Differential distribution of aggrecan isoforms in perineuronal nets of the human cerebral cortex

The "Loss" of Perineuronal Nets in Alzheimer's Disease: Missing or Hiding in Plain Sight?

Perineuronal nets (PNNs) are chondroitin-sulfate glycosaminoglycan (CS-GAG) containing extracellular matrix structures that assemble around neurons involved in learning, memory, and cognition. Owing to the unique patterning of negative charges stemming from sulfate modifications to the attached CS-GAGs, these matrices play key roles in mediating glycan-protein binding, signaling interactions, and charged ion buffering of the underlying circuitry. Histochemical loss of PNN matrices has been reported for a range of neurocognitive and neurodegenerative diseases, implying that PNNs might be a key player in the pathogenesis of neurological disorders. In this hypothesis and theory article, we begin by highlighting PNN changes observed in human postmortem brain tissue associated with Alzheimer's disease (AD) and corresponding changes reported in rodent models of AD neuropathology. We then discuss the technical limitations surrounding traditional methods for PNN analyses and propose alternative explanations to these historical findings. Lastly, we embark on a global re-evaluation of the interpretations for PNN changes across brain regions, across species, and in relation to other neurocognitive disorders.

Recovery of Post-Stroke Spatial Memory and Thalamocortical Connectivity Following Novel Glycomimetic and rhBDNF Treatment

Stroke-induced cognitive impairments remain of significant concern, with very few treatment options available. The involvement of glycosaminoglycans in neuroregenerative processes is becoming better understood and recent advancements in technology have allowed for cost-effective synthesis of novel glycomimetics. The current study evaluated the therapeutic potential of two novel glycomimetics, compound A and G, when administered systemically five-days post-photothrombotic stroke to the PFC. As glycosaminoglycans are thought to facilitate growth factor function, we also investigated the combination of our glycomimetics with intracerebral, recombinant human brain-derived neurotrophic factor (rhBDNF). C56BL/6J mice received sham or stroke surgery and experimental treatment (day-5), before undergoing the object location recognition task (OLRT). Four-weeks post-surgery, animals received prelimbic injections of the retrograde tracer cholera toxin B (CTB), before tissue was collected for quantification of thalamo-PFC connectivity and reactive astrogliosis. Compound A or G treatment alone modulated a degree of reactive astrogliosis yet did not influence spatial memory performance. Contrastingly, compound G+rhBDNF treatment significantly improved spatial memory, dampened reactive astrogliosis and limited stroke-induced loss of connectivity between the PFC and midline thalamus. As rhBDNF treatment had negligible effects, these findings support compound A acted synergistically to enhance rhBDNF to restrict secondary degeneration and facilitate functional recovery after PFC stroke.

Glycomaterials to Investigate the Functional Role of Aberrant Glycosylation in Glioblastoma

Glioblastoma (GBM) is a stage IV astrocytoma that carries a dismal survival rate of ≈10 months postdiagnosis and treatment. The highly invasive capacity of GBM and its ability to escape therapeutic challenges are key factors contributing to the poor overall survival rate. While current treatments aim to target the cancer cell itself, they fail to consider the significant role that the GBM tumor microenvironment (TME) plays in promoting tumor progression and therapeutic resistance. The GBM tumor glycocalyx and glycan-rich extracellular matrix (ECM), which are important constituents of the TME have received little attention as therapeutic targets. A wide array of aberrantly modified glycans in the GBM TME mediate tumor growth, invasion, therapeutic resistance, and immunosuppression. Here, an overview of the landscape of aberrant glycan modifications in GBM is provided, and the design and utility of 3D glycomaterials are discussed as a tool to evaluate glycan-mediated GBM progression and therapeutic efficacy. The development of alternative strategies to target glycans in the TME can potentially unveil broader mechanisms of restricting tumor growth and enhancing the efficacy of tumor-targeting therapeutics.

Microglia facilitate loss of perineuronal nets in the Alzheimer's disease brain

BACKGROUND

Microglia, the brain's principal immune cell, are increasingly implicated in Alzheimer's disease (AD), but the molecular interfaces through which these cells contribute to amyloid beta (Aβ)-related neurodegeneration are unclear. We recently identified microglial contributions to the homeostatic and disease-associated modulation of perineuronal nets (PNNs), extracellular matrix structures that enwrap and stabilize neuronal synapses, but whether PNNs are altered in AD remains controversial.

METHODS

Extensive histological analysis was performed on male and female 5xFAD mice at 4, 8, 12, and 18 months of age to assess plaque burden, microgliosis, and PNNs. Findings were validated in postmortem AD tissue. The role of neuroinflammation in PNN loss was investigated via LPS treatment, and the ability to prevent or rescue disease-related reductions in PNNs was assessed by treating 5xFAD and 3xTg-AD model mice with colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 to deplete microglia.

FINDINGS

Utilizing the 5xFAD mouse model and human cortical tissue, we report that PNNs are extensively lost in AD in proportion to plaque burden. Activated microglia closely associate with and engulf damaged nets in the 5xFAD brain, and inclusions of PNN material are evident in mouse and human microglia, while aggrecan, a critical PNN component, deposits within human dense-core plaques. Disease-associated reductions in parvalbumin (PV)+ interneurons, frequently coated by PNNs, are preceded by PNN coverage and integrity impairments, and similar phenotypes are elicited in wild-type mice following microglial activation with LPS. Chronic pharmacological depletion of microglia prevents 5xFAD PNN loss, with similar results observed following depletion in aged 3xTg-AD mice, and this occurs despite plaque persistence.

INTERPRETATION

We conclude that phenotypically altered microglia facilitate plaque-dependent PNN loss in the AD brain.

FUNDING

The NIH (NIA, NINDS) and the Alzheimer's Association.

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.

Sialylated keratan sulfate proteoglycans are Siglec-8 ligands in human airways

Human siglecs are a family of 14 sialic acid-binding proteins, most of which are expressed on subsets of immune cells where they regulate immune responses. Siglec-8 is expressed selectively on human allergic inflammatory cells—primarily eosinophils and mast cells—where engagement causes eosinophil apoptosis and inhibits mast cell mediator release. Evidence supports a model in which human eosinophils and mast cells bind to Siglec-8 sialoglycan ligands on inflammatory target tissues to resolve allergic inflammation and limit tissue damage. To identify Siglec-8-binding sialoglycans from human airways, proteins extracted from postmortem human trachea were resolved by size-exclusion chromatography and composite agarose–acrylamide gel electrophoresis, blotted and probed by Siglec-8-Fc blot overlay. Three size classes of Siglec-8 ligands were identified: 250 kDa, 600 kDa and 1 MDa, each of which was purified by affinity chromatography using a recombinant pentameric form of Siglec-8. Proteomic mass spectrometry identified all size classes as the proteoglycan aggrecan, a finding validated by immunoblotting. Glycan array studies demonstrated Siglec-8 binding to synthetic glycans with a terminal Neu5Acα2-3(6-sulfo)-Gal determinant, a quantitatively minor terminus on keratan sulfate (KS) chains of aggrecan. Treating human tracheal extracts with sialidase or keratanase eliminated Siglec-8 binding, indicating sialylated KS chains as Siglec-8-binding determinants. Treating human tracheal histological sections with keratanase also completely eliminated the binding of Siglec-8-Fc. Finally, Siglec-8 ligand purified from human trachea extracts induced increased apoptosis of freshly isolated human eosinophils in vitro. We conclude that sialylated KS proteoglycans are endogenous human airway ligands that bind Siglec-8 and may regulate allergic inflammation.

Normal Development of the Perineuronal Net in Humans; In Patients with and without Epilepsy

The perineuronal net (PN), a highly organized extracellular matrix structure, is believed to play an important role in synaptic function, including maturation and stabilization. In addition to its role in restricting plasticity, alterations in the PN are implicated in disorders such as epilepsy and schizophrenia. However, the time course of PN development is not known in humans. Therefore we set out to document the developmental timeline of the PN formation in humans in 14 frontal and hippocampal specimens from donors aged 27 days to 31 years old. Using immunohistochemistry and western blotting, we demonstrate that the PN begins to form as early as the second month of life but does not reach its robust, mature appearance until around 8 years of age, though aggrecan cleavage products are observed prior to this. A similar developmental time course was observed in specimens from epilepsy patients. Our data suggest that aggrecan is present early in development but the structured PN develops throughout early childhood, similar to what has been observed in rodents. This timeline provides information for future pathological studies on the role of the PN in disease and an additional parallel between human and rodent development.

Keratan sulfate, a complex glycosaminoglycan with unique functional capability

From an evolutionary perspective keratan sulfate (KS) is the newest glycosaminoglycan (GAG) but the least understood. KS is a sophisticated molecule with a diverse structure, and unique functional roles continue to be uncovered for this GAG. The cornea is the richest tissue source of KS in the human body but the central and peripheral nervous systems also contain significant levels of KS and a diverse range of KS-proteoglycans with essential functional roles. KS also displays important cell regulatory properties in epithelial and mesenchymal tissues and in bone and in tumor development of diagnostic and prognostic utility. Corneal KS-I displays variable degrees of sulfation along the KS chain ranging from non-sulfated polylactosamine, mono-sulfated and disulfated disaccharide regions. Skeletal KS-II is almost completely sulfated consisting of disulfated disaccharides interrupted by occasional mono-sulfated N-acetyllactosamine residues. KS-III also contains highly sulfated KS disaccharides but differs from KS-I and KS-II through 2-O-mannose linkage to serine or threonine core protein residues on proteoglycans such as phosphacan and abakan in brain tissue. Historically, the major emphasis on the biology of KS has focused on its sulfated regions for good reason. The sulfation motifs on KS convey important molecular recognition information and direct cell behavior through a number of interactive proteins. Emerging evidence also suggest functional roles for the poly-N-acetyllactosamine regions of KS requiring further investigation. Thus further research is warranted to better understand the complexities of KS.

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.

Regulation of glycosaminoglycan biogenesis is critical for sensitive-period-dependent vocal ontogeny

In the brain, the extracellular matrix (ECM) plays a central role during neural development and thus modulates critical-period regulated behavioral ontogeny. The major components of the ECM are glycosaminoglycans (GAGs) including chondroitin sulfate (CS). However, the specific roles of GAGs in behavioral development are largely unknown. It has been shown that xylosides affect the biological functions of GAGs through modulating GAG biosynthesis. Particularly, xylosides affect GAG biosynthesis through priming of GAG chains (priming activity), competing with endogenous core proteins that carry GAG initiation sites (decoy activity), or both. Using birdsong as our model, we investigated, for the first time, how xyloside-mediated modulation of GAG biogenesis affects song development. Xylosides infused into motor cortex of juvenile birds alter song development by specifically affecting ontogeny of the stereotyped sequence rather than the acoustic structure of syllables. Further analyses reveal that observed changes can be attributed to the priming activity rather than the decoy activity of xylosides. Collectively, these results suggest that regulation of GAG biogenesis through chemical biology approaches may allow promising therapeutic interventions of critical-period-dependent central nervous system plasticity. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1401-1412, 2017.

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

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

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.

Transcriptional maturation of the mouse auditory forebrain

Background

The maturation of the brain involves the coordinated expression of thousands of genes, proteins and regulatory elements over time. In sensory pathways, gene expression profiles are modified by age and sensory experience in a manner that differs between brain regions and cell types. In the auditory system of altricial animals, neuronal activity increases markedly after the opening of the ear canals, initiating events that culminate in the maturation of auditory circuitry in the brain. This window provides a unique opportunity to study how gene expression patterns are modified by the onset of sensory experience through maturity. As a tool for capturing these features, next-generation sequencing of total RNA (RNAseq) has tremendous utility, because the entire transcriptome can be screened to index expression of any gene. To date, whole transcriptome profiles have not been generated for any central auditory structure in any species at any age. In the present study, RNAseq was used to profile two regions of the mouse auditory forebrain (A1, primary auditory cortex; MG, medial geniculate) at key stages of postnatal development (P7, P14, P21, adult) before and after the onset of hearing (~P12). Hierarchical clustering, differential expression, and functional geneset enrichment analyses (GSEA) were used to profile the expression patterns of all genes. Selected genesets related to neurotransmission, developmental plasticity, critical periods and brain structure were highlighted. An accessible repository of the entire dataset was also constructed that permits extraction and screening of all data from the global through single-gene levels. To our knowledge, this is the first whole transcriptome sequencing study of the forebrain of any mammalian sensory system. Although the data are most relevant for the auditory system, they are generally applicable to forebrain structures in the visual and somatosensory systems, as well.

Results

The main findings were: (1) Global gene expression patterns were tightly clustered by postnatal age and brain region; (2) comparing A1 and MG, the total numbers of differentially expressed genes were comparable from P7 to P21, then dropped to nearly half by adulthood; (3) comparing successive age groups, the greatest numbers of differentially expressed genes were found between P7 and P14 in both regions, followed by a steady decline in numbers with age; (4) maturational trajectories in expression levels varied at the single gene level (increasing, decreasing, static, other); (5) between regions, the profiles of single genes were often asymmetric; (6) GSEA revealed that genesets related to neural activity and plasticity were typically upregulated from P7 to adult, while those related to structure tended to be downregulated; (7) GSEA and pathways analysis of selected functional networks were not predictive of expression patterns in the auditory forebrain for all genes, reflecting regional specificity at the single gene level.

Conclusions

Gene expression in the auditory forebrain during postnatal development is in constant flux and becomes increasingly stable with age. Maturational changes are evident at the global through single gene levels. Transcriptome profiles in A1 and MG are distinct at all ages, and differ from other brain regions. The database generated by this study provides a rich foundation for the identification of novel developmental biomarkers, functional gene pathways, and targeted studies of postnatal maturation in the auditory forebrain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1709-8) contains supplementary material, which is available to authorized users.

Physical and biological regulation of neuron regenerative growth and network formation on recombinant dragline silks

Recombinant spider silks produced in transgenic goat milk were studied as cell culture matrices for neuronal growth. Major ampullate spidroin 1 (MaSp1) supported neuronal growth, axon extension and network connectivity, with cell morphology comparable to the gold standard poly-lysine. In addition, neurons growing on MaSp1 films had increased neural cell adhesion molecule (NCAM) expression at both mRNA and protein levels. The results indicate that MaSp1 films present useful surface charge and substrate stiffness to support the growth of primary rat cortical neurons. Moreover, a putative neuron-specific surface binding sequence GRGGL within MaSp1 may contribute to the biological regulation of neuron growth. These findings indicate that MaSp1 could regulate neuron growth through its physical and biological features. This dual regulation mode of MaSp1 could provide an alternative strategy for generating functional silk materials for neural tissue engineering.

Aggrecan, link protein and tenascin-R are essential components of the perineuronal net to protect neurons against iron-induced oxidative stress

In Alzheimer's disease (AD), different types of neurons and different brain areas show differential patterns of vulnerability towards neurofibrillary degeneration, which provides the basis for a highly predictive profile of disease progression throughout the brain that now is widely accepted for neuropathological staging. In previous studies we could demonstrate that in AD cortical and subcortical neurons are constantly less frequently affected by neurofibrillary degeneration if they are enwrapped by a specialized form of the hyaluronan-based extracellular matrix (ECM), the so called ‘perineuronal net' (PN). PNs are basically composed of large aggregating chondroitin sulphate proteoglycans connected to a hyaluronan backbone, stabilized by link proteins and cross-linked via tenascin-R (TN-R). Under experimental conditions in mice, PN-ensheathed neurons are better protected against iron-induced neurodegeneration than neurons without PN. Still, it remains unclear whether these neuroprotective effects are directly mediated by the PNs or are associated with some other mechanism in these neurons unrelated to PNs. To identify molecular components that essentially mediate the neuroprotective aspect on PN-ensheathed neurons, we comparatively analysed neuronal degeneration induced by a single injection of FeCl₃ on four different mice knockout strains, each being deficient for a different component of PNs. Aggrecan, link protein and TN-R were identified to be essential for the neuroprotective properties of PN, whereas the contribution of brevican was negligible. Our findings indicate that the protection of PN-ensheathed neurons is directly mediated by the net structure and that both the high negative charge and the correct interaction of net components are essential for their neuroprotective function.

Developmental pattern of perineuronal nets in the human prefrontal cortex and their deficit in schizophrenia

BACKGROUND

Perineuronal nets (PNNs) are extracellular matrix structures that enwrap many neurons in the brain. They regulate the postnatal experience-dependent maturation of brain circuits and maintain their functional integrity in the mature brain by stabilizing their synaptic architecture.

METHODS

Eighty-six postmortem human brains were included in this study. We used Wisteria Floribunda agglutinin histochemistry to visualize PNNs to investigate whether the densities of PNNs in the prefrontal cortex (PFC) and primary visual cortex were altered in subjects with schizophrenia or bipolar disorder. In addition, we quantified the normal postnatal development of PNNs in the human PFC.

RESULTS

The densities of PNNs were decreased by 70%-76% in layers 3 and 5 of the PFC in schizophrenia, compared with the normal control subjects, but not in bipolar disorder. This finding was replicated in a separate group of schizophrenia and normal control subjects. In addition, PNN densities in the primary visual cortex were unaltered in either condition. Finally, the number of PNNs in the PFC increased during postnatal development through the peripubertal period until late adolescence and early adulthood.

CONCLUSIONS

These findings suggest that PNN deficit contributes to PFC dysfunction in schizophrenia. That the timing of PNN development overlaps with the period when schizophrenia symptomatology gradually emerges raises the possibility that aberrant PNN formation might contribute to the onset of illness. Thus, characterization of the molecular mechanisms underlying PNN deficit might have important implications for the conceptualization of novel strategies for the diagnosis, treatment, early intervention, and prevention of schizophrenia.

NG2/CSPG4-collagen type VI interplays putatively involved in the microenvironmental control of tumour engraftment and local expansion

In soft-tissue sarcoma patients, enhanced expression of NG2/CSPG4 proteoglycan in pre-surgical primary tumours predicts post-surgical metastasis formation and thereby stratifies patients into disease-free survivors and patients destined to succumb to the disease. Both primary and secondary sarcoma lesions also up-regulate collagen type VI, a putative extracellular matrix ligand of NG2, and this matrix alteration potentiates the prognostic impact of NG2. Enhanced constitutive levels of the proteoglycan in isolated sarcoma cells closely correlate with a superior engraftment capability and local growth in xenogenic settings. This apparent NG2-associated malignancy was also corroborated by the diverse tumorigenic behaviour in vitro and in vivo of immunoselected NG2-expressing and NG2-deficient cell subsets, by RNAi-mediated knock down of endogenous NG2, and by ectopic transduction of full-length or deletion constructs of NG2. Cells with modified expression of NG2 diverged in their interaction with purified Col VI, matrices supplemented with Col VI, and cell-free matrices isolated from wild-type and Col VI null fibroblasts. The combined use of dominant-negative NG2 mutant cells and purified domain fragments of the collagen allowed us to pinpoint the reciprocal binding sites within the two molecules and to assert the importance of this molecular interaction in the control of sarcoma cell adhesion and motility. The NG2-mediated binding to Col VI triggered activation of convergent cell survival- and cell adhesion/migration-promoting signal transduction pathways, implicating PI-3K as a common denominator. Thus, the findings point to an NG2-Col VI interplay as putatively involved in the regulation of the cancer cell-host microenvironment interactions sustaining sarcoma progression.

Perineuronal and perisynaptic extracellular matrix in the human spinal cord

Extracellular matrix (ECM) forms an active interface around neurons of the central nervous system (CNS). Whilst the components, chemical heterogeneity and cellular recruitment of this intercellular assembly in various parts of the brain have been discussed in detail, the spinal cord received limited attention in this context. This is in sharp contrast to its clinical relevance since the overall role of ECM especially that of its chondroitin sulphate-based proteoglycan components (CSPGs) was repeatedly addressed in neuropathology, regeneration, CNS repair and therapy models. Based on two post-mortem human specimen, this study gives the first and detailed description of major ECM components of the human spinal cord. Immunohistochemical investigations were restricted to the systematic mapping of aggrecan, brevican, proteoglycan link-protein as well as tenascin-R and hyaluronan containing matrices in the whole cranio-caudal dimension of the human spinal cord. Other proteoglycans like versican, neurocan and NG2 were exemplarily investigated in restricted areas. We show the overall presence of tenascin-R and hyaluronan in both white and grey matters whereas aggrecan, proteoglycan link-protein and brevican were restricted to the grey matter. In the grey matter, the ECM formed aggrecan-based perineuronal nets in the ventral and lateral horns but established single perisynaptic assemblies, axonal coats (ACs), containing link-protein and brevican in all regions except of the Lissauer's zone. Intersegmental differences were reflected in the appearance of segment-specific nuclei but not in overall matrix distribution pattern or chemical heterogeneity. Perineuronal nets were typically associated with long-range projection neurons including cholinergic ventral horn motorneurons or dorsal spinocerebellar tract neurons of the Clarke-Stilling nuclei. Multiple immunolabelling revealed that nociceptive afferents were devoid of individual matrix assemblies unlike glycinergic or GABAergic synapses. The detailed description of ECM distribution in the human spinal cord shall support clinical approaches in injury and regenerative therapy.

Mapping the differential distribution of proteoglycan core proteins in the adult human retina, choroid, and sclera

PURPOSE

To examine the presence and distribution of proteoglycan (PG) core proteins in the adult human retina, choroid, and sclera.

METHODS

Postmortem human eye tissue was dissected into Bruch's membrane/choroid complex, isolated Bruch's membrane, or neurosensory retina. PGs were extracted and partially purified by anion exchange chromatography. Trypsinized peptides were analyzed by tandem mass spectrometry and PG core proteins identified by database search. The distribution of PGs was examined by immunofluorescence microscopy on human macular tissue sections.

RESULTS

The basement membrane PGs perlecan, agrin, and collagen-XVIII were identified in the human retina, and were present in the internal limiting membrane, blood vessel walls, and Bruch's membrane. The hyalectans versican and aggrecan were also detected. Versican was identified in Bruch's membrane, while aggrecan was distributed throughout the retina, choroid, and sclera. The cartilage link protein HAPLN1 was abundant in the interphotoreceptor matrix and sclera, while HAPLN4 (brain link protein 2) was found throughout the retina and choroid. The small leucine-rich repeat PG (SLRP) family members biglycan, decorin, fibromodulin, lumican, mimecan, opticin, and prolargin were present, with different patterns of distribution in the retina, choroid, and sclera.

CONCLUSIONS

A combination of proteomics and immunohistochemistry approaches has provided for the first time a comprehensive analysis of the presence and distribution of PG core proteins throughout the human retina, choroid, and sclera. This complements our knowledge of glycosaminoglycan chain distribution in the human eye, and has important implications for understanding the structure and functional regulation of the eye in health and disease.

Unique features of extracellular matrix in the mouse medial nucleus of trapezoid body--implications for physiological functions

The medial nucleus of the trapezoid body (MNTB) is a vital structure of sound localization circuits in the auditory brainstem. Each principal cell of MNTB is contacted by a very large presynaptic glutamatergic terminal, the calyx of Held. The MNTB principal cells themselves are surrounded by extracellular matrix components forming prominent perineuronal nets (PNs). Throughout the CNS, PNs, which form lattice-like structures around the somata and proximal dendrites, are associated with distinct types of neurons. PNs are highly enriched in hyaluronan and chondroitin sulfate proteoglycans therefore providing a charged surface structure surrounding the cell body and proximal neurites of these neurons. The localization and composition of PNs have lead investigators to a number of hypotheses about their functions including: creating a specific extracellular ionic milieu around these neurons, stabilizing synapses, and influencing the outgrowth of axons. However, presently the precise functions of PNs are still quite unclear primarily due to the lack of an ideal experimental model system that is highly enriched in PNs and in which the synaptic transmission properties can be precisely measured. The MNTB principal cells could offer such a model, since they have been extensively characterized electrophysiologically. However, extracellular matrix (ECM) in these neurons has not yet been precisely detailed. The present study gives a detailed examination of the ECM organization and structural differences in PNs of the mouse MNTB. The different PN components and their distribution pattern are scrutinized throughout the MNTB. The data are complemented by electron microscopic investigations of the unique ultrastructural localization of PN-components and their interrelation with distinct pre- and postsynaptic MNTB cell structures. Therefore, we believe this work identifies the MNTB as an ideal system for studying PN function.

Involvement of perineuronal and perisynaptic extracellular matrix in Alzheimer's disease neuropathology

Brain extracellular matrix (ECM) is organized in specific patterns assumed to mirror local features of neuronal activity and synaptic plasticity. Aggrecan-based perineuronal nets (PNs) and brevican-based perisynaptic axonal coats (ACs) form major structural phenotypes of ECM contributing to the laminar characteristics of cortical areas. In Alzheimer's disease (AD), the deposition of amyloid proteins and processes related to neurofibrillary degeneration may affect the integrity of the ECM scaffold. In this study we investigate ECM organization in primary sensory, secondary and associative areas of the temporal and occipital lobe. By detecting all major PN components we show that the distribution, structure and molecular properties of PNs remain unchanged in AD. Intact PNs occurred in close proximity to amyloid plaques and were even located within their territory. Counting of PNs revealed no significant alteration in AD. Moreover, neurofibrillary tangles never occurred in neurons associated with PNs. ACs were only lost in the core of amyloid plaques in parallel with the loss of synaptic profiles. In contrast, hyaluronan was enriched in the majority of plaques. We conclude that the loss of brevican is associated with the loss of synapses, whereas PNs and related matrix components resist disintegration and may protect neurons from degeneration.

Progesterone induction of chondroitin sulfate proteoglycan aggrecan expression in human endometrial epithelial cells

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan species in the human endometrium, but the expression profile of CS proteoglycans (PGs) in this mucosal tissue remains fully undetermined. In this study, we aimed to clarify the expression of CSPGs including aggrecan, neurocan, melanoma-associated CSPG, neuroglycan C, and brevican in the human cycling endometrium. By reverse transcription-polymerase chain reaction, the gene transcripts for aggrecan core protein were detected in all samples examined, while other CSPGs were not. Western blotting showed the immunoreactivity for aggrecan core protein at approximately 370 kDa size after enzymatic digestion of CS-A and CS-C side chains. The expression level of aggrecan core protein was significantly higher in the secretory phase than in the proliferative phase. The immunostaining for aggrecan was detected in the endometrial microvascular endothelium throughout the menstrual cycle. The immunostaining in the glandular epithelium was faint during the proliferative and early secretory phase, but distinct during the mid-to-late-secretory phase. Progesterone, but not 17β-estradiol, induced aggrecan core protein expression in cultured endometrial epithelial cells. The endometrial expression pattern of aggrecan was distinct from that of other known CSPGs, suggesting the unique role of this proteoglycan at the implantation site.

Neurons associated with aggrecan-based perineuronal nets are protected against tau pathology in subcortical regions in Alzheimer's disease

The biological basis for the selective vulnerability of neurons in Alzheimer's disease (AD) is elusive. Aggrecan-based perineuronal nets (PNs) of the extracellular matrix have been considered to contribute to neuroprotection in the cerebral cortex. In the present study, we investigated the organization of the aggrecan-based extracellular matrix in subcortical regions known to be preferentially affected by tau pathology in AD. Immunocytochemistry of aggrecan core protein was combined with detection of neurofibrillary degeneration. The results show that many regions affected by tau pathology in AD, such as the basal nucleus of Meynert, the dorsal thalamus, hypothalamic nuclei, raphe nuclei, and the locus coeruleus were devoid of a characteristic aggrecan-based extracellular matrix. Regions composed of nuclei with clearly different intensity of tau pathology, such as the amygdala, the thalamus and the oculomotor complex, showed largely complementary distribution patterns of neurofibrillary tangles and PNs. Quantification in the rostral interstitial nucleus of the longitudinal fascicle potentially affected by tau pathology in AD revealed that tau pathology was not accompanied by loss of aggrecan-based PNs. Neuro-fibrillary tangles in net-associated neurons extremely rarely occurred in the pontine reticular formation. We conclude that the low vulnerability of neurons ensheathed by PNs previously described for cortical areas in AD represents a more general phenomenon that also applies to subcortical regions. The aggrecan-based extracellular matrix of PNs may thus, be involved in neuroprotection.

Distribution of perineuronal nets in the human superior olivary complex

Perineuronal nets (PNNs) are specialized assemblies of chondroitin sulfate proteoglycans (CSPGs) in the central nervous system that form a lattice-like covering over the cell body, primary dendrites and initial axon segment of select neuronal populations. PNNs appear to play significant roles in development of the central nervous system, neuronal protection, synaptic plasticity and local ion homeostasis. In seven human brainstems (average age=81 years), we have utilized Wisteria floribunda (WFA) histochemistry and immunocytochemistry for CSPG to map the distribution of PNNs within the nuclei of the human superior olivary complex (SOC). Within the SOC, the majority of net-bearing neurons are situated in the most medially situated nuclei, especially the superior paraolivary nucleus and medial nucleus of the trapezoid body. Net-bearing neurons are consistently found in the ventral nucleus of the trapezoid body and posterior periolivary nucleus, but to a lesser extent in the lateral nucleus of the trapezoid body. Finally, perineuronal nets are typically absent from the lateral and medial superior olives.