Cell adhesion and aggregation

Carbohydrate-carbohydrate interactions have been suggested as mediators of cell adhesion and aggregation. Studies of four different interactions— sponge cell aggregation, embryo and myelin compaction, and melanoma cell adhesion— have provided insights into the role of the saccharides in these events. The biological context of these associations as well as the results of experiments using biophysical and chemical model systems are described. 

G. Knedlitschek, F. Schneider, E. Gottwald, T. Schaller, E. Eschbach, and K.F. Weibezahn, A tissue-like culture system using microstructures Influence of extracellular matrix material on cell adhesion and aggregation, JBiomech Eng-T Asme, 121 (1), 35-39,1999. 

Apart fi-om effects on the nucleus, retinol has been found to have a stabilizing effect on cell membranes. More specifically retinol seems to take part in glycosyl-transfer reactions and the synthesis of various glycoconjugates (page 407). Effects on cell surface components may mediate changes in intracellular recognition and interactions and also in the process of cell adhesion and aggregation. 

We investigated the efficiency of NSC expansion on surfaces with EGF-His immobilized in the correct orientation. NSCs were obtained from neurosphere cultures prepared from fetal rat striatum harvested on embryonic day 16. NSCs were cultured for 5 days on EGF-His-immobilized substrates prepared with mixed SAMs of different COOH-thiol contents. Cells adhered and formed network structures at a density that increased with the COOH-thiol content of the surface. As a control, cells were seeded onto surfaces without immobilized EGF-His. This resulted in poor cell adhesion during the entire culture period. In addition, when EGF-His adsorbed to SAMs with 100% COOH-thiol or SAMs with NTA-derivatized COOH that lacked Ni2+ chelation, we observed poor initial cell adhesion, and the cells formed aggregates within 5 days. Interestingly, the substrate used to covalently immobilize EGF-His with the standard carbodiimide chemistry was not a suitable surface for cell adhesion and proliferation. The control experimental results contrasted markedly with results from EGF-His-chelated surfaces. 

Dictyostelium has been shown thus far to only have relatively weak contacts with the substratum. Observations by interference reflection microscopy show that highly chemotactic Dictyostelium cells have relatively small areas of contact with the substratum [193, 231]. They do not demonstrate the focal contacts that are seen with mesenchymal cells. The contact areas with the substratum do not show focal accumulations of cytoskeletal proteins, consistent with the lack of focal contacts. Flow force measurements of cell adhesion and detachment show that mutations in cytoskeletal proteins can reduce the adhesion strength [55, 161, 208, 221]. Dictyostelium cells can form eupodia on their dorsal surfaces when in contact with agarose on that surface [74, 75]. These structures may represent more localized adhesion sites, which are present when the appropriate substratum is available. In addition, during aggregation, chemotactic responses may be modified by cell-cell adhesion. 

Internal and external surfaces of substitutes have been studied in order to determine topographical cues and create favorable conditions for cell adhesion and proliferation. It was highlighted that the high specific surface and porosity of fibrous structure encourage cell adhesion and nutriment transport. However, dimensional incoherence between fibers, pores, and cells results in aggregates rather than neo-endothelium at the inner wall surface. Adjustments of the fibrous structure at the subcellular level allows endothelial cells to cross over fibrous interstices that previously acted as barrier to cell migration. 

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