Atypical antipsychotic drugs upregulate synapsin II in the prefrontal cortex of post-mortem samples obtained from patients with schizophrenia

An updated reappraisal of synapsins: structure, function and role in neurological and psychiatric disorders

Synapsins (Syns) are phosphoproteins strongly involved in neuronal development and neurotransmitter release. Three distinct genes SYN1, SYN2 and SYN3, with elevated evolutionary conservation, have been described to encode for Synapsin I, Synapsin II and Synapsin III, respectively. Syns display a series of common features, but also exhibit distinctive localization, expression pattern, post-translational modifications (PTM). These characteristics enable their interaction with other synaptic proteins, membranes and cytoskeletal components, which is essential for the proper execution of their multiple functions in neuronal cells. These include the control of synapse formation and growth, neuron maturation and renewal, as well as synaptic vesicle mobilization, docking, fusion, recycling. Perturbations in the balanced expression of Syns, alterations of their PTM, mutations and polymorphisms of their encoding genes induce severe dysregulations in brain networks functions leading to the onset of psychiatric or neurological disorders. This review presents what we have learned since the discovery of Syn I in 1977, providing the state of the art on Syns structure, function, physiology and involvement in central nervous system disorders.

The prefrontal cortex as a target for atypical antipsychotics in schizophrenia, lessons of neurodevelopmental animal models

Prefrontal cortex (PFC) inflammatory imbalance, oxidative/nitrosative stress (O/NS) and impaired neuroplasticity in schizophrenia are thought to have neurodevelopmental origins. Animal models are not only useful to test this hypothesis, they are also effective to establish a relationship among brain disturbances and behavior with the atypical antipsychotics (AAPs) effects. Here we review data of PFC post-mortem and in vivo neuroimaging, human induced pluripotent stem cells (hiPSC), and peripheral blood studies of inflammatory, O/NS, and neuroplasticity alterations in the disease as well as about their modulation by AAPs. Moreover, we reviewed the PFC alterations and the AAP mechanisms beyond their canonical antipsychotic action in four neurodevelopmental animal models relevant to the study of schizophrenia with a distinct approach in the generation of schizophrenia-like phenotypes, but all converge in O/NS and altered neuroplasticity in the PFC. These animal models not only reinforce the neurodevelopmental risk factor model of schizophrenia but also arouse some novel potential therapeutic targets for the disease including the reestablishment of the antioxidant response by the perineuronal nets (PNNs) and the nuclear factor erythroid 2-related factor (Nrf2) pathway, as well as the dendritic spine dynamics in the PFC pyramidal cells.

Reduced expression of synapsin II in a chronic phencyclidine preclinical rat model of schizophrenia

Schizophrenia is a mental disorder characterized by positive symptoms, negative symptoms, and cognitive dysfunction. Phencyclidine (PCP)-a N-methyl-D-aspartate (NMDA) receptor antagonist-induces symptoms indistinguishable from those of schizophrenia. A reduction of the phosphoprotein synapsin II has also been implicated in schizophrenia and has a well-known role in the maintenance of the presynaptic reserve pool and vesicle mobilization. This study assessed the behavioral and biochemical outcomes of chronic NMDA receptor antagonism in rodents and its implications for the pathophysiology of schizophrenia. Sprague Dawley rats received saline or chronic PCP (5 mg/kg/day) for 14 days via surgically implanted Alzet® osmotic mini-pumps. Following the treatment period, rats were tested with a series of behavioral paradigms, including locomotor activity, social interaction, and sensorimotor gating. Following behavioral assessment, the medial prefrontal cortex (mPFC) of all rats was isolated for synapsin II protein analysis. Chronic PCP treatment yielded a hyper-locomotive state (p = 0.0256), reduced social interaction (p = 0.0005), and reduced pre-pulse inhibition (p < 0.0001) in comparison to saline-treated controls. Synapsin IIa (p < 0.0001) and IIb (p < 0.0071) levels in the mPFC of chronically treated PCP rats were reduced in comparison to the saline group. Study results confirm that rats subject to chronic PCP treatment display behavioral phenotypes similar to established preclinical animal models of schizophrenia. Reduction of synapsin II expression in this context implicates the role of this protein in the pathophysiology of schizophrenia and sheds light on the longer-term consequences of NMDA receptor antagonism facilitated by chronic PCP treatment.

Role of presynaptic phosphoprotein synapsin II in schizophrenia

Synapsin II is a member of the neuronal phosphoprotein family. These phosphoproteins are evolutionarily conserved across many organisms and are important in a variety of synaptic functions, including synaptogenesis and the regulation of neurotransmitter release. A number of genome-wide scans, meta-analyses, and genetic susceptibility studies have implicated the synapsin II gene (3p25) in the etiology of schizophrenia (SZ) and other psychiatric disorders. Further studies have found a reduction of synapsin II mRNA and protein in the prefrontal cortex in post-mortem samples from schizophrenic patients. Disruptions in the expression of this gene may cause synaptic dysfunction, which can result in neurotransmitter imbalances, likely contributing to the pathogenesis of SZ. SZ is a costly, debilitating psychiatric illness affecting approximately 1.1% of the world’s population, amounting to 51 million people today. The disorder is characterized by positive (hallucinations, paranoia), negative (social withdrawal, lack of motivation), and cognitive (memory impairments, attention deficits) symptoms. This review provides a comprehensive summary of the structure, function, and involvement of the synapsin family, specifically synapsin II, in the pathophysiology of SZ and possible target for therapeutic intervention/implications.

Nitric oxide synthase 1 adaptor protein, a protein implicated in schizophrenia, controls radial migration of cortical neurons

BACKGROUND

Where a neuron is positioned in the brain during development determines neuronal circuitry and information processing needed for normal brain function. When aberrations in this process occur, cognitive disorders may result. Patients diagnosed with schizophrenia have been reported to show altered neuronal connectivity and heterotopias. To elucidate pathways by which this process occurs and become aberrant, we have chosen to study the long isoform of nitric oxide synthase 1 adaptor protein (NOS1AP), a protein encoded by a susceptibility gene for schizophrenia.

METHODS

To determine whether NOS1AP plays a role in cortical patterning, we knocked down or co-overexpressed NOS1AP and a green fluorescent protein or red fluorescent protein (TagRFP) reporter in neuronal progenitor cells of the embryonic rat neocortex using in utero electroporation. We analyzed sections of cortex (ventricular zone, intermediate zone, and cortical plate [CP]) containing green fluorescent protein or red fluorescent protein TagRFP positive cells and counted the percentage of positive cells that migrated to each region from at least three rats for each condition.

RESULTS

NOS1AP overexpression disrupts neuronal migration, resulting in increased cells in intermediate zone and less cells in CP, and decreases dendritogenesis. Knockdown results in increased migration, with more cells reaching the CP. The phosphotyrosine binding region, but not the PDZ-binding motif, is necessary for NOS1AP function. Amino acids 181 to 307, which are sufficient for NOS1AP-mediated decreases in dendrite number, have no effect on migration.

CONCLUSIONS

Our studies show for the first time a critical role for the schizophrenia-associated gene NOS1AP in cortical patterning, which may contribute to underlying pathophysiology seen in schizophrenia.

Change in expression of vesicular protein synapsin II by chronic treatment with D2 allosteric modulator PAOPA

The hallmark symptoms of schizophrenia include profound disturbances in thought, perception, cognition etc., which negatively impacts an individual's quality of life. Current antipsychotic drugs are not effective in treating all symptoms of this disorder, and often cause severe movement and metabolic side effects. Consequently, there remains a strong impetus to develop safer and more efficacious therapeutics for patients, as well as elucidating the etiology of schizophrenia. Previous work in our lab has introduced a novel candidate for the treatment of this disease: the dopamine D2 receptor (D2R) allosteric modulator, 3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA). We have previously shown that PAOPA, by selectively modulating D2R, can ameliorate schizophrenia-like symptoms in animal models, although the precise mechanism is presently not understood. Synapsin II is a presynaptic vesicular protein which has been strongly implicated in schizophrenia, as it is reduced in the prefrontal cortex of patients, and knockdown of this protein elicits schizophrenia-like phenotypes in animal models. Given the therapeutic effects of PAOPA and the role of synapsin II in schizophrenia, the objective of this study was to investigate the effect of chronic administration of PAOPA (45 days) on neuronal synapsin II protein expression in rodents. Immunoblot results revealed that the synapsin IIa, but not the IIb isoform, was increased in the dopaminergic regions of the striatum, nucleus accumbens, and medial prefrontal cortex. The results of this study implicate a role for modulation of synapsin II as a possible therapeutic mechanism of action for potential antipsychotic drug PAOPA.

Synapsin II gene expression in the dorsolateral prefrontal cortex of brain specimens from patients with schizophrenia and bipolar disorder: effect of lifetime intake of antipsychotic drugs

Synapsins are neuronal phosphoproteins crucial to regulating the processes required for normal neurotransmitter release. Synapsin II, in particular, has been implied as a candidate gene for schizophrenia. This study investigated synapsin II mRNA expression, using Real Time RT-PCR, in coded dorsolateral prefrontal cortical samples provided by the Stanley Foundation Neuropathology Consortium. Synapsin IIa was decreased in patients with schizophrenia when compared to both healthy subjects and patients with bipolar disorder, whereas the synapsin IIb was only significantly reduced in patients with schizophrenia when compared to healthy subjects, but not patients with bipolar disorder. Furthermore, lifetime antipsychotic drug use was positively associated with synapsin IIa expression in patients with schizophrenia. Results suggest that impairment of synaptic transmission by synapsin II reduction may contribute to dysregulated convergent molecular mechanisms which result in aberrant neural circuits that characterize schizophrenia, while implicating involvement of synapsin II in therapeutic mechanisms of currently prescribed antipsychotic drugs.

Long-lasting hippocampal synaptic protein loss in a mouse model of posttraumatic stress disorder

Despite intensive research efforts, the molecular pathogenesis of posttraumatic stress disorder (PTSD) and especially of the hippocampal volume loss found in the majority of patients suffering from this anxiety disease still remains elusive. We demonstrated before that trauma-induced hippocampal shrinkage can also be observed in mice exhibiting a PTSD-like syndrome. Aiming to decipher the molecular correlates of these trans-species posttraumatic hippocampal alterations, we compared the expression levels of a set of neurostructural marker proteins between traumatized and control mice at different time points after their subjection to either an electric footshock or mock treatment which was followed by stressful re-exposure in several experimental groups. To our knowledge, this is the first systematic in vivo study analyzing the long-term neuromolecular sequelae of acute traumatic stress combined with re-exposure. We show here that a PTSD-like syndrome in mice is accompanied by a long-lasting reduction of hippocampal synaptic proteins which interestingly correlates with the strength of the generalized and conditioned fear response but not with the intensity of hyperarousal symptoms. Furthermore, we demonstrate that treatment with the serotonin reuptake inhibitor (SSRI) fluoxetine is able to counteract both the PTSD-like syndrome and the posttraumatic synaptic protein loss. Taken together, this study demonstrates for the first time that a loss of hippocampal synaptic proteins is associated with a PTSD-like syndrome in mice. Further studies will have to reveal whether these findings are transferable to PTSD patients.