Recovery of Forearm and Fine Digit Function After Chronic Spinal Cord Injury by Simultaneous Blockade of Inhibitory Matrix Chondroitin Sulfate Proteoglycan Production and the Receptor PTPσ

Spinal cord injuries (SCI), for which there are limited effective treatments, result in enduring paralysis and hypoesthesia, in part because of the inhibitory microenvironment that develops and limits regeneration/sprouting, especially during chronic stages. Recently, we discovered that targeted enzymatic removal of the inhibitory chondroitin sulfate proteoglycan (CSPG) component of the extracellular and perineuronal net (PNN) matrix via Chondroitinase ABC (ChABC) rapidly restored robust respiratory function to the previously paralyzed hemi-diaphragm after remarkably long times post-injury (up to 1.5 years) following a cervical level 2 lateral hemi-transection. Importantly, ChABC treatment at cervical level 4 in this chronic model also elicited improvements in gross upper arm function. In the present study, we focused on arm and hand function, seeking to highlight and optimize crude as well as fine motor control of the forearm and digits at lengthy chronic stages post-injury. However, instead of using ChABC, we utilized a novel and more clinically relevant systemic combinatorial treatment strategy designed to simultaneously reduce and overcome inhibitory CSPGs. Following a 3-month upper cervical spinal hemi-lesion using adult female Sprague Dawley rats, we show that the combined treatment had a profound effect on functional recovery of the chronically paralyzed forelimb and paw, as well as on precision movements of the digits. The regenerative and immune system related events that we describe deepen our basic understanding of the crucial role of CSPG-mediated inhibition via the PTPσ receptor in constraining functional synaptic plasticity at lengthy time points following SCI, hopefully leading to clinically relevant translational benefits.

Augmented Chondroitin Sulfate Proteoglycan Has Therapeutic Potential for Intervertebral Disc Degeneration by Stimulating Anabolic Turnover in Bovine Nucleus Pulposus Cells under Changes in Hydrostatic Pressure

Nucleus pulposus (NP) cells are exposed to changes in hydrostatic pressure (HP) and osmotic pressure within the intervertebral disc. We focused on main disc matrix components, chondroitin sulfate proteoglycan (CSPG) and hyaluronan (HA) to elucidate the capability of augmented CSPG to enhance the anabolism of bovine NP (bNP) cells under repetitive changes in HP at high osmolality. Aggrecan expression with CSPG in the absence of HP was significantly upregulated compared to the no-material control (phosphate buffer saline) under no HP at 3 days, and aggrecan expression with CSPG under HP was significantly higher than the control with HA under HP at 12 days. Collagen type I expression under no HP was significantly lower with CSPG than in controls at 3 days. Although matrix metalloproteinase 13 expression under HP was downregulated compared to no HP, it was significantly greater with HA than the control and CSPG, even under HP. Immunohistology revealed the involvement of mechanoreceptor of transient receptor potential vanilloid-4 activation under HP, suggesting an HP transduction mechanism. Addition of CSPG had anabolic and anti-fibrotic effects on bNP cells during the early culture period under no HP; furthermore, it showed synergy with dynamic HP to increase bNP-cell anabolism at later time points.

Lumican Inhibits SNAIL-Induced Melanoma Cell Migration Specifically by Blocking MMP-14 Activity

Lumican, a small leucine rich proteoglycan, inhibits MMP-14 activity and melanoma cell migration in vitro and in vivo. Snail triggers epithelial-mesenchymal transitions endowing epithelial cells with migratory and invasive properties during tumor progression. The aim of this work was to investigate lumican effects on MMP-14 activity and migration of Snail overexpressing B16F1 (Snail-B16F1) melanoma cells and HT-29 colon adenocarcinoma cells. Lumican inhibits the Snail induced MMP-14 activity in B16F1 but not in HT-29 cells. In Snail-B16F1 cells, lumican inhibits migration, growth, and melanoma primary tumor development. A lumican-based strategy targeting Snail-induced MMP-14 activity might be useful for melanoma treatment.

NME2 associates with PTPσ to transduce signals from chondroitin sulfate proteoglycans

Chondroitin sulfate proteoglycans (CSPGs) are a major component of glial scars, inhibiting axonal growth in the central nervous system. Protein tyrosine phosphatase, receptor type S (PTPσ) has been identified as a receptor for CSPGs, whereas its downstream signaling pathway remains to be fully understood. Here, we report that nucleoside diphosphate kinase 2 (NME2) interacts with PTPσ. We screened proteins associated with PTPσ by mass spectrometry, and obtained NME2. Immunoprecipitation analysis revealed that NME2 associated with the PTPσ intracellular domain in HEK-293T cells. NME2 was expressed in the cytoplasm and nucleus of cortical neurons, and knockdown of NME2 in the cortical neurons completely rescued neurite outgrowth inhibition induced by CSPGs. These results demonstrate that NME2 associates with PTPσ to elicit neurite outgrowth inhibition in response to CSPGs.

A chemical genetic approach identifies piperazine antipsychotics as promoters of CNS neurite growth on inhibitory substrates

Injury to the central nervous system (CNS) can result in lifelong loss of function due in part to the regenerative failure of CNS neurons. Inhibitory proteins derived from myelin and the astroglial scar are major barriers for the successful regeneration of injured CNS neurons. Previously, we described the identification of a novel compound, F05, which promotes neurite growth from neurons challenged with inhibitory substrates in vitro, and promotes axonal regeneration in vivo (Usher et al., 2010). To identify additional regeneration-promoting compounds, we used F05-induced gene expression profiles to query the Broad Institute Connectivity Map, a gene expression database of cells treated with >1300 compounds. Despite no shared chemical similarity, F05-induced changes in gene expression were remarkably similar to those seen with a group of piperazine phenothiazine antipsychotics (PhAPs). In contrast to antipsychotics of other structural classes, PhAPs promoted neurite growth of CNS neurons challenged with two different glial derived inhibitory substrates. Our pharmacological studies suggest a mechanism whereby PhAPs promote growth through antagonism of calmodulin signaling, independent of dopamine receptor antagonism. These findings shed light on mechanisms underlying neurite-inhibitory signaling, and suggest that clinically approved antipsychotic compounds may be repurposed for use in CNS injured patients.

Lumican promotes corneal epithelial wound healing

Lumican regulates collagenous matrix assembly as a keratan sulfate proteoglycan in the cornea and is also present in the connective tissues of other organs and embryonic corneal stroma as a glycoprotein. In normal unwounded cornea, lumican is expressed by stromal keratocytes. Interestingly, injured mouse corneal epithelium ectopically and transiently expresses lumican during the early phase of wound healing, suggesting a potential lumican functionality unrelated to regulation of collagen fibrillogenesis, e.g., modulation of epithelial cell adhesion or migration. Healing of a corneal epithelial injury in lumican knockout (Lum(-/-)) mice was significantly delayed compared with Lum(+/-) mice. Addition of purified lumican to cultured medium promoted re-epithelialization and enhanced cell proliferation of wild-type mouse corneal epithelial cells in an organ culture. Therefore, administration of lumican may be beneficial for treating epithelial defects in the cornea and other tissues.

Lumican inhibits B16F1 melanoma cell lung metastasis

BACKGROUND

Lumican is a small leucine-rich proteoglycan (SLRP) of the extracellular matrix (ECM) involved in the control of melanoma growth and invasion. The aim of the present study was to analyse the role of lumican in the regulation of the development of lung metastasis.

METHODS

B16F1 melanoma cells stably transfected with lumican expressing plasmid (Lum-B16F1) were injected to syngenic mice. The lung metastasis was compared to mice injected with mock-transfected B16F1 cells (Mock-B16F1). The expression of lumican, cyclin D1, apoptotic markers, vascular endothelium growth factor (VEGF) and Von Willebrand Factor (vWF) within lung metastasis nodules was investigated by immunohistochemistry. In parallel, cells cultured in presence of lumican were assayed for apoptosis and motility.

RESULTS

We observed that the number and the size of lung metastasis nodules were significantly decreased in mice injected with Lum-B16F1 cells in comparison to Mock-B16F1 cells. This was associated with an increase of tumour cell apoptosis within metastasis nodules but the cell proliferation rate remained constant in the two mice groups. In contrast, the VEGF immunostaining and the number of blood vessels within the lung metastasis nodules were decreased in the lumican-expressing tumours. In vitro, a significant decrease of apoptotic markers in wild type B16F1 cells incubated with increasing amounts of lumican core protein was observed. In addition, pseudotubes formation on Matrigel(R) and the migratory capacity of endothelial cells was inhibited by lumican. Altogether, our results indicate that lumican decreases lung metastasis development not only by inducing tumour cell apoptosis but also by inhibiting angiogenesis.

[Axonal growth inhibition by chondroitin sulfate proteoglycans in the central nervous system]

Chondroitin sulphate proteoglycans (CSPG) are components of the extracellular matrix, consisting of peptides chemically attached covalently to chains of glycosaminoglycans. There are 4 families of CSPG including lecticans, which are found mainly in the central nervous system (CNS) of vertebrates. In vitro studies have shown a negative effect of these proteoglycans on axonal growth, mediated by depolymerization of actin filaments in the neuronal cytoskeleton. In some neurodegenerative diseases, and especially after traumatic injuries of adult CNS, there are increased levels of CSPG expression. Axonal growth inhibition by CSPG has been observed also in vivo, and therefore a strategy aimed to counteract the inhibition of axonal growth might lead to new therapies designed to restore neural circuits. There is compelling in vivo evidence that CSPG degradation by Chondroitinase ABC allows both axonal growth and functional recovery in models of injury in the mammalian CNS. These data suggest that manipulation of the response to damage could result in effective ways to promote recovery of nerve functions in neurological disorders that affect humans, such as spinal cord lesions or Parkinson disease.

Two faces of chondroitin sulfate proteoglycan in spinal cord repair: a role in microglia/macrophage activation

BACKGROUND

Chondroitin sulfate proteoglycan (CSPG) is a major component of the glial scar. It is considered to be a major obstacle for central nervous system (CNS) recovery after injury, especially in light of its well-known activity in limiting axonal growth. Therefore, its degradation has become a key therapeutic goal in the field of CNS regeneration. Yet, the abundant de novo synthesis of CSPG in response to CNS injury is puzzling. This apparent dichotomy led us to hypothesize that CSPG plays a beneficial role in the repair process, which might have been previously overlooked because of nonoptimal regulation of its levels. This hypothesis is tested in the present study.

METHODS AND FINDINGS

We inflicted spinal cord injury in adult mice and examined the effects of CSPG on the recovery process. We used xyloside to inhibit CSPG formation at different time points after the injury and analyzed the phenotype acquired by the microglia/macrophages in the lesion site. To distinguish between the resident microglia and infiltrating monocytes, we used chimeric mice whose bone marrow-derived myeloid cells expressed GFP. We found that CSPG plays a key role during the acute recovery stage after spinal cord injury in mice. Inhibition of CSPG synthesis immediately after injury impaired functional motor recovery and increased tissue loss. Using the chimeric mice we found that the immediate inhibition of CSPG production caused a dramatic effect on the spatial organization of the infiltrating myeloid cells around the lesion site, decreased insulin-like growth factor 1 (IGF-1) production by microglia/macrophages, and increased tumor necrosis factor alpha (TNF-alpha) levels. In contrast, delayed inhibition, allowing CSPG synthesis during the first 2 d following injury, with subsequent inhibition, improved recovery. Using in vitro studies, we showed that CSPG directly activated microglia/macrophages via the CD44 receptor and modulated neurotrophic factor secretion by these cells.

CONCLUSIONS

Our results show that CSPG plays a pivotal role in the repair of injured spinal cord and in the recovery of motor function during the acute phase after the injury; CSPG spatially and temporally controls activity of infiltrating blood-borne monocytes and resident microglia. The distinction made in this study between the beneficial role of CSPG during the acute stage and its deleterious effect at later stages emphasizes the need to retain the endogenous potential of this molecule in repair by controlling its levels at different stages of post-injury repair.

[Proteoglycans of L6J1 myoblast extracellular matrix. Characteristics and effect on myoblast adhesion]

Proteoglycans were isolated from extracellular matrix of L6J1 rat myoblasts and their influence on myoblast adhesion was studied. Proteoglycan digestion with chondroitinase AC and heparinase III degrading the polysaccharide moieties revealed that chondroitin sulfate proteoglycans are the main class of myoblast extracellular matrix proteoglycans. Electrophoresis of enzymatically processed proteoglycans was used to examine their core proteins. Myoblast adhesion was suppressed by proteoglycans or the mixture of proteoglycans and fibronectin/extracellular matrix. When being processed with chondroitinase AC the combined substrate of fibronectin and proteoglycans lost the capability of myoblast adhesion suppression. Thus, as a result of presented work the proteoglycans of L6J1 rat myoblast extracellular matrix were isolated and purified. The main class of proteoglycans was chondroitin sulphate proteoglycans. Isolated proteoglycans suppressed myoblast adhesion and this effect was mediated by polysaccharide moieties of proteoglycans.

Overcoming Chondroitin Sulphate Proteoglycan Inhibition of Axon Growth in the Injured Brain: Lessons from Chondroitinase ABC

The presence of numerous axon-inhibitory molecules limits the capacity of injured neurons in the adult mammalian central nervous system (CNS) to regenerate damaged axons. Among others, chondroitin sulphate proteoglycans (CSPGs) enriched in glycosaminoglycan (GAG) chains, acting intracellularly via Rho GTPase activation and cytoskeletal modification, prevent axon re-growth after injury. However, axon regeneration can be induced by modulating the extrinsic environment or the intrinsic neural response to axon extension. Among other strategies, the use of chondroitinase ABC (ChABC) to degrade GAGs and decrease CSPG-associated inhibition has been analyzed. Recent reports have extended the use of this enzyme, in combination with cell transplantation or pharmacological treatment. The steady advances made in these combinations offer promising perspectives for the development of new therapies to repair the injured nervous system.

A novel role of the lumican core protein in bacterial lipopolysaccharide-induced innate immune response

Lumican is an extracellular matrix protein modified as a proteoglycan in some tissues. The core protein with leucine-rich repeats, characteristic of the leucine-rich-repeat superfamily, binds collagen fibrils and regulates its structure. In addition, we believe that lumican sequestered in the pericellular matrix interacts with cell surface proteins for specific cellular functions. Here we show that bacterial lipopolysaccharide sensing by the Toll-like receptor 4 signaling pathway and innate immune response is regulated by lumican. Primary cultures of lumican-deficient (Lum(-/-)) macrophages show impaired innate immune response to lipopolysaccharides with lower induction of tumor necrosis factor alpha (TNFalpha) and interleukin-6. Macrophage response to other pathogen-associated molecular patterns is not adversely affected by lumican deficiency, suggesting a specific role for the lumican core protein in the Toll-like receptor 4 pathway. An exogenous recombinant lumican core protein increases lipopolysaccharide-mediated TNFalpha induction and partially rescues innate immune response in Lum(-/-) macrophages. We further show that the core protein binds lipopolysaccharide. Immunoprecipitation of lumican from peritoneal lavage co-precipitates CD14, a cell surface lipopolysaccharide-binding protein that is involved in its presentation to Toll-like receptor 4. The Lum(-/-) mice are hypo-responsive to lipopolysaccharide-induced septic shock, with poor induction of pro-inflammatory cytokines, TNFalpha, and interleukins 1beta and 6 in the serum. Taken together, the data indicates a novel role for lumican in the presentation of bacterial lipopolysaccharide to CD14 and host response to this bacterial endotoxin.

Inhibition of Rho kinase (ROCK) increases neurite outgrowth on chondroitin sulphate proteoglycan in vitro and axonal regeneration in the adult optic nerve in vivo

Inhibitory molecules derived from CNS myelin and glial scar tissue are major causes for insufficient functional regeneration in the mammalian CNS. A multitude of these molecules signal through the Rho/Rho kinase (ROCK) pathway. We evaluated three inhibitors of ROCK, Y- 27632, Fasudil (HA-1077), and Dimethylfasudil (H-1152), in models of neurite outgrowth in vitro. We show, that all three ROCK inhibitors partially restore neurite outgrowth of Ntera-2 neurons on the inhibitory chondroitin sulphate proteoglycan substrate. In the rat optic nerve crush model Y-27632 dose-dependently increased regeneration of retinal ganglion cell axons in vivo. Application of Dimethylfasudil showed a trend towards increased axonal regeneration in an intermediate concentration. We demonstrate that inhibition of ROCK can be an effective therapeutic approach to increase regeneration of CNS neurons. The selection of a suitable inhibitor with a broad therapeutic window, however, is crucial in order to minimize unwanted side effects and to avoid deleterious effects on nerve fiber growth.

Chondroitin Sulfate-Derived Disaccharide Protects Retinal Cells from Elevated Intraocular Pressure in Aged and Immunocompromised Rats

PURPOSE

A disaccharide (DS) derived from the naturally occurring compound chondroitin sulfate proteoglycan (CSPG) was recently shown to have neuroprotective activity. The authors examined the ability of this compound (CSPG-DS) to protect retinal ganglion cells (RGCs) from death caused by elevated intraocular pressure (IOP).

METHODS

With the use of chronic and acute models of elevated IOP, the authors examined the effects of CSPG-DS on RGC survival in adult ( approximately 2 months old), aged (10-12 months old), and immunocompromised Lewis rats. Systemic, topical, and oral routes of administration were examined.

RESULTS

CSPG-DS protected RGCs from IOP-induced death. Treatment was effective in all three examined rat populations (normal adult, aged, and immunocompromised rats) and with all routes of administration, possibly in part through its control of microglial activity.

CONCLUSIONS

Results point to the therapeutic potential of CSPG-DS for glaucoma, particularly in elderly populations for whom disease prevalence is high.

Hyaluronic acid inhibits the adherence and growth of monolayer keratinocytes but does not affect the growth of keratinocyte epithelium

Hyaluronic acid (HA) is involved in epidermal biology but evidence for its functional significance is sparse. In this study, low-calcium monolayer and high-calcium epithelium cultures of human keratinocytes were used to study the effect of up to four different HA preparations on keratinocyte growth and on the adherence of proliferating keratinocytes onto the plastic surface coated with different matrix proteins. In suboptimally growing monolayer culture, up to 1,000 microg/ml rooster comb HA and streptococcus equi HA inhibited keratinocyte growth. Instead, all HA preparations tested did not affect the growth and migration of keratinocyte epithelium using optimal or suboptimal growth conditions. In the cell adherence assays, up to 1,000 microg/ml rooster comb HA and streptococcus equi HA inhibited the keratinocyte adherence onto the fibronectin- and collagen-coated substratum. In contrast to other HA preparations, HA from human umbilical cord did not affect the growth of monolayer keratinocytes and it increased markedly the cell adherence onto the collagen-coated substratum. This increase, however, can be attributed to chonroitin sulphate proteoglycan contaminant present in this HA preparation. In conclusion, HA can inhibit the growth and adherence of proliferating monolayer keratinocytes, but it has no apparent effect on the growth and migration of keratinocyte epithelium.

Neurotrophins support regenerative axon assembly over CSPGs by an ECM-integrin-independent mechanism

Chondroitin sulfate proteoglycans (CSPGs) and myelin-based inhibitors are the most studied inhibitory molecules in the adult central nervous system. Unlike myelin-based inhibitors, few studies have reported ways to overcome the inhibitory effect of CSPGs. Here, by using regenerating adult dorsal root ganglion (DRG) neurons, we show that chondroitin sulfate proteoglycans inhibit axon assembly by a different mechanism from myelin-based inhibitors. Furthermore, we show that neither Rho inhibition nor cAMP elevation rescues extracellular factor-induced axon assembly inhibited by CSPGs. Instead, our data suggest that CSPGs block axon assembly by interfering with integrin signaling. Surprisingly, we find that nerve growth factor (NGF) promotes robust axon growth of regenerating DRG neurons over CSPGs. We have found that, unlike naive neurons that require simultaneous activation of neurotrophin and integrin pathways for axon assembly, either neurotrophin or integrin signaling alone is sufficient to induce axon assembly of regenerating neurons. Thus, our results suggest that the ability of NGF to overcome CSPG inhibition in regenerating neurons is probably due to the ability of regenerating neurons to assemble axons using an integrin-independent pathway. Finally, our data show that the GSK-3β-APC pathway, previously shown to mediate developing axon growth, is also necessary for axon regeneration.

Human intervertebral disc cells promote nerve growth over substrata of human intervertebral disc aggrecan

STUDY DESIGN

Coculture assays of the migration and interaction of human intervertebral disc cells and chick sensory nerves on alternate substrata of collagen and aggrecan.

OBJECTIVE

To examine the effects of aggrecan on disc cell migration, how disc cells and sensory nerves interact, and whether disc cells affect previously reported inhibitory effects of aggrecan on sensory nerve growth.

SUMMARY OF BACKGROUND DATA

Human intervertebral disc aggrecan is inhibitory to sensory nerve growth in vitro, suggesting that a loss of aggrecan from the disc may have a role in the increased innervation seen in disc degeneration. Endothelial cells that appear to co-migrate with nerves into degenerated intervertebral disc express neurotrophic factors, but the effects of disc cells on nerve growth are not known.

METHODS

Human disc cells were seeded onto tissue culture plates that had been coated with type I collagen and human intervertebral disc aggrecan. Explants of chick dorsal root ganglions (DRGs) were subsequently added to the plates and sensory neurite outgrowth stimulated by the addition of nerve growth factor. Time-lapse video and fluorescence microscopy were used to examine the migration and interaction of the disc cells and sensory neurites, in the context of the different matrix substrata. The effects of disc cell conditioned medium on nerve growth were also examined.

RESULTS

Disc cells spread and migrated on collagen until they encountered the aggrecan substrata, where some cells, but not all, were repelled. In coculture, DRG neurites extended onto the collagen/disc cells until they encountered the aggrecan, where, like the disc cells, many were repelled. However, in the presence of disc cells, some neurites were able to cross onto this normally inhibitory substratum. The number of neurite crossings onto aggrecan correlated significantly with the number of disc cells present on the aggrecan. In control experiments using DRG alone, all extending neurites were repelled at the collagen/aggrecan border. Conditioned medium from disc cell cultures stimulated DRG neurite outgrowth on collagen but did not increase neurite crossing onto aggrecan substrata.

CONCLUSIONS

Human disc cells migrate across aggrecan substrata that are repellent to sensory DRG neurites. Disc cells synthesize neurotrophic factors in vitro that promote neurite outgrowth. Furthermore, the presence of disc cells in coculture with DRG partially abrogates the inhibitory effects of aggrecan on nerve growth. These findings have important implications for the regulation of nerve growth into the intervertebral disc, but whether disc cells promote nerve growth in vivo remains to be determined.

The accumulation of intracellular ITEGE and DIPEN neoepitopes in bovine articular chondrocytes is mediated by CD44 internalization of hyaluronan

OBJECTIVE

A dramatic loss of aggrecan proteoglycan from cartilage is associated with osteoarthritis. The fate of residual G1 domains of aggrecan is unknown, but inefficient turnover of these domains may impede subsequent repair and retention of newly synthesized aggrecan. Thus, the objective of this study was to determine whether ITEGE- and DIPEN-containing G1 domains, generated in situ, are internalized by articular chondrocytes, and whether these events are dependent on hyaluronan (HA) and its receptor, CD44.

METHODS

ITEGE and DIPEN neoepitopes were detected by immunofluorescence staining of bovine articular cartilage chondrocytes treated with or without interleukin-1alpha (IL-1alpha). Additionally, purified ITEGE- or DIPEN-containing G1 domains were aggregated with HA and then added to articular chondrocytes, articular chondrocytes transfected with CD44delta67, or COS-7 cells transfected with or without full-length CD44. Internalized epitopes were distinguished by their resistance to extensive trypsinization of the cell surface.

RESULTS

Both ITEGE and DIPEN were visualized within the extracellular cell-associated matrix of chondrocytes as well as within intracellular vesicles. Following trypsinization, the intracellular accumulation of both epitopes was clearly visible. IL-1 treatment increased extracellular as well as intracellular ITEGE epitope accumulation. Once internalized, the ITEGE neoepitope became localized within the nucleus and displayed little colocalization with HA, DIPEN, or other G1 domain epitopes. The internalization of both ITEGE and DIPEN G1 domains was dependent on the presence of HA and CD44.

CONCLUSION

One important mechanism for the elimination of residual G1 domains following extracellular degradation of aggrecan is CD44-mediated co-internalization with HA.

Chondroitinase ABC combined with neural stem/progenitor cell transplantation enhances graft cell migration and outgrowth of growth-associated protein-43-positive fibers after rat spinal cord injury

We previously reported that the transplantation of neural stem/progenitor cells (NSPCs) can contribute to the repair of injured spinal cord in adult rats and monkeys. In some cases, however, most of the transplanted cells adhered to the cavity wall and failed to migrate and integrate into the host spinal cord. In this study we focused on chondroitin sulfate proteoglycan (CSPG), a known constituent of glial scars that is strongly expressed after spinal cord injury (SCI), as a putative inhibitor of NSPC migration in vivo. We hypothesized that the digestion of CSPG by chondroitinase ABC (C-ABC) might promote the migration of transplanted cells and neurite outgrowth after SCI. An in vitro study revealed that the migration of NSPC-derived cells was inhibited by CSPG and that this inhibitory effect was attenuated by C-ABC pre-treatment. Consistently, an in vivo study of C-ABC treatment combined with NSPC transplantation into injured spinal cord revealed that C-ABC pre-treatment promoted the migration of the transplanted cells, whereas CSPG-immunopositive scar tissue around the lesion cavity prevented their migration into the host spinal cord in the absence of C-ABC pre-treatment. Furthermore, this combined treatment significantly induced the outgrowth of a greater number of growth-associated protein-43-positive fibers at the lesion epicentre, compared with NSPC transplantation alone. These findings suggested that the application of C-ABC enhanced the benefits of NSPC transplantation for SCI by reducing the inhibitory effects of the glial scar, indicating that this combined treatment may be a promising strategy for the regeneration of injured spinal cord.

Fibulin-2 is present in murine vascular lesions and is important for smooth muscle cell migration

OBJECTIVE

The vascular extracellular matrix (ECM) can affect smooth muscle cell (SMC) adhesion, migration and proliferation-events that are important during the atherosclerotic process. Fibulin-2 is a member of the ECM protein family of fibulins and has been found to cross-link versican/hyaluronan complexes, an ECM network that has been suggested to be important during tissue repair. In this study we have analysed the presence of fibulin-2 in two different models of murine vascular lesions. We have also examined how the fibulin-2/versican network influences SMC migration.

METHODS

Presence of fibulin-2 was analysed by immunohistochemistry in atherosclerotic aortas and in mechanically injured carotid arteries from mice. Fibulin-2 protein levels were also studied by Western blotting during rat aortic SMC phenotypic modulation in vitro. The importance of a fibulin-2/versican interaction for SMC migration was studied in the presence of two inhibiting peptides (FN III 3-5 and aggrecan C-type lectin-like domain).

RESULTS

Fibulin-2 is expressed in SMC rich regions of atherosclerotic lesions where it colocalises with versican and hyaluronan. It is also present in injury-induced vascular lesions and is upregulated during SMC phenotypic modulation in cell culture. Moreover, treatments with peptides that block the interaction between versican and fibulin-2 inhibit SMC migration in vitro.

CONCLUSIONS

Fibulin-2 can be produced by SMC as a response to injury and may participate in the ECM organisation that regulates SMC migration during vessel wall repair.

A sulfated disaccharide derived from chondroitin sulfate proteoglycan protects against inflammation-associated neurodegeneration

Chondroitin sulfate proteoglycan (CSPG), a matrix protein that occurs naturally in the central nervous system (CNS), is considered to be a major inhibitor of axonal regeneration and is known to participate in activation of the inflammatory response. The degradation of CSPG by a specific enzyme, chondroitinase ABC, promotes repair. We postulated that a disaccharidic degradation product of this glycoprotein (CSPG-DS), generated following such degradation, participates in the modulation of the inflammatory responses and can, therefore, promote recovery in immune-induced neuropathologies of the CNS, such as experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune uveitis (EAU). In these pathologies, the dramatic increase in T cells infiltrating the CNS is far in excess of the numbers needed for regular maintenance. Here, we show that CSPG-DS markedly alleviated the clinical symptoms of EAE and protected against the neuronal loss in EAU. The last effect was associated with a reduction in the numbers of infiltrating T cells and marked microglia activation. This is further supported by our in vitro results indicating that CSPG-DS attenuated T cell motility and decreased secretion of the cytokines interferon-gamma and tumor necrosis factor-alpha. Mechanistically, these effects are associated with an increase in SOCS-3 levels and a decrease in NF-kappaB. Our results point to a potential therapeutic modality, in which a compound derived from an endogenous CNS-resident molecule, known for its destructive role in CNS recovery, might be helpful in overcoming inflammation-induced neurodegenerative conditions.

BMP stimulation of alkaline phosphatase activity in pluripotent mouse C2C12 cells is inhibited by dermatopontin, one of the most abundant low molecular weight proteins in demineralized bone matrix

Demineralized bone matrix (DBM) is a complex mixture of osteoinductive bone morphogenetic proteins (BMPs), as well as BMP-binding proteins that regulate BMP bioactivity and localization. Our aim was to use modern proteomic methods to identify additional BMP-binding proteins in DBM, with initial emphasis on the most abundant. Relatively large, water-soluble noncollagenous proteins (NCPs) were preferentially extracted from DBM with alkalinized urea. The insoluble residue, which contained the BMP activity, was extracted with GuHCl/CaCl2, dialyzed versus citrate, defatted, resuspended in GuHCl, dialyzed sequentially against Triton X-100 and water, pelleted, and lyophilized. The proteins in this pellet were fractionated by hydroxyapatite affinity chromatography. Proteins that copurified with BMP bioactivity were separated by SDS-PAGE. Distinct bands were excised, and the proteins in them were reduced and alkylated, digested with trypsin, eluted, and subjected to MALDI/ToF MS (matrix-assisted laser-desorption ionization time-of-flight mass spectrometry). Computer-assisted peptide fingerprint analysis of the MS profiles was used to identify C-terminal lysine-6-oxidase; dermatopontin (DPT); histones H2A2, H2A3, and H2B; and trace amounts of gamma-actin. DPT is a 22-kDa, tyrosine-rich acidic matrix protein not previously recognized to be among the most abundant small proteins to copurify with BMP bioactivity in DBM. We tested the effects of DPT on BMP-2 stimulation of alkaline phosphatase (ALP) activity in C2C12 cells. BMP-2 stimulated ALP activity in C2C12 cells by 6.2-fold above basal levels. DPT alone had no effect on ALP activity in C2C12 cells. When added with BMP-2, DPT blocked 40% of the stimulatory effect of BMP-2 on ALP activity in C2C12 cells. DPT is an abundant protein in DBM, and it can inhibit the stimulatory effects of BMP-2 on ALP activity in C2C12 cells.

Axon regeneration in peripheral nerves is enhanced by proteoglycan degradation

Regeneration of axons in the peripheral nervous system is enhanced by the removal of glycosaminoglycan side chains (GAGs) of chondroitin sulfate proteoglycans. However, some axons regenerate poorly despite such treatment, suggesting the existence of additional inhibitors. We compared the effects of enzymatic removal of GAGs from chondroitin sulfate proteoglycans versus two other proteoglycan species, heparan sulfate and keratan sulfate proteoglycans, on the regeneration of peripheral axons. Common fibular (CF) nerves of thy-1-YFP-H mice were cut and repaired using short segments of CF nerves harvested from wild-type littermates and pre-treated with a GAG-degrading enzyme for 1 h prior to nerve repair. Axonal regeneration was assayed by measuring the lengths of profiles of YFP+ axons in optical sections of the grafted nerves 1 week later. Except for grafts treated with keratanase, more and longer axon profiles were encountered in enzyme-treated grafts than in control grafts. Heparinase III treatments induced the greatest number of axons to enter into the graft. The proportions of axon profiles longer than 1000 microm were greater in grafts treated with chondroitinase ABC or heparinase I, but not with either keratanase or heparinase III. More regenerative sprouts were observed after treatment with heparinase I than any other enzymes. Treatment with a mixture of all four enzymes resulted in an enhancement of axon regeneration which was greater than that observed after treatment with any of the enzymes individually. The effects of chondroitinase ABC and heparinase III were correlated with specific GAG degradation. We believe that enzymatic removal of GAGs is especially effective in promoting the ability of regenerating axons to select their pathway in the distal stump (or nerve graft) and, in the case of chondroitinase ABC or heparinase I, it may also promote growth within that pathway.

Pleiotrophin inhibits HIV infection by binding the cell surface-expressed nucleolin

The growth factor pleiotrophin (PTN) has been reported to bind heparan sulfate and nucleolin, two components of the cell surface implicated in the attachment of HIV-1 particles to cells. Here we show that PTN inhibits HIV-1 infection by its capacity to inhibit HIV-1 particle attachment to the surface of permissive cells. The beta-sheet domains of PTN appear to be implicated in this inhibitory effect on the HIV infection, in particular the domain containing amino acids 60-110. PTN binding to the cell surface is mediated by high and low affinity binding sites. Other inhibitors of HIV attachment known to bind specifically surface expressed nucleolin, such as the pseudopeptide HB-19 and the cytokine midkine prevent the binding of PTN to its low affinity-binding site. Confocal immunofluorescence laser microscopy revealed that the cross-linking of surface-bound PTN with a specific antibody results in the clustering of cell surface-expressed nucleolin and the colocalization of both PTN and nucleolin signals. Following its binding to surface-nucleolin, PTN is internalized by a temperature sensitive mechanism, a process which is inhibited by HB-19 and is independent of heparan and chondroitin sulfate proteoglycans. Nevertheless, proteoglycans might play a role in the concentration of PTN on the cell surface for a more efficient interaction with nucleolin. Our results demonstrate for the first time that PTN inhibits HIV infection and suggest that the cell surface-expressed nucleolin is a low affinity receptor for PTN binding to cells and it is also implicated in PTN entry into cells by an active process.

Extracellular Muscle Myosin II Promotes Sensory Axon Formation

Myosin II is an intracellular force-generating enzyme with no known extracellular action. In the course of experiments involving trituration loading of skeletal myosin II into embryonic sensory neurons we observed that extracellular application of myosin II to neurons resulted in a robust increase in the number of axons initiated by each neuron, but did not alter the rate of axon extension. Substratum bound myosin II in the presence of laminin was sufficient to elicit increases in axon formation. However, in the absence of laminin, extracellular myosin II alone was not sufficient to promote axon formation, although it allowed neuron survival in the presence of neurotrophin. Myosin II promoted the attachment of neurons to the substratum in the absence or presence of laminin. In addition to promoting the initiation of axons, extracellular myosin II also increased the frequency of axon collateral branching. Finally, extracellular myosin II did not affect growth cone collapse in response to semaphorin-IIIA, but attenuated the inhibitory action of chondroitin sulfate proteoglycans on axon extension. Surprisingly, these results demonstrate that extracellular myosin II promotes attachment of neurons and increases axon formation and branching. The potential significance of these observations is discussed in the context of myosin II release from injured muscle and a previous demonstration of extracellular myosin II association with the extracellular matrix.

Regulation of MDR1 expression and drug resistance by a positive feedback loop involving hyaluronan, phosphoinositide 3-kinase, and ErbB2

Multidrug resistance is a potent barrier to effective, long term therapy in cancer patients. It is frequently attributed to enhanced expression of multidrug transporters or to the action of receptor kinases, such as ErbB2, and downstream anti-apoptotic signaling pathways, such as the phosphoinositide 3-kinase/Akt pathway. However, very few connections have been made between receptor kinases or anti-apoptotic pathways and multidrug transporter expression or function. Data presented herein show that constitutive interaction of the pericellular polysaccharide, hyaluronan, with its receptor, CD44, regulates assembly and activation of an ErbB2-containing signaling complex, which in turn stimulates phosphoinositide 3-kinase activity in multidrug-resistant MCF-7/Adr human breast carcinoma cells. Phosphoinositide 3-kinase activates Akt and downstream anti-apoptotic events, which contribute to drug resistance. However, hyaluronan and phosphoinositide 3-kinase stimulate expression of the multidrug transporter, MDR1 (P-glycoprotein), in an interdependent, but Akt-independent, manner. Furthermore, constitutively active phosphoinositide 3-kinase, but not Akt, stimulates hyaluronan production. These Akt-independent effects are dominant over the effects of Akt on doxorubicin resistance in MCF-7/Adr cells. Thus hyaluronan, phosphoinositide 3-kinase, and ErbB2 form a positive feedback loop that strongly amplifies MDR1 expression and regulates drug resistance in these cells. This pathway may also be important in progression of other malignant characteristics. These results illustrate the potential importance of hyaluronan as a therapeutic target in multidrug-resistant carcinomas.

Soluble lumican glycoprotein purified from human amniotic membrane promotes corneal epithelial wound healing

PURPOSE

To purify and characterize the glycoprotein lumican, isolated from human amniotic membrane (AM), and to examine its efficacy in treating corneal epithelium debridement.

METHODS

An affinity-purified, anti-human lumican antibody-conjugated protein A Sepharose column was used to purify soluble lumican protein from human AM. The purified AM lumican was characterized by two-dimensional and SDS gel electrophoresis, plus Western blot analysis with anti-lumican antibody. The effects of lumican on corneal epithelial wound healing were examined in an organ culture mouse eye model.

RESULTS

Lumican was found to be abundantly present in the stroma of human AM. It was extracted from the AM by isotonic, 1 M NaCl, and 4 M guanidine HCl solutions, suggesting that it is present in both the soluble and matrix-bound states. In two-dimensional gel electrophoresis, the 50-kDa human amniotic lumican purified by antibody-conjugated affinity chromatography migrated in a smear between pH 3.0 and 6.0. After endo-beta-galactosidase digestion, it existed as a single core protein at pH 6.0, suggesting that native human amniotic lumican is a glycoprotein with short sugar moiety. Addition of purified human AM lumican to cultured medium promoted re-epithelialization and enhanced cell proliferation of wild-type mouse corneal epithelial cells in an organ culture. In lumican-knockout (lum(-/-)) mice, the effect of human lumican on promoting corneal epithelial wound healing was even more dramatic than in wild-type mice.

CONCLUSIONS

The diversified functions of lumican include modulation of epithelial cells in wound healing and serving as an extracellular matrix component. Administration of lumican may be beneficial for treating epithelial defects in the cornea and other tissues.

Retinal ganglion cell neurotrophin receptor levels and trophic requirements following target ablation in the neonatal rat

Superior colliculus (SC) ablation in neonatal rats results in a rapid increase in retinal ganglion cell (RGC) death. This injury-induced death is reduced by exogenous brain-derived neurotrophic factor or neurotrophin-4/5 (NT-4/5), but the protective effect of these molecules is transient, delaying but not preventing neuronal loss. We sought to discover why neurotrophins only temporarily reduce RGC death after target ablation, focusing on changes in neurotrophin receptor expression and possible changes in growth factor dependency. In unlesioned rats, receptor tyrosine kinase B (trkB) immunohistochemistry revealed no change in the number of trkB positive cells in the RGC layer 24 h after intraocular NT-4/5 injection. However, after SC lesions there were significantly less immunoreactive cells and, surprisingly, even fewer immunoreactive cells in NT-4/5 injected eyes. Semi-quantitative confocal analysis of immunofluorescence intensity revealed an increase in trkB staining in the RGC layer in unlesioned rats 24 h after NT-4/5 injection, whereas in SC-lesioned animals exposed to NT-4/5 there was a significant decrease in staining. To determine whether injured neonatal RGCs can switch their trophic requirements, different doses of ciliary neurotrophic factor were given intraocularly, either alone or combined with NT-4/5. We also tested an SC-derived chondroitin sulfate proteoglycan that has been reported to promote neonatal RGC survival. None of these interventions reduced lesion-induced RGC death 24 or 36 h after SC ablation. In summary, we show that developing RGCs do not shift their trophic dependence to other survival factors following injury; rather, the application of neurotrophins causes a down-regulation of the cognate trkB receptor, presumably altering the long-term responsiveness of neonatal RGCs to exogenous neurotrophins. These data highlight the difficulty in promoting long-term neuronal survival when using one-off administration of recombinant growth factors.

V3 versican isoform expression alters the phenotype of melanoma cells and their tumorigenic potential

Versican is a large chondroitin sulfate proteoglycan produced by several tumor cell types, including malignant melanoma. The expression of increased amounts of versican in the extracellular matrix may play a role in tumor cell growth, adhesion and migration. We have expressed the V3 isoform of versican in human and canine melanoma cell lines. Retroviral overexpression of V3 did not change the morphology of any of the cell lines but markedly reduces cell growth in the V3 versican expressing melanoma cells. The V3-overexpressing melanoma cells retain their diminished growth potential in vivo because primary tumors arising from these cell lines growth more slowly than their vector only counterparts. This effect was accompanied by increases in cell adhesion on hyaluronan and an enhanced ability to migrate on hyaluronan-coated transwell chambers. This enhanced migration is blocked when cells are preincubated with soluble hyaluronan, or anti-CD44 antibodies, suggesting that V3 acts by altering the hyaluronan-CD44 interaction. Hyaluronan content and CD44 expression are not altered in V3-overexpressing cells compared to vector-transduced cells. Our results show that V3 overproduction modulates the in vitro behavior of human and canine melanoma cell lines and reduces their tumorigenicity in vivo.

A disaccharide derived from chondroitin sulphate proteoglycan promotes central nervous system repair in rats and mice

Chondroitin sulphate proteoglycan (CSPG) inhibits axonal regeneration in the central nervous system (CNS) and its local degradation promotes repair. We postulated that the enzymatic degradation of CSPG generates reparative products. Here we show that an enzymatic degradation product of CSPG, a specific disaccharide (CSPG-DS), promoted CNS recovery by modulating both neuronal and microglial behaviour. In neurons, acting via a mechanism that involves the PKCalpha and PYK2 intracellular signalling pathways, CSPG-DS induced neurite outgrowth and protected against neuronal toxicity and axonal collapse in vitro. In microglia, via a mechanism that involves ERK1/2 and PYK2, CSPG-DS evoked a response that allowed these cells to manifest a neuroprotective phenotype ex vivo. In vivo, systemically or locally injected CSPG-DS protected neurons in mice subjected to glutamate or aggregated beta-amyloid intoxication. Our results suggest that treatment with CSPG-DS might provide a way to promote post-traumatic recovery, via multiple cellular targets.

Melanoma chondroitin sulfate proteoglycan enhances FAK and ERK activation by distinct mechanisms

Melanoma chondroitin sulfate proteoglycan (MCSP) is an early cell surface melanoma progression marker implicated in stimulating tumor cell proliferation, migration, and invasion. Focal adhesion kinase (FAK) plays a pivotal role in integrating growth factor and adhesion-related signaling pathways, facilitating cell spreading and migration. Extracellular signal–regulated kinase (ERK) 1 and 2, implicated in tumor growth and survival, has also been linked to clinical melanoma progression. We have cloned the MCSP core protein and expressed it in the MCSP-negative melanoma cell line WM1552C. Expression of MCSP enhances integrin-mediated cell spreading, FAK phosphorylation, and activation of ERK1/2. MCSP transfectants exhibit extensive MCSP-rich microspikes on adherent cells, where it also colocalizes with α4 integrin. Enhanced activation of FAK and ERK1/2 by MCSP appears to involve independent mechanisms because inhibition of FAK activation had no effect on ERK1/2 phosphorylation. These results indicate that MCSP may facilitate primary melanoma progression by enhancing the activation of key signaling pathways important for tumor invasion and growth.

The small leucine-rich proteoglycan lumican inhibits melanoma progression

Lumican is a member of the small leucine-rich proteoglycan (SLRP) family. It contributes to the organisation of the collagen network and plays an important role in cell migration and tissue repair. The present study aimed to determine the influence of lumican expression on adhesion, anchorage-dependent and -independent growth, migration, in vitro invasion and in vivo melanoma growth. For that purpose, B16F1 mouse melanoma cells were stably transfected with an expression plasmid containing the complete lumican cDNA. Lumican expression by tumor cells did not change the proliferative activity of mouse melanoma cells in monolayer culture and did not influence either cell adhesion to extracellular matrix gel or type I collagen or cell spreading on these substrates. In contrast, lumican-transfected cells were characterized by a strong reduction of their anchorage-independent proliferation in agarose gel and capacity to invade extracellular matrix gel. After subcutaneous injections of transfected B16F1 cells in syngenic mice, lumican expression significantly decreased subcutaneous tumor formation in vivo, with a concomitant decrease of cyclin D1 expression. Lumican induced and/or increased the apoptosis of B16F1 cells. The results suggest that lumican is involved in the control of melanoma growth and invasion and may be considered, like decorin, as an anti-tumor factor from the extracellular matrix.

Regulation of RPTPbeta/phosphacan expression and glycosaminoglycan epitopes in injured brain and cytokine-treated glia

Several chondroitin sulfate proteoglycans (CSPGs) are upregulated after CNS injury and are thought to limit axonal regeneration in the adult mammalian CNS. Therefore, we examined the expression of the CSPG, receptor protein tyrosine phosphatase beta (RPTPbeta)/phosphacan, after a knife lesion to the cerebral cortex and after treatment of glial cultures with regulatory factors. The three splice variants of this CSPG gene, the secreted isoform, phosphacan, and the two transmembrane isoforms, the long and short RPTPbeta, were examined. Western blot and immunostaining analysis of injured and uninjured tissue revealed a transient decrease of phosphacan protein levels, but not of short RPTPbeta, in the injured tissue from 1 to 7 days postlesion (dpl). By real time RT-PCR, we show that phosphacan and long RPTPbeta mRNA levels are transiently down-regulated at 2 dpl, unlike those of short RPTPbeta which increased after 4 dpl. In contrast to the core glycoprotein, the phosphacan chondroitin sulfate (CS) glycosaminoglycan epitope DSD-1 was up-regulated after 7 dpl. Phosphacan was expressed by cultivated astrocytes and oligodendrocyte precursors but was more glycanated in oligodendrocyte precursors, which produce more of DSD-1 epitope than astrocytes. Epidermal growth factor/transforming growth factor alpha strongly increased the astrocytic expression of long RPTPbeta and phosphacan and slightly the short RPTPbeta protein levels, while interferon gamma and tumor necrosis factor alpha reduced astrocytic levels of phosphacan, but not of the receptor forms. Examining the effects of phosphacan on axon growth from rat E17 cortical neurons, we found that phosphacan stimulates outgrowth in a largely CS dependent manner, while it blocks the outgrowth-promoting effects of laminin through an interaction that is not affected by removal of the CS chains. These results demonstrate complex injury-induced modifications in phosphacan expression and glycanation that may well influence axonal regeneration and repair processes in the damaged CNS.

The globular domains of PG-M/versican modulate the proliferation-apoptosis equilibrium and invasive capabilities of tumor cells

To dissect the role of the globular domains of PGM/versican--a large hyaluronan binding proteoglycan (PG) enriched in tumor lesions--we have stably transduced a human leiomyosarcoma cell line with either the G1 or G3 domain of the PG and subsequently assayed the effect of this manipulation on several cellular processes in vitro and in vivo. G1- and G3-overexpressing cells were found to exhibit an enhanced growth that was more accentuated in the absence of serum components and was seen both when cells were cultured on ECM substrates and in the absence of ECM anchorage. Accordingly, if inoculated subcutaneously into nude mice, G1 transfectants formed larger tumor masses than control cells at the site of implantation, albeit after a certain latency period. Upon binding to cell surface CD44, proliferation of G1-, but not G3-, overexpressing cells were dose dependently inhibited by exogenous hyaluronan (HA) or HA fragments. G1- and G3-transduced cells did not differ in their intrinsic ability to adhere and migrate on various purified ECM components, whereas G1-overproducing sarcoma cells were more invasive than the corresponding G3 mutants, and their locomotion was perturbed by exogenous HA. The augmented anchorage-independent growth exhibited solely by G1-transduced was largely ascribable to a reduced apoptotic rate, thereby indicating a shift in the proliferation--apoptosis equilibrium of the cells toward the former. In fact, G1-overexpressing cells appeared resistant to both cytotoxic drug-induced and Fas-dependent programmed cell death, and this resistance implicated mitochondrial apoptotic genes. The results indicate that the terminal domains of versican may differentially control propagation of tumor cells and diversely modulate their responses to environmental HA.

PKC mediates inhibitory effects of myelin and chondroitin sulfate proteoglycans on axonal regeneration

Successful axon regeneration in the mammalian central nervous system (CNS) is at least partially compromised due to the inhibitors associated with myelin and glial scar. However, the intracellular signaling mechanisms underlying these inhibitory activities are largely unknown. Here we provide biochemical and functional evidence that conventional isoforms of protein kinase C (PKC) are key components in the signaling pathways that mediate the inhibitory activities of myelin components and chondroitin sulfate proteoglycans (CSPGs), the major class of inhibitors in the glial scar. Both the myelin inhibitors and CSPGs induce PKC activation. Blocking PKC activity pharmacologically and genetically attenuates the ability of CNS myelin and CSPGs to activate Rho and inhibit neurite outgrowth. Intrathecal infusion of a PKC inhibitor, Gö6976, into the site of dorsal hemisection promotes regeneration of dorsal column axons across and beyond the lesion site in adult rats. Thus, perturbing PKC activity could represent a therapeutic approach to stimulating axon regeneration after brain and spinal cord injuries.

Directed nerve outgrowth is enhanced by engineered glial substrates

In the present study, the influence of astrocyte alignment on the direction and length of regenerating neurites was examined in vitro. Astrocytes were experimentally manipulated by different approaches to create longitudinally aligned monolayers. When cultured on the aligned monolayers, dorsal root ganglion neurites grew parallel to the long axis of the aligned astrocytes and were significantly longer than controls. Engineered monolayers expressed linear arrays of fibronectin, laminin, neural cell adhesion molecule, and chondroitin sulfate proteoglycan that were organized parallel to one another, suggesting that a particular spatial arrangement of these molecules on the astrocyte surface may be necessary to direct nerve regeneration in vivo. In contrast, no bias in directional outgrowth was observed for neurites growing on unorganized monolayers. The results suggest that altering the organization of astrocytes and their scar-associated matrix at the lesion site may be used to influence the direction and the length of adjacent regenerating axons in the damaged brain and spinal cord.

Chondroitin sulfate anticoagulant activity is linked to water transfer: relevance to proteoglycan structure in atherosclerosis

OBJECTIVE

Changes in chondroitin sulfate (CS) proteoglycan (PG) during atherosclerosis are associated with chronic inflammatory changes and increased incidence of thrombosis. To explore how glycosaminoglycan changes could influence the thrombogenicity of atherosclerotic lesions, water-transfer reactions were examined during activation of antithrombin by CS.

METHODS AND RESULTS

Advanced type IV atherosclerotic lesions prone to thrombosis contained CSPG (versican) with undersulfated CS relative to CS of the adjacent healthy aorta. Approximately 11% of the CS disaccharide in versican from healthy arteries was oversulfated, but this proportion decreased markedly to 3% in atherosclerotic lesions. Oversulfated CS functionally bound antithrombin with a dissociation constant of 3.3+/-1.9 micromol/L. Measured by osmotic stress (OS) techniques with an approximately 26-A probe, the reaction was linked to transfer of approximately 2500 mol water per mole of coagulation factor Xa inhibited. Under OS, the anticoagulant efficiency of CS was 1.3 (micromol/L)(-1) x s(-1), approximately 5- and 15-fold higher than heparan sulfate efficiency measured under OS and standard conditions, respectively.

CONCLUSIONS

Decreased sulfation of high molecular weight CSPG in the advancing atherosclerotic lesions may predispose the lesions to thrombosis by disrupting osmotic regulation, limiting avidity for antithrombin and decreasing activation efficiency.

Neurite elongation on chondroitin sulfate proteoglycans is characterized by axonal fasciculation

In the developing or regenerating nervous system, migrating growth cones are exposed to regulatory molecules that positively and/or negatively affect guidance. Chondroitin sulfate proteoglycans (CSPGs) are complex macromolecules that are typically negative regulators of growth cone migration in vivo and in vitro. However, in certain cases, neurites sometimes traverse regions expressing relatively high levels of CSPGs, seemingly a paradox. In our continuing efforts to characterize CSPG inhibition in vitro, we manipulated the ratio of CSPGs to growth-promoting laminin-1 to produce a substratum that supports outgrowth of a subpopulation of dorsal root ganglia (DRG) neurites, while still being inhibitory to other populations of DRG neurons [Exp. Neurol. 109 (1990), 111; J. Neurobiol. 51 (2002), 285]. This model comprises a useful tool in the analysis of mechanisms of growth cone guidance and is particularly useful to analyze how CSPGs can be inhibitory under some conditions, and growth permissive under others. We grew embryonic (E9-10) chicken DRG neurons on nervous system-isolated, substratum-bound CSPGs at a concentration that supports an intermittent pattern of outgrowth, alternating with regions adsorbed with growth-promoting laminin-1 alone, and analyzed outgrowth behaviors qualitatively and quantitatively. A novel finding of the study was that DRG neurites that elongated onto CSPGs were predominantly fasciculated, but immediately returned to a defasciculated state upon contact with laminin-1. Further, cursory inspection suggests that outgrowth onto CSPGs may be initially accomplished by pioneer axons, along which subsequent axons migrate. The outgrowth patterns characterized in vitro may accurately reflect outgrowth in vivo in locations where inhibitory CSPGs and growth-promoting molecules are coexpressed, e.g., in the developing retina where fasciculated outgrowth may be instrumental in the guidance of retinal ganglion cells from the periphery to the optic fissure.

Phosphacan and neurocan are repulsive substrata for adhesion and neurite extension of adult rat dorsal root ganglion neurons in vitro

Phosphacan (PC) and neurocan (NC) are major chondroitin sulfate proteoglycans (CS-PGs) in nervous tissue and are involved in the modulation of cell adhesion and neurite outgrowth during neural development and regeneration. In the present study, we examined the effects of PC and NC on the attachment and neurite extension of adult rat dorsal root ganglion (DRG) neurons in vitro. Treatment with PC and NC on poly-L-lysine (PL) significantly impaired both neuronal attachment and neurite extension in a concentration-dependent manner (10 microg/ml > 1 microg/ml >> 0.1 microg/ml), and they were partially suppressed by chondroitinase ABC (ChABC) digestion. The CS-PGs applied to culture medium (1 microg/ml) also displayed inhibitory effects on neurite extension, which were not altered by ChABC treatment. These results show that PC and NC are repulsive substrata for adhesion and neurite regeneration of adult DRG neurons in vitro and suggest that both chondroitin sulfate moieties and core proteins are responsible for the inhibitory actions of the CS-PGs. We also conducted immunohistochemical analyses with the monoclonal antibodies to core proteins of PC (mAb 6B4) and NC (mAb 1G2), which revealed that only a few neurons in the DRG section were stained with these antibodies. In contrast, most DRG neurons at different stages (12 h, 1 day, 2 days, and 4 days) in culture were immunoreactive to mAb 6B4 and mAb 1G2. Taking these findings together, it is plausible that both CS-PGs expressed in the cultured neurons may play a role in the modulation of attachment, survival, and neurite regeneration.

Extracellular matrix effects on neurosphere cell motility

There is a paucity of information on the roles of extracellular matrix (ECM) and substrate molecules in general with regard to the growth and differentiation of neural stem and progenitor cells. There are well-established findings of a dense, presumably astrocyte-derived ECM in the persistently neurogenic subependymal zone and its migratory extension the rostral migratory stream. Cells cultured from this region, as well as from early postnatal cerebellum, generate multipotent neurospheres, but at present there is little information as to the ECM regulation of these neural stem cell populations. The present study examined the behavior of cerebellar-derived neurospheres on the matrix components laminin, fibronectin, and chondroitin sulfate proteoglycan. The results showed that laminin and fibronectin significantly increase cell migration velocity as compared to CSPG. Fibronectin effected a maximal velocity after 48 h, whereas maximal velocity on laminin and CSPG was not reached until 72 h. Both laminin and fibronectin were very permissive substrates for cellular outgrowth. Chondroitin sulfate proteoglcyan showed a significant inhibition of migratory outgrowth and velocity. These ECM molecules did not appear to affect the fate choice of neurons and glia, thus their role in neuropoietic structures may be to facilitate or deter cell movement and process outgrowth.

The Rho/ROCK pathway mediates neurite growth-inhibitory activity associated with the chondroitin sulfate proteoglycans of the CNS glial scar

Axons fail to regenerate in the central nervous system after injury. Chondroitin sulfate proteoglycans (CSPG) expressed in the scar significantly contribute to the nonpermissive properties of the central nervous system environment. To examine the inhibitory activity of a CSPG mixture on retina ganglion cell (RGC) axon growth, we employed both a stripe assay and a nerve fiber outgrowth assay. We show that the inhibition exerted by CSPGs in vitro can be blocked by application of either C3 transferase, a specific inhibitor of the Rho GTPase, or Y27632, a specific inhibitor of the Rho kinase. These results demonstrate that CSPG-associated inhibition of neurite outgrowth is mediated by the Rho/ROCK signaling pathway. Consistent with these results, we found that retina ganglion cell axon growth on glial scar tissue was enhanced in the presence of C3 transferase and Y27632, respectively. In addition, we show that the recently identified inhibitory CSPG Te38 is upregulated in the lesioned spinal cord.

Versican is upregulated in CNS injury and is a product of oligodendrocyte lineage cells

Chondroitin sulfate proteoglycan (CS-PG) expression is increased in response to CNS injury and limits the capacity for axonal regeneration. Previously we have shown that neurocan is one of the CS-PGs that is upregulated (Asher et al., 2000). Here we show that another member of the aggrecan family, versican, is also upregulated in response to CNS injury. Labeling of frozen sections 7 d after a unilateral knife lesion to the cerebral cortex revealed a clear increase in versican immunoreactivity around the lesion. Western blot analysis of extracts prepared from injured and uninjured tissue also revealed considerably more versican in the injured tissue extract. In vitro studies revealed versican to be a product of oligodendrocyte lineage cells (OLCs). Labeling was seen between the late A2B5-positive stage and the O1-positive pre-oligodendrocyte stage. Neither immature, bipolar A2B5-positive cells, nor differentiated, myelin-forming oligodendrocytes were labeled. The amount of versican in conditioned medium increased as these cells differentiated. Versican and tenascin-R colocalized in OLCs, and coimmunoprecipitation indicated that the two exist as a complex in oligodendrocyte-conditioned medium. Treatment of pre-oligodendrocytes with hyaluronidase led to the release of versican, indicating that its retention at the cell surface is dependent on hyaluronate (HA). In rat brain, approximately half of the versican is bound to hyaluronate. We also provide evidence of a role for CS-PGs in the axon growth-inhibitory properties of oligodendrocytes. Because large numbers of OLCs are recruited to CNS lesions, these results suggest that OLC-derived versican contributes to the inhospitable environment of the injured CNS.

Roles of the telencephalic cells and their chondroitin sulfate proteoglycans in delimiting an anterior border of the retinal pathway

The axons of the retinal ganglion cells run on the diencephalotelencephalic boundary on their way to the tectum; however, they do not invade the telencephalon anteriorly. To investigate the mechanisms that prevent the retinal axons from entering the telencephalic territory, the effects of the telencephalic cells were examined on the outgrowth of the retinal axons in vitro; the retinal outgrowth was selectively inhibited by the cellular substrate derived from the telencephalon. The responsible factor for the selective inhibition was, furthermore, found in the telencephalic membranes and the fraction of peripheral membrane molecules from the telencephalon. Because the inhibitory effect was destroyed by chondroitinase ABC but not by heat, this inhibition was attributable to the carbohydrate chains of chondroitin sulfate proteoglycans (CSPGs) adhering to the membranes of the telencephalic cells. To understand the function of the telencephalic CSPGs on the retinal pathfinding in vivo, their carbohydrate chains [chondroitin sulfate glycosaminoglycan (CS-GAG)] were removed from the embryonic brains by intraventricular injection of chondroitinase ABC; the removal of CS-GAG resulted in an anterior enlargement of the optic tract. The results indicate that the telencephalic cells delimit the anterior border of the optic tract with their CSPGs and prevent the retinal axons from aberrantly entering the anterior territory.

Fibronectin and laminin elicit differential behaviors from SH-SY5Y growth cones contacting inhibitory chondroitin sulfate proteoglycans

Neuronal growth cones integrate signals from outgrowth-promoting molecules, e.g., laminin (LN) or fibronectin (FN), and outgrowth-inhibiting molecules, e.g., chondroitin sulfate proteoglycans (CSPGs), to navigate through extracellular matrix (ECM). Sensory neurons on LN typically turn to avoid areas rich in inhibitory CSPGs, whereas neuron-like cells of human origin (SH-SY5Y) preferentially stop/stall. These different behaviors may reflect differences in neuron type, response to outgrowth-promoters, or the mechanisms involved in outgrowth vs. inhibition. We used image analysis to determine the effects of different outgrowth promoters on the response of SH-SY5Y cells to inhibitory CSPGs. LN increased neurite initiation and elongation compared to cells plated either on endogenous matrix or FN. On a patterned substratum consisting of alternating stripes of FN and CSPGs, 59.6 +/- 9.3% of SH-SY5Y growth cones turned upon CSPG contact, whereas only 31.9 +/- 8.2% of growth cones turned at a LN/CSPG border. Growth cones on LN spread more upon contact with CSPG than growth cones on FN, whereas growth cones on LN or FN not contacting CSPGs were morphologically similar. Because it is known that integrins are involved in outgrowth on promoters, we analyzed integrin expression in response to inhibitory CSPGs in a choice assay. CSPGs did not induce increases or redistribution of several integrin subunits in SH-SY5Y cells. Furthermore, an anti-beta1 integrin function-blocking antibody did not alter growth cone behavior at a CSPG border. These results indicate that significant mechanistic differences may exist between outgrowth on homogenous outgrowth promoters and growth cone turning at inhibitory molecules.

Identification of a neurite outgrowth-promoting motif within the alternatively spliced region of human tenascin-C

Our work centers on understanding how the extracellular matrix molecule tenascin-C regulates neuronal growth. We have found that the region of tenascin-C containing only alternately spliced fibronectin type-III repeat D, called fnD, when used by itself, dramatically increases neurite outgrowth in culture. We used overlapping synthetic peptides to localize the neurite outgrowth-promoting site within fnD to a 15 amino acid sequence, called D5. An antibody against D5 blocked promotion of neurite outgrowth by fnD as well as tenascin-C, indicating that this peptide sequence is functional in the context of the native molecule. Further testing of shorter synthetic peptides restricted the neurite outgrowth-promoting site to eight amino acids, VFDNFVLK. Of these, "FD" and "FV" are conserved in tenascin-C sequences derived from all the species available in the GenBank. To investigate the hypothesis that FD and FV are critical for the interaction with neurons, we tested a recombinant fnD protein and synthetic peptides with alterations in FD and/or FV. These molecules did not facilitate process extension, suggesting that the conserved amino acids are required for formation of the active site in fnD. We next investigated whether VFDNFVLK could be used as a reagent to overcome the neurite outgrowth inhibitory properties of chondroitin sulfate proteoglycans, the major inhibitory molecules in the glial scar. The peptide significantly enhanced outgrowth on proteoglycans and was more effective than laminin-1, L1-Fc, or intact tenascin-C, thus demonstrating the potential applicability of tenascin-C regions as therapeutic reagents.

Nervous system-derived chondroitin sulfate proteoglycans regulate growth cone morphology and inhibit neurite outgrowth: a light, epifluorescence, and electron microscopy study

Proteoglycans influence aging and plasticity in the nervous system. Particularly prominent are the chondroitin sulfate proteoglycans (CSPGs), which are generally inhibitory to neurite outgrowth. During development, CSPGs facilitate normal guidance, but following nervous system injury and in diseases of aging (e.g., Alzheimer's disease), they block successful regeneration, and are associated with axon devoid regions and degenerating nerve cells. Whereas previous studies used non-nervous system sources of CSPGs, this study analyzed the morphology and behavior of sensory (dorsal root ganglia) neurons, and a human nerve cell model (SH-SY5Y neuroblastoma cells) as they contacted nervous system-derived CSPGs, using a variety of microscopy techniques. The results of these qualitative analyses show that growth cones of both nerve cell types contact CSPGs via actin-based filopodia, sample the CSPGs repeatedly without collapse, and alter their trajectory to avoid nervous system-derived CSPGs. Turning and branching are correlated with increased filopodial sampling, and are common to both neurons and Schwann cells. We show that CSPG expression by rat CNS astrocytes in culture is correlated with sensory neuron avoidance. Further, we show for the first time the ultrastructure of sensory growth cones at a CSPG-laminin border and reveal details of growth cone and neurite organization at this choice point. This type of detailed analysis of the response of growth cones to nervous system-derived CSPGs may lead to an understanding of CSPG function following injury and in diseases of aging, where CSPGs are likely to contribute to aberrant neurite outgrowth, failed or reduced synaptic connectivity, and/or ineffective plasticity.

Inhibitory effects of neurocan and phosphacan on neurite outgrowth from retinal ganglion cells in culture

PURPOSE

Neurocan and phosphacan are nervous tissue-specific chondroitin sulfate proteoglycans (CSPGs) that are highly expressed in postnatal rat retina. To elucidate potential roles of neurocan and phosphacan on neurite outgrowth from retinal ganglion cells (RGCs), in vitro experiments were conducted with purified RGCs.

METHODS

Neurocan and phosphacan were purified from postnatal rat brain by DEAE-column chromatography and subsequent gel chromatography. RGCs were obtained from postnatal rat retinas by a two-step immunopanning procedure using an anti-Thy 1,1 antibody and an anti-macrophage antibody. Neurite outgrowth from RGCs was examined on poly-L-lysine (PLL)-conditioned plates, and PLL-conditioned plates treated with neurocan or phosphacan.

RESULTS

Compared with PLL-conditioned plates, neurocan and phosphacan inhibited neurite outgrowth from RGCs at 48 and 72 hours after seeding. When chondroitin sulfate side chains linked to the core proteins were digested by chondroitinase ABC, the inhibitory effect remained, indicating that the core proteins are related to the effect. Furthermore, the digestion of chondroitin sulfate side chains linked to phosphacan core protein significantly promoted the inhibitory effect of phosphacan on neurite outgrowth from RGCs.

CONCLUSIONS

Neurocan and phosphacan, which are highly expressed in postnatal rat retina, inhibit neurite outgrowth from postnatal rat RGCs, indicating that these proteoglycans may be inhibitory factors against neurite outgrowth from RGCs during retinal development.

Recombinant core protein fragment of phosphacan, a brain specific chondroitin sulfate proteoglycan, promote excitotoxic cell death of cultured rat hippocampal neurons

We investigated the role of phosphacan, a chondroitin sulfate proteoglycan that is constitutively expressed in the adult hippocampus, and recombinant core proteins of phosphacan in excitotoxic cell death of primary cultured rat hippocampal neurons. Phosphacan had no significant effect on excitotoxic neuronal death. Surprisingly, one of three recombinant proteins corresponding to N-terminal portions of phosphacan core protein dramatically promoted excitotoxic neuronal death. Moreover, the recombinant protein induced cell death of rat hippocampal neurons, even when neurons were not exposed to glutamate. These results suggest that proteolytic degradation of phosphacan and resultant core protein fragments may contribute to neuronal degeneration of hippocampal neurons in various neuropathological conditions.

Specific endocytosis and catabolism in the scavenger endothelial cells of cod (Gadus morhua L.) generate high-energy metabolites

The catabolic fate of circulating hyaluronan and the proteoglycan chondroitin sulphate (CSPG) was studied in the Atlantic cod (Gadus morhua L.). Distribution studies using radio-iodinated ligand demonstrated that CSPG was rapidly eliminated from the blood by the endocardial endothelial cells (EECs) of the heart atrium and ventricle. The presence of excess amounts of hyaluronan or CSPG inhibited uptake of [125I]hyaluronan into cultured atrial EECs (aEECs) by 46% and 84%, respectively. Neither formaldehyde-treated serum albumin (FSA) nor mannose inhibited this uptake. The presence of excess amounts of CSPG and hyaluronan inhibited uptake of [125I]CSPG by 90% and 42%, respectively, suggesting that aEECs express a specific hyaluronan binding site that also recognizes CSPG. FSA inhibited endocytosis of [1251]CSPG by 65%, indicating that CSPG is also recognized by the scavenger receptor. Approximately 17% and 57% of added [125I]hyaluronan and 15% and 65% of the added [125I]CSPG were endocytosed after 1 and 24h, respectively. High-performance liquid chromatographic analyses of the spent medium after endocytosis of hyaluronan and CSPG serglycin labelled biosynthetically with 3H in the acetyl groups identified labelled the low-molecular-mass degradation products as [3H]acetate, indicating that aEECs operate anaerobically. These findings suggest that acetate released from cod EECs following catabolism of endocytosed hyaluronan and CSPG represents a high-energy metabolite that may fuel cardiomyocytes.

Carbohydrate-protein interactions between HNK-1-reactive sulfoglucuronyl glycolipids and the proteoglycan lectin domain mediate neuronal cell adhesion and neurite outgrowth

Lecticans, a family of chondroitin sulfate proteoglycans, represent the largest group of proteoglycans expressed in the nervous system. We previously showed that the C-type lectin domains of lecticans bind two classes of sulfated cell surface glycolipids, sulfatides and HNK-1-reactive sulfoglucuronylglycolipids (SGGLs). In this paper, we demonstrate that the interaction between the lectin domain of brevican, a nervous system-specific lectican, and cell surface SGGLs acts as a novel cell recognition system that promotes neuronal adhesion and neurite outgrowth. The Ig chimera of the brevican lectin domain bind to the surface of SGGL-expressing rat hippocampal neurons. The substrate of the brevican chimera promotes adhesion and neurite outgrowth of hippocampal neurons. The authentic, full-length brevican also promotes neuronal cell adhesion and neurite outgrowth. These activities of brevican substrates are neutralized by preincubation of cells with HNK-1 monoclonal antibodies and by pretreatment of the brevican substrates with purified SGGLs. Brevican and HNK-1 carbohydrates are coexpressed in specific layers of the developing hippocampus where axons from entorhinal neurons elongate. Our observations suggest that cell surface SGGLs and extracellular lecticans comprise a novel cell-substrate recognition system operating in the developing nervous system.