Zill P, Baghai TC, Zwanzger P, Schüle C, Eser D, Rupprecht R,
Möller HJ, Bondy B, Ackenheil M
SNP and haplotype
analysis of a novel tryptophan hydroxylase isoform (TPH2) gene provide evidence
for association with major depression.
2004 May 4;
Tryptophan hydroxylase (TPH), being the rate-limiting enzyme in
the biosynthesis of serotonin plays a major role as candidate gene in several
psychiatric disorders. Recently, a second TPH isoform (TPH2) was identified in
mice, which was exclusively present in the brain. In a previous post-mortem study
of our own group, we could demonstrate that TPH2 is also expressed in the human
brain, but not in peripheral tissues. This is the first report of an association
study between polymorphisms in the TPH2 gene and major depression (MD). We performed
single-nucleotide polymorphism (SNP), haplotype and linkage disequlibrium studies
on 300 depressed patients and 265 healthy controls with 10 SNPs in the TPH2 gene.
Significant association was detected between one SNP (P=0.0012, global P=0.0051)
and MD. Haplotype analysis produced additional support for association (P<0.0001,
global P=0.0001). Our findings provide evidence for an involvement of genetic
variants of the TPH2 gene in the pathogenesis of MD and might be a hint on the
repeatedly discussed duality of the serotonergic system. These results may open
up new research strategies for the analysis of the observed disturbances in the
serotonergic system in patients suffering from several other psychiatric disorders.
EJ, Slager SL, McGrath PJ, Knowles JA, Hamilton SP
of serotonin-related genes in antidepressant response.
Psychiatry. 2004 Sep;9(9):879-89.
In this study, we sought out to test the
hypothesis that genetic factors may influence antidepressant response to fluoxetine.
The investigation focused on seven candidate genes in the serotonergic pathway
involved in the synthesis, transport, recognition, and degradation of serotonin.
Our clinical sample consisted of 96 subjects with unipolar major depression treated
with fluoxetine with response variables assessed after a 12-week trial. Patient
data were also collected to investigate the pattern of drug response. Using a
high-throughput single-nucleotide polymorphism (SNP) genotyping platform and capillary
electrophoresis, we genotyped patients at 110 SNPs and four repeat polymorphisms
located in seven candidate genes (HTR1A, HTR2A, HTR2C, MAOA, SLC6A4, TPH1, and
TPH2). Statistical tests performed included single-locus and haplotype association
tests, and linkage disequilibrium (LD) estimation. Little evidence of population
stratification was observed in the sample with 20 random SNPs using a genomic
control procedure. Our most intriguing result involved three SNPs in the TPH1
gene and one SNP in the SLC6A4 gene, which show significant single-locus association
when response to fluoxetine is compared to nonresponse (P=0.02-0.04). All odds
ratios indicated an increased risk of not responding to fluoxetine. In the specific
response vs nonspecific and nonresponse comparison, three SNPs in the TPH2 gene
(P=0.02-0.04) were positively associated and one SNP in the HTR2A gene (P=0.02)
was negatively associated. When comparing specific response to nonspecific response,
we found significant negative associations in three SNPs in the HTR2A gene (P=0.001-0.03)
and two SNPs in the MAOA gene (P=0.03-0.05). We observed variable, although strong
LD, in each gene and unexpectedly low numbers of estimated haplotypes, formed
from tagged SNPs. Significant haplotype associations were found in all but the
HTR1A and HTR2C genes. Although these data should be interpreted cautiously due
to the small sample size, these results implicate TPH1 and SLC6A4 in general response,
and HTR2A, TPH2, and MAOA in the specificity of response to fluoxetine. Intriguingly,
we observe that a number of the less frequent alleles of many of the SNP markers
were associated with the nonresponse and nonspecific phenotypes. [Abstract]
SE, White DJ, Glatt CE
Identification of genetic variants
in the neuronal form of tryptophan hydroxylase (TPH2).
Genet. 2004 Jun;14(2):69-72.
OBJECTIVE: We screened the complete protein coding
sequence of the newly identified neuronal form of tryptophan hydroxylase (TPH2)
for genetic variants. METHODS: Genomic DNA samples from 24 African-Americans and
24 Caucasian-Americans in the Coriell human variation collection were screened
by denaturing high-performance liquid chromatography followed by sequencing. RESULTS:
We identified a number of genetic variants in both the coding and exon-flanking
intronic sequences. Only one variant was identified that predicts a structural
change in the TPH2 protein, and this was seen in only one out of 96 chromosomes.
CONCLUSIONS: The gene for TPH2 contains a number of polymorphisms that might serve
as useful markers for association analyses of complex behavioral phenotypes or
as actual risk factors. Structural polymorphisms are extremely rare in TPH2 and
cannot therefore act as substantial risk factors for behavioral disorders in African-American
and Caucasian populations. [Abstract]
X, Beaulieu JM, Sotnikova TD, Gainetdinov RR, Caron MG
hydroxylase-2 controls brain serotonin synthesis.
2004 Jul 9;305(5681):217.
Dysregulation of brain serotonin contributes to many
psychiatric disorders. Tryptophan hydroxylase-2 (Tph2), rather than Tph1, is preferentially
expressed in the brain. We report a functional (C1473G) single-nucleotide polymorphism
in mouse Tph2 that results in the substitution of Pro447 with Arg447 and leads
to decreased serotonin levels in PC12 cells. Moreover, in BALB/cJ and DBA/2 mice
that are homozygous for the 1473G allele, brain serotonin tissue content and synthesis
are reduced in comparison to C57Bl/6 and 129X1/SvJ mice that are homozygous for
the 1473C allele. Our data provide direct evidence for a fundamental role of Tph2
in brain serotonin synthesis. [Abstract]
M, Shink E, Tremblay M, Gagné B, Raymond C, Labbé M, Walther DJ, Bader M, Barden
Support for the involvement of TPH2 gene in affective
Mol Psychiatry. 2004 Jul 20; [Abstract]
Luca V, Mueller DJ, Tharmalingam S, King N, Kennedy JL
of the novel TPH2 gene in bipolar disorder and suicidality.
Psychiatry. 2004 Jun 15; [Abstract]
Walther DJ, Bader M
unique central tryptophan hydroxylase isoform.
Pharmacol. 2003 Nov 1;66(9):1673-80.
Serotonin (5-hydroxytryptophan, 5-HT)
is a neurotransmitter synthesized in the raphe nuclei of the brain stem and involved
in the central control of food intake, sleep, and mood. Accordingly, dysfunction
of the serotonin system has been implicated in the pathogenesis of psychiatric
diseases. At the same time, serotonin is a peripheral hormone produced mainly
by enterochromaffin cells in the intestine and stored in platelets, where it is
involved in vasoconstriction, haemostasis, and the control of immune responses.
Moreover, serotonin is a precursor for melatonin and is therefore synthesized
in high amounts in the pineal gland. Tryptophan hydroxylase (TPH) catalyzes the
rate limiting step in 5-HT synthesis. Until recently, only one gene encoding TPH
was described for vertebrates. By gene targeting, we functionally ablated this
gene in mice. To our surprise, the resulting animals, although being deficient
for serotonin in the periphery and in the pineal gland, exhibited close to normal
levels of 5-HT in the brain stem. This led us to the detection of a second TPH
gene in the genome of humans, mice, and rats, called TPH2. This gene is predominantly
expressed in the brain stem, while the classical TPH gene, now called TPH1, is
expressed in the gut, pineal gland, spleen, and thymus. These findings clarify
puzzling data, which have been collected over the last decades about partially
purified TPH proteins with different characteristics and justify a new concept
of the serotonin system. In fact, there are two serotonin systems in vertebrates,
independently regulated and with distinct functions. [Abstract]
J, Cook EH
Knockout mouse points to second form of
Mol Interv. 2003 Mar;3(2):72-5,
A second form of tryptophan hydroxylase (TPH) is expressed in the brain
by the gene Tph2. The presence of the gene was discovered when Tph 1(-/-)mice
were found to express normal amounts of serotonin in brain, but not in the periphery.
Additionally, Tph1(-/-) mice showed no observed behavioral differences from wild-type
littermates. Veenstra-Vanderweele and Cook discuss the ramifications of these
findings and what they might mean for designing drugs that target the expression
and activity of TPH in differing tissues. [Abstract]
PD, Pontrello C, Burke S
Robust and tissue-specific
expression of TPH2 versus TPH1 in rat raphe and pineal gland.
Psychiatry. 2004 Feb 15;55(4):428-33.
BACKGROUND: Regulation of raphe serotonergic
cells is fundamental to the prevailing hypothesis of major depression pathophysiology.
Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin biosynthesis,
but brainstem TPH mRNA expression has been difficult to measure and study. Recently,
a novel paralog of TPH, TPH2 (or neuronal TPH), was described, but its anatomic
expression is unknown. METHODS: In situ hybridization histochemical survey was
conducted across Sprague-Dawley rat brain for TPH1 and TPH2 mRNA. Semiquantitative
techniques were used to estimate relative mRNA levels in individual cells. RESULTS:
Almost exclusively, TPH2 mRNA is expressed in raphe, in a pattern overlapping
the histologically defined raphe nuclei. In sharp contrast, TPH1 (the previously
known TPH) is expressed predominantly in pineal gland. There is no appreciable
overlap in the expression of these paralogs. The level of TPH2 mRNA expression
in individual raphe cells is approximately 2.5-fold greater than the level of
TPH1 expression in pinealocytes. CONCLUSIONS: TPH2 mRNA has an anatomic expression
pattern consistent with brainstem raphe nuclei and is likely to be the gene giving
rise to the majority of TPH activity in these cells. The robust expression of
TPH2 in brainstem should facilitate studies on the transcriptional regulation
of raphe serotonin biosynthesis. [Abstract]
P, Büttner A, Eisenmenger W, Bondy B, Ackenheil M
mRNA expression of a second tryptophan hydroxylase isoform in postmortem tissue
samples of two human brains.
Tryptophan hydroxylase (TPH) as rate limiting enzyme
in the biosynthesis of serotonin plays a major role as candidate gene in several
psychiatric disorders. Recently a second TPH isoform (TPH2) was identified in
mice, which was exclusively expressed in the brain. We investigated whether the
mRNA of the human homologue of this new TPH2 isoform is expressed in the human
brain but not in peripheral tissues. The study was performed with postmortem specimen
obtained from two subjects who died on cardiovascular failure. TPH2 mRNA levels
were determined by quantitative real time RT-PCR. TPH2 mRNA was exclusively present
in the human brains but not in the investigated peripheral tissues. Our finding
may open up new research strategies for the analysis of the repeatedly observed
disturbances in the serotonergic system in patients suffering from several psychiatric
Comparison of circadian expression of tryptophan
hydroxylase isoform mRNAs in the rat pineal gland using real-time PCR.
Neurochem. 2003 Sep;86(5):1308-11.
A second gene encoding a functional tryptophan
hydroxylase activity has recently been described (TPH2), which is expressed abundantly
in brainstem, the primary site of serotonergic neurons in the CNS. As serotonin
(5-HT) has an important role as a precursor of the nocturnal synthesis of the
pineal gland hormone, melatonin, it was of interest to determine the relative
expression of TPH1 and 2 mRNA in the rat pineal during the light:dark (L:D) cycle
using sensitive real-time RT-PCR assays which were developed for each TPH isoform.
TPH1 mRNA expression was 105-fold more abundant in rat pineal than TPH2, and showed
a significant approximately 4-fold nocturnal increase in expression which may
contribute to the previously described nocturnal increase in pineal tryptophan
hydroxylase activity. TPH2 expression within the gland showed no significant variation
with time of day and was very low (approximately 300 copies/gland) indicating
expression in the small proportion of "non-pinealocyte" cells in the
J, Wessel JH, Iuvone PM, Tosini G, Fukuhara C
rhythms of tryptophan hydroxylase 1 and 2 mRNA expression in the rat retina.
2004 Jun 28;15(9):1497-500.
Tryptophan hydroxylase is the first of four enzymes
in the melatonin biosynthetic pathway. Recent studies have shown that there are
two genes, Tph1 and Tph2, that encode tryptophan hydroxylase in mammals. In this
study, we investigated which of the two genes is expressed in the rat retina.
To that end, we measured Tph1 (classical Tph) and Tph2 mRNA levels using real-time
quantitative RT-PCR in the retina. Our data demonstrate that Tph1 mRNA is the
prevalent form expressed in the retina; Tph2 mRNA is also present but the level
is very low. We also measured Tph1 expression levels in the outer nuclear layer,
inner nuclear layer, and ganglion cell layer by combining laser capture microdissection
and real-time RT-PCR. Tph1 mRNA is more abundant in the photoreceptors of the
outer nuclear layer than in the inner nuclear layer or ganglion cell layer. Tph1
and Tph2 transcripts showed robust diurnal rhythms of abundance, with highest
levels at night. Our results support the hypothesis that Tph1 is involved in melatonin
synthesis in retinal photoreceptor cells. [Abstract]