Posts in Category: Vascular Biology

Translational Implications of Platelets as Vascular First Responders

Translational Implications of Platelets as Vascular First Responders

Richard C. Becker, Travis Sexton, Susan S. Smyth

Platelet participation in neutrophil extracellular trap formation (NETosis). Activated platelets interact with neutrophils via platelet P-selectin and neutrophil PSGL-1 (P-selectin glycoprotein ligand-1), with interactions stabilized by a series of secondary adhesion interactions, including the ones mediated by platelet GP (glycoprotein) Ib and leukocyte Mac-1 (αMβ2). This interaction can contribute to trigger the release of NETs, consisting of chromatin containing citrullinated histones complexed with antimicrobial proteases, such as elastase and myeloperoxidase, in a process called NETosis. NETs serve to enhance the clearance of pathogens. They also contribute to clot formation by forming a mesh with platelets and fibrin and accumulating coagulation factors, such as tissue factor (TF). [Powerpoint File]

Translational Implications of Platelets as Vascular First Responders

Translational Implications of Platelets as Vascular First Responders

Richard C. Becker, Travis Sexton, Susan S. Smyth

Role for platelets in inflammation and response to pathogens. At sites of damaged or inflamed endothelium, platelet adhesion occurs through various interactions, such as with exposed subendothelium, P-selectin expression on activated endothelium, and release of ultralarge vWF (von Willebrand factor). Adherent platelets, in turn, recruit white blood cells (WBCs), which can subsequently transmigrate across the endothelium. Heterotypic cell interactions between platelets and WBCs or red blood cells (RBCs) can occur and are associated with increases in systemic inflammation. Activated platelets can trigger the release of neutrophil extracellular traps (NETs), which contribute to microbial clearance and clot formation. Platelets also interact with viral and bacterial pathogens to contribute to their clearance and respond to gut microbiota that can modulate platelet function. [Powerpoint File]

Circulating Platelets as Mediators of Immunity, Inflammation, and Thrombosis

Circulating Platelets as Mediators of Immunity, Inflammation, and Thrombosis

Milka Koupenova, Lauren Clancy, Heather A. Corkrey, Jane E. Freedman

Platelet and circulating cell interactions during infection initiate the innate or adaptive immune response. Platelets achieve cell-to-cell communication during bacterial or viral infection either by direct interaction with white blood cells (WBCs) through surface expression of platelet proteins or through indirect protein release from their α- or δ-granules. Encephalomyocarditis virus (EMCV)–activated platelets interact with neutrophils in a TLR7 (Toll-like receptor 7)-dependent manner. Coxsackievirus B (CVB)–activated platelets bind to neutrophils in a phosphatidylserine (PS)-dependent manner. Dengue and influenza increase microparticle release; dengue-mediated microparticles contain IL-1β (interleukin 1β). Human cytomegalovirus (HCMV)–activated platelets interact with neutrophils, monocytes, B cells, T cells, and dendritic cells (DCs), suggesting activation of innate and adaptive immune responses. Vaccinia-bound platelets have reduced aggregation potential in the presence of ADP, collagen, or thrombin. The specific pathways by which platelets respond to herpes simplex virus (HSV) 1 or HSV2 are currently unknown. During bacterial infection, platelet interactions with complement C3 opsonized bacteria through GP1b (glycoprotein 1b; CD42) lead to slowing of bacterial clearance. DCs recognize the platelet–bacterial complexes, thereby inducing adaptive immunity. These platelet–bacterial interactions are true for Gram-positive or Gram-negative bacteria. 5HT includes serotonin; and VEGF, vascular endothelial growth factor. [Powerpoint File]

Circulating Platelets as Mediators of Immunity, Inflammation, and Thrombosis

Circulating Platelets as Mediators of Immunity, Inflammation, and Thrombosis

Milka Koupenova, Lauren Clancy, Heather A. Corkrey, Jane E. Freedman

Platelet-mediated interactions with vascular or circulating cells. Platelets interact with endothelial and immune cells in the circulation, orchestrating a response to microbes, inflammatory stimuli, and vessel damage. Through their TLRs (Toll-like receptors; or inflammatory signals), platelets can change their surface expression and release their granule content, thereby engaging different immune cells. Platelets form heterotypic aggregates (HAGs) and initiate innate immune responses in the presence of TLR agonists and viruses such as encephalomyocarditis virus (EMCV), coxsackievirus B (CVB), dengue, flu, HIV. Platelets can interact with dendritic cells (DC) through their P-selectin (platelet selectin), activate them to become antigen (Ag) presenting through their CD154. By releasing α- or δ-granule content which leads to IgG (IgG1, IgG2, IgG3) production and control of T-cell function, platelets engage the adaptive immune response. Similarly, platelets are able to activate the endothelium, make it more permeable, and mediate leukocyte trafficking to the inflamed endothelium. Proteins in bold represent changes of expression on the platelet surface. Continuous lines represent direct binding; dotted lines represent interaction through secretion. 5HT indicates serotonin; CMV, cytomegalovirus; ICAM-1, intercellular adhesion molecule 1; IL, interleukin; PF4, platelet factor 4; PSGL1, P-selectin glycoprotein ligand 1; RANTES, regulated on activation, normal T cell expressed and secreted; TGF-β; transforming growth factor-β; and VCAM-1, vascular cell adhesion molecule 1. [Powerpoint File]

Multifunctional Role of Chymase in Acute and Chronic Tissue Injury and Remodeling

Multifunctional Role of Chymase in Acute and Chronic Tissue Injury and Remodeling

Louis J. Dell’Italia, James F. Collawn, Carlos M. Ferrario

Evidence from human pathology and preclinical animal models supports the important role for chymase in cardiovascular stress. Upper left, Demonstrates a cross-section of a human renal artery with marked increase in chymase (brown) extending from the endothelium to adventitia in a patient with diabetes mellitus (reprinted from Koka et al60 with permission. Copyright ©2006, Wolters Kluwer Health). Center and upper right, Cartoons demonstrate the potential role of chymase in attenuating ischemia/reperfusion injury and promoting stabilization of the vulnerable atherosclerotic plaque (reprinted from Bentzon et al249 with permission. Copyright ©2014, Wolters Kluwer Health). Bottom right, Demonstrate the marked increase in left ventricular (LV) volume and LV wall thinning in a patient with chronic mitral regurgitation (MR; right) compared with a normal subject (left; reprinted from Zheng et al250 with permission. Copyright ©2014, Wolters Kluwer Health). Bottom left, Demonstrates the increase in LV volume and apical wall thinning in a patient 6 mo after an antero-apical myocardial infarction (MI; right) compared with 3 d after MI (left; reprinted from Foster et al251 with permission. Copyright ©1998, Elsevier). Targeting the multifunctional roles of chymase (Figure 2) in each of these conditions by chymase inhibition will complement conventional renin–angiotensin system (RAS) blockade in promoting better outcomes and tissue protection. [Powerpoint File]

Bioresorbable Scaffold: The Emerging Reality and Future Directions

Bioresorbable Scaffold: The Emerging Reality and Future Directions

Yohei Sotomi, Yoshinobu Onuma, Carlos Collet, Erhan Tenekecioglu, Renu Virmani, Neal S. Kleiman, Patrick W. Serruys

Strut thickness and platelet activation. The thick protruding strut disrupts the laminar flow and induces flow disturbances, and thereby endothelial shear stress (ESS) microgradients (upper panel). The shear microgradients can induce the formation of stabilized discoid platelet aggregates, the size of which is directly regulated by the magnitude and spatial distribution of the gradient.72,73 Shear microgradient–dependent platelet aggregation requires 3 principal features: shear acceleration phase, peak shear phase, and shear deceleration phase. During shear acceleration, platelets in the central regions of blood flow exposed to laminar flow (constant physiological shear) are suddenly accelerated through the shear microgradient. During the peak shear phase, a proportion of the discoid platelets that are accelerated into the peak shear zone adhere to exposed thrombogenic surfaces through platelet membrane glycoprotein (GP) Ib/IX/V. Exposure of these platelets to elevated hemodynamic drag leads to the extrusion of thin filamentous membrane tethers. Membrane tether formation initiates discoid platelet adhesion with the thrombogenic surface and also facilitates the recruitment of discoid platelets into the downstream deceleration zone. During the shear deceleration phase, platelets transitioning into the flow deceleration zone experience decreasing hemodynamic drag forces. Reduced shear within this zone progressively favors the formation of integrin αIIbβ3 adhesion contacts. Integrin αIIbβ3 engagement is associated with low-frequency calcium spikes that trigger tether restructuring, leading to the stabilization of discoid platelet aggregates. Ongoing discoid platelet recruitment drives the propagation of the thrombus in the downstream deceleration zone, which may in turn amplify the shear microgradient and promote further platelet aggregation. Thus, the shear microgradients caused by the thick struts induce platelet aggregation, formation of microthrombi with potential embolization, and micromyocardial necrosis (so-called a nidus of thrombus). The magnitude of flow disturbance depends on the degree of protrusion of the strut into the lumen. Therefore, thin struts could be a potential solution for the less flow disturbance and thus less thrombogenic status (lower panel). There is another cascade of von Willebrand factor (VWF)/GPIb activation, namely agglutination-elicited GPIb signaling.73 In contrast to shear stress–induced GPIb-elicited signaling, agglutination-elicited GPIb signaling that activates integrin αIIbβ3 requires thromboxane A2 (TXA2). Agglutination-elicited TXA2 production is independent of Ca2+ influx and mobilization of internal Ca2+ stores. [Powerpoint File]

Bioresorbable Scaffold: The Emerging Reality and Future Directions

Bioresorbable Scaffold: The Emerging Reality and Future Directions

Yohei Sotomi, Yoshinobu Onuma, Carlos Collet, Erhan Tenekecioglu, Renu Virmani, Neal S. Kleiman, Patrick W. Serruys

Design and optical coherence tomography (OCT) appearance of first and next generation bioresorbable scaffolds (BRSs). [Powerpoint File]

Circulating Noncoding RNAs as Biomarkers of Cardiovascular Disease and Injury

Circulating Noncoding RNAs as Biomarkers of Cardiovascular Disease and Injury

Janika Viereck, Thomas Thum

Biogenesis and function of microRNAs (miRNAs). MiRNAs are transcribed from longer precursors with protein or other noncoding gene sequences and further processed via 2 endonucleolytic processing steps. Mature miRNAs associate with Argonaute proteins (Ago2) forming the RNA-induced silencing complex (miRISC). Within this complex, miRNAs recognize their target sequence and block their expression by translational repression or degradation. MiRNAs can be released or actively secreted into the extracellular space and circulatory system stabilized in vesicles or proteinous binding partners. DGCR8, DiGeorge syndrome critical region 8; TRBP, transactivation-responsive RNA-binding protein. [Powerpoint File]

Circulating Noncoding RNAs as Biomarkers of Cardiovascular Disease and Injury

Circulating Noncoding RNAs as Biomarkers of Cardiovascular Disease and Injury

Janika Viereck, Thomas Thum

Molecular mechanism of long noncoding RNA (lncRNA) activities. LncRNAs regulate the expression of genes in the nucleus by interacting directly with DNA recruiting chromatin modifying complexes and various transcriptional regulators. Cytoplasmatic noncoding transcripts act as sponges for other transcripts like microRNAs (miRNAs) or for proteins, serve as templates for small peptide synthesis or regulate messenger RNA (mRNA) degradation and translation. These transcripts enter the bloodstream bound to proteinous carriers or incorporated into extracellular vesicles that leads to a stabilization of transcripts. Ago2, Argonaute protein 2. [Powerpoint File]

MicroRNA Biomarkers and Platelet Reactivity: The Clot Thickens

MicroRNA Biomarkers and Platelet Reactivity: The Clot Thickens

Nicholas Sunderland, Philipp Skroblin, Temo Barwari, Rachael P. Huntley, Ruifang Lu, Abhishek Joshi, Ruth C. Lovering, Manuel Mayr

MiRNAs and platelet reactivity. Association of miR-126 and miR-223 levels in platelet-poor plasma (PPP) to the VerifyNow P2Y12 aggregation test (A) and the vasodilator-stimulated phosphoprotein (VASP) phosphorylation assay (B) in patients on dual antiplatelet therapy for 30 days postacute coronary syndrome. Note that fewer samples were measured with the VerifyNow (n=39) compared with the VASP assay (n=123). PRU denotes P2Y12 reaction units (x axis). Higher PRU values reflect higher P2Y12-mediated platelet reactivity. [Powerpoint File]

MicroRNA Biomarkers and Platelet Reactivity: The Clot Thickens

MicroRNA Biomarkers and Platelet Reactivity: The Clot Thickens

Nicholas Sunderland, Philipp Skroblin, Temo Barwari, Rachael P. Huntley, Ruifang Lu, Abhishek Joshi, Ruth C. Lovering, Manuel Mayr

Choice of samples. A, Workflow for the preparation of platelet-poor plasma (PPP) from platelet-rich plasma (PRP). Addition of prostacyclin inhibits platelet activation during centrifugation. B, Concerns with regards to miRNA measurements in the different samples range from a contamination with leukocytes in PRP, proteolytic activity in serum to residual platelets in plasma. PRP and serum should reflect platelet miRNA content; PPP platelet miRNA release; plasma samples will reflect extracellular miRNA content but may additionally reflect either, platelet miRNA content or release. This depends on the amount of residual platelets in the plasma samples or platelet activation during plasma preparation, in particular during centrifugation. [Powerpoint File]

Pleiotropic Effects of Statins on the Cardiovascular System

Pleiotropic Effects of Statins on the Cardiovascular System

Adam Oesterle, Ulrich Laufs, James K. Liao

Regulation of the Rho GTPase cycle. Rho cycles between an inactive, cytoplasmic, GDP bound form and after geranylgeranylation is translocated to the plasma membrane and activated when it is bound to GTP. Inhibition of mevalonate synthesis by statins decreases geranylgeranyl (GG) pyrophosphate and prevents the geranylgeranylation of Rho and therefore its activation of Rho kinase (ROCK). ROCK mediates the downstream effects of Rho and has effect on endothelial cells, inflammatory cells, fibroblasts, cardiomyocytes, and vascular smooth muscle cells (SMC) that promote atherosclerosis and cardiac remodeling and may be responsible for the pleiotropic effects of statins. CRD indicates cysteine-rich domain; eNOS, endothelial nitric oxide synthase; GAP, GTPase-activating proteins; GDI, guanine nucleotide dissociation inhibitors; GEF, guanine nucleotide exchange factors; PI3K, phosphatidylinositol 3-kinase; and RBD, Rho-binding domain. Illustration Credit: Ben Smith. [Powerpoint File]

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

Yulia A. Komarova, Kevin Kruse, Dolly Mehta, Asrar B. Malik

Mechanotransduction at adherens junctions (AJs). The mechanosensory complex in endothelial cells is composed of vascular endothelial (VE)-cadherin, platelet endothelial cell adhesion molecule (PECAM)-1, and vascular endothelial growth factor receptor (VEGFR) 2. Mechanosensing of shear stress occurs through PECAM-1–dependent activation of Fyn, which in turn facilitates VEGFR2-mediated signaling in a ligand-independent manner and activates phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K). PI3K activates both Rac1 and endothelial nitric oxide synthase (eNOS) signaling pathways. Rac1 relieves tension at AJs, whereas NO concomitantly promotes vasorelaxation of smooth muscle cells. PECAM-1–dependent sensing of shear stress also promotes α2β1 integrin signaling and consequently activation of protein kinase A (PKA) in atheroresistant regions. PKA phosphorylates RhoA and decreases RhoA-dependent cellular stiffness allowing the endothelial cell to align in the direction of blood flow. GPCR indicates G-protein–coupled receptor; and sGC, soluble guanylyl cyclase. [Powerpoint File]

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

Yulia A. Komarova, Kevin Kruse, Dolly Mehta, Asrar B. Malik

Role of actomyosin apparatus in stabilizing adherens junctions (AJs). A, Domain structure of nonmuscle myosin-II (NM-II). The NM-II consists of a globular head domain containing both actin-binding and motor domains, essential light chains (ELCs), regulatory light chains (RLCs), and heavy chains. NM-II possesses a head-to-tail interaction in the absence of phosphorylation. Phosphorylation of regulatory light chain at Thr18/Ser19 by myosin light chain kinase (MLCK) unfolds the molecule, enabling assembly of antiparallel filaments through interactions between their rod domains. Activation of Rho-associated kinase (ROCK), which inhibits phosphatase activity of myosin light chain phosphatase (MLCP) in a phosphorylation-dependent manner, also favors RLC phosphorylation. NM-II filaments bind to actin filaments, which slide along each other, and cause a cell contraction. Modified from Vicente-Manzanares et al415 with permission of the publisher. Copyright ©2009, Nature Publishing Group. B, Proposed mechanism of regulation of NM-II activity at AJs in confluent endothelium. NM-II regulates attachment of the vascular endothelial (VE)-cadherin adhesion complex to the actin cytoskeleton, thereby generating mechanical tension required for binding of α-catenin to both β-catenin and f-actin. NM-II phosphorylation is controlled by MLCK and MLCP activities. In the model, we propose that Src and Cdc42 pathways cooperate in regulating NM-II activity at AJs. Cdc42 facilitates activation of NM-II through myotonic dystrophy kinase–related Cdc42-binding kinase (MRCK)–dependent phosphorylation of MLCP, whereas Src phosphorylates MLCK at sites of VE-cadherin adhesion. CaM indicates calmodulin; GAP, GTPase-activating protein; and GEF, guanine nucleotide exchange factor. [Powerpoint File]

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

Yulia A. Komarova, Kevin Kruse, Dolly Mehta, Asrar B. Malik

Composition of interendothelial junctions. A, Schematic representation of interendothelial junctions composed of tight junctions (TJs), adherens junctions (AJs), and gap junctions (GJs). TJs are mediated by adhesion proteins such as claudins, occludin, and junctional adhesion molecules (JAMs), whereas the zona occludin proteins (ZO-1, ZO-2, and ZO-3) connect adhesion molecules to the actin cytoskeleton. AJs are composed of vascular endothelial (VE)-cadherin and associated β- and p120-catenins. α-catenin binds β-catenin to connect AJs to the actin cytoskeleton. GJs are composed of 2 connexin hexamers forming hemichannels. B, VE-cadherin mediates adhesion by trans-dimerization of tryptophan 2 and tryptophan 4 residues in a hydrophobic pocket of the opposing VE-cadherin molecule. Ribbon presentations of VE-cadherin trans-dimer. C, Strand swap dimerization occurs through the insertion of a tryptophan residue into the hydrophobic binding pocket of the opposing cadherin. D, Trans-dimerization (between endothelial cell [EC] 1 and EC1 of opposing cadherins) orients VE-cadherin molecules and facilitates cis interactions (between EC1 and EC2 of neighboring cadherins). Panels B, C, and D are modified from Brasch et al115 with permission of the publisher. Copyright ©2012, Elsevier. [Powerpoint File]