Kinetics of adventitial repair in the rat carotid model

BACKGROUND

Discrepancies between success in experimental animals with a variety of pharmacologic strategies and failure with such agents in clinical trials have raised questions concerning the mechanism of restenosis. Recent observations suggest a potential implication for the adventitial (Adv) layer in neointimal formation.

METHODS

The purpose of this study was to examine the Adv changes in the rat carotid artery subjected to balloon injury. These changes were characterized by morphometric, immunohistochemical, and electron microscopy analyses, with special attention devoted to early time-points post-injury.

RESULTS

We report that the most important adventitial changes occurred in the first 48 h post-injury. Within 2 h there was extensive cell-loss by apoptosis and oncosis in the Adv and in the media; this was followed by the rapid onset of proliferation and a parallel slow increase in Adv thickening, reaching a maximum at 7 days. We further demonstrate an early migration of these Adv cells to the media and neointima. Moreover, we characterize the Adv cell phenotype with a panel of antibodies. Within 48 h after injury, a population of Adv cells expressed alpha-actin and vinculin with a maximum expression 7 days post-injury. At that time, these Adv cells started to express smooth muscle myosin heavy chain, a specific marker of smooth muscle cells. In parallel, we report an impaired production of elastic fibres in the Adv and medial layer.

CONCLUSIONS

We reported a detailed time-course of adventitial changes after rat carotid injury (cell death, proliferation, migration and differentiation) that supports an important role of adventitia in neointima formation.

[The mechanisms of angiogenesis. Medical and therapeutic applications]

PURPOSE

Endothelial and smooth muscle cells interact with each other to form new blood vessels. In this review, the cellular and molecular mechanism underlying the formation of the primary vascular plexus (vasculogenesis), the sprouting of further blood vessels (angiogenesis) and their maturation via recruitment of smooth muscle cells (arteriogenesis) during physiological and pathological conditions are summarized.

CURRENT KNOWLEDGE AND KEY POINT

The concept of angiogenesis is studied in tumoral and cardiovascular pathology. Promoting the formation of new collateral vessels in ischemic tissues using angiogenic growth factors (therapeutic angiogenesis) is a promising approach in cardiovascular diseases. Conversely, inhibition of the action of key regulators of angiogenesis is a new pathway for the treatment of solid tumors and metastasis.

FUTURE PROSPECTS AND PROJECTS

These concepts are being tested now in clinical trials in the oncology or cardiovascular fields. Some trials are reported in this review with their potential adverse effects, limits and developments in the future.

Nitric oxide reduces vascular smooth muscle cell elastase activity through cGMP-mediated suppression of ERK phosphorylation and AML1B nuclear partitioning

Nitric oxide (NO) reduces the severity of pulmonary vascular disease in rats as do elastase inhibitors. We therefore hypothesized that NO inhibits elastase by suppressing mitogen-activated protein kinases that trans-activate AML1B, a transcription factor for elastase. We used cultured pulmonary artery smooth muscle cells in which serum-treated elastin (STE) induces a > threefold increase in elastase activity as evaluated by solubilization of [(3)H]-elastin. NO donors (SNAP and DETA NONOate) inhibited elastase in a dose-dependent manner as did a cGMP mimetic (8-pCPT-cGMP). SNAP inhibition of elastase was reversed by coadministration of a cGMP-PKG inhibitor (Rp-8-pCPT-cGMP). The STE-induced increase in phospho-ERK was suppressed by NO donors and the cGMP mimetic, and reversed by cGMP-PKG inhibitor, as was expression of AML1B and DNA binding in nuclear extracts. A concomitant increase in p38 phosphorylation was also inhibited by SNAP, but whereas MEK inhibitor (PD98059) suppressed elastase and AML1B-DNA binding, a p38 inhibitor (SB202190) did not. Our study uniquely links NO with inhibition of elastase-dependent matrix remodeling in vascular disease by suggesting a cGMP-PKG-related mechanism suppressing ERK-mediated partitioning of AML1B in nuclear extracts.

Expression pattern of mouse sFRP-1 and mWnt-8 gene during heart morphogenesis

The Wnt genes encode a large family of secreted proteins that play a key role in embryonic development and tissue differentiation in many species (Rijsewijk et al., 1987; Nusse and Varmus, 1992). Genetic and biochemical studies have suggested that the frizzled proteins are cell surface receptors for Wnts (Vinson et al., 1989; Chan et al. , 1992; Bhanot et al., 1996; Wang et al., 1996). In parallel, a number of secreted frizzled-like proteins with a conserved N-terminal frizzled motif have been identified (Finch et al., 1997; Melkonyan et al., 1997; Rattner et al., 1997). One of these proteins, FrzA, the bovine counterpart of the murine sFRP-1 (93% identity) is involved in vascular cell growth control, binds Wg in vitro and antagonizes Xwnt-8 and hWnt-2 signaling in Xenopus embryos (Xu et al. , 1998; Duplàa et al., 1999). In this study, we report that sFRP-1 is expressed in the heart and in the visceral yolk sac during mouse development, and that sFRP-1 and mWnt-8 display overlapping expression patterns during heart morphogenesis. From 8.5 to 12.5 d.p. c., sFRP-1 is expressed in cardiomyocytes together with mWnt-8 but neither in the pericardium nor in the endocardium; at 17.5 d.p.c., they are no longer present in the heart. In mouse adult tissues, while sFRP-1 is highly detected in the aortic endothelium and media and in cardiomyocytes, mWnt-8 is not detected in these areas. Immunoprecipitation experiments demonstrates that FrzA binds to mWnt-8 in cell culture experiments.

RNA interference can target pre-mRNA: consequences for gene expression in a Caenorhabditis elegans operon

In nematodes, flies, trypanosomes, and planarians, introduction of double-stranded RNA results in sequence-specific inactivation of gene function, a process termed RNA interference (RNAi). We demonstrate that RNAi against the Caenorhabditis elegans gene lir-1, which is part of the lir-1/lin-26 operon, induced phenotypes very different from a newly isolated lir-1 null mutation. Specifically, lir-1(RNAi) induced embryonic lethality reminiscent of moderately strong lin-26 alleles, whereas the lir-1 null mutant was viable. We show that the lir-1(RNAi) phenotypes resulted from a severe loss of lin-26 gene expression. In addition, we found that RNAi directed against lir-1 or lin-26 introns induced similar phenotypes, so we conclude that lir-1(RNAi) targets the lir-1/lin-26 pre-mRNA. This provides direct evidence that RNA interference can prevent gene expression by targeting nuclear transcripts. Our results highlight that caution may be necessary when interpreting RNA interference without the benefit of mutant alleles.

lir-2, lir-1 and lin-26 encode a new class of zinc-finger proteins and are organized in two overlapping operons both in Caenorhabditis elegans and in Caenorhabditis briggsae

lin-26, which encodes a unique Zn-finger protein, is required for differentiation of nonneuronal ectodermal cells in Caenorhabditis elegans. Here, we show that the two genes located immediately upstream of lin-26 encode LIN-26-like Zn-finger proteins; hence their names are lir-1 and lir-2 (lin-26 related). lir-2, lir-1, and lin-26 generate several isoforms by alternative splicing and/or trans-splicing at different positions. On the basis of their trans-splicing pattern, their intergenic distances, and their expression, we suggest that lir-2, lir-1, and lin-26 form two overlapping transcriptional operons. The first operon, which is expressed in virtually all cells, includes lir-2 and long lir-1 isoforms. The second operon, which is expressed in the nonneuronal ectoderm, includes short lir-1 isoforms, starting at exon 2 and lin-26. This unusual genomic organization has been conserved in C. briggsae, as shown by cloning the C. briggsae lir-2, lir-1, and lin-26 homologs. Particularly striking is the sequence conservation throughout the first lir-1 intron, which is very long in both species. Structural conservation is functionally meaningful as C. briggsae lin-26 is also expressed in the nonneuronal ectoderm and can complement a C. elegans lin-26 null mutation.

A tissue-specific knock-out strategy reveals that lin-26 is required for the formation of the somatic gonad epithelium in Caenorhabditis elegans

The Caenorhabditis elegans LIN-26 protein is required to specify and/or maintain the fates of all non-neuronal ectodermal cells. Here we show that lin-26 is expressed until the somatic gonad primordium stage in all cells of the somatic gonad, except in distal tip cells, and later in all uterine cells. To determine if lin-26 functions in the somatic gonad, we have generated gonad-specific lin-26 alleles obtained by integration of lin-26 promoter deletion derivatives into a lin-26 null mutant background. In this way, we rescued the lethal phenotype imparted by lin-26 null mutations and uncovered a highly penetrant sterile phenotype. Specifically, the strongest of these new alleles was characterized by the absence of lin-26 expression in the somatic gonad, the presence of endomitotic oocytes, decreased germline proliferation, a protruding vulva and a less penetrant absence of gonad arms. Lineage analysis of mutant somatic gonads and examination of several markers expressed in the spermatheca, sheath cells, distal tip cells and the uterus, suggest that LIN-26 is required in sheath, spermatheca and uterine precursors, and in uterine cells. We conclude that lin-26 performs a similar function in the non-neuronal ectoderm and the somatic gonad, a mesoderm derivative, and we speculate that lin-26 is required to express epithelial characteristics.

Vitronectin expression and interaction with receptors in smooth muscle cells from human atheromatous plaque

Vitronectin (VN) is a plasma glycoprotein that promotes cell attachment and induces migration of human smooth muscle cells (SMCs) in culture. VN has been observed to accumulate in human atherosclerotic plaques, although its origin and role in atherosclerosis are not yet established. In the present experiments, synthesis of VN by intimal cells and its colocalization with receptors, alphavbeta3 and alphavbeta5, were studied by in situ hybridization and immunohistochemistry on 15 human atherosclerotic plaques from carotid arteries obtained after surgery. Strong VN protein and mRNA expression was observed in the intima and in the media. In the intima, VN mRNA expression was colocalized with SMCs, indicating that these cells produce VN, which may account for its accumulation in atherosclerotic plaques. In SMCs in culture, immunoprecipitation after metabolic labeling demonstrated that human SMCs do synthesize vitronectin. Confocal microscopic examination showed that VN colocalized with its receptors, alphavbeta3 and alphavbeta5, in the atherosclerotic intima. However, the distribution of the VN receptors on SMCs in culture in contact with VN was different. These observations suggest that VN plays various parts in atherogenesis via different SMC membrane receptors.

Phenotypic modification of arterial smooth muscle cells in response to medial dissection

BACKGROUND

In the treatment of peripheral arteries, percutaneous transluminal angioplasty is commonly associated with intimal tears and dissections.

OBJECTIVE

To investigate the influence of medial dissection on the remodelling of the vessel wall after balloon injury.

METHODS

Aortae were obtained from 14 Fauve de Bourgogne rabbits that had been fed a normal diet. Seven days after the initial pull-back injury, the aortae were examined using morphometric and immunocytochemical methods.

RESULTS

Eight rabbits (57%) had a tear that extended into the media. Morphometric measurements showed that the intima was significantly thinner when there was a medial dissection [(18.3 +/- 6.9) x 10(-3) versus (39.1 +/- 3.5) x 10(-3) mm without dissection, P < 0.001]. In the media of injured vessels, medial dissection was associated with a greater accumulation of extracellular matrix proteins (50.5 +/- 9.7 versus 12.4 +/- 2.2% of the surface area), a marked reduction in alpha-smooth muscle actin content (36.6 +/- 5.4 versus 47.4 +/- 7.5% of the surface area), a higher expression of a smooth muscle activation antigen (21.2 +/- 5.7 versus 8.9 +/- 1.5% of the 2P1A2-immunostained surface area) and an increase in the number of medial proliferating cell nuclear antigen-positive nuclei (8.2 versus 1.2% of labelled nuclei).

CONCLUSION

These observations indicated that mechanical injury of the arterial wall induces a phenotypic activation of medial smooth muscle cells. In the case of acute distension, the response of the smooth muscle cells in the media was mainly responsible for wound healing in the presence of medial dissection; moreover, acute distension induced a significant higher state of activation and a medial repairing that could prevent migration towards the intimal space.

The integrin very late antigen-4 is expressed in human smooth muscle cell. Involvement of alpha 4 and vascular cell adhesion molecule-1 during smooth muscle cell differentiation

Vascular cell adhesion molecule-1 (VCAM-1) and its counterreceptor, the integrin very late antigen-4 (VLA-4), have recently been identified in smooth muscle cells during intimal thickening in humans and in newly forming vessels during ontogeny in mice, respectively. We examined the coexpression of VCAM-1 and the alpha 4 integrin subunit in human smooth muscle cells. The expression of VCAM-1 and alpha 4 subunit were studied during development of the aorta. In the 10-week-old human fetal aorta, VCAM-1 and alpha 4 were strongly expressed in smooth muscle cells. Their expression was dramatically reduced within the 24th week of gestation and disappeared in the adult aortic media. However, smooth muscle cells from intimal atherosclerotic thickening of adult aorta reexpressed both VCAM-1 and alpha 4. In a culture model mimicking smooth muscle differentiation, VCAM-1 mRNA and protein and alpha 4 integrin protein were coexpressed with smooth muscle-specific variants of cytoskeletal and contractile proteins, smooth muscle myosin heavy chain, caldesmon heavy chain, and desmin. Treatment with antibodies against VCAM-1 or alpha 4 integrin subunit interfered with the mRNA induction of smooth muscle-specific markers of differentiation. These results in vitro, associated with the transitory expression of VCAM-1 and VLA-4 during vascular ontogeny and the atherosclerosis process, point to a possible role of VCAM-1 and VLA-4 in the induction of smooth muscle differentiation.

Functional characterization of the proteolytic activity of the tomato black ring nepovirus RNA-1-encoded polyprotein

Translation of tomato black ring virus (TBRV) RNA-1 in a rabbit reticulocyte lysate leads to the synthesis of a 250K polyprotein which cleaves itself into smaller proteins of 50, 60, 120, and 190K. Polypeptides synthesized from synthetic transcripts corresponding to different regions of TBRV RNA-1 are processed only when they encode the 23K protein delimited earlier by sequence homology with the cowpea mosaic virus 24K protease. The proteolytic activity of this protein is completely lost by mutating residues C170 (to I) or L188 (to H), residues which align with conserved residues of the viral serine-like proteases. The 120K protein is generated by cleavage of the dipeptide K/A localized in front of the VPg but is not further cleaved in vitro at the K/S site (at the C terminus of the VPg) or between the protease and polymerase domains. However, both the protein VPgProPol (120K) and the protein ProPol (117K) produced in vitro from synthetic transcripts can cleave in trans the RNA-2-encoded 150K polyprotein, but they cannot cleave in trans polypeptides containing a cleavage site expressed from RNA-1 transcripts in which the protease cistron is absent or modified.

Influence of pentoxifylline on membrane thrombomodulin levels in endothelial cells submitted to hypoxic conditions

Thrombomodulin (TM) expression at the surface of endothelial cells is upregulated by cAMP analogues, whereas hypoxic conditions induce a decrease in this expression. Pentoxifylline (PTX) enhances the intracellular levels of cAMP in human umbilical vein endothelial cells (HUVECs). We therefore investigated the influence of this drug on TM expression in cells submitted to hypoxia. TM expression was quantified at the surface of HUVECs in the presence or absence of PTX during 18 h of incubation. Membrane TM was immunolabeled with a fluorescent monoclonal antibody and the expression was quantified by flow cytometric analysis. Our preliminary data revealed that PTX at 0.01 microM significantly increased TM expression levels compared with cells in hypoxia without the drug. Therefore, at this low dose PTX appears able to counterbalance the procoagulant effect of hypoxia.

Plasma thrombomodulin: new approach of endothelium damage

Endothelium damage is associated with thrombotic risk in a variety of diseases including atherosclerosis, gram negative sepsis, viral infections and neoplastic disease. Therefore, it appears necessary to find a mean for the clinical investigation for such a damage. Among the markers of these cells, thrombomodulin which is a membrane glycoprotein, seems to be of great interest for this purpose. Actually, thrombomodulin is also found in plasma, following an endothelial lesion. Plasma levels of thrombomodulin are increased in a certain number of pathologies associated with endothelium lesion: atheromatous arterial disease, disseminated intravascular coagulation syndrome and also in systemic lupus erythematosus where the levels of plasma thrombomodulin are related to the severity of the pathology. Moreover, previous in vitro studies confirm the fact that the release of thrombomodulin from the endothelial cell membrane occurs during the course of injury by activated leukocytes or hydrogen peroxide. So, one can suppose a prospective interest in the measurement of plasma thrombomodulin as a diagnostic tool for the approach of endothelium damage.

Levels of plasma thrombomodulin are increased in atheromatous arterial disease

The plasma thrombomodulin (TM) level depends on the integrity of the endothelium and the clearance of the molecule. In several different pathological conditions, plasma TM levels increase with damage to the endothelium. We studied plasma TM levels in patients with various localizations of atheromatous arterial disease who had normal serum creatinine levels. Two groups of patients had a single symptomatic localization, which was either peripheral occlusive arterial disease (POAD) or ischemic heart disease (IHD) and a third group of patients had multiple symptomatic localizations (polyvascular). We compared the plasma TM levels with the plasma levels of other specific markers of endothelial cell activation such as: prostacyclin (PGI2), tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI-1). Plasma TM levels were significantly increased in all three individual groups and when all patients were considered (total patients), as compared with normal controls. When all patients were considered, there was a significant positive correlation between plasma TM levels and t-PA and between plasma TM levels and PGI2. A significant positive correlation was also found between the plasma TM levels and PAI-1 for patients with POAD. Thus, our findings suggest that an increased influx of TM into the plasma may be caused by endothelial cell damage in patients with atheromatous arterial disease. However in our study, the plasma TM levels obtained were similar for all three types of atheromatous arterial disease. Though plasma thrombomodulin is a marker of endothelial cell injury, it cannot be of a clinical interest until its levels are related to the extend of the atheromatous lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycoproteins and lectins in cell adhesion and cell recognition processes

The discovery of endogenous lectins having specific and high affinity for the carbohydrate portions of glycoproteins has opened up new directions in the field of cell adhesion and cell recognition. Two endogenous lectins, termed as CSL and R1, initially isolated from the rat cerebellum and having a wide distribution in mammalian tissues, have been shown to participate in essential mechanisms of cell adhesion. The membrane-bound lectin R1 seems to be involved in transient recognition between neuronal cells, followed by elimination of the glycoprotein ligands at the surface of the recognized cell. In contrast, CSL is a molecule involved in adhesion between various normal or transformed cells since it participates in the formation of tight junctions. The glycoprotein ligands recognized with higher affinity by these two lectins seem to possess a special structure which defines a sub-class of oncofetal HNK-1 glycans. The over-expression of the glycoprotein ligands of these lectins in most transformed cells provides new tools for understanding the underlying mechanism of malignant transformation as well as the generation of signals through cell adhesion.