Imputed expression of schizophrenia-associated genes and cognitive measures in patients with schizophrenia

Background: Cognitive dysfunction is a core manifestation of schizophrenia and one of the best predictors of long-term disability. Genes increasing risk for schizophrenia may partly act through the modulation of cognition.Methods: We imputed the expression of 130 genes recently prioritized for association with schizophrenia, using PsychENCODE variant weights and genotypes of patients with schizophrenia in CATIE. Processing speed, reasoning, verbal memory, working memory, vigilance, and a composite cognitive score were used as phenotypes. We performed linear regression models for each cognitive measure and gene expression score, adjusting for age, years of education, antipsychotic treatment, years since the first antipsychotic treatment and population principal components.Results: We included 425 patients and expression scores of 91 genes (others had no heritable expression; Bonferroni corrected alpha = 5.49e-4). No gene expression score was associated with cognitive measures, though ENOX1 expression was very close to the threshold for verbal memory (p = 6e-4) and processing speed (p = 7 e-4). Other genes were nominally associated with multiple phenotypes (MAN2A1 and PCGF3).Conclusion: A better understanding of the mechanisms mediating cognitive dysfunction in schizophrenia may help in the definition of disease prognosis and in the identification of new treatments, as the treatment of cognitive impairment remains an unmet therapeutic need

Therapeutic Challenges of Post-traumatic Stress Disorder: Focus on the Dopaminergic System

Post-traumatic stress disorder (PTSD) is a mental illness developed by vulnerable individuals exposed to life-threatening events. The pharmacological unresponsiveness displayed by the vast majority of PTSD patients has raised considerable interest in understanding the poorly known pathophysiological mechanisms underlying this disorder. Most studies in the field focused, so far, on noradrenergic mechanisms, because of their well-established role in either tuning arousal or in encoding emotional memories. However, less attention has been paid to other neural systems. Manipulations of the dopaminergic system alter behavioral responses to stressful situations and recent findings suggest that dopaminergic dysfunction might play an overriding role in the pathophysiology of PTSD. In the present review, dopaminergic mechanisms relevant for the pathogenesis of PTSD, as well as potential dopaminergic-based pharmacotherapies are discussed in the context of addressing the unmet medical need for new and effective drugs for treatment of PTSD

Enhanced expression of PACAP and of its high affinity receptor (PAC1) in the hippocampus and cerebral cortex of dopamine D3 knockout mice

Dopamine (DA) D3 receptor (D3R) is a pre-synaptic autoreceptor whose main role is to modulate DA release through a negative feedback regulatory loop. Immunolocalization studies from our research group have previously described that these receptors, despite being relatively low expressed in the central nervous system (CNS), may still be detected in less discreet brain regions normally associated to memory function, including the hippocampus and the cerebral cortex (1). Consistent with these findings, genetic deletion of the D3R in mice (D3R-/-) has been shown to have profound repercussions on the formation of new memories, especially fear associative memories (2). While it is now well-accepted that such pro-cognitive effects in these mice are presumably due to the increased DA bioavailability caused by the lack of autoreceptor function, it still remains to be established if there are molecular determinants directly or indirectly involved in ameliorating this specific type of associative learning. Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous peptide which is gaining scientific relevance because of its prominent “cognitive enhancer” function and the recent developments suggesting its active participation in the acquisition and consolidation of fear memories (3, 4). Based on these evidences, we thought it could have been of scientific relevance to assess whether PACAP expression, as well as that of its binding receptors, are affected in knockout mice showing this peculiar behavioural phenotype. We found that PACAP immunoreactivity (IR) was present at low levels in CA1 hippocampal subfield while moderate staining was observed in CA2-CA3 fields and in the dentate gyrus (DG) of wild-type (WT) mice. In sharp contrast, PACAP-IR was remarkably increased in all CA subfields, and particularly in CA1, CA3 and the DG regions of D3R-/- mice. Regarding the cerebral cortex (CX), PACAP expression was restricted to the V cortical layer in WT mice, whereas in D3R-/- mice, stained neurons were apparent both in the IV, V and VI cortical layers, with an overall increased staining score. In line with these findings, the expression of the PACAP-preferring PAC1 receptor, which was detectable only at moderate levels in the CA2 subfield of WTs, was enhanced in both CA2 and CA3 of D3R-/- mice. Interestingly, PAC1-IR was already present at moderate levels in the II-III cortical layers of WT mice, but genetic deletion of the D3R caused a remarkable spread of PAC1-stained neurons throughout all cortical layers, with the exception of layer I. We conclude that the absence or blockade of functional D3Rs from the brain enhances both PACAP and PAC1 receptor expression levels in the hippocampus and cerebral cortex. Considering the ameliorative role mediated by PACAP-PAC1 signalling in cognition, we infer that enhanced PACAP peptide and receptor expression may relate to the specific behavioural phenotype of these mice

Behavioural and neurochemical changes induced by stress-related conditions are counteracted by the neurokinin-2 receptor antagonist saredutant.

Abstract These experiments were undertaken to assess the mechanisms underlying the antidepressant-like effects of the neurokinin-2 (NK2) receptor antagonist saredutant (SR48968) in rats tested in the forced swim test (FST), by analysing hippocampal brain-derived neurotrophic factor (BDNF) and plasma corticosterone [as index of hypothalamic-pituitary-adrenal (HPA) axis activity]. Male Wistar rats received three intraperitoneal injections over 24 h of vehicle, saredutant (5 mg/kg), citalopram (15 mg/kg), clomipramine (50 mg/kg). Rats were subjected to restraint stress (4 h) 24 h prior to the FST procedure. This stress procedure increased immobility and decreased swimming behaviour in the FST; furthermore, it lowered hippocampal BDNF protein expression and increased plasma corticosterone levels. Saredutant and clomipramine or citalopram, used here as positive controls, reduced the immobility time in the FST both under basal conditions and after stress exposure. This effect was not attributable to changes in locomotion, because locomotor activity was unchanged when assessed in the open field test. Pretreatment with para-cholorophenylalanine (150 mg/kg, 72 h and 48 h prior to FST) abolished the effect of citalopram and saredutant on immobility time. At neurochemical level, saredutant attenuated activation of HPA axis in stressed animals more than clomipramine or citalopram. The behavioural effects of saredutant support the hypothesis that NK2 receptor activity is involved in stress-related disorders. These effects of saredutant may be related to normalization of the HPA axis. Moreover, saredutant increases BDNF expression in the hippocampus, confirming the role of NK2 receptor blockade in BDNF activation following stressor application

Dopamine D3 receptor knockout mice exhibit increased hippocampal cAMP response element binding protein (CREB) following acquisition of passive avoidance memory

The dopamine D3 (D3R) receptor seems to be implicated in synaptic plasticity and memory-related processes as identified by several pharmacological and behavioral approaches (Laszy et al., 2005; Swant 2008). In a previous study we have shown that D3Rs mediate an inhibitory effect on learning, since D3R knockout (D3-/-) mice display enhanced cognitive performance in the single trial step-through passive avoidance task (PA) as compared to WTs (Micale et al., 2010; D’Amico et al., 2013). Formation of new memories is known to require de novo synthesis of proteins related to synaptic function, possibly through the activation of a number of signaling pathways including the mitogen-activated protein kinases (MAPKs), protein kinase B (namely Akt) and the activation of nuclear transcription factors such as the cAMP response element binding protein (CREB). However, no clear indications have yet been provided regarding the specific involvement of D3Rs in the activation of these signaling cascades after acquisition of PA. Therefore, in the present study we assessed whether activity/phosphorylation levels of several MAPKs, Akt and CREB were differentially affected by PA in both wild-type (WT) and D3-/- mice. Animals were divided into four groups: naive, unconditioned stimulus trained (USTA), conditioned stimulus trained (CSTA) and conditioned (CA) animals. Phosphorylation of MAPKs, including extracellular signal-regulated kinase 1/2 (ERK 1/2), c-Jun-N-terminal kinase (JNK) and p38, as well as of Akt and CREB were assessed by immunoblotting and immunohistochemical analyses. Results showed that acquisition of PA induced a significant increase in hippocampal pCREB levels both in WT and D3-/- mice. However, the extent of PA-driven increase in pCREB levels was significantly higher in mice lacking D3Rs. Similarly, hippocampal pERK 1/2 were further augmented in D3-/- mice subjected to PA as compared to trained WTs. JNK and p38 phosphorylation was not affected neither by PA nor by genetic background. Finally, a significantly increased Akt activation was observed only when comparing naïve WT and D3-/- mice, but not in response to PA acquisition. This result suggests that the Akt signaling cascade is influenced by the absence of the receptor, but only under basal conditions. In conclusion, the data here presented supports the notion that D3Rs might modulate CREB phosphorylation after acquisition of PA, probably via activation of the ERK signaling pathway

Retinal Protection and Distribution of Curcumin in Vitro and in Vivo

Diabetic retinopathy (DR), a secondary complication of diabetes, is a leading cause of irreversible blindness accounting for 5% of world blindness cases in working age. Oxidative stress and inflammation are considered causes of DR. Curcumin, a product with anti-oxidant and anti-inflammatory properties, is currently proposed as oral supplementation therapy for retinal degenerative diseases, including DR. In this study we predicted the pharmacodynamic profile of curcumin through an in silico approach. Furthermore, we tested the anti-oxidant and anti-inflammatory activity of curcumin on human retinal pigmented epithelial cells exposed to oxidative stress, human retinal endothelial and human retinal pericytes (HRPCs) cultured with high glucose. Because currently marketed curcumin nutraceutical products have not been so far evaluated for their ocular bioavailability; we assessed retinal distribution of curcumin, following oral administration, in rabbit eye. Curcumin (10 μM) decreased significantly (p < 0.01) ROS concentration and TNF-α release in retinal pigmented epithelial cells and retinal endothelial cells, respectively. The same curcumin concentration significantly (p < 0.01) protected retinal pericytes from high glucose damage as assessed by cell viability and LDH release. Among the tested formulations, only that containing a hydrophilic carrier provided therapeutic levels of curcumin in rabbit retina. In conclusion, our data suggest that curcumin, when properly formulated, may be of value in clinical practice to manage retinal diseases

Bark in Experimental Early Diabetic Retinopathy

Diabetic retinopathy is a complex condition where inflammation and oxidative stress represent crucial pathways in the pathogenesis of the disease. Aim of the study was to investigate the effects of a fortified extract of red berries, Ginkgo biloba and white willow bark containing carnosine and -lipoic acid in early retinal and plasma changes of streptozotocin-induced diabetic rats. Diabetes was induced by a single streptozotocin injection in Sprague Dawley rats. Diabetics and nondiabetic (control) rats were treated daily with the fortified extract for the ten days. Retina samples were collected and analyzed for their TNF-and VEGF content. Moreover, plasma oxidative stress was evaluated by thiobarbituric acid reacting substances (TBARS). Increased TNF-and VEGF levels were observed in the retina of diabetic rats. Treatment with the fortified extract significantly lowered retinal cytokine levels and suppressed diabetes-related lipid peroxidation. These data demonstrate that the fortified extract attenuates the degree of retinal inflammation and plasma lipid peroxidation preserving the retina in early diabetic rats

Dopamine D3 receptor modulates tissue type plasminogen activator (tPA) activity in mouse brain

Growing amount of evidence points to the dopamine D3 receptor (D3R) as an important mediator in the broad array of events that regulate memory function, perhaps through the modulation of molecular pathways involved in neurotrophic factor activation. Tissue type plasminogen activator (tPA) is a proteolytic enzyme that cleaves the precursor of brain derived neurotrophic factor (proBDNF) into the biologically active form of mature BDNF. However, whether D3Rs modulate tPA activity on BDNF in brain has not been ascertained yet. Here in the present study, using D3R knock-out (D3-/-) mice, we demonstrate that receptor inactivation is associated with increased tPA expression both in prefrontal cortex and, to a greater extent, in the hippocampus, two regions associated with memory processes. The heightened tPA levels observed in D3-/- mice inversely correlated with proBDNF protein expression, whereas they positively correlated with both BDNF mRNA and mature BDNF protein levels. In conclusion, our finding strongly suggest that D3Rs might modulate tPAmediated post-transcriptional processing of BDNF in brain regions critical to memory function