Role of p38 MAPK and STAT3 in lipopolysaccharide-stimulated mouse alveolar macrophages

Excessive production of inflammatory mediators is an important feature of inflammatory lung disease. In macrophages, mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription-3 (STAT3) are crucial mediators for the production of proinflammatory cytokines. In the present study, the role of MAPK and STAT3 on tumor necrosis factor (TNF)-alpha and interleukin (IL)-10 production was investigated in mouse alveolar macrophages. The levels of TNF-alpha and IL-10 in lipopolysaccharide (LPS; 100 ng/mI)-stimulated MH-S cell lines were measured by an enzyme-linked inmmunosorbent assay,with or without p38 inhibitor (SB203580; 5, 10 or 15 mu M) intervention. Phosphorylated STAT3 (p-STAT3) expression was examined by western blot analysis and immunocytochemistry following LPS stimulation for 15 or 30 min. Antibodies against STAT3 were used to verify comparable sample loading. Cells stimulated with LPS showed significantly increased levels of p-STAT3 protein (P<0.05) when compared with the baseline levels. TNF-alpha and IL-10 protein levels also increased following LPS stimulation (P<0.05). By contrast, treatment with the p38 inhibitor, SB203580, decreased the levels of p-STAT3, TNF-alpha and IL-10 (P<0.05) following LPS stimulation. SB203580 was shown to inhibit LPS-stimulated TNF-alpha expression (P<0.05) in a concentration-dependent manner, reaching significance at a concentration of 10 mu M. However, the inhibition of IL-10 expression was not concentration-dependent. Therefore, LPS-stimulated overproduction of TNF-alpha and IL-10 is mediated at least partially by the MAPK pathway. Inhibition of p38 prevented LPS-induced STAT3 phosphorylation, indicating an interaction between the STAT3 and MAPK signaling pathways.