Cross talk between endothelial and red blood cell glycocalyces via near-field flow

Prevention of Protein Adsorption and Macrophage Phagocytosis of Perfluorocarbon-Based Microsized Core-Shell Artificial Oxygen Carriers by Facile PEG Coatings

Polyethylene glycol (PEG)-coated microsized artificial oxygen carriers (AOCs) with a perfluorooctyl bromide (PFOB) core and poly(lactide-co-caprolactone) (PLC) shell were successfully fabricated using Shirasu porous glass (SPG) membrane emulsification. The PEG coating was achieved by adding the polylactide-b-polyethylene glycol-b-polylactide (PLA-PEG-PLA) block copolymer to the disperse phase during the SPG membrane emulsification process. During the DCM evaporation process, the three-layer structure of the PEG layer, PLC shell, and PFOB core of the AOCs spontaneously formed by phase separation. By adjustment of the ratio of PLA to PLA-PEG-PLA, the PEG chain density on the AOC surface was controlled and estimated as 0.1-2.4 chains nm-2 based on quantitative proton nuclear magnetic resonance analysis. It was expected that a loop PEG brush structure was formed on the surface of the AOCs owing to the ABA block copolymer structure of PLA-PEG-PLA. With the increase in PEG chain density, nonspecific adsorption of bovine serum albumin, γ-globulin, and fibrinogen to AOCs decreased drastically and reached below 10 μg cm-2. Additionally, phagocytosis of the AOCs, evaluated using the macrophage cell line RAW 264.7, was effectively prevented and the phagocytosis index decreased from 2 to almost 0. Finally, the PEG-coated core-shell AOCs exhibited excellent higher cell viability to RAW 264.7 than bare AOCs and showed oxygen delivery to hypoxia-responsive HeLa cells. Effective facile PEG coating on PFOB/PLC core-shell AOCs was successfully achieved simultaneously with membrane emulsification and subsequent evaporation-induced phase separation. It will be an effective strategy for membrane emulsification technology as well as the preparation of AOCs.

RBCs regulate platelet function and hemostasis under shear conditions through biophysical and biochemical means

ABSTRACT

Red blood cells (RBCs) have been hypothesized to support hemostasis by facilitating platelet margination and releasing platelet-activating factors such as adenosine 5'-diphosphate (ADP). Significant knowledge gaps remain regarding how RBCs influence platelet function, especially in (patho)physiologically relevant hemodynamic conditions. Here, we present results showing how RBCs affect platelet function and hemostasis in conditions of anemia, thrombocytopenia, and pancytopenia and how the biochemical and biophysical properties of RBCs regulate platelet function at the blood and vessel wall interface and in the fluid phase under flow conditions. We found that RBCs promoted platelet deposition to collagen under flow conditions in moderate (50 × 103/μL) but not severe (10 × 103/μL) thrombocytopenia in vitro. Reduction in hematocrit by 45% increased bleeding in mice with hemolytic anemia. In contrast, bleeding diathesis was observed in mice with a 90% but not with a 60% reduction in platelet counts. RBC transfusion improved hemostasis by enhancing fibrin clot formation at the site of vascular injury in mice with severe pancytopenia induced by total body irradiation. Altering membrane deformability changed the ability of RBCs to promote shear-induced platelet aggregation. RBC-derived ADP contributed to platelet activation and aggregation in vitro under pathologically high shear stresses, as observed in patients supported by left ventricular assist devices. These findings demonstrate that RBCs support platelet function and hemostasis through multiple mechanisms, both at the blood and vessel wall interface and in the fluidic phase of circulation.

Interplay between endothelial glycocalyx layer and red blood cell in microvascular blood flow: A numerical study

The endothelial glycocalyx layer (EGL) plays a crucial role in regulating blood flow in microvessels. Experimental evidence suggests that there is greater blood flow resistance in vivo compared to in vitro, partially due to the presence of the EGL. However, the complex relationship between EGL deformation and blood cell behavior in shear flow and its quantification remains incompletely understood. To address this gap, we employ a particle-based numerical simulation technique to examine the interaction of the EGL with flowing red blood cells (RBCs) in microtubes. We examine changes in EGL deformation in response to variations in shear rate, EGL graft density, and contour height. Our results indicate that the alterations in EGL height are influenced by the mechanical properties of the EGL, flow conditions, and the RBC-EGL interaction. The flowing RBC compresses the EGL, causing a notable reduction in EGL height near the RBC flow. Additionally, we find that the presence of the EGL in the microtube results in increased RBC deformation and a wider gap between the RBC and tube wall due to spatial occupancy. The significant impact of the EGL on RBC flow is particularly evident in microtubes with diameters ranging from 7 to 10µm, a range consistent with notable differences in vascular flow resistance observed between in vivo and in vitro experiments. The simulation results shed insight on the dynamic interplay between RBC and the EGL in microvascular blood flow.

High salt intake and HIV infection on endothelial glycocalyx shedding in salt-sensitive hypertension

The endothelial glycocalyx is closely associated with various physiological and pathophysiological events. Significant modification of the endothelial glycocalyx is an early process in the pathogenesis of cardiovascular disease. High dietary salt and HIV infection damages the endothelial glycocalyx causing endothelial dysfunction and increasing the risk for salt-sensitive hypertension and cardiovascular disease. The two factors, HIV infection and dietary salt are critical independent predictors of hypertension and cardiovascular disease and often synergize to exacerbate and accelerate disease pathogenesis. Salt-sensitive hypertension is more common among people living with HIV and is associated with risk for cardiovascular disease, stroke, heart attack and even death. However, the underlying mechanisms linking endothelial glycocalyx damage to dietary salt and HIV infection are lacking. Yet, both HIV infection/treatment and dietary salt are closely linked to endothelial glycocalyx damage and development of salt-sensitive hypertension. Moreover, the majority of individuals globally, consume more salt than is recommended and the burden of HIV especially in sub-Sahara Africa is disproportionately high. In this review, we have discussed the missing link between high salt and endothelial glycocalyx shedding in the pathogenesis of salt-sensitive hypertension. We have further elaborated the role played by HIV infection and treatment in modifying endothelial glycocalyx integrity to contribute to the development of hypertension and cardiovascular disease.

Role of blood flow in endothelial functionality: a review

Endothelial cells, located on the surface of blood vessel walls, are constantly stimulated by mechanical forces from the blood flow. The mechanical forces, i.e., fluid shear stress, induced by the blood flow play a pivotal role in controlling multiple physiological processes at the endothelium and in regulating various pathways that maintain homeostasis and vascular function. In this review, research looking at different blood fluid patterns and fluid shear stress in the circulation system is summarized, together with the interactions between the blood flow and the endothelial cells. This review also highlights the flow profile as a response to the configurational changes of the endothelial glycocalyx, which is less revisited in previous reviews. The role of endothelial glycocalyx in maintaining endothelium health and the strategies for the restoration of damaged endothelial glycocalyx are discussed from the perspective of the fluid shear stress. This review provides a new perspective regarding our understanding of the role that blood flow plays in regulating endothelial functionality.

Influence of the vessel wall geometry on the wall-induced migration of red blood cells

The geometry of the blood vessel wall plays a regulatory role on the motion of red blood cells (RBCs). The overall topography of the vessel wall depends on many features, among which the endothelial lining of the endothelial surface layer (ESL) is an important one. The endothelial lining of vessel walls presents a large surface area for exchanging materials between blood and tissues. The ESL plays a critical role in regulating vascular permeability, hindering leukocyte adhesion as well as inhibiting coagulation during inflammation. Changes in the ESL structure are believed to cause vascular hyperpermeability and entrap immune cells during sepsis, which could significantly alter the vessel wall geometry and disturb interactions between RBCs and the vessel wall, including the wall-induced migration of RBCs and the thickening of a cell-free layer. To investigate the influence of the vessel wall geometry particularly changed by the ESL under various pathological conditions, such as sepsis, on the motion of RBCs, we developed two models to represent the ESL using the immersed boundary method in two dimensions. In particular, we used simulations to study how the lift force and drag force on a RBC near the vessel wall vary with different wall thickness, spatial variation, and permeability associated with changes in the vessel wall geometry. We find that the spatial variation of the wall has a significant effect on the wall-induced migration of the RBC for a high permeability, and that the wall-induced migration is significantly inhibited as the vessel diameter is increased.

Red blood cell lingering modulates hematocrit distribution in the microcirculation

The distribution of red blood cells (RBCs) in the microcirculation determines the oxygen delivery and solute transport to tissues. This process relies on the partitioning of RBCs at successive bifurcations throughout the microvascular network, and it has been known since the last century that RBCs partition disproportionately to the fractional blood flow rate, therefore leading to heterogeneity of the hematocrit (i.e., volume fraction of RBCs in blood) in microvessels. Usually, downstream of a microvascular bifurcation, the vessel branch with a higher fraction of blood flow receives an even higher fraction of RBC flux. However, both temporal and time-average deviations from this phase-separation law have been observed in recent studies. Here, we quantify how the microscopic behavior of RBC lingering (i.e., RBCs temporarily residing near the bifurcation apex with diminished velocity) influences their partitioning, through combined in vivo experiments and in silico simulations. We developed an approach to quantify the cell lingering at highly confined capillary-level bifurcations and demonstrate that it correlates with deviations of the phase-separation process from established empirical predictions by Pries et al. Furthermore, we shed light on how the bifurcation geometry and cell membrane rigidity can affect the lingering behavior of RBCs; e.g., rigid cells tend to linger less than softer ones. Taken together, RBC lingering is an important mechanism that should be considered when studying how abnormal RBC rigidity in diseases such as malaria and sickle-cell disease could hinder the microcirculatory blood flow or how the vascular networks are altered under pathological conditions (e.g., thrombosis, tumors, aneurysm).

Accommodation in allogeneic and xenogeneic organ transplantation: Prevalence, impact, and implications for monitoring and for therapeutics

Accommodation refers to acquired resistance of organs or tissues to immune or inflammatory reactions that might otherwise cause severe injury or rejection. As first observed in ABO-incompatible kidney transplants and heterotopic cardiac xenografts, accommodation was identified when organ transplants continued to function despite the presence of anti-graft antibodies and/or other reactants in the blood of recipients. Recent evidence suggests many and perhaps most organ transplants have accommodation, as most recipients mount B cell responses specific for the graft. Wide interest in the impact of graft-specific antibodies on the outcomes of transplants prompts questions about which mechanisms confer protection against such antibodies, how accommodation might be detected and whether and how rejection could be superimposed on accommodation. Xenotransplantation offers a unique opportunity to address these questions because immune responses to xenografts are easily detected and the pathogenic impact of immune responses is so severe. Xenotransplantation also provides a compelling need to apply these and other insights to decrease the intensity and toxicity of immunosuppression that otherwise could limit clinical application.

Effects of Preconditioning on RBC Deformability in Critically Ill Patients

RBCs from critically ill patients have depressed deformability, especially in sepsis. Prolonged exposure of RBCs from healthy volunteers to physiologic shear stress (the preconditioning technique) has been associated with improved deformability, but the effect of preconditioning on RBCs from critically ill patients with or without sepsis has never been studied.

OSCILLATORS IN THE MICROVASCULATURE - GLYCOCALYX AND BEYOND

The growing recognition of abundance of oscillating functions in biological systems has motivated this brief overview which narrows down on the microvasculature. Specifically, it encompasses self-sustained oscillations of blood flow, hematocrit and viscosity at bifurcations; their effects on the oscillations of endothelial glycocalyx, mechanotransduction and its termination to prime endothelial cells for the subsequent mechanical signaling event; oscillating affinity of hyaluronan-CD44 binding domain; spontaneous contractility of actomyosin complexes in the cortical actin web, its effects on the tension of the plasma membrane; reversible effects of sirtuin-1 on endothelial glycocalyx; and effects of plasma membrane tension on endo-and exocytosis. Some potential interactions between those oscillators - their coupling - are discussed together with their transition into chaotic movements. Future in-depth understanding of the oscillatory activities in the microvasculature could serve as a guide to its chronotherapy under pathological conditions.

Ways and Means of Cellular Reconditioning for Kidney Regeneration

BACKGROUND

Mitochondrial, lysosomal, and peroxisomal dysfunction; defective autophagy; mitophagy; and pexophagy, as well as the loss of glycocalyx integrity are known contributors to initiation and progression of diverse kidney diseases. Those cellular organelles are tightly interactive in health, and during development of a disease, damage in one may propagate to others. By extension, it follows that restoring an individual defect may culminate in a broader restorative spectrum and improvement of cell and organ functions.

SUMMARY

A novel strategy of reconditioning cellular organellar dysfunction, which we define as refurbishment of pathogenically pivotal intra- or extracellular elements, damaged in the course of disease and impeding restoration, is briefly outlined in this overview. Individual therapeutic reconditioning approaches targeting selected organelles are cataloged. We anticipate that the proposed reconditioning strategy in the future may enrich the arsenal of regenerative medicine and nephrology.

KEY MESSAGE

The arsenal of regenerative medicine and nephrology consisting of organ transplantation, use of stem cells, cell-free approaches, cell reprogramming strategies, and organ engineering has been enriched by the reconditioning strategy. The latter is based on the recognition of two facts that (a) impairment of diverse cellular organelles contributes to pathogenesis of kidney disease and (b) individual organelles are functionally interactively coupled, which explains the "domino effect" leading to their dysfunction. Reconditioning takes advantage of these facts and, while initially directed to restore the function of individual cellular organelles, culminates in the propagation of a therapeutic intervention to account for improved cell and organ function. Examples of such interventions are briefly summarized along the presentation of defective cellular organelles contributing to pathogenesis of kidney disease.

Biomechanical properties of endothelial glycocalyx: An imperfect pendulum

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This review seeks to fuse the discoveries in cell biology with mechanical engineering to produce a comprehensive biophysical model of endothelial glycocalyx.

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The aperiodic oscillatory motions of glycocalyx and cortical actin web underlie our prediction of two functional pacemakers and their participation in the outside-in signaling, the basis for mechanotransduction, and the dampening action of the inside-out signaling.

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Advancing an idea that the glycocalyx, plasma membrane, and cortical actin web represent a structure-functional unit and proposing the concept of tensegrity model.

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Presentation of our recent data suggesting that erythrocytes are gliding or havering and rotating over the surface of intact glycocalyx, whereas the rotational and hovering components of their passage along the capillaries are lost when glycocalyx of either is degraded.

Endothelial glycocalyx plays a crucial role in hemodynamics in health and disease, yet studying it is met by multiple technical hindrances. We attempted to outline our views on some biomechanical properties of endothelial glycocalyx, which are potentially amenable to mathematical modeling. We start with the null-hypothesis ascribing to glycocalyx the properties of a pendulum and reject this hypothesis on the grounds of multiple obstacles for pendulum behavior, such as rich decoration with flexible negatively charged side-chains, variable length and density, fluid fixation to the plasma membrane. We next analyze the current views on membrane attachments to the cortical actin web, its pulsatile contraction-relaxation cycles which rebound to the changes in tension of the plasma membrane. Based on this, we consider the outside-in signaling, the basis for mechanotransduction, and the dampening action of the inside-out signaling. The aperiodic oscillatory motions of glycocalyx and cortical actin web underlie our prediction of two functional pacemakers. We next advance an idea that the glycocalyx, plasma membrane, and cortical actin web represent a structure-functional unit and propose the concept of tensegrity model. Finally, we present our recent data suggesting that erythrocytes are gliding or hovering and rotating over the surface of intact glycocalyx, whereas the rotational and hovering components of their passage along the capillaries are lost when glycocalyx of either is degraded. These insights into the mechanics of endothelial glycocalyx motions may be of value in crosspollination between biomechanics, physiology, and pathophysiology for deeper appreciation of its rich untapped resources in health and pharmacotherapy in disease.

Understanding the Role of Endothelial Glycocalyx in Mechanotransduction via Computational Simulation: A Mini Review

Endothelial glycocalyx (EG) is a forest-like structure, covering the lumen side of blood vessel walls. EG is exposed to the mechanical forces of blood flow, mainly shear, and closely associated with vascular regulation, health, diseases, and therapies. One hallmark function of the EG is mechanotransduction, which means the EG senses the mechanical signals from the blood flow and then transmits the signals into the cells. Using numerical modelling methods or in silico experiments to investigate EG-related topics has gained increasing momentum in recent years, thanks to tremendous progress in supercomputing. Numerical modelling and simulation allows certain very specific or even extreme conditions to be fulfilled, which provides new insights and complements experimental observations. This mini review examines the application of numerical methods in EG-related studies, focusing on how computer simulation contributes to the understanding of EG as a mechanotransducer. The numerical methods covered in this review include macroscopic (i.e., continuum-based), mesoscopic [e.g., lattice Boltzmann method (LBM) and dissipative particle dynamics (DPD)] and microscopic [e.g., molecular dynamics (MD) and Monte Carlo (MC) methods]. Accounting for the emerging trends in artificial intelligence and the advent of exascale computing, the future of numerical simulation for EG-related problems is also contemplated.