.1% LA.After 10 wk, oxidative stress biomarkers including malondialdehyde, superoxide dismutase, catalase, total antioxidant capacity, reduced glutathione/oxidized glutathione ratio, reactive oxygen species (ROS), and immune parameters were examined. HFD led to a significant oxidative stress and a potent weakened antioxidant defenses in mice. Flow cytometric analysis results indicated the CD4+/CD8+, and percent of B lymphocytes, and lymphocytes transformation rate significantly decreased with HFD mice. Apoptotic percentages of spleen lymphocytes were significantly increased with HFD mice. LA as a possible effective supplement with HFD, both to prevent the development of oxidative stress and to attenuate lymphocytes immunosuppression which inhibited by HFD.Cytokines such as IFN-γ, IL-4, IL-6, TNF-αand IL-10 was examined after 10 wk, respectively. Gene expression related to oxidative stress and inflammation were confirmed by QRT-PCR. HFD significantly increased levels of IFN-γ,IL-6 and TNF-α, and decreased levels of IL-4 and IL-10 in mice plasma. QRT-PCR results showed an up-regulated in inflammation related gene and a down-regulated in antioxidant related gene. LA as a possible effective supplementation with HFD to prevent the development of chronic inflammation.2. Molecular mechanism for HFD-induced lymphocytes immunosuppressionRNA was extracted and gene expressions were analyzed using the Affymetrix MOE430A Genchip according to standard Affymetrix protocols. Results from On-tools analysis tool revealed that HFD feeding triggered a widespread response in spleen. Significant changed signal pathway terms were studied by On-tools, which revealed that the differentially expressed genes were mainly related to ROS metabolism, MAPK, insulin signaling pathway, cell cycle, apoptosis, calcium signaling pathway and immune response including BCR, TCR, toll-like receptor, natural killer cell mediated cytotoxicity, JAK-STAT, cytokine-cytokine receptor interaction, and complement and coagulation cascades. LA up-regulated the expression of genes related to ROS scavenger enzymes and proteins. Then, the immune response, insulin signaling pathway, cell cycle and calcium signaling pathway related gene were up-regulated, while those involved in apoptosis were down-regulated. These results suggested LA can improve immune function of HFD fed mice. We analyzed the concentration of SIgA and the gene expression patterns of lymphocyte related signal transduction genes in jejunum of C57BL/6 mice in order to gain insight on the possible molecular mechanism by which HFD induced mucosal immunosuppression. Results of present study showed that HFD induced down-regulated expressions of the gene involved in ROS scavenger enzymes and proteins, BCR (including Cd19,Cr2,Ighg,Igh-6,Cd79b), TCR (including Il2ra,Syk,Lck,Cd28,Cd86), and antigen processing and presentation signaling pathway. LA supplement ameliorated that HFD induced oxidative stress and immunosuppression by recovering expressions of these genes. The present study indicates that a HFD can decrease the concentration of SIgA, induce chronic oxidative stress, suppress signal transduction of gut-associated lymphocytes, and lead to an inhibition of mucosal immunity.3. Influence of HFD-induced oxidative stress on spleen proteins expressionThe objective of this investigation was to explore possible molecular changes for role of a HFD-induced oxidative stress in spleen, and whether a dietary LA supplement could attenuate these changes. Two-dimensional gel electrophoresis was used to compare the proteomes of spleen with three dietary groups. Differentially expressed spots whose expression altered over 3-fold were identified by MALDI-TOF MS. Bioinformatic evaluation results of MALDI-TOF MS showed that 20 differentially expressed protein spots were known to be involved in many processes associated with cell function, such as cytoskeleton(CORONIN, VIM), energy metabolism and oxidative stress (ACO2, TKT, PRDX1), apoptosis (HLX,DAPK1) and cell cycle (CITRON-K,GPRIN1). In conclusion, these results indicate that HFD-induced oxidative stress could lead to the functional decline of spleen, and LA supplement restores the redox balance and enhances the intracellular energy metabolism and synthesis of biological macromolecules by scavenging ROS.4. Influence of redox status on lymphocytes function and energy metabolismThe objective of this investigation was to verify the molecular mecanism of HFD-induced immunosuppression by studying ATP level, mitochondrial functionsplenic, and lymphocytes function of splenic lymphocytes in different week HFD. H2O2, GSH/GSSG and MDA were examined after 5wk. The transformation rate of lymphocytes, cellular ATP level and mitochondrial membrane potential of lymphocytes were examined after 3 and 5 wk, respectively. Gene expression related to oxidative stress, glucose metabolism and immune function were confirmed by QRT-PCR. The transformation rate of lymphocytes, ATP level and mitochondrial membrane potential of lymphocytes significantly increased with HFD mice after 3 wk and significantly decreased with HFD mice after 5 wk. Gene expression related to oxidative stress (Mt-1, Prdx1, Prdx4), glucose metabolism (Inr, Slc2, Pik3cd, Akt3, Rac-1) and immune function (Il2, Ilr2α, CD19, Igh-6) were significantly decreased with HFD mice after 5 wk. LA as a possible effective supplement with HFD, both to prevent the development of oxidative stress and to attenuate lymphocytes suppression which inhibited by HFD.In clusion, dietary oxidative stress induced glucose metabolism inhibition and ATP level decrease may be the important reason of the reduction of lymphocyte number and dysfunction. LA could effectively protect the function of lymphocytes by changing redox status.