Differential expression of the small chondroitin/dermatan sulfate proteoglycans decorin and biglycan after injury of the adult rat brain

Expression of OASIS, a CREB/ATF family transcription factor, in CNS lesion and its transcriptional activity

We reported the expression patterns of a novel member of the CREB/ATF family, OASIS, in central nervous system (CNS) lesions and its transcriptional activity. OASIS gene expression was upregulated in the stab-injured spinal cord. Double labeling experiments revealed that the distribution of OASIS mRNA-positive cells overlapped with a population of GFAP-immunoreactive cells. This finding suggested that OASIS might regulate expression of important downstream molecules in certain subset of the reactive astrocytes (e.g. inhibitory substances in injured brain). In gel shift assays, OASIS was able to specifically bind to CRE as CREB family members were. We then examined transcriptional activity of full-length OASIS with GAL4-UAS-luciferase reporter assay in COS7 cells. OASIS protein activated transcription, but did not inhibit basal transcription driven by AdML promoter. To determine critical portion(s) of the OASIS protein in transcriptional activation, we examined the activity of various deletion constructs of OASIS gene. The assay revealed that a strong transcriptional activation domain lay in the N-terminal region where acidic amino acids clustered and a possible repression domain, which had not been reported for other CREB/ATF family members, lay in the more C-terminal region. We therefore proposed that OASIS protein positively regulated gene transcription in a subset of reactive astrocytes, and thereby influenced the reaction of injured CNS tissues.

Water ADC, extracellular space volume, and tortuosity in the rat cortex after traumatic injury

The diffusion parameters in rat cortex were studied 3-35 days following a cortical stab wound, using diffusion-weighted MR to determine the apparent diffusion coefficient of water (ADC(W)) in the tissue, and the real-time iontophoretic tetramethylammonium (TMA) method to measure the extracellular space (ECS) diffusion parameters: ECS volume fraction alpha and the ADC of TMA(+) (ADC(TMA)). Severe astrogliosis was found close to the wound, and mild astrogliosis was found in the ipsilateral but not the contralateral cortex. Chondroitin sulfate proteoglycan (CSPG) expression was increased throughout the ipsilateral cortex. In the hemisphere contralateral to the wound, alpha, ADC(TMA), and ADC(W) were not significantly different from control values. ECS volume fraction was increased only in the vicinity of the wound, in the region of cell death and severe astrogliosis, at 3 and 7 days after injury. However, both ADC(TMA) and ADC(W) were significantly decreased after lesion in the vicinity of the wound as well as in the rest of the ipsilateral hemisphere distant from the wound. Thus, both ADC(W) and ADC(TMA) decreased in regions wherein alpha did not change but CSPG increased. An increase in extracellular matrix expression may therefore impose diffusion barriers for water as well as for TMA molecules.

Facilitation of learning and modulation of frontal cortex acetylcholine by ventral pallidal injection of heparin glucosaminoglycan

We examined the effects of heparin on learning and frontal cortex acetylcholine parameters following injection of the glucosaminoglycan into the ventral pallidum. In Experiment 1, possible mnemoactive effects of intrapallidal heparin injection were assessed. Rats with chronically implanted cannulae were administered heparin (0.1, 1.0, 10 ng) or vehicle (0.5 microl) and were tested on a one-trial step-through avoidance task. Two retention tests were carried out in each animal, one at 1.5 h after training to measure short-term memory and another at 24 h to measure long-term memory. Post-trial intrapallidal injection of 1.0 ng heparin improved both short- and long-term retention of the task, whereas the lower and the higher dose of the glucosaminoglycan had no effect. When the effective dose of heparin was injected 5 h, rather than immediately after training, it no longer facilitated long-term retention of the conditioned avoidance response. In Experiment 2, the effects of ventral pallidal heparin injection on frontal cortex acetylcholine and choline concentrations were investigated with in vivo microdialysis in anaesthetized rats. Heparin, administered in the dose of 1.0 ng, which was effective in facilitating avoidance performance, produced a delayed increase in cortical acetylcholine levels ipsi- and contralaterally to the side of intrabasalis injection, resembling the known neurochemical effects obtained for another glycosaminoglycan, chondroitin sulfate, which recently was shown to facilitate inhibitory avoidance learning and to increase frontal cortex acetylcholine. The present findings indicate that heparin, like other extracellular matrix proteoglycans, can exert beneficial effects on memory and strengthen the presumptive relationship between such promnestic effects of proteoglycans and basal forebrain cholinergic mechanisms. The data are discussed with respect to the presumed roles of matrix molecules in extrasynaptic volume transmission and in the 'cross-talk' between synapses.

Proteoglycans in retina

In this article, we summarize the roles of proteoglycans in retinal tissue. Chondroitin sulfate and heparan sulfate proteoglycans are the major constituents in proteoglycans expressed in retinal tissue. Soluble heparan sulfate proteoglycans are found in the extracellular matrices of the basement membrane, such as the inner limiting membrane and Bruch's membrane, whereas heparan sulfate proteoglycans with their membrane-binding domain are localized primarily in the neurites of retinal neuronal cells, indicating their role as receptors for cytokines. The distribution of chondroitin sulfate proteoglycans is classified into two regions: nerve fiber-rich layers such as the optic nerve, inner plexiform layer and outer plexiform layer, and the interphotoreceptor matrix (IPM). The expression in the nerve fiber-rich layers of several chondroitin sulfate proteoglycans, such as neurocan and phosphacan, is restricted in the nervous tissues, and is upregulated as retinal development proceeds, then decreases after maturation of the retina. In vitro data suggest that these proteoglycans regulate axon guidance and synapse formation during the development of nervous tissue. In contrast, in adult vertebrate retina, the IPM is a rich source of chondroitin sulfate proteoglycans. Histologic data from animals with experimental retinitis pigmentosa, and the existence of the hyaluronan-binding domain in their core proteins, indicate that these proteoglycans contribute to the structural link between the neural retina and retinal pigment epithelium via the interaction with hyaluronan, which is also abundant in the IPM. Furthermore, several chondroitin sulfate proteoglycans in the nerve fiber-rich layers contain the hyaluronan-binding domain, so it is likely that the interaction of proteoglycans with hyaluronan plays an important role in neural network formation in the central nervous system.

Gene modulation in total brain induced by exposure to the bicyclic phosphorus ester trimethylolpropane phosphate (TMPP)

The effect of a single subconvulsive dose of the GABAergic convulsant trimethylolpropane phosphate (TMPP) on gene expression in total rat brain was examined using cDNA array analysis. Using threshold criteria that reduce the number of false positives to <1 gene per 3551 actively transcribed genes on the cDNA array, 41 genes/EST sequences were reproducibly modulated in response to 0.25 mg/kg TMPP. Several genes that were consistent with epileptogenesis and/or neuronal damage and repair mechanisms, such as trkB, alphaB-crystallin, and decorin, were modulated by TMPP exposure in the absence of clinical convulsions. Previous research indicates that rats exposed to subconvulsive doses of TMPP exhibit both "absence-like" EEG paroxysms and persisting central nervous system (CNS) sensitization, as evidenced by increased susceptibility to audiogenic seizures (AGS). Results of this study suggest that cDNA arrays can be used to identify gene modulation events induced by low-level exposure to a chemical convulsant in a reproducible manner.

White matter extracellular matrix chondroitin sulfate/dermatan sulfate proteoglycans in multiple sclerosis

Extracellular matrix (ECM) alterations in the central nervous system (CNS) of multiple sclerosis (MS) patients result from blood-brain barrier breakdown, release and activation of proteases, and synthesis of ECM components. To elucidate their potential pathophysiologic roles, we analyzed expression of major CNS ECM proteoglycans (PGs) in MS and control CNS tissues. In active MS plaque edges, 3 CNS lecticans (versican, aggrecan, and neurocan) and dermatan sulfate PG were increased in association with astrocytosis; in active plaque centers they were decreased in the ECM and accumulated in foamy macrophages, suggesting that these ECM PGs are injured and phagocytosed along with myelin. In inactive lesions they were diminished and in normal-appearing white matter they showed heretofore-unappreciated abnormal heterogeneous aggregation. Phosphacan, an ECM PG abundant in both gray and white matter, was less markedly altered. Since in development the spaciotemporal expression of ECM PGs influences neurite outgrowth, cell migration, axon guidance, and myelination, these data suggest that 1) enhanced white matter lectican and dermatan sulfate PG expression in the pro-inflammatory milieu of expanding lesion edges contributes to their sharp boundaries and the failure of neuronal ingrowth; 2) decreases in plaque centers may preclude regeneration and repair; and 3) diffuse ECM PG damage relates to axon degeneration outside of overt lesions. Thus, ECM PG alterations are specific, temporally dynamic, and widespread in MS patients and may play critical roles in lesion pathogenesis and CNS dysfunction.

Proteoglycans in the nervous system--the quest for functional roles in vivo

Large numbers of different proteoglycans are expressed in tightly regulated spatio-temporal patterns by both the nerve cells (neurons) and the supporting glial cells of the nervous system. Several of these proteoglycans have been shown by studies in vitro to affect the migration of neural precursor cells, the elongation and pathfinding of neurites and the formation and stabilization of synapses. Such processes are important for the accurate wiring of the nervous system, and so it has been postulated that proteoglycans play an essential role during neural development. However, with few exceptions, the phenotypes of null mutations in mice and some human genetic diseases have provided little support for this view. Here we will review recent data from both in vitro and in vivo studies analyzing the function of proteoglycans in the nervous system in order to provide possible explanations for their apparent lack of function.

Collagen IV deposits do not prevent regrowing axons from penetrating the lesion site in spinal cord injury

Scarring is suggested to impede axon regrowth across the lesion site in the injured adult mammalian central nervous system. Collagen Type IV, as a major component of the scar formed after injury, is an impediment for successful axonal regeneration and a decrease in its amount is a prerequisite for regrowing axons to cross the lesion in the postcommissural fornix in the injured adult rat (Stichel et al. [1999] Neurosci. 93:321-333). The aim of the present study was to analyze the relationship between collagen IV deposits and regrowing axons at various times after dorsal hemi-section of the adult rat spinal cord. Immunohistochemical double staining revealed that penetrating neurofilament-positive axons and collagen IV deposits were co-localized in the lesion site in the initial stages of axonal sprouting (between 7 and 14 days post-operatively) and were still present 1 and 2 months post-operatively. Interestingly, collagen IV-immunoreactive areas located around cystic cavities formed at the site of injury 1 month post-operatively, were devoid of axons. In conclusion, our observations indicate that collagen IV deposits after spinal cord injury do not prevent neurofilament-positive regrowing axons from penetrating the lesion site.

The polarity and magnitude of ambient charge influences three-dimensional neurite extension from DRGs

Sulfated proteoglycans have inhibitory effects on neurite extension, and the negative charge of the glycosaminoglycan side chains may be involved in the inhibitory process. The main goal of this study is to investigate the effects of charge on three-dimensional neurite extension. Various concentrations of dermatan sulfate (DS), a chondroitin sulfate glycosaminoglycan, and consequently, various degrees of negative charge were presented on three-dimensional agarose hydrogels and the effect of charge on neurite extension from primary neurons was investigated. Dose-response experiments were also performed with the polycationic (positively charged) polysaccharide chitosan covalently coupled to agarose. The amount of DS or chitosan coupled to the agarose gel was quantified via metachromatic dye or Fourier transform infrared spectroscopy methods, respectively. The length of embryonic day 9 (E9) chick dorsal root ganglia neurites extended through charged agarose gels is dependent on the polarity and quantity of ambient charge. The inhibitory effects of the sulfated DS and the enhancing effects of the polycationic chitosan on neurite extension decrease as the amount of DS or chitosan coupled to agarose is decreased. These findings indicate that primary neural process extension is influenced by the polarity of ambient charge in a dose-responsive manner.

Nervous system proteoglycans as modulators of neurite outgrowth

The proteoglycans are multifunctional macromolecules composed of a core polypeptide and a variable number of glycosaminoglycan chains. The structural diversity and complexities of proteoglycan expression in the developing and adult Nervous System underlies the variety of biological functions that these molecules fulfill. Thus, in the Nervous System, proteoglycans regulate the structural organisation of the extracellular matrix, modulate growth factor activities and cellular adhesive and motility events, such as cell migration and axon outgrowth. This review summarises the evidences indicating that proteoglycans have an important role as modulators of neurite outgrowth and neuronal polarity. Special emphasis will be placed on those studies that have shown that proteoglycans of certain subtypes inhibit neurite extension either during the development and/or the regeneration of the vertebrate Central Nervous System.

Neurocan is upregulated in injured brain and in cytokine-treated astrocytes

Injury to the CNS results in the formation of the glial scar, a primarily astrocytic structure that represents an obstacle to regrowing axons. Chondroitin sulfate proteoglycans (CSPG) are greatly upregulated in the glial scar, and a large body of evidence suggests that these molecules are inhibitory to axon regeneration. We show that the CSPG neurocan, which is expressed in the CNS, exerts a repulsive effect on growing cerebellar axons. Expression of neurocan was examined in the normal and damaged CNS. Frozen sections labeled with anti-neurocan monoclonal antibodies 7 d after a unilateral knife lesion to the cerebral cortex revealed an upregulation of neurocan around the lesion. Western blot analysis of extracts prepared from injured and uninjured tissue also revealed substantially more neurocan in the injured CNS. Western blot analysis revealed neurocan and the processed forms neurocan-C and neurocan-130 to be present in the conditioned medium of highly purified rat astrocytes. The amount detected was increased by transforming growth factor beta and to a greater extent by epidermal growth factor and was decreased by platelet-derived growth factor and, to a lesser extent, by interferon gamma. O-2A lineage cells were also capable of synthesizing and processing neurocan. Immunocytochemistry revealed neurocan to be deposited on the substrate around and under astrocytes but not on the cells. Astrocytes therefore lack the means to retain neurocan at the cell surface. These findings raise the possibility that neurocan interferes with axonal regeneration after CNS injury.

Nogo-A, a potent inhibitor of neurite outgrowth and regeneration

The lack of regrowth of injured neurons in the adult central nervous system (CNS) of higher vertebrates was accepted as a fact for many decades. In the last few years a very different view emerged; regeneration of lesioned fibre tracts in vivo could be induced experimentally, and molecules that are responsible for inhibition and repulsion of growing neurites have been defined. Mechanisms that link cellular phenomena like growth cone turning or growth cone collapse to intracellular changes in second messenger systems and cytoskeletal dynamics became unveiled. This article reviews recent developments in this field, focusing especially on one of the best characterised neurite out-growth inhibitory molecules found in CNS myelin that was recently cloned: Nogo-A. Nogo-A is a high molecular weight transmembrane protein and an antigen of the monoclonal antibody mAb IN-1 that was shown to promote long-distance regeneration and functional recovery in vivo when applied to spinal cord-injured adult rats. Nogo-A is expressed by oligodendrocytes in white matter of the CNS. With the molecular characterisation of this factor new possibilities open up to achieve structural and functional repair of the injured CNS.

Chondroitin sulfates expressed on oligodendrocyte-derived tenascin-R are involved in neural cell recognition. Functional implications during CNS development and regeneration

Tenascin-R (TN-R), an extracellular matrix constituent of the central nervous system (CNS), has been implicated in a variety of cell-matrix interactions underlying axon growth inhibition/guidance, myelination and neural cell migration during development and regeneration. Although most of the functional analyses have concentrated exclusively on the role of the core protein, the contribution of TN-R glycoconjugates present on many potential sites for N- and O-glycosylation is presently unknown. Here we provide first evidence that TN-R derived from whole rat brain or cultured oligodendrocytes expresses chondroitin sulfate (CS) glycosaminoglycans (GAGs), i.e., C-4S and C-6S, that are recognized by CS-56, a CS/dermatan sulfate-specific monoclonal antibody. Based on different in vitro approaches utilizing substrate-bound glycoprotein, we found that TN-R-linked CS GAGs (1) promote oligodendrocyte migration from white matter microexplants and increase the motility of oligodendrocyte lineage cells; (2) similar to soluble CS GAGs, induce the formation of glial scar-like structures by cultured cerebral astrocytes; and (3) contribute to the antiadhesive properties of TN-R for neuronal cell adhesion in an F3/F11-independent manner, but not to neurite outgrowth inhibition, by mechanism(s) sensitive to chondroitinase or CS-56 treatments. Furthermore, after transection of the postcommissural fornix in adult rat, CS-bearing TN-R was found to be stably upregulated at the lesion site. Our findings suggest the functional impact of TN-R-linked CS on neural cell adhesion and migration during brain morphogenesis and the contribution of TN-R to astroglial scar formation (CS-dependent) and axon growth inhibition (CS-independent), i.e., suppression of axon regeneration after CNS injury.

Chondroitin sulfate proteoglycan immunoreactivity increases following spinal cord injury and transplantation

Extrinsic factors appear to contribute to the lack of regeneration in the injured adult spinal cord. It is likely that these extrinsic factors include a group of putative growth inhibitory molecules known as chondroitin sulfate proteoglycans (CSPGs). The aims of this study were to determine: (1) the consequences of spinal cord contusion injury on CSPG expression, (2) if CSPGs can be degraded in vivo by exogenous enzyme application, and (3) the effects of intraspinal transplantation on the expression of CSPGs. Chondroitin 6-sulfate proteoglycan immunoreactivity (CSPG-IR) dramatically increased following spinal cord contusion injury both at and adjacent to the injury site compared to normal controls (no surgical procedure) and laminectomy-only controls by 4 days postinjury. The dramatic increase in CSPG-IR persisted around the lesion and in the dorsal one-half to two-thirds of the spinal cord for at least 40 days postinjury. Glial fibrillary acidic protein (GFAP)-IR patterns were similarly intensified and spatially restricted as CSPG-IR patterns. These results suggest that: (1) CSPGs may contribute to the lack of regeneration following spinal cord injury and (2) astrocytes may contribute to the production of CSPGs. In addition, our results show that CSPGs could be cleaved in vivo with exogenous chondroitinase ABC application. This demonstration of cleavage may the basis for a model to directly assess CSPGs' role in growth inhibition in vivo (studies in progress) and hold potential as a therapeutic approach to enhance growth. Interestingly, the robust, injury-induced CSPG-IR patterns were not altered by intraspinal grafts of fetal spinal cord. The CSPG expression profile in the host spinal cord was similar to time-matched contusion-only animals. This was also true of GFAP-IR patterns. Furthermore, the fetal spinal cord tissue, which was generally CSPG negative at the time of transplantation, developed robust CSPG expression by 30 days posttransplantation. This increase in CSPG expression in the graft was paired with a moderate increase in GFAP-IR. CSPG-IR patterns suggest that these molecules may contribute to the limited regeneration seen following intraspinal transplantation. In addition, it suggests that the growth permissiveness of the graft may change overtime as CSPG expression develops within the graft. These correlations in the injured and transplanted spinal cord support CSPGs' putative growth inhibitory effect in the adult spinal cord.

Diffusion barriers evoked in the rat cortex by reactive astrogliosis

Changes in extracellular space (ECS) diffusion parameters in astrogliotic tissue around a unilateral cortical stab wound were determined from concentration-time profiles of tetramethylammonium (TMA(+)) using TMA(+)-selective microelectrodes. Three diffusion parameters-ECS volume fraction alpha (alpha = ECS volume/ total tissue volume), tortuosity lambda (lambda(2) = D/ADC; where D is the free and ADC is the apparent diffusion coefficient of TMA(+) in the brain), and nonspecific TMA(+)uptake k'-were determined at 3, 7, 21, and 35 days postwounding (dpw), in the hemispheres ipsilateral and contralateral to the lesion. Following diffusion experiments, tissue sections were immunostained for glial fibrillary acidic protein (GFAP) and chondroitin-sulphate proteoglycans (CSPG). In the area 300-1000 micron around the wound, alpha was increased at 3, 7, and 21 dpw by about 20% but returned to control values at 35 dpw; lambda was increased at all four intervals, reaching a maximum at 7 dpw. k' was lower than in the contralateral hemisphere at 7, 21, and 35 dpw. Measurements 1,500-2,000 micron from the wound revealed only an increase in lambda at 7 dpw. The time course of changes in ECS diffusion parameters closely correlated with increased staining for GFAP and CSPG. Our results show that astrogliosis significantly changes the diffusion properties of nervous tissue, making it less permissive. Both hypertrophied astrocytic processes and an enhanced formation of some extracellular matrix molecules could affect, through changes in the diffusion of molecules in the ECS, neuron-glia communication, "cross-talk" between synapses, extrasynaptic transmission, and regenerative processes.

Decorin attenuates gliotic scar formation in the rat cerebral hemisphere

The transforming growth factor-betas (TGF-betas) are potent fibrogenic factors implicated in numerous CNS pathologies in which fibrosis and neural dysfunction are causally associated. In this study, we aimed to demonstrate significant inhibition of fibrogenesis, glial scarring, and inflammation in penetrating incisional wounds of the rat brain using the proteoglycan decorin, which effectively inhibits TGF-beta activity. Adult rats were assigned to two treatment groups each receiving 14 daily intraventricular injections of 10 microliter total volume of: (i) saline plus 0.3% autologous rat serum = 30 microgram protein); or (ii) saline plus 30 microgram recombinant human decorin. On day 0 of the experiment, a stereotactically defined unilateral incisional lesion was placed through the cerebral cortex into the lateral ventricle and, after 14 days, brains were processed for immunohistochemical analysis of the lesion site. Specific antibodies were used to visualize the deposition within the wound of matrix molecules and the extent and nature of reactive astrocytosis and inflammation. Quantitative and qualitative image analysis of the fibrous scar was performed in sections from a defined anatomical plane through the wound to detect the antifibrotic effects of decorin treatment. Treatment of wounds with decorin led to a marked attenuation of all aspects of CNS scarring including matrix deposition, formation of an accessory glial limiting membrane, and inflammation. Our findings suggest that decorin is potentially applicable to a number of human CNS fibrotic diseases to arrest the deposition of excessive extracellular matrix components and maintain and/or restore functional integrity.

Expression of different extracellular matrix components in human brain tumor and melanoma cells in respect to variant culture conditions

Local tumor invasion into the surrounding brain tissue is a major characteristic of malignant gliomas. These processes critically depend on the interaction of tumor cells with various extracellular matrix (ECM) components. Because only little quantitative information about expression of ECM gene products in general and expression in response to alterations of the surrounding environment is available, the present study was designed. Four human glioblastoma cell lines (U373MG, U138MG, U251MG, GaMG) as well as four human melanoma cell lines (MV3, BLM, 530, IF6) were tested with semiquantitative RT-PCR for their ability to express mRNA of different human ECM components (fibronectin, decorin, tenascin, collagen I, collagen IV, versican). In addition, two human medulloblastoma (MHH-Med 1, MHH-Med 4) and two fibrosarcoma (HT1080, U2OS) cell lines were analyzed. Cells which were grown in DMEM medium containing 10% FCS expressed most of the analyzed protein components. When the same medium, but depleted of ECM proteins by filtrating through a membrane with cut-off at > 100 kD was used, basal mRNA expression of the ECM proteins was changed in most of the examined cell lines. Using serum free conditions, most of the cell lines again showed a variation in the expression pattern of mRNA encoding for the different ECM proteins compared to the other medium conditions. Comparing different cell lines from one tumor entity or different tumor groups, ECM expression was heterogeneous with regard to the different tumor entities as well as within the entities themselves. Migration assays revealed heterogeneous responses between the different cell lines, ECM components and culture conditions, making it difficult to correlate ECM expression patterns and migratory behavior. Our results revealed that all examined cell lines are able to produce ECM proteins in vitro. This suggests that tumor cells can modulate their microenvironment in vitro which has to be taken into consideration for studies related to migration and invasion.

The glial scar and central nervous system repair

Damage to the central nervous system (CNS) results in a glial reaction, leading eventually to the formation of a glial scar. In this environment, axon regeneration fails, and remyelination may also be unsuccessful. The glial reaction to injury recruits microglia, oligodendrocyte precursors, meningeal cells, astrocytes and stem cells. Damaged CNS also contains oligodendrocytes and myelin debris. Most of these cell types produce molecules that have been shown to be inhibitory to axon regeneration. Oligodendrocytes produce NI250, myelin-associated glycoprotein (MAG), and tenascin-R, oligodendrocyte precursors produce NG2 DSD-1/phosphacan and versican, astrocytes produce tenascin, brevican, and neurocan, and can be stimulated to produce NG2, meningeal cells produce NG2 and other proteoglycans, and activated microglia produce free radicals, nitric oxide, and arachidonic acid derivatives. Many of these molecules must participate in rendering the damaged CNS inhibitory for axon regeneration. Demyelinated plaques in multiple sclerosis consists mostly of scar-type astrocytes and naked axons. The extent to which the astrocytosis is responsible for blocking remyelination is not established, but astrocytes inhibit the migration of both oligodendrocyte precursors and Schwann cells which must restrict their access to demyelinated axons.

Inhibition of collagen IV deposition promotes regeneration of injured CNS axons

Scarring impedes axon regrowth across the lesion site and is one major extrinsic constraint to effective regeneration in the adult mammalian central nervous system. In the present study we determined whether specific biochemical or immunochemical modulation of one major component of the scar, the basal membrane (BM), would provide a means to stimulate axon regeneration in the mechanically transected postcommissural fornix of the adult rat. Basal membrane developed within the first 2 weeks after transection in spatiotemporal coincidence with the abrupt growth arrest of spontaneously regrowing axons. Local injection of anticollagen IV antibodies or alpha, alpha'-dipyridyl, an inhibitor of collagen triple helix formation and synthesis, significantly reduced lesion-induced BM deposition. This treatment allowed massive axon elongation across the lesion site. Anterograde tracing provided unequivocal evidence that regenerating axons follow their original pathway, reinnervate the appropriate target, the mammillary body, and become remyelinated with compact myelin. Presynaptic electrophysiological recordings of regenerated fibre tracts showed recovery to nearly normal conduction properties. Our results indicate that lesion-induced BM is an impediment for successful axonal regeneration and its reduction is a prerequisite and sufficient condition for regrowing axons to cross the lesion site.

Fibroblast growth factor receptor-1 expression in the cortex and hippocampus in Alzheimer's disease

Localization of fibroblast growth receptor (FGFR)-1 immunoreactivity was investigated immunochemically in postmortem brain tissue of Alzheimer's disease (AD) and age-matched control cases using a rabbit polyclonal antibody and a mouse monoclonal antibody specific for FGFR-1. In control cases, FGFR-1 immunoreactivity was identified in astrocytes in white matter and in hippocampal pyramidal neurons. In AD cases, the immunoreactivity in reactive astrocytes surrounding senile plaques was increased. The pattern of FGFR-1 immunoreactivity was confirmed in selected cases by in situ hybridization for FGFR-1 mRNA. Immunoreactivity using a monoclonal antibody demonstrated a similar distribution pattern. The localization of FGFR-1 is consistent with previous reports on the involvement of FGF-1 and FGF-2 in AD.

Developmental regulation of decorin expression in postnatal rat brain

Here, we report on the expression of the small chondroitin/dermatan sulfate proteoglycan decorin in the developing postnatal rat brain. Northern analysis of brain RNA demonstrated decorin transcripts with peak expression on postnatal day 3 followed by a slow decline to the lower adult level. In situ hybridization and immunohistochemistry revealed postnatal decorin expression in the grey matter of neocortex, hippocampus and thalamus, in myelinated fibre tracts and in several mesenchymal tissues (blood vessels, pia mater and the choroid plexus). In the neocortex, decorin is expressed in a specific laminar pattern with intense staining of the cortical plate and its derivatives, which differs remarkably from the distributions observed for other proteoglycans [B. Miller, A.M. Sheppard, A.R. Bicknese, A.L. Pearlman, Chondroitin sulfate proteoglycans in the developing cerebral cortex: the distribution of neurocan distinguishes forming afferent and efferent axonal pathways, J. Comp. Neurol. 355 (1995) 615-28]. Thus, decorin seems to serve yet unknown functions in the developing rat brain parenchyma in addition to its well-established role as a constituent of the mesenchymal extracellular matrix.

Structural alterations and changes in cytoskeletal proteins and proteoglycans after focal cortical ischemia

In order to study structural alterations which occur after a defined unilateral cortical infarct, the hindlimb region of the rat cortex was photochemically lesioned. The infarcts caused edema restricted to the perilesional cortex which affected allocortical and isocortical areas differently. Postlesional changes in cytoskeletal marker proteins such as microtubule-associated protein 2, non-phosphorylated (SMI32) and phosphorylated (SMI35, SMI31 and 200,000 mol. wt) neurofilaments and 146,000 mol. wt glycoprotein Py as well as changes in proteoglycans visualized with Wisteria floribunda lectin binding (WFA) were studied at various time points and related to glial scar formation. The results obtained by the combination of these markers revealed six distinct regions in which transient, epitope-specific changes occurred: the core, demarcation zone, rim, perilesional cortex, ipsilateral thalamus and contralateral homotopic cortical area. Within the core immunoreactivity for microtubule-associated protein 2 and SMI32 decreased and the cellular components showed structural disintegration 4 h post lesion, but partial recovery of somatodendritic staining was seen after 24 h. Microtubule-associated protein 2 and SMI32 persisted up to days 7 and 5 respectively in the core, whereas the number of glial fibrillary acidic protein- and WFA-positive cells decreased between days 7 and 14. The demarcation zone showed a dramatic loss of immunoreactivity for all epitopes 4 h post lesion which was not followed by a phase of recovery. In the inner region of the demarcation zone there was an invasion and accumulation of non-neuronal WFA-positive cells which formed a tight capsule around the core. Neuronal immunoreactivities for microtubule-associated protein 2, SMI31 and Py as well as astrocytic glial fibrillary acidic protein increased strongly within an approximately 0.4-1.0 mm-wide rim region directly bordering the demarcation zone. Py immunoreactivity increased significantly in the perilesional cortex, whereas glial fibrillary acidic protein-positive astrocytes became transiently more numerous in the entire lesioned hemisphere including strongly enhanced immunoreactivity in the thalamus by days 5-7 post lesion. Glial fibrillary acidic protein immunoreactivity increased in the corpus callosum and the homotopic cortical area of the unlesioned hemisphere by days 5-7. In this homotopic area additional changes in SMI31 immunoreactivity occurred. Our results showed that a cortical infarct is not only a locally restricted lesion, but leads to a variety of cytoskeletal and other structural changes in widely-distributed functionally-related areas of the brain.

Elevated synthesis of biglycan and decorin in an ovine annular lesion model of experimental disc degeneration

The aim of this study was to extend our earlier observations on the changes that occur in the proteoglycans (PGs) of discs subjected to experimental injury to the annulus fibrosus (AF). We employed the alginate bead culture method to examine the metabolism of the dermatan sulphate (DS) containing PGs by cells derived from different regions of ovine discs that had been subjected to experimental annular injury. This was compared with the metabolism of the DS-PGs by cells isolated from equivalent regions of normal sham-operated discs. Six months after induction of the annular lesion, AF cells isolated from the lesion produced significantly higher levels of decorin and biglycan in alginate bead culture than did cells from equivalent zones of the controls. Decorin and biglycan were identified in culture media samples by immunoblotting, using specific antibodies (6-B-6, LF-96), and also by positive identification of their de-glycosylated core proteins. The core protein of the DS-PGs has been shown to inhibit type I/II collagen fibrillogenesis, to negatively regulate the action of transforming growth factor-beta (TGF-beta) and to diminish cellular proliferation in vitro; events which may be detrimental to tissue repair. The findings are therefore consistent with our previous observation the annular lesions in the avascular inner annulus have no capacity to heal.

Glypican and biglycan in the nuclei of neurons and glioma cells: presence of functional nuclear localization signals and dynamic changes in glypican during the cell cycle

We have investigated the expression patterns and subcellular localization in nervous tissue of glypican, a major glycosylphosphatidylinositol-anchored heparan sulfate proteoglycan that is predominantly synthesized by neurons, and of biglycan, a small, leucine-rich chondroitin sulfate proteoglycan. By laser scanning confocal microscopy of rat central nervous tissue and C6 glioma cells, we found that a significant portion of the glypican and biglycan immunoreactivity colocalized with nuclear staining by propidium iodide and was also seen in isolated nuclei. In certain regions, staining was selective, insofar as glypican and biglycan immunoreactivity in the nucleus was seen predominantly in a subpopulation of large spinal cord neurons. The amino acid sequences of both proteoglycans contain potential nuclear localization signals, and these were demonstrated to be functional based on their ability to target beta-galactosidase fusion proteins to the nuclei of transfected 293 cells. Nuclear localization of glypican beta-galactosidase or Fc fusion proteins in transfected 293 cells and C6 glioma cells was greatly reduced or abolished after mutation of the basic amino acids or deletion of the sequence containing the nuclear localization signal, and no nuclear staining was seen in the case of heparan sulfate and chondroitin sulfate proteoglycans that do not possess a nuclear localization signal, such as syndecan-3 or decorin (which is closely related in structure to biglycan). Transfection of COS-1 cells with an epitope-tagged glypican cDNA demonstrated transport of the full-length proteoglycan to the nucleus, and there are also dynamic changes in the pattern of glypican immunoreactivity in the nucleus of C6 cells both during cell division and correlated with different phases of the cell cycle. Our data therefore suggest that in certain cells and central nervous system regions, glypican and biglycan may be involved in the regulation of cell division and survival by directly participating in nuclear processes.

Changes in decorin expression with hyperoxic injury to developing rat lung

Proteoglycans are extracellular matrix components that appear to play important roles in lung development and in the response to injury. Decorin, a small extracellular matrix-associated proteoglycan, is known to be involved in collagen fibrillogenesis and is a likely participant in the pathogenesis of lung injury. We hypothesized that chronic exposure of the developing lung to hyperoxia would result in temporal and spatial changes in decorin expression. To determine the expression of decorin in normal and oxygen-injured lung, newborn rats were exposed to hyperoxia for 6 wk. Decorin mRNA abundance was determined using Northern hybridization analyses, and decorin expression was localized by in situ hybridization and immunohistochemistry. Decorin mRNA expression in type II pneumocytes was studied using reverse transcription-polymerase chain reaction. Oxygen exposure is associated with a 77% reduction in decorin mRNA in whole lung and a decrease in decorin immunoreactivity in connective tissues surrounding large airways and blood vessels, but an increase in decorin mRNA and protein expression at the tips of alveolar septa. Studies using isolated cells indicate that macrophages and polymorphonuclear neutrophils contain decorin core protein but not decorin mRNA. Type II pneumocytes do not contain either decorin mRNA or core protein. These findings demonstrate that hyperoxic lung injury is associated with localized changes in decorin expression, changes that are not reflected in whole lung RNA studies. It is likely that regional changes in lung decorin expression are influenced by factors produced and acting locally, and that such changes may contribute to the morphologic alterations characteristic of oxygen-induced lung injury.