Polychlorinated Biphenyl–Induced Reduction of Dopamine Transporter Expression as a Precursor to Parkinson's Disease–Associated Dopamine Toxicity

Abstract

Epidemiological and laboratory studies have suggested that exposure to polychlorinated biphenyls (PCBs) may be a risk factor for Parkinson's disease. The purpose of this study was to examine the potential mechanisms by which PCBs may disrupt normal functioning of the nigrostriatal dopamine (DA) system. We utilized an environmentally relevant exposure of PCBs (7.5 or 15 mg/kg/day Aroclor 1,254:1,260 for 30 days by oral gavage) to identify early signs of damage to the DA system. This dosing regimen, which resulted in PCB levels similar to those found in human brain samples, did not cause overt degeneration to the DA system as shown by a lack of change in striatal DA levels or tyrosine hydroxylase levels. However, we did observe a dramatic dose-dependent decrease in striatal dopamine transporter (DAT) levels. The observed reductions appear to be specific to the DAT populations located in the striatum, as no change was observed in other dopaminergic brain regions or to other neurotransmitter transporters present in the striatum. These data demonstrate that PCB tissue concentrations similar to those found in postmortem human brain specifically disrupt DA transport, which acts as a precursor to subsequent damage to the DA system. Furthermore, DAT imaging may be useful in evaluating alterations in brain function in human populations exposed to PCBs.

Reduced Vesicular Storage of Dopamine Causes Progressive Nigrostriatal Neurodegeneration

“…Western blots were used to quantify the amount of dopamine transporter (DAT), manganese superoxide dismutase (MnSOD), 3-nitrotyrosine (3-NT), tyrosine hydroxylase (TH), VMAT2, and ␣-tubulin present in samples of striatal tissue and were performed as described previously (Caudle et al, 2006). Briefly, striata samples were homogenized and subjected to PAGE and electrophoretically transferred to polyvinylidene difluoride membranes.…”

“…Tissue staining was performed as described previously (Miller et al, , 1999bCaudle et al, 2006). Briefly, VMAT2 wild-type and hypomorph mice were perfused transcardially with 4% paraformaldehyde.…”

“…Dopamine uptake studies were performed as described previously (Caudle et al, 2006). Briefly, crude synaptosomes were prepared from fresh striatal tissue and incubated in assay buffer (4 mM Tris, 6.25 mM HEPES, 120 mM NaCl, 5 mM KCl, 1.2 mM CaCl2, 1.2 mM MgSO 4 , 0.6 mM ascorbic acid, 5.5 mM glucose, 10 M pargyline, pH 7.4) containing a saturating concentration of dopamine (1 M final concentration) and a tracer amount of […”

“…After determination of protein concentrations (Bradford, 1976), uptake rates were calculated as pmol/min Ϫ mg protein and expressed as raw values. (Caudle et al, 2006). Binding studies with crude striatal synaptosomes were conducted with a single concentration (10 nM) of [ 3 H] WIN 35,428 in 25 mM sodium phosphate buffer (125 mM NaCl, 5 mM KCl, pH 7.4) for 1 h at 4°C in 96-well plates.…”

Synaptic vesicle glycoprotein 2C (SV2C) modulates dopamine release and is disrupted in Parkinson’s disease

“…Brains were sectioned to 40µm. Staining was conducted as described previously (60,63), except that all washes and dilutions were conducted in PBS with 0.2% Triton X-100. Immunoprecipitation of SV2C and α-synuclein: Coimmunoprecipitation experiments were performed using the Pierce Co-Immunoprecipitation Kit (Thermo Scientific) according to manufacturer's protocols.…”