Neurodevelopment and mood stabilizers

Serotonin-related rodent models of early-life exposure relevant for neurodevelopmental vulnerability to psychiatric disorders

Mental disorders including depression and anxiety are continuously rising their prevalence across the globe. Early-life experience of individuals emerges as a main risk factor contributing to the developmental vulnerability to psychiatric disorders. That is, perturbing environmental conditions during neurodevelopmental stages can have detrimental effects on adult mood and emotional responses. However, the possible maladaptive neural mechanisms contributing to such psychopathological phenomenon still remain poorly understood. In this review, we explore preclinical rodent models of developmental vulnerability to psychiatric disorders, focusing on the impact of early-life environmental perturbations on behavioral aspects relevant to stress-related and psychiatric disorders. We limit our analysis to well-established models in which alterations in the serotonin (5-HT) system appear to have a crucial role in the pathophysiological mechanisms. We analyze long-term behavioral outcomes produced by early-life exposures to stress and psychotropic drugs such as the selective 5-HT reuptake inhibitor (SSRI) antidepressants or the anticonvulsant valproic acid (VPA). We perform a comparative analysis, identifying differences and commonalities in the behavioral effects produced in these models. Furthermore, this review discusses recent advances on neurodevelopmental substrates engaged in these behavioral effects, emphasizing the possible existence of maladaptive mechanisms that could be shared by the different models.

Histone deacetylase 4 (HDAC4): a new player in anorexia nervosa?

Anorexia nervosa (AN) and other eating disorders continue to constitute significant challenges for individual and public health. AN is thought to develop as a result of complex interactions between environmental triggers, psychological risk factors, sociocultural influences, and genetic vulnerability. Recent research developments have highlighted a novel potentially relevant component in the AN etiology-activity of the histone deacetylase 4 (HDAC4) gene that has emerged in several recent studies related to AN. HDAC4 is a member of the ubiquitously important family of epigenetic modifier enzymes called histone deacetylases and has been implicated in processes related to the formation and function of the central nervous system (CNS), bone, muscle, and metabolism. In a family affected by eating disorders, a missense mutation in HDAC4 (A786T) was found to segregate with the illness. The relevance of this mutation in eating-related behaviors was further confirmed with mouse models. Despite  the fact that HDAC4 has not been identified as a significant signal in genome-wide association studies in AN, several studies have found significant or near-significant methylation differences in HDAC4 locus in peripheral tissues of actively ill AN patients in comparison with different control groups. Limitations of these studies include a lack of understanding of to what extent the changes in methylation are predictive of AN as such changes might also occur as a consequence of the disease. It remains to be determined how methylation in peripheral tissues correlates with that in the CNS and how different methylation patterns affect HDAC4 expression. The present review discusses the findings and potential roles of HDAC4 in AN. Its emerging roles in learning and neuroplasticity may be specific and relevant for the etiology of AN and potentially lead to novel therapeutic approaches.

Epigenetic regulation of G protein coupled receptor signaling and its implications in psychiatric disorders

G protein-coupled receptors (GPCRs) act as a relay center through which extracellular signals, in the form of neurotransmitters or therapeutics, are converted into an intracellular response, which ultimately shapes the overall response at the tissue and behavioral level. Remarkably in similar ways, epigenetic mechanisms also modulate the expression pattern of a large number of genes in response to the dynamic environment inside and outside of the body, and consequently overall response. Emerging evidences from the pharmacogenomics and preclinical studies clearly suggest that these two distinct mechanisms criss-cross each other in several neurological disorders. At one hand such cross-talks between two distinct mechanisms make disease etiology more challenging to understand, while on the other hand if dealt appropriately, such situations might provide an opportunity to find novel druggable target and strategy for the treatment of complex diseases. In this review article, we have summarized and highlighted the main findings that tie epigenetic mechanisms to GPCR mediated signaling in the pathophysiology of central nervous system (CNS) disorders, including depression, addiction and pain.

A genome-wide association study of bipolar disorder with comorbid eating disorder replicates the SOX2-OT region

BACKGROUND

Bipolar disorder is a heterogeneous mood disorder associated with several important clinical comorbidities, such as eating disorders. This clinical heterogeneity complicates the identification of genetic variants contributing to bipolar susceptibility. Here we investigate comorbidity of eating disorders as a subphenotype of bipolar disorder to identify genetic variation that is common and unique to both disorders.

METHODS

We performed a genome-wide association analysis contrasting 184 bipolar subjects with eating disorder comorbidity against both 1370 controls and 2006 subjects with bipolar disorder only from the Bipolar Genome Study (BiGS).

RESULTS

The most significant genome-wide finding was observed bipolar with comorbid eating disorder vs. controls within SOX2-OT (p=8.9×10(-8) for rs4854912) with a secondary peak in the adjacent FXR1 gene (p=1.2×10(-6) for rs1805576) on chromosome 3q26.33. This region was also the most prominent finding in the case-only analysis (p=3.5×10(-7) and 4.3×10(-6), respectively). Several regions of interest containing genes involved in neurodevelopment and neuroprotection processes were also identified.

LIMITATIONS

While our primary finding did not quite reach genome-wide significance, likely due to the relatively limited sample size, these results can be viewed as a replication of a recent study of eating disorders in a large cohort.

CONCLUSIONS

These findings replicate the prior association of SOX2-OT with eating disorders and broadly support the involvement of neurodevelopmental/neuroprotective mechanisms in the pathophysiology of both disorders. They further suggest that different clinical manifestations of bipolar disorder may reflect differential genetic contributions and argue for the utility of clinical subphenotypes in identifying additional molecular pathways leading to illness.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

NF-κB mediated regulation of adult hippocampal neurogenesis: relevance to mood disorders and antidepressant activity

Adult hippocampal neurogenesis is a peculiar form of process of neuroplasticity that in recent years has gained great attention for its potential implication in cognition and in emotional behavior in physiological conditions. Moreover, a vast array of experimental studies suggested that adult hippocampal neurogenesis may be altered in various neuropsychiatric disorders, including major depression, where its disregulation may contribute to cognitive impairment and/or emotional aspects associated with those diseases. An intriguing area of interest is the potential influence of drugs on adult neurogenesis. In particular, several psychoactive drugs, including antidepressants, were shown to positively modulate adult hippocampal neurogenesis. Among molecules which could regulate adult hippocampal neurogenesis the NF-κB family of transcription factors has been receiving particular attention from our and other laboratories. Herein we review recent data supporting the involvement of NF-κB signaling pathways in the regulation of adult neurogenesis and in the effects of drugs that are endowed with proneurogenic and antidepressant activity. The potential implications of these findings on our current understanding of the process of adult neurogenesis in physiological and pathological conditions and on the search for novel antidepressants are also discussed.

Epigenetics of the depressed brain: role of histone acetylation and methylation

Major depressive disorder is a chronic, remitting syndrome involving widely distributed circuits in the brain. Stable alterations in gene expression that contribute to structural and functional changes in multiple brain regions are implicated in the heterogeneity and pathogenesis of the illness. Epigenetic events that alter chromatin structure to regulate programs of gene expression have been associated with depression-related behavior, antidepressant action, and resistance to depression or 'resilience' in animal models, with increasing evidence for similar mechanisms occurring in postmortem brains of depressed humans. In this review, we discuss recent advances in our understanding of epigenetic contributions to depression, in particular the role of histone acetylation and methylation, which are revealing novel mechanistic insight into the syndrome that may aid in the development of novel targets for depression treatment.

HDAC modulation and cell death in the clinic

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two opposing classes of enzymes, which finely regulate the balance of histone acetylation affecting chromatin packaging and gene expression. Imbalanced acetylation has been associated with carcinogenesis and cancer progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. This implies that epigenetic alterations are amenable to pharmacological interventions. Accordingly, some epigenetic-based drugs (epidrugs) have been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment. Here, we focus on the biological features of HDAC inhibitors (HDACis), analyzing the mechanism(s) of action and their current use in clinical practice.

A non-invasive method to isolate the neuronal linage from the nasal epithelium from schizophrenic and bipolar diseases

Brain imaging and histopathological studies suggest that neurodevelopmental anomalies play a key role in the etiology of schizophrenia (SZ) and bipolar disorder (BD). New neuron formation and maturation occur in human olfactory epithelium throughout life. Therefore, the olfactory epithelium has been proposed as a model to study alterations in neurodevelopment, particularly in some psychiatric diseases. However, former studies were done with olfactory epithelium biopsies taken post mortem or under anesthesia from patients with SZ and BD. In this work we have developed a new method to obtain viable neural precursors by exfoliation of the anterior region of the medial lateral turbinate of the nasal cavity from healthy controls, and ambulatory patients. Cells were propagated to establish neural precursor banks. Thawed cells showed cytoskeletal phenotypes typical of developing neurons. They also conserved the ability to differentiate in presence of 2mM dibutyril-cyclic adenosine monophosphate, and maintained voltage-operated Ca(2+) currents in culture. Moreover, proportions of neuronal maturation stages were maintained in cultured exfoliates obtained from SZ and BD patients. Data support that neural precursors obtained from a nasal exfoliate are an excellent experimental model to later approach studies on biomarkers, neural development and cellular alterations in the pathophysiology of SZ and BD.

The polyketide MPBD initiates the SDF-1 signaling cascade that coordinates terminal differentiation in Dictyostelium

Dictyostelium uses a wide array of chemical signals to coordinate differentiation as it switches from a unicellular to a multicellular organism. MPBD, the product of the polyketide synthase encoded by stlA, regulates stalk and spore differentiation by rapidly stimulating the release of the phosphopeptide SDF-1. By analyzing specific mutants affected in MPBD or SDF-1 production, we delineated a signal transduction cascade through the membrane receptor CrlA coupled to Gα1, leading to the inhibition of GskA so that the precursor of SDF-1 is released. It is then processed by the extracellular protease of TagB on prestalk cells. SDF-1 apparently acts through the adenylyl cyclase ACG to activate the cyclic AMP (cAMP)-dependent protein kinase A (PKA) and trigger the production of more SDF-1. This signaling cascade shows similarities to the SDF-2 signaling pathway, which acts later to induce rapid spore encapsulation.

Prolyl endopeptidase is involved in cellular signalling in human neuroblastoma SH-SY5Y cells

Prolyl endopeptidase (PREP), probably acting through the inositol cycle, has been implicated in memory and learning. However, the physiological role of PREP is unknown. It has been shown that PREP expression, regulated in cerebellar granule cells, has probably a role in cell proliferation and differentiation. Here, we report the levels and subcellular distribution of PREP in human neuroblastoma SH-SY5Y cells in proliferating conditions and under differentiation induced by retinoic acid (RA). We analysed the levels of cell signalling intermediates, growth behavior and gene expression, and differentiation morphology changes, upon PREP inhibition. After induction of differentiation, PREP activity was found decreased in the nucleus but increased to high levels in the cytoplasm, due in part to increased PREP transcription. The levels of inositol (1,4,5)-trisphosphate revealed no correlation with PREP activity, but phosphorylated extracellular signal-regulated kinases 1 and 2 were decreased by PREP inhibition during early stages of differentiation. Morphological evaluation indicated that PREP inhibition retarded the onset of differentiation. PREP activity regulated gene expression of protein synthesis machinery, intracellular transport and kinase complexes. We conclude that PREP is a regulatory target and a regulatory element in cell signalling. This is the first report of a direct influence of a cell signalling molecule, RA, on PREP expression.

Disruption of glycogen synthase kinase-3-beta activity leads to abnormalities in physiological measures in mice

Dysregulation of glycogen synthase kinase-3-beta (GSK-3β) signaling pathways is thought to underlie the pathophysiology of mood disorders. In order to demonstrate that the loss of normal GSK-3β activity results in disturbances of physiological measures, we attempted to determine whether sleep-wake architecture, circadian rhythms of core body temperature and activity were altered in transgenic mice overexpressing GSK-3β activity specifically in the brain. Cortical electroencephalographic activity, body temperature (BT) and body locomotor activity (LMA) were continuously monitored using a biopotential telemetry probe. Normal circadian patterns were maintained for different measurements in both genotypes. No differences were found in total time spent asleep and waking over the 24-h recording session. However, transgenic animals overexpressing GSK-3β showed alteration in sleep continuity characterized by an increases in number of non rapid eye movement (NREM) sleep episodes (GSK-3β, 227.2 ± 1.7 vs. WT, 172.6 ± 1.4, p < 0.05) and decreases in mean episode duration (GSK-3β, 3.0 ± 0.1 vs. WT, 4.4 ± 0.2, p < 0.05). Additionally, transgenic animals exhibited marked enhancement of basal LMA and BT levels during the first part of the dark period, under both light-dark and free running dark-dark circadian cycles. Our findings indicate that transgenic mice overexpressing GSK-3β activity exhibit severe fragmentation of sleep-wake cycle during both the light and dark periods, without showing deviancy in total durations of vigilance states. The results strongly suggest that GSK-3β activity is elemental for the maintenance of circadian motor behavior levels required for proper regulation of BT and sleep-wake organization.

Effects of diverse psychopharmacological substances on the activity of brain prolyl oligopeptidase

Prolyl oligopeptidase (POP) has been connected to learning, memory and mood. Changes in serum or plasma POP activity have been linked to psychiatric disorders. POP has been thought to interfere in these conditions by cleaving neuroactive peptides or via the phosphatidylinositol second messenger system. However, little is known about the possible POP inhibition of commonly used psychoactive drugs. In this study, we measured the effects of various psychotropic drugs, including antidepressants, antipsychotics, mood stabilisers and anxiolytics, on the activity of the rat brain homogenate POP. Of the 38 compounds tested, 18 inhibited POP by at least 20% at 10 μM (buspirone, chlorpromazine, citalopram, clozapine, desipramine, duloxetine, escitalopram, flupenthixol, imipramine, ketanserin, lamotrigine, levomepromazine, prazosin, prochlorperazine, promazine, risperidone ritanserin and thioridazine). Thioridazine and valproate (VPA) acted at therapeutic plasma levels. Kinetically, VPA was a competitive inhibitor, thioridazine a non-competitive inhibitor and ketanserin a mixed type inhibitor. Being lipophilic, many of the psychoactive compounds are present in the brain at several-times higher concentrations than in plasma. At concentrations reported to be reached in the brain, chlorpromazine, clozapine, desipramine, imipramine, prochlorperazine and promazine inhibited POP by 30-50% suggesting that they could inhibit POP in vivo. However, when studied ex vivo, a single dose of 10 mg/kg thioridazine caused a deep sedation in the mice but did not inhibit the activity of POP. In conclusion, compared with conventional POP inhibitors, all psychopharmacological compounds tested are very weak inhibitors in vitro, and we doubt that their POP inhibition would be therapeutically meaningful.

GSK-3β activity and hyperdopamine-dependent behaviors

Dopamine plays important roles in normal brain function and many neuropsychiatric disorders. Classically, dopamine receptors are positively coupled to G protein-mediated signaling to regulate cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA)-dopamine and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) and Ca(2+) pathways. However, emerging evidence indicates that under hyperdopaminergic conditions, the protein kinase B (Akt)-glycogen synthase kinase 3β (GSK-3β) signaling cascade may mediate dopamine actions via D(2)-like receptors. This cAMP-independent signaling pathway involves the regulation of downstream synaptic targets, e.g., AMPA receptor, NMDA receptors, and thus synaptic plasticity. Here we provide an overview of how this novel signaling pathway relays dopamine receptor-mediated responses, particularly hyperdopamine-dependent behaviors. We discuss the relevance of the Akt/GSK-3β signaling cascade for the expression of dopamine-dependent behaviors and the drug actions associated with dopaminergic systems.

Valproic acid inhibits Abeta production, neuritic plaque formation, and behavioral deficits in Alzheimer's disease mouse models

Neuritic plaques in the brains are one of the pathological hallmarks of Alzheimer's disease (AD). Amyloid β-protein (Aβ), the central component of neuritic plaques, is derived from β-amyloid precursor protein (APP) after β- and γ-secretase cleavage. The molecular mechanism underlying the pathogenesis of AD is not yet well defined, and there has been no effective treatment for AD. Valproic acid (VPA) is one of the most widely used anticonvulsant and mood-stabilizing agents for treating epilepsy and bipolar disorder. We found that VPA decreased Aβ production by inhibiting GSK-3β–mediated γ-secretase cleavage of APP both in vitro and in vivo. VPA treatment significantly reduced neuritic plaque formation and improved memory deficits in transgenic AD model mice. We also found that early application of VPA was important for alleviating memory deficits of AD model mice. Our study suggests that VPA may be beneficial in the prevention and treatment of AD.

Shared gene expression alterations in schizophrenia and bipolar disorder

BACKGROUND

Schizophrenia and bipolar disorder together affect approximately 2.5% of the world population, and their etiologies are thought to involve multiple genetic variants and environmental influences. The analysis of gene expression patterns in brain may provide a characteristic signature for each disorder.

METHODS

RNA samples from the dorsolateral prefrontal cortex (Brodmann area 46) consisting of individuals with schizophrenia (SZ), bipolar disorder (BPD), and control subjects were tested on the Codelink Human 20K Bioarray platform. Selected transcripts were validated by quantitative real-time polymerase chain reaction (PCR). The strong effects of age, gender, and pH in the analysis of differential gene expression were controlled by analysis of covariance (ANCOVA). Criteria for differential gene expression were 1) a gene was significantly dysregulated in both BPD and SZ compared with control subjects and 2) significant in ANCOVA analysis with samples that have a pH above the median of the sample.

RESULTS

A list of 78 candidate genes passed these two criteria in BPD and SZ and was overrepresented for functional categories of nervous system development, immune system development and response, and cell death. Five dysregulated genes were confirmed with quantitative Q-PCR in both BPD and SZ. Three genes were highly enriched in brain expression (AGXT2L1, SLC1A2, and TU3A). The distribution of AGXT2L1 expression in control subjects versus BPD and SZ was highly significant (Fisher's Exact Test, p < 10(-06)).

CONCLUSIONS

These results suggest a partially shared molecular profile for both disorders and offer a window into discovery of common pathophysiology that might lead to core treatments.

Gene and expression analyses reveal enhanced expression of pericentrin 2 (PCNT2) in bipolar disorder

BACKGROUND

DISC1 has been suggested as a causative gene for psychoses in a large Scottish kindred. PCNT2 has recently been identified as an interacting partner of DISC1. In this study, we investigated the role of PCNT2 in bipolar disorder, by gene expression analysis and genetic association study.

METHODS

By TaqMan real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), we examined the messenger RNA (mRNA) levels of PCNT2 in the postmortem prefrontal cortex of bipolar disorder (n = 34), schizophrenia (n = 31), and control subjects (n = 32), obtained from Stanley Array Collection. We also compared the mRNA levels of PCNT2 in the peripheral blood lymphocytes of bipolar disorder (n = 21), schizophrenia (n = 21), depression (n = 33), and control subjects (n = 57). For the association study, 23 single nucleotide polymorphisms (SNPs) were analyzed in 285 bipolar disorder patients and 287 age-and gender-matched control subjects, all of Japanese origin. The genotypes were determined by TaqMan assay.

RESULTS

Significantly higher expression of PCNT2 was observed in the brain samples of bipolar group, compared with the control (p = .001) and schizophrenia (p = .018) groups. In the peripheral blood lymphocytes also, a significantly higher expression of PCNT2 was observed in the bipolar group, compared with the control subjects (p = .043). However, none of the SNPs analyzed in our study showed a significant association with bipolar disorder; a weak tendency toward association was observed for two intronic SNPs.

CONCLUSIONS

Our findings suggest that elevated levels of PCNT2 might be implicated in the pathophysiology of bipolar disorder.

Causality of stem cell based neurogenesis and depression--to be or not to be, is that the question?

Mood disorders compose a considerable portion of the worldwide prevailing diseases with high suicide rates and urgent demand for novel therapeutic interventions as efficacious treatment is still lacking. Depression is thought to feature distinct morphological correlatives in the brain and has recently been linked to adult neurogenesis (NG) in the hippocampal formation. Numerous findings give rise to the hypothesis that depression and declining NG in the hippocampus may be causally connected. This implies that depressive symptoms could originate from impairments in NG and, vice versa, that improved NG could mediate antidepressant action and alleviate symptoms. Thus, great hopes rest on the question whether the observed increase in NG following antidepression treatment may have the potential to become a novel drug target and specific mechanism in the development of the next generation of antidepressants that specifically involves targeting of neuropoetic factors in addition to their "traditional" effects as modulators of synaptic transmission. Along the still hypothetical association of depression and NG, however, several controversies and unresolved questions exist with respect to the presently available data and interpretation. This article highlights and summarizes some of the most pressing issues and identifies the crucial ones that await urgent clarification and resolving. Without their reliable answering, the fascinating notion of a neurogenic basis for depression will remain to be greatly speculative.

Specificity of mood stabilizer action on neuronal growth cones

OBJECTIVES

Lithium, valproic acid (VPA) and carbamazepine (CBZ) are commonly used mood stabilizers, but their therapeutic mechanism is unclear. These drugs all cause the same morphological effects on postnatal rat neuronal dorsal root ganglia (DRG) growth cones via an inositol-reversible mechanism. However, due to limitations in earlier analysis, the effects of combining drugs, drug specificity and inositol stereoisomer specificity are unknown. We devised an improved analytical method to address these issues.

METHODS

Dorsal root ganglia explants were cultured individually and incubated with combinations of psychotropic drugs and inositol stereoisomers. We recorded axonal growth cone morphology and calculated growth cone area per a modified method described by Williams et al. (Nature 2002; 417: 292-295). Statistically significant changes in area were calculated using non-parametric statistical testing.

RESULTS

(i) Lithium and VPA showed an additive effect on growth cone spreading. (ii) Among eight additional psychotropic drugs to those previously tested, only imipramine and chlorpromazine altered DRG growth cone morphology. As this effect was not reversed by myo-inositol, it arises from a different mechanism to the mood stabilizers lithium, VPA and CBZ. (iii) Myo-inositol, but not scyllo- or epi-inositol, causes a significant reversal of the lithium effect on the growth cones spreading, consistent with the inositol depletion hypothesis.

CONCLUSIONS

These results show that lithium, VPA and CBZ are unique in causing altered neuronal morphology via myo-inositol depletion.

Schizophrenia as a GSK-3 dysregulation disorder

Converging evidence suggests that the regulation of glycogen synthase kinase 3 (GSK-3) might be important in schizophrenia. Atypical and typical antipsychotic drugs alter GSK-3 activity, as do drugs that induce psychosis. GSK-3 regulatory pathways are altered in schizophrenia, and many of the genes associated with schizophrenia directly or indirectly regulate GSK-3 activity. We propose a variant on the neurodevelopment and dopamine hypotheses of schizophrenia, whereby (i) an early dysfunction in GSK-3 regulation has neurodevelopmental consequences that predispose to disease and (ii) dysfunction in GSK-3 regulation in the adult brain alters dopamine signalling events, causing psychotic symptoms and cognitive dysfunction. If, as we suggest, GSK-3 regulation is crucial to schizophrenia, the Wnt and insulin signalling pathways become targets for therapy.

On the role of prolyl oligopeptidase in health and disease

Prolyl oligopeptidase (POP) is a serine peptidase which digests small peptide-like hormones, neuroactive peptides, and various cellular factors. Therefore, this peptidase has been implicated in many physiological processes as well as in some psychiatric disorders, most probably through interference in inositol cycle. Intense research has been performed to elucidate, on the one hand, the basic structure, ligand binding, and kinetic properties of POP, and on the other, the pharmacology of its inhibitors. There is fairly strong evidence of in vivo importance of POP on substance P, arginine vasopressin, thyroliberin and gonadoliberin metabolism. However, information about the biological relevance of POP is not yet conclusive. Evidence regarding the physiological role of POP is lacking, which is surprising considering that peptidase inhibitors have been exploited for drug development, some of which are currently in clinical trials as memory enhancers for the aged and in a variety of neurological disorders. Here we review the recent progress on POP research and evaluate the relevance of the peptidase in the metabolism of various neuropeptides. The recognition of novel forms and relatives of POP may improve our understanding of how this family of proteins functions in normal and in neuropathological conditions.

Valproate and copper accelerate TRH-like peptide synthesis in male rat pancreas and reproductive tissues

Treatment with valproate (Valp) facilitates the synthesis of TRH-like peptides (pGlu-X-Pro-NH(2)) in rat brain where "X" can be any amino acid residue. Because high levels of TRH-like peptides occur in the pancreas and pGlu-Glu-Pro-NH(2) (Glu-TRH) has been shown to be a fertilization promoting peptide, we hypothesized that these peptides mediate some of the metabolic and reproductive side effects of Valp. Male WKY rats were treated with Valp acutely (AC), chronically (CHR) or chronically followed by a 2 day withdrawal (WD). AC, CHR and WD treatments significantly altered TRH and/or TRH-like peptide levels in pancreas and reproductive tissues. Glu-TRH was the predominant TRH-like peptide in epididymis, consistent with its fertilization promoting activity. Glu-TRH levels in the epididymis increased 3-fold with AC Valp. Phe-TRH, the most abundant TRH-like peptide in the pancreas, increased 4-fold with AC Valp. Phe-TRH inhibits both basal and TRH-stimulated insulin release. Large dense core vesicles (LDCV's) contain a copper-dependent enzyme responsible for the post-translational processing of precursors of TRH and TRH-like peptides. Copper (500 microM) increased the in vitro C-terminal amidation of TRH-like peptides by 8- and 4-fold during 24 degrees C incubation of homogenates of pancreas and testis, respectively. Valp (7 microM) accelerated 3-fold the processing of TRH and TRH-like peptide precursors in pancreatic LDCV's incubated at 24 degrees C. We conclude that copper, an essential cofactor for TRH and TRH-like peptide biosynthesis that is chelated by Valp, mediates some of the metabolic and reproductive effects of Valp treatment via acceleration of intravesicular synthesis and altered release of these peptides.

The human reelin gene: Transcription factors (+), repressors (−) and the methylation switch (+/−) in schizophrenia

A recent report suggests that the down-regulation of reelin and glutamic acid decarboxylase (GAD(67)) mRNAs represents 2 of the more consistent findings thus far described in post-mortem material from schizophrenia (SZ) patients [reviewed in. Neurochemical markers for schizophrenia, bipolar disorder amd major depression in postmortem brains. Biol Psychiatry 57, 252-260]. To study mechanisms responsible for this down-regulation, we have analyzed the promoter of the human reelin gene. Collectively, our studies suggest that SZ is characterized by a gamma-amino butyric acid (GABA)-ergic neuron pathology presumably mediated by promoter hypermethylation facilitated by the over-expression of the methylating enzyme DNA methyltransferase (Dnmt) 1. Using transient expression assays, promoter deletions and co-transfection assays with various transcription factors, we have shown a clear synergistic action that is a critical component of the mechanism of the trans-activation process. Equally important is the observation that the reelin promoter is more heavily methylated in brain regions in patients diagnosed with SZ as compared to non-psychiatric control subjects [Grayson, D. R., Jia, X., Chen, Y., Sharma, R. P., Mitchell, C. P., & Guidotti, A., et al. (2005). Reelin promoter hypermethylation in schizophrenia. Proc Natl Acad Sci U S A 102, 9341-9346]. The combination of studies in cell lines and in animal models of SZ, coupled with data obtained from post-mortem human material provides compelling evidence that aberrant methylation may be part of a core dysfunction in this psychiatric disease. More interestingly, the hypermethylation concept provides a coherent mechanism that establishes a plausible link between the epigenetic misregulation of multiple genes that are affected in SZ and that collectively contribute to the associated symptomatology.

Variations in genes regulating neuronal migration predict reduced prefrontal cognition in schizophrenia and bipolar subjects from mediterranean Spain: A preliminary study

Both neural development and prefrontal cortex function are known to be abnormal in schizophrenia and bipolar disorder. In order to test the hypothesis that these features may be related with genes that regulate neuronal migration, we analyzed two genomic regions: the lissencephaly critical region (chromosome 17p) encompassing the LIS1 gene and which is involved in human lissencephaly; and the genes related to the platelet-activating-factor, functionally related to LIS1, in 52 schizophrenic patients, 36 bipolar I patients and 65 normal control subjects. In addition, all patients and the 25 control subjects completed a neuropsychological battery. Thirteen (14.8%) patients showed genetic variations in either two markers related with lissencephaly or in the platelet-activating-factor receptor gene. These patients performed significantly worse in the Wisconsin Card Sorting Test-Perseverative Errors in comparison with patients with no lissencephaly critical region/platelet-activating-factor receptor variations. The presence of lissencephaly critical region/platelet-activating-factor receptor variations was parametrically related to perseverative errors, and this accounted for 17% of the variance (P = 0.0001). Finally, logistic regression showed that poor Wisconsin Card Sorting Test-Perseverative Errors performance was the only predictor of belonging to the positive lissencephaly critical region/platelet-activating-factor receptor group. These preliminary findings suggest that the variations in genes involved in neuronal migration predict the severity of the prefrontal cognitive deficits in both disorders.

Lithium- and valproate-induced alterations in circadian locomotor behavior in Drosophila

Lithium and valproate are commonly used mood stabilizers, but their action pathways are not clearly understood. They also suffer from multiple toxic effects that limit their utility. Elucidating their action mechanisms could lead to newer agents and better understanding of the etiopathogenesis of bipolar disorder. We have expanded the study of signaling mechanisms of lithium and valproate by using Drosophila circadian locomotor activity as a robust behavioral assay that is amenable to genetic manipulations. We demonstrate that lithium affects the circadian system of Drosophila similarly to what has been reported in the mammalian studies. We show that lithium and valproate share effects on the circadian locomotor activity of Drosophila: they lengthen the period of circadian rhythms and increase arrhythmicity. Valproate exerts these effects in a weaker fashion than does lithium. We also tested the circadian alterations in multiple mutant lines of Drosophila bearing defects in the GSK-3beta gene and other clock genes in response to lithium administration. We show that lithium partially rescues the shortening of circadian period when the GSK-3beta gene is overexpressed only in specific circadian pacemaker neurons, thus implicating GSK-3beta as a component in lithium's effect on the circadian oscillator. Moreover, lithium also lengthens the period in GSK-3beta heterozygous mutants and doubletime long mutants. These results establish a basis for using Drosophila genetics to investigate more fully lithium and valproate action mechanisms.

Two Sides of the Same Coin: Wnt Signaling in Neurodegeneration and Neuro-Oncology

Wnts function through the activation of at least three intracellular signal transduction pathways, of which the canonical β-catenin mediated pathway is the best understood. Aberrant canonical Wnt signaling has been involved in both neurodegeneration and cancer. An impairment of Wnt signals appears to be associated with aspects of neurodegenerative pathologies while overactivation of Wnt signaling is a common theme in several types of human tumors. Therefore, although therapeutic approaches aimed at modulating Wnt signaling in neurodegenerative and hyperproliferative diseases might impinge on the same molecular mechanisms, different pharmacological outcomes are required. Here we review recent developments on the understanding of the role of Wnt signaling in Alzheimer's disease and CNS tumors, and identify possible avenues for therapeutic intervention within a complex and multi-faceted signaling pathway.

Decreased prefrontal Myo-inositol in major depressive disorder

BACKGROUND

Postmortem studies have shown robust prefrontal cortex glial losses and more subtle neuronal changes in major depressive disorder (MDD). Earlier proton magnetic resonance spectroscopy (1H-MRS) studies of the glial marker myo-inositol in MDD were subject to potential confounds. The primary hypothesis of this study was that MDD patients would show reduced prefrontal/anterior cingulate cortex levels of myo-inositol.

METHODS

Thirteen nonmedicated moderate-severe MDD patients and 13 matched control subjects were studied (six male, seven female per group). Proton magnetic resonance spectroscopy stimulated echo acquisition mode spectra (3.0 T; echo time=168 msec; mixing time=28 msec; repetition time=3000 msec) were obtained from prefrontal/anterior cingulate cortex. Metabolite data were adjusted for tissue composition.

RESULTS

Patients with MDD showed significantly lower myo-inositol/creatine ratios (.94+/-.23) than control subjects (1.32+/-.37) [F(1,23)=6.9; p=.016].

CONCLUSIONS

These data suggest a reduction of myo-inositol in prefrontal/anterior cingulate cortex in MDD, which could be a consequence of glial loss or altered glial metabolism. Additional in vivo studies of glial markers could add to the understanding of the pathophysiology of MDD.

Concerted Structural Changes in the Peptidase and the Propeller Domains of Prolyl Oligopeptidase are Required for Substrate Binding

Prolyl oligopeptidase contains a peptidase domain and its catalytic triad is covered by the central tunnel of a seven-bladed beta-propeller. This domain makes the enzyme an oligopeptidase by excluding large structured peptides from the active site. The apparently rigid crystal structure does not explain how the substrate can approach the catalytic groups. Two possibilities of substrate access were investigated: either blades 1 and 7 of the propeller domain move apart, or the peptidase and/or propeller domains move to create an entry site at the domain interface. Engineering disulfide bridges to the expected oscillating structures prevented such movements, which destroyed the catalytic activity and precluded substrate binding. This indicated that concerted movements of the propeller and the peptidase domains are essential for the enzyme action.