The high affinity neurotensin receptor gene (NTSR1): comparative sequencing and association studies in schizophrenia

Neurotensin induces sustainable activation of the ErbB-ERK1/2 pathway, which is required for developmental competence of oocytes in mice

Purpose

LH induces the expression of EGF-like factors and their shedding enzyme (ADAM17) in granulosa cells (GCs), which is essential for ovulation via activation of the ErbB-ERK1/2 pathway in cumulus cells (CCs). Neurotensin (NTS) is reported as a novel regulator of ovulation, whereas the NTS-induced maturation mechanism in oocytes remains unclear. In this study, we focused on the role of NTS in the expression of EGF-like factors and ErbBs, and ADAM17 activity, during oocyte maturation and ovulation in mice.

Methods

The expression and localization in GC and CC were examined. Next, hCG and NTS receptor 1 antagonist (SR) were injected into eCG-primed mice, and the effects of SR on ERK1/2 phosphorylation were investigated. Finally, we explored the effects of SR on the expression of EGF-like factors and ErbBs, and ADAM17 activity in GC and CC.

Results

NTS was significantly upregulated in GC and CC following hCG injection. SR injection suppressed oocyte maturation and ERK1/2 phosphorylation. SR also downregulated part of the expression of EGF-like factors and their receptors, and ADAM17 activity.

Conclusions

NTS induces oocyte maturation through the sustainable activation of the ERK1/2 signaling pathway by upregulating part of the EGF-like factor-induced pathway during oocyte maturation in mice.

Cortical patterning of abnormal morphometric similarity in psychosis is associated with brain expression of schizophrenia-related genes

Schizophrenia has been conceived as a disorder of brain connectivity, but it is unclear how this network phenotype is related to the underlying genetics. We used morphometric similarity analysis of MRI data as a marker of interareal cortical connectivity in three prior case-control studies of psychosis: in total, n = 185 cases and n = 227 controls. Psychosis was associated with globally reduced morphometric similarity in all three studies. There was also a replicable pattern of case-control differences in regional morphometric similarity, which was significantly reduced in patients in frontal and temporal cortical areas but increased in parietal cortex. Using prior brain-wide gene expression data, we found that the cortical map of case-control differences in morphometric similarity was spatially correlated with cortical expression of a weighted combination of genes enriched for neurobiologically relevant ontology terms and pathways. In addition, genes that were normally overexpressed in cortical areas with reduced morphometric similarity were significantly up-regulated in three prior post mortem studies of schizophrenia. We propose that this combined analysis of neuroimaging and transcriptional data provides insight into how previously implicated genes and proteins as well as a number of unreported genes in their topological vicinity on the protein interaction network may drive structural brain network changes mediating the genetic risk of schizophrenia.

Contributions of dopamine-related genes and environmental factors to highly sensitive personality: a multi-step neuronal system-level approach

Traditional behavioral genetic studies (e.g., twin, adoption studies) have shown that human personality has moderate to high heritability, but recent molecular behavioral genetic studies have failed to identify quantitative trait loci (QTL) with consistent effects. The current study adopted a multi-step approach (ANOVA followed by multiple regression and permutation) to assess the cumulative effects of multiple QTLs. Using a system-level (dopamine system) genetic approach, we investigated a personality trait deeply rooted in the nervous system (the Highly Sensitive Personality, HSP). 480 healthy Chinese college students were given the HSP scale and genotyped for 98 representative polymorphisms in all major dopamine neurotransmitter genes. In addition, two environment factors (stressful life events and parental warmth) that have been implicated for their contributions to personality development were included to investigate their relative contributions as compared to genetic factors. In Step 1, using ANOVA, we identified 10 polymorphisms that made statistically significant contributions to HSP. In Step 2, these polymorphism's main effects and interactions were assessed using multiple regression. This model accounted for 15% of the variance of HSP (p<0.001). Recent stressful life events accounted for an additional 2% of the variance. Finally, permutation analyses ascertained the probability of obtaining these findings by chance to be very low, p ranging from 0.001 to 0.006. Dividing these loci by the subsystems of dopamine synthesis, degradation/transport, receptor and modulation, we found that the modulation and receptor subsystems made the most significant contribution to HSP. The results of this study demonstrate the utility of a multi-step neuronal system-level approach in assessing genetic contributions to individual differences in human behavior. It can potentially bridge the gap between the high heritability estimates based on traditional behavioral genetics and the lack of reproducible genetic effects observed currently from molecular genetic studies.

Neurotensin receptor 1 gene (NTSR1) polymorphism is associated with working memory

BACKGROUND

Recent molecular genetics studies showed significant associations between dopamine-related genes (including genes for dopamine receptors, transporters, and degradation) and working memory, but little is known about the role of genes for dopamine modulation, such as those related to neurotensin (NT), in working memory. A recent animal study has suggested that NT antagonist administration impaired working memory in a learning task. The current study examined associations between NT genes and working memory among humans.

METHODS

Four hundred and sixty healthy undergraduate students were assessed with a 2-back working memory paradigm. 5 SNPs in the NTSR1 gene were genotyped. 5 ANOVA tests were conducted to examine whether and how working memory differed by NTSR1 genotype, with each SNP variant as the independent variable and the average accuracy on the working memory task as the dependent variable.

RESULTS

ANOVA results suggested that two SNPs in the NTSR1 gene (rs4334545 and rs6090453) were significantly associated with working memory. These results survived corrections for multiple comparisons.

CONCLUSIONS

Our results demonstrated that NTSR1 SNP polymorphisms were significantly associated with variance in working memory performance among healthy adults. This result extended previous rodent studies showing that the NT deficiency impairs the working memory function. Future research should replicate our findings and extend to an examination of other dopamine modulators.

P2RX7: A bipolar and unipolar disorder candidate susceptibility gene?

The chromosomal region 12q24 has been previously implicated by linkage studies of both bipolar disorder and unipolar mood disorder and we have reported two pedigrees segregating both bipolar disorder and Darier's disease that show linkage across this region. The gene P2RX7 is located in this chromosomal region and has been recently reported as a susceptibility gene for bipolar disorder and unipolar depression. The non-synonymous SNP rs2230912 (resulting in amino-acid polymorphism Q460R) showed the strongest association and has been postulated to be pathogenically relevant. We have investigated this gene in a large UK case-control sample (bipolar I disorder N = 687, unipolar recurrent major depression N = 1,036, controls N = 1,204). Neither rs2230912 nor any of 8 other SNPs genotyped across P2RX7 was found to be associated with mood disorder in general, nor specifically with bipolar or unipolar disorder. Further, sequencing of our two chromosome 12-linked bipolar-Darier families showed no evidence of rare variants at P2RX7 that could explain the linkage. Our data do not provide support for rs2230912 or the other polymorphisms studied within the P2RX7 locus, being involved in susceptibility to mood disorders.

Selectively increased trace conditioning under the neurotensin agonist PD 149163 in an aversive procedure in which SR 142948A was without intrinsic effect

There is evidence to suggest that neurotensin (NT) may enhance cognitive function. The present study, therefore, examined the role of NT in associative learning between a conditioned stimulus (CS) and an unconditioned stimulus (UCS). This was tested in a trace procedure using conditioned suppression of drinking with a noise CS and foot shock UCS. We compared the effects of an NT agonist (PD 149163, 0.25 and 1 mg/kg) with those of an NT antagonist (SR 142948A, 0.01 and 0.1 mg/kg). Conditioning after drug treatment was followed by drug-free tests of associative learning. At 0.25 but not 1 mg/kg, PD 149163 selectively increased conditioning over the trace interval: there was no such increased conditioning in the 0s group. This increased conditioning over the trace is an effect that is reliably produced by dopamine (DA) agonists in the same procedure. However, dissimilar to the effects of DA agonists, conditioning to box context, was reduced under PD 149163. Doses of SR 142948A, selected on the basis of their effects in similar aversively motivated tests of latent inhibition, were without intrinsic effect in the present procedure. The dose-related dissociation between trace and contextual conditioning effects under PD 149163 is considered as cognitive enhancement.

Involvement of neuropeptide systems in schizophrenia: human studies

Neuropeptides are heterogeneously distributed throughout the digestive, circulatory, and nervous systems and serve as neurotransmitters, neuromodulators, and hormones. Neuropeptides are phylogenetically conserved and have been demonstrated to regulate numerous behaviors. They have been hypothesized to be pathologically involved in several psychiatric disorders, including schizophrenia. On the basis of preclinical data, numerous studies have sought to examine the role of neuropeptide systems in schizophrenia. This chapter reviews the clinical data, linking alterations in neuropeptide systems to the etiology, pathophysiology, and treatment of schizophrenia. Data for the following neuropeptide systems are included: arginine-vasopressin, cholecystokinin (CCK), corticotropin-releasing factor (CRF), interleukins, neuregulin 1 (NRG1), neurotensin (NT), neuropeptide Y (NPY), opioids, secretin, somatostatin, tachykinins, thyrotropin-releasing hormone (TRH), and vasoactive intestinal peptide (VIP). Data from cerebrospinal fluid (CSF), postmortem and genetic studies, as well as clinical trials are described. Despite the inherent difficulties associated with human studies (including small sample size, variable duration of illness, medication status, the presence of comorbid psychiatric disorders, and diagnostic heterogeneity), several findings are noteworthy. Postmortem studies support disease-related alterations in several neuropeptide systems in the frontal and temporal cortices. The strongest genetic evidence supporting a role for neuropeptides in schizophrenia are those studies linking polymorphisms in NRG1 and the CCKA receptor with schizophrenia. Finally, the only compounds that act directly on neuropeptide systems that have demonstrated therapeutic efficacy in schizophrenia are neurokinin receptor antagonists. Clearly, additional investigation into the role of neuropeptide systems in the etiology, pathophysiology, and treatment of schizophrenia is warranted.

Neurotensin: role in psychiatric and neurological diseases

Neurotensin (NT), an endogenous brain-gut peptide, has a close anatomical and functional relationship with the mesocorticolimbic and neostriatal dopamine system. Dysregulation of NT neurotransmission in this system has been hypothesized to be involved in the pathogenesis of schizophrenia. Additionally, NT containing circuits have been demonstrated to mediate some of the mechanisms of action of antipsychotic drugs, as well as the rewarding and/or sensitizing properties of drugs of abuse. NT receptors have been suggested to be novel targets for the treatment of psychoses or drug addiction.

Bipolar disorder and polymorphisms in the dysbindin gene (DTNBP1)

BACKGROUND

Several studies support the dysbindin (dystrobrevin binding protein 1) gene (DTNBP1) as a susceptibility gene for schizophrenia. We previously reported that variation at a specific 3-locus haplotype influences susceptibility to schizophrenia in a large United Kingdom (UK) Caucasian case-control sample.

METHODS

Using similar methodology to our schizophrenia study, we have investigated this same 3-locus haplotype in a large, well-characterized bipolar sample (726 Caucasian UK DSM-IV bipolar I patients; 1407 ethnically matched controls).

RESULTS

No significant differences were found in the distribution of the 3-locus haplotype in the full sample. Within the subset of bipolar I cases with predominantly psychotic episodes of mood disturbance (n = 133) we found nominally significant support for association at this haploptype (p < .042) and at SNP rs2619538 (p = .003), with a pattern of findings similar to that in our schizophrenia sample. This finding was not significant after correction for multiple testing.

CONCLUSIONS

Our data suggest that variation at the polymorphisms examined does not make a major contribution to susceptibility to bipolar disorder in general. They are consistent with the possibility that DTNBP1 influences susceptibility to a subset of bipolar disorder cases with psychosis. However, our subset sample is small and the hypothesis requires testing in independent, adequately powered samples.

Mutation screening and LD mapping in the VCFS deleted region of chromosome 22q11 in schizophrenia using a novel DNA pooling approach

We examined whether variation within six genes from the VCFS critical region at 22q11 (DGSC, Stk22A1, DGSI, Gscl, Slc25A1 and Znf74) confers susceptibility to schizophrenia. We screened the exons and flanking intronic sequence of each gene for mutations in 14 individuals with DSM-IV schizophrenia using DHPLC. All polymorphisms identified were characterised and genotyped in a sample of 184 schizophrenics and matched controls, using novel DNA pooling methods. Of the polymorphisms identified, 17 were located within exons, six were within coding sequence, and two were non-synonymous. Pooled genotyping revealed no differences in the allele frequencies for any polymorphism between cases and controls that met our pre-defined criterion (P < or = 0.1). In a complementary approach we also attempted to define the location of a schizophrenia susceptibility locus more precisely by performing association mapping using seven microsatellites spanning the VCFS region with an average inter-marker distance of 450 kb. Conventional chi(2) analysis of genotypes in 368 cases and 368 controls revealed that none of the markers was significantly associated (P < 0.05) with schizophrenia. However, evidence for significant association (P = 0.003) was obtained for D22S944 when alleles were combined. TDT analysis of D22S944 genotyped in a further 278 cases of schizophrenia and their parents failed to find any overall allele-wise significant transmission disequilibrium (chi(2) = 18.3, P = 0.17). However, individual analysis of the alleles revealed that allele 12 was excessively non-transmitted and that this almost reached significance when corrected for multiple alleles (chi(2) = 7.35, P = 0.006, P = 0.078 corrected for 13 alleles).

Detailed analysis of PRODH and PsPRODH reveals no association with schizophrenia

People with deletion of the chromosome 22q11 region associated with velo cardio-facial syndrome (VCFS) have a remarkably high risk of developing schizophrenia. Recently, the gene proline dehydrogenase (PRODH) which maps to 22q11 and is also an excellent functional candidate gene for psychosis, has been reported to show genetic association with schizophrenia. We have screened all the exons and adjacent intronic sequences of PRODH for the presence of sequence variation in 14 DSM IV schizophrenic subjects. Similarly, we also screened all putative exons of a sequence that is similar to proline dehydrogenase (PsPRODH) and which also maps within the deleted region. A total of nine single nucleotide polymorphisms (SNPs) were identified in PRODH, eight of which were exonic, while in PsPRODH, five SNPs were identified, one of which was in a putative exon. All samples were tested for association in a pooled sample of 368 DSM IV diagnosed schizophrenic subjects and 368 matched controls. None of the variants identified in PRODH gave even modest evidence for allelic association (P < 0.1). In PsPRODH, two variants (-3864G > A and 226G > A) gave P values < 0.1. These were individually genotyped in the same subjects that had been used to construct the pools. Although a trend for association was confirmed, neither showed evidence for association at the P </= 0.05 level. These results do not suggest that PRODH or PsPRODH contribute to the aetiology of schizophrenia, and that the putative schizophrenia susceptibility gene in 22q11 remains unknown.

A decade of high-resolution liquid chromatography of nucleic acids on styrene-divinylbenzene copolymers

The introduction of alkylated, nonporous poly-(styrene-divinylbenzene) microparticles in 1992 enabled the subsequent development of denaturing HPLC that has emerged as the most sensitive screening method for mutations to date. Denaturing HPLC has provided unprecedented insight into human origins and prehistoric migrations, accelerated the cloning of genes involved in mono- and polygenic traits, and facilitated the mutational analysis of more than a hundred candidate genes of human disease. A significant step toward increased sample-throughput and information content was accomplished by the recent introduction of monolithic poly(styrene-divinylbenzene) capillary columns. They have enabled the construction of capillary arrays amenable to multiplex analysis of fluorescent dye-labeled nucleic acids by laser-induced fluorescence detection. Hyphenation of denaturing HPLC with electrospray ionization mass spectrometry, on the other hand, has allowed the direct elucidation of the chemical nature of DNA variation and determination of phase of multiple alleles on a chromosome.

Neuropeptides involved in the pathophysiology of schizophrenia and major depression

The present review summarizes the findings on the role of neuropeptides in the pathophysiology of schizophrenia and major depression. Several neuropeptides as vasopressin and endorphins in particular, beta-endorphin and gamma-type endorphins, cholecystokinin (CCK), neurotensin, somatostatin and Neuropeptide Y have been implicated in schizophrenia. During the last decade, however, few attempts to explore the significance of most of these and other neuropeptides in the pathophysiology of the disease or their therapeutic potential are found in the literature. An exception is neurotensin, which exerts neuroleptic-like effects in animal studies, while CSF, brain and blood studies are inconclusive. Things are different in major depression. Here much attention is paid to the endocrine abnormalities found in this disorder in particular the increased activity of the hypothalamic-pituitary-adrenal (HPA) axis. Neuropeptides as corticotropin-releasing hormone (CRH), vasopressin and corticosteroids are implicated in the symptomatology of this disorder. As a consequence much work is going on investigating the influence of CRH and corticosteroid antagonists or inhibitors of the synthesis of corticosteroids as potential therapeutic agents. This review emphasizes the role of vasopressin in the increased activity of the HPA axis in major depression and suggests exploration of the influence of the now available non-peptidergic vasopressin orally active V1 antagonists.

Neurotensin receptor binding abnormalities in the entorhinal cortex in schizophrenia and affective disorders

BACKGROUND

Convergent evidence from in vivo and in vitro studies of schizophrenia have implicated the mesial temporal lobe as a primary site of pathological change in this disorder. We have previously reported decreased neurotensin receptor density in layer II of the intermediate entorhinal cortex (ERC) in schizophrenia, a finding seen elsewhere but not seen in more caudal ERC.

METHODS

To study neuroanatomic and diagnostic specificity, we measured the density of neurotensin receptors in the intermediate and caudal ERC and hippocampal formation of schizophrenic, affective disorder control subjects, and normal control subjects. Slide-based radioligand binding was used to perform these studies.

RESULTS

Not only schizophrenic but also affective disorder subjects had decreased neurotensin receptor density in layer II of the intermediate ERC. Affective disorder subjects had significantly decreased neurotensin receptor density in layers V/VI of the intermediate ERC, and schizophrenic subjects trended in the same direction.

CONCLUSIONS

These findings demonstrate region-specific changes in neurotensin receptor binding levels in the mesial temporal lobe; however, there is no clear diagnostic specificity for these changes, because they were seen to varying degrees in both schizophrenia and affective disorders.

Recent advances in the genetics of schizophrenia

The genetic etiology of schizophrenia, a common and debilitating psychiatric disorder, is supported by a wealth of data. Review of the current findings suggests that considerable progress has been made in recent years, with a number of chromosomal regions consistently implicated by linkage analysis. Three groups have shown linkage to 1q21-22 using similar models, with HLOD scores of 6.5, 3.2, and 2.4. Other replicated loci include 13q32 that has been implicated by two independent groups with significant HLOD scores (4.42) or NPL values (4.18), and 5pl4.1-13.1, 5q21-33, 8p2l-22, and 10p11-15, each of which have been reported as suggestive by at least three separate groups. Different studies have also replicated evidence for a modest number of candidate genes that were not ascertained through linkage. Of these, the greatest support exists for the DRD3 (3q13.3), HTR2A (13q14.2), and CHRNA7 (15q13-q14) genes. The refinement of phenotypes, the use of endophenotypes, reduction of heterogeneity, and extensive genetic mapping have all contributed to this progress. The rapid expansion of information from the human genome project will likely further accelerate this progress and assist in the discovery of susceptibility genes for schizophrenia. A greater understanding of disease mechanisms and the application of pharmacogenetics should also lead to improvements in therapeutic interventions.

Denaturing high-performance liquid chromatography: A review

Denaturing high-performance liquid chromatography (DHPLC) compares two or more chromosomes as a mixture of denatured and reannealed PCR amplicons, revealing the presence of a mutation by the differential retention of homo- and heteroduplex DNA on reversed-phase chromatography supports under partial denaturation. Temperature determines sensitivity, and its optimum can be predicted by computation. Single-nucleotide substitutions, deletions, and insertions have been detected successfully by on-line UV or fluorescence monitoring within 2-3 minutes in unpurified amplicons as large as 1.5 Kb. Sensitivity and specificity of DHPLC consistently exceed 96%. These features and its low cost make DHPLC one of the most powerful tools for the re-sequencing of the human and other genomes. Aside from its application to the mutational analysis of candidate genes, DHPLC has proven instrumental in elucidating human evolution and in the mapping of genes. Employing completely denaturing conditions, the utility of DHPLC has been extended to the genotyping of known polymorphisms by utilizing the ability of poly(styrene-divinylbenzene) to resolve single-stranded DNA molecules of identical size that differ in a single base. Under completely denaturing conditions, it is thus possible to resolve all possible base substitutions with the single exception of C-->G transversions. Improvements in throughput became feasible with the recent introduction of monolithic poly(styrene-divinylbenzene) capillaries that lend themselves to the fabrication of arrays connected to a multi-color laser induced fluorescence scanner or a mass spectrometer.