Zinc induced apoptotic death of mouse dendritic cells

Zinc ions (Zn(2+)) are food components with favourable effects in infectious disease. Zn(2+) is taken up into dendritic cells (DCs), key players in the regulation of innate and adaptive immunity. In other cell types, Zn(2+) has been shown to stimulate the formation of ceramide, which is in turn known to trigger suicidal cell death. The present study explored whether Zn(2+) modifies ceramide formation and survival of bone marrow derived DCs. To this end, DCs were isolated from acid sphingomyelinase knockout (asm (-/-)) and corresponding wild type (asm (+/+)) mice and treated with different concentrations of Zn(2+). Ceramide formation was assessed with anti-ceramide antibodies in FACS and immunohistochemical analysis, sub-G1 cell population by FACS analysis, break down of phosphatidylserine asymmetry by annexin V binding, cell death by propidium iodide incorporation, metabolic cell activity by MTT assay, ROS production from dichlorofluorescein fluorescence and activation of MAPKs by Western blotting. The treatment of asm (+/+) DCs with low Zn(2+) concentrations (up to 100 μM) was followed by ceramide formation, increase in sub-G1 cell population and phosphatidylserine exposure, effects blunted in asm (-/-) DCs. The treatment of DCs with C2-ceramide increased the percentage of sub-G1 and apoptotic DCs from both genotypes. Zn(2+) led to similar activation of MAPKs in asm (+/+) and asm (-/-) DCs and did not affect ROS production. Higher concentrations of Zn(2+) led to a marked increase of propidium iodide incorporation in DCs of both genotypes. The present study reveals that in DCs Zn(2+) triggers ceramide formation, which in turn compromises cell survival.