Neuroprotective effect of chondroitinase ABC on primary and secondary brain injury after stroke in hypertensive rats

Out of the core: the impact of focal ischemia in regions beyond the penumbra

The changes in the necrotic core and the penumbra following induction of focal ischemia have been the focus of attention for some time. However, evidence shows, that ischemic injury is not confined to the primarily affected structures and may influence the remote areas as well. Yet many studies fail to probe into the structures beyond the penumbra, and possibly do not even find any significant results due to their short-term design, as secondary damage occurs later. This slower reaction can be perceived as a therapeutic opportunity, in contrast to the ischemic core defined as irreversibly damaged tissue, where the window for salvation is comparatively short. The pathologies in remote structures occur relatively frequently and are clearly linked to the post-stroke neurological outcome. In order to develop efficient therapies, a deeper understanding of what exactly happens in the exo-focal regions is necessary. The mechanisms of glia contribution to the ischemic damage in core/penumbra are relatively well described and include impaired ion homeostasis, excessive cell swelling, glutamate excitotoxic mechanism, release of pro-inflammatory cytokines and phagocytosis or damage propagation via astrocytic syncytia. However, little is known about glia involvement in post-ischemic processes in remote areas. In this literature review, we discuss the definitions of the terms "ischemic core", "penumbra" and "remote areas." Furthermore, we present evidence showing the array of structural and functional changes in the more remote regions from the primary site of focal ischemia, with a special focus on glia and the extracellular matrix. The collected information is compared with the processes commonly occurring in the ischemic core or in the penumbra. Moreover, the possible causes of this phenomenon and the approaches for investigation are described, and finally, we evaluate the efficacy of therapies, which have been studied for their anti-ischemic effect in remote areas in recent years.

Chondroitinase as a therapeutic enzyme: Prospects and challenges

The chondroitinases (Chase) are bacterial lyases that specifically digest chondroitin sulfate and/or dermatan sulfate glycosaminoglycans via a β-elimination reaction and generate unsaturated disaccharides. In recent decades, these enzymes have attracted the attention of many researchers due to their potential applications in various aspects of medicine from the treatment of spinal cord injury to use as an analytical tool. In spite of this diverse spectrum, the application of Chase is faced with several limitations and challenges such as thermal instability and lack of a suitable delivery system. In the current review, we address potential therapeutic applications of Chase with emphasis on the challenges ahead. Then, we summarize the latest achievements to overcome the problems by considering the studies carried out in the field of enzyme engineering, drug delivery, and combination-based therapy.

Inhibition of CSPG receptor PTPσ promotes migration of newly born neuroblasts, axonal sprouting, and recovery from stroke

In addition to neuroprotective strategies, neuroregenerative processes could provide targets for stroke recovery. However, the upregulation of inhibitory chondroitin sulfate proteoglycans (CSPGs) impedes innate regenerative efforts. Here, we examine the regulatory role of PTPσ (a major proteoglycan receptor) in dampening post-stroke recovery. Use of a receptor modulatory peptide (ISP) or Ptprs gene deletion leads to increased neurite outgrowth and enhanced NSCs migration upon inhibitory CSPG substrates. Post-stroke ISP treatment results in increased axonal sprouting as well as neuroblast migration deeply into the lesion scar with a transcriptional signature reflective of repair. Lastly, peptide treatment post-stroke (initiated acutely or more chronically at 7 days) results in improved behavioral recovery in both motor and cognitive functions. Therefore, we propose that CSPGs induced by stroke play a predominant role in the regulation of neural repair and that blocking CSPG signaling pathways will lead to enhanced neurorepair and functional recovery in stroke.

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.

The Potential Role of Inflammation in Modulating Endogenous Hippocampal Neurogenesis After Spinal Cord Injury

Currently there are approximately 291,000 people suffering from a spinal cord injury (SCI) in the United States. SCI is associated with traumatic changes in mobility and neuralgia, as well as many other long-term chronic health complications, including metabolic disorders, diabetes mellitus, non-alcoholic steatohepatitis, osteoporosis, and elevated inflammatory markers. Due to medical advances, patients with SCI survive much longer than previously. This increase in life expectancy exposes them to novel neurological complications such as memory loss, cognitive decline, depression, and Alzheimer's disease. In fact, these usually age-associated disorders are more prevalent in people living with SCI. A common factor of these disorders is the reduction in hippocampal neurogenesis. Inflammation, which is elevated after SCI, plays a major role in modulating hippocampal neurogenesis. While there is no clear consensus on the mechanism of the decline in hippocampal neurogenesis and cognition after SCI, we will examine in this review how SCI-induced inflammation could modulate hippocampal neurogenesis and provoke age-associated neurological disorders. Thereafter, we will discuss possible therapeutic options which may mitigate the influence of SCI associated complications on hippocampal neurogenesis.

Xuesaitong exerts long-term neuroprotection for stroke recovery by inhibiting the ROCKII pathway, in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Xuesaitong (XST) is a traditional Chinese medicine injection with neuroprotective properties and has been extensively used to treat stroke for many years. The main component of XST is Panax notoginseng saponins (PNS), which is the main extract of the Chinese herbal medicine Panax notoginseng.

AIM OF THE STUDY

In this study, we investigated whether XST provided long-term neuroprotection by inhibiting neurite outgrowth inhibitor-A (Nogo-A) and the ROCKII pathway in experimental rats after middle cerebral artery occlusion (MCAO) and in SH-SY5Y cells exposed to oxygen-glucose deprivation/reperfusion (OGD/R).

MATERIALS AND METHODS

Rats with permanent MCAO were administered XST, Y27632, XST plus Y27632, and nimodipine for 14 and 28 days. Successful MCAO onset was confirmed by 2,3,5-triphenyl tetrazolium chloride (TTC) staining. Neurological deficit score (NDS) was used to assess neurological impairment. Hematoxylin-eosin (HE) staining and immunohistochemical (IHC) analysis of synaptophysin (SYN) and postsynaptic density protein-95 (PSD-95) were performed to evaluate cerebral ischemic injury and the neuroprotective capability of XST. Nogo-A levels and the ROCKII pathway were detected by IHC analysis, western blotting, and quantitative real-time polymerase chain reaction (qRT-PCR) to explore the protective mechanism of XST. OGD/R model was established in SH-SY5Y cells. Cell counting kit 8 (CCK8) was applied to detect the optimum OGD time and XST concentration. The expression levels Nogo-A and ROCKII pathway were determined using western blotting.

RESULTS

Our results showed that XST reduced neurological dysfunction and pathological damage, promoted weight gain and synaptic regeneration, reduced Nogo-A mRNA and protein levels, and inhibited the ROCKII pathway in MCAO rats. CCK8 assay displayed that the optimal OGD time and optimal XST concentration were 7 h and 20 μg/mL respectively in SH-SY5Y cells. XST could evidently inhibit OGD/R-induced Nogo-A protein expression and ROCKII pathway activation in SH-SY5Y cells.

CONCLUSIONS

The present study suggested that XST exerted long-term neuroprotective effects that assisted in stroke recovery, possibly through inhibition of the ROCKII pathway.

Effect of Tetramethylpyrazine on Neuroplasticity after Transient Focal Cerebral Ischemia Reperfusion in Rats

Tetramethylpyrazine (TMP) has been widely used in ischemic stroke in China. The regulation of neuroplasticity may underlie the recovery of some neurological functions in ischemic stroke. Middle cerebral artery occlusion (MCAO) model was established in this study. Rats were divided into three groups: sham group, model group, and TMP group. The neurological function was evaluated using modified neurological severity score (mNSS). Following the neurological function test, expression of synaptophysin (SYP) and growth-associated protein 43 (GAP-43) were analyzed through immunohistochemistry at 3 d, 7 d, 14 d, and 28 d after MCAO. Finally, the synaptic structural plasticity was investigated using transmission electron microscopy (TEM). The TMP group showed better neurological function comparing to the model group. SYP levels increased gradually in ischemic penumbra (IP) in the model group and could be enhanced by TMP treatment at 7 d, 14 d, and 28 d, whereas GAP-43 levels increased from 3 d to 7 d and thereafter decreased gradually from 14 d to 28 d in the model group, which showed no significant improvement in the TMP group. The results of TEM showed a flatter synaptic interface, a thinner postsynaptic density (PSD), and a wider synaptic cleft in the model group, and the first two alterations could be ameliorated by TMP. Then, a Pearson's correlation test revealed mNSS markedly correlated with SYP and synaptic ultrastructures. Taken together, TMP is capable of promoting functional outcome after ischemic stroke, and the mechanisms may be partially associated with regulation of neuroplasticity.

Neurogenic Niche Conversion Strategy Induces Migration and Functional Neuronal Differentiation of Neural Precursor Cells Following Brain Injury

Glial scars formed after brain injuries provide permissive cues for endogenous neural precursor/stem cells (eNP/SCs) to undergo astrogenesis rather than neurogenesis. Following brain injury, eNP/SCs from the subventricular zone leave their niche, migrate to the injured cortex, and differentiate into reactive astrocytes that contribute to glial scar formation. In vivo neuronal reprogramming, directly converting non-neuronal cells such as reactive astrocytes or NG2 glia into neurons, has greatly improved brain injury repair strategies. However, reprogramming carries a high risk of future clinical applications such as tumorigenicity, involving virus. In this study, we constructed a neural matrix to alter the adverse niche at the injured cortex, enabling eNP/SCs to differentiate into functional neurons. We found that the neural matrix functioned as a "glial trap" that largely concentrated and limited reactive astrocytes to the core of the lesion area, thus altering the adverse niche. The eNP/SCs migrated toward the injured cortex and differentiated into functional neurons. In addition, regenerated neurites extended across the boundary of the injured cortex. Mice treated with the neural matrix demonstrated significant behavioral recovery. For the first time, we induced eNP/SC-derived functional neurons in the cortex after brain injury without the use of viruses, microRNAs, or small molecules. Our novel strategy of applying this "glial trap" to obtain functional neurons in the injured cortex may provide a safer and more natural therapeutic alternative to reprogramming in future clinical applications.

Targeting chondroitinase ABC to axons enhances the ability of chondroitinase to promote neurite outgrowth and sprouting

BACKGROUND

There is currently no effective treatment for promoting regeneration of injured nerves in patients who have sustained injury to the central nervous system such as spinal cord injury. Chondroitinase ABC is an enzyme, which promotes neurite outgrowth and regeneration. It has shown considerable promise as a therapy for these conditions. The aim of the study is to determine if targeting chondroitinase ABC expression to the neuronal axon can further enhance its ability to promote axon outgrowth. Long-distance axon regeneration has not yet been achieved, and would be a significant step in attaining functional recovery following spinal cord injury.

METHODOLOGY/PRINCIPAL FINDINGS

To investigate this, neuronal cultures were transfected with constructs encoding axon-targeted chondroitinase, non-targeted chondroitinase or GFP, and the effects on neuron outgrowth and sprouting determined on substrates either permissive or inhibitory to neuron regeneration. The mechanisms underlying the observed effects were also explored. Targeting chondroitinase to the neuronal axon markedly enhances its ability to promote neurite outgrowth. The increase in neurite length is associated with an upregulation of β-integrin staining at the axonal cell surface. Staining for phosphofocal adhesion kinase, is also increased, indicating that the β-integrins are in an activated state. Expression of chondroitinase within the neurons also resulted in a decrease in expression of PTEN and RhoA, molecules which present a block to neurite outgrowth, thus identifying two of the pathways by which ChABC promotes neurite outgrowth.

CONCLUSIONS / SIGNIFICANCE

The novel finding that targeting ChABC to the axon significantly enhances its ability to promote neurite extension, suggests that this may be an effective way of promoting long-distance axon regeneration following spinal cord injury. It could also potentially improve its efficacy in the treatment of other pathologies, where it has been shown to promote recovery, such as myocardial infarction, stroke and Parkinson's disease.

Recent advances in the therapeutic uses of chondroitinase ABC

Many studies, using pre-clinical models of SCI, have demonstrated the efficacy of chondroitinase ABC as a treatment for spinal cord injury and this has been confirmed in laboratories worldwide and in several animal models. The aim of this review is report the current state of research in the field and to compare the relative efficacies of these new interventions to improve outcomes in both acute and chronic models of SCI. We also report new methods of chondroitinase delivery and the outcomes of two clinical trials using the enzyme to treat spinal cord injury in dogs and disc herniation in human patients. Recent studies have assessed the outcomes of combining chondroitinase with other strategies known to promote recovery following spinal cord injury and new approaches. Evidence is emerging that one of the most powerful combinations is that of chondroitinase with cell transplants. The particular benefits of each of the different cell types used for these transplant experiments are discussed. Combining chondroitinase with rehabilitation also improves outcomes. Gene therapy is an efficient method of enzyme delivery to the injured spinal cord and circumvents the issue of the enzyme's thermo-instability. Other methods of delivery, such as via nanoparticles or synthetic scaffolds, have shown promise; however, the outcomes from these experiments suggest that these methods of delivery require further optimization to achieve similar levels of efficacy to that obtained by a gene therapy approach. Pre-clinical models have also shown chondroitinase is efficacious in the treatment of other conditions, such as peripheral nerve injury, stroke, coronary reperfusion, Parkinson's disease and certain types of cancer. The wide range of conditions where the benefits of chondroitinase treatment have been demonstrated reflects the complex roles that chondroitin sulphate proteoglycans (its substrate) play in health and disease and warrants the enzyme's further development as a therapy.

Involvement of Epigenetic Mechanisms and Non-coding RNAs in Blood-Brain Barrier and Neurovascular Unit Injury and Recovery After Stroke

Cessation of blood flow leads to a complex cascade of pathophysiological events at the blood-vascular-parenchymal interface which evolves over time and space, and results in damage to neural cells and edema formation. Cerebral ischemic injury evokes a profound and deleterious upregulation in inflammation and triggers multiple cell death pathways, but it also induces a series of the events associated with regenerative responses, including vascular remodeling, angiogenesis, and neurogenesis. Emerging evidence suggests that epigenetic reprograming could play a pivotal role in ongoing post-stroke neurovascular unit (NVU) changes and recovery. This review summarizes current knowledge about post-stroke recovery processes at the NVU, as well as epigenetic mechanisms and modifiers (e.g., DNA methylation, histone modifying enzymes and microRNAs) associated with stroke injury, and NVU repair. It also discusses novel drug targets and therapeutic strategies for enhancing post-stroke recovery.

The impact of metallothionein-II on microglial response to tumor necrosis factor-alpha (TNFα) and downstream effects on neuronal regeneration

Background

The extracellular environment plays an important role in supporting the regeneration of axons after injury. Metallothionein-II (MTII) is a metal-binding protein known for its neuroprotective effect by directly stimulating the growth of axons after injury. Previous studies have shown that MTII also modulates the response of astrocytes and microglia after injury. However, a detailed analysis describing how MTII modulates the interaction between microglia and neurons is lacking.

Methods

We introduced fluorescently labelled MTII into the cortex at the time of needlestick injury to investigate the cellular uptake of MTII using immunohistochemistry with antibodies against cell-type-specific markers. The role of MTII in modulating the effect of microglia on axon outgrowth following an inflammatory response is further investigated using a co-culture model involving primary rodent microglia pre-treated with TNFα and primary rodent cortical neurons. The axon lengths were assessed 24 h after the plating of the neurons onto treated microglia. We also utilised siRNA to knockdown the expression of LRP1, which allows us to investigate the role of LRP1 receptors in the MTII-mediated effect of microglia on axon outgrowth.

Results

Fluorescently labelled MTII was found to be associated with neurons, astrocytes and microglia following injury in vivo. Microglia-neuron co-culture experiments demonstrated that exogenous MTII altered the response of microglia to TNFα. The neurons plated onto the TNFα-stimulated microglia pre-treated with MTII have shown a significantly longer axonal length compare to the TNFα-stimulated microglia without the MTII treatment. This suggested that MTII reduce cytokine-stimulated activation of microglia, which would ordinarily impair neurite outgrowth. This inhibitory effect of MTII on activated microglia was blocked by siRNA-mediated downregulation of LRP1 receptor expression in microglia, suggesting that MTII acts via the LRP1 receptor on microglia.

Conclusions

This study demonstrates that exogenous MTII acts via the LRP1 receptor to alter the inflammatory response of microglia following TNFα stimulation, providing a more supportive environment for axon growth.

Chondroitinase ABC for neurological recovery after acute brain injury: systematic review and meta-analyses of preclinical studies

OBJECTIVES

Damage to critical brain regions causes deficits in important neurological functions. Chondroitinase ABC (ChABC) has been shown to promote neuroplasticity and may ameliorate neurological deficits caused by disease or trauma. This systematic review identifies and evaluates preclinical studies of ChABC as a treatment for acute brain injury.

METHODS

Four databases were searched for studies relating to ChABC and brain or brain injuries. Controlled studies in mammals with acute brain injuries treated with ChABC were included in meta-analyses of neurobehavioural outcomes. Means and standard deviations from the fifth day of treatment were extracted, and normalised mean differences were calculated.

RESULTS

Of 775 identified records, 16 studies administered ChABC after acute brain injury, of which 9 reported neurobehavioural outcomes. The estimated treatment effect on neurological recovery over the duration of included studies was 49.4% (CI: 30.3-68.4% with Hartung-Knapp-Sidik-Jonkman adjustment, p = 0.0002). The mechanisms of action may involve decreasing astroglial scar formation, promoting neuronal sprouting, and selective synaptic strengthening of sprouting neurites and activated neural pathways.

CONCLUSIONS

The summary of published evidence suggests that ChABC treatment is effective in improving neurological outcomes in preclinical models of acute brain injury. However, more studies are needed for better assessment of the specific translational potential of ChABC.

ABBREVIATIONS

AVM - Arteriovenous Malformation; ChABC - Chondroitinase ABC; CI - Confidence Interval; CSPG - Chondroitin Sulphate Proteoglycans; HKSJ - Hartung-Knapp-Sidik-Jonkman; MCA - Middle Cerebral Artery; NMD - Normalised Mean Difference; NSPC - Neural Stem/Progenitor Cells; PI - Prediction Interval; SD - Standard Deviation; SMD - Standardised Mean Difference; TBI - Traumatic Brain Injury.

Netrin-1 Ameliorates Blood-Brain Barrier Impairment Secondary to Ischemic Stroke via the Activation of PI3K Pathway

Secondary impairment of blood-brain barrier (BBB) occurs in the remote thalamus after ischemic stroke. Netrin-1, an axonal guidance molecule, presents bifunctional effects on blood vessels through receptor-dependent pathways. This study investigates whether netrin-1 protects BBB against secondary injury. Netrin-1 (600 ng/d for 7 days) was intracerebroventricularly infused 24 h after middle cerebral artery occlusion (MCAO) in hypertensive rats. Neurological function was assessed 8 and 14 days after MCAO, and the permeability of BBB in the ipsilateral thalamus was detected. The viability of brain microvascular endothelial cells was determined after being disposed with netrin-1 (50 ng/mL) before oxygen-glucose deprivation (OGD). The role of netrin-1 was further explored by examining its receptors and their function. We found that netrin-1 infusion improved neurological function, attenuated secondary impairment of BBB by up-regulating the levels of tight junction proteins and diminishing extravasation of albumin, with autophagy activation 14 days after MCAO. Netrin-1 also enhanced cell survival and autophagy activity in OGD-treated cells, inhibited by UNC5H2 siRNA transfection. Furthermore, the beneficial effects of netrin-1 were suppressed by PI3K inhibitors 3-Methyladenine and LY294002. Our results showed that netrin-1 ameliorated BBB impairment secondary to ischemic stroke by promoting tight junction function and endothelial survival. PI3K-mediated autophagy activation depending on UNC5H2 receptor could be an underlying mechanism.

Damaged Neocortical Perineuronal Nets Due to Experimental Focal Cerebral Ischemia in Mice, Rats and Sheep

As part of the extracellular matrix (ECM), perineuronal nets (PNs) are polyanionic, chondroitin sulfate proteoglycan (CSPG)-rich coatings of certain neurons, known to be affected in various neural diseases. Although these structures are considered as important parts of the neurovascular unit (NVU), their role during evolution of acute ischemic stroke and subsequent tissue damage is poorly understood and only a few preclinical studies analyzed PNs after acute ischemic stroke. By employing three models of experimental focal cerebral ischemia, this study was focused on histopathological alterations of PNs and concomitant vascular, glial and neuronal changes according to the NVU concept. We analyzed brain tissues obtained 1 day after ischemia onset from: (a) mice after filament-based permanent middle cerebral artery occlusion (pMCAO); (b) rats subjected to thromboembolic MACO; and (c) sheep at 14 days after electrosurgically induced focal cerebral ischemia. Multiple fluorescence labeling was applied to explore simultaneous alterations of NVU and ECM. Serial mouse sections labeled with the net marker Wisteria floribunda agglutinin (WFA) displayed largely decomposed and nearly erased PNs in infarcted neocortical areas that were demarcated by up-regulated immunoreactivity for vascular collagen IV (Coll IV). Subsequent semi-quantitative analyses in mice confirmed significantly decreased WFA-staining along the ischemic border zone and a relative decrease in the directly ischemia-affected neocortex. Triple fluorescence labeling throughout the three animal models revealed up-regulated Coll IV and decomposed PNs accompanied by activated astroglia and altered immunoreactivity for parvalbumin, a calcium-binding protein in fast-firing GABAergic neurons which are predominantly surrounded by neocortical PNs. Furthermore, ischemic neocortical areas in rodents simultaneously displayed less intense staining of WFA, aggrecan, the net components neurocan, versican and the cartilage link protein (CRTL) as well as markers in net-bearing neurons such as the potassium channel subunit Kv3.1b and neuronal nuclei (NeuN). In summary, theconsistent observations based on three different stroke models confirmed that PNs are highly sensitive constituents of the NVU along with impaired associated GABAergic neurons. These results suggest that PNs could be promising targets of future stroke treatment, and further studies should address their reorganization and plasticity in both stabilizing the acute stroke as well as supportive effects during the chronic phase of stroke.

Transient global cerebral ischemia induces rapid and sustained reorganization of synaptic structures

Ischemia can cause rapid neuronal damage. Previous studies have suggested that synaptic structures and cortical functions can be rescued if therapeutic interventions are applied in time, but the structural basis for this resilience remains incompletely understood. Here, we investigated the restoration of synaptic structures and postischemic plasticity of dendritic spines in the somatosensory cortices of mice by taking advantage of a reversible global cerebral ischemia model. Intravital two-photon imaging revealed that although dendritic structures were rapidly distorted after global ischemia, only a small percentage of spines were actually lost after transient ischemia. Electron microscopy indicated that most presynaptic electron-dense structures were still apposed to postsynaptic densities, and that the majority of disrupted synaptic structures were rapidly reinstated following reperfusion after transient ischemia. Repeated imaging suggested that restored dendrites survived the initial ischemia -reperfusion challenge. Importantly, spines on the restored dendrites underwent a rapid and sustained structural reorganization following transient ischemia. These findings suggested that disrupted synapses during transient ischemia could be rapidly restored after ischemia/reperfusion, and that restored dendritic structures remained plastic to rebuild the cortical network.

Intravenous infusion of human bone marrow mesenchymal stromal cells promotes functional recovery and neuroplasticity after ischemic stroke in mice

Transplantation of human bone marrow mesenchymal stromal cells (hBM-MSC) promotes functional recovery after stroke in animal models, but the mechanisms underlying these effects remain incompletely understood. We tested the efficacy of Good Manufacturing Practices (GMP) compliant hBM-MSC, injected intravenously 3.5 hours after injury in mice subjected to transient middle cerebral artery occlusion (tMCAo). We addressed whether hBM-MSC are efficacious and if this efficacy is associated with cortical circuit reorganization using neuroanatomical analysis of GABAergic neurons (parvalbumin; PV-positive cells) and perineuronal nets (PNN), a specialized extracellular matrix structure which acts as an inhibitor of neural plasticity. tMCAo mice receiving hBM-MSC, showed early and lasting improvement of sensorimotor and cognitive functions compared to control tMCAo mice. Furthermore, 5 weeks post-tMCAo, hBM-MSC induced a significant rescue of ipsilateral cortical neurons; an increased proportion of PV-positive neurons in the perilesional cortex, suggesting GABAergic interneurons preservation; and a lower percentage of PV-positive cells surrounded by PNN, indicating an enhanced plastic potential of the perilesional cortex. These results show that hBM-MSC improve functional recovery and stimulate neuroprotection after stroke. Moreover, the downregulation of “plasticity brakes” such as PNN suggests that hBM-MSC treatment stimulates plasticity and formation of new connections in the perilesional cortex.

Matrix Metalloproteinases, Neural Extracellular Matrix, and Central Nervous System Pathology

The functionality and stability of the central nervous system (CNS) pabulum, called neural extracellular matrix (nECM), is paramount for the maintenance of a healthy network. The loosening or the damage of the scaffold disrupts synaptic transmission with the consequent imbalance of the neurotransmitters, reactive cells invasion, astrocytosis, new matrix deposition, digestion of the previous structure and ultimately, maladaptive plasticity with the loss of neuronal viability. nECM is constantly affected by CNS disorders, particularly in chronic modifying such as neurodegenerative disease, or in acute/subacute with chronic sequelae, like cerebrovascular and inflammatory pathology. Matrix metalloproteinases (MMPs) are the main interfering agent of nECM, guiding the balance of degradation and new deposition of proteins such as proteoglycans and glycoproteins, or glycosaminoglycans, such as hyaluronic acid. Activation of these enzymes is modulated by their physiologic inhibitors, the tissue inhibitors of MMPs or via other proteases inhibitors, as well as genetic or epigenetic up- or downregulation through molecular interaction or receptor activation. The appropriate understanding of the pathways underlying nECM modifications in CNS pathology is probably one of the pivotal future directions to identify the healthy brain network and subsequently design new therapies to interfere with the progression of the CNS disease and eventually find appropriate therapies.

Reactive astrogliosis in stroke: Contributions of astrocytes to recovery of neurological function

Alterations in neuronal connectivity, particularly in the "peri-infarct" tissue adjacent to the region of ischemic damage, are important contributors to the spontaneous recovery of function that commonly follows stroke. Peri-infarct astrocytes undergo reactive astrogliosis and play key roles in modulating the adaptive responses in neurons. This reactive astrogliosis shares many features with that induced by other forms of damage to the central nervous system but also differs in details that potentially influence neurological recovery. A subpopulation of astrocytes within a few hundred micrometers of the infarct proliferate and are centrally involved in the development of the glial scar that separates the damaged tissue in the infarct from surrounding normal brain. The intertwined processes of astrocytes adjacent to the infarct provide the core structural component of the mature scar. Interventions that cause early disruption of glial scar formation typically impede restoration of neurological function. Marked reactive astrogliosis also develops in cells more distant from the infarct but these cells largely remain in the spatial territories they occupied prior to stroke. These cells play important roles in controlling the extracellular environment and release proteins and other molecules that are able to promote neuronal plasticity and improve functional recovery. Treatments manipulating aspects of reactive astrogliosis can enhance neuronal plasticity following stroke. Optimising these treatments for use in human stroke would benefit from a more complete characterization of the specific responses of peri-infarct astrocytes to stroke as well as a better understanding of the influence of other factors including age, sex, comorbidities and reperfusion of the ischemic tissue.

Trafficking and processing of bacterial proteins by mammalian cells: Insights from chondroitinase ABC

BACKGROUND

There is very little reported in the literature about the relationship between modifications of bacterial proteins and their secretion by mammalian cells that synthesize them. We previously reported that the secretion of the bacterial enzyme Chondroitinase ABC by mammalian cells requires the strategic removal of at least three N-glycosylation sites. The aim of this study was to determine if it is possible to enhance the efficacy of the enzyme as a treatment for spinal cord injury by increasing the quantity of enzyme secreted or by altering its cellular location.

METHODOLOGY/PRINCIPAL FINDINGS

To determine if the efficiency of enzyme secretion could be further increased, cells were transfected with constructs encoding the gene for chondroitinase ABC modified for expression by mammalian cells; these contained additional modifications of strategic N-glycosylation sites or alternative signal sequences to direct secretion of the enzyme from the cells. We show that while removal of certain specific N-glycosylation sites enhances enzyme secretion, N-glycosylation of at least two other sites, N-856 and N-773, is essential for both production and secretion of active enzyme. Furthermore, we find that the signal sequence directing secretion also influences the quantity of enzyme secreted, and that this varies widely amongst the cell types tested. Last, we find that replacing the 3'UTR on the cDNA encoding Chondroitinase ABC with that of β-actin is sufficient to target the enzyme to the neuronal growth cone when transfected into neurons. This also enhances neurite outgrowth on an inhibitory substrate.

CONCLUSION/SIGNIFICANCE

Some intracellular trafficking pathways are adversely affected by cryptic signals present in the bacterial gene sequence, whilst unexpectedly others are required for efficient secretion of the enzyme. Furthermore, targeting chondroitinase to the neuronal growth cone promotes its ability to increase neurite outgrowth on an inhibitory substrate. These findings are timely in view of the renewed prospects for gene therapy, and of direct relevance to strategies aimed at expressing foreign proteins in mammalian cells, in particular bacterial proteins.

Abolished perineuronal nets and altered parvalbumin-immunoreactivity in the nucleus reticularis thalami of wildtype and 3xTg mice after experimental stroke

Treatment strategies for ischemic stroke are still limited, since numerous attempts were successful only in preclinical research but failed under clinical condition. To overcome this translational roadblock, clinical relevant stroke models should consider co-morbidities, age-related effects and the complex neurovascular unit (NVU) concept. The NVU includes neurons, vessels and glial cells with astrocytic endfeet in close relation to the extracellular matrix (ECM). However, the role of the ECM after stroke-related tissue damage is poorly understood and mostly neglected for treatment strategies. This study is focused on alterations of perineuronal nets (PNs) as ECM constituents and parvalbumin-containing GABAergic neurons in mice with emphasis on the nucleus reticularis thalami (NRT) in close proximity to the ischemic lesion as induced by a filament-based stroke model. One day after ischemia onset, immunofluorescence-based quantitative analyses revealed drastically declined PNs in the ischemia-affected NRT from 3- and 12-month-old wildtype and co-morbid triple-transgenic (3xTg) mice with Alzheimer-like alterations. Parvalbumin-positive cells decreased numerically in the ischemia-affected NRT, while staining intensity did not differ between the affected and non-affected hemisphere. Additional qualitative analyses demonstrated ischemia-induced loss of PNs and allocated neuropil ECM immunoreactive for aggrecan and neurocan, and impaired immunoreactivity for calbindin, the potassium channel subunit Kv3.1b and the glutamate decarboxylase isoforms GAD65 and GAD67 in the NRT. In conclusion, these data confirm PNs as highly sensitive constituents of the ECM along with impaired neuronal integrity of GABAergic neurons. Therefore, specific targeting of ECM components might appear as a promising strategy for future treatment strategies in stroke.

Exercise Training Inhibits the Nogo-A/NgR1/Rho-A Signals in the Cortical Peri-infarct Area in Hypertensive Stroke Rats

OBJECTIVE

The aim of this study was to test the hypothesis that exercise training promotes motor recovery after stroke by facilitating axonal remodeling via inhibition of the Nogo-A/NgR1 and Rho-A pathway.

DESIGN

A distal middle cerebral artery occlusion model was generated in stroke-prone renovascular hypertensive rats. Stroke-prone renovascular hypertensive rats were randomly divided into a control group, an exercise training group, and a sham group. Motor function was measured using the grip strength test. Axon and myelin remodeling markers, growth-associated protein 43, myelin basic protein, Tau, and amyloid precursor protein were detected by immunofluorescence. The expression of Nogo-A, NgR1, and Rho-A was demonstrated by immunofluorescence and Western blotting in the peri-infarction area at 7, 14, 28, and 52 days after distal middle cerebral artery occlusion.

RESULTS

Grip strength was higher in the exercise training group (P < 0.05). Exercise training increased the expression of growth-associated protein 43, myelin basic protein (at 7, 14, and 28 days), and Tau (at 7 and 14 days), and decreased the expression of axonal damage amyloid precursor protein (at 7 and 14 days), compared with the control group. The protein levels of Nogo-A (at 7 and 14 days), NgR1 (at 7, 14, and 28 days), and Rho-A (at 14 and 28 days) were reduced after exercise training.

CONCLUSIONS

Exercise training promotes axonal recovery, which is associated with functional improvement after cerebral infarction. Down-regulation of the Nogo-A/NgR1/Rho-A may mediate the axonal remodeling induced by exercise training.

Asynchronous therapy targeting Nogo-A enhances neurobehavioral recovery by reducing neuronal loss and promoting neurite outgrowth after cerebral ischemia in mice

Therapeutics targeting the Nogo-A signal pathway hold promise to promote recovery following brain injury. Based on the temporal characteristics of Nogo-A expression in the process of cerebral ischemia and reperfusion, we tested a novel asynchronous treatment, in which TAT-M9 was used in the early stage to decrease neuronal loss, and TAT-NEP1-40 was used in the delayed stage to promote neurite outgrowth after bilateral common carotid artery occlusion (BCCAO) in mice. Both TAT-M9 and TAT-NEP1-40 were efficiently delivered into the brains of mice by intraperitoneal injection. TAT-M9 treatment promoted neuron survival and inhibited neuronal apoptosis. Asynchronous therapy with TAT-M9 and TAT-NEP1-40 increased the expression of Tau, GAP43 and MAP-2 proteins, and enhanced short-term and long-term cognitive functions. In conclusion, the asynchronous treatment had a long-term neuroprotective effect, which reduced neurologic injury and apoptosis, promoted neurite outgrowth and enhanced functional recovery after ischemia. It suggests that this asynchronous treatment could be a promising therapy for cerebral ischemia in humans.

Chondroitin sulfate proteoglycans impede myelination by oligodendrocytes after perinatal white matter injury

Hypomyelination is the major cause of neurodevelopmental deficits that are associated with perinatal white matter injury. Chondroitin sulfate proteoglycans (CSPGs) are known to exert inhibitory effects on the migration and differentiation of oligodendrocytes (OLs). However, few studies describe the roles of CSPGs in myelination by OLs and the cognitive dysfunction that follows perinatal white matter injury. Here, we examined the alterations in the expression of CSPGs and their functional impact on the maturation of OLs and myelination in a neonatal rat model of hypoxic-ischemic (HI) brain injury. Three-day-old Sprague-Dawley rats underwent a right common carotid artery ligation and were exposed to hypoxia (6% oxygen for 2.5h). Rats were given chondroitinase ABC (cABC) via an intracerebroventricular injection to digest CSPGs. Animals were sacrificed at 7, 14, 28 and 56days after HI injury and the accompanying surgical procedure. We found that the expression of CSPGs was significantly up-regulated in the cortical regions surrounding the white matter after HI injury. cABC successfully degraded CSPGs in the rats that received cABC. Immunostaining showed decreased expression of the pre-oligodendrocyte marker O4 in the cingulum, external capsule and corpus callosum in HI+cABC rats compared to HI rats. However HI+cABC rats exhibited greater maturation of OLs than did HI rats, with increased expression of O1 and myelin basic protein in the white matter. Furthermore, using electron microscopy, we demonstrated that myelin formation was enhanced in HI+cABC rats, which had an increased number of myelinated axons and decreased G-ratios of myelin compared to HI rats. Finally, HI+cABC rats performed better in the Morris water maze task than HI rats, which indicates an improvement in cognitive ability. Our results suggest that CSPGs inhibit both the maturation of OLs and the process of myelination after neonatal HI brain injury. The data also raise the possibility that modifying CSPGs may repair this type of lesion associated with demyelination.

Enzyme activity enhancement of chondroitinase ABC I from Proteus vulgaris by site-directed mutagenesis

Arg660 was found as a new active site and Asn795Ala and Trp818Ala mutants showed higher activities than the wild type based on molecular docking simulation analysis for the first time.

Targeting RPTPσ with lentiviral shRNA promotes neurites outgrowth of cortical neurons and improves functional recovery in a rat spinal cord contusion model

After spinal cord injury (SCI), the rapidly upregulated chondroitin sulfate proteoglycans (CSPGs), the prominent chemical constituents and main repulsive factors of the glial scar, play an important role in the extremely limited ability to regenerate in adult mammals. Although many methods to overcome the inhibition have been tested, no successful method with clinical feasibility has been devised to date. It was recently discovered that receptor protein tyrosine phosphatase sigma (RPTPσ) is a functional receptor for CSPGs-mediated inhibition. In view of the potential clinical application of RNA interference (RNAi), here we investigated whether silencing RPTPσ via lentivirus-mediated RNA interference can promote axon regeneration and functional recovery after SCI. Neurites of primary rat cerebral cortical neurons with depleted RPTPσ exhibited a significant enhancement in elongation and crossing ability when they encountered CSPGs in vitro. A contusion model of spinal cord injury in Wistar rats (the New York University (NYU) impactor) was used for in vivo experiments. Local injection of lentivirus encoding RPTPσ shRNA at the lesion site promoted axon regeneration and synapse formation, but did not affect the scar formation. Meanwhile, in vivo functional recovery (motor and sensory) was also enhanced after RPTPσ depletion. Therefore, strategies directed at silencing RPTPσ by RNAi may prove to be a beneficial, efficient and valuable approach for the treatment of SCI.

Influence of the extracellular matrix on endogenous and transplanted stem cells after brain damage

The limited regeneration capacity of the adult central nervous system (CNS) requires strategies to improve recovery of patients. In this context, the interaction of endogenous as well as transplanted stem cells with their environment is crucial. An understanding of the molecular mechanisms could help to improve regeneration by targeted manipulation. In the course of reactive gliosis, astrocytes upregulate Glial fibrillary acidic protein (GFAP) and start, in many cases, to proliferate. Beside GFAP, subpopulations of these astroglial cells coexpress neural progenitor markers like Nestin. Although cells express these markers, the proportion of cells that eventually give rise to neurons is limited in many cases in vivo compared to the situation in vitro. In the first section, we present the characteristics of endogenous progenitor-like cells and discuss the differences in their neurogenic potential in vitro and in vivo. As the environment plays an important role for survival, proliferation, migration, and other processes, the second section of the review describes changes in the extracellular matrix (ECM), a complex network that contains numerous signaling molecules. It appears that signals in the damaged CNS lead to an activation and de-differentiation of astrocytes, but do not effectively promote neuronal differentiation of these cells. Factors that influence stem cells during development are upregulated in the damaged brain as part of an environment resembling a stem cell niche. We give a general description of the ECM composition, with focus on stem cell-associated factors like the glycoprotein Tenascin-C (TN-C). Stem cell transplantation is considered as potential treatment strategy. Interaction of transplanted stem cells with the host environment is critical for the outcome of stem cell-based therapies. Possible mechanisms involving the ECM by which transplanted stem cells might improve recovery are discussed in the last section.