Cannabinoid receptor agonists upregulate and enhance serotonin 2A (5‐HT_2A) receptor activity via ERK1/2 signaling

Abstract

Recent behavioral studies suggest that non-selective agonists of cannabinoid receptors may regulate serotonin 2A (5-HT2A) receptor neurotransmission. Two cannabinoids receptors are found in brain, CB1 and CB2 receptors, but the molecular mechanism by which cannabinoid receptors would regulate 5-HT2A receptor neurotransmission remains unknown. Interestingly, we have recently found that certain cannabinoid receptor agonists can specifically upregulate 5-HT2A receptors. Here, we present experimental evidence that rats treated with a non-selective cannabinoid receptor agonist (CP 55,940, 50μg/kg, 7 days) showed increases in 5-HT2A receptor protein levels, 5-HT2A receptor mRNA levels, and 5-HT2A receptor-mediated phospholipase C Beta (PLCβ) activity in prefrontal cortex (PFCx). Similar effects were found in neuronal cultured cells treated with CP 55,940 but these effects were prevented by selective CB2, but not selective CB1, receptor antagonists. CB2 receptors couple to the extracellular kinase (ERK) signaling pathway by Gαi/o class of G-proteins. Noteworthy, GP 1a (selective CB2 receptor agonist) produced a strong upregulation of 5-HT2A receptor mRNA and protein, an effect that was prevented by selective CB2 receptor antagonists and by an ERK1/2 inhibitor, PD 198306. In summary, our results identified a strong cannabinoid-induced upregulation of 5-HT2A receptor signaling in rat PFCx. Our cultured cell studies suggest that selective CB2 receptor agonists upregulate 5-HT2A receptor signaling by activation of the ERK1/2 signaling pathway. Activity of cortical 5-HT2A receptors has been associated with several physiological functions and neuropsychiatric disorders such as stress response, anxiety & depression and schizophrenia. Therefore, these results might provide a molecular mechanism by which activation of cannabinoid receptors might be relevant to the pathophysiology of some cognitive and mood disorders in humans.

Cannabinoid receptor-specific mechanisms to alleviate pain in sickle cell anemia via inhibition of mast cell activation and neurogenic inflammation

“…CP55,940, via the CB2R, was demonstrated to stimulate serotonin 2A receptor activity in the pre-frontal cortex of rats, suggesting of an influence on cognitive and mood disorders. 51 The effect of cannabinoids on neuropsychiatric conditions in SCA does, therefore, require consideration.…”

G-protein Receptor Kinase 5 Regulates the Cannabinoid Receptor 2-induced Up-regulation of Serotonin 2A Receptors

“…Here we treated cells with CP55940 for 72 h in order to assess the effect of repeated cannabinoid agonist exposure on the expression of GRKs because our previous findings show that repeated, but not single, exposure to cannabinoid agonists up-regulates 5-HT 2A receptor protein expression (1)(2)(3)(4). CP55940 treatment in these cells significantly (p Ͻ 0.01) increased GRK5 protein levels (67 Ϯ 3% increase compared with vehicle-treated controls) without significant (p Ͼ 0.05) changes in the protein levels of GRK6 (Fig.…”

“…Effect of Selective CB 1 or CB 2 Receptor Agonists on GRK5 mRNA-CLU213 cells were incubated with either vehicle (ethanol, 0.01% final concentration), GP1a 1 nM (selective CB 2 agonist, K i ϭ 0.037 and 353 nM for CB 2 and CB 1 receptors, respectively) (30), or 15 nM ACEA (selective CB 1 agonist, K i ϭ 1.4 nM and 3.1 M for CB 1 and CB 2 receptors, respectively) (31) for 72 h. Cells were washed (three times) with PBS every 24 h, and fresh vehicle, GP1a, or ACEA was added. qRT-PCR for GRK5 was performed.…”

“…Effect of GRK5 shRNA Lentivirus Transfection on Cannabinoid-induced CB 2 Receptor Phosphorylation or ␤-Arrestin 2/ERK Interaction-Cells stably transfected with control or GRK5 shRNA lentivirus particles were treated with vehicle (ethanol, 0.01% final concentration) or GP1a (1 nM) for 72 h. Cells were washed (three times) with Kreb's buffer every 24 h, and fresh vehicle or GP1a was added. Phosphorylated proteins were isolated from cells, and Western blot was used to determine the expression of phosphorylated CB 2 receptors as described above.…”

“…We have recently reported that repeated exposure to cannabinoid agonists induces a strong up-regulation and increases the activity of 5-HT 2A 2 receptors in rat prefrontal cortex (PFCx) and in two neuronal cell models (1)(2)(3)(4). This cannabinoid-mediated up-regulation of 5-HT 2A receptors was 1) induced by nonselective CB 1 /CB 2 and selective CB 2 receptor agonists (2, 4) and 2) inhibited by selective CB 2 , but not CB 1 , shRNA lentiviral particles, suggesting that CB 2 receptors mediate this phenomenon (3).…”