Cannabis Users Show Enhanced Expression of CB1-5HT2A Receptor Heteromers in Olfactory Neuroepithelium Cells

Abstract

Cannabinoid CB1 receptors (CBR) and serotonergic 2A receptors (5HTR) form heteromers in the brain of mice where they mediate the cognitive deficits produced by delta-9-tetrahydrocannabinol. However, it is still unknown whether the expression of this heterodimer is modulated by chronic cannabis use in humans. In this study, we investigated the expression levels and functionality of CBR-5HTR heteromers in human olfactory neuroepithelium (ON) cells of cannabis users and control subjects, and determined their molecular characteristics through adenylate cyclase and the ERK 1/2 pathway signaling studies. We also assessed whether heteromer expression levels correlated with cannabis consumption and cognitive performance in neuropsychological tests. ON cells from controls and cannabis users expressed neuronal markers such as βIII-tubulin and nestin, displayed similar expression levels of genes related to cellular self-renewal, stem cell differentiation, and generation of neural crest cells, and showed comparable Na currents in patch clamp recordings. Interestingly, CBR-5HTR heteromer expression was significantly increased in cannabis users and positively correlated with the amount of cannabis consumed, and negatively with age of onset of cannabis use. In addition, a negative correlation was found between heteromer expression levels and attention and working memory performance in cannabis users and control subjects. Our findings suggest that cannabis consumption regulates the formation of CBR-5HTR heteromers, and may have a key role in cognitive processing. These heterodimers could be potential new targets to develop treatment alternatives for cognitive impairments.

Modulatory effects of cannabinoids on brain neurotransmission

“…Recently, Galindo et al . () presented evidence that cognitive function impairment that have been found among cannabis users, have been associated with an increased expression of CB 1 ‐5‐HT 2A receptors heteromer. Moreover, this alteration was positively correlated with the amount of cannabis consumed and negatively with the age of onset of cannabis use.…”

“…An impaired activity of cortical 5-HT 2A has been observed in several neurological and psychopathologies such as Alzheimer's disease, depression, anxiety, addiction, and schizophrenia (Nacmias et al, 2001;Meltzer et al, 2003;Bubar & Cunningham, 2006). Interestingly, several human studies have provided evidence for an association between specific 5-HT receptors and 5-HT transporter gene polymorphisms and cannabis user (Ewing et al, 2012;Verdejo-Garc ıa et al, 2013;Galindo et al, 2018). Variations of 5-HT receptor allele have been found to affect treatment responsiveness in adolescent cannabis users who seek psychosocial treatment.…”

“…They have found that in short allele carriers, but not in non-carriers, cannabis use has been positively associated with higher levels of anxiety symptoms, suggesting that interplay between the regulation of 5-HT functioning and cannabis use may underlie some of the adverse effects associated with cannabis use (Otten et al, 2017). Recently, Galindo et al (2018) presented evidence that cognitive function impairment that have been found among cannabis users, have been associated with an increased expression of CB 1 -5-HT 2A receptors heteromer. Moreover, this alteration was positively correlated with the amount of cannabis consumed and negatively with the age of onset of cannabis use.…”

Dimers of serotonin receptors: Impact on ligand affinity and signaling

“…The relation between the amnesic effects of THC and heterodimers is also supported by a human study comparing cannabis users and non-users. Although the acute effect of cannabis on memory was not directly addressed in this study, the authors observed a positive correlation between the amount of heterodimers in primary cell cultures from the subjects and their consumption of cannabis, and a negative correlation with their memory performance [71]. In contrast, some of the effects of CB1 receptors agonists, which are therapeutically interesting like their antinociceptive effects, are preserved in Htr2a -/mice and not inhibited by heterodimerization-blocking peptides in wild-type mice, indicating that they do not require heterodimerization of CB1 with 5-HT 2A receptors [28].…”

“…The Gi/o-coupled CB1 and Gq-coupled 5-HT 2A receptors are both expressed in specific brain regions involved in emotion and memory, and it has been shown that the amnesic and anxiolytic effects of the CB1 receptor agonist delta9-tetrahydrocannabinol (THC) require the presence of Gq-coupled 5-HT 2A receptors. These functional interactions seem to be related to the existence of heterodimers that have been detected in an exhaustive study using several combined techniques including BRET saturation, PLA verified in knockout animals, bimolecular complementation assays, both in-vivo, in behavioral tests, and in transfected cell lines [28] or in ex-vivo primary cultures of human olfactory epithelial cells [71]. Functionally, pharmacological data on CB1-5-HT 2A heterodimers support the existence of a switch in 5-HT 2A -receptor coupling from Gq to Gi/o proteins (thus agonists for any of the two receptors will inhibit cAMP production) and of an antagonist transinhibition (antagonist binding to one receptor blocks signaling of the other receptor) (Figure 3 Right) [28].…”