Heat shock response inhibits NF-kappaB activation and cytokine production in murine Kupffer cells

BACKGROUND: Kupffer cells play a crucial role in the pathogenesis of sepsis through production of proinflammatory mediators and control of systemic endotoxemia. The anti-inflammatory effects of heat shock response (HSP) have been well documented. However, the role of HSP in lipopolysaccharide (LPS) induced Kupffer cell activation has not been fully investigated. In this study, we investigated the effects of HSP on LPS induced Kupffer cell NF-kappaB activation and cytokine production. MATERIALS AND METHODS: Kupffer cells were isolated from mice by collagenase digestion and HSP was induced by culturing Kupffer cells with sodium arsenite. Kupffer cells were stimulated in vitro by LPS. Heat shock protein (HSP)-70 expression and cytoplasmic IkappaBalpha protein was determined by Western blot. Supernatant tumor necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-10 levels were measured by ELISA. NF-kappaB activation was analyzed by electrophoresis mobility shift assay. Cytokine and IkappaBalpha mRNA expression were determined by RT-PCR. Toll-like receptor 4 expression on Kupffer cells was determined by flow cytometry. RESULTS: HSP pre-conditioning significantly inhibited LPS-induced cytokine TNF-alpha and IL-6 production and mRNA expression. NF-kappaB activation and IkappaBalpha degradation induced by LPS were attenuated by HSP. HSP up-regulated expression of IkappaBalpha mRNA. No effect of HSP on cell surface expression of TLR4 was observed. CONCLUSIONS: Increased IkappaBalpha stability and up-regulation of IkappaBalpha gene expression may be one of the mechanisms of the inhibition of LPS induced Kupffer cell activation by HSP. HSP also inhibited expression of the anti-inflammatory cytokine IL-10, and the mechanism and biological significance of this effect merit further investigation.