Proteoglycans in brain development and pathogenesis

Glycosaminoglycans' for brain health: Harnessing glycosaminoglycan based biomaterials for treating central nervous system diseases and in-vitro modeling

Dysfunction of the central nervous system (CNS) following traumatic brain injuries (TBI), spinal cord injuries (SCI), or strokes remains challenging to address using existing medications and cell-based therapies. Although therapeutic cell administration, such as stem cells and neuronal progenitor cells (NPCs), have shown promise in regenerative properties, they have failed to provide substantial benefits. However, the development of living cortical tissue engineered grafts, created by encapsulating these cells within an extracellular matrix (ECM) mimetic hydrogel scaffold, presents a promising functional replacement for damaged cortex in cases of stroke, SCI, and TBI. These grafts facilitate neural network repair and regeneration following CNS injuries. Given that natural glycosaminoglycans (GAGs) are a major constituent of the CNS, GAG-based hydrogels hold potential for the next generation of CNS healing therapies and in vitro modeling of CNS diseases. Brain-specific GAGs not only offer structural and biochemical signaling support to encapsulated neural cells but also modulate the inflammatory response in lesioned brain tissue, facilitating host integration and regeneration. This review briefly discusses different roles of GAGs and their related proteoglycan counterparts in healthy and diseases brain and explores current trends and advancements in GAG-based biomaterials for treating CNS injuries and modeling diseases. Additionally, it examines injectable, 3D bioprintable, and conductive GAG-based scaffolds, highlighting their clinical potential for in vitro modeling of patient-specific neural dysfunction and their ability to enhance CNS regeneration and repair following CNS injury in vivo.

Endogenous retroviruses in multiple sclerosis: A network-based etiopathogenic model

The present perspective article proposes an etiopathological model for multiple sclerosis pathogenesis and progression associated with the activation of human endogenous retroviruses. We reviewed preclinical, clinical, epidemiological, and evolutionary evidence indicating how the complex, multi-level interplay of genetic traits and environmental factors contributes to multiple sclerosis. We propose that endogenous retroviruses transactivation acts as a critical node in disease development. We also discuss the rationale for combined anti-retroviral therapy in multiple sclerosis as a disease-modifying therapeutic strategy. Finally, we propose that the immuno-pathogenic process triggered by endogenous retrovirus activation can be extended to aging and aging-related neurodegeneration. In this regard, endogenous retroviruses can be envisioned to act as epigenetic noise, favoring the proliferation of disorganized cellular subpopulations and accelerating system-specific "aging". Since inflammation and aging are two sides of the same coin (plastic dis-adaptation to external stimuli with system-specific degree of freedom), the two conditions may be epiphenomenal products of increased epigenomic entropy. Inflammation accelerates organ-specific aging, disrupting communication throughout critical systems of the body and producing symptoms. Overlapping neurological symptoms and syndromes may emerge from the activity of shared molecular networks that respond to endogenous retroviruses' reactivation.

CNS/PNS proteoglycans functionalize neuronal and astrocyte niche microenvironments optimizing cellular activity by preserving membrane polarization dynamics, ionic microenvironments, ion fluxes, neuronal activation, and network neurotransductive capacity

Central and peripheral nervous system (CNS/PNS) proteoglycans (PGs) have diverse functional roles, this study examined how these control cellular behavior and tissue function. The CNS/PNS extracellular matrix (ECM) is a dynamic, responsive, highly interactive, space-filling, cell supportive, stabilizing structure maintaining tissue compartments, ionic microenvironments, and microgradients that regulate neuronal activity and maintain the neuron in an optimal ionic microenvironment. The CNS/PNS contains a high glycosaminoglycan content (60% hyaluronan, HA) and a diverse range of stabilizing PGs. Immobilization of HA in brain tissues by HA interactive hyalectan PGs preserves tissue hydration and neuronal activity, a paucity of HA in brain tissues results in a pro-convulsant epileptic phenotype. Diverse CS, KS, and HSPGs stabilize the blood-brain barrier and neurovascular unit, provide smart gel neurotransmitter neuron vesicle storage and delivery, organize the neuromuscular junction basement membrane, and provide motor neuron synaptic plasticity, and photoreceptor and neuron synaptic functions. PG-HA networks maintain ionic fluxes and microgradients and tissue compartments that contribute to membrane polarization dynamics essential to neuronal activation and neurotransduction. Hyalectans form neuroprotective perineuronal nets contributing to synaptic plasticity, memory, and cognitive learning. Sialoglycoprotein associated with cones and rods (SPACRCAN), an HA binding CSPG, stabilizes the inter-photoreceptor ECM. HSPGs pikachurin and eyes shut stabilize the photoreceptor synapse aiding in phototransduction and neurotransduction with retinal bipolar neurons crucial to visual acuity. This is achieved through Laminin G motifs in pikachurin, eyes shut, and neurexins that interact with the dystroglycan-cytoskeleton-ECM-stabilizing synaptic interconnections, neuronal interactive specificity, and co-ordination of regulatory action potentials in neural networks.

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.

Chondroitin sulfate glycan sulfation patterns influence histochemical labeling of perineuronal nets: a comparative study of interregional distribution in human and mouse brain

Perineuronal nets (PNNs) are a condensed subtype of extracellular matrix that form a net-like coverings around certain neurons in the brain. PNNs are primarily composed of chondroitin sulfate (CS) proteoglycans from the lectican family that consist of CS-glycosaminoglycan side chains attached to a core protein. CS disaccharides can exist in various isoforms with different sulfation patterns. Literature suggests that CS disaccharide sulfation patterns can influence the function of PNNs as well as their labeling. This study was conducted to characterize such interregional CS disaccharide sulfation pattern differences in adult human (n = 81) and mouse (n = 19) brains. Liquid chromatography tandem mass spectrometry was used to quantify five different CS disaccharide sulfation patterns, which were then compared to immunolabeling of PNNs using Wisteria Floribunda Lectin (WFL) to identify CS-glycosaminoglycans and anti-aggrecan to identify CS proteoglycans. In healthy brains, significant regional and species-specific differences in CS disaccharide sulfation and single versus double-labeling pattern were identified. A secondary analysis to investigate how early-life stress impacts these PNN features discovered that although early-life stress increases WFL+ PNN density, the CS-glycosaminoglycan sulfation code and single versus double PNN-labeling distributions remained unaffected in both species. These results underscore PNN complexity in traditional research, emphasizing the need to consider their heterogeneity in future experiments.

Chondroitin sulfate glycan sulfation patterns influence histochemical labeling of perineuronal nets: a comparative study of interregional distribution in human and mouse brain

Perineuronal nets (PNNs) are a condensed subtype of extracellular matrix that form a net-like coverings around certain neurons in the brain. PNNs are primarily composed of chondroitin sulfate (CS) proteoglycans from the lectican family that consist of CS-glycosaminoglycan (CS-GAG) side chains attached to a core protein. CS disaccharides can exist in various isoforms with different sulfation patterns. Literature suggests that CS disaccharide sulfation patterns can influence the function of PNNs as well as their labeling. This study was conducted to characterize such interregional CS disaccharide sulfation pattern differences in adult human (N = 81) and mouse (N = 19) brains. Liquid chromatography tandem mass spectrometry was used to quantify five different CS disaccharide sulfation patterns, which were then compared to immunolabeling of PNNs using Wisteria Floribunda Lectin (WFL) to identify CS-GAGs and anti-aggrecan to identify CS proteoglycans. In healthy brains, significant regional and species-specific differences in CS disaccharide sulfation and single versus double-labeling pattern were identified. A secondary analysis to investigate how early-life stress (ELS) impacts these PNN features discovered that although ELS increases WFL+ PNN density, the CS-GAG sulfation code and single versus double PNN-labeling distributions remained unaffected in both species. These results underscore PNN complexity in traditional research, emphasizing the need to consider their heterogeneity in future experiments.

Heterogeneity of brain extracellular matrix and astrocyte activation

From the blood brain barrier to the synaptic space, astrocytes provide structural, metabolic, ionic, and extracellular matrix (ECM) support across the brain. Astrocytes include a vast array of subtypes, their phenotypes and functions varying both regionally and temporally. Astrocytes' metabolic and regulatory functions poise them to be quick and sensitive responders to injury and disease in the brain as revealed by single cell sequencing. Far less is known about the influence of the local healthy and aging microenvironments on these astrocyte activation states. In this forward-looking review, we describe the known relationship between astrocytes and their local microenvironment, the remodeling of the microenvironment during disease and injury, and postulate how they may drive astrocyte activation. We suggest technology development to better understand the dynamic diversity of astrocyte activation states, and how basal and activation states depend on the ECM microenvironment. A deeper understanding of astrocyte response to stimuli in ECM-specific contexts (brain region, age, and sex of individual), paves the way to revolutionize how the field considers astrocyte-ECM interactions in brain injury and disease and opens routes to return astrocytes to a healthy quiescent state.

Molecular recognition and proteoglycan mimic arrangement: modulating cisplatin toxicity

We have demonstrated that cisplatin (CP), an anticancer drug, showed a preference for binding the sulfated-L-iduronic acid (S-L-IdoA) unit over the sulfated-D-glucuronic acid unit of heparan sulfate. The multivalency of S-L-IdoA, such as in the proteoglycan mimic, resulted in distinct modes of cell-surface engineering in normal and cancer cells, with these disparities having a significant impact on CP-mediated toxicity.

Kallikrein-related peptidase's significance in Alzheimer's disease pathogenesis: A comprehensive survey

Alzheimer's disease (AD) and related dementias constitute an important global health challenge. Detailed understanding of the multiple molecular mechanisms underlying their pathogenesis constitutes a clue for the management of the disease. Kallikrein-related peptidases (KLKs), a lead family of serine proteases, have emerged as potential biomarkers and therapeutic targets in the context of AD and associated cognitive decline. Hence, KLKs were proposed to display multifaceted impacts influencing various aspects of neurodegeneration, including amyloid-beta aggregation, tau pathology, neuroinflammation, and synaptic dysfunction. We propose here a comprehensive survey to summarize recent findings, providing an overview of the main kallikreins implicated in AD pathophysiology namely KLK8, KLK6 and KLK7. We explore the interplay between KLKs and key AD molecular pathways, shedding light on their significance as potential biomarkers for early disease detection. We also discuss their pertinence as therapeutic targets for disease-modifying interventions to develop innovative therapeutic strategies aimed at halting or ameliorating the progression of AD and associated dementias.

Alteration of mechanical stresses in the murine brain by age and hemorrhagic stroke

Residual mechanical stresses, also known as solid stresses, emerge during rapid differential growth or remodeling of tissues, as observed in morphogenesis and tumor growth. While residual stresses typically dissipate in most healthy adult organs, as the growth rate decreases, high residual stresses have been reported in mature, healthy brains. However, the origins and consequences of residual mechanical stresses in the brain across health, aging, and disease remain poorly understood. Here, we utilized and validated a previously developed method to map residual mechanical stresses in the brains of mice across three age groups: 5-7 days, 8-12 weeks, and 22 months. We found that residual solid stress rapidly increases from 5-7 days to 8-12 weeks and remains high in mature 22 months mice brains. Three-dimensional mapping revealed unevenly distributed residual stresses from the anterior to posterior coronal brain sections. Since the brain is rich in negatively charged hyaluronic acid, we evaluated the contribution of charged extracellular matrix (ECM) constituents in maintaining solid stress levels. We found that lower ionic strength leads to elevated solid stresses, consistent with its unshielding effect and the subsequent expansion of charged ECM components. Lastly, we demonstrated that hemorrhagic stroke, accompanied by loss of cellular density, resulted in decreased residual stress in the murine brain. Our findings contribute to a better understanding of spatiotemporal alterations of residual solid stresses in healthy and diseased brains, a crucial step toward uncovering the biological and immunological consequences of this understudied mechanical phenotype in the brain.

Cell-type brain-region specific changes in prefrontal cortex of a mouse model of alcohol dependence

The prefrontal cortex is a crucial regulator of alcohol drinking, and dependence, and other behavioral phenotypes associated with AUD. Comprehensive identification of cell-type specific transcriptomic changes in alcohol dependence will improve our understanding of mechanisms underlying the excessive alcohol use associated with alcohol dependence and will refine targets for therapeutic development. We performed single nucleus RNA sequencing (snRNA-seq) and Visium spatial gene expression profiling on the medial prefrontal cortex (mPFC) obtained from C57BL/6 J mice exposed to the two-bottle choice-chronic intermittent ethanol (CIE) vapor exposure (2BC-CIE, defined as dependent group) paradigm which models phenotypes of alcohol dependence including escalation of alcohol drinking. Gene co-expression network analysis and differential expression analysis identified highly dysregulated co-expression networks in multiple cell types. Dysregulated modules and their hub genes suggest novel understudied targets for studying molecular mechanisms contributing to the alcohol dependence state. A subtype of inhibitory neurons was the most alcohol-sensitive cell type and contained a downregulated gene co-expression module; the hub gene for this module is Cpa6, a gene previously identified by GWAS to be associated with excessive alcohol consumption. We identified an astrocytic Gpc5 module significantly upregulated in the alcohol-dependent group. To our knowledge, there are no studies linking Cpa6 and Gpc5 to the alcohol-dependent phenotype. We also identified neuroinflammation related gene expression changes in multiple cell types, specifically enriched in microglia, further implicating neuroinflammation in the escalation of alcohol drinking. Here, we present a comprehensive atlas of cell-type specific alcohol dependence mediated gene expression changes in the mPFC and identify novel cell type-specific targets implicated in alcohol dependence.

Zebrafish as a model for study of disorders in pyrimidine nucleotide metabolism

Pyrimidine nucleotides are not only the building blocks of DNA and RNA but also participate in multiple cellular metabolic processes, including protein, lipid and polysaccharide biosynthesis. Pyrimidine nucleotides are synthesized by two distinct pathways-the de novo and salvage pathways. Disorders in pyrimidine nucleotide metabolism cause severe neurodegenerative disorders in human. For example, deficiency in thymidylate kinase, an essential enzyme in dTTP synthesis, causes severe microcephaly in human patients. Zebrafish mutants selected by insertion mutagenesis that results in inactive enzymes in pyrimidine metabolism showed also neurological and developmental disorders. In this work I have summarized current data on neurological and developmental disorders caused by defects in enzymes in pyrimidine nucleotide metabolism in zebrafish and compared to human. All these data suggest that zebrafish is a useful animal model to study pathogenic mechanism of neurological disorders due to defect in pyrimidine nucleotide metabolism.

Global impact of proteoglycan science on human diseases

In this comprehensive review, we will dissect the impact of research on proteoglycans focusing on recent developments involved in their synthesis, degradation, and interactions, while critically assessing their usefulness in various biological processes. The emerging roles of proteoglycans in global infections, specifically the SARS-CoV-2 pandemic, and their rising functions in regenerative medicine and biomaterial science have significantly affected our current view of proteoglycans and related compounds. The roles of proteoglycans in cancer biology and their potential use as a next-generation protein-based adjuvant therapy to combat cancer is also emerging as a constructive and potentially beneficial therapeutic strategy. We will discuss the role of proteoglycans in selected and emerging areas of proteoglycan science, such as neurodegenerative diseases, autophagy, angiogenesis, cancer, infections and their impact on mammalian diseases.

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

Hyaluronan hydrates and compartmentalises the CNS/PNS extracellular matrix and provides niche environments conducive to the optimisation of neuronal activity

The central nervous system/peripheral nervous system (CNS/PNS) extracellular matrix is a dynamic and highly interactive space-filling, cell-supportive, matrix-stabilising, hydrating entity that creates and maintains tissue compartments to facilitate regional ionic micro-environments and micro-gradients that promote optimal neural cellular activity. The CNS/PNS does not contain large supportive collagenous and elastic fibrillar networks but is dominated by a high glycosaminoglycan content, predominantly hyaluronan (HA) and collagen is restricted to the brain microvasculature, blood-brain barrier, neuromuscular junction and meninges dura, arachnoid and pia mater. Chondroitin sulphate-rich proteoglycans (lecticans) interactive with HA have stabilising roles in perineuronal nets and contribute to neural plasticity, memory and cognitive processes. Hyaluronan also interacts with sialoproteoglycan associated with cones and rods (SPACRCAN) to stabilise the interphotoreceptor matrix and has protective properties that ensure photoreceptor viability and function is maintained. HA also regulates myelination/re-myelination in neural networks. HA fragmentation has been observed in white matter injury, multiple sclerosis, and traumatic brain injury. HA fragments (2 × 105  Da) regulate oligodendrocyte precursor cell maturation, myelination/remyelination, and interact with TLR4 to initiate signalling cascades that mediate myelin basic protein transcription. HA and its fragments have regulatory roles over myelination which ensure high axonal neurotransduction rates are maintained in neural networks. Glioma is a particularly invasive brain tumour with extremely high mortality rates. HA, CD44 and RHAMM (receptor for HA-mediated motility) HA receptors are highly expressed in this tumour. Conventional anti-glioma drug treatments have been largely ineffective and surgical removal is normally not an option. CD44 and RHAMM glioma HA receptors can potentially be used to target gliomas with PEP-1, a cell-penetrating HA-binding peptide. PEP-1 can be conjugated to a therapeutic drug; such drug conjugates have successfully treated dense non-operative tumours in other tissues, therefore similar applications warrant exploration as potential anti-glioma treatments.

SuPreme Study: a protocol to study the neuroprotective potential of sulfate among very/extremely preterm infants

INTRODUCTION

Antenatal maternal magnesium sulfate (MgSO4) administration is a proven efficacious neuroprotective treatment reducing the risk of cerebral palsy (CP) among infants born preterm. Identification of the neuroprotective component with target plasma concentrations could lead to neonatal treatment with greater efficacy and accessibility.

METHODS AND ANALYSIS

This is a prospective observational cohort study, in three tertiary Australian centres. Participants are preterm infants, irrespective of antenatal MgSO4 exposure, born in 2013-2020 at 24+0 to 31+6 weeks gestation, and followed up to 2 years corrected age (CA) (to September 2023). 1595 participants are required (allowing for 17% deaths/loss to follow-up) to detect a clinically significant reduction (30% relative risk reduction) in CP when sulfate concentration at 7 days of age is 1 SD above the mean.A blood sample is collected on day 7 of age for plasma sulfate and magnesium measurement. In a subset of participants multiple blood and urine samples are collected for pharmacokinetic studies, between days 1-28, and in a further subset mother/infant blood is screened for genetic variants of sulfate transporter genes.The primary outcome is CP. Surviving infants are assessed for high risk of CP at 12-14 weeks CA according to Prechtl's Method to assess General Movements. Follow-up at 2 years CA includes assessments for CP, cognitive, language and motor development, and social/behavioural difficulties.Multivariate analyses will examine the association between day 7 plasma sulfate/magnesium concentrations with adverse neurodevelopmental outcomes. A population pharmacokinetic model for sulfate in the preterm infant will be created using non-linear mixed-effects modelling.

ETHICS AND DISSEMINATION

The study has been approved by Mater Misericordiae Ltd Human Research Ethics Committee (HREC/14/MHS/188). Results will be disseminated in peer-reviewed journal publications, and provided to the funding bodies. Using consumer input, a summary will be prepared for participants and consumer groups.

The therapeutic potential of the neuroactive peptides of soluble amyloid precursor protein-alpha in Alzheimer's disease and related neurological disorders

Soluble amyloid precursor protein-alpha (sAPPα) is a multi-functional brain-derived protein that has neuroprotective, neurogenic and neurotropic properties. Moreover, it is known to facilitate synaptic function and promote neural repair. These properties suggest sAPPα may be useful as a therapeutic agent for the treatment of neurological diseases characterized by synaptic failure and neuronal loss, such as occurs in Alzheimer's disease, and for neural repair following traumatic brain injury and stroke. However, sAPPα's relatively large size and the difficulty of ongoing delivery of therapeutics to the brain mean this is not currently practicable. Importantly, however, sAPPα is composed of several neuroactive domains that each possess properties that collectively are remarkably similar to those of sAPPα itself. Here, we review the molecular structure of sAPPα and identify the domains that contribute to its overall functionality. Four peptide motifs present as possible targets for therapeutic development. We review their physiochemical and neuroactive properties, both within sAPPα and as isolated peptides, and discuss their potential for future development as multipurpose therapeutic agents for the treatment of Alzheimer's disease and other disorders of neuronal function. Further, we discuss the role of heparin binding sites, found within sAPPα's structure and overlapping with the neuroactive domains, as sites for interactions with effector proteins and synaptic receptors. The potential role of the neuroactive peptides known as Cationic Arginine-Rich Peptides (CARPs) as neuroprotective motifs is also reviewed. Mechanisms of peptide delivery to the brain are briefly discussed. Finally, we summarise the potential benefits and pitfalls of using the isolated peptides, either individually or in combination, for the treatment of neurological diseases.

Biocompatible Macroion/Growth Factor Assemblies for Medical Applications

Growth factors are a class of proteins that play a role in the proliferation (the increase in the number of cells resulting from cell division) and differentiation (when a cell undergoes changes in gene expression becoming a more specific type of cell) of cells. They can have both positive (accelerating the normal healing process) and negative effects (causing cancer) on disease progression and have potential applications in gene therapy and wound healing. However, their short half-life, low stability, and susceptibility to degradation by enzymes at body temperature make them easily degradable in vivo. To improve their effectiveness and stability, growth factors require carriers for delivery that protect them from heat, pH changes, and proteolysis. These carriers should also be able to deliver the growth factors to their intended destination. This review focuses on the current scientific literature concerning the physicochemical properties (such as biocompatibility, high affinity for binding growth factors, improved bioactivity and stability of the growth factors, protection from heat, pH changes or appropriate electric charge for growth factor attachment via electrostatic interactions) of macroions, growth factors, and macroion-growth factor assemblies, as well as their potential uses in medicine (e.g., diabetic wound healing, tissue regeneration, and cancer therapy). Specific attention is given to three types of growth factors: vascular endothelial growth factors, human fibroblast growth factors, and neurotrophins, as well as selected biocompatible synthetic macroions (obtained through standard polymerization techniques) and polysaccharides (natural macroions composed of repeating monomeric units of monosaccharides). Understanding the mechanisms by which growth factors bind to potential carriers could lead to more effective delivery methods for these proteins, which are of significant interest in the diagnosis and treatment of neurodegenerative and civilization diseases, as well as in the healing of chronic wounds.

A Dedicated 21-Plex Proximity Extension Assay Panel for High-Sensitivity Protein Biomarker Detection Using Microdialysis in Severe Traumatic Brain Injury: The Next Step in Precision Medicine?

Cerebral protein profiling in traumatic brain injury (TBI) is needed to better comprehend secondary injury pathways. Cerebral microdialysis (CMD), in combination with the proximity extension assay (PEA) technique, has great potential in this field. By using PEA, we have previously screened >500 proteins from CMD samples collected from TBI patients. In this study, we customized a PEA panel prototype of 21 selected candidate protein biomarkers, involved in inflammation (13), neuroplasticity/-repair (six), and axonal injury (two). The aim was to study their temporal dynamics and relation to age, structural injury, and clinical outcome. Ten patients with severe TBI and CMD monitoring, who were treated in the Neurointensive Care Unit, Uppsala University Hospital, Sweden, were included. Hourly CMD samples were collected for up to 7 days after trauma and analyzed with the 21-plex PEA panel. Seventeen of the 21 proteins from the CMD sample analyses showed significantly different mean levels between days. Early peaks (within 48 h) were noted with interleukin (IL)-1β, IL-6, IL-8, granulocyte colony-stimulating factor, transforming growth factor alpha, brevican, junctional adhesion molecule B, and neurocan. C-X-C motif chemokine ligand 10 peaked after 3 days. Late peaks (>5 days) were noted with interleukin-1 receptor antagonist (IL-1ra), monocyte chemoattractant protein (MCP)-2, MCP-3, urokinase-type plasminogen activator, Dickkopf-related protein 1, and DRAXIN. IL-8, neurofilament heavy chain, and TAU were biphasic. Age (above/below 22 years) interacted with the temporal dynamics of IL-6, IL-1ra, vascular endothelial growth factor, MCP-3, and TAU. There was no association between radiological injury (Marshall grade) or clinical outcome (Extended Glasgow Outcome Scale) with the protein expression pattern. The PEA method is a highly sensitive molecular tool for protein profiling from cerebral tissue in TBI. The novel TBI dedicated 21-plex panel showed marked regulation of proteins belonging to the inflammation, plasticity/repair, and axonal injury families. The method may enable important insights into complex injury processes on a molecular level that may be of value in future efforts to tailor pharmacological TBI trials to better address specific disease processes and optimize timing of treatments.

Transcriptomic Analysis of Glycosylation and Neuroregulatory Pathways in Rodent Models in Response to Psychedelic Molecules

The potential for psychedelic molecules in impacting cognitive flexibility has long been supported and acknowledged across scientific reports. In the current study, an approach leveraging knowledge-based gene-set information analysis has been adopted to explore the potential impact of psychedelic molecules on both glycosylation, (a post-translational modifications (PTM)) and on neuro-regulatory pathways. Though limitations and restrictions rise from the scarcity of publicly available 'omics' data, targeted analysis enabled us to identify a number of key glycogenes (Hexb, Hs6st2, Col9a2, B3gat2, Mgat5, Bgn) involved the structural organization of extracellular matrix and neuroprotective factors (Kl, Pomc, Oxt, Gal, Avp, Cartpt) which play vital roles in neuron protection, development as well as synaptic stability. In response to psychedelic molecules, we found that these genes and associated pathways are transcriptional altered in rodent models. The approach used indicates the potential to exploit existing datasets for hypothesis generation and testing for the molecular processes which play a role in the physiological response to psychedelic molecule effects. These reported findings, which focused on alterations in glycogenes and neuro-regulatory factors may provide a novel range of biomarkers to track the beneficial, as well as potential toxicological effects of psychedelic molecules.

Amplitudes of resting-state functional networks - investigation into their correlates and biophysical properties

Resting-state fMRI studies have shown that multiple functional networks, which consist of distributed brain regions that share synchronised spontaneous activity, co-exist in the brain. As these resting-state networks (RSNs) have been thought to reflect the brain's intrinsic functional organization, intersubject variability in the networks' spontaneous fluctuations may be associated with individuals' clinical, physiological, cognitive, and genetic traits. Here, we investigated resting-state fMRI data along with extensive clinical, lifestyle, and genetic data collected from 37,842 UK Biobank participants, with the object of elucidating intersubject variability in the fluctuation amplitudes of RSNs. Functional properties of the RSN amplitudes were first examined by analyzing correlations with the well-established between-network functional connectivity. It was found that a network amplitude is highly correlated with the mean strength of the functional connectivity that the network has with the other networks. Intersubject clustering analysis showed the amplitudes are most strongly correlated with age, cardiovascular factors, body composition, blood cell counts, lung function, and sex, with some differences in the correlation strengths between sensory and cognitive RSNs. Genome-wide association studies (GWASs) of RSN amplitudes identified several significant genetic variants reported in previous GWASs for their implications in sleep duration. We provide insight into key factors determining RSN amplitudes and demonstrate that intersubject variability of the amplitudes primarily originates from differences in temporal synchrony between functionally linked brain regions, rather than differences in the magnitude of raw voxelwise BOLD signal changes. This finding additionally revealed intriguing differences between sensory and cognitive RSNs with respect to sex effects on temporal synchrony and provided evidence suggesting that synchronous coactivations of functionally linked brain regions, and magnitudes of BOLD signal changes, may be related to different genetic mechanisms. These results underscore that intersubject variability of the amplitudes in health and disease need to be interpreted largely as a measure of the sum of within-network temporal synchrony and amplitudes of BOLD signals, with a dominant contribution from the former.

Introduction to the Complexity of Cell Surface and Tissue Matrix Glycoconjugates

This chapter provides an overview of structures and functions of complex carbohydrates (commonly called glycans) that are covalently linked to proteins or lipids to form glycoconjugates known as glycoproteins, glycolipids, and proteoglycans. To understand the complexity of the glycan structures, the nature of their monosaccharide building blocks, how the monomeric units are covalently linked to each other, and how the resulting glycans are attached to proteins or lipids are discussed. Then, the classification, nomenclature, structural features, and functions of the glycan moieties of animal glycoconjugates are briefly described. All three classes of glycoconjugates are constituents of plasma membranes of all animal cells, including those of the nervous system. Glycoproteins and proteoglycans are also found abundantly as constituents of tissue matrices. Additionally, glycan-rich mucin glycoproteins are the major constituents of mucus secretions of epithelia of various organs. Furthermore, the chapter draws attention to the incredible structural complexity and diversity of the glycan moieties of cell surface and extracellular glycoconjugates. Finally, the involvement of glycans as informational molecules in a wide range of essential functions in almost all known biological processes, which are crucial for development, differentiation, and normal functioning of animals, is discussed.

Glucocorticoid Effects on Proteoglycans and Glycosaminoglycans

Glucocorticoids are steroid hormones that play diverse roles in numerous normal and pathological processes. They are actively used to treat a wide variety of diseases, including neurodegenerative and inflammatory diseases, cancers, and COVID-19, among others. However, the long-term use of glucocorticoids is associated with numerous side effects. Molecular mechanisms of these negative side effects are not completely understood. Recently, arguments have been made that one such mechanisms may be related to the influence of glucocorticoids on O-glycosylated components of the cell surface and extracellular matrix, in particular on proteoglycans and glycosaminoglycans. The potential toxic effects of glucocorticoids on these glycosylated macromolecules are particularly meaningful for brain physiology because proteoglycans/glycosaminoglycans are the main extracellular components of brain tissue. Here, we aim to review the known effects of glucocorticoids on proteoglycan expression and glycosaminoglycan content in different tissues, with a specific focus on the brain.

Emerging cellular themes in leukodystrophies

Leukodystrophies are a broad spectrum of neurological disorders that are characterized primarily by deficiencies in myelin formation. Clinical manifestations of leukodystrophies usually appear during childhood and common symptoms include lack of motor coordination, difficulty with or loss of ambulation, issues with vision and/or hearing, cognitive decline, regression in speech skills, and even seizures. Many cases of leukodystrophy can be attributed to genetic mutations, but they have diverse inheritance patterns (e.g., autosomal recessive, autosomal dominant, or X-linked) and some arise from de novo mutations. In this review, we provide an updated overview of 35 types of leukodystrophies and focus on cellular mechanisms that may underlie these disorders. We find common themes in specialized functions in oligodendrocytes, which are specialized producers of membranes and myelin lipids. These mechanisms include myelin protein defects, lipid processing and peroxisome dysfunction, transcriptional and translational dysregulation, disruptions in cytoskeletal organization, and cell junction defects. In addition, non-cell-autonomous factors in astrocytes and microglia, such as autoimmune reactivity, and intercellular communication, may also play a role in leukodystrophy onset. We hope that highlighting these themes in cellular dysfunction in leukodystrophies may yield conceptual insights on future therapeutic approaches.

Pathogenic variants damage cell composition and single cell transcription in cardiomyopathies

Pathogenic variants in genes that cause dilated cardiomyopathy (DCM) and arrhythmogenic cardiomyopathy (ACM) convey high risks for the development of heart failure through unknown mechanisms. Using single-nucleus RNA sequencing, we characterized the transcriptome of 880,000 nuclei from 18 control and 61 failing, nonischemic human hearts with pathogenic variants in DCM and ACM genes or idiopathic disease. We performed genotype-stratified analyses of the ventricular cell lineages and transcriptional states. The resultant DCM and ACM ventricular cell atlas demonstrated distinct right and left ventricular responses, highlighting genotype-associated pathways, intercellular interactions, and differential gene expression at single-cell resolution. Together, these data illuminate both shared and distinct cellular and molecular architectures of human heart failure and suggest candidate therapeutic targets.

A novel cytoskeletal action of xylosides

Proteoglycan glycosaminoglycan (GAG) chains are attached to a serine residue in the protein through a linkage series of sugars, the first of which is xylose. Xylosides are chemicals which compete with the xylose at the enzyme xylosyl transferase to prevent the attachment of GAG chains to proteins. These compounds have been employed at concentrations in the millimolar range as tools to study the role of GAG chains in proteoglycan function. In the course of our studies with xylosides, we conducted a dose-response curve for xyloside actions on neural cells. To our surprise, we found that concentrations of xylosides in the nanomolar to micromolar range had major effects on cell morphology of hippocampal neurons as well as of Neuro2a cells, affecting both actin and tubulin cytoskeletal dynamics. Such effects/morphological changes were not observed with higher xyloside concentrations. We found a dose-dependent alteration of GAG secretion by Neuro2a cells; however, concentrations of xylosides which were effective in altering neuronal morphology did not cause a large change in the rate of GAG chain secretion. In contrast, both low and high concentrations of xylosides altered HS and CS composition. RNAseq of treated cells demonstrated alterations in gene expression only after treatment with millimolar concentration of xylosides that had no effect on cell morphology. These observations support a novel action of xylosides on neuronal cells.

Distributed genetic architecture across the hippocampal formation implies common neuropathology across brain disorders

Despite its major role in complex human functions across the lifespan, most notably navigation, learning and memory, much of the genetic architecture of the hippocampal formation is currently unexplored. Here, through multivariate genome-wide association analysis in volumetric data from 35,411 white British individuals, we reveal 177 unique genetic loci with distributed associations across the hippocampal formation. We identify genetic overlap with eight brain disorders with typical onset at different stages of life, where common genes suggest partly age- and disorder-independent mechanisms underlying hippocampal pathology.

Proteoglycans and Glycosaminoglycans in Central Nervous System Injury

The brain and spinal cord constitute the central nervous system (CNS), which when injured, can be exceedingly devastating. The mechanistic roles of proteoglycans (PGs) and their glycosaminoglycan (GAG) side chains in such injuries have been extensively studied. CNS injury immediately alters endothelial and extracellular matrix (ECM) PGs and GAGs. Subsequently, these alterations contribute to acute injury, post-injury fibrosis, and post-injury repair. These effects are central to the pathophysiology of CNS injury. This review focuses on the importance of PGs and GAGs in multiple forms of injury including traumatic brain injury, spinal cord injury, and stroke. We highlight the causes and consequences of degradation of the PG and GAG-enriched endothelial glycocalyx in early injury and discuss the pleiotropic roles of PGs in neuroinflammation. We subsequently evaluate the dualistic effects of PGs on recovery: both PG/GAG-mediated inhibition and facilitation of repair. We then report promising therapeutic strategies that may prove effective for repair of CNS injury including PG receptor inhibition, delivery of endogenous, pro-repair PGs and GAGs, and direct degradation of pathologic GAGs. Last, we discuss importance of two PG- and GAG-containing ECM structures (synapses and perineuronal nets) in CNS injury and recovery.

Sulfation Pathways During Neurodevelopment

Sulfate is an important nutrient that modulates a diverse range of molecular and cellular functions in mammalian physiology. Over the past 2 decades, animal studies have linked numerous sulfate maintenance genes with neurological phenotypes, including seizures, impaired neurodevelopment, and behavioral abnormalities. Despite sulfation pathways being highly conserved between humans and animals, less than one third of all known sulfate maintenance genes are clinically reportable. In this review, we curated the temporal and spatial expression of 91 sulfate maintenance genes in human fetal brain from 4 to 17 weeks post conception using the online Human Developmental Biology Resource Expression. In addition, we performed a systematic search of PubMed and Embase, identifying those sulfate maintenance genes linked to atypical neurological phenotypes in humans and animals. Those findings, together with a search of the Online Mendelian Inheritance in Man database, identified a total of 18 candidate neurological dysfunction genes that are not yet considered in clinical settings. Collectively, this article provides an overview of sulfate biology genes to inform future investigations of perturbed sulfate homeostasis associated with neurological conditions.

Emerging therapeutic role of chondroitinase (ChABC) in neurological disorders and cancer

Abstract:

Proteoglycans are essential biomacromolecules that participate in matrix structure and organization, cell proliferation and migration, and cell surface signal transduction. However, their roles in physiology, particularly in CNS remain incompletely deciphered. Numerous studies highlight the elevated levels of chondroitin sulphate proteoglycans (CSPGs) in various diseases like cancers and neurological disorders like spinal cord injury (SCI), traumatic brain damage, neurodegenerative diseases, and are mainly implicated to hinder tissue repair. In such a context, chondroitinase ABC (ChABC), a therapeutic enzyme has shown immense hope to treat these diseases in several preclinical studies, primarily attributed to the digestion of the side chains of the proteoglycan chondroitin sulphate (CS) molecule. Despite extensive research, the progress in evolving the concept of therapeutic targeting of proteoglycans is still in its infancy. This review thus provides fresh insights into the emerging therapeutic applications of ChABC in various diseases apart from SCI and the underlying mechanisms.

Biallelic variants in SLC35B2 cause a novel chondrodysplasia with hypomyelinating leukodystrophy

Sulfated proteoglycans are essential in skeletal and brain development. Recently, pathogenic variants in genes encoding proteins involved in the proteoglycan biosynthesis have been identified in a range of chondrodysplasia associated with intellectual disability. Nevertheless, several patients remain with unidentified molecular basis. This study aimed to contribute to the deciphering of new molecular bases in patients with chondrodysplasia and neuro-developmental disease. Exome sequencing was performed to identify pathogenic variants in patients presenting with chondrodysplasia and intellectual disability. The pathogenic effects of the potentially causative variants were analyzed by functional studies. We identified homozygous variants (c.1218_1220del and c.1224_1225del) in SLC35B2 in two patients with pre- and postnatal growth retardation, scoliosis, severe motor and intellectual disabilities and hypomyelinating leukodystrophy. By functional analyses, we showed that the variants affect SLC35B2 mRNA expression and protein subcellular localization leading to a functional impairment of the protein. Consistent with those results, we detected proteoglycan sulfation impairment in SLC35B2 patient fibroblasts and serum. Our data support that SLC35B2 functional impairment causes a novel syndromic chondrodysplasia with hypomyelinating leukodystrophy, most likely through a proteoglycan sulfation defect. This is the first time that SLC35B2 variants are associated with bone and brain development in human.

Protective Effects of a synthetic glycosaminoglycan mimetic (OTR4132) in a rat immunotoxic lesion model of septohippocampal cholinergic degeneration

Using a partial hippocampal cholinergic denervation model, we assessed the effects of the RGTA^® named OTR4132, a synthetic heparan-mimetic biopolymer with neuroprotective/neurotrophic properties. Long-Evans male rats were injected with the cholinergic immunotoxin 192 IgG-saporin into the medial septum/diagonal band of Broca (0.37 µg); vehicle injections served as controls. Immediately after surgery, OTR4132 was injected into the lateral ventricles (0.25 µg/5 µl/rat) or intramuscularly (1.5 mg/kg). To determine whether OTR4132 reached the lesion site, some rats received intracerebroventricular (ICV) or intramuscular (I.M.) injections of fluorescent OTR4132. Rats were sacrificed at 4, 10, 20, or 60 days post-lesion (DPL). Fluorescein-labeled OTR4132 injected ICV or I.M. was found in the lesion from 4 to 20 DPL. Rats with partial hippocampal cholinergic denervation showed decreases in hippocampal acetylcholinesterase reaction products and in choline acetyltransferase-positive neurons in the medial septum. These lesions were the largest at 10 DPL and then remained stable until 60 DPL. Both hippocampal acetylcholinesterase reaction products and choline acetyltransferase-positive neurons in the medial septum effects were significantly attenuated in OTR4132-treated rats. These effects were not related to competition between OTR4132 and 192 IgG-saporin for the neurotrophin receptor P75 (p75^NTR), as OTR4132 treatment did not alter the internalization of Cy3-labelled 192 IgG. OTR4132 was more efficient at reducing the acetylcholinesterase reaction products and choline acetyltransferase-positive neurons than a comparable heparin dose used as a comparator. Using the slice superfusion technique, we found that the lesion-induced decrease in muscarinic autoreceptor sensitivity was abolished by intramuscular OTR4132. After partial cholinergic damage, OTR4132 was able to concentrate at the brain lesion site possibly due to the disruption of the blood-brain barrier and to exert structural and functional effects that hold promises for neuroprotection/neurotrophism.

Mammalian brain glycoproteins exhibit diminished glycan complexity compared to other tissues

Glycosylation is essential to brain development and function, but prior studies have often been limited to a single analytical technique and excluded region- and sex-specific analyses. Here, using several methodologies, we analyze Asn-linked and Ser/Thr/Tyr-linked protein glycosylation between brain regions and sexes in mice. Brain N-glycans are less complex in sequence and variety compared to other tissues, consisting predominantly of high-mannose and fucosylated/bisected structures. Most brain O-glycans are unbranched, sialylated O-GalNAc and O-mannose structures. A consistent pattern is observed between regions, and sex differences are minimal compared to those in plasma. Brain glycans correlate with RNA expression of their synthetic enzymes, and analysis of glycosylation genes in humans show a global downregulation in the brain compared to other tissues. We hypothesize that this restricted repertoire of protein glycans arises from their tight regulation in the brain. These results provide a roadmap for future studies of glycosylation in neurodevelopment and disease.

The cerebrospinal fluid proteome of preterm infants predicts neurodevelopmental outcome

BACKGROUND

Survival rate increases for preterm infants, but long-term neurodevelopmental outcome predictors are lacking. Our primary aim was to determine whether a specific proteomic profile in cerebrospinal fluid (CSF) of preterm infants differs from that of term infants and to identify novel biomarkers of neurodevelopmental outcome in preterm infants.

METHODS

Twenty-seven preterm infants with median gestational age 27 w + 4 d and ten full-term infants were enrolled prospectively. Protein profiling of CSF were performed utilizing an antibody suspension bead array. The relative levels of 178 unique brain derived proteins and inflammatory mediators, selected from the Human Protein Atlas, were measured.

RESULTS

The CSF protein profile of preterm infants differed from that of term infants. Increased levels of brain specific proteins that are associated with neurodevelopment and neuroinflammatory pathways made up a distinct protein profile in the preterm infants. The most significant differences were seen in proteins involved in neurodevelopmental regulation and synaptic plasticity, as well as components of the innate immune system. Several proteins correlated with favorable outcome in preterm infants at 18-24 months corrected age. Among the proteins that provided strong predictors of outcome were vascular endothelial growth factor C, Neurocan core protein and seizure protein 6, all highly important in normal brain development.

CONCLUSION

Our data suggest a vulnerability of the preterm brain to postnatal events and that alterations in protein levels may contribute to unfavorable neurodevelopmental outcome.

Impaired neural differentiation of MPS IIIA patient induced pluripotent stem cell-derived neural progenitor cells

Mucopolysaccharidosis type IIIA (MPS IIIA) is characterised by a progressive neurological decline leading to early death. It is caused by bi-allelic loss-of-function mutations in SGSH encoding sulphamidase, a lysosomal enzyme required for heparan sulphate glycosaminoglycan (HS GAG) degradation, that results in the progressive build-up of HS GAGs in multiple tissues most notably the central nervous system (CNS). Skin fibroblasts from two MPS IIIA patients who presented with an intermediate and a severe clinical phenotype, respectively, were reprogrammed into induced pluripotent stem cells (iPSCs). The intermediate MPS IIIA iPSCs were then differentiated into neural progenitor cells (NPCs) and subsequently neurons. The patient derived fibroblasts, iPSCs, NPCs and neurons all displayed hallmark biochemical characteristics of MPS IIIA including reduced sulphamidase activity and increased accumulation of an MPS IIIA HS GAG biomarker. Proliferation of MPS IIIA iPSC-derived NPCs was reduced compared to control, but could be partially rescued by reintroducing functional sulphamidase enzyme, or by doubling the concentration of the mitogen fibroblast growth factor 2 (FGF2). Whilst both control heparin, and MPS IIIA HS GAGs had a similar binding affinity for FGF2, only the latter inhibited FGF signalling, suggesting accumulated MPS IIIA HS GAGs disrupt the FGF2:FGF2 receptor:HS signalling complex. Neuronal differentiation of MPS IIIA iPSC-derived NPCs was associated with a reduction in the expression of neuronal cell marker genes βIII-TUBULIN, NF-H and NSE, revealing reduced neurogenesis compared to control. A similar result was achieved by adding MPS IIIA HS GAGs to the culture medium during neuronal differentiation of control iPSC-derived NPCs. This study demonstrates the generation of MPS IIIA iPSCs, and NPCs, the latter of which display reduced proliferation and neurogenic capacity. Reduced NPC proliferation can be explained by a model in which soluble MPS IIIA HS GAGs compete with cell surface HS for FGF2 binding. The mechanism driving reduced neurogenesis remains to be determined but appears downstream of MPS IIIA HS GAG accumulation.

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.

Protein post-translational modifications after spinal cord injury

Deficits in intrinsic neuronal capacities in the spinal cord, a lack of growth support, and suppression of axonal outgrowth by inhibitory molecules mean that spinal cord injury almost always has devastating consequences. As such, one of the primary targets for the treatment of spinal cord injury is to develop strategies to antagonize extrinsic or intrinsic axonal growth-inhibitory factors or enhance the factors that support axonal growth. Among these factors, a series of individual protein level disorders have been identified during the generation of axons following spinal cord injury. Moreover, an increasing number of studies have indicated that post-translational modifications of these proteins have important implications for axonal growth. Some researchers have discovered a variety of post-translational modifications after spinal cord injury, such as tyrosination, acetylation, and phosphorylation. In this review, we reviewed the post-translational modifications for axonal growth, functional recovery, and neuropathic pain after spinal cord injury, a better understanding of which may elucidate the dynamic change of spinal cord injury-related molecules and facilitate the development of a new therapeutic strategy for spinal cord injury.

Is Galactose a Hormetic Sugar? An Exploratory Study of the Rat Hippocampal Redox Regulatory Network

SCOPE

Galactose, a ubiquitous monosaccharide with incompletely understood physiology is often exploited for inducing oxidative-stress mediated aging in animals. Recent research demonstrates that galactose can conserve cellular function during periods of starvation and prevent/alleviate cognitive deficits in a rat model of sporadic Alzheimer's disease. The present aim is to examine the acute effects of oral galactose on the redox regulatory network (RRN).

METHODS AND RESULTS

Rat plasma and hippocampal RRNs are analyzed upon acute orogastric gavage of galactose (200 mg kg^-1 ). No systemic RRN disbalance is observed; however, a mild pro-oxidative shift accompanied by a paradoxical increment in tissue reductive capacity suggesting overcompensation of endogenous antioxidant systems is observed in the hippocampus. Galactose-induced increment of reductive capacity is accompanied by inflation of the hippocampal pool of nicotinamide adenine dinucleotide phosphates indicating ROS detoxification through disinhibition of the oxidative pentose phosphate pathway flux, reduced neuronal activity, and upregulation of Leloir pathway gatekeeper enzyme galactokinase-1.

CONCLUSION

Based on the observed findings, and in the context of previous work on galactose, a hormetic hypothesis of galactose is proposed suggesting that the protective effects may be inseparable from its pro-oxidative action at the biochemical level.

Quantitative Proteomics Reveals Significant Differences between Mouse Brain Formations in Expression of Proteins Involved in Neuronal Plasticity during Aging

Aging is associated with a general decline in cognitive functions, which appears to be due to alterations in the amounts of proteins involved in the regulation of synaptic plasticity. Here, we present a quantitative analysis of proteins involved in neurotransmission in three brain regions, namely, the hippocampus, the cerebral cortex and the cerebellum, in mice aged 1 and 22 months, using the total protein approach technique. We demonstrate that although the titer of some proteins involved in neurotransmission and synaptic plasticity is affected by aging in a similar manner in all the studied brain formations, in fact, each of the formations represents its own mode of aging. Generally, the hippocampal and cortical proteomes are much more unstable during the lifetime than the cerebellar proteome. The data presented here provide a general picture of the effect of physiological aging on synaptic plasticity and might suggest potential drug targets for anti-aging therapies.

STAU2 binds a complex RNA cargo that changes temporally with production of diverse intermediate progenitor cells during mouse corticogenesis

STAU2 is a double-stranded RNA-binding protein enriched in the nervous system. During asymmetric divisions in the developing mouse cortex, STAU2 preferentially distributes into the intermediate progenitor cell (IPC), delivering RNA molecules that can impact IPC behavior. Corticogenesis occurs on a precise time schedule, raising the hypothesis that the cargo STAU2 delivers into IPCs changes over time. To test this, we combine RNA-immunoprecipitation with sequencing (RIP-seq) over four stages of mouse cortical development, generating a comprehensive cargo profile for STAU2. A subset of the cargo was 'stable', present at all stages, and involved in chromosome organization, macromolecule localization, translation and DNA repair. Another subset was 'dynamic', changing with cortical stage, and involved in neurogenesis, cell projection organization, neurite outgrowth, and included cortical layer markers. Notably, the dynamic STAU2 cargo included determinants of IPC versus neuronal fates and genes contributing to abnormal corticogenesis. Knockdown of one STAU2 target, Taf13, previously linked to microcephaly and impaired myelination, reduced oligodendrogenesis in vitro. We conclude that STAU2 contributes to the timing of corticogenesis by binding and delivering complex and temporally regulated RNA cargo into IPCs.

Chemotherapy-Induced Degradation of Glycosylated Components of the Brain Extracellular Matrix Promotes Glioblastoma Relapse Development in an Animal Model

Adjuvant chemotherapy with temozolomide (TMZ) is an intrinsic part of glioblastoma multiforme (GBM) therapy targeted to eliminate residual GBM cells. Despite the intensive treatment, a GBM relapse develops in the majority of cases resulting in poor outcome of the disease. Here, we investigated off-target negative effects of the systemic chemotherapy on glycosylated components of the brain extracellular matrix (ECM) and their functional significance. Using an elaborated GBM relapse animal model, we demonstrated that healthy brain tissue resists GBM cell proliferation and invasion, thereby restricting tumor development. TMZ-induced [especially in combination with dexamethasone (DXM)] changes in composition and content of brain ECM proteoglycans (PGs) resulted in the accelerated adhesion, proliferation, and invasion of GBM cells into brain organotypic slices ex vivo and more active growth and invasion of experimental xenograft GBM tumors in SCID mouse brain in vivo. These changes occurred both at core proteins and polysaccharide chain levels, and degradation of chondroitin sulfate (CS) was identified as a key event responsible for the observed functional effects. Collectively, our findings demonstrate that chemotherapy-induced changes in glycosylated components of brain ECM can impact the fate of residual GBM cells and GBM relapse development. ECM-targeted supportive therapy might be a useful strategy to mitigate the negative off-target effects of the adjuvant GBM treatment and increase the relapse-free survival of GBM patients.

Characterization of the Striatal Extracellular Matrix in a Mouse Model of Parkinson's Disease

Parkinson’s disease’s etiology is unknown, although evidence suggests the involvement of oxidative modifications of intracellular components in disease pathobiology. Despite the known involvement of the extracellular matrix in physiology and disease, the influence of oxidative stress on the matrix has been neglected. The chemical modifications that might accumulate in matrix components due to their long half-live and the low amount of extracellular antioxidants could also contribute to the disease and explain ineffective cellular therapies. The enriched striatal extracellular matrix from a mouse model of Parkinson’s disease was characterized by Raman spectroscopy. We found a matrix fingerprint of increased oxalate content and oxidative modifications. To uncover the effects of these changes on brain cells, we morphologically characterized the primary microglia used to repopulate this matrix and further quantified the effects on cellular mechanical stress by an intracellular fluorescence resonance energy transfer (FRET)-mechanosensor using the U-2 OS cell line. Our data suggest changes in microglia survival and morphology, and a decrease in cytoskeletal tension in response to the modified matrix from both hemispheres of 6-hydroxydopamine (6-OHDA)-lesioned animals. Collectively, these data suggest that the extracellular matrix is modified, and underscore the need for its thorough investigation, which may reveal new ways to improve therapies or may even reveal new therapies.

Rabbit PrP Is Partially Resistant to in vitro Aggregation Induced by Different Biological Cofactors

Prion diseases have been described in humans and other mammals, including sheep, goats, cattle, and deer. Since mice, hamsters, and cats are susceptible to prion infection, they are often used to study the mechanisms of prion infection and conversion. Mammals, such as horses and dogs, however, do not naturally contract the disease and are resistant to infection, while others, like rabbits, have exhibited low susceptibility. Infection involves the conversion of the cellular prion protein (PrP^C) to the scrapie form (PrP^Sc), and several cofactors have already been identified as important adjuvants in this process, such as glycosaminoglycans (GAGs), lipids, and nucleic acids. The molecular mechanisms that determine transmissibility between species remain unclear, as well as the barriers to transmission. In this study, we examine the interaction of recombinant rabbit PrP^C (RaPrP) with different biological cofactors such as GAGs (heparin and dermatan sulfate), phosphatidic acid, and DNA oligonucleotides (A1 and D67) to evaluate the importance of these cofactors in modulating the aggregation of rabbit PrP and explain the animal’s different degrees of resistance to infection. We used spectroscopic and chromatographic approaches to evaluate the interaction with cofactors and their effect on RaPrP aggregation, which we compared with murine PrP (MuPrP). Our data show that all cofactors induce RaPrP aggregation and exhibit pH dependence. However, RaPrP aggregated to a lesser extent than MuPrP in the presence of any of the cofactors tested. The binding affinity with cofactors does not correlate with these low levels of aggregation, suggesting that the latter are related to the stability of PrP at acidic pH. The absence of the N-terminus affected the interaction with cofactors, influencing the efficiency of aggregation. These findings demonstrate that the interaction with polyanionic cofactors is related to rabbit PrP being less susceptible to aggregation in vitro and that the N-terminal domain is important to the efficiency of conversion, increasing the interaction with cofactors. The decreased effect of cofactors in rabbit PrP likely explains its lower propensity to prion conversion.

Heparan Sulfate Proteoglycans in Viral Infection and Treatment: A Special Focus on SARS-CoV-2

Heparan sulfate proteoglycans (HSPGs) encompass a group of glycoproteins composed of unbranched negatively charged heparan sulfate (HS) chains covalently attached to a core protein. The complex HSPG biosynthetic machinery generates an extraordinary structural variety of HS chains that enable them to bind a plethora of ligands, including growth factors, morphogens, cytokines, chemokines, enzymes, matrix proteins, and bacterial and viral pathogens. These interactions translate into key regulatory activity of HSPGs on a wide range of cellular processes such as receptor activation and signaling, cytoskeleton assembly, extracellular matrix remodeling, endocytosis, cell-cell crosstalk, and others. Due to their ubiquitous expression within tissues and their large functional repertoire, HSPGs are involved in many physiopathological processes; thus, they have emerged as valuable targets for the therapy of many human diseases. Among their functions, HSPGs assist many viruses in invading host cells at various steps of their life cycle. Viruses utilize HSPGs for the attachment to the host cell, internalization, intracellular trafficking, egress, and spread. Recently, HSPG involvement in the pathogenesis of SARS-CoV-2 infection has been established. Here, we summarize the current knowledge on the molecular mechanisms underlying HSPG/SARS-CoV-2 interaction and downstream effects, and we provide an overview of the HSPG-based therapeutic strategies that could be used to combat such a fearsome virus.

Bioinformatic analysis of the human brain extracellular matrix proteome in neurodegenerative disorders

Alzheimer's, Parkinson's, and Huntington's diseases are characterized by selective degeneration of specific brain areas. Although increasing number of studies report alteration of the extracellular matrix on these diseases, an exhaustive characterization at the brain's matrix level might contribute to the development of more efficient cell restoration therapies. In that regard, proteomics-based studies are a powerful approach to uncover matrix changes. However, to date, the majority of proteomics studies report no or only a few brain matrix proteins with altered expression. This study aims to reveal the changes in the brain extracellular matrix by integrating several proteomics-based studies performed with postmortem tissue. In total, 67 matrix proteins with altered expression were collected. By applying a bioinformatic approach, we were able to reveal the dysregulated biological processes. Among them are processes related to the organization of the extracellular matrix, glycosaminoglycans and proteoglycans' metabolism, blood coagulation, and response to injury and oxidative stress. In addition, a protein was found altered in all three diseases-collagen type I alpha 2-and its binding partners further identified. A ClueGO network was created, depicting the GO groups associated with these binding partners, uncovering the processes that may consequently be affected. These include cellular adhesion, cell signaling through membrane receptors, inflammatory processes, and apoptotic cell death in response to oxidative stress. Overall, we were able to associate the contribution of the modification of extracellular matrix components to essential biological processes, highlighting the investment needed on proteomics studies with specific focus on the extracellular matrix in neurodegeneration.

Maturation-Dependent Differences in the Re-innervation of the Denervated Dentate Gyrus by Sprouting Associational and Commissural Mossy Cell Axons in Organotypic Tissue Cultures of Entorhinal Cortex and Hippocampus

Sprouting of surviving axons is one of the major reorganization mechanisms of the injured brain contributing to a partial restoration of function. Of note, sprouting is maturation as well as age-dependent and strong in juvenile brains, moderate in adult and weak in aged brains. We have established a model system of complex organotypic tissue cultures to study sprouting in the dentate gyrus following entorhinal denervation. Entorhinal denervation performed after 2 weeks postnatally resulted in a robust, rapid, and very extensive sprouting response of commissural/associational fibers, which could be visualized using calretinin as an axonal marker. In the present study, we analyzed the effect of maturation on this form of sprouting and compared cultures denervated at 2 weeks postnatally with cultures denervated at 4 weeks postnatally. Calretinin immunofluorescence labeling as well as time-lapse imaging of virally-labeled (AAV2-hSyn1-GFP) commissural axons was employed to study the sprouting response in aged cultures. Compared to the young cultures commissural/associational sprouting was attenuated and showed a pattern similar to the one following entorhinal denervation in adult animals in vivo. We conclude that a maturation-dependent attenuation of sprouting occurs also in vitro, which now offers the chance to study, understand and influence maturation-dependent differences in brain repair in these culture preparations.

The CNS/PNS Extracellular Matrix Provides Instructive Guidance Cues to Neural Cells and Neuroregulatory Proteins in Neural Development and Repair

Background. The extracellular matrix of the PNS/CNS is unusual in that it is dominated by glycosaminoglycans, especially hyaluronan, whose space filling and hydrating properties make essential contributions to the functional properties of this tissue. Hyaluronan has a relatively simple structure but its space-filling properties ensure micro-compartments are maintained in the brain ultrastructure, ensuring ionic niches and gradients are maintained for optimal cellular function. Hyaluronan has cell-instructive, anti-inflammatory properties and forms macro-molecular aggregates with the lectican CS-proteoglycans, forming dense protective perineuronal net structures that provide neural and synaptic plasticity and support cognitive learning. Aims. To highlight the central nervous system/peripheral nervous system (CNS/PNS) and its diverse extracellular and cell-associated proteoglycans that have cell-instructive properties regulating neural repair processes and functional recovery through interactions with cell adhesive molecules, receptors and neuroregulatory proteins. Despite a general lack of stabilising fibrillar collagenous and elastic structures in the CNS/PNS, a sophisticated dynamic extracellular matrix is nevertheless important in tissue form and function. Conclusions. This review provides examples of the sophistication of the CNS/PNS extracellular matrix, showing how it maintains homeostasis and regulates neural repair and regeneration.

Perineuronal net abnormalities in Slc13a4+/- mice are rescued by postnatal administration of N-acetylcysteine

Disruptions to either sulfate supply or sulfation enzymes can affect brain development and have long-lasting effects on brain function, yet our understanding of the molecular mechanisms governing this are incomplete. Perineuronal nets (PNNs) are highly sulfated, specialized extracellular matrix structures that regulate the maturation of synaptic connections and neuronal plasticity. We have previously shown that mice heterozygous for the brain sulfate transporter Slc13a4 have abnormal social interactions, memory, exploratory behaviors, stress and anxiety of postnatal origin, pointing to potential deficits in PNN biology, and implicate SLC13A4 as a critical factor required for regulating normal synaptic connectivity and function. Here, we sought to investigate aberrant PNN formation as a potential mechanism contributing to the functional deficits displayed by Slc13a4^+/- mice. Following social interactions, we reveal reduced neuronal activation in the somatosensory cortex of Slc13a4^+/- mice, and altered inhibitory and excitatory postsynaptic currents. In line with this, we found a reduction in parvalbumin-expressing neurons decorated with PNNs, as well as reduced expression of markers for PNN maturation. Finally, we reveal that postnatal administration of N-acetylcysteine prevented PNN abnormalities from manifesting in Slc13a4^+/- adult animals. Collectively, these data highlight a central role for postnatal SLC13A4 in normal PNN formation, circuit function and subsequent animal behavior.