BioMed Research International

Volume 2014 (2014), Article ID 516028, 9 pages

http://dx.doi.org/10.1155/2014/516028

Review Article

Towards Understanding the Roles of Heparan Sulfate Proteoglycans in Alzheimer’s Disease

Gan-lin Zhang,¹ Xiao Zhang,² Xiao-min Wang,¹ and Jin-Ping Li³

¹Beijing Hospital of Traditional Chinese Medicine, Capital Medical University, Beijing 100010, China

²Department of Neuroscience, Pharmacology, University of Uppsala, The Biomedical Center, 751 23 Uppsala, Sweden

³Department of Medical Biochemistry and Microbiology, University of Uppsala, The Biomedical Center, 751 23 Uppsala, Sweden

Received 3 May 2014; Accepted 12 July 2014; Published 23 July 2014

Academic Editor: Ilona Kovalszky

Copyright © 2014 Gan-lin Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Alzheimer’s disease (AD) is the most common form of dementia, characterized by progressive loss of memory and cognitive dysfunctions. A central pathological event of AD is accumulation and deposition of cytotoxic amyloid-β peptide (Aβ) in the brain parenchyma. Heparan sulfate proteoglycans (HSPGs) and the side chains heparan sulfate (HS) are found associated with Aβ deposits in the brains of AD patients and transgenic animal models of AD. A growing body of evidence from in vitro and in vivo studies suggests functional roles of HSPG/HS in Aβ pathogenesis. Although the question of “how and why HSPG/HS is codeposited with Aβ?” still remains, it is within reach to understand the mechanisms of the events. Recent progress by immunohistochemical examination with advanced antibodies shed light on molecular structures of HS codeposited with Aβ. Several recent reports have provided important new insights into the roles of HSPG in Aβ pathogenesis. Particularly, experiments on mouse models revealed indispensible functions of HSPG in modulating Aβ-associated neuroinflammation and clearance of Aβ from the brain. Application of molecules to interfere with the interaction between HS and Aβ peptides has demonstrated beneficial effects on AD mouse models. Elucidating the functions of HSPG/HS in Aβ deposition and toxicity is leading to further understanding of the complex pathology of AD. The progress is encouraging development of new treatments for AD by targeting HS-Aβ interactions.

1. Introduction

Structure of Heparan Sulfate Proteoglycans. Heparan sulfate proteoglycans (HSPGs) are heavily glycosylated proteins, in which several heparan sulfate (HS) glycosaminoglycan (GAG) chains are covalently attached to a core protein. HSPGs are expressed on the cell surface and in the extracellular matrix (ECM) in all tissues. Cell surface HSPGs are membrane-spanning syndecans (SDCs) and lipid-anchored glypicans (GPCs). There are four members in SDC family (SDC 1–4) and six in GPC family (GPC 1–6). Secreted HSPGs are agrin, collagen type XVIII, and perlecan [1]. HS polysaccharide chains are characterized by highly structural heterogeneity with respect to the chain length and sulfation pattern, generated by a complex biosynthetic process within the Golgi apparatus [2, 3]. Functions of HSPGs are mainly attributed to the HS side chains that interact with a spectrum of protein ligands including growth factors, cytokines, enzymes, lipase, apolipoproteins, and protein components of the ECM, exerting biological activities in development, homeostasis, and diseases [3, 4].

The diverse functions of HS in different biological settings have been extensively studied, and substantial information is obtained. One of the most studied molecular mechanisms of HS is in signal transduction process, particularly growth factor medicated signaling. For example, HS mediates high affinity binding of fibroblast growth factor-2 (FGF-2) to its receptor promoting the formation of a stable tertiary signal complex of FGF-2-HS-FGF-2 receptor [5]. Apart from mediating growth factor activities, HS also functions as coreceptors in other biological activities, for example, modulating the interaction of neuropeptide agouti-related protein with melanocortin receptors 3 and 4 (MC3R and MC4R) in the hypothalamus and regulating food consumption [6–8]. Moreover, membrane HSPGs also act as endocytic receptors for diverse macromolecules such as lipid, growth factors, receptor ligands, and morphogens [1, 9].

Secreted HSPGs, agrin [10] and perlecan [11], constitute major structural molecules in the ECM and basement membrane (BM) along with collagens and other proteins (for review, see [12]). In the ECM, HSPG serves as storage for a number of molecules, such as growth factors and chemokines. In addition, HSPG also plays important roles in maintaining the integrity of ECM and BM [13, 14] and modulating cell mobility [15–17] (also for review, see [4]). In the BM, HSPG, along with collagen IV and laminin-entactin/nidogen complex, controls blood vessel permeability and takes a part in transportation of solutes between vessels and ECM [18, 19]. The ultrastructure of BM can be changed in disease conditions [20] and aging [21], probably due to abnormal production and breakdown of BM components including HSPGs [20].

Heparanase. Heparanase is an endo--glucuronidase that specifically cleaves HS side chains of HSPG, releasing oligosaccharide products at the size of 4–7 kDa (10–20 sugar units) [22]. Heparanase is normally expressed at a low level in majority of tissues including the brain [23]. Surprisingly, this unique HS-specific glycosidase is not essential for animal development and homeostasis, as demonstrated by targeted interruption of the heparanase gene in mouse [24]. The heparanase null mice produce longer HS chains in comparison to wildtype mice; however, there is no accumulation of the polysaccharide in organs, indicating that heparanase is not an indispensible enzyme for HS catabolism. In contrast, overexpression of heparanase in mice resulted in extensive modification of HS chains, producing short fragments with increased sulfation that exert higher potency for FGF-2-HS-FGF-2 receptor resembling [25]. This makes the heparanase transgenic mouse (Hpa-tg) a valuable tool for study of HS functions in different diseases [26–29]. Changes in expression of heparanase in tissues, mainly upregulation, have been reported in several diseases, particularly in cancers [30]. Increased expression of heparanase is detected in brain tumor glioma tissues from human and animal models, where heparanase is suggested to play an important role in the control of tumor cell proliferation and invasion [31]. Cerebral ischemia markedly increased heparanase levels in endothelial cells and astrocytes of mouse [32] and rat [33] brains. Available information suggests that heparanase may function as a regulatory factor in different pathological conditions, including tumor and inflammation, exerting its functions through modification of HS structure [34]. Moreover, heparanase has been shown to have nonenzymatic activities, most likely through direct interaction with cell surface receptors, which needs further investigations [35].

A Pathology of Alzheimer’s Disease. Alzheimer’s disease (AD) is a major central nervous system disease characterized by a progressive neurodegeneration with a clinical phenotype of cognitive impairment. A histopathological hallmark of AD is extracellular A deposition in brain parenchyma manifested as senile A plaques [36]. The pathological A peptides of 40 or 42 amino acids are products of sequential cleavage of the amyloid precursor protein (APP), a transmembrane glycoprotein, by -secretase (-site APP cleaving enzyme 1: BACE1) [37] and -secretase, a multisubunit protease complex composed of at least 4 proteins including presenilin 1 and 2 [38]. Deposition of A in the brain is attributed to excessive accumulation and aggregation of A in the brain. Accumulation and deposition of A most probably resulted from overproduction in the brain or/and impaired removal of A from the brain [39]. Autosomal dominant mutations in three genes, that is, APP gene (APP) and presenilin 1 and 2 genes (PSEN1 and PSEN2), can cause early onset familial AD, accounting for <10% of AD cases [40–42]. All these mutations can result in overproduction of the A peptides, leading to their accumulation and aggregation in the brain [43–45]. In clinic, the most common form of AD is late-onset sporadic AD accounting for about 90% of AD cases. Sporadic AD is not associated with genetic mutations, and no overproduction of A was found. In these cases, it is generally believed that overall A clearance is impaired, resulting in accumulation of A peptides [46, 47]. In the brains of AD patients and some aging individuals with no clear diagnosis of dementia, A is found to accumulate and deposit in blood vessel walls, named cerebral amyloid angiopathy (CAA), which has been interpreted as a sign of impaired A clearance from the brain [48].

There are several ways for A clearance, including degradation by proteolytic enzymes [49], receptor mediated A transport across the blood-brain barrier (BBB) in which the main receptor is low-density lipoprotein receptor related protein-1 (LRP-1) [50], phagocytosis by innate immune cells (macrophages) [51], and perivascular drainage along the BM of blood vessels [52].

2. Interaction of HS with A

Several in vitro studies demonstrate interaction of A with GAGs including HS and heparin (a HS analogue with higher sulfation degree) [53–56]. It has been found that the HHQK domain at the N-terminus of A is a HS binding motif and this sequence has also been shown to bind microglial cells, suggesting that microglia interact with A through membrane associated HS [57]. Concurrently, a HS sequence of -sulfated hexasaccharide domain containing critical 2-O-sulfated iduronic acid residues binds fibrillar A and was identified in human cerebral cortex. Interestingly, this HS domain also serves as a binding site for the neuroprotective growth factor FGF-2. This evidence suggests that, in AD brain, neurotoxic A may compete with neuroprotective FGF-2 for a common HS binding site [58]. Affinity of HS binding to A is associated with its sulfation pattern, as heparin shows a higher affinity to A, while desulfated HS essentially lost binding capacity to A. This interaction is also dependent on chain length of the GAGs, as heparin fragments shorter than 6-sugar units do not bind to A [58]. Furthermore, it has been proposed that the A-HS interaction is mutually protective, such that HS is protected from heparanase degradation [53] and A is protected from protease degradation [59].

3. Codeposition of HS with A in AD Brain—Updated Findings

The presence of glycosaminoglycans (GAGs) in A plaques in AD brain was first identified using Congo red staining for A fibrils and Alcian blue dye for sulfated GAGs in brain sections of autopsy specimens of AD patients about 30 years ago [60]. The presence of HSPGs in A plaques and CAA was later revealed by immunostaining with specific antibodies recognizing the core proteins of HSPGs [61–63]. With these antibodies, subtypes of HSPGs including SDC 1–3, GPC 1, and agrin have been immunolocalized in A plaques and CAA of AD brains [64, 65]. Development of antibodies recognizing different A fragments further promoted characterization of interaction between A and HS.

Recent studies employed advanced type of anti-HS antibodies that differentially recognizes certain structures of HS polysaccharide chains [66, 67]. For example, phage display antibodies EV3C3 and HS4C3 recognize fully N-sulfated motifs in HS chain, while RB4EA12 and HS4E4 recognize partially N-sulfated and N-acetylated HS motifs [66, 68, 69]. Availability of these unique antibodies allowed us to analyze the molecular structure of HS codeposited with A in the brain. By costaining the AD brain sections with an anti-HS phage display antibody HS4E4 and antibodies specific for A species, we found that HS is differentially deposited with A40 or A42 in neuritic and diffuse plaques [70]. In sporadic AD cases, HS4E4 immunosignals are preferentially colocalized with A40 in the cores of senile plaques; however, the HS4E4 signals are absent from A42-rich diffuse deposits. In a recent study, antibodies (EV3C3 and HS4C3) recognizing highly N-sulfated HS detected strongest immunosignals in both fibrillar and nonfibrillar A plaques, while antibodies (RB4EA12 and HS4E4) recognizing HS regions with lower degree of N-sulfation only stained fibrillar A plaques [68], indicating a distinct property of HS structures in interaction with different A aggregates in vivo. These reports are in agreement with our findings, confirming that only fibrillar A plaques of A40 deposits are colocalized with lower sulfated HS motifs. We have identified the membrane bound HSPGs, GPC 1, and SDC 3 in glial cells associated with A deposits in dense core plaques, proximal to sites of HS accumulation, and suggested that HS codeposited with A40 in neuritic plaques is mainly derived from glial cells [70]. RB4CD12 is another phage display antibody that recognizes highly sulfated domains of HS [71]. This antibody strongly stained both diffuse and neuritic A plaques in the brains of AD and several transgenic AD mouse models. Interestingly, the RB4CD12 epitope accumulated in A plaques can be demolished by extracellular sulfatases (Sulf-1 and Sulf-2) ex vivo [72], suggesting that 6-O-sulfated glucosamine residues are within the HS sequence interacting with A.

These recent findings of selective deposition of HS with different species and forms of A strongly suggest distinct roles of HS in A aggregation and deposition. These studies point that HS/HSPG constitutes a part of A plaques and the findings support the notion that HS plays a role in A plaque formation and persistence.

4. HS Mediated A Uptake—Implications in A Cytotoxicity and Clearance

In the brain, A are present in both extracellular and intracellular pools and extracellular A contributes to intracellular A through internalization mechanisms [73]. Cell types in the brain are known to engulf A including neurons, endothelial cells [74], smooth muscle cells [75], and glial cells (microglia and astrocytes) [76, 77]. Internalization of A into cells has been shown to be associated with A cytotoxicity [78, 79]. Several cell surface macromolecules of microglia/macrophages are reported to play roles in A uptake, including toll-like receptor [80], complement receptors [81], scavenger receptors [76, 82], LRP-1 [83], and transmembrane protein CD33, a member of the sialic acid-binding immunoglobulin-like lectins [84] (also for review, see [85]). HSPG functions as a cell surface receptor for entry of diverse macromolecules into cells; in this context, both the core protein and the HS side chains of HSPG are attributed to regulation of endocytosis (for review, see [9]). Having this in mind, we studied A40 uptake and associated toxicity in Chinese hamster ovary (CHO) cell lines. After exposure to A40, the CHO wildtype cells (CHO-WT) survived poorly, whereas the HS-deficient CHO pgsD-677 cells were resistant to the treatment. In correlation with A cytotoxicity, the added A40 was substantially uptaken by CHO-WT but barely by CHO pgsD-677 cells [86]. Likewise, A40 cytotoxicity was attenuated in human embryonic kidney cells (HEK293) overexpressing heparanase due to extensive degradation of HS chains [86]. These findings suggest that cell surface HS mediates A internalization and toxicity.

According to “amyloid hypothesis,” the cause of the majority form of AD, that is, late-onset sporadic, is due to impaired clearance of A from the brain [47, 87]. Transport of A across the BBB from brain to blood is an important route for A clearance, where transcytosis requires A to attach to cell surface after which it is internalized and subsequently released at the luminal side of the endothelium. LRP-1 at the surface of blood vessel endothelial and smooth muscle cells has been reported to function as A cargo in this process [50, 75]. It has been recently reported that LRP-1 and HSPGs mediate A internalization in a seemingly cooperative manner, in which HSPG is more important for A binding to cell surface than LRP-1 [88]. Another important player in this context is apolipoprotein E (ApoE). ApoE and HS are consistently codetected in A deposits and have been ascribed various roles in the pathogenesis of AD [89, 90]. ApoE can bind to HSPG forming functional complex of ApoE/HSPG; alternatively, it joins HSPG/LRP-1 uptake pathway in which ApoE first binds to HSPG and then presents to LRP-1 for uptake (for review, see [91]). The finding of codistribution of ApoE, HS, and LRP1 in A40-positive microvasculature in the hippocampus of individuals with Down’s syndrome (DS), diagnosed with AD, encouraged us to investigate correlation of these molecules in A uptake and clearance [92]. We investigated the functional relationship between A and ApoE and their interactions with cell surface HS and LRP-1 [92]. Coincubation of A with CHO cells either deficient in HS (CHO pgsD677) or in LRP-1 (CHO 13-5-1) along with CHO-WT revealed that addition of ApoE in the cell culture increased A association to the cells, which is dependent on presence of HSPG and LRP-1 on the cell surface. ApoE uptake by the cells does not require presence of both HSPG and LRP1; however, lack of HS in the CHO pgsD677 cells resulted in aberrant intracellular ApoE processing. These data propose that the complex interactions of ApoE, LRP-1, and HSPG facilitate A internalization, which may represent one of major routes for A clearance through transportation of ECM A across BBB into the vessel lumen [92].

5. Heparanase in Aging and AD—Implications in Transmigration of Blood-Borne Monocytes

Heparanase expression in the brain is at marginally detectable level [23, 29], while, in several pathological conditions of the brain, expression of heparanase has been found elevated [31, 32]. Although limited information is available regarding the impact of heparanase on AD pathogenesis, A40 has been shown to protect heparanase-catalyzed degradation of HSPGs in vitro with predicted effect contributing to the stability and persistence of A plaques [53]. Our recent study has revealed increased vasculature expression of heparanase in the brains of AD patients and a mouse model that overexpresses human APP (Tg2576 mice) [29]. Since HS is involved in almost every step of A pathogenesis found in AD (Figure 1), it is of great importance to study expression and activity of heparanase in the brain of aging subjects, both human and animal models.

Figure 1: Heparan sulfate (HS) is involved in essentially each step of amyloid- (A) pathological development in Alzheimer’s disease. HS modulates -secretase (BACE) activity and accelerates A aggregation and fibrillization. It is unclear whether HS is involved in formation of the toxic oligomers/protofibrils; however, HS mediates toxic effect of different types of A fibrils. HS in the basement membrane participates in clearance of A.

In the brain, perivascular macrophages derived from blood-borne mononuclear cells play an important role in A clearance [51, 93, 94]; A peptides are uptaken and subsequently degraded by proteases [95]. Several in vivo studies have demonstrated the multiple functions of HS and heparanase in inflammatory reactions with regard to infiltration of blood-borne immune cells into infected tissues [28, 96]. In this scenario, molecular structures of HS, for example, sulfation pattern and chain length, are pivotal in interaction between endothelial cells and leukocytes as well as with the soluble inflammatory cytokines. Accordingly, we have recently studied the potential roles of heparanase and HS in mediating blood-borne monocytes across blood vessel wall into the brain parenchyma on the transgenic mouse model overexpressing heparanase (Hpa-tg). Overexpression of heparanase resulted in shorter HS chains in the brain of Hpa-tg mouse [29]. In the study, we applied two experimental regimens, that is, localized cerebral microinjection of aggregated A42 and systemic challenge by intraperitoneal injection of lipopolysaccharide (LPS), a bacterial endotoxin. Microinjection of aggregated A42 into the brain elicited an inflammatory response restricted to the injection site of the wildtype mice, characterized by massive infiltration of microglia/macrophages. This inflammatory reaction clearly showed a beneficial effect for clearance of the injected A. In comparison, recruitment and activation of immune cells (microglia and blood-borne monocytes) were significantly attenuated around the injection site of Hpa-tg mouse brain, which resulted in detainment of the injected A42 [29]. The LPS-treated wildtype mice also showed massive activation of resident microglia as well as recruitment of monocyte-derived macrophages in the brain parenchyma, whereas Hpa-tg mice exhibited restricted inflammation with significantly fewer infiltrated macrophages. The mechanism for the reduced recruitment of inflammatory cells into the brain of Hpa-tg mice was verified with an in vitro BBB model constituted with primary endothelia cells and pericytes [29].

The integrity of ECM and the capillary vascular basement membrane (VBM) scaffold is often found severely damaged in association with A deposition [97, 98], which may be responsible for perturbed elimination of solutes and A from parenchyma, consequently leading to development of CAA [99]. As HSPGs are major components of the ECM and VBM and heparanase activity is strongly implicated in structural remodeling of the ECM and BM through degradation of HS, heparanase expression may markedly contribute to pathological changes in the ECM and VBM in AD brain, accordingly affecting A clearance. There is essentially no information with this regard and studies are needed to explore the implications of HS in A transportation and clearance.

6. Conclusion and Perspectives

Principle treatments for AD with regard to A pathology are to reduce production, improve clearance, and prevent aggregation of the pathological peptides. Considering that HS-A interaction contributes to every stage of the A pathogenesis in AD, including production, clearance and accumulation, aggregation, and toxicity of A (Figure 1), it is rational to hypothesize that interfering HS-A interaction may have multiple beneficial effects. Earlier studies show that treatment with low molecular weight heparin (LMWH) reduced A burden in the brain of an AD mouse model overexpressing human APP [100]; the effect is probably that the LMWH competes with endogenous HS, blocking the HS-A interaction. This assumption is supported by our findings that the fragmentation of HS by overexpressed heparanase in mouse attenuated deposition of serum A amyloid (SAA; another amyloid protein) [27]. Though it is improper to use LMWH for treatment of AD, it is possible to apply non-anticoagulant LMWH or HS mimetics for the purpose. With the progress in characterization of HS molecular structures dissected from A plaques, it should be possible to design compounds mimic to the HS structures that interact with A to block its aggregation as well as to neutralize its toxicity. Moreover, targeting A producing enzymes, that is, BACE1 and γ-secretase, constitutes one of the potential treatments for AD. Interestingly, HSPG has been found to modulate BACE activity [101, 102], and efforts are being made to synthesize HS-oligosaccharides as inhibitors of BACE [103]. In light of experimental and clinical evidences addressing the role of HS in A pathology, it is plausible to expect that novel treatments by targeting HS-A interaction may contribute to AD treatment and to improve effects of other treatments. Apart from designed synthesis of HS mimetics, natural anionic oligosaccharides, such as glycosaminoglycans isolated from marine animals and natural herbs, should also be explored for the potential to be developed as drug candidates for this particular application.

Conflict of Interests

The authors declare that they have no conflict of interests regarding the publication of this paper.

Acknowledgments

This work was supported by Grants from the Swedish Heart and Lung Foundation (20110131), Swedish Research Council (K2012-67X-21128-01-4), Stint (IB2012-4524), Polysackaridforskning Foundation (Uppsala), and National Natural Science Foundation of China (81373815 and 81202840).

References

S. Sarrazin, W. C. Lamanna, and J. D. Esko, “Heparan sulfate proteoglycans,” Cold Spring Harbor Perspectives in Biology, vol. 3, no. 7, 2011.

J. Kreuger and L. Kjellén, “Heparan sulfate biosynthesis: regulation and variability,” Journal of Histochemistry and Cytochemistry, vol. 60, no. 12, pp. 898–907, 2012.

U. Lindahl and J. Li, “Interactions between heparan sulfate and proteins-design and functional implications,” International Review of Cell and Molecular Biology, vol. 276, pp. 105–159, 2009.

J. R. Bishop, M. Schuksz, and J. D. Esko, “Heparan sulphate proteoglycans fine-tune mammalian physiology,” Nature, vol. 446, no. 7139, pp. 1030–1037, 2007.

A. Yayon, M. Klagsbrun, J. D. Esko, P. Leder, and D. M. Ornitz, “Cell surface, heparin-like molecules are required for binding of basic fibroblast growth factor to its high affinity receptor,” Cell, vol. 64, no. 4, pp. 841–848, 1991.

L. Karlsson-Lindahl, L. Schmidt, D. Haage et al., “Heparanase affects food intake and regulates energy balance in mice,” PLoS ONE, vol. 7, no. 3, Article ID e34313, 2012.

O. Reizes, S. C. Benoit, A. D. Strader, D. J. Clegg, S. Akunuru, and R. J. Seeley, “Syndecan-3 modulates food intake by interacting with the melanocortin/AgRP pathway,” Annals of the New York Academy of Sciences, vol. 994, pp. 66–73, 2003.

A. D. Strader, O. Reizes, S. C. Woods, S. C. Benoit, and R. J. Seeley, “Mice lacking the syndecan-3 gene are resistant to diet-induced obesity,” Journal of Clinical Investigation, vol. 114, no. 9, pp. 1354–1360, 2004.

H. C. Christianson and M. Belting, “Heparan sulfate proteoglycan as a cell-surface endocytosis receptor,” Matrix Biology, vol. 35, pp. 51–55, 2014.

G. Tsen, W. Halfter, S. Kroger, and G. J. Cole, “Agrin is a heparan sulfate proteoglycan,” The Journal of Biological Chemistry, vol. 270, no. 7, pp. 3392–3399, 1995.

A. D. Murdoch, G. R. Dodge, I. Cohen, R. S. Tuan, and R. V. Iozzo, “Primary structure of the human heparan sulfate proteoglycan from basement membrane (HSPG2/perlecan). A chimeric molecule with multiple domains homologous to the low density lipoprotein receptor, laminin, neural cell adhesion molecules, and epidermal growth factor,” Journal of Biological Chemistry, vol. 267, no. 12, pp. 8544–8557, 1992.

R. Kalluri, “Basement membranes: structure, assembly and role in tumour angiogenesis,” Nature Reviews Cancer, vol. 3, no. 6, pp. 422–433, 2003.

H. J. Guretzki, E. Schleicher, K. D. Gerbitz, and B. Olgemoller, “Heparin induces endothelial extracellular matrix alterations and barrier dysfunction,” American Journal of Physiology, vol. 267, no. 4, part 1, pp. C946–C954, 1994.

M. Costell, E. Gustafsson, A. Aszódi et al., “Perlecan maintains the integrity of cartilage and some basement membranes,” Journal of Cell Biology, vol. 147, no. 5, pp. 1109–1122, 1999.

A. Asplund, G. Östergren-Lundén, G. Camejo, P. Stillemark-Billton, and G. Bondjers, “Hypoxia increases macrophage motility, possibly by decreasing the heparan sulfate proteoglycan biosynthesis,” Journal of Leukocyte Biology, vol. 86, no. 2, pp. 381–388, 2009.

J. J. Moon, M. Matsumoto, S. Patel, L. Lee, J. Guan, and S. Li, “Role of cell surface heparan sulfate proteoglycans in endothelial cell migration and mechanotransduction,” Journal of Cellular Physiology, vol. 203, no. 1, pp. 166–176, 2005.

S. Floris, J. van den Born, S. M. A. van der Pol, C. D. Dijkstra, and H. E. de Vries, “Heparan sulfate proteoglycans modulate monocyte migration across cerebral endothelium,” Journal of Neuropathology and Experimental Neurology, vol. 62, no. 7, pp. 780–790, 2003.

P. D. Yurchenco and J. C. Schittny, “Molecular architecture of basement membranes,” The FASEB Journal, vol. 4, no. 6, pp. 1577–1590, 1990.

M. Paulsson, “Basement membrane proteins: structure, assembly, and cellular interactions,” Critical Reviews in Biochemistry and Molecular Biology, vol. 27, no. 1-2, pp. 93–127, 1992.

E. Farkas and P. G. M. Luiten, “Cerebral microvascular pathology in aging and Alzheimer's disease,” Progress in Neurobiology, vol. 64, no. 6, pp. 575–611, 2001.

C. A. Hawkes, M. Gatherer, M. M. Sharp et al., “Regional differences in the morphological and functional effects of aging on cerebral basement membranes and perivascular drainage of amyloid-β from the mouse brain,” Aging Cell, vol. 12, no. 2, pp. 224–236, 2013.

D. S. Pikas, J. Li, I. Vlodavsky, and U. Lindahl, “Substrate specificity of heparanases from human hepatoma and platelets,” Journal of Biological Chemistry, vol. 273, no. 30, pp. 18770–18777, 1998.

E. Zcharia, S. Metzger, T. Chajek-Shaul et al., “Transgenic expression of mammalian heparanase uncovers physiological functions of heparan sulfate in tissue morphogenesis, vascularization, and feeding behavior,” The FASEB Journal, vol. 18, no. 2, pp. 252–263, 2004.

E. Zcharia, J. Jia, X. Zhang et al., “Newly generated heparanase knock-out mice unravel co-regulation of heparanase and matrix metalloproteinases,” PLoS ONE, vol. 4, no. 4, Article ID e5181, 2009.

M. L. Escobar Galvis, J. Jia, X. Zhang et al., “Transgenic or tumor-induced expression of heparanase upregulates sulfation of heparan sulfate,” Nature Chemical Biology, vol. 3, no. 12, pp. 773–778, 2007.

A. B. Baker, W. J. Gibson, V. B. Kolachalama et al., “Heparanase regulates thrombosis in vascular injury and stent-induced flow disturbance,” Journal of the American College of Cardiology, vol. 59, no. 17, pp. 1551–1560, 2012.

J. Li, M. L. Escobar Galvis, F. Gong et al., “In vivo fragmentation of heparan sulfate by heparanase overexpression renders mice resistant to amyloid protein a amyloidosis,” Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 18, pp. 6473–6477, 2005.

S. Massena, G. Christoffersson, E. Hjertström et al., “Achemotactic gradient sequestered on endothelial heparan sulfate induces directional intraluminal crawling of neutrophils,” Blood, vol. 116, no. 11, pp. 1924–1931, 2010.

X. Zhang, B. Wang, P. O'Callaghan et al., “Heparanase overexpression impairs inflammatory response and macrophage-mediated clearance of amyloid-β in murine brain,” Acta Neuropathologica, vol. 124, no. 4, pp. 465–478, 2012.

N. Ilan, M. Elkin, and I. Vlodavsky, “Regulation, function and clinical significance of heparanase in cancer metastasis and angiogenesis,” International Journal of Biochemistry and Cell Biology, vol. 38, no. 12, pp. 2018–2039, 2006.

X. Hong, K. K. Nelson, A. C. deCarvalho, and S. N. Kalkanis, “Heparanase expression of glioma in human and animal models: laboratory investigation,” Journal of Neurosurgery, vol. 113, no. 2, pp. 261–269, 2010.

J. Li, X. Zhang, Z. Lu, S. P. Yu, and L. Wei, “Expression of heparanase in vascular cells and astrocytes of the mouse brain after focal cerebral ischemia,” Brain Research, vol. 1433, pp. 137–144, 2012.

H. Takahashi, H. Matsumoto, Y. Kumon et al., “Expression of heparanase in nestin-positive reactive astrocytes in ischemic lesions of rat brain after transient middle cerebral artery occlusion,” Neuroscience Letters, vol. 417, no. 3, pp. 250–254, 2007.

I. Vlodavsky, P. Beckhove, I. Lerner et al., “Significance of heparanase in cancer and inflammation,” Cancer Microenvironment, vol. 5, no. 2, pp. 115–132, 2012.

A. Riaz, N. Ilan, I. Vlodavsky, J. Li, and S. Johansson, “Characterization of heparanase-induced phosphatidylinositol 3-kinase-AKT activation and its integrin dependence,” The Journal of Biological Chemistry, vol. 288, no. 17, pp. 12366–12375, 2013.

J. Hardy and D. J. Selkoe, “The amyloid hypothesis of Alzheimer's disease: progress and problems on the road to therapeutics,” Science, vol. 297, no. 5580, pp. 353–356, 2002.

H. Cai, Y. Wang, D. McCarthy et al., “BACE1 is the major β-secretase for generation of Aβ peptides by neurons,” Nature Neuroscience, vol. 4, no. 3, pp. 233–234, 2001.

B. A. Bergmans and B. de Strooper, “-secretases: from cell biology to therapeutic strategies,” The Lancet Neurology, vol. 9, no. 2, pp. 215–226, 2010.

J. A. Hardy and G. A. Higgins, “Alzheimer's disease: the amyloid cascade hypothesis,” Science, vol. 256, no. 5054, pp. 184–185, 1992.

J. C. Janssen, J. A. Beck, T. A. Campbell et al., “Early onset familial Alzheimer's disease: mutation frequency in 31 families,” Neurology, vol. 60, no. 2, pp. 235–239, 2003.

G. Raux, L. Guyant-Maréchal, C. Martin et al., “Molecular diagnosis of autosomal dominant early onset Alzheimer's disease: an update,” Journal of Medical Genetics, vol. 42, no. 10, pp. 793–795, 2005.

D. Campion, C. Dumanchin, D. Hannequin et al., “Early-onset autosomal dominant Alzheimer disease: prevalence, genetic heterogeneity, and mutation spectrum,” American Journal of Human Genetics, vol. 65, no. 3, pp. 664–670, 1999.

C. Haass, A. Y. Hung, D. J. Selkoe, and D. B. Teplow, “Mutations associated with a locus for familial Alzheimer's disease result in alternative processing of amyloid β-protein precursor,” Journal of Biological Chemistry, vol. 269, no. 26, pp. 17741–17748, 1994.

M. Citron, T. Oltersdorf, C. Haass et al., “Mutation of the β-amyloid precursor protein in familial Alzheimer's disease increases β-protein production,” Nature, vol. 360, no. 6405, pp. 672–674, 1992.

X.-D. Cai, T. E. Golde, and S. G. Younkin, “Release of excess amyloid β protein from a mutant amyloid β protein precursor,” Science, vol. 259, no. 5094, pp. 514–516, 1993.

K. G. Mawuenyega, W. Sigurdson, V. Ovod et al., “Decreased clearance of CNS β-amyloid in Alzheimer's disease,” Science, vol. 330, no. 6012, p. 1774, 2010.

R. E. Tanzi, R. D. Moir, and S. L. Wagner, “Clearance of Alzheimer's Aβ peptide: the many roads to perdition,” Neuron, vol. 43, no. 5, pp. 605–608, 2004.

R. O. Weller, A. Massey, T. A. Newman, M. Hutchings, Y. Kuo, and A. E. Roher, “Cerebral amyloid angiopathy: amyloid β accumulates in putative interstitial fluid drainage pathways in Alzheimer's disease,” American Journal of Pathology, vol. 153, no. 3, pp. 725–733, 1998.

J. S. Miners, S. Baig, J. Palmer, L. E. Palmer, P. G. Kehoe, and S. Love, “Aβ-degrading enzymes in Alzheimer's disease,” Brain Pathology, vol. 18, no. 2, pp. 240–252, 2008.

R. Deane, R. D. Bell, A. Sagare, and B. V. Zlokovic, “Clearance of amyloid-β peptide across the blood-brain barrier: implication for therapies in Alzheimer's disease,” CNS and Neurological Disorders, Drug Targets, vol. 8, no. 1, pp. 16–30, 2009.

D. Gate, K. Rezai-Zadeh, D. Jodry, A. Rentsendorj, and T. Town, “Macrophages in Alzheimer's disease: the blood-borne identity,” Journal of Neural Transmission, vol. 117, no. 8, pp. 961–970, 2010.

R. O. Weller, M. Subash, S. D. Preston, I. Mazanti, and R. O. Carare, “Perivascular drainage of amyloid-β peptides from the brain and its failure in cerebral amyloid angiopathy and Alzheimer's disease,” Brain Pathology, vol. 18, no. 2, pp. 253–266, 2008.

K. J. Bame, J. Danda, A. Hassall, and S. Tumova, “Aβ(1-40) prevents heparanase-catalyzed degradation of heparan sulfate glycosaminoglycans and proteoglycans in vitro. A role for heparan sulfate proteoglycan turnover in Alzheimer's disease,” Journal of Biological Chemistry, vol. 272, no. 27, pp. 17005–17011, 1997.

L. Buée, W. Ding, J. P. Anderson et al., “Binding of vascular heparan sulfate proteoglycan to Alzheimer's amyloid precursor protein is mediated in part by the N-terminal region of A4 peptide,” Brain Research, vol. 627, no. 2, pp. 199–204, 1993.

B. Leveugle, A. Scanameo, W. Ding, and H. Fillit, “Binding of heparan sulfate glycosaminoglycan to β-amyloid peptide: inhibition by potentially therapeutic polysulfated compounds,” NeuroReport, vol. 5, no. 11, pp. 1389–1392, 1994.

D. J. Watson, A. D. Lander, and D. J. Selkoe, “Heparin-binding properties of the amyloidogenic peptides Aβ and amylin: dependence on aggregation state and inhibition by Congo red,” The Journal of Biological Chemistry, vol. 272, no. 50, pp. 31617–31624, 1997.

D. Giulian, L. J. Haverkamp, J. Yu et al., “The HHQK domain of -amyloid provides a structural basis for the immunopathology of Alzheimer's disease,” The Journal of Biological Chemistry, vol. 273, no. 45, pp. 29719–29726, 1998.

B. Lindahl, C. Westling, G. Giménez-Gallego, U. Lindahl, and M. Salmivirta, “Common binding sites for β-amyloid fibrils and fibroblast growth factor-2 in heparan sulfate from human cerebral cortex,” Journal of Biological Chemistry, vol. 274, no. 43, pp. 30631–30635, 1999.

R. Gupta-Bansal, R. C. Frederickson, and K. R. Brunden, “Proteoglycan-mediated inhibition of Aβ proteolysis: a potential cause of senile plaque accumulation,” The Journal of Biological Chemistry, vol. 270, no. 31, pp. 18666–18671, 1995.

A. D. Snow, J. Willmer, and R. Kisilevsky, “Sulfated glycosaminoglycans: a common constituent of all amyloids?” Laboratory Investigation, vol. 56, no. 1, pp. 120–123, 1987.

L. S. Perlmutter, H. C. Chui, D. Saperia, and J. Athanikar, “Microangiography and the colocalization of heparan sulfate proteoglycan with amyloid in senile plaques of Alzheimer's disease,” Brain Research, vol. 508, no. 1, pp. 13–19, 1990.

A. D. Snow, H. Mar, D. Nochlin et al., “The presence of heparan sulfate proteoglycans in the neuritic plaques and congophilic angiopathy in Alzheimer's disease,” American Journal of Pathology, vol. 133, no. 3, pp. 456–463, 1988.

J. H. Su, B. J. Cummings, and C. W. Cotman, “Localization of heparan sulfate glycosaminoglycan and proteoglycan core protein in aged brain and Alzheimer's disease,” Neuroscience, vol. 51, no. 4, pp. 801–813, 1992.

J. E. Donahue, T. M. Berzin, M. S. Rafii et al., “Agrin in Alzheimer's disease: altered solubility and abnormal distribution within microvasculature and brain parenchyma,” Proceedings of the National Academy of Sciences of the United States of America, vol. 96, no. 11, pp. 6468–6472, 1999.

J. van Horssen, J. Kleinnijenhuis, C. N. Maass et al., “Accumulation of heparan sulfate proteoglycans in cerebellar senile plaques,” Neurobiology of Aging, vol. 23, no. 4, pp. 537–545, 2002.

S. Kurup, T. J. M. Wijnhoven, G. J. Jenniskens et al., “Characterization of anti-heparan sulfate phage display antibodies AO4B08 and HS4E4,” The Journal of Biological Chemistry, vol. 282, no. 29, pp. 21032–21042, 2007.

T. H. van Kuppevelt, M. A. Dennisseni, W. J. van Venrooij, R. M. A. Hoet, and J. H. Veerkamp, “Generation and application of type-specific anti-heparan sulfate antibodies using phage display technology: further evidence for heparan sulfate heterogeneity in the kidney,” The Journal of Biological Chemistry, vol. 273, no. 21, pp. 12960–12966, 1998.

I. B. Bruinsma, L. te Riet, T. Gevers et al., “Sulfation of heparan sulfate associated with amyloid-β plaques in patients with Alzheimer's disease,” Acta Neuropathologica, vol. 119, no. 2, pp. 211–220, 2010.

G. B. T. Dam, S. Kurup, E. M. A. Van De Westerlo et al., “3-O-sulfated oligosaccharide structures are recognized by anti-heparan sulfate antibody HS₄C₃,” The Journal of Biological Chemistry, vol. 281, no. 8, pp. 4654–4662, 2006.

P. O'Callaghan, E. Sandwall, J. Li et al., “Heparan sulfate accumulation with Aβ deposits in Alzheimer's disease and Tg2576 mice is contributed by glial cells,” Brain Pathology, vol. 18, no. 4, pp. 548–561, 2008.

M. A. B. A. Dennissen, G. J. Jenniskens, M. Pieffers et al., “Large, tissue-regulated domain diversity of heparan sulfates demonstrated by phage display antibodies,” The Journal of Biological Chemistry, vol. 277, no. 13, pp. 10982–10986, 2002.

T. Hosono-Fukao, S. Ohtake-Niimi, H. Hoshino et al., “Heparan sulfate subdomains that are degraded by sulf accumulate in cerebral amyloid ß plaques of alzheimer's disease: evidence from mouse models and patients,” The American Journal of Pathology, vol. 180, no. 5, pp. 2056–2067, 2012.

F. M. LaFerla, K. N. Green, and S. Oddo, “Intracellular amyloid-β in Alzheimer's disease,” Nature Reviews Neuroscience, vol. 8, no. 7, pp. 499–509, 2007.

K. K. Kandimalla, O. G. Scott, S. Fulzele, M. W. Davidson, and J. F. Poduslo, “Mechanism of neuronal versus endothelial cell uptake of Alzheimer's disease amyloid β protein,” PLoS ONE, vol. 4, no. 2, Article ID e4627, 2009.

T. Kanekiyo, C. Liu, M. Shinohara, J. Li, and G. Bu, “LRP1 in brain vascular smooth muscle cells mediates local clearance of Alzheimer's amyloid-β,” Journal of Neuroscience, vol. 32, no. 46, pp. 16458–16465, 2012.

D. M. Paresce, R. N. Ghosh, and F. R. Maxfield, “Microglial cells internalize aggregates of the Alzheimer's disease amyloid β-protein via a scavenger receptor,” Neuron, vol. 17, no. 3, pp. 553–565, 1996.

H. M. Nielsen, S. D. Mulder, J. A. M. Beliën, R. J. P. Musters, P. Eikelenboom, and R. Veerhuis, “Astrocytic Aβ1-42 uptake is determined by Aβ-aggregation state and the presence of amyloid-associated proteins,” GLIA, vol. 58, no. 10, pp. 1235–1246, 2010.

A. Y. Lai and J. McLaurin, “Mechanisms of amyloid-β peptide uptake by neurons: the role of lipid rafts and lipid raft-associated proteins,” International Journal of Alzheimer's Disease, vol. 2011, Article ID 548380, 11 pages, 2011.

M. Sakono and T. Zako, “Amyloid oligomers: formation and toxicity of Aβ oligomers,” FEBS Journal, vol. 277, no. 6, pp. 1348–1358, 2010.

K. Tahara, H. Kim, J. Jin, J. A. Maxwell, L. Li, and K. Fukuchi, “Role of toll-like receptor signalling in Aβ uptake and clearance,” Brain, vol. 129, no. 11, pp. 3006–3019, 2006.

H. Fu, B. Liu, J. L. Frost et al., “Complement component C3 and complement receptor type 3 contribute to the phagocytosis and clearance of fibrillar Aβ by microglia,” GLIA, vol. 60, no. 6, pp. 993–1003, 2012.

C. N. Yang, Y. J. Shiao, F. S. Shie et al., “Mechanism mediating oligomeric Aβ clearance by naïve primary microglia,” Neurobiology of Disease, vol. 42, no. 3, pp. 221–230, 2011.

A. N’Songo, T. Kanekiyo, and G. Bu, “LRP1 plays a major role in the amyloid-β clearance in microglia,” Molecular Neurodegeneration, vol. 8, supplement 1, p. P33, 2013.

A. Griciuc, A. Serrano-Pozo, A. R. Parrado et al., “Alzheimer's disease risk gene cd33 inhibits microglial uptake of amyloid β,” Neuron, vol. 78, no. 4, pp. 631–643, 2013.

D. Doens and P. L. Fernandez, “Microglia receptors and their implications in the response to amyloid for Alzheimer's disease pathogenesis,” Journal of Neuroinflammation, vol. 11, p. 48, 2014.

E. Sandwall, P. O'Callaghan, X. Zhang, U. Lindahl, L. Lannfelt, and J. Li, “Heparan sulfate mediates amyloid-beta internalization and cytotoxicity,” Glycobiology, vol. 20, no. 5, pp. 533–541, 2010.

B. V. Zlokovic, “The blood-brain barrier in health and chronic neurodegenerative disorders,” Neuron, vol. 57, no. 2, pp. 178–201, 2008.

T. Kanekiyo, J. Zhang, Q. Liu, C. Liu, L. Zhang, and G. Bu, “Heparan sulphate proteoglycan and the low-density lipoprotein receptor-related protein 1 constitute major pathways for neuronal amyloid-β uptake,” The Journal of Neuroscience, vol. 31, no. 5, pp. 1644–1651, 2011.

D. M. Holtzman, K. R. Bales, T. Tenkova et al., “Apolipoprotein E isoform-dependent amyloid deposition and neuritic degeneration in a mouse model of Alzheimer's disease,” Proceedings of the National Academy of Sciences of the United States of America, vol. 97, no. 6, pp. 2892–2897, 2000.

Q. Jiang, C. Y. D. Lee, S. Mandrekar et al., “ApoE promotes the proteolytic degradation of Aβ,” Neuron, vol. 58, no. 5, pp. 681–693, 2008.

T. Kanekiyo, H. Xu, and G. Bu, “ApoE and Aβ in Alzheimer's disease: accidental encounters or partners?” Neuron, vol. 81, no. 4, pp. 740–754, 2014.

P. O'Callaghan, F. Noborn, D. Sehlin et al., “Apolipoprotein E increases cell association of amyloid-β 40 through heparan sulfate and LRP1 dependent pathways,” Amyloid, vol. 21, no. 2, pp. 76–87, 2014.

A. R. Simard, D. Soulet, G. Gowing, J. Julien, and S. Rivest, “Bone marrow-derived microglia play a critical role in restricting senile plaque formation in Alzheimer's disease,” Neuron, vol. 49, no. 4, pp. 489–502, 2006.

D. Frenkel, K. Wilkinson, L. Zhao et al., “Scara1 deficiency impairs clearance of soluble amyloid- by mononuclear phagocytes and accelerates Alzheimer's-like disease progression,” Nature Communications, vol. 4, article 2030, 2013.

M. Fiala, J. Lin, J. Ringman et al., “Ineffective phagocytosis of amyloid-β by macrophages of Alzheimer's disease patients,” Journal of Alzheimer's Disease, vol. 7, no. 3, pp. 221–232, 2005.

L. Wang, M. Fuster, P. Sriramarao, and J. D. Esko, “Endothelial heparan sulfate deficiency impairs L-selectin- and chemokine-mediated neutrophil trafficking during inflammatory responses,” Nature Immunology, vol. 6, no. 9, pp. 902–910, 2005.

C. Zarow, E. Barron, H. C. Chui, and L. S. Perlmutter, “Vascular basement membrane pathology and Alzheimer's disease,” Annals of the New York Academy of Sciences, vol. 826, pp. 147–160, 1997.

D. Bonneh-Barkay and C. A. Wiley, “Brain extracellular matrix in neurodegeneration,” Brain Pathology, vol. 19, no. 4, pp. 573–585, 2009.

C. A. Hawkes, W. Härtig, J. Kacza et al., “Perivascular drainage of solutes is impaired in the ageing mouse brain and in the presence of cerebral amyloid angiopathy,” Acta Neuropathologica, vol. 121, no. 4, pp. 431–443, 2011.

L. Bergamaschini, E. Rossi, C. Storini et al., “Peripheral treatment with enoxaparin, a low molecular weight heparin, reduces pl aques and β-amyloid accumulation in a mouse model of Alzheimer's disease,” Journal of Neuroscience, vol. 24, no. 17, pp. 4181–4186, 2004.

Z. Scholefield, E. A. Yates, G. Wayne, A. Amour, W. McDowell, and J. E. Turnbull, “Heparan sulfate regulates amyloid precursor protein processing by BACE1, the Alzheimer's β-secretase,” Journal of Cell Biology, vol. 163, no. 1, pp. 97–107, 2003.

D. H. Small, D. W. Klaver, and M. Beckman, “Regulation of proBACE1 by glycosaminoglycans,” Neurodegenerative Diseases, vol. 5, no. 3-4, pp. 206–208, 2008.

R. Schwörer, O. V. Zubkova, J. E. Turnbull, and P. C. Tyler, “Synthesis of a targeted library of heparan sulfate hexa- to dodecasaccharides as inhibitors of β-secretase: potential therapeutics for Alzheimer's disease,” Chemistry A, vol. 19, no. 21, pp. 6817–6823, 2013.