| Gene Symbol | HTR6 |
|---|---|
| Full Name | 5-Hydroxytryptamine Receptor 6 |
| Chromosome | 1p35.3 |
| NCBI Gene ID | [3362](https://www.ncbi.nlm.nih.gov/gene/3362) |
| OMIM | [604111](https://www.omim.org/entry/604111) |
| Ensembl ID | [ENSG00000158708](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000158708) |
| UniProt ID | [P50406](https://www.uniprot.org/uniprot/P50406) |
| Protein Class | G protein-coupled receptor (GPCR) |
| Protein Size | 440 amino acids (~46 kDa) |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), Schizophrenia, Parkinson's Disease, Epilepsy |
| Expression | CNS (brain), primarily cortex and hippocampus |
The HTR6 gene (5-Hydroxytryptamine Receptor 6) encodes the 5-HT6 receptor, a G protein-coupled receptor (GPCR) primarily expressed in the central nervous system. The 5-HT6 receptor has attracted significant interest as a therapeutic target for cognitive disorders, particularly Alzheimer's disease and schizophrenia, due to its role in modulating neurotransmitter release and neuronal signaling in brain regions critical for learning and memory [1][2].
The 5-HT6 receptor was first cloned in 1993 and represents one of the more recently identified serotonin receptor subtypes. Like all serotonin receptors, it belongs to the GPCR superfamily, characterized by seven transmembrane domains that signal through Gs proteins to stimulate adenylate cyclase activity. This signaling cascade ultimately leads to increased cAMP levels and activation of downstream effectors including protein kinase A (PKA) and the cAMP response element-binding protein (CREB).
The receptor's brain distribution is largely restricted to the central nervous system, with highest expression in brain regions associated with learning and memory, including the hippocampus and cerebral cortex. This localization, combined with its signaling properties, makes the 5-HT6 receptor an attractive target for cognitive enhancement strategies [3][4].
The HTR6 gene is located on chromosome 1p35.3 and encodes a 440-amino acid protein. Like other serotonin receptors, 5-HT6 contains seven transmembrane domains, an extracellular N-terminus, and an intracellular C-terminus. The receptor couples preferentially to Gs proteins, stimulating adenylate cyclase activity and increasing intracellular cAMP levels.
5-HT6 receptors show highest expression in:
The receptor is almost exclusively neuronal, expressed on both glutamatergic and GABAergic neurons where it modulates neurotransmitter release and neuronal excitability.
The 5-HT6 receptor has emerged as a promising target for cognitive enhancement in AD [5][6][7]:
The failed clinical trials of idalopirdine and intepirdine in 2016-2018 highlighted the challenges of translating preclinical findings to human cognitive benefits. However, research continues on alternative approaches including combination therapies and biased agonists.
5-HT6 receptors are implicated in both motor and non-motor symptoms of PD [8]:
Multiple 5-HT6 ligands have been developed:
| Drug | Type | Development Status | Notes |
|---|---|---|---|
| Idalopirdine | Antagonist | Phase III (completed) | Failed to meet endpoints |
| Intepirdine | Antagonist | Phase III (completed) | Failed to meet endpoints |
| SAM-760 | Antagonist | Phase II | Cognitive enhancement |
| PRX-07034 | Antagonist | Phase I/II | Cognitive enhancement |
Woolley ML, Marsden CA, Fone KC. 5-HT6 receptors. Curr Drug Targets CNS Neurol Disord. 2004. ↩︎
Holenz J, et al. 5-HT6 receptor pharmacology. Pharmacol Ther. 2005. ↩︎
Meneses A. 5-HT6 receptors and learning. Behav Brain Res. 2007. ↩︎
Ramirez MJ. 5-HT6 receptors and cognitive dysfunction. Curr Opin Pharmacol. 2013. ↩︎
Garcia-Alloza M, Hirst WD, Chen CP, et al. 5-HT6 receptor antagonism facilitates amyloidogenic processing of APP. J Neurochem. 2011. ↩︎
Geldenhuys WJ, et al. 5-HT6 receptors in Alzheimer's disease. Neurochem Res. 2019. ↩︎
Maher-Edwards G, Zvartau-Hind M, Hunter AJ, et al. Idalopirdine (Lu AE58054): a phase 3 clinical study for Alzheimer's disease. J Prev Alzheimers Dis. 2015. ↩︎
Dayer AG, et al. 5-HT6 receptors in Parkinson's disease. Mov Disord. 2018. ↩︎
Codony X, et al. 5-HT6 receptor ligands as cognitive enhancers. Prog Med Chem. 2011. ↩︎
Hume R, et al. 5-HT6 receptor inverse agonists for obesity. J Med Chem. 2013. ↩︎