Contributions of astrocytes to synapse formation and maturation - Potential functions of the perisynaptic extracellular matrix

Integrity of neural extracellular matrix is required for microglia-mediated synaptic remodeling

Microglia continuously remodel synapses, which are embedded in the extracellular matrix (ECM). However, the mechanisms, which govern this process remain elusive. To investigate the influence of the neural ECM in synaptic remodeling by microglia, we disrupted ECM integrity by injection of chondroitinase ABC (ChABC) into the retrosplenial cortex of healthy adult mice. Using in vivo two-photon microscopy we found that ChABC treatment increased microglial branching complexity and ECM phagocytic capacity and decreased spine elimination rate under basal conditions. Moreover, ECM attenuation largely prevented synaptic remodeling following synaptic stress induced by photodamage of single synaptic elements. These changes were associated with less stable and smaller microglial contacts at the synaptic damage sites, diminished deposition of calreticulin and complement proteins C1q and C3 at synapses and impaired expression of microglial CR3 receptor. Thus, our findings provide novel insights into the function of the neural ECM in deposition of complement proteins and synaptic remodeling by microglia.

A disinhibitory microcircuit of the orbitofrontal cortex mediates cocaine preference in mice

Both clinical and animal studies showed that the impaired functions of the orbitofrontal cortex (OFC) underlie the compulsive drug-seeking behavior of drug addiction. However, the functional changes of the microcircuit in the OFC and the underlying molecular mechanisms in drug addiction remain elusive, and little is known for whether microcircuits in the OFC contributed to drug addiction-related behaviors. Utilizing the cocaine-induced conditioned-place preference model, we found that the malfunction of the microcircuit led to disinhibition in the OFC after cocaine withdrawal. We further showed that enhanced Somatostatin-Parvalbumin (SST-PV) inhibitory synapse strength changed microcircuit function, and SST and PV inhibitory neurons showed opposite contributions to the drug addiction-related behavior of mice. Brevican of the perineuronal nets of PV neurons regulated SST-PV synapse strength, and the knockdown of Brevican alleviated cocaine preference. These results reveal a novel molecular mechanism of the regulation of microcircuit function and a novel circuit mechanism of the OFC in gating cocaine preference.

Perineuronal nets as regulators of parvalbumin interneuron function: Factors implicated in their formation and degradation

The brain extracellular matrix (ECM) has garnered increasing attention as a fundamental component of brain function in a predominantly "neuron-centric" paradigm. Particularly, the perineuronal nets (PNNs), a specialized net-like structure formed by ECM aggregates, play significant roles in brain development and physiology. PNNs enwrap synaptic junctions in various brain regions, precisely balancing new synaptic formation and long-term stabilization, and are highly dynamic entities that change in response to environmental stimuli, especially during the neurodevelopmental period. They are found mainly surrounding parvalbumin (PV)-expressing GABAergic interneurons, being proposed to promote PV interneuron maturation and protect them against oxidative stress and neurotoxic agents. This structural and functional proximity underscores the crucial role of PNNs in modulating PV interneuron function, which is critical for the excitatory/inhibitory balance and, consequently, higher-level behaviours. This review delves into the molecular underpinnings governing PNNs formation and degradation, elucidating their functional interactions with PV interneurons. In the broader physiological context and brain-related disorders, we also explore their intricate relationship with other molecules, such as reactive oxygen species and metalloproteinases, as well as glial cells. Additionally, we discuss potential therapeutic strategies for modulating PNNs in brain disorders.

Astrocytic GABAergic Regulation in Alcohol Use and Major Depressive Disorders

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). Most GABAergic neurons synthesize GABA from glutamate and release it in the synaptic cleft in the CNS. However, astrocytes can also synthesize and release GABA, activating GABA receptors in the neighboring neurons in physiological and pathological conditions. As the primary homeostatic glial cells in the brain, astrocytes play a crucial role in regulating GABA homeostasis and synaptic neurotransmission. Accumulating evidence demonstrates that astrocytic GABA dysregulation is implicated in psychiatric disorders, including alcohol use disorder (AUD) and major depressive disorder (MDD), the most prevalent co-occurring psychiatric disorders. Several current medications and emerging pharmacological agents targeting GABA levels are in clinical trials for treating AUD and MDD. This review offers a concise summary of the role of astrocytic GABA regulation in AUD and MDD. We also provide an overview of the current understanding and areas of debate regarding the mechanisms by which astrocytes regulate GABA in the CNS and their potential significance in the molecular basis of AUD and MDD, paving the way toward future research directions and potential therapeutic target areas within this field.

Building a pathway to recovery: Targeting ECM remodeling in CNS injuries

Extracellular matrix (ECM) is a complex and dynamic network of proteoglycans, proteins, and other macromolecules that surrounds cells in tissues. The ECM provides structural support to cells and plays a critical role in regulating various cellular functions. ECM remodeling is a dynamic process involving the breakdown and reconstruction of the ECM. This process occurs naturally during tissue growth, wound healing, and tissue repair. However, in the context of central nervous system (CNS) injuries, dysregulated ECM remodeling can lead to the formation of fibrotic and glial scars. CNS injuries encompass various traumatic events, including concussions and fractures. Following CNS trauma, the formation of glial and fibrotic scars becomes prominent. Glial scars primarily consist of reactive astrocytes, while fibrotic scars are characterized by an abundance of ECM proteins. ECM remodeling plays a pivotal and tightly regulated role in the development of these scars after spinal cord and brain injuries. Various factors like ECM components, ECM remodeling enzymes, cell surface receptors of ECM molecules, and downstream pathways of ECM molecules are responsible for the remodeling of the ECM. The aim of this review article is to explore the changes in ECM during normal physiological conditions and following CNS injuries. Additionally, we discuss various approaches that target various factors responsible for ECM remodeling, with a focus on promoting axon regeneration and functional recovery after CNS injuries. By targeting ECM remodeling, it may be possible to enhance axonal regeneration and facilitate functional recovery after CNS injuries.

ADAR1 suppression causes interferon signaling and transposable element transcript accumulation in human astrocytes

Neuroinflammation is a central mechanism of brain aging and Alzheimer's disease (AD), but the exact causes of age- and AD-related neuroinflammation are incompletely understood. One potential modulator of neuroinflammation is the enzyme adenosine deaminase acting on RNA 1 (ADAR1), which regulates the accumulation of endogenous double-stranded RNA (dsRNA), a pro-inflammatory/innate immune activator. However, the role of ADAR1 and its transcriptomic targets in astrocytes, key mediators of neuroinflammation, have not been comprehensively investigated. Here, we knock down ADAR1 in primary human astrocytes via siRNA transfection and use transcriptomics (RNA-seq) to show that this results in: (1) increased expression of type I interferon and pro-inflammatory signaling pathways and (2) an accumulation of transposable element (TE) transcripts with the potential to form dsRNA. We also show that our findings may be clinically relevant, as ADAR1 gene expression declines with brain aging and AD in humans, and this is associated with a similar increase in TE transcripts. Together, our results suggest an important role for ADAR1 in preventing pro-inflammatory activation of astrocytes in response to endogenous dsRNA with aging and AD.

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.

Regulation of the E/I-balance by the neural matrisome

In the mammalian cortex a proper excitatory/inhibitory (E/I) balance is fundamental for cognitive functions. Especially γ-aminobutyric acid (GABA)-releasing interneurons regulate the activity of excitatory projection neurons which form the second main class of neurons in the cortex. During development, the maturation of fast-spiking parvalbumin-expressing interneurons goes along with the formation of net-like structures covering their soma and proximal dendrites. These so-called perineuronal nets (PNNs) represent a specialized form of the extracellular matrix (ECM, also designated as matrisome) that stabilize structural synapses but prevent the formation of new connections. Consequently, PNNs are highly involved in the regulation of the synaptic balance. Previous studies revealed that the formation of perineuronal nets is accompanied by an establishment of mature neuronal circuits and by a closure of critical windows of synaptic plasticity. Furthermore, it has been shown that PNNs differentially impinge the integrity of excitatory and inhibitory synapses. In various neurological and neuropsychiatric disorders alterations of PNNs were described and aroused more attention in the last years. The following review gives an update about the role of PNNs for the maturation of parvalbumin-expressing interneurons and summarizes recent findings about the impact of PNNs in different neurological and neuropsychiatric disorders like schizophrenia or epilepsy. A targeted manipulation of PNNs might provide an interesting new possibility to indirectly modulate the synaptic balance and the E/I ratio in pathological conditions.

3D biocomposite culture enhances differentiation of dopamine-like neurons from SH-SY5Y cells: A model for studying Parkinson's disease phenotypes

Studies of underlying neurodegenerative processes in Parkinson's Disease (PD) have traditionally utilized cell cultures grown on two-dimensional (2D) surfaces. Biomimetic three-dimensional (3D) cell culture platforms have been developed to better emulate features of the brain's natural microenvironment. We here use our bioengineered brain-like tissue model, composed of a silk-hydrogel composite, to study the 3D microenvironment's contributions on the development and performance of dopaminergic-like neurons (DLNs). Compared with 2D culture, SH-SY5Y cells differentiated in 3D microenvironments were enriched for DLNs concomitant with a reduction in proliferative capacity during the neurodevelopmental process. Additionally, the 3D DLN cultures were more sensitive to oxidative stresses elicited by the PD-related neurotoxin 1-methyl-4-phenylpyridinium (MPP). MPP induced transcriptomic profile changes specific to 3D-differentiated DLN cultures, replicating the dysfunction of neuronal signaling pathways and mitochondrial dynamics implicated in PD. Overall, this physiologically-relevant 3D platform resembles a useful tool for studying dopamine neuron biology and interrogating molecular mechanisms underlying neurodegeneration in PD.

Connexins Signatures of the Neurovascular Unit and Their Physio-Pathological Functions

Central nervous system (CNS) homeostasis is closely linked to the delicate balance of the microenvironment in which different cellular components of the neurovascular unit (NVU) coexist. Intercellular communication plays a pivotal role in exchanges of signaling molecules and mediators essential for survival functions, as well as in the removal of disturbing elements that can lead to related pathologies. The specific signatures of connexins (Cxs), proteins which form either gap junctions (GJs) or hemichannels (HCs), represent the biological substrate of the pathophysiological balance. Connexin 43 (Cx43) is undoubtedly one of the most important factors in glia–neuro–vascular crosstalk. Herein, Cxs signatures of every NVU component are highlighted and their critical influence on functional processes in healthy and pathological conditions of nervous microenvironment is reviewed.

Role of Perineuronal nets in the cerebellar cortex in cocaine-induced conditioned preference, extinction, and reinstatement

Perineuronal nets (PNNs) are cartilage-like structures of extracellular matrix molecules that enwrap in a net-like manner the cell-body and proximal dendrites of special subsets of neurons. PNNs stabilize their incoming connections and restrict plasticity. Consequently, they have been proposed as a candidate mechanism for drug-induced learning and memory. In the cerebellum, PNNs surround Golgi inhibitory interneurons and both inhibitory and excitatory neurons in the deep cerebellar nuclei (DCN). Previous studies from the lab showed that cocaine-induced conditioned memory increased PNN expression in the granule cell layer of the posterior vermis. The present research aimed to investigate the role of cerebellar PNNs in cocaine-induced conditioned preference. For this purpose, we use the enzyme chondroitinase ABC (ChABC) to digest PNNs at different time points of the learning process to ascertain whether their removal can affect drug-induced memory. Our results show that PNN digestion using ChABC in the posterior vermis (Lobule VIII) did not affect the acquisition of cocaine-induced conditioned preference. However, the removal of PNNs in Lobule VIII -but not in the DCN- disrupted short-term memory of conditioned preference. Moreover, although PNN digestion facilitated the formation of extinction, reinstatement of cocaine-induced conditioned preference was encouraged under PNN digestion. The present findings suggests that PNNs around Golgi interneurons are needed to maintain cocaine-induced Pavlovian memory but also to stabilize extinction memory. Conversely, PNN degradation within the DCN did not affect stability of cocaine-induced memories. Therefore, degradation of PNNs in the vermis might be used as a promising tool to manipulate drug-induced memory.

Chondroitin Sulphate Proteoglycan Axonal Coats in the Human Mediodorsal Thalamic Nucleus

Mounting evidence supports a key involvement of the chondroitin sulfate proteoglycans (CSPGs) NG2 and brevican (BCAN) in the regulation of axonal functions, including axon guidance, fasciculation, conductance, and myelination. Prior work suggested the possibility that these functions may, at least in part, be carried out by specialized CSPG structures surrounding axons, termed axonal coats. However, their existence remains controversial. We tested the hypothesis that NG2 and BCAN, known to be associated with oligodendrocyte precursor cells, form axonal coats enveloping myelinated axons in the human brain. In tissue blocks containing the mediodorsal thalamic nucleus (MD) from healthy donors (n = 5), we used dual immunofluorescence, confocal microscopy, and unbiased stereology to characterize BCAN and NG2 immunoreactive (IR) axonal coats and measure the percentage of myelinated axons associated with them. In a subset of donors (n = 3), we used electron microscopy to analyze the spatial relationship between axons and NG2- and BCAN-IR axonal coats within the human MD. Our results show that a substantial percentage (∼64%) of large and medium myelinated axons in the human MD are surrounded by NG2- and BCAN-IR axonal coats. Electron microscopy studies show NG2- and BCAN-IR axonal coats are interleaved with myelin sheets, with larger axons displaying greater association with axonal coats. These findings represent the first characterization of NG2 and BCAN axonal coats in the human brain. The large percentage of axons surrounded by CSPG coats, and the role of CSPGs in axonal guidance, fasciculation, conductance, and myelination suggest that these structures may contribute to several key axonal properties.

Astrocyte depletion alters extracellular matrix composition in the demyelinating phase of Theiler's murine encephalomyelitis

Astrocytes produce extracellular matrix (ECM) glycoproteins contributing to the blood-brain barrier and regulating the immune response in the central nervous system (CNS). The aim of this study was to investigate the impact of astrocyte depletion upon the clinical outcome and the composition of ECM glycoproteins in a virus-induced animal model of demyelination. Glial fibrillary acidic protein (GFAP)-thymidine-kinase transgenic SJL (GFAP-knockout) and wildtype mice were infected with Theiler’s murine encephalomyelitis virus (TMEV). Astrocyte depletion was induced during the progressive, demyelinating disease phase by ganciclovir administration once daily between 56 and 77 days post infection (dpi). At 77 dpi GFAP-knockout mice showed a significant deterioration of clinical signs associated with a reduction of azan and picrosirius red stained ECM-molecules in the thoracic spinal cord. Basement-membrane-associated ECM-molecules including laminin, entactin/nidogen-1 and Kir4.1 as well as non-basement membrane-associated ECM-molecules like collagen I, decorin, tenascin-R and CD44 were significantly reduced in the spinal cord of GFAP-knockout mice. The reduction of the investigated ECM-molecules demonstrates that astrocytes play a key role in the production of ECM-molecules. The present findings indicate that the detected loss of Kir4.1 and CD44 as well as the disruption of the integrity of perineuronal nets led to the deterioration of clinical signs in GFAP-knockout mice.

Brevican, Neurocan, Tenascin-C, and Tenascin-R Act as Important Regulators of the Interplay Between Perineuronal Nets, Synaptic Integrity, Inhibitory Interneurons, and Otx2

Fast-spiking parvalbumin interneurons are critical for the function of mature cortical inhibitory circuits. Most of these neurons are enwrapped by a specialized extracellular matrix (ECM) structure called perineuronal net (PNN), which can regulate their synaptic input. In this study, we investigated the relationship between PNNs, parvalbumin interneurons, and synaptic distribution on these cells in the adult primary visual cortex (V1) of quadruple knockout mice deficient for the ECM molecules brevican, neurocan, tenascin-C, and tenascin-R. We used super-resolution structured illumination microscopy (SIM) to analyze PNN structure and associated synapses. In addition, we examined parvalbumin and calretinin interneuron populations. We observed a reduction in the number of PNN-enwrapped cells and clear disorganization of the PNN structure in the quadruple knockout V1. This was accompanied by an imbalance of inhibitory and excitatory synapses with a reduction of inhibitory and an increase of excitatory synaptic elements along the PNNs. Furthermore, the number of parvalbumin interneurons was reduced in the quadruple knockout, while calretinin interneurons, which do not wear PNNs, did not display differences in number. Interestingly, we found the transcription factor Otx2 homeoprotein positive cell population also reduced. Otx2 is crucial for parvalbumin interneuron and PNN maturation, and a positive feedback loop between these parameters has been described. Collectively, these data indicate an important role of brevican, neurocan, tenascin-C, and tenascin-R in regulating the interplay between PNNs, inhibitory interneurons, synaptic distribution, and Otx2 in the V1.

Neonatal Rat Glia Cultured in Physiological Normoxia for Modeling Neuropathological Conditions In Vitro

Cell culture conditions were proven to highly affect crucial biological processes like proliferation, differentiation, intercellular crosstalk, and senescence. Oxygen tension is one of the major factors influencing cell metabolism and thus, modulating cellular response to pathophysiological conditions. In this context, the presented study aimed at the development of a protocol for efficient culture of rat neonatal glial cells (microglia, astrocytes, and oligodendrocytes) in oxygen concentrations relevant to the nervous tissue. The protocol allows for obtaining three major cell populations, which play crucial roles in sustaining tissue homeostasis and are known to be activated in response to a wide spectrum of external stimuli. The cells are cultured in media without supplement addition to avoid potential modulation of cell processes. The application of active biomolecules for coating culturing surfaces might be useful for mirroring physiological cell interactions with extracellular matrix components. The cell fractions can be assembled as cocultures to further evaluate investigated mechanisms, intercellular crosstalk, or cell response to tested pharmacological compounds. Applying additional procedures, like transient oxygen and glucose deprivation, allows to mimic in vitro the selected pathophysiological conditions. The presented culture system for neonatal rat glial cells is a highly useful tool for in vitro modeling selected neuropathological conditions.

Memristive Circuit Implementation of a Self-Repairing Network Based on Biological Astrocytes in Robot Application

A large number of studies have shown that astrocytes can be combined with the presynaptic terminals and postsynaptic spines of neurons to constitute a triple synapse via an endocannabinoid retrograde messenger to achieve a self-repair ability in the human brain. Inspired by the biological self-repair mechanism of astrocytes, this work proposes a self-repairing neuron network circuit that utilizes a memristor to simulate changes in neurotransmitters when a set threshold is reached. The proposed circuit simulates an astrocyte-neuron network and comprises the following: 1) a single-astrocyte-neuron circuit module; 2) an astrocyte-neuron network circuit; 3) a module to detect malfunctions; and 4) a neuron PR (release probability of synaptic transmission) enhancement module. When faults occur in a synapse, the neuron module becomes silent or near silent because of the low PR of the synapses. The circuit can detect faults automatically. The damaged neuron can be repaired by enhancing the PR of other healthy neurons, analogous to the biological repair mechanism of astrocytes. This mechanism helps to repair the damaged circuit. A simulation of the circuit revealed the following: 1) as the number of neurons in the circuit increases, the self-repair ability strengthens and 2) as the number of damaged neurons in the astrocyte-neuron network increases, the self-repair ability weakens, and there is a significant degradation in the performance of the circuit. The self-repairing circuit was used for a robot, and it effectively improved the robots' performance and reliability.

Neurocan regulates vulnerability to stress and the anti-depressant effect of ketamine in adolescent rats

Depression is more prevalent among adolescents than adults, but the underlying mechanisms remain largely unknown. Using a subthreshold chronic stress model, here we show that developmentally regulated expressions of the perineuronal nets (PNNs), and one of the components, Neurocan in the prelimbic cortex (PrL) are important for the vulnerability to stress and depressive-like behaviors in both adolescent and adult rats. Reduction of PNNs or Neurocan with pharmacological or viral methods to mimic the expression of PNNs in the PrL during adolescence compromised resilience to stress in adult rats, while virally mediated overexpression of Neurocan reversed vulnerability to stress in adolescent rats. Ketamine, a recent-approved drug for treatment-resistant depression rescued impaired function of Parvalbumin-positive neurons function, increased expression of PNNs in the PrL, and reversed depressive-like behaviors in adolescent rats. Furthermore, we show that Neurocan mediates the anti-depressant effect of ketamine, virally mediated reduction of Neurocan in the PrL abolished the anti-depressant effect of ketamine in adolescent rats. Our findings show an important role of Neurocan in depression in adolescence, and suggest a novel mechanism for the anti-depressant effect of ketamine.

Vav3-Deficient Astrocytes Enhance the Dendritic Development of Hippocampal Neurons in an Indirect Co-culture System

Vav proteins belong to the class of guanine nucleotide exchange factors (GEFs) that catalyze the exchange of guanosine diphosphate (GDP) by guanosine triphosphate (GTP) on their target proteins. Here, especially the members of the small GTPase family, Ras homolog family member A (RhoA), Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 homolog (Cdc42) can be brought into an activated state by the catalytic activity of Vav-GEFs. In the central nervous system (CNS) of rodents Vav3 shows the strongest expression pattern in comparison to Vav2 and Vav1, which is restricted to the hematopoietic system. Several studies revealed an important role of Vav3 for the elongation and branching of neurites. However, little is known about the function of Vav3 for other cell types of the CNS, like astrocytes. Therefore, the following study analyzed the effects of a Vav3 knockout on several astrocytic parameters as well as the influence of Vav3-deficient astrocytes on the dendritic development of cultured neurons. For this purpose, an indirect co-culture system of native hippocampal neurons and Vav3-deficient cortical astrocytes was used. Interestingly, neurons cultured in an indirect contact with Vav3-deficient astrocytes showed a significant increase in the dendritic complexity and length after 12 and 17 days in vitro (DIV). Furthermore, Vav3-deficient astrocytes showed an enhanced regeneration in the scratch wound heal assay as well as an altered profile of released cytokines with a complete lack of CXCL11, reduced levels of IL-6 and an increased release of CCL5. Based on these observations, we suppose that Vav3 plays an important role for the development of dendrites by regulating the expression and the release of neurotrophic factors and cytokines in astrocytes.

Microglia as hackers of the matrix: sculpting synapses and the extracellular space

Microglia shape the synaptic environment in health and disease, but synapses do not exist in a vacuum. Instead, pre- and postsynaptic terminals are surrounded by extracellular matrix (ECM), which together with glia comprise the four elements of the contemporary tetrapartite synapse model. While research in this area is still just beginning, accumulating evidence points toward a novel role for microglia in regulating the ECM during normal brain homeostasis, and such processes may, in turn, become dysfunctional in disease. As it relates to synapses, microglia are reported to modify the perisynaptic matrix, which is the diffuse matrix that surrounds dendritic and axonal terminals, as well as perineuronal nets (PNNs), specialized reticular formations of compact ECM that enwrap neuronal subsets and stabilize proximal synapses. The interconnected relationship between synapses and the ECM in which they are embedded suggests that alterations in one structure necessarily affect the dynamics of the other, and microglia may need to sculpt the matrix to modify the synapses within. Here, we provide an overview of the microglial regulation of synapses, perisynaptic matrix, and PNNs, propose candidate mechanisms by which these structures may be modified, and present the implications of such modifications in normal brain homeostasis and in disease.

Parvalbumin Interneurons and Perineuronal Nets in the Hippocampus and Retrosplenial Cortex of Adult Male Mice After Early Social Isolation Stress and Perinatal NMDA Receptor Antagonist Treatment

Both early life aversive experiences and intrinsic alterations in early postnatal neurodevelopment are considered predisposing factors for psychiatric disorders, such as schizophrenia. The prefrontal cortex and the hippocampus have protracted postnatal development and are affected in schizophrenic patients. Interestingly, similar alterations have been observed in the retrosplenial cortex (RSC). Studies in patients and animal models of schizophrenia have found alterations in cortical parvalbumin (PV) expressing interneurons, making them good candidates to study the etiopathology of this disorder. Some of the alterations observed in PV+ interneurons may be mediated by perineuronal nets (PNNs), specialized regions of the extracellular matrix, which frequently surround these inhibitory neurons. In this study, we have used a double hit model (DHM) combining a single perinatal injection of an NMDAR antagonist (MK801) to disturb early postnatal development and post-weaning social isolation as an early life aversive experience. We have investigated PV expressing interneurons and PNNs in the hippocampus and the RSC of adult male mice, using unbiased stereology. In the CA1, but not in the CA3 region, of the hippocampus, the number of PNNs and PV + PNN+ cells was affected by the drug treatment, and a significant decrease of these parameters was observed in the groups of animals that received MK801. The percentage of PNNs surrounding PV+ cells was significantly decreased after treatment in both hippocampal regions; however, the impact of isolation was observed only in CA1, where isolated animals presented lower percentages. In the RSC, we observed significant effects of isolation, MK801 and the interaction of both interventions on the studied parameters; in the DHM, we observed a significantly lower number of PV+, PNNs, and PV+PNN+cells when compared to control mice. Similar significant decreases were observed for the groups of animals that were just isolated or treated with MK801. To our knowledge, this is the first report on such alterations in the RSC in an animal model combining neurodevelopmental alterations and aversive experiences during infancy/adolescence. These results show the impact of early-life events on different cortical regions, especially on the structure and plasticity of PV+ neurons and their involvement in the emergence of certain psychiatric disorders.

Parallels between the extracellular matrix roles in developmental biology and cancer biology

Interaction of a tumor with its microenvironment is an emerging field of investigation, and the crosstalk between cancer cells and the extracellular matrix is of particular interest, since cancer patients with abundant and stiff extracellular matrices display a poorer prognosis. At the post-juvenile stage, the extracellular matrix plays predominantly a structural role by providing support to cells and tissues; however, during development, matrix proteins exert a plethora of diverse signals to guide the movement and determine the fate of pluripotent cells. Taking a closer look at the communication between the extracellular matrix and cells of a developing body may bring new insights into cancer biology and identify cancer weaknesses. This review discusses parallels between the extracellular matrix roles during development and tumor growth.

Engineering 3D Cortical Spheroids for an In Vitro Ischemic Stroke Model

Three-dimensional (3D) spheroids composed of brain cells have shown great potential to mimic the pathophysiology of the brain. However, a 3D spheroidal brain-disease model for cerebral ischemia has not been reported. This study investigated an ultralow attachment (ULA) surface-mediated formation of 3D cortical spheroids using primary rat cortical cells to recapitulate the cerebral ischemic responses in stroke by oxygen-glucose deprivation-reoxygenation (OGD-R) treatment. Comparison between two-dimensional (2D) and 3D cell culture models confirmed the better performance of the 3D cortical spheroids as normal brain models. The cortical cells cultured in 3D maintained their healthy physiological morphology of a less activated state and suppressed mRNA expressions of pathological stroke markers, S100B, IL-1β, and MBP, selected based on in vivo stroke model. Interestingly, the spheroids formed on the ULA surface exhibited striking aggregation dynamics involving active cell-substrate interactions, whereas those formed on the agarose surface aggregated passively by the convective flow of the media. Accordingly, ULA spheroids manifested a layered arrangement of neurons and astrocytes with higher expressions of integrin β1, integrin α5, N-cadherin, and fibronectin than the agarose spheroids. OGD-R-induced stroke model of the ULA spheroids successfully mimicked the ischemic response as evidenced by the upregulated mRNA expressions of the key markers for stroke, S100B, IL-1β, and MBP. Our study suggested that structurally and functionally distinct cortical spheroids could be generated by simply tuning the cell-substrate binding activities during dynamic spheroidal formation, which should be an essential factor to consider in establishing a brain-disease model.

Role of glucose 6-phosphate dehydrogenase (G6PD) deficiency and its association to Autism Spectrum Disorders

Autism Spectrum Disorder (ASD) is a common group of neurodevelopmental disorders which causes significant alterations in social and communication skills along with repetitive behavior and limited interests. The physiological understanding of ASD is ambiguous. Several reports suggested that environmental, genetic and epigenetic changes, neuroinflammation, mitochondrial dysfunction and metabolic alterations orchestrate the pathological outcomes of ASD. A recent report from Saudi Arabia found a mutation in X-chromosomal housekeeping glucose 6-phosphate dehydrogenase (G6PD) gene in two male ASD patients. Although, the involvement of G6PD-deficiency in the pathogenesis of ASD is poorly understood. Several reports suggested that G6PD deficiency impedes cellular detoxification of reactive oxygen species (ROS), which may result in neuronal damage and neuroinflammation. A deficiency of G6PD in newborn children may play a fundamental role in the pathogenesis of ASD. In this review, we will discuss the implications of G6PD deficiency in pathogenesis, male biasness and theranostics in ASD patients.

Engineering in vitro human neural tissue analogs by 3D bioprinting and electrostimulation

There is a fundamental need for clinically relevant, reproducible, and standardized in vitro human neural tissue models, not least of all to study heterogenic and complex human-specific neurological (such as neuropsychiatric) disorders. Construction of three-dimensional (3D) bioprinted neural tissues from native human-derived stem cells (e.g., neural stem cells) and human pluripotent stem cells (e.g., induced pluripotent) in particular is appreciably impacting research and conceivably clinical translation. Given the ability to artificially and favorably regulate a cell's survival and behavior by manipulating its biophysical environment, careful consideration of the printing technique, supporting biomaterial and specific exogenously delivered stimuli, is both required and advantageous. By doing so, there exists an opportunity, more than ever before, to engineer advanced and precise tissue analogs that closely recapitulate the morphological and functional elements of natural tissues (healthy or diseased). Importantly, the application of electrical stimulation as a method of enhancing printed tissue development in vitro, including neuritogenesis, synaptogenesis, and cellular maturation, has the added advantage of modeling both traditional and new stimulation platforms, toward improved understanding of efficacy and innovative electroceutical development and application.

Review of Design Considerations for Brain-on-a-Chip Models

In recent years, the need for sophisticated human in vitro models for integrative biology has motivated the development of organ-on-a-chip platforms. Organ-on-a-chip devices are engineered to mimic the mechanical, biochemical and physiological properties of human organs; however, there are many important considerations when selecting or designing an appropriate device for investigating a specific scientific question. Building microfluidic Brain-on-a-Chip (BoC) models from the ground-up will allow for research questions to be answered more thoroughly in the brain research field, but the design of these devices requires several choices to be made throughout the design development phase. These considerations include the cell types, extracellular matrix (ECM) material(s), and perfusion/flow considerations. Choices made early in the design cycle will dictate the limitations of the device and influence the end-point results such as the permeability of the endothelial cell monolayer, and the expression of cell type-specific markers. To better understand why the engineering aspects of a microfluidic BoC need to be influenced by the desired biological environment, recent progress in microfluidic BoC technology is compared. This review focuses on perfusable blood-brain barrier (BBB) and neurovascular unit (NVU) models with discussions about the chip architecture, the ECM used, and how they relate to the in vivo human brain. With increased knowledge on how to make informed choices when selecting or designing BoC models, the scientific community will benefit from shorter development phases and platforms curated for their application.

Cell type-specific changes in transcriptomic profiles of endothelial cells, iPSC-derived neurons and astrocytes cultured on microfluidic chips

In vitro neuronal models are essential for studying neurological physiology, disease mechanisms and potential treatments. Most in vitro models lack controlled vasculature, despite its necessity in brain physiology and disease. Organ-on-chip models offer microfluidic culture systems with dedicated micro-compartments for neurons and vascular cells. Such multi-cell type organs-on-chips can emulate neurovascular unit (NVU) physiology, however there is a lack of systematic data on how individual cell types are affected by culturing on microfluidic systems versus conventional culture plates. This information can provide perspective on initial findings of studies using organs-on-chip models, and further optimizes these models in terms of cellular maturity and neurovascular physiology. Here, we analysed the transcriptomic profiles of co-cultures of human induced pluripotent stem cell (hiPSC)-derived neurons and rat astrocytes, as well as one-day monocultures of human endothelial cells, cultured on microfluidic chips. For each cell type, large gene expression changes were observed when cultured on microfluidic chips compared to conventional culture plates. Endothelial cells showed decreased cell division, neurons and astrocytes exhibited increased cell adhesion, and neurons showed increased maturity when cultured on a microfluidic chip. Our results demonstrate that culturing NVU cell types on microfluidic chips changes their gene expression profiles, presumably due to distinct surface-to-volume ratios and substrate materials. These findings inform further NVU organ-on-chip model optimization and support their future application in disease studies and drug testing.

Brain-derived neurotrophic factor protects against acrylamide-induced neuronal and synaptic injury via the TrkB-MAPK-Erk1/2 pathway

Acrylamide has been shown to be neurotoxic. Brain-derived neurotrophic factor (BDNF) can alleviate acrylamide-induced synaptic injury; however, the underlying mechanism remains unclear. In this study, dibutyryl-cyclic adenosine monophosphate-induced mature human neuroblastoma (NB-1) cells were exposed with 0–100 μg/mL acrylamide for 24–72 hours. Acrylamide decreased cell viability and destroyed synapses. Exposure of co-cultured NB-1 cells and Schwann cells to 0–100 μg/mL acrylamide for 48 hours resulted in upregulated expression of synapsin I and BDNF, suggesting that Schwann cells can activate self-protection of neurons. Under co-culture conditions, activation of the downstream TrkB-MAPK-Erk1/2 pathway strengthened the protective effect. Exogenous BDNF can increase expression of TrkB, Erk1/2, and synapsin I, while exogenous BDNF or the TrkB inhibitor K252a could inhibit these changes. Taken together, Schwann cells may act through the BDNF-TrkB-MAPK-Erk1/2 signaling pathway, indicating that BDNF plays an important role in this process. Therefore, exogenous BDNF may be an effective treatment strategy for acrylamide-induced nerve injury. This study was approved by the Laboratory Animal Welfare and Ethics Committee of the National Institute of Occupational Health and Poison Control, a division of the Chinese Center for Disease Control and Prevention (approval No. EAWE-2017-008) on May 29, 2017.

Extracellular Matrix in Neural Plasticity and Regeneration

The extracellular matrix (ECM) is a fundamental component of biological tissues. The ECM in the central nervous system (CNS) is unique in both composition and function. Functions such as learning, memory, synaptogenesis, and plasticity are regulated by numerous ECM molecules. The neural ECM acts as a non-specific physical barrier that modulates neuronal plasticity and axon regeneration. There are two specialized types of ECM in the CNS, diffuse perisynaptic ECM and condensed ECM, which selectively surround the perikaryon and initial part of dendritic trees in subtypes of neurons, forming perineuronal nets. This review presents the current knowledge about the role of important neuronal ECM molecules in maintaining the basic functions of a neuron, including electrogenesis and the ability to form neural circuits. The review mainly focuses on the role of ECM components that participate in the control of key events such as cell survival, axonal growth, and synaptic remodeling. Particular attention is drawn to the numerous molecular partners of the main ECM components. These regulatory molecules are integrated into the cell membrane or disposed into the matrix itself in solid or soluble form. The interaction of the main matrix components with molecular partners seems essential in molecular mechanisms controlling neuronal functions. Special attention is paid to the chondroitin sulfate proteoglycan 4, type 1 transmembrane protein, neural-glial antigen 2 (NG2/CSPG4), whose cleaved extracellular domain is such a molecular partner that it not only acts directly on neural and vascular cells, but also exerts its influence indirectly by binding to resident ECM molecules.

The enigmatic fetal subplate compartment forms an early tangential cortical nexus and provides the framework for construction of cortical connectivity

The most prominent transient compartment of the primate fetal cortex is the deep, cell-sparse, synapse-containing subplate compartment (SPC). The developmental role of the SPC and its extraordinary size in humans remain enigmatic. This paper evaluates evidence on the development and connectivity of the SPC and discusses its role in the pathogenesis of neurodevelopmental disorders. A synthesis of data shows that the subplate becomes a prominent compartment by its expansion from the deep cortical plate (CP), appearing well-delineated on MR scans and forming a tangential nexus across the hemisphere, consisting of an extracellular matrix, randomly distributed postmigratory neurons, multiple branches of thalamic and long corticocortical axons. The SPC generates early spontaneous non-synaptic and synaptic activity and mediates cortical response upon thalamic stimulation. The subplate nexus provides large-scale interareal connectivity possibly underlying fMR resting-state activity, before corticocortical pathways are established. In late fetal phase, when synapses appear within the CP, transient the SPC coexists with permanent circuitry. The histogenetic role of the SPC is to provide interactive milieu and capacity for guidance, sorting, "waiting" and target selection of thalamocortical and corticocortical pathways. The new evolutionary role of the SPC and its remnant white matter neurons is linked to the increasing number of associative pathways in the human neocortex. These roles attributed to the SPC are regulated using a spatiotemporal gene expression during critical periods, when pathogenic factors may disturb vulnerable circuitry of the SPC, causing neurodevelopmental cognitive circuitry disorders.

Integrating GWAS and Transcriptomics to Identify the Molecular Underpinnings of Thermal Stress Responses in Drosophila melanogaster

Thermal tolerance of an organism depends on both the ability to dynamically adjust to a thermal stress and preparatory developmental processes that enhance thermal resistance. However, the extent to which standing genetic variation in thermal tolerance alleles influence dynamic stress responses vs. preparatory processes is unknown. Here, using the model species Drosophila melanogaster, we used a combination of Genome Wide Association mapping (GWAS) and transcriptomic profiling to characterize whether genes associated with thermal tolerance are primarily involved in dynamic stress responses or preparatory processes that influence physiological condition at the time of thermal stress. To test our hypotheses, we measured the critical thermal minimum (CTmin) and critical thermal maximum (CTmax) of 100 lines of the Drosophila Genetic Reference Panel (DGRP) and used GWAS to identify loci that explain variation in thermal limits. We observed greater variation in lower thermal limits, with CTmin ranging from 1.81 to 8.60°C, while CTmax ranged from 38.74 to 40.64°C. We identified 151 and 99 distinct genes associated with CTmin and CTmax, respectively, and there was strong support that these genes are involved in both dynamic responses to thermal stress and preparatory processes that increase thermal resistance. Many of the genes identified by GWAS were involved in the direct transcriptional response to thermal stress (72/151 for cold; 59/99 for heat), and overall GWAS candidates were more likely to be differentially expressed than other genes. Further, several GWAS candidates were regulatory genes that may participate in the regulation of stress responses, and gene ontologies related to development and morphogenesis were enriched, suggesting many of these genes influence thermal tolerance through effects on development and physiological status. Overall, our results suggest that thermal tolerance alleles can influence both dynamic plastic responses to thermal stress and preparatory processes that improve thermal resistance. These results also have utility for directly comparing GWAS and transcriptomic approaches for identifying candidate genes associated with thermal tolerance.

Neonatal Ethanol Disturbs the Normal Maturation of Parvalbumin Interneurons Surrounded by Subsets of Perineuronal Nets in the Cerebral Cortex: Partial Reversal by Lithium

Reduction in parvalbumin-positive (PV+) interneurons is observed in adult mice exposed to ethanol at postnatal day 7 (P7), a late gestation fetal alcohol spectrum disorder model. To evaluate whether PV+ cells are lost, or PV expression is reduced, we quantified PV+ and associated perineuronal net (PNN)+ cell densities in barrel cortex. While PNN+ cell density was not reduced by P7 ethanol, PV cell density decreased by 25% at P90 with no decrease at P14. PNN+ cells in controls were virtually all PV+, whereas more than 20% lacked PV in ethanol-treated adult animals. P7 ethanol caused immediate apoptosis in 10% of GFP+ cells in G42 mice, which express GFP in a subset of PV+ cells, and GFP+ cell density decreased by 60% at P90 without reduction at P14. The ethanol effect on PV+ cell density was attenuated by lithium treatment at P7 or at P14-28. Thus, reduced PV+ cell density may be caused by disrupted cell maturation, in addition to acute apoptosis. This effect may be regionally specific: in the dentate gyrus, P7 ethanol reduced PV+ cell density by 70% at P14 and both PV+ and PNN+ cell densities by 50% at P90, and delayed lithium did not alleviate ethanol's effect.

Hyaluronic Acid and Regenerative Medicine: New Insights into the Stroke Therapy

Stroke is known as one of the very important public health problems that are related to societal burden and tremendous economic losses. It has been shown that there are few therapeutic approaches for the treatment of this disease. In this regard, the present therapeutic platforms aim to obtain neuroprotection, reperfusion, and neuro recovery. Among these therapies, regenerative medicine-based therapies have appeared as new ways of stroke therapy. Hyaluronic acid (HA) is a new candidate, which could be applied as a regenerative medicine-based therapy in the treatment of stroke. HA is a glycosaminoglycan composed of disaccharide repeating elements (N-acetyl-Dglucosamine and D-glucuronic acid). Multiple lines of evidence demonstrated that HA has critical roles in normal tissues. It can be a key player in different physiological and pathophysiological conditions such as water homeostasis, multiple drug resistance, inflammatory processes, tumorigenesis, angiogenesis, and changed viscoelasticity of the extracellular matrix. HA has very important physicochemical properties i.e., availability of reactive functional groups and its solubility, which make it a biocompatible material for application in regenerative medicine. Given that HAbased bioscaffolds and biomaterials do not induce inflammation or allergies and are hydrophilic, they are used as soft tissue fillers and injectable dermal fillers. Several studies indicated that HA could be employed as a new therapeutic candidate in the treatment of stroke. These studies documented that HA and HA-based therapies exert their pharmacological effects via affecting stroke-related processes. Herein, we summarized the role of the extracellular matrix in stroke pathogenesis. Moreover, we highlighted the HA-based therapies for the treatment of stroke.

Immunomodulatory role of the extracellular matrix protein tenascin-C in neuroinflammation

The extracellular matrix (ECM) consists of a dynamic network of various macromolecules that are synthesized and released by surrounding cells into the intercellular space. Glycoproteins, proteoglycans and fibrillar proteins are main components of the ECM. In addition to general functions such as structure and stability, the ECM controls several cellular signaling pathways. In this context, ECM molecules have a profound influence on intracellular signaling as receptor-, adhesion- and adaptor-proteins. Due to its various functions, the ECM is essential in the healthy organism, but also under pathological conditions. ECM constituents are part of the glial scar, which is formed in several neurodegenerative diseases that are accompanied by the activation and infiltration of glia as well as immune cells. Remodeling of the ECM modulates the release of pro- and anti-inflammatory cytokines affecting the fate of immune, glial and neuronal cells. Tenascin-C is an ECM glycoprotein that is expressed during embryonic central nervous system (CNS) development. In adults it is present at lower levels but reappears under pathological conditions such as in brain tumors, following injury and in neurodegenerative disorders and is highly associated with glial reactivity as well as scar formation. As a key modulator of the immune response during neurodegeneration in the CNS, tenascin-C is highlighted in this mini-review.

The Interstitial System of the Brain in Health and Disease

The brain interstitial fluid (ISF) and the cerebrospinal fluid (CSF) cushion and support the brain cells. The ISF occupies the brain interstitial system (ISS), whereas the CSF fills the brain ventricles and the subarachnoid space. The brain ISS is an asymmetrical, tortuous, and exceptionally confined space between neural cells and the brain microvasculature. Recently, with a newly developed in vivo measuring technique, a series of discoveries have been made in the brain ISS and the drainage of ISF. The goal of this review is to confer recent advances in our understanding of the brain ISS, including its structure, function, and the various processes mediating or disrupting ISF drainage in physiological and pathological conditions. The brain ISF in the deep brain regions has recently been demonstrated to drain in a compartmentalized ISS instead of a highly connected system, together with the drainage of ISF into the cerebrospinal fluid (CSF) at the surface of the cerebral cortex and the transportation from CSF into cervical lymph nodes. Besides, accumulation of tau in the brain ISS in conditions such as Alzheimer’s disease and its link to the sleep-wake cycle and sleep deprivation, clearance of ISF in a deep sleep via increased CSF flow, novel approaches to remove beta-amyloid from the brain ISS, and obstruction to the ISF drainage in neurological conditions are deliberated. Moreover, the role of ISS in the passage of extracellular vesicles (EVs) released from neural cells and the rapid targeting of therapeutic EVs into neural cells in the entire brain following an intranasal administration, and the promise and limitations of ISS based drug delivery approaches are discussed

Decreased Density of Perineuronal Net in Prelimbic Cortex Is Linked to Depressive-Like Behavior in Young-Aged Rats

Perineuronal nets (PNNs) are condensed extracellular matrix (ECM) structures regulating developmental plasticity and protecting neurons against oxidative stress. PNN abnormalities have been observed in various psychiatric disorders such as schizophrenia and bipolar disorder, but the relationship between PNN density and depression still remains unclear. In the present study, we examined the density and components of PNNs including aggrecan, neurocan and Tenascin-R in the prelimbic cortex (PrL) after chronic unpredictable mild stress (CUMS). We found that depressive-like behaviors were induced after 30 days of CUMS accompanied by decreases in PNN⁺ cell density and aggrecan expression in the PrL. In addition, rats subjected to 20 days of CUMS were separated into vulnerable and resilient subpopulations that differ along several behavioral domains. Consistently, the density of PNNs and the expression level of neurocan in the vulnerable group were decreased compared to control and resilient groups. Finally, we examined individual differences based on locomotion in a novel context and classified rats as high responding (HR) and low responding (LR) phenotypes. The density of PNNs and the expression level of neurocan in the LR group were lower than the HR group. Moreover, the LR rats were more susceptible to depressive-like behaviors compared with HR rats. Altogether, these results suggest that the density of PNNs in the PrL is associated with depressive-like behaviors in young-aged rats, and it may serve as a potential endophenotype or therapeutic target for depression.

Dopamine Receptor Activation Modulates the Integrity of the Perisynaptic Extracellular Matrix at Excitatory Synapses

In the brain, Hebbian-type and homeostatic forms of plasticity are affected by neuromodulators like dopamine (DA). Modifications of the perisynaptic extracellular matrix (ECM), which control the functions and mobility of synaptic receptors as well as the diffusion of transmitters and neuromodulators in the extracellular space, are crucial for the manifestation of plasticity. Mechanistic links between synaptic activation and ECM modifications are largely unknown. Here, we report that neuromodulation via D1-type DA receptors can induce targeted ECM proteolysis specifically at excitatory synapses of rat cortical neurons via proteases ADAMTS-4 and -5. We showed that receptor activation induces increased proteolysis of brevican (BC) and aggrecan, two major constituents of the adult ECM both in vivo and in vitro. ADAMTS immunoreactivity was detected near synapses, and shRNA-mediated knockdown reduced BC cleavage. We have outlined a molecular scenario of how synaptic activity and neuromodulation are linked to ECM rearrangements via increased cAMP levels, NMDA receptor activation, and intracellular calcium signaling.

Distribution and classification of the extracellular matrix in the olfactory bulb

Extracellular matrix (ECM) became an important player over the last few decades when studying the plasticity and regeneration of the central nervous system. In spite of the established role of ECM in these processes throughout the central nervous system (CNS), only few papers were published on the ECM of the olfactory system, which shows a lifelong plasticity, synaptic remodeling and postnatal neurogenesis. In the present study, we have described the localization and organization of major ECM molecules, the hyaluronan, the lecticans, tenascin-R and HAPLN1 link protein in the olfactory bulb (OB) of the rat. We detected all of these molecules in the OB showing differences in the molecular composition, staining intensity, and organization of ECM between the layers and in some cases within a single layer. One of the striking features of ECM staining pattern in the OB was that the reactions are shown dominantly in the neuropil, the PNNs were found rarely and they exhibited thin or diffuse appearance Similar organization was shown in human and mice samples. As the PNN limits the neural plasticity, its rare appearance may be related to the high degree of plasticity in the OB.

Urokinase-type plasminogen activator (uPA) protects the tripartite synapse in the ischemic brain via ezrin-mediated formation of peripheral astrocytic processes

Cerebral ischemia has a harmful effect on the synapse associated with neurological impairment. The "tripartite synapse" is assembled by the pre- and postsynaptic terminals, embraced by astrocytic elongations known as peripheral astrocytic processes (PAPs). Ischemic stroke induces the detachment of PAPs from the synapse, leading to synaptic dysfunction and neuronal death. Ezrin is a membrane-associated protein, required for the formation of PAPs, that links the cell surface to the actin cytoskeleton. Urokinase-type plasminogen activator (uPA) is a serine proteinase that upon binding to its receptor (uPAR) promotes neurite growth during development. In the adult brain, neurons release uPA and astrocytes recruit uPAR to the plasma membrane during the recovery phase from an ischemic stroke, and uPA/uPAR binding promotes functional improvement following an ischemic injury. We found that uPA induces the synthesis of ezrin in astrocytes, with the subsequent formation of PAPs that enter in direct contact with the synapse. Furthermore, either the release of neuronal uPA or intravenous treatment with recombinant uPA (ruPA) induces the formation of PAPs in the ischemic brain, and the interaction of these PAPs with the pre- and postsynaptic terminals protects the integrity of the "tripartite synapse" from the harmful effects of the ischemic injury.

A TBR1-K228E Mutation Induces Tbr1 Upregulation, Altered Cortical Distribution of Interneurons, Increased Inhibitory Synaptic Transmission, and Autistic-Like Behavioral Deficits in Mice

Mutations in Tbr1, a high-confidence ASD (autism spectrum disorder)-risk gene encoding the transcriptional regulator TBR1, have been shown to induce diverse ASD-related molecular, synaptic, neuronal, and behavioral dysfunctions in mice. However, whether Tbr1 mutations derived from autistic individuals cause similar dysfunctions in mice remains unclear. Here we generated and characterized mice carrying the TBR1-K228E de novo mutation identified in human ASD and identified various ASD-related phenotypes. In heterozygous mice carrying this mutation (Tbr1^+/K228E mice), levels of the TBR1-K228E protein, which is unable to bind target DNA, were strongly increased. RNA-Seq analysis of the Tbr1^+/K228E embryonic brain indicated significant changes in the expression of genes associated with neurons, astrocytes, ribosomes, neuronal synapses, and ASD risk. The Tbr1^+/K228E neocortex also displayed an abnormal distribution of parvalbumin-positive interneurons, with a lower density in superficial layers but a higher density in deep layers. These changes were associated with an increase in inhibitory synaptic transmission in layer 6 pyramidal neurons that was resistant to compensation by network activity. Behaviorally, Tbr1^+/K228E mice showed decreased social interaction, increased self-grooming, and modestly increased anxiety-like behaviors. These results suggest that the human heterozygous TBR1-K228E mutation induces ASD-related transcriptomic, protein, neuronal, synaptic, and behavioral dysfunctions in mice.

Elimination of the four extracellular matrix molecules tenascin-C, tenascin-R, brevican and neurocan alters the ratio of excitatory and inhibitory synapses

The synaptic transmission in the mammalian brain is not limited to the interplay between the pre- and the postsynapse of neurons, but involves also astrocytes as well as extracellular matrix (ECM) molecules. Glycoproteins, proteoglycans and hyaluronic acid of the ECM pervade the pericellular environment and condense to special superstructures termed perineuronal nets (PNN) that surround a subpopulation of CNS neurons. The present study focuses on the analysis of PNNs in a quadruple knockout mouse deficient for the ECM molecules tenascin-C (TnC), tenascin-R (TnR), neurocan and brevican. Here, we analysed the proportion of excitatory and inhibitory synapses and performed electrophysiological recordings of the spontaneous neuronal network activity of hippocampal neurons in vitro. While we found an increase in the number of excitatory synaptic molecules in the quadruple knockout cultures, the number of inhibitory synaptic molecules was significantly reduced. This observation was complemented with an enhancement of the neuronal network activity level. The in vivo analysis of PNNs in the hippocampus of the quadruple knockout mouse revealed a reduction of PNN size and complexity in the CA2 region. In addition, a microarray analysis of the postnatal day (P) 21 hippocampus was performed unravelling an altered gene expression in the quadruple knockout hippocampus.

Sensory deafferentation modulates and redistributes neurocan in the rat auditory brainstem

INTRODUCTION

Cochlear ablation causing sensory deafferentation (SD) of the cochlear nucleus triggers complex re-arrangements in the cellular and molecular communication networks of the adult mammalian central auditory system. Participation of the extracellular matrix (ECM) in these processes is not well understood.

METHODS

We investigated consequences of unilateral SD for the expression and distribution of the chondroitin sulfate proteoglycans, neurocan (Ncan) and aggrecan (Agg), alongside various plasticity markers in the auditory brainstem of the adult rat using immunohistochemical techniques.

RESULTS

In the deafferented ventral cochlear nucleus (VCN), Ncan expression increased massively within 3 postoperative days (POD), but rapidly decreased thereafter. Agg showed a similar but less pronounced progression. Decrease in Ncan was spatially and temporally related to the re-innervation of VCN documented by the emergence of growth-associated protein Gap43 contained in nerve fibers and presynaptic boutons. Concurrently, astrocytes grew and expressed matrix metalloproteinase-2 (MMP2), an enzyme known to emerge only under re-innervation of VCN. MMP2 is capable of cleaving both Ncan and Agg when released. A transient modulation of the ECM in the central inferior colliculus on the side opposite to SD occurred by POD1. Modulations of glutamatergic synapses and Gap43 expression were detected, reflecting state changes of the surrounding tissue induced by transsynaptic effects of SD.

CONCLUSIONS

The ECM variously participates in adaptive responses to sudden deafness by SD on several levels along the central auditory pathway, with a striking spatial and temporal relationship of Ncan modulation to astrocytic activation and to synaptogenesis.

Hapln2 in Neurological Diseases and Its Potential as Therapeutic Target

Hyaluronan and proteoglycan link protein 2 (Hapln2) is important for the binding of chondroitin sulfate proteoglycans to hyaluronan. Hapln2 deficiency leads to the abnormal expression of extracellular matrix (ECM) proteins and dysfunctional neuronal conductivity, demonstrating the vital role of Hapln2 in these processes. Studies have revealed that Hapln2 promotes the aggregation of α-synuclein, thereby contributing to neurodegeneration in Parkinson’s disease (PD), and it was recently suggested to be in intracellular neurofibrillary tangles (NFTs). Additionally, the expression levels of Hapln2 showed lower in the anterior temporal lobes of individuals with schizophrenia than those of healthy subjects. Together, these studies implicate the involvement of Hapln2 in the pathological processes of neurological diseases. A better understanding of the function of Hapln2 in the central nervous system (CNS) will provide new insights into the molecular mechanisms of these diseases and help to establish promising therapeutic strategies. Herein, we review the recent progress in defining the role of Hapln2 in brain physiology and pathology.

The Application of Omics Technologies to Study Axon Regeneration and CNS Repair

Traumatic brain and spinal cord injuries cause permanent disability. Although progress has been made in understanding the cellular and molecular mechanisms underlying the pathophysiological changes that affect both structure and function after injury to the brain or spinal cord, there are currently no cures for either condition. This may change with the development and application of multi-layer omics, new sophisticated bioinformatics tools, and cutting-edge imaging techniques. Already, these technical advances, when combined, are revealing an unprecedented number of novel cellular and molecular targets that could be manipulated alone or in combination to repair the injured central nervous system with precision. In this review, we highlight recent advances in applying these new technologies to the study of axon regeneration and rebuilding of injured neural circuitry. We then discuss the challenges ahead to translate results produced by these technologies into clinical application to help improve the lives of individuals who have a brain or spinal cord injury.

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.

Keratan sulfate (KS)-proteoglycans and neuronal regulation in health and disease: the importance of KS-glycodynamics and interactive capability with neuroregulatory ligands

Compared to the other classes of glycosaminoglycans (GAGs), that is, chondroitin/dermatan sulfate, heparin/heparan sulfate and hyaluronan, keratan sulfate (KS), have the least known of its interactive properties. In the human body, the cornea and the brain are the two most abundant tissue sources of KS. Embryonic KS is synthesized as a linear poly-N-acetyllactosamine chain of d-galactose-GlcNAc repeat disaccharides which become progressively sulfated with development, sulfation of GlcNAc is more predominant than galactose. KS contains multi-sulfated high-charge density, monosulfated and non-sulfated poly-N-acetyllactosamine regions and thus is a heterogeneous molecule in terms of chain length and charge distribution. A recent proteomics study on corneal KS demonstrated its interactivity with members of the Slit-Robbo and Ephrin-Ephrin receptor families and proteins which regulate Rho GTPase signaling and actin polymerization/depolymerization in neural development and differentiation. KS decorates a number of peripheral nervous system/CNS proteoglycan (PG) core proteins. The astrocyte KS-PG abakan defines functional margins of the brain and is up-regulated following trauma. The chondroitin sulfate/KS PG aggrecan forms perineuronal nets which are dynamic neuroprotective structures with anti-oxidant properties and roles in neural differentiation, development and synaptic plasticity. Brain phosphacan a chondroitin sulfate, KS, HNK-1 PG have roles in neural development and repair. The intracellular microtubule and synaptic vesicle KS-PGs MAP1B and SV2 have roles in metabolite transport, storage, and export of neurotransmitters and cytoskeletal assembly. MAP1B has binding sites for tubulin and actin through which it promotes cytoskeletal development in growth cones and is highly expressed during neurite extension. The interactive capability of KS with neuroregulatory ligands indicate varied roles for KS-PGs in development and regenerative neural processes.