Chronic pulsatile shear stress impacts synthesis of proteoglycans by endothelial cells: effect on platelet aggregation and coagulation

Glomerular endothelial glycocalyx-derived heparan sulfate inhibits glomerular leukocyte influx and attenuates experimental glomerulonephritis

Proliferative forms of glomerulonephritis are characterized by the influx of leukocytes, albuminuria, and loss of kidney function. The glomerular endothelial glycocalyx is a thick carbohydrate layer that covers the endothelium and is comprised of heparan sulfate (HS), which plays a pivotal role in glomerular inflammation by facilitating endothelial-leukocyte trafficking. We hypothesize that the exogenous glomerular glycocalyx may reduce the glomerular influx of inflammatory cells during glomerulonephritis. Indeed, administration of mouse glomerular endothelial cell (mGEnC)-derived glycocalyx constituents, or the low-molecular-weight heparin enoxaparin, reduced proteinuria in mice with experimental glomerulonephritis. Glomerular influx of granulocytes and macrophages, as well as glomerular fibrin deposition, was reduced by the administration of mGEnC-derived glycocalyx constituents, thereby explaining the improved clinical outcome. HS_glx also inhibited granulocyte adhesion to human glomerular endothelial cells in vitro. Notably, a specific HS_glx fraction inhibited both CD11b and L-selectin binding to activated mGEnCs. Mass spectrometry analysis of this specific fraction revealed six HS oligosaccharides, ranging from tetra- to hexasaccharides with 2-7 sulfates. In summary, we demonstrate that exogenous HS_glx reduces albuminuria during glomerulonephritis, which is possibly mediated via multiple mechanisms. Our results justify the further development of structurally defined HS-based therapeutics for patients with (acute) inflammatory glomerular diseases, which may be applicable to non-renal inflammatory diseases as well.

Pulsatility protects the endothelial glycocalyx during extracorporeal membrane oxygenation

BACKGROUND

Pulsatile flow protects vital organ function and improves microcirculatory perfusion during extracorporeal membrane oxygenation (ECMO). Studies revealed that pulsatile shear stress plays a vital role in microcirculatory function and integrity. The objective of this study was to investigate how pulsatility affects wall shear stress and endothelial glycocalyx components during ECMO.

METHODS

Using the i-Cor system, sixteen canine ECMO models were randomly allocated into the pulsatile or the non-pulsatile group (eight canines for each). Hemodynamic parameters, peak wall shear stress (PWSS), serum concentration of syndecan-1, and heparan sulfate were measured at different time points during ECMO. Pulsatile shear stress experiments were also performed in endothelial cells exposed to different magnitudes of pulsatility (five plates for each condition), with cell viability, the expressions of syndecan-1, and endothelial-to-mesenchymal transformation (EndMT) markers analyzed.

RESULTS

The pulsatile flow generated more surplus hemodynamic energy and preserved higher PWSS during ECMO. Serum concentrations of both syndecan-1 and heparan sulfate were negatively correlated with PWSS, and significantly lower levels were observed in the pulsatile group. Besides, non-pulsatility triggered EndMT and endothelial cells exposed to low pulsatility had the lowest possibility of EndMT.

CONCLUSION

The maintenance of the PWSS by pulsatility during ECMO possesses beneficial effects on glycocalyx integrity. Moreover, pulsatility prevents EndMT in endothelial cells, and low pulsatility exhibits the best protective effects. The augmentation of pulsatility may be a plausible future direction to improve the clinical outcome in ECMO.

Fabrication of Adipose-Derived Stem Cell-Based Self-Assembled Scaffold under Hypoxia and Mechanical Stimulation for Urethral Tissue Engineering

Long urethral strictures are often treated with autologous genital skin and buccal mucosa grafts; however, risk of hair ingrowth and donor site morbidity, restrict their application. To overcome this, we introduced a tissue-engineered human urethra comprising adipose-derived stem cell (ASC)-based self-assembled scaffold, human urothelial cells (UCs) and smooth muscle cells (SMCs). ASCs were cultured with ascorbic acid to stimulate extracellular matrix (ECM) production. The scaffold (ECM) was stained with collagen type-I antibody and the thickness was measured under a confocal microscope. Results showed that the thickest scaffold (28.06 ± 0.59 μm) was achieved with 3 × 10⁴ cells/cm² seeding density, 100 μg/mL ascorbic acid concentration under hypoxic and dynamic culture condition. The biocompatibility assessment showed that UCs and SMCs seeded on the scaffold could proliferate and maintain the expression of their markers (CK7, CK20, UPIa, and UPII) and (α-SMA, MHC and Smootheline), respectively, after 14 days of in vitro culture. ECM gene expression analysis showed that the ASC and dermal fibroblast-based scaffolds (control) were comparable. The ASC-based scaffold can be handled and removed from the plate. This suggests that multiple layers of scaffold can be stacked to form the urothelium (seeded with UCs), submucosal layer (ASCs only), and smooth muscle layer (seeded with SMCs) and has the potential to be developed into a fully functional human urethra for urethral reconstructive surgeries.

Differential binding of chemokines CXCL1, CXCL2 and CCL2 to mouse glomerular endothelial cells reveals specificity for distinct heparan sulfate domains

INTRODUCTION

Proliferative glomerulonephritis manifests in a range of renal diseases and is characterized by the influx of inflammatory cells into the glomerulus. Heparan sulfate (HS) is an important (co-)receptor for binding of chemokines, cytokines and leukocytes to the endothelial glycocalyx, a thick glycan layer that covers the inside of blood vessels. During glomerulonephritis, HS in the glomerular endothelial glycocalyx plays a central role in chemokine presentation and oligomerization, and in binding of selectins and integrins expressed by leukocytes. We hypothesize that distinct endothelial HS domains determine the binding of different chemokines. In this study we evaluated the interaction of three pro-inflammatory chemokines (CXCL1, CXCL2 and CCL2) with mouse glomerular endothelial cells (mGEnC-1) in ELISA in competition with different HS preparations and anti-HS single chain variable fragment (scFv) antibodies specific for distinct HS domains.

RESULTS

HS appeared to be the primary ligand mediating chemokine binding to the glomerular endothelial glycocalyx in vitro. We found differential affinities of CXCL1, CXCL2 and CCL2 for HS in isolated mGEnC-1 glycocalyx, heparan sulfate from bovine kidney or low molecular weight heparin in competition ELISAs using mGEnC-1 as a substrate, indicating that chemokine binding is affected by the domain structure of the different HS preparations. Blocking of specific HS domains with anti-HS scFv antibodies revealed a domain-specific interaction of the tested chemokines to HS on mGEnC-1. Furthermore, chemokines did not compete for the same binding sites on mGEnC-1.

CONCLUSION

CXCL1, CXCL2 and CCL2 binding to the glomerular endothelial glycocalyx appears differentially mediated by specific HS domains. Our findings may therefore contribute to the development of HS-based treatments for renal and possibly other inflammatory diseases specifically targeting chemokine-endothelial cell interactions.

Subverting the mechanisms of cell death: flavivirus manipulation of host cell responses to infection

Viruses exploit host metabolic and defence machinery for their own replication. The flaviviruses, which include Dengue (DENV), Yellow Fever (YFV), Japanese Encephalitis (JEV), West Nile (WNV) and Zika (ZIKV) viruses, infect a broad range of hosts, cells and tissues. Flaviviruses are largely transmitted by mosquito bites and humans are usually incidental, dead-end hosts, with the notable exceptions of YFV, DENV and ZIKV. Infection by flaviviruses elicits cellular responses including cell death via necrosis, pyroptosis (involving inflammation) or apoptosis (which avoids inflammation). Flaviviruses exploit these mechanisms and subvert them to prolong viral replication. The different effects induced by DENV, WNV, JEV and ZIKV are reviewed. Host cell surface proteoglycans (PGs) bearing glycosaminoglycan (GAG) polysaccharides — heparan/chondroitin sulfate (HS/CS) — are involved in initial flavivirus attachment and during the expression of non-structural viral proteins play a role in disease aetiology. Recent work has shown that ZIKV-infected cells are protected from cell death by exogenous heparin (a GAG structurally similar to host cell surface HS), raising the possibility of further subtle involvement of HS PGs in flavivirus disease processes. The aim of this review is to synthesize information regarding DENV, WNV, JEV and ZIKV from two areas that are usually treated separately: the response of host cells to infection by flaviviruses and the involvement of cell surface GAGs in response to those infections.

Body Perfusion during Adult Cardiopulmonary Bypass is Improved by Pulsatile flow with Intra-Aortic Balloon Pump

Purpose

To evaluate if the use of an intra-aortic balloon pump (IABP) during cardioplegic arrest improves body perfusion.

Methods

158 coronary artery bypass graft (CABG) patients were randomized to linear cardiopulmonary bypass (CPB) (n=71, Group A) or automatic 80 bpm intra-aortic ballon pump (IABP) induced pulsatile CPB (n=87, Group B). We evaluated hemodynamic response by Swan-Ganz catheter, inflammation by cytokines, coagulation and fibrinolysis, transaminase, bilirubin, amylase, lactate and renal function (estimated glomerular filtration rate (eGFR), creatinine, and incidence of renal insufficiency and failure).

Results

IABP induced Surplus Hemodynamic Energy was 15.8±4.9 mmHg, with higher mean arterial pressure during cross-clamping (p=0.001), and lower indexed systemic vascular resistances during cross-clamping (p=0.001) and CPB discontinuation (p=0.034). IL-2 and IL-6 were lower, while IL-10 proved higher in Group B (p<0.05). Group B showed lower chest drainage (p<0.05), transfusions (p<0.05), INR (p<0.05), and AT-III (p=0.001), together with higher platelets, aPTT (p<0.05), fibrinogen (p<0.05) and D-dimer (p<0.05). Transaminases, bilirubin, amylase, lactate were lower in Group B (p<0.05); eGFR was better in Group B from ITU-arrival to 48 hours, both in preoperative kidney disease Stages 1–2 (p<0.03) and Stage 3 (p<0.05), resulting in lower creatinine from ITU-arrival to 48 hours (p<0.03). Incidence of renal insufficiency (p=0.004) and need for renal replacement therapy (p=0.044) was lower in Group B Stage 3. Group B PaO2/FiO2 and lung compliance improved from aortic declamping to the first day (p<0.003) with shorter intubation time (p=0.01).

Conclusion

Pulsatile flow by IABP improves whole-body perfusion during CPB.

Surface functionalization and dynamics of polymeric cell culture substrates

The promise of growing tissues to replace or improve the function of failing ones, a practice often referred to as regenerative medicine, has been driven in recent years by the development of stem cells and cell lines. Stem cells are typically cultured outside the body to increase cell number or differentiate the cells into mature cell types. In order to maximize the regenerative potential of these cells, there is a need to understand cell-material interactions that direct cell behavior and cell-material dynamics. Most synthetic surfaces used for growth and differentiation of cells in the lab are impractical and cost prohibitive in clinical labs. This review focuses on the modification of low cost polymer substrates that are already widely used for cell culture so that they may be used to control and understand cell-material interactions. In addition, we discuss the ability of cells to exert dynamic control over the microenvironment leading to a more complex, less controlled surface.

Shear stress-induced redistribution of the glycocalyx on endothelial cells in vitro

The glycocalyx is the inner most layer of the endothelium that is in direct contact with the circulating blood. Shear stress affects its synthesis and reorganization. This study focuses on changes in the spatial distribution of the glycocalyx caused by shear stimulation and its recovery following the removal of the shear stress. Sialic acid components of the glycocalyx on human umbilical vain endothelial cells are observed using confocal microscopy. The percentage area of the cell membrane covered by the glycocalyx, as well as the average fluorescence intensity ratio between the apical and edge areas of the cell is used to assess the spatial distribution of the glycocalyx on the cell membrane. Our results show that following 24 h shear stimulation, the glycocalyx relocates near the edge of endothelial cells (i.e., cell-cell junction regions). Following the removal of the shear stress, the glycocalyx redistributes and gradually appears in the apical region of the cell membrane. This redistribution is faster in the early hours (<4 h) after shear stimulation than that in the later stage (e.g., between 8 and 24 h). We further investigate the recovery of the glycocalyx after its enzyme degradation under either static or shear flow conditions. Our results show that following 24 h recovery under shear flow, the glycocalyx reappears predominantly near the edge of endothelial cells. Static and shear flow conditions result in notable changes in the spatial recovery of the glycocalyx, but the difference is not statistically significant. We hypothesize that newly synthesized glycocalyx is not structurally well developed. Its weak interaction with flow results in less than significant redistribution, contrary to what has been observed for a well-developed glycocalyx layer.

Dynamic culture induces a cell type-dependent response impacting on the thickness of engineered connective tissues

Mesenchymal cells are central to connective tissue homeostasis and are widely used for tissue-engineering applications. Dermal fibroblasts and adipose-derived stromal cells (ASCs) allow successful tissue reconstruction by the self-assembly approach of tissue engineering. This method leads to the production of multilayered tissues, devoid of exogenous biomaterials, that can be used as stromal compartments for skin or vesical reconstruction. These tissues are formed by combining cell sheets, generated through cell stimulation with ascorbic acid, which favours the cell-derived production/organization of matrix components. Since media motion can impact on cell behaviour, we investigated the effect of dynamic culture on mesenchymal cells during tissue reconstruction, using the self-assembly method. Tissues produced using ASCs in the presence of a wave-like movement were nearly twice thicker than under standard conditions, while no difference was observed for tissues produced from dermal fibroblasts. The increased matrix deposition was not correlated with an increased proliferation of ASCs, or by higher transcript levels of fibronectin or collagens I and III. A 30% increase of type V collagen mRNA was observed. Interestingly, tissues engineered from dermal fibroblasts featured a four-fold higher level of MMP-1 transcripts under dynamic conditions. Mechanical properties were similar for tissues reconstructed using dynamic or static conditions. Finally, cell sheets produced using ASCs under dynamic conditions could readily be manipulated, resulting in a 2 week reduction of the production time (from 5 to 3 weeks). Our results describe a distinctive property of ASCs' response to media motion, indicating that their culture under dynamic conditions leads to optimized tissue engineering.

Endothelial cell capture of heparin-binding growth factors under flow

Circulation is an important delivery method for both natural and synthetic molecules, but microenvironment interactions, regulated by endothelial cells and critical to the molecule's fate, are difficult to interpret using traditional approaches. In this work, we analyzed and predicted growth factor capture under flow using computer modeling and a three-dimensional experimental approach that includes pertinent circulation characteristics such as pulsatile flow, competing binding interactions, and limited bioavailability. An understanding of the controlling features of this process was desired. The experimental module consisted of a bioreactor with synthetic endothelial-lined hollow fibers under flow. The physical design of the system was incorporated into the model parameters. The heparin-binding growth factor fibroblast growth factor-2 (FGF-2) was used for both the experiments and simulations. Our computational model was composed of three parts: (1) media flow equations, (2) mass transport equations and (3) cell surface reaction equations. The model is based on the flow and reactions within a single hollow fiber and was scaled linearly by the total number of fibers for comparison with experimental results. Our model predicted, and experiments confirmed, that removal of heparan sulfate (HS) from the system would result in a dramatic loss of binding by heparin-binding proteins, but not by proteins that do not bind heparin. The model further predicted a significant loss of bound protein at flow rates only slightly higher than average capillary flow rates, corroborated experimentally, suggesting that the probability of capture in a single pass at high flow rates is extremely low. Several other key parameters were investigated with the coupling between receptors and proteoglycans shown to have a critical impact on successful capture. The combined system offers opportunities to examine circulation capture in a straightforward quantitative manner that should prove advantageous for biologicals or drug delivery investigations.

Reversible secretion of glycosaminoglycans and proteoglycans by cyclically stretched valvular cells in 3D culture

Mitral valve leaflets and chordae have been shown to contain different amounts and proportions of glycosaminoglycans (GAGs) and proteoglycans (PGs) corresponding to in vivo normal or diseased cyclic strain patterns. To understand the effect of cyclic strains on GAG/PG synthesis by valvular interstitial cells (VICs) isolated from valve leaflet and chordae separately, porcine VICs were seeded within collagen gels and alternately stretched or relaxed for 24 h periods for one week in a custom-designed tissue engineering bioreactor. We found cyclic-stretch-induced upregulation of total GAGs and of individual GAG classes secreted into the culture medium. Leaflet cells showed a delayed response to stretching compared to chordal cells, but altered the proportions of various GAG classes they secreted during the culture duration. Decorin and biglycan PGs were slightly responsive to stretch. We demonstrated that mechanical stretch and relaxation conditions reversibly regulate GAG and PG production in a novel 3D model of valve tissues. This is the first study using cyclic strains to modulate GAG/PG synthesis by valve cells and our results may have implications for the remodeling of the mitral valve as well as other tissues.

Influence of strain on proteoglycan synthesis by valvular interstitial cells in three-dimensional culture

Differently loaded regions of the mitral valve contain distinct amounts and types of proteoglycans (PGs); these PG profiles are altered in abnormal loading and disease conditions. We developed an in vitro three-dimensional model to analyze PGs secreted by valvular interstitial cells (VICs) isolated from distinct regions of porcine mitral valves (leaflet or chordae) and subjected to either biaxial or uniaxial mechanical constraints. In addition, the PGs, DNA and collagen content of the collagen gels was monitored over time. All three PGs previously found in heart valves (decorin, biglycan and versican) were present in the collagen gels and the conditioned medium. Compared to unconstrained gels, the constrained collagen gels (whether biaxially or uniaxially loaded) retained more decorin and biglycan but less versican. However, the conditioned medium from constrained collagen gels contained higher amounts of all three PGs than did medium from unconstrained gels. Constrained collagen gels containing leaflet cells retained more decorin and biglycan than did those containing chordal cells. DNA content was maintained early in the culture period but was reduced by 55-80% after 7 days, whereas PG synthesis increased over time. At the end of the culture period, the cell density was highest in the biaxial region of gels seeded with leaflet cells. In contrast, collagen content in both constrained and unconstrained gels remained consistent over culture duration. This study provides valuable information about the role of applied loading on proteoglycan segregation, which should aid in tissue engineering applications and for understanding valve biology and pathology.

Utility and control of proteoglycans in tissue engineering

This review addresses various methods of integrating proteoglycans (PGs) into the design of engineered tissues and provides insight for designing tissue-engineered disease models that leverage current knowledge of PG biology. Even though PGs show immense possibilities in tissue-engineering applications, they have seldom been used to their full potential. The most common tissue-engineering application of PGs has been in scaffolds (matrigels and collagen-chondroitin sulfate matrices), in which PGs or their glycosaminoglycan (GAG) chains are incorporated into the scaffold to promote cell growth, tissue remodeling, and intracellular signaling. In addition, many studies have reported the total amount of PGs synthesized within engineered tissues but have not delineated which specific PGs or GAG classes are involved in engineered tissue development. In native tissues, various PGs are dynamically and differentially regulated to achieve specific biophysical and biological functions, such as compressibility and transparency. Therefore, the targeted modulation of specific PGs (via exogenous addition, endogenous stimulation with growth factors, or mechanical stimulation) may help engineered tissues to achieve native tissue properties. The PG composition of engineered tissues could also be modified to achieve disease models in vitro and thus provide a way to study the effect of external agents on PG-related disease mechanisms.

Vasculoprotective properties of the endothelial glycocalyx: effects of fluid shear stress

The endothelial glycocalyx exerts a wide array of vasculoprotective effects via inhibition of coagulation and leucocyte adhesion, by contributing to the vascular permeability barrier and by mediating shear stress-induced NO release. In this review, we will focus on the relationship between fluid shear stress and the endothelial glycocalyx. We will address the hypothesis that modulation of glycocalyx synthesis by fluid shear stress may contribute to thinner glycocalyces, and therefore more vulnerable endothelium, at lesion-prone sites of arterial bifurcations. Finally, we will discuss the effects of known atherogenic stimuli such as hyperglycaemia on whole body glycocalyx volume in humans and its effect on endothelial function.

Implementation of an Optical Method for the Real-Time Determination of Uniaxial Strain and Vessel Mechanics

The determination of the mechanical properties of vascular growth substrates has seen increasing interest in the bioengineering field. Mechanical features such as rupture strength, compliance characteristics, and viscoelastic properties of vascular grafts are important for their design and are indicative of their success in vivo. Thus a simple inexpensive measurement technique for these parameters would be useful. In this report we describe the implementation of an optical method for the measurement of vessel distention under a transluminal pressure gradient. It is based on the concept of laser light occlusion and allows for real time noncontact diameter measurements of hollow vessels < or = 2 cm. We demonstrate precise and reproducible measurements of diameter changes of less than 10 microm and, further, with the simultaneous determination of both strain and luminal pressure, were able to determine the elastic modulus of commercially available polymeric vessels. Comparison of the manufacturer specifications and our own measurement of the elastic modulus of these vessels, validate the effectiveness of our system. The advantages of this technique are its relative low cost, ease of implementation, high resolution, and flexibility stemming from its modular setup.

Exercise-induced changes in coagulation and fibrinolysis in healthy populations and patients with cardiovascular disease

This review highlights the clinical significance of coagulation and fibrinolytic responses, and adaptations in healthy individuals and patients with cardiovascular disease (CVD). Much of the review focuses on indicators of the potential for coagulation and fibrinolysis. The terms 'coagulation potential' and 'fibrinolytic potential' are used frequently, as much of the literature in the area of exercise haemostasis evaluates factors that reflect an increased potential for coagulation, while coagulation per se, may or may not be occurring. Similarly, fibrinolysis is definitively the lysis of inappropriate or excessive blood clot, which may or may not be occurring when the enzymes that stimulate fibrinolysis are activated. Nevertheless, markers of coagulation and fibrinolytic potential are associated with CVD, ischaemic events, and cardiovascular mortality. Additionally, fibrinolytic potential is associated with other established CVD risk factors. Ischaemic events triggered by physical exertion are more likely to occur due to an occlusive thrombus, suggesting the exercise-induced responses related to haemostasis are of clinical significance. The magnitude of increase in coagulation potential, platelet aggregation and fibrinolysis appears to be primarily determined by exercise intensity. Patients with CVD may also have a larger increase in coagulation potential during acute exercise than healthy individuals. Additionally, the magnitude of the fibrinolytic response is largely related to the resting fibrinolytic profile of the individual. In particular, high resting plasminogen activator inhibitor-1 may diminish the magnitude of tissue plasminogen activator response during acute exercise. Therefore, acute responses to exercise may increase the risk of ischaemic event. However, chronic aerobic exercise training may decrease coagulation potential and increase fibrinolytic potential in both healthy individuals and CVD patients. Due to the aforementioned importance of resting fibrinolysis on the fibrinolytic response to exercise, chronic aerobic exercise training may cause favourable adaptations that could contribute to decreased risk for ischaemic event, both at rest and during physical exertion.