The response of smooth muscle cells to alpha-thrombin depends on its arterial origin: comparison among different species

Viscoelastic properties of multi-layered cellularized vascular tissues fabricated from collagen gel

Since collagen is one of the major extracellular matrix components in vascular tissues, its use for vascular tissue engineering has several advantages. However, collagen extraction and processing for tissue engineering application alters its structure. As a result, collagen-based vascular constructs show poor mechanical properties compared to native tissues. In this work, multi-layer (single, double, and triple) vascular tissue constructs were engineered from porcine smooth muscle cells (PSMCs) entrapped in collagen gel by concentrically and sequentially layering after compaction of the previous layer(s). The engineered tissues were matured for either 14 or 21 days to allow the collagen gel to remodel before viscoelasticity, compliance, histological, and protein expression studies were conducted. While there was no significant difference upon addition of the different layers on the elastic modulus (p > .05), the viscous modulus of the single layer construct was significantly lower than the double and triple layer constructs (p < .05). Increasing the number of layers of the cellularized collagen construct increased the wall thickness and the viscous modulus of the construct. Furthermore, the cellularized single-layer construct had a relatively high compliance, but the double and triple layer constructs had compliance values comparable to both engineered vessels and native vessels. PSMCs were uniformly distributed throughout the cross-section and expressed the anticipated marker proteins smooth muscle-α actin, calponin, and smooth muscle myosin heavy chain. Taken together, this study demonstrated the viscoelastic responsiveness of multi-layer collagen-gel based vascular tissues.

Preparation and characterization of a scaffold for vascular tissue engineering by direct-assembling of collagen and cells in a cylindrical geometry

In the past 25 years, several efforts have been focused on developing vascular substitutes showing long-term patency when implanted in humans. In this study, we present our last findings in an ongoing project aiming to develop a tissue-regenerated blood vessel from collagen-based scaffolds. A collagen-based scaffold with adequate biological properties was developed by directly assembling collagen and cells in a cylindrical geometry. The technique mainly involves the use of a ventilated rotating tube allowing smooth muscle cells to grow in a cylindrical collagen matrix. Scanning electron microscopy (SEM), histology, and cell cycle analyses were carried out in order to assess the biological potential of the cell-based scaffold for further maturation. Compliance results showed that this technique allows cells to assemble in the collagen matrix, thus providing enough rigidity to the structure to be handled and mounted in a perfusion bioreactor for further growth and maturation.

Neuron-derived orphan receptor-1 (NOR-1) is induced by thrombin and mediates vascular endothelial cell growth

BACKGROUND AND AIM

Neuron-derived orphan receptor-1 (NOR-1) is a transcription factor overexpressed in human atherosclerotic plaques that is involved in vascular smooth muscle cell (VSMC) proliferation. The aim of this study was to analyze the role of NOR-1 in thrombin-induced endothelial cell growth.

RESULTS

Thrombin induced an early and transient up-regulation of NOR-1 in human umbilical vein endothelial cells (HUVEC). NOR-1 up-regulation by thrombin is dependent on multiple pathways, including cytosolic Ca(2+), activation of protein kinase C (PKC), mitogen-activated protein kinase (MAPK) pathways [both extracellular-regulated kinase (ERK) and p38 MAPK], and downstream activation of cAMP response element binding protein (CREB). The critical role of CREB in the induction of NOR-1 by thrombin was demonstrated using a dominant-negative of CREB. By site-direct mutagenesis we identified two CRE sites present at -79 and -53 bp in the NOR-1 promoter involved in the up-regulation of NOR-1 by thrombin. Inhibition of thrombin receptor PAR-1 abolished CREB activation, NOR-1 up-regulation and DNA synthesis (used as an index of cell proliferation). TRAP-6 mimicked both NOR-1 up-regulation and CREB activation induced by thrombin, while PPACK (an irreversible thrombin inhibitor) prevented such an effect. Direct inhibition of thrombin-induced NOR-1 up-regulation, using antisense oligonucleotides or siRNA against NOR-1, reduced DNA synthesis and endothelial cell re-growth after injury in an in vitro model of wound repair.

CONCLUSIONS

These results indicate that NOR-1 up-regulation plays a key role in thrombin-induced endothelial cell growth. Strategies aimed to block NOR-1 could be useful to prevent vascular effects triggered by thrombin.

Biological performances of collagen-based scaffolds for vascular tissue engineering

Collagen is widely used for biomedical applications and it could represent a valid alternative scaffold material for vascular tissue engineering. In this work, reconstituted collagen films were prepared from neutralized acid-soluble solutions for subsequent haemocompatibility and cell viability performance assays. First, haemoglobin-free, thrombelastography and platelet adhesion tests were performed in order to investigate the blood contact performance. Secondly, specimens were seeded with endothelial cells and smooth muscle cells, and cell viability tests were carried out by MTT and SEM. Results show that neutralized acid-soluble type I collagen films do not enhance blood coagulation, do not alter normal viscoelastic properties of blood and slightly activate platelet adhesion and aggregation. Cell culture shows that the samples are adequate substrates to support the adhesion and proliferation of endothelial and smooth muscle cells.

Intracellular lipid accumulation, low-density lipoprotein receptor-related protein expression, and cell survival in vascular smooth muscle cells derived from normal and atherosclerotic human coronaries

BACKGROUND

Vascular smooth muscle cell (VSMC) regulation during atherosclerotic plaque progression is determinant for plaque stability.

AIMS

To study lipid accumulation, low-density lipoprotein receptor-related protein (LRP) expression, and cell survival in VSMCs isolated from nonatherosclerotic areas (normal VSMCs) and advanced atherosclerotic plaques (plaque-VSMCs) of human coronaries.

DESIGN

Normal or plaque-VSMCs were obtained from the intima by modification of the explant technique.

RESULTS

Aggregated low-density lipoprotein (agLDL) (100 micro g mL(-1)) internalization induced higher intracellular cholesteryl ester (CE) accumulation in plaque-VSMC compared with normal VSMCs (89.28 +/- 6.1 vs. 60.34 +/- 4.1 micro g CE mg(-1) of protein; P < 0.05). This internalization was associated with LRP expression, as plaque-VSMCs show higher levels of LRP mRNA (6.06 +/- 0.55 vs. 3.87 +/- 0.28; P < 0.05) and LRP protein expression than normal VSMCs. However, plaque-VSMCs showed a lower proliferative response than normal VSMCs (6536 +/- 636 vs. 11151 +/- 815 c.p.m. [(3)H]thymidine; P < 0.05) and did not respond to platelet-derived growth factor BB (PDGF-BB) stimulus. In agreement, the Bcl(2)/BAX ratio was significantly lower in plaque-VSMCs compared with normal VSMCs (0.14 +/- 0.05 vs. 0.51 +/- 0.07; P < 0.05) and it was independent of lipid loading.

CONCLUSIONS

These results indicate that higher intracellular lipid deposition in plaque-VSMCs is related to higher LRP expression levels. However, LRP-mediated agLDL internalization is not directly related to the reduced survival of plaque-VSMCs.

Neovascularización en arterias coronarias humanas con distintos grados de lesión

INTRODUCTION AND OBJECTIVES

Endothelial function can be modulated by growth factors produced by activated smooth muscle cells, inflammatory cells and plasma products that infiltrate the lesion. The aim of this study was to quantify neovessels in human coronary arteries with atherosclerotic lesions of different severity and analyze their relationship with inflammatory cell and plasma product infiltrates.

PATIENTS AND METHOD

We studied 60 coronary arteries from patients who underwent heart transplant. Cellular markers (smooth muscle cell, monocyte/macrophage), the presence thrombin/prothrombin and expression of vascular endothelial growth factor (VEGF) were analyzed and quantified by conventional histology, immunohistochemistry and image analysis techniques.

RESULTS

Neovessels were detected in advanced lesions, and a positive correlation was observed with the degree of vessel remodeling, monocyte/macrophage infiltration and lipid deposition. Smooth muscle cells were the main producers of VEGF in both the intima and media layers of advanced lesions. In these lesions thrombin/prothrombin-positive areas colocalized with activated smooth muscle cells.

CONCLUSIONS

The presence of neovessels in coronary arteries correlated with inflammatory cell infiltration, lipid deposition and thrombin/prothrombin content. VEGF expression was mainly associated with smooth muscle cells, indicating a key role of these cells in the modulation of endothelial cell function.

[Cellular and molecular biology of atherosclerotic lesions]

The association of atherosclerosis with the most common risk factors including elevation of low density lipoprotein (LDL) levels, diabetes, hypertension and cigarette smoking, led to the hypothesis of "response to injury" to explain how the lesions develop. According to this hypothesis, one of the earliest events in atherogenesis is the accumulation of LDL in the arterial wall where they undergo oxidation. These LDL impair endothelial function, and thus, all the antiatherogenic properties of the endothelium. In addition, macrophages and smooth muscle cells take up these LDL, through different receptors, and become foam cells. The accumulation of foam cells in the arterial wall contributes to lesion development. Therefore, lesion development involves the activation of endothelial cells, as well as smooth muscle cells and monocytes/macrophages. In this activation different growth factors (PDGF, EGF, etc.), cytokines (IL-1b, TNFa, etc.) and the modified LDL themselves, play an important role. Through several signal transduction pathways these molecules activate transcription factors, such as the nuclear factor kappa B (NF-kB) or protooncogenes such as c-fos, c-myc, that regulate the expression of genes involved in the inflammatory/proliferative response of the lesions.

Inhibition of cellular action of thrombin by N3-cyclopropyl-7-[[4-(1-methylethyl)phenyl]methyl]-7H-pyrrolo[3, 2-f]quinazoline-1,3-diamine (SCH 79797), a nonpeptide thrombin receptor antagonist

A growing body of evidence suggests an important contribution of the cellular actions of thrombin to thrombosis and restenosis following angioplasty. Recently we reported on SCH 79797 (N3-cyclopropyl-7-¿[4-(1-methylethyl)phenyl]methyl¿-7H-pyrrolo[3, 2-f]quinazoline-1,3-diamine) and its analogs as new potent, nonpeptide thrombin receptor antagonists. This study further characterizes the biochemical and pharmacological actions of pyrroloquinazoline inhibitors of protease activated receptor-1 (PAR-1) in human platelets and coronary artery smooth muscle cells (hCASMC). SCH 79797 and its N-methyl analog (SCH 203099) inhibited binding of a high-affinity thrombin receptor-activating peptide ([(3)H]haTRAP, Ala-Phe(p-F)-Arg-ChA-HArg-[(3)H]Tyr-NH(2)) to PAR-1 with IC(50) values of 70 and 45 nM, respectively. SCH 79797 inhibited [(3)H]haTRAP binding in a competitive manner. SCH 79797 and SCH 203099 inhibited alpha-thrombin- and haTRAP-induced aggregation of human platelets, but did not inhibit human platelet aggregation induced by the tethered ligand agonist for protease-activated receptor-4 (PAR-4), gamma-thrombin, ADP, or collagen. SCH 203099 inhibited surface expression of P-selectin induced by haTRAP and thrombin, and it did not increase P-selectin expression or prevent thrombin cleavage of the receptor. Thrombin and TFLLRNPNDK-NH(2) (TK), a PAR-1-selective agonist, produced transient increases in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) in hCASMC. This increase in [Ca(2+)](i) was inhibited effectively by SCH 79797. However, the Ca(2+) transients induced by SLIGKV-NH(2,) a PAR-2-selective agonist, were not inhibited by SCH 79797. Thrombin- and TK-stimulated [(3)H]thymidine incorporation also was inhibited completely by SCH 79797. The results of this study demonstrate that SCH 79797 and SCH 203099 are potent, selective antagonists of PAR-1 in human platelets and hCASMC. These data also suggest that the thrombin stimulation of Ca(2+) transients and mitogenesis in hCASMC is mediated primarily through activation of PAR-1.