No description available.

Epidemiological evidence indicates that selenium supplementation may increase risk for ocular hypertension and glaucoma. The purpose of this project was to determine the effects of selenium on the conventional "trabecular" aqueous outflow pathway, a likely site of pathology for glaucoma. Human trabecular meshwork (HTM) cells and human umbilical vein endothelial cells (HUVECs) were treated with selenium (MSeA) at or near physiologically relevant concentrations. Selenium uptake by cells was monitored using mass spectrometry. While detectible changes in intracellular selenium were observed after exposure to 1-10 uM MSeA for 24 hours, the majority remained in the conditioned medium. The high concentrations of extracellular selenium we observed raised the possibility that selenium has an extracellular target.To investigate the role of selenium in extracellular matrix turnover, I examined alterations in protein secretion and intracellular signaling. MSeA treatment (5-10 uM) led to a significant decrease in the secretion of matrix metalloproteinase -2 and its inhibitor after 6-24 hours and to a dose-dependent decrease in kinase signaling. Later, I investigated the possibility that integrins are an extracellular target of selenium by monitoring morphological changes in HTM cells and by treating them with divalent cations. MSeA stimulated morphological changes consistent with a decrease in integrin function. These occurred before (less than 3 hours) alterations in protein secretion and intracellular signaling (3-6 hours). Zinc treatment prevented MSeA-mediated alterations in protein secretion and changes in cell-matrix adhesion.Finally markers of HTM cell homeostasis were examined. MSeA treatment (5 uM) led to a 60% decrease in protein synthesis after 3 hours and a 60% reduction in protein secretion, without causing significant alterations in cell viability and total ATP. To assess the physiological relevance of my results, anterior segments were perfused with MSeA to determine its effects on aqueous outflow facility. Preliminary results suggest that MSeA leads to a decrease in outflow facility.The combination of MSeA-induced decreases in several indicators of HTM cell homeostasis (without adversely effects on cell viability at physiologically relevant doses) and decreases in outflow facility provide a possible mechanism for selenium-associated ocular hypertension.

Fibrillin-1 is the main component of the 10-12 nm microfibrils, which are found in several elastic and non-elastic tissues. Human fibrillin-1 contains multiple calcium-binding epidermal growth factor-like (cbEGF) domains interspersed with transforming growth factor β-binding protein-like (TB) domains. TB4 domain contains a flexible RGD loop which mediates cell adhesion via αVβ3, α5β1 and αVβ6 integrins. Mutations which introduce amino acid substitutions into TB4 are associated with a wide spectrum of diseases such as Marfan syndrome (MFS), ectopia lentis, Stiff skin syndrome (SSS). Amino acid substitutions such as W1570C, C1564S and C1577G in the TB4 domain have been found to cause SSS. The upstream TB5 domain has been predicted to modulate integrin binding and a deletion in the domain has been found in Weill-Marchesani syndrome (WMS), phenotype of which is similar to SSS (skin fibrosis and short stature), thereby suggesting that the underlying pathogenic mechanism might be similar. This study has used cellular, biochemical and biophysical methods to investigate the effects of SSS substitutions C1564S and W1570C on domain structure and function and compared it to a MFS substitution C1564Y in the TB4 domain and WMS deletion in the TB5 domain. Effects of the SSS mutations on structure of the domains were studied using limited proteolysis, nuclear magnetic resonance spectroscopy and calcium chelation experiments. Subsequently, the ability of human fibroblasts to secrete wild-type and mutant fibrillin-1 was examined to identify the effect of the mutations on the trafficking of the protein. Finally, cell binding assays and SPR was employed to investigate the effect of disease-causing mutations on fibrillin-1/integrin interactions. The results demonstrate that the SSS mutations affect TB4-cbEGF23 interface and calcium-binding to cbEGF23 but do not alter secretion of recombinant fibrillin-1 mutant fragments from the cell. On the other hand, intracellular retention was observed for MFS substitution C1564Y which was shown to be more susceptible to proteolysis than SSS substitution C1564S. WMS deletion also gives rise to partial retention of the recombinant fragment, suggesting a different pathogenic mechanism for these disorders. Cell binding assays and surface plasmon resonance (SPR) experiments show that SSS mutations affect binding to αvβ3 integrin, but not αvβ6 integrin suggesting that selectively impaired integrin interactions may contribute to pathogenesis of SSS.

Naegleria fowleri (N. fowleri) and Naegleria lovaniensis (N. lovaniensis) are closely related amebae found in the environment. N. fowleri causes Primary Amebic Meningoencephalitis (PAM), a fatal disease of the central nervous system, while N. lovaniensis is nonpathogenic. N. fowleri infection occurs when amebae enter the nasal passages, and migrate to the brain. The molecular mechanisms involved in the pathogenesis of PAM are not well-defined. Therefore, the purpose of this study was to define phenotypic characteristics that may be functionally linked to the pathogenicity associated with N. fowleri. Studies revealed that N. fowleri has a faster growth rate and is more resistant to complement-mediated lysis when compared to N. lovaniensis. Additionally, contact-independent cytotoxicity was observed only for N. fowleri. The ability to invade tissues can be a characteristic that distinguishes pathogens from nonpathogens. Therefore, adhesion to extracellular matrix components (ECM), laminin-1, fibronectin, and collagen I, was assessed. N. fowleri exhibited a higher level of adhesion to ECM components and was shown to invade tri-dimensional ECM scaffolds (matrigel and collagen I) to a greater extent than N. lovaniensis. Scanning electron microscopy revealed that N. fowleri attached on ECM substrata exhibited a spread-out appearance that included the presence of focal adhesion-like structures. Attachment of N. fowleri to ECM components was decreased significantly when amebae were pretreated with trypsin, suggesting a role for a surface protein in this process. Pretreatment of N. fowleri amebae with periodate, a sugar oxidant, led to a decrease in attachment to laminin-1 and fibronectin suggesting that the surface component contained a sugar moiety. Western immunoblotting revealed two integrin-like proteins for both species. However, one with a molecular mass of approximately 70 kDa, was detected at a higher level for N. fowleri. Confocal microscopy indicated that the integrin-like proteins co-localized to the focal adhesion-like structures. An anti-integrin antibody decreased adhesion of N. fowleri to ECM components. Zymographic analysis demonstrated differential expression of proteases occurs when N. fowleri and N. lovaniensis invade ECM components using an in vitro invasion assay. These results indicate a distinction in adhesion to, and invasion of, extracellular matrix proteins between N. fowleri and N. lovaniensis.

Cartilage has limited intrinsic healing potential upon injury, due to the low cell density and the lack of blood supply. Degenerative disease of the cartilage, such as osteoarthritis (OA), is challenging to treat without clear mechanistic understandings of cartilage development. With over 90% of the cartilage tissue occupied by extracellular matrix (ECM), understanding the cellular and molecular effects of cartilage ECM on chondrogenesis and chondrocyte behavior is crucial for therapeutic development. The focus of this work is to study the regulation of chondrogenesis and hypertrophic maturation of human mesenchymal stem cells (MSCs) by cartilage ECM in the context of potential therapeutic applications. To study the cartilage ECM, we created a decellularized ECM digest from native porcine cartilage and examined its effects on MSCs. Since native cartilage ECM maintains chondrocyte homeostasis without progressing to hypertrophic degeneration, we hypothesized that the decellularized ECM would promote MSC chondrogenesis and inhibit hypertrophy. Indeed, we showed that ECM promoted MSC chondrogenesis and matrix production, and inhibited hypertrophy and endochondral ossification. The chondrogenic effect was shown to potentially involve the PI3K-Akt-Foxo1 and Hif1 pathways. By recapitulating the activated Hif1 pathway, roxadustat, a small molecule stabilizer of Hif, was able to reproduce the chondrogenic and anti-hypertrophic effects of the cartilage ECM. It also reduced the expression of matrix metalloproteases (MMPs) in MSCs, healthy chondrocytes, and OA chondrocytes, and alleviated matrix degradation in bovine cartilage explants. We also attempted to identify ECM components that display chondrogenic properties. Collagen XI, a minor component of articular cartilage, was shown to promote cartilage matrix formation in MSCs and healthy chondrocytes, and to reduce matrix degradation in bovine cartilage explants. Taken together, this study reveals the dual roles of cartilage ECM in promoting chondrogenesis and matrix production and inhibiting cartilage hypertrophy. Importantly, small molecule drugs that recapitulate the signaling pathways of ECM regulation, and collagen XI, a component of the ECM, may serve as leads for further therapeutic development for cartilage injury and degenerative disease.

The infectious first-stage larvae of the nematode Trichinella spiralis is an intracellular parasite of altered skeletal muscle. Invasion of the muscle cell initiates a series of morphological changes in the host muscle cell which ultimately results in a specialized unit called the nurse cell. The completed nurse cell consists of a collagenous capsule, matrix of altered sarcoplasm, and a circulatory rete. The purpose of this study was to determine the types of collagen present in the nurse cell capsule. Additionally, the presence of the gl ycoproteins, laminin and tenascin was determined. This study also sought to demonstrate the location of the selected extracellular matrix proteins within the capsule. Nurse cells were isolated from infected host muscle by sequential protease treatment with pronase, collagenase, and hyaluronidase. Nurse cells were digested with pepsin to produce characteristic pepsin-resistant triple helical fragments of collagen. The nurse cellpepsin digest was characterized by SDS-page, under reduced and nonreduced conditions, with type VI collagen and the ala2a3 chains of type XI collagen. Frozen tissue sections of infected and non-infected rat diaphragms were screened with specific polyclonal antibodies against types I, m, IV, V/Xl, and VI collagen, laminin, and tenascin. Indirect immunofluorescence using FITC secondary antibodies was used to locate the protein in the capsule and host tissue. SDS-page of the nurse cell-pepsin digest produced an electrophoretic pattern of resistant fragments characteristic for types I, III, IV, V, and VI collagen. Additionally, fragments migrated with an apparent molecular weight expected for pepsin resistant fragments of laminin. Indirect immunofluorescence showed types I, III, IV, and VI collagen, and laminin were distributed throughout the capsule. Serum No. 4876, which recognizes type V /XJ collagen, localized to the larvae. Tenascin failed to stain the nurse cell or host tissue. The results show that the capsule is a heterogenic structure with types I, III, IV, V, and VI collagens, and laminin distributed throughout the structure. The immunolocalization of Serum No. 4876 to the larvae suggests that a nematode collagen shares an amino acid sequence in common with mammalian type V /XI collagen.

No description available.

Thesis (M.Orth.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves [102]-122) Also available in print.

During early embryonic development, endodermal cells leave the inner cell mass (ICM) and migrate over an extracellular matrix (ECM), located on the blastocoelic side of the trophectoderm, to form a continuous layer of extraembryonic endoderm. Cell migration events depend on a family of cell surface proteins known as integrins that bind specific ECM proteins. In an effort to understand the mechanisms involved in bovine endodermal cell migration, two experiments were conducted. In the first experiment, expression of the ECM proteins fibronectin, laminin and vitronectin was evaluated by immunofluorescent staining in in vivo and in vitro developing embryos during Day 6-10 and Day 7-10, respectively (Day 0=onset of estrus). Fibronectin was detected in all stages of in vivo and in vitro embryos, however no difference (P>0.10) was observed due to day or developmental stage. Laminin staining was moderately expressed in all stages of in vivo embryos, with an increase (P<0.05) in Day 10 in vivo embryos. Laminin staining in Day 9 in vitro embryos was less intense (P<0.05) than Day 7 and 8 in vitro embryos. Higher (P<0.05) expression of laminin was observed in Day l0 in vivo embryos as compared to Day 10 in vitro. Vitronectin staining was expressed throughout all stages of development. Day 6 in vivo embryos exhibited more intense (P<0.05) staining compared to Day 8 in vivo embryos. Day 10 in vivo embryos expressed more (P<0.05) vitronectin than Day 10 in vitro embryos. In the second experiment, the effects of ECM-type and inhibitors of integrin binding on bovine endodermal cell outgrowth from the ICM were evaluated. Day 7 embryos were nonsurgically collected and cultured for 96 h on either fibronectin-layered microdrops containing 0 (control), 0.5 or 1.0 mg/ml RGD and/or EILDV peptides or vitronectin-layered microdrops containing 0, 0.5 or 1.0 mg/ml RGD peptides. At 24-h intervals, ICM were photographed and the numbers of cells leaving the ICM were counted. Areas of cellular outgrowth were calculated from the photomicrographs. Compared to the control, addition of 0.5 or 1.0 mg/ml RGD, EILDV or RGD and EILDV did not (P>0.10) reduce the areas of cellular outgrowth from the ICM on matrices of fibronectin. Numbers of cells in outgrowths were greater (P<0.05) in control ICM compared to 0.5 mg/ml RGD, but this effect was eliminated (P>0.10) when the inhibitor concentration was increased to 1.0 mg/ml. Addition of 0.5 or 1.0 mg/ml RGD did not reduce (P>0.10) the area of cellular outgrowth from the ICM on vitronectin and had no effect (P>0.10) on numbers of cells in the outgrowths. Detection of fibronectin, laminin and vitronectin by immunofluorescence suggests these proteins are present in the developing bovine embryo to support endodermal cell migration and stabilization in extraembryonic endoderm formation. Because cell migration over fibronectin and vitronectin was not inhibited by the RGD and EILDV peptides, endodermal cells must use either an integrin that recognizes alternative binding sites in fibronectin and vitronectin or an alternative cell adhesion system. / Graduation date: 2003

Graduation date: 1997