The Crucial Role Of PPARγ-Egr-1-Pro-Inflammatory Mediators Axis In IgG Immune Complex-Induced Acute Lung Injury

Research BackgroundAcute Lung Injury(ALI)and Acute Respiratory Distress Syndrome(ARDS)refer to acute and progressive hypoxic respiratory failure caused by various intrapulmonary and extrapulmonary pathogenic factors other than cardiac,with an annual incidence of about 64/100,000 and an extremely high mortality rate of approximately 40%,ARDS/ALI represents an important global public health problem.ARDS is caused by a variety of primary diseases,the pathogenesis of ARDS is complicated,and IgG immune complex(IgG-IC)lung deposition is an important factor.IgG immune complex-induced acute lung injury in mice is a classic model of acute lung injury,and the complex regulatory mechanisms of inflammation in the model needs intensive investigation.The ligand-activated transcription factor peroxisome proliferators-activated receptor(PPAR)γ plays crucial roles in a variety of biological processes including cellular metabolism,differentiation,development,and immune responses.Activation of PPARγ results in beneficial effects as well as adverse side effects.The role of early growth response factor(Egr-1)in the inflammatory response has also been extensively investigated,but its effect and mechanism on acute lung inflammation are not fully understood.The regulatory function and underlying mechanism of Egr-1 in lung injury induced by IgG-IC intrapulmonary deposition remain a mystery.In this study,we will discuss the roles of PPARγ and Egr-1 in IgG-IC-induced acute lung injury,their interactions and specific mechanisms,then provide new ideas for ARDS/ALI treatment strategies.Research PurposeThis study aimed to determine the effect and mechanism of PPARγ and Egr-1 on IgG-IC-induced acute pulmonary inflammation,and to provide insights for the treatment of acute pulmonary inflammation.Research MethodsVarious plasmids were constructed by conventional PCR;sh RNA was used to downregulate target gene expression;macrophage RAW264.7 cells were treated with DMSO or 10 μM PPARγagonist rosiglitazone(ROSI);adenovirus was used as a vector to achieve PPARγ overexpression in mouse lung tissue;IgG-IC-induced acute lung injury models in mice were constructed;bronchoalveolar lavage fluid(BALF)and whole lungs were collected,lung permeability indexes were analyzed,pulmonary myeloperoxidase(MPO)content,total white blood cells and percentage of neutrophils in the liquid were measured;RT-q PCR was used to detect the RNA expression levels of the target genes;Western Blot technology was used to detect the protein expression levels of the target genes;ELISA was used to analyse the protein expression levels of TNF-α,MCP-1,MIP-1α and MIP-2 in the supernatant level;software(JASPAR)predicts the potential Early Growth Response-1(Egr-1)binding sites in the promoter regions of pro-inflammatory mediators TNF-α,MCP-1 and MIP-1α;twenty-four hours after plasmid transfection,cells were lysed then the luciferase activity in cell lysates was measured with Dual-Luciferase Reporter Assay System.Research Results1.PPARγ negatively regulates IgG-IC-induced acute lung injury.2.In IgG-IC-treated macrophages PPARγ alleviates inflammation.3.In IgG-IC-treated macrophages Egr-1 expression is reduced by PPARγ.4.In macrophages Egr-1 increases IgG-IC-induced expression of pro-inflammatory me-diators by binding to its promoter region.5.During IgG-IC-induced acute lung injury,Egr-1 expression is reduced by PPARγ.6.Egr-1 aggravates IgG-IC-induced acute lung injury by increasing the expression of pro-inflammatory mediators.ConclusionsThe anti-inflammatory effect of PPARγ following IgG-IC lung deposition is mediated by inhibiting the production of Egr-1,which can bind to the promoter regions of pro-inflammatory mediators including TNF-α,MCP-1 and MIP-1α.Regulation of the PPARγ-Egr-1-proinflammatory mediator axis by the PPARγ agonist ROSI may represent a novel strategy to treat acute lung injury.