Reelin Supplementation Into the Hippocampus Rescues Abnormal Behavior in a Mouse Model of Neurodevelopmental Disorders

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic- and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice 24 h post-treatment. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than anxiolytic effects.

ΔFosB is part of a homeostatic mechanism that protects the epileptic brain from further deterioration

Activity induced transcription factor ΔFosB plays a key role in different CNS disorders including epilepsy, Alzheimer's disease, and addiction. Recent findings suggest that ΔFosB drives cognitive deficits in epilepsy and together with the emergence of small molecule inhibitors of ΔFosB activity makes it an interesting therapeutic target. However, whether ΔFosB contributes to pathophysiology or provides protection in drug-resistant epilepsy is still unclear. In this study, ΔFosB was specifically downregulated by delivering AAV-shRNA into the hippocampus of chronically epileptic mice using the drug-resistant pilocarpine model of mesial temporal epilepsy (mTLE). Immunohistochemistry analyses showed that prolonged downregulation of ΔFosB led to exacerbation of neuroinflammatory markers of astrogliosis and microgliosis, loss of mossy fibers, and hippocampal granule cell dispersion. Furthermore, prolonged inhibition of ΔFosB using a ΔJunD construct to block ΔFosB signaling in a mouse model of Alzheimer's disease, that exhibits spontaneous recurrent seizures, led to similar findings, with increased neuroinflammation and decreased NPY expression in mossy fibers. Together, these data suggest that seizure-induced ΔFosB, regardless of seizure-etiology, is part of a homeostatic mechanism that protects the epileptic brain from further deterioration.

Reelin Signaling and Synaptic Plasticity in Schizophrenia

Recent research emphasizes the significance of studying the quality of life of schizophrenia patients, considering the complex nature of the illness. Identifying neuronal markers for early diagnosis and treatment is crucial. Reelin (RELN) stands out among these markers, with genetic studies highlighting its role in mental health. Suppression of RELN expression may contribute to cognitive deficits by limiting dendritic proliferation, affecting neurogenesis, and leading to improper neuronal circuits. Although the physiological function of reelin is not fully understood, it plays a vital role in hippocampal cell stratification and neuroglia formation. This analysis explores reelin's importance in the nervous system, shedding light on its impact on mental disorders such as schizophrenia, paving the way for innovative therapeutic approaches, and at the same time, raises the following conclusions: increased methylation levels of the RELN gene in patients with a diagnosis of schizophrenia results in a multiple decrease in the expression of reelin, and monitoring of this indicator, i.e., methylation levels, can be used to monitor the severity of symptoms in the course of schizophrenia.

Reelin Signaling in Neurodevelopmental Disorders and Neurodegenerative Diseases

Reelin is an extracellular matrix glycoprotein involved in neuronal migration during embryonic brain development and synaptic plasticity in the adult brain. The role of Reelin in the developing central nervous system has been extensively characterized. Indeed, a loss of Reelin or a disruption in its signaling cascade leads to neurodevelopmental defects and is associated with ataxia, intellectual disability, autism, and several psychiatric disorders. In the adult brain, Reelin is critically involved in neurogenesis and synaptic plasticity. Reelin's signaling potentiates glutamatergic and GABAergic neurotransmission, induces synaptic maturation, and increases AMPA and NMDA receptor subunits' expression and activity. As a result, there is a growing literature reporting that a loss of function and/or reduction of Reelin is implicated in numerous neurodegenerative diseases. The present review summarizes the current state of the literature regarding the implication of Reelin and Reelin-mediated signaling during aging and neurodegenerative disorders, highlighting Reelin as a possible target in the prevention or treatment of progressive neurodegeneration.

Emotional behaviors as well as the hippocampal reelin expression in C57BL/6N male mice chronically treated with corticosterone

Depression is a common psychiatric disorder affecting around 300 million people worldwide. Serum cortisol and glucocorticoid levels in humans are reportedly higher in patients with depression compared to controls. Furthermore, rodents repeatedly treated with exogenous corticosterone (CORT), a glucocorticoid in rodents, exhibit deficits in emotional behaviors. To confirm the availability of mice with chronic CORT treatment as an animal model of depression, we investigated the effect of chronic CORT treatment on depression-like behavioral and neuropathological phenotypes in C57BL/6N male mice. Behavioral studies showed depression- and anxiety-like behaviors in mice treated with CORT compared with control mice in the forced-swim and elevated-plus maze tests. Additionally, treated mice represented anhedonia and social behavior impairments in the sucrose preference and social interaction tests, respectively. Brains of depression patients have altered expression of reelin, an extracellular matrix protein involved in neuronal development and function. Likewise, in the present study, mice with chronic CORT treatment also exhibited reelin downregulation in cells of the hippocampus. Hence, we investigated therapeutic effects of reelin supplementation on CORT-induced behavioral abnormalities in mice. Microinjections of recombinant reelin protein into the hippocampus did not rescue behavioral deficits in mice with chronic CORT treatment. These results suggest that C57BL/6N male mice chronically treated with CORT are a suitable animal depression model, in which depressive behaviors may occur independently of the alternation of hippocampal Reelin expression.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT 2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic-and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice 24 h post-treatment. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than an anxiolytic effects.

Central repeat fragment of reelin leads to active reelin intracellular signaling and rescues cognitive deficits in a mouse model of reelin deficiency

Reelin and its receptor, ApoER2, play important roles in prenatal brain development and postnatally in synaptic plasticity, learning, and memory. Previous reports suggest that reelin's central fragment binds to ApoER2 and receptor clustering is involved in subsequent intracellular signaling. However, limitations of currently available assays have not established cellular evidence of ApoER2 clustering upon binding of the central reelin fragment. In the present study, we developed a novel, cell-based assay of ApoER2 dimerization using a "split-luciferase" approach. Specifically, cells were co-transfected with one recombinant ApoER2 receptor fused to the N-terminus of luciferase and one ApoER2 receptor fused to the C-terminus of luciferase. Using this assay, we directly observed basal ApoER2 dimerization/clustering in transfected HEK293T cells and, significantly, an increase in ApoER2 clustering in response to that central fragment of reelin. Furthermore, the central fragment of reelin activated intracellular signal transduction of ApoER2, indicated by increased levels of phosphorylation of Dab1, ERK1/2, and Akt in primary cortical neurons. Functionally, we were able to demonstrate that injection of the central fragment of reelin rescued phenotypic deficits observed in the heterozygous reeler mouse. These data are the first to test the hypothesis that the central fragment of reelin contributes to facilitating the reelin intracellular signaling pathway through receptor clustering.

Postnatal injection of Reelin protein into the cerebellum ameliorates the motor functions in reeler mouse

Reelin is a large secreted protein important for brain development and functions. In both humans and mice, the lack of Reelin gene causes cerebellar hypoplasia and ataxia. Treatment against Reelin deficiency is currently unavailable. Here, we show that the injection of recombinant Reelin protein into the cerebellum of Reelin-deficient reeler mice at postnatal day 3 ameliorates the forelimb coordination and mice are noted to stand up along cage wall more frequently. A mutant Reelin protein resistant to proteases has no better effect than the wild-type Reelin. Such ameliorations were not observed when a mutant Reelin protein that does not bind to Reelin receptors was injected and the injection of Reelin protein did not ameliorate the behavior of Dab1-mutant yotari mice, indicating that its effect is dependent on the canonical Reelin receptor-Dab1 pathway. Additionally, a Purkinje cell layer in reeler mice was locally induced by Reelin protein injection. Our results indicate that the reeler mouse cerebellum retains the ability to react to Reelin protein in the postnatal stage and that Reelin protein has the potential to benefit Reelin-deficient patients.

Maternal Immune Activation Induces Adolescent Cognitive Deficits Preceded by Developmental Perturbations in Cortical Reelin Signalling

Exposure to maternal immune activation (MIA) in utero significantly elevates the risk of developing schizophrenia and other neurodevelopmental disorders. To understand the biological mechanisms underlying the link between MIA and increased risk, preclinical animal models have focussed on specific signalling pathways in the brain that mediate symptoms associated with neurodevelopmental disorders such as cognitive dysfunction. Reelin signalling in multiple brain regions is involved in neuronal migration, synaptic plasticity and long-term potentiation, and has been implicated in cognitive deficits. However, how regulation of Reelin expression is affected by MIA across cortical development and associated cognitive functions remains largely unclear. Using a MIA rat model, here we demonstrate cognitive deficits in adolescent object-location memory in MIA offspring and reductions in Reln expression prenatally and in the adult prefrontal cortex. Further, developmental disturbances in gene/protein expression and DNA methylation of downstream signalling components occurred subsequent to MIA-induced Reelin dysregulation and prior to cognitive deficits. We propose that MIA-induced dysregulation of Reelin signalling contributes to the emergence of prefrontal cortex-mediated cognitive deficits through altered NMDA receptor function, resulting in inefficient long-term potentiation. Our data suggest a developmental window during which attenuation of Reelin signalling may provide a possible therapeutic target.

Reelin regulates the migration of late-born hippocampal CA1 neurons via cofilin phosphorylation

Reelin, a large secreted glycoprotein, plays an important role in neuronal migration during brain development. The C-terminal region (CTR) of Reelin is involved in the efficient activation of downstream signaling and its loss leads to abnormal hippocampal layer formation. However, the molecular mechanism by which Reelin CTR regulates hippocampal development remains unknown. Here, we showed that the migration of late-born, but not early-born, neurons is impaired in the knock-in mice in which Reelin CTR is deleted (ΔC-KI mice). The phosphorylation of cofilin, an actin-depolymerizing protein, was remarkably decreased in the hippocampus of the ΔC-KI mice. Exogenous expression of pseudo-phosphorylated cofilin rescued the ectopic positioning of neurons in the hippocampus of ΔC-KI mice. These results suggest that Reelin CTR is required for the migration of late-born neurons in the hippocampus and that this event involves appropriate phosphorylation of cofilin.

Immune Activation in Pregnant Rats Affects Brain Glucose Consumption, Anxiety-like Behaviour and Recognition Memory in their Male Offspring

PURPOSE

Prenatal infection during pregnancy is a risk factor for schizophrenia, as well as for other developmental psychiatric disorders, such as autism and bipolar disorder. Schizophrenia patients were reported to have altered brain metabolism and neuroinflammation. However, the link between prenatal infection, altered brain inflammation and metabolism, and schizophrenia remains unclear. In this project, we aimed to evaluate whether there are changes in brain glucose consumption and microglia activation in the offspring of pregnant rats exposed to maternal immune activation (MIA), and if so, whether these changes occur before or after the initiation of schizophrenia-like behaviour.

PROCEDURES

Pregnant rats were treated with the viral mimic polyinosinic-polycytidylic acid (MIA group) or saline (control group) on gestational day 15. Static PET scans of the male offspring were acquired on postnatal day (PND) 21, 60, and 90, using [11C]-PK11195 and deoxy-2-[18F]fluoro-D-glucose ([18F]-FDG) as tracers to measure TSPO expression in activated microglia and brain glucose consumption, respectively. On PND60 and PND90, anxiety-like behaviour, recognition memory, and sensorimotor gating were measured using the open field test (OFT), novel object recognition test (NOR), and prepulse inhibition test (PPI).

RESULTS

[18F]-FDG PET demonstrated that MIA offspring displayed higher brain glucose consumption in the whole brain after weaning (p = 0.017), and in the frontal cortex during late adolescence (p = 0.001) and adulthood (p = 0.037) than control rats. [11C]-PK11195 PET did not reveal any changes in TSPO expression in MIA offspring. Prenatal infection induced age-related behavioural alterations. Adolescent MIA offspring displayed a more anxious state in the OFT than controls (p = 0.042). Adult MIA offspring showed recognition memory deficits in the NOR (p = 0.003). Our study did not show any PPI deficits.

CONCLUSIONS

Our results suggest that prenatal immune activation changed neurodevelopment, resulting in increased brain glucose consumption, but not in microglia activation. The increased brain glucose consumption in the frontal cortex of MIA offspring remained until adulthood and was associated with increased anxiety-like behaviour during adolescence and recognition memory deficits in adulthood.

Reelin central fragment supplementation improves cognitive deficits in a mouse model of Fragile X Syndrome

Fragile X Syndrome (FXS) is the most common form of inherited intellectual disability and is characterized by autistic behaviors, childhood seizures, and deficits in learning and memory. FXS has a loss of function of the FMR1 gene that leads to a lack of Fragile X Mental Retardation Protein (FMRP) expression. FMRP is critical for synaptic plasticity, spatial learning, and memory. Reelin is a large extracellular glycoprotein essential for synaptic plasticity and numerous neurodevelopmental processes. Reduction in Reelin signaling is implicated as a contributing factor in disease etiology in several neurological disorders, including schizophrenia, and autism. However, the role of Reelin in FXS is poorly understood. We demonstrate a reduction in Reelin in Fmr1 knock-out (KO) mice, suggesting that a loss of Reelin activity may contribute to FXS. We demonstrate here that Reelin signaling enhancement via a single intracerebroventricular injection of the Reelin central fragment into Fmr1 KO mice can profoundly rescue cognitive deficits in hidden platform water maze and fear conditioning, as well as hyperactivity during the open field. Improvements in behavior were associated with rescued levels of post synaptic marker in Fmr1 KO mice when compared to controls. These data suggest that increasing Reelin signaling in FXS could offer a novel therapeutic for improving cognition in FXS.

Reelin Alterations, Behavioral Phenotypes, and Brain Anomalies in Schizophrenia: A Systematic Review of Insights From Rodent Models

Reelin is an extracellular matrix glycoprotein reduced in brain regions (the prefrontal cortex and the hippocampus) of patients with schizophrenia. There are diverse rodent models of schizophrenia that mimic patient symptoms based on various causal theories; however, likely shared reelin alterations have not yet been systematically assessed in those models. A systematic review of the literature was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) model. Articles focused on psychotic disorders or schizophrenia and their relationship with reelin in rodent models were selected. Data (first author, publication year, results, both open field and prepulse inhibition test results, and type of reelin alteration) were extracted in duplicate by two independent reviewers. The 37 reviewed articles reported about various schizophrenia models and their reelin alterations, brain morphology, and behavioral defects. We conclude that reelin is an altered preclinical biomarker common to all models included, mainly prenatal or genetic models, and a key protein in schizophrenia disease, making the reelin signaling pathway in prenatal stages a target of special interest for future preclinical and clinical studies. All models presented at least one of the four described reelin alteration types.

Systematic Review Registration: [https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021210568], identifier [CRD42021210568].

Visualization of Reelin secretion from primary cultured neurons by bioluminescence imaging

Reelin is a secreted glycoprotein important for brain development and synaptic plasticity in the adult brain. Some reports suggest that Reelin is secreted from the nerve terminals and functions as a neurotransmitter. However, the mechanism of Reelin secretion is unknown. In this study, we visualized Reelin secretion by bioluminescence imaging using a fusion protein of Reelin and Gaussia luciferase (GLase-Reelin). GLase-Reelin expressed in HEK293T cells was correctly processed and secreted. Luminescence signals from the secreted GLase-Reelin of primary cultured neurons were visualized by bioluminescence microscopy. Reelin secretory events were observed at neurites and cell bodies. Bioluminescence imaging was also performed before and after KCl depolarization to compare the secretory events of Reelin and brain-derived neurotrophic factor (BDNF). The secretion of BDNF increased markedly shortly after depolarization. In contrast, the frequency of Reelin secretion did not change significantly by depolarization. Thus, Reelin secretion from neurites might not be regulated in a neuronal activity-dependent manner.

New Strategies for the Treatment of Neuropsychiatric Disorders Based on Reelin Dysfunction

Reelin is an extracellular matrix protein that is mainly produced in Cajal-Retzius cells and controls neuronal migration, which is important for the proper formation of cortical layers in the developmental stage of the brain. In the adult brain, Reelin plays a crucial role in the regulation of N-methyl-D-aspartate receptor-dependent synaptic function, and its expression decreases postnatally. Clinical studies showed reductions in Reelin protein and mRNA expression levels in patients with psychiatric disorders; however, the causal relationship remains unclear. Reelin-deficient mice exhibit an abnormal neuronal morphology and behavior, while Reelin supplementation ameliorates learning deficits, synaptic dysfunctions, and spine loss in animal models with Reelin deficiency. These findings suggest that the neuronal deficits and brain dysfunctions associated with the down-regulated expression of Reelin are attenuated by enhancements in its expression and functions in the brain. In this review, we summarize findings on the role of Reelin in neuropsychiatric disorders and discuss potential therapeutic approaches for neuropsychiatric disorders associated with Reelin dysfunctions.

Genotoxic Damage During Brain Development Presages Prototypical Neurodegenerative Disease

Western Pacific Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex (ALS/PDC) is a disappearing prototypical neurodegenerative disorder (tau-dominated polyproteinopathy) linked with prior exposure to phytogenotoxins in cycad seed used for medicine and/or food. The principal cycad genotoxin, methylazoxymethanol (MAM), forms reactive carbon-centered ions that alkylate nucleic acids in fetal rodent brain and, depending on the timing of systemic administration, induces persistent developmental abnormalities of the cortex, hippocampus, cerebellum, and retina. Whereas administration of MAM prenatally or postnatally can produce animal models of epilepsy, schizophrenia or ataxia, administration to adult animals produces little effect on brain structure or function. The neurotoxic effects of MAM administered to rats during cortical brain development (specifically, gestation day 17) are used to model the histological, neurophysiological and behavioral deficits of human schizophrenia, a condition that may precede or follow clinical onset of motor neuron disease in subjects with sporadic ALS and ALS/PDC. While studies of migrants to and from communities impacted by ALS/PDC indicate the degenerative brain disorder may be acquired in juvenile and adult life, a proportion of indigenous cases shows neurodevelopmental aberrations in the cerebellum and retina consistent with MAM exposure in utero. MAM induces specific patterns of DNA damage and repair that associate with increased tau expression in primary rat neuronal cultures and with brain transcriptional changes that parallel those associated with human ALS and Alzheimer's disease. We examine MAM in relation to neurodevelopment, epigenetic modification, DNA damage/replicative stress, genomic instability, somatic mutation, cell-cycle reentry and cellular senescence. Since the majority of neurodegenerative disease lacks a solely inherited genetic basis, research is needed to explore the hypothesis that early-life exposure to genotoxic agents may trigger or promote molecular events that culminate in neurodegeneration.

Microinjection of Reelin into the mPFC prevents MK-801-induced recognition memory impairment in mice

Reelin, a large extracellular matrix protein, helps to regulate neuronal plasticity and cognitive function. Several studies have shown that Reelin dysfunction, resulting from factors such as mutations in gene RELN or low Reelin expression, is associated with schizophrenia (SCZ). We previously reported that microinjection of Reelin into cerebral ventricle prevents phencyclidine-induced cognitive and sensory-motor gating deficits. However, it remains unclear whether and how Reelin ameliorates behavioral abnormalities in the animal model of SCZ. In the present study, we evaluated the effect of recombinant Reelin microinjection into the medial prefrontal cortex (mPFC) on abnormal behaviors induced by MK-801, an N-methyl-D-aspartate receptor antagonist. Microinjection of Reelin into the mPFC prevented impairment of recognition memory of MK-801-treated mice in the novel object recognition test (NORT). On the other hand, the same treatment had no effect on deficits in sensory-motor gating and short-term memory in the pre-pulse inhibition and Y-maze tests, respectively. To establish the neural substrates that respond to Reelin, the number of c-Fos-positive cells in the mPFC was determined. A significant increase in c-Fos-positive cells in the mPFC of MK-801-treated mice was observed when compared with saline-treated mice, and this change was suppressed by microinjection of Reelin into the mPFC. A K2360/2467A Reelin that cannot bind to its receptor failed to ameliorate MK-801-induced cognitive deficits in NORT. These results suggest that Reelin prevents MK-801-induced recognition memory impairment by acting on its receptors to suppress neural activity in the mPFC of mice.

Regulation of Reelin functions by specific proteolytic processing in the brain

The secreted glycoprotein Reelin plays important roles in both brain development and function. During development, Reelin regulates neuronal migration and dendrite development. In the mature brain, the glycoprotein is involved in synaptogenesis and synaptic plasticity. It has been suggested that Reelin loss or decreased function contributes to the onset and/or deterioration of neuropsychiatric diseases, including schizophrenia and Alzheimer's disease. While the molecular mechanisms underpinning Reelin function remain unclear, recent studies have suggested that the specific proteolytic cleavage of Reelin may play central roles in the embryonic and postnatal brain. In this review, we focus on Reelin proteolytic processing and review its potential physiological roles.

Reelin changes hippocampal learning in aging and Alzheimer's disease

The hippocampal formation (HF) is a neuroanatomical region essential for learning and memory. As one of the earliest regions to display the histopathological hallmarks of Alzheimer's disease (AD), determining the specific mechanisms of the HF's vulnerability is of capital importance. Reelin, a glycoprotein crucial in cortical lamination during embryonic neurogenesis, has an uncommon expression pattern within the HF and has been implicated in both learning and AD pathogenesis. We hypothesized that Reelin deficiency would expedite behavioral impairments which accompany normal aging. Additionally, we hypothesized that Reelin deficiency in the presence of mutated human microtubule associated protein tau (MAPT) would further impair hippocampal function. To test our hypothesis, we utilized cohorts of aged mice, aged mice with Reelin conditional knockout (RcKO), and adult mice with both RcKO and MAPT in the Barnes maze and Trace fear conditioning. Consistent with prior literature, increased age in wild-type mice was sufficient to reduce spatial searching in the Barnes maze. Increased age both exacerbated spatial impairments and altered context learning in RcKO mice. Lastly, adult mice with both RcKO and the MAPT transgene displayed both the lowest age-of-onset and most severe spatial learning deficits. In conclusion, Reelin deficiency when combined with AD risk-factors produced consistent impairments in spatial memory tasks. Furthermore, our results further implicate Reelin's importance in both HF homeostasis and AD pathogenesis.

Maternal immune activation in rodent models: A systematic review of neurodevelopmental changes in gene expression and epigenetic modulation in the offspring brain

Maternal immune activation (mIA) during pregnancy is hypothesised to disrupt offspring neurodevelopment and predispose offspring to neurodevelopmental disorders such as schizophrenia. Rodent models of mIA have explored possible mechanisms underlying this paradigm and provide a vital tool for preclinical research. However, a comprehensive analysis of the molecular changes that occur in mIA-models is lacking, hindering identification of robust clinical targets. This systematic review assesses mIA-driven transcriptomic and epigenomic alterations in specific offspring brain regions. Across 118 studies, we focus on 88 candidate genes and show replicated changes in expression in critical functional areas, including elevated inflammatory markers, and reduced myelin and GABAergic signalling proteins. Further, disturbed epigenetic markers at nine of these genes support mIA-driven epigenetic modulation of transcription. Overall, our results demonstrate that current outcome measures have direct relevance for the hypothesised pathology of schizophrenia and emphasise the importance of mIA-models in contributing to the understanding of biological pathways impacted by mIA and the discovery of new drug targets.

Analysis of Reelin signaling and neurodevelopmental trajectory in primary cultured cortical neurons with RELN deletion identified in schizophrenia

Reelin, an extracellular matrix protein, is secreted by Cajal-Retzius cells and plays crucial roles in the development of brain structures and neuronal functions. Reductions in Reelin cause the brain dysfunctions associated with mental disorders, such as schizophrenia. A recent genome-wide copy number variation analysis of Japanese schizophrenia patients identified a novel deletion in RELN encoding Reelin. To clarify the pathophysiological role of the RELN deletion, we developed transgenic mice carrying the RELN deletion (Reln-del) and found abnormalities in their brain structures and social behavior. In the present study, we performed an in vitro analysis of Reelin expression, intracellular Reelin signaling, and the morphology of primary cultured cortical neurons from wild-type (WT) and Reln-del mice. Reelin protein levels were lower in Reln-del neurons than in WT neurons. Dab1 expression levels were significantly higher in Reln-del neurons than in WT neurons, suggesting that Reelin signaling was decreased in Reln-del neurons. Reelin was mainly expressed in γ-aminobutyric acid (GABA)-ergic inhibitory neurons, but not in parvalbumin (PV)-positive neurons. A small proportion of Ca²⁺/calmodulin-dependent protein kinase II α subunit (CaMKIIα)-positive excitatory neurons also expressed Reelin. In comparisons with WT neurons, significant decreases were observed in neurite lengths and branch points as well as in the number of postsynaptic density protein 95 (PSD95) immunoreactive puncta in Reln-del neurons. A disintegrin and metalloproteinase with thrombospondin motifs-3 (ADAMTS-3) is a protease that inactivates Reelin by cleavage at the N-t site. The knockdown of ADAMTS-3 by short hairpin RNAs suppressed Reelin cleavage in conditioned medium and reduced Dab1 expression, indicating that Reelin signaling was enhanced in the primary cultured cortical neurons of WT and heterozygous Reln-del. Accordingly, the inhibition of ADAMTS-3 may be a potential candidate in the clinical treatment of schizophrenia by enhancing Reelin signaling in the brain.