Role Of Fatty Acid Binding Protein 4 In Regulating Apoptosis Of Macrophage Induced By Bacillus Calmette-Guerin Infection

Background:Macrophage is the main target cell of Mycobacterium tuberculosis(M.tb).Studies revealed that M.tb infection can induce alveolar macrophage apoptosis which is helpful in suppress mycobacteria infection.During this process,the metabolic pathway will also change to meet cell's energy needs.As an important component of energy metabolism,fatty acids(FAs)metabolism could produce energy through oxidation process and provide stable energetic support.One the other hand,some FAs and the intermediate products produced by fatty acids metabolism process are signaling molecules which were involved in the activation of many pathways.However,FAs need bind together with protein to reduce its toxicity.Fatty acid binding protein4(FABP4)is the apolipoprotein which is abundant in macrophage.Studies has shown that FABP4 could combine with FAs and is involved in regulating apoptosis.However,the function of FABP4 in macrophage during M.tb infection remains obscure.Method:The present study aimed to investigate the role of FABP4 in regulating apoptosis of RAW264.7 cell with Mycobacterium infection.Small interfering RNA was used to knock down the expression of FABP4.FCS WB and IF were used to detect the function of FABP4 on RAW264.7 cell apoptosis and fatty oxidation during BCG infection.The results we got showed below:1.BCG infection increased the expression of FABP4 on time-dependent manner.Compared with un-infection group,the expression was significantly increased 12h after infection(p<0.001).2.BCG infection enhanced the expression of apoptosis and FAO related factors.The apoptotic rate and the expression of Caspase3 and PARP were significantly increased(p<0.001)12h after BCG infection.In the meantime,the expression of FAO related factors PPAR-? and CPT1A were significantly enhanced(p<0.001)which accomplished the accumulation of fatty acid.3.Knockdown of FABP4 decreased fatty acid accumulation in BCG infected RAW264.7 cells.Furthermore,knockdown of FABP4 increased the expression of fatty acid ?-oxidation factors CPT1A and AC ADM(p<0.001)which further promoted the accumulation of ROS and ATP production.4.In BCG infected RAW264.7 cells,knockdown of FABP4 increased level of Ca2+ accomplished with up-regulated the expression of PERK p-eIF2? and Chop which are the ER stress markers.Meanwhile,the knockdown of FABP4 promoted MMP loss and decreased the expression of antiapoptotic protein Bcl-2 but enhanced the expression of proapoptotic factors Bax and Caspase-9 which all are biomarkers of intrinsic apoptosis pathway.Moreover,the knockdown of FABP4 increased apoptotic rate and the expression of Caspase3 PARP in BCG infected RAW264.7 cells.Conclusion:BCG infection promoted macrophage apoptosis and fatty acid oxidation which accomplished with upregulation of FABP4 expression.The knockdown of FABP4 enhanced fatty acid oxidation and aggravate BCG-induced apoptosis of RAW264.7 via ER stress pathway.