Mapping heparanase expression in the spinal cord of adult rats

Heparanome-Mediated Rescue of Oligodendrocyte Progenitor Quiescence following Inflammatory Demyelination

The proinflammatory cytokine IFN-γ, which is chronically elevated in multiple sclerosis, induces pathologic quiescence in human oligodendrocyte progenitor cells (OPCs) via upregulation of the transcription factor PRRX1. In this study using animals of both sexes, we investigated the role of heparan sulfate proteoglycans in the modulation of IFN-γ signaling following demyelination. We found that IFN-γ profoundly impaired OPC proliferation and recruitment following adult spinal cord demyelination. IFN-γ-induced quiescence was mediated by direct signaling in OPCs as conditional genetic ablation of IFNγR1 (Ifngr1) in adult NG2⁺ OPCs completely abrogated these inhibitory effects. Intriguingly, OPC-specific IFN-γ signaling contributed to failed oligodendrocyte differentiation, which was associated with hyperactive Wnt/Bmp target gene expression in OPCs. We found that PI-88, a heparan sulfate mimetic, directly antagonized IFN-γ to rescue human OPC proliferation and differentiation in vitro and blocked the IFN-γ-mediated inhibitory effects on OPC recruitment in vivo Importantly, heparanase modulation by PI-88 or OGT2155 in demyelinated lesions rescued IFN-γ-mediated axonal damage and demyelination. In addition to OPC-specific effects, IFN-γ-augmented lesions were characterized by increased size, reactive astrogliosis, and proinflammatory microglial/macrophage activation along with exacerbated axonal injury and cell death. Heparanase inhibitor treatment rescued many of the negative IFN-γ-induced sequelae suggesting a profound modulation of the lesion environment. Together, these results suggest that the modulation of the heparanome represents a rational approach to mitigate the negative effects of proinflammatory signaling and rescuing pathologic quiescence in the inflamed and demyelinated human brain.SIGNIFICANCE STATEMENT The failure of remyelination in multiple sclerosis contributes to neurologic dysfunction and neurodegeneration. The activation and proliferation of oligodendrocyte progenitor cells (OPCs) is a necessary step in the recruitment phase of remyelination. Here, we show that the proinflammatory cytokine interferon-γ directly acts on OPCs to induce pathologic quiescence and thereby limit recruitment following demyelination. Heparan sulfate is a highly structured sulfated carbohydrate polymer that is present on the cell surface and regulates several aspects of the signaling microenvironment. We find that pathologic interferon-γ can be blocked by modulation of the heparanome following demyelination using either a heparan mimetic or by treatment with heparanase inhibitor. These studies establish the potential for modulation of heparanome as a regenerative approach in demyelinating disease.

Heparanase attenuates axon degeneration following sciatic nerve transection

Axon degeneration underlies many nervous system diseases; therefore understanding the regulatory signalling pathways is fundamental to identifying potential therapeutics. Previously, we demonstrated heparan sulphates (HS) as a potentially new target for promoting CNS repair. HS modulate cell signalling by both acting as cofactors in the formation of ligand-receptor complexes and in sequestering ligands in the extracellular matrix. The enzyme heparanase (Hpse) negatively regulates these processes by cleaving HS and releasing the attached proteins, thereby attenuating their ligand-receptor interaction. To explore a comparative role for HS in PNS axon injury/repair we data mined published microarrays from distal sciatic nerve injury. We identified Hpse as a previously unexplored candidate, being up-regulated following injury. We confirmed these results and demonstrated inhibition of Hpse led to an acceleration of axonal degeneration, accompanied by an increase in β-catenin. Inhibition of β-catenin and the addition of Heparinase I both attenuated axonal degeneration. Furthermore the inhibition of Hpse positively regulates transcription of genes associated with peripheral neuropathies and Schwann cell de-differentiation. Thus, we propose Hpse participates in the regulation of the Schwann cell injury response and axo-glia support, in part via the regulation of Schwann cell de-differentiation and is a potential therapeutic that warrants further investigation.

Heparanase: Potential roles in multiple sclerosis

Heparanase is a heparan sulfate degrading enzyme that cleaves heparan sulfate (HS) chains present on HS proteoglycans (HSPGs), and has been well characterized for its roles in tumor metastasis and inflammation. However, heparanase is emerging as a contributing factor in the genesis and severity of a variety of neurodegenerative diseases and conditions. This is in part due to the wide variety of HSPGs on which the presence or absence of HS moieties dictates protein function. This includes growth factors, chemokines, cytokines, as well as components of the extracellular matrix (ECM) which in turn regulate leukocyte infiltration into the CNS. Roles for heparanase in stroke, Alzheimer's disease, and glioma growth have been described; roles for heparanase in other disease such as multiple sclerosis (MS) are less well established. However, given its known roles in inflammation and leukocyte infiltration, it is likely that heparanase also contributes to MS pathology. In this review, we will briefly summarize what is known about heparanase roles in the CNS, and speculate as to its potential role in regulating disease progression in MS and its animal model EAE (experimental autoimmune encephalitis), which may justify testing of heparanase inhibitors for MS treatment.

Endothelial cell heparanase taken up by cardiomyocytes regulates lipoprotein lipase transfer to the coronary lumen after diabetes

After diabetes, the heart has a singular reliance on fatty acid (FA) for energy production, which is achieved by increased coronary lipoprotein lipase (LPL) that breaks down circulating triglycerides. Coronary LPL originates from cardiomyocytes, and to translocate to the vascular lumen, the enzyme requires liberation from myocyte surface heparan sulfate proteoglycans (HSPGs), an activity that needs to be sustained after chronic hyperglycemia. We investigated the mechanism by which endothelial cells (EC) and cardiomyocytes operate together to enable continuous translocation of LPL after diabetes. EC were cocultured with myocytes, exposed to high glucose, and uptake of endothelial heparanase into myocytes was determined. Upon uptake, the effect of nuclear entry of heparanase was also investigated. A streptozotocin model of diabetes was used to expand our in vitro observations. In high glucose, EC-derived latent heparanase was taken up by cardiomyocytes by a caveolae-dependent pathway using HSPGs. This latent heparanase was converted into an active form in myocyte lysosomes, entered the nucleus, and upregulated gene expression of matrix metalloproteinase-9. The net effect was increased shedding of HSPGs from the myocyte surface, releasing LPL for its onwards translocation to the coronary lumen. EC-derived heparanase regulates the ability of the cardiomyocyte to send LPL to the coronary lumen. This adaptation, although acutely beneficial, could be catastrophic chronically because excess FA causes lipotoxicity. Inhibiting heparanase function could offer a new strategy for managing cardiomyopathy observed after diabetes.

Urofacial syndrome: a genetic and congenital disease of aberrant urinary bladder innervation

The urofacial, or Ochoa, syndrome is characterised by congenital urinary bladder dysfunction together with an abnormal grimace upon smiling, laughing and crying. It can present as fetal megacystis. Postnatal features include urinary incontinence and incomplete bladder emptying due to simultaneous detrusor muscle and bladder outlet contractions. Vesicoureteric reflux is often present, and the condition can be complicated by urosepsis and end-stage renal disease. The syndrome has long been postulated to have neural basis, and it can be familial when it is inherited in an autosomal recessive manner. Most individuals with urofacial syndrome genetically studied to date carry biallelic, postulated functionally null mutations of HPSE2 or, less commonly, of LRIG2. Little is known about the biology of the respective encoded proteins, heparanase 2 and leucine-rich repeats and immunoglobulin-like domains 2. Nevertheless, the observations that heparanase 2 can bind heparan sulphate proteolgycans and inhibit heparanase 1 enzymatic activity and that LRIG2 can modulate receptor tyrosine kinase growth factor signalling each point to biological roles relevant to tissue differentiation. Moreover, both heparanase 2 and LRIG2 proteins are detected in autonomic nerves growing into fetal bladders. The collective evidence is consistent with the hypothesis that urofacial syndrome genes code for proteins which work in a common pathway to facilitate neural growth into, and/or function within, the bladder. This molecular pathway may also have relevance to our understanding of the pathogenesis of other lower tract diseases, including Hinman-Allen syndrome, or non-neurogenic neurogenic bladder, and of the subset of individuals who have primary vesicoureteric reflux accompanied by bladder dysfunction.

LRIG2 mutations cause urofacial syndrome

Urofacial syndrome (UFS) (or Ochoa syndrome) is an autosomal-recessive disease characterized by congenital urinary bladder dysfunction, associated with a significant risk of kidney failure, and an abnormal facial expression upon smiling, laughing, and crying. We report that a subset of UFS-affected individuals have biallelic mutations in LRIG2, encoding leucine-rich repeats and immunoglobulin-like domains 2, a protein implicated in neural cell signaling and tumorigenesis. Importantly, we have demonstrated that rare variants in LRIG2 might be relevant to nonsyndromic bladder disease. We have previously shown that UFS is also caused by mutations in HPSE2, encoding heparanase-2. LRIG2 and heparanase-2 were immunodetected in nerve fascicles growing between muscle bundles within the human fetal bladder, directly implicating both molecules in neural development in the lower urinary tract.

Heparanase enhances nerve-growth-factor-induced PC12 cell neuritogenesis via the p38 MAPK pathway

Heparanase is involved in the cleavage of the HS (heparan sulfate) chain of HSPGs (HS proteoglycans) and hence participates in remodelling of the ECM (extracellular matrix) and BM (basement membrane). In the present study we have shown that NGF (nerve growth factor) promoted nuclear enrichment of EGR1 (early growth response 1), a transcription factor for heparanase, and markedly induced heparanase expression in rat adrenal pheochromocytoma (PC12) cells. K252a, an antagonist of the NGF receptor TrkA (tyrosine kinase receptor A), decreased heparanase protein expression induced by NGF in PC12 cells. Suramin, a heparanase inhibitor, decreased heparanase in PC12 cells and blocked NGF-induced PC12 neuritogenesis. Stable overexpression of heparanase activated p38 MAPK (mitogen-activated protein kinase) by phosphorylation and enhanced the neurite outgrowth induced by NGF, whereas knock down of heparanase impaired this process. However, overexpression of latent pro-heparanase with a Y156A mutation still led to enhanced NGF-induced neurite outgrowth and increased p38 MAPK phosphorylation. Inhibition of p38 MAPK by SB203580 suppressed the promotion of NGF-induced neuritogenesis by the wild-type and mutant heparanase. The impaired differentiation by knock down of heparanase could be restored by transfection of wild-type or mutant heparanase in PC12 cells. The results of the present study suggest that heparanase, at least in the non-enzymatic form, may promote NGF-induced neuritogenesis via the p38 MAPK pathway.

Expression of heparanase in vascular cells and astrocytes of the mouse brain after focal cerebral ischemia

Heparanase is a heparan sulfate degrading endoglycosidase. Previous work has demonstrated that heparanase plays important roles in various biological processes including angiogenesis, wound healing and metastasis. However, the role of heparanase in the post-ischemic brain is not well defined. Transient focal cerebral ischemia in adult mice was induced by ligations of the right middle cerebral artery (MCA) and both common carotid arteries (CCAs). All mice were subjected to bromodeoxyuridine (BrdU) injection and sacrificed at different time points after stroke for immunohistochemical and Western blot analyses. Heparanase expression increased after ischemia in both cell-specific and time-dependent manners. Three to 7 days after stroke, levels of the 50-kD heparanase, basic fibroblast growth factor (FGF-2), and angiopoietin-2 (Ang-2) increased in the peri-infarct region. At early time points, heparanase expression was largely confined to proliferating vascular endothelial cells. At 14 days after ischemia, this expression had shifted to astrocytes in the same region. These data show that cerebral ischemia markedly increases heparanase levels in endothelial cells and then in astrocytes. The unique features of the heparanase upregulation imply that heparanase may play specific roles in the pathological and regenerative processes during the acute and sub-acute/chronic phases in the post-stroke brain.

Deoxyribozyme-mediated knockdown of xylosyltransferase-1 mRNA promotes axon growth in the adult rat spinal cord

In the injured spinal cord, proteoglycans (PGs) within scar tissue obstruct axon growth through their glycosaminoglycan (GAG)-side chains. The formation of GAG-side chains (glycosylation) is catalysed by xylosyltransferase-1 (XT-1). Here, we knocked down XT-1 mRNA using a tailored deoxyribozyme (DNAXTas) and hypothesized that this would decrease the amount of glycosylated PGs and, consequently, promote axon growth in the adult rat spinal cord. A continuous 2-week delivery of DNAXTas near the rostral border of a peripheral nerve graft bridging the transected dorsal columns in the thoracic spinal cord resulted in an 81% decrease in XT-1 mRNA, an average of 1.4-fold reduction in GAG-side chains of chondroitin sulphate or heparan sulphate-PGs and 2.2-fold reduction in neurocan and brevican core proteins in scar tissue. Additionally, compared to control deoxyribozyme, the DNAXTas treatment resulted in a 9-fold increase in length and a 4-fold increase in density of ascending axons growing through the nerve graft and scar tissue present at the rostral spinal cord. Together our data showed that treatment with a deoxyribozyme against XT-1 mRNA decreased the amount of glycosylated PGs and promoted axon growth through scar tissue in the injured spinal cord. The deoxyribozyme approach may become a contributing factor in spinal cord repair strategies.

Brain heparanase expression is up-regulated during postnatal development and hypoxia-induced neovascularization in adult rats

Heparanase is an endo-beta-d-glucuronidase which specifically cleaves extracellular and cell surface heparan sulphates at intra-chain sites. Its enzymatic activity is strongly implicated in cell dissemination associated with tumor metastasis and inflammation. Indeed, heparanase gene is expressed in various tumors and its over-expression is correlated with increased tumor vascularity and metastatic potential of tumor cells. However, heparanase expression in non-invasive and non-immune tissue, including brain, has received less attention. Using RT-qPCR, western blot and histological analysis, we demonstrate in the adult rat that heparanase transcript is differentially expressed according to brain area, and that heparanase protein is mainly detected in neurons. Furthermore, we provide evidence that heparanase transcript and protein reach their greatest levels at early postnatal stages, in particular within the neocortex characterized by intensive structural plasticity. Using the in vitro model of PC12-induced neuronal differentiation, we suggest that developmental regulation of heparanase may coincide with axonal and dendritic pathfinding. At adulthood, we demonstrate that the increased heparanase transcript level correlates in the hippocampus with enhanced angiogenesis following repeated hypoxia exposures. Taken together, our results emphasize the potential importance of heparanase in brain homeostasis, both during development and adaptative responses to severe environmental challenges.

Expression of heparanase in nestin-positive reactive astrocytes in ischemic lesions of rat brain after transient middle cerebral artery occlusion

Heparanase is an enzyme that cleaves heparan sulfate proteoglycans, an important component of the extracellular matrix to generate heparan sulfate fragments, leading to the remodeling of the extracellular matrix and the basement membrane particularly during cancer metastasis. A growing body of evidence suggests that heparanase serves multiple functions in normal tissues including the central nervous system. In this study, we showed that heparanase is expressed in reactive astrocytes in the peri-infarct lesion of a rat brain whose middle cerebral artery was transiently occluded for 90 min. RT-PCR and Western blot analyses revealed that heparanase expression was markedly upregulated during the subacute phase of ischemia (from 3 to 7 days post-reperfusion (dpr)). As revealed by immunohistochemical study, heparanase was localized in astrocytes located in the peri-infarct region. Heparanase+ astrocytes expressed nestin that is known as a marker of reactive astrocytes. Infiltrated neutrophils were weakly heparanase+. After 7 dpr, the expression level of heparanase+ astrocytes considerably decreased. Therefore, the maximum expression of heparanase by astrocytes may correlate with the time of migration of reactive astrocytes toward the ischemic core, which may result in astrogliosis. These findings suggest a novel role of heparanase in the pathophysiology of brain ischemia.