2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced inflammatory activation is mediated by intracellular free calcium in microglial cells

- TCDD induces inflammatory activation by increasing levels of Ca2+ in microglial cells.
- TCDD upregulates the expression and secretion of TNF-α in HAPI microglial cells.
- TCDD activates NF-κB signaling pathways in HAPI microglial cells.
- TCDD causes a rapid activation of cPLA2 and COX-2 in HAPI microglial cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been known to induce inflammatory signaling in a number of cell types and tissues. However, the adverse effects of TCDD on the central nervous system (CNS) have not been entirely elucidated. In this study, using reverse transcriptase PCR (RT-PCR) and ELISA, we showed that TCDD up-regulated the expression and secretion of tumor necrosis factor-alpha (TNF-α) in a time-dependent manner in cultured HAPI microglial cells. TCDD also caused a fast (within 30 min as judged by the increase in its mRNA level) activation of cytosolic phospholipase A2 (cPLA2). This initial action was accompanied by up-regulation of cyclooxygenase-2 (COX-2), an important inflammation marker within 1 h after TCDD treatment. These pro-inflammatory responses were inhibited by two types of Ca2+ blockers, bis-(o-aminophenoxy) ethane-N,N,N′,N′-tetra-acetic acid acetoxymethyl ester (BAPTA-AM) and nifedipine, thus, indicating that the effects are triggered by initial increase in the intracellular concentration of free Ca2+ ([Ca2+]i). Further, TCDD exposure could induce phosphorylation- and ubiquitination-dependent degradation of IкBα, and the translocation of NF-κB p65 from the cytosol to the nucleus in this microglial cell line. Thus, the NF-κB signaling pathway can be activated after TCDD treatment. However, Ca2+ blockers also obviously attenuated NF-κB activation and transnuclear transport induced by TCDD. In concert with these results, we highlighted that the secretion of pro-inflammatory cytokine and NF-κB activation induced by TCDD can be mediated by elevation of [Ca2+]i in HAPI microglial cells.