Molecular Maps of Red Cell Deformation: Hidden Elasticity and in Situ Connectivity

Abstract

Fluorescence-imaged micropipette aspiration was used to map redistribution of the proteins and lipids in highly extended human red blood cell membranes. Whereas the fluid bilayer distributed uniformly (+/- 10 percent), the underlying, solidlike cytoskeleton of spectrin, actin, and protein 4.1 exhibited a steep gradient in density along the aspirated projection, which was reversible on release from deformation. Quantitation of the cytoskeletal protein density gradients showed that skeletal elasticity is well represented by a grafted polymer network with a ratio of surface dilation modulus to shear modulus of approximately 2:1. Fractionally mobile integral proteins, such as band 3, and highly mobile receptors, such as CD59 as well as glycophorin C in protein 4.1-deficient cells, appeared to be squeezed out of areas dense in the underlying network and enriched in areas of network dilation. This complementary segregation demonstrates patterning of cell surface components by cytoskeletal dilation.

Equilibrium physics breakdown reveals the active nature of red blood cell flickering

“…By comparing membrane fluctuations directly between healthy RBCs and cells depleted of ATP (adenosine triphosphate), recent experiments find a decrease of fluctuations upon ATP-depletion, hence suggesting that an active process may contribute to membrane undulations 6,[14][15][16] . However, the passive mechanical properties of the RBC membrane themselves depend strongly on ATP, as illustrated by the stiffening of the RBC membrane on starvation [17][18][19]6,15 , that correlates with a sudden transition from discocyte to spiculated echinocyte shapes 20,21 . Therefore a direct and compelling explanation for the decrease of fluctuations observed in ATP-depleted cells is the stiffening of the membrane 22,23 rather than the loss of putative active (that is, non-equilibrium) fluctuations.…”

Rh-RhAG/Ankyrin-R, a New Interaction Site between the Membrane Bilayer and the Red Cell Skeleton, Is Impaired by Rhnull-associated Mutation

“…Supporting such a role, several studies indicate that Rh, RhAG, and CD47 are, in great part, resistant to membrane solubilization by non-ionic detergent and therefore remain predominantly associated with the detergent-insoluble material (DIM) of erythroid precursor cells cultured and differentiated in vitro, mature red cells, and erythroleukemic cell lines (14 -16). Evidence that these results currently account for an association of the Rh complex with the erythroid membrane skeleton rather than with lipid rafts (defined as detergent insoluble lipid rich membrane microdomains) (17), has been recently provided by fluorescence imaged microdeformation (FIMD) analysis of intact RBCs (18). In these studies, the behavior of Rh and CD47 proteins were intermediate between that of actin and band 3, whereas that of RhAG was similar to that of GPC and actin (19,20).…”

Red blood cell-mimicking synthetic biomaterial particles

“…In this context, red blood cells (RBCs), the most abundant cells in blood, represent a remarkably engineered biological entity designed for complex biological functionality including oxygen delivery (16). RBCs possess unique physical and chemical properties in terms of size, shape, flexibility, and chemical composition, all of which are essential to their biological functions (17,18). Inspired by the unique ability of these cells to perform complex tasks and motivated by the need to design particles that adopt the sophistication exhibited by biological entities, we sought to design synthetic carriers that mimic the key structural attributes of RBCs including size, shape, and mechanical properties, yet offer engineering control required in synthetic carriers.…”