Uncoupling of ATP-Mediated Calcium Signaling and Dysregulated Interleukin-6 Secretionin Dendritic Cells by Nanomolar Thimerosal

Abstract

Dendritic cells (DCs), a rare cell type widely distributed in the soma, are potent antigen-presenting cells that initiate primary immune responses. DCs rely on intracellular redox state and calcium (Ca2+) signals for proper development and function, but the relationship between these two signaling systems is unclear. Thimerosal (THI) is a mercurial used to preserve vaccines and consumer products, and is used experimentally to induce Ca2+ release from microsomal stores. We tested adenosine triphosphate (ATP)-mediated Ca2+ responses of DCs transiently exposed to nanomolar THI. Transcriptional and immunocytochemical analyses show that murine myeloid immature DCs (IDCs) and mature DCs (MDCs) express inositol 1,4,5-trisphosphate receptor (IP3R) and ryanodine receptor (RyR) Ca2+ channels, known targets of THI. IDCs express the RyR1 isoform in a punctate distribution that is densest near plasma membranes and within dendritic processes, whereas IP3Rs are more generally distributed. RyR1 positively and negatively regulates purinergic signaling because ryanodine (Ry) blockade a) recruited 80% more ATP responders, b) shortened ATP-mediated Ca2+ transients > 2-fold, and c) produced a delayed and persistent rise (≥ 2-fold) in baseline Ca2+. THI (100 nM, 5 min) recruited more ATP responders, shortened the ATP-mediated Ca2+ transient (≥ 1.4-fold), and produced a delayed rise (≥ 3-fold) in the Ca2+ baseline, mimicking Ry. THI and Ry, in combination, produced additive effects leading to uncoupling of IP3R and RyR1 signals. THI altered ATP-mediated interleukin-6 secretion, initially enhancing the rate of cytokine secretion but suppressing cytokine secretion overall in DCs. DCs are exquisitely sensitive to THI, with one mechanism involving the uncoupling of positive and negative regulation of Ca2+ signals contributed by RyR1.

Mycobacterial and mouse HSP70 have immuno-modulatory effects on dendritic cells

“…In addition, production of the anti-inflammatory cytokine IL-10 did not reach levels above detection limit after HSP70 treatment. The increased IL-6 production after HSP70 treatment was not caused by contaminants like endotoxins or nucleotides (Bendz et al 2008;Goth et al 2006;Takeuchi et al 1999). BMDC treatment with proteinase K-digested Mtor mouse HSP70 in order to degrade the protein but not the possible contaminants, showed no increased IL-6 secretion compared to untreated BMDC.…”

Sensitization effect of thimerosal is mediated in vitro via reactive oxygen species and calcium signaling

“…Indeed, a change in redox glutathione (GSH/GSSG) imbalance caused by sensitizers was reported to play a crucial role in triggering DC maturation (Kantengwa et al, 2003;Mizuashi et al, 2005;Yamada et al, 2006). However, although DC maturation was recently reported to be relevant to reactive oxygen species (ROS) and in particular to thiol groups (Rutault et al, 1999;Bruchhausen et al, 2003;Becker et al, 2003;Hirota et al, 2009;Suzuki et al, 2009;Kagatani et al, 2010), few studies have investigated the direct effect of thimerosal on DCs (Goth et al, 2006;Agrawal et al, 2007;Trompezinski et al, 2008). The aim of this study was to identify more accurately the role of oxidative stress induced by thimerosal and mercury derivatives in U937 activation (CD86 overexpression and interleukin (IL)-8 secretion) through the measurement of glutathione (GSH) depletion and ROS.…”

Ca2+ signaling through ryanodine receptor 1 enhances maturation and activation of human dendritic cells

“…These effects are unveiled when subthreshold concentrations of LPS are used. DCs express both IP 3 R and RyR1 intracellular Ca 2+ channels (Hosoi et al, 2001;Stolk et al, 2006;Goth et al, 2006) and the involvement of Ca 2+ -dependent signaling events in their activation has been clearly established. In fact, (1) treatment of human iDCs with the Ca 2+ ionophore A23187 induces upregulation of major histocompatibility complex (MHC) and costimulatory molecules and CD83 expression (Czerniecki et al, 1997) and activates the transcription of IL23A (this study), and (2) promotes T-cell activation (Faries et al, 2001).…”