Neuronal activity enhances aryl hydrocarbon receptor‐mediated gene expression and dioxin neurotoxicity in cortical neurons

Abstract

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that belongs to the basic helix-loop-helix/ Per-Arnt-Sim transcription factor superfamily (reviewed by Rowlands and Gustafsson 1997;Hahn 1998 ] i , intracellular calcium concentration; AhR, aryl hydrocarbon receptor; ARNT, aryl hydrocarbon receptor nuclear translocator; BME, basal medium Eagles; CaMK, calcium/calmodulindependent protein kinase; CBP, cAMP-responsive-element binding protein; ChIP, chromatin immunoprecipitation; CYP1A1, cytochrome P450 1A1; DCF, 2,7-dichlorodihydrofluorescein; DIV, days in vitro; DRE, dioxin-responsive elements; FBS, fetal bovine serum; fura-2AM, fura-2 acetoxymethyl ester; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; LDH, lactate dehydrogenase; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NMDA-R, NMDA receptor; PBS, phosphate-buffered saline; ROS, reactive oxygen species; SD, Sprague-Dawley; siAhR, AhR small interfering RNA; siRNA, small interfering RNA; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; TTX, tetrodotoxin. AbstractThe aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor activated by dioxin and polyaromatic hydrocarbons. Recent studies have revealed that AhR activity in central neurons depends on the NMDA receptor. In this study, we investigated how the neuronal activity influence AhR-mediated dioxin-responsive gene expression and neurotoxicity. Our results show that activation of AhR by the selective agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin induced dioxin-responsive gene expression and calcium entry, which were attenuated by AhR small interfering RNA, the NMDA receptor channel blocker MK801, and the action potential blocker tetrodotoxin (TTX). In addition, AhR-mediated gene expression was enhanced in neurons during synaptogenesis (10 days in vitro) compared with younger neurons (4 days in vitro), as was sensitivity to TTX and MK801. Furthermore, TTX and MK801 differentially affected the association of AhR and its transcriptional co-activator cAMP-responsive-element binding protein with the cytochrome P450 1A1 (cyp1A1) gene enhancer. Calcium/calmodulin-dependent protein kinase IV, the cAMP-responsive-element binding protein activating enzyme, was also activated by 2,3,7,8-tetrachlorodibenzop-dioxin in an activity-dependent manner. Finally, we found that neuronal susceptibility to dioxin insult was also maturation and activity-dependent. Together, the results suggest that neuronal activity may facilitate AhR-mediated calcium signaling, which in turn enhances AhR-mediated gene regulation and mediated maturation-dependent dioxin neurotoxicity. Keywords: aryl hydrocarbon receptor, calcium/calmodulindependent protein kinase IV, CREB binding protein, neuronal activity, neuronal survival, NMDA receptor.

Activation of the Aryl Hydrocarbon Receptor by the Calcium/Calmodulin-Dependent Protein Kinase Kinase Inhibitor 7-Oxo-7H-benzimidazo[2,1-a]benz[de]isoquinoline-3-carboxylic Acid (STO-609)

“…As described for TCDD and other AhR ligands (NЈDiaye et al, 2006;Lin et al, 2008;Monteiro et al, 2008) (Monteiro et al, 2008). The exact mechanisms implicated in the phosphorylation of CaMKI␣ in response to AhR ligands remain to be determined.…”

Knockdown of the aryl hydrocarbon receptor attenuates excitotoxicity and enhances NMDA‐induced BDNF expression in cortical neurons

“…Toxicological and epidemiological studies revealed that exposure to environmental AhR ligands are associated with delayed development of brain sexual dimorphism, social behavior, learning ability, and neuropsychiatric disorders in both animal models and humans (Ikeda et al 2005;Nishijo et al 2007;Piedrafita et al 2008;Patandin et al 1999;Goetz et al 1994). Although AhR-mediated neurotoxicity has been demonstrated in various experimental systems (Kim and Yang 2005;Akahoshi et al 2006;Lin et al 2008), information were limited to its up-regulation of CYP1A1 and oxidative stress. The extent to which AhR participates in neuronal survival and plasticity remains poorly understood.…”

“…Activation of AhR by these environmental toxins leads to cytotoxicity and carcinogenesis via induction of cytochrome P450 1A1/1A2 expression that generates toxic metabolites and induces oxidative stress (Nebert et al 2004). In mammalian brains, AhR is widely expressed in the cerebral cortex, hippocampus, hypothalamus, brainstem, and cerebellum (Petersen et al 2000;Powers et al 2005;Lin et al 2008). Information regarding the physiological roles of AhR in the brain is limited.…”

Glucocorticoid Protection of Oligodendrocytes against Excitotoxin Involving Hypoxia-Inducible Factor-1 in a Cell-Type-Specific Manner

“…Chromatin immunoprecipitation assay (Lin et al, 2008). Antibodies used for immunoprecipitation were mouse anti-GR (2 g; Abcam), mouse anti-HIF-1␣ (2 g; Novus), and rabbit anti-CREB (cAMP response element-binding) protein binding protein (CBP) (2 g; Santa Cruz Biotechnology) antibodies.…”