Transforming growth factor-β inhibits lipopolysaccharide-stimulated expression of inflammatory cytokines in mouse macrophages through downregulation of activation protein 1 and CD14 receptor expression

The septic shock that occurs in gram-negative infections is caused by a cascade of inflammatory cytokines. Several studies showed that transforming growth factor-beta 1 (TGF-beta 1) inhibits this septic shock through suppression of expression of the lipopolysaccharide (LPS)-induced inflammatory cytokines. In this study, we investigated whether TGF-beta 1 inhibition of LPS-induced expression of inflammatory cytokines in the septic shock results from downregulation of LPS-stimulated expression of CD14, an LPS receptor. TGF-beta 1 markedly inhibited LPS stimulation of CD14 mRNA and protein levers in mouse macrophages, LPS-stimulated expression of CD14 was dramatically inhibited by addition of antisense, but not sense, c-fos and c-jun oligonucleotides. Since TGF-beta 1 pretreatment inhibited LPS-stimulated expression of c-fos and c-jun genes and also the binding of nuclear proteins to the consensus sequence of the binding site for activation protein 1 (AP-1), a heterodimer of c-Fos and c-Jun, in the cells, TGF-beta 1 inhibition of CD14 expression may be a consequence of downregulation of AP-1. LPS-stimulated expression of interleukin-1 beta and tumor necrosis factor alpha genes in the cells was inhibited by addition of CD14 antisense oligonucleotide. Also, TGF-beta 1 inhibited the LPS-stimulated production of both inflammatory cytokines by the macrophages. In addition, TGF-beta 1 inhibited expression of the two cytokines in several organs of mice receiving LPS. Thus, our results suggest that TGF-beta 1 inhibition of LPS-stimulated inflammatory responses resulted from downregulation of CD14 and also may be a possible mechanism of TGF-beta 1 inhibition of LPS-induced septic shock.