Thesis (M.D) -- University of Texas Southwestern Medical Center at Dallas, 2007. / Vita. Bibliography: pp. 35-37.

<p>Heparan sulfate (HS) is a glycosaminoglycan present in all cell types covalently attached to core proteins forming proteoglycans. HS interacts with different proteins and thereby affects a variety of processes. The biosynthesis of HS takes place in the Golgi network where a complex of the enzymes EXT1 and EXT2 adds N-acetyl glucosamine and glucuronic acid units to the growing chain. The HS chain is <i>N</i>-sulfated by the enzyme <i>N</i>-deacetylase <i>N</i>-sulfotransferase (NDST). <i>N</i>-Sulfation occurs in domains where further modifications (including <i>O</i>-sulfations) take place, giving the chain a complex sulfation pattern.</p><p>In this thesis, new data about the regulation of NDST enzyme activity is presented. By studying NDST1 with active site mutations overexpressed in HEK 293 cells we show that <i>N</i>-deacetylation is the rate-limiting step in HS <i>N</i>-sulfation and that two different NDST molecules can work on the same GlcN unit.</p><p>By analyzing recombinant forms of NDST1 and NDST2 we determined the smallest substrate for <i>N</i>-deacetylation to be an octasaccharide. Importantly, the sulfate donor PAPS was shown to regulate the NDST enzymes to modify the HS chain in domains and that binding of PAPS had a stimulating effect on <i>N</i>-deacetylase activity. </p><p>We could also show that increased levels of NDST1 were obtained when NDST1 was coexpressed with EXT2, while coexpression with EXT1 had the opposite effect. We suggest that EXT2 binds to NDST1, promoting the transport of functional NDST1 to the Golgi network and that EXT1 competes for binding to EXT2. </p><p>Using cell lines overexpressing EXT proteins, it was demonstrated that overexpression of EXT1 increases HS chain length and coexpression of EXT2 results in even longer chains. The enhancing effect of EXT2 was lost when EXT2 was carrying mutations identical to those found in patients with hereditary multiple exostoses, a syndrome characterized by cartilage-capped bony outgrowths at the long bones.</p><p>.</p>

Heparan sulfate (HS) is a glycosaminoglycan present in all cell types covalently attached to core proteins forming proteoglycans. HS interacts with different proteins and thereby affects a variety of processes. The biosynthesis of HS takes place in the Golgi network where a complex of the enzymes EXT1 and EXT2 adds N-acetyl glucosamine and glucuronic acid units to the growing chain. The HS chain is N-sulfated by the enzyme N-deacetylase N-sulfotransferase (NDST). N-Sulfation occurs in domains where further modifications (including O-sulfations) take place, giving the chain a complex sulfation pattern. In this thesis, new data about the regulation of NDST enzyme activity is presented. By studying NDST1 with active site mutations overexpressed in HEK 293 cells we show that N-deacetylation is the rate-limiting step in HS N-sulfation and that two different NDST molecules can work on the same GlcN unit. By analyzing recombinant forms of NDST1 and NDST2 we determined the smallest substrate for N-deacetylation to be an octasaccharide. Importantly, the sulfate donor PAPS was shown to regulate the NDST enzymes to modify the HS chain in domains and that binding of PAPS had a stimulating effect on N-deacetylase activity. We could also show that increased levels of NDST1 were obtained when NDST1 was coexpressed with EXT2, while coexpression with EXT1 had the opposite effect. We suggest that EXT2 binds to NDST1, promoting the transport of functional NDST1 to the Golgi network and that EXT1 competes for binding to EXT2. Using cell lines overexpressing EXT proteins, it was demonstrated that overexpression of EXT1 increases HS chain length and coexpression of EXT2 results in even longer chains. The enhancing effect of EXT2 was lost when EXT2 was carrying mutations identical to those found in patients with hereditary multiple exostoses, a syndrome characterized by cartilage-capped bony outgrowths at the long bones. .

Proteoglycans (PGs) are composed of highly sulfated glycosaminoglycans chains (GAGs) attached to specific core proteins. They are present in extracellular matrices, on the cell surface and in storage granules of hematopoietic cells. Heparan sulfate (HS) and chondroitin/dermatan sulfate (CS/DS) GAGs play indispensable roles in a wide range of biological processes, where they can serve as protein carriers, be involved in growth factor or morphogen gradient formation and act as co-receptors in signaling processes. Protein binding abilities of GAGs are believed to be predominantly dependent on the arrangement of the sugar modifications, sulfation and epimerization, into specific oligosaccharide sequences. Although the process of HS and CS/DS assembly and modification is not fully understood, a set of GAG biosynthetic enzymes have been fairly well studied and several mutations in genes encoding for this Golgi machinery have been linked to human genetic disorders. This thesis focuses on the zebrafish N-deacetylase/N-sulfotransferase gene family, encoding key enzymes in HS chain modification, as well as glycosyltransferases responsible for chondroitin/dermatan sulfate elongation present in zebrafish. Our data illustrates the strict spatio-temporal expression of both the NDST enzymes (Paper I) and CS/DS glycosyltransferases (Paper II) in the developing zebrafish embryo. In Paper III we took advantage of the four preexisting zebrafish mutants with defective GAG biosynthesis. We could demonstrate a relation between HS content and the severity of the pectoral fin defects, and additionally correlate impaired HS biosynthesis with altered chondrocyte intercalation. Interestingly, altered CS biosynthesis resulted in loss of the chondrocyte extracellular matrix. One of the main findings was the demonstration of the ratio between the HS biosynthesis enzyme Extl3 and the Csgalnact1/Csgalnact2 proteins, as a main factor influencing the HS/CS ratio. In Paper IV we used the newly developed CRISPR/Cas9 technique to create a collection of zebrafish mutants with defective GAG biosynthetic machineries. Lack of phenotypes linked to null-mutations of most of the investigated genes is striking in this study.

The aim of the study was to investigate the expression NDST transcripts in a wide variety of tissues using RNA-sequencing experimental data from five published studies, using two common in silico tools: the Tophat-Cufflink pipeline and the HTSeq-DEXSeq pipeline. We show that to detect NDST alternative transcripts, paired-end sequencing should be used with replicates of samples or conditions together with 100 base read length to allow for reliable detection of the low expressed transcripts in the NDST family.  As a demonstration project, we also characterized HS synthesized by the adrenal carcinoma (ACC) cell line H295R and determined expression of NDSTs in the cells and in ACC tumor samples. We could show that roughly 65% of newly synthesized proteoglycans isolated after metabolic 35S-sulfate labeling of the cells are made up of heparan sulfate (HS) with an average chain length of 45 kDa. The HS chains show a high frequency of N-sulfation and a high total degree of sulfation. Interestingly, disaccharide analysis demonstrated a three-time higher amount of stored chondroitin sulfate (CS) compared to HS in the ACC cell line.

No description available.

Sulfatide is a galactolipid and a major lipid component of the myelin sheath. Its production is catalyzed by the enzyme cerebroside sulfotransferase (CST). To determine the functions of sulfatide, the gene encoding CST was genetically disrupted resulting in mice incapable of sulfatide synthesis. Using these mice, it has been shown in the central nervous system (CNS) that sulfatide is essential for normal myelin synthesis and stability even though the onset of myelination is not impaired. Additionally, proper initial clustering of paranodal proteins and cluster maintenance of nodal proteins is impaired suggesting that paranodal domains are important for long-term node stability. In contrast to the CNS, a requirement for sulfatide in the initiation of myelination, and in initiation of paranodal and nodal clustering or in the long-term maintenance of these clusters in the peripheral nervous system (PNS) has not been analyzed. Therefore, we have employed a combination of electron microscopic, immunocytochemical, and confocal microscopic analyses of the CST KO mice to determine the role of sulfatide in PNS myelination and onset of protein domain formation and maintenance. For these studies we have quantified myelin thickness, paranodal structural integrity, and the number of paranodal and nodal protein clusters in the CST KO and wild type mice at 4 days, 7 days, and 10 months of age. Our findings indicate that myelination onset is not delayed in the absence of sulfatide and that both the node and paranode are grossly normal; however, closer analysis reveals that paranodal junctions are compromised, Schwann cell microvilli are disoriented and the myelin-axon interface along the internodal region is transiently disrupted. In addition, we report that the paranodal myelin protein neurofascin 155 (Nfasc155) shows a transient decrease in initial clustering in the CST null mice at 4 days of age that is restored to WT levels by 7 days of age that is also maintained in the adult mice. Whereas nodal clustering of neuronal voltage-gated sodium channels is initially normal, cluster number is significantly but also transiently reduced by 7 days of age. By 10 months of age, the number of sodium channel clusters is restored to normal levels. In contrast, clustering of neither the paranodal neuronal protein contactin nor the myelin nodal protein gliomedin is altered at any of the ages studied. Together our findings suggest that sulfatide is not essential for PNS myelination or for protein domain formation in contrast to its more vital role in the development and maintenance of the CNS.

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.

<p>In the extracellular space, many specialized proteins are located to support cells and to mediate cell-cell signalling. One class of such molecules is heparan sulfate (HS) proteoglycans, which are proteins with different properties and locations but all of them decorated with long unbranched HS polysaccharide chains. During biosynthesis the HS chains are modified by sulfation and a C5-epimerase converts some glucuronic acid residues to iduronic acid. The patterns of the modifications vary distinctly between tissues and developing stages and give HS chains different affinity for biologically important proteins. Thus, the regulation of HS biosynthesis is likely to influence a wide variety of biological events.</p><p>This thesis focuses on the biosynthesis of HS in animals with targeted disruptions in genes important for HS production. The N-deacetylase N-sulfotransferase (NDST) is a key enzyme in HS biosynthesis, directing other modifications. We show that NDST isoforms have very different roles in HS biosynthesis. Inactivation of NDST1 affects HS biosynthesis in all tissues. In embryonic liver HS from NDST1-/- mice the N-sulfation was decresed with twothirds, while the absence of NDST2 did not affect HS structure. In the absence of NDST1 in the liver, however, NDST2 is active in HS N-sulfation. </p><p>In a study of embryonic stem cells lacking both NDST1 and NDST2, no N-sulfate groups could be detected. 6-O-sulfate groups were, however, still present at half of its normal level. This was an unexpected finding since 6-O-sulfotransferases have been thought to be strictly dependent on N-sulfate groups for substrate recognition.</p><p>By adapting an automated method for HS analysis to mammalian tissues, we could extend our analyses to more tissues and other transgene models. We also developed a protocol to create a sensitive “fingerprint” of HS structure. With these methods we could determine the individual HS structure of different mouse tissues. </p>

<p>Heparan sulfate (HS) proteoglycans consist of sulfated HS chains covalently bound to core proteins. They are ubiquitously expressed, on the cell surface and in the extracellular matrix, throughout the body. During biosynthesis the HS chain is modified to generate a highly variable pattern of sulfated residues, able to interact with a wide variety of ligands, such as growth factors, morphogens and extracellular matrix molecules. The presence of HS proteoglycans is crucial during various developmental processes as they are involved in generation of morphogen gradients and influence the function of several growth factor pathways essential for tissue assembly and differentiation.</p><p>In this thesis the phenotypes of two mouse strains, deficient in different isoforms of the HS biosynthetic enzyme N-deacetylase/N-sulfotransferase (NDST) have been analyzed. In addition, NDST deficient embryonic stem (ES) cells have been analyzed with regard to HS structure and differentiation capacity. Mice deficient in NDST1 die peri-natally. The embryos display an overall low-sulfated HS and several developmental defects, with a lung phenotype as the predominant cause of death. Mice deficient in NDST2 lack sulfated heparin in connective tissue type mast cells while HS structure is unaltered. These results indicate that NDST1 is the isoform mainly responsible for HS biosynthesis during development. However, NDST1/2 deficient embryos do not survive beyond E5.5 and have a greatly disturbed morphology, suggesting that NDST2 has an essential role during early embryonic development. HS synthesized by NDST1/2 deficient ES cells had a total lack of N-sulfate groups while, interestingly, about half of the 6-O-sulfate groups remained. This result was unexpected since 6-O-sulfotransferases have been thought to be strictly dependent on N-sulfate groups for substrate recognition. Further characterization of the NDST1/2 deficient ES cells during in vitro differentiation demonstrated that the expression pattern of markers for all three germ layers was disturbed. In addition, it was demonstrated that NDST1 is not needed for mast cell development, that lack of NDST2 results in abnormal mast cells and that no mast cells is formed from NDST1/2 deficient ES cells.</p>