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PubMed1992

Changes in Molecular Size Distribution of Cellulose during Attack by White Rot and Brown Rot Fungi.

The kinetics of cotton cellulose depolymerization by the brown rot fungus Postia placenta and the white rot fungus Phanerochaete chrysosporium were investigated with solid-state cultures. The degree of polymerization (DP; the average number of glucosyl residues per cellulose molecule) of cellulose removed from soil-block cultures during degradation by P. placenta was first determined viscosimetrically. Changes in molecular size distribution of cellulose attacked by either fungus were then determined by size exclusion chromatography as the tricarbanilate derivative. The first study with P. placenta revealed two phases of depolymerization: a rapid decrease to a DP of approximately 800 and then a slower decrease to a DP of approximately 250. Almost all depolymerization occurred before weight loss. Determination of the molecular size distribution of cellulose during attack by the brown rot fungus revealed single major peaks centered over progressively lower DPs. Cellulose attacked by P. chrysosporium was continuously consumed and showed a different pattern of change in molecular size distribution than cellulose attacked by P. placenta. At first, a broad peak which shifted at a slightly lower average DP appeared, but as attack progressed the peak narrowed and the average DP increased slightly. From these results, it is apparent that the mechanism of cellulose degradation differs fundamentally between brown and white rot fungi, as represented by the species studied here. We conclude that the brown rot fungus cleaved completely through the amorphous regions of the cellulose microfibrils, whereas the white rot fungus attacked the surfaces of the microfibrils, resulting in a progressive erosion.

Journal Article↗

PubMed2002

Cellulose synthase (CesA) genes in the green alga Mesotaenium caldariorum.

Cellulose, a microfibrillar polysaccharide consisting of bundles of beta-1,4-glucan chains, is a major component of plant and most algal cell walls and is also synthesized by some prokaryotes. Seed plants and bacteria differ in the structures of their membrane terminal complexes that make cellulose and, in turn, control the dimensions of the microfibrils produced. They also differ in the domain structures of their CesA gene products (the catalytic subunit of cellulose synthase), which have been localized to terminal complexes and appear to help maintain terminal complex structure. Terminal complex structures in algae range from rosettes (plant-like) to linear forms (bacterium-like). Thus, algal CesA genes may reveal domains that control terminal complex assembly and microfibril structure. The CesA genes from the alga Mesotaenium caldariorum, a member of the order Zygnematales, which have rosette terminal complexes, are remarkably similar to seed plant CesAs, with deduced amino acid sequence identities of up to 59%. In addition to the putative transmembrane helices and the D-D-D-QXXRW motif shared by all known CesA gene products, M. caldariorum and seed plant CesAs share a region conserved among plants, an N-terminal zinc-binding domain, and a variable or class-specific region. This indicates that the domains that characterize seed plant CesAs arose prior to the evolution of land plants and may play a role in maintaining the structures of rosette terminal complexes. The CesA genes identified in M. caldariorum are the first reported for any eukaryotic alga and will provide a basis for analyzing the CesA genes of algae with different types of terminal complexes.

Algal Proteins↗

PubMed1997

epsilon(gamma-Glutamyl)lysine crosslinks are concentrated in a non-collagenous microfibrillar fraction of cartilage.

Fractions of rib cartilage were obtained by homogenization and extracted with 4 M guanidinium chloride, and the washed residue was digested with purified collagenase. Differential centrifugation of the insoluble residue from this digestion yielded a non-collagenous fraction that earlier work had shown to contain microfibrils. This material contains a much higher concentration of epsilon(gamma-glutamyl)lysine than the ribs or any of the other cartilage fractions. This transglutaminase-derived crosslink may be a common component of extracellular matrix microfibrils.

Animals↗

PubMed1990

Nonamyloidotic fibrillar glomerulopathy and recurrent gestational anasarca.

Congo-red-negative microfibrils have been described in various glomerular diseases, some of which have no known etiology. We report the unusual case of a young woman who, over a period of 17 years, developed recurrent gestational anasarca but was asymptomatic between pregnancies except for proteinuria. Her blood pressure and renal function have remained normal over the years. A renal biopsy done 5 years after her third pregnancy showed diffuse mesangial expansion and irregular thickening of the glomerular basement membrane, both caused by the deposition of nonamyloidotic microfibrils. We discuss the differential diagnosis of this case and review the pertinent literature.

Adult↗

PubMed1981

Glomerular basement membrane and mesangial matrix: a comparative study in different vertebrates.

Perfusion fixation of the rat kidneys with aldehydes and alcian blue demonstrates within the glomerular mesangium various components displaying anionic binding sites. These are the surface coat of the mesangial cells, numerous mesangial microfibrils (probably glycoproteins), and polygonal particles (Presumably proteoglycans). These particles lie close to the mesangial cells and form assemblies of various extension within the mesangial matrix as well. In addition, a discontinuous basement membrane can be recognized which surrounds the mesangial cells. In the hagfish glomeruli (fixed without cationic dye), a prominent layer of microfibrils is interposed between mesangial and endothelial cells. Both these cells show incomplete basement membranes.

Animals↗

PubMed1995

Fibrillary glomerulonephritis in a 9-year-old girl.

A 9-year-old girl presented with mild proteinuria and microscopic hematuria. Renal biopsy disclosed highly organized fibrillary deposits in glomerular mesangial areas by ultrastructural examination. The microfibrils were 10-15 nm in diameter, up to 1,200 nm in length and in parallel array. They did not have a microtubular appearance. The diameter of the microfibrils was larger than that of amyloid fibrils. Congo red and crystal violet stains were negative. There was no clinical or serologic evidence of paraproteinemia, cryoglobulinemia, light chain disease or systemic lupus erythematosus. To date, most of the reported cases of fibrillary glomerulonephritis have occurred in adults; this disorder is extremely rare in children. We believe that this glomerulopathy can occur in the pediatric age group and should be considered in renal biopsy diagnoses.

Biopsy↗

PubMed1999

Surface roughness enhances upward migration of bacteria on polymer fibers above liquid cultures.

Monofilament polypropylene (PP) fibers, very similar to fibers that have been used as monofilament tailstrings of interuterine contraceptive devices, were suspended vertically in bacterial liquid monocultures so that a portion of a fiber extended above the liquid surface. In some cases these highly oriented, cold drawn fibers were abraded prior to insertion in the cultures in order to produce surface roughness characterized by axial channels and protruding microfibrils that partially peeled from the fiber surface thereby forming the channels. Extent of migration on a fiber was assessed by aseptically cutting it into small segments, followed by culturing each segment on agar containing growth medium. Such assessment of the PP fibers after 48 h of incubation in the cultures revealed upward migration of Eschericia coli, Pseudomonas aeruginosa, and Staphylococcus aureus over significantly longer distances on the pre-roughened fibers than on those not so pre-treated. Mean measured distances of migration during 48 h were: for E. coli 2.7+/-0.6 mm on roughened fibers (n = 16) and 0.4+/-0.7 mm on fibers not roughened (n = 17); for S. aureus 9.0+/-4.3 mm on roughened fibers (n = 13) and 0.2+/-0.3 mm on fibers not roughened (n = 14); for P. aeruginosa 8.5+/-3.7 mm on roughened fibers (n = 26) and 0.2+/-0.5 mm on fibers not roughened (n = 5). Although no statistically significant (95% confidence level) difference could be discerned between the migration distances of S. aureus and P. aeruginosa, each of these species migrated a greater distance on the PP than did E. coli. The migrations observed are attributed predominantly to wicking of the liquid cultures upward in the axial grooves developed on the surface of the PP by the eruption and peeling of microfibrils from the surface. Surface tension of the growth medium was significantly lower than that of water and its contact angle on PP was less than 90 deg, thereby indicating a tendency to wet the PP. Bacterial growth in the medium further reduced its contact angle on PP, thereby indicating an even greater tendency to wet PP after such growth.

Animals↗

PubMed2006

Comparing the mechanical properties of high performances polymer nanocomposites from biological sources.

There are numerous examples where animals or plants synthesize extracellular high-performance skeletal biocomposites consisting of a matrix reinforced by fibrous biopolymers. Cellulose and chitin are classical examples of these reinforcing elements, which occur as whisker-like microfibrils that are biosynthesized and deposited in a continuous fashion. In many cases, this mode of biogenesis leads to crystalline microfibrils that are almost defect-free, with the consequence of axial physical properties approaching those of perfect crystals. Starch is another example of natural semicrystalline polymer that is produced by many plants and occurs as microscopic granules. It acts as a storage polymer in cereals and tubers. These abundant and natural polymers can be used to create high performance nanocomposites presenting outstanding properties. Aqueous suspensions of crystallites can be prepared by acid hydrolysis of the purified substrates. The object of this treatment is to dissolve away regions of low lateral order so that the water-insoluble, highly crystalline residue may be converted into a stable suspension by subsequent vigorous mechanical shearing action. For cellulose and chitin, these monocrystals appear as rod-like nanoparticles which dimensions depend on the biological source of the substrate. In the case of starch they consist of platelet-like nanoparticles. High reinforcing capability was reported resulting from the intrinsic chemical nature of these polymers and from their hierarchical structure. During the last decade, many works have been devoted to mimic biocomposites by blending cellulose whiskers from different sources with polymer matrices.

Acids↗

PubMed2003

Distribution of myocilin and extracellular matrix components in the corneoscleral meshwork of human eyes.

PURPOSE: To examine ultrastructurally the composition of major extracellular matrix (ECM) components and the distribution of myocilin in the trabecular lamellae of corneoscleral (CS) meshwork in normal human eyes. The codistribution of myocilin with ECM components was also investigated. METHODS: Postembedding immunoelectron microscopic studies were performed with antibodies against myocilin and other ECM components, including fibronectin, laminin, vitronectin, tenascin, elastin, fibrillin-1, microfibril-associated glycoprotein (MAGP)-1, decorin, versican, hyaluronic acid, and five types of collagen (I, III, IV, V, and VI). Double labeling of myocilin with other ECM components was performed with different sized gold particles. RESULTS: In the trabecular beams of CS meshwork, fibronectin, laminin, and collagen type IV were associated with basement membranes, whereas elastin was specifically localized to the core of elastic-like fibers. Several types of collagens, glycoproteins, proteoglycans, and hyaluronic acid were detected both in the collagen fibers and ground substances. Myocilin predominantly localized in the long-spacing collagens and sheath materials surrounding elastic-like fibers, codistributed with fibronectin, fibrillin-1, MAGP-1, decorin, and type VI collagen. CONCLUSIONS: This study illustrated the composition of ECM materials in the trabecular lamellae of CS meshwork. Myocilin was specifically localized to long-spacing collagens and the surrounding sheath of elastic-like fibers interacting with microfibril-associated elements where changes have been documented to occur in glaucomatous and aging eyes.

Adult↗

PubMed2005

Differential gene expression in pseudoexfoliation syndrome.

PURPOSE: To identify and characterize genes differentially expressed in anterior segment tissues of eyes with pseudoexfoliation (PEX) syndrome and glaucoma. METHODS: Anterior segment tissues (iris, ciliary processes, lens epithelium) were obtained from eight surgically enucleated eyes with PEX-associated open-angle or closed-angle glaucomas and eight age-matched glaucomatous control eyes without PEX. cDNA libraries were generated from three PEX and three control specimens, and their gene expression patterns were compared by means of cDNA subtraction. Differentially expressed clones from the subtracted cDNA libraries were sequenced, and their differential expression was verified by means of RT-PCR, virtual Northern blot analysis, and in situ hybridization with specific RNA probes. RESULTS: Subtraction of cDNA libraries identified 27 candidate genes for differential expression in PEX tissues, of which 23 genes were confirmed by virtual Northern blot, RT-PCR, and in situ hybridization. One set of genes consistently upregulated in anterior segment tissues from different patients with PEX comprised latent transforming growth factor binding proteins (LTBP-1 and -2), which are structural components of elastic microfibrils, the cross-linking enzyme transglutaminase-2 (TGase-2), tissue inhibitor of matrix metalloproteinase-2 (TIMP-2), A-kinase anchor protein-2 (AKAP-2), apolipoprotein D, and the adenosine receptor-A3 (AdoR-A3). Genes reproducibly downregulated in PEX tissues included TIMP-1, clusterin, microsomal glutathione-S-transferase-1 (mGST-1), and serum amyloid A1. Further transcripts, such as elastase, GST-T1, integrin beta4, and dehydrocholesterol reductase, did not show a consistent differential expression pattern in tissues obtained from different patients. Although fibrillin-1 was not isolated from subtracted cDNA libraries, upregulated expression of this elastic microfibrillar component was also demonstrated by RT-PCR and in situ hybridization. CONCLUSIONS: Differentially expressed genes with a high level of reproducibility in different tissues and different patients with PEX syndrome are mainly related to extracellular matrix metabolism and cellular stress. The underlying pathophysiology of PEX syndrome appears to be associated with an excessive production of elastic microfibril components, enzymatic cross-linking processes, a proteolytic imbalance between matrix metalloproteinases and their inhibitors, and increased cellular and oxidative stress supporting the notion of PEX syndrome as a stress-induced elastic microfibrillopathy.

Aged↗

PubMed1994

Quantitative differences in biosynthesis and extracellular deposition of fibrillin in cultured fibroblasts distinguish five groups of Marfan syndrome patients and suggest distinct pathogenetic mechanisms.

Pulse-chase studies of [35S]cysteine-labeled fibrillin were performed on fibroblast strains from 55 patients with Marfan syndrome (MFS), including 13 with identified mutations in the fibrillin-1 gene and 10 controls. Quantitation of the soluble intracellular and insoluble extracellular fibrillin allowed discrimination of five groups. Groups I (n = 8) and II (n = 19) synthesize reduced amounts of normal-sized fibrillin, while synthesis is normal in groups III (n = 6), IV (n = 18), and V (n = 4). When extracellular fibrillin deposition is measured, groups I and III deposit between 35 and 70% of control values, groups II and IV < 35%, and group V > 70%. A deletion mutant with a low transcript level from the mutant allele and seven additional patients have the group I protein phenotype. Disease in these patients is caused by a reduction in microfibrils associated with either a null allele, an unstable transcript, or an altered fibrillin product synthesized in low amounts. In 68% of the MFS individuals (groups II and IV), a dominant negative effect is invoked as the main pathogenetic mechanism. Products made by the mutant allele in these fibroblasts are proposed to interfere with microfibril formation. Insertion, deletion, and exon skipping mutations, resulting in smaller fibrillin products, exhibit the group II phenotype. A truncated form of fibrillin of 60 kD was identified with specific fibrillin antibodies in one of the group II cell culture media. Seven of the nine known missense mutations, giving rise to abnormal, but normal-sized fibrillin molecules, are in group IV.

Cells, Cultured↗

PubMed1997

Age-related changes of elastic fibers in the superficial layer of the lamina propria of vocal folds.

An investigation was carried out to determine the morphologic characteristics of elastic fibers in the superficial layer of the lamina propria of aged vocal folds (EFAVFs). Excised human adult vocal folds served as the material for this study. Scanning and transmission electron microscopic observations were made. The results can be summarized as follows. First, the EFAVFs were composed of amorphous substances and microfibrils. The amorphous substances increased in amount and the microfibrils became less numerous. Second, the EFAVFs ran in various directions, were branched, and formed a complicated network. The surface of the fibers was rough, and the fibers appeared to vary in size. Some EFAVFs united to form a sheet with a rough surface. Third, the EFAVFs could not be easily digested by elastase compared with those of younger adults. We conclude that the morphologic and metabolic changes of elastic fibers in the most important vibrating portion (superficial layer of the lamina propria) of the aged vocal folds contribute partially to aging of the voice.

Adult↗

PubMed2002

Gene expression and accumulation of fibrillin-1, fibrillin-2, and tropoelastin in cultured periodontal fibroblasts.

The elastic system fibers consist of three types--oxytalan, elaunin, and elastic fibers--differing in their relative microfibril and elastin contents. All three types are found in human gingiva, but human periodontal ligaments contain only elastin-free fibers. We examined cultured human gingival fibroblasts (HGF) and cultured human periodontal ligament fibroblasts (HPLF) to determine the gene expression of fibrillin-1 and fibrillin-2 (the major components of microfibrils) and of tropoelastin. In addition, we assessed the degree of accumulation of these proteins in the extracellular matrix. Northern blot analysis revealed that the level of expression of fibrillin-1 and fibrillin-2 was higher in HGF than in HPLF. However, examination of matrix samples from HGF and HPLF cell layers showed that there was no difference in fibrillin-1 accumulation, although fibrillin-2 accumulated to a much greater extent in the HGF-derived matrix. Tropoelastin was expressed only in and around HGF. These results show a correlation between gene expression and the accumulation of tropoelastin and fibrillin-2 in HGF.

Adolescent↗

PubMedDate not supplied

Genetic fibrillinopathies: new insights in molecular diagnosis and clinical management.

The Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder with a prevalence of 2-3 per 10,000 individuals and symptoms ranging from skeletal overgrowth, cutaneous striae to ectopia lentis and aortic dilatation leading to dissection. Mutation in the gene for fibrillin-1 (FBN1) cause MFS and other related disorders of connective tissue, grouped as fibrillinopathies. Fibrillin-1 is the main constituent of extracellular microfibrils. Microfibrils can exist as individual structures or associate with elastin to form elastic fibers. This article provides an overview of the current diagnostic criteria and medical management, estimates the role of fibrillin-1 mutation analysis, sheds new light on genotype-phenotype correlations and summarizes new insights on the pathogenesis of this disorder based on mouse models.

Animals↗

PubMed1992

Chondrons from articular cartilage. V. Immunohistochemical evaluation of type VI collagen organisation in isolated chondrons by light, confocal and electron microscopy.

The pericellular microenvironment around articular cartilage chondrocytes must play a key role in regulating the interaction between the cell and its extracellular matrix. The potential contribution of type VI collagen to this interaction was investigated in this study using isolated canine tibial chondrons embedded in agarose monolayers. The immunohistochemical distribution of an anti-type VI collagen antibody was assessed in these preparations using fluorescence, peroxidase and gold particle probes in combination with light, confocal and transmission electron microscopy. Light and confocal microscopy both showed type VI collagen concentrated in the pericellular capsule and matrix around the chondrocyte with reduced staining in the tail region and the interconnecting segments between adjacent chondrons. Minimal staining was recorded in the territorial and interterritorial matrices. At higher resolution, type VI collagen appeared both as microfibrils and as amorphous deposits that accumulated at the junction of intersecting capsular fibres and microfibrils. Electron microscopy also showed type VI collagen anchored to the chondrocyte membrane at the articular pole of the pericellular capsule and tethered to the radial collagen network through the tail at the basal pole of the capsule. We suggest that type VI collagen plays a dual role in the maintenance of chondron integrity. First, it could bind to the radial collagen network and stabilise the collagens, proteoglycans and glycoproteins of the pericellular microenvironment. Secondly, specific cell surface receptors exist, which could mediate the interaction between the chondrocyte and type VI collagen, providing firm anchorage and signalling potentials between the pericellular matrix and the cell nucleus. In this way type VI collagen could provide a close functional interrelationship between the chondrocyte, its pericellular microenvironment and the load bearing extracellular matrix of adult articular cartilage.

Animals↗

PubMed1996

Expression of fibulin-2 by fibroblasts and deposition with fibronectin into a fibrillar matrix.

The extracellular matrix protein fibulin-2 was shown to be a typical product of cultured human and mouse fibroblasts by several immunological assays. It is secreted and deposited in cells and tissues as a disulfide-bonded oligomer identical in size to the previously described recombinant fibulin-2. Most of the fibroblast fibulin-2 is deposited into a dense fibrillar meshwork which requires treatment with EDTA and/or 6 M urea for solubilization. Fibulin-2 and fibronectin are synthesized at equivalent levels and both colocalize in the fibrils as shown by immunofluorescence. Metabolic labelling and pulse-chase studies demonstrated fibulin-2 oligomers in detergent extracts of cells and their rapid translocation to extracellular EDTA-sensitive assembly forms. Unlike for fibronectin and fibulin-1 only a little fibulin-2 was found in the cell culture medium. Immunogold staining of confluent human fibroblasts showed localization of fibulin-2 to a fine meshwork or bundles of amorphous microfibrils in the matrix. This also demonstrated a distinct colocalization of fibulin-2 and fibronectin at the electron microscope level, indicating that the interaction between these two protein shown in in vitro assays may also exist in situ. No distinct colocalization of both proteins could, however, be observed with cross-striated fibrils of collagen I and collagen VI microfibrils.

Animals↗

PubMed1991

Isolation and ultrastructural analysis of microfibrillar structures from foetal bovine elastic tissues. Relative abundance and supramolecular architecture of type VI collagen assemblies and fibrillin.

Extensive intact assemblies of matrix macromolecules have been solubilized from foetal calf skin, nuchal ligament and aorta by a new procedure that includes bacterial collagenase digestion under non-reducing, non-denaturing conditions and gel filtration chromatography. Type VI collagen was identified as the major microfibrillar element of these tissues by SDS-PAGE analysis and Western blotting. Rotary shadowing electron microscopy of these preparations revealed by far the most abundant and extensive arrays of intact collagen VI microfibrils isolated to date. The distinct microfibrillar species, fibrillin, which was identified on the basis of its periodicity and morphology, was also solubilized in abundance by this protocol. Analysis of these complex polymers has generated new information on their supramolecular architecture and relative abundance in these tissues. The protocol also demonstrates that the release of intact collagen VI microfibrils from these tissues is largely dependent on the removal of the major collagen fibrils.

Animals↗

PubMed2002

Floppy aortic valves without aortic root dilatation: clinical, histologic, and ultrastructural studies.

Gross anatomic, histologic and ultrastructural studies were made on 32 floppy aortic valves (FAVs) resected at the time of aortic valvular replacement for aortic regurgitation. Patients with the FAVs had relatively long clinical courses and had severe aortic regurgitation with mild symptoms of heart failure. The sizes of the mechanical valves implanted in the patients with FAVs were not large, indicating that the aortic regurgitation in these patients was not worsened by dilatation of the aortic ring. Two types of FAVs were recognized grossly, according to whether they showed abnormal cuspal thickening or thinning. Accumulations of myxoid material in the spongiosa were found in all FAVs, regardless of cuspal gross morphology. Histologically, the collagen fibers were sparse and irregularly arranged and elastic fibers were disrupted and finely granular in the myxomaotus areas of FAVs. Ultrastructurally, the myxomatous material consisted of numerous star-shaped proteoglycan granules associated with spiraling collagen fibrils and abnormal elastic fibers. Numerous spiraling collagen fibrils were observed especially at the border area of myxomatous change that extended from the spongiosa into the fibrosa. Abnormal elastic fibers had either a granular appearance of their amorphous components without microfibrils, or irregularly arranged masses of microfibrils without amorphous components. These abnormalities of connective tissue components, resulting from defective formation and/or increased degradation were similar to those in floppy mitral valves, and were related to the floppiness of cardiac valves.

Adolescent↗