Cloning and expression of the human 5-HT1B-type receptor gene

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

5-HT Receptor Nomenclature: Naming Names, Does It Matter? A Tribute to Maurice Rapport

The naming of 5-HT receptors has been challenging, especially in the early days when the concept of multiple receptors for a single neurotransmitter was considered to be unrealistic at best. Yet pharmacological (rank orders of potency in functional or biochemical settings) and transductional evidence (second messengers, electrophysiology) clearly indicated the existence of receptor families and subfamilies. The genetic revolution, with the cloning and study of recombinantly expressed receptors, and eventually the cloning of the human and other genomes have made such reservations obsolete. Further, the advances in structural biology, with the possibility to study ligand receptor complexes as crystals and/or using solution NMR have largely confirmed the complexity of the 5-HT receptor system: species differences, existence of multiple receptor active and inactive states, splice variants, editing variants, complexes with multiple interacting proteins and transduction bias. This is a short personal history on how advances in biochemistry, molecular biology, biophysics, imaging and medicinal chemistry, some lateral thinking, and a decent amount of collaborative spirit within the 5-HT receptor nomenclature committee and the 5-HT community at large have helped to better define the pharmacology of the 5-HT receptor family.

The serotonergic system in Parkinson's disease

Although the cardinal manifestations of Parkinson's disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding.

The use of serotonergic drugs to treat obesity--is there any hope?

Surgical interventional strategies for the treatment of obesity are being implemented at an increasing rate. The safety and feasibility of these procedures are questionable for most overweight or obese individuals. The use of long-term pharmacotherapy options, on the other hand, can target a greater portion of the obese population and provide early intervention to help individuals maintain a healthy lifestyle to promote weight loss. Medications that act on the central serotonergic pathways have been a relative mainstay for the treatment of obesity for the last 35 years. The clinical efficacy of these drugs, however, has been encumbered by the potential for drug-associated complications. Two drugs that act, albeit by different mechanisms, on the central serotonergic system to reduce food intake and decrease body weight are sibutramine and lorcaserin. Sibutramine is a serotonin and norepinephrine reuptake inhibitor, whereas lorcaserin is a selective 5HT_2C receptor agonist. The recent worldwide withdrawal of sibutramine and FDA rejection of lorcaserin has changed the landscape not only for serotonin-based therapeutics specifically, but for obesity pharmacotherapy in general. The purpose of this review is to focus on the importance of the serotonergic system in the control of feeding and its potential as a target for obesity pharmacotherapy. Advances in refining and screening more selective receptor agonists and a better understanding of the potential off-target effects of serotonergic drugs are needed to produce beneficial pharmacotherapy.

The effect of genetic variation of the serotonin 1B receptor gene on impulsive aggressive behavior and suicide

Impulsive-aggressive behaviors (IABs) are regarded as possible suicide intermediate phenotypes, mediating the relationship between genes and suicide outcome. In this study, we aimed to investigate the putative relationship between genetic variation at the 5-HT1B receptor gene, which in animal models is involved in impulse-aggression control, IABs, and suicide risk. We investigated the relationship of variation at five 5-HT1B loci and IAB measures in a sample of 696 subjects, including 338 individuals who died by suicide and 358 normal epidemiological controls. We found that variation at the 5-HT1B promoter A-161T locus had a significant effect on levels of IABs, as measured by the Buss-Durkee Hostility Inventory (BDHI). Suicides also differed from controls in distribution of variants at this locus. The A-161T locus, which seems to impact 5-HT1B transcription, could play a role in suicide predisposition by means of mediating impulsive-aggressive behaviors.

Depression and adipose polyunsaturated fatty acids in an adolescent group

The purpose of the present study was to investigate the relation between adipose tissue polyunsaturated fatty acids, an index of long-term or habitual fatty acid dietary intake and depression. The sample consisted of 90 adolescents from the island of Crete. There were 54 girls and 36 boys, aged 13-18. The mean age was 15.2 years. Subjects were examined by the Preventive Medicine and Nutrition Clinic of the University of Crete. Depression was assessed through the use of the Beck Depression Inventory (BDI) and the Center for Epidemiologic Studies Depression Scale (CES-D). Unlike other studies, there were no significant relations between adipose tissue n-3 or n-6 polyunsaturated fatty acids and depression. BDI correlated positively with adipose tissue C20:3n-6/C18:3n-6 ratio, while CES-D correlated positively with adipose tissue (C20:3n-6+C22:5n-3)/(C18:3n-6+C20:5n-3) ratio. Depressed subjects (BDI>16, CES-D>16) had significantly elevated adipose tissue C20:3n-6/C18:3n-6 and (C20:3n-6+C22:5n-3)/(C18:3n-6+C20:5n-3) ratios, than non-depressed subjects. The observed positive relation between depression and the particular fatty acid ratios, in the present study, appears to indicate increasing activity of elongases, the enzymes responsible for elongating polyunsaturated fatty acids into their longer-chain derivatives, with increasing depression. This is the first literature report of a possible relation between elongases and depression. The observed relation may stem from a possible over-expression of the HELO1 (ELOVL5) gene, the gene encoding a protein responsible for elongating long-chain polyunsaturated fatty acids, in the adipose tissue of depressed adolescents.

Association study of novel human serotonin 5-HT(1B) polymorphisms with alcohol dependence in Taiwanese Han

BACKGROUND

Abnormal serotonergic pathways are implicated in numerous neuropsychiatric disorders, such as depression, anxiety, migraine, substance abuse, and alcoholism. The human serotonin receptor 1B, encoded by the HTR1B gene, is a presynaptic serotonin autoreceptor that plays a role in regulating serotonin synthesis and release. Because the linkage of antisocial alcoholism to the HTR1B gene was recently reported in two populations, it was of interest to identify genetic variants at the HTR1B locus and study their association with alcoholism in the Taiwanese Han population.

METHODS

We sequenced DNA from Taiwanese Han to screen for genetic variation in the coding, promoter, and partial 3' untranslated regions of the HTR1B locus of 158 alcohol-dependent cases with withdrawal symptoms and 149 control subjects, who either never drank or drank only occasionally and in low quantities.

RESULTS

Seven variants were identified. Positive associations were found between variant A-161T and alcohol dependence at both the allelic and genotypic level. In addition, an expression study showed that the A-161T variant affected reporter gene activity.

CONCLUSIONS

Our results support an association between HTR1B and alcohol dependence. The HTR1B A-161T polymorphism may be valuable both as a functional and as an anonymous genetic marker for HTR1B.

Assignment of the human serotonin 1F receptor gene (HTR1F) to the short arm of chromosome 3 (3p13-p14.1)

In the present study, we report the chromosomal localization of the human 5-HT1F receptor gene (HTR1F) by the analysis of somatic cell hybrids. Based upon the HTR1F cDNA sequence, a primer set that reacted with human genomic DNA but not mouse or hamster genomic DNA was derived from the relatively nonconserved 5'-untranslated and coding region. Using monochromosomal hybrid cell lines of the NIGMS Mapping Panel 2 we localized the HTR1F to human chromosome 3. To confirm the localization on chromosome 3 and to further sublocalize the HTR1F gene, a set of human cell hybrids regionally separating chromosome 3 into 7 regions was similarly analysed. Analysis of this regional panel showed that the HTR1F gene was located proximal to the 3p14.1 breakpoint in hybrid APH14 and distal to the breakpoint in 3p13 in hybrid APH13. This localizes the HTR1F gene to human chromosome 3p13-p14.1.

Molecular biology of serotonin (5-HT) receptors

The hypothesis that multiple serotonin (5-hydroxytryptamine; 5-HT) receptors exist was first developed in the 1950s. However, unequivocal proof of 5-HT receptor multiplicity required the availability of molecular biological technologies. Indeed, the multiplicity of 5-HT receptor subtypes, both within and between species, has far exceeded most of the predictions that might have been made on the basis of pharmacological data. Over the past few years, and especially in 1992 and 1993, numerous "new" 5-HT receptors were reported. In this review, the extensive data generated in the past few years are summarized in an evolutionary context.

Cloning, sequencing and phylogenetic analysis of a human 5-hydroxytryptamine 1D receptor pseudogene

A third member of the human 5HT1D gene family has been identified using a combination of homology cloning and DNA sequence analysis. This human gene is most related to the 5HT1D alpha subtype (77% shared identity) and is a pseudogene, based on the lack of an open reading frame (ORF) caused by multiple in-frame stop codons and nucleotide (nt) deletions relative to the functional 5HT1D alpha gene (encoding the 5-hydroxytryptamine 1D alpha receptor). The 5HT1D pseudogene also contained an insertion that shares 87% identity to the Alu consensus sequence. Phylogenetic analysis of the three human genes in this family reveals that although the two functional genes, 5HT1D alpha and 5HT1D beta, are detected in all mammalian species examined, the 5HT1D pseudogene is only detected in a subset of primates (catarrhines) that evolved approximately 35-45 million years (Myr) ago. Alternatively, based on the 23% divergence between the functional 5HT1D alpha gene and the 5HT1D pseudogene, we estimate that these two genes began to diverge approximately 50 Myr ago.

A new wave of serotonin receptors

The neurotransmitter serotonin mediates diverse effects through multiple receptor subtypes. Recently, many of these receptor subtypes have been identified, molecularly cloned and characterized, advancing our understanding of their functional roles in the central and peripheral nervous systems.