Polymorphism screening of PIP5K2A: a candidate gene for chromosome 10p-linked psychiatric disorders

NRG1, PIP4K2A, and HTR2C as Potential Candidate Biomarker Genes for Several Clinical Subphenotypes of Depression and Bipolar Disorder

GSK3B, BDNF, NGF, NRG1, HTR2C, and PIP4K2A play important roles in molecular mechanisms of psychiatric disorders. GSK3B occupies a central position in these molecular mechanisms and is also modulated by psychotropic drugs. BDNF regulates a number of key aspects in neurodevelopment and synaptic plasticity. NGF exerts a trophic action and is implicated in cerebral alterations associated with psychiatric disorders. NRG1 is active in neural development, synaptic plasticity, and neurotransmission. HTR2C is another important psychopharmacological target. PIP4K2A catalyzes the phosphorylation of PI5P to form PIP2, the latter being implicated in various aspects of neuronal signal transduction. In the present study, the six genes were sequenced in a cohort of 19 patients with bipolar affective disorder, 41 patients with recurrent depressive disorder, and 55 patients with depressive episode. The study revealed a number of genetic variants associated with antidepressant treatment response, time to recurrence of episodes, and depression severity. Namely, alleles of rs35641374 and rs10508649 (NRG1 and PIP4K2A) may be prognostic biomarkers of time to recurrence of depressive and manic/mixed episodes among patients with bipolar affective disorder. Alleles of NC_000008.11:g.32614509_32614510del, rs61731109, and rs10508649 (also NRG1 and PIP4K2A) seem to be predictive biomarkers of response to pharmacological antidepressant treatment on the 28th day assessed by the HDRS-17 or CGI-I scale. In particular, the allele G of rs10508649 (PIP4K2A) may increase resistance to antidepressant treatment and be at the same time protective against recurrent manic/mixed episodes. These results support previous data indicating a biological link between resistance to antidepressant treatment and mania. Bioinformatic functional annotation of associated variants revealed possible impact for transcriptional regulation of PIP4K2A. In addition, the allele A of rs2248440 (HTR2C) may be a prognostic biomarker of depression severity. This allele decreases expression of the neighboring immune system gene IL13RA2 in the putamen according to the GTEx portal. The variant rs2248440 is near rs6318 (previously associated with depression and effects of psychotropic drugs) that is an eQTL for the same gene and tissue. Finally, the study points to several protein interactions relevant in the pathogenesis of mood disorders. Functional studies using cellular or animal models are warranted to support these results.

PIP4K2A regulates intracellular cholesterol transport through modulating PI(4,5)P2 homeostasis

The transport of LDL-derived cholesterol from lysosomes to peroxisomes is facilitated by membrane contacts formed between the lysosomal protein synaptotagmin VII and the peroxisomal lipid phosphatidylinositol 4, 5-bisphosphate [PI(4,5)P₂]. Here, we used RNA interference to search for regulators of PI(4,5)P₂ and to study the effects of altered PI(4,5)P₂ homeostasis on cholesterol transport. We found that knockdown of phosphatidylinositol 5-phosphate 4-kinase type-2 α (PIP4K2A) reduced peroxisomal PI(4,5)P₂ levels, decreased lysosome-peroxisome membrane contacts, and increased accumulation of lysosomal cholesterol in human SV-589 fibroblasts. Forced expression of peroxisome-localized, kinase-active PIP4K2A in the knockdown cells reduced cholesterol accumulation, and in vitro addition of recombinant PIP4K2A restored membrane contacts. These results suggest that PIP4K2A plays a critical role in intracellular cholesterol transport by upregulating PI(4,5)P₂ levels in the peroxisomal membrane. Further research into PIP4K2A activity may inform future therapeutic interventions for managing lysosomal storage disorders.

[Association of polymorphic variants of PIP5K2A and HTR2C genes with response to antidepressant therapy of patients with a current depressive episode]

AIM

To study the association between polymorphisms of PIP5K2A and HTR2C genes and response to antidepressant therapy in patients with a current depressive episode.

MATERIAL AND METHODS

The study included 222 patients (168 women and 54 men) with a current depressive episode. The assessment of the severity of the current depressive episode and the efficacy of treatment was performed using the Hamilton depression scale (HDRS-17) and the Clinical global impression scale (CGI-S, CGI-I). The association of treatment efficacy with PIP5K2A polymorphisms rs10430590, rs10828317 and HTR2C polymorphisms rs6318, rs569959, rs3813929, rs12858300 was studied.

RESULTS AND CONCLUSION

Polymorphisms rs10828317 and rs10430590 in the PIP5K2A gene were associated with the CGI-S total score at day 28 of therapy. Polymorphism rs6318 in the HTR2C gene was associated with response to antidepressant therapy followed by clinical improvement of patients with current depressive episode on the 28th day of antidepressant therapy.

Detecting Gene-Gene Interactions Associated with Multiple Complex Traits with U-Statistics

Many complex diseases, such as psychiatric and behavioral disorders, are commonly characterized through various measurements that reflect physical, behavioral and psychological aspects of diseases. While it remains a great challenge to find a unified measurement to characterize a disease, the available multiple phenotypes can be analyzed jointly in the genetic association study. Simultaneously testing these phenotypes has many advantages, including considering different aspects of the disease in the analysis, and utilizing correlated phenotypes to improve the power of detecting disease-associated variants. Furthermore, complex diseases are likely caused by the interplay of multiple genetic variants through complicated mechanisms. Considering gene-gene interactions in the joint association analysis of complex diseases could further increase our ability to discover genetic variants involving complex disease pathways. In this article, we propose a stepwise U-test for joint association analysis of multiple loci and multiple phenotypes. Through simulations, we demonstrated that testing multiple phenotypes simultaneously could attain higher power than testing one single phenotype at a time, especially when there are shared genes contributing to multiple phenotypes. We also illustrated the proposed method with an application to Nicotine Dependence (ND), using datasets from the Study of Addition, Genetics and Environment (SAGE). The joint analysis of three ND phenotypes identified two SNPs, rs10508649 and rs2491397, and reached a nominal P-value of 3.79e-13. The association was further replicated in two independent datasets with P-values of 2.37e-05 and 7.46e-05.

Control of diverse subcellular processes by a single multi-functional lipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]

Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] is a multi-functional lipid that regulates several essential subcellular processes in eukaryotic cells. In addition to its well-established function as a substrate for receptor-activated signalling at the plasma membrane (PM), it is now recognized that distinct PI(4,5)P2 pools are present at other organelle membranes. However, a long-standing question that remains unresolved is the mechanism by which a single lipid species, with an invariant functional head group, delivers numerous functions without loss of fidelity. In the present review, we summarize studies that have examined the molecular processes that shape the repertoire of PI(4,5)P2 pools in diverse eukaryotes. Collectively, these studies indicate a conserved role for lipid kinase isoforms in generating functionally distinct pools of PI(4,5)P2 in diverse metazoan species. The sophistication underlying the regulation of multiple functions by PI(4,5)P2 is also shaped by mechanisms that regulate its availability to enzymes involved in its metabolism as well as molecular processes that control its diffusion at nanoscales in the PM. Collectively, these mechanisms ensure the specificity of PI(4,5)P2 mediated signalling at eukaryotic membranes.

Cellular and molecular interactions of phosphoinositides and peripheral proteins

Anionic lipids act as signals for the recruitment of proteins containing cationic clusters to biological membranes. A family of anionic lipids known as the phosphoinositides (PIPs) are low in abundance, yet play a critical role in recruitment of peripheral proteins to the membrane interface. PIPs are mono-, bis-, or trisphosphorylated derivatives of phosphatidylinositol (PI) yielding seven species with different structure and anionic charge. The differential spatial distribution and temporal appearance of PIPs is key to their role in communicating information to target proteins. Selective recognition of PIPs came into play with the discovery that the substrate of protein kinase C termed pleckstrin possessed the first PIP binding region termed the pleckstrin homology (PH) domain. Since the discovery of the PH domain, more than ten PIP binding domains have been identified including PH, ENTH, FYVE, PX, and C2 domains. Representative examples of each of these domains have been thoroughly characterized to understand how they coordinate PIP headgroups in membranes, translocate to specific membrane docking sites in the cell, and function to regulate the activity of their full-length proteins. In addition, a number of novel mechanisms of PIP-mediated membrane association have emerged, such as coincidence detection-specificity for two distinct lipid headgroups. Other PIP-binding domains may also harbor selectivity for a membrane physical property such as charge or membrane curvature. This review summarizes the current understanding of the cellular distribution of PIPs and their molecular interaction with peripheral proteins.

Regulation of phosphatidylinositol-5-phosphate signaling by Pin1 determines sensitivity to oxidative stress

Oxidative signaling and oxidative stress contribute to aging, cancer, and diseases resulting from neurodegeneration. Pin1 is a proline isomerase that recognizes phosphorylated substrates and regulates the localization and conformation of its targets. Pin1(-/-) mice show phenotypes associated with premature aging, yet mouse embryonic fibroblasts (MEFs) from these mice are resistant to hydrogen peroxide (H(2)O(2))-induced cell death. We found that the abundance of phosphatidylinositol-5-phosphate (PtdIns5P) was increased in response to H(2)O(2), an effect that was enhanced in Pin1(-/-) MEFs. Reduction of H(2)O(2)-induced PtdIns5P compromised cell viability in response to oxidative stress, suggesting that PtdIns5P contributed to the enhanced cell viability of Pin1(-/-) MEFs exposed to oxidative stress. The increased PtdIns5P in the Pin1(-/-) MEFs stimulated the expression of genes involved in defense against oxidative stress and reduced the accumulation of reactive oxygen species. Pin1 and PtdIns5P 4-kinases (PIP4Ks), enzymes that phosphorylate and thereby reduce the amount of PtdIns5P, interacted in a manner dependent on the phosphorylation of PIP4K. Although reintroduction of Pin1 into the Pin1(-/-) MEFs reduced the amount of PtdIns5P produced in response to H(2)O(2), in vitro assays indicated that the isomerase activity of Pin1 inhibited PIP4K activity. Whether this isomerise-mediated inhibition of PIP4K occurs in cells remains an open question, but the data suggest that the regulation of PIP4K by Pin1 may be complex.

Wnt signaling: role in Alzheimer disease and schizophrenia

Wnt signaling function starts during the development of the nervous system and is crucial for synaptic plasticity in the adult brain. Clearly Wnt effects in synaptic and plastic processes are relevant, however the implication of this pathway in the prevention of neurodegenerative diseases that produce synaptic impairment, is even more interesting. Several years ago our laboratory found a relationship between the loss of Wnt signaling and the neurotoxicity of the amyloid-β-peptide (Aβ), one of the main players in Alzheimer's disease (AD). Moreover, the activation of the Wnt signaling cascade prevents Aβ-dependent cytotoxic effects. In fact, disrupted Wnt signaling may be a direct link between Aβ-toxicity and tau hyperphosphorylation, ultimately leading to impaired synaptic plasticity and/or neuronal degeneration, indicating that a single pathway can account for both neuro-pathological lesions and altered synaptic function. These observations, suggest that a sustained loss of Wnt signaling function may be a key relevant factor in the pathology of AD. On the other hand, Schizophrenia remains one of the most debilitating and intractable illness in psychiatry. Since Wnt signaling is important in organizing the developing brain, it is reasonable to propose that defects in Wnt signaling could contribute to Schizophrenia, particularly since the neuro-developmental hypothesis of the disease implies subtle dys-regulation of brain development, including some core components of the Wnt signaling pathways such as GSK-3β or Disrupted in Schizophrenia-1 (DISC-1). This review focuses on the relationship between Wnt signaling and its potential relevance for the treatment of neurodegenerative and neuropsychiatric diseases including AD and Schizophrenia.

Convergent functional genomic studies of ω-3 fatty acids in stress reactivity, bipolar disorder and alcoholism

Omega-3 fatty acids have been proposed as an adjuvant treatment option in psychiatric disorders. Given their other health benefits and their relative lack of toxicity, teratogenicity and side effects, they may be particularly useful in children and in females of child-bearing age, especially during pregnancy and postpartum. A comprehensive mechanistic understanding of their effects is needed. Here we report translational studies demonstrating the phenotypic normalization and gene expression effects of dietary omega-3 fatty acids, specifically docosahexaenoic acid (DHA), in a stress-reactive knockout mouse model of bipolar disorder and co-morbid alcoholism, using a bioinformatic convergent functional genomics approach integrating animal model and human data to prioritize disease-relevant genes. Additionally, to validate at a behavioral level the novel observed effects on decreasing alcohol consumption, we also tested the effects of DHA in an independent animal model, alcohol-preferring (P) rats, a well-established animal model of alcoholism. Our studies uncover sex differences, brain region-specific effects and blood biomarkers that may underpin the effects of DHA. Of note, DHA modulates some of the same genes targeted by current psychotropic medications, as well as increases myelin-related gene expression. Myelin-related gene expression decrease is a common, if nonspecific, denominator of neuropsychiatric disorders. In conclusion, our work supports the potential utility of omega-3 fatty acids, specifically DHA, for a spectrum of psychiatric disorders such as stress disorders, bipolar disorder, alcoholism and beyond.

Phosphatidylinositol-4-phosphate 5-kinases and phosphatidylinositol 4,5-bisphosphate synthesis in the brain

The predominant pathway for phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P(2)) synthesis is thought to be phosphorylation of phosphatidylinositol 4-phosphate at the 5 position of the inositol ring by type I phosphatidylinositol phosphate kinases (PIPK): PIPKIalpha, PIPKIbeta, and PIPKIgamma. PIPKIgamma has been shown to play a role in PI(4,5)P(2) synthesis in brain, and the absence of PIPKIgamma is incompatible with postnatal life. Conversely, mice lacking PIPKIalpha or PIPKIbeta (isoforms are referred to according to the nomenclature of human PIPKIs) live to adulthood, although functional effects in specific cell types are observed. To determine the contribution of PIPKIalpha and PIPKIbeta to PI(4,5)P(2) synthesis in brain, we investigated the impact of disrupting multiple PIPKI genes. Our results show that a single allele of PIPKIgamma, in the absence of both PIPKIalpha and PIPKIbeta, can support life to adulthood. In addition, PIPKIalpha alone, but not PIPKIbeta alone, can support prenatal development, indicating an essential and partially overlapping function of PIPKIalpha and PIPKIgamma during embryogenesis. This is consistent with early embryonic expression of PIPKIalpha and PIPKIgamma but not of PIPKIbeta. PIPKIbeta expression in brain correlates with neuronal differentiation. The absence of PIPKIbeta does not impact embryonic development in the PIPKIgamma knock-out (KO) background but worsens the early postnatal phenotype of the PIPKIgamma KO (death occurs within minutes rather than hours). Analysis of PIP(2) in brain reveals that only the absence of PIPKIgamma significantly impacts its levels. Collectively, our results provide new evidence for the dominant importance of PIPKIgamma in mammals and imply that PIPKIalpha and PIPKIbeta function in the generation of specific PI(4,5)P(2) pools that, at least in brain, do not have a major impact on overall PI(4,5)P(2) levels.

Association study of NRG1, DTNBP1, RGS4, G72/G30, and PIP5K2A with schizophrenia and symptom severity in a Hungarian sample

Genetic association studies have yielded extensive but frequently inconclusive data about genetic risk factors for schizophrenia. Clinical and genetic heterogeneity are possible factors explaining the inconsistent findings. The objective of this study was to test the association of commonly incriminated candidate genes with two clinically divergent subgroups, non-deficit (SZ-ND) and deficit-schizophrenia (SZ-D), and symptom severity, in order to test for replication of previously reported results. A homogeneous sample of 280 schizophrenia patients and 230 healthy controls of Hungarian, Caucasian descent were genotyped for polymorphisms in schizophrenia candidate genes NRG1, DTNBP1, RGS4, G72/G30, and PIP5K2A. Patients were divided into the diagnostic subgroups of SZ-ND and SZ-D using the Schedule for Deficit Syndrome (SDS), and assessed clinically by the Positive and Negative Symptom Scale (PANSS). SNP8NRG241930 in NRG1 and rs1011313 in DTNBP1 were associated with SZ-ND (P = 0.04 and 0.03, respectively). Polymorphisms in RGS4, G72/G30, and PIP5K2A were neither associated with SZ-ND nor with SZ-D. SNP8NRG241930 showed association with the PANSS cognitive and hostility/excitability factors, rs1011313 with the negative factor and SDS total score, and rs10917670 in RGS4 was associated with the depression factor. Although these results replicate earlier findings about the genetic background of SZ-ND and SZ-D only partially, our data seem to confirm previously reported association of NRG1 with schizophrenia without prominent negative symptoms. It was possible to detect associations of small-to-medium effect size between the investigated candidate genes and symptom severity. Such studies have the potential to unravel the possible connection between genetic and clinical heterogeneity in schizophrenia.

Association analysis of the PIP4K2A gene on chromosome 10p12 and schizophrenia in the Irish study of high density schizophrenia families (ISHDSF) and the Irish case-control study of schizophrenia (ICCSS)

Molecular studies support pharmacological evidence that phosphoinositide signaling is perturbed in schizophrenia and bipolar disorder. The phosphatidylinositol-4-phosphate-5-kinase type-II alpha (PIP4K2A) gene is located on chromosome 10p12. This region has been implicated in both diseases by linkage, and PIP4K2A directly by association. Given linkage evidence in the Irish Study of High Density Schizophrenia Families (ISHDSF) to a region including 10p12, we performed an association study between genetic variants at PIP4K2A and disease. No association was detected through single-marker or haplotype analysis of the whole sample. However, stratification into families positive and negative for the ISHDSF schizophrenia high-risk haplotype (HRH) in the DTNBP1 gene and re-analysis for linkage showed reduced amplitude of the 10p12 linkage peak in the DTNBP1 HRH positive families. Association analysis of the stratified sample showed a trend toward association of PIP4K2A SNPs rs1417374 and rs1409395 with schizophrenia in the DTNBP1 HRH positive families. Despite this apparent paradox, our data may therefore suggest involvement of PIP4K2A in schizophrenia in those families for whom genetic variation in DTNBP1 appears also to be a risk factor. This trend appears to arise from under-transmission of common alleles to female cases. Follow-up association analysis in a large Irish schizophrenia case-control sample (ICCSS) showed significant association with disease of a haplotype comprising these same SNPs rs1417374-rs1409395, again more so in affected females, and in cases with negative family history of the disease. This study supports a minor role for PIP4K2A in schizophrenia etiology in the Irish population.

PIP5K2A-dependent regulation of excitatory amino acid transporter EAAT3

INTRODUCTION

According to previous observations, the gene encoding the phosphatidylinositol-4-phosphate 5-kinase II alpha (PIP5K2A) is associated with schizophrenia. Specifically, the mutation (N251S)PIP5K2A has been discovered in schizophrenic patients but not in healthy individuals. A defect of the excitatory amino acid transporter EAAT3 has similarly been implicated in the development of schizophrenia. The present study thus explored whether PIP5K2A is involved in the regulation of EAAT3 activity.

MATERIALS AND METHODS

EAAT3 was expressed in Xenopus oocytes either without or with PIP5K2A, and EAAT3 transporter activity was estimated from the glutamate (2-mM)-induced current (I(glu)) in dual electrode voltage clamp experiments. EAAT3 protein abundance in the cell membrane was estimated by Western blotting and confocal microscopy.

RESULTS

In EAAT3-expressing oocytes, I(glu) was enhanced by coexpression of wild type PIP5K2A. Coexpression of the schizophrenia-associated mutant (N251S)PIP5K2A significantly decreased I(glu) in oocytes expressing EAAT3 with or without additional expression of wild type PIP5K2A. Thus, (N251S)PIP5K2A exerts a dominant inhibitory effect.

DISCUSSION

Membrane abundance of EAAT3 was increased by wild type PIP5K2A and decreased by (N251S)PIP5K2A in both EAAT3-expressing oocytes and human embryonic kidney cells. The present observations disclose a novel mechanism of EAAT3 regulation, which may contribute to the deranged regulation of excitability in schizophrenic patients.

PtdIns(3,4,5)P3 and inositol depletion as a cellular target of mood stabilizers

Lithium (Li+) is the mood stabilizer most frequently used in the treatment of bipolar mood disorder; however, its therapeutic mechanism is unknown. In the 1980s, Berridge and colleagues proposed that Li+ treatment acts via inhibition of IMPase (inositol monophosphatase) to deplete the cellular concentration of myo-inositol. Inositol depletion is also seen with the alternative mood stabilizers VPA (valproic acid) and CBZ (carbamazepine), suggesting a common therapeutic action. All three drugs cause changes in neuronal cell morphology and cell chemotaxis; however, it is unclear how reduced cellular inositol modulates these changes in cell behaviour. It is often assumed that reduced inositol suppresses Ins(1,4,5)P3, a major intracellular signal molecule, but there are other important phosphoinostide-based signal molecules in the cell. In the present paper, we discuss evidence that Li+ has a substantial effect on PtdIns(3,4,5)P3, an important signal molecule within the nervous system. As seen for Ins(1,4,5)P3 signalling, suppression of PtdIns(3,4,5)P3 signalling also occurs via an inositol-depletion mechanism. This has implications for the cellular mechanisms controlling phosphoinositide signalling, and offers insight into the genetics underlying risk of bipolar mood disorder.

Mammalian phosphoinositide kinases and phosphatases

Phosphoinositides are lipids that are present in the cytoplasmic leaflet of a cell's plasma and internal membranes and play pivotal roles in the regulation of a wide variety of cellular processes. Phosphoinositides are molecularly diverse due to variable phosphorylation of the hydroxyl groups of their inositol rings. The rapid and reversible configuration of the seven known phosphoinositide species is controlled by a battery of phosphoinositide kinases and phosphoinositide phosphatases, which are thus critical for phosphoinositide isomer-specific localization and functions. Significantly, a given phosphoinositide generated by different isozymes of these phosphoinositide kinases and phosphatases can have different biological effects. In mammals, close to 50 genes encode the phosphoinositide kinases and phosphoinositide phosphatases that regulate phosphoinositide metabolism and thus allow cells to respond rapidly and effectively to ever-changing environmental cues. Understanding the distinct and overlapping functions of these phosphoinositide-metabolizing enzymes is important for our knowledge of both normal human physiology and the growing list of human diseases whose etiologies involve these proteins. This review summarizes the structural and biological properties of all the known mammalian phosphoinositide kinases and phosphoinositide phosphatases, as well as their associations with human disorders.

Mutations in phosphoinositide metabolizing enzymes and human disease

Phosphoinositides are implicated in the regulation of a wide variety of cellular functions. Their importance in cellular and organismal physiology is underscored by the growing number of human diseases linked to perturbation of kinases and phosphatases that catalyze interconversion from one phosphoinositide to another. Many such enzymes are attractive targets for therapeutic interventions. Here, we review diseases linked to inheritable or somatic mutations of these enzymes.

Association study between the PIK4CA gene and methamphetamine use disorder in a Japanese population

Accumulating evidence suggests that phosphatidylinositol (PI) pathways have been involved in the secretion of dopamine (DA) and the regulation of DA transporter, which is a target of methamphetamine (METH). A recent large-scale gene-association study in a Dutch population demonstrated that the PIK4CA gene was closely linked to schizophrenia [Jungerius et al. (2007); Mol Psychiatry]. Here, we conducted a case (N = 232)-control (N = 233) study of the PIK4CA gene on Japanese METH abusers, which can manifest severe psychosis similar to schizophrenia. The genotype and allelic distributions of all four single nucleotide polymorphisms (SNPs) did not differ significantly between the METH abusers and the controls. The comparisons based on the classification of the psychosis as transient or prolonged and on the presence or absence of spontaneous relapse revealed no significant distribution of the four SNPs compared to the controls. Furthermore, haplotype analyses showed almost the same frequencies between the METH abusers and the controls. The present study suggests that the PIK4CA gene does not play a significant role in the vulnerability to METH use disorder in the Japanese population.

Association of PIP5K2A with schizophrenia: a study in an indonesian family sample

PIP5K2A variants have been shown to be associated with schizophrenia in Caucasian populations. This study tested 12 PIP5K2A SNPs for association with schizophrenia in a sample of 152 sib-pair families of Indonesian descent. All SNPs had previously been tested for association with schizophrenia in a German family sample by Schwab et al. [2006; Mol Psychiatry] and seven SNPs were nominally associated with schizophrenia in this previous study. The purpose of the study was to examine whether previously implicated PIP5K2A variants influence susceptibility to schizophrenia in populations of non-European descent. No single markers showed nominal association with schizophrenia in this Indonesian family sample, however multi-marker haplotypes including a previously associated exonic SNP marker revealed nominally significant association (P = 0.03). Power to detect association was greater than 80% for all previously implicated variants except for rs11013052, where power was greatly reduced due to the low minor allele frequency of this marker in the Indonesian sample. An explorative study combining the results of this study with those of our previous study indicated that rs11013052 was significantly associated with schizophrenia in the combined sample (P = 0.002). The results of this study suggest that any contribution of previously implicated DNA variants within the PIP5K2A gene to schizophrenia susceptibility in the Indonesian population is only minor.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

A schizophrenia-linked mutation in PIP5K2A fails to activate neuronal M channels

RATIONALE

Evidence for an association between phosphatidylinositol-4-phosphate 5-kinase II alpha (PIP5K2A) and schizophrenia was recently obtained and replicated in several samples. PIP5K2A controls the function of KCNQ channels via phosphatidylinositol-4,5-bisphosphate (PIP2) synthesis. Interestingly, recent data suggest that KCNQ channels suppress basal activity of dopaminergic neurons and dopaminergic firing. Activation of KCNQ accordingly attenuates the central stimulating effects of dopamine, cocaine, methylphenidate, and phenylcyclidine.

OBJECTIVE

The aim of this study was to explore the functional relevance of PIP5K2A, which might influence schizophrenic behavior.

MATERIALS AND METHODS

Here, we study the effects of the neuronal PIP5K2A on KCNQ2, KCNQ5, KCNQ2/KCNQ3, and KCNQ3/KCNQ5 in the Xenopus expression system.

RESULTS

We find that wild-type PIP5K2A but not the schizophrenia-associated mutant (N251S)-PIP5K2A activates heteromeric KCNQ2/KCNQ3 and KCNQ3/KCNQ5, the molecular correlate of neuronal M channels. Homomeric KCNQ2 and KCNQ5 channels were not activated by the kinase indicating that the presence of KCNQ3 in the channel complex is required for the kinase-mediated effects. Acute application of PI(4,5)P2 and a PIP2 scavenger indicates that the mutation N251S renders the kinase PIP5K2A inactive.

CONCLUSIONS

Our results suggest that the schizophrenia-linked mutation of the kinase results in reduced KCNQ channel function and thereby might explain the loss of dopaminergic control in schizophrenic patients. Moreover, the addictive potential of dopaminergic drugs often observed in schizophrenic patients might be explained by this mechanism. At least, the insufficiency of (N251S)-PIP5K2A to stimulate neuronal M channels may contribute to the clinical phenotype of schizophrenia.

The physiology of phosphoinositides

Phosphoinositides are a family of phosphorylated derivatives of the membrane lipid phosphatidylinositol. These lipids are highly concentrated in distinct pools located in a cell's plasma membrane, endosomes or nucleus, where they function as ligands for phosphoinositide-binding proteins. Protein domains that bind phosphoinositides include the pleckstrin homology (PH) domain, the phox homology (PX) domain and the Fab1p-YOPB-Vps27p-EEA1 (FYVE) domain. These domains are found in many proteins involved in intracellular signaling, membrane trafficking and cytoskeletal rearrangement. Recent studies have identified potential links between alterations to various signaling pathways involving phosphoinositides and the etiology of many human diseases.

The PIP5K2A gene and schizophrenia in the Chinese population--a case-control study

Results from a number of molecular and pharmacological studies suggest that the phosphatidylinositol-4-phosphate 5-kinase IIalpha (PIP5K2A) gene may be involved in the development of schizophrenia. A recent family-based transmission disequilibrium test in the German and Israeli populations found that four single nucleotide polymorphisms, rs1417374, rs10828317, rs746203 and rs8341 in this gene or nearby intergenic regions are significantly associated with schizophrenia. The objective of our study was to investigate whether these four SNPs are also associated with schizophrenia in the Chinese population. Our study found that SNP rs8341 (p=0.0045, Odds Ratio=1.415, 95%CI=1.113-1.799 for the minor allele) and a haplotype (p=0.0039, Odds Ratio=1.440, 95%CI=1.123-1.845) are significantly associated with schizophrenia. Our results confirm that the PIP5K2A gene merits further study as a susceptible gene for schizophrenia.

Attenuation of phospholipid signaling provides a novel mechanism for the action of valproic acid

Valproic acid (VPA) is used to treat epilepsy and bipolar disorder and to prevent migraine. It is also undergoing trials for cancer therapy. However, the biochemical and molecular biological actions of VPA are poorly understood. Using the social amoeba Dictyostelium discoideum, we show that an acute effect of VPA is the inhibition of chemotactic cell movement, a process partially dependent upon phospholipid signaling. Analysis of this process shows that VPA attenuates the signal-induced translocation of PH(Crac)-green fluorescent protein from cytosol to membrane, suggesting the inhibition of phosphatidylinositol-(3,4,5)-trisphosphate (PIP(3)) production. Direct labeling of lipids in vivo also shows a reduction in PIP and PIP(2) phosphorylation following VPA treatment. We further show that VPA acutely reduces endocytosis and exocytosis-processes previously shown to be dependent upon PIP(3) production. These results suggest that in Dictyostelium, VPA rapidly attenuates phospholipid signaling to reduce endocytic trafficking. To examine this effect in a mammalian model, we also tested depolarization-dependent neurotransmitter release in rat nerve terminals, and we show that this process is also suppressed upon application of VPA and an inhibitor of phosphatidylinositol 3-kinase. Although a more comprehensive analysis of the effect of VPA on lipid signaling will be necessary in mammalian systems, these results suggest that VPA may function to reduce phospholipid signaling processes and thus may provide a novel therapeutic effect for this drug.

PtdIns-4,5-P2 as a potential therapeutic target for pathologic angiogenesis

A variety of diseases arise, at least in part, when the events controlling the formation and stability of blood vessels are deregulated. For instance, the growth and survival of solid tumors are tightly linked to their ability to undergo vascularization. Similarly, pathologic angiogenesis of the retina or choroid underscores blinding diseases that afflict a substantial percentage of the world's population. Therefore, it is of great interest to develop antiangiogenic drugs that will relieve the burden of vascular diseases such as cancer, age-related macular degeneration and proliferative diabetic retinopathy. In this article, the authors highlight their recent discovery that PtdIns-4,5-P2)can regulate vessel stability. This finding identifies PtdIns-4,5-P2 as a novel target for angiogenesis therapies.

ThePIP5K2AandRGS4genes are differentially associated with deficit and non-deficit schizophrenia

Several putative schizophrenia susceptibility genes have recently been reported, but it is not clear whether these genes are associated with schizophrenia in general or with specific disease subtypes. In a previous study, we found an association of the neuregulin 1 (NRG1) gene with non-deficit schizophrenia only. We now report an association study of four schizophrenia candidate genes in patients with and without deficit schizophrenia, which is characterized by severe and enduring negative symptoms. Single-nucleotide polymorphisms (SNPs) were genotyped in the DTNBP1 (dysbindin), G72/G30 and RGS4 genes, and the relatively unknown PIP5K2A gene, which is located in a region of linkage with both schizophrenia and bipolar disorder. The sample consisted of 273 Dutch schizophrenia patients, 146 of whom were diagnosed with deficit schizophrenia and 580 controls. The strongest evidence for association was found for the A-allele of SNP rs10828317 in the PIP5K2A gene, which was associated with both clinical subtypes (P = 0.0004 in the entire group; non-deficit P = 0.016, deficit P = 0.002). Interestingly, this SNP leads to a change in protein composition. In RGS4, the G-allele of the previously reported SNP RGS4-1 (single and as part of haplotypes with SNP RGS4-18) was associated with non-deficit schizophrenia (P = 0.03) but not with deficit schizophrenia (P = 0.79). SNPs in the DTNBP1 and G72/G30 genes were not significantly associated in any group. In conclusion, our data provide further evidence that specific genes may be involved in different schizophrenia subtypes and suggest that the PIP5K2A gene deserves further study as a general susceptibility gene for schizophrenia.

The 2',3'-cyclic nucleotide 3'-phosphodiesterase and oligodendrocyte lineage transcription factor 2 genes do not appear to be associated with schizophrenia in the Japanese population

Several lines of evidence suggest that disturbance of myelin-related genes is associated with the etiology of schizophrenia. Recently, the 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) gene and the oligodendrocyte lineage transcription factor 2 (OLIG2) gene were reported to be related to the development of schizophrenia, based on the results of genetic association and microarray studies. In the present study, no significant association with schizophrenia was observed by single-marker or haplotype analysis for 6 tag SNPs of these genes (759 cases, 757 controls). These findings suggest that CNP and OLIG2 are unlikely to be related to the development of schizophrenia in the Japanese population.

Association study between genetic variants at the PIP5K2A gene locus and schizophrenia and bipolar affective disorder

Results from molecular and pharmacological studies point to involvement of the gene coding for the phosphatidylinositol-4-phosphate 5-kinase type II-alpha (PIP5K2A) in the development of schizophrenia and bipolar affective disorder (BPAD). The PIP5K2A gene locus, which is located on chromosomal region 10p12, has been implicated in the development of both disorders by independent linkage and association studies. On a cellular level, PIP5K2A is an enzyme component of the metabolism of inositol phosphate, which has been considered a potential target for the therapeutic action of lithium in BPAD patients. Given that the PIP5K2A gene is a promising candidate for the development of both disorders, we performed an association study between genetic variants at the PIP5K2A locus and 268 patients with schizophrenia, 260 patients with BPAD and 325 ethnically matched healthy controls. We failed to detect association to either disorder using PIP5K2A gene variants through single-marker and haplotype analysis. Therefore, our data does not support an involvement of the PIP5K2A locus in the etiology of either schizophrenia or BPAD in the German population.

Evidence for association of DNA sequence variants in the phosphatidylinositol-4-phosphate 5-kinase IIalpha gene (PIP5K2A) with schizophrenia

Linkage studies in schizophrenia have identified a candidate region on chromosome 10p14-11 as reported for several independent samples. We investigated association of DNA sequence variants in a plausible candidate gene located in this region, the gene for phosphatidylinositol-4-phosphate 5-kinase IIalpha (PIP5K2A), in a sample of 65 sib-pair families for which linkage had been reported. Evidence for association was obtained for 15 polymorphisms spanning 73.6 kb in the genomic region of the gene between intron 4 and the 3' untranslated region, a region with high degree of linkage disequilibrium. Single nucleotide polymorphism (SNP) rs10828317 located in exon 7 and causing a non-synonymous amino-acid exchange (asparagine/serine) produced a P-value of 0.001 (experiment-wide significance level 0.00275) for over-transmission of the major allele coding for serine, analysed by transmission disequilibrium test using FAMHAP. Association of this SNP with schizophrenia has been also described in a sample of 273 Dutch schizophrenic patients and 580 controls (P=0.0004). PIP5K2A is involved in the biosynthesis of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2), one of the key metabolic crossroads in phosphoinositide signalling. PI(4,5)P2 plays a role in membrane transduction of neurotransmitter signals as well as in intracellular signalling, pathways that may be impaired in schizophrenia.

Schizophrenia proteomics: biomarkers on the path to laboratory medicine?

Over two million Americans are afflicted with schizophrenia, a debilitating mental health disorder with a unique symptomatic and epidemiological profile. Genomics studies have hinted towards candidate schizophrenia susceptibility chromosomal loci and genes. Modern proteomic tools, particularly mass spectrometry and expression scanning, aim to identify both pathogenic-revealing and diagnostically significant biomarkers. Only a few studies on basic proteomics have been conducted for psychiatric disorders relative to the plethora of cancer specific experiments. One such proteomic utility enables the discovery of proteins and biological marker fingerprinting profiling techniques (SELDI-TOF-MS), and then subjects them to tandem mass spectrometric fragmentation and de novo protein sequencing (MALDI-TOF/TOF-MS) for the accurate identification and characterization of the proteins. Such utilities can explain the pathogenesis of neuro-psychiatric disease, provide more objective testing methods, and further demonstrate a biological basis to mental illness. Although clinical proteomics in schizophrenia have yet to reveal a biomarker with diagnostic specificity, methods that better characterize the disorder using endophenotypes can advance findings. Schizophrenia biomarkers could potentially revolutionize its psychopharmacology, changing it into a more hypothesis and genomic/proteomic-driven science.

An emerging role for PtdIns(4,5)P2-mediated signalling in human disease

Although an established regulator of many cellular functions, the phosphoinositide phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P2) appears to have evaded the attention of drug-discovery companies. An increasing number of reports have identified potential links between PtdIns(4,5)P2-mediated signalling pathways and the aetiology of many human diseases. Here, we review current knowledge of the regulation and function of PtdIns(4,5)P2 and discuss how aberrant PtdIns(4,5)P2-mediated signalling might contribute to human pathologies such as cardiac failure, bipolar disorder, channelopathies and the genetic disorder Lowe syndrome.

Screening of PIP5K2A promoter region for mutations in bipolar disorder and schizophrenia

OBJECTIVE

To analyze the promoter region of PIP5K2A, a phosphatidylinositol 4-phosphate 5-kinase that maps to 10p in a region linked to both bipolar disorder and schizophrenia.

METHODS

The promoter region was screened by single-strand conformation polymorphism analysis and DNA sequencing. Allele frequencies were determined in a case-control study. Functional significance of a promoter variant was determined by electromobility gel shift assays.

RESULTS

Homozygosity for a rare putative promoter variant, -1007C-->T, was found in only two patients with schizophrenia and in no controls or bipolar patients. The variant forms a 7/8 base match for the binding site of Oct-1, a member of the POU homeodomain family. Electromobility gel shift assays revealed increased binding of a brain-specific nuclear protein to the -1007T allele compared with -1007C.

CONCLUSION

The data suggest that homozygosity for -1007T could be a rare genetic factor in the development of schizophrenia.

Association of schizophrenia in African Americans to polymorphism in synapsin III gene

Linkage studies in families with schizophrenia have pointed to chromosome 22q12-q13 as one of several regions of the genome that may contain a susceptibility gene. The gene coding for synapsin III, an intrinsic synaptic vesicle membrane protein, maps to this target region. Two tightly linked single-nucleotide polymorphisms were recently found in a small subset of patients with SZ - a synonymous variant, L469L (469G>A), and a non-synonymous variant, S470N (470G>A) - which results in the loss of a mitogen-activated protein kinase serine phosphorylation site. We also found a slight increase in 470A in Caucasian patients from the US with schizophrenia. But, the sample size and allele frequency were too small to draw definitive conclusions. However, both single-nucleotide polymorphisms were much more polymorphic in African American controls than in Caucasian controls, thereby providing a better sample cohort to analyze for schizophrenia involvement. For the codon 469 single-nucleotide polymorphisms, a 50-fold increase was observed in the frequency of 469A in African Americans compared with Caucasians. Furthermore, there was an increase in the percentage of African American patients with schizophrenia who were homozygous for the 469A allele compared with controls who were homozygous (11 versus 5%; AA vs. all other genotypes - Fisher statistic=3.08, P=0.04, one-tailed). An increase in 470A heterozygotes was also found, but the results fell short of being statistically significant. The findings support a role for synapsin III in a subset of African American patients with schizophrenia and raises questions about selective pressure in Africa to account for the extraordinary disparity of the 469 and 470 single-nucleotide polymorphisms in different ethnic populations.

Genetic tests of biologic systems in affective disorders

To liberate candidate gene analyses from criticisms of inexhaustiveness of examination of specific candidate genes, or incompleteness in the choice of candidate genes to study for specific neurobiological pathways, study of sizeable sets of genes pertinent to each putative pathophysiological pathway is required. For many years, genes have been tested in a 'one by one' manner for association with major affective disorders, primarily bipolar illness. However, it is conceivable that not individual genes but abnormalities in several genes within a system or in several neuronal, neural, or hormonal systems are implicated in the functional hypotheses for etiology of affective disorders. Compilation of candidate genes for entire pathways is a challenge, but can reasonably be carried out for the major affective disorders as discussed here. We present here five groupings of genes implicated by neuropharmacological and other evidence, which suggest 252 candidate genes worth examining. Inexhaustiveness of gene interrogation would apply to many studies in which only one polymorphism per gene is analyzed. In contrast to whole-genome association studies, a study of a limited number of candidate genes can readily exploit information on genomic sequence variations obtained from databases and/or resequencing, and has an advantage of not having the complication of an extremely stringent statistical criterion for association.

Genetic models of schizophrenia and bipolar disorder: overlapping inheritance or discrete genotypes?

Schizophrenia and affective disorder have been considered to be nosologically and etiologically distinct disorders. This postulate is challenged by progress in new biological research. Both disorders are strongly influenced by genetic factors; thus genetic research is a main contributor to this discussion. We review current evidence of the genetic relationship between schizophrenia and affective disorders, mainly bipolar disorder (the various genetic research methods have been particularly applied to bipolar disorder). Recent family and twin studies reveal a growing consistency in demonstrating cosegregation between both disorders which is difficult to detect with certainty given the low base rates. Systematic molecular genetic search for specific genes impacting on either disorder has now identified one gene which is apparently involved in both disorders (G72/G30); other candidate genes reveal some evidence to present as susceptibility genes with very modest effects for each of both disorders, although not consistently so (e. g., COMT, BDNF). There is room for speculation about other common susceptibility genes, given the overlap between candidate regions for schizophrenia and those for bipolar disorder emerging from linkage studies.

Analysis of SYNJ1, a candidate gene for 21q22 linked bipolar disorder: a replication study

Linkage analysis has shown that chromosome 21q22 may contain a candidate gene for bipolar disorder (BPD). One potential 21q22 candidate gene we previously analyzed is SYNJ1, which encodes synaptojanin 1, an inositol 5-phosphatase. Previous mutation screening of SYNJ1 identified three rare functional variants, one of which is a polymorphic variant near the intron 12-oxon 12 border. The rare variants were found only in a total of four BPD patients and no controls, and a trend toward significance was found for the intron 12 polymorphism. In an analysis of a new set of 84 bipolar patients, none of the rare variants were detected. There was an increase in allele 2 for the intron 12 polymorphism, similar to our original study, but the result was not significant. The combined data from both studies continue to show a trend toward significance for allele 2 homozygotes in BPD.

Identification of PIK3C3 promoter variant associated with bipolar disorder and schizophrenia

BACKGROUND

Genes involved in phosphoinositide (PI) lipid metabolism are excellent candidates to consider in the pathogenesis of bipolar disorder (BD) and schizophrenia (SZ). One is PIK3C3, a member of the phosphatidylinositide 3-kinase family that maps closely to markers on 18q linked to both BD and SZ in a few studies.

METHODS

The promoter region of PIK3C3 was analyzed for mutations by single-strand conformation polymorphism analysis and sequencing. A case-control association study was conducted to determine the distribution of variant alleles in unrelated patients from three cohorts. Electromobility gel shift assays (EMSA) were performed to assess the functional significance of variants.

RESULTS

Two polymorphisms in complete linked disequilibrium with each other were identified, -432C- > T and a "C" insert at position -86. The -432T allele occurs within an octamer containing an ATTT motif resembling members of the POU family of transcription factors. In each population analyzed, an increase in -432T was found in patients. EMSAs showed that a -432T containing oligonucleotide binds to brain proteins that do not recognize -432C.

CONCLUSIONS

A promoter mutation in a PI regulator affecting the binding of a POU-type transcription factor may be involved in BD and SZ in a subset of patients.