Activation-Induced Cell Death of Dendritic Cells Is Dependent on Sphingosine Kinase 1

Abstract

Sphingosine 1-phosphate (S1P) is an immune modulatory lipid mediator and has been implicated in numerous pathophysiological processes. S1P is produced by sphingosine kinase 1 (Sphk1) and Sphk2. Dendritic cells (DCs) are central for the direction of immune responses and crucially involved in autoimmunity and cancerogenesis. In this study we examined the function and survival of bone marrow-derived DCs under long-term inflammatory stimulation. We observed that differentiated cells undergo activation-induced cell death (AICD) upon LPS stimulation with an increased metabolic activity shortly after stimulation, followed by a rapid activation of caspase 3 and subsequent augmented apoptosis. Importantly, we highlight a profound role of Sphk1 in secretion of inflammatory cytokines and survival of dendritic cells that might be mediated by a change in sphingolipid levels as well as by a change in STAT3 expression. Cell growth during differentiation of Sphk1-deficient cells treated with the functional S1P receptor antagonist FTYP was reduced. Importantly, in dendritic cells we did not observe a compensatory regulation of Sphk2 mRNA in Sphk1-deficient cells. Instead, we discovered a massive increase in Sphk1 mRNA concentration upon long-term stimulation with LPS in wild type cells that might function as an attempt to rescue from inflammation-caused cell death. Taken together, in this investigation we describe details of a crucial involvement of sphingolipids and Sphk1 in AICD during long-term immunogenic activity of DCs that might play an important role in autoimmunity and might explain the differences in immune response observed in in vivo studies of Sphk1 modulation.

Biglycan- and Sphingosine Kinase-1 Signaling Crosstalk Regulates the Synthesis of Macrophage Chemoattractants

“…There are extensive studies, which show promoting effects of SphK1 on LPS- [20,23,42] and Mycobacterium smegmatis -triggered [43] expression of pro-inflammatory cytokines. Moreover, LPS cooperates with S1P to augment the expression of adhesion molecules and pro-inflammatory modulators [44].…”

Nuclear Translocation of SGPP-1 and Decrease of SGPL-1 Activity Contribute to Sphingolipid Rheostat Regulation of Inflammatory Dendritic Cells

“…Isolation, differentiation, and stimulation of bone marrow cells were performed as described before [ 2 ]. In brief, female C57BL/6 wild-type mice (Janvier, Saint-Berthevin Cedex, France) were used.…”

“…Besides its migratory effects, S1P importantly contributes to inflammatory processes by intracellular signaling [ 1 ]. Its production, metabolism, and transportation define the sphingolipid rheostat which plays a critical role in dendritic cell (DC) survival as well as cytokine secretion and antigen capture [ 2 – 4 ]. S1P can function intracellularly as a second messenger or be secreted out of the cell and act extracellularly by signaling through S1P receptors in autocrine and paracrine manners.…”

“…We and others demonstrated that high extracellular concentrations of S1P lead to the differentiation of DC populations producing less IL-12p70 after TLR4 stimulation [ 3 , 5 ] and a limited capacity to initiate Th1 responses [ 6 ]. Deletion of one major S1P-producing enzyme sphingosine kinase 1 (Sphk1) in dendritic cells leads to a reduction of cell survival and metabolic activity [ 2 ].…”

“…Despite the obvious importance of S1P-degrading pathways, only a sparse set of investigations focuses on S1P phosphatases during cellular differentiation and cancer, with actually no study dealing with SGPP-1 in immune cells. Previously, we have described a dominant loss of S1P upon TLR activation on dendritic cells [ 2 ]. Thus, in this consecutive study, we investigated S1P dephosphorylating enzyme SGPP-1 and the terminally degrading enzyme SGPL-1, as well as other possible mechanisms to reduce intracellular S1P levels in inflammatory dendritic cells.…”