Lipid bilayer and cytoskeletal interactions in a red blood cell

Abstract

We study the biomechanical interactions between the lipid bilayer and the cytoskeleton in a red blood cell (RBC) by developing a general framework for mesoscopic simulations. We treated the lipid bilayer and the cytoskeleton as two distinct components and developed a unique whole-cell model of the RBC, using dissipative particle dynamics (DPD). The model is validated by comparing the predicted results with measurements from four different and independent experiments. First, we simulated the micropipette aspiration and quantified the cytoskeletal deformation. Second, we studied the membrane fluctuations of healthy RBCs and RBCs parasitized to different intraerythrocytic stages by the malaria-inducing parasite Plasmodium falciparum. Third, we subjected the RBC to shear flow and investigated the dependence of its tank-treading frequency on shear rate. Finally, we simulated the bilayer-cytoskeletal detachment in channel flow to quantify the strength of such interactions when the corresponding bonds break. Taken together, these experiments and corresponding systematic DPD simulations probe the governing constitutive response of the cytoskeleton, elastic stiffness, viscous friction, and strength of bilayer-cytoskeletal interactions as well as membrane viscosities. Hence, the DPD simulations and comparisons with available independent experiments serve as validation of the unique two-component model and lead to useful insights into the biomechanical interactions between the lipid bilayer and the cytoskeleton of the RBC. Furthermore, they provide a basis for further studies to probe cell mechanistic processes in health and disease in a manner that guides the design and interpretation of experiments and to develop simulations of phenomena that cannot be studied systematically by experiments alone.coarse graining | worm-like chain | multiscale modeling | adhesion energy | erythrocyte T he red blood cell (RBC) membrane consists of two components: a lipid bilayer and an attached 2D spectrin network that acts as the cytoskeleton. The resistance of the lipid bilayer to bending is controlled by the bending rigidity, k c , whereas the spectrin network's resistance to shear strain is characterized by the in-plane shear modulus, μ s . Under normal conditions, the cytoskeleton is tightly attached to the lipid bilayer from the cytoplasmic side. However, under certain pathological conditions, e.g., in sickle cell disease, the cytoskeleton may become dissociated from the lipid bilayer (1). Although the biomechanics of the two-component erythrocyte membrane have been studied extensively for decades (2), the mechanical properties of the interactions between the lipid bilayer and the cytoskeleton (such as elastic stiffness, viscous friction, and strength) via the pinning connections of transmembrane proteins are still largely unknown. This is at least in part ascribed to the fact that it is difficult to measure these interactions directly from experiments, because the length scale of these connections is too small compared with the chara...

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