Modulation of microvascular signaling by heparan sulfate matrix: studies in syndecan-4 transgenic mice

Sulodexide Inhibits Arterial Contraction via the Endothelium-Dependent Nitric Oxide Pathway

Background/Objectives: Sulodexide (SDX) is a drug known for restoring the glycocalyx, thereby offering endothelial protection and regulating permeability. Additionally, it has antithrombotic and anti-inflammatory properties and has shown arterial vasodilatory effects. Endothelial cells play a crucial role in maintaining homeostasis, with their dysfunction being a key contributor to loss in vasodilatory response, especially in arterial pathologies. The aim of this study was to investigate the effects of SDX on stimulated vascular tonus in human arterial samples and to assess the function of the endothelial layer as a source of nitric oxide (NO). Methods: A total of 16 internal mammary artery remnants from coronary artery bypass graft surgeries were dissected into endothelium-intact and endothelium-denuded groups (n = 8 each). The arterial rings were equilibrated under tension, with their basal tonus recorded before and after phenylephrine stimulation. SDX's impact on arterial contraction was assessed through cumulative dose-response curves. NO synthase inhibitor (Nω-nitro-L-arginine methyl ester) was used to assess SDX's vasodilatory effect over the NO pathway. Results: SDX application resulted in concentration-dependent vasorelaxation in both endothelium-intact and endothelium-denuded groups at certain doses. However, the inhibitory effect of SDX was more pronounced in endothelium-intact rings at higher doses compared to endothelium-denuded rings (p < 0.05). Similar inhibition of contraction curves was achieved for both endothelium-intact and endothelium-denuded rings after L-NAME pre-incubation, suggesting a necessity for NO-related endothelial pathways. Conclusions: SDX exerts a concentration-dependent inhibition on arterial contraction, emphasizing the critical role of an intact endothelium and NO-mediated pathways in this process. This underscores SDX's potential in treating endothelial dysfunction-related pathologies.

Acute protein kinase C beta inhibition preserves coronary endothelial function after cardioplegic hypoxia/reoxygenation

Objective

Protein kinase C (PKC) influences myocardial contractility and susceptibility to long-term cardiac dysfunction after ischemia-reperfusion injury. In diabetes, PKC inhibition has a protective effect in terms of microvascular dysfunction. SK-channel dysfunction also influences endothelial dysfunction in cardioplegic hypoxia-reoxygenation (CP-H/R). Here, we examine whether acute inhibition of PKC beta protects against CP-H/R-induced coronary endothelial and SK channel dysfunction.

Methods

Isolated mouse coronary arterioles, half pretreated with selective PKC inhibitor ruboxistaurin (RBX), were subjected to hyperkalemic, cardioplegic hypoxia (1 hour), and reoxygenation (1 hour) with Krebs buffer. Sham control vessels were continuously perfused with oxygenated Krebs buffer without CP-H/R. After 1 hour of reoxygenation, responses to the endothelium-dependent vasodilator adenosine-diphosphate (ADP) and the SK-channel activator NS309 were examined. Endothelial SK-specific potassium currents from mouse heart endothelial cells were examined using whole-cell path clamp configurations in response to NS309 and SK channel blockers apamin and TRAM34.

Results

CP-H/R significantly decreased coronary relaxation responses to ADP (P = .006) and NS309 (P = .0001) compared with the sham control group. Treatment with selective PKC beta inhibitor RBX significantly increased recovery of coronary relaxation responses to ADP (P = .031) and NS309 (P = .004) after CP-H/R. Treatment with RBX significantly increased NS309-mediated potassium currents following CP-H/R (P = .0415). Apamin and TRAM34 sensitive currents were significantly greater in CP-H/R + RBX versus CP-H/R mouse heart endothelial cells (P = .0027).

Conclusions

Acute inhibition of PKC beta significantly protected mouse coronary endothelial function after CP-H/R injury. This suggests that acute PKC beta inhibition may be a novel approach for preventing microvascular dysfunction during CP-H/R.

HS, an Ancient Molecular Recognition and Information Storage Glycosaminoglycan, Equips HS-Proteoglycans with Diverse Matrix and Cell-Interactive Properties Operative in Tissue Development and Tissue Function in Health and Disease

Heparan sulfate is a ubiquitous, variably sulfated interactive glycosaminoglycan that consists of repeating disaccharides of glucuronic acid and glucosamine that are subject to a number of modifications (acetylation, de-acetylation, epimerization, sulfation). Variable heparan sulfate chain lengths and sequences within the heparan sulfate chains provide structural diversity generating interactive oligosaccharide binding motifs with a diverse range of extracellular ligands and cellular receptors providing instructional cues over cellular behaviour and tissue homeostasis through the regulation of essential physiological processes in development, health, and disease. heparan sulfate and heparan sulfate-PGs are integral components of the specialized glycocalyx surrounding cells. Heparan sulfate is the most heterogeneous glycosaminoglycan, in terms of its sequence and biosynthetic modifications making it a difficult molecule to fully characterize, multiple ligands also make an elucidation of heparan sulfate functional properties complicated. Spatio-temporal presentation of heparan sulfate sulfate groups is an important functional determinant in tissue development and in cellular control of wound healing and extracellular remodelling in pathological tissues. The regulatory properties of heparan sulfate are mediated via interactions with chemokines, chemokine receptors, growth factors and morphogens in cell proliferation, differentiation, development, tissue remodelling, wound healing, immune regulation, inflammation, and tumour development. A greater understanding of these HS interactive processes will improve therapeutic procedures and prognoses. Advances in glycosaminoglycan synthesis and sequencing, computational analytical carbohydrate algorithms and advanced software for the evaluation of molecular docking of heparan sulfate with its molecular partners are now available. These advanced analytic techniques and artificial intelligence offer predictive capability in the elucidation of heparan sulfate conformational effects on heparan sulfate-ligand interactions significantly aiding heparan sulfate therapeutics development.

Assessment of syndecan-4 expression in the hearts of Trypanosoma cruzi-infected mice and human subjects with chronic Chagas disease cardiomyopathy

Background

Chronic Chagas cardiomyopathy (CCC) is characterized by the presence of a multifocal inflammatory response and myocardial damage, leading to fibrosis, arrhythmias and ventricular dysfunction. The expression of syndecan-4, a transmembrane proteoglycan, was previously found to be increased in the hearts of mice chronically infected with Trypanosoma cruzi. The possible involvement of syndecan-4 in the disease pathogenesis, however, remains unknown. Here we evaluated the pattern of expression of syndecan-4 in the heart tissue of T. cruzi infected mice and subjects with Chagas cardiomyopathy, correlating with the degree of inflammation and fibrosis.

Methods

The expression of syndecan-4 was evaluated by immunofluorescence and RT-qPCR in the hearts of C57Bl/6 mice at different time points after infection with the Colombian strain of T. cruzi. Immunostainings for syndecan-4 were performed in heart samples obtained from CCC patients and other etiologies of heart failure. The number of infiltrating inflammatory cells and area of fibrosis were also evaluated and quantified.

Results

In the experimental model, the number of infiltrating inflammatory cells and fibrosis area in the hearts progressively increased after the acute phase of infection, while syndecan-4 expression remained elevated in similar levels in both the acute and chronic phases. Confocal microscopy analysis demonstrated the localization of syndecan-4 expression in blood vessels, co-localized with α-SMA, a marker for vascular smooth muscle cells (VSMCs). Confocal microscopy analysis of human hearts samples showed a similar pattern of syndecan-4 expression in blood vessels. No correlation between syndecan-4 expression and inflammation or fibrosis was found in the hearts from subjects with CCC. We also compared the expression of syndecan-4 evaluated in subjects with CCC, idiopathic dilated cardiomyopathy and ischemic cardiomyopathy. No differences in the number of syndecan-4 positive vessels/mm2 were found comparing the three groups (P = 0.466), whereas CCC patients presented a higher number of infiltrating inflammatory cells, compared to the other etiologies of heart failure. Additionally, no correlation between syndecan-4 and fibrosis or numbers of inflammatory cells was found.

Conclusions

Syndecan-4 is expressed in the heart during the acute and chronic phases of Chagas disease, in association with VSMCs, independently of the degree of myocardial fibrosis or the number of infiltrating inflammatory cells.

Rapid insulin-mediated increase in microvascular glycocalyx accessibility in skeletal muscle may contribute to insulin-mediated glucose disposal in rats

It has been demonstrated that insulin-mediated recruitment of microvascular blood volume is associated with insulin sensitivity. We hypothesize that insulin rapidly stimulates penetration of red blood cells (RBC) and plasma into the glycocalyx and thereby promotes insulin-mediated glucose uptake by increasing intracapillary blood volume. Experiments were performed in rats; the role of the glycocalyx was assessed by enzymatic degradation using a bolus of hyaluronidase. First, the effect of insulin on glycocalyx accessibility was assessed by measuring the depth of penetration of RBCs into the glycocalyx in microvessels of the gastrocnemius muscle with Sidestream Dark-field imaging. Secondly, peripheral insulin sensitivity was determined using intravenous insulin tolerance tests (IVITT). In addition, in a smaller set of experiments, intravital microscopy of capillary hemodynamics in cremaster muscle and histological analysis of the distribution of fluorescently labeled 40 kDa dextrans (D40) in hindlimb muscle was used to evaluate insulin-mediated increases in capillary blood volume. Insulin increased glycocalyx penetration of RBCs by 0.34±0.44 µm (P<0.05) within 10 minutes, and this effect of insulin was greatly impaired in hyaluronidase treated rats. Further, hyaluronidase treated rats showed a 35±25% reduction in whole-body insulin-mediated glucose disposal compared to control rats. Insulin-mediated increases in capillary blood volume were reflected by a rapid increase in capillary tube hematocrit from 21.1±10.1% to 29.0±9.8% (P<0.05), and an increase in D40 intensity in individual capillaries of 134±138% compared to baseline at the end of the IVITT. These effects of insulin were virtually abolished in hyaluronidase treated animals. In conclusion, insulin rapidly increases glycocalyx accessibility for circulating blood in muscle, and this is associated with an increased blood volume in individual capillaries. Hyaluronidase treatment of the glycocalyx abolishes the effects of insulin on capillary blood volume and impairs insulin-mediated glucose disposal.

Related transcriptional enhancer factor 1 increases endothelial-dependent microvascular relaxation and proliferation

OBJECTIVE

Related transcriptional enhancer factor 1 (RTEF-1) is a key transcriptional regulator in endothelial function. In this study, we investigated a possible role for RTEF-1 in the regulation of microvascular relaxation and the underlying mechanism involved. Activation of fibroblast growth factor receptor 1 (FGFR1) by FGFs increases vasodilation, although transcriptional control of the molecular mechanisms underlying FGFR1 is still unclear.

MATERIALS AND METHODS

We demonstrated that RTEF-1 stimulated FGFR1 expression at the transcriptional level, specifically an area including Sp1 elements, as evidenced by promoter assays. Additionally, RTEF-1 increased FGFR1 mRNA and protein expression in vitro and in VE-cadherin-promoted RTEF-1 (VE-Cad/RTEF-1) transgenic mice, whereas RTEF-1 siRNA blocked the upregulation of FGFR1 expression. Furthermore, increased endothelial-dependent microvessel relaxation was observed in the coronary arteries of VE-Cad/RTEF-1 mice, and increased proliferation was observed in RTEF-1-overexpressing cells, both of which correlated to increased FGF/FGFR1 signaling and endothelial nitric oxide synthase (eNOS) upregulation. Our results indicate that RTEF-1 acts as a transcriptional stimulator of FGFR1 and is involved in FGF pathways by increasing microvessel dilatation via eNOS.

CONCLUSIONS

These findings suggest that RTEF-1 plays an important role in FGFR1- stimulated vasodilatation. Understanding the effect of RTEF-1 in microvessel relaxation may provide beneficial knowledge in improving treatments in regards to ischemic vascular disorders.

Prostaglandin E(2) primes the angiogenic switch via a synergic interaction with the fibroblast growth factor-2 pathway

RATIONALE

Prostaglandin (PG)E(2) exerts temporally distinct actions on blood vessels, immediate vasodilatation, and long-term activation of angiogenesis.

OBJECTIVE

To study the mechanism of PGE(2) induction of angiogenesis, we characterized its effect on fibroblast growth factor (FGF)-2 signaling in cultured endothelial cells and in ex vivo and in vivo assays of blood vessel formation.

METHODS AND RESULTS

Using Western blotting assay, we demonstrated that PGE(2) induced upregulation of components of the FGF-2 pathway: FGF-2 protein, phosphorylation of FGF receptor type 1 (FGFR1), activation of FRS2alpha (FGFR substrate 2alpha), phospholipase Cgamma, endothelial nitric oxide synthase, extracellular signal-regulated kinase 1/2, and the transcription factor STAT-3. Synergism between PGE(2) and FGF-2 promoted endothelial cell proliferation and robust angiogenesis in vivo, in rabbit cornea and Matrigel assays. The magnitude of the angiogenic response to PGE(2) was directly related to FGF-2 availability which determined the extent of FGFR1 activation. In fact, PGE(2) induction of angiogenesis in vitro was impaired in FGF-2(-/-) endothelial cells and FGFR1 blockade abrogated PGE(2) action on the endothelium, preventing the activation of FGF-2 signaling.

CONCLUSION

We propose a model for the angiogenic switch based on the autocrine/paracrine FGF-2/FGFR1 activation by PGE(2) and FGF-2 synergistic interaction. The synergism between the PGE(2) and FGF-2 signaling pathways here described may explain the mechanism of action of drug combinations, the most notable being cyclooxygenase inhibitors with growth factors or growth factor receptor inhibitors.

Syndecan-4 regulates subcellular localization of mTOR Complex2 and Akt activation in a PKCalpha-dependent manner in endothelial cells

Mammalian target of rapamycin (mTOR) activity is regulated by assembly of two functionally distinct complexes, mTORC1 and mTORC2. In syndecan-4 (S4) null endothelial cells, mTORC2 activity is reduced, resulting in decreased Akt activation, while mTORC1 activity is increased. Levels of rictor, mLST8, and mSin-1 are unchanged in total cell lysates but decreased in the rafts of S4(-/-) endothelial cells, as is the level of PKCalpha. Expression of myristoylated-PKCalpha in S4(-/-) cells restores rictor, mLST8, and mSin-1 presence in the rafts and rescues Akt phosphorylation. PKCalpha knockdown mimics the effect of S4 deletion on mTORC2 localization and Akt activation. Reduced mTORC2 activity in S4(-/-) endothelial cells results in decreased FoxO1/3a and eNOS phosphorylation, decreased endothelial cell size, and increased arterial blood pressure in S4(-/-) mice. Thus, S4-dependent targeting of PKCalpha to the plasma membrane is required for recruitment of mTORC2 components to the rafts and Akt activation.

Heparin impairs glycocalyx barrier properties and attenuates shear dependent vasodilation in mice

The endothelial glycocalyx is a hydrated mesh of polysaccharides and adsorbed plasma proteins that forms the true interface between the flowing blood and the endothelium. We hypothesized in the present study that competitive binding of heparin to glycocalyx-associated proteins would affect glycocalyx barrier properties and mechanotransduction of shear stress to the endothelium. In anesthetized mice, the clearance of 70-kDa dextrans from the circulation was increased (P<0.05 versus saline) 1 hour after heparin (1.25 U) and glycocalyx degradation with hyaluronidase (35 U; amount cleared in 30 minutes after saline: 11+/-5%; after heparin: 45+/-8%; after hyaluronidase: 30+/-3%). Clearance of 40-kDa dextrans increased (P<0.05 versus saline) to a lesser extent after both treatments (saline: 46+/-3%; heparin: 60+/-5%; hyaluronidase: 60+/-2%). The dilator response of second-order arterioles in cremaster muscle during reactive hyperemia was reduced for < or =90 minutes after heparin as reflected by a decrease (P=0.008) in t(50) of diameter recovery, and this effect was associated with a diminished NO bioavailability. Infusion of hyaluronidase resulted in reductions (P<0.05) in baseline and peak reactive hyperemic diameter, whereas, despite an increase in wall shear rate at the beginning of reactive hyperemia, t(50) of diameter recovery was not affected. In conclusion, our data in mice show that a heparin challenge is associated with increased vascular leakage of dextrans and impaired arteriolar vasodilation during reactive hyperemia. Our data suggest that protein-heparan sulfate interactions are important for a functional glycocalyx.

Regulated expression of syndecan-4 in rat calvaria osteoblasts induced by fibroblast growth factor-2

Fibroblast growth factor-2 (FGF2) is a member of a prominent growth factor family that drives proliferation in a wide variety of cell types, including osteoblasts. The binding and signal transduction triggered by these mitogens is dependent on glycosaminoglycan (GAG) sugars, particularly of the heparan sulfate (HS) class. These are secreted in proteoglycan (PG) complexes, some of which become FGF co-receptors. The syndecans, the transmembrane forms of HSPG of which there are four members, act as multifunctional receptors for a variety of ligands involved in cell-extracellular matrix (ECM) adhesion as well as growth factor binding. To understand the role of syndecans in developing osteoblasts, the effects of exogenous FGF2 on syndecan expression were examined using primary rat calvarial osteoblasts. All four syndecan mRNAs were expressed in the osteoblasts, although only syndecan-4 was upregulated by FGF2 treatment in a dose-dependent manner. This upregulation could be abrogated by pretreatment with the protein synthesis inhibitor cycloheximide, suggesting that the upregulation of syndecan-4 by FGF2 is not a primary response. Osteoblast proliferation and mineralization were enhanced by exogenous FGF2 treatment, but could be specifically diminished by anti-syndecan-4 antibody pretreatment. This treatment also blocked FGF2-induced extracellular signal-regulated kinase activation, but not the expression of the bone-specific transcription factor Runx2. These results demonstrate that mitogen-triggered syndecan-4 expression is an intrinsic part of the pathways subtending osteoblast proliferation and mineralization.

Syndecans in wound healing, inflammation and vascular biology

Syndecans are heparan sulphate proteoglycans consisting of a type I transmembrane core protein modified by heparan sulphate and sometimes chondroitin sulphate chains. They are major proteoglycans of many organs including the vasculature, along with glypicans and matrix proteoglycans. Heparan sulphate chains have potential to interact with a wide array of ligands, including many growth factors, cytokines, chemokines and extracellular matrix molecules relevant to growth regulation in vascular repair, hypoxia, angiogenesis and immune cell function. This is consistent with the phenotypes of syndecan knock-out mice, which while viable and fertile, show deficits in tissue repair. Furthermore, there are potentially important changes in syndecan distribution and function described in a variety of human vascular diseases. The purpose of this review is to describe syndecan structure and function, consider the role of syndecan core proteins in transmembrane signalling and also their roles as co-receptors with other major classes of cell surface molecules. Current debates include potential redundancy between syndecan family members, the significance of multiple heparan sulphate interactions, regulation of the cytoskeleton and cell behaviour and the switch between promoter and inhibitor of important cell functions, resulting from protease-mediated shedding of syndecan ectodomains.

The role of syndecans in disease and wound healing

Syndecans are a family of transmembrane heparan sulfate proteoglycans widely expressed in both developing and adult tissues. Until recently, their role in pathogenesis was largely unexplored. In this review, we discuss the reported involvement of syndecans in human cancers, infectious diseases, obesity, wound healing and angiogenesis. In some cancers, syndecan expression has been shown to regulate tumor cell function (e.g. proliferation, adhesion, and motility) and serve as a prognostic marker for tumor progression and patient survival. The ectodomains and heparan sulfate glycosaminoglycan chains of syndecans can also act as receptors/co-receptors for some bacterial and viral pathogens, mediating infection. In addition, syndecans bind to obesity-related factors and regulate their signaling, in turn modulating food consumption and weight balance. In vivo animal models of tissue injury and in vitro data also implicate syndecans in processes necessary for wound healing, including fibroblast and endothelial proliferation, cell motility, angiogenesis, and extracellular matrix organization. These new insights into the involvement of syndecans in disease and tissue repair coupled with the emergence of syndecan-specific molecular tools may lead to novel therapies for a variety of human diseases.

Syndecans: new kids on the signaling block

Cell-associated proteoglycans provide highly complex and sophisticated systems to control interactions of extracellular cell matrix components and soluble ligands with the cell surface. Syndecans, a conserved family of heparan- and chondroitin-sulfate carrying transmembrane proteins, are emerging as central players in these interactions. Recent studies have demonstrated the essential role of syndecans in modulating cellular signaling in embryonic development, tumorigenesis, and angiogenesis. In this review, we focus on new advances in our understanding of syndecan-mediated cell signaling.

Effects of l -Arginine on Fibroblast Growth Factor 2–Induced Angiogenesis in a Model of Endothelial Dysfunction

Background— Nitric oxide availability, which is decreased in advanced coronary artery disease associated with endothelial dysfunction, is an important mediator of fibroblast growth factor-2 (FGF-2)–induced angiogenesis. This could explain the disappointing results of FGF-2 therapy in clinical trials despite promising preclinical studies. We examined the influence of l -arginine supplementation to FGF-2 therapy on myocardial microvascular reactivity and perfusion in a porcine model of endothelial dysfunction.

Methods and Results— Eighteen pigs were fed either a normal (NORM, n=6) or high cholesterol diet, with (HICHOL-ARG, n=6) or without (HICHOL, n=6) l -arginine. All pigs underwent ameroid placement on the circumflex artery and 3 weeks later received surgical FGF-2 treatment. Four weeks after treatment, endothelial-dependent coronary microvascular responses and lateral myocardial perfusion were assessed. Endothelial cell density was determined by immunohistochemistry. FGF-2, fibroblast growth receptor-1, endothelial-derived nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and syndecan-4 levels were determined by immunoblotting. Pigs from the HICHOL group showed endothelial dysfunction in the circumflex territory, which was normalized by l -arginine supplementation. FGF-2 treatment was ineffective in the HICHOL group (circumflex/left anterior descending blood flow ratios: 1.01 (rest) and 1.01 (pace), after and before treatment). Addition of l -arginine improved myocardial perfusion in response to FGF-2 at rest (ratio 1.13, P =0.02 versus HICHOL) but not during pacing (ratio 0.94, P =NS), and was associated with increased protein levels of iNOS and eNOS.

Conclusion— l -arginine supplementation can partially restore the normal response to endothelium-dependent vasorelaxants and myocardial perfusion in response to FGF-2 treatment in a swine model of hypercholesterolemia-induced endothelial dysfunction. These findings suggest a role for l -arginine in combination with FGF-2 therapy for end-stage coronary artery disease.

A synthetic glycosaminoglycan mimetic (RGTA) modifies natural glycosaminoglycan species during myogenesis

Crucial events in myogenesis rely on the highly regulated spatiotemporal distribution of cell surface heparan sulfate proteoglycans to which are associated growth factors, thus creating a specific microenvironment around muscle cells. Most growth factors involved in control of myoblast growth and differentiation are stored in the extracellular matrix through interaction with specific sequences of glycosaminoglycan oligosaccharides, mainly heparan sulfate (HS). Different HS subspecies revealed by specific antibodies, have been shown to provide spatiotemporal regulation during muscle development. We have previously shown that glycosaminoglycan (GAG) mimetics called RGTA (ReGeneraTing Agent), stimulate muscle precursor cell growth and differentiation. These data suggest an important role of GAGs during myogenesis; however, little is yet known about the different species of GAGs synthesized during myogenesis and their metabolic regulation. We therefore quantified GAGs during myogenesis of C2.7 cells and show that the composition of GAG species was modified during myogenic differentiation. In particular, HS levels were increased during this process. In addition, the GAG mimetic RGTA, which stimulated both growth and differentiation of C2.7 cells, increased the total amount of GAG produced by these cells without significantly altering their rate of sulfation. RGTA treatment further enhanced HS levels and changed its sub-species composition. Although mRNA levels of the enzymes involved in HS biosynthesis were almost unchanged during myogenic differentiation, heparanase mRNA levels decreased. RGTA did not markedly alter these levels. Here we show that the effects of RGTA on myoblast growth and differentiation are in part mediated through an alteration of GAG species and provide an important insight into the role of these molecules in normal or pathologic myogenic processes.

Heparan Sulfate Proteoglycan Is a Mechanosensor on Endothelial Cells

The objective of this study was to test whether a glycosaminoglycan component of the surface glycocalyx layer is a fluid shear stress sensor on endothelial cells (ECs). Because enhanced nitric oxide (NO) production in response to fluid shear stress is a characteristic and physiologically important response of ECs, we evaluated NO x (NO 2 − and NO 3 − ) production in response to fluid shear stress after enzymatic removal of heparan sulfate, the dominant glycosaminoglycan of the EC glycocalyx, from cultured ECs. The significant NO x production induced by steady shear stress (20 dyne/cm 2 ) was inhibited completely by pretreatment with 15 mU/mL heparinase III (E.C.4.2.2.8) for 2 hours. Oscillatory shear stress (10±15 dyne/cm 2 ) induced an even greater NO x production than steady shear stress that was completely inhibited by pretreatment with heparinase III. Addition of bradykinin (BK) induced significant NO x production that was not inhibited by heparinase pretreatment, demonstrating that the cells were still able to produce abundant NO after heparinase treatment. Fluorescent imaging with a heparan sulfate antibody revealed that heparinase III treatments removed a substantial fraction of the heparan sulfate bound to the surfaces of ECs. In summary, these experiments demonstrate that a heparan sulfate component of the EC glycocalyx participates in mechanosensing that mediates NO production in response to shear stress. The full text of this article is available online at http://www.circresaha.org.