Role of silent polymorphisms within the dopamine D1 receptor associated with schizophrenia on D1–D2 receptor hetero-dimerization

Polymorphisms of Dopamine Receptor Genes and Parkinson's Disease: Clinical Relevance and Future Perspectives

Parkinson’s disease (PD) is a neurodegenerative disease caused by loss of dopaminergic neurons in the midbrain. PD is clinically characterized by a variety of motor and nonmotor symptoms, and treatment relies on dopaminergic replacement. Beyond a common pathological hallmark, PD patients may present differences in both clinical progression and response to drug therapy that are partly affected by genetic factors. Despite extensive knowledge on genetic variability of dopaminergic receptors (DR), few studies have addressed their relevance as possible influencers of clinical heterogeneity in PD patients. In this review, we summarized available evidence regarding the role of genetic polymorphisms in DR as possible determinants of PD development, progression and treatment response. Moreover, we examined the role of DR in the modulation of peripheral immunity, in light of the emerging role of the peripheral immune system in PD pathophysiology. A better understanding of all these aspects represents an important step towards the development of precise and personalized disease-modifying therapies for PD.

Rare-variant pathogenicity triage and inclusion of synonymous variants improves analysis of disease associations of orphan G protein-coupled receptors

The pace of deorphanization of G protein-coupled receptors (GPCRs) has slowed, and new approaches are required. Small molecule targeting of orphan GPCRs can potentially be of clinical benefit even if the endogenous receptor ligand has not been identified. Many GPCRs lack common variants that lead to reproducible genome-wide disease associations, and rare-variant approaches have emerged as a viable alternative to identify disease associations for such genes. Therefore, our goal was to prioritize orphan GPCRs by determining their associations with human diseases in a large clinical population. We used sequence kernel association tests to assess the disease associations of 85 orphan or understudied GPCRs in an unselected cohort of 51,289 individuals. Using rare loss-of-function variants, missense variants predicted to be pathogenic or likely pathogenic, and a subset of rare synonymous variants that cause large changes in local codon bias as independent data sets, we found strong, phenome-wide disease associations shared by two or more variant categories for 39% of the GPCRs. To validate the bioinformatics and sequence kernel association test analyses, we functionally characterized rare missense and synonymous variants of GPR39, a family A GPCR, revealing altered expression or Zn²⁺-mediated signaling for members of both variant classes. These results support the utility of rare variant analyses for identifying disease associations for GPCRs that lack impactful common variants. We highlight the importance of rare synonymous variants in human physiology and argue for their routine inclusion in any comprehensive analysis of genomic variants as potential causes of disease.

A pharmacogenetic study of patients with schizophrenia from West Siberia gets insight into dopaminergic mechanisms of antipsychotic-induced hyperprolactinemia

BACKGROUND

Hyperprolactinemia (HPRL) is a classical side effect of antipsychotic drugs primarily attributed to blockade of dopamine D2 receptors (DRD2s) on the membranes of lactotroph cells within the pituitary gland. Certain antipsychotic drugs, e.g. risperidone, are more likely to induce HPRL because of relative accumulation within the adenohypophysis. Nevertheless, due to competition for pituitary DRD2s by high dopamine levels may limit antipsychotic-induced HPRL. Moreover, the activity of prolactin-producing lactotrophs also depends on other hormones which are regulated by the extra-pituitary activity of dopamine receptors, dopamine transporters, enzymes of neurotransmitter metabolism and other factors. Polymorphic variants in the genes coding for these receptors and proteins can have functional significance and influence on the development of hyperprolactinemia.

METHODS

A set of 41 SNPs of genes for dopamine receptors DRD1, DRD2, DRD3, DRD4, the dopamine transporter SLC6A3 and dopamine catabolizing enzymes MAOA and MAOB was investigated in a population of 446 Caucasians (221 males/225 females) with a clinical diagnosis of schizophrenia (according to ICD-10: F20) with and without HPRL who were treated with classical and/or atypical antipsychotic drugs. Additive genetic model was tested and the analysis was carried out in the total group and in subgroup stratified by the use of risperidone/paliperidone.

RESULTS

One statistically significant association between polymorphic variant rs1799836 of MAOB gene and HPRL in men was found in the total group. Furthermore, the rs40184 and rs3863145 variants in SLC6A3 gene appeared to be associated with HPRL in the subgroup of patients using the risperidone/paliperidone, but not with HPRL induced by other antipsychotic drugs.

CONCLUSIONS

Our results indicate that genetic variants of MAOB and SLC6A3 may have consequences on the modulation of prolactin secretion. A further search for genetic markers associated with the development of antipsychotic-related hyperprolactinemia in schizophrenic patients is needed.

A silent mutation in human alpha-A crystallin gene in patients with age-related nuclear or cortical cataract

A cataract is a complex multifactorial disease that results from alterations in the cellular architecture, i.e. lens proteins. Genes associated with the development of lens include crystallin genes. Although crystallins are highly conserved proteins among vertebrates, a significant number of polymorphisms exist in human population. In this study, we screened for polymorphisms in crystallin alpha A (CRYAA) and alpha B (CRYAB) genes in 200 patients over 40 years of age, diagnosed with age-related cataract (ARC; nuclear and cortical cataracts). Genomic DNA was extracted from the peripheral blood. The coding regions of the CRYAA and CRYAB gene were amplified using polymerase chain reaction and subjected to restriction digestion. Restriction fragment length polymorphism (RFLP) was performed using known restriction enzymes for CRYAA and CRYAB genes. Denaturing high performance liquid chromatography and direct sequencing were performed to detect sequence variation in CRYAA gene. In silico analysis of secondary CRYAA mRNA structure was performed using CLC RNA Workbench. RFLP analysis did not show any changes in the restriction sites of CRYAA and CRYAB genes. In 6 patients (4 patients with nuclear cataract and 2 with cortical cataract), sequence analysis of the exon 1 in the CRYAA gene showed a silent single nucleotide polymorphism [D2D] (CRYAA: C to T transition). One of the patients with nuclear cataract was homozygous for this allele. The in silico analysis revealed that D2D mutation results in a compact CRYAA mRNA secondary structure, while the wild type CRYAA mRNA has a weak or loose secondary structure. D2D mutation in the CRYAA gene may be an additional risk factor for progression of ARC.

Evidence for limited D1 and D2 receptor coexpression and colocalization within the dorsal striatum of the neonatal mouse

The striatum is the major input nucleus of the basal ganglia involved in reward processing, goal-directed behaviors, habit learning, and motor control. The striatum projects to the basal ganglia output nuclei via the "direct" and "indirect" pathways, which can be distinguished by their projection fields and their opposing effects on behavior. In adult animals, the functional opposition is modulated by the differential actions of D1 and D2 dopamine receptors (D1R, D2R), the expression of which is largely separated between these pathways. To determine whether a similar degree of separation exists earlier in development, we used dual-label immunohistochemistry to map dorsal-striatal D1R and D2R expression at the promoter level in postnatal day 0 (PD0) Drd1a-tdTomato/Drd2-GFP BAC transgenic mice, and at the receptor level by costaining for native D1R and D2R in wildtype (WT) PD0 animals. To assess for potential molecular interactions between D1R and D2R we also employed a recently developed proximity-ligation assay (PLA). Limited coexpression and colocalization of the D1R and D2R proteins was found in clusters of neurons endemic to the "patch" compartment as identified by costaining with tyrosine hydroxylase, but not outside these clusters. Moreover, in contrast to our recent findings where we failed to detect a D1R-D2R PLA signal in the adult striatum, in PD0 striatum we did identify a clear PLA signal for this pair of receptors. This colocalization at close proximity points to a possible role for D1R/D2R-mediated crosstalk in early striatal ontogeny.

Pharmacology of Ultrasonic Vocalizations in adult Rats: Significance, Call Classification and Neural Substrate

Pharmacological studies of emotional arousal and initiation of emotional states in rats measured by their ultrasonic vocalizations are reviewed. It is postulated that emission of vocalizations is an inseparable feature of emotional states and it evolved from mother-infant interaction. Positive emotional states are associated with emission of 50 kHz vocalizations that could be induced by rewarding situations and dopaminergic activation of the nucleus accumbens and are mediated by D1, D2, and partially D3 dopamine receptors. Three biologically significant subtypes of 50 kHz vocalizations have been identified, all expressing positive emotional states: (1) flat calls without frequency modulation that serve as contact calls during social interactions; (2) frequencymodulated calls without trills that signal rewarding and significantly motivated situation; and (3) frequency-modulated calls with trills or trills themselves that are emitted in highly emotional situations associated with intensive affective state. Negative emotional states are associated with emission of 22 kHz vocalizations that could be induced by aversive situations, muscarinic cholinergic activation of limbic areas of medial diencephalon and forebrain, and are mediated by M2 muscarinic receptors. Two biologically significant subtypes of 22 kHz vocalizations have been identified, both expressing negative emotional sates: (1) long calls that serve as alarm calls and signal external danger; and (2) short calls that express a state of discomfort without external danger. The positive and negative states with emission of vocalizations are initiated by two ascending reticular activating subsystems: the mesolimbic dopaminergic subsystem as a specific positive arousal system, and the mesolimbic cholinergic subsystem as a specific negative arousal system.

Risk-associated coding synonymous SNPs in type 2 diabetes and neurodegenerative diseases: genetic silence and the underrated association with splicing regulation and epigenetics

Single nucleotide polymorphisms (SNPs) are tentatively critical with regard to disease predisposition, but coding synonymous SNPs (sSNPs) are generally considered "neutral". Nevertheless, sSNPs in serine/arginine-rich (SR) and splice-site (SS) exonic splicing enhancers (ESEs) or in exonic CpG methylation targets, could be decisive for splicing, particularly in aging-related conditions, where mis-splicing is frequently observed. We presently identified 33 genes T2D-related and 28 related to neurodegenerative diseases, by investigating the impact of the corresponding coding sSNPs on splicing and using gene ontology data and computational tools. Potentially critical (prominent) sSNPs comply with the following criteria: changing the splicing potential of prominent SR-ESEs or of significant SS-ESEs by >1.5 units (Δscore), or formation/deletion of ESEs with maximum splicing score. We also noted the formation/disruption of CpGs (tentative methylation sites of epigenetic sSNPs). All disease association studies involving sSNPs are also reported. Only 21/670 coding SNPs, mostly epigenetic, reported in 33 T2D-related genes, were found to be prominent coding synonymous. No prominent sSNPs have been recorded in three key T2D-related genes (GCGR, PPARGC1A, IGF1). Similarly, 20/366 coding synonymous were identified in ND related genes, mostly epigenetic. Meta-analysis showed that 17 of the above prominent sSNPs were previously investigated in association with various pathological conditions. Three out of four sSNPs (all epigenetic) were associated with T2D and one with NDs (branch site sSNP). Five were associated with other or related pathological conditions. None of the four sSNPs introducing new ESEs was found to be disease-associated. sSNPs introducing smaller Δscore changes (<1.5) in key proteins (INSR, IRS1, DISC1) were also correlated to pathological conditions. This data reveals that genetic variation in splicing-regulatory and particularly CpG sites might be related to disease predisposition and that in-silico analysis is useful for identifying sSNPs, which might be falsely identified as silent or synonymous.

Are polymorphisms in oestrogen receptors genes associated with lipid levels in response to hormone therapy?

BACKGROUND

Polymorphisms in the oestrogen receptor 1 (ESR1) and oestrogen receptor 2 (ESR2) genes are associated with intermediate or endpoint markers of cardiovascular disease and with the efficacy of postmenopausal hormone therapy (HT). Contradictory findings have been described in the past and the role of these genetics variants remains unclear.

METHODS

A cross-sectional study was carried out with 266 postmenopausal women, of whom 115 received oral HT (HT+) and 151 did not receive any HT (HT-). We analysed three single-nucleotide polymorphisms (SNPs) in ESR1 (rs1801132, rs7757956 and rs2813544) and two in ESR2 (rs3020450 and rs7154455) and derived haplotypes with three additional polymorphisms that had been previously investigated by our group (ESR1 rs2234693 and ESR2 rs1256049 and rs4986938).

RESULTS

The ESR1 rs2813544 polymorphism was associated with low-density lipoprotein cholesterol (LDL-C) in HT+ postmenopausal women (p = 0.044; pC = 0.388), while one ESR2 gene haplotype was associated with total cholesterol (T-chol) (p = 0.015; pC = 0.090) and LDL-C in HT+ postmenopausal women (p = 0.021; pC = 0.126).

CONCLUSION

Our findings suggest that, in HT+ postmenopausal women, the rs2813544 polymorphism may influence LDL-C levels and, as previously described, ESR2 rs1256049 is associated with T-chol and LDL-C. No previous study has investigated the association of this SNP set with lipoprotein levels in women while taking into account the hormonal status of the patients.

Effect of clozapine on the dimerization of serotonin 5-HT(2A) receptor and its genetic variant 5-HT(2A)H425Y with dopamine D(2) receptor

Oligomerization of G protein-coupled receptors has become a very important issue in a present molecular pharmacology. In the present study the level of the serotonin 5-HT(2A) and the dopamine D(2) receptor interactions have been studied since it may have a key significance in understanding the mechanism of action of drugs used to treat schizophrenia. With the use of fluorescence resonance energy transfer we demonstrated that the serotonin 5-HT(2A) receptors form homo- and hetero-dimers with the dopamine D(2) receptors and polymorphism H452Y within the 5-HT(2A) receptor, implicated as a cause of altered response to antipsychotic treatment, disturbs both processes. Clozapine affected the hetero-dimers (5-HT(2A)H452Y/D(2)) complexes and increased the otherwise weakened dimerization to the value observed for combination of both wild type receptors, and had no effect on the serotonin receptor homo-dimers (5-HT(2A)H452Y/5-HT(2A)), while haloperidol has restored the weakened interaction within homo-complexes and did not effect the hetero-complexes. The obtained data suggest that H452Y polymorphism has an influence not only on the level of constitutive oligomerization of investigated receptors but also it changes their pharmacological properties within both homo- and hetero-complexes.

Association and haplotype analysis of candidate genes in five genomic regions linked to sow maternal infanticide in a white Duroc × Erhualian resource population

Background

Maternal infanticide is an extreme and failed maternal behavior, which is defined as an active attack on piglets using the jaws, resulting in serious or fatal bite wounds. It brings big economic loss to the pig industry and severe problems to piglets' welfare. But little is known about the genetic background of this behavior. Quantitative trait loci (QTL) for maternal infanticide were identified in a White Duroc × Erhualian intercross by a non-parametric linkage analysis (NPL) in our previous study. In this study, associations of 194 microsatellite markers used in NPL analysis with maternal infanticide behavior were further analyzed by transmission-disequilibrium test (TDT). On this basis, seven genes (ESR2, EAAT2, BDNF, OXTR, 5-HTR2C, DRD1 and GABRA6) at five genomic regions were selected and further analyzed. Associations of single nucleotide polymorphisms (SNPs) and haplotypes in each gene with maternal infanticide behavior were evaluated.

Results

Microsatellite markers on pig chromosome (SSC) 2, 13, 15, and X displayed significance at P < 0.05 by both TDT and NPL. Of the seven candidate genes, three ESR2 SNPs had nominal evidence for association (P < 0.05). Allele A at EAAT2 g. 233G > A and allele T at DRD1 g.1013C > G > T also showed evidence of overtransmission to infanticidal sows. In the overall tests of association of haplotypes, candidate genes of ESR2, EAAT2 and DRD1 achieved overall significance level (P < 0.05). Haplotype [A; A; G], [G; A; G], [A; G; G] and [C; C], respectively, from ESR2, EAAT2 and DRD1 showed higher frequencies to infanticidal sows (P < 0.05). Alleles among haplotypes and SNPs which showed an overtransmission to infanticidal sows were from White Duroc.

Conclusions

From association tests of SNPs and haplotypes, ESR2, EAAT2 and DRD1 showed significant associations with maternal infanticide. This result supported the existence of QTL for maternal infanticide behavior on SSC1, SSC2 and SSC16.

Hetero-dimerization of serotonin 5-HT(2A) and dopamine D(2) receptors

In the present study, detailed information is presented on the hetero-dimerization of the serotonin 5-HT(2A) receptor and the dopamine D(2) receptor. Biophysical approaches (fluorescence spectroscopy as well as fluorescence lifetime microscopy) were used to determine the degree of fluorescence resonance energy transfer (FRET) between cyan and yellow fluorescent protein labeled receptor variants co-expressed in human embryonic kidney 293 cells (HEK293). Recorded data demonstrate the existence of energy transfer between the wild-type forms of 5-HT(2A)R and D(2)R, pointing toward the formation of hetero-5-HT(2A)R/D(2)R dimers and homo-5-HT(2A)R/5-HT(2A)R dimers. Moreover, the present study investigates the role of specific motifs (one containing adjacent arginine residues (217RRRRKR222) in the third intracellular loop (ic3) of D(2)R, and the other consisting of acidic glutamate residues (454EE455) in the C-tail of (5-HT(2A)R) in the formation of noncovalent complexes between these receptors. Our results suggest that these regions of 5-HT(2A)R and D(2)R may be involved in the interaction between these two proteins. On the other hand, the above-mentioned motifs do not play an important role in the homo-dimerization of these receptors. Furthermore, we estimated the influence of specific receptor ligands on the dimerization processes. Agonists (DOI and quinpirole) and antagonists (ketanserin and butaclamol) cause different effects on FRET efficiency depending on whether homo- or hetero-complexes are present. These data may have therapeutic implications, since (using the immunofluorescence double labeling protocols) the co-localization of these two receptors was demonstrated in the medial prefrontal cortex and pars reticulate of the substantia nigra of the rat brain.