An association study between PPP1R1B gene and schizophrenia in the Chinese population

Lower density of calretinin-immunopositive neurons in the putamen of subjects with schizophrenia

Schizophrenia (SCH) is a chronic and serious mental illness which puts an enormous burden on the individual, families, and society. It is well established that altered dopamine signaling and excitatory-inhibitory imbalance contributes to the symptoms of schizophrenia. Recent neuroimaging and histological studies suggest that the striatum is a key area involved in SCH, however, our knowledge of how specific cell neuronal subtypes of certain subcortical structures may be impaired is incomplete. To this date, no detailed investigation of the putamen has ever been published regarding neuroanatomical changes in SCH. Here we tested whether the density of calretinin immunopositive (CR+) neurons and DARPP32+ neurons is altered in the putamen of patients with SCH. We used immunohistochemistry to reveal CR+ and DARPP32+ neurons in six samples from patients with SCH and six age- and gender-matched control subjects. In line with previous studies, we detected small, medium, and large CR+ neurons. The density of small CR+ neurons was significantly lower in SCH (p = 0.0076). Medium and large CR+ and DARPP32+ neuronal density was not significantly different between groups. The present study substantiates previous results showing significantly lower density of small CR+ interneurons in the caudate nucleus in samples from patients with schizophrenia, highlighting the involvement of the striatum in the disorder. Our results warrant further studies focusing on the role of CR+ interneurons in the regulation of information processing in the fronto-striatal networks, evidently key structures in schizophrenia.

The involvement of DARPP-32 in the pathophysiology of schizophrenia

Schizophrenia is one of the most devastating heterogeneous psychiatric disorders. The dopamine hypothesis is the longest standing pathoetiologic theory of schizophrenia based on neurochemical evidences of elevated brain striatal dopamine synthesis capacity and increased dopamine release in response to stress. Dopamine and cyclic AMP-regulated phosphoprotein of relative molecular mass 32,000 (DARPP-32) is a cytosolic protein highly enriched in the medium spiny neurons of the neostriatum, considered as the most important integrator between the cortical input and the basal ganglia, and associated with motor control. Accumulating evidences has indicated the involvement of DARPP-32 in the development of schizophrenia; i. DARPP-32 phosphorylation is regulated by several neurotransmitters, including dopamine and glutamate, neurotransmitters implicated in schizophrenia pathogenesis; ii. decrease of both total and phosphorylated DARPP-32 in the prefrontal cortex are observed in schizophrenic animal models; iii. postmortem brain studies indicated decreased expression of DARPP-32 protein in the superior temporal gyrus and dorsolateral prefrontal cortex in patients with schizophrenia; iv. DARPP-32 phosphorylation is increased upon therapy with antipsychotic drugs, such as haloperidol and risperidone which improve behavioral performance in experimental animal models and patients; v. Genetic analysis of the gene coding for DARPP-32 propose an association with schizophrenia. Cumulatively, these findings implicate DARPP-32 protein in schizophrenia and propose it as a potential therapeutic target. Here, we summarize the possible roles of DARPP-32 during the development of schizophrenia and make some recommendations for future research. We propose that DARPP-32 and its interacting proteins may serve as potential therapeutic targets in the treatment of schizophrenia.

Genetic and Developmental Perspective of Language Abnormality in Autism and Schizophrenia

Language and communication through it are two of the defining features of normally developed human beings. However, both these functions are often impaired in autism and schizophrenia. In the former disorder, the problem usually emerges in early childhood (~2 years old) and typically includes a lack of communication. In the latter condition, the language problems usually occur in adolescence and adulthood and presents as disorganized speech. What are the fundamental mechanisms underlying these two disorders? Is there a shared genetic basis? Are the traditional beliefs about them true? Are there any common strategies for their prevention and management? To answer these questions, we searched PubMed by using autism, schizophrenia, gene, and language abnormality as keywords, and we reconsidered the basic concepts about these two diseases or syndromes. We found many functional genes, for example, FOXP2, COMT, GABRB3, and DISC1, are actually implicated in both of them. After observing the symptoms, genetic correlates, and temporal progression of these two disorders as well as their relationships more carefully, we now infer that the occurrence of these two diseases is likely developmentally regulated via interaction between the genome and the environment. Furthermore, we propose a unified view of autism and schizophrenia: a single age-dependently occurred disease that is newly named as Systemic Integral Disorder: if occurring in children before age 2, it is called autism; if in adolescence or a later age, it is called schizophrenia.

Revisiting DARPP-32 in postmortem human brain: changes in schizophrenia and bipolar disorder and genetic associations with t-DARPP-32 expression

Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32 or PPP1R1B) has been of interest in schizophrenia owing to its critical function in integrating dopaminergic and glutaminergic signaling. In a previous study, we identified single-nucleotide polymorphisms (SNPs) and a frequent haplotype associated with cognitive and imaging phenotypes that have been linked with schizophrenia, as well as with expression of prefrontal cortical DARPP-32 messenger RNA (mRNA) in a relatively small sample of postmortem brains. In this study, we examined the association of expression of two major DARPP-32 transcripts, full-length (FL-DARPP-32) and truncated (t-DARPP-32), with genetic variants of DARPP-32 in three brain regions receiving dopaminergic input and implicated in schizophrenia (the dorsolateral prefrontal cortex (DLPFC), hippocampus and caudate) in a much larger set of postmortem samples from patients with schizophrenia, bipolar disorder, major depression and normal controls (>700 subjects). We found that the expression of t-DARPP-32 was increased in the DLPFC of patients with schizophrenia and bipolar disorder, and was strongly associated with genotypes at SNPs (rs879606, rs90974 and rs3764352), as well as the previously identified 7-SNP haplotype related to cognitive functioning. The genetic variants that predicted worse cognitive performance were associated with higher t-DARPP-32 expression. Our results suggest that variation in PPP1R1B affects the abundance of the splice variant t-DARPP-32 mRNA and may reflect potential molecular mechanisms implicated in schizophrenia and affective disorders.

Association between a casein kinase 1 ε gene polymorphism and schizophrenia in a Chinese Han population

The casein kinase 1 (Csnk1) family of serine/threonine kinases regulates dopamine receptor (DR) signaling by phosphorylating the 32-kDa dopamine- and cAMP-regulated phosphoprotein DARPP-32, leading to inhibition of protein phosphatase 1 and a shift in the phosphorylation state of many downstream proteins. By modulating DR-activated phosphorylation cascades, Csnk1 plays a central role in neuropsychiatric disorders and modulates the stimulant response to amphetamine. No published study, however, has established a correlation between Csnk1 gene polymorphisms and schizophrenia. We genotyped the rs135745C/G polymorphism of the Csnk1ε gene in 384 schizophrenic patients and 502 healthy controls drawn from the Chinese Han population. There were significantly higher CG and CC genotype frequencies in schizophrenic patients compared to control subjects (CG, p = 0.0086, odds ratio (OR) = 1.477, 95% confidence interval (CI), 1.103-1.978; CC, p = 0.0431, OR = 2.571; 95% CI, 0.998-6.624). The C allele frequency was also higher in the schizophrenics (p = 0.0022; OR = 1.474; 95% CI, 1.149-1.891). In the dominant model, subjects with genotypes CC or CG were at greater risk for schizophrenia (p = 0.0032; OR = 1.532; 95% CI, 1.153-2.037), suggesting that a genetic variant in the Csnk1ε gene significantly enhances the probability of schizophrenia in the Chinese Han population.

Detailed DARPP-32 expression profiles in postmortem brains from patients with schizophrenia: an immunohistochemical study

The prevalence of dopamine and cAMP-regulated phosphoprotein 32kD (DARPP-32) is associated with the pathogenesis of schizophrenia. To date, the findings on DARPP-32 cellular expression and distribution in postmortem brains from patients with schizophrenia have been inconsistent. To clarify the detailed cellular expression of DARPP-32 in patients with schizophrenia, we immunohistochemically stained sections from postmortem brains using specific antibodies. We measured the density of immunopositive cells in various brain regions including the prefrontal cortex and compared the data from nine schizophrenia subjects with those of nine age- and sex-matched control subjects. The density of DARPP-32-immunoreactive (IR) neurons was significantly lower in layers II-V of the dorsolateral prefrontal cortex (DLPFC) from subjects with schizophrenia. In contrast, there were no marked differences in DARPP-32 expression in other brain regions. In addition, the density of threonine (Thr34)-phosphorylated DARPP-32-IR neurons was significantly higher in layer V of DLPFC from subjects with schizophrenia. These results suggest that the decrease in DARPP-32 in schizophrenia was more marked in neurons of DLPFC than in other cells or other brain regions, and that this decrease might be partly compensated for by an increase in expression of Thr34-phosphorylated DARPP-32 in DLPFC.

DARPP-32, Jack of All Trades… Master of Which?

DARPP-32 (PPP1R1B) was discovered as a substrate of cAMP-dependent protein kinase (PKA) enriched in dopamine-innervated brain areas. It is one of three related, PKA-regulated inhibitors of protein phosphatase-1 (PP1). These inhibitors seem to have appeared in early vertebrate ancestors, possibly Gnathostomes. DARPP-32 has additional important biochemical properties including inhibition of PKA when phosphorylated by Cdk5 and regulation by casein kinases 1 and 2. It is highly enriched in specific neuronal populations, especially striatal medium-size spiny neurons. As PP1 inhibitor DARPP-32 amplifies and/or mediates many actions of PKA at the plasma membrane and in the cytoplasm, with a broad spectrum of potential targets and functions. DARPP-32 also undergoes a continuous and tightly regulated cytonuclear shuttling. This trafficking is controlled by phosphorylation of Ser-97, which is necessary for nuclear export. When phosphorylated on Thr-34 and dephosphorylated on Ser-97, DARPP-32 can inhibit PP1 in the nucleus and modulate signaling pathways involved in the regulation of chromatin response. Recent work with multiple transgenic and knockout mutant mice has allowed the dissection of DARPP-32 function in striato-nigral and striato-pallidal neurons. It is implicated in the action of therapeutic and abused psychoactive drugs, in prefrontal cortex function, and in sexual behavior. However, the contribution of DARPP-32 in human behavior remains poorly understood. Post-mortem studies in humans suggest possible alterations of DARPP-32 levels in schizophrenia and bipolar disorder. Genetic studies have revealed a polymorphism with possible association with psychological and psychopathological traits. In addition, a short isoform of DARPP-32, t-DARPP, plays a role in cancer, indicating additional signaling properties. Thus, DARPP-32 is a non-essential but tightly regulated signaling hub molecule which may improve the general performance of the neuronal circuits in which it is expressed.

Beyond the dopamine receptor: regulation and roles of serine/threonine protein phosphatases

Dopamine plays an important modulatory role in the central nervous system, helping to control critical aspects of motor function and reward learning. Alteration in normal dopaminergic neurotransmission underlies multiple neurological diseases including schizophrenia, Huntington’s disease, and Parkinson’s disease. Modulation of dopamine-regulated signaling pathways is also important in the addictive actions of most drugs of abuse. Our studies over the last 30 years have focused on the molecular actions of dopamine acting on medium spiny neurons, the predominant neurons of the neostriatum. Striatum-enriched phosphoproteins, particularly dopamine and adenosine 3′:5′-monophosphate-regulated phosphoprotein of 32 kDa (DARPP-32), regulator of calmodulin signaling (RCS), and ARPP-16, mediate pleiotropic actions of dopamine. Notably, each of these proteins, either directly or indirectly, regulates the activity of one of the three major subclasses of serine/threonine protein phosphatases, PP1, PP2B, and PP2A, respectively. For example, phosphorylation of DARPP-32 at Thr34 by protein kinase A results in potent inhibition of PP1, leading to potentiation of dopaminergic signaling at multiple steps from the dopamine receptor to the nucleus. The discovery of DARPP-32 and its emergence as a critical molecular integrator of striatal signaling will be discussed, as will more recent studies that highlight novel roles for RCS and ARPP-16 in dopamine-regulated striatal signaling pathways.

Variation of the gene coding for DARPP-32 (PPP1R1B) and brain connectivity during associative emotional learning

Associative emotional learning, which is important for the social emotional functioning of individuals and is often impaired in psychiatric illnesses, is in part mediated by dopamine and glutamate pathways in the brain. The protein DARPP-32 is involved in the regulation of dopaminergic and glutaminergic signaling. Consequently, it has been suggested that the haplotypic variants of the gene PPP1R1B that encodes DARPP-32 are associated with working memory and emotion processing. We hypothesized that PPP1R1B should have a significant influence on the network of brain regions involved in associative emotional learning that are rich in DARPP-32, namely the striatum, prefrontal cortex (comprising the medial frontal gyrus and inferior frontal gyrus (IFG)), amygdala and parahippocampal gyrus (PHG). Dynamic causal models were applied to functional MRI data to investigate how brain connectivity during an associative emotional learning task is affected by different single-nucleotide polymorphisms (SNPs) of PPP1R1B: rs879606, rs907094 and rs3764352. Compared to heterozygotes, homozygotes with GTA alleles displayed increased intrinsic connectivity between the IFG and PHG, as well as increased excitability of the PHG for negative emotional stimuli. We have also elucidated the directionality of these genetic influences. Our data suggest that homozygotes with GTA alleles involve stronger functional connections between brain areas in order to maintain activation of these regions. Homozygotes might engage a greater degree of motivational learning and integration of information to perform the emotional learning task correctly. We conclude that PPP1R1B is associated with the neural network involved in associative emotional learning.

Association between DARPP-32 gene polymorphism and personality traits in healthy Chinese-Han subjects

The 32-kDa dopamine- and cAMP-regulated phosphoprotein (DARPP-32) is a key signaling factor in several neurotransmitter pathways (including dopamine and serotonin) that impact personality traits. Therefore, different DARPP-32 alleles may influence the biological determination of distinct personality types. We established an association between the DARPP-32 gene polymorphisms (rs12601930C/T, rs879606A/G, and rs3764352A/G) and personality traits as measured by the Tridimensional Personality Questionnaire in 502 healthy Chinese-Han subjects. Of the three polymorphic sites examined, rs12601930C/T was associated with novelty seeking (χ² = 13.06, P = 0.001), while both rs879606A/G and rs3764352A/G were associated with harm avoidance (rs879606: χ² = 7.74, P = 0.021; rs3764352: χ² = 8.53, P = 0.014). There was no significant association between reward dependence scores and DARPP-32 gene polymorphisms. Our results suggest that polymorphisms in the DARPP-32 gene are involved in the biological mechanisms that confer the traits of novelty seeking and harm avoidance.

The physiology, signaling, and pharmacology of dopamine receptors

G protein-coupled dopamine receptors (D1, D2, D3, D4, and D5) mediate all of the physiological functions of the catecholaminergic neurotransmitter dopamine, ranging from voluntary movement and reward to hormonal regulation and hypertension. Pharmacological agents targeting dopaminergic neurotransmission have been clinically used in the management of several neurological and psychiatric disorders, including Parkinson's disease, schizophrenia, bipolar disorder, Huntington's disease, attention deficit hyperactivity disorder (ADHD(1)), and Tourette's syndrome. Numerous advances have occurred in understanding the general structural, biochemical, and functional properties of dopamine receptors that have led to the development of multiple pharmacologically active compounds that directly target dopamine receptors, such as antiparkinson drugs and antipsychotics. Recent progress in understanding the complex biology of dopamine receptor-related signal transduction mechanisms has revealed that, in addition to their primary action on cAMP-mediated signaling, dopamine receptors can act through diverse signaling mechanisms that involve alternative G protein coupling or through G protein-independent mechanisms via interactions with ion channels or proteins that are characteristically implicated in receptor desensitization, such as β-arrestins. One of the future directions in managing dopamine-related pathologic conditions may involve a transition from the approaches that directly affect receptor function to a precise targeting of postreceptor intracellular signaling modalities either directly or through ligand-biased signaling pharmacology. In this comprehensive review, we discuss dopamine receptor classification, their basic structural and genetic organization, their distribution and functions in the brain and the periphery, and their regulation and signal transduction mechanisms. In addition, we discuss the abnormalities of dopamine receptor expression, function, and signaling that are documented in human disorders and the current pharmacology and emerging trends in the development of novel therapeutic agents that act at dopamine receptors and/or on related signaling events.

A case-control association study between the CYP3A4 and CYP3A5 genes and schizophrenia in the Chinese Han population

In this study, variants of two genes coding for cytochrome P450 enzyme (CYP3A4 and CYP3A5) were analysed in a case-control sample using 398 schizophrenic patients and 391 healthy controls. All subjects were unrelated Han Chinese from Shanghai. No difference was observed on the allelic or genotypic distribution of CYP3A4 and CYP3A5 gene polymorphisms between the groups. However, the two-marker haplotypes covering components CYP3A41G and CYP3A53 were observed to be significantly associated with schizophrenia (corrected global p=0.0009). In addition, we identified one common risk haplotype, G/G (present in 59.5% of the general population). The results suggest that CYP3A4 and CYP3A5 might play a role in genetic susceptibility to schizophrenia. However, confirmatory studies in independent samples are needed.