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

摘要

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 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.