Neural functions of matrix metalloproteinases: plasticity, neurogenesis, and disease

Interplays Between Matrix Metalloproteinases and Neurotropic Viruses: An Overview

Matrix metalloproteinases (MMPs) are a diverse group of proteases involved in various physiological and pathological processes through modulation of extracellular matrix (ECM) components, cytokines, and growth factors. In the central nervous system (CNS), MMPs play a major role in CNS development, plasticity, repair, and reorganisation contributing to learning, memory, and neuroimmune response to injury. MMPs are also linked to various neurological disorders such as Alzheimer's disease, Parkinson's disease, cerebral aneurysm, stroke, epilepsy, multiple sclerosis, and brain cancer suggesting these proteases as key regulatory factors in the nervous system. Moreover, MMPs have been involved in the pathogenesis of neurotropic viral infections via dysregulation of various cellular processes, which may highlight these factors as potential targets for the treatment and control of neurological complications associated with viral pathogens. This review provides an overview of the roles of MMPs in various physiological processes of the CNS and their interactions with neurotropic viral pathogens.

Investigation of the Neuroprotective Effect of Riluzole on Matrix Metalloproteinases in an Experimental Model of Glaucoma

Purpose

To investigate the neuroprotective effect of riluzole through matrix metalloproteinase-2 (MMP-2) and MMP-9 in rats, in an experimental glaucoma model.

Methods

A total of 28 Wistar albino rats, 3-4 months old, weighing 250-300 g, were divided into four groups; Group I (control), Group II (glaucoma), Group III (glaucoma + corn oil + dimethyl sulfoxide (DMSO), and Group IV (glaucoma + corn oil + DMSO + riluzole). A glaucoma model was created by episcleral vein cauterization in the left eyes of Group II, III, and IV subjects. After the formation of the model, daily intraperitoneal riluzole (5 mg/kg) administration was started. At the end of 7 weeks, retinal tissues were taken and some parts of them were stained with hematoxylin and eosin for histopathological examinations. In the other part, MMP-2 and MMP-9 expressions were determined using real-time quantitative PCR and immunohistochemical techniques.

Results

As a result, a statistically significant increase in intraocular pressures (IOP) was found in Groups II, III, and IV when compared with the control eyes after 7 weeks (P < 0.001). There was a decrease in IOP in the riluzole group compared to the glaucoma group. Expression levels in both genes decreased slightly with riluzole administration. In the histopathological evaluation of the groups, it was observed that there were no significant differences between the findings of degeneration in ganglion cells, hemorrhage, and differentiation in layers.

Conclusions

MMP-2 and MMP-9 exhibited decreased expression levels in both Group III (glaucoma + corn oil + DMSO) and Group IV (glaucoma + corn oil + DMSO + 5 mg/kg riluzole) compared to the glaucoma groups in Group II. Given that both Group III and Group IV received injections of corn oil + DMSO, this conclusion was drawn.

Regional Microglial Response in Entorhino-Hippocampal Slice Cultures to Schaffer Collateral Lesion and Metalloproteinases Modulation

Microglia and astrocytes are essential in sustaining physiological networks in the central nervous system, with their ability to remodel the extracellular matrix, being pivotal for synapse plasticity. Recent findings have challenged the traditional view of homogenous glial populations in the brain, uncovering morphological, functional, and molecular heterogeneity among glial cells. This diversity has significant implications for both physiological and pathological brain states. In the present study, we mechanically induced a Schaffer collateral lesion (SCL) in mouse entorhino-hippocampal slice cultures to investigate glial behavior, i.e., microglia and astrocytes, under metalloproteinases (MMPs) modulation in the lesioned area, CA3, and the denervated region, CA1. We observed distinct response patterns in the microglia and astrocytes 3 days after the lesion. Notably, GFAP-expressing astrocytes showed no immediate changes post-SCL. Microglia responses varied depending on their anatomical location, underscoring the complexity of the hippocampal neuroglial network post-injury. The MMPs inhibitor GM6001 did not affect microglial reactions in CA3, while increasing the number of Iba1-expressing cells in CA1, leading to a withdrawal of their primary branches. These findings highlight the importance of understanding glial regionalization following neural injury and MMPs modulation and pave the way for further research into glia-targeted therapeutic strategies for neurodegenerative disorders.

System biology approaches to identify hub genes linked with ECM organization and inflammatory signaling pathways in schizophrenia pathogenesis

Schizophrenia (SZ) is a chronic and devastating mental illness that affects around 20 million individuals worldwide. Cognitive deficits and structural and functional changes of the brain, abnormalities of brain ECM components, chronic neuroinflammation, and devastating clinical manifestation during SZ are likely etiological factors shown by affected individuals. However, the pathophysiological events associated with multiple regulatory pathways involved in the brain of this complex disorder are still unclear. This study aimed to develop a pipeline based on bioinformatics and systems biology approaches for identifying potential therapeutic targets involving possible biological mechanisms from SZ patients and healthy volunteers. About 420 overlapping differentially expressed genes (DEGs) from three RNA-seq datasets were identified. Gene ontology (GO), and pathways analysis showed several biological mechanisms enriched by the commonly shared DEGs, including extracellular matrix organization (ECM) organization, collagen fibril organization, integrin signaling pathway, inflammation mediated by chemokines and cytokines signaling pathway, and GABA-B receptor II and IL4 mediated signaling. Besides, 15 hub genes (FN1, COL1A1, COL3A1, COL1A2, COL5A1, COL2A1, COL6A2, COL6A3, MMP2, THBS1, DCN, LUM, HLA-A, HLA-C, and FBN1) were discovered by comprehensive analysis, which was mainly involved in the ECM organization and inflammatory signaling pathway. Furthermore, the miRNA target of the hub genes was analyzed with the random-forest-based approach software miRTarBase. In addition, the transcriptional factors and protein kinases regulating overlapping DEGs in SZ, namely, SUZ12, EZH2, TRIM28, TP53, EGR1, CSNK2A1, GSK3B, CDK1, and MAPK14, were also identified. The results point to a new understanding that the hub genes (fibronectin 1, collagen, matrix metalloproteinase-2, and lumican) in the ECM organization and inflammatory signaling pathways may be involved in the SZ occurrence and pathogenesis.

Cerebrospinal fluid exploratory proteomics and ketamine metabolite pharmacokinetics in human volunteers after ketamine infusion

Ketamine is a treatment for both refractory depression and chronic pain syndromes. In order to explore ketamine's potential mechanism of action and whether ketamine or its metabolites cross the blood brain barrier, we examined the pharmacokinetics of ketamine and its metabolites-norketamine (NK), dehydronorketamine (DHNK), and hydroxynorketamines (HNKs)-in cerebrospinal fluid (CSF) and plasma, as well as in an exploratory proteomic analysis in the CSF of nine healthy volunteers who received ketamine intravenously (0.5 mg/kg IV). We found that ketamine, NK, and (2R,6R;2S,6S)-HNK readily crossed the blood brain barrier. Additionally, 354 proteins were altered in the CSF in at least two consecutive timepoints (p < 0.01). Proteins in the classes of tyrosine kinases, cellular adhesion molecules, and growth factors, including insulin, were most affected, suggesting an interplay of altered neurotransmission, neuroplasticity, neurogenesis, synaptogenesis, and neural network functions following ketamine administration.

Involvement of the peroxisome proliferator-activated receptor gamma (Pparγ) and matrix metalloproteinases-2 and -9 (Mmp-2 and -9) in the mechanism of action of di(2-ethylhexyl)phthalate (DEHP) in cultured mouse brain astrocytes and neurons

Di(2-ethylhexyl)phthalate (DEHP) is one of the most widely used phthalates in industry. It has been shown that, after entering the body, DEHP has the ability to cross the blood-placenta and blood-brain barriers. One of the proposed mechanisms of action of DEHP is the activation of peroxisome proliferator-activated receptors (PPARs). Many different functions of PPARγ in cells have been demonstrated, one of which is the modulation of the activation of matrix metalloproteinases (MMPs). The aim of this study was to investigate the role of Pparγ, Mmp-2, and Mmp-9 in the mechanism of action of DEHP. The experiments were performed on in vitro primary murine neurons and astrocytes. The results showed that DEHP has a pro-apototic effect on neurons, causing an increase in caspase-3 activity and in the number of apoptotic bodies. However, in astrocytes, the increase in caspase-3 activity was not related to the apoptosis process, as no increase in the formation of apoptotic bodies was observed. Moreover, DEHP increased the proliferation of astrocytes, which was confirmed by the increase in the amount and expression of the Ki-67 protein. In astrocytes, DEHP decreased the expression of the Pparγ and Mmp-9 proteins but increased the expression of the Mmp-2 protein. In DEHP neurons, it increased the expression of the Pparγ protein but decreased the expression of the Mmp-2 and Mmp-9 proteins.

Retrosplenial cortex microglia and perineuronal net densities are associated with memory impairment in aged rhesus macaques

Synapse loss and altered plasticity are significant contributors to memory loss in aged individuals. Microglia, the innate immune cells of the brain, play critical roles in maintaining synapse function, including through a recently identified role in regulating the brain extracellular matrix. This study sought to determine the relationship between age, microglia, and extracellular matrix structure densities in the macaque retrosplenial cortex. Twenty-nine macaques ranging in age from young adult to aged were behaviorally characterized on 3 distinct memory tasks. Microglia, parvalbumin (PV)-expressing interneurons and extracellular matrix structures, known as perineuronal nets (PNNs), were immuno- and histochemically labeled. Our results indicate that microglia densities increase in the retrosplenial cortex of aged monkeys, while the proportion of PV neurons surrounded by PNNs decreases. Aged monkeys with more microglia had fewer PNN-associated PV neurons and displayed slower learning and poorer performance on an object recognition task. Stepwise regression models using age and the total density of aggrecan, a chondroitin sulfate proteoglycan of PNNs, better predicted memory performance than did age alone. Together, these findings indicate that elevated microglial activity in aged brains negatively impacts cognition in part through mechanisms that alter PNN assembly in memory-associated brain regions.

Inhibition of matrix metalloproteinases by HIV-1 integrase strand transfer inhibitors

More than fifteen million women with the human immunodeficiency virus type-1 (HIV-1) infection are of childbearing age world-wide. Due to improved and affordable access to antiretroviral therapy (ART), the number of in utero antiretroviral drug (ARV)-exposed children has exceeded a million and continues to grow. While most recommended ART taken during pregnancy suppresses mother to child viral transmission, the knowledge of drug safety linked to fetal neurodevelopment remains an area of active investigation. For example, few studies have suggested that ARV use can be associated with neural tube defects (NTDs) and most notably with the integrase strand transfer inhibitor (INSTI) dolutegravir (DTG). After risk benefit assessments, the World Health Organization (WHO) made recommendations for DTG usage as a first and second-line preferred treatment for infected populations including pregnant women and those of childbearing age. Nonetheless, long-term safety concerns remain for fetal health. This has led to a number of recent studies underscoring the need for biomarkers to elucidate potential mechanisms underlying long-term neurodevelopmental adverse events. With this goal in mind, we now report the inhibition of matrix metalloproteinases (MMPs) activities by INSTIs as an ARV class effect. Balanced MMPs activities play a crucial role in fetal neurodevelopment. Inhibition of MMPs activities by INSTIs during neurodevelopment could be a potential mechanism for adverse events. Thus, comprehensive molecular docking testing of the INSTIs, DTG, bictegravir (BIC), and cabotegravir (CAB), against twenty-three human MMPs showed broad-spectrum inhibition. With a metal chelating chemical property, each of the INSTI were shown to bind Zn++ at the MMP's catalytic domain leading to MMP inhibition but to variable binding energies. These results were validated in myeloid cell culture experiments demonstrating MMP-2 and 9 inhibitions by DTG, BIC and CAB and even at higher degree than doxycycline (DOX). Altogether, these data provide a potential mechanism for how INSTIs could affect fetal neurodevelopment.

CD147 and MMPs as key factors in physiological and pathological processes

Cluster of differentiation 147 (CD147) or extracellular matrix metalloproteinase inducer (EMMPRIN) is a transmembrane glycoprotein that induces the synthesis of matrix metalloproteinases (MMPs). MMPs, as zinc-dependent proteases and versatile enzymes, play critical roles in the degradation of the extracellular matrix (ECM) components, cleaving of the receptors of cellular surfaces, signaling molecules, and other precursor proteins, which may lead to attenuation or activation of such targets. CD147 and MMPs play essential roles in physiological and pathological conditions and any disorder in the expression, synthesis, or function of CD147 and MMPs may be associated with various types of disease. In this review, we have focused on the roles of CD147 and MMPs in some major physiological and pathological processes.

HIV-1 Integrase Strand Transfer Inhibitors and Neurodevelopment

Children born to mothers, with or at risk, of human immunodeficiency virus type-1 (HIV-1) infection are on the rise due to affordable access of antiretroviral therapy (ART) to pregnant women or those of childbearing age. Each year, up to 1.3 million HIV-1-infected women on ART have given birth with recorded mother-to-child HIV-1 transmission rates of less than 1%. Despite this benefit, the outcomes of children exposed to antiretroviral drugs during pregnancy, especially pre- and post- natal neurodevelopment remain incompletely understood. This is due, in part, to the fact that pregnant women are underrepresented in clinical trials. This is underscored by any potential risks of neural tube defects (NTDs) linked, in measure, to periconceptional usage of dolutegravir (DTG). A potential association between DTG and NTDs was first described in Botswana in 2018. Incidence studies of neurodevelopmental outcomes associated with DTG, and other integrase strand transfer inhibitors (INSTIs) are limited as widespread use of INSTIs has begun only recently in pregnant women. Therefore, any associations between INSTI use during pregnancy, and neurodevelopmental abnormalities remain to be explored. Herein, United States Food and Drug Administration approved ARVs and their use during pregnancy are discussed. We provide updates on INSTI pharmacokinetics and adverse events during pregnancy together with underlying mechanisms which could affect fetal neurodevelopment. Overall, this review seeks to educate both clinical and basic scientists on potential consequences of INSTIs on fetal outcomes as a foundation for future scientific investigations.

Matrix Metalloproteinases and Glaucoma

Matrix metalloproteinases (MMPs) are enzymes that decompose extracellular matrix (ECM) proteins. MMPs are thought to play important roles in cellular processes, such as cell proliferation, differentiation, angiogenesis, migration, apoptosis, and host defense. MMPs are distributed in almost all intraocular tissues and are involved in physiological and pathological mechanisms of the eye. MMPs are also associated with glaucoma, a progressive neurodegenerative disease of the eyes. MMP activity affects intraocular pressure control and apoptosis of retinal ganglion cells, which are the pathological mechanisms of glaucoma. It also affects the risk of glaucoma development based on genetic pleomorphism. In addition, MMPs may affect the treatment outcomes of glaucoma, including the success rate of surgical treatment and side effects on the ocular surface due to glaucoma medications. This review discusses the various relationships between MMP and glaucoma.

Sexually dimorphic transcriptional programs of early-phase response in regenerating peripheral nerves

The convergence of transcriptional and epigenetic changes in the peripheral nervous system (PNS) reshapes the spatiotemporal gene expression landscape in response to nerve transection. The control of these molecular programs exhibits sexually dimorphic characteristics that remain not sufficiently characterized. In the present study, we recorded genome-wide and sex-dependent early-phase transcriptional changes in regenerating (proximal) sciatic nerve 24 h after axotomy. Male nerves exhibited more extensive transcriptional changes with male-dominant upregulation of cytoskeletal binding and structural protein genes. Regulation of mRNAs encoding ion and ionotropic neurotransmitter channels displayed prominent sexual dimorphism consistent with sex-specific mRNA axonal transport in an early-phase regenerative response. Protein kinases and axonal transport genes showed sexually dimorphic regulation. Genes encoding components of synaptic vesicles were at high baseline expression in females and showed post-injury induction selectively in males. Predictive bioinformatic analyses established patterns of sexually dimorphic regulation of neurotrophic and immune genes, including activation of glial cell line-derived neurotrophic factor Gfra1 receptor and immune checkpoint cyclin D1 (Ccnd1) potentially linked to X-chromosome encoded tissue inhibitor of matrix metallo proteinases 1 (Timp1). Regulatory networks involving Olig1, Pou3f3/Oct6, Myrf, and Myt1l transcription factors were linked to sex-dependent reprogramming in regenerating nerves. Differential expression patterns of non-coding RNAs motivate a model of sexually dimorphic nerve regenerative responses to injury determined by epigenetic factors. Combined with our findings in the corresponding dorsal root ganglia (DRG), unique early-phase sex-specific molecular triggers could enrich the mechanistic understanding of peripheral neuropathies.

Cerebral blood flow is associated with matrix metalloproteinase levels during the early symptomatic phase of concussion

Concussion is associated with disrupted cerebral blood flow (CBF), although there appears to be substantial inter-individual variability in CBF response. At present, the mechanisms of variable CBF response remain incompletely understood, but one potential contributor is matrix metalloproteinase (MMP) expression. In more severe forms of acquired brain injury, MMP up-regulation contributes to CBF impairments via increased blood-brain barrier permeability. A similar relationship is hypothesized for concussion, where recently concussed individuals with higher MMP levels have lower CBF. To test this hypothesis, 35 concussed athletes were assessed longitudinally at early symptomatic injury (median: 5 days post-injury) and at medical clearance (median: 24 days post-injury), along with 71 athletic controls. For all athletes, plasma MMPs were measured and arterial spin labelling was used to measure CBF. Consistent with our hypothesis, higher concentrations of MMP-2 and MMP-3 were correlated with lower global CBF. The correlations between MMPs and global CBF were also significantly diminished for concussed athletes at medical clearance and for athletic controls. These results indicate an inverse relationship between plasma MMP levels and CBF that is specific to the symptomatic phase of concussion. Analyses of regional CBF further showed that correlations with MMP levels exhibited some spatial specificity, with greatest effects in occipital, parietal and temporal lobes. These findings provide new insights into the mechanisms of post-concussion cerebrovascular dysfunction.

Dynamics of biomarkers across the stages of traumatic spinal cord injury - implications for neural plasticity and repair

BACKGROUND

Traumatic spinal cord injury (SCI) is a complex medical condition causing significant physical disability and psychological distress. While the adult spinal cord is characterized by poor regenerative potential, some recovery of neurological function is still possible through activation of neural plasticity mechanisms. We still have limited knowledge about the activation of these mechanisms in the different stages after human SCI.

OBJECTIVE

In this review, we discuss the potential role of biomarkers of SCI as indicators of the plasticity mechanisms at work during the different phases of SCI.

METHODS

An extensive review of literature related to SCI pathophysiology, neural plasticity and humoral biomarkers was conducted by consulting the PubMed database. Research and review articles from SCI animal models and SCI clinical trials published in English until January 2021 were reviewed. The selection of candidates for humoral biomarkers of plasticity after SCI was based on the following criteria: 1) strong evidence supporting involvement in neural plasticity (mandatory); 2) evidence supporting altered expression after SCI (optional).

RESULTS

Based on selected findings, we identified two main groups of potential humoral biomarkers of neural plasticity after SCI: 1) neurotrophic factors including: Brain derived neurotrophic factor (BDNF), Nerve growth factor (NGF), Neurotrofin-3 (NT-3), and Insulin-like growth factor 1 (IGF-1); 2) other factors including: Tumor necrosis factor-alpha (TNF-α), Matrix Metalloproteinases (MMPs), and MicroRNAs (miRNAs). Plasticity changes associated with these biomarkers often can be both adaptive (promoting functional improvement) and maladaptive. This dual role seems to be influenced by their concentrations and time-window during SCI.

CONCLUSIONS

Further studies of dynamics of biomarkers across the stages of SCI are necessary to elucidate the way in which they reflect the remodeling of neural pathways. A better knowledge about the mechanisms underlying plasticity could guide the selection of more appropriate therapeutic strategies to enhance positive spinal network reorganization.

Dolutegravir Inhibition of Matrix Metalloproteinases Affects Mouse Neurodevelopment

Dolutegravir (DTG) is a first-line antiretroviral drug (ARV) used in combination therapy for the treatment of human immunodeficiency virus type-1 (HIV-1) infection. The drug is effective, safe, and well tolerated. Nonetheless, concerns have recently emerged for its usage in pregnant women or those of child-bearing age. Notably, DTG-based ARV regimens have been linked to birth defects seen as a consequence of periconceptional usages. To this end, uncovering an underlying mechanism for DTG-associated adverse fetal development outcomes has gained clinical and basic research interest. We now report that DTG inhibits matrix metalloproteinases (MMPs) activities that could affect fetal neurodevelopment. DTG is a broad-spectrum MMPs inhibitor and binds to Zn⁺⁺ at the enzyme’s catalytic domain. Studies performed in pregnant mice show that DTG readily reaches the fetal central nervous system during gestation and inhibits MMP activity. Postnatal screenings of brain health in mice pups identified neuroinflammation and neuronal impairment. These abnormalities persist as a consequence of in utero DTG exposure. We conclude that DTG inhibition of MMPs activities during gestation has the potential to affect prenatal and postnatal neurodevelopment.

Role of matrix metalloproteinase-9 in neurodevelopmental deficits and experience-dependent plasticity in Xenopus laevis

Matrix metalloproteinase-9 (MMP-9) is a secreted endopeptidase targeting extracellular matrix proteins, creating permissive environments for neuronal development and plasticity. Developmental dysregulation of MMP-9 may also lead to neurodevelopmental disorders (ND). Here, we test the hypothesis that chronically elevated MMP-9 activity during early neurodevelopment is responsible for neural circuit hyperconnectivity observed in Xenopus tadpoles after early exposure to valproic acid (VPA), a known teratogen associated with ND in humans. In Xenopus tadpoles, VPA exposure results in excess local synaptic connectivity, disrupted social behavior and increased seizure susceptibility. We found that overexpressing MMP-9 in the brain copies effects of VPA on synaptic connectivity, and blocking MMP-9 activity pharmacologically or genetically reverses effects of VPA on physiology and behavior. We further show that during normal neurodevelopment MMP-9 levels are tightly regulated by neuronal activity and required for structural plasticity. These studies show a critical role for MMP-9 in both normal and abnormal development.

Emerging roles of MT-MMPs in embryonic development

Membrane-type matrix metalloproteinases (MT-MMPs) are cell membrane-tethered proteinases that belong to the family of the MMPs. Apart from their roles in degradation of the extracellular milieu, MT-MMPs are able to activate through proteolytic processing at the cell surface distinct molecules such as receptors, growth factors, cytokines, adhesion molecules, and other pericellular proteins. Although most of the information regarding these enzymes comes from cancer studies, our current knowledge about their contribution in distinct developmental processes occurring in the embryo is limited. In this review, we want to summarize the involvement of MT-MMPs in distinct processes during embryonic morphogenesis, including cell migration and proliferation, epithelial-mesenchymal transition, cell polarity and branching, axon growth and navigation, synapse formation, and angiogenesis. We also considered information about MT-MMP functions from studies assessed in pathological conditions and compared these data with those relevant for embryonic development.

Postnatal Fluoxetine Treatment Alters Perineuronal Net Formation and Maintenance in the Hippocampus

Elevation of serotonin via postnatal fluoxetine (PNFlx) treatment during critical temporal windows is hypothesized to perturb the development of limbic circuits thus establishing a substratum for persistent disruption of mood-related behavior. We examined the impact of PNFlx treatment on the formation and maintenance of perineuronal nets (PNNs), extracellular matrix (ECM) structures that deposit primarily around inhibitory interneurons, and mark the closure of critical period plasticity. PNFlx treatment evoked a significant decline in PNN number, with a robust reduction in PNNs deposited around parvalbumin (PV) interneurons, within the CA1 and CA3 hippocampal subfields at postnatal day (P)21 in Sprague Dawley rat pups. While the reduction in CA1 subfield PNN number was still observed in adulthood, we observed no change in colocalization of PV-positive interneurons with PNNs in the hippocampi of adult PNFlx animals. PNFlx treatment did not alter hippocampal PV, calretinin (CalR), or Reelin-positive neuron numbers in PNFlx animals at P21 or in adulthood. We did observe a small, but significant increase in somatostatin (SST)-positive interneurons in the DG subfield of PNFlx-treated animals in adulthood. This was accompanied by altered GABA-A receptor subunit composition, increased dendritic complexity of apical dendrites of CA1 pyramidal neurons, and enhanced neuronal activation revealed by increased c-Fos-positive cell numbers within hippocampi of PNFlx-treated animals in adulthood. These results indicate that PNFlx treatment alters the formation of PNNs within the hippocampus, raising the possibility of a disruption of excitation-inhibition (E/I) balance within this key limbic brain region.

Activity-dependent regulome of human GABAergic neurons reveals new patterns of gene regulation and neurological disease heritability

Neuronal activity-dependent gene expression is essential for brain development. Although transcriptional and epigenetic effects of neuronal activity have been explored in mice, such an investigation is lacking in humans. Because alterations in GABAergic neuronal circuits are implicated in neurological disorders, we conducted a comprehensive activity-dependent transcriptional and epigenetic profiling of human induced pluripotent stem cell-derived GABAergic neurons similar to those of the early developing striatum. We identified genes whose expression is inducible after membrane depolarization, some of which have specifically evolved in primates and/or are associated with neurological diseases, including schizophrenia and autism spectrum disorder (ASD). We define the genome-wide profile of human neuronal activity-dependent enhancers, promoters and the transcription factors CREB and CRTC1. We found significant heritability enrichment for ASD in the inducible promoters. Our results suggest that sequence variation within activity-inducible promoters of developing human forebrain GABAergic neurons contributes to ASD risk.

Scrap and Build for Functional Neural Circuits: Spatiotemporal Regulation of Dendrite Degeneration and Regeneration in Neural Development and Disease

Dendrites are cellular structures essential for the integration of neuronal information. These elegant but complex structures are highly patterned across the nervous system but vary tremendously in their size and fine architecture, each designed to best serve specific computations within their networks. Recent in vivo imaging studies reveal that the development of mature dendrite arbors in many cases involves extensive remodeling achieved through a precisely orchestrated interplay of growth, degeneration, and regeneration of dendritic branches. Both degeneration and regeneration of dendritic branches involve precise spatiotemporal regulation for the proper wiring of functional networks. In particular, dendrite degeneration must be targeted in a compartmentalized manner to avoid neuronal death. Dysregulation of these developmental processes, in particular dendrite degeneration, is associated with certain types of pathology, injury, and aging. In this article, we review recent progress in our understanding of dendrite degeneration and regeneration, focusing on molecular and cellular mechanisms underlying spatiotemporal control of dendrite remodeling in neural development. We further discuss how developmental dendrite degeneration and regeneration are molecularly and functionally related to dendrite remodeling in pathology, disease, and aging.

Spreading Depressions and Periinfarct Spreading Depolarizations in the Context of Cortical Plasticity

Studies of cortical function-recovery require a comparison between normal and post-stroke conditions that lead to changes in cortical metaplasticity. Focal cortical stroke impairs experience-dependent plasticity in the neighboring somatosensory cortex and usually evokes periinfarct depolarizations (PiDs) - spreading depression-like waves. Experimentally induced spreading depressions (SDs) affect gene expression and some of these changes persist for at least 30 days. In this study we compare the effects of non-stroke depolarizations that impair cortical experience-dependent plasticity to the effects of stroke, by inducing experience-dependent plasticity in rats with SDs or PiDs by a month of contralateral partial whiskers deprivation. We found that whiskers' deprivation after SDs resulted in normal cortical representation enlargement suggesting that SDs and PiDs depolarization have no influence on experience-dependent plasticity cortical map reorganization. PiDs and the MMP-9, -3, -2 or COX-2 proteins, which are assumed to influence metaplasticity in rats after stroke were compared between SDs induced by high osmolarity KCl solution and the PiDs that followed cortical photothrombotic stroke (PtS). We found that none of these factors directly caused cortical post-stroke metaplasticity changes. The only significant difference between stoke and induced SD was a greater imbalance in interhemispheric activity equilibrium after stroke. The interhemispheric interactions that were modified by stroke may therefore be promising targets for future studies of post-stroke experience-dependent plasticity and of recuperation studies.

Matrix metalloproteinases deregulation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the loss of upper and lower motor neurons that results in progressive paralysis and muscular atrophy. There are many molecules and genes involved in neuromuscular degeneration in ALS; among these, matrix metalloproteinases (MMPs). MMPs play an important role in the pathology of ALS, and MMP-1, 2, 3, and 9 might serve as disease progression markers. Tissue inhibitors of metalloproteinases (TIMPS) might also function as progression markers in ALS because they participate in regulating the proteolytic activity of MMPs. Moreover, a diversity of genes also plays a role in the pathogenesis of ALS; most MMPs-coding genes present variants related to the pathological proteolytic activity. This short review, however, will focus on the role of matrix metalloproteinases in ALS.

Targeting the Wnt/β-catenin pathway in neurodegenerative diseases: recent approaches and current challenges

INTRODUCTION

Wnt/β-catenin signaling is an evolutionarily conserved pathway having a crucial role in embryonic and adult life. Specifically, the Wnt/β-catenin axis is pivotal to the development and homeostasis of the nervous system, and its dysregulation has been associated with various neurological disorders, including neurodegenerative diseases. Therefore, this signaling pathway has been proposed as a potential therapeutic target against neurodegeneration.

AREAS COVERED

This review focuses on the role of Wnt/β-catenin pathway in the pathogenesis of neurodegenerative diseases, including Parkinson's, Alzheimer's Diseases and Amyotrophic Lateral Sclerosis. The evidence showing that defects in the signaling might be involved in the development of these diseases, and the pharmacological approaches tested so far, are discussed. The possibilities that this pathway offers in terms of new therapeutic opportunities are also considered.

EXPERT OPINION

The increasing interest paid to the role of Wnt/β-catenin pathway in the onset of neurodegenerative diseases demonstrates how targeting this signaling for therapeutic purposes could be a great opportunity for both neuroprotection and neurorepair. Without overlooking some licit concerns about drug safety and delivery to the brain, there is growing and more convincing evidence that restoring this signaling in neurodegenerative diseases may strongly increase the chance to develop disease-modifying treatments for these brain pathologies.

Molecular Biomarkers Predictive of Sertraline Treatment Response in Young Children With Autism Spectrum Disorder

Sertraline is one among several selective serotonin reuptake inhibitors (SSRIs) that exhibited improvement of language development in Autism Spectrum Disorder (ASD); however, the molecular mechanism has not been elucidated. A double blind, randomized, 6-month, placebo-controlled, clinical trial of low-dose sertraline in children ages (3-6 years) with ASD was conducted at the UC Davis MIND Institute. It aimed at evaluating the efficacy and benefit with respect to early expressive language development and global clinical improvement. This study aimed to identify molecular biomarkers that might be key players in the serotonin pathway and might be predictive of a clinical response to sertraline. Fifty eight subjects with the diagnosis of ASD were randomized to sertraline or placebo. Eight subjects from the sertraline arm and five from the placebo arm discontinued from the study. Furthermore, four subjects did not have a successful blood draw. Hence, genotypes for 41 subjects (20 on placebo and 21 on sertraline) were determined for several genes involved in the serotonin pathway including the serotonin transporter-linked polymorphic region (5-HTTLPR), the tryptophan hydroxylase 2 (TPH2), and the Brain-Derived Neurotrophic Factor (BDNF). In addition, plasma levels of BDNF, Matrix metallopeptidase 9 (MMP-9) and a selected panel of cytokines were determined at baseline and post-treatment. Intent-to-treat analysis revealed several primary significant correlations between molecular changes and the Mullen Scales of Early Learning (MSEL) and Clinical Global Impression Scale - Improvement (CGI-I) of treatment and control groups but they were not significant after adjustment for multiple testing. Thus, sertraline showed no benefit for treatment of young children with ASD in language development or changes in molecular markers in this study. These results indicate that sertraline may not be beneficial for the treatment of children with ASD; however, further investigation of larger groups as well as longer term follow-up studies are warranted.

A conceptualized model linking matrix metalloproteinase-9 to schizophrenia pathogenesis

Matrix metalloproteinase 9 (MMP-9) is an extracellularly operating zinc-dependent endopeptidase that is commonly expressed in the brain, other tissues. It is synthesized in a latent zymogen form known as pro-MMP-9 that is subsequently converted to the active MMP-9 enzyme following cleavage of the pro-domain. Within the central nervous system, MMP-9 is localized and released from neurons, astrocytes and microglia where its expression levels are modulated by cytokines and growth factors during both normal and pathological conditions as well as by reactive oxygen species generated during oxidative stress. MMP-9 is involved in a number of key neurodevelopmental processes that are thought to be affected in schizophrenia, including maturation of the inhibitory neurons that contain the calcium-binding protein parvalbumin, developmental formation of the specialized extracellular matrix structure perineuronal net, synaptic pruning, and myelination. In this context, the present article provides a narrative synthesis of the existing evidence linking MMP-9 dysregulation to schizophrenia pathogenesis. We start by providing an overview of MMP-9 involvement in brain development and physiology. We then discuss the potential mechanisms through which MMP-9 dysregulation may affect neural circuitry maturation as well as how these anomalies may contribute to the disease process of schizophrenia. We conclude by articulating a comprehensive, cogent, and experimentally testable hypothesis linking MMP-9 to the developmental pathophysiologic cascade that triggers the onset and sustains the chronicity of the illness.

The role of matrix metalloproteinase-9 in negative reinforcement learning and plasticity in alcohol dependence

A role for matrix metalloproteinases (MMPs) in plasticity-dependent learning has been established. MMPs degrade the extracellular matrix (ECM) when synaptic reorganization is warranted. Previously, we showed that escalation of alcohol self-administration is a learned plasticity-dependent process that requires an intact MMP system. To identify the MMP subtypes within specific brain regions that are associated with plasticity underlying the negative reinforcing effects of alcohol (as measured by escalated alcohol self-administration) during acute withdrawal in alcohol dependence, male Wistar rats were trained to self-administer alcohol in an operant paradigm, subjected to one month of intermittent alcohol vapor exposure to induce alcohol dependence and then allowed to self-administer alcohol during repeated acute withdrawal self-administration sessions. Subsequently, rat brains were extracted after initial or stable escalated alcohol self-administration phases of acute withdrawal and analyzed by immunoblot to detect MMP-2, -3, and -9 levels in the anterior cingulate cortex (ACC), bed nucleus of the stria terminalis, central amygdala (CeA), hippocampus, and nucleus accumbens (NAc). The results showed that MMP-9 expression in the CeA and NAc of alcohol-dependent rats was increased, however, MMP-9 expression in the ACC was decreased during negative reinforcement learning. Subsequently, the importance of plasticity mediated by MMP-9 in escalated alcohol self-administration during acute withdrawal was functionally assessed through site-specific intra-CeA MMP-9 inhibition during repeated acute withdrawal self-administration sessions. MMP-9 inhibition prevented acute withdrawal-induced escalation of alcohol self-administration in a manner that was not confounded by locomotor effects or a permanent inability to learn about the negative reinforcing effects of alcohol.

Evolving paradigms on the interplay of mitochondrial Hsp70 chaperone system in cell survival and senescence

The role of mitochondria within a cell has grown beyond being the prime source of cellular energy to one of the major signaling platforms. Recent evidence provides several insights into the crucial roles of mitochondrial chaperones in regulating the organellar response to external triggers. The mitochondrial Hsp70 (mtHsp70/Mortalin/Grp75) chaperone system plays a critical role in the maintenance of proteostasis balance in the organelle. Defects in mtHsp70 network result in attenuated protein transport and misfolding of polypeptides leading to mitochondrial dysfunction. The functions of Hsp70 are primarily governed by J-protein cochaperones. Although human mitochondria possess a single Hsp70, its multifunctionality is characterized by the presence of multiple specific J-proteins. Several studies have shown a potential association of Hsp70 and J-proteins with diverse pathological states that are not limited to their canonical role as chaperones. The role of mitochondrial Hsp70 and its co-chaperones in disease pathogenesis has not been critically reviewed in recent years. We evaluated some of the cellular interfaces where Hsp70 machinery associated with pathophysiological conditions, particularly in context of tumorigenesis and neurodegeneration. The mitochondrial Hsp70 machinery shows a variable localization and integrates multiple components of the cellular processes with varied phenotypic consequences. Although Hsp70 and J-proteins function synergistically in proteins folding, their precise involvement in pathological conditions is mainly idiosyncratic. This machinery is associated with a heterogeneous set of molecules during the progression of a disorder. However, the precise binding to the substrate for a specific physiological response under a disease subtype is still an undocumented area of analysis.

Matrix metalloproteinases in the CNS: interferons get nervous

Matrix metalloproteinases (MMPs) have been investigated in context of chronic inflammatory diseases and demonstrated to degrade multiple components of the extracellular matrix (ECM). However, following several disappointing MMP clinical trials, recent studies have demonstrated unexpected novel functions of MMPs in viral infections and autoimmune inflammatory diseases in unanticipated locations. Thus, MMPs play additional functions in inflammation than just ECM degradation. They can regulate the activity of chemokines and cytokines of the immune response by precise proteolytic processing resulting in activation or inactivation of signaling pathways. MMPs have been demonstrated to cleave multiple substrates of the central nervous systems (CNS) and contribute to promoting and dampening diseases of the CNS. Initially, believed to be solely promoting pathologies, more than 10 MMPs to date have been shown to have protective functions. Here, we present some of the beneficial and destructive roles of MMPs in CNS pathologies and discuss strategies for the use of MMP inhibitors.

MMP-1 overexpression selectively alters inhibition in D1 spiny projection neurons in the mouse nucleus accumbens core

Protease activated receptor-1 (PAR-1) and its ligand, matrix metalloproteinase-1 (MMP-1), are altered in several neurodegenerative diseases. PAR-1/MMP-1 signaling impacts neuronal activity in various brain regions, but their role in regulating synaptic physiology in the ventral striatum, which is implicated in motor function, is unknown. The ventral striatum contains two populations of GABAergic spiny projection neurons, D1 and D2 SPNs, which differ with respect to both synaptic inputs and projection targets. To evaluate the role of MMP-1/PAR-1 signaling in the regulation of ventral striatal synaptic function, we performed whole-cell recordings (WCR) from D1 and D2 SPNs in control mice, mice that overexpress MMP-1 (MMP-1OE), and MMP-1OE mice lacking PAR-1 (MMP-1OE/PAR-1KO). WCRs from MMP1-OE mice revealed an increase in spontaneous inhibitory post-synaptic current (sIPSC), miniature IPSC, and miniature excitatory PSC frequency in D1 SPNs but not D2 SPNs. This alteration may be partially PAR-1 dependent, as it was not present in MMP-1OE/PAR-1KO mice. Morphological reconstruction of D1 SPNs revealed increased dendritic complexity in the MMP-1OE, but not MMP-1OE/PAR-1KO mice. Moreover, MMP-1OE mice exhibited blunted locomotor responses to amphetamine, a phenotype also observed in MMP-1OE/PAR-1KO mice. Our data suggest PAR-1 dependent and independent MMP-1 signaling may lead to alterations in striatal neuronal function.

Enhancement of matrix metalloproteinases 2 and 9 accompanied with neurogenesis following collagen glycosaminoglycan matrix implantation after surgical brain injury

Surgical brain injury may result in irreversible neurological deficits. Our previous report showed that partial regeneration of a traumatic brain lesion is achieved by implantation of collagen glycosaminoglycan (CGM). Matrix metalloproteinases (MMPs) may play an important role in neurogenesis but there is currently a lack of studies displaying the relationship between the stimulation of MMPs and neurogenesis after collagen glycosaminoglycan implantation following surgical brain trauma. The present study was carried out to further examine the expression of MMP2 and MMP9 after implantation of collagen glycosaminoglycan (CGM) following surgical brain trauma. Using the animal model of surgically induced brain lesion, we implanted CGM into the surgical trauma. Rats were thus divided into three groups: (1) sham operation group: craniotomy only; (2) lesion (L) group: craniotomy + surgical trauma lesion; (3) lesion + CGM (L + CGM) group: CGM implanted following craniotomy and surgical trauma lesion. Cells positive for SOX2 (marker of proliferating neural progenitor cells) and matrix metalloproteinases (MMP2 and MMP9) in the lesion boundary zone were assayed and analyzed by immunofluorescence and ELISA commercial kits, respectively. Our results demonstrated that following implantation of CGM after surgical brain trauma, significant increases in MMP2+/SOX2+ cells and MMP9+/SOX2+ cells were seen within the lesion boundary zone in the L + CGM group. Tissue protein concentrations of MMP2 and MMP9 also increased after CGM scaffold implantation. These findings suggest that implantation of a CGM scaffold alone after surgical brain trauma can enhance the expression of MMP2 and MMP9 accompanied by neurogenesis.

miR-9 regulates basal ganglia-dependent developmental vocal learning and adult vocal performance in songbirds

miR-9 is an evolutionarily conserved miRNA that is abundantly expressed in Area X, a basal ganglia nucleus required for vocal learning in songbirds. Here, we report that overexpression of miR-9 in Area X of juvenile zebra finches impairs developmental vocal learning, resulting in a song with syllable omission, reduced similarity to the tutor song, and altered acoustic features. miR-9 overexpression in juveniles also leads to more variable song performance in adulthood, and abolishes social context-dependent modulation of song variability. We further show that these behavioral deficits are accompanied by downregulation of FoxP1 and FoxP2, genes that are known to be associated with language impairments, as well as by disruption of dopamine signaling and widespread changes in the expression of genes that are important in circuit development and functions. These findings demonstrate a vital role for miR-9 in basal ganglia function and vocal communication, suggesting that dysregulation of miR-9 in humans may contribute to language impairments and related neurodevelopmental disorders.

A novel Drosophila injury model reveals severed axons are cleared through a Draper/MMP-1 signaling cascade

Neural injury triggers swift responses from glia, including glial migration and phagocytic clearance of damaged neurons. The transcriptional programs governing these complex innate glial immune responses are still unclear. Here, we describe a novel injury assay in adult Drosophila that elicits widespread glial responses in the ventral nerve cord (VNC). We profiled injury-induced changes in VNC gene expression by RNA sequencing (RNA-seq) and found that responsive genes fall into diverse signaling classes. One factor, matrix metalloproteinase-1 (MMP-1), is induced in Drosophila ensheathing glia responding to severed axons. Interestingly, glial induction of MMP-1 requires the highly conserved engulfment receptor Draper, as well as AP-1 and STAT92E. In MMP-1 depleted flies, glia do not properly infiltrate neuropil regions after axotomy and, as a consequence, fail to clear degenerating axonal debris. This work identifies Draper-dependent activation of MMP-1 as a novel cascade required for proper glial clearance of severed axons.

Generation and intracellular trafficking of a polysialic acid-carrying fragment of the neural cell adhesion molecule NCAM to the cell nucleus

Polysialic acid (PSA) and its major protein carrier, the neural cell adhesion molecule NCAM, play important roles in many nervous system functions during development and in adulthood. Here, we show that a PSA-carrying NCAM fragment is generated at the plasma membrane by matrix metalloproteases and transferred to the cell nucleus via endosomes and the cytoplasm. Generation and nuclear import of this fragment in cultured cerebellar neurons is induced by a function-triggering NCAM antibody and a peptide comprising the effector domain (ED) of myristoylated alanine-rich C kinase substrate (MARCKS) which interacts with PSA within the plane of the plasma membrane. These treatments lead to activation of the fibroblast growth factor (FGF) receptor, phospholipase C (PLC), protein kinase C (PKC) and phosphoinositide-3-kinase (PI3K), and subsequently to phosphorylation of MARCKS. Moreover, the NCAM antibody triggers calmodulin-dependent activation of nitric oxide synthase, nitric oxide (NO) production, NO-dependent S-nitrosylation of matrix metalloprotease 9 (MMP9) as well as activation of matrix metalloprotease 2 (MMP2) and MMP9, whereas the ED peptide activates phospholipase D (PLD) and MMP2, but not MMP9. These results indicate that the nuclear PSA-carrying NCAM fragment is generated by distinct and functionally defined signal transducing mechanisms.

Clearance of cerebral Aβ in Alzheimer's disease: reassessing the role of microglia and monocytes

Deficiency in cerebral amyloid β-protein (Aβ) clearance is implicated in the pathogenesis of the common late-onset forms of Alzheimer’s disease (AD). Accumulation of misfolded Aβ in the brain is believed to be a net result of imbalance between its production and removal. This in turn may trigger neuroinflammation, progressive synaptic loss, and ultimately cognitive decline. Clearance of cerebral Aβ is a complex process mediated by various systems and cell types, including vascular transport across the blood–brain barrier, glymphatic drainage, and engulfment and degradation by resident microglia and infiltrating innate immune cells. Recent studies have highlighted a new, unexpected role for peripheral monocytes and macrophages in restricting cerebral Aβ fibrils, and possibly soluble oligomers. In AD transgenic (ADtg) mice, monocyte ablation or inhibition of their migration into the brain exacerbated Aβ pathology, while blood enrichment with monocytes and their increased recruitment to plaque lesion sites greatly diminished Aβ burden. Profound neuroprotective effects in ADtg mice were further achieved through increased cerebral recruitment of myelomonocytes overexpressing Aβ-degrading enzymes. This review summarizes the literature on cellular and molecular mechanisms of cerebral Aβ clearance with an emphasis on the role of peripheral monocytes and macrophages in Aβ removal.

Three-dimensional culture of single embryonic stem-derived neural/stem progenitor cells in fibrin hydrogels: neuronal network formation and matrix remodelling

In an attempt to improve the efficacy of neural stem/progenitor cell (NSPC) based therapies, fibrin hydrogels are being explored to provide a favourable microenvironment for cell survival and differentiation following transplantation. In the present work, the ability of fibrin to support the survival, proliferation, and neuronal differentiation of NSPCs derived from embryonic stem (ES) cells under monolayer culture was explored. Single mouse ES-NSPCs were cultured within fibrin (fibrinogen concentration: 6 mg/ml) under neuronal differentiation conditions up to 14 days. The ES-NSPCs retained high cell viability and proliferated within small-sized spheroids. Neuronal differentiation was confirmed by an increase in the levels of βIII-tubulin and NF200 over time. At day 14, cell-matrix constructs mainly comprised NSPCs and neurons (46.5% βIII-tubulin⁺ cells). Gamma-aminobutyric acid (GABA)ergic and dopaminergic/noradrenergic neurons were also observed, along with a network of synaptic proteins. The ES-NSPCs expressed matriptase and secreted MMP-2/9, with MMP-2 activity increasing along time. Fibronectin, laminin and collagen type IV deposition was also detected. Fibrin gels prepared with higher fibrinogen concentrations (8/10 mg/ml) were less permissive to neurite extension and neuronal differentiation, possibly owing to their smaller pore area and higher rigidity. Overall, it is shown that ES-NSPCs within fibrin are able to establish neuronal networks and to remodel fibrin through MMP secretion and extracellular matrix (ECM) deposition. This three-dimensional (3D) culture system was also shown to support cell viability, neuronal differentiation and ECM deposition of human ES-NSPCs. The settled 3D platform is expected to constitute a valuable tool to develop fibrin-based hydrogels for ES-NSPC delivery into the injured central nervous system. Copyright © 2016 John Wiley & Sons, Ltd.

Marine pharmacology: therapeutic targeting of matrix metalloproteinases in neuroinflammation

Alterations in matrix metalloproteinase (MMP) expression and activity are recognized as key pathogenetic events in several neurological disorders. This evidence makes MMPs possible therapeutic targets. The search for substances that can inhibit MMPs is moving progressively toward the screening of natural products. In particular, marine bioprospecting could be promising for the discovery of marine natural products with anti-MMP activities. Despite recent advances in this field, the possibility of using marine MMP inhibitors (MMPIs) for the treatment of neuroinflammation is still under-investigated. Here, we review the latest findings in this promising research field and the potential that marine MMPIs can have in the management and treatment of various neurological diseases.

The multifaceted role of metalloproteinases in physiological and pathological conditions in embryonic and adult brains

Matrix metalloproteinases (MMPs) are a large family of ubiquitous extracellular endopeptidases, which play important roles in a variety of physiological and pathological conditions, from the embryonic stages throughout adult life. Their extraordinary physiological "success" is due to concomitant broad substrate specificities and strict regulation of their expression, activation and inhibition levels. In recent years, MMPs have gained increasing attention as significant effectors in various aspects of central nervous system (CNS) physiology. Most importantly, they have been recognized as main players in a variety of brain disorders having different etiologies and evolution. A common aspect of these pathologies is the development of acute or chronic neuroinflammation. MMPs play an integral part in determining the result of neuroinflammation, in some cases turning its beneficial outcome into a harmful one. This review summarizes the most relevant studies concerning the physiology of MMPs, highlighting their involvement in both the developing and mature CNS, in long-lasting and acute brain diseases and, finally, in nervous system repair. Recently, a concerted effort has been made in identifying therapeutic strategies for major brain diseases by targeting MMP activities. However, from this revision of the literature appears clear that MMPs have multifaceted functional characteristics, which modulate physiological processes in multiple ways and with multiple consequences. Therefore, when choosing MMPs as possible targets, great care must be taken to evaluate the delicate balance between their activation and inhibition and to determine at which stage of the disease and at what level they become active in order maximize chances of success.

Matrix Metalloproteinases in Non-Neoplastic Disorders

The matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases belonging to the metzincin superfamily. There are at least 23 members of MMPs ever reported in human, and they and their substrates are widely expressed in many tissues. Recent growing evidence has established that MMP not only can degrade a variety of components of extracellular matrix, but also can cleave and activate various non-matrix proteins, including cytokines, chemokines and growth factors, contributing to both physiological and pathological processes. In normal conditions, MMP expression and activity are tightly regulated via interactions between their activators and inhibitors. Imbalance among these factors, however, results in dysregulated MMP activity, which causes tissue destruction and functional alteration or local inflammation, leading to the development of diverse diseases, such as cardiovascular disease, arthritis, neurodegenerative disease, as well as cancer. This article focuses on the accumulated evidence supporting a wide range of roles of MMPs in various non-neoplastic diseases and provides an outlook on the therapeutic potential of inhibiting MMP action.

Matrix metalloproteinases in neural development: a phylogenetically diverse perspective

The matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases originally characterized as secreted proteases responsible for degrading extracellular matrix proteins. Their canonical role in matrix remodelling is of significant importance in neural development and regeneration, but emerging roles for MMPs, especially in signal transduction pathways, are also of obvious importance in a neural context. Misregulation of MMP activity is a hallmark of many neuropathologies, and members of every branch of the MMP family have been implicated in aspects of neural development and disease. However, while extraordinary research efforts have been made to elucidate the molecular mechanisms involving MMPs, methodological constraints and complexities of the research models have impeded progress. Here we discuss the current state of our understanding of the roles of MMPs in neural development using recent examples and advocate a phylogenetically diverse approach to MMP research as a means to both circumvent the challenges associated with specific model organisms, and to provide a broader evolutionary context from which to synthesize an understanding of the underlying biology.

Characterization, biomedical and agricultural applications of protease inhibitors: A review

This review describes Protease Inhibitors (PIs) which target or inhibit proteases, protein digesting enzymes. These proteases play a crucial task in many biological events including digestion, blood coagulation, apoptosis etc. Regardless of their crucial roles, they need to be checked regularly by PIs as their excess may possibly damage host organism. On basis of amino acid composition of PIs where Protease-PI enzymatic reactions occur i.e. serine, cysteine, and aspartic acid, they are classified. Nowadays, various PIs are being worked upon to fight various parasitic or viral diseases including malaria, schistosomiasis, colds, flu', dengue etc. They prevent an ongoing process begun by carcinogen exposure by keeping a check on metastasis. They also possess potential to reduce carcinogen-induced, increased levels of gene amplification to almost normal levels. Some PIs can principally be used for treatment of hypertension and congestive heart failure by blocking conversion of angiotensin I to angiotensin II for example Angiotensin-converting enzyme inhibitors (ACEIs). Also PIs target amyloid β-peptide (Aβ) level in brain which is prime responsible for development of Alzheimer's Disease (AD). Also, PIs inhibit enzymatic activity of HIV-1 Protease Receptor (PR) by preventing cleavage events in Gag and Gag-Pol that result in production of non-virulent virus particles.

Matrix Metalloproteinases During Axonal Regeneration, a Multifactorial Role from Start to Finish

By proteolytic cleavage, matrix metalloproteinases (MMPs) not only remodel the extracellular matrix (ECM) but they also modify the structure and activity of other proteinases, growth factors, signaling molecules, cell surface receptors, etc. Their vast substrate repertoire adds a complex extra dimension of biological control and turns MMPs into important regulatory nodes in the protease web. In the central nervous system (CNS), the detrimental impact of elevated MMP activities has been well-described for traumatic injuries and many neurodegenerative diseases. Nonetheless, there is ample proof corroborating MMPs as fine regulators of CNS physiology, and well-balanced MMP activity is instrumental to development, plasticity, and repair. In this manuscript, we review the emerging evidence for MMPs as beneficial modulators of axonal regeneration in the mammalian CNS. By exploring the multifactorial causes underlying the inability of mature axons to regenerate, and describing how MMPs can help to overcome these hurdles, we emphasize the benign actions of these Janus-faced proteases.

Rotary orbital suspension culture of embryonic stem cell-derived neural stem/progenitor cells: impact of hydrodynamic culture on aggregate yield, morphology and cell phenotype

Embryonic stem (ES)-derived neural stem/progenitor cells (ES-NSPCs) constitute a promising cell source for application in cell therapies for the treatment of central nervous system disorders. In this study, a rotary orbital hydrodynamic culture system was applied to single-cell suspensions of ES-NSPCs, to obtain homogeneously-sized ES-NSPC cellular aggregates (neurospheres). Hydrodynamic culture allowed the formation of ES-NSPC neurospheres with a narrower size distribution than statically cultured neurospheres, increasing orbital speeds leading to smaller-sized neurospheres and higher neurosphere yield. Neurospheres formed under hydrodynamic conditions (72 h at 55 rpm) showed higher cell compaction and comparable percentages of viable, dead, apoptotic and proliferative cells. Further characterization of cellular aggregates provided new insights into the effect of hydrodynamic shear on ES-NSPC behaviour. Rotary neurospheres exhibited reduced protein levels of N-cadherin and β-catenin, and higher deposition of laminin (without impacting fibronectin deposition), matrix metalloproteinase-2 (MMP-2) activity and percentage of neuronal cells. In line with the increased MMP-2 activity levels found, hydrodynamically-cultured neurospheres showed higher outward migration on laminin. Moreover, when cultured in a 3D fibrin hydrogel, rotary neurospheres generated an increased percentage of neuronal cells. In conclusion, the application of a constant orbital speed to single-cell suspensions of ES-NSPCs, besides allowing the formation of homogeneously-sized neurospheres, promoted ES-NSPC differentiation and outward migration, possibly by influencing the expression of cell-cell adhesion molecules and the secretion of proteases/extracellular matrix proteins. These findings are important when establishing the culture conditions needed to obtain uniformly-sized ES-NSPC aggregates, either for use in regenerative therapies or in in vitro platforms for biomaterial development or pharmacological screening. Copyright © 2016 John Wiley & Sons, Ltd.

Two classes of matrix metalloproteinases reciprocally regulate synaptogenesis

Synaptogenesis requires orchestrated intercellular communication between synaptic partners, with trans-synaptic signals necessarily traversing the extracellular synaptomatrix separating presynaptic and postsynaptic cells. Extracellular matrix metalloproteinases (Mmps) regulated by secreted tissue inhibitors of metalloproteinases (Timps), cleave secreted and membrane-associated targets to sculpt the extracellular environment and modulate intercellular signaling. Here, we test the roles of Mmp at the neuromuscular junction (NMJ) model synapse in the reductionist Drosophila system, which contains just two Mmps (secreted Mmp1 and GPI-anchored Mmp2) and one secreted Timp. We found that all three matrix metalloproteome components co-dependently localize in the synaptomatrix and show that both Mmp1 and Mmp2 independently restrict synapse morphogenesis and functional differentiation. Surprisingly, either dual knockdown or simultaneous inhibition of the two Mmp classes together restores normal synapse development, identifying a reciprocal suppression mechanism. The two Mmp classes co-regulate a Wnt trans-synaptic signaling pathway modulating structural and functional synaptogenesis, including the GPI-anchored heparan sulfate proteoglycan (HSPG) Wnt co-receptor Dally-like protein (Dlp), cognate receptor Frizzled-2 (Frz2) and Wingless (Wg) ligand. Loss of either Mmp1 or Mmp2 reciprocally misregulates Dlp at the synapse, with normal signaling restored by co-removal of both Mmp classes. Correcting Wnt co-receptor Dlp levels in both Mmp mutants prevents structural and functional synaptogenic defects. Taken together, these results identify an Mmp mechanism that fine-tunes HSPG co-receptor function to modulate Wnt signaling to coordinate synapse structural and functional development.

Spinal cord injury induced neuropathic pain: Molecular targets and therapeutic approaches

Neuropathic pain, especially that resulting from spinal cord injury, is a tremendous clinical challenge. A myriad of biological changes have been implicated in producing these pain states including cellular interactions, extracellular proteins, ion channel expression, and epigenetic influences. Physiological consequences of these changes are varied and include functional deficits and pain responses. Developing therapies that effectively address the cause of these symptoms require a deeper knowledge of alterations in the molecular pathways. Matrix metalloproteinases and tissue inhibitors of metalloproteinases are two promising therapeutic targets. Matrix metalloproteinases interact with and influence many of the studied pain pathways. Gene expression of ion channels and inflammatory mediators clearly contributes to neuropathic pain. Localized and time dependent targeting of these proteins could alleviate and even prevent neuropathic pain from developing. Current therapeutic options for neuropathic pain are limited primarily to analgesics targeting the opioid pathway. Therapies directed at molecular targets are highly desirable and in early stages of development. These include transplantation of exogenously engineered cell populations and targeted gene manipulation. This review describes specific molecular targets amenable to therapeutic intervention using currently available delivery systems.

Dystroglycan controls dendritic morphogenesis of hippocampal neurons in vitro

Dendritic outgrowth and arborization are important for establishing neural circuit formation. To date, little information exists about the involvement of the extracellular matrix (ECM) and its cellular receptors in these processes. In our studies, we focus on the role of dystroglycan (DG), a cell adhesion molecule that links ECM components to the actin cytoskeleton, in dendritic development and branching. Using a lentiviral vector to deliver short-hairpin RNA (shRNA) that specifically silences DG in cultured hippocampal neurons, we found that DG knockdown exerted an inhibitory effect on dendritic tree growth and arborization. The structural changes were associated with activation of the guanosine triphosphatase Cdc42. The overexpression of DG promoted dendritic length and branching. Furthermore, exposure of the cultures to autoactivating matrix metalloproteinase-9 (aaMMP-9), a β-DG-cleaving protease, decreased the complexity of dendritic arbors. This effect was abolished in neurons that overexpressed a β-DG mutant that was defective in MMP-9-mediated cleavage. Altogether, our results indicate that DG controls dendritic arborization in vitro in MMP-9-dependent manner.

Multifaceted role of matrix metalloproteinases (MMPs)

Matrix metalloproteinases (MMPs), a large family of calcium-dependent zinc-containing endopeptidases, are involved in the tissue remodeling and degradation of the extracellular matrix. MMPs are widely distributed in the brain and regulate various processes including microglial activation, inflammation, dopaminergic apoptosis, blood-brain barrier disruption, and modulation of α-synuclein pathology. High expression of MMPs is well documented in various neurological disorders including Parkinson's disease (PD), Alzheimer's disease (AD), Japanese encephalitis (JE), and Glaucoma. Although potentially critical, the role of MMPs in neuronal disorders is under-investigated. The present review summarizes the role of MMPs in neurodegeneration with a particular emphasis on PD, AD, JE, and Glaucoma.

Serum matrix metalloproteinase-9 levels and severity of symptoms in boys with attention deficit hyperactivity disorder ADHD/hyperkinetic disorder HKD

The serum levels of matrix metalloproteinase-9 (MMP-9) in neuropsychiatric disorders of adults have been widely investigated. So far, no studies have been conducted on the relationship of MMP-9 and cognitive domains in children with two phenotype models, attention deficit/hyperactivity disorder and hyperkinetic disorder (ADHD/HKD). The aim of this research was to evaluate and test the hypothesis that serum MMP-9 levels are associated with the severity of symptoms in children with ADHD/HKD and to compare the results in two models of this disorder. The study group comprised 37 Caucasian boys aged 7-12 years with HKD, being a subset of the combined ADHD subtype. Intellectual functions were measured using Wechsler Intelligence Scale for Children-Revised. The analysis of serum concentrations of MMP-9 was based on a quantitative sandwich ELISA. The statistical regression analysis revealed a correlation between increased serum MMP-9 levels and severity of symptoms in the ADHD (β = 0.33; p = 0.043) and HKD (β = 0.34, p = 0.037) model. According to the results, elevated levels of serum MMP-9 in boys with HKD may be associated with clinical impulsivity domain (β = 0.38; p = 0.019).