Genetic analysis of the role of the PI3K-Akt pathway in lipopolysaccharide-induced cytokine and tissue factor gene expression in monocytes/macrophages

LPS stimulation of monocytes/macrophages induces the expression of genes encoding proinflammatory cytokines and the procoagulant protein, tissue factor. Induction of these genes is mediated by various signaling pathways, including mitogen-activated protein kinases, and several transcription factors, including Egr-1, AP-1, ATF-2, and NF-kappa B. We used a genetic approach to determine the role of the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) pathway in the regulation of LPS signaling and gene expression in isolated macrophages and in mice. The PI3K-Akt pathway is negatively regulated by the phosphatase and tensin homologue (PTEN). We used peritoneal exudate cells from Pik3r1-deficient mice, which lack the p85 alpha regulatory subunit of PI3K and have reduced PI3K activity, and peritoneal macrophages from PTENflox/flox/LysMCre mice (PTEN-/-), which have increased Akt activity. Analysis of LPS signaling in Pik3r1(-/-) and PTEN-/- cells indicated that the PI3K-Akt pathway inhibited activation of the ERK1/2, JNK1/2, and p38 mitogen-activated protein kinases and reduced the levels of nuclear Egr-1 protein and phosphorylated ATF-2. Modulating the PI3K-Akt pathway did not affect LPS-induced degradation of I kappa B alpha or NF-kappa B nuclear translocation. LPS induction of TNF-alpha, IL-6, and tissue factor gene expression was increased in Pik3r1(-/-) peritoneal exudate cells and decreased in PTEN-/- peritoneal macrophages compared with wild-type (WT) cells. Furthermore, LPS-induced inflammation and coagulation were enhanced in WT mice containing Pik3r1(-/-) bone marrow compared with WT mice containing WT bone marrow and in mice lacking the p85a subunit in all cells. Taken together, our results indicate that the PI3K-Akt pathway negatively regulates LPS signaling and gene expression in monocytes/macrophages.