Modulation of vesicle adhesion and spreading kinetics by hyaluronan cushions
Résumé
The adhesion of giant unilamellar phospholipid vesicles to planar substrates coated with extra-cellular matrix mimetic cushions of hyaluronan is studied using quantitative reflection interference contrast microscopy (RICM). The absolute height of the vesicle membrane at the vicinity of the substrate is measured by considering, for the first time, the refractive indices of the reflecting media. The thickness of the cushion is varied in the range of about 50 to 100 nm, by designing various coupling strategies. On bare protein coated substrates, the vesicles spread fast (0.5 sec) and form a uniform adhesion-disc, with the average membrane height about 4 nm. On thick hyaluronan cushions (>80 nm), the membrane height is about the same as the thickness of the cushion implying that the vesicle lies on top of the cushion. On a thin and inhomogeneous hyaluronan cushion, the adhesion is modified but not prevented. The spreading is slow (~20 sec) compared to the no-cushion case. The average membrane height is about 10 nm and the adhesion-disc is studded with blister like structures. Observations with fluorescent-hyaluronan indicate that the polymer is compressed under rather than expelled from the adhesion-disc. The adhesion energy density is about three-fold higher in the no-cushion case (1.2 mJ/m2) as compared to the thin-cushion case (0.54 mJ/m2). In the thin-cushion case, the presence of short (~4 nm) glyco-polymers on the vesicles results in a hitherto unreported stable 'partial' adhesion state - the membrane height ranges from zero to about 250 nm. The minimal model-system presented here mimics in-vitro the hyaluronan modulated early stages of cell adhesion, and demonstrates that the presence of a polymer cushion influences both the final equilibrium adhesion-state and the spreading kinetics.
Domaines
Biophysique [physics.bio-ph]
Origine : Fichiers produits par l'(les) auteur(s)
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