In dendritic cells Toll-like receptor-dependent induction of IL-12p70 is accompanied by a profound down regulation of sphingosine-1-phosphate lyase mRNA (P1348)

Abstract

Abstract Sphingosine-1-phosphate (S1P) is an immune modulator produced by sphingosine kinase (SphK)1 and SphK2 and dephosphorylated by two S1P phosphatases or irreversibly degraded by a lyase. We recently showed that Toll-like receptor (TLR)4-induced IL-12p70 is selectively counter regulated by SphK1 and extracellular S1P/S1PR1. Others demonstrated that specific SphK1-dependent binding of intracellular S1P to TRAF2 enhances TNF signaling. In an ongoing investigation to determine the influence of extra- and intracellular S1P on dendritic cell signaling our experiments revealed that activation of TLR4 by lipopolysaccharide dose and time dependently decreased S1P lyase mRNA expression of murine bone marrow-derived dendritic cells by up to 70%. This set of realtime PCR data was further confirmed by semi-quantitative RT-PCR using exon-specific primers for murine sgpl1. Systematic analysis with dose-optimized ligands of TLRs 1/2, 5, 2/6, 7/8 and TLR9 showed a differential pattern of S1P lyase down regulation with concomitant increase of intracellular S1P. Although S1P lyase defcient mice are immune compromised, we found that TLR-induced transient S1P lyase downregulation resulted in a TLR adaptor-dependent upregulation of IL-12p70, IL-23 and IL-6 expression on mRNA and protein level. Further experiments including cell compartment-specific quantification of S1P, hexadecenal and, possibly counter regulatory, sphingolipid enzymes are necessary to understand the role of sphingolipids in DC.