Low Density Lipoprotein-Receptor Related Protein 1 Is Differentially Expressed by Neuronal and Glial Populations in the Developing and Mature Mouse Central Nervous System

Human iPSC-derived neural stem cells displaying radial glia signature exhibit long-term safety in mice

Human induced pluripotent stem cell-derived neural stem/progenitor cells (hiPSC-NSCs) hold promise for treating neurodegenerative and demyelinating disorders. However, comprehensive studies on their identity and safety remain limited. In this study, we demonstrate that hiPSC-NSCs adopt a radial glia-associated signature, sharing key epigenetic and transcriptional characteristics with human fetal neural stem cells (hfNSCs) while exhibiting divergent profiles from glioblastoma stem cells. Long-term transplantation studies in mice showed robust and stable engraftment of hiPSC-NSCs, with predominant differentiation into glial cells and no evidence of tumor formation. Additionally, we identified the Sterol Regulatory Element Binding Transcription Factor 1 (SREBF1) as a regulator of astroglial differentiation in hiPSC-NSCs. These findings provide valuable transcriptional and epigenetic reference datasets to prospectively define the maturation stage of NSCs derived from different hiPSC sources and demonstrate the long-term safety of hiPSC-NSCs, reinforcing their potential as a viable alternative to hfNSCs for clinical applications.

Adipocyte metabolic state regulates glial phagocytic function

Obesity and type 2 diabetes are well-established risk factors for neurodegenerative disorders1-4, yet the underlying mechanisms remain poorly understood. The adipocyte-brain axis is crucial for brain function, as adipocytes secrete signaling molecules, including lipids and adipokines, that impinge on neural circuits to regulate feeding and energy expenditure5. Disruptions in the adipocyte-brain axis are associated with neurodegenerative conditions6, but the causal links are not fully understood. Neural debris accumulates with age and injury, and glial phagocytic function is crucial for clearing this debris and maintaining a healthy brain microenvironment7-9. Using adult Drosophila, we investigate how adipocyte metabolism influences glial phagocytic activity in the brain. We demonstrate that a prolonged obesogenic diet increases adipocyte fatty acid oxidation and ketogenesis. Genetic manipulations that mimic obesogenic diet-induced changes in adipocyte lipid and mitochondrial metabolism unexpectedly reduce the expression of the phagocytic receptor Draper in Drosophila microglia-like cells in the brain. We identify Apolpp-the Drosophila equivalent of human apolipoprotein B (ApoB)-as a critical adipocyte-derived signal that regulates glial phagocytosis. Additionally, we show that Lipoprotein Receptor 1 (LpR1), the LDL receptor on phagocytic glia, is required for glial capacity to clear injury-induced neuronal debris. Our findings establish that adipocyte-brain lipoprotein signaling regulates glial phagocytic function, revealing a novel pathway that links adipocyte metabolic disorders with neurodegeneration.

Somatostatin and the pathophysiology of Alzheimer's disease

Among the central features of Alzheimer's disease (AD) progression are altered levels of the neuropeptide somatostatin (SST), and the colocalisation of SST-positive interneurons (SST-INs) with amyloid-β plaques, leading to cell death. In this theoretical review, I propose a molecular model for the pathogenesis of AD based on SST-IN hypofunction and hyperactivity. Namely, hypofunctional and hyperactive SST-INs struggle to control hyperactivity in medial regions in early stages, leading to axonal Aβ production through excessive presynaptic GABAB inhibition, GABAB1a/APP complex downregulation and internalisation. Concomitantly, excessive SST-14 release accumulates near SST-INs in the form of amyloids, which bind to Aβ to form toxic mixed oligomers. This leads to differential SST-IN death through excitotoxicity, further disinhibition, SST deficits, and increased Aβ release, fibrillation and plaque formation. Aβ plaques, hyperactive networks and SST-IN distributions thereby tightly overlap in the brain. Conversely, chronic stimulation of postsynaptic SST2/4 on gulutamatergic neurons by hyperactive SST-INs promotes intense Mitogen-Activated Protein Kinase (MAPK) p38 activity, leading to somatodendritic p-tau staining and apoptosis/neurodegeneration - in agreement with a near complete overlap between p38 and neurofibrillary tangles. This model is suitable to explain some of the principal risk factors and markers of AD progression, including mitochondrial dysfunction, APOE4 genotype, sex-dependent vulnerability, overactive glial cells, dystrophic neurites, synaptic/spine losses, inter alia. Finally, the model can also shed light on qualitative aspects of AD neuropsychology, especially within the domains of spatial and declarative (episodic, semantic) memory, under an overlying pattern of contextual indiscrimination, ensemble instability, interference and generalisation.

Iron homeostasis and post-hemorrhagic hydrocephalus: a review

Iron physiology is regulated by a complex interplay of extracellular transport systems, coordinated transcriptional responses, and iron efflux mechanisms. Dysregulation of iron metabolism can result in defects in myelination, neurotransmitter synthesis, and neuronal maturation. In neonates, germinal matrix-intraventricular hemorrhage (GMH-IVH) causes iron overload as a result of blood breakdown in the ventricles and brain parenchyma which can lead to post-hemorrhagic hydrocephalus (PHH). However, the precise mechanisms by which GMH-IVH results in PHH remain elusive. Understanding the molecular determinants of iron homeostasis in the developing brain may lead to improved therapies. This manuscript reviews the various roles iron has in brain development, characterizes our understanding of iron transport in the developing brain, and describes potential mechanisms by which iron overload may cause PHH and brain injury. We also review novel preclinical treatments for IVH that specifically target iron. Understanding iron handling within the brain and central nervous system may provide a basis for preventative, targeted treatments for iron-mediated pathogenesis of GMH-IVH and PHH.

Amyloid precursor protein and its interacting proteins in neurodevelopment

Amyloid precursor protein (APP) is a key molecule in the pathogenesis of Alzheimer's disease (AD) as the pathogenic amyloid-β peptide is derived from it. Two closely related APP family proteins (APPs) have also been identified in mammals. Current knowledge, including genetic analyses of gain- and loss-of-function mutants, highlights the importance of APPs in various physiological functions. Notably, APPs consist of multiple extracellular and intracellular protein-binding regions/domains. Protein-protein interactions are crucial for many cellular processes. In past decades, many APPs interactors have been identified which assist the revelation of the putative roles of APPs. Importantly, some of these interactors have been shown to influence several APPs-mediated neuronal processes which are found defective in AD and other neurodegenerative disorders. Studying APPs-interactor complexes would not only advance our understanding of the physiological roles of APPs but also provide further insights into the association of these processes to neurodegeneration, which may lead to the development of novel therapies. In this mini-review, we summarize the roles of APPs-interactor complexes in neurodevelopmental processes including neurogenesis, neurite outgrowth, axonal guidance and synaptogenesis.

Low-density lipoprotein receptor-related protein-1 (LRP1) in the glial lineage modulates neuronal excitability

The low-density lipoprotein related protein receptor 1 (LRP1), also known as CD91 or α-Macroglobulin-receptor, is a transmembrane receptor that interacts with more than 40 known ligands. It plays an important biological role as receptor of morphogens, extracellular matrix molecules, cytokines, proteases, protease inhibitors and pathogens. In the CNS, it has primarily been studied as a receptor and clearance agent of pathogenic factors such as Aβ-peptide and, lately, Tau protein that is relevant for tissue homeostasis and protection against neurodegenerative processes. Recently, it was found that LRP1 expresses the Lewis-X (Lex) carbohydrate motif and is expressed in the neural stem cell compartment. The removal of Lrp1 from the cortical radial glia compartment generates a strong phenotype with severe motor deficits, seizures and a reduced life span. The present review discusses approaches that have been taken to address the neurodevelopmental significance of LRP1 by creating novel, lineage-specific constitutive or conditional knockout mouse lines. Deficits in the stem cell compartment may be at the root of severe CNS pathologies.

LRP1 Deficiency Promotes Mitostasis in Response to Oxidative Stress: Implications for Mitochondrial Targeting after Traumatic Brain Injury

The brain undergoes oxidative stress and mitochondrial dysfunction following physiological insults such as Traumatic brain injury (TBI), ischemia-reperfusion, and stroke. Pharmacotherapeutics targeting mitochondria (mitoceuticals) against oxidative stress include antioxidants, mild uncouplers, and enhancers of mitochondrial biogenesis, which have been shown to improve pathophysiological outcomes after TBI. However, to date, there is no effective treatment for TBI. Studies have suggested that the deletion of LDL receptor-related protein 1 (LRP1) in adult neurons or glial cells could be beneficial and promote neuronal health. In this study, we used WT and LRP1 knockout (LKO) mouse embryonic fibroblast cells to examine mitochondrial outcomes following exogenous oxidative stress. Furthermore, we developed a novel technique to measure mitochondrial morphometric dynamics using transgenic mitochondrial reporter mice mtD2g (mitochondrial-specific Dendra2 green) in a TBI model. We found that oxidative stress increased the quantity of fragmented and spherical-shaped mitochondria in the injury core of the ipsilateral cortex following TBI, whereas rod-like elongated mitochondria were seen in the corresponding contralateral cortex. Critically, LRP1 deficiency significantly decreased mitochondrial fragmentation, preserving mitochondrial function and cell growth following exogenous oxidative stress. Collectively, our results show that targeting LRP1 to improve mitochondrial function is a potential pharmacotherapeutic strategy against oxidative damage in TBI and other neurodegenerative diseases.

High affinity of β-amyloid proteins to cerebral capillaries: implications in chronic lead exposure-induced neurotoxicity in rats

Lead (Pb) is a known environmental risk factor in the etiology of Alzheimer's disease (AD). The existing reports suggest that Pb exposure increases beta-amyloid (Aβ) levels in brain tissues and cerebrospinal fluid (CSF) and facilitates the formation of amyloid plaques, which is a pathological hallmark for AD. Pb exposure has long been associated with cerebral vasculature injury. Yet it remained unclear if Pb exposure caused excessive Ab buildup in cerebral vasculature, which may damage the blood-brain barrier and cause abnormal Ab accumulation. This study was designed to investigate the impact of chronic Pb exposure on Aβ accumulation in cerebral capillary and the expression of low-density lipoprotein receptor protein-1 (LRP1), a critical Aβ transporter, in brain capillary and parenchyma. Sprague-Dawley rats received daily oral gavage at doses of 0, 14 (low-dose), and 27 (high-dose) mg Pb/kg as Pb acetate, 5 d/wk, for 4 or 8 wks. At the end of Pb exposure, a solution containing Aβ40 was infused into the brain via the cannulated internal carotid artery. Data by ELISA showed a strikingly high affinity of Ab to cerebral vasculature, which was approximately 7-14 times higher than that to the parenchymal fractions collected from control brains. Pb exposure further aggravated the Aβ accumulation in cerebral vasculature in a dose-dependent manner. Western blot analyses revealed that Pb exposure decreased LRP1 expression in cortical capillaries and hippocampal parenchyma. Immunohistochemistry (IHC) studies further revealed a disrupted distribution of LRP1 alongside hippocampal vasculature accompanied with a decreased expression in hippocampal neurons by Pb exposure. Taken together, the current study demonstrated that the cerebral vasculature naturally possessed a high affinity to Aβ present in circulating blood. Pb exposure significantly increased Aβ accumulation in cerebral vasculature; such an increased Aβ accumulation was due partly to the diminished expression of LRP1 in response to Pb in tested brain regions. Perceivably, Pb-facilitated Ab aggravation in cerebral vasculature may contribute to Pb-associated amyloid alterations.

Potential Molecular Mechanisms of Alzheimer's Disease from Genetic Studies

The devastating effects of Alzheimer's disease (AD) are yet to be ameliorated due to the absence of curative treatment options. AD is an aging-related disease that affects cognition, and molecular imbalance is one of its hallmarks. There is a need to identify common causes of molecular imbalance in AD and their potential mechanisms for continuing research. A narrative synthesis of molecular mechanisms in AD from primary studies that employed single-cell sequencing (scRNA-seq) or spatial genomics was conducted using Embase and PubMed databases. We found that differences in molecular mechanisms in AD could be grouped into four key categories: sex-specific features, early-onset features, aging, and immune system pathways. The reported causes of molecular imbalance were alterations in bile acid (BA) synthesis, PITRM1, TREM2, olfactory mucosa (OM) cells, cholesterol catabolism, NFkB, double-strand break (DSB) neuronal damage, P65KD silencing, tau and APOE expression. What changed from previous findings in contrast to results obtained were explored to find potential factors for AD-modifying investigations.

Lactoferrin as a Component of Pharmaceutical Preparations: An Experimental Focus

Lactoferrin is an 80 kDa monomeric glycoprotein that exhibits multitask activities. Lactoferrin properties are of interest in the pharmaceutical field for the design of products with therapeutic potential, including nanoparticles and liposomes, among many others. In antimicrobial preparations, lactoferrin has been included either as a main bioactive component or as an enhancer of the activity and potency of first-line antibiotics. In some proposals based on nanoparticles, lactoferrin has been included in delivery systems to transport and protect drugs from enzymatic degradation in the intestine, favoring the bioavailability for the treatment of inflammatory bowel disease and colon cancer. Moreover, nanoparticles loaded with lactoferrin have been formulated as delivery systems to transport drugs for neurodegenerative diseases, which cannot cross the blood-brain barrier to enter the central nervous system. This manuscript is focused on pharmaceutical products either containing lactoferrin as the bioactive component or formulated with lactoferrin as the carrier considering its interaction with receptors expressed in tissues as targets of drugs delivered via parenteral or mucosal administration. We hope that this manuscript provides insights about the therapeutic possibilities of pharmaceutical Lf preparations with a sustainable approach that contributes to decreasing the resistance of antimicrobials and enhancing the bioavailability of first-line drugs for intestinal chronic inflammation and neurodegenerative diseases.

Enhanced glaucomatous damage accompanied by glial response in a new multifactorial mouse model

Introduction

Glaucoma is a complex, multifactorial neurodegenerative disease, which can lead to blindness if left untreated. It seems that, among others, immune processes, elevated intraocular pressure (IOP), or a combination of these factors are responsible for glaucomatous damage. Here, we combined two glaucoma models to examine if a combination of risk factors (IOP and immune response) results in a more severe damage of retinal ganglion cells (RGCs) and the optic nerves as well as an additional glia activation.

Methods

Six-week-old wildtype (WT+ONA) and βB1-Connective Tissue Growth Factor (CTGF) mice (CTGF+ONA) were immunized with 1 mg ONA (optic nerve antigen). A WT and a CTGF control group (CTGF) received sodium chloride instead. IOP was measured before and every two weeks after immunization. After six weeks, electroretinogram (ERG) measurements were performed. Then, retinae and optic nerves were processed for (immuno-) histology. Further, mRNA levels of corresponding genes in optic nerve and retina were analyzed via RT-qPCR.

Results

Six weeks after immunization, the IOP in CTGF and CTGF+ONA mice was increased. The optic nerve of CTGF+ONA animals displayed the most severe cell inflammation, demyelination, and macroglia activation. Fewer numbers of oligodendrocytes were only observed in WT+ONA optic nerves, while more apoptotic cells triggered by the extrinsic pathway could be revealed in all three glaucoma groups. The number of microglia/macrophages was not altered within the optic nerves of all groups. The loss of neuronal cells, especially RGCs was most pronounced in CTGF+ONA retinae in the central part and this was accompanied by an enhanced activation of microglia/macrophages. Also, Müller cell activation could be noted in CTGF and CTGF+ONA retinae.

Discussion

In this new model, an additive degeneration could be noted in optic nerves as well as in the number of RGCs. These results suggest a potential additive role of high IOP and immune factors in glaucoma development, which will aid for understanding this multifactorial disease more precisely in the future.

PICALM and Alzheimer's Disease: An Update and Perspectives

Genome-wide association studies (GWAS) have identified the PICALM (Phosphatidylinositol binding clathrin-assembly protein) gene as the most significant genetic susceptibility locus after APOE and BIN1. PICALM is a clathrin-adaptor protein that plays a critical role in clathrin-mediated endocytosis and autophagy. Since the effects of genetic variants of PICALM as AD-susceptibility loci have been confirmed by independent genetic studies in several distinct cohorts, there has been a number of in vitro and in vivo studies attempting to elucidate the underlying mechanism by which PICALM modulates AD risk. While differential modulation of APP processing and Aβ transcytosis by PICALM has been reported, significant effects of PICALM modulation of tau pathology progression have also been evidenced in Alzheimer's disease models. In this review, we summarize the current knowledge about PICALM, its physiological functions, genetic variants, post-translational modifications and relevance to AD pathogenesis.

Intracerebroventricular dosing of N-sulfoglucosamine sulfohydrolase in mucopolysaccharidosis IIIA mice reduces markers of brain lysosomal dysfunction

Mucopolysaccharidosis type IIIA (MPS IIIA) is a lysosomal storage disorder caused by N-sulfoglucosamine sulfohydrolase (SGSH) deficiency. SGSH removes the sulfate from N-sulfoglucosamine residues on the nonreducing end of heparan sulfate (HS-NRE) within lysosomes. Enzyme deficiency results in accumulation of partially degraded HS within lysosomes throughout the body, leading to a progressive severe neurological disease. Enzyme replacement therapy has been proposed, but further evaluation of the treatment strategy is needed. Here, we used Chinese hamster ovary cells to produce a highly soluble and fully active recombinant human sulfamidase (rhSGSH). We discovered that rhSGSH utilizes both the CI-MPR and LRP1 receptors for uptake into patient fibroblasts. A single intracerebroventricular (ICV) injection of rhSGSH in MPS IIIA mice resulted in a tissue half-life of 9 days and widespread distribution throughout the brain. Following a single ICV dose, both total HS and the MPS IIIA disease-specific HS-NRE were dramatically reduced, reaching a nadir 2 weeks post dose. The durability of effect for reduction of both substrate and protein markers of lysosomal dysfunction and a neuroimmune response lasted through the 56 days tested. Furthermore, seven weekly 148 μg doses ICV reduced those markers to near normal and produced a 99.5% reduction in HS-NRE levels. A pilot study utilizing every other week dosing in two animals supports further evaluation of less frequent dosing. Finally, our dose-response study also suggests lower doses may be efficacious. Our findings show that rhSGSH can normalize lysosomal HS storage and markers of a neuroimmune response when delivered ICV.

APOE in the bullseye of neurodegenerative diseases: impact of the APOE genotype in Alzheimer's disease pathology and brain diseases

ApoE is the major lipid and cholesterol carrier in the CNS. There are three major human polymorphisms, apoE2, apoE3, and apoE4, and the genetic expression of APOE4 is one of the most influential risk factors for the development of late-onset Alzheimer's disease (AD). Neuroinflammation has become the third hallmark of AD, together with Amyloid-β plaques and neurofibrillary tangles of hyperphosphorylated aggregated tau protein. This review aims to broadly and extensively describe the differential aspects concerning apoE. Starting from the evolution of apoE to how APOE's single-nucleotide polymorphisms affect its structure, function, and involvement during health and disease. This review reflects on how APOE's polymorphisms impact critical aspects of AD pathology, such as the neuroinflammatory response, particularly the effect of APOE on astrocytic and microglial function and microglial dynamics, synaptic function, amyloid-β load, tau pathology, autophagy, and cell-cell communication. We discuss influential factors affecting AD pathology combined with the APOE genotype, such as sex, age, diet, physical exercise, current therapies and clinical trials in the AD field. The impact of the APOE genotype in other neurodegenerative diseases characterized by overt inflammation, e.g., alpha- synucleinopathies and Parkinson's disease, traumatic brain injury, stroke, amyotrophic lateral sclerosis, and multiple sclerosis, is also addressed. Therefore, this review gathers the most relevant findings related to the APOE genotype up to date and its implications on AD and CNS pathologies to provide a deeper understanding of the knowledge in the APOE field.

Assessment of endocytic traffic and Ocrl function in the developing zebrafish neuroepithelium

Endocytosis allows cells to internalise a wide range of molecules from their environment and to maintain their plasma membrane composition. It is vital during development and for maintenance of tissue homeostasis. The ability to visualise endocytosis in vivo requires suitable assays to monitor the process. Here, we describe imaging-based assays to visualise endocytosis in the neuroepithelium of living zebrafish embryos. Injection of fluorescent tracers into the brain ventricles followed by live imaging was used to study fluid-phase or receptor-mediated endocytosis, for which we used receptor-associated protein (RAP, encoded by Lrpap1) as a ligand for low-density lipoprotein receptor-related protein (LRP) receptors. Using dual-colour imaging combined with expression of endocytic markers, it is possible to track the progression of endocytosed tracers and to monitor trafficking dynamics. Using these assays, we reveal a role for the Lowe syndrome protein Ocrl in endocytic trafficking within the neuroepithelium. We also found that the RAP-binding receptor Lrp2 (encoded by lrp2a) appears to contribute only partially to neuroepithelial RAP endocytosis. Altogether, our results provide a basis to track endocytosis within the neuroepithelium in vivo and support a role for Ocrl in this process.

This article has an associated First Person interview with the first author of the paper.

Insights into the mechanisms of non-coding RNAs' implication in the pathogenesis of Alzheimer's disease

Non-coding RNAs including long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are implicated in the regulation of gene expression at transcriptional, posttranscriptional, and epigenetic levels. Several studies in cell lines, animal models, and humans, have revealed that non-coding RNAs play crucial roles in the pathogenesis of Alzheimer's disease (AD). Detailed knowledge on their mechanism of implication in the AD pathogenesis can help to develop novel therapeutic and disease management strategies. The two main pathological hallmarks of AD are amyloid plaques resulting from the β-amyloid accumulation, and neurofibrillary tangles (NFT) due to the phosphorylated tau accumulation. Several lncRNAs and miRNAs play crucial roles in both these hallmarks of the AD pathogenesis and other AD-related pathological procedures such as neuronal and synaptic plasticity, neuroinflammation, neuronal differentiation and neuronal apoptosis. In this review, we outlined the non-coding RNAs and further discussed how they are implicated in these AD-related pathological procedures.

Protocadherin 15 suppresses oligodendrocyte progenitor cell proliferation and promotes motility through distinct signalling pathways

Oligodendrocyte progenitor cells (OPCs) express protocadherin 15 (Pcdh15), a member of the cadherin superfamily of transmembrane proteins. Little is known about the function of Pcdh15 in the central nervous system (CNS), however, Pcdh15 expression can predict glioma aggression and promote the separation of embryonic human OPCs immediately following a cell division. Herein, we show that Pcdh15 knockdown significantly increases extracellular signal-related kinase (ERK) phosphorylation and activation to enhance OPC proliferation in vitro. Furthermore, Pcdh15 knockdown elevates Cdc42-Arp2/3 signalling and impairs actin kinetics, reducing the frequency of lamellipodial extrusion and slowing filopodial withdrawal. Pcdh15 knockdown also reduces the number of processes supported by each OPC and new process generation. Our data indicate that Pcdh15 is a critical regulator of OPC proliferation and process motility, behaviours that characterise the function of these cells in the healthy CNS, and provide mechanistic insight into the role that Pcdh15 might play in glioma progression.

Protocadherin 15 promotes lamellipodial and filopodial dynamics in oligodendrocyte progenitor cells by regulating Cdc42-Arp2/3 activity, but also suppresses ERK1/2 phosphorylation to reduce proliferation.

Spatiotemporal mapping of gene expression landscapes and developmental trajectories during zebrafish embryogenesis

A major challenge in understanding vertebrate embryogenesis is the lack of topographical transcriptomic information that can help correlate microenvironmental cues within the hierarchy of cell-fate decisions. Here, we employed Stereo-seq to profile 91 zebrafish embryo sections covering six critical time points during the first 24 h of development, obtaining a total of 152,977 spots at a resolution of 10 × 10 × 15 μm³ (close to cellular size) with spatial coordinates. Meanwhile, we identified spatial modules and co-varying genes for specific tissue organizations. By performing the integrated analysis of the Stereo-seq and scRNA-seq data from each time point, we reconstructed the spatially resolved developmental trajectories of cell-fate transitions and molecular changes during zebrafish embryogenesis. We further investigated the spatial distribution of ligand-receptor pairs and identified potentially important interactions during zebrafish embryo development. Our study constitutes a fundamental reference for further studies aiming to understand vertebrate development.

Oligodendrogenesis increases in hippocampal grey and white matter prior to locomotor or memory impairment in an adult mouse model of tauopathy

Myelin and axon losses are associated with cognitive decline in healthy ageing but are worse in people diagnosed with tauopathy. To determine whether tauopathy is also associated with enhanced myelin plasticity, we evaluated the behaviour of OPCs in mice that expressed a human pathological variant of microtubule-associated protein tau (MAPTP301S ). By 6 months of age (P180), MAPTP301S mice overexpressed hyperphosphorylated tau and had developed reactive gliosis in the hippocampus but had not developed overt locomotor or memory impairment. By performing cre-lox lineage tracing of adult OPCs, we determined that the number of newborn oligodendrocytes added to the hippocampus, entorhinal cortex and fimbria was equivalent in control and MAPTP301S mice prior to P150. However, between P150 and P180, significantly more new oligodendrocytes were added to these regions in the MAPTP301S mouse brain. This large increase in new oligodendrocyte number was not the result of increased OPC proliferation, nor did it alter oligodendrocyte density in the hippocampus, entorhinal cortex or fimbria, which was equivalent in P180 wild-type and MAPTP301S mice. Furthermore, the proportion of hippocampal and fimbria axons with myelin was unaffected by tauopathy. However, the proportion of myelinated axons that were ensheathed by immature myelin internodes was significantly increased in the hippocampus and fimbria of P180 MAPTP301S mice, when compared with their wild-type littermates. These data suggest that MAPTP301S transgenic mice experience significant oligodendrocyte turnover, with newborn oligodendrocytes compensating for myelin loss early in the development of tauopathy.

Phagocytic Glial Cells in Brain Homeostasis

Phagocytosis by glial cells has been shown to play an important role in maintaining brain homeostasis. Microglia are currently considered to be the major phagocytes in the brain parenchyma, and these cells phagocytose a variety of materials, including dead cell debris, abnormally aggregated proteins, and, interestingly, the functional synapses of living neurons. The intracellular signaling mechanisms that regulate microglial phagocytosis have been studied extensively, and several important factors, including molecules known as "find me" signals and "eat me" signals and receptors on microglia that are involved in phagocytosis, have been identified. In addition, recent studies have revealed that astrocytes, which are another major glial cell in the brain parenchyma, also have phagocytic abilities. In this review, we will discuss the roles of microglia and astrocytes in phagocytosis-mediated brain homeostasis, focusing on the characteristics and differences of their phagocytic abilities.

Surface Functionalization of PLGA Nanoparticles to Increase Transport across the BBB for Alzheimer’s Disease

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder that accounts for about 60% of all diagnosed cases of dementia worldwide. Although there are currently several drugs marketed for its treatment, none are capable of slowing down or stopping the progression of AD. The role of the blood-brain barrier (BBB) plays a key role in the design of a successful treatment for this neurodegenerative disease. Nanosized particles have been proposed as suitable drug delivery systems to overcome BBB with the purpose of increasing bioavailability of drugs in the brain. Biodegradable poly (lactic-co-glycolic acid) nanoparticles (PLGA-NPs) have been particularly regarded as promising drug delivery systems as they can be surface-tailored with functionalized molecules for site-specific targeting. In this review, a thorough discussion about the most recent functionalization strategies based on PLGA-NPs for AD and their mechanisms of action is provided, together with a description of AD pathogenesis and the role of the BBB in brain targeting.

From the low-density lipoprotein receptor-related protein 1 to neuropathic pain: a potentially novel target

The low-density lipoprotein receptor–related protein 1 plays a major role in the regulation of neuroinflammation, neurodegeneration, neuroregeneration, neuropathic pain, and deficient cognitive functions.

This review describes the roles of the low-density lipoprotein receptor–related protein 1 (LRP-1) in inflammatory pathways, nerve nerve degeneration and -regeneration and in neuropathic pain. Induction of LRP-1 is able to reduce the activation of the proinflammatory NFκB-mediated pathway and the mitogen-activated protein kinase (MAPK) c-Jun N-terminal kinase and p38 signaling pathways, in turn decreasing the production of inflammatory mediators. Low-density lipoprotein receptor-related protein 1 activation also decreases reactive astrogliosis and polarizes microglial cells and macrophages from a proinflammatory phenotype (M1) to an anti-inflammatory phenotype (M2), attenuating the neuroinflammatory environment. Low-density lipoprotein receptor-related protein 1 can also modulate the permeability of the blood–brain barrier and the blood–nerve barrier, thus regulating the infiltration of systemic insults and cells into the central and the peripheral nervous system, respectively. Furthermore, LRP-1 is involved in the maturation of oligodendrocytes and in the activation, migration, and repair phenotype of Schwann cells, therefore suggesting a major role in restoring the myelin sheaths upon injury. Low-density lipoprotein receptor-related protein 1 activation can indirectly decrease neurodegeneration and neuropathic pain by attenuation of the inflammatory environment. Moreover, LRP-1 agonists can directly promote neural cell survival and neurite sprouting, decrease cell death, and attenuate pain and neurological disorders by the inhibition of MAPK c-Jun N-terminal kinase and p38-pathway and activation of MAPK extracellular signal–regulated kinase pathway. In addition, activation of LRP-1 resulted in better outcomes for neuropathies such as Alzheimer disease, nerve injury, or diabetic peripheral neuropathy, attenuating neuropathic pain and improving cognitive functions. To summarize, LRP-1 plays an important role in the development of different experimental diseases of the nervous system, and it is emerging as a very interesting therapeutic target.

Brain penetrating peptides and peptide-drug conjugates to overcome the blood-brain barrier and target CNS diseases

Nearly one in six people worldwide suffer from disorders of the central nervous system (CNS). There is an urgent need for effective strategies to improve the success rates in CNS drug discovery and development. The lack of effective technologies for delivering drugs and genes to the brain due to the blood-brain barrier (BBB), a structural barrier that effectively blocks most neurotherapeutic agents from reaching the brain, has posed a formidable hurdle for CNS drug development. Brain-homing and brain-penetrating molecular transport vectors, such as brain permeable peptides or BBB shuttle peptides, have shown promise in overcoming the BBB and ferrying the drug molecules to the brain. The BBB shuttle peptides are discovered by phage display technology or derived from natural neurotropic proteins or certain viruses and harness the receptor-mediated transcytosis molecular machinery for crossing the BBB. Brain permeable peptide-drug conjugates (PDCs), composed of BBB shuttle peptides, linkers, and drug molecules, have emerged as a promising CNS drug delivery system by taking advantage of the endogenous transcytosis mechanism and tricking the brain into allowing these bioactive molecules to pass the BBB. Here, we examine the latest development of brain-penetrating peptide shuttles and brain-permeable PDCs as molecular vectors to deliver small molecule drug payloads across the BBB to reach brain parenchyma. Emerging knowledge of the contribution of the peptides and their specific receptors expressed on the brain endothelial cells, choice of drug payloads, the design of PDCs, brain entry mechanisms, and delivery efficiency to the brain are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

Deletion of LRP1 From Astrocytes Modifies Neuronal Network Activity in an in vitro Model of the Tripartite Synapse

The low-density lipoprotein receptor-related protein 1 (LRP1) is a transmembrane receptor that binds over 40 potential ligands and is involved in processes such as cell differentiation, proliferation, and survival. LRP1 is ubiquitously expressed in the organism and enriched among others in blood vessels, liver, and the central nervous system (CNS). There, it is strongly expressed by neurons, microglia, immature oligodendrocytes, and astrocytes. The constitutive LRP1 knockout leads to embryonic lethality. Therefore, previous studies focused on conditional LRP1-knockout strategies and revealed that the deletion of LRP1 causes an increased differentiation of neural stem and precursor cells into astrocytes. Furthermore, astrocytic LRP1 is necessary for the degradation of Aβ and the reduced accumulation of amyloid plaques in Alzheimer’s disease. Although the role of LRP1 in neurons has intensely been investigated, the function of LRP1 with regard to the differentiation and maturation of astrocytes and their functionality is still unknown. To address this question, we generated an inducible conditional transgenic mouse model, where LRP1 is specifically deleted from GLAST-positive astrocyte precursor cells. The recombination with resulting knockout events was visualized by the simultaneous expression of the fluorescent reporter tdTomato. We observed a significantly increased number of GLT-1 expressing astrocytes in LRP1-depleted astrocytic cultures in comparison to control astrocytes. Furthermore, we investigated the influence of astrocytic LRP1 on neuronal activity and synaptogenesis using the co-culture of hippocampal neurons with control or LRP1-depleted astrocytes. These analyses revealed that the LRP1-deficient astrocytes caused a decreased number of single action potentials as well as a negatively influenced neuronal network activity. Moreover, the proportion of pre- and postsynaptic structures was significantly altered in neurons co-cultured with LPR1-depleted astrocytes. However, the number of structural synapses was not affected. Additionally, the supernatant of hippocampal neurons co-cultured with LRP1-deficient astrocytes showed an altered set of cytokines in comparison to the control condition, which potentially contributed to the altered neuronal transmission and synaptogenesis. Our results suggest astrocytic LRP1 as a modulator of synaptic transmission and synaptogenesis by altering the expression of the glutamate transporter on the cell surface on astrocytes and the release of cytokines in vitro.

Brain cell type-specific endocytosis of arylsulfatase A identifies limitations of enzyme-based therapies for metachromatic leukodystrophy

Enzyme replacement therapies, allogeneic bone marrow transplantation and gene therapies are treatment options for lysosomal storage diseases caused by inherited deficiencies of soluble lysosomal enzymes. Independent from the approach, the enzyme must be delivered to lysosomes of deficient patient cells. Little is known about the dissemination of enzyme within a tissue where cells compete for uptake via different receptor systems, binding affinities and endocytic rates. To evaluate dissemination and lysosomal targeting of a lysosomal enzyme in the CNS, we analysed receptor-mediated endocytosis of arylsulfatase A (ASA) by different types of brain-derived cell lines and primary murine brain cells. For ASA expressed by chinese hamster ovary cells for enzyme replacement therapy of metachromatic leukodystrophy, endocytic rates decline from microglia to neurons and astrocytes and to oligodendrocytes. Only immature oligodendrocytes endocytose significant amounts of enzyme. Uptake by non-microglial cells is due to mannose 6-phosphate receptors, whereas several receptor systems participate in endocytosis by microglial cells. Interestingly, ASA expressed by microglial cells cannot be taken up in a mannose 6-phosphate dependent manner. The resulting failure to correct non-microglial cells corroborates in vivo data and indicates that therapeutic effects of allogeneic bone marrow transplantation and hematopoietic stem cell gene therapy on metachromatic leukodystrophy are independent of metabolic cross-correction of neurons, astrocytes and oligodendrocytes by receptor-mediated endocytosis.

Kif3a deletion prevents primary cilia assembly on oligodendrocyte progenitor cells, reduces oligodendrogenesis and impairs fine motor function

Primary cilia are small microtubule‐based organelles capable of transducing signals from growth factor receptors embedded in the cilia membrane. Developmentally, oligodendrocyte progenitor cells (OPCs) express genes associated with primary cilia assembly, disassembly, and signaling, however, the importance of primary cilia for adult myelination has not been explored. We show that OPCs are ciliated in vitro and in vivo, and that they disassemble their primary cilia as they progress through the cell cycle. OPC primary cilia are also disassembled as OPCs differentiate into oligodendrocytes. When kinesin family member 3a (Kif3a), a gene critical for primary cilium assembly, was conditionally deleted from adult OPCs in vivo (Pdgfrα‐CreER™:: Kif3a^fl/fl transgenic mice), OPCs failed to assemble primary cilia. Kif3a‐deletion was also associated with reduced OPC proliferation and oligodendrogenesis in the corpus callosum and motor cortex and a progressive impairment of fine motor coordination.

Low-Density Lipoprotein Receptor-Related Protein 1 (LRP1) Is a Negative Regulator of Oligodendrocyte Progenitor Cell Differentiation in the Adult Mouse Brain

Low-density lipoprotein receptor-related protein 1 (LRP1) is a large, endocytic cell surface receptor that is highly expressed by oligodendrocyte progenitor cells (OPCs) and LRP1 expression is rapidly downregulated as OPCs differentiate into oligodendrocytes (OLs). We report that the conditional deletion of Lrp1 from adult mouse OPCs (Pdgfrα-CreER :: Lrp1^fl/fl) increases the number of newborn, mature myelinating OLs added to the corpus callosum and motor cortex. As these additional OLs extend a normal number of internodes that are of a normal length, Lrp1-deletion increases adult myelination. OPC proliferation is also elevated following Lrp1 deletion in vivo, however, this may be a secondary, homeostatic response to increased OPC differentiation, as our in vitro experiments show that LRP1 is a direct negative regulator of OPC differentiation, not proliferation. Deleting Lrp1 from adult OPCs also increases the number of newborn mature OLs added to the corpus callosum in response to cuprizone-induced demyelination. These data suggest that the selective blockade of LRP1 function on adult OPCs may enhance myelin repair in demyelinating diseases such as multiple sclerosis.

Knockin' on heaven's door: Molecular mechanisms of neuronal tau uptake

Since aggregates of the microtubule‐binding protein tau were found to be the main component of neurofibrillary tangles more than 30 years ago, their contribution to neurodegeneration in Alzheimer's disease (AD) and tauopathies has become well established. Recent work shows that both tau load and its distribution in the brain of AD patients correlate with cognitive decline more closely compared to amyloid plaque deposition. In addition, the amyloid cascade hypothesis has been recently challenged because of disappointing results of clinical trials designed to treat AD by reducing beta‐amyloid levels, thus fuelling a renewed interest in tau. There is now robust evidence to indicate that tau pathology can spread within the central nervous system via a prion‐like mechanism following a stereotypical pattern, which can be explained by the trans‐synaptic inter‐neuronal transfer of pathological tau. In the receiving neuron, tau has been shown to take multiple routes of internalisation, which are partially dependent on its conformation and aggregation status. Here, we review the emerging mechanisms proposed for the uptake of extracellular tau in neurons and the requirements for the propagation of its pathological conformers, addressing how they gain access to physiological tau monomers in the cytosol. Furthermore, we highlight some of the key mechanistic gaps of the field, which urgently need to be addressed to expand our understanding of tau propagation and lead to the identification of new therapeutic strategies for tauopathies.

In vitro Validation of Chimeric β-Galactosylceramidase Enzymes With Improved Enzymatic Activity and Increased Secretion

Globoid Cell Leukodystrophy (GLD) is a lysosomal storage disease (LSD) caused by inherited defects of the β-galactosylceramidase (GALC) gene. The infantile forms display a rapid and aggressive central and peripheral nervous system (CNS and PNS) dysfunction. No treatments are available for GLD patients. Effective gene therapy (GT) strategies for GLD require a safe and widespread delivery of the functional GALC enzyme to all affected tissues/organs, and particularly to the CNS. The use of chimeric lysosomal enzymes with increased secretion and enhanced transport across the blood-brain barrier (BBB) that boost the efficacy of GT approaches in pre-clinical models of similar neurodegenerative LSDs may benefit GLD as well. Here, we tested the safety and biological efficacy of chimeric GALC enzymes engineered to express an alternative signal peptide (iduronate-2-sulfatase - IDSsp) and the low-density lipoprotein receptor (LDLr)-binding domain from the Apolipoprotein E II (ApoE II) in GLD murine neural and hematopoietic stem/progenitor cells and progeny, which are relevant cells types in the context of in vivo and ex vivo GT platforms. We show that the lentiviral vector-mediated expression of the chimeric GALC enzymes is safe and leads to supranormal enzymatic activity in both neural and hematopoietic cells. The IDSsp.GALC shows enhanced expression and secretion in comparison to the unmodified GALC. The chimeric GALC enzymes produced by LV-transduced cells reduce intracellular galactosylceramide (GalCer) storage and effectively cross-correct GLD murine neurons and glial cells, indicating that the transgenic enzymes are delivered to lysosomes, efficiently secreted, and functional. Of note, the expression of LDLr and LDLr-related proteins in GLD neurons and glial cells supports the exploitation of this system to enhance the GALC supply in affected CNS cells and tissues. These in vitro studies support the use of chimeric GALC enzymes to develop novel and more effective GT approaches for GLD.

Lipoprotein receptor loss in forebrain radial glia results in neurological deficits and severe seizures

The Alzheimer disease-associated multifunctional low-density lipoprotein receptor-related protein-1 is expressed in the brain. Recent studies uncovered a role of this receptor for the appropriate functioning of neural stem cells, oligodendrocytes, and neurons. The constitutive knock-out (KO) of the receptor is embryonically lethal. To unravel the receptors' role in the developing brain we generated a mouse mutant by specifically targeting radial glia stem cells of the dorsal telencephalon. The low-density lipoprotein receptor-related protein-1 lineage-restricted KO female and male mice, in contrast to available models, developed a severe neurological phenotype with generalized seizures during early postnatal development. The mechanism leading to a buildup of hyperexcitability and emergence of seizures was traced to a failure in adequate astrocyte development and deteriorated postsynaptic density integrity. The detected impairments in the astrocytic lineage: precocious maturation, reactive gliosis, abolished tissue plasminogen activator uptake, and loss of functionality emphasize the importance of this glial cell type for synaptic signaling in the developing brain. Together, the obtained results highlight the relevance of astrocytic low-density lipoprotein receptor-related protein-1 for glutamatergic signaling in the context of neuron-glia interactions and stage this receptor as a contributing factor for epilepsy.

Amyloidosis is associated with thicker myelin and increased oligodendrogenesis in the adult mouse brain

In Alzheimer's disease, amyloid plaque formation is associated with the focal death of oligodendrocytes and soluble amyloid β impairs the survival of oligodendrocytes in vitro. However, the response of oligodendrocyte progenitor cells (OPCs) to early amyloid pathology remains unclear. To explore this, we performed a histological, electrophysiological, and behavioral characterization of transgenic mice expressing a pathological form of human amyloid precursor protein (APP), containing three single point mutations associated with the development of familial Alzheimer's disease (PDGFB‐APP^Sw.Ind, also known as J20 mice). PDGFB‐APP^Sw.Ind transgenic mice had impaired survival from weaning, were hyperactive by 2 months of age, and developed amyloid plaques by 6 months of age, however, their spatial memory remained intact over this time course. Hippocampal OPC density was normal in P60‐P180 PDGFB‐APP^Sw.Ind transgenic mice and, by performing whole‐cell patch‐clamp electrophysiology, we found that their membrane properties, including their response to kainate (100 µM), were largely normal. However, by P100, the response of hippocampal OPCs to GABA was elevated in PDGFB‐APP^Sw.Ind transgenic mice. We also found that the nodes of Ranvier were shorter, the paranodes longer, and the myelin thicker for hippocampal axons in young adult PDGFB‐APP^Sw.Ind transgenic mice compared with wildtype littermates. Additionally, oligodendrogenesis was normal in young adulthood, but increased in the hippocampus, entorhinal cortex, and fimbria of PDGFB‐APP^Sw.Ind transgenic mice as pathology developed. As the new oligodendrocytes were not associated with a change in total oligodendrocyte number, these cells are likely required for cell replacement.

LRP1 is a master regulator of tau uptake and spread

The spread of protein aggregates during disease progression is a common theme underlying many neurodegenerative diseases. The microtubule-associated protein tau (MAPT) plays a central role in the pathogenesis of several forms of dementia known as tauopathies, including Alzheimer’s disease (AD), frontotemporal dementia (FTD) and chronic traumatic encephalopathy (CTE)¹. Progression of these diseases is characterized by the sequential spread and deposition of protein aggregates in a predictable pattern that correlates with clinical severity². This observation and complementary experimental studies^3,4 have suggested that tau can spread in a prion-like manner by passing to naïve cells where it templates misfolding and aggregation. However, while tau propagation has been extensively studied, the underlying cellular mechanisms remain poorly understood. Here we show that the low-density lipoprotein (LDL) receptor-related protein 1 (LRP1) controls tau endocytosis and subsequent spread. Knockdown of LRP1 significantly reduced tau uptake in H4 neuroglioma cells and iPS-derived neurons. The interaction between tau and LRP1 is mediated by lysine residues in the microtubule binding repeat region of tau. Furthermore, we find that downregulation of LRP1 in an in vivo mouse model of tau spread effectively reduced tau propagation between neurons. Our results identify LRP1 as a key regulator of tau spread in the brain and, thus, as a novel target for diseases of tau spread and aggregation.

The active contribution of OPCs to neuroinflammation is mediated by LRP1

Oligodendrocyte progenitor cells (OPCs) account for about 5% of total brain and spinal cord cells, giving rise to myelinating oligodendrocytes that provide electrical insulation to neurons of the CNS. OPCs have also recently been shown to regulate inflammatory responses and glial scar formation, suggesting functions that extend beyond myelination. Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifaceted phagocytic receptor that is highly expressed in several CNS cell types, including OPCs. Here, we have generated an oligodendroglia-specific knockout of LRP1, which presents with normal myelin development, but is associated with better outcomes in two animal models of demyelination (EAE and cuprizone). At a mechanistic level, LRP1 did not directly affect OPC differentiation into mature oligodendrocytes. Instead, animals lacking LRP1 in OPCs in the demyelinating CNS were characterized by a robust dampening of inflammation. In particular, LRP1-deficient OPCs presented with impaired antigen cross-presentation machinery, suggesting a failure to propagate the inflammatory response and thus promoting faster myelin repair and neuroprotection. Our study places OPCs as major regulators of neuroinflammation in an LRP1-dependent fashion.

PLGA-PEG-ANG-2 Nanoparticles for Blood-Brain Barrier Crossing: Proof-of-Concept Study

The treatment of diseases that affect the central nervous system (CNS) represents a great research challenge due to the restriction imposed by the blood-brain barrier (BBB) to allow the passage of drugs into the brain. However, the use of modified nanomedicines engineered with different ligands that can be recognized by receptors expressed in the BBB offers a favorable alternative for this purpose. In this work, a BBB-penetrating peptide, angiopep-2 (Ang-2), was conjugated to poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles through pre- and post-formulation strategies. Then, their ability to cross the BBB was qualitatively assessed on an animal model. Proof-of-concept studies with fluorescent and confocal microscopy studies highlighted that the brain-targeted PLGA nanoparticles were able to cross the BBB and accumulated in neuronal cells, thus showing a promising brain drug delivery system.

Conditional Deletion of LRP1 Leads to Progressive Loss of Recombined NG2-Expressing Oligodendrocyte Precursor Cells in a Novel Mouse Model

The low-density lipoprotein receptor-related protein 1 (LRP1) is a transmembrane receptor, mediating endocytosis and activating intracellular signaling cascades. LRP1 is highly expressed in the central nervous system (CNS), especially in oligodendrocyte precursor cells (OPCs). Previous studies have suggested LRP1 as a regulator in early oligodendrocyte development, repair of chemically induced white matter lesions, and cholesterol homeostasis. To circumvent embryonic lethality observed in the case of global LRP1 deletion, we generated a new inducible conditional knockout (KO) mouse model, which enabled an NG2-restricted LRP1 deficiency (NG2-CreERT2^ct2/wtxR26eGFP^flox/floxxLRP1^flox/flox). When characterizing our triple transgenic mouse model, we noticed a substantial and progressive loss of recombined LRP1-deficient cells in the oligodendrocyte lineage. On the other hand, we found comparable distributions and fractions of oligodendroglia within the Corpus callosum of the KO and control animals, indicating a compensation of these deficits. An initial study on experimental autoimmune encephalomyelitis (EAE) was performed in triple transgenic and control mice and the cell biology of oligodendrocytes obtained from the animals was studied in an in vitro myelination assay. Differences could be observed in these assays, which, however, did not achieve statistical significance, presumably because the majority of recombined LRP1-deficient cells has been replaced by non-recombined cells. Thus, the analysis of the role of LRP1 in EAE will require the induction of acute recombination in the context of the disease process. As LRP1 is necessary for the survival of OPCs in vivo, we assume that it will play an important role in myelin repair.

Truncating variant burden in high-functioning autism and pleiotropic effects of LRP1 across psychiatric phenotypes

BACKGROUND

Previous research has implicated de novo and inherited truncating mutations in autism-spectrum disorder. We aim to investigate whether the load of inherited truncating mutations contributes similarly to high-functioning autism, and to characterize genes that harbour de novo variants in high-functioning autism.

METHODS

We performed whole-exome sequencing in 20 high-functioning autism families (average IQ = 100).

RESULTS

We observed no difference in the number of transmitted versus nontransmitted truncating alleles for high-functioning autism (117 v. 130, p = 0.78). Transmitted truncating and de novo variants in high-functioning autism were not enriched in gene ontology (GO) or Kyoto Encyclopedia of Genes and Genomes (KEGG) categories, or in autism-related gene sets. However, in a patient with high-functioning autism we identified a de novo variant in a canonical splice site of LRP1, a postsynaptic density gene that is a target for fragile X mental retardation protein (FRMP). This de novo variant leads to in-frame skipping of exon 29, removing 2 of 6 blades of the β-propeller domain 4 of LRP1, with putative functional consequences. Large data sets implicate LRP1 across a number of psychiatric disorders: de novo variants are associated with autism-spectrum disorder (p = 0.039) and schizophrenia (p = 0.008) from combined sequencing projects; common variants using genome-wide association study data sets from the Psychiatric Genomics Consortium show gene-based association in schizophrenia (p = 6.6 × E−07) and in a meta-analysis across 7 psychiatric disorders (p = 2.3 × E−03); and the burden of ultra-rare pathogenic variants has been shown to be higher in autism-spectrum disorder (p = 1.2 × E−05), using whole-exome sequencing from 6135 patients with schizophrenia, 1778 patients with autism-spectrum disorder and 7875 controls.

LIMITATIONS

We had a limited sample of patients with high-functioning autism, related to difficulty in recruiting probands with high cognitive performance and no family history of psychiatric disorders.

CONCLUSION

Previous studies and ours suggest an effect of truncating mutations restricted to severe autism-spectrum disorder phenotypes that are associated with intellectual disability. We provide evidence for pleiotropic effects of common and rare variants in the LRP1 gene across psychiatric phenotypes.

Low Density Receptor-Related Protein 1 Interactions With the Extracellular Matrix: More Than Meets the Eye

The extracellular matrix (ECM) is a biological substrate composed of collagens, proteoglycans and glycoproteins that ensures proper cell migration and adhesion and keeps the cell architecture intact. The regulation of the ECM composition is a vital process strictly controlled by, among others, proteases, growth factors and adhesion receptors. As it appears, ECM remodeling is also essential for proper neuronal and glial development and the establishment of adequate synaptic signaling. Hence, disturbances in ECM functioning are often present in neurodegenerative diseases like Alzheimer’s disease. Moreover, mutations in ECM molecules are found in some forms of epilepsy and malfunctioning of ECM-related genes and pathways can be seen in, for example, cancer or ischemic injury. Low density lipoprotein receptor-related protein 1 (Lrp1) is a member of the low density lipoprotein receptor family. Lrp1 is involved not only in ligand uptake, receptor mediated endocytosis and lipoprotein transport—functions shared by low density lipoprotein receptor family members—but also regulates cell surface protease activity, controls cellular entry and binding of toxins and viruses, protects against atherosclerosis and acts on many cell signaling pathways. Given the plethora of functions, it is not surprising that Lrp1 also impacts the ECM and is involved in its remodeling. This review focuses on the role of Lrp1 and some of its major ligands on ECM function. Specifically, interactions with two Lrp1 ligands, integrins and tissue plasminogen activator are described in more detail.

Genetic Elimination of Connective Tissue Growth Factor in the Forebrain Affects Subplate Neurons in the Cortex and Oligodendrocytes in the Underlying White Matter

Connective tissue growth factor (CTGF) is a secreted extracellular matrix-associated protein, which play a role in regulating various cellular functions. Although the expression of CTGF has been reported in the cortical subplate, its function is still not clear. Thus, to explore the significance of CTGF in the brain, we created a forebrain-specific Ctgf knockout (FbCtgf KO) mouse model. By crossing Ctgf^fl/fl mice with Emx1-Cre transgenic mice, in which the expression of Cre is prenatally initiated, the full length Ctgf is removed in the forebrain structures. In young adult (2–3 months old) FbCtgf KO mice, subplate markers such as Nurr1 and Cplx3 are still expressed in the cortical layer VIb; however, the density of the subplate neurons is increased. Interestingly, in these mutants, we found a reduced structural complexity in the subplate neurons. The distribution patterns of neurons and glial cells, examined by immunohistochemistry, are comparable between genotypes in the somatosensory cortex. However, increased densities of mature oligodendrocytes, but not immature ones, were noticed in the external capsule underneath the cortical layer VIb in young adult FbCtgf KO mice. The features of myelinated axons in the external capsule were then examined using electron microscopy. Unexpectedly, the thickness of the myelin sheath was reduced in middle-aged (>12 months old), but not young adult FbCtgf KO mice. Our results suggest a secretory function of the subplate neurons, through the release of CTGF, which regulates the density and dendritic branching of subplate neurons as well as the maturation and function of nearby oligodendrocytes in the white matter.

LRP1 deficiency in microglia blocks neuro-inflammation in the spinal dorsal horn and neuropathic pain processing

Following injury to the peripheral nervous system (PNS), microglia in the spinal dorsal horn (SDH) become activated and contribute to the development of local neuro-inflammation, which may regulate neuropathic pain processing. The molecular mechanisms that control microglial activation and its effects on neuropathic pain remain incompletely understood. We deleted the gene encoding the plasma membrane receptor, LDL Receptor-related Protein-1 (LRP1), conditionally in microglia using two distinct promoter-Cre recombinase systems in mice. LRP1 deletion in microglia blocked development of tactile allodynia, a neuropathic pain-related behavior, after partial sciatic nerve ligation (PNL). LRP1 deletion also substantially attenuated microglial activation and pro-inflammatory cytokine expression in the SDH following PNL. Because LRP1 shedding from microglial plasma membranes generates a highly pro-inflammatory soluble product, we demonstrated that factors which activate spinal cord microglia, including lipopolysaccharide (LPS) and colony-stimulating factor-1, promote LRP1 shedding. Proteinases known to mediate LRP1 shedding, including ADAM10 and ADAM17, were expressed at increased levels in the SDH after PNL. Furthermore, LRP1-deficient microglia in cell culture expressed significantly decreased levels of interleukin-1β and interleukin-6 when treated with LPS. We conclude that in the SDH, microglial LRP1 plays an important role in establishing and/or amplifying local neuro-inflammation and neuropathic pain following PNS injury. The responsible mechanism most likely involves proteolytic release of LRP1 from the plasma membrane to generate a soluble product that functions similarly to pro-inflammatory cytokines in mediating crosstalk between cells in the SDH and in regulating neuropathic pain.

Hemopexin increases the neurotoxicity of hemoglobin when haptoglobin is absent

Hemopexin (Hpx) binds heme with extraordinary affinity, and after haptoglobin may provide a second line of defense against the toxicity of extracellular hemoglobin (Hb). In this series of experiments, the hypothesis that Hpx protects neurons from Hb neurotoxicity was evaluated in murine primary cultures containing neurons and glial cells. Contrary to hypothesis, Hpx increased neuronal loss due to micromolar concentrations of Hb by 4- to 12-fold, as measured by LDH release assay; conversely, the neurotoxicity of hemin was completely prevented. The endogenous fluorescence of Hpx was quenched by Hb, consistent with transfer of Hb-bound heme to Hpx. This was associated with precipitation of globin chains, as detected by immunostaining and fluorescent Hb labeling. A portion of this precipitate attached firmly to cells and could not be removed by multiple washes. Concomitant treatment with haptoglobin (Hp) prevented globin precipitation and most of the increase in neuronal loss. Hpx weakly attenuated the increase in culture non-heme iron produced by Hb treatment, quantified by ferrozine assay. However, Hb-Hpx toxicity was iron-dependent, and was blocked by deferoxamine and ferrostatin-1. Up-regulation of cell ferritin expression, a primary cell defense against Hb toxicity, was not observed on western blots of culture lysates that had been concomitantly treated with Hpx. These results suggest that Hpx destabilizes Hb in the absence of haptoglobin, leading to globin precipitation and exacerbation of iron-dependent oxidative cell injury. Combined therapy with hemopexin plus haptoglobin may be preferable to hemopexin alone after CNS hemorrhage.

LRP1 regulates peroxisome biogenesis and cholesterol homeostasis in oligodendrocytes and is required for proper CNS myelin development and repair

Low-density lipoprotein receptor-related protein-1 (LRP1) is a large endocytic and signaling molecule broadly expressed by neurons and glia. In adult mice, global inducible (Lrp1^flox/flox;CAG-CreER) or oligodendrocyte (OL)-lineage specific ablation (Lrp1^flox/flox;Pdgfra-CreER) of Lrp1 attenuates repair of damaged white matter. In oligodendrocyte progenitor cells (OPCs), Lrp1 is required for cholesterol homeostasis and differentiation into mature OLs. Lrp1-deficient OPC/OLs show a strong increase in the sterol-regulatory element-binding protein-2 yet are unable to maintain normal cholesterol levels, suggesting more global metabolic deficits. Mechanistic studies revealed a decrease in peroxisomal biogenesis factor-2 and fewer peroxisomes in OL processes. Treatment of Lrp1^−/− OPCs with cholesterol or activation of peroxisome proliferator-activated receptor-γ with pioglitazone alone is not sufficient to promote differentiation; however, when combined, cholesterol and pioglitazone enhance OPC differentiation into mature OLs. Collectively, our studies reveal a novel role for Lrp1 in peroxisome biogenesis, lipid homeostasis, and OPC differentiation during white matter development and repair.

Microglial-mediated PDGF-CC activation increases cerebrovascular permeability during ischemic stroke

Treatment of acute ischemic stroke with the thrombolytic tissue plasminogen activator (tPA) can significantly improve neurological outcomes; however, thrombolytic therapy is associated with an increased risk of intra-cerebral hemorrhage (ICH). Previously, we demonstrated that during stroke tPA acting on the parenchymal side of the neurovascular unit (NVU) can increase blood–brain barrier (BBB) permeability and ICH through activation of latent platelet-derived growth factor-CC (PDGF-CC) and signaling by the PDGF receptor-α (PDGFRα). However, in vitro, activation of PDGF-CC by tPA is very inefficient and the mechanism of PDGF-CC activation in the NVU is not known. Here, we show that the integrin Mac-1, expressed on brain microglia/macrophages (denoted microglia throughout), acts together with the endocytic receptor LRP1 in the NVU to promote tPA-mediated activation of PDGF-CC. Mac-1-deficient mice (Mac-1^−/−) are protected from tPA-induced BBB permeability but not from permeability induced by intracerebroventricular injection of active PDGF-CC. Immunofluorescence analysis demonstrates that Mac-1, LRP1, and the PDGFRα all localize to the NVU of arterioles, and following middle cerebral artery occlusion (MCAO) Mac-1^−/− mice show significantly less PDGFRα phosphorylation, BBB permeability, and infarct volume compared to wild-type mice. Bone-marrow transplantation studies indicate that resident CD11b⁺ cells, but not bone-marrow-derived leukocytes, mediate the early activation of PDGF-CC by tPA after MCAO. Finally, using a model of thrombotic stroke with late thrombolysis, we show that wild-type mice have an increased incidence of spontaneous ICH following thrombolysis with tPA 5 h after MCAO, whereas Mac-1^−/− mice are resistant to the development of ICH even with late tPA treatment. Together, these results indicate that Mac-1 and LRP1 act as co-factors for the activation of PDGF-CC by tPA in the NVU, and suggest a novel mechanism for tightly regulating PDGFRα signaling in the NVU and controlling BBB permeability.

Oleocanthal ameliorates amyloid-β oligomers' toxicity on astrocytes and neuronal cells: In vitro studies

Extra-virgin olive oil (EVOO) has several health promoting effects. Evidence have shown that EVOO attenuates the pathology of amyloid-β (Aβ) and improves cognitive function in experimental animal models, suggesting it's potential to protect and reduce the risk of developing Alzheimer's disease (AD). Available studies have linked this beneficial effect to oleocanthal, one of the active components in EVOO. The effect of oleocanthal against AD pathology has been linked to its ability to attenuate Aβ and tau aggregation in vitro, and enhance Aβ clearance from the brains of wild-type and AD transgenic mice in vivo. However, the ability of oleocanthal to alter the toxic effect of Aβ on brain parenchymal cells is unknown. In the current study, we investigated oleocanthal effect on modulating Aβ oligomers (Aβo) pathological events in neurons and astrocytes. Our findings demonstrated oleocanthal prevented Aβo-induced synaptic proteins, SNAP-25 and PSD-95, down-regulation in neurons, and attenuated Aβo-induced inflammation, glutamine transporter (GLT1) and glucose transporter (GLUT1) down-regulation in astrocytes. Aβo-induced inflammation was characterized by interleukin-6 (IL-6) increase and glial fibrillary acidic protein (GFAP) upregulation that were reduced by oleocanthal. In conclusion, this study provides further evidence to support the protective effect of EVOO-derived phenolic secoiridoid oleocanthal against AD pathology.

Evaluating Tissue-Specific Recombination in a Pdgfrα-CreERT2 Transgenic Mouse Line

In the central nervous system (CNS) platelet derived growth factor receptor alpha (PDGFRα) is expressed exclusively by oligodendrocyte progenitor cells (OPCs), making the Pdgfrα promoter an ideal tool for directing transgene expression in this cell type. Two Pdgfrα-CreER^T2 mouse lines have been generated for this purpose which, when crossed with cre-sensitive reporter mice, allow the temporally restricted labelling of OPCs for lineage-tracing studies. These mice have also been used to achieve the deletion of CNS-specific genes from OPCs. However the ability of Pdgfrα-CreER^T2 mice to induce cre-mediated recombination in PDGFRα⁺ cell populations located outside of the CNS has not been examined. Herein we quantify the proportion of PDGFRα⁺ cells that become YFP-labelled following Tamoxifen administration to adult Pdgfrα-CreER^T2::Rosa26-YFP transgenic mice. We report that the vast majority (>90%) of PDGFRα⁺ OPCs in the CNS, and a significant proportion of PDGFRα⁺ stromal cells within the bone marrow (~38%) undergo recombination and become YFP-labelled. However, only a small proportion of the PDGFRα⁺ cell populations found in the sciatic nerve, adrenal gland, pituitary gland, heart, gastrocnemius muscle, kidney, lung, liver or intestine become YFP-labelled. These data suggest that Pdgfrα-CreER^T2 transgenic mice can be used to achieve robust recombination in OPCs, while having a minimal effect on most PDGFRα⁺ cell populations outside of the CNS.