Zinc induced apoptotic death of mouse dendritic cells

Zinc ions (Zn²⁺) are food components with favourable effects in infectious disease. Zn²⁺ is taken up into dendritic cells (DCs), key players in the regulation of innate and adaptive immunity. In other cell types, Zn²⁺ has been shown to stimulate the formation of ceramide, which is in turn known to trigger suicidal cell death. The present study explored whether Zn²⁺ 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 Zn²⁺. 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 Zn²⁺ 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. Zn²⁺ led to similar activation of MAPKs in asm ^+/+ and asm ^−/− DCs and did not affect ROS production. Higher concentrations of Zn²⁺ led to a marked increase of propidium iodide incorporation in DCs of both genotypes. The present study reveals that in DCs Zn²⁺ triggers ceramide formation, which in turn compromises cell survival.