Reelin: Neurodevelopmental Architect and Homeostatic Regulator of Excitatory Synapses

Reelin marks cocaine-activated striatal neurons, promotes neuronal excitability, and regulates cocaine reward

Drugs of abuse activate defined neuronal populations in reward structures such as the nucleus accumbens (NAc), which promote the enduring synaptic, circuit, and behavioral consequences of drug exposure. While the molecular and cellular effects arising from experience with drugs like cocaine are increasingly well understood, mechanisms that dictate NAc neuronal recruitment remain unknown. Here, we leveraged unbiased single-nucleus transcriptional profiling and targeted in situ detection to identify Reln (encoding the secreted glycoprotein, Reelin) as a marker of cocaine-activated neuronal populations within the rat NAc. A CRISPR interference approach enabling selective Reln knockdown in the adult NAc altered expression of calcium signaling genes, promoted a transcriptional trajectory consistent with loss of cocaine sensitivity, and decreased MSN excitability. Behaviorally, Reln knockdown prevented cocaine locomotor sensitization, abolished cocaine place preference memory, and decreased cocaine self-administration behavior. These results identify Reelin as a critical mechanistic link between neuronal activation and cocaine-induced behavioral adaptations.

Genetic or therapeutic disruption of the Reelin/Apoer2 signaling pathway improves inflammatory arthritis outcomes

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation, pannus formation, and progressive joint destruction. The inflammatory milieu in RA drives endothelial cell activation and upregulation of adhesion molecules, thus facilitating leukocyte infiltration into the synovium. Reelin, a circulating glycoprotein previously implicated in endothelial activation and leukocyte recruitment in diseases such as atherosclerosis and multiple sclerosis, has emerged as a potential upstream regulator of these processes. However, its role in RA pathogenesis remains poorly understood. Here, we demonstrate that Reelin levels are markedly elevated in the plasma of both RA patients and mouse models of arthritis, with higher concentrations correlating with greater disease severity. Genetic deletion of the Reelin receptor Apoer2 conferred significant protection against serum transfer arthritis (STA), underscoring the relevance of this pathway in disease progression. Furthermore, therapeutic inhibition of Reelin using the CR-50 antibody yielded robust anti-inflammatory effects in multiple preclinical arthritis models, including STA, K/BxN, and collagen-induced arthritis. Notably, CR-50 treatment not only reduced leukocyte infiltration and synovial inflammation but also mitigated pannus formation. Importantly, these benefits were achieved without the gastrointestinal side effects commonly associated with nonsteroidal anti-inflammatory drugs like diclofenac. Our findings position Reelin as a proinflammatory endothelial biomarker and therapeutic target in RA. By modulating endothelial activation and leukocyte recruitment, anti-Reelin strategies offer an alternative approach to attenuate synovial inflammation and joint damage. These results provide a compelling rationale for further exploration of Reelin-targeted therapies as alternatives to conventional immunosuppressive treatments in RA and other chronic inflammatory diseases.

Effects of Oral Administration of the Probiotic Lactobacillus rhamnosus GG on the Proteomic Profiles of Cerebrospinal Fluid and Immunoregulatory Signaling in the Hippocampus of Adult Male Rats

INTRODUCTION

The microbiome-gut-brain axis, by modulating bidirectional immune, metabolic, and neural signaling pathways in the host, has emerged as a target for the prevention and treatment of psychiatric and neurological disorders. Oral administration of the probiotic bacterium Lactobacillus rhamnosus GG (LGG; ATCC 53103) exhibits anti-inflammatory effects, although the precise mechanisms by which LGG benefits host physiology and behavior are not known. The goal of this study was to explore the general effects of LGG on the cerebrospinal fluid (CSF) proteome and a biological signature of anti-inflammatory signaling in the central nervous system (CNS) of undisturbed, adult male rats.

METHODS

Liquid chromatography-tandem mass spectrometry-based proteomics were conducted using CSF samples collected after 21 days of oral treatment with live LGG (3.34 × 107 colony-forming units (CFU)/mL in the drinking water (resulting in an estimated delivery of ∼1.17 × 109 CFU/day/rat) or water vehicle. Gene enrichment analysis (using DAVID, v. 6.8) and protein-protein interactions (using STRING, v. 11) were used to explore physiological network changes in CSF. Real-time reverse transcription polymerase chain reaction (real-time RT-PCR) was performed to assess gene expression changes of anti-inflammatory cytokines in the hippocampus. Genes associated with anti-inflammatory signaling that were analyzed included Il10, Tgfb1, Il4, and IL-4-responsive genes, Cd200, Cd200r1, and Mrc1 (Cd206).

RESULTS

Oral LGG administration altered the abundance of CSF proteins, increasing the abundance of five proteins (cochlin, NPTXR, reelin, Sez6l, and VPS13C) and decreasing the abundance of two proteins (CPQ, IGFBP-7) in the CSF. Simultaneously, LGG increased the expression of Il10 mRNA, encoding the anti-inflammatory cytokine interleukin 10, in the hippocampus.

CONCLUSION

Oral LGG altered the abundance of CSF proteins associated with extracellular scaffolding, synaptic plasticity, and glutamatergic signaling. These data are consistent with the hypothesis that oral administration of LGG improves memory and cognition, and promotes a physiological resilience to neurodegenerative disease, by increasing glutamatergic signaling and promoting an anti-inflammatory environment in the brain.

Repeated social defeat in male mice induced unique RNA profiles in projection neurons from the amygdala to the hippocampus

Chronic stress increases the incidence of psychiatric disorders including anxiety, depression, and posttraumatic stress disorder. Repeated Social Defeat (RSD) in mice recapitulates several key physiological, immune, and behavioral changes evident after chronic stress in humans. For instance, neurons in the prefrontal cortex, amygdala, and hippocampus are involved in the interpretation of and response to fear and threatful stimuli after RSD. Therefore, the purpose of this study was to determine how stress influenced the RNA profile of hippocampal neurons and neurons that project into the hippocampus from threat appraisal centers. Here, RSD increased anxiety-like behavior in the elevated plus maze and reduced hippocampal-dependent novel object location memory in male mice. Next, pan-neuronal (Baf53 b-Cre) RiboTag mice were generated to capture ribosomal bound mRNA (i.e., active translation) activated by RSD in the hippocampus. RNAseq revealed that there were 1694 differentially expressed genes (DEGs) in hippocampal neurons after RSD. These DEGs were associated with an increase in oxidative stress, synaptic long-term potentiation, and neuroinflammatory signaling. To further examine region-specific neural circuitry associated with fear and anxiety, a retrograde-adeno-associated-virus (AAV2rg) expressing Cre-recombinase was injected into the hippocampus of male RiboTag mice. This induced expression of a hemagglutinin epitope in neurons that project into the hippocampus. These AAV2rg-RiboTag mice were subjected to RSD and ribosomal-bound mRNA was collected from the amygdala for RNA-sequencing. RSD induced 677 DEGs from amygdala projections. Amygdala neurons that project into the hippocampus had RNA profiles associated with increased synaptogenesis, interleukin-1 signaling, nitric oxide, and reactive oxygen species production. Using a similar approach, there were 1132 DEGs in neurons that project from the prefrontal cortex. These prefrontal cortex neurons had RNA profiles associated with increased synaptogenesis, integrin signaling, and dopamine feedback signaling after RSD. Collectively, there were unique RNA profiles of stress-influenced projection neurons and these profiles were associated with hippocampal-dependent behavioral and cognitive deficits.

Analysis of distribution and localization of proteins of the reelin signalling pathway in mesial temporal lobe epilepsy

INTRODUCTION

Granule cell dispersion (GCD) is pathognomonic of hippocampal sclerosis seen in the mesial temporal lobe epilepsy (MTLE). Current animal studies indicate deficiency of Reelin is associated with abnormal granule cell migration leading to GCD. The present study aimed to evaluate complete Reelin signalling pathway to assess whether Reelin deficiency is related to MTLE.

MATERIALS AND METHODS

Hippocampal sclerosis was confirmed by H and E stain. To explore the amount and cellular location of the Reelin cascade molecules, the hippocampal tissues from MTLE surgery and controls (n = 15 each) were studied using Immuno-histochemistry (IHC). Additionally, confocal imaging was used to validate the IHC findings by co-localization of different proteins. Quantification of IHC images was performed using histo-score and confocal images by Image J software.

RESULTS

Immune expression of active Reelin was significantly reduced in patients. Reelin receptors were deranged, apolipoprotein E receptor 2 was increased while very low-density lipoprotein receptor was reduced. Disabled-1, a downstream molecule was significantly reduced in MTLE. Its ultimate target, cofilin was thus disinhibited and expressed more in MTLE. Reelin cleaving protease, matrix metalloprotease-9 (MMP-9) and MMP-9 inhibitor, tissue inhibitor of matrix protease-1, showed reduced expression in extracellular matrix. Semi-quantification of immunohistochemistry was done using Histo (H) score. H score of Reelin in diseased patients was 15 against 125 for control patients. These results were validated by confocal fluorescence microscopy.

CONCLUSIONS

Reelin signalling cascade was deranged in chronic MTLE. Pharmacological manipulation of Reelin cascade can be done at various levels and it may provide novel treatment options for MTLE.

Do specific myelin autoantibodies and increased cerebral dopamine neurotrophic factor in the context of inflammation predict the diagnosis of attention deficit hyperactivity disorder in medication-free children?

BACKGROUND

The aim of this study was to investigate the serum levels of anti-myelin basic protein (anti-MBP), anti-myelin oligodentrocyte glycoprotein (anti-MOG), myelin-associated glycoprotein (MAG), high-sensitivity C-reactive protein (hs-CRP), cerebral dopamine neurotrophic factor (CDNF), cerebellin-1, and reelin and their relationships with clinical severity and irritability behaviours in children with attention deficit (AD) hyperactivity disorder (ADHD) and typically developing (TD) healthy controls.

METHODS

In this study, 141 children with ADHD between the ages of 8 and 14 years who were medication-free and 135 TD healthy controls were included. The serum levels of anti-MBP, anti-MOG, MAG, CDNF, hs-CRP, cerebellin, and reelin were measured using enzyme-linked immunosorbent assay kits. The Turgay Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)-based Screening and Evaluation Scale for Attention Deficit and Disruptive Behavior Disorders-Parent Form (TDSM-IV-O) and the affective reactivity index (ARI) scale were used to assess clinical severity and irritability behaviours in the children.

RESULTS

The MAG, CDNF, hs-CRP, reelin, and cerebellin levels were significantly higher in the ADHD group than in the control group, but no significant differences in anti-MBP and anti-MOG levels were found between the groups. Compared with the controls, the patients with ADHD showed significantly higher scores on the ARI self- and parent-report scales. The reelin, hs-CRP, and MAG levels were significantly associated with the TDSM-IV-O AD scores, AD and oppositional defiant (OD) disorder scores and hyperactivity, and OD and conduct disorder scores, respectively. Hs-CRP was significantly associated with anti-MBP and cerebellin levels. In an analysis of covariance, the results were unchanged even after controlling for potential confounders such as age, body mass index, and sex.

CONCLUSION

This study demonstrates that MAG, CDNF, hs-CRP, reelin, and cerebellin levels may play a potential role in the pathogenesis of ADHD.

Shared molecular signature in Alzheimer's disease and schizophrenia: A systematic review of the reelin signaling pathway

The Reelin signaling pathway, particularly the RELN-APOER2-DAB1 complex, has emerged as a key contributor to the neuropathology of Alzheimer's disease (AD) and Schizophrenia (SZ). Despite being distinct clinical conditions, these disorders exhibit similar patterns of cognitive decline, including early disruptions in synaptic function and memory impairments. Notably, individuals with SZ have a 2-4 fold increased risk of developing AD or other dementias, highlighting potential shared molecular mechanisms, and positioning Reelin as a pivotal link between them. This systematic review explores the role of Reelin and its signaling components across these disorders. In AD, Reelin disruption correlates with hallmark features such as Tau hyperphosphorylation, amyloid-beta accumulation, and cognitive deficits. In SZ, alterations in Reelin signaling, including epigenetic modifications affecting RELN expression, are linked to disruptions in neuronal development and synaptic plasticity, particularly in the parietal and prefrontal cortices. Additionally, genomic studies reveal specific RELN variants and allelic imbalances that may influence disease severity and treatment response in SZ, suggesting RELN's role as a potential biomarker for therapeutic outcomes. Region-specific Reelin alterations in both AD and SZ suggest differing impacts yet underscore a potential common molecular origin. Our findings highlight the Reelin pathway as a molecular convergence point, warranting further investigation as a therapeutic and diagnostic target for AD, SZ, and potentially other neuropsychiatric disorders. The interplay between genetic and epigenetic regulation of RELN may provide novel insights into neurodegeneration, with implications for personalized intervention strategies in AD and SZ.

DNA methylation and histone modifications associated with antipsychotic treatment: a systematic review

Antipsychotic medications are essential when treating schizophrenia spectrum and other psychotic disorders, but the efficacy and tolerability of these medications vary from person to person. This interindividual variation is likely mediated, at least in part, by epigenomic processes that have yet to be fully elucidated. Herein, we systematically identified and evaluated 65 studies that examine the influence of antipsychotic drugs on epigenomic changes, including global methylation (9 studies), genome-wide methylation (22 studies), candidate gene methylation (16 studies), and histone modification (18 studies). Our evaluation revealed that haloperidol was consistently associated with increased global hypermethylation, which corroborates with genome-wide analyses, mostly performed by methylation arrays. In contrast, clozapine seems to promote hypomethylation across the epigenome. Candidate-gene methylation studies reveal varying effects post-antipsychotic therapy. Some genes like Glra1 and Drd2 are frequently found to undergo hypermethylation, whereas other genes such as SLC6A4, DUSP6, and DTNBP1 are more likely to exhibit hypomethylation in promoter regions. In examining histone modifications, the literature suggests that clozapine changes histone methylation patterns in the prefrontal cortex, particularly elevating H3K4me3 at the Gad1 gene and affecting the transcription of genes like mGlu2 by modifying histone acetylation and interacting with HDAC2 enzymes. Risperidone and quetiapine, however, exhibit distinct impacts on histone marks across different brain regions and cell types, with risperidone reducing H3K27ac in the striatum and quetiapine modifying global H3K9me2 levels in the prefrontal cortex, suggesting antipsychotics demonstrate selective influence on histone modifications, which demonstrates a complex and targeted mode of action. While this review summarizes current knowledge, the intricate dynamics between antipsychotics and epigenetics clearly warrant more exhaustive exploration with the potential to redefine our understanding and treatment of psychiatric conditions. By deciphering the epigenetic changes associated with drug treatment and therapeutic outcomes, we can move closer to personalized medicine in psychiatry.

Bnip3 expression is strongly associated with reelin-positive entorhinal cortex layer II neurons

In layer II of the entorhinal cortex, the principal neurons that project to the dentate gyrus and the CA3/2 hippocampal fields markedly express the large glycoprotein reelin (Re + ECLII neurons). In rodents, neurons located at the dorsal extreme of the EC, which border the rhinal fissure, express the highest levels, and the expression gradually decreases at levels successively further away from the rhinal fissure. Here, we test two predictions deducible from the hypothesis that reelin expression is strongly correlated with neuronal metabolic rate. Since the mitochondrial turnover rate serves as a proxy for energy expenditure, the mitophagy rate arguably also qualifies as such. Because messenger RNA of the canonical promitophagic BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (Bnip3) is known to be highly expressed in the EC, we predicted that Bnip3 would be upregulated in Re + ECLII neurons, and that the degree of upregulation would strongly correlate with the expression level of reelin in these neurons. We confirm both predictions, supporting that the energy requirement of Re + ECLII neurons is generally high and that there is a systematic increase in metabolic rate as one moves successively closer to the rhinal fissure. Intriguingly, the systematic variation in energy requirement of the neurons that manifest the observed reelin gradient appears to be consonant with the level of spatial and temporal detail by which they encode information about the external environment.

Herbal Formula Extract Ameliorates Anxiety and Cognitive Impairment via Regulation of the Reelin/Dab-1 Pathway in a Murine Model of Post-Traumatic Stress Disorder

We investigated the effects of epigenetic modifications on post-traumatic stress disorder (PTSD) using a novel combination of herbal medicines from Panax ginseng, Astragalus membranaceus, Atractylodes macrocephala, and Glycyrrhiza uralensis. The herbal formula extract (HFE) (250 mg/kg) was administered orally once daily for 14 days to determine its effects on PTSD in mice by combining prolonged stress and foot shock. The open field and Y-maze tests determined the effect of HFE on PTSD-induced anxiety and cognition. Hippocampal neuronal plastic changes and molecular mechanism were verified. Treatment with HFE decreased anxiety-like behavior and enhanced cognition. Moreover, it reduced the number of PTSD-related hilar ectopic granule cells in the dentate gyrus (DG). PTSD mice showed reduced neuronal plasticity of doublecortin+ cells in the DG, which was restored by HFE treatment. HFE reversed PTSD-induced inhibition of the Reelin/Dab1 pathway, a critical signaling cascade involved in brain development, and regulated Reelin methylation. Furthermore, DNA methylation, methyl-CpG binding protein 2, and DNA methyltransferase 1, which were elevated in the hippocampus of PTSD mice, were restored following HFE treatment. HFE increased the expression of synaptic plasticity-related factors in the hippocampus of PTSD mice. Our findings suggest that HFE can facilitate PTSD treatment by alleviating behavioral abnormalities through the restoration of hippocampal dysfunction via regulation of the Reelin/Dab-1 pathway and DNA methylation in the hippocampus.

OCRL1 Deficiency Affects the Intracellular Traffic of ApoER2 and Impairs Reelin-Induced Responses

Lowe Syndrome (LS) is a rare X-linked disorder characterized by renal dysfunction, cataracts, and several central nervous system (CNS) anomalies. The mechanisms underlying the neurological dysfunction in LS remain unclear, albeit they share some phenotypic characteristics similar to the deficiency or dysfunction of the Reelin signaling, a relevant pathway with roles in CNS development and neuronal functions. In this study, we investigated the role of OCRL1, an inositol polyphosphate 5-phosphatase encoded by the OCRL gene, mutated in LS, focusing on its impact on endosomal trafficking and receptor recycling in human neuronal cells. Specifically, we tested the effects of OCRL1 deficiency in the trafficking and signaling of ApoER2/LRP8, a receptor for the ligand Reelin. We found that loss of OCRL1 impairs ApoER2 intracellular trafficking, leading to reduced receptor expression and decreased levels at the plasma membrane. Additionally, human neurons deficient in OCRL1 showed impairments in ApoER2/Reelin-induced responses. Our findings highlight the critical role of OCRL1 in regulating ApoER2 endosomal recycling and its impact on the ApoER2/Reelin signaling pathway, providing insights into potential mechanisms underlying the neurological manifestations of LS.

Reelin marks cocaine-activated striatal ensembles, promotes neuronal excitability, and regulates cocaine reward

Drugs of abuse activate defined neuronal ensembles in brain reward structures such as the nucleus accumbens (NAc), which are thought to promote the enduring synaptic, circuit, and behavioral consequences of drug exposure. While the molecular and cellular effects arising from experience with drugs like cocaine are increasingly well understood, the mechanisms that sculpt NAc ensemble participation are largely unknown. Here, we leveraged unbiased single-nucleus transcriptional profiling to identify expression of the secreted glycoprotein Reelin (encoded by the Reln gene) as a marker of cocaine-activated neuronal ensembles within the rat NAc. Multiplexed in situ detection confirmed selective expression of the immediate early gene Fos in Reln+ neurons after cocaine experience, and also revealed enrichment of Reln mRNA in Drd1 + medium spiny neurons (MSNs) in both the rat and human brain. Using a novel CRISPR interference strategy enabling selective Reln knockdown in the adult NAc, we observed altered expression of genes linked to calcium signaling, emergence of a transcriptional trajectory consistent with loss of cocaine sensitivity, and a striking decrease in MSN intrinsic excitability. At the behavioral level, loss of Reln prevented cocaine locomotor sensitization, abolished cocaine place preference memory, and decreased cocaine self-administration behavior. Together, these results identify Reelin as a critical mechanistic link between ensemble participation and cocaine-induced behavioral adaptations.

Early developmental changes in a rat model of malformations of cortical development: Abnormal neuronal migration and altered response to NMDA-induced excitotoxic injury

Malformations of cortical development (MCDs) are caused by abnormal neuronal migration processes during the fetal period and are a major cause of intractable epilepsy in infancy. However, the timing of hyperexcitability or epileptogenesis in MCDs remains unclear. To identify the early developmental changes in the brain of the MCD rat model, which exhibits increased seizure susceptibility during infancy (P12-15), we analyzed the pathological changes in the brains of MCD model rats during the neonatal period and tested NMDA-induced seizure susceptibility. Pregnant rats were injected with two doses of methylazoxymethanol acetate (MAM, 15 mg/kg, i.p.) to induce MCD, while controls were administered normal saline. The cortical development of the offspring was measured by performing magnetic resonance imaging (MRI) on postnatal days (P) 1, 5, and 8. At P8, some rats were sacrificed for immunofluorescence, Golgi staining, and Western analysis. In another set of rats, the number and latency to onset of spasms were monitored for 90 min after the NMDA (5 mg/kg i.p.) injection at P8. In MCD rats, in vivo MR imaging showed smaller brain volume and thinner cortex from day 1 after birth (p < 0.001). Golgi staining and immunofluorescence revealed abnormal neuronal migration, with a reduced number of neuronal cell populations and less dendritic arborization at P8. Furthermore, MCD rats exhibited a significant reduction in the expression of NMDA receptors and AMPAR4, along with an increase in AMPAR3 expression (p < 0.05). Although there was no difference in the latency to seizure onset between MCD rats and controls, the MCD rats survived significantly longer than the controls. These results provide insights into the early developmental changes in the cortex of a MCD rat model and suggest that delayed and abnormal neuronal development in the immature brain is associated with a blunted response to NMDA-induced excitotoxic injury. These developmental changes may be involved in the sudden onset of epilepsy in patients with MCD or prenatal brain injury.

The Role of RIN3 Gene in Alzheimer's Disease Pathogenesis: a Comprehensive Review

Alzheimer's disease (AD) is a globally prevalent form of dementia that impacts diverse populations and is characterized by progressive neurodegeneration and impairments in executive memory. Although the exact mechanisms underlying AD pathogenesis remain unclear, it is commonly accepted that the aggregation of misfolded proteins, such as amyloid plaques and neurofibrillary tau tangles, plays a critical role. Additionally, AD is a multifactorial condition influenced by various genetic factors and can manifest as either early-onset AD (EOAD) or late-onset AD (LOAD), each associated with specific gene variants. One gene of particular interest in both EOAD and LOAD is RIN3, a guanine nucleotide exchange factor. This gene plays a multifaceted role in AD pathogenesis. Firstly, upregulation of RIN3 can result in endosomal enlargement and dysfunction, thereby facilitating the accumulation of beta-amyloid (Aβ) peptides in the brain. Secondly, RIN3 has been shown to impact the PICLAM pathway, affecting transcytosis across the blood-brain barrier. Lastly, RIN3 has implications for immune-mediated responses, notably through its influence on the PTK2B gene. This review aims to provide a concise overview of AD and delve into the role of the RIN3 gene in its pathogenesis.

Chronic corticosterone exposure in rats induces sex-specific alterations in hypothalamic reelin fragments, MeCP2, and DNMT3a protein levels

Women are disproportionately affected by stress-related disorders like depression. In our prior research, we discovered that females exhibit lower basal hypothalamic reelin levels, and these levels are differentially influenced by chronic stress induced through repeated corticosterone (CORT) injections. Although epigenetic mechanisms involving DNA methylation and the formation of repressor complexes by DNA methyl-transferases (DNMTs) and Methyl-CpG binding protein 2 (MeCP2) have been recognized as regulators of reelin expression in vitro, there is limited understanding of the impact of stress on the epigenetic regulation of reelin in vivo and whether sex differences exist in these mechanisms. To address these questions, we conducted various biochemical analyses on hypothalamic brain samples obtained from male and female rats previously treated with either 21 days of CORT (40 mg/kg) or vehicle (0.9 % saline) subcutaneous injections. Upon chronic CORT treatment, a reduction in reelin fragment NR2 was noted in males, while the full-length molecule remained unaffected. This decrease paralleled with an elevation in MeCP2 and a reduction in DNMT3a protein levels only in males. Importantly, sex differences in baseline and CORT-induced reelin protein levels were not associated with changes in the methylation status of the Reln promoter. These findings suggest that CORT-induced reelin decreases in the hypothalamus may be a combination of alterations in downstream processes beyond gene transcription. This research brings novel insights into the sexually distinct consequences of chronic stress, an essential aspect to understand, particularly concerning its role in the development of depression.

The Reelin receptor ApoER2 is a cargo for the adaptor protein complex AP-4: Implications for Hereditary Spastic Paraplegia

Adaptor protein complex 4 (AP-4) is a heterotetrameric complex that promotes export of selected cargo proteins from the trans-Golgi network. Mutations in each of the AP-4 subunits cause a complicated form of Hereditary Spastic Paraplegia (HSP). Herein, we report that ApoER2, a receptor in the Reelin signaling pathway, is a cargo of the AP-4 complex. We identify the motif ISSF/Y within the ApoER2 cytosolic domain as necessary for interaction with the canonical signal-binding pocket of the µ4 (AP4M1) subunit of AP-4. AP4E1- knock-out (KO) HeLa cells and hippocampal neurons from Ap4e1-KO mice display increased co-localization of ApoER2 with Golgi markers. Furthermore, hippocampal neurons from Ap4e1-KO mice and AP4M1-KO human iPSC-derived cortical i3Neurons exhibit reduced ApoER2 protein expression. Analyses of biosynthetic transport of ApoER2 reveal differential post-Golgi trafficking of the receptor, with lower axonal distribution in KO compared to wild-type neurons, indicating a role of AP-4 and the ISSF/Y motif in the axonal localization of ApoER2. Finally, analyses of Reelin signaling in mouse hippocampal and human cortical KO neurons show that AP4 deficiency causes no changes in Reelin-dependent activation of the AKT pathway and only mild changes in Reelin-induced dendritic arborization, but reduces Reelin-induced ERK phosphorylation, CREB activation, and Golgi deployment. This work thus establishes ApoER2 as a novel cargo of the AP-4 complex, suggesting that defects in the trafficking of this receptor and in the Reelin signaling pathway could contribute to the pathogenesis of HSP caused by mutations in AP-4 subunits.

Intersectin - many facets of a scaffold protein

Intersectin (ITSN) is a multi-domain scaffold protein with a diverse array of functions including regulation of endocytosis, vesicle transport, and activation of various signal transduction pathways. There are two ITSN genes located on chromosomes 21 and 2 encoding for proteins ITSN1 and ITSN2, respectively. Each ITSN gene encodes two major isoforms, ITSN-Long (ITSN-L) and ITSN-Short (ITSN-S), due to alternative splicing. ITSN1 and 2, collectively referred to as ITSN, are implicated in many physiological and pathological processes, such as neuronal maintenance, actin cytoskeletal rearrangement, and tumor progression. ITSN is mis-regulated in many tumors, such as breast, lung, neuroblastomas, and gliomas. Altered expression of ITSN is also found in several neurodegenerative diseases, such as Down Syndrome and Alzheimer's disease. This review summarizes recent studies on ITSN and provides an overview of the function of this important family of scaffold proteins in various biological processes.

The Inflammation-Induced Dysregulation of Reelin Homeostasis Hypothesis of Alzheimer's Disease

Alzheimer's disease (AD) accounts for most dementia cases, but we lack a complete understanding of the mechanisms responsible for the core pathology associated with the disease (e.g., amyloid plaque and neurofibrillary tangles). Inflammation has been identified as a key contributor of AD pathology, with recent evidence pointing towards Reelin dysregulation as being associated with inflammation. Here we describe Reelin signaling and outline existing research involving Reelin signaling in AD and inflammation. Research is described pertaining to the inflammatory and immunological functions of Reelin before we propose a mechanism through which inflammation renders Reelin susceptible to dysregulation resulting in the induction and exacerbation of AD pathology. Based on this hypothesis, it is predicted that disorders of both inflammation (including peripheral inflammation and neuroinflammation) and Reelin dysregulation (including disorders associated with upregulated Reelin expression and disorders of Reelin downregulation) have elevated risk of developing AD. We conclude with a description of AD risk in various disorders involving Reelin dysregulation and inflammation.

The Reelin Receptor ApoER2 is a Cargo for the Adaptor Protein Complex AP-4: Implications for Hereditary Spastic Paraplegia

Adaptor protein complex 4 (AP-4) is a heterotetrameric complex that promotes protein export from the trans -Golgi network. Mutations in each of the AP-4 subunits cause a complicated form of Hereditary Spastic Paraplegia (HSP). Herein, we report that ApoER2, a receptor in the Reelin signaling pathway, is a cargo of the AP-4 complex. We identify the motif ISSF/Y within the ApoER2 cytosolic domain as necessary for interaction with the canonical signal-binding pocket of the µ4 (AP4M1) subunit of AP-4. AP4E1 -knock-out (KO) HeLa cells and hippocampal neurons from Ap4e1 -KO mice display increased Golgi localization of ApoER2. Furthermore, hippocampal neurons from Ap4e1 -KO mice and AP4M1 -KO human iPSC-derived cortical i3Neurons exhibit reduced ApoER2 protein expression. Analyses of biosynthetic transport of ApoER2 reveal differential post-Golgi trafficking of the receptor, with lower axonal distribution in KO compared to wild-type neurons, indicating a role of AP-4 and the ISSF/Y motif in the axonal localization of ApoER2. Finally, analyses of Reelin signaling in mouse hippocampal and human cortical KO neurons show that AP4 deficiency causes no changes in Reelin-dependent activation of the AKT pathway and only mild changes in Reelin-induced dendritic arborization, but reduces Reelin-induced ERK phosphorylation, CREB activation, and Golgi deployment. Altogether, this work establishes ApoER2 as a novel cargo of the AP-4 complex, suggesting that defects in the trafficking of this receptor and in the Reelin signaling pathway could contribute to the pathogenesis of HSP caused by mutations in AP-4 subunits.

Activation of adenosine A1 receptor potentiates metabotropic glutamate receptor 1-mediated Ca2+ mobilization in the rat hippocampal marginal zone

Two subtypes of group I metabotropic glutamate receptors (mGluRs), mGluR1 and mGluR5, participate in the regulation of cell excitability and synaptic plasticity in the central nervous system. They couple to the Gq/11 protein and release Ca2+ from the intracellular stores. In the marginal zone of the neonatal hippocampus, Cajal-Retzius (CR) cells, which control radial migration of neurons, express the subtype mGluR1. The adenosine A1 receptor (A1R) is also G-protein coupled and is extensively expressed in the central nervous system. The interactions among G-protein-coupled receptors have been predicted previously, however, there is insufficient evidence of functional interactions between naturally occurring receptors. In this study, potentiation of the mGluR1-mediated response by A1R activation was demonstrated in hippocampal CR cells. Fluorescence imaging revealed that the application of A1R agonists intensified mGluR1-induced elevation of intracellular Ca2+ concentration ([Ca2+]i). Activation of A1R did not change [Ca2+]i. The potentiated responses were independent of extracellular Ca2+ and prevented by the Gi inhibitor. The potentiation of mGluR1-induced [Ca2+]i. elevation was also enhanced by mGluR2/3 activation. These results suggest that mGluR1 and A1R cooperatively influence postnatal hippocampal development by facilitating Ca2+ mobilization in CR cells.

Accelerating Alzheimer's therapeutic development: The past and future of clinical trials

Alzheimer's disease (AD) research has entered a new era with the recent positive phase 3 clinical trials of the anti-Aβ antibodies lecanemab and donanemab. Why did it take 30 years to achieve these successes? Developing potent therapies for reducing fibrillar amyloid was key, as was selection of patients at relatively early stages of disease. Biomarkers of the target pathologies, including amyloid and tau PET, and insights from past trials were also critical to the recent successes. Moving forward, the challenge will be to develop more efficacious therapies with greater efficiency. Novel trial designs, including combination therapies and umbrella and basket protocols, will accelerate clinical development. Better diversity and inclusivity of trial participants are needed, and blood-based biomarkers may help to improve access for medically underserved groups. Incentivizing innovation in both academia and industry through public-private partnerships, collaborative mechanisms, and the creation of new career paths will be critical to build momentum in these exciting times.

Regulation of the hippocampal translatome by Apoer2-ICD release

BACKGROUND

ApoE4, the most significant genetic risk factor for late-onset Alzheimer's disease (AD), sequesters a pro-synaptogenic Reelin receptor, Apoer2, in the endosomal compartment and prevents its normal recycling. In the adult brain, Reelin potentiates excitatory synapses and thereby protects against amyloid-β toxicity. Recently, a gain-of-function mutation in Reelin that is protective against early-onset AD has been described. Alternative splicing of the Apoer2 intracellular domain (Apoer2-ICD) regulates Apoer2 signaling. Splicing of juxtamembraneous exon 16 alters the γ-secretase mediated release of the Apoer2-ICD as well as synapse number and LTP, and inclusion of exon 19 ameliorates behavioral deficits in an AD mouse model. The Apoer2-ICD has also been shown to alter transcription of synaptic genes. However, the role of Apoer2-ICD release upon transcriptional regulation and its role in AD pathogenesis is unknown.

METHODS

To assess in vivo mRNA-primed ribosomes specifically in hippocampi transduced with Apoer2-ICD splice variants, we crossed wild-type, cKO, and Apoer2 cleavage-resistant mice to a Cre-inducible translating ribosome affinity purification (TRAP) model. This allowed us to perform RNA-Seq on ribosome-loaded mRNA harvested specifically from hippocampal cells transduced with Apoer2-ICDs.

RESULTS

Across all conditions, we observed ~4,700 altered translating transcripts, several of which comprise key synaptic components such as extracellular matrix and focal adhesions with concomitant perturbation of critical signaling cascades, energy metabolism, translation, and apoptosis. We further demonstrated the ability of the Apoer2-ICD to rescue many of these altered transcripts, underscoring the importance of Apoer2 splicing in synaptic homeostasis. A variety of these altered genes have been implicated in AD, demonstrating how dysregulated Apoer2 splicing may contribute to neurodegeneration.

CONCLUSIONS

Our findings demonstrate how alternative splicing of the APOE and Reelin receptor Apoer2 and release of the Apoer2-ICD regulates numerous translating transcripts in mouse hippocampi in vivo. These transcripts comprise a wide range of functions, and alterations in these transcripts suggest a mechanistic basis for the synaptic deficits seen in Apoer2 mutant mice and AD patients. Our findings, together with the recently reported AD-protective effects of a Reelin gain-of-function mutation in the presence of an early-onset AD mutation in Presenilin-1, implicate the Reelin/Apoer2 pathway as a target for AD therapeutics.

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.

Reelin Rescues Behavioral, Electrophysiological, and Molecular Metrics of a Chronic Stress Phenotype in a Similar Manner to Ketamine

Over the past decade, ketamine, an NMDA receptor antagonist, has demonstrated fast-acting antidepressant effects previously unseen with monoaminergic-based therapeutics. Concerns regarding psychotomimetic effects limit the use of ketamine for certain patient populations. Reelin, an extracellular matrix glycoprotein, has shown promise as a putative fast-acting antidepressant in a model of chronic stress. However, research has not yet demonstrated the changes that occur rapidly after peripheral reelin administration. To address this key gap in knowledge, male Long-Evans rats underwent a chronic corticosterone (CORT; or vehicle) paradigm (40 mg/kg, 21 d). On day 21, rats were then administered an acute dose of ketamine (10 mg/kg, i.p.), reelin (3 µg, i.v.), or vehicle. Twenty-four hours after administration, rats underwent behavioral or in vivo electrophysiological testing before killing. Immunohistochemistry was used to confirm changes in hippocampal reelin immunoreactivity. Lastly, the hippocampus was microdissected from fresh tissue to ascertain whole cell and synaptic-specific changes in protein expression through Western blotting. Chronic corticosterone induced a chronic stress phenotype in the forced swim test and sucrose preference test (SPT). Both reelin and ketamine rescued immobility and swimming, however reelin alone rescued latency to immobility. In vivo electrophysiology revealed decreases in hippocampal long-term potentiation (LTP) after chronic stress which was increased significantly by both ketamine and reelin. Reelin immunoreactivity in the dentate gyrus paralleled the behavioral and electrophysiological findings, but no significant changes were observed in synaptic-level protein expression. This exploratory research supports the putative rapid-acting antidepressant effects of an acute dose of reelin across behavioral, electrophysiological, and molecular measures.

Apoer2-ICD-dependent regulation of hippocampal ribosome mRNA loading

Background ApoE4, the most significant genetic risk factor for late-onset Alzheimer's disease (AD), sequesters a pro-synaptogenic Reelin receptor, Apoer2, in the endosomal compartment and prevents its normal recycling. In the adult brain, Reelin potentiates excitatory synapses and thereby protects against amyloid-β toxicity. Recently, a gain-of-function mutation in Reelin that is protective against early-onset AD has been described. Alternative splicing of the Apoer2 intracellular domain (Apoer2-ICD) regulates Apoer2 signaling. Splicing of juxtamembraneous exon 16 alters the g-secretase mediated release of the Apoer2-ICD as well as synapse number and LTP, and inclusion of exon 19 ameliorates behavioral deficits in an AD mouse model. The Apoer2-ICD has also been shown to alter transcription of synaptic genes. However, the role of Apoer2 splicing for transcriptional regulation and its role in AD pathogenesis is unknown. Methods To assess in vivo mRNA-primed ribosomes specifically in hippocampi transduced with Apoer2-ICD splice variants, we crossed wild-type, cKO, and Apoer2 cleavage-resistant mice to a Cre-inducible translating ribosome affinity purification (TRAP) model. This allowed us to perform RNA-Seq on ribosome-loaded mRNA harvested specifically from hippocampal cells transduced with Apoer2-ICDs. Results Across all conditions, we observed ~ 4,700 altered ribosome-associated transcripts, several of which comprise key synaptic components such as extracellular matrix and focal adhesions with concomitant perturbation of critical signaling cascades, energy metabolism, translation, and apoptosis. We further demonstrated the ability of the Apoer2-ICD to rescue many of these altered transcripts, underscoring the importance of Apoer2 splicing in synaptic homeostasis. A variety of these altered genes have been implicated in AD, demonstrating how dysregulated Apoer2 splicing may contribute to neurodegeneration. Conclusions Our findings demonstrate how alternative splicing of the APOE and Reelin receptor Apoer2 and release of the Apoer2-ICD regulates numerous ribosome-associated transcripts in mouse hippocampi in vivo . These transcripts comprise a wide range of functions, and alterations in these transcripts suggest a mechanistic basis for the synaptic deficits seen in Apoer2 mutant mice and AD patients. Our findings, together with the recently reported AD-protective effects of a Reelin gain-of-function mutation in the presence of an early-onset AD mutation in Presenilin-1, implicate the Reelin/Apoer2 pathway as a target for AD therapeutics.

Resilience to autosomal dominant Alzheimer's disease in a Reelin-COLBOS heterozygous man

We characterized the world's second case with ascertained extreme resilience to autosomal dominant Alzheimer's disease (ADAD). Side-by-side comparisons of this male case and the previously reported female case with ADAD homozygote for the APOE3 Christchurch (APOECh) variant allowed us to discern common features. The male remained cognitively intact until 67 years of age despite carrying a PSEN1-E280A mutation. Like the APOECh carrier, he had extremely elevated amyloid plaque burden and limited entorhinal Tau tangle burden. He did not carry the APOECh variant but was heterozygous for a rare variant in RELN (H3447R, termed COLBOS after the Colombia-Boston biomarker research study), a ligand that like apolipoprotein E binds to the VLDLr and APOEr2 receptors. RELN-COLBOS is a gain-of-function variant showing stronger ability to activate its canonical protein target Dab1 and reduce human Tau phosphorylation in a knockin mouse. A genetic variant in a case protected from ADAD suggests a role for RELN signaling in resilience to dementia.

Extracellular matrix and synapse formation

The extracellular matrix (ECM) is a complex molecular network distributed throughout the extracellular space of different tissues as well as the neuronal system. Previous studies have identified various ECM components that play important roles in neuronal maturation and signal transduction. ECM components are reported to be involved in neurogenesis, neuronal migration, and axonal growth by interacting or binding to specific receptors. In addition, the ECM is found to regulate synapse formation, the stability of the synaptic structure, and synaptic plasticity. Here, we mainly reviewed the effects of various ECM components on synapse formation and briefly described the related diseases caused by the abnormality of several ECM components.

Reelin Signaling Pathway and Mesial Temporal Lobe Epilepsy: A Causative Link

Introduction

Mesial temporal lobe epilepsy (MTLE) is the most frequent form of partial epilepsy. Granule cell dispersion, resulting from aberrant neuronal migration in the hippocampus, is pathognomonic of MTLE. Reelin, a secreted neurodevelopmental glycoprotein has a crucial role in controlling the radial migration of neurons. Several animal studies have implicated Reelin in the MTLE pathogenesis Mesial temporal lobe epilepsy (MTLE) is the most frequent form of partial epilepsy. Granule cell dispersion, resulting from aberrant neuronal migration in the hippocampus, is pathognomonic of MTLE. Reelin, a secreted neurodevelopmental glycoprotein has a crucial role in controlling the radial migration of neurons. Several animal studies have implicated Reelin in the MTLE pathogenesis.

Methods

The aim of this study was to investigate the Reelin signalling pathway in the MTLE patients. Therefore, we studied each step in the Reelin signalling pathway for the gene and protein expressions, in the hippocampal tissue obtained from patients undergoing surgery for MTLE and compared it with age matched normal autopsy cases.

Results

We found statistically significant decrease (P<0.001) in the Reelin mRNA expression in MTLE patients. Among the two reelin receptors, apolipoprotein E receptor 2 (ApoER2) was significantly increased whereas very low density lipoprotein receptor (VLDLR) was decreased among the patients. Disabled 1 (Dab1), the downstream target of reelin, was found to be decreased. Dab1 in turn inhibits Cofilin, which is responsible for cytoskeletal reorganization, thus limiting aberrant neuronal migration. Statistically significant over expression of Cofilin protein was found in the patient group. Matrix metalloproteinase 9 (MMP-9) and tissue inhibitor of metalloproteases-1 (TIMP-1), both of which are involved in processing of Reelin, were down regulated in 70-85% of cases.

Conclusion

The whole pathway was found to be deranged in MTLE. These results indicate that Reelin signalling pathway is disturbed at various points in the MTLE patients and might be involved in the pathogenesis & progression of MTLE. Our results extend the existing information regarding the components of the Reelin pathway and further, establish a link between pathway disturbance and MTLE.

Altered resting-state functional connectivity in hiPSCs-derived neuronal networks from schizophrenia patients

Schizophrenia (SZ) is a severe mental disorder that arises from abnormal neurodevelopment, caused by genetic and environmental factors. SZ often involves distortions in reality perception and it is widely associated with alterations in brain connectivity. In the present work, we used Human Induced Pluripotent Stem Cells (hiPSCs)-derived neuronal cultures to study neural communicational dynamics during early development in SZ. We conducted gene and protein expression profiling, calcium imaging recordings, and applied a mathematical model to quantify the dynamism of functional connectivity (FC) in hiPSCs-derived neuronal networks. Along the neurodifferentiation process, SZ networks displayed altered gene expression of the glutamate receptor-related proteins HOMER1 and GRIN1 compared to healthy control (HC) networks, suggesting a possible tendency to develop hyperexcitability. Resting-state FC in neuronal networks derived from HC and SZ patients emerged as a dynamic phenomenon exhibiting connectivity configurations reoccurring in time (hub states). Compared to HC, SZ networks were less thorough in exploring different FC configurations, changed configurations less often, presented a reduced repertoire of hub states and spent longer uninterrupted time intervals in this less diverse universe of hubs. Our results suggest that alterations in the communicational dynamics of SZ emerging neuronal networks might contribute to the previously described brain FC anomalies in SZ patients, by compromising the ability of their neuronal networks for rapid and efficient reorganization through different activity patterns.

Single-nucleus and spatial transcriptome profiling of pancreatic cancer identifies multicellular dynamics associated with neoadjuvant treatment

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal and treatment-refractory cancer. Molecular stratification in pancreatic cancer remains rudimentary and does not yet inform clinical management or therapeutic development. Here, we construct a high-resolution molecular landscape of the cellular subtypes and spatial communities that compose PDAC using single-nucleus RNA sequencing and whole-transcriptome digital spatial profiling (DSP) of 43 primary PDAC tumor specimens that either received neoadjuvant therapy or were treatment naive. We uncovered recurrent expression programs across malignant cells and fibroblasts, including a newly identified neural-like progenitor malignant cell program that was enriched after chemotherapy and radiotherapy and associated with poor prognosis in independent cohorts. Integrating spatial and cellular profiles revealed three multicellular communities with distinct contributions from malignant, fibroblast and immune subtypes: classical, squamoid-basaloid and treatment enriched. Our refined molecular and cellular taxonomy can provide a framework for stratification in clinical trials and serve as a roadmap for therapeutic targeting of specific cellular phenotypes and multicellular interactions.

Metabolic Syndrome and Vascular-Associated Cognitive Impairment: a Focus on Preclinical Investigations

PURPOSE OF REVIEW

Metabolic syndrome is associated with an increased risk of vascular cognitive impairment or, in the more extreme, vascular dementia. Animal models are used to investigate the relationship between pathology and behaviour. This review summarizes the latest understanding of the role of the hippocampus and prefrontal cortex in vascular cognitive impairment, the influence of inflammation in this association while also commenting on some of the latest interventions proposed.

RECENT FINDINGS

Models of vascular cognitive impairment and vascular dementia, whether they develop from an infarct or non-infarct base, demonstrate increased neuroinflammation, reduced neuronal function and deficits in prefrontal and hippocampal-associated cognitive domains. Promising new research shows agents and environmental interventions that inhibit central oxidative stress and inflammation can reverse both pathology and cognitive dysfunction. While preclinical studies suggest that reversal of deficits in vascular cognitive impairment models is possible, replication in patients still needs to be demonstrated.

Considering the Role of Extracellular Matrix Molecules, in Particular Reelin, in Granule Cell Dispersion Related to Temporal Lobe Epilepsy

The extracellular matrix (ECM) of the nervous system can be considered as a dynamically adaptable compartment between neuronal cells, in particular neurons and glial cells, that participates in physiological functions of the nervous system. It is mainly composed of carbohydrates and proteins that are secreted by the different kinds of cell types found in the nervous system, in particular neurons and glial cells, but also other cell types, such as pericytes of capillaries, ependymocytes and meningeal cells. ECM molecules participate in developmental processes, synaptic plasticity, neurodegeneration and regenerative processes. As an example, the ECM of the hippocampal formation is involved in degenerative and adaptive processes related to epilepsy. The role of various components of the ECM has been explored extensively. In particular, the ECM protein reelin, well known for orchestrating the formation of neuronal layer formation in the cerebral cortex, is also considered as a player involved in the occurrence of postnatal granule cell dispersion (GCD), a morphologically peculiar feature frequently observed in hippocampal tissue from epileptic patients. Possible causes and consequences of GCD have been studied in various in vivo and in vitro models. The present review discusses different interpretations of GCD and different views on the role of ECM protein reelin in the formation of this morphological peculiarity.

Prenatal exposure to valproic acid alters Reelin, NGF expressing neuron architecture and impairs social interaction in their autistic-like phenotype male offspring

Maternal exposure to anti-epileptic drug Valproic acid (VPA) during pregnancy increases the risk for the development of autism spectrum disorders (ASD). In this study, we have examined whether prenatal exposure to VPA will alter expression of key genes, synaptic morphology of nerve growth factor (NGF) and Reelin expressing neurons in the cortex of male offspring. To characterize in animal models, rat fetuses were exposed to VPA on 12.5 gestational day. The offspring of the VPA-exposed individuals (42%) resembles ASD-related phenotype (facial malformation, crooked-like tail, flattened paw, toenails and in-turning-ankles). Furthermore, we have observed deficit in social interaction accompanied by deregulation in expression of genes such as Caspase-3, focal adhesion kinase (FAK), Reelin, glial fibrillary acidic protein (GFAP), proliferating cell nuclear antigen (PCNA) and NGF. Subsequently, immunohistochemistry analysis revealed that exposure to VPA alters the cytoarchitecture (area, diameter) and reduced the dendritic arborization of Reelin, NGF expressing neurons in cortex. The compromised neurodevelopment by altered expression of Caspase-3, FAK, Reelin, GFAP, PCNA and NGF may cause defects in neuronal architecture, synaptic formation, synaptic plasticity and neuronal communication which could be linked with observed ASD-like phenotype and deficit social interaction.

Lipid Peroxidation Induced ApoE Receptor-Ligand Disruption as a Unifying Hypothesis Underlying Sporadic Alzheimer's Disease in Humans

BACKGROUND

Sporadic Alzheimer's disease (sAD) lacks a unifying hypothesis that can account for the lipid peroxidation observed early in the disease, enrichment of ApoE in the core of neuritic plaques, hallmark plaques and tangles, and selective vulnerability of entorhinal-hippocampal structures.

OBJECTIVE

We hypothesized that 1) high expression of ApoER2 (receptor for ApoE and Reelin) helps explain this anatomical vulnerability; 2) lipid peroxidation of ApoE and ApoER2 contributes to sAD pathogenesis, by disrupting neuronal ApoE delivery and Reelin-ApoER2-Dab1 signaling cascades.

METHODS

In vitro biochemical experiments; Single-marker and multiplex fluorescence-immunohistochemistry (IHC) in postmortem specimens from 26 individuals who died cognitively normal, with mild cognitive impairment or with sAD.

RESULTS

ApoE and ApoER2 peptides and proteins were susceptible to attack by reactive lipid aldehydes, generating lipid-protein adducts and crosslinked ApoE-ApoER2 complexes. Using in situ hybridization alongside IHC, we observed that: 1) ApoER2 is strongly expressed in terminal zones of the entorhinal-hippocampal 'perforant path' projections that underlie memory; 2) ApoE, lipid aldehyde-modified ApoE, Reelin, ApoER2, and the downstream Reelin-ApoER2 cascade components Dab1 and Thr19-phosphorylated PSD95 accumulated in the vicinity of neuritic plaques in perforant path terminal zones in sAD cases; 3) several ApoE/Reelin-ApoER2-Dab1 pathway markers were higher in sAD cases and positively correlated with histological progression and cognitive deficits.

CONCLUSION

Results demonstrate derangements in multiple ApoE/Reelin-ApoER2-Dab1 axis components in perforant path terminal zones in sAD and provide proof-of-concept that ApoE and ApoER2 are vulnerable to aldehyde-induced adduction and crosslinking. Findings provide the foundation for a unifying hypothesis implicating lipid peroxidation of ApoE and ApoE receptors in sAD.

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.

Genetics of otosclerosis: finally catching up with other complex traits?

Otosclerosis is a relatively common cause of hearing impairment, characterized by abnormal bone remodeling of the middle and inner ear. In about 50-60% of the patients, the disease is present in a familial form. In most of these families, otosclerosis seems to be caused by a small number of genetic factors (oligogenic) while only in a small number of families the disease seems to be truly monogenic. In the remaining patients a complex genetic form of otosclerosis is present. Several studies have aimed to identify the genetic factors underlying otosclerosis, which has led to the identification of eight published loci for monogenic otosclerosis, as well as several genes and one chromosomal region (11q13.1) with a clear association with otosclerosis. Implementation of next-generation sequencing (NGS) in otosclerosis research has led to the identification of pathogenic variants in MEPE, ACAN and SERPINF1, although the pathogenic role of the latter is under debate. In addition, a recent GWAS can be considered a breakthrough for otosclerosis as it identified several strong associations with otosclerosis and suggested new potential candidate genes. These recent findings are important for unraveling the genetic architecture of otosclerosis. More future studies will help to understand the complete pathogenesis of the disease.

Physiological Characterization and Transcriptomic Properties of GnRH Neurons Derived From Human Stem Cells

Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus play a key role in the regulation of reproductive function. In this study, we sought an efficient method for generating GnRH neurons from human embryonic and induced pluripotent stem cells (hESC and hiPSC, respectively). First, we found that exposure of primitive neuroepithelial cells, rather than neuroprogenitor cells, to fibroblast growth factor 8 (FGF8), was more effective in generating GnRH neurons. Second, addition of kisspeptin to FGF8 further increased the efficiency rates of GnRH neurogeneration. Third, we generated a fluorescent marker mCherry labeled human embryonic GnRH cell line (mCh-hESC) using a CRISPR-Cas9 targeting approach. Fourth, we examined physiological characteristics of GnRH (mCh-hESC) neurons: similar to GnRH neurons in vivo, they released the GnRH peptide in a pulsatile manner at ~60 min intervals; GnRH release increased in response to high potassium, kisspeptin, estradiol, and neurokinin B challenges; and injection of depolarizing current induced action potentials. Finally, we characterized developmental changes in transcriptomes of GnRH neurons using hESC, hiPSC, and mCh-hESC. The developmental pattern of transcriptomes was remarkably similar among the 3 cell lines. Collectively, human stem cell-derived GnRH neurons will be an important tool for establishing disease models to understand diseases, such as idiopathic hypothalamic hypogonadism, and testing contraceptive drugs.

Hepatic stellate cells: current state and open questions

This review article summarizes 20 years of our research on hepatic stellate cells within the framework of two collaborative research centers CRC575 and CRC974 at the Heinrich Heine University. Over this period, stellate cells were identified for the first time as mesenchymal stem cells of the liver, and important functions of these cells in the context of liver regeneration were discovered. Furthermore, it was determined that the space of Disse - bounded by the sinusoidal endothelium and hepatocytes - functions as a stem cell niche for stellate cells. Essential elements of this niche that control the maintenance of hepatic stellate cells have been identified alongside their impairment with age. This article aims to highlight previous studies on stellate cells and critically examine and identify open questions and future research directions.

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.

Structural studies of reelin N-terminal region provides insights into a unique structural arrangement and functional multimerization

The large, secreted glycoprotein reelin regulates embryonic brain development as well as adult brain functions. Although reelin binds to its receptors via its central part, the N-terminal region directs multimer formation and is critical for efficient signal transduction. In fact, the inhibitory antibody CR-50 interacts with the N-terminal region and prevents higher-order multimerization and signalling. Reelin is a multidomain protein in which the central part is composed of eight characteristic repeats, named reelin repeats, each of which is further divided by insertion of a epidermal growth factor (EGF) module into two subrepeats. In contrast, the N-terminal region shows unique 'irregular' domain architecture since it comprises three consecutive subrepeats without the intervening EGF module. Here, we determined the crystal structure of the murine reelin fragment named RX-R1 including the irregular region and the first reelin repeat at 2.0-Å resolution. The overall structure of RX-R1 has a branched Y-shaped form. Interestingly, two incomplete subrepeats cooperatively form one entire subrepeat structure, though an additional subrepeat is inserted between them. We further reveal that Arg335 of RX-R1 is crucial for binding CR-50. A possible self-association mechanism via the N-terminal region is proposed based on our results.

The structure-function relationship of a signaling-competent, dimeric Reelin fragment

Reelin operates through canonical and non-canonical pathways that mediate several aspects of brain development and function. Reelin's dimeric central fragment (CF), generated through proteolytic cleavage, is required for the lipoprotein-receptor-dependent canonical pathway activation. Here, we analyze the signaling properties of a variety of Reelin fragments and measure the differential binding affinities of monomeric and dimeric CF fragments to lipoprotein receptors to investigate the mode of canonical signal activation. We also present the cryoelectron tomography-solved dimeric structure of Reelin CF and support it using several other biophysical techniques. Our findings suggest that Reelin CF forms a covalent parallel dimer with some degree of flexibility between the two protein chains. As a result of this conformation, Reelin binds to lipoprotein receptors in a manner inaccessible to its monomeric form and is capable of stimulating canonical pathway signaling.

Increased Callosal Connectivity in Reeler Mice Revealed by Brain-Wide Input Mapping of VIP Neurons in Barrel Cortex

The neocortex is composed of layers. Whether layers constitute an essential framework for the formation of functional circuits is not well understood. We investigated the brain-wide input connectivity of vasoactive intestinal polypeptide (VIP) expressing neurons in the reeler mouse. This mutant is characterized by a migration deficit of cortical neurons so that no layers are formed. Still, neurons retain their properties and reeler mice show little cognitive impairment. We focused on VIP neurons because they are known to receive strong long-range inputs and have a typical laminar bias toward upper layers. In reeler, these neurons are more dispersed across the cortex. We mapped the brain-wide inputs of VIP neurons in barrel cortex of wild-type and reeler mice with rabies virus tracing. Innervation by subcortical inputs was not altered in reeler, in contrast to the cortical circuitry. Numbers of long-range ipsilateral cortical inputs were reduced in reeler, while contralateral inputs were strongly increased. Reeler mice had more callosal projection neurons. Hence, the corpus callosum was larger in reeler as shown by structural imaging. We argue that, in the absence of cortical layers, circuits with subcortical structures are maintained but cortical neurons establish a different network that largely preserves cognitive functions.

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.

Molecular mechanisms for targeted ASD treatments

The possibility to generate construct valid animal models enabled the development and testing of therapeutic strategies targeting the core features of autism spectrum disorders (ASDs). At the same time, these studies highlighted the necessity of identifying sensitive developmental time windows for successful therapeutic interventions. Animal and human studies also uncovered the possibility to stratify the variety of ASDs in molecularly distinct subgroups, potentially facilitating effective treatment design. Here, we focus on the molecular pathways emerging as commonly affected by mutations in diverse ASD-risk genes, on their role during critical windows of brain development and the potential treatments targeting these biological processes.

Reelin functions beyond neuronal migration: from synaptogenesis to network activity modulation

Reelin, a glycoprotein of the extracellular matrix, has been the focus of several studies over the years, mostly for its role in cell migration. Here we report the role of this molecule and of its downstream pathways in post-mitotic neurons and how they contribute to neural circuit assembly, refinement and function. Accumulating evidence has pointed at a major role for Reelin in axonal guidance, synaptogenesis and dendritic spine formation. In particular, new evidence points at a direct role in axonal targeting and refinement at the target site. In addition, recent advances highlight new functions of Reelin in the modulation of synaptic activity, plasticity and behavior and in the direct regulation of GABA receptors expression and stability. We discuss these findings in the context of neurodevelopmental disorders.

Rare single-nucleotide DAB1 variants and their contribution to Schizophrenia and autism spectrum disorder susceptibility

Disabled 1 (DAB1) is an intracellular adaptor protein in the Reelin signaling pathway and plays an essential role in correct neuronal migration and layer formation in the developing brain. DAB1 has been repeatedly reported to be associated with neurodevelopmental disorders including schizophrenia (SCZ) and autism spectrum disorders (ASD) in genetic, animal, and postmortem studies. Recently, increasing attention has been given to rare single-nucleotide variants (SNVs) found by deep sequencing of candidate genes. In this study, we performed exon-targeted resequencing of DAB1 in 370 SCZ and 192 ASD patients using next-generation sequencing technology to identify rare SNVs with a minor allele frequency <1%. We detected two rare missense mutations (G382C, V129I) and then performed a genetic association study in a sample comprising 1763 SCZ, 380 ASD, and 2190 healthy control subjects. Although no statistically significant association with the detected mutations was observed for either SCZ or ASD, G382C was found only in the case group, and in silico analyses and in vitro functional assays suggested that G382C alters the function of the DAB1 protein. The rare variants of DAB1 found in the present study should be studied further to elucidate their potential functional relevance to the pathophysiology of SCZ and ASD.