Dissertation (Ph.D.)--University of South Florida, 2007. / Includes vita. Includes bibliographical references. Also available online.

The misfolding and aggregation of the beta cell hormone islet amyloid polypeptide (IAPP) into amyloid fibrils is the main pathological finding in islets of Langerhans in type 2 diabetes. Pathological assemblies of IAPP are cytotoxic and believed to contribute to the loss of insulin-producing beta cells. Changes in the microenvironment that could trigger the aggregation of IAPP are largely unknown. So is the possibility that islet amyloid can spread within or between tissues. The present thesis have explored the roles of glycosaminoglycan heparan sulfate (HS) and the novel anti-amyloid chaperone Bri2 BRICHOS domain in the assembly of IAPP amyloid and cytotoxic IAPP aggregates. Furthermore, cross-seeding as a molecular interaction between the observed connection of type 2 diabetes and Alzheimer disease has been examined. The N-terminal region of IAPP was required for binding to HS structures and induction of binding promoted amyloid formation. Interference in the HS-IAPP interaction by heparanase degradation of HS or by introducing short, soluble HS-structure fragments reduced amyloid deposition in cultured islets. Cytotoxicity induced by extracellular, aggregating IAPP was mediated via interactions with cell-surface HS. This suggests that HS plays an important role in islet amyloid deposition and associated toxicity. BRICHOS domain containing protein Bri2 was highly expressed in human beta cells and colocalized with IAPP intracellularly and in islet amyloid deposits. The BRICHOS domain effectively attenuated both IAPP amyloid formation and IAPP-induced cytotoxicity. These results propose Bri2 BRICHOS as a novel chaperone preventing IAPP aggregation in beta cells. The intravenous injection of IAPP, proIAPP or amyloid-β (Aβ) fibrils enhanced islet amyloidosis in transgenic human IAPP mice, demonstrating that both homologous- and heterologous seeding of islet amyloid can occur in vivo. IAPP colocalized with Aβ in brain amyloid from AD patients, and AD patients diagnosed with T2D displayed increased proportions of neuritic plaques, the more pathogenic plaque subtype. In conclusion, both IAPP amyloid formation and the cytotoxic effects of IAPP is dependent on interactions with HS whereas interactions with Bri2 BRICHOS is protective. Cross-seeding between Aβ and IAPP can occur in vivo and the two peptides colocalize in brain amyloid in AD patients.

Articular cartilage plays a vital role in load-bearing joints, providing an almost frictionless surface to articulating bones. However, the avascular nature and low cell density of the tissue means that following injury, there is limited potential for regeneration and repair. With the ageing population, the prevalence and economic burden associated with osteoarthritis (OA) is increasing rapidly, but as of yet there are no fully effective ways to treat the condition. Research into novel therapies has therefore become a popular avenue of investigation, and human mesenchymal stem/stromal cells (hMSCs) have been highlighted as particularly promising targets. However, current, methods for inducing the chondrogenic differentiation of hMSCs, which typically employ the use of transforming growth factor beta 1 or 3 (TGFβ1/3), result in the production of hypertrophic rather than hyaline tissue, hampering translational progress. Growth differentiation factor 5 (GDF5) belongs to the TGFβ superfamily of proteins and is vital for skeletal formation, however its use in cartilage tissue engineering (TE) strategies has been somewhat neglected. Here we demonstrate that GDF5 significantly increases aggrecan gene expression (a marker of articular cartilage), without affecting collagen type X expression (a marker of chondrocyte hypertrophy), in chondrocyte pellet cultures derived from hMSCs, making it a promising target for the formation of permanent articular cartilage. The therapeutic application of growth factors is, at present, limited due to their expense, susceptibility to proteolytic degradation, and rapid clearance, leading to large quantities being required to get anywhere near the desired outcome. The highly sulfated glycosaminoglycan (GAG), heparin, is already extensively used in the clinic as an anticoagulant, and is also able to bind and potentiate the activity of a wide range of growth factors. As such, researchers are now using it to enhance stem cell expansion/ differentiation protocols, as well as to improve the delivery/ activity of growth factors in TE strategies. Here, we identify GDF5 as a novel heparin/heparan sulfate (HS)-binding protein, and show that endogenous HS proteoglycans (HSPGs) are vital for localizing GDF5 to the cell surface, but are not required for its signalling activity. Importantly, we report that clinically relevant doses of heparin (≥ 10 nM), but not equivalent concentrations of HS, inhibit GDF5’s biological activity, in both hMSC-derived chondrocyte pellet cultures, and in the skeletal cell line ATDC5. We demonstrate that these inhibitory effects are due to heparin (but not HS) inhibiting both GDF5 binding to endogenous HSPGs and GDF5-induced induction of Smad 1/5/8 signalling. This study may therefore explain the variable (and disappointing) results seen with heparin-loaded biomaterials for skeletal TE, and the adverse skeletal effects, such as osteoporosis, that have been reported in the clinic following long-term heparin treatment. Together, our results caution the use of heparin in the clinic and in TE applications, and prompt the transition to using more specific GAGs (e.g. HS derivatives or synthetics), with better-defined structures and fewer off-target effects, if optimal therapy is to be achieved. In the case of GDF5, we have used a variety of developed techniques to begin uncovering important structural and functional information regarding the HS-GDF5 interaction, which are hoped to ultimately pave the way towards achieving this aim. Although further analysis is necessary, our data indicate that relatively long HS sequences are required for binding, and that both ionic and non-ionic interactions play a role in the interaction. In addition we suggest that low- rather than high-affinity HS variants may be key to potentiating the activity of this growth factor.

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.

L'interferon-γ (IFNγ) est une cytokine immunomodulatrice puissante, également dotée d'une activité antivirale. Il possède deux ligands de haute affinité : un récepteur par lequel il transmet ses signaux et des polysaccharides complexes de la famille des héparanes sulfates (HS), tous deux situés à la surface cellulaire. In vivo, la liaison aux HS permet de concentrer localement la cytokine et de réguler son activité biologique par le biais d'une protection partielle du domaine C-terminal de la protéine. Ce domaine C-terminal, caractérisé par deux domaines basiques D1 et D2, est impliqué dans la reconnaissance du récepteur et des HS. Dans ce contexte, nos travaux se sont attachés à définir les aspects structuraux de l'interaction de l'IFNg, et plus précisément de son extrémité C-terminale, avec ses deux ligands. Pour cela, de divers mutants ponctuels, multiples et de délétion de l'IFNg ont été produites, purifiées et étudiées. Leur capacité à lier les HS et le récepteur de l'IFNg est déterminée par SPR puis leur influence sur l'activité antivirale de l'IFNg est déterminée. Les paramètres thermodynamiques de l'interaction IFNg:HS-oligosaccharides sont investigués. Par ailleurs, nous avons préparé une banque oligosaccharidique dérivée d'HS. Le criblage de cette banque, pour sa capacité à lier l'IFNγ, a permis de démontrer que l'IFNg reconnaissait des motifs de sulfatation particuliers. Finalement, nous avons tenté de cristallisé le complexe IFNg:HS-oligosaccharide, jusqu'à présent sans obtention de cristaux qui diffractent. Ces différentes approches visent à élucider le mécanisme de reconnaissance d'IFNg par des HS. Ceci afin de concevoir un mime de ce site d'interaction inhibant la signalisation de l'IFNg. Enfin, une compréhension plus détaillé de l'interaction de l'IFNg avec les HS et son récepteur reste à établir afin d'entièrement comprendre comment l'IFNg migre des HS vers l'IFNgR. / Interferon-γ (IFNγ) is a strong immunomodulating cytokine with some antiviral activity. It has two ligands for which it has high affinities: a receptor through which it transmits its signals, and complex polysaccharides of the heparan sulphate (HS) family. Both are situated on the cellular surface. In vivo, binding on the HS permits local concentration of the cytokine, and regulates its biological activity via a partial protection of the C-terminal region. This C-terminal region, characterised by two basic domains, D1 and D2, is implicated in the recognition of the receptor and the HS. In this context, we investigated the structural features for the interaction of IFNγ, and more specifically the importance of his C-terminus, with both of his cellular ligands. Therefore, we produced, purified and examined various mutants of IFNγ, including points, multiples and deletions mutants. There ability to bind to HS and the IFNγ receptor is examined by SPR and there influence on IFNγ's antiviral activity is determined. The thermodynamics complexation of IFNγ with the HS-oligosaccharides is examined. Moreover, we have prepared an oligosaccharidic library derived from HS. By screening this library for its capacity to bind IFNγ, we have demonstrated that the cytokine recognizes a particular sulphated pattern. Finely, we tried to crystallize the IFNγ:HS-oligosaccharide complex, without obtaining diffracting crystals yet. These studies contribute to clarify the mechanism of recognition of IFNγ by the HS. This would enable us to design a mimic of the interaction site for IFNγ on the HS, who inhibits inappropriate signaling of the cytokine. Finely, a detailed comprehension of the interaction of IFNγ with his receptor and with the HS needs to be established to fully understand how IFNγ migrates for the HS to its receptor.

Elastin-like peptides (ELPs) are stimulus-responsive protein-based polymers which are attractive material for biomedical research due to their biocompatibility and unique properties. The physical properties of ELPs are dependent on the chain length and the chosen amino acid at the guest residue position. This imparts unlimited flexibility in designing ELP based biomaterials with the desired physical properties. We have shown that in addition to their physical properties, ELPs have biological activities that are conducive to tissue regeneration. Specifically, we found that ELPs induce fibroblast proliferation via cell surface heparan sulfate proteoglycans (HSPG). Furthermore, our data suggests that ELP based materials with differential proliferative potential can be designed by controlling the interaction of ELPs with HSPGs by incorporating either hydrophobic or positively charged residues within the ELP sequence. Fibroblast proliferation is important for granulation tissue formation which is important in chronic wounds as well as in healing of other tissues. The customizable biological activity of ELPs coupled with their unique physical properties will enable us to design novel, sustainable and cost effective therapies for different tissue regeneration applications. ELPs can be genetically fused to biologically active peptides or proteins. These fusions can be expressed and readily purified since they maintain the phase transitioning property of the fused ELP domain. Moreover, depending on the ELP sequence chosen the chimeric fusion sequences can self-assemble into unique structures such as nanoparticles. These structures can then be applied to the injury site where they not only provide unique topographical cues or structural support but also act as delivery vehicles for the fused bioactive protein. We developed a multifunctional nanoparticle that is comprised of PMP-D2-ELP fusion protein and different functional peptide ELP fusion proteins to preserve the bioactivity of the functional group with the existence of elastase. These heterogeneous particles will be beneficial for the delivery of combination therapies to solve multiple problems that often existed in chronic wound healing or other tissue regeneration process. In summary, this study adds to our understanding of the biological activity of ELP and the interaction mechanism that allow the regulation of cellular behavior. Furthermore this work also investigated the potential therapeutic application of ELP as a delivery platform for chronic wound healing.

Hepatic lipase (HL) plays a pivotal role in the catabolism of apolipoprotein (apo)B-containing lipoproteins and high density lipoprotein (HDL) particles through its reported catalytic and non-catalytic extracellular functions. The current study tested the hypothesis that HL expression might impair formation and secretion of hepatic derived very low density lipoproteins (VLDL) and apoA-I (nascent HDL). Stable or transient expression of human HL (hHL) in McA-RH7777 cells resulted in decreased incorporation of [3H]glycerol into cell-associated and secreted (VLDL-associated) 3H-triacylglcyerol (TAG) relative to control cells. Stable expression of catalytically-inactive hHL (hHLSG) also resulted in decreased secretion of VLDL-associated 3H-TAG whereas cell-associated 3H-TAG levels were unchanged. Expression of hHL or hHLSG increased cell-associated 35S-apoB100 with relatively no change in secreted 35S-apoB100. Importantly, hHL or hHLSG expression resulted in reduced 3H-TAG associated with the microsomal lumen lipid droplets (LLD), and increased relative expression of ApoB and genes involved in lipogenesis and fatty acyl oxidation. Transient expression of hHL in HL-null primary hepatocytes, mediated by adenoviral gene transfer, resulted in decreased steady-state levels of cell-associated and secreted apoA-I and reduced rates of synthesis and secretion of 35S-apoA-I. HL-null hepatocytes exhibited increased levels of secreted 35S-apoA-I relative to wildtype hepatocytes while cell-associated 35S-apoA-I levels were normal. Transient expression of a hHL chimera (hHLmt), in which the C-terminus of hHL was replaced with mouse HL sequences, exerted an inhibitory effect on apoA-I production similar to that of hHL even though hHLmt was secreted less effectively than hHL with impaired exit from the endoplasmic reticulum (ER) as compared with hHL. In contrast, stable expression of hHL in McA-RH7777 cells resulted in a dose-dependent increase in cell-associated and secreted 35S-apoA-I levels. These studies demonstrate that hHL has an intracellular (but non-catalytic) role in reducing the content of the LLD and ultimately the buoyancy of secreted VLDL particles, and that the N-terminal sequences of ER-residing hHL directly or indirectly modulates the production and secretion of apoA-I (nascent HDL) from hepatocytes.

L’entrée du virus de l’hépatite C (VHC) dans les hépatocytes est un événement multi-étapes complexe, impliquant un certain nombre de facteurs cellulaires. Elle est initiée par la fixation des particules virales sur des structures d’héparanes sulfates (HS) présentes à la surface de l’hépatocyte. Cette étape initiale reste cependant peu comprise. En effet, en raison de l’interaction de la particule virale du VHC avec des lipoprotéines, la contribution exacte des différents composants du virion à cette interaction reste controversée. Au cours de cette thèse, nous avons étudié le rôle potentiel de protéines d'enveloppe du VHC et de l'apolipoprotéine E dans l'étape de liaison aux HS. Nous avons d’abord montré que la délétion de la région hypervariable 1 (HVR1), une région précédemment proposée pour participer à l’interaction avec les HS, n'avait aucun effet sur la liaison du virion aux HS, indiquant que cette région n'est pas impliquée dans cette interaction. Nous avons également utilisé des anticorps monoclonaux neutralisants reconnaissant différentes régions des glycoprotéines d'enveloppe du VHC dans un test de compétition utilisant des billes d’agarose couplées à l’héparine, un homologue structural des HS, pour précipiter le virus. Bien que les glycoprotéines d’enveloppe du VHC dissociées de la particule virale interagissaient avec l'héparine, aucun de ces anticorps n’était capable d'interférer avec l'interaction entre la particule virale et l’héparine, suggérant fortement que les glycoprotéines d'enveloppe du VHC présente à la surface des virions ne sont pas accessibles pour interagir avec les HS. En revanche, nos résultats d’études cinétiques, d’interaction avec l’héparine ainsi que les expériences d'inhibition avec des anticorps anti-apolipoprotéine E indiquent que cette apolipoprotéine joue un rôle majeur dans l'interaction initiale entre le VHC et les HS. Enfin, la caractérisation des déterminants structuraux des HS nécessaires à l'infection par le VHC, à l’aide d’ARN interférents ciblant des enzymes impliquées dans la voie de biosynthèse des HS et par compétition avec des héparines modifiées, indique que la N-sulfatation et la 6-O-sulfatation sont nécessaires pour l’initiation de l'infection par le VHC. Par contre la 2-O-sulfatation n’est pas indispensable pour l’étape d’entrée cellulaire du VHC. Enfin, nous avons également montré que la taille minimale des oligosaccharides d’HS requise pour l'infection par le VHC est un decasaccharide. En conclusion, l’ensemble de ces données indique que le VHC détourne l'apolipoprotéine E pour initier son interaction avec des structures d’HS spécifiques. / Hepatitis C virus (HCV) entry into hepatocytes is a complex multistep process involving a series of cellular factors. HCV entry is initiated by the binding of viral particles to cell surface heparan sulfate (HS) structures. However, due to the lipoprotein-like structure of HCV, the exact contribution of virion components to this interaction remains controversial. Here, we investigated the relative contribution of HCV envelope proteins and apolipoprotein E in the HS-binding step. Deletion of hypervariable region 1, a region previously proposed to be involved in HS-binding, did not alter HCV virion binding to HS, indicating that this region is not involved in this interaction. Neutralizing monoclonal antibodies recognizing different regions of HCV envelope glycoproteins were also used in a pull-down assay with beads coated with heparin, a close HS structural homologue. Although isolated HCV envelope glycoproteins could interact with heparin, none of these antibodies was able to interfere with virion-heparin interaction, strongly suggesting that, at the virion surface HCV envelope glycoproteins are not accessible for HS binding. In contrast, results from kinetic studies, heparin pull-down and inhibition experiments with anti-apolipoprotein E antibodies indicate that this apolipoprotein plays a major role in HCV-HS interaction. Finally, characterization of HS structural determinants required for HCV infection by silencing enzymes involved in the HS biosynthesis pathway and by competition with modified heparin indicated that N- and 6-O-sulfation but not 2-O-sulfation are required for HCV infection, and that the minimum HS oligosaccharide length required for HCV infection is a decasaccharide. Together, these data indicate that HCV hijacks apolipoprotein E to initiate its interaction with specific HS structures.

Les GAGs, en particulier les HS et les CS, sont des polysaccharides linéaires sulfatés situés à la surface des cellules et la matrice extracellulaire où ils influencent les fonctions des cellules. Les GAGs sont connus pour se lier et réguler l'activité d'un certain nombre de protéines différentes appelées «protéines de liaison héparine», y compris les chimiokines, facteurs de croissance, des enzymes et des molécules d'adhésion. Dans le cas du développement de la tumeur, la surexpression de l'héparanase a été observée. En conséquence, une variété d'oligosaccharides de HS et de CS est libérée. Néanmoins, leurs structures et leurs effets biologiques sont inconnus.De nombreux outils existent pour la caractérisation des GAG cependant, le développement de nouvelles technologies pour isoler des fragments du HS endogènes est nécessaire. Dans ce contexte, nous proposons d'utiliser la technologie d'empreinte moléculaire, ce qui permettrait d'obtenir des polymères avec des cavités capables de reconnaître certains types d'oligosaccharides mimétiques de HS, et par la suite d'étudier les HS endogènes.Les GAGs extraits de tumeurs xénogreffes et du sang, de 3 à 8 semaines au cours de la croissance tumorale, ont été quantifiés par dosage colorimétrique. Nous avons observé une diminution de la quantité des GAG tumoraux et une augmentation des GAG sanguin, au cours de la croissance de la tumeur. En outre, les GAGs tumoraux montrent une affinité croissante pour le FGF-2 au cours de la croissance tumorale.Nous avons étudié l'applicabilité de la «technique d'empreinte moléculaire» pour la production d'hydrogels imprimés capables de reconnaître spécifiquement le fondaparinux, un oligosaccharide analogue de l'héparine. Nous avons préparé une bibliothèque d'hydrogels imprimés afin d'optimiser leur synthèse et obtenir des matériaux qui reconnaissent spécifique et sélectivement cette molécule cible. Nos résultats montrent que, par un contrôle minutieux de la stœchiométrie et de la proportion de l'agent de réticulation utilisé lors de leur synthèse ainsi que la détermination des conditions de reconnaissance, les hydrogels imprimés reconnaissent spécifiquement les oligosaccharides mimétiques de HS.Ces travaux ouvrent des intéressantes perspectives d'application de la technologie d'impression moléculaire à l'analyse des séquences de GAGs extraits d'un milieu biologique. / GAGs, and particularly heparan sulfate (HS) and chondoitin sulfate (CS), are linear and sulfated polysaccharides located at the cell surface and extracellular matrix from where they influence the functions of cells. GAGs are known to bind and regulate the activity of a number of distinct proteins known as ‘heparin binding proteins' including chemokines, growth factors, enzymes and adhesion molecules. In the case of tumor development, heparanase over-expression has been observed. As a consequence, a variety of HS and CS oligosaccharides are released which structures and biological effects are unknown.Many tools exist for GAG characterization and a need to develop a new technology to isolate fragments of endogenous HS is required. In this context, we propose to use molecular imprinting technology that could allow to obtain polymers owing cavities able to recognize specific types of HS mimetic oligosaccharides and therefore the endogenous HS.GAGs extracted from xenografted tumors and blood, at 3 to 8 weeks during tumor growth, were quantified by a colorimetric assay. We observed a decrease in the amount of GAGs tumors and an increase of GAGs blood, during the tumor growth. Moreover, tumor GAGs were tested by competition toward growth factor with enzyme immunoassay showing increasing affinity for FGF-2 during tumor growth.We investigated the applicability of ‘Molecular Imprinting Technology' to the generation of imprinted hydrogels able of specifically recognize fondaparinux, an oligosaccharide analogue of heparin. We have prepared a library of imprinted hydrogels in order to optimize their synthesis and obtain materials that specifically and selectively recognize that oligosaccharide. Our results show that, by a careful control of the stoichiometry and crossliking choice for their synthesis and by adapting rebinding conditions, namely the temperature, imprinted hydrogels can readily be prepared to specifically recognize the HS mimetic used as model.This work opens an interesting outlook to analyze GAGs extracted from a biological medium by molecular imprinting technology

Heparin glycosaminoglycans mediate a range of biological events, including anticoagulation as well as a diversity of cell proliferation and differentiation processes. Heparin saccharides have been shown to act as inhibitors against angiogenesis and metastasis of tumour cells. This thesis describes work developing chemistry towards varying length oligosaccharide sequences with potential to offer variable sulfation patterns. The main synthetic components to this work were contribution to developing scalable syntheses of an orthogonally protected L-Iduronic acid unit and a differentially protected D-glucosamine unit. The synthetic work also evaluated a recently reported diazo transfer reagent, which allowed for earlier placement of azide protection over that of previously developed routes within the group. This provided a cheaper, more atom efficient route towards protected D-glucosamine building blocks. Glycosylation of the developed D-GlcN donor units with the L-Ido acceptor allowed the production of key disaccharides which facilitated an efficient iterative glycosylation strategy towards longer oligosaccharides, ultimately providing a differentially protected pentasaccharide. The project evaluated methods towards generating various dimeric heparin type systems through forming new O4 ether linkages between GlcN residues across various short linker fragments. The most successful of these dimerisations used a methallyl dichloride core which allowed for further derivatisation towards dihydroxylated species, the analysis of which highlighted some interesting proton NMR data. The final aspect of this project began development of chemistry towards non-reducing end-labelled oligosaccharide sequences by implementation of a masked aldehyde unit on the C4 hydroxyl of GlcN synthesised from the allylated GlcN precursor via dihydroxylation chemistry. Incorporation of this moiety (protected as a 1,2-dibenzyl glycol) within both a trisaccharide and a pentasaccharide was achieved. Further development of this chemistry should allow for late step oxidative cleavage to reveal the reactive aldehyde, potentially allowing for attachment of various amine functionalised fluorophores via reductive amination. Radiolabelling of such a species should also be possible through sodium borotritide reduction for example.