Downregulation of cannabinoid receptor 1 from neuropeptide Y interneurons in the basal ganglia of patients with Huntington's disease and mouse models

Abstract

Cannabinoid receptor 1 (CB1 receptor) controls several neuronal functions, including neurotransmitter release, synaptic plasticity, gene expression and neuronal viability. Downregulation of CB1 expression in the basal ganglia of patients with Huntington’s disease (HD) and animal models represents one of the earliest molecular events induced by mutant huntingtin (mHtt). This early disruption of neuronal CB1 signaling is thought to contribute to HD symptoms and neurodegeneration. Here we determined whether CB1 downregulation measured in patients with HD and mouse models was ubiquitous or restricted to specific striatal neuronal subpopulations. Using unbiased semi-quantitative immunohistochemistry, we confirmed previous studies showing that CB1 expression is downregulated in medium spiny neurons of the indirect pathway, and found that CB1 is also downregulated in neuropeptide Y (NPY)/neuronal nitric oxide synthase (nNOS)-expressing interneurons while remaining unchanged in parvalbumin- and calretinin-expressing interneurons. CB1 downregulation in striatal NPY/nNOS-expressing interneurons occurs in R6/2 mice, HdhQ150/Q150 mice and the caudate nucleus of patients with HD. In R6/2 mice, CB1 downregulation in NPY/nNOS-expressing interneurons correlates with diffuse expression of mHtt in the soma. This downregulation also occludes the ability of cannabinoid agonists to activate the pro-survival signaling molecule cAMP response element-binding protein in NPY/nNOS-expressing interneurons. Loss of CB1 signaling in NPY/nNOS-expressing interneurons could contribute to the impairment of basal ganglia functions linked to HD.

Biased Type 1 Cannabinoid Receptor Signaling Influences Neuronal Viability in a Cell Culture Model of Huntington Disease

“…*P , 0.01 compared with vehicle-treated cells within cell type, †P , 0.01 compared with STHdh Q7/Q7 cells within treatment group, as determined using two-way ANOVA followed by Bonferroni post-hoc analysis. data provide support for Ga i/o -and Gbg-selective activation of CB 1 to maintain CB 1 levels and the cellular function and viability of cells expressing mHtt (Blázquez et al, 2011(Blázquez et al, , 2015Mievis et al, 2011;Horne et al, 2013;Chiarlone et al, 2014;Naydenov et al, 2014).…”

“…Recently, three studies have demonstrated that increasing CB 1 levels in medium spiny projection neurons in the R6/2 mouse model of HD via adenovirus-mediated overexpression normalizes brain-derived neurotrophic factor levels, reduces striatal atrophy, and prevents decreases in dendritic spine density and levels of excitatory synaptic markers, such as synaptophysin and vesicular glutamate transporter, but does not improve deficits in motor coordination (Chiarlone et al, 2014;Naydenov et al, 2014;Blázquez et al, 2015). In accordance with this, knockdown or knockout of CB 1 in medium spiny projection neurons of R6/2, N171-82Q, or Hdh Q150/Q150 HD mice further reduces the pool of CB 1 and exacerbates deficits in motor control, enhances striatal atrophy, and reduces survival (Blázquez et al, 2011;Mievis et al, 2011;Horne et al, 2013). Further, individuals with HD and a variant of the CB 1 gene (CNR1 rs4707436) that is associated with lower levels of CB 1 begin displaying motor-related symptoms of HD earlier than individuals with HD and normal CNR1 (Kloster et al, 2013).…”

ABHD6 Blockade Exerts Antiepileptic Activity in PTZ-Induced Seizures and in Spontaneous Seizures in R6/2 Mice

“…Staining was performed as described in Horne et al (Horne et al, 2012). Images were collected on a Leica SP1 Confocal Laser Scanning microscope with a 63x oil objective, and on an Olympus Fluoview-1000 Confocal microscope equipped with an automated stage and a 20x air or 63X oil objective.…”

“…Images were analyzed using automated macros in a Fiji distribution of ImageJ (Schindelin et al, 2012). Thresholding was performed to remove background staining (threshold = mean+SD for all stains except NPY, threshold=mean+2*SD for NPY), and mean intensity of remaining pixels was calculated, a method we have previously validated (Horne et al, 2012). …”

“…Specifically, R6/2 mice display both spontaneous and audiogenic seizures (Cepeda-Prado et al, 2012; Mangiarini et al, 1996) and reproduce the profound dysregulation of eCB signaling described in Huntington's disease (HD) patients (Bisogno et al, 2008; Centonze et al, 2005). R6/2 mice have both decreased 2-AG availability (Bisogno et al, 2008) and CB 1 receptor down-regulation in select neuronal populations (Dowie et al, 2009; Glass et al, 2000; 1993; Horne et al, 2012). Here too, we hypothesized that ABHD6 inhibition would prevent spontaneous seizures in R6/2 mice by augmenting 2-AG signaling.…”