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

摘要

Dendritic cells (DCs), a rare cell type widely distributed in the soma, arepotent antigen-presenting cells that initiate primary immune responses. DCsrely on intracellular redox state and calcium (Ca2+) signals for proper development and function, but the relationship betweenthese two signaling systems is unclear. Thimerosal (THI) is a mercurialused to preserve vaccines and consumer products, and is used experimentallyto induce Ca2+ release from microsomal stores. We tested adenosine triphosphate (ATP)-mediatedCa2+ responses of DCs transiently exposed to nanomolar THI. Transcriptionaland immunocytochemical analyses show that murine myeloid immature DCs (IDCs) andmature 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 punctatedistribution that is densest near plasma membranes and within dendriticprocesses, whereas IP3Rs are more generally distributed. RyR1 positively and negatively regulatespurinergic 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 baselineCa2+. THI (100 nM, 5 min) recruited more ATP responders, shortened the ATP-mediatedCa2+ transient (≥ 1.4-fold), and produced a delayed rise (≥ 3-fold) inthe Ca2+ baseline, mimicking Ry. THI and Ry, in combination, produced additiveeffects leading to uncoupling of IP3R and RyR1 signals. THI altered ATP-mediated interleukin-6 secretion, initiallyenhancing the rate of cytokine secretion but suppressing cytokinesecretion overall in DCs. DCs are exquisitely sensitive to THI, withone mechanism involving the uncoupling of positive and negative regulationof Ca2+ signals contributed by RyR1.