AhR-Mediated Effects of Dioxin on Neuronal Acetylcholinesterase Expression in Vitro

Abstract

Background: Deficits in cognitive functioning have been reported in humans exposed to dioxins and dioxin-like compounds. Evidence suggests that dioxins induce cholinergic dysfunction mediated by hypothyroidism. However, little is known about direct effects of dioxins on the cholinergic system.Objectives: We investigated the action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on acetylcholinesterase (AChE), a key enzyme in cholinergic neurotransmission.Methods: We used SK-N-SH human-derived neuronal cells to evaluate the effect of dioxin exposure on AChE.Results: We consistently found a significant decrease in enzymatic activity of AChE in cultured neurons treated with TCDD. We also found that, unlike organophosphate pesticides that directly act on the catalytic center of AChE, the suppressive effect of dioxin was through transcriptional regulation. The addition of CH223191, an inhibitor of the aryl hydrocarbon receptor (AhR)-dependent pathway, counteracted the TCDD-induced suppression of AChE, suggesting involvement of the AhR-dependent pathway. The existence of putative dioxin-responsive element (DRE) consensus sequences in the human ACHE promoter region further supported this hypothesis. Consistent with the absence of DRE elements in mouse or rat ACHE promoter regions, suppression of AChE by TCDD did not occur in rat neuronal cells, indicating a potential species-specific effect.Conclusions: In SK-N-SH cells, dioxin suppressed the activity of neuronal AChE via AhR-mediated transcriptional down-regulation. This is the first study to report direct interference by dioxin with the cholinergic neurotransmission system.

Dioxin and Dioxin-Like Compounds Suppress Acetylcholinesterase Activity via Transcriptional Downregulations In Vitro

“…In this study, we showed that similar to dioxin (Xie et al 2013), DLCs decreased the enzymatic activity of neuronal AChE in SK-N-SH cells (Fig 1). Based on our previous study and the well-accepted transcriptional action mechanism of dioxin via DRE, we examined the alterations in promoter activity of ACHE upon DLC exposures to further explore the action mechanism.…”

“…Our previous study has shown that 2,3,7,8-TCDD (10 −10 to 10 −9 M) could decrease AChE enzymatic activity in neurons (Xie et al 2013). Similarly, the present findings showed that exposure to DLCs, including polychlorinated dibenzo-p-dioxins, furans, and polybrominated dibenzo-p-dioxins with TEQs equivalent to 10 −10 to 10 −9 M of 2,3,7,8-TCDD could also reduce the enzymatic activity of AChE (Fig.…”

“…Our previous study has shown that 2, 3,7,3,7,, the most potent congener among dioxins, could decrease the enzymatic activity of AChE via aryl hydrocarbon receptor (AhR)-mediated transcriptional downregulation in human neuronal cells. Such results indicate that dioxins may interfere with the cholinergic function via AChE (Xie et al 2013).…”

“…V Total reaction volume in milliliter ε The molar extinction coefficient for the product, 5-thio-2-nitrobenzoate, ε =1.36×10 4 L/mol/cm (Ellman et al 1961) L Light path length measured in centimeters, L =0.8 cm Reporter Gene Construction, Transfection, and Luciferase Activity Determination pAChE-Luc and the mutated construct, pAChE-M-Luc (derived from pAChE-Luc), with mutated sequence on the 5′ putative DRE site were constructed as in Xie et al (2013). The cells were seeded in 96-well plates at 10,000 cells/well 24 h before transient transfection using PolyJet TM reagent following the manufacturer's instructions (SignaGen Laboratories, Rockville, MD, USA).…”

New perspectives for multi-level regulations of neuronal acetylcholinesterase by dioxins

“…Our previous work demonstrated that dioxin decreased AChE activity by transcriptional suppression of the AChE T subunit, a major variant of AChE transcript in the nervous system, in SK-N-SH human neuroblastoma cells: this suppression was mediated via AhR-dependent pathway [10]. This transcriptional alteration of AChE led to a decrease in the protein expression, which consequently caused the decrease in AChE enzymatic activity [10].…”