Page 48 - Handbook of Adhesion Promoters

2.13 Cellular adhesion 41

Figure 2.46. (a) Magnetic resonance image of octopus arm with one sucker, the scale bar equals 1 cm; (b) ultra-
sound image of a sucker, the scale bar equals 0.5 cm; (c) histological image of octopus arm with one sucker, the
scale bar equals 0.5 cm; (d) detail of denticle located in the infundibular portion, the scale bar equals 2 μm; (e)
3D reconstruction from full set of 70 magnetic resonance images with 1 millimeter thickness. [Adapted, by per-
mission, from Tramacere, F; Beccai, L; Sinibaldi, E; Laschi, C; Mazzolai, B, Procedia Computer Sci., 7, 192-3,
2011.]
2.13 CELLULAR ADHESION

The cell surface recognition is the interaction of the cell with the surfaces of other cells
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and with extracellular matrices in surroundings. The cell-extracellular matrix interac-
tions provide cells with anchorage, traction for cell migration, and signals for growth and
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differentiation. Most cell-surroundings interactions depend on the recognition of the
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simple tripeptide Arg-Gly-Asp, RDG, by cell surface receptors, integrins. Multiple inte-
grins endow a cell with a great capacity to differentiate between the own extracellular
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matrix and the matrices secreted by other cells.
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Epithelium forms a barrier between the outside and the inside of an organism. The
apical plasma membrane contacts opposing cells and an extracellular matrix. Cell-cell
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adhesion complexes hold epithelial cells together.
Cells can form tissues by directly adhering to one another, using transmembrane
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receptors. Another means of adhesion is to attach the cell to the extracellular matrix,
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ECM, (dynamic, highly crosslinked mesh of insoluble proteins). This is primarily medi-
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ated by the transmembrane integrin receptors. They anchor the cell and provide an indi-
rect means of cell-cell adhesion when different cells connect to a common ECM between
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them. These features play critical roles in the construction and maintenance of tissues
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during development and adult life.
Keratin is a protein of human hair but it is also a protein which regulates the func-
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tions of the liver. Hepatocytes are the cells of the liver tissue. Hepatocytes make up 70-
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85% of the liver's mass. The keratin biomaterials researchers, aiming at regulating phys-
iological events through surface-mediated control of cellular behavior, are interested in
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adhesion between human hair keratins and hypatocytes. The hepatocyte adhesion to ker-
atin substrates was not mediated by integrins of the β - or β -subtype but by hepatic glyco-
1
2
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protein receptor. Glycopolymer surfaces preserve the differentiated state of mature
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hepatocytes and help maintain their ability to perform liver-specific functions.
Scanning near-field optical microscopy, SNOM, has been employed to simultane-
ously acquire high-resolution fluorescence images along with shear-force atomic force
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microscopy from cell membranes (Figure 2.47). The application of the technique to
investigate cell-cell adhesion has revealed the interactions of filopodia (or microspikes are
cytoplasmic projections that extend beyond the leading edge of cells) and their functional
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relationship in establishing adherens junctions. The filopodia from each cell extend
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across the intercellular region (Figure 2.47a). The filopodia have diameters ranging from
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110 to 270 nm. These nanostructures extend approximately 4-5 μm from their originat-
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ing lamellipodium, while some protrude over 10 mm into the intercellular space. Filopo-