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Biomedical subjects

D E Birk

Publications and source records attributed to D E Birk.

69 records · Page 4Linked to original sources
PubMed1986

Organization of collagen types I and V in the embryonic chicken cornea.

The distribution and organization of type I and type V collagens were studied in the embryonic chicken cornea using anti-collagen, type specific, monoclonal antibodies and immunoelectron microscopy. These studies were performed on lathyritic 17-day corneas treated at 4 degrees C or 37 degrees C. At the lower temperature, collagen fibril structure is disrupted; at the higher temperature, normal fibril structure is maintained. Corneas from non-lathyritic 17-day chick embryos, reacted at the two different temperatures, were studied for comparison. In Bowman's membrane, the thin (20 nm) fibrils were labelled by antibodies against both type I and type V collagen under all conditions studied. In the corneal stroma, the striated collagen fibrils (25 nm) were labelled with the antibodies against type I collagen in all cases, and by antibodies against type V collagen under conditions where fibril structure was disrupted. These results are consistent with the concept of heteropolymeric fibrils consisting of both type I and type V collagen molecules assembled such that the epitopes on the type V molecule are unavailable to antibody unless the fibrillar structure is disrupted. We suggest that the interaction of type V collagen with type I collagen may be responsible for the small diameter fibrils and the rigid control of fibril structure found in the cornea.

Animals↗
PubMed1985

The fibroblast in morphogenesis and fibrosis: cell topography and surface-related functions.

'Fibroblast' is a generic term for a population of cells responsible for the establishment, maintenance and repair of three-dimensional form in multicellular organisms. These cells are a major, semi-permanent resident of the 'extracellular space' and the fibroblast compartmentalizes this space to various purposes during the formation of collagen fibrils and fibril bundles. The boundaries of these extracellular compartments blend and overlap, but discrete regions can be identified which are involved in collagen fibril assembly and fibril bundle assembly. The formation of these extracellular compartments in both the tendon and cornea results from a series of fusions of membrane-limited structures, beginning with collagen secretory vacuoles fusing with the cell surface to form deep surface recesses within which fibrils assemble; and progressing through the lateral fusion of these recesses with the consequent formation of fibril bundles. The topography of the fibroblast is also specialized for matrix anchorage, for matrix and cell repositioning, and for matrix degradation.

Animals↗
PubMed1985

Fibroblasts create compartments in the extracellular space where collagen polymerizes into fibrils and fibrils associate into bundles.

Morphogenesis in the animal kingdom is closely coupled with the intracellular synthesis and the extracellular deposition of collagen. These morphogenetically important events involve multiple steps which begin in compartments inside the cell and continue in compartments outside the cell. The movement of matrix components from the intracellular compartments to the extracellular compartments is a functional continuum. Studies of embryonic chick tendon and cornea fibroblasts with the high-voltage (1000 kV) transmission electron microscope have provided the beginnings of an understanding of how this functional continuum is related to the structural compartments which the cells create. This series of compartments, both inside and outside the cell, is involved in collagen fibrillogenesis, collagen fibril bundle formation, and tissue morphogenesis.

Animals↗
PubMed1984

Collagen fibrillogenesis in vitro: comparison of types I, II, and III.

The self-assembly of pepsin-extracted types I, II, and III collagen was studied to determine how differences in the triple-helical structure between collagen types influence in vitro collagen fibrillogenesis. Collagen types I, II, and III were extracted and purified from bovine sources, and were studied in solution by laser light scattering, pH titration, and determination of turbidity-time curves. The molecular weights were between 280,000 and 289,000, while the translational diffusion coefficients and particle scattering factors at 175.5 degrees were consistent with those expected for single collagen molecules. Titration of collagen types I, II, and III between pH 7.0 and 2.0 using HCl indicated that type I collagen had the most titratable carboxylic groups with type II and III having significantly fewer titratable groups. The self-assembly of these collagens was studied in vitro in phosphate-buffered saline. The time course and extent of fibril formation were studied turbidimetrically, and were found to be dependent on collagen type. Apparent rate constants were determined for both the lag and growth phases of fibril formation. The rates of both phases were greater for type III than for type I collagen, with the rates for type II collagen being intermediate. The extent of fibril formation was based on the turbidity per unit concentration (specific turbidity) extrapolated to zero concentration (intrinsic turbidity), which was found to be greater for type I than for type III collagen. Type II collagen had the smallest intrinsic turbidity. The specific and intrinsic turbidity values were consistent with the relative fibril diameters seen in dermis and cartilage by transmission electron microscopy. These observations indicate that helix-helix interactions are important in the regulation of the rate and extent of collagen fibrillogenesis and may be involved in the determination of fibril structure.

Animals↗
PubMed1984

Attachment to and degradation of collagen substrata by adenovirus-transformed cells of varying tumorigenicity.

The interaction of adenovirus-transformed cells of different tumorigenicity with different collagen substrata has been investigated. The adenovirus type 2 (Ad2)-transformed cells are nontumorigenic in syngeneic rats while, the adenovirus type 12 (Ad12)-transformed cells induce tumors with high efficiency. Cells transformed with Ad2 preferentially attach to collagen type I and this attachment is enhanced by fibronectin. Highly tumorigenic Ad12-transformed cells attach less efficiently to collagen type I and their attachment ability is unaffected by fibronectin. These cells, however, strongly attach to type IV collagen and this attachment is considerably enhanced by laminin. Ad2-transformed cells attach less efficiently to collagen type IV and laminin has no effect on this process. The ability of adenovirus-transformed cells to degrade collagen also has been examined. The nontumorigenic cells secrete significant amounts of collagenolytic activity directed against type I collagen into the medium, but very little type IV collagenolytic activity is secreted. The highly tumorigenic cells secrete collagenolytic activity directed against both collagen types I and IV. In addition, their secreted type IV collagenolytic activity is significantly higher than that of the nontumorigenic cells. These results suggest that laminin mediated attachment to and degradation of type IV collagen may play a significant role in determining the tumorigenic and invasive potential of adenovirus-transformed cells.

Adenoviridae↗
PubMed1984

Kinetic analysis of collagen fibrillogenesis: II. Corneal and scleral type I collagen.

Fibril formation of neutral salt soluble and pepsin-treated type I collagen from rabbit corneal stroma or sclera was compared using a turbidimetric analysis which permits the determination of apparent rate constants and activation energies for the lag and growth phase of collagen fibrillogenesis. Information regarding the lateral growth of fibrils was obtained from the final turbidity values. Neutral salt soluble corneal collagen had smaller rate constants for both the lag and growth phases of fibrillogenesis than scleral collagen. Pepsin treatment decreased the rate constants for both collagens proportionately. The activation energies were higher for type I collagen from cornea than sclera. Pepsin treatment increased the activation energy for both phases of corneal fibril formation but only the growth phase of scleral collagen fibrillogenesis was affected. The extent of lateral fibril growth was compared using the intrinsic turbidity values which are related to the mass per unit fibril length. Neutral salt soluble scleral type I collagen had a significantly higher intrinsic turbidity than did neutral salt soluble corneal collagen indicating that scleral collagen formed thicker fibrils; however, this difference was not retained after pepsin treatment, demonstrating that a helical-telopeptide interaction occurs in corneal type I collagen which influences fibril diameter. The observed differences in the rate constants, activation energies and intrinsic turbidity values indicates that there are molecular differences which are responsible for fibrillar differences of corneal and scleral type I collagens.

Animals↗
PubMed1984

Extracellular compartments in matrix morphogenesis: collagen fibril, bundle, and lamellar formation by corneal fibroblasts.

The regulation of collagen fibril, bundle, and lamella formation by the corneal fibroblasts, as well as the organization of these elements into an orthogonal stroma, was studied by transmission electron microscopy and high voltage electron microscopy. Transmission and high voltage electron microscopy of chick embryo corneas each demonstrated a series of unique extracellular compartments. Collagen fibrillogenesis occurred within small surface recesses. These small recesses usually contained between 5 and 12 collagen fibrils with typically mature diameters and constant intrafibrillar spacing. The lateral fusion of the recesses resulted in larger recesses and consequent formation of prominent cell surface foldings. Within these surface foldings, bundles that contained 50-100 collagen fibrils were formed. The surface foldings continued to fuse and the cell surface retracted, forming large surface-associated compartments in which bundles coalesced to form lamellae. High voltage electron microscopy of 0.5 micron sections cut parallel to the corneal surface revealed that the corneal fibroblasts and their processes had two major axes at approximately right angles to one another. The surface compartments involved in the production of the corneal stroma were aligned along the fibroblast axes and the orthogonality of the cell was in register with that of the extracellular matrix. In this manner, corneal fibroblasts formed collagen fibrils, bundles, and lamellae within a controlled environment and thereby determined the architecture of the corneal stroma by the configuration of the cell and its associated compartments.

Animals↗
PubMed1983

Kinetic analysis of collagen fibrillogenesis: I. Use of turbidity--time data.

A method is presented for analyzing turbidity-time curves characterizing biological assembly and disassembly processes. The method allows for the determination of apparent rate constants for the turbidity lag and growth phases of collagen fibrillogenesis. Plots of concentration/lag time versus concentration for type I collagen and concentration/(time to complete growth phase) versus concentration are shown to be straight lines. The slopes of these plots are defined as the apparent rate constants for the lag and growth phases. Activation energies are obtained from the temperature dependence of these slopes. The slopes of the growth portion of turbidity-time curves as well as the final turbidity are directly proportional to the collagen concentration. These observations are consistent with the hypothesis that the rate limiting steps for both lag and growth phases are apparent first order with respect to collagen concentration. Sample calculations based on light scattering theory suggest that the turbidimetric growth phase begins when the number of collagen molecules per unit length is greater than 100 and that the extent of fibril formation is proportional to the turbidity per unit concentration. These studies indicate that the turbidimetric lag phase involves both linear and lateral growth of collagen linear aggregates.

Animals↗
PubMed1982

Collagen fibrillogenesis in tissues, in a solution and from modeling: a synthesis.

Collagen fibril formation has been studied in tissues by light and electron microscopy; in solution by light scattering and microscopy; and from modeling based on the amino acid sequence of type I collagen. Taken together these studies indicate that collagen fibril assembly involves a stepwise formation of intermediate aggregates in which each intermediate is formed from earlier aggregates. In this sequence, monomeric collagen contributes only to the formation of early aggregates; and fibrils grow in length by the addition of intermediate aggregates to the end of a subfibril and in width by lateral wrapping of subfibrils. Modeling based on amino acid sequence data of possible intermolecular charge-charge interactions indicate 2 different kinds, one which promotes linear aggregation and the other which promotes linear aggregation. The effects of different collagens and coprecipitants such as glycoproteins and proteoglycans can begin to be explained by their influence on the character of intermediate subassemblies. Ultrastructural data from 2 tissues, embryonic cornea and tendon, indicate that the site of fibril growth and assembly is at the cell surface.

Animals↗
PubMed1981

Corneal and scleral collagen fiber formation in vitro.

We have investigated the role of structural differences in collagen molecules and the effect of proteoglycan preparations on the control of collagen fibril formation. Collagen and proteoglycans were extracted, purified and characterized from two structurally and functionally different connective tissues, rabbit corneal stroma and sclera. Corneal collagen was found to form fibers 6- to 7-times more slowly than scleral type I collagen. Proteoglycans from both sources retard fibrillogenesis, with corneal proteoglycans having approximately 3-times the effect observed with scleral proteoglycans. The morphology of the fibers formed was normal in all cases. Therefore, the changes observed may reflect a true control mechanism related to the strict morphological arrangement associated with corneal transparency.

Amino Acids↗
PubMed1981

Phagocytic properties of human keratocyte cultures.

The uptake of polystyrene latex beads (approximately 0.75 micrometers) and glutaraldehyde-treated erythrocytes by human corneal stromal keratocytes maintained in culture has been studied. Combined phase-contrast and scanning electron microscopic observations on individual cells after exposure to either beads or erythrocytes demonstrated that the majority of these particles were present intracellularly. Transmission electron microscopy revealed that the beads were membrane-bound within the cytoplasm of these cells. Thus the human keratocytes in culture are phagocytic and able to internalize particles ranging in size from approximately 0.75 to 6 micrometer. Kinetic studies showed continuous uptake of the polystyrene latex beads for at least 72 hr, with an approximate linear uptake rate between 4 and 48 hr. The extent of bead uptake was dependent on the initial bead concentration. The human keratocyte cultures were markedly more phagocytic than human skin fibroblasts or rabbit chondrocytes. It was also found that after extensive bead uptake the normal growth pattern of the keratocytes was affected. It is suggested that the phagocytic ability of the human keratocytes is involved in the turnover of the corneal stromal matrix as well as in the initial response of this avascular tissue to injury or bacterial infection.

Cells, Cultured↗
PubMedDate not supplied

Topographies of extracytoplasmic compartments in developing chick tendon fibroblasts.

The complex topography of the fibroblast leading to the formation of extracellular compartments is demonstrated in the native three-dimensional state in cryofractured chick embryo tendon at different stages of development. Tendon collagen fibrils, fibril bundles, and macroaggregates are intimately associated with these extracytoplasmic domains. The localization of fibrils within narrow channels, bundles within peripheral compartments, and the coalescence of bundles into macroaggregates within larger extracytoplasmic compartments is illustrated at different stages of development. Changing patterns of matrix organization are apparent as morphogenesis proceeds. Our interpretation is that collagen fibrils, oriented along the tendon axis, appear in extracytoplasmic channels defined by the fibroblast which are added at the periphery of the cell until a row of fibrils outlines the cellular border at Day 10. By Day 14, cytoplasmic processes have partitioned the fibrils into groups and then into round bundles. New fibrils are continually added to the fibril bundles through fusion of the extracytoplasmic channels. As the bundles grow larger, the cell boundaries between the bundles retract and bundles begin to coalesce into macroaggregates. The fibroblast becomes attenuated, bundle-forming compartments disappear as processes retract, bundles coalesce, and macroaggregates predominate by Day 17. This work is consistent with the model proposed for the compartmentalization of the extracellular space by the fibroblast, providing distinct microenvironments where collagen fibrillogenesis and matrix morphogenesis occur under close cellular regulation.

Animals↗