Gene Expression Profiling of LPS‐Stimulated Murine Macrophages and Role of the NF‐κB and PI3K/mTOR Signaling Pathways

Abstract

Lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria, activates a broad spectrum of signaling pathways in immune cells. In this article, RAW264.7 cells have been stimulated for 4 h with 1 microg/mL of LPS in the presence or not of specific inhibitors of the NF-kappaB pathway (BAY 11-7082) and the PI3K pathway (LY294002). Gene expression profiles were characterized using the DNA microarray "Dual Chip Mouse Inflammation." This array monitors the expression of 233 genes encoding proteins playing a role in inflammation. Both signaling pathways exert an important role in the response to LPS, but they are not completely overlapping. For example, genes encoding the PAF receptor, PAI-1, PlA2 (group V), IL-13 receptor (alpha2), and GTP cyclohydrolase 1, were upregulated after LPS treatment, but this upregulation was counteracted by LY294002. The same was observed for BAY 11-7082: genes encoding the kit ligand, TLR2, or TNFRSF5 were mainly under the control of NF-kappaB. NF-kappaB plays an important role in the macrophage response to LPS, but we have also shown that the PI3K pathway partially contributes to it. Further experiments with the specific inhibitor of mTOR (rapamycin) will provide more information on the specific contribution of the PI3K/mTOR pathway in the inflammatory response in LPS-stimulated macrophages.

Lipopolysaccharide Induces Chronic Kidney Injury and Fibrosis through Activation of mTOR Signaling in Macrophages

“…The inhibition of mTOR markedly ameliorated macrophage infiltrates, tubular injuries and fibrosis, which may work through a suppression of inflammatory chemokines in macrophages. These findings are in agreement with previous reports that LPS could induce an abundant expression of chemokines in macrophages through the activation of mTOR signaling, which could be significantly suppressed by rapamycin [36,37] . It will be challenging to further explore the role of mTOR in macrophage dynamics and its correlation with outcomes of kidney disease.…”

Regulatory effects of TLR2 on megakaryocytic cell function

“…Only COX2 and NFB1 were solely regulated by the NFB pathway. Increases in the gene expression of MCP-1 and TLR2 was also affected by both the PI3K/Akt [44][45] and the ERK-MAPK [46][47] pathways in megakaryocytes, as has been shown in other cell types.…”

A novel mTOR inhibitor is efficacious in a murine model of colitis

“…The inability of P2281 to inhibit in vivo LPSinduced TNF-␣ production was not because of pharmacokinetic issues because sufficient levels (C max : 38 g/ml, i.e., 180 M) of P2281 were seen in the plasma of mice after administration of 100 mg/kg P2281 (data not shown). These observations, combined with the fact that LPS stimulates mTOR activity (13,27), indicate that mTOR activation plays little if any role in induced TNF-␣ production. Furthermore, P2281 had little if any effect on LPS-induced IL-6, IL-8, and IL-1 production from hPBMCs (data not shown).…”