Metabolic remodeling of the human red blood cell membrane

Abstract

The remarkable deformability of the human red blood cell (RBC) results from the coupled dynamic response of the phospholipid bilayer and the spectrin molecular network. Here we present quantitative connections between spectrin morphology and membrane fluctuations of human RBCs by using dynamic full-field laser interferometry techniques. We present conclusive evidence that the presence of adenosine 5′-triphosphate (ATP) facilitates nonequilibrium dynamic fluctuations in the RBC membrane that are highly correlated with the biconcave shape of RBCs. Spatial analysis of the fluctuations reveals that these non-equilibrium membrane vibrations are enhanced at the scale of spectrin mesh size. Our results indicate that the dynamic remodeling of the coupled membranes powered by ATP results in non-equilibrium membrane fluctuations manifesting from both metabolic and thermal energies and also maintains the biconcave shape of RBCs.ATP | imaging technique | membrane fluctuation | RBC | spectrin A s they travel through small blood vessels and organs, RBCs undergo repeated severe deformation. The coupling and interactions between the phospholipid bilayer and the spectrin network govern the deformability of RBCs (1). The fluid-like lipid bilayer is coupled to the two-dimensional spectrin network that comprises an approximately hexagonal lattice via protein junctional complexes. The RBC membrane is remarkably soft and elastic, and thus exhibits fluctuations with amplitudes of the order of tens of nanometers. The dynamics of the RBC membrane is strongly related to the membrane structure and mechanical properties and has been explored extensively (2-6). However, experimental results available to date on RBC membrane fluctuations have provided only limited information on select regions of the cell membrane with limited spatial and/or temporal resolution (7-9). No full-field measurements of membrane fluctuations in the entire RBC arising in response to well-controlled metabolic activity have been made so far and, consequently, different techniques have led to different interpretations of the mechanistic origins of dynamic RBC membrane fluctuations with and without metabolic activity (7-9).The RBC membrane is not a static but a metabolically regulated active structure. It is known that biochemical energy controls its static and dynamic characteristics. The presence of ATP is not only crucial in maintaining the biconcave shape of the RBC membrane (10), but was also shown to increase the dynamic membrane fluctuations (7, 9). However, the regulatory mechanism of ATP in RBC membranes still remains elusive. Furthermore, these static and dynamic effects of ATP on RBC membrane fluctuations have hitherto been regarded as separate phenomena and have never been explored simultaneously.Here, we present dynamic, full-field, and quantitative measurements of ATP effects on RBC membrane morphology and fluctuations. We show that in the presence of ATP, the RBC membrane fluctuations have a non-equilibrium, metabolic component in addition to a thermal o...

Stiffness increase of red blood cells during storage

“…The structure and the interactions between these proteins change during RBC storage due to the degradation of several biochemical parameters, such as SNO and ATP [40][41][42] . The degradation of these biochemical parameters over the RBC storage process has been widely reported, and the depletion of SNO and ATP has been speculated to play important roles in regulating RBCs' mechanical properties 39,[43][44][45] . During RBC storage, the SNO level becomes lower, leading to a lower activity of S-nitrosylation 40 .…”

“…Meanwhile, gradual ATP depletion is known to occur during RBC storage 41 . Due to insufficient energy provided by ATP for the detachment of glycophorin from the spectrin network 39 , glycophorin tends to re-attach to spectrin by protein 4.1 44 , and the higher affinity between glycophorin and spectrin can also contribute to the increase in RBC membrane stiffness.…”

Direct Cytoskeleton Forces Cause Membrane Softening in Red Blood Cells

“…The elastic properties of RBCs are dominated by the interaction between the lipid bilayer and the underlying spectrin cytoskeleton (8,9), which is a dynamical meshwork mainly consisting of spectrin filaments linked by reconfigurable junctional complexes (5,6). The transient binding capacity of these complexes depends on their phosphorylation state (10)(11)(12).…”

“…This structural network endows the spectrin skeleton with the basic role of globally imparting structural rigidity to the cell membrane (13) and locally regulating its flexibility through reversible phosphorylation at the anchoring nodes (6,14). Indeed, the ability of RBCs to undergo reversible large deformations cannot be rationalized on the basis of a fixed connectivity of the cytoskeleton, but instead requires a model that attributes metabolically driven forces to active remodeling of the RBC cytoskeleton (6,14). Therefore, RBC dynamics has been postulated to be metabolically regulated by continuous remodeling of the junctional nodes of the spectrin skeleton (6)(7)(8)14).…”

“…Indeed, the ability of RBCs to undergo reversible large deformations cannot be rationalized on the basis of a fixed connectivity of the cytoskeleton, but instead requires a model that attributes metabolically driven forces to active remodeling of the RBC cytoskeleton (6,14). Therefore, RBC dynamics has been postulated to be metabolically regulated by continuous remodeling of the junctional nodes of the spectrin skeleton (6)(7)(8)14). Under the optical microscope, normal RBCs experience large membrane undulations at the equatorial emplacement, a phenomenon originally referred to as the RBC flicker (15,16).…”