Heparan sulfate (HS), an unbranched sulfated carbohydrate chain, and the HS-degrading enzyme heparanase play important roles in physiological and pathological processes during all stages of life, from early embryogenesis to ageing. Accumulated information shows that HS and heparanase are involved in inflammatory processes and associated diseases, e.g. rheumatoid arthritis (RA) and Alzheimer’s disease. In this thesis I have investigated the role of HS and heparanase (Hpa) in inflammatory-related pathologies. In the first project, Hpa overexpressing mice (Hpa-tg) were induced with a murine model of RA. We found a pro-inflammatory role of Hpa through enhancing the activity of T-cells and innate immune cells, which contributed to an augmented severity of clinical symptoms in the Hpa-tg mice. In my second project, we revealed co-current interaction of heparin with both ApoA1 and SAA of HDL isolated from plasma of inflamed mouse. Mass spectrometry analysis indicated close proximity of ApoA1 and SAA on the HDL surface, providing a molecular and structural mechanism for the simultaneous binding of heparin to apoA1 and SAA. In my third project, we investigated the role of Hpa in AA amyloid formation and resolution in mice in a model of AA-amyloidosis. We found a similar degree of amyloid formation in Hpa-KO mice compared to the wildtype control mice, but the resolution process was faster in Hpa-KO mice. The rapid clearance of deposited SAA in Hpa-KO mice was associated with upregulated expression of matrix metalloproteases. The results suggest an associated function of ECM proteases with heparanase in the process of AA amyloid resolution. In my fourth project, we found that overexpression of heparanase impaired inflammation associated beta amyloid (Aβ) clearance in the brain of an Alzheimer’s disease mouse model. Examination of the cytokine profile of brain lysates revealed an overall lower inflammatory reaction in the double transgenic (tgHpa*Swe) mice compared to single APP-tg (tg-Swe) mice in response to LPS-induced inflammation.

En accordance avec son haut prévalence dans le monde, parmi tous les cas de démence, la maladie d'Alzheimer (MA) est considérée comme la principal pathologie affectant les personnes plus âgées que 65 ans. Depuis son première description en 1907, de la recherche important et des observations innovants ont été faites concernant des aspects histopathologiques et moléculaires la neurodégénération associée à la maladie. Cependant, les mécanismes moléculaires de la pathogenèse et de la progression de la MA restent toujours partiellement compris. Outre, des stratégies thérapeutiques efficaces soit pour la prévention, soit pour l'arrêt de la progression de la maladie ne sont pas encore développées. Il semble donc crucial le développement de la recherche dans des domaines émergeants, nés à partir des concepts innovants et basés sur des approches mécanistiques novateurs à fin de découvrir des aspects dans la physiopathologie de la neurodégénérescence qui puissent conduire à des stratégies thérapeutiques pour soigner ces maladies.Les études présentées ici sont centrées dans le rôle des héparanes sulfates (HS), un membre particulier de la famille des glycosaminoglycannes, dans la physiopathologie des troubles neurodégénératifs, tels que la MA et démences associées, nommées taupathies. Ce travail de recherche, basé sur plusieurs observations isolées suggérant une association entre la pathologie de tau caractéristique des taupathies et les HS, explore par des moyens de études moléculaires, cellulaires et animaux les implications pathologiques de telle interaction. Comme résultat, je montre ici des évidences suggérant une participation clé des HS dans les évènements pathologiques de tau, tels que la phosphorylation anormale, la formation des inclusions intracellulaires, et la propagation des amas de tau.Globalement, le travail présenté ici dévoile une implication importante des HS hautement sulfatés dans la pathologie de tau associée à la MA, et au même temps ouvre une gamme de voies de recherche novatrices pour approfondir dans la caractérisation de l'interaction tau/HS et ses consequences physiopathologiques. De plus, ceci suggère des cibles pharmacologiques alternatives qui puisèrent donner d'espoir pour trouver un traitement effectif pour la MA. / According to its higher prevalence worldwide among all dementia cases, Alzheimer's disease (AD) is placed as the first pathology affecting people aged of more than 65 years old. Since it first description in 1907, profound research and groundbreaking observations have been made concerning the histopathological and molecular aspects of its associated neurodegeneration. However, the molecular mechanisms of AD pathogenesis and progression remain still poorly understood. In addition, an efficient therapeutic approach to either prevent or stop the disease progression has not yet been developed. It becomes hence crucial to develop research in emerging areas raising from groundbreaking concepts and supported by new mechanistic approaches in order to unveil novel aspects of the physiopathology of neurodegeneration and therefore design new therapeutic approaches to treat these pathologies.The present study is focused on the role of heparan sulfate (HS), a particular member of the glycosaminoglycan family, in the physiopathology of neurodegenerative disorders, such as AD and related dementias, termed tauopathies. Based on numerous separate observations suggesting an association between tau pathology characteristic of tauopathies and HS, this research explores the pathological implications of such interaction by the means of molecular, cellular, and animal studies. As a result, I hereby present evidence suggesting a crucial involvement of HS in tau pathological events, such as abnormal phosphorylation, inclusion formation, and assembly propagation.Globally, the present work unveils a strong implication of highly sulfated HS in tau pathology associated to AD and related tauopathies, and opens a wide array of novel research pathways to deepen into the characterization of tau /HS interplay and its pathophysiologic consequences. In addition, it suggests alternative pharmacological targets that could bring some hope in finding an effective treatment for AD.

Les protéines solubles sont généralement faiblement immunogènes, ce qui constitue unelimite pour le développement de vaccins sous unitaires à base de protéines. Mes travaux de thèseont eu pour objectif de décrypter certains mécanismes moléculaires et cellulaires qui contribuent àl’immunogénicité et d’en tirer partie pour développer des approches originales permettantd’améliorer la capacité des protéines à déclencher la réponse immunitaire. Pour cela, j’aiprincipalement utilisé le transactivateur transcriptionnel (Tat) du VIH-1. J’ai montré quel’oligomérisation de Tat permet à un mécanisme de collaboration B-TH-2 d’induire la réponseimmunitaire en absence d’adjuvant. J’ai identifié le déterminant minimal responsable de l’effet etmontré qu’il confère la propriété adjuvante à d’autres antigènes. J’ai ensuite montré que laprésentation aux cellules T restreinte aux CMH I et CMH II est accrue lorsque les protéines sontdotées de la capacité à lier des sucres sulfatés d’expression ubiquitaire: les héparanes sulfate. Cestravaux ont permis de définir de nouvelles approches pour améliorer l’immunogénicité de protéinessusceptibles d’être intégrées dans des préparations vaccinales. / Soluble proteins are usually poorly immunogenic, which is a limit to the development ofsubunit vaccines based on proteins. My thesis work aimed to decipher some molecular and cellularmechanisms that contribute to the immunogenicity and to exploit them to develop innovativeapproaches to improve the ability of proteins to trigger the immune response. For this purpose, Imainly used the transcriptional transactivator (Tat) of HIV-1. I showed that the oligomerization of Tatenables a B-TH-2 collaborative mechanism to induce the immune response in the absence ofadjuvant. I identified the minimum region determining the effect and showed that it confers the selfadjuvantingproperty to other antigens. In the second part of my work, I showed that the MHC I andMHC II restricted presentation to T cells is increased when the proteins are endowed with the abilityto bind ubiquitous sulfated polysaccharides: heparan sulfates. This work helped to define newapproaches to improve the immunogenicity of proteins that are likely to be included in vaccinepreparations.

Tissue repair is a complex process that is difficult to emulate. The addition of the glycosaminoglycan heparan sulfate (HS), a multi-potential regulator of numerous growth factors and cytokines endogenously expressed during the repair process, may represent a valuable tool for tissue engineering. The addition of exogenous HS into wound site has previously been shown to promote tissue repair in a number of models, however, the incorporation of HS into controlled release systems or biomaterials for tissue engineering had not been explored prior to the work presented here. Thus, this thesis explores the incorporation of HS and its analogue heparin into synthetic biodegradable polymer biomaterials with different potential applications, either as a slow releasing drug reservoir, or as a drug releasing cell scaffold. Polycaprolactone was used to make microcapsules and electrospun fibers for HS or heparin entrapment. These materials were characterized for their drug release profiles, biocompatibility and bioactivity. Microcapsules encapsulating heparin or HS were made by the oil - in - water solvent evaporation method which allowed fabrication of slow releasing drug reservoirs. Either pure water or a poly(vinyl alcohol) solution was used in the drug phase which resulted in capsules with similar size and drug loading. However the internal morphology and drug release profiles showed differences depending on the drug phase, in either case release was sustained for over 30 days. These capsules elicited no pro-inflammatory response from macrophages in vitro, and the released HS retained its bioactivity to induce the proliferation of human mesenchymal stem cells, an important cell type for bone tissue engineering. Heparin and HS were incorporated into electrospun fibers as a drug releasing scaffold for two different tissue engineering applications. Heparin fibers were studied as a drug releasing membrane that could be used in vascular repair to prevent the unwanted proliferation of vascular smooth muscle cells. Heparin release was sustained from the fibers for at least 2 weeks. The fibers did not induce a pro-inflammatory response from macrophages in vitro and the released heparin retained the ability to inhibit the proliferation in vascular smooth muscle cells. HS fibers were studied as a tissue engineering scaffold for bone repair using human mesenchymal stem cells. HS release was maintained for over 30 days which is thought to be an appropriate time for bone repair applications. The release profiles depended on the HS concentration in the spinning solution which affected the morphology of the fibers. The fibers did not elicit a pro-inflammatory response in cultured macrophages and supported the proliferation and mineralization of human mesechymal stem cells. The HS fibers were then taken through to an in vivo model to study ectopic bone formation of pre-osteoblast cells on HS releasing scaffolds. The fibers produced a chronic inflammatory response in vivo, which lead to the clearance of implanted cells and no mineralization of the scaffold. The HS and heparin materials made in this work showed sustained release over appropriate time frames for different tissue repair applications. The released HS and heparin maintained bioactivity and showed good biocompatibility in vitro, however, further in vivo studies are required to fully test their efficacy for tissue engineering.

<p>Fibroblast growth factors (FGFs) constitute a family (currently FGF-1 to FGF-23) of polypeptides that are essential in embryonal development and adult physiology, in animals from nematodes to humans. FGFs bind to four receptor tyrosine kinases, denoted FGFR-1 to FGFR-4. For proper function, the FGFs and their receptors depend on specific polysaccharide co-receptors, denoted heparan sulfate (HS). This thesis describes HS regulation of FGFR-1 signal transduction using blood vessel endothelial cells as a model.</p><p>We have determined HS structural features, necessary for FGF-2 induced FGFR-1 activation, using chemically modified heparin, which is structurally related to HS. Modified heparin, lacking sulfation at the 6-O position was inhibitory for FGFR-1 kinase activation and FGF-2 induced angiogenesis. Inhibition of blood vessel formation using modified heparin could be useful in treatment of diseases characterized by excess blood vessel formation. The critical role of HS sulfation for proper growth factor function was further underscored using an embryonal stem (ES) cell model. ES cells lacking expression of two isoforms of N-deacetyl N-sulfotransferase, NDST-1 and –2, failed to undergo embryonal development and to establish a vascular system. Exogenous heparin could not support development, but HS delivered from other ES cells allowed formation of primitive vessels and subsequent sprouting angiogenesis.</p><p>We have, furthermore, shown that the mechanism whereby HS supports FGF receptor activation is qualitative, as well as quantitative. Kinase activity could be induced by FGF-2 in the absence of HS, but this allowed only selected phosphorylation. In the presence of HS, the kinase activity was stabilized, allowing a broader spectrum of phosphorylation of sites on the FGF receptor itself as well as on cytoplasmic substrates. Finally, using selected microarrays, we have examined the potential regulation of enzymes in the HS biosynthesis pathway and of different proteoglycans to which HS is attached. Overall, we found no evidence for dramatic regulation on the transcriptional level, but could identify specific upregulation of HS proteoglycan syndecan-2, during blood vessel formation in vitro.</p><p>In conclusion, our studies demonstrate selective and complex regulation of HS synthesis and structure, essential in guiding growth factor function during health and disease.</p>

<p>Heparan sulfate (HS), a linear negatively charged polysaccharide located at the cell surface and in the extracellular matrix, interacts with, and thereby regulates the functions of numerous proteins. HS-protein interactions depend on the fine structure of HS, especially its sulfation pattern. This thesis aimed to understand how differently sulfated domains in HS are generated. Specifically, the substrate specificities of HS hexuronic acid 2-<i>O</i>-sulfotransferase (2OST) and HS glucosaminyl 6-<i>O</i>-sulfotransferases (6OSTs) were investigated. </p><p>Three different 6OSTs (6OST1-3) have been cloned and characterized. To study the mechanisms controlling 6-<i>O</i>-sulfation we incubated the recombinant purified 6-OST isoforms with different 6-<i>O</i>-desulfated poly- and oligosaccharide substrates and the active sulfate donor 3'-phosphoadenosine 5'-phospho[³⁵S]sulfate (³⁵S-labeled PAPS). All three enzymes catalyzed 6-<i>O</i>-sulfation of both <i>N</i>-acetylated (GlcNAc) as well as <i>N</i>-sulfated (GlcNS) glucosamines next to a nonreducing iduronic acid (IdoA) or glucuronic acid (GlcA). Similar specificities were demonstrated, although some differences in substrate preferences were noted.</p><p>To understand how pre-existing 2-<i>O</i>-sulfates affects 6-<i>O</i>-sulfation, 6OST2 and 6OST3 were incubated with pair-wise mixed octasaccharide substrates with different contents of 2-<i>O</i>-sulfates. The specificities for substrates with two or three 2-<i>O</i>-sulfates were higher compared to octasaccharides with no or one 2-<i>O</i>-sulfate indicating that 2-<i>O</i>-sulfate groups substantially promote the subsequent 6-<i>O</i>-sulfation. </p><p>Overexpression of the 6OSTs in a mammalian cell line resulted in increased 6-<i>O</i>-sulfation of -GlcA-GlcNS- and -GlcA-GlcNAc- sequences. The results were not isoform specific, but affected by the overexpression level. </p><p>The 2OST catalyzes 2-<i>O</i>-sulfation of both IdoA and GlcA residues, with high preference for IdoA units. To study how 2-<i>O</i>-sulfation of GlcA and IdoA is regulated, we incubated the enzyme with different substrates and ³⁵S-labeled PAPS. Our findings revealed that the 2OST almost exclusively sulfated IdoA also with a ratio of GlcA to IdoA of 99:1, suggesting that 2-<i>O</i>-sulfation of GlcA occurs before IdoA is formed.</p>

<p>Blood vessels transport blood with essential nutrients and oxygen to the cells in our body. In a healthy adult, formation of new vessels (angiogenesis) occurs only in case of tissue repair and growth. Physiological angiogenesis requires precise regulation of multiple signaling components, a process which is deregulated in a number of pathological conditions, such as cancer. This thesis is focused on the role of laminins, heparan sulfate proteoglycans (HSPGs) and vascular endothelial growth factor (VEGF)-A in regulation of vascular development and angiogenesis. As a model, we have used embryonic stem cells that differentiate to form blood vessels in a manner faithfully recapitulating the <i>in vivo</i> processes. </p><p>We show that the basement membrane (BM) protein laminin-111 promotes maturation of endothelial cells in the presence of fibroblast growth factor-2, a known endothelial cell mitogen. However, embryonic stem cells are able to differentiate into endothelial cells also in the absence of laminin deposition in the vascular BM. Sprouting angiogenesis, induced by VEGF-A, is also not strictly dependent on laminin deposition. On the other hand, in the absence of laminins, vessels are enlarged. These data suggest an important role for laminins in regulation of the vessel diameter.</p><p>We also show that HSPGs serve as coreceptors for VEGF-A to regulate vascular development. The mode of presentation of HSPGs, <i>in</i> <i>cis</i> (on the endothelial cell) or <i>in</i> <i>trans</i> (on an adjacent cell such as pericytes), is critical in regulation of VEGF receptor-2 activation and stimulation of vascular development. Binding of VEGF-A to HSPGs <i>in</i> <i>trans</i> leads to accumulation of activated VEGFR-2 in endothelial cells and to prolonged signaling. This demonstrates a potential role for HSPGs in regulation of receptor trafficking and signaling kinetics, with possible implications also for other HS-binding ligand/receptor systems.</p>

Fibroblast growth factors (FGFs) constitute a family (currently FGF-1 to FGF-23) of polypeptides that are essential in embryonal development and adult physiology, in animals from nematodes to humans. FGFs bind to four receptor tyrosine kinases, denoted FGFR-1 to FGFR-4. For proper function, the FGFs and their receptors depend on specific polysaccharide co-receptors, denoted heparan sulfate (HS). This thesis describes HS regulation of FGFR-1 signal transduction using blood vessel endothelial cells as a model. We have determined HS structural features, necessary for FGF-2 induced FGFR-1 activation, using chemically modified heparin, which is structurally related to HS. Modified heparin, lacking sulfation at the 6-O position was inhibitory for FGFR-1 kinase activation and FGF-2 induced angiogenesis. Inhibition of blood vessel formation using modified heparin could be useful in treatment of diseases characterized by excess blood vessel formation. The critical role of HS sulfation for proper growth factor function was further underscored using an embryonal stem (ES) cell model. ES cells lacking expression of two isoforms of N-deacetyl N-sulfotransferase, NDST-1 and –2, failed to undergo embryonal development and to establish a vascular system. Exogenous heparin could not support development, but HS delivered from other ES cells allowed formation of primitive vessels and subsequent sprouting angiogenesis. We have, furthermore, shown that the mechanism whereby HS supports FGF receptor activation is qualitative, as well as quantitative. Kinase activity could be induced by FGF-2 in the absence of HS, but this allowed only selected phosphorylation. In the presence of HS, the kinase activity was stabilized, allowing a broader spectrum of phosphorylation of sites on the FGF receptor itself as well as on cytoplasmic substrates. Finally, using selected microarrays, we have examined the potential regulation of enzymes in the HS biosynthesis pathway and of different proteoglycans to which HS is attached. Overall, we found no evidence for dramatic regulation on the transcriptional level, but could identify specific upregulation of HS proteoglycan syndecan-2, during blood vessel formation in vitro. In conclusion, our studies demonstrate selective and complex regulation of HS synthesis and structure, essential in guiding growth factor function during health and disease.

Heparan sulfate (HS), a linear negatively charged polysaccharide located at the cell surface and in the extracellular matrix, interacts with, and thereby regulates the functions of numerous proteins. HS-protein interactions depend on the fine structure of HS, especially its sulfation pattern. This thesis aimed to understand how differently sulfated domains in HS are generated. Specifically, the substrate specificities of HS hexuronic acid 2-O-sulfotransferase (2OST) and HS glucosaminyl 6-O-sulfotransferases (6OSTs) were investigated. Three different 6OSTs (6OST1-3) have been cloned and characterized. To study the mechanisms controlling 6-O-sulfation we incubated the recombinant purified 6-OST isoforms with different 6-O-desulfated poly- and oligosaccharide substrates and the active sulfate donor 3'-phosphoadenosine 5'-phospho[35S]sulfate (35S-labeled PAPS). All three enzymes catalyzed 6-O-sulfation of both N-acetylated (GlcNAc) as well as N-sulfated (GlcNS) glucosamines next to a nonreducing iduronic acid (IdoA) or glucuronic acid (GlcA). Similar specificities were demonstrated, although some differences in substrate preferences were noted. To understand how pre-existing 2-O-sulfates affects 6-O-sulfation, 6OST2 and 6OST3 were incubated with pair-wise mixed octasaccharide substrates with different contents of 2-O-sulfates. The specificities for substrates with two or three 2-O-sulfates were higher compared to octasaccharides with no or one 2-O-sulfate indicating that 2-O-sulfate groups substantially promote the subsequent 6-O-sulfation. Overexpression of the 6OSTs in a mammalian cell line resulted in increased 6-O-sulfation of -GlcA-GlcNS- and -GlcA-GlcNAc- sequences. The results were not isoform specific, but affected by the overexpression level. The 2OST catalyzes 2-O-sulfation of both IdoA and GlcA residues, with high preference for IdoA units. To study how 2-O-sulfation of GlcA and IdoA is regulated, we incubated the enzyme with different substrates and 35S-labeled PAPS. Our findings revealed that the 2OST almost exclusively sulfated IdoA also with a ratio of GlcA to IdoA of 99:1, suggesting that 2-O-sulfation of GlcA occurs before IdoA is formed.

Blood vessels transport blood with essential nutrients and oxygen to the cells in our body. In a healthy adult, formation of new vessels (angiogenesis) occurs only in case of tissue repair and growth. Physiological angiogenesis requires precise regulation of multiple signaling components, a process which is deregulated in a number of pathological conditions, such as cancer. This thesis is focused on the role of laminins, heparan sulfate proteoglycans (HSPGs) and vascular endothelial growth factor (VEGF)-A in regulation of vascular development and angiogenesis. As a model, we have used embryonic stem cells that differentiate to form blood vessels in a manner faithfully recapitulating the in vivo processes. We show that the basement membrane (BM) protein laminin-111 promotes maturation of endothelial cells in the presence of fibroblast growth factor-2, a known endothelial cell mitogen. However, embryonic stem cells are able to differentiate into endothelial cells also in the absence of laminin deposition in the vascular BM. Sprouting angiogenesis, induced by VEGF-A, is also not strictly dependent on laminin deposition. On the other hand, in the absence of laminins, vessels are enlarged. These data suggest an important role for laminins in regulation of the vessel diameter. We also show that HSPGs serve as coreceptors for VEGF-A to regulate vascular development. The mode of presentation of HSPGs, in cis (on the endothelial cell) or in trans (on an adjacent cell such as pericytes), is critical in regulation of VEGF receptor-2 activation and stimulation of vascular development. Binding of VEGF-A to HSPGs in trans leads to accumulation of activated VEGFR-2 in endothelial cells and to prolonged signaling. This demonstrates a potential role for HSPGs in regulation of receptor trafficking and signaling kinetics, with possible implications also for other HS-binding ligand/receptor systems.