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Yuen, Yee Lok. / On t.p. "alpha" appears as the Greek letter. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 165-177). / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.iv / Acknowledgement --- p.vii / Table of Contents --- p.viii / List of Abbreviations --- p.xiii / List of Figures --- p.xv / List of Tables --- p.xx / Chapter Chapter 1 --- Literature review --- p.1 / Chapter 1.1 --- Peroxisome proliferator-activated receptor (PPAR) --- p.1 / Chapter 1.1.1 --- PPARα isoforms --- p.1 / Chapter 1.2 --- PPARα ligands --- p.2 / Chapter 1.3 --- Biological roles of PPARα --- p.3 / Chapter 1.3.1 --- Lipid metabolism --- p.3 / Chapter 1.3.2 --- Bile acid metabolism --- p.4 / Chapter 1.3.3 --- Biotransformation --- p.6 / Chapter 1.4 --- Roles of PPARα in hepatocarcinogenesis --- p.7 / Chapter 1.4.1 --- Cell proliferation and apoptosis --- p.7 / Chapter 1.4.2 --- Oxidative stress --- p.8 / Chapter 1.5 --- Discovery of novel PPARα target genes --- p.9 / Chapter 1.5.1 --- Identification of a novel PPARα-regulated gene L5#55 by fluorescent differential mRNA display (FDD) analysis --- p.9 / Chapter 1.6 --- Sulfotransferase (SULT) --- p.15 / Chapter 1.7 --- Objective of the present study --- p.16 / Chapter Chapter 2 --- Molecular cloning and characterization of mouse liver sulfotransferase-like (mL-STL) gene --- p.17 / Chapter 2.1 --- Introduction --- p.17 / Chapter 2.2 --- Materials and methods --- p.17 / Chapter 2.2.1 --- Animals --- p.17 / Chapter 2.2.2 --- Treatments --- p.18 / Chapter 2.2.3 --- Total RNA extraction --- p.18 / Chapter 2.2.3.1 --- Materials --- p.18 / Chapter 2.2.3.2 --- Methods --- p.19 / Chapter 2.2.4 --- Rapid amplification of cDNA ends (RACE) --- p.19 / Chapter 2.2.4.1 --- Materials --- p.19 / Chapter 2.2.4.2 --- Methods --- p.20 / Chapter 2.2.4.2.1 --- Primer design --- p.20 / Chapter 2.2.4.2.2 --- Rapid amplification of 5'- and 3'-cDNA ends --- p.20 / Chapter 2.2.5 --- Cloning of the 5'- and 3' RACE products --- p.25 / Chapter 2.2.5.1 --- Materials --- p.25 / Chapter 2.2.5.2 --- Methods --- p.25 / Chapter 2.2.6 --- Northern blot analysis --- p.28 / Chapter 2.2.6.1 --- Materials --- p.28 / Chapter 2.2.6.2 --- Methods --- p.28 / Chapter 2.2.6.2.1 --- Formaldehyde-agarose gel electrophoresis and blotting of RNA --- p.31 / Chapter 2.2.6.2.2 --- PCR DIG-labeling --- p.31 / Chapter 2.2.6.2.3 --- Hybridization and signal detection --- p.32 / Chapter 2.2.7 --- Reverse transcription (RT)-PCR --- p.34 / Chapter 2.2.7.1 --- Materials --- p.34 / Chapter 2.2.7.2 --- Methods --- p.34 / Chapter 2.3 --- Results and discussion --- p.37 / Chapter 2.3.1 --- Cloning of the full-length mL-STL cDNA --- p.37 / Chapter 2.3.2 --- In silico analysis of the mL-STL cDNAs --- p.50 / Chapter 2.3.3 --- Genomic organization of the mL-STL gene --- p.61 / Chapter 2.3.4 --- Tissue distribution of mL-STL mRNA transcript --- p.68 / Chapter 2.3.5 --- "PPARα-dependent regulation of mL-STL mRNA expression by fasting and Wy-14,643 treatment" --- p.74 / Chapter Chapter 3 --- Identification of the native mL-STL protein in mouse liver --- p.86 / Chapter 3.1 --- Introduction --- p.86 / Chapter 3.2 --- Materials and methods --- p.87 / Chapter 3.2.1 --- Animal and treatments --- p.87 / Chapter 3.2.2 --- Cloning of the mL-STL cDNA into a modified pRSET (mpRSET) expression vector --- p.88 / Chapter 3.2.2.1 --- Materials --- p.88 / Chapter 3.2.2.2 --- Methods --- p.88 / Chapter 3.2.2.2.1 --- Amplification of mL-STL cDNA fragments --- p.88 / Chapter 3.2.2.2.2 --- Preparation of mpRSET expression vector --- p.92 / Chapter 3.2.2.2.3 --- "Ligation, transformation, and screening of recombinants" --- p.92 / Chapter 3.2.3 --- Over-expression of the mL-STL recombinant proteins in E coli strains --- p.94 / Chapter 3.2.3.1 --- Materials --- p.94 / Chapter 3.2.3.2 --- Methods --- p.94 / Chapter 3.2.4 --- Mass spectrometry analysis of the mL-STL recombinant proteins --- p.95 / Chapter 3.2.4.1 --- Materials --- p.96 / Chapter 3.2.4.2 --- Methods --- p.96 / Chapter 3.2.4.2.1 --- Trypsin digestion and peptide extraction --- p.96 / Chapter 3.2.4.2.2 --- Matrix-assisted laser desorption/ionization time-of- flight (MALDI-TOF) mass spectrometry --- p.97 / Chapter 3.2.5 --- Purification of the mL-STL recombinant proteins --- p.98 / Chapter 3.2.5.1 --- Materials --- p.98 / Chapter 3.2.5.2 --- Methods --- p.98 / Chapter 3.2.5.2.1 --- Semi-purification of the mL-STL recombinant proteins by preparative SDS-PAGE --- p.98 / Chapter 3.2.5.2.2 --- Purification of mL-STL recombinant proteins by column chromatography --- p.99 / Chapter 3.2.6 --- Rabbit immunization using purified mL-STL recombinant proteins --- p.101 / Chapter 3.2.7 --- Subcellular fractionation of mouse liver by ultracentrifugation --- p.101 / Chapter 3.2.7.1 --- Materials --- p.101 / Chapter 3.2.7.2 --- Methods --- p.102 / Chapter 3.2.8 --- Western blot analysis of the native mL-STL protein --- p.104 / Chapter 3.2.8.1 --- Materials --- p.104 / Chapter 3.2.8.2 --- Methods --- p.104 / Chapter 3.2.8.2.1 --- SDS-PAGE and electro-blotting of proteins --- p.104 / Chapter 3.2.8.2.2 --- Immunostaining and signal detection --- p.105 / Chapter 3.3 --- Results and discussion --- p.106 / Chapter 3.3.1 --- Cloning of the mL-STLl and mL-STL2 cDNAs into a modified pRSET (mpRSET) vector --- p.106 / Chapter 3.3.2 --- IPTG induction of the mpRSET-mL-STL protein expression --- p.106 / Chapter 3.3.3 --- Confirmation of mL-STL recombinant proteins by mass spectrometry --- p.118 / Chapter 3.3.4 --- Purification of mL-STL recombinant proteins for rabbit immunization and polyclonal antisera production --- p.130 / Chapter 3.3.5 --- Antigenicity of mL-STL antisera --- p.134 / Chapter 3.3.6 --- Identification of mL-STL native protein and its induction pattern in mouse liver --- p.139 / Chapter 3.3.7 --- "Time-course of fasting and Wy-14,643 treatment on the mL- STLl native protein expression" --- p.147 / Chapter Chapter 4 --- Overall discussion --- p.153 / Future study --- p.163 / References --- p.165 / "Appendix A. Alignment of nucleotide sequences of mouse chromosome 7，Riken2810007J24, mL-STLl, and mL-STL2 cDNA sequences" --- p.178 / Appendix Bl. Theoretical tryptic peptide masses of mpRSET- mL-STLl protein --- p.217 / Appendix B2. Raw data from mass spectrometry analysis of mpRSET-mL-STLl protein --- p.218 / Appendix C1. Residue molecular mass of amino acids --- p.219 / Appendix C2. Di-peptide table --- p.220 / Appendix D1. Theoretical tryptic peptide masses of mpRSET- mL-STL2 protein --- p.221 / Appendix D2. Raw data from mass spectrometry analysis of mpRSET-mL-STL2 protein --- p.222

Xu, Jian. / Thesis Ph.D. Chinese University of Hong Kong 2015. / Includes bibliographical references (leaves 238-255). / Abstracts also in Chinese. / Title from PDF title page (viewed on 24, October, 2016).

Industrial chemicals known as polychlorinated biphenyls (PCBs) were widely used for decades until their production was banned worldwide due to their persistence and toxicities to humans and other animals. Upon oxidative metabolism by cytochrome P450, hydroxylated metabolites of PCBs (OHPCBs) are formed. OHPCBs have been shown to competitively displace thyroxine from transthyretin, block normal hormonal activity, and inhibit phenol or family 1 sulfotransferases (SULTs) which catalyze sulfation of thyroid hormones and estrogens. Recently, three OHPCBs were shown to also interact with hydroxysteroid or family 2 sulfotransferases that play a role in the homeostasis of steroid hormones such as dehydroepiandrosterone (DHEA). The objectives of the studies presented in this thesis were to further examine the effects of selected OHPCBs on the activity of human hydroxysteroid sulfotransferase (hSULT2A1), to develop a three-dimensional quantitative structure activity relationship (3D-QSAR) model for OHPCBs as inhibitors of DHEA-sulfation catalyzed by this enzyme, and to investigate the mechanism of inhibition and binding of OHPCBs to hSULT2A1. All 15 OHPCBs examined inhibited the sulfation of 1 μ M [3H] DHEA, catalyzed by hSULT2A1 with IC50 values ranging from 0.6 to 96 μ M. The OHPCBs with a 3, 5-dichloro-4-hydroxy substitution were the most potent inhibitors of DHEA sulfation, and they were also shown to be substrates for hSULT2A1. Eight OHPCBs were substrates for hSULT2A1, and seven were solely inhibitors (i.e. they inhibited the sulfation of DHEA, yet they were not themselves sulfuryl-acceptors in hSULT2A1-catalyzed reactions). A 3D-QSAR model was developed utilizing comparative molecular field analysis (CoMFA). The model fit the data well and also had good predictability. The kinetics of inhibition showed that these OHPCBs were noncompetitive inhibitors of hSULT2A1. Binding studies utilizing the displacement of a fluorescent probe, 8-anilino-1-naphthalene sulfonic acid, revealed that several of the OHPCBs interact either at more than one binding site or with more than one enzyme conformation. Further exploration of this binding by molecular modeling showed that OHPCBs bind similarly to different conformations of the enzyme. This work has helped in our understanding of the roles of sulfotransferases in the metabolism and toxicities of OHPCBs, and it opens new avenues for future work.

<p>Heparan sulfates (HSs) are linear, negatively charged polysaccharides composed of alternating hexuronic acid (glucuronic acid or iduronic acid) and glucosamine residues that can be substituted to varying degrees with sulfate groups. HS, localized in the extracellular matrix and on the surface of most cells, interacts with a large number of proteins. The actions of HS largely depend on the amount and distribution of its sulfate groups, that provide binding sites for proteins. </p><p>This thesis focuses on the regulation of the structural diversity in HS, in particular the regulation of its 6-<i>O</i>-sulfation patterns that are generated by the combined action of 6-<i>O</i>-sulfotransferases (6OSTs) during biosynthesis, and 6-<i>O</i>-endosulfatases (Sulfs) after completed biosynthesis. In addition, a new model organism is introduced that offers good prospects for investigating the evolutional aspects of HS structural heterogeneity.</p><p>Our studies showed that the three mouse 6OSTs (6OST1-3) exhibit similar substrate specificities <i>in vitro</i>, with minor differences in target preferences. Overexpression of the 6OSTs in cells resulted in increased 6-<i>O</i>-sulfation of both <i>N</i>-sulfated and <i>N</i>-acetylated glucosamine residues. The changes were independent of enzyme isoform but positively correlated to the level of enzyme expressed.</p><p>Quail Sulf1 and Sulf2 enzymes were shown to be cell surface HS 6-<i>O-</i>endosulfatases with preference towards a subset of trisulfated disaccharides within HS chains. The Sulfs contain a “hydrophilic domain” that was shown to be essential for binding of HS, anchorage to the cell surface and endosulfatase activity. QSulf1 was also shown to promote Wnt-Frizzled signaling in cells. </p><p>An HS-like polysaccharide was isolated from the sea anemone <i>Nematostella vectensis</i> and characterized, and all the enzyme families involved in HS biosynthesis and modification in mammalian model systems were also identified. Our results suggest that <i>Nematostella</i> may be a useful tool for understanding the role of evolution in generating HS structural diversity.</p>

<P align=justify>Aromatische Amine und Amide (aAA) sind aufgrund ihrer starken Verbreitung in der menschlichen Umwelt und ihres kanzerogenen Potenzials von großer toxikologischer Bedeutung. Die Kanzerogenität der aAA wird durch die Mutagenität hochreaktiver Stoffwechselprodukte vermittelt, die in zwei sequenziellen katalytischen Reaktionen entstehen. Die erste ist meistens eine <I>N</I>-Hydroxylierung, die oft durch Cytochrom P450 1A2 (CYP1A2) katalysiert wird. Daran schließt sich eine <I>O</I>-Konjugation durch Sulfotransferasen (SULT) oder <I>N</I>-Acetyltransferasen (NAT) an. Die Bioaktivierung ist ein kritischer Parameter für die Übertragbarkeit von Ergebnissen aus Tiermodellen auf den Menschen. </P><P align=justify>Rekombinante <I>in vitro</I> Systeme, die fremdstoffmetabolisierende Enzyme verschiedener Spezies exprimieren, ermöglichen die vergleichende Untersuchung der Bioaktivierung im Menschen und in Versuchstieren. Ziel des Projektes war die Aufklärung der Bioaktivierung der aAA durch humane Enzyme. Im Vordergrund stand die Untersuchung der Rolle humaner SULT in diesem Prozess. Es wurden rekombinante <I>in vitro</I> Systeme, konstruiert, die CYP1A2 und SULT des Menschen koexprimieren. SULT-cDNAs wurden in den Säugerzell Expressionsvektor pMPSV kloniert und in Standardindikatorzellen für Mutagenitätsuntersuchungen (V79 Zellen aus dem Chinesischen Hamster) transfiziert. Das Expressionsniveau von CYP1A2 und SULT wurde mittels Immunblotanalyse und radiometrischen Aktivitätsmessungen charakterisiert. In den rekombinanten Zellen wurden vier aAA als Modellsubstanzen (2-Acetylaminofluoren, 2-Aminoanthracen, 3&prime;-Methyl-4-dimethylaminoazobenzol, 2,4-Diaminotoluol) auf ihre Mutagenität am <I>hprt</I>-Locus hin untersucht.</P><P align=justify>Die aAA waren in Zellen, die keine rekombinanten Enzyme oder lediglich CYP1A2 exprimierten, nicht mutagen. In Zellen, die CYP1A2 und SULT der Subfamilie 1A koexprimierten, erzeugten sie bereits in geringen Konzentrationen klare mutagene Effekte (0,3 &#181;M für 2-Acetylaminofluoren <br /> und 3&prime;-Methyl-4-dimethylaminoazobenzol; 0,1 &#181;M für 2-Aminoanthracen; 10 &#181;M für 2,4-Diaminotoluol). Die stärkste Aktivierung von 2-Acetylaminofluoren und 3&prime;-Methyl-4-dimethylaminoazobenzol erfolgte in der Zelllinie, die CYP1A2 und SULT1A2 koexprimierte; die stärkste Aktivierung von 2,4-Diaminotoluol und 2-Aminoanthracen erfolgte in der Zelllinie, die CYP1A2 und SULT1A1 koexprimierte. </P><P align=justify>Sowohl SULT1A1 als auch SULT1A2 sind im Menschen genetisch polymorph. Ein unterschiedlich starkes Aktivierungspotenzial der Alloenzyme könnte eine individuell unterschiedliche Suszeptibilität für die durch aAA ausgelöste Kanzerogenese bedingen. In HPRT-Mutationsuntersuchungen mit rekombinanten Zellen zeigten die allelischen Varianten der SULT1A2 starke Unterschiede in ihrem Aktivierungpotenzial. Nur in der Zelllinie, die das Alloenzym SULT1A2*1 mit CYP1A2 koexprimierte, wurde 2-Acetylaminofluoren zum Mutagen aktiviert. Zur Aktivierung von 3&prime;-Methyl-4-dimethylaminoazobenzol waren jedoch sowohl das Alloenzym SULT1A2*1 als auch das Alloenzym SULT1A2*2 in der Lage. Die Alloenzyme der SULT1A1 zeigten ein ähnlich gutes Aktivierungspotenzial für aAA. </P><P align=justify>In früheren Studien wurde gezeigt, dass die SULT1C1 der Ratte eine wichtige Rolle bei der Aktivierung der aAA in dieser Spezies spielt. Dahingegen war die humane SULT1C1 nicht in der Lage die untersuchten aAA zu aktivieren. Die Kenntnis solcher Spezieunterschiede könnte wichtig sein um unterschiedliche Organotropismen aAA in Menschen und Tiermodellen zu erklären, da SULT mit starker Gewebespezifität exprimiert werden und das Expressionsmuster für die einzelnen SULT-Formen in Menschen und Ratten sich stark unterscheidet.</P><br> / <P align=justify>Aromatic amines and amides (aAA) represent a group of chemicals with great toxicological importance due to their wide distribution in the environment and their carcinogenic potency. The carcinogenicity of aAA is mediated by the mutagenic action of highly reactive metabolites. They are frequently formed by <I>N</I>-hydroxylation of the exocyclic amino group, usually catalysed by cytochrome P450 1A2 (CYP1A2) and subsequent <I>O</I>-conjugation by phase-II enzymes e.g. sulfotransferases (SULT) or <I>N</I>-acetyltransferases. </P> <P align=justify>The bioactivation constitutes a critical parameter for the transfer of results from animal models on man. Recombinant <I>in vitro</I> systems expressing xenobiotic metabolizing enzymes of different species allow the comparative study of the bioactivation in humans and animal models. <BR>The aim of this project was to elucidate the bioactivation of aAA by human xenobiotic enzymes. The investigation focused on the role of SULT in this process. SULT-cDNAs were cloned into the mammalian expression vector pMPSV and transfected in V79 Chinese Hamster cells, which represent standard indicator cells for mutagenicity tests. Selected SULT-cDNAs were also co-expressed with human CYP1A2. These cells were able to catalyse internally both enzymatic reactions that are necessary for the bioactivation of aAA. The expression level of CYP1A2 and SULT in the co-expressing cell clones was characterised by immunoblot analysis and radiometric SULT-activity measurement. The mutagenicity of four aAA model compounds, 2-aminoanthracene, 2-acetylaminofluorene, 3'-methyl-4-dimethylaminoazobenzene and 2,4-diaminotoluene, at the <I>hprt</I> locus of the recombinant cell lines was investigated.</P><br /> <P align=justify>These aAA were not or only marginally mutagenic in wild type cells or in recombinant cells expressing CYP1A2 alone. If CYP1A2 was co-expressed with SULT forms of the 1A subfamily clear mutagenic effects occured in low concentrations of the aAA (0,3 &#181;M for 2-acetylaminofluorene and 3&prime;-methyl-4-dimethylaminoazobenzene; 0,1 &#181;M for 2-aminoanthracene; 10 &#181;M for 2,4-diaminotoluene). The strongest activation of 2-acetylaminofluorene and 3'-methyl-4-dimethylaminoazobenzene was mediated by SULTA2 and of 2-aminoanthracene and 2,4-diaminotoluene by SULT1A1. </P><br /> <P align=justify>SULT1A1 and SULT1A2 are expressed polymorphically in humans. Differences in the activation potency of distinct alloenzymes for aAA may cause divergent individual susceptibilities for cancer induced by aAA. Briefly, the allelic variants of SULT1A2 showed substantial differences regarding their activation potencies for the investigated aAA. Only alloenzyme SULT1A2*1 was able to activate 2-acetylaminofluorene to a mutagen whereas 3&prime;-methyl-4-di-methylaminoazobenzene was activated by alloenzymes SULT1A2*1 and SULT1A2*2. The investigated alloenzymes of SULT1A1 showed equal activation potencies for aAA. </P><br /> <P align=justify>In previous studies it had been shown that the SULT1C1 plays an important role in the activation of aAA in rats. However, the human SULT1C1 was not able to activate the investigated aAA in the study presented here. Such species differences might be important for the elucidation of divergent organotropisms of aAA in humans and animal models, since SULT are expressed with strong tissue specificities and the pattern of expression in humans and rats is severely different.</P><br>

Heparan sulfates (HSs) are linear, negatively charged polysaccharides composed of alternating hexuronic acid (glucuronic acid or iduronic acid) and glucosamine residues that can be substituted to varying degrees with sulfate groups. HS, localized in the extracellular matrix and on the surface of most cells, interacts with a large number of proteins. The actions of HS largely depend on the amount and distribution of its sulfate groups, that provide binding sites for proteins. This thesis focuses on the regulation of the structural diversity in HS, in particular the regulation of its 6-O-sulfation patterns that are generated by the combined action of 6-O-sulfotransferases (6OSTs) during biosynthesis, and 6-O-endosulfatases (Sulfs) after completed biosynthesis. In addition, a new model organism is introduced that offers good prospects for investigating the evolutional aspects of HS structural heterogeneity. Our studies showed that the three mouse 6OSTs (6OST1-3) exhibit similar substrate specificities in vitro, with minor differences in target preferences. Overexpression of the 6OSTs in cells resulted in increased 6-O-sulfation of both N-sulfated and N-acetylated glucosamine residues. The changes were independent of enzyme isoform but positively correlated to the level of enzyme expressed. Quail Sulf1 and Sulf2 enzymes were shown to be cell surface HS 6-O-endosulfatases with preference towards a subset of trisulfated disaccharides within HS chains. The Sulfs contain a “hydrophilic domain” that was shown to be essential for binding of HS, anchorage to the cell surface and endosulfatase activity. QSulf1 was also shown to promote Wnt-Frizzled signaling in cells. An HS-like polysaccharide was isolated from the sea anemone Nematostella vectensis and characterized, and all the enzyme families involved in HS biosynthesis and modification in mammalian model systems were also identified. Our results suggest that Nematostella may be a useful tool for understanding the role of evolution in generating HS structural diversity.

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 chaînes de glycosaminoglycanes (GAGs) des protéoglycanes (PGs) jouent un rôle majeur dans la régulation de multiples événements cellulaires et le maintien de l'architecture des tissus. Des perturbations de la synthèse des GAGs sont impliquées dans des pathologies d'origine dégénérative, tumorale et génétique, tel que le syndrome progéroïde d'Ehlers-Danlos (ED). Ce déficit résulte de mutations de la [bêta]1,4-galactosyltransférase 7 ([bêta]4GalT7) humaine associées à des atteintes sévères du système musculo-squelettique. En effet, cette enzyme catalyse une étape essentielle de l?initiation de la synthèse des GAGs à partir de la protéine "core" des PGs et de xylosides exogènes. Notre travail a porté sur l'étude structure-fonction de la [bêta]4GalT7 recombinante humaine. Nous avons associé des approches in vitro et ex vivo afin d?explorer le rôle des acides aminés des motifs 163DVD165, 221FWGWGREDDD230 et 257HLH259, strictement conservés au sein des [bêta]4GalTs. L'étude des conséquences de mutations systématiques sur les propriétés cinétiques et fonctionnelles de la [bêta]4GalT7 recombinante a permis d'identifier des acides aminés essentiels du site actif. Nous avons montré que les résidus D165 et H257 forment des liaisons de coordination avec le cation Mn2+ et proposé le rôle du résidu D228 dans la catalyse. Nous avons mis en évidence un rôle central du résidu W224 dans les interactions avec les substrats donneur et accepteur. Nous avons également établi les bases moléculaires des mutations de la [bêta]4GalT7 associées au syndrome ED. Enfin, l'étude de mécanismes de régulation épigénétique des voies de biosynthèse des GAGs dans les cellules H-EMC-SS de chondrosarcome humain a mis en évidence une hyperméthylation spécifique des gènes de la famille des 3-O-sulfotransférases, associée à un phénotype invasif. L'ensemble de ce travail ouvre des perspectives vers de nouvelles stratégies thérapeutiques dans le traitement des arthropathies / Proteoglycans (PGs) and their glycosaminoglycan chains (GAGs), play a major role in the architecture of extracellular matrices and are implicated in numerous cell events. The impairment of GAG synthesis and sulfation is involved in degenerative, tumor and genetic diseases, such as the progeroid form of Ehlers-Danlos (ED) syndrome. This inherited disorder is due to mutations of human [bêta]4GalT7 ([bêta]4GalT7) causing a defect in GAG synthesis, associated with severe musculo-skeletal alterations. Indeed, this enzyme catalyzes a key step in GAG synthesis linked to the core protein of PGs and from exogenous xylosides. Our work has been focused on the structural and functional characterization of human recombinant [bêta]4GalT7 enzyme. We combined in vitro and ex vivo approaches to explore the role of amino acids located in 163DVD165, 221FWGWGREDDD230 and 257HLH259 motifs, which are highly conserved within [bêta]4GalTs. The study of the consequences of site-directed mutations on kinetic and functional properties of the [bêta]4GalT7 enzyme allowed us to identify key active site amino acids. Our results indicate that D165 and H257 residues form coordination bonds with Mn2+ divalent cations. Furthermore, we suggested a catalytic role for D228 residue and highlighted a central role of W224 residue via interactions with the donor and acceptor substrates. We also determined the molecular basis of [bêta]4GalT7 mutations associated with ED syndrome. Finally, the study of epigenetic regulation mechanisms by DNA methylation of GAG biosynthesis in human chondrosarcoma cells (H-EMC-SS) revealed the specific hypermethylation of the 3-O-sulfotransferase gene family, associated with the invasive phenotype of these cells. Together, this work paves the way towards innovative strategies in the treatment of arthropathies