Molecular analysis of arterial stenosis in rat carotids

Pro-inflammatory cytokines activate hypoxia-inducible factor 3α via epigenetic changes in mesenchymal stromal/stem cells

Human mesenchymal stromal/stem cells (hMSCs) emerged as a promising therapeutic tool for ischemic disorders, due to their ability to regenerate damaged tissues, promote angiogenesis and reduce inflammation, leading to encouraging, but still limited results. The outcomes in clinical trials exploring hMSC therapy are influenced by low cell retention and survival in affected tissues, partially influenced by lesion's microenvironment, where low oxygen conditions (i.e. hypoxia) and inflammation coexist. Hypoxia and inflammation are pathophysiological stresses, sharing common activators, such as hypoxia-inducible factors (HIFs) and NF-κB. HIF1α and HIF2α respond essentially to hypoxia, activating pathways involved in tissue repair. Little is known about the regulation of HIF3α. Here we investigated the role of HIF3α in vitro and in vivo. Human MSCs expressed HIF3α, differentially regulated by pro-inflammatory cytokines in an oxygen-independent manner, a novel and still uncharacterized mechanism, where NF-κB is critical for its expression. We investigated if epigenetic modifications are involved in HIF3α expression by methylation-specific PCR and histone modifications. Robust hypermethylation of histone H3 was observed across HIF3A locus driven by pro-inflammatory cytokines. Experiments in a murine model of arteriotomy highlighted the activation of Hif3α expression in infiltrated inflammatory cells, suggesting a new role for Hif3α in inflammation in vivo.

Vascular smooth muscle cell proliferation depends on caveolin-1-regulated polyamine uptake

Much evidence highlights the importance of polyamines for VSMC (vascular smooth muscle cell) proliferation and migration. Cav-1 (caveolin-1) was recently reported to regulate polyamine uptake in intestinal epithelial cells. The aim of the present study was to assess the importance of Cav-1 for VSMC polyamine uptake and its impact on cell proliferation and migration. Cav-1 KO (knockout) mouse aortic cells showed increased polyamine uptake and elevated proliferation and migration compared with WT (wild-type) cells. Both Cav-1 KO and WT cells expressed the smooth muscle differentiation markers SM22 and calponin. Cell-cycle phase distribution analysis revealed a higher proportion of Cav-1 KO than WT cells in the S phase. Cav-1 KO cells were hyper-proliferative in the presence but not in the absence of extracellular polyamines, and, moreover, supplementation with exogenous polyamines promoted proliferation in Cav-1 KO but not in WT cells. Expression of the solute carrier transporters Slc7a1 and Slc43a1 was higher in Cav-1 KO than in WT cells. ODC (ornithine decarboxylase) protein and mRNA expression as well as ODC activity were similar in Cav-1 KO and WT cells showing unaltered synthesis of polyamines in Cav-1 KO cells. Cav-1 was reduced in migrating cells in vitro and in carotid lesions in vivo. Our data show that Cav-1 negatively regulates VSMC polyamine uptake and that the proliferative advantage of Cav-1 KO cells is critically dependent on polyamine uptake. We provide proof-of-principle for targeting Cav-1-regulated polyamine uptake as a strategy to fight unwanted VSMC proliferation as observed in restenosis.

Novel potential targets for prevention of arterial restenosis: insights from the pre-clinical research

Restenosis is the pathophysiological process occurring in 10-15% of patients submitted to revascularization procedures of coronary, carotid and peripheral arteries. It can be considered as an excessive healing reaction of the vascular wall subjected to arterial/venous bypass graft interposition, endarterectomy or angioplasty. The advent of bare metal stents, drug-eluting stents and of the more recent drug-eluting balloons, have significantly reduced, but not eliminated, the incidence of restenosis, which remains a clinically relevant problem. Biomedical research in pre-clinical animal models of (re)stenosis, despite its limitations, has contributed enormously to the identification of processes involved in restenosis progression, going well beyond the initial dogma of a primarily proliferative disease. Although the main molecular and cellular mechanisms underlying restenosis have been well described, new signalling molecules and cell types controlling the progress of restenosis are continuously being discovered. In particular, microRNAs and vascular progenitor cells have recently been shown to play a key role in this pathophysiological process. In addition, the advanced highly sensitive high-throughput analyses of molecular alterations at the transcriptome, proteome and metabolome levels occurring in injured vessels in animal models of disease and in human specimens serve as a basis to identify novel potential therapeutic targets for restenosis. Molecular analyses are also contributing to the identification of reliable circulating biomarkers predictive of post-interventional restenosis in patients, which could be potentially helpful in the establishment of an early diagnosis and therapy. The present review summarizes the most recent and promising therapeutic strategies identified in experimental models of (re)stenosis and potentially translatable to patients subjected to revascularization procedures.

Stimulatory interactions between human coronary smooth muscle cells and dendritic cells

Despite inflammatory and immune mechanisms participating to atherogenesis and dendritic cells (DCs) driving immune and non-immune tissue injury response, the interactions between DCs and vascular smooth muscle cells (VSMCs) possibly relevant to vascular pathology including atherogenesis are still unclear. To address this issue, immature DCs (iDCs) generated from CD14+ cells isolated from healthy donors were matured either with cytokines (mDCs), or co-cultured (ccDCs) with human coronary artery VSMCs (CASMCs) using transwell chambers. Co-culture induced DC immunophenotypical and functional maturation similar to cytokines, as demonstrated by flow cytometry and mixed lymphocyte reaction. In turn, factors from mDCs and ccDCs induced CASMC migration. MCP-1 and TNFα, secreted from DCs, and IL-6 and MCP-1, secreted from CASMCs, were primarily involved. mDCs adhesion to CASMCs was enhanced by CASMC pre-treatment with IFNγ and TNFα ICAM-1 and VCAM-1 were involved, since the expression of specific mRNAs for these molecules increased and adhesion was inhibited by neutralizing antibodies to the counter-receptors CD11c and CD18. Adhesion was also inhibited by CASMC pre-treatment with the HMG-CoA-reductase inhibitor atorvastatin and the PPARγ agonist rosiglitazone, which suggests a further mechanism for the anti-inflammatory action of these drugs. Adhesion of DCs to VSMCs was shown also in vivo in rat carotid 7 to 21 days after crush and incision injury. The findings indicate that DCs and VSMCs can interact with reciprocal stimulation, possibly leading to perpetuate inflammation and vascular wall remodelling, and that the interaction is enhanced by a cytokine-rich inflammatory environment and down-regulated by HMGCoA-reductase inhibitors and PPARγ agonists.

Asymmetric radial expansion and contraction of rat carotid artery observed using a high-resolution ultrasound imaging system

The geometry of carotid artery bifurcation is of high clinical interest because it determines the characteristics of blood flow that is closely related to the formation and development of atherosclerotic plaque. However, information on the dynamic changes in the vessel wall of carotid artery bifurcation during a pulsatile cycle is limited. This pilot study investigated the cyclic changes in carotid artery geometry caused by blood flow pulsation in rats. A high-resolution ultrasound imaging system with a broadband scanhead centered at 40 MHz was used to obtain longitudinal images of the rat carotid artery. A high frame rate retrospective B-scan imaging technique based on the use of electrocardiogram to trigger signal acquisition was used to examine precisely the fast arterial wall motion. Two-dimensional geometry data obtained from nine rats showed that the rat carotid artery asymmetrically contracts and dilates during each cardiac cycle. Systolic/diastolic vessel diameters near the upstream and downstream regions from the bifurcation were 0.976 ± 0.011/0.825 ± 0.015 mm and 0.766 ± 0.015/0.650 ± 0.016 mm, respectively. Their posterior/anterior wall displacement ratios in the radial direction were 41.0 ± 14.9% and 2.9 ± 1.6%, respectively. These results indicate that in the vicinity of bifurcation, the carotid artery favorably expands to the anterior side during the systolic phase. This phenomenon was observed to be more prominent in the downstream region near the bifurcation. The cyclic variation pattern in wall movement varies depending on the measurement site, which shows different patterns at far upstream and downstream of the bifurcation. The asymmetric radial expansion and contraction of the rat carotid artery observed in this study may be useful in studying the hemodynamic etiology of cardiovascular diseases because the pulsatile changes in vessel geometry may affect the local hemodynamics that determines the spatial distribution of wall shear stress, one of important cardiovascular risk factors. Further systematic study is needed to clarify the effects of wall elasticity, branch angle and vessel diameter ratio on the asymmetric wall motion of carotid artery bifurcation.

Local inhibition of ornithine decarboxylase reduces vascular stenosis in a murine model of carotid injury

OBJECTIVES

Polyamines are organic polycations playing an essential role in cell proliferation and differentiation, as well as in cell contractility, migration and apoptosis. These processes are known to contribute to restenosis, a pathophysiological process often occurring in patients submitted to revascularization procedures. We aimed to test the effect of α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, on vascular cell pathophysiology in vitro and in a rat model of carotid arteriotomy-induced (re)stenosis.

METHODS

The effect of DFMO on primary rat smooth muscle cells (SMCs) and mouse microvascular bEnd.3 endothelial cells (ECs) was evaluated through the analysis of DNA synthesis, polyamine concentration, cell viability, cell cycle phase distribution and by RT-PCR targeting cyclins and genes belonging to the polyamine pathway. The effect of DFMO was then evaluated in arteriotomy-injured rat carotids through the analysis of cell proliferation and apoptosis, RT-PCR and immunohistochemical analysis of differential gene expression.

RESULTS

DFMO showed a differential effect on SMCs and on ECs, with a marked, sustained anti-proliferative effect of DFMO at 3 and 8 days of treatment on SMCs and a less pronounced, late effect on bEnd.3 ECs at 8 days of DFMO treatment. DFMO applied perivascularly in pluronic gel at arteriotomy site reduced subsequent cell proliferation and preserved smooth muscle differentiation without affecting the endothelial coverage. Lumen area in DFMO-treated carotids was 49% greater than in control arteries 4 weeks after injury.

CONCLUSIONS

Our data support the key role of polyamines in restenosis and suggest a novel therapeutic approach for this pathophysiological process.

Stem cell therapy for arterial restenosis: potential parameters contributing to the success of bone marrow-derived mesenchymal stromal cells

PURPOSE

Restenosis is a complex and heterogeneous pathophysiological phenomenon occurring in patients submitted to revascularization procedures. Previous studies proved the antirestenotic properties of injected allogenic mesenchymal stromal cells (MSCs) in an experimental model of rat carotid (re)stenosis induced through arteriotomy. In this study we describe some of the effects subsequent to MSC treatment of rats submitted to carotid arteriotomy and possibly responsible for their antirestenotic effect.

METHODS

Rat MSCs were isolated from bone marrow, expanded in vitro and characterized. Subsequently, we evaluated the effects of MSC administration via tail vein at 3 and 7 days after carotid arteriotomy both in rat serum and in injured carotids, focusing on DNA oxidative damage (8-oxo-dG detection), cell proliferation index (BrdU incorporation assay), apoptotic index (TUNEL assay), the expression of inflammation- and proliferation-related genes (RT-PCR), the release of growth factors and of inflammation-related cytokines (antibody arrays and ELISA).

RESULTS

MSC administration induced a greater cell proliferation in carotids after arteriotomy, together with an increased level of VEGF in the serum and with the higher expression of VEGF mRNA in injured carotids. Serum analysis also revealed a decreased level of the pro-inflammatory cytokines CXCL1, CXCL5, L-Selectin, ICAM-1 and LIX, and of TIMP1 and SDF-1alpha in MSC-treated rats. The MSC immunomodulatory activity was confirmed by the decreased expression of TLR2 and TLR4 in injured carotids.

CONCLUSIONS

MSCs play an immunomodulatory paracrine role when injected in rats submitted to carotid arteriotomy, accompanied by the release of VEGF, possibly contributing to the accelerated repair of the injured vascular wall.

LCAT cholesterol esterification is associated with the increase of ApoE/ApoA-I ratio during atherosclerosis progression in rabbit

Apolipoprotein A-I and Apolipoprotein E promote different steps of reverse cholesterol transport, including lecithin-cholesterol acyltransferase stimulation. Our aim was to study the changes in the levels of Apolipoprotein A-I, Apolipoprotein E, and lecithin-cholesterol acyltransferase activity during atherosclerosis progression in rabbits. Quantitative echocardiographic parameters were analyzed in order to evaluate, for the first time, whether atherosclerosis progression in rabbit is associated to apolipoproteins changes and alteration of indices of cardiac function, such as systolic strain and strain rate of the left ventricle. Atherosclerosis was induced by feeding rabbits for 8 weeks with 2 % cholesterol diet. The HDL levels of cholesterol and cholesteryl esters were measured by HPLC. The lecithin-cholesterol acyltransferase activity was evaluated both ex vivo, as cholesteryl esters/cholesterol molar ratio, and in vitro. Apolipoproteins levels were analyzed by ELISA. The HDL levels of cholesterol and cholesteryl esters increased, during treatment, up to 3.7- and 2.5-fold, respectively, compared to control animals. The lecithin-cholesterol acyltransferase activity in vitro was halved after 4 weeks. During cholesterol treatment, Apolipoprotein A-I level significantly decreased, whereas Apolipoprotein E concentration markedly increased. The molar ratio Apolipoprotein E/Apolipoprotein A-I was negatively correlated with the enzyme activity, and positively correlated with both increases in the intima-media thickness of common carotid wall and cardiac dysfunction signs, such as systolic strain and strain rate of the left ventricle.

Rosiglitazone reduces the inflammatory response in a model of vascular injury in rats

Thiazolidinediones are ligands that bind to and activate the nuclear peroxisome proliferator-activated receptor gamma. They are widely used as insulin sensitizers for the treatment of type 2 diabetes. Several studies have implicated the peroxisome proliferator-activated receptor gamma agonists rosiglitazone and pioglitazone in inflammatory events. To assess the anti-inflammatory properties of rosiglitazone, we investigated its effects on the molecular and cellular inflammatory response induced by a carotid injury in the rat. Male Wistar rats were randomized into a rosiglitazone-treated group (10 mg kg(-1) day(-1)) and a control group (0.9% w/v NaCl). The drug or vehicle was administered by gavage for 7 days before carotid injury and for up to 21 days after injury. The inflammatory markers p38 mitogen-activated protein kinase, cyclooxygenase 2, nuclear factor-kappaB, and heat shock protein 47 and the influx and activity of cells in response to injury were measured. Rosiglitazone treatment significantly reduced the expression of the inflammatory markers compared with control group. p38 mitogen-activated protein kinase and nuclear factor-kappaB started to decrease a few hours after injury, whereas cyclooxygenase 2 and heat shock protein 47 expression decreased 7 and 14 days, respectively, after injury. Rosiglitazone also reduced neointima formation and inflammatory cell infiltration. In conclusion, rosiglitazone negatively regulated the inflammatory events involved in tissue repair at molecular and cellular levels. These results suggest that rosiglitazone plays a protective role in inflammatory vascular diseases.

DNA damage and repair in a model of rat vascular injury

Restenosis rate following vascular interventions still limits their long-term success. Oxidative stress plays a relevant role in this pathophysiological phenomenon, but less attention has been devoted to its effects on DNA damage and to the subsequent mechanisms of repair. We analysed in a model of arteriotomy-induced stenosis in rat carotids the time-dependent expression of DNA damage markers and of DNA repair genes, together with the assessment of proliferation and apoptosis indexes. The expression of the oxidative DNA damage marker 7,8-dihydro-8-oxo-2'-deoxyguanosine was increased at 3 and 7 days after arteriotomy, with immunostaining distributed in the injured vascular wall and in perivascular tissue. The expression of the DNA damage marker phospho-H2A.X was less relevant but increasing from 4 hrs to 7 days after arteriotomy, with immunostaining prevalently present in the adventitia and, to a lesser extent, in medial smooth muscle cells at the injury site. RT-PCR indicated a decrease of 8 out of 12 genes of the DNA repair machinery we selected from 4 hrs to 7 days after arteriotomy with the exception of increased Muyth and Slk genes (p<0.05). Western Blot revealed a decrease of p53 and catalase at 3 days after arteriotomy (p<0.05). A maximal 7% of BrdU-positive cells in endothelium and media occurred at 7 days after arteriotomy, while the apoptotic index peaked at 3 days after injury (p<0.05). Our results highlight a persistent DNA damage presumably related to a temporary decreased expression of the DNA repair machinery and of the antioxidant enzyme catalase, playing a role in stenosis progression.

From the laboratory bench to the patient's bedside: an update on clinical trials with mesenchymal stem cells

Mesenchymal Stem Cells (MSCs) are non-hematopoietic multi-potent stem-like cells that are capable of differentiating into both mesenchymal and non-mesenchymal lineages. In fact, in addition to bone, cartilage, fat, and myoblasts, it has been demonstrated that MSCs are capable of differentiating into neurons and astrocytes in vitro and in vivo. MSCs are of interest because they are isolated from a small aspirate of bone marrow and can be easily expanded in vitro. As such, these cells are currently being tested for their potential use in cell and gene therapy for a number of human diseases. Nevertheless, there are still some open questions about origin, multipotentiality, and anatomical localization of MSCs. In this review, we discuss clinical trials based on the use of MSCs in cardiovascular diseases, such as treatment of acute myocardial infarction, endstage ischemic heart disease, or prevention of vascular restenosis through stem cell-mediated injury repair. We analyze data from clinical trials for treatment of osteogenesis imperfecta (OI), which is a genetic disease characterized by production of defective type I collagen. We describe progress for neurological disease treatment with MSC transplants. We discuss data on amyotrophic lateral sclerosis (ALS) and on lysosomal storage diseases (Hurler syndrome and metachromatic leukodystrophy). A section of review is dedicated to ongoing clinical trials, involving MSCs in treatment of steroid refractory Graft Versus Host Disease (GVHD); periodontitis, which is a chronic disease affecting periodontium and causing destruction of attachment apparatus, heart failure, and bone fractures. Finally, we will provide information about biotech companies developing MSC therapy.

Inflammatory events in a vascular remodeling model induced by surgical injury to the rat carotid artery

1.--The aim of our study was to gain insight into the molecular and cellular mechanisms of the inflammatory response to arterial injury in a rat experimental model. 2.--Rats (five for each experimental time) were subjected to brief clamping and longitudinal incision of a carotid artery and monitored for 30 days. Subsequently, Nuclear Factor-kappaB (NF-kappaB) expression was measured by electrophoretic mobility shift assay. Heat shock protein (HSP) 27, HSP47 and HSP70 were evaluated by Western blot. Morphological changes of the vessel wall were investigated by light and electron microscopy. 3.--In injured rat carotid artery NF-kappaB activity started immediately upon injury, and peaked between 2 and 3 weeks later. Western blot showed a significant increase of HSP47 and HSP70 7 days after injury. At 2 weeks postinjury, HSP27 expression peaked. Light microscopy showed a neointima formation, discontinuity of the media layer and a rich infiltrate. Among infiltrating cells electron microscopy identified dendritic-like cells in contact with lymphocytes. 4.--Our model of surgical injury induces a significant inflammatory process characterized by enhanced NF-kappaB activity and HSPs hyperexpression. Dendritic-like cells were for the first time identified as a novel component of tissue repair consequent to acute arterial injury.

Rat carotid arteriotomy: c-myc is involved in negative remodelling and apoptosis

OBJECTIVE

c-myc is the main proto-oncogene responsible for restenosis in cardiovascular surgery. The aim of our study was to evaluate the effects of c-myc antisense (AS) phosphorothioate oligodeoxynucleotides (ODNs) in the remodelling process induced by surgical carotid arteriotomy on an experimental rat model.

METHODS

Fifty-five rats with carotid stenosis and apoptosis induced by arteriotomy were submitted to gene expression analysis 4 h after surgery, to TUNEL assay 48 h after surgery and to histological analysis 30 days later.

RESULTS

AS ODNs induced a 60% decrease in target c-myc mRNA in injured carotid arteries compared to control sense and scrambled ODN-treated carotid arteries (P < 0.05). Histological evaluation revealed that stenosis stimulated by arteriotomy was mainly due to adventitial constrictive remodelling rather than to neointimal hyperplasia, observed only in a limited number of samples. Morphometric analysis showed that lumen area in c-myc AS ODN-treated carotid arteries was 35% greater than in control arteries (P < 0.05), whereas the media/lumen area ratio showed a 63% reduction in AS ODN-treated carotid arteries in comparison to control arteries (P < 0.05). Surgical injury affected the expression of apoptosis-related genes Bcl-2, Bax, Bcl-xL and Bcl-xS, inducing a mean 3.5-fold decrease in the Bcl-2/ Bax ratio and a 9-fold decrease in the Bcl-xL/S ratio 4 h after injury as compared with uninjured carotid arteries. TUNEL assay experiments revealed increased apoptosis in AS ODN-treated carotid arteries in comparison to control carotid arteries.

CONCLUSIONS

c-myc AS ODNs reduce the negative remodelling induced by arteriotomy. The imbalance between proliferative stimulus represented by surgery and the c-myc mRNA decrease induced greater apoptosis in AS ODN-treated carotid arteries without further affecting mRNA levels of Bcl-2, Bax, Bcl-xL and Bcl-xS genes.

c-Myc antisense oligonucleotides preserve smooth muscle differentiation and reduce negative remodelling following rat carotid arteriotomy

OBJECTIVES

The vascular biology of restenosis is complex and not fully understood, thus explaining the lack of effective therapy for its prevention in clinical settings. The role of c-Myc in arteriotomy-induced stenosis, smooth muscle cell (SMC) differentiation and apoptosis was investigated in rat carotids applying full phosphorothioate antisense (AS) oligonucleotides (ODNs).

METHODS

Carotid arteries from WKY rats were submitted to arteriotomy and to local application of ODNs through pluronic gel. Apoptosis (deoxynucleotidyl transferase-mediated dUTP nick end-labelling), SMC differentiation (SM22 immunofluorescence) and vessel morphology and morphometry (image analysis) were determined 2, 5 and 30 days after injury, respectively.

RESULTS

AS ODNs induced a 60% decrease of target c-Myc mRNA 4 h after surgery in comparison to control sense (S) and scrambled ODN-treated carotids (p < 0.05). A significant 37 and 50% decrease in SM22 protein in the media of S ODN-treated and untreated carotids was detected when compared to uninjured contralateral arteries (p < 0.05). This reduction in SM22 expression was prevented in AS ODN-treated carotids. Stenosis was mainly due to adventitial constrictive remodelling. Lumen area in AS ODN-treated carotids was 35% greater than in control arteries 30 days after surgery (p < 0.05). TUNEL assay revealed increased apoptosis in AS ODN-treated carotids (p < 0.05).

CONCLUSIONS

c-Myc AS ODNs reduce arteriotomy-induced negative remodelling. This is accompanied by maintained SMC differentiation and greater apoptosis. The combination of reduced c-Myc-induced proliferation and increased apoptosis may thus underlie the less severe remodelling upon treatment with c-Myc mRNA AS ODN.

Surgical injury of rat arteries: genetic control of the remodelling process

OBJECTIVES

Remodelling and restenosis are complex biological processes responsible for bypass and percutaneous transluminal coronary angioplasty failures which are likely to affect many hundreds of genes. We evaluated the effectiveness of topically applied antisense oligonucleotides in reducing the translation of the messenger RNA for the transcription factor c-myc and in reducing stenosis.

METHODS

Surgery was performed under sterile conditions; 60 Wistar-Kyoto male rats were anaesthetized by ketamine. The carotid arteries were isolated through a median incision in the anterior neck region. At the same point, 0.5 mm longitudinal incisions were performed. Haemostasis was obtained by an adventitial 8.0 stitch. Thirty animals were given 150 microg of c-myc antisense oligonucleotide (Group A) while the other 30 animals received 150 microg of c-myc control sense oligonucleotide (Group B). Oligo molecules were locally applied through 100 microl of 20% pluronic gel. Rats were sacrificed at 30 days; carotid arteries were explanted and stained. Qualitative histological analysis was performed in all cases; serial sections were made every 25 micro in seven consecutive rats for each group. Morphometric analysis was also performed, luminal and medial area values recorded and the ratio between the two areas calculated. Data from each animal were compared with the corresponding contralateral carotid artery and expressed as mean+/-standard deviation. Statistical comparison between the two groups was carried out by one-way ANOVA text.

RESULTS

Qualitative histological analysis showed marked remodelling with complete disarray of vessel wall, neointima accumulation and evidence of elastic fibres in the adventitia of all animals of Group B versus Group A. Morphometric analysis showed a significant reduction in the lumen area in Group A animals together with increased values of the medial area versus Group B animals. In addition, the ratio between the lumen and medial area was significantly higher in Group A than in Group B (2.61+/-0.18 versus 1.14+/-0.33, P<0.0001).

CONCLUSIONS

c-myc antisense oligonucleotides applied intraoperatively can reduce post-operative stenosis.

Attenuated retinoblastoma gene product and associated E2F/retinoblastoma imbalance in anastomotic intimal hyperplasia

OBJECTIVE

The retinoblastoma gene product is a cell cycle control protein that when inhibited allows cell proliferation to progress by releasing E2F. Retinoblastoma manipulation has been attempted to prevent intimal hyperplasia (IH) in injured native vessels by arresting vascular smooth muscle cell proliferation. However, no studies have identified the role, if any, of retinoblastoma in anastomotic IH formation after prosthetic arterial grafting. The goal of this study was to describe the relation of retinoblastoma and E2F to anastomotic IH with analyzing retinoblastoma/E2F levels, retinoblastoma phosphorylation, and transcription of retinoblastoma and E2F in prosthetic arterial grafting.

METHODS

Six-mm-diameter expanded polytetrafluoroethylene carotid interposition grafts (n = 12) were implanted in 25-kg mongrel dogs. The intervening arterial segments were harvested as controls. The distal anastomoses were harvested at 14 and 30 days after implantation for immunoblot, messenger RNA (mRNA), and immunohistochemistry analyses. Tissue homogenate was separated with sodium dodecylsulfate-polyacrylamide gel electrophoresis and probed with antibody to total retinoblastoma, phosphorylated retinoblastoma at serine 795, serine 780, and serine 807/811, and E2F-1. Bands at each time point were quantitated and compared with control artery (n = 12). Each lane was standardized with reprobing with antibody to beta-tubulin. Immunohistochemistry was performed with antibody to retinoblastoma. Retinoblastoma and E2F mRNA expression levels in anastomotic IH and control artery were analyzed with an oligonucleotide microarray.

RESULTS

Total retinoblastoma, from immunoblot analysis, was decreased at the 14-day and 30-day distal anastomoses by 35.7% and 33.6%, respectively, compared with control (P <.01). Furthermore, retinoblastoma at these time points was unphosphorylated at phosphorylation sites serine 795, serine 780, and serine 807/811. E2F-1 levels at 14 days and 30 days were unchanged compared with control. Positive staining for retinoblastoma was seen in endothelial and vascular smooth muscle cell from control, 14-day, and 30-day tissue. A qualitative decrease appeared to be seen in retinoblastoma in the neointima at 14 and 30 days compared with the native wall. No differential expression of retinoblastoma and E2F mRNA was seen in anastomotic IH compared with control.

CONCLUSION

This study showed that total retinoblastoma levels are decreased and E2F-1 levels remain unchanged in anastomotic IH. Attenuated retinoblastoma is a novel concept to anastomotic IH after prosthetic arterial grafting. Retinoblastoma/E2F imbalance may not be the result of transcriptional regulation and may increase unbound E2F to promote cell proliferation. Hypophosphorylation of remaining retinoblastoma may minimize uncontrolled proliferation by preventing further increases in unbound E2F. Therefore, retinoblastoma/E2F imbalance may lead to the early but limited increase in cell proliferation seen after prosthetic arterial grafting and appears to contribute to the development and progression of anastomotic IH.

c-Myc oncoprotein: a dual pathogenic role in neoplasia and cardiovascular diseases?

A growing body of evidence indicates that c-Myc can play a pivotal role both in neoplasia and cardiovascular diseases. Indeed, alterations of the basal machinery of the cell and perturbations of c-Myc-dependent signaling network are involved in the pathogenesis of certain cardiovascular disorders. Down-regulation of c-Myc induced by intervention with antioxidants or by antisense technology may protect the integrity of the arterial wall as well as neoplastic tissues. Further intervention studies are necessary to investigate the effects of tissue-specific block of c-Myc overexpression in the development of cardiovascular diseases.

Gene expression and morphological changes in surgically injured carotids of spontaneously hypertensive rats

The expression profiles of genes involved in cell proliferation, differentiation and programmed death were investigated in carotids of spontaneously hypertensive rats (SHR) treated with a model of surgical injury that mimics events occurring during arterial grafts, endarterectomy and organ transplantation. The mRNA level of the c-myc, angiotensin II receptor 1 (AT1), Rb/p105, Rb2/p130, Bcl-2 and Bax-alpha genes was assessed by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) technique at different times up to 48 h after injury, while the morphological changes were evaluated 30 days after injury. The proliferation marker c-myc increases almost immediately, peaks after 4 h and returns to basal levels after 24 h; the AT1 receptor mRNA reaches its maximal level 48 h after injury. The level of cell cycle exit markers Rb/p105 and Rb2/p130 gradually decreases after injury. The apoptosis marker Bcl-2/Bax-alpha ratio shows a significant reduction only 4 h after injury, resuming the initial value after 24 and 48 h. Morphological analysis reveals that surgical injury in SHR induces adventitial and medial constrictive remodeling changes rather than intima proliferation as in balloon angioplasty. Both molecular and histological data show substantial differences with respect to normotensive rats.

Endothelin-1 increases cholinergic nerve-mediated contraction of human bronchi via tachykinin synthesis induction

1. In some asthmatics, muscarinic receptor antagonists are effective in limiting bronchoconstrictor response, suggesting an abnormal cholinergic drive in these subjects. There is a growing body of evidences indicating that cholinergic neurotransmission is also enhanced by endothelin-1 (ET-1) in rabbit bronchi, mouse trachea and in human isolated airway preparations. 2. We investigated the role of secondary mediators in ET-1 induced potentiation of cholinergic nerve-mediated contraction in human bronchi, in particular the possible role of neuropeptides in this phenomenon. 3. Bronchial tissues after endothelin treatment were exposed to a standard electrical field stimulation (EFS) (30% of EFS 30 Hz)-induced contraction. In addition, in some experiments, preparations were treated with a tachykinin NK(2) receptor antagonist and subsequently exposed to the same protocol. HPLC and RIA were performed on organ bath fluid samples. Moreover, the human bronchi were used for the beta-PPT (preprotachykinin) mRNA extraction and semiquantitative reverse transcription polymerase chain reaction (RT - PCR), prior to and 30-40 min following ET-1 challenge. 4. The selective tachykinin NK(2) receptor antagonist, SR48968, was effective to reduce ET-1 potentiation of EFS mediated contraction. HPLC or RIA showed significant increased quantities of NKA in organ bath effluents after EFS stimulation in bronchi pretreated with ET-1. Finally, beta-PPT mRNA level after stimulation of bronchi with ET-1 was increased about 2 fold respect to control untreated bronchi. 5. In conclusion, this study demonstrated that, at least in part, the ET-1 potentiation of cholinergic nerve-mediated contraction is mediated by tachykinin release, suggesting that in addition to nerves, several type of cells, such as airway smooth muscle cell, may participate to neuropeptide production.