Heparan sulphate proteoglycans in glia and in the normal and injured CNS: expression of sulphotransferases and changes in sulphation

A role for decorin in improving motor deficits after traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death and disability due to injury worldwide. Extracellular matrix (ECM) remodeling is known to significantly contribute to TBI pathophysiology. Glycosaminoglycans, which are long-chain, variably sulfated polysaccharides abundant within the ECM, have previously been shown to be substantially altered after TBI. In this study, we sought to delineate the dynamics of glycosaminoglycan alterations after TBI and discover the precise biologic processes responsible for observed glycosaminoglycan changes after injury. We performed state-of-the art mass spectrometry on brain tissues isolated from mice after TBI or craniotomy-alone. We observed dynamic changes in glycosaminoglycans at Day 1 and 7 post-TBI, with heparan sulfate, chondroitin sulfate, and hyaluronan remaining significantly increased after a week vis-à-vis craniotomy-alone tissues. We did not observe appreciable changes in circulating glycosaminoglycans in mice after experimental TBI compared to craniotomy-alone nor in patients with TBI and severe polytrauma compared to control patients with mild injuries, suggesting increases in injury site glycosaminoglycans are driven by local synthesis. We subsequently performed an unbiased whole genome transcriptomics analysis on mouse brain tissues 7 days post-TBI and discovered a significant induction of hyaluronan synthase 2, glypican-3, and decorin. The functional role of decorin after injury was further examined through multimodal behavioral testing comparing wild-type and Dcn-/- mice. We discovered that genetic ablation of Dcn led to an overall negative effect of TBI on function, exacerbating motor impairments after TBI. Collectively, our results provide a spatiotemporal characterization of post-TBI glycosaminoglycan alterations in the brain ECM and support an important adaptive role for decorin upregulation after TBI.

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.

CXCL9 recombinant adeno-associated virus (AAV) virotherapy sensitizes glioblastoma (GBM) to anti-PD-1 immune checkpoint blockade

The promise of immunotherapy to induce long-term durable responses in conventionally treatment resistant tumors like glioblastoma (GBM) has given hope for patients with a dismal prognosis. Yet, few patients have demonstrated a significant survival benefit despite multiple clinical trials designed to invigorate immune recognition and tumor eradication. Insights gathered over the last two decades have revealed numerous mechanisms by which glioma cells resist conventional therapy and evade immunological detection, underscoring the need for strategic combinatorial treatments as necessary to achieve appreciable therapeutic effects. However, new combination therapies are inherently difficult to develop as a result of dose-limiting toxicities, the constraints of the blood-brain barrier, and the suppressive nature of the GBM tumor microenvironment (TME). GBM is notoriously devoid of lymphocytes driven in part by a paucity of lymphocyte trafficking factors necessary to prompt their recruitment, infiltration, and activation. We have developed a novel recombinant adeno-associated virus (AAV) gene therapy strategy that enables focal and stable reconstitution of the GBM TME with C-X-C motif ligand 9 (CXCL9), a powerful call-and-receive chemokine for cytotoxic T lymphocytes (CTLs). By precisely manipulating local chemokine directional guidance, AAV-CXCL9 increases tumor infiltration by CD8-postive cytotoxic lymphocytes, sensitizing GBM to anti-PD-1 immune checkpoint blockade (ICB). These effects are accompanied by immunologic signatures evocative of an inflamed and responsive TME. These findings support targeted AAV gene therapy as a promising adjuvant strategy for reconditioning GBM immunogenicity given its excellent safety profile, TME-tropism, modularity, and off-the-shelf capability, where focal delivery bypasses the constrains of the blood-brain barrier, further mitigating risks observed with high-dose systemic therapy.

Astrocytes Are a Key Target for Neurotropic Viral Infection

Astrocytes are increasingly recognized as important viral host cells in the central nervous system. These cells can produce relatively high quantities of new virions. In part, this can be attributed to the characteristics of astrocyte metabolism and its abundant and dynamic cytoskeleton network. Astrocytes are anatomically localized adjacent to interfaces between blood capillaries and brain parenchyma and between blood capillaries and brain ventricles. Moreover, astrocytes exhibit a larger membrane interface with the extracellular space than neurons. These properties, together with the expression of various and numerous viral entry receptors, a relatively high rate of endocytosis, and morphological plasticity of intracellular organelles, render astrocytes important target cells in neurotropic infections. In this review, we describe factors that mediate the high susceptibility of astrocytes to viral infection and replication, including the anatomic localization of astrocytes, morphology, expression of viral entry receptors, and various forms of autophagy.

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.

Low sulfated heparan sulfate mimetic differentially affects repair in immune-mediated and toxin-induced experimental models of demyelination

There is an urgent need for therapies that target the multicellular pathology of central nervous system (CNS) disease. Modified, nonanticoagulant heparins mimic the heparan sulfate glycan family and are known regulators of multiple cellular processes. In vitro studies have demonstrated that low sulfated modified heparin mimetics (LS-mHeps) drive repair after CNS demyelination. Herein, we test LS-mHep7 (an in vitro lead compound) in experimental autoimmune encephalomyelitis (EAE) and cuprizone-induced demyelination. In EAE, LS-mHep7 treatment resulted in faster recovery and rapidly reduced inflammation which was accompanied by restoration of animal weight. LS-mHep7 treatment had no effect on remyelination or on OLIG2 positive oligodendrocyte numbers within the corpus callosum in the cuprizone model. Further in vitro investigation confirmed that LS-mHep7 likely mediates its pro-repair effect in the EAE model by sequestering inflammatory cytokines, such as CCL5 which are upregulated during immune-mediated inflammatory attacks. These data support the future clinical translation of this next generation modified heparin as a treatment for CNS diseases with active immune system involvement.

Validation of Recombinant Heparan Sulphate Reagents for CNS Repair

Therapies that target the multicellular pathology of central nervous system (CNS) disease/injury are urgently required. Modified non-anticoagulant heparins mimic the heparan sulphate (HS) glycan family and have been proposed as therapeutics for CNS repair since they are effective regulators of numerous cellular processes. Our in vitro studies have demonstrated that low-sulphated modified heparan sulphate mimetics (LS-mHeps) drive CNS repair. However, LS-mHeps are derived from pharmaceutical heparin purified from pig intestines, in a supply chain at risk of shortages and contamination. Alternatively, cellular synthesis of heparin and HS can be achieved using mammalian cell multiplex genome engineering, providing an alternative source of recombinant HS mimetics (rHS). TEGA Therapeutics (San Diego) have manufactured rHS reagents with varying degrees of sulphation and we have validated their ability to promote repair in vitro using models that mimic CNS injury, making comparisons to LS-mHep7, a previous lead compound. We have shown that like LS-mHep7, low-sulphated rHS compounds promote remyelination and reduce features of astrocytosis, and in contrast, highly sulphated rHS drive neurite outgrowth. Cellular production of heparin mimetics may, therefore, offer potential clinical benefits for CNS repair.

Proteoglycan Sulphation in the Function of the Mature Central Nervous System

Chondroitin sulphate and heparan sulphate proteoglycans (CSPGS and HSPGs) are found throughout the central nervous system (CNS). CSPGs are ubiquitous in the diffuse extracellular matrix (ECM) between cells and are a major component of perineuronal nets (PNNs), the condensed ECM present around some neurons. HSPGs are more associated with the surface of neurons and glia, with synapses and in the PNNs. Both CSPGs and HSPGs consist of a protein core to which are attached repeating disaccharide chains modified by sulphation at various positions. The sequence of sulphation gives the chains a unique structure and local charge density. These sulphation codes govern the binding properties and biological effects of the proteoglycans. CSPGs are sulphated along their length, the main forms being 6- and 4-sulphated. In general, the chondroitin 4-sulphates are inhibitory to cell attachment and migration, while chondroitin 6-sulphates are more permissive. HSPGs tend to be sulphated in isolated motifs with un-sulphated regions in between. The sulphation patterns of HS motifs and of CS glycan chains govern their binding to the PTPsigma receptor and binding of many effector molecules to the proteoglycans, such as growth factors, morphogens, and molecules involved in neurodegenerative disease. Sulphation patterns change as a result of injury, inflammation and ageing. For CSPGs, attention has focussed on PNNs and their role in the control of plasticity and memory, and on the soluble CSPGs upregulated in glial scar tissue that can inhibit axon regeneration. HSPGs have key roles in development, regulating cell migration and axon growth. In the adult CNS, they have been associated with tau aggregation and amyloid-beta processing, synaptogenesis, growth factor signalling and as a component of the stem cell niche. These functions of CSPGs and HSPGs are strongly influenced by the pattern of sulphation of the glycan chains, the sulphation code. This review focuses on these sulphation patterns and their effects on the function of the mature CNS.

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.

THAP1 modulates oligodendrocyte maturation by regulating ECM degradation in lysosomes

Mechanisms controlling myelination during central nervous system (CNS) maturation play a pivotal role in the development and refinement of CNS circuits. The transcription factor THAP1 is essential for timing the inception of myelination during CNS maturation through a cell-autonomous role in the oligodendrocyte lineage. Here, we demonstrate that THAP1 modulates the extracellular matrix (ECM) composition by regulating glycosaminoglycan (GAG) catabolism within oligodendrocyte progenitor cells (OPCs). Thap1 ^-/- OPCs accumulate and secrete excess GAGs, inhibiting their maturation through an autoinhibitory mechanism. THAP1 controls GAG metabolism by binding to and regulating the GusB gene encoding β-glucuronidase, a GAG-catabolic lysosomal enzyme. Applying GAG-degrading enzymes or overexpressing β-glucuronidase rescues Thap1 ^-/- OL maturation deficits in vitro and in vivo. Our studies establish lysosomal GAG catabolism within OPCs as a critical mechanism regulating oligodendrocyte development.

Axonal Regeneration by Glycosaminoglycan

Like other biomolecules including nucleic acid and protein, glycan plays pivotal roles in various cellular processes. For instance, it modulates protein folding and stability, organizes extracellular matrix and tissue elasticity, and regulates membrane trafficking. In addition, cell-surface glycans are often utilized as entry receptors for viruses, including SARS-CoV-2. Nevertheless, its roles as ligands to specific surface receptors have not been well understood with a few exceptions such as selectins and siglecs. Recent reports have demonstrated that chondroitin sulfate and heparan sulfate, both of which are glycosaminoglycans, work as physiological ligands on their shared receptor, protein tyrosine phosphatase sigma (PTPσ). These two glycans differentially determine the fates of neuronal axons after injury in our central nervous system. That is, heparan sulfate promotes axonal regeneration while chondroitin sulfate inhibits it, inducing dystrophic endbulbs at the axon tips. In our recent study, we demonstrated that the chondroitin sulfate (CS)-PTPσ axis disrupted autophagy flux at the axon tips by dephosphorylating cortactin. In this minireview, we introduce how glycans work as physiological ligands and regulate their intracellular signaling, especially focusing on chondroitin sulfate.

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.

Type IIa RPTPs and Glycans: Roles in Axon Regeneration and Synaptogenesis

Type IIa receptor tyrosine phosphatases (RPTPs) play pivotal roles in neuronal network formation. It is emerging that the interactions of RPTPs with glycans, i.e., chondroitin sulfate (CS) and heparan sulfate (HS), are critical for their functions. We highlight here the significance of these interactions in axon regeneration and synaptogenesis. For example, PTPσ, a member of type IIa RPTPs, on axon terminals is monomerized and activated by the extracellular CS deposited in neural injuries, dephosphorylates cortactin, disrupts autophagy flux, and consequently inhibits axon regeneration. In contrast, HS induces PTPσ oligomerization, suppresses PTPσ phosphatase activity, and promotes axon regeneration. PTPσ also serves as an organizer of excitatory synapses. PTPσ and neurexin bind one another on presynapses and further bind to postsynaptic leucine-rich repeat transmembrane protein 4 (LRRTM4). Neurexin is now known as a heparan sulfate proteoglycan (HSPG), and its HS is essential for the binding between these three molecules. Another HSPG, glypican 4, binds to presynaptic PTPσ and postsynaptic LRRTM4 in an HS-dependent manner. Type IIa RPTPs are also involved in the formation of excitatory and inhibitory synapses by heterophilic binding to a variety of postsynaptic partners. We also discuss the important issue of possible mechanisms coordinating axon extension and synapse formation.

Overcoming the inhibitory microenvironment surrounding oligodendrocyte progenitor cells following experimental demyelination

Chronic demyelination in the human CNS is characterized by an inhibitory microenvironment that impairs recruitment and differentiation of oligodendrocyte progenitor cells (OPCs) leading to failed remyelination and axonal atrophy. By network-based transcriptomics, we identified sulfatase 2 (Sulf2) mRNA in activated human primary OPCs. Sulf2, an extracellular endosulfatase, modulates the signaling microenvironment by editing the pattern of sulfation on heparan sulfate proteoglycans. We found that Sulf2 was increased in demyelinating lesions in multiple sclerosis and was actively secreted by human OPCs. In experimental demyelination, elevated OPC Sulf1/2 expression directly impaired progenitor recruitment and subsequent generation of oligodendrocytes thereby limiting remyelination. Sulf1/2 potentiates the inhibitory microenvironment by promoting BMP and WNT signaling in OPCs. Importantly, pharmacological sulfatase inhibition using PI-88 accelerated oligodendrocyte recruitment and remyelination by blocking OPC-expressed sulfatases. Our findings define an important inhibitory role of Sulf1/2 and highlight the potential for modulation of the heparanome in the treatment of chronic demyelinating disease.

Demyelination results in impairments in oligodendrocyte progenitor cell recruitment. Here the authors identify sulfatase 1/2 as a potential modulator of myelination by modulating the microenvironment around oligodendrocyte progenitor cells.

Application of Force to a Syndecan-4 Containing Complex With Thy-1-αVβ3 Integrin Accelerates Neurite Retraction

Inflammation contributes to the genesis and progression of chronic diseases, such as cancer and neurodegeneration. Upregulation of integrins in astrocytes during inflammation induces neurite retraction by binding to the neuronal protein Thy-1, also known as CD90. Additionally, Thy-1 alters astrocyte contractility and movement by binding to the mechano-sensors α_Vβ₃ integrin and Syndecan-4. However, the contribution of Syndecan-4 to neurite shortening following Thy-1-α_Vβ₃ integrin interaction remains unknown. To further characterize the contribution of Syndecan-4 in Thy-1-dependent neurite outgrowth inhibition and neurite retraction, cell-based assays under pro-inflammatory conditions were performed. In addition, using Optical Tweezers, we studied single-molecule binding properties between these proteins, and their mechanical responses. Syndecan-4 increased the lifetime of Thy-1-α_Vβ₃ integrin binding by interacting directly with Thy-1 and forming a ternary complex (Thy-1-α_Vβ₃ integrin + Syndecan-4). Under in vitro-generated pro-inflammatory conditions, Syndecan-4 accelerated the effect of integrin-engaged Thy-1 by forming this ternary complex, leading to faster neurite retraction and the inhibition of neurite outgrowth. Thus, Syndecan-4 controls neurite cytoskeleton contractility by modulating α_Vβ₃ integrin mechano-receptor function. These results suggest that mechano-transduction, cell-matrix and cell-cell interactions are likely critical events in inflammation-related disease development.

Glycan sulfation patterns define autophagy flux at axon tip via PTPRσ-cortactin axis

Chondroitin sulfate (CS) and heparan sulfate (HS) are glycosaminoglycans that both bind the receptor-type protein tyrosine phosphatase PTPRσ, affecting axonal regeneration. CS inhibits axonal growth, while HS promotes it. Here, we have prepared a library of HS octasaccharides and, together with synthetic CS oligomers, we found that PTPRσ preferentially interacts with CS-E-a rare sulfation pattern in natural CS-and most HS oligomers bearing sulfate and sulfamate groups. Consequently, short and long stretches of natural CS and HS, respectively, bind to PTPRσ. CS activates PTPRσ, which dephosphorylates cortactin-herein identified as a new PTPRσ substrate-and disrupts autophagy flux at the autophagosome-lysosome fusion step. Such disruption is required and sufficient for dystrophic endball formation and inhibition of axonal regeneration. Therefore, sulfation patterns determine the length of the glycosaminoglycan segment that bind to PTPRσ and define the fate of axonal regeneration through a mechanism involving PTPRσ, cortactin and autophagy.

Low sulfated heparins target multiple proteins for central nervous system repair

The lack of endogenous repair following spinal cord injury (SCI) accounts for the frequent permanent deficits for which effective treatments are absent. Previously, we demonstrated that low sulfated modified heparin mimetics (LS-mHeps) attenuate astrocytosis, suggesting they may represent a novel therapeutic approach. mHeps are glycomolecules with structural similarities to resident heparan sulfates (HS), which modulate cell signaling by both sequestering ligands, and acting as cofactors in the formation of ligand-receptor complexes. To explore whether mHeps can affect the myelination and neurite outgrowth necessary for repair after SCI, we created lesioned or demyelinated neural cell co-cultures and exposed them with a panel of mHeps with varying degrees and positions of their sulfate moieties. LS-mHep7 enhanced neurite outgrowth and myelination, whereas highly sulfated mHeps (HS-mHeps) had attenuating effects. LS-mHeps had no effects on myelination or neurite extension in developing, uninjured myelinating cultures, suggesting they might exert their proregenerating effects by modulating or sequestering inhibitory factors secreted after injury. To investigate this, we examined conditioned media from cultures using chemokine arrays and conducted an unbiased proteomics approach by applying TMT-LC/MS to mHep7 affinity purified conditioned media from these cultures. Multiple protein factors reported to play a role in damage or repair mechanisms were identified, including amyloid betaA4. Amyloid beta peptide (1-42) was validated as an important candidate by treating myelination cultures and shown to inhibit myelination. Thus, we propose that LS-mHeps exert multiple beneficial effects on mechanisms supporting enhanced repair, and represent novel candidates as therapeutics for CNS damage.

The influence of microenvironment and extracellular matrix molecules in driving neural stem cell fate within biomaterials

Transplantation of stem cells is a promising potential therapy for central nervous system disease and injury. The capacity for self-renewal, proliferation of progenitor cells, and multi-lineage potential underscores the need for controlling stem cell fate. Furthermore, transplantation within a hostile environment can lead to significant cell death and limited therapeutic potential. Tissue-engineered materials have been developed to both regulate stem cell fate, increase transplanted cell viability, and improve therapeutic outcomes. Traditionally, regulation of stem cell differentiation has been driven through soluble signals, such as growth factors. While these signals are important, insoluble factors from the local microenvironment or extracellular matrix (ECM) molecules also contribute to stem cell activity and fate. Understanding the microenvironment factors that influence stem cell fate, such as mechanical properties, topography, and presentation of specific ECM ligands, is necessary for designing improved biomaterials. Here we review some of the microenvironment factors that regulate stem cell fate and how they can be incorporated into biomaterials as part of potential CNS therapies.

Wide Profiling of Circulating MicroRNAs in Spinocerebellar Ataxia Type 7

Spinocerebellar ataxia type 7 (SCA7), a neurodegenerative disease characterized by cerebellar ataxia and retinal degeneration, is caused by a CAG repeat expansion in the ATXN7 gene coding region. Disease onset and progression are highly variable between patients, thus identification of specific/sensitive biomarkers that can improve the monitoring of disease progression is an immediate need. Because altered expression of circulating microRNAs (miRNAs) has been shown in various neurological diseases, they could be useful biomarkers for SCA7. In this study, we showed, to our knowledge for the first time, the expression profile of circulating miRNAs in SCA7. Using the TaqMan profiling low density array (TLDA), we found 71 differentially expressed miRNAs in the plasma of SCA7 patients, compared with healthy controls. The reliability of TLDA data was validated independently by quantitative real-time polymerase chain reaction in an independent cohort of patients and controls. We identified four validated miRNAs that possesses the diagnostic value to discriminate between healthy controls and patients (hsa-let-7a-5p, hsa-let7e-5p, hsa-miR-18a-5p, and hsa-miR-30b-5p). The target genes of these four miRNAs were significantly enriched in cellular processes that are relevant to central nervous system function, including Fas-mediated cell-death, heparansulfate biosynthesis, and soluble-N-ethylmaleimide-sensitive factor activating protein receptor pathways. Finally, we identify a signature of four miRNAs associated with disease severity that discriminate between early onset and adult onset, highlighting their potential utility to surveillance disease progression. In summary, circulating miRNAs might provide accessible biomarkers for disease stage and progression and help to identify novel cellular processes involved in SCA7.

Proteoglycans in brain development and pathogenesis

Proteoglycans are diverse, complex extracellular/cell surface macromolecules composed of a central core protein with covalently linked glycosaminoglycan (GAG) chains; both of these components contribute to the growing list of important bio-active functions attributed to proteoglycans. Increasingly, attention has been paid to the roles of proteoglycans in nervous tissue development due to their highly regulated spatio/temporal expression patterns, whereby they promote/inhibit neurite outgrowth, participate in specification and maturation of various precursor cell types, and regulate cell behaviors like migration, axonal pathfinding, synaptogenesis and plasticity. These functions emanate from both the environments proteoglycans create around cells by retaining ions and water or serving as scaffolds for cell shaping or motility, and from dynamic interactions that modulate signaling fields for cytokines, growth factors and morphogens, which may bind to either the protein or GAG portions. Also, genetic abnormalities impacting proteoglycan synthesis during critical steps of brain development and response to environmental insults and injuries, as well as changes in microenvironment interactions leading to tumors in the central nervous system, all suggest roles for proteoglycans in behavioral and intellectual disorders and malignancies.

Cell adhesion and matricellular support by astrocytes of the tripartite synapse

Astrocytes contribute to the formation, function, and plasticity of synapses. Their processes enwrap the neuronal components of the tripartite synapse, and due to this close interaction they are perfectly positioned to modulate neuronal communication. The interaction between astrocytes and synapses is facilitated by cell adhesion molecules and matricellular proteins, which have been implicated in the formation and functioning of tripartite synapses. The importance of such neuron-astrocyte integration at the synapse is underscored by the emerging role of astrocyte dysfunction in synaptic pathologies such as autism and schizophrenia. Here we review astrocyte-expressed cell adhesion molecules and matricellular molecules that play a role in integration of neurons and astrocytes within the tripartite synapse.

Role of proteoglycans in neuro-inflammation and central nervous system fibrosis

Fibrosis is defined as the thickening and scarring of connective tissue, usually as a consequence of tissue damage. The central nervous system (CNS) is special in the sense that fibrogenic cells are restricted to vascular and meningeal areas. Inflammation and the disruption of the blood-brain barrier can lead to the infiltration of fibroblasts and trigger fibrotic response. While the initial function of the fibrotic tissue is to restore the blood-brain barrier and to limit the site of injury, it also demolishes the structure of extracellular matrix and impedes the healing process by producing inhibitory molecules and forming a physical and biochemical barrier that prevents axon regeneration. As a major constituent in the extracellular matrix, proteoglycans participate in the neuro-inflammation, modulating the fibrotic process. In this review, we will discuss the pathophysiology of fibrosis during acute injuries of the CNS, as well as during chronic neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis and age-related neurodegeneration with focus on the functional roles of proteoglycans.

Extracellular matrix and traumatic brain injury

The brain extracellular matrix (ECM) plays a crucial role in both the developing and adult brain by providing structural support and mediating cell-cell interactions. In this review, we focus on the major constituents of the ECM and how they function in both normal and injured brain, and summarize the changes in the composition of the ECM as well as how these changes either promote or inhibit recovery of function following traumatic brain injury (TBI). Modulation of ECM composition to facilitates neuronal survival, regeneration and axonal outgrowth is a potential therapeutic target for TBI treatment.

Exploiting Heparan Sulfate Proteoglycans in Human Neurogenesis-Controlling Lineage Specification and Fate

Unspecialized, self-renewing stem cells have extraordinary application to regenerative medicine due to their multilineage differentiation potential. Stem cell therapies through replenishing damaged or lost cells in the injured area is an attractive treatment of brain trauma and neurodegenerative neurological disorders. Several stem cell types have neurogenic potential including neural stem cells (NSCs), embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs). Currently, effective use of these cells is limited by our lack of understanding and ability to direct lineage commitment and differentiation of neural lineages. Heparan sulfate proteoglycans (HSPGs) are ubiquitous proteins within the stem cell microenvironment or niche and are found localized on the cell surface and in the extracellular matrix (ECM), where they interact with numerous signaling molecules. The glycosaminoglycan (GAG) chains carried by HSPGs are heterogeneous carbohydrates comprised of repeating disaccharides with specific sulfation patterns that govern ligand interactions to numerous factors including the fibroblast growth factors (FGFs) and wingless-type MMTV integration site family (Wnts). As such, HSPGs are plausible targets for guiding and controlling neural stem cell lineage fate. In this review, we provide an overview of HSPG family members syndecans and glypicans, and perlecan and their role in neurogenesis. We summarize the structural changes and subsequent functional implications of heparan sulfate as cells undergo neural lineage differentiation as well as outline the role of HSPG core protein expression throughout mammalian neural development and their function as cell receptors and co-receptors. Finally, we highlight suitable biomimetic approaches for exploiting the role of HSPGs in mammalian neurogenesis to control and tailor cell differentiation into specific lineages. An improved ability to control stem cell specific neural lineage fate and produce abundant cells of lineage specificity will further advance stem cell therapy for the development of improved repair of neurological disorders. We propose a deeper understanding of HSPG-mediated neurogenesis can potentially provide novel therapeutic targets of neurogenesis.

Heparin interacts with the adhesion GPCR GPR56, reduces receptor shedding, and promotes cell adhesion and motility

GPR56 is an adhesion-class G-protein-coupled receptor responsible for bilateral frontoparietal polymicrogyria (BFPP), a severe disorder of cortical formation. Additionally, GPR56 is involved in biological processes as diverse as hematopoietic stem cell generation and maintenance, myoblast fusion, muscle hypertrophy, immunoregulation and tumorigenesis. Collagen III and tissue transglutaminase 2 (TG2) have been revealed as the matricellular ligands of GPR56 involved in BFPP and melanoma development, respectively. In this study, we identify heparin as a glycosaminoglycan interacting partner of GPR56. Analyses of truncated and mutant GPR56 proteins reveal two basic-residue-rich clusters, R(26)GHREDFRFC(35) and L(190)KHPQKASRRP(200), as the major heparin-interacting motifs that overlap partially with the collagen III- and TG2-binding sites. Interestingly, the GPR56-heparin interaction is modulated by collagen III but not TG2, even though both ligands are also heparin-binding proteins. Finally, we show that the interaction with heparin reduces GPR56 receptor shedding, and enhances cell adhesion and motility. These results provide novel insights into the interaction of GPR56 with its multiple endogenous ligands and have functional implications in diseases such as BFPP and cancer.

Inhibition of herpes virus infection in oligodendrocyte cultured cells by valproic acid

Valproic acid (VPA) is a small fatty acid used for treatment of different neurologic diseases such as epilepsy, migraines or bipolar disorders. VPA modulates different processes of cell metabolism that can lead to alterations in susceptibility of several cell types to the infection of Human Immunodeficiency Virus (HIV), Epstein-Barr virus (EBV), as well as to exert an inhibitory effect on the replication of different enveloped viruses in cultured cells. Taken these data into account and the fact that HSV-1 has been involved in some neuropathies, we have characterized the effect of VPA on this herpesvirus infection of the differentiation/maturation-inducible human oligodendrocyte cell line HOG, which resulted more susceptible to VPA inhibition of virus growth after cell differentiation. In these cells, the role of VPA in virus entry was tackled. Incubation with VPA induced a slight but reproducible inhibition in the virus particles uptake mainly observed when the drug was added in the adsorption or early upon infection. In addition, transcription and expression of viral proteins were significantly downregulated in the presence of VPA. Remarkably, when the infective viral production was assessed, VPA dramatically blocked the detection of infectious HSV-1 particles. Herein, our results indicate that VPA treatment of HOG cells significantly reduces the effect of HSV-1 infection, virus entry and productivity without affecting cellular viability.

Sulf1 and Sulf2 Differentially Modulate Heparan Sulfate Proteoglycan Sulfation during Postnatal Cerebellum Development: Evidence for Neuroprotective and Neurite Outgrowth Promoting Functions

Introduction

Sulf1 and Sulf2 are cell surface sulfatases, which remove specific 6-O-sulfate groups from heparan sulfate (HS) proteoglycans, resulting in modulation of various HS-dependent signaling pathways. Both Sulf1 and Sulf2 knockout mice show impairments in brain development and neurite outgrowth deficits in neurons.

Methodology and Main Findings

To analyze the molecular mechanisms behind these impairments we focused on the postnatal cerebellum, whose development is mainly characterized by proliferation, migration, and neurite outgrowth processes of precursor neurons. Primary cerebellar granule cells isolated from Sulf1 or Sulf2 deficient newborns are characterized by a reduction in neurite length and cell survival. Furthermore, Sulf1 deficiency leads to a reduced migration capacity. The observed impairments in cell survival and neurite outgrowth could be correlated to Sulf-specific interference with signaling pathways, as shown for FGF2, GDNF and NGF. In contrast, signaling of Shh, which determines the laminar organization of the cerebellar cortex, was not influenced in either Sulf1 or Sulf2 knockouts. Biochemical analysis of cerebellar HS demonstrated, for the first time in vivo, Sulf-specific changes of 6-O-, 2-O- and N-sulfation in the knockouts. Changes of a particular HS epitope were found on the surface of Sulf2-deficient cerebellar neurons. This epitope showed a restricted localization to the inner half of the external granular layer of the postnatal cerebellum, where precursor cells undergo final maturation to form synaptic contacts.

Conclusion

Sulfs introduce dynamic changes in HS proteoglycan sulfation patterns of the postnatal cerebellum, thereby orchestrating fundamental mechanisms underlying brain development.

Drug and gene delivery across the blood-brain barrier with focused ultrasound

The blood-brain barrier (BBB) remains one of the most significant limitations to treatments of central nervous system (CNS) disorders including brain tumors, neurodegenerative diseases and psychiatric disorders. It is now well-established that focused ultrasound (FUS) in conjunction with contrast agent microbubbles may be used to non-invasively and temporarily disrupt the BBB, allowing localized delivery of systemically administered therapeutic agents as large as 100nm in size to the CNS. Importantly, recent technological advances now permit FUS application through the intact human skull, obviating the need for invasive and risky surgical procedures. When used in combination with magnetic resonance imaging, FUS may be applied precisely to pre-selected CNS targets. Indeed, FUS devices capable of sub-millimeter precision are currently in several clinical trials. FUS mediated BBB disruption has the potential to fundamentally change how CNS diseases are treated, unlocking potential for combinatorial treatments with nanotechnology, markedly increasing the efficacy of existing therapeutics that otherwise do not cross the BBB effectively, and permitting safe repeated treatments. This article comprehensively reviews recent studies on the targeted delivery of therapeutics into the CNS with FUS and offers perspectives on the future of this technology.

The role of neuronal versus astrocyte-derived heparan sulfate proteoglycans in brain development and injury

Astrocytes modulate many aspects of neuronal function, including synapse formation and the response to injury. Heparan sulfate proteoglycans (HSPGs) mediate some of the effects of astrocytes on synaptic function, and participate in the astrocyte-mediated brain injury response. HSPGs are a highly conserved class of proteoglycans, with variable heparan sulfate (HS) chains that play a major role in determining the function of these proteins, such as binding to growth factors and receptors. Expression of both the core proteins and their HS chains can vary depending on cellular origin, thus the functional impact of HSPGs may be determined by the cell type in which they are expressed. In the brain, HSPGs are expressed by both neurons and astrocytes; however, the specific contribution of neuronal HSPGs compared with astrocyte-derived HSPGs to development and the injury response is largely unknown. The present review examines the current evidence regarding the roles of HSPGs in the brain, describes the cellular origins of HSPGs, and interrogates the roles of HSPGs from astrocytes and neurons in synaptogenesis and injury. The importance of considering cell-type-specific expression of HSPGs when studying brain function is discussed.

Glycosaminoglycans and glycomimetics in the central nervous system

With recent advances in the construction of synthetic glycans, selective targeting of the extracellular matrix (ECM) as a potential treatment for a wide range of diseases has become increasingly popular. The use of compounds that mimic the structure or bioactive function of carbohydrate structures has been termed glycomimetics. These compounds are mostly synthetic glycans or glycan-binding constructs which manipulate cellular interactions. Glycosaminoglycans (GAGs) are major components of the ECM and exist as a diverse array of differentially sulphated disaccharide units. In the central nervous system (CNS), they are expressed by both neurons and glia and are crucial for brain development and brain homeostasis. The inherent diversity of GAGs make them an essential biological tool for regulating a complex range of cellular processes such as plasticity, cell interactions and inflammation. They are also involved in the pathologies of various neurological disorders, such as glial scar formation and psychiatric illnesses. It is this diversity of functions and potential for selective interventions which makes GAGs a tempting target. In this review, we shall describe the molecular make-up of GAGs and their incorporation into the ECM of the CNS. We shall highlight the different glycomimetic strategies that are currently being used in the nervous system. Finally, we shall discuss some possible targets in neurological disorders that may be addressed using glycomimetics.

Proteoglycans of reactive rat cortical astrocyte cultures: abundance of N-unsubstituted glucosamine-enriched heparan sulfate

"Reactive" astrocytes and other glial cells in the injured CNS produce an altered extracellular matrix (ECM) that influences neuronal regeneration. We have profiled the glycosaminoglycan (GAG) component of proteoglycans (PGs) produced by reactive neonatal rat cortical astrocytes, and have quantified their neurite-outgrowth inhibitory activity. PGs extracted from cell layers and medium were fractionated on DEAE-Sephacel with a gradient of NaCl from 0.15 to 1.0 M. Monosaccharide analysis of the major peaks eluting at 0.6 M NaCl indicated an excess of GlcNH₂ to GalNH₂, suggesting an approximate HS/CS ratio of 6.2 in the cell layer and 4.2 in the medium. Chondroitinase ABC-generated disaccharide analysis of cell and medium PGs showed a >5-fold excess of chondroitin 4-sulfate over chondroitin 6-sulfate. Heparin lyase-generated disaccharides characteristic of the highly sulfated S-domain regions within HS were more abundant in cell layer than medium-derived PGs. Cell layer and medium HS disaccharides contained ~20% and ~40% N-unsubstituted glucosamine respectively, which is normally rare in HS isolated from most tissues. NGF-stimulated neurite outgrowth assays using NS-1 (PC12) neuronal cells on adsorbed substrata of PGs isolated from reactive astrocyte medium showed pronounced inhibition of neurite outgrowth, and aggregation of NS-1 cells. Cell layer PGs from DEAE-Sephacel pooled fractions having high charge density permitted greater NGF-stimulated outgrowth than PGs with lower charge density. Our results indicate the synthesis of both inhibitory and permissive PGs by activated astrocytes that may correlate with sulfation patterns and HS/CS ratios.

Effect of valproic acid and injury on lesion size and endothelial glycocalyx shedding in a rodent model of isolated traumatic brain injury

BACKGROUND

In isolated traumatic brain injury (TBI), little is known about the endothelial response and the effects of endothelial glycocalyx shedding. We have previously shown that treatment with valproic acid (VPA) improves outcomes following TBI and hemorrhagic shock.In this model, we hypothesized that severe isolated TBI would cause shedding of the endothelial glycocalyx, as measured by serum syndecan-1 (sSDC-1) levels. We further hypothesized that VPA treatment would reduce this response and reduce lesion size volume.

METHODS

Forty Sprague-Dawley rats were allocated to TBI + VPA (n = 8), TBI + saline vehicle control infusion (n = 8), sham + saline vehicle control infusion (n = 6), or sham + VPA (n = 8). TBI animals were subjected to severe controlled cortical impact and killed 6 hours after injury. VPA 300 mg/kg was given as an intravenous bolus 30 minutes after injury. Serum samples were analyzed for sSDC-1, and lesion size was determined on Nissl-stained cryosections.

RESULTS

sSDC-1 was significantly elevated in injured compared with uninjured animals at 3 hours (p = 0.0009) and 6 hours (p = 0.0007) after injury. This effect was significantly more pronounced in the animals treated with VPA (p = 0.019) 3 hours after injury, in which sSDC-1 levels were also significantly inversely correlated with lesion size (ρ = -0.55, p = 0.038).Lesion size was significantly smaller in TBI + VPA (40.45 mm ± 13.83 mm) as compared with vehicle control (59.57 mm ± 16.83 mm) (p = 0.023).

CONCLUSION

Severe isolated TBI caused shedding of the endothelial glycocalyx. Treatment with VPA was associated with increased glycocalyx shedding and reduced lesion size volume in injured animal.

Extracellular matrix regulation of inflammation in the healthy and injured spinal cord

Throughout the body, the extracellular matrix (ECM) provides structure and organization to tissues and also helps regulate cell migration and intercellular communication. In the injured spinal cord (or brain), changes in the composition and structure of the ECM undoubtedly contribute to regeneration failure. Less appreciated is how the native and injured ECM influences intraspinal inflammation and, conversely, how neuroinflammation affects the synthesis and deposition of ECM after CNS injury. In all tissues, inflammation can be initiated and propagated by ECM disruption. Molecules of ECM newly liberated by injury or inflammation include hyaluronan fragments, tenascins, and sulfated proteoglycans. These act as "damage-associated molecular patterns" or "alarmins", i.e., endogenous proteins that trigger and subsequently amplify inflammation. Activated inflammatory cells, in turn, further damage the ECM by releasing degradative enzymes including matrix metalloproteinases (MMPs). After spinal cord injury (SCI), destabilization or alteration of the structural and chemical compositions of the ECM affects migration, communication, and survival of all cells - neural and non-neural - that are critical for spinal cord repair. By stabilizing ECM structure or modifying their ability to trigger the degradative effects of inflammation, it may be possible to create an environment that is more conducive to tissue repair and axon plasticity after SCI.

Syndecan promotes axon regeneration by stabilizing growth cone migration

Growth cones facilitate the repair of nervous system damage by providing the driving force for axon regeneration. Using single-neuron laser axotomy and in vivo time-lapse imaging, we show that syndecan, a heparan sulfate (HS) proteoglycan, is required for growth cone function during axon regeneration in C. elegans. In the absence of syndecan, regenerating growth cones form but are unstable and collapse, decreasing the effective growth rate and impeding regrowth to target cells. We provide evidence that syndecan has two distinct functions during axon regeneration: (1) a canonical function in axon guidance that requires expression outside the nervous system and depends on HS chains and (2) an intrinsic function in growth cone stabilization that is mediated by the syndecan core protein, independently of HS. Thus, syndecan is a regulator of a critical choke point in nervous system repair.

Traffic lights for axon growth: proteoglycans and their neuronal receptors

Axon growth is a central event in the development and post-injury plasticity of the nervous system. Growing axons encounter a wide variety of environmental instructions. Much like traffic lights in controlling the migrating axons, chondroitin sulfate proteoglycans (CSPGs) and heparan sulfate proteoglycans (HSPGs) often lead to "stop" and "go" growth responses in the axons, respectively. Recently, the LAR family and NgR family molecules were identified as neuronal receptors for CSPGs and HSPGs. These discoveries provided molecular tools for further study of mechanisms underlying axon growth regulation. More importantly, the identification of these proteoglycan receptors offered potential therapeutic targets for promoting post-injury axon regeneration.

The effect of cellular differentiation on HSV-1 infection of oligodendrocytic cells

Herpes simplex type 1 (HSV-1) is a neurotropic virus that infects many types of cells. Previous studies have demonstrated that oligodendrocytic cells are highly susceptible to HSV-1 infection. Here we analysed HSV-1 infection of a human oligodendrocytic cell line, HOG, and oligodendrocyte precursor cells (OPCs) cultured under growth or differentiation conditions. In addition to cell susceptibility, the role of the major cell receptors for viral entry was assessed. Our results revealed that OPCs and HOG cells cultured under differentiation conditions became more susceptible to HSV-1. On the other hand, viral infection induced morphological changes corresponding to differentiated cells, suggesting that HSV-1 might be inducing cell differentiation. We also observed colocalization of HVEM and nectin-1 with viral particles, suggesting that these two major HSV-1 receptors are functional in HOG cells. Finally, electron microscopy assays indicated that HSV-1 may be also entering OLs by macropinocytosis depending on their differentiation stage. In addition, vesicles containing intracellular enveloped virions observed in differentiated cells point to an endocytic mechanism of virus entry. All these data are indicative of diverse entry pathways dependent on the maturation stage of OLs.

Tick-borne encephalitis virus infects rat astrocytes but does not affect their viability

Tick-borne encephalitis virus (TBEV) causes one of the most dangerous human neuroinfections in Europe and Asia. To infect neurons it must cross the blood-brain-barrier (BBB), and presumably also cells adjacent to the BBB, such as astrocytes, the most abundant glial cell type. However, the knowledge about the viral infection of glial cells is fragmental. Here we studied whether TBEV infects rat astrocytes. Rats belong to an animal group serving as a TBEV amplifying host. We employed high resolution quantitative fluorescence microscopy to investigate cell entry and cytoplasmic mobility of TBEV particles along with the effect on the cell cytoskeleton and cell survival. We report that infection of astrocytes with TBEV increases with time of exposure to TBEV and that with post-infection time TBEV particles gained higher mobility. After several days of infection actin cytoskeleton was affected, but cell survival was unchanged, indicating that rat astrocytes resist TBEV-mediated cell death, as reported for other mammalian cells. Therefore, astrocytes may present an important pool of dormant TBEV infections and a new target for therapeutic intervention.

Evidence of association of human papillomavirus with prognosis worsening in glioblastoma multiforme

BACKGROUND

Glioblastoma multiforme (GBM) is the most malignant brain tumor in adults, but its etiology still remains unknown. Recently, a role of viruses such as cytomegalovirus and JC virus in gliomagenesis has been suggested. Since human papillomavirus (HPV) is considered the most common oncogenic virus in humans, we evaluated its occurrence in GBM samples.

MATERIAL AND METHODS

Fifty-two formalin-fixed paraffin-embedded primary glioblastoma specimens were retrospectively analyzed. The presence of HPV genome on tumor DNA was assessed by MY/GP nested PCR. Confirmation of HPV detection was obtained by chromogenic in situ hybridization (CISH) and immunohistochemistry (IHC) with an antibody directed against the L1 capsidic protein. Finally, univariate and multivariate proportional-hazards models were used to compare the risk of death among HPV-positive and HPV-negative patients.

RESULTS

Strikingly, viral DNA was detected after PCR in 12 cases (23%). HPV16 genome was present in 25% infected samples, whereas the remaining samples tested positive for HPV6. CISH confirmed positivity in all infected samples for which enough material was available. Moreover, IHC positivity suggested that production of viral proteins from HPV genome is an ongoing process in GBM cancer cells. Finally an association between HPV infection and a worse prognosis was found in patients upon age stratification with a univariate analysis (HR, 2.10; 95% CI, 1.00-4.44; log-rank P = .045).

CONCLUSIONS

HPV infection status may be considered an independent prognostic factor in GBM patients and suggests that prevention may be considered, should HPV be recognized as a causative agent in gliomagenesis.

Heparin-binding correlates with increased efficiency of AAV1- and AAV6-mediated transduction of striated muscle, but negatively impacts CNS transduction

Gene delivery vectors derived from adeno-associated virus (AAV) have great potential as therapeutic agents. rAAV1 and rAAV6, efficiently target striated muscle, but the mechanisms that determine their tropism remain unclear. It is known that AAV6, but not AAV1, interacts with heparin-sulfate proteoglycans (HSPG). HSPGs are not primary receptors for AAV6, but heparin interactions may affect tissue tropism and transduction. To investigate these possibilities, we generated rAAV1 and rAAV6 capsids that do or do not bind heparin. We evaluated the transduction profile of these vectors in vivo across multiple routes of administration, and found that heparin-binding capability influences tissue transduction in striated muscle and neuronal tissues. Heparin-binding capsids transduce striated muscle more efficiently than non-binding capsids, via both intramuscular and intravenous injection. However, rAAV6 achieved greater muscle transduction than the heparin-binding rAAV1 variant, suggesting that there are additional factors that influence differences in transduction efficiency between AAV1 and AAV6. Interestingly, the opposite trend was found when vectors were delivered via intracranial injection. Non-binding vectors achieved robust and widespread gene expression, whereas transduction via heparin-binding serotypes was substantially reduced. These data indicate that heparin-binding capability is an important determinant of transduction that should be considered in the design of rAAV-mediated gene therapies.

Noninvasive and targeted gene delivery into the brain using microbubble-facilitated focused ultrasound

Recombinant adeno-associated viral (rAAV) vectors are potentially powerful tools for gene therapy of CNS diseases, but their penetration into brain parenchyma is severely limited by the blood-brain barrier (BBB) and current delivery relies on invasive stereotactic injection. Here we evaluate the local, targeted delivery of rAAV vectors into the brains of mice by noninvasive, reversible, microbubble-facilitated focused ultrasound (FUS), resulting in BBB opening that can be monitored and controlled by magnetic resonance imaging (MRI). Using this method, we found that IV-administered AAV2-GFP (green fluorescence protein) with a low viral vector titer (1×10(9) vg/g) can successfully penetrate the BBB-opened brain regions to express GFP. We show that MRI monitoring of BBB-opening could serve as an indicator of the scale and distribution of AAV transduction. Transduction peaked at 3 weeks and neurons and astrocytes were affected. This novel, noninvasive delivery approach could significantly broaden the application of AAV-viral-vector-based genes for treatment of CNS diseases.

Proteoglycans in the central nervous system: role in development, neural repair, and Alzheimer's disease

Proteoglycans (PGs) are major components of the cell surface and extracellular matrix and play critical roles in development and maintenance of the central nervous system (CNS). PGs are a family of proteins, all of which contain a core protein to which glycosaminoglycan side chains are covalently attached. PGs possess diverse physiological roles, particularly in neural development, and are also implicated in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). The main functions of PGs in the CNS are reviewed as are the roles of PGs in brain injury and in the development or treatment of AD.

Anti-neurotrophic effects from autoantibodies in adult diabetes having primary open angle glaucoma or dementia

AIM

To test for anti-endothelial and anti-neurotrophic effects from autoantibodies in subsets of diabetes having open-angle glaucoma, dementia, or control subjects.

METHODS

Protein-A eluates from plasma of 20 diabetic subjects having glaucoma or suspects and 34 age-matched controls were tested for effects on neurite outgrowth in rat pheochromocytoma PC12 cells or endothelial cell survival. The mechanism of the diabetic glaucoma autoantibodies' neurite-inhibitory effect was investigated in co-incubations with the selective Rho kinase inhibitor Y27632 or the sulfated proteoglycan synthesis inhibitor sodium chlorate. Stored protein-A eluates from certain diabetic glaucoma or dementia subjects which contained long-lasting, highly stable cell inhibitory substances were characterized using mass spectrometry and amino acid sequencing.

RESULTS

Diabetic primary open angle glaucoma (POAG) or suspects (n = 20) or diabetic dementia (n = 3) autoantibodies caused significantly greater mean inhibition of neurite outgrowth in PC12 cells (p < 0.0001) compared to autoantibodies in control diabetic (n = 24) or non-diabetic (n = 10) subjects without glaucoma (p < 0.01). Neurite inhibition by the diabetic glaucoma autoantibodies was completely abolished by 10 μM concentrations of Y27632 (n = 4). It was substantially reduced by 30 mM concentrations of sodium chlorate (n = 4). Peak, long-lasting activity survived storage ×5 years at 0-4°C and was associated with a restricted subtype of Ig kappa light chain. Diabetic glaucoma or dementia autoantibodies (n = 5) caused contraction and process retraction in quiescent cerebral cortical astrocytes effects which were blocked by 5 μM concentrations of Y27632.

CONCLUSION

These data suggest that autoantibodies in subsets of adult diabetes having POAG (glaucoma suspects) and/or dementia inhibit neurite outgrowth and promote a reactive astrocyte morphology by a mechanism which may involve activation of the RhoA/p160 ROCK signaling pathway.

Endothelial heparan sulfate 6-O-sulfation levels regulate angiogenic responses of endothelial cells to fibroblast growth factor 2 and vascular endothelial growth factor

Fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor 165 (VEGF(165)) are potent pro-angiogenic growth factors that play a pivotal role in tumor angiogenesis. The activity of these growth factors is regulated by heparan sulfate (HS), which is essential for the formation of FGF2/FGF receptor (FGFR) and VEGF(165)/VEGF receptor signaling complexes. However, the structural characteristics of HS that determine activation or inhibition of such complexes are only partially defined. Here we show that ovarian tumor endothelium displays high levels of HS sequences that harbor glucosamine 6-O-sulfates when compared with normal ovarian vasculature where these sequences are also detected in perivascular area. Reduced HS 6-O-sulfotransferase 1 (HS6ST-1) or 6-O-sulfotransferase 2 (HS6ST-2) expression in endothelial cells impacts upon the prevalence of HS 6-O-sulfate moieties in HS sequences, which consist of repeating short, highly sulfated S domains interspersed by transitional N-acetylated/N-sulfated domains. 1-40% reduction in 6-O-sulfates significantly compromises FGF2- and VEGF(165)-induced endothelial cell sprouting and tube formation in vitro and FGF2-dependent angiogenesis in vivo. Moreover, HS on wild-type neighboring endothelial or smooth muscle cells fails to restore endothelial cell sprouting and tube formation. The affinity of FGF2 for HS with reduced 6-O-sulfation is preserved, although FGFR1 activation is inhibited correlating with reduced receptor internalization. These data show that 6-O-sulfate moieties in endothelial HS are of major importance in regulating FGF2- and VEGF(165)-dependent endothelial cell functions in vitro and in vivo and highlight HS6ST-1 and HS6ST-2 as potential targets of novel antiangiogenic agents.

Matrix metalloproteinase dependent cleavage of cell adhesion molecules in the pathogenesis of CNS dysfunction with HIV and methamphetamine

Physiologically appropriate levels of matrix metalloproteinases (MMPs) are likely important to varied aspects of CNS function. In particular, these enzymes may contribute to neuronal activity dependent synaptic plasticity and to cell mobility in processes including stem cell migration and immune surveillance. Levels of MMPs may, however, be substantially increased in the setting of HIV infection with methamphetamine abuse. Elevated MMP levels might in turn influence integrity of the blood brain barrier, as has been demonstrated in published work. Herein we suggest that elevated levels of MMPs can also contribute to microglial activation as well as neuronal and synaptic injury through a mechanism that involves cleavage of specific cell and synaptic adhesion molecules.

Normal sulfation levels regulate spinal cord neural precursor cell proliferation and differentiation

Background

Sulfated glycosaminoglycan chains are known for their regulatory functions during neural development and regeneration. However, it is still unknown whether the sulfate residues alone influence, for example, neural precursor cell behavior or whether they act in concert with the sugar backbone. Here, we provide evidence that the unique 473HD-epitope, a representative chondroitin sulfate, is expressed by spinal cord neural precursor cells in vivo and in vitro, suggesting a potential function of sulfated glycosaminoglycans for spinal cord development.

Results

Thus, we applied the widely used sulfation inhibitor sodium chlorate to analyze the importance of normal sulfation levels for spinal cord neural precursor cell biology in vitro. Addition of sodium chlorate to spinal cord neural precursor cell cultures affected cell cycle progression accompanied by changed extracellular signal-regulated kinase 1 or 2 activation levels. This resulted in a higher percentage of neurons already under proliferative conditions. In contrast, the relative number of glial cells was largely unaffected. Strikingly, both morphological and electrophysiological characterization of neural precursor cell-derived neurons demonstrated an attenuated neuronal maturation in the presence of sodium chlorate, including a disturbed neuronal polarization.

Conclusions

In summary, our data suggest that sulfation is an important regulator of both neural precursor cell proliferation and maturation of the neural precursor cell progeny in the developing mouse spinal cord.