Mapping of aggrecan, hyaluronic acid, heparan sulphate proteoglycans and aquaporin 4 in the central nervous system of the mouse

GSK-3β orchestrates the inhibitory innervation of adult-born dentate granule cells in vivo

Adult hippocampal neurogenesis enhances brain plasticity and contributes to the cognitive reserve during aging. Adult hippocampal neurogenesis is impaired in neurological disorders, yet the molecular mechanisms regulating the maturation and synaptic integration of new neurons have not been fully elucidated. GABA is a master regulator of adult and developmental neurogenesis. Here we engineered a novel retrovirus encoding the fusion protein Gephyrin:GFP to longitudinally study the formation and maturation of inhibitory synapses during adult hippocampal neurogenesis in vivo. Our data reveal the early assembly of inhibitory postsynaptic densities at 1 week of cell age. Glycogen synthase kinase 3 Beta (GSK-3β) emerges as a key regulator of inhibitory synapse formation and maturation during adult hippocampal neurogenesis. GSK-3β-overexpressing newborn neurons show an increased number and altered size of Gephyrin+ postsynaptic clusters, enhanced miniature inhibitory postsynaptic currents, shorter and distanced axon initial segments, reduced synaptic output at the CA3 and CA2 hippocampal regions, and impaired pattern separation. Moreover, GSK-3β overexpression triggers a depletion of Parvalbumin+ interneuron perineuronal nets. These alterations might be relevant in the context of neurological diseases in which the activity of GSK-3β is dysregulated.

Tau Protein Modulates Perineuronal Extracellular Matrix Expression in the TauP301L-acan Mouse Model

Tau mutations promote the formation of tau oligomers and filaments, which are neuropathological signs of several tau-associated dementias. Types of neurons in the CNS are spared of tau pathology and are surrounded by a specialized form of extracellular matrix; called perineuronal nets (PNs). Aggrecan, the major PN proteoglycans, is suggested to mediate PNs neuroprotective function by forming an external shield preventing the internalization of misfolded tau. We recently demonstrated a correlation between aggrecan amount and the expression and phosphorylation of tau in a TauP310L-acan mouse model, generated by crossbreeding heterozygous aggrecan mice with a significant reduction of aggrecan and homozygous TauP301L mice. Neurodegenerative processes have been associated with changes of PN structure and protein signature. In this study, we hypothesized that the structure and protein expression of PNs in this TauP310L-acan mouse is regulated by tau. Immunohistochemical and biochemical analyses demonstrate that protein levels of PN components differ between TauP301L^HET-acan^WT and TauP301L^HET-acan^HET mice, accompanied by changes in the expression of protein phosphatase 2 A. In addition, tau can modulate PN components such as brevican. Co-immunoprecipitation experiments revealed a physical connection between PN components and tau. These data demonstrate a complex, mutual interrelation of tau and the proteoglycans of the PN.

Disease-specific glycosaminoglycan patterns in the extracellular matrix of human lung and brain

A wide variety of diseases throughout the mammalian organism is characterized by abnormal deposition of various components of the extracellular matrix (ECM), including the heterogeneous family of glycosaminoglycans (GAGs), which contribute considerably to the ECM architecture as part of the so-called proteoglycans. The GAG's unique sulfation pattern, derived from highly dynamic and specific modification processes, has a massive impact on critical mediators such as cytokines and growth factors. Due to the strong connection between the specific sulfation pattern and GAG function, slight alterations of this pattern are often associated with enormous changes at the cell as well as at the organ level. This review aims to investigate the connection between modifications of GAG sulfation patterns and the wide range of pathological conditions, mainly focusing on a range of chronic diseases of the central nervous system (CNS) as well as the respiratory tract.

Glia and extracellular matrix molecules: What are their importance for the electrographic and MRI changes in the epileptogenic zone?

Glial cells and extracellular matrix (ECM) molecules are crucial for the maintenance of brain homeostasis. Especially because of their actions regarding neurotransmitter and ionic control, and synaptic function, these cells can potentially contribute to the hyperexcitability seen in the epileptogenic, while ECM changes are linked to synaptic reorganization. The present review will explore glial and ECM homeostatic roles and their potential contribution to tissue plasticity. Finally, we will address how glial, and ECM changes in the epileptogenic zone can be seen in magnetic resonance imaging (MRI), pointing out their importance as markers for the extension of the epileptogenic area. This article is part of the Special Issue "NEWroscience 2018".

Integrin β3 organizes dendritic complexity of cerebral cortical pyramidal neurons along a tangential gradient

Dysfunctional dendritic arborization is a key feature of many developmental neurological disorders. Across various human brain regions, basal dendritic complexity is known to increase along a caudal-to-rostral gradient. We recently discovered that basal dendritic complexity of layer II/III cortical pyramidal neurons in the mouse increases along a caudomedial-to-rostrolateral gradient spanning multiple regions, but at the time, no molecules were known to regulate that exquisite pattern. Integrin subunits have been implicated in dendritic development, and the subunit with the strongest associations with autism spectrum disorder and intellectual disability is integrin β3 (Itgb3). In mice, global knockout of Itgb3 leads to autistic-like neuroanatomy and behavior. Here, we tested the hypothesis that Itgb3 is required for increasing dendritic complexity along the recently discovered tangential gradient among layer II/III cortical pyramidal neurons. We targeted a subset of layer II/III cortical pyramidal neurons for Itgb3 loss-of-function via Cre-loxP-mediated excision of Itgb3. We tracked the rostrocaudal and mediolateral position of the targeted neurons and reconstructed their dendritic arbors. In contrast to controls, the basal dendritic complexity of Itgb3 mutant neurons was not related to their cortical position. Basal dendritic complexity of mutant and control neurons differed because of overall changes in branch number across multiple branch orders (primary, secondary, etc.), rather than any changes in the average length at those branch orders. Furthermore, dendritic spine density was related to cortical position in control but not mutant neurons. Thus, the autism susceptibility gene Itgb3 is required for establishing a tangential pattern of basal dendritic complexity among layer II/III cortical pyramidal neurons, suggesting an early role for this molecule in the developing brain.

Diverse Roles for Hyaluronan and Hyaluronan Receptors in the Developing and Adult Nervous System

Hyaluronic acid (HA) plays a vital role in the extracellular matrix of neural tissues. Originally thought to hydrate tissues and provide mechanical support, it is now clear that HA is also a complex signaling molecule that can regulate cell processes in the developing and adult nervous systems. Signaling properties are determined by molecular weight, bound proteins, and signal transduction through specific receptors. HA signaling regulates processes such as proliferation, differentiation, migration, and process extension in a variety of cell types including neural stem cells, neurons, astrocytes, microglia, and oligodendrocyte progenitors. The synthesis and catabolism of HA and the expression of HA receptors are altered in disease and influence neuroinflammation and disease pathogenesis. This review discusses the roles of HA, its synthesis and breakdown, as well as receptor expression in neurodevelopment, nervous system function and disease.

Aggrecan modulates the expression and phosphorylation of tau in a novel bigenic TauP301L - Acan mouse model

Selected types of neurons in the central nervous system are associated with a specialized form of extracellular matrix. These so-called perineuronal nets (PNs) are supramolecular structures surrounding neuronal somata, proximal dendrites and axon initial segments. PNs are involved in the regulation of plasticity and synaptic physiology. In addition, PNs were proposed to carry neuroprotective functions as PN-ensheathed neurons are mostly spared of tau pathology in brains of Alzheimer patients. Recently, the neuroprotective action of PNs was confirmed experimentally, demonstrating (i) that mainly aggrecan mediates the neuroprotective function of PNs and (ii) that aggrecan seems to generate an external shielding preventing the internalization of pathological forms of tau. In the present study, we aimed at extending these findings and hypothesized that aggrecan further provides an intracellular protection by preventing mutation-triggered formation of pathological forms of tau. We used crossbreds of TauP301L mice and heterozygous aggrecan mice which are characterized by spontaneous deletion of the aggrecan allele. We analysed the extent of tau pathology in dependence of aggrecan protein amount by applying immunohistochemistry, Western blotting and ELISA. The results clearly indicate that aggrecan has no significant impact on tau aggregation in the brainstem of our mouse model. Still, reduced aggrecan levels were accompanied by increased levels of tau protein and reduced number of Tau-1-positive neurons, which indicate an increase in phosphorylation of tau. In conclusion, these data demonstrate a correlation between aggrecan and P301L mutation-triggered tau expression and phosphorylation in our bigenic mouse model.

Protective Mechanism and Treatment of Neurogenesis in Cerebral Ischemia

Stroke is the fifth leading cause of death worldwide and is a main cause of disability in adults. Neither currently marketed drugs nor commonly used treatments can promote nerve repair and neurogenesis after stroke, and the repair of neurons damaged by ischemia has become a research focus. This article reviews several possible mechanisms of stroke and neurogenesis and introduces novel neurogenic agents (fibroblast growth factors, brain-derived neurotrophic factor, purine nucleosides, resveratrol, S-nitrosoglutathione, osteopontin, etc.) as well as other treatments that have shown neuroprotective or neurogenesis-promoting effects.

An Activity-Based Nanosensor for Traumatic Brain Injury

Currently, traumatic brain injury (TBI) is detected by medical imaging; however, medical imaging requires expensive capital equipment, is time- and resource-intensive, and is poor at predicting patient prognosis. To date, direct measurement of elevated protease activity has yet to be utilized to detect TBI. In this work, we engineered an activity-based nanosensor for TBI (TBI-ABN) that responds to increased protease activity initiated after brain injury. We establish that a calcium-sensitive protease, calpain-1, is active in the injured brain hours within injury. We then optimize the molecular weight of a nanoscale polymeric carrier to infiltrate into the injured brain tissue with minimal renal filtration. A calpain-1 substrate that generates a fluorescent signal upon cleavage was attached to this nanoscale polymeric carrier to generate an engineered TBI-ABN. When applied intravenously to a mouse model of TBI, our engineered sensor is observed to locally activate in the injured brain tissue. This TBI-ABN is the first demonstration of a sensor that responds to protease activity to detect TBI.

Proteomics, Glycomics, and Glycoproteomics of Matrisome Molecules

The most straightforward applications of proteomics database searching involve intracellular proteins. Although intracellular gene products number in the thousands, their well-defined post-translational modifications (PTMs) makes database searching practical. By contrast, cell surface and extracellular matrisome proteins pass through the secretory pathway where many become glycosylated, modulating their physicochemical properties, adhesive interactions, and diversifying their functions. Although matrisome proteins number only a few hundred, their high degree of complex glycosylation multiplies the number of theoretical proteoforms by orders of magnitude. Given that extracellular networks that mediate cell-cell and cell-pathogen interactions in physiology depend on glycosylation, it is important to characterize the proteomes, glycomes, and glycoproteomes of matrisome molecules that exist in a given biological context. In this review, we summarize proteomics approaches for characterizing matrisome molecules, with an emphasis on applications to brain diseases. We demonstrate the availability of methods that should greatly increase the availability of information on matrisome molecular structure associated with health and disease.

The ontogeny of memory persistence and specificity

Interest in the ontogeny of memory blossomed in the twentieth century following the initial observations that memories from infancy and early childhood are rapidly forgotten. The intense exploration of infantile amnesia in subsequent years has led to a thorough characterization of its psychological determinants, although the neurobiology of memory persistence has long remained elusive. By contrast, other phenomena in the ontogeny of memory like infantile generalization have received relatively less attention. Despite strong evidence for reduced memory specificity during ontogeny, infantile generalization is poorly understood from psychological and neurobiological perspectives. In this review, we examine the ontogeny of memory persistence and specificity in humans and nonhuman animals at the levels of behavior and the brain. To this end, we first describe the behavioral phenotypes associated with each phenomenon. Looking into the brain, we then discuss neurobiological mechanisms in the hippocampus that contribute to the ontogeny of memory. Hippocampal neurogenesis and critical period mechanisms have recently been discovered to underlie amnesia during early development, and at the same time, we speculate that similar processes may contribute to the early bias towards memory generalization.

miR‑29a ameliorates ischemic injury of astrocytes in vitro by targeting the water channel protein aquaporin 4

Ischemic stroke is the main cause of brain injury and results in a high rate of morbidity, disability and mortality. In the present study, we aimed to determine whether miR-29a played a protective role in oxygen glucose deprivation (OGD) injury via regulation of the water channel protein aquaporin 4 (AQP4). Real-time PCR and western blotting were used to assess miR-29a levels and AQP4 protein levels, respectively. Apoptosis was detected by flow cytometry, and lactate dehydrogenase (LDH) was determined by enzyme-linked immunosorbent assay (ELISA). Overexpression of miR-29a was significantly downregulated in OGD-induced primary astrocytes, and transfection with a miR-29a mimic decreased LDH release and apoptosis, and improved cell health in OGD-induced astrocytes. AQP4 was the target of miR-29a, which suppressed AQP4 expression, and knockdown of AQP4 mitigated OGD-induced astrocyte injury. Furthermore, miR-29a regulated AQP4 expression in OGD-induced astrocytes. AQP4 exacerbated astrocyte injury following ischemic stroke, and knockdown of AQP4 protected OGD/RX-induced primary cultured astrocytes against injury. The effect of miR-29a inhibitor on primary astrocytes was lost following AQP4 knockdown. These findings indicated that miR-29a prevented astrocyte injury in vitro by inhibiting AQP4. Thus, miR-29a may protect primary cultured astrocytes after OGD-induced injury by targeting AQP4, and may be a potential therapeutic target for ischemic injury of astrocytes.

Traditional Japanese Herbal Medicine Yokukansan Targets Distinct but Overlapping Mechanisms in Aged Mice and in the 5xFAD Mouse Model of Alzheimer's Disease

Yokukansan (YKS) is a traditional Japanese herbal medicine that has been used in humans for the treatment of several neurological conditions, such as age-related anxiety and behavioral and psychological symptoms (BPSD) related to multiple forms of dementia, including Alzheimer’s disease (AD). However, the cellular and molecular mechanisms targeted by YKS in the brain are not completely understood. Here, we compared the efficacy of YKS in ameliorating the age- and early-onset familial AD-related behavioral and cellular defects in two groups of animals: 18- to 22-month-old C57BL6/J wild-type mice and 6- to 9-month-old 5xFAD mice, as a transgenic mouse model of this form of AD. Animals were fed food pellets that contained YKS or vehicle. After 1–2 months of YKS treatment, we evaluated the cognitive improvements in both the aged and 5xFAD transgenic mice, and their brain tissues were further investigated to assess the molecular and cellular changes that occurred following YKS intake. Our results show that both the aged and 5xFAD mice exhibited impaired behavioral performance in novel object recognition and contextual fear conditioning (CFC) tasks, which was significantly improved by YKS. Further analyses of the brain tissue from these animals indicated that in aged mice, this improvement was associated with a reduction in astrogliosis, microglia activation and downregulation of the extracellular matrix (ECM), whereas in 5xFAD mice, none of these mechanisms were evident. These results show the differential action of YKS in healthy aged and 5xFAD mice. However, both aged and 5xFAD YKS-treated mice showed increased neuroprotective signaling through protein kinase B/Akt as the common mode of action. Our data suggest that YKS may impart its beneficial effects through Akt signaling in both 5xFAD mice and aged mice, with multiple additional mechanisms potentially contributing to its beneficial effects in aged animals.

Hydrogel-assisted neuroregeneration approaches towards brain injury therapy: A state-of-the-art review

Recent years have witnessed the development of an enormous variety of hydrogel-based systems for neuroregeneration. Formed from hydrophilic polymers and comprised of up to 90% of water, these three-dimensional networks are promising tools for brain tissue regeneration. They can assist structural and functional restoration of damaged tissues by providing mechanical support and navigating cell fate. Hydrogels also show the potential for brain injury therapy due to their broadly tunable physical, chemical, and biological properties. Hydrogel polymers, which have been extensively implemented in recent brain injury repair studies, include hyaluronic acid, collagen type I, alginate, chitosan, methylcellulose, Matrigel, fibrin, gellan gum, self-assembling peptides and proteins, poly(ethylene glycol), methacrylates, and methacrylamides. When viewed as tools for neuroregeneration, hydrogels can be divided into: (1) hydrogels suitable for brain injury therapy, (2) hydrogels that do not meet basic therapeutic requirements and (3) promising hydrogels which meet the criteria for further investigations. Our analysis shows that fibrin, collagen I and self-assembling peptide-based hydrogels display very attractive properties for neuroregeneration.

Perineuronal nets in brain physiology and disease

Perineuronal nets (PNNs) in the brain are condensed glycosaminoglycan-rich extracellular matrix structures with heterogeneous composition yet specific organization. They typically assemble around a subset of fast-spiking interneurons that are implicated in learning and memory. Owing to their unique structural organization, PNNs have neuroprotective capacities but also participate in signal transduction and in controlling neuronal activity and plasticity. In this review, we define PNN structure in detail and describe its various biochemical and physiological functions. We further discuss the role of PNNs in brain disorders such as schizophrenia, bipolar disorder, Alzheimer disease and addictions. Lastly, we describe therapeutic approaches that target PNNs to alter brain physiology and counter brain dysfunction.

TDP-43 regulation of stress granule dynamics in neurodegenerative disease-relevant cell types

Stress granules (SGs) are cytoplasmic foci that form in response to various external stimuli and are essential to cell survival following stress. SGs are studied in several diseases, including ALS and FTD, which involve the degeneration of motor and cortical neurons, respectively, and are now realized to be linked pathogenically by TDP-43, originally discovered as a component of ubiquitin-positive aggregates within patients’ neurons and some glial cells. So far, studies to undercover the role of TDP-43 in SGs have used primarily transformed cell lines, and thus rely on the extrapolation of the mechanisms to cell types affected in ALS/FTD, potentially masking cell specific effects. Here, we investigate SG dynamics in primary motor and cortical neurons as well as astrocytes. Our data suggest a cell and stress specificity and demonstrate a requirement for TDP-43 for efficient SG dynamics. In addition, based on our in vitro approach, our data suggest that aging may be an important modifier of SG dynamics which could have relevance to the initiation and/or progression of age-related neurodegenerative diseases.

Quantification of the Extracellular Matrix Molecule Thrombospondin 1 and Its Pericellular Association in the Brain Using a Semiautomated Computerized Approach

The structure and functions of the extracellular matrix (ECM), its spatial distribution and pericellular association of ECM molecules remain poorly understood. Colocalization of ECM molecules with cell phenotypes through immunohistochemistry can provide crucial insights into their juxtacrine signaling role as well as their structural relevance to tissue architecture. As manual quantification of images introduces intra- and inter-user bias and is cumbersome for high-throughput approaches, we implemented an automated high-throughput method to quantify the spatial distribution and cellular association of one ECM molecule, thrombospondin 1 (TSP1) with two major cell phenotypes, neurons, and astrocytes. The distribution of TSP1 was homogeneous throughout the striatum and cortex along the anterior-posterior axis. TSP1 occupied 8.85% of the striatum and 7.40% in the cortex. TSP1 also associated with 94.58% and 88.45% of neurons in the striatum and cortex. The association with astrocytes was significantly lower at 47.55% and 28.09%. These findings highlight the key role that TSP1 plays in neuron physiology in a healthy brain, but also highlights key regional difference in astrocytes secreting ECM molecules. The semiautomated approach implemented here will improve the throughput and reliability of measuring the distribution and cellular colocalization of ECM molecules.

Perineuronal nets in subcortical auditory nuclei of four rodent species with differing hearing ranges

Perineuronal nets (PNs) are aggregates of extracellular matrix molecules that surround some neurons in the brain. While PNs occur widely across many cortical areas, subcortical PNs are especially associated with motor and auditory systems. The auditory system has recently been suggested as an ideal model system for studying PNs and their functions. However, descriptions of PNs in subcortical auditory areas vary, and it is unclear whether the variation reflects species differences or differences in staining techniques. Here, we used two staining techniques (one lectin stain and one antibody stain) to examine PN distribution in the subcortical auditory system of four different species: guinea pigs (Cavia porcellus), mice (Mus musculus, CBA/CaJ strain), Long-Evans rats (Rattus norvegicus), and naked mole-rats (Heterocephalus glaber). We found that some auditory nuclei exhibit dramatic differences in PN distribution among species while other nuclei have consistent PN distributions. We also found that PNs exhibit molecular heterogeneity, and can stain with either marker individually or with both. PNs within a given nucleus can be heterogeneous or homogenous in their staining patterns. We compared PN staining across the frequency axes of tonotopically organized nuclei and among species with different hearing ranges. PNs were distributed non-uniformly across some nuclei, but only rarely did this appear related to the tonotopic axis. PNs were prominent in all four species; we found no systematic relationship between the hearing range and the number, staining patterns or distribution of PNs in the auditory nuclei.

Hippocampal area CA2: properties and contribution to hippocampal function

This review focuses on area CA2 of the hippocampus, as recent results have revealed the unique properties and surprising role of this region in encoding social, temporal and contextual aspects of memory. Originally identified and described by Lorente de No, in 1934, this region of the hippocampus has unique intra-and extra-hippocampal connectivity, sending and receiving input to septal and hypothalamic regions. Recent in vivo studies have indicated that CA2 pyramidal neurons encode spatial information during immobility and play an important role in the generation of sharp-wave ripples. Furthermore, CA2 neurons act to control overall excitability in the hippocampal network and have been found to be consistently altered in psychiatric diseases, indicating that normal function of this region is necessary for normal cognition. With its unique role, area CA2 has a unique molecular profile, interneuron density and composition. Furthermore, this region has an unusual manifestation of synaptic plasticity that does not occur post-synaptically at pyramidal neuron dendrities but through the local network of inhibitory neurons. While much progress has recently been made in understanding the large contribution of area CA2 to social memory formation, much still needs to be learned.

Unaltered Glutamate Transporter-1 Protein Levels in Aquaporin-4 Knockout Mice

Maintenance of glutamate and water homeostasis in the brain is crucial to healthy brain activity. Astrocytic glutamate transporter-1 (GLT1) and aquaporin-4 (AQP4) are the main regulators of extracellular glutamate and osmolarity, respectively. Several studies have reported colocalization of GLT1 and AQP4, but the existence of a physical interaction between the two has not been well studied. Therefore, we used coimmunoprecipitation to determine whether a strong interaction exists between these two important molecules in mice on both a CD1 and C57BL/6 background. Furthermore, we used Western blot and immunohistochemistry to examine GLT1 levels in AQP4 knockout (AQP4^−/−) mice. An AQP4-GLT1 precipitate was not detected, suggesting the lack of a strong physical interaction between AQP4 and GLT1. In addition, GLT1 protein levels remained unaltered in tissue from CD1 and C57BL/6 AQP4^−/− mice. Finally, immunohistochemical analysis revealed that AQP4 and GLT1 do colocalize, but only in a region-specific manner. Taken together, these findings suggest that AQP4 and GLT1 do not have a strong physical interaction between them and are, instead, differentially regulated.

The absence of brain-specific link protein Bral2 in perineuronal nets hampers auditory temporal resolution and neural adaptation in mice

Brain-specific link protein Bral2 represents a substantial component of perineuronal nets (PNNs) enwrapping neurons in the central nervous system. To elucidate the role of Bral2 in auditory signal processing, the hearing function in knockout Bral2(-/-) (KO) mice was investigated using behavioral and electrophysiological methods and compared with wild type Bral2(+/+) (WT) mice. The amplitudes of the acoustic startle reflex (ASR) and the efficiency of the prepulse inhibition of ASR (PPI of ASR), produced by prepulse noise stimulus or gap in continuous noise, was similar in 2-week-old WT and KO mice. Over the 2-month postnatal period the increase of ASR amplitudes was significantly more evident in WT mice than in KO mice. The efficiency of the PPI of ASR significantly increased in the 2-month postnatal period in WT mice, whereas in KO mice the PPI efficiency did not change. Hearing thresholds in 2-month-old WT mice, based on the auditory brainstem response (ABR) recordings, were significantly lower at high frequencies than in KO mice. However, amplitudes and peak latencies of individual waves of click-evoked ABR did not differ significantly between WT and KO mice. Temporal resolution and neural adaptation were significantly better in 2-month-old WT mice than in age-matched KO mice. These results support a hypothesis that the absence of perineuronal net formation at the end of the developmental period in the KO mice results in higher hearing threshold at high frequencies and weaker temporal resolution ability in adult KO animals compared to WT mice.

Perineuronal Nets Suppress Plasticity of Excitatory Synapses on CA2 Pyramidal Neurons

Long-term potentiation of excitatory synapses on pyramidal neurons in the stratum radiatum rarely occurs in hippocampal area CA2. Here, we present evidence that perineuronal nets (PNNs), a specialized extracellular matrix typically localized around inhibitory neurons, also surround mouse CA2 pyramidal neurons and envelop their excitatory synapses. CA2 pyramidal neurons express mRNA transcripts for the major PNN component aggrecan, identifying these neurons as a novel source for PNNs in the hippocampus. We also found that disruption of PNNs allows synaptic potentiation of normally plasticity-resistant excitatory CA2 synapses; thus, PNNs play a role in restricting synaptic plasticity in area CA2. Finally, we found that postnatal development of PNNs on CA2 pyramidal neurons is modified by early-life enrichment, suggesting that the development of circuits containing CA2 excitatory synapses are sensitive to manipulations of the rearing environment.

SIGNIFICANCE STATEMENT

Perineuronal nets (PNNs) are thought to play a major role in restricting synaptic plasticity during postnatal development, and are altered in several models of neurodevelopmental disorders, such as schizophrenia and Rett syndrome. Although PNNs have been predominantly studied in association with inhibitory neurons throughout the brain, we describe a dense expression of PNNs around excitatory pyramidal neurons in hippocampal area CA2. We also provide insight into a previously unrecognized role for PNNs in restricting plasticity at excitatory synapses and raise the possibility of an early critical period of hippocampal plasticity that may ultimately reveal a key mechanism underlying learning and memory impairments of PNN-associated neurodevelopmental disorders.

Morphological, histological and immunohistochemical study of the area postrema in the dog

Circumventricular organs are specialized brain structures that are located mainly at the midsagittal line, around the third and fourth ventricles, often protruding into the lumen. They are positioned at the interface between the neuroparenchyma and the ventricular system of the brain. These highly vascularized nervous tissue structures differ from the brain parenchyma, as they lack a blood-brain barrier. Circumventricular organs have specialized sensory and secretory functions. It is essential for any pathologist who evaluates brain sections to have a solid knowledge of microscopic neuroanatomy and to recognize these numerous specialized structures within the nervous system as normal and not mistake them for pathological changes. The purpose of this study was to provide, for the first time, a detailed and complete histological description of the healthy canine area postrema and to determine its resemblance to that of other mammalian species. Anatomical dissections with routine histological and immunohistochemical techniques were carried out on ten canine brains. The cellular composition of area postrema proved to be largely comparable to that of other mammal species.

Down-regulated expression of aquaporin-4 in the cerebellum after status epilepticus

Status epilepticus (SE) is a common neurological condition associated with high rates of mortality and permanent brain injury. SE usually leads to neuronal death which may be accompanied by edema, epileptogenesis and learning impairment. Aquaporin-4 (AQP4), is a transmembrane water channel protein in the neuropil of the central nervous system that has an important role in water transport in the brain; AQP4 expression is altered in many pathological conditions such as changes in the blood- brain barrier and/or astrocytic activation, including seizures. AQP4 was shown to be downregulated in the piriform cortex and the hippocampus after SE. Although it is normally expressed at a high level in the cerebellum, little is known about AQP4 levels in the cerebellum following SE. We addressed this in the present study in a mouse model of pilocarpine-induced SE. We found that AQP4 expression was reduced from 3 h to 3 days after SE, with the levels recovering on day 7. Moreover, mice in the acute post-SE stages exhibited impaired motor coordination and learning. These results indicate that cerebellar damage following SE involves changes in AQP4 expression.

Rediscovering area CA2: unique properties and functions

Hippocampal area CA2 has several features that distinguish it from CA1 and CA3, including a unique gene expression profile, failure to display long-term potentiation and relative resistance to cell death. A recent increase in interest in the CA2 region, combined with the development of new methods to define and manipulate its neurons, has led to some exciting new discoveries on the properties of CA2 neurons and their role in behaviour. Here, we review these findings and call attention to the idea that the definition of area CA2 ought to be revised in light of gene expression data.

Wisteria Floribunda Agglutinin-Labeled Perineuronal Nets in the Mouse Inferior Colliculus, Thalamic Reticular Nucleus and Auditory Cortex

Perineuronal nets (PNNs) are specialized extracellular matrix molecules that are associated with the closing of the critical period, among other functions. In the adult brain, PNNs surround specific types of neurons, however the expression of PNNs in the auditory system of the mouse, particularly at the level of the midbrain and forebrain, has not been fully described. In addition, the association of PNNs with excitatory and inhibitory cell types in these structures remains unknown. Therefore, we sought to investigate the expression of PNNs in the inferior colliculus (IC), thalamic reticular nucleus (TRN) and primary auditory cortex (A1) of the mouse brain by labeling with wisteria floribunda agglutinin (WFA). To aid in the identification of inhibitory neurons in these structures, we employed the vesicular GABA transporter (VGAT)-Venus transgenic mouse strain, which robustly expresses an enhanced yellow-fluorescent protein (Venus) natively in nearly all gamma-amino butyric acid (GABA)-ergic inhibitory neurons, thus enabling a rapid and unambiguous assessment of inhibitory neurons throughout the nervous system. Our results demonstrate that PNNs are expressed throughout the auditory midbrain and forebrain, but vary in their local distribution. PNNs are most dense in the TRN and least dense in A1. Furthermore, PNNs are preferentially associated with inhibitory neurons in A1 and the TRN, but not in the IC of the mouse. These data suggest regionally specific roles for PNNs in auditory information processing.

Heterogeneous expression of extracellular matrix molecules in the red nucleus of the rat

Previous studies in our laboratory showed that the organization and heterogeneous molecular composition of extracellular matrix is associated with the variable cytoarchitecture, connections and specific functions of the vestibular nuclei and two related areas of the vestibular neural circuits, the inferior olive and prepositus hypoglossi nucleus. The aim of the present study is to reveal the organization and distribution of various molecular components of extracellular matrix in the red nucleus, a midbrain premotor center. Morphologically and functionally the red nucleus is comprised of the magno- and parvocellular parts, with overlapping neuronal population. By using histochemical and immunohistochemical methods, the extracellular matrix appeared as perineuronal net, axonal coat, perisynaptic matrix or diffuse network in the neuropil. In both parts of the red nucleus we have observed positive hyaluronan, tenascin-R, link protein, and lectican (aggrecan, brevican, versican, neurocan) reactions. Perineuronal nets were detected with each of the reactions and the aggrecan showed the most intense staining in the pericellular area. The two parts were clearly distinguished on the basis of neurocan and HAPLN1 expression as they have lower intensity in the perineuronal nets of large cells and in the neuropil of the magnocellular part. Additionally, in contrast to this pattern, the aggrecan was heavily labeled in the magnocellular region sharply delineating from the faintly stained parvocellular area. The most characteristic finding was that the appearance of perineuronal nets was related with the neuronal size independently from its position within the two subdivisions of red nucleus. In line with these statements none of the extracellular matrix molecules were restricted exclusively to the magno- or parvocellular division. The chemical heterogeneity of the perineuronal nets may support the recently accepted view that the red nucleus comprises more different populations of neurons than previously reported.

Extracellular matrix protein expression is brain region dependent

In the brain, extracellular matrix (ECM) components form networks that contribute to structural and functional diversity. Maladaptive remodeling of ECM networks has been reported in neurodegenerative and psychiatric disorders, suggesting that the brain microenvironment is a dynamic structure. A lack of quantitative information about ECM distribution in the brain hinders an understanding of region-specific ECM functions and the role of ECM in health and disease. We hypothesized that each ECM protein as well as specific ECM structures, such as perineuronal nets (PNNs) and interstitial matrix, are differentially distributed throughout the brain, contributing to the unique structure and function in the various regions of the brain. To test our hypothesis, we quantitatively analyzed the distribution, colocalization, and protein expression of aggrecan, brevican, and tenascin-R throughout the rat brain utilizing immunohistochemistry and mass spectrometry analysis and assessed the effect of aggrecan, brevican, and/or tenascin-R on neurite outgrowth in vitro. We focused on aggrecan, brevican, and tenascin-R as they are especially expressed in the mature brain, and have established roles in brain development, plasticity, and neurite outgrowth. The results revealed a differentiated distribution of all three proteins throughout the brain and indicated that their presence significantly reduces neurite outgrowth in a 3D in vitro environment. These results underline the importance of a unique and complex ECM distribution for brain physiology and suggest that encoding the distribution of distinct ECM proteins throughout the brain will aid in understanding their function in physiology and in turn assist in identifying their role in disease. J. Comp. Neurol. 524:1309-1336, 2016. © 2016 Wiley Periodicals, Inc.

Expression of the Astrocyte Water Channel Aquaporin-4 in the Mouse Brain

Aquaporin-4 (AQP4) is a bidirectional water channel that is found on astrocytes throughout the central nervous system. Expression is particularly high around areas in contact with cerebrospinal fluid, suggesting that AQP4 plays a role in fluid exchange between the cerebrospinal fluid compartments and the brain. Despite its significant role in the brain, the overall spatial and region-specific distribution of AQP4 has yet to be fully characterized. In this study, we used Western blotting and immunohistochemical techniques to characterize AQP4 expression and localization throughout the mouse brain. We observed AQP4 expression throughout the forebrain, subcortical areas, and brainstem. AQP4 protein levels were highest in the cerebellum with lower expression in the cortex and hippocampus. We found that AQP4 immunoreactivity was profuse on glial cells bordering ventricles, blood vessels, and subarachnoid space. Throughout the brain, AQP4 was expressed on astrocytic end-feet surrounding blood vessels but was also heterogeneously expressed in brain tissue parenchyma and neuropil, often with striking laminar specificity. In the cerebellum, we showed that AQP4 colocalized with the proteoglycan brevican, which is synthesized by and expressed on cerebellar astrocytes. Despite the high abundance of AQP4 in the cerebellum, its functional significance has yet to be investigated. Given the known role of AQP4 in synaptic plasticity in the hippocampus, the widespread and region-specific expression pattern of AQP4 suggests involvement not only in fluid balance and ion homeostasis but also local synaptic plasticity and function in distinct brain circuits.

Proteolytic regulation of synaptic plasticity in the mouse primary visual cortex: analysis of matrix metalloproteinase 9 deficient mice

The extracellular matrix (ECM) is known to play important roles in regulating neuronal recovery from injury. The ECM can also impact physiological synaptic plasticity, although this process is less well understood. To understand the impact of the ECM on synaptic function and remodeling in vivo, we examined ECM composition and proteolysis in a well-established model of experience-dependent plasticity in the visual cortex. We describe a rapid change in ECM protein composition during Ocular Dominance Plasticity (ODP) in adolescent mice, and a loss of ECM remodeling in mice that lack the extracellular protease, matrix metalloproteinase-9 (MMP9). Loss of MMP9 also attenuated functional ODP following monocular deprivation (MD) and reduced excitatory synapse density and spine density in sensory cortex. While we observed no change in the morphology of existing dendritic spines, spine dynamics were altered, and MMP9 knock-out (KO) mice showed increased turnover of dendritic spines over a period of 2 days. We also analyzed the effects of MMP9 loss on microglia, as these cells are involved in extracellular remodeling and have been recently shown to be important for synaptic plasticity. MMP9 KO mice exhibited very limited changes in microglial morphology. Ultrastructural analysis, however, showed that the extracellular space surrounding microglia was increased, with concomitant increases in microglial inclusions, suggesting possible changes in microglial function in the absence of MMP9. Taken together, our results show that MMP9 contributes to ECM degradation, synaptic dynamics and sensory-evoked plasticity in the mouse visual cortex.

"GAG-ing with the neuron": The role of glycosaminoglycan patterning in the central nervous system

Proteoglycans (PGs) are a diverse family of proteins that consist of one or more glycosaminoglycan (GAG) chains, covalently linked to a core protein. PGs are major components of the extracellular matrix (ECM) and play critical roles in development, normal function and damage-response of the central nervous system (CNS). GAGs are classified based on their disaccharide subunits, into the following major groups: chondroitin sulfate (CS), heparan sulfate (HS), heparin (HEP), dermatan sulfate (DS), keratan sulfate (KS) and hyaluronic acid (HA). All except HA are modified by sulfation, giving GAG chains specific charged structures and binding properties. While significant neuroscience research has focused on the role of one PG family member, chondroitin sulfate proteoglycan (CSPG), there is ample evidence in support of a role for the other PGs in regulating CNS function in normal and pathological conditions. This review discusses the role of all the identified PG family members (CS, HS, HEP, DS, KS and HA) in normal CNS function and in the context of pathology. Understanding the pleiotropic roles of these molecules in the CNS may open the door to novel therapeutic strategies for a number of neurological conditions.

Update on biomarkers in neuromyelitis optica

Neuromyelitis optica (NMO) (and NMO spectrum disorder) is an autoimmune inflammatory disease of the CNS primarily affecting spinal cord and optic nerves. Reliable and sensitive biomarkers for onset, relapse, and progression in NMO are urgently needed because of the heterogeneous clinical presentation, severity of neurologic disability following relapses, and variability of therapeutic response. Detecting aquaporin-4 (AQP4) antibodies (AQP4-IgG or NMO-IgG) in serum supports the diagnosis of seropositive NMO. However, whether AQP4-IgG levels correlate with disease activity, severity, response to therapy, or long-term outcomes is unclear. Moreover, biomarkers for patients with seronegative NMO have yet to be defined and validated. Collaborative international studies hold great promise for establishing and validating biomarkers that are useful in therapeutic trials and clinical management. In this review, we discuss known and potential biomarkers for NMO.

Aquaporin 4-dependent expression of glial fibrillary acidic protein and tenascin-C in activated astrocytes in stab wound mouse brain and in primary culture

We previously reported that aquaporin 4 (AQP4) has a neuroimmunological function via astrocytes and microglial cells involving osteopontin. AQP4 is a water channel localized in the endofoot of astrocytes in the brain, and its expression is upregulated after a stab wound to the mouse brain or the injection of methylmercury in common marmosets. In this study, the correlation between the expression of AQP4 and the expression of glial fibrillary acidic protein (GFAP) or tenascin-C (TN-C) in reactive astrocytes was examined in primary cultures and brain tissues of AQP4-deficient mice (AQP4/KO). In the absence of a stab wound to the brain or of any stimulation of the cells, the expressions of both GFAP and TN-C were lower in astrocytes from AQP4/KO mice than in those from wild-type (WT) mice. High levels of GFAP and TN-C expression were observed in activated astrocytes after a stab wound to the brain in WT mice; however, the expressions of GFAP and TN-C were insignificant in AQP4/KO mice. Furthermore, lipopolysaccharide (LPS) stimulation activated primary culture of astrocytes and upregulated GFAP and TN-C expression in cells from WT mice, whereas the expressions of GFAP and TN-C were slightly upregulated in cells from AQP4/KO mice. Moreover, the stimulation of primary culture of astrocytes with LPS also upregulated inflammatory cytokines in cells from WT mice, whereas modest increases were observed in cells from AQP4/KO mice. These results suggest that AQP4 expression accelerates GFAP and TN-C expression in activated astrocytes induced by a stab wound in the mouse brain and LPS-stimulated primary culture of astrocytes.

Biologic scaffold for CNS repair

Injury to the CNS typically results in significant morbidity and endogenous repair mechanisms are limited in their ability to restore fully functional CNS tissue. Biologic scaffolds composed of individual purified components have been shown to facilitate functional tissue reconstruction following CNS injury. Extracellular matrix scaffolds derived from mammalian tissues retain a number of bioactive molecules and their ability for CNS repair has recently been recognized. In addition, novel biomaterials for dural mater repairs are of clinical interest as the dura provides barrier function and maintains homeostasis to CNS. The present article describes the application of regenerative medicine principles to the CNS tissues and dural mater repair. While many approaches have been exploring the use of cells and/or therapeutic molecules, the strategies described herein focus upon the use of extracellular matrix scaffolds derived from mammalian tissues that are free of cells and exogenous factors.

Extracellular matrix components mark the territories of circumventricular organs

In the central nervous system the extracellular matrix has important roles, e.g. supporting the extracellular space, controlling the tissue hydration, binding soluble factors and influencing their diffusion. The distribution of the extracellular matrix components in the brain has been mapped but data on the circumventricular organs (CVOs) is not available yet. The CVOs lack the blood-brain barrier and have relatively large perivascular spaces. The present study investigates tenascin-R and the lecticans: aggrecan, brevican, neurocan, and versican in the median eminence, the area postrema, the vascular organ of the lamina terminalis, the subfornical organ, the pineal body and the subcommissural organ of the rat applying immunohistochemical methods, and lectin histochemistry, using Wisteria floribunda agglutinin (WFA). The extracellular matrix components were found intensely expressed in the CVOs with two exceptions: aggrecan immunoreactivity visualized only neurons in the arcuate nucleus, and the subcommissural organ was not labeled with either WFA, or lecticans, or tenascin-R. The different labelings usually overlapped each other. The distribution of the extracellular matrix components marked the territories of the CVOs. Considering these we suppose that the extracellular matrix is essential in the maintenance of CVO functions providing the large extracellular space which is required for diffusion and other processes important in their chemosensitive and neurosecretory activities. The decrease of extracellular matrix beyond the border of the organs may contribute to the control of the diffusion of molecules from the CVOs into the surrounding brain substance.

Gene expression profiling of mesenteric lymph nodes from sheep with natural scrapie

BACKGROUND

Prion diseases are characterized by the accumulation of the pathogenic PrPSc protein, mainly in the brain and the lymphoreticular system. Although prions multiply/accumulate in the lymph nodes without any detectable pathology, transcriptional changes in this tissue may reflect biological processes that contribute to the molecular pathogenesis of prion diseases. Little is known about the molecular processes that occur in the lymphoreticular system in early and late stages of prion disease. We performed a microarray-based study to identify genes that are differentially expressed at different disease stages in the mesenteric lymph node of sheep naturally infected with scrapie. Oligo DNA microarrays were used to identify gene-expression profiles in the early/middle (preclinical) and late (clinical) stages of the disease.

RESULTS

In the clinical stage of the disease, we detected 105 genes that were differentially expressed (≥2-fold change in expression). Of these, 43 were upregulated and 62 downregulated as compared with age-matched negative controls. Fewer genes (50) were differentially expressed in the preclinical stage of the disease. Gene Ontology enrichment analysis revealed that the differentially expressed genes were largely associated with the following terms: glycoprotein, extracellular region, disulfide bond, cell cycle and extracellular matrix. Moreover, some of the annotated genes could be grouped into 3 specific signaling pathways: focal adhesion, PPAR signaling and ECM-receptor interaction. We discuss the relationship between the observed gene expression profiles and PrPSc deposition and the potential involvement in the pathogenesis of scrapie of 7 specific differentially expressed genes whose expression levels were confirmed by real time-PCR.

CONCLUSIONS

The present findings identify new genes that may be involved in the pathogenesis of natural scrapie infection in the lymphoreticular system, and confirm previous reports describing scrapie-induced alterations in the expression of genes involved in protein misfolding, angiogenesis and the oxidative stress response. Further studies will be necessary to determine the role of these genes in prion replication, dissemination and in the response of the organism to this disease.

Perineuronal nets and GABAergic cells in the inferior colliculus of guinea pigs

Perineuronal nets (PNs) are aggregates of extracellular matrix that have been associated with neuronal plasticity, critical periods, fast-spiking cells and protection from oxidative stress. Although PNs have been reported in the auditory system in several species, there is disagreement about the distribution of PNs within the inferior colliculus (IC), an important auditory hub in the midbrain. Furthermore, PNs in many brain areas are preferentially associated with GABAergic cells, but whether such an association exists in the IC has not been addressed. We used Wisteria floribunda agglutinin staining and immunohistochemistry in guinea pigs to examine PNs within the IC. PNs are present in all IC subdivisions and are densest in the central portions of the IC. Throughout the IC, PNs are preferentially associated with GABAergic cells. Not all GABAergic cells are surrounded by PNs, so the presence of PNs can be used to subdivide IC GABAergic cells into “netted” and “non-netted” categories. Finally, PNs in the IC, like those in other brain areas, display molecular heterogeneity that suggests a multitude of functions.

Adolescent binge ethanol treatment alters adult brain regional volumes, cortical extracellular matrix protein and behavioral flexibility

Adolescents binge drink more than any other age group, increasing risk of disrupting the development of the frontal cortex. We hypothesized that adolescent binge drinking would lead to persistent alterations in adulthood. In this study, we modeled adolescent weekend underage binge-drinking, using adolescent mice (post-natal days [P] 28-37). The adolescent intermittent binge ethanol (AIE) treatment includes 6 binge intragastric doses of ethanol in an intermittent pattern across adolescence. Assessments were conducted in adulthood following extended abstinence to determine if there were persistent changes in adults. Reversal learning, open field and other behavioral assessments as well as brain structure using magnetic imaging and immunohistochemistry were determined. We found that AIE did not impact adult Barnes Maze learning. However, AIE did cause reversal learning deficits in adults. AIE also caused structural changes in the adult brain. AIE was associated with adulthood volume enlargements in specific brain regions without changes in total brain volume. Enlarged regions included the orbitofrontal cortex (OFC, 4%), cerebellum (4.5%), thalamus (2%), internal capsule (10%) and genu of the corpus callosum (7%). The enlarged OFC volume in adults after AIE is consistent with previous imaging studies in human adolescents. AIE treatment was associated with significant increases in the expression of several extracellular matrix (ECM) proteins in the adult OFC including WFA (55%), Brevican (32%), Neurocan (105%), Tenacin-C (25%), and HABP (5%). These findings are consistent with AIE causing persistent changes in brain structure that could contribute to a lack of behavioral flexibility.

ADAMTS1, ADAMTS5, ADAMTS9 and aggrecanase-generated proteoglycan fragments are induced following spinal cord injury in mouse

ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) proteinases are involved in a variety of biological processes such as angiogenesis, cancer and arthritis. ADAMTSs appears to be responsible for the cleavage of proteoglycans in several tissues including brain and cartilage. Chondroitin sulfate proteoglycans (CSPGs) maintains the integrity of the brain extracellular matrix and major inhibitory contributors for glial scar and neural plasticity. The activity of aggrecanases in the central nervous system (CNS) has been reported. ADAMTSs are an enzyme degrading CSPGs in the brain. However, there is a little knowledge regarding ADAMTSs in the CNS. We investigated the expression levels of ADAMTSs mRNAs by RT-PCR after spinal cord injury in mouse. Transcripts encoding 4 of the 19 known ADAMTSs were evaluated in the mouse spinal cord following injury. ADAMTS1, -5 and -9 expression levels were found to be upregulated. No change was observed in ADAMTS4 expression. By means of immunohistochemistry, ADAMTSs were detected in the astrocytes implying its cellular source in SCI. Western blot analyses indicated that aggrecanase-generated proteoglycan fragments are produced after SCI.

Hyaluronic acid-based scaffold for central neural tissue engineering

Central nervous system (CNS) regeneration with central neuronal connections and restoration of synaptic connections has been a long-standing worldwide problem and, to date, no effective clinical therapies are widely accepted for CNS injuries. The limited regenerative capacity of the CNS results from the growth-inhibitory environment that impedes the regrowth of axons. Central neural tissue engineering has attracted extensive attention from multi-disciplinary scientists in recent years, and many studies have been carried out to develop cell- and regeneration-activating biomaterial scaffolds that create an artificial micro-environment suitable for axonal regeneration. Among all the biomaterials, hyaluronic acid (HA) is a promising candidate for central neural tissue engineering because of its unique physico-chemical and biological properties. This review attempts to outline current biomaterials-based strategies for CNS regeneration from a tissue engineering point of view and discusses the main progresses in research of HA-based scaffolds for central neural tissue engineering in detail.

Gene expression profiling and association with prion-related lesions in the medulla oblongata of symptomatic natural scrapie animals

The pathogenesis of natural scrapie and other prion diseases remains unclear. Examining transcriptome variations in infected versus control animals may highlight new genes potentially involved in some of the molecular mechanisms of prion-induced pathology. The aim of this work was to identify disease-associated alterations in the gene expression profiles of the caudal medulla oblongata (MO) in sheep presenting the symptomatic phase of natural scrapie. The gene expression patterns in the MO from 7 sheep that had been naturally infected with scrapie were compared with 6 controls using a Central Veterinary Institute (CVI) custom designed 4×44K microarray. The microarray consisted of a probe set on the previously sequenced ovine tissue library by CVI and was supplemented with all of the Ovis aries transcripts that are currently publicly available. Over 350 probe sets displayed greater than 2-fold changes in expression. We identified 148 genes from these probes, many of which encode proteins that are involved in the immune response, ion transport, cell adhesion, and transcription. Our results confirm previously published gene expression changes that were observed in murine models with induced scrapie. Moreover, we have identified new genes that exhibit differential expression in scrapie and could be involved in prion neuropathology. Finally, we have investigated the relationship between gene expression profiles and the appearance of the main scrapie-related lesions, including prion protein deposition, gliosis and spongiosis. In this context, the potential impacts of these gene expression changes in the MO on scrapie development are discussed.