M1 Macrophages Increase Endothelial Permeability and Enhance p38 Phosphorylation via PPAR-γ/CXCL13-CXCR5 in Sepsis

Abstract

<b><i>Purpose:</i></b> Vascular endothelial hyperpermeability and barrier disruption are involved in the initiation and development of sepsis. M1 macrophages promote inflammation in sepsis by releasing pro-inflammatory cytokines and chemokines. This study was designed to investigate the functional relationships between M1 macrophages and human umbilical vein endothelial cells (HUVECs), as well as the underlying molecular mechanisms. <b><i>Methods:</i></b> HUVECs were co-cultured with THP-1-derived M1 macrophages pretreated with or without rosiglitazone (RSG), a peroxisome proliferator-activated receptor (PPAR)-γ agonist. C-X-C chemokine receptor type (CXCR)5 was knocked down by short hairpin RNA lentivirus. Cecal ligation and puncture were used to induce sepsis in a mouse model. Endothelial permeability was evaluated using transendothelial electrical resistance and fluorescein isothiocyanate (FITC)-dextran assays. <b><i>Results:</i></b> Chemokine ligand (CXCL)13 was upregulated in M1 macrophages than M0 macrophages, as well as in the culture medium. In HUVECs co-cultured with M1 macrophages, transendothelial electrical resistance decreased, FITC-dextran flux increased, p38 phosphorylation was strengthened, and the expression of tight junction proteins (zonula occludens protein-1, occludin, and claudin-4) decreased. CXCR5 RNA interference or RSG pretreatment partially reversed these effects. A luciferase reporter assay revealed that CXCL13 was a direct target of PPAR-γ. RSG treatment decreased serum levels of creatinine, blood urea nitrogen, CXCL13, tumor necrosis factor-α, and interleukin-6, downregulated CXCL13 in peritoneal macrophages, and enhanced the survival rate of sepsis mice. <b><i>Conclusion:</i></b> M1 macrophages induced endothelial hyperpermeability and promoted p38 phosphorylation in sepsis by inhibiting PPAR-γ to increase CXCL13 production. PPAR-γ/CXCL13-CXCR5 signaling could be a promising novel therapeutic target for sepsis.