tPA promotes ADAMTS-4-induced CSPG degradation, thereby enhancing neuroplasticity following spinal cord injury

Fibrinolytic Agents in Thromboembolic Diseases: Historical Perspectives and Approved Indications

Fibrinolytic agents catalyze the conversion of the inactive proenzyme plasminogen into the active protease plasmin, degrading fibrin within the thrombus and recanalizing occluded vessels. The history of these medications dates to the discovery of the first fibrinolytic compound, streptokinase, from bacterial cultures in 1933. Over time, researchers identified two other plasminogen activators in human samples, namely urokinase and tissue plasminogen activator (tPA). Subsequently, tPA was cloned using recombinant DNA methods to produce alteplase. Several additional derivatives of tPA, such as tenecteplase and reteplase, were developed to extend the plasma half-life of tPA. Over the past decades, fibrinolytic medications have been widely used to manage patients with venous and arterial thromboembolic events. Currently, alteplase is approved by the U.S. Food and Drug Administration (FDA) for use in patients with pulmonary embolism with hemodynamic compromise, ST-segment elevation myocardial infarction (STEMI), acute ischemic stroke, and central venous access device occlusion. Reteplase and tenecteplase have also received FDA approval for treating patients with STEMI. This review provides an overview of the historical background related to fibrinolytic agents and briefly summarizes their approved indications across various thromboembolic diseases.

Therapeutic administration of mouse mast cell protease 6 improves functional recovery after traumatic spinal cord injury in mice by promoting remyelination and reducing glial scar formation

Traumatic spinal cord injury (SCI) most often leads to permanent paralysis due to the inability of axons to regenerate in the adult mammalian central nervous system (CNS). In the past, we have shown that mast cells (MCs) improve the functional outcome after SCI by suppressing scar tissue formation at the lesion site via mouse mast cell protease 6 (mMCP6). In this study, we investigated whether recombinant mMCP6 can be used therapeutically to improve the functional outcome after SCI. Therefore, we applied mMCP6 locally via an intrathecal catheter in the subacute phase after a spinal cord hemisection injury in mice. Our findings showed that hind limb motor function was significantly improved in mice that received recombinant mMCP6 compared with the vehicle-treated group. In contrast to our previous findings in mMCP6 knockout mice, the lesion size and expression levels of the scar components fibronectin, laminin, and axon-growth-inhibitory chondroitin sulfate proteoglycans were not affected by the treatment with recombinant mMCP6. Surprisingly, no difference in infiltration of CD4+ T cells and reactivity of Iba-1+ microglia/macrophages at the lesion site was observed between the mMCP6-treated mice and control mice. Additionally, local protein levels of the pro- and anti-inflammatory mediators IL-1β, IL-2, IL-4, IL-6, IL-10, TNF-α, IFNγ, and MCP-1 were comparable between the two treatment groups, indicating that locally applied mMCP6 did not affect inflammatory processes after injury. However, the increase in locomotor performance in mMCP6-treated mice was accompanied by reduced demyelination and astrogliosis in the perilesional area after SCI. Consistently, we found that TNF-α/IL-1β-astrocyte activation was decreased and that oligodendrocyte precursor cell (OPC) differentiation was increased after recombinant mMCP6 treatment in vitro. Mechanistically, this suggests effects of mMCP6 on reducing astrogliosis and improving (re)myelination in the spinal cord after injury. In conclusion, these data show for the first time that recombinant mMCP6 is therapeutically active in enhancing recovery after SCI.

Matrix disequilibrium in Alzheimer's disease and conditions that increase Alzheimer's disease risk

Alzheimer's Disease (AD) and related dementias are a leading cause of death globally and are predicted to increase in prevalence. Despite this expected increase in the prevalence of AD, we have yet to elucidate the causality of the neurodegeneration observed in AD and we lack effective therapeutics to combat the progressive neuronal loss. Throughout the past 30 years, several non-mutually exclusive hypotheses have arisen to explain the causative pathologies in AD: amyloid cascade, hyper-phosphorylated tau accumulation, cholinergic loss, chronic neuroinflammation, oxidative stress, and mitochondrial and cerebrovascular dysfunction. Published studies in this field have also focused on changes in neuronal extracellular matrix (ECM), which is critical to synaptic formation, function, and stability. Two of the greatest non-modifiable risk factors for development of AD (aside from autosomal dominant familial AD gene mutations) are aging and APOE status, and two of the greatest modifiable risk factors for AD and related dementias are untreated major depressive disorder (MDD) and obesity. Indeed, the risk of developing AD doubles for every 5 years after ≥ 65, and the APOE4 allele increases AD risk with the greatest risk in homozygous APOE4 carriers. In this review, we will describe mechanisms by which excess ECM accumulation may contribute to AD pathology and discuss pathological ECM alterations that occur in AD as well as conditions that increase the AD risk. We will discuss the relationship of AD risk factors to chronic central nervous system and peripheral inflammation and detail ECM changes that may follow. In addition, we will discuss recent data our lab has obtained on ECM components and effectors in APOE4/4 and APOE3/3 expressing murine brain lysates, as well as human cerebrospinal fluid (CSF) samples from APOE3 and APOE4 expressing AD individuals. We will describe the principal molecules that function in ECM turnover as well as abnormalities in these molecular systems that have been observed in AD. Finally, we will communicate therapeutic interventions that have the potential to modulate ECM deposition and turnover in vivo.

Epigenetic Up-Regulation of ADAMTS4 in Sympathetic Ganglia is Involved in the Maintenance of Neuropathic Pain Following Nerve Injury

Sympathetic axonal sprouting into dorsal root ganglia is a major phenomenon implicated in neuropathic pain, and sympathetic ganglia blockage may relieve some intractable chronic pain in animal pain models and clinical conditions. These suggest that sympathetic ganglia participated in the maintenance of chronic pain. However, the molecular mechanism underlying sympathetic ganglia-mediated chronic pain is not clear. Here, we found that spared nerve injury treatment upregulated the expression of ADAMTS4 and AP-2α protein and mRNA in the noradrenergic neurons of sympathetic ganglia during neuropathic pain maintenance. Knockdown the ADAMTS4 or AP-2α by injecting specific retro scAAV-TH (Tyrosine Hydroxylase)-shRNA ameliorated the mechanical allodynia induced by spared nerve injury on day 21 and 28. Furthermore, chromatin immunoprecipitation and coimmunoprecipitation assays found that spared nerve injury increased the recruitment of AP-2α to the ADAMTS4 gene promoter, the interaction between AP-2α and histone acetyltransferase p300 and the histone H4 acetylation on day 28. Finally, knockdown the AP-2α reduced the acetylation of H4 on the promoter region of ADAMTS4 gene and suppressed the increase of ADAMTS4 expression induced by spared nerve injury. Together, these results suggested that the enhanced interaction between AP-2α and p300 mediated the epigenetic upregulation of ADAMTS4 in sympathetic ganglia noradrenergic neurons, which contributed to the maintenance of spared nerve injury induced neuropathic pain.

Parvalbumin interneuron-derived tissue-type plasminogen activator shapes perineuronal net structure

Background

Perineuronal nets (PNNs) are specialized extracellular matrix structures mainly found around fast-spiking parvalbumin (FS-PV) interneurons. In the adult, their degradation alters FS-PV-driven functions, such as brain plasticity and memory, and altered PNN structures have been found in neurodevelopmental and central nervous system disorders such as Alzheimer’s disease, leading to interest in identifying targets able to modify or participate in PNN metabolism. The serine protease tissue-type plasminogen activator (tPA) plays multifaceted roles in brain pathophysiology. However, its cellular expression profile in the brain remains unclear and a possible role in matrix plasticity through PNN remodeling has never been investigated.

Result

By combining a GFP reporter approach, immunohistology, electrophysiology, and single-cell RT-PCR, we discovered that cortical FS-PV interneurons are a source of tPA in vivo. We found that mice specifically lacking tPA in FS-PV interneurons display denser PNNs in the somatosensory cortex, suggesting a role for tPA from FS-PV interneurons in PNN remodeling. In vitro analyses in primary cultures of mouse interneurons also showed that tPA converts plasminogen into active plasmin, which in turn, directly degrades aggrecan, a major structural chondroitin sulfate proteoglycan (CSPG) in PNNs.

Conclusions

We demonstrate that tPA released from FS-PV interneurons in the central nervous system reduces PNN density through CSPG degradation. The discovery of this tPA-dependent PNN remodeling opens interesting insights into the control of brain plasticity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01419-8.

Neuroserpin Is Strongly Expressed in the Developing and Adult Mouse Neocortex but Its Absence Does Not Perturb Cortical Lamination and Synaptic Proteome

Neuroserpin is a serine protease inhibitor that regulates the activity of tissue-type plasminogen activator (tPA) in the nervous system. Neuroserpin is strongly expressed during nervous system development as well as during adulthood, when it is predominantly found in regions eliciting synaptic plasticity. In the hippocampus, neuroserpin regulates developmental neurogenesis, synaptic maturation and in adult mice it modulates synaptic plasticity and controls cognitive and social behavior. High expression levels of neuroserpin in the neocortex starting from prenatal stage and persisting during adulthood suggest an important role for the serpin in the formation of this brain region and in the maintenance of cortical functions. In order to uncover neuroserpin function in the murine neocortex, in this work we performed a comprehensive investigation of its expression pattern during development and in the adulthood. Moreover, we assessed the role of neuroserpin in cortex formation by comparing cortical lamination and neuronal maturation between neuroserpin-deficient and control mice. Finally, we evaluated a possible regulatory role of neuroserpin at cortical synapses in neuroserpin-deficient mice. We observed that neuroserpin is expressed starting from the beginning of corticogenesis until adulthood throughout the neocortex in several classes of glutamatergic projection neurons and GABA-ergic interneurons. However, in the absence of neuroserpin we did not detect any alteration either in cortical layer formation, or in neuronal soma size and dendritic length. Furthermore, no significant quantitative changes were observed in the proteome of cortical synapses upon neuroserpin deficiency. We conclude that, although strongly expressed in the neocortex, absence of neuroserpin does not lead to gross developmental abnormalities, and does not perturb the composition of the cortical synaptic proteome.

Protein Degradome of Spinal Cord Injury: Biomarkers and Potential Therapeutic Targets

Degradomics is a proteomics sub-discipline whose goal is to identify and characterize protease-substrate repertoires. With the aim of deciphering and characterizing key signature breakdown products, degradomics emerged to define encryptic biomarker neoproteins specific to certain disease processes. Remarkable improvements in structural and analytical experimental methodologies as evident in research investigating cellular behavior in neuroscience and cancer have allowed the identification of specific degradomes, increasing our knowledge about proteases and their regulators and substrates along with their implications in health and disease. A physiologic balance between protein synthesis and degradation is sought with the activation of proteolytic enzymes such as calpains, caspases, cathepsins, and matrix metalloproteinases. Proteolysis is essential for development, growth, and regeneration; however, inappropriate and uncontrolled activation of the proteolytic system renders the diseased tissue susceptible to further neurotoxic processes. In this article, we aim to review the protease-substrate repertoires as well as emerging therapeutic interventions in spinal cord injury at the degradomic level. Several protease substrates and their breakdown products, essential for the neuronal structural integrity and functional capacity, have been characterized in neurotrauma including cytoskeletal proteins, neuronal extracellular matrix glycoproteins, cell junction proteins, and ion channels. Therefore, targeting exaggerated protease activity provides a potentially effective therapeutic approach in the management of protease-mediated neurotoxicity in reducing the extent of damage secondary to spinal cord injury.

Local Serpin Treatment via Chitosan-Collagen Hydrogel after Spinal Cord Injury Reduces Tissue Damage and Improves Neurologic Function

Spinal cord injury (SCI) results in massive secondary damage characterized by a prolonged inflammation with phagocytic macrophage invasion and tissue destruction. In prior work, sustained subdural infusion of anti-inflammatory compounds reduced neurological deficits and reduced pro-inflammatory cell invasion at the site of injury leading to improved outcomes. We hypothesized that implantation of a hydrogel loaded with an immune modulating biologic drug, Serp-1, for sustained delivery after crush-induced SCI would have an effective anti-inflammatory and neuroprotective effect. Rats with dorsal column SCI crush injury, implanted with physical chitosan-collagen hydrogels (CCH) had severe granulomatous infiltration at the site of the dorsal column injury, which accumulated excess edema at 28 days post-surgery. More pronounced neuroprotective changes were observed with high dose (100 µg/50 µL) Serp-1 CCH implanted rats, but not with low dose (10 µg/50 µL) Serp-1 CCH. Rats treated with Serp-1 CCH implants also had improved motor function up to 20 days with recovery of neurological deficits attributed to inhibition of inflammation-associated tissue damage. In contrast, prolonged low dose Serp-1 infusion with chitosan did not improve recovery. Intralesional implantation of hydrogel for sustained delivery of the Serp-1 immune modulating biologic offers a neuroprotective treatment of acute SCI.

New Insights into ADAMTS Metalloproteases in the Central Nervous System

Components of the extracellular matrix (ECM) are key players in regulating cellular functions throughout the whole organism. In fact, ECM components not only participate in tissue organization but also contribute to processes such as cellular maintenance, proliferation, and migration, as well as to support for various signaling pathways. In the central nervous system (CNS), proteoglycans of the lectican family, such as versican, aggrecan, brevican, and neurocan, are important constituents of the ECM. In recent years, members of this family have been found to be involved in the maintenance of CNS homeostasis and to participate directly in processes such as the organization of perineural nets, the regulation of brain plasticity, CNS development, brain injury repair, axonal guidance, and even the altering of synaptic responses. ADAMTSs are a family of “A disintegrin and metalloproteinase with thrombospondin motifs” proteins that have been found to be involved in a multitude of processes through the degradation of lecticans and other proteoglycans. Recently, alterations in ADAMTS expression and activity have been found to be involved in neuronal disorders such as stroke, neurodegeneration, schizophrenia, and even Alzheimer’s disease, which in turn may suggest their potential use as therapeutic targets. Herein, we summarize the different roles of ADAMTSs in regulating CNS events through interactions and the degradation of ECM components (more specifically, the lectican family of proteoglycans).

Astrocyte-selective AAV-ADAMTS4 gene therapy combined with hindlimb rehabilitation promotes functional recovery after spinal cord injury

Chondroitin sulphate proteoglycans (CSPGs) are inhibitors to axon regeneration and plasticity. A disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS4) is a human enzyme that catalyses the proteolysis of CSPG protein cores. Infusion of ADAMTS4 into the damaged spinal cord was previously shown to improve functional recovery SCI, however, this therapy is limited in its enzyme form. Adeno-associated viral (AAV) vector gene therapy has emerged as the vector of choice for safe, robust and long-term transgene expression in the central nervous system. Here, an AAV expression cassette containing ADAMTS4 under the control of the astrocytic GfaABC₁D promoter was packaged into an AAV5 vector. Sustained expression of ADAMTS4 was achieved in vitro and in vivo leading to degradation of CSPGs. Compared to a contusion only group, AAV-ADAMTS4 resulted in significantly decreased lesion size, increased sprouting of hindlimb corticospinal tract axons, increased serotonergic fiber density caudal to a contusive spinal cord injury. Hindlimb-specific exercise rehabilitation was used to drive neuroplasticity towards improving functional connections. The combination of hindlimb rehabilitation with AAV-ADAMTS4 led to functional recovery after SCI compared to a contusion only group. Thus, long-term degradation of CSPGs through AAV-ADAMTS4 gene therapy in a combinational approach with rehabilitation represents a candidate for further preclinical development.

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

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

Deficits in developmental neurogenesis and dendritic spine maturation in mice lacking the serine protease inhibitor neuroserpin

Neuroserpin is a serine protease inhibitor of the nervous system required for normal synaptic plasticity and regulating cognitive, emotional and social behavior in mice. The high expression level of neuroserpin detected at late stages of nervous system formation in most regions of the brain points to a function in neurodevelopment. In order to evaluate the contribution of neuroserpin to brain development, we investigated developmental neurogenesis and neuronal differentiation in the hippocampus of neuroserpin-deficient mice. Moreover, synaptic reorganization and composition of perineuronal net were studied during maturation and stabilization of hippocampal circuits. We showed that absence of neuroserpin results in early termination of neuronal precursor proliferation and premature neuronal differentiation in the first postnatal weeks. Additionally, at the end of the critical period neuroserpin-deficient mice had changed morphology of dendritic spines towards a more mature phenotype. This was accompanied by increased protein levels and reduced proteolytic cleavage of aggrecan, a perineuronal net core protein. These data suggest a role for neuroserpin in coordinating generation and maturation of the hippocampus, which is essential for establishment of an appropriate neuronal network.

Intra- and Extracellular Pillars of a Unifying Framework for Homeostatic Plasticity: A Crosstalk Between Metabotropic Receptors and Extracellular Matrix

In the face of chronic changes in incoming sensory inputs, neuronal networks are capable of maintaining stable conditions of electrical activity over prolonged periods of time by adjusting synaptic strength, to amplify or dampen incoming inputs [homeostatic synaptic plasticity (HSP)], or by altering the intrinsic excitability of individual neurons [homeostatic intrinsic plasticity (HIP)]. Emerging evidence suggests a synergistic interplay between extracellular matrix (ECM) and metabotropic receptors in both forms of homeostatic plasticity. Activation of dopaminergic, serotonergic, or glutamate metabotropic receptors stimulates intracellular signaling through calmodulin-dependent protein kinase II, protein kinase A, protein kinase C, and inositol trisphosphate receptors, and induces changes in expression of ECM molecules and proteolysis of both ECM molecules (lecticans) and ECM receptors (NPR, CD44). The resulting remodeling of perisynaptic and synaptic ECM provides permissive conditions for HSP and plays an instructive role by recruiting additional signaling cascades, such as those through metabotropic glutamate receptors and integrins. The superimposition of all these signaling events determines intracellular and diffusional trafficking of ionotropic glutamate receptors, resulting in HSP and modulation of conditions for inducing Hebbian synaptic plasticity (i.e., metaplasticity). It also controls cell-surface delivery and activity of voltage- and Ca2+-gated ion channels, resulting in HIP. These mechanisms may modify epileptogenesis and become a target for therapeutic interventions.

MAP‑1B, PACS‑2 and AHCYL1 are regulated by miR‑34A/B/C and miR‑449 in neuroplasticity following traumatic spinal cord injury in rats: Preliminary explorative results from microarray data

Spinal cord injury (SCI) is a specific type of damage to the central nervous system causing temporary or permanent changes in its function. The present aimed to identify the genetic changes in neuroplasticity following SCI in rats. The GSE52763 microarray dataset, which included 15 samples [3 sham (1 week), 4 injury only (1 week), 4 injury only (3 weeks), 4 injury + treadmill (3 weeks)] was downloaded from the Gene Expression Omnibus database. An empirical Bayes linear regression model in limma package was used to identify the differentially expressed genes (DEGs) in injury vs. sham and treadmill vs. non‑treadmill comparison groups. Subsequently, time series and enrichment analyses were performed using pheatmap and clusterProfile packages, respectively. Additionally, protein‑protein interaction (PPI) and transcription factor (TF)‑microRNA (miRNA)‑target regulatory networks were constructed using Cytoscape software. In total, 159 and 105 DEGs were identified in injury vs. sham groups and treadmill vs. non‑treadmill groups, respectively. There were 40 genes in cluster 1 that presented increased expression levels in the injury (1 week/3 weeks) groups compared with the sham group, and decreased expression levels in the injury + treadmill group compared with the injury only groups; conversely, 52 genes in cluster 2 exhibited decreased expression levels in the injury (1 week/3 weeks) groups compared with the sham group, and increased expression levels in the injury + treadmill group compared with the injury only groups. Enrichment analysis indicated that clusters 1 and 2 were associated with immune response and signal transduction, respectively. Furthermore, microtubule associated protein 1B, phosphofurin acidic cluster sorting protein 2 and adenosylhomocysteinase‑like 1 exhibited the highest degrees in the regulatory network, and were regulated by miRNAs including miR‑34A, miR‑34B, miR‑34C and miR‑449. These miRNAs and their target genes may serve important roles in neuroplasticity following traumatic SCI in rats. Nevertheless, additional in‑depth studies are required to confirm these data.

Protease-independent action of tissue plasminogen activator in brain plasticity and neurological recovery after ischemic stroke

Emerging evidence suggests that tissue plasminogen activator (tPA), currently the only FDA-approved medication for ischemic stroke, exerts important biological actions on the CNS besides its well-known thrombolytic effect. In this study, we investigated the role of tPA on primary neurons in culture and on brain recovery and plasticity after ischemic stroke in mice. Treatment with recombinant tPA stimulated axonal growth in culture, an effect independent of its protease activity and achieved through epidermal growth factor receptor (EGFR) signaling. After permanent focal cerebral ischemia, tPA knockout mice developed more severe sensorimotor and cognitive deficits and greater axonal and myelin injury than wild-type mice, suggesting that endogenously expressed tPA promotes long-term neurological recovery after stroke. In tPA knockout mice, intranasal administration of recombinant tPA protein 6 hours poststroke and 7 more times at 2 d intervals mitigated white matter injury, improved axonal conduction, and enhanced neurological recovery. Consistent with the proaxonal growth effects observed in vitro, exogenous tPA delivery increased poststroke axonal sprouting of corticobulbar and corticospinal tracts, which might have contributed to restoration of neurological functions. Notably, recombinant mutant tPA-S478A lacking protease activity (but retaining the EGF-like domain) was as effective as wild-type tPA in rescuing neurological functions in tPA knockout stroke mice. These findings demonstrate that tPA improves long-term functional outcomes in a clinically relevant stroke model, likely by promoting brain plasticity through EGFR signaling. Therefore, treatment with the protease-dead recombinant tPA-S478A holds particular promise as a neurorestorative therapy, as the risk for triggering intracranial hemorrhage is eliminated and tPA-S478A can be delivered intranasally hours after stroke.

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

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

The Biology of Regeneration Failure and Success After Spinal Cord Injury

Since no approved therapies to restore mobility and sensation following spinal cord injury (SCI) currently exist, a better understanding of the cellular and molecular mechanisms following SCI that compromise regeneration or neuroplasticity is needed to develop new strategies to promote axonal regrowth and restore function. Physical trauma to the spinal cord results in vascular disruption that, in turn, causes blood-spinal cord barrier rupture leading to hemorrhage and ischemia, followed by rampant local cell death. As subsequent edema and inflammation occur, neuronal and glial necrosis and apoptosis spread well beyond the initial site of impact, ultimately resolving into a cavity surrounded by glial/fibrotic scarring. The glial scar, which stabilizes the spread of secondary injury, also acts as a chronic, physical, and chemo-entrapping barrier that prevents axonal regeneration. Understanding the formative events in glial scarring helps guide strategies towards the development of potential therapies to enhance axon regeneration and functional recovery at both acute and chronic stages following SCI. This review will also discuss the perineuronal net and how chondroitin sulfate proteoglycans (CSPGs) deposited in both the glial scar and net impede axonal outgrowth at the level of the growth cone. We will end the review with a summary of current CSPG-targeting strategies that help to foster axonal regeneration, neuroplasticity/sprouting, and functional recovery following SCI.

Glycans and glycosaminoglycans in neurobiology: key regulators of neuronal cell function and fate

The aim of the present study was to examine the roles of l-fucose and the glycosaminoglycans (GAGs) keratan sulfate (KS) and chondroitin sulfate/dermatan sulfate (CS/DS) with selected functional molecules in neural tissues. Cell surface glycans and GAGs have evolved over millions of years to become cellular mediators which regulate fundamental aspects of cellular survival. The glycocalyx, which surrounds all cells, actuates responses to growth factors, cytokines and morphogens at the cellular boundary, silencing or activating downstream signaling pathways and gene expression. In this review, we have focused on interactions mediated by l-fucose, KS and CS/DS in the central and peripheral nervous systems. Fucose makes critical contributions in the area of molecular recognition and information transfer in the blood group substances, cytotoxic immunoglobulins, cell fate-mediated Notch-1 interactions, regulation of selectin-mediated neutrophil extravasation in innate immunity and CD-34-mediated new blood vessel development, and the targeting of neuroprogenitor cells to damaged neural tissue. Fucosylated glycoproteins regulate delivery of synaptic neurotransmitters and neural function. Neural KS proteoglycans (PGs) were examined in terms of cellular regulation and their interactive properties with neuroregulatory molecules. The paradoxical properties of CS/DS isomers decorating matrix and transmembrane PGs and the positive and negative regulatory cues they provide to neurons are also discussed.

Biodiversity of CS–proteoglycan sulphation motifs: chemical messenger recognition modules with roles in information transfer, control of cellular behaviour and tissue morphogenesis

Chondroitin sulphate (CS) glycosaminoglycan chains on cell and extracellular matrix proteoglycans (PGs) can no longer be regarded as merely hydrodynamic space fillers. Overwhelming evidence over recent years indicates that sulphation motif sequences within the CS chain structure are a source of significant biological information to cells and their surrounding environment. CS sulphation motifs have been shown to interact with a wide variety of bioactive molecules, e.g. cytokines, growth factors, chemokines, morphogenetic proteins, enzymes and enzyme inhibitors, as well as structural components within the extracellular milieu. They are therefore capable of modulating a panoply of signalling pathways, thus controlling diverse cellular behaviours including proliferation, differentiation, migration and matrix synthesis. Consequently, through these motifs, CS PGs play significant roles in the maintenance of tissue homeostasis, morphogenesis, development, growth and disease. Here, we review (i) the biodiversity of CS PGs and their sulphation motif sequences and (ii) the current understanding of the signalling roles they play in regulating cellular behaviour during tissue development, growth, disease and repair.

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.

ADAMTS-4 in oligodendrocytes contributes to myelination with an impact on motor function

Myelination is a late developmental process regulated by a set of inhibitory and stimulatory factors, including extracellular matrix components. Accordingly, chondroitin sulfate proteoglycans (CSPGs) act as negative regulators of myelination processes. A disintegrin and metalloproteinase with thrombospondin motifs type 4 (ADAMTS-4) is an extracellular protease capable of degrading CSPGs. Although exogenous ADAMTS-4 has been proven to be beneficial in several models of central nervous system (CNS) injuries, the physiological functions of endogenous ADAMTS-4 remain poorly understood. We first used Adamts4/LacZ reporter mice to reveal that ADAMTS-4 is strongly expressed in the CNS, especially in the white matter, with a cellular profile restricted to mature oligodendrocytes. Interestingly, we evidenced an abnormal myelination in Adamts4^-/- mice, characterized by a higher diameter of myelinated axons with a shifting g-ratio. Accordingly, lack of ADAMTS-4 is accompanied by motor deficits and disturbed nervous electrical activity. In conclusion, we demonstrate that ADAMTS-4 is a new marker of mature oligodendrocytes contributing to the myelination processes and thus to the control of motor capacities.

Extracellular Matrix Modulation Is Driven by Experience-Dependent Plasticity During Stroke Recovery

Following stroke, complete cellular death in the ischemic brain area may ensue, with remaining brain areas undergoing tissue remodelling to various degrees. Experience-dependent brain plasticity exerted through an enriched environment (EE) promotes remodelling after central nervous system injury, such as stroke. Post-stroke tissue reorganization is modulated by growth inhibitory molecules differentially expressed within the ischemic hemisphere, like chondroitin sulfate proteoglycans found in perineuronal nets (PNNs). PNNs in the neocortex predominantly enwrap parvalbumin-containing GABAergic (PV/GABA) neurons, important in sensori-information processing. Here, we investigate how extracellular matrix (ECM) proteases and their inhibitors may participate in the regulation of PNN integrity during stroke recovery. Rats were subjected to photothrombotic stroke in the motor cortex, and functional deficits were assessed at 7 days of recovery. Sham and stroked rats were housed in either standard or EE conditions for 5 days, and infarct volumes were calculated. PNNs were visualized by immunohistochemistry and counted in the somatosensory cortex of both hemispheres. mRNA expression levels of ECM proteases and protease inhibitors were assessed by RT-qPCR and their activity analyzed by gel zymography. PNNs and protease activity were also studied in brains from stroke patients where similar results were observed. EE starting 2 days after stroke and continuing for 5 days stimulated behavioral recovery of limb-placement ability without affecting infarct size. EE promoted a decrease of PNNs around PV/GABA neurons and a concomitant modulation of the proteolytic activity and mRNA expression of ECM proteases and protease inhibitors in the somatosensory cortex. This study provides molecular targets for novel therapies that could support rehabilitation of stroke patients.

Lack of collagen XV is protective after ischemic stroke in mice

Collagens are key structural components of basement membranes, providing a scaffold for other components or adhering cells. Collagens and collagen-derived active fragments contribute to biological activities such as cell growth, differentiation and migration. Here, we report that collagen XV knock-out (ColXV KO) mice are resistant to experimental ischemic stroke. Interestingly, the infarcts of ColXV KO mice were as small as those of wild-type (WT) mice thrombolysed with recombinant tissue plasminogen activator (rtPA), the actual treatment for ischemic stroke. Importantly, there were no differences in the architecture of cerebrovascular anatomy between WT and ColXV KO mice. We found a twofold increase of the most potent pro-angiogenic factor, type A vascular growth endothelial factor (VEGF-A) in the ipsilateral cortex of rtPA-treated ischemic WT mice compared with untreated ischemic and sham-operated counterparts. A similar increase of VEGF-A was also found in both rtPA and untreated ischemic ColXV KO mice compared with sham ColXV KO mice. Finally, we evidenced that the levels of ColXV were increased in the plasma of WT mice treated with rtPA compared with untreated ischemic counterparts. Altogether, this study indicates that the lack ColXV is protective after stroke and that the degradation of endothelial ColXV may contribute to the beneficial effect of rtPA after ischemic stroke. The neuroprotection observed in ColXV KO mice may be attributed to the increased VEGF-A production following stroke in the ischemic territory.

Tissue-type plasminogen activator controls neuronal death by raising surface dynamics of extrasynaptic NMDA receptors

N-methyl-d-aspartate receptors (NMDARs) are ion channels whose synaptic versus extrasynaptic localization critically influences their functions. This distribution of NMDARs is highly dependent on their lateral diffusion at the cell membrane. Each obligatory subunit of NMDARs (GluN1 and GluN2) contains two extracellular clamshell-like domains with an agonist-binding domain and a distal N-terminal domain (NTD). To date, the roles and dynamics of the NTD of the GluN1 subunit in NMDAR allosteric signaling remain poorly understood. Using single nanoparticle tracking in mouse neurons, we demonstrate that the extracellular neuronal protease tissue-type plasminogen activator (tPA), well known to have a role in the synaptic plasticity and neuronal survival, leads to a selective increase of the surface dynamics and subsequent diffusion of extrasynaptic NMDARs. This process explains the previously reported ability of tPA to promote NMDAR-mediated calcium influx. In parallel, we developed a monoclonal antibody capable of specifically blocking the interaction of tPA with the NTD of the GluN1 subunit of NMDAR. Using this original approach, we demonstrate that the tPA binds the NTD of the GluN1 subunit at a lysine in position 178. Accordingly, when applied to mouse neurons, our selected antibody (named Glunomab) leads to a selective reduction of the tPA-mediated surface dynamics of extrasynaptic NMDARs, subsequent signaling and neurotoxicity, both in vitro and in vivo. Altogether, we demonstrate that the tPA is a ligand of the NTD of the obligatory GluN1 subunit of NMDAR acting as a modulator of their dynamic distribution at the neuronal surface and subsequent signaling.

Adaptive preconditioning in neurological diseases - therapeutic insights from proteostatic perturbations

In neurological disorders, both acute and chronic neural stress can disrupt cellular proteostasis, resulting in the generation of pathological protein. However in most cases, neurons adapt to these proteostatic perturbations by activating a range of cellular protective and repair responses, thus maintaining cell function. These interconnected adaptive mechanisms comprise a 'proteostasis network' and include the unfolded protein response, the ubiquitin proteasome system and autophagy. Interestingly, several recent studies have shown that these adaptive responses can be stimulated by preconditioning treatments, which confer resistance to a subsequent toxic challenge - the phenomenon known as hormesis. In this review we discuss the impact of adaptive stress responses stimulated in diverse human neuropathologies including Parkinson׳s disease, Wolfram syndrome, brain ischemia, and brain cancer. Further, we examine how these responses and the molecular pathways they recruit might be exploited for therapeutic gain. This article is part of a Special Issue entitled SI:ER stress.

CSPGs inhibit axon branching by impairing mitochondria-dependent regulation of actin dynamics and axonal translation

Chondroitin sulfate proteoglycans (CSPGs) inhibit the formation of axon collateral branches. The regulation of the axonal cytoskeleton and mitochondria are important components of the mechanism of branching. Actin-dependent axonal plasticity, reflected in the dynamics of axonal actin patches and filopodia, is greatest along segments of the axon populated by mitochondria. It is reported that CSPGs partially depolarize the membrane potential of axonal mitochondria, which impairs the dynamics of the axonal actin cytoskeleton and decreases the formation and duration of axonal filopodia, the first steps in the mechanism of branching. The effects of CSPGs on actin cytoskeletal dynamics are specific to axon segments populated by mitochondria. In contrast, CSPGs do not affect the microtubule content of axons, or the localization of microtubules into axonal filopodia, a required step in the mechanism of branch formation. It is also reported that CSPGs decrease the mitochondria-dependent axonal translation of cortactin, an actin associated protein involved in branching. Finally, the inhibitory effects of CSPGs on axon branching, actin cytoskeletal dynamics and the axonal translation of cortactin are reversed by culturing neurons with acetyl-l-carnitine, which promotes mitochondrial respiration. Collectively these data indicate that CSPGs impair mitochondrial function in axons, an effect which contributes to the inhibition of axon branching. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419-437, 2017.

Anti-inflammatory effects of ADAMTS-4 in a mouse model of ischemic stroke

ADAMTS-4 (a disintegrin and metalloproteinase with thrombospondin motifs type 4) is a metalloprotease capable to degrade chondroitin sulfate proteoglycans leading to cartilage destruction during arthritis or to neuroplasticity during spinal cord injury (SCI). Although ADAMTS-4 is an inflammatory-regulated enzyme, its role during inflammation has never been investigated. The aim of this study was to investigate the role of ADAMTS-4 in neuroinflammation. First, we evidenced an increase of ADAMTS-4 expression in the ischemic brain hemisphere of mouse and human patients suffering from ischemic stroke. Then, we described that ADAMTS-4 has predominantly an anti-inflammatory effect in the CNS. Treatment of primary microglia or astrocyte cultures with low doses of a human recombinant ADAMTS-4 prior to LPS exposure decreased NO production and the synthesis/release of pro-inflammatory cytokines including NOS2, CCL2, TNF-α, IL-1β and MMP-9. Accordingly, when cell cultures were transfected with silencing siRNA targeting ADAMTS-4 prior to LPS exposure, the production of NO and the synthesis/release of pro-inflammatory cytokines were increased. Finally, the feasibility of ADAMTS-4 to modulate neuroinflammation was investigated in vivo after permanent middle cerebral artery occlusion in mice. Although ADAMTS-4 treatment did not influence the lesion volume, it decreased astrogliosis and macrophage infiltration, and increased the number of microglia expressing arginase-1, a marker of alternatively activated cells with inflammation inhibiting functions. Additionally, ADAMTS-4 increased the production of IL-10 and IL-6 in the peri-ischemic area. By having anti-inflammatory and neuroregenerative roles, ADAMTS-4 may represent an interesting target to treat acute CNS injuries, such as ischemic stroke, SCI or traumatic brain injury. GLIA 2016;64:1492-1507.

ADAMTS-4 promotes neurodegeneration in a mouse model of amyotrophic lateral sclerosis

Background

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) proteoglycanases are specialized in the degradation of chondroitin sulfate proteoglycans and participate in mechanisms mediating neuroplasticity. Despite the beneficial effect of ADAMTS-4 on neurorepair after spinal cord injury, the functions of ADAMTS proteoglycanases in other CNS disease states have not been studied. Therefore, we investigated the expression, effects and associated mechanisms of ADAMTS-4 during amyotrophic lateral sclerosis (ALS) in the SOD1^G93A mouse model.

Results

ADAMTS-4 expression and activity were reduced in the spinal cord of SOD1^G93A mice at disease end-stage when compared to WT littermates. To counteract the loss of ADAMTS-4, SOD1^G93A and WT mice were treated with saline or a recombinant ADAMTS-4 before symptom onset. Administration of ADAMTS-4 worsened the prognosis of SOD1^G93A mice by accelerating clinical signs of neuromuscular dysfunctions. The worsened prognosis of ADAMTS-4-treated SOD1^G93A mice was accompanied by increased degradation of perineuronal nets enwrapping motoneurons and increased motoneuron degeneration in the lumbar spinal cord. Motoneurons of ADAMTS-4-treated SOD1^G93A mice were more vulnerable to degeneration most likely due to the loss of their extracellular matrix envelopes. The decrease of neurotrophic factor production induced by ADAMTS-4 in vitro and in vivo may also contribute to a hostile environment for motoneuron especially when devoid of a net.

Conclusions

This study suggests that the reduction of ADAMTS-4 activity during the progression of ALS pathology may be an adaptive change to mitigate its neurodegenerative impact in CNS tissues. Therapies compensating the compromized ADAMTS-4 activity are likely not promising approaches for treating ALS.

The story of an exceptional serine protease, tissue-type plasminogen activator (tPA)

The only acute treatment of ischemic stroke approved by the health authorities is tissue recombinant plasminogen activator (tPA)-induced thrombolysis. Under physiological conditions, tPA, belonging to the serine protease family, is secreted by endothelial and brain cells (neurons, astrocytes, microglia, oligodendrocytes). Although revascularisation induced by tPA is beneficial during a stroke, research over the past 20 years shows that tPA can also be deleterious for the brain parenchyma. Thus, in this review of the literature, after a brief history on the discovery of tPA, we reviewed current knowledge of mechanisms by which tPA can influence brain function in physiological and pathological conditions.

Extracellular proteolysis in structural and functional plasticity of mossy fiber synapses in hippocampus

Brain is continuously altered in response to experience and environmental changes. One of the underlying mechanisms is synaptic plasticity, which is manifested by modification of synapse structure and function. It is becoming clear that regulated extracellular proteolysis plays a pivotal role in the structural and functional remodeling of synapses during brain development, learning and memory formation. Clearly, plasticity mechanisms may substantially differ between projections. Mossy fiber synapses onto CA3 pyramidal cells display several unique functional features, including pronounced short-term facilitation, a presynaptically expressed long-term potentiation (LTP) that is independent of NMDAR activation, and NMDA-dependent metaplasticity. Moreover, structural plasticity at mossy fiber synapses ranges from the reorganization of projection topology after hippocampus-dependent learning, through intrinsically different dynamic properties of synaptic boutons to pre- and postsynaptic structural changes accompanying LTP induction. Although concomitant functional and structural plasticity in this pathway strongly suggests a role of extracellular proteolysis, its impact only starts to be investigated in this projection. In the present report, we review the role of extracellular proteolysis in various aspects of synaptic plasticity in hippocampal mossy fiber synapses. A growing body of evidence demonstrates that among perisynaptic proteases, tissue plasminogen activator (tPA)/plasmin system, β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) and metalloproteinases play a crucial role in shaping plastic changes in this projection. We discuss recent advances and emerging hypotheses on the roles of proteases in mechanisms underlying mossy fiber target specific synaptic plasticity and memory formation.

Chondroitin sulfate proteoglycans: Key modulators in the developing and pathologic central nervous system

Chondroitin Sulfate Proteoglycans (CSPGs) are a major component of the extracellular matrix in the central nervous system (CNS) and play critical role in the development and pathophysiology of the brain and spinal cord. Developmentally, CSPGs provide guidance cues for growth cones and contribute to the formation of neuronal boundaries in the developing CNS. Their presence in perineuronal nets plays a crucial role in the maturation of synapses and closure of critical periods by limiting synaptic plasticity. Following injury to the CNS, CSPGs are dramatically upregulated by reactive glia which form a glial scar around the lesion site. Increased level of CSPGs is a hallmark of all CNS injuries and has been shown to limit axonal plasticity, regeneration, remyelination, and conduction after injury. Additionally, CSPGs create a non-permissive milieu for cell replacement activities by limiting cell migration, survival and differentiation. Mounting evidence is currently shedding light on the potential benefits of manipulating CSPGs in combination with other therapeutic strategies to promote spinal cord repair and regeneration. Moreover, the recent discovery of multiple receptors for CSPGs provides new therapeutic targets for targeted interventions in blocking the inhibitory properties of CSPGs following injury. Here, we will provide an in depth discussion on the impact of CSPGs in normal and pathological CNS. We will also review the recent preclinical therapies that have been developed to target CSPGs in the injured CNS.