Activation of mitogen-activated protein kinases and IL-6 release in response to lipopolysaccharides in Kupffer cells is modulated by anisoosmolarity

Background/Aims: The influence of anisoosmolarity on the activation of the extracellular signal-regulated kinases-1 and -2 and on interleukin-6 release was studied in lipopolysaccharide-stimulated rat liver macrophages. Methods: Experiments were performed with rat liver macrophages. Activation of the extracellular signal-regulated kinases was determined by kinase shift assay and immune complex kinase assay. Interleukin-6 mRNA was measured by Northern blot analysis and interleukin-6 production by enzyme-linked immunosorbent assay. Results: Lipopolysaccharide-induced activation of the extracellular signal-regulated kinases-1 and -2 was enhanced in hypoosmotic media (205 mosm/l) and diminished by hyperosmotic (405 mosm/l) exposure when compared to normoosmotic (305 mosm/l) conditions. These effects were paralleled by changes in lipopolysaccharide-stimulated interleukin-6 mRNA expression, when determined after 4 h and interleukin-6 release after 18 h. The mitogen-activated protein kinase-kinase inhibitor PD 098059 abolished phosphorylation of the extracellular signal-regulated kinases-1 and -2 in response to lipopolysaccharide, irrespective of the medium osmolarity, and diminished lipopolysaccharide-induced interleukin-6 mRNA expression and interleukin-6 production under normo- and hypoosmotic conditions by about 50%; it also resulted under hyperosmotic conditions in an about 80% inhibition. SB 203580, a specific inhibitor of p38 largely abolished interleukin-6 mRNA expression and interleukin-6 production, irrespective of medium osmolarity, whereas phosphorylation of the extracellular signal-regulated kinases was not affected. Conclusions: The data indicate a modulation of lipopolysaccharide-induced interleukin-6 production by ambient osmolarity and an involvement of both p38 and the extracellular signal-regulated kinases-1 and -2 in the stimulation of interleukin-6 production by lipopolysaccharide.