Structure, expression and regulation of the cannabinoid receptor gene (CB1) in Huntington's disease transgenic mice

Abstract

Loss of cannabinoid receptors (CB1) occurs prior to neurodegeneration in Huntington's disease (HD). The levels and distribution of CB1 RNA were equivalent in 3-week-old mice regardless of genotype demonstrating that the specific factors and appropriate chromatin structure that lead to the transcription of CB1 were present in the striatum of young R6/2 and R6/1 transgenic HD mice. The expression of the mutant HD transgene led progressively to decreased steadystate levels of CB1 mRNA in neurons of the lateral striatum, which was dependent on the size of the CAG repeat and relative expression of the gene encoding mutant huntingtin (HD). Although it is known that the coding region of CB1 is contained within a single exon in mice, rats and humans, the 5¢-untranslated region of the mouse gene remained to be defined. CB1 mRNA is encoded by two exons separated by an 18.4-kb intron. Transcription of CB1 occurred at multiple sites within a GC-rich promoter region upstream of exon 1 encoding the 5¢-UTR of CB1. There was no difference in the selection of specific transcription initiation sites associated with higher levels of CB1 expression in the striatum compared to the cortex or between the striata of wild-type and HD transgenic mice. The progressive decline in CB1 mRNA levels in R6 compared to wild-type mice was due to decreased transcription, which is consistent with the hypothesis that mutant huntingtin exerts its effects by altering transcription factor activity. The cell-specific conditions that allow for increased transcription of CB1 in the lateral striatum compared to other forebrain regions from all transcription start sites were affected by the expression of mutant huntingtin in a time-dependent manner.Keywords: mutant huntingtin; striatum; transcription initiation sites; quantitative PCR.Huntington's disease (HD) is a progressive neurodegenerative disorder, characterized by a decline in motor function and cognition, as well as the development of psychiatric symptoms [1]. HD develops when an individual inherits one copy of the HD gene with an extended polyglutamineencoding CAG repeat [2]. The number of CAG repeats is inversely correlated with the age of onset of the disorder [3]. The extended polyglutamine tract in mutant huntingtin confers an abnormal function that ultimately causes neurodegeneration of a subpopulation of cells in the basal ganglia. In addition, a reduction in the level of normal huntingtin may also be detrimental to the survival and function of neurons [4,5].One of the earliest known changes in human HD patients is the loss of cannabinoid receptors [6]. Immunohistochemistry and radio-ligand binding assays of postmortem human brains at different ages and stages of HD have demonstrated that CB1 receptors decrease on nerve terminals in the globus pallidus [7] and substantia nigra [6,8] prior to cell loss. Similarly, CB1 mRNA levels decline in the striatum of transgenic HD mice [8,9]. The mechanism by which mutant huntingtin causes changes in CB1 mRNA levels has not yet been determined and it is ...

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

“…Early in HD progression, levels of type 1 cannabinoid receptor (CB 1 ) mRNA and protein decrease in medium spiny projection neurons of the caudate and putamen (Denovan-Wright and Robertson, 2000;Glass et al, 2000;Van Laere et al, 2010). CB 1 transcription is inhibited by mHtt (McCaw et al, 2004;Laprairie et al, 2013). The reduction in CB 1 and loss of CB 1 function have been shown to contribute to the cognitive, behavioral, and motor deficits of HD pathology in animal models of HD (Blázquez et al, 2011;2015;Chiarlone et al, 2014).…”

Transcriptional Regulation of Cannabinoid Receptor-1 Expression in the Liver by Retinoic Acid Acting via Retinoic Acid Receptor-γ

“…Core consensus sequences of transcription factor binding sites, including an RAR element, have been mapped in the mouse CB 1 R promoter (32). However, direct evidence for their role in transcriptional regulation has not been explored, with the exception of the STAT6 sequence S2, which was shown to be involved in the interleukin-4-inducible expression of CB 1 R in T lymphocytes (33).…”

A restricted population of CB 1 cannabinoid receptors with neuroprotective activity

“…This devastating disease constitutes so far the best paradigm to study the specific role of CB 1 receptors located on glutamatergic or GABAergic terminals because CB 1 receptors are expressed in the striatum at synapses established by neurons containing GABA (especially MSNs, the cells that primarily degenerate in HD) or glutamate (especially corticostriatal projecting neurons, which critically control MSN function) as transmitters, and play a key role in the control of motor behavior, one of the processes that is most typically affected in HD (11,12). Moreover, a remarkable down-regulation of CB 1 receptors has been documented as one of the earliest and most characteristic neurochemical alterations found in the MSNs of HD animal models (13,14) and patients with HD (15,16). In striking contrast, CB 1 receptors located on glutamatergic terminals are fully preserved in (i) the striatum of symptomatic R6/2 mice (17) (Fig.…”