Vascular Smooth Muscle Cell Content Research Articles

Neutrophil-specific STAT4 deficiency attenuates atherosclerotic burden and improves plaque stability via reduction in neutrophil activation and recruitment into aortas of Ldlr-/- mice.

Neutrophils drive atheroprogression and directly contribute to plaque instability. We recently identified signal transducer and activator of transcription 4 (STAT4) as a critical component for bacterial host defense in neutrophils. The STAT4-dependent functions of neutrophils in atherogenesis are unknown. Therefore, we investigated a contributory role of STAT4 in neutrophils during advanced atherosclerosis. We generated myeloid-specific Stat4ΔLysMLdlr-/-, neutrophil-specific Stat4ΔS100A8Ldlr-/-, and control Stat4fl/flLdlr-/- mice. All groups were fed a high-fat/cholesterol diet (HFD-C) for 28 weeks to establish advanced atherosclerosis. Aortic root plaque burden and stability were assessed histologically by Movat pentachrome staining. Nanostring gene expression analysis was performed on isolated blood neutrophils. Flow cytometry was utilized to analyze hematopoiesis and blood neutrophil activation. In vivo homing of neutrophils to atherosclerotic plaques was performed by adoptively transferring prelabeled Stat4ΔLysMLdlr-/- and Stat4fl/flLdlr-/- bone marrow cells into aged atherosclerotic Apoe-/- mice and detected by flow cytometry. STAT4 deficiency in both myeloid-specific and neutrophil-specific mice provided similar reductions in aortic root plaque burden and improvements in plaque stability via reduction in necrotic core size, improved fibrous cap area, and increased vascular smooth muscle cell content within the fibrous cap. Myeloid-specific STAT4 deficiency resulted in decreased circulating neutrophils via reduced production of granulocyte-monocyte progenitors in the bone marrow. Neutrophil activation was dampened in HFD-C fed Stat4ΔLysMLdlr-/- mice via reduced mitochondrial superoxide production, attenuated surface expression of degranulation marker CD63, and reduced frequency of neutrophil-platelet aggregates. Myeloid-specific STAT4 deficiency diminished expression of chemokine receptors CCR1 and CCR2 and impaired in vivo neutrophil trafficking to atherosclerotic aorta. Our work indicates a pro-atherogenic role for STAT4-dependent neutrophil activation and how it contributes to multiple factors of plaque instability during advanced atherosclerosis in mice.

Establishment of a New Abdominal Aortic Aneurysm Model in Rats by a Retroperitoneal Approach.

BackgroundConstructing an ideal model of abdominal aortic aneurysm (AAA) is of great significance to elucidate its complex pathogenesis. Therefore, we introduce a new and simple method to simulate human AAA and construct a rat AAA model through a retroperitoneal approach.MethodsForty healthy adult Sprague Dawley (SD) rats were randomly divided into a control group, elastase + calcium chloride group (PPE+CaCl2), elastase group (PPE), and elastase + beta aminopropionitrile group (PPE+BAPN) according to a male-female ratio of 1:1, with 10 rats in each group. A retroperitoneal approach was used to free the infrarenal abdominal aorta in all four groups. In the PPE + CaCl2 group, 0.1 ml of elastase (approximately 5 U) was perfused into the arterial cavity for 20 min, and 1.0 mol/L calcium chloride was infiltrated out of the arterial cavity for 10 min. In the PPE group, 0.1 mL of elastase (approximately 5U) was perfused into the arterial cavity for 20 min, and normal saline was infiltrated out of arterial cavity for 10 min; the PPE + BAPN group combined with 0.3% BAPN drinking water/day on the basis of PPE group; the control group was treated with saline instead of elastase and calcium chloride. Abdominal aortic specimens were collected after 4 weeks of feeding. The diagnostic criteria of AAA were 50% dilation of the abdominal aorta or rupture of the aneurysm at 4 weeks after the operation. Histopathology, immunohistochemistry, quantitative PCR (qPCR), western blotting assay, gelatine zymogram, and other methods were used.ResultsThe operation time of the four groups was controlled at approximately 40 min, and the success rate of the operation was 100%. Survival rate: Control Group (100%) = PPE Group (100%) > PPE + CaCl2 Group (90%) > PPE + BAPN Group (40%); Aneurysm formation rate: PPE + BAPN Group (100%) > PPE + CaCl2 Group (80%) > PPE Group (60%) > Control Group (0%); Aneurysm rupture rate: PPE + BAPN group (60%) > PPE + CaCl2 group (12.5%) > PPE group (0%);Inflammatory cells (macrophages, T cells, B cells, dendritic cells) infiltrated in different degrees in the PPE + CaCl2, PPE and PPE + BAPN groups. Vascular thickness, elastic fiber content, collagen fiber content, and vascular smooth muscle cell content in the PPE + CaCl2 group and PPE + BNPA group were significantly lower than those in Control group (P < 0.05). The content of elastic fibers and vascular smooth muscle cells in the PPE group were significantly lower than that in Control group (P < 0.05). The expression and activity of matrix metalloproteinase 2 (MMP2) and MMP9 in the PPE + CaCl2 group, PPE group, and PPE + BNPA group were significantly higher than those in the control group (P < 0.05).ConclusionsA new, simple, and reproducible rat AAA model can be constructed by a retroperitoneal approach. The pathological features of the three models are effective simulation of human AAA inflammatory cell infiltration, protease activity enhancement, and extracellular matrix destruction. The PPE+ CaCl2 model has the advantages of a high survival rate, high aneurysm formation rate, good stability, and reproducibility. It is an ideal animal model for studying the pathogenesis of AAA. The PPE + BAPN model can simulate the characteristics of spontaneous rupture of aneurysms. It is an ideal animal model to study the mechanism of AAA rupture.

Improved Quantification of Cell Density in the Arterial Wall-A Novel Nucleus Splitting Approach Applied to 3D Two-Photon Laser-Scanning Microscopy.

Accurate information on vascular smooth muscle cell (VSMC) content, orientation, and distribution in blood vessels is indispensable to increase understanding of arterial remodeling and to improve modeling of vascular biomechanics. We have previously proposed an analysis method to automatically characterize VSMC orientation and transmural distribution in murine carotid arteries under well-controlled biomechanical conditions. However, coincident nuclei, erroneously detected as one large nucleus, were excluded from the analysis, hampering accurate VSMC content characterization and distorting transmural distributions. In the present study, therefore, we aim to (1) improve the previous method by adding a “nucleus splitting” procedure to split coinciding nuclei, (2) evaluate the accuracy of this novel method, and (3) test this method in a mouse model of VSMC apoptosis. After euthanasia, carotid arteries from SM22α-hDTR Apoe–/– and control Apoe–/– mice were bluntly dissected, excised, mounted in a biaxial biomechanical tester and brought to in vivo axial stretch and a pressure of 100 mmHg. Nuclei and elastin fibers were then stained using Syto-41 and Eosin-Y, respectively, and imaged using 3D two-photon laser scanning microscopy. Nuclei were segmented from images and coincident nuclei were split. The nucleus splitting procedure determines the likelihood that voxel pairs within coincident nuclei belong to the same nucleus and utilizes these likelihoods to identify individual nuclei using spectral clustering. Manual nucleus counts were used as a reference to assess the performance of our splitting procedure. Before and after splitting, automatic nucleus counts differed −26.6 ± 9.90% (p < 0.001) and −1.44 ± 7.05% (p = 0.467) from the manual reference, respectively. Whereas the slope of the relative difference between the manual and automated counts as a function of the manual count was significantly negative before splitting (p = 0.008), this slope became insignificant after splitting (p = 0.653). Smooth muscle apoptosis led to a 33.7% decrease in VSMC density (p = 0.008). Nucleus splitting improves the accuracy of automated cell content quantification in murine carotid arteries and overcomes the progressively worsening problem of coincident nuclei with increasing cell content in vessels. The presented image analysis framework provides a robust tool to quantify cell content, orientation, shape, and distribution in vessels to inform experimental and advanced computational studies on vascular structure and function.

Quantification of spiral artery remodelling using an Adobe Photoshop-based technique.

Uterine spiral arteries undergo remodelling in normal pregnancy, with replacement of the musculoelastic arterial media by fibrinoid containing extravillous trophoblast cells. Deficient spiral artery remodelling is associated with several adverse pregnancy outcomes. Although there are distinct components of spiral artery remodelling, assessment is subjective and often based on an overall impression of morphology. We aimed to develop a quantitative approach for assessment of uterine spiral artery remodelling. Placental bed biopsies were immunostained using smooth muscle markers, digital images of spiral arteries were captured and Adobe Photoshop was used to analyse positive immunostaining. The method was then used to investigate variation in the same vessel at different levels within a paraffin block, and the effect of parity, pre-eclampsia or miscarriage on vascular smooth muscle cell content. Results were also compared with a more subjective morphology-based assessment system. There was good intra- and interobserver agreement and the method correlated well with the more subjective assessment system. There was an overall reduction in vascular smooth muscle, as detected by caldesmon 1 (h-caldesmon) immunopositivity, with increasing gestational age from 8 weeks to term. A previous pregnancy did not affect the amount of spiral artery smooth muscle. Comparison of pre-eclampsia and late miscarriage samples with controls of the appropriate gestational age demonstrated increased medial smooth muscle in pathological samples. This technique provides a simple, rapid, reproducible and inexpensive approach to quantitative assessment of spiral artery remodelling in normal and pathological human pregnancy, a process which although fundamental for successful pregnancy, is still incompletely understood.

Broad-spectrum chemokine inhibition blocks inflammation-induced angiogenesis, but preserves ischemia-driven angiogenesis.

M3 is a broad-spectrum chemokine-binding protein that inactivates inflammatory chemokines, including CCL2, CCL5, and CX3CL1. The aim of this study was to compare whether M3 could inhibit angiogenesis driven by inflammation or ischemia. Here, apolipoprotein E-/- mice were injected with adenoviral M3 (AdM3) or control adenoviral green fluorescent protein (AdGFP) 3 d prior to stimulating angiogenesis using 2 established models that distinctly represent inflammatory or ischemia-driven angiogenesis, namely the periarterial femoral cuff and hind limb ischemia. AdM3 reduced intimal thickening, adventitial capillary density, and macrophage accumulation in femoral arteries 21 d after periarterial femoral cuff placement compared with AdGFP-treated mice (P < 0.05). AdM3 also reduced mRNA expression of proangiogenic VEGF, inflammatory markers IL-6 and IL-1β, and vascular smooth muscle cell (VSMC)-activated synthetic markers Krüppel-like family of transcription factor 4 (KLF4) and platelet-derived growth factor receptor β (PDGFRβ) in the inflammatory cuff model. In contrast, capillary density, VSMC content, blood flow perfusion, and VEGF gene expression were unaltered between groups in skeletal muscle following hind limb ischemia. In vitro, AdM3 significantly reduced human microvascular endothelial cell 1 proliferation, migration, and tubule formation by ∼17, 71.3, and 8.7% (P < 0.05) in macrophage-conditioned medium associating with reduced VEGF and hypoxia-inducible factor 1α mRNA but not in hypoxia (1% O2). Compared with AdGFP, AdM3 also inhibited VSMC proliferation and migration and reduced mRNA expression of KLF4 and PDGFRβ under inflammatory conditions. In contrast, AdM3 had no effect on VSMC processes in response to hypoxia in vitro. Our findings show that broad-spectrum inhibition of inflammatory chemokines by M3 inhibits inflammatory-driven but not ischemia-driven angiogenesis, presenting a novel strategy for the treatment of diseases associated with inflammatory-driven angiogenesis.-Ravindran, D., Cartland, S. P., Bursill, C. A., Kavurma, M. M. Broad-spectrum chemokine inhibition blocks inflammation-induced angiogenesis, but preserves ischemia-driven angiogenesis.

P3114Protective effect of SOCS1-based therapy in experimental abdominal aortic aneurysm

Abstract Introduction Abdominal aortic aneurysm (AAA) is a multifactorial vascular disease characterized by chronic inflammation, oxidative stress and proteolytic activity in the aortic wall, which contribute to extracellular matrix degradation and aortic dilation. Altered expression and activation of Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway have been implicated in several cardiovascular diseases including atherosclerosis and aneurysm formation. Suppressors of cytokine signaling (SOCS) are key negative regulators of JAK/STAT pathway and have been considered an attractive target for therapeutic intervention. AIM We hypothesize that SOCS1 protein could influence AAA development by inhibiting JAK activity and, consequently, STAT activation and target gene expression. Therefore, this study investigates the effect of a SOCS1-derived synthetic peptide in a rodent model of AAA and in cultured vascular smooth muscle cells (VSMC). Methods Experimental AAA was induced in C57BL/6 mice (males, 12 weeks old) by transient elastase perfusion of the aorta. Mice were randomly divided into control (vehicle, i.p.) and treatment (SOCS1 peptide, 3 mg/kg/day, i.p.) groups. Fourteen days after AAA induction, mice were sacrificed, and aorta segments were collected for histology (n=10/group) and mRNA and protein expression analysis (n=8/group). Results Compared to the AAA control group, SOCS1-treated mice exhibited a significant decrease in aortic diameter (68±6% vs. control; p&lt;0.005) and aortic wall thickness, (67±3% vs. control; p&lt;0.001). Histological analyses of aortic tissues showed a higher content of VSMC (α-actin) along with reduced leukocyte infiltration (macrophages, neutrophils and T-cells) and oxidative stress markers (superoxide anion and 8-hydroxyguanosine) in SOCS1-treated mice. SOCS1 therapy also attenuated the gene expression of inflammatory cytokines (CCL2, CCL5, TNF, IFNγ) and matrix metalloproteinases (MMP2, MMP9) in aortic lesions, and altered the expression levels of macrophage M1 (ArgII, iNOS) and M2 (ArgI, CD206) polarization markers. In vitro experiments in murine VSMC revealed that SOCS1 peptide prevented the expression of cytokines and chemokines induced by non-toxic dose of elastase (5 ug/ml, 24 hours). Effects of SOCS1 treatment were accompanied by a reduction in STAT1 and STAT3 phosphorylation and gene expression, both in AAA lesions and cultured VSMC. Conclusion Our results suggest that SOCS1 peptide presents protective effects in experimental AAA by suppressing JAK/STAT pathway-mediated inflammation. Acknowledgement/Funding MINECO-FEDER (SAF2015-63696-R), ISCII (FIS-FEDER PI17/01495), Spanish Society of Arteriosclerosis.

Silencing Nogo-B receptor inhibits penile corpus cavernosum vascular smooth muscle cell apoptosis of rats with diabetic erectile dysfunction by down-regulating ICAM-1.

Erectile dysfunction (ED) is a major sexual problem for men. Nogo-B receptor (NgBR) has been found to be involved in the regulation of vascular remodeling and angiogenesis. The present study explores the effects of NgBR in penile corpus cavernosum in rats with diabetic ED. Firstly, the ED model of Sprague Dawley rats was established. Hematoxylin-eosin staining and Masson staining were conducted to observe pathological morphology. Immunochemical assay was adopted to detect α-smooth muscle actin (α-SMA), NgBR and intercellular cell adhesion molecule-1 (ICAM-1) expression. Reverse transcription quantitative polymerase chain reaction assay and Western blot analysis were carried out for the assessment of NgBR, factors correlated to ICAM-1, including steroid receptor coactivator (SRC) and proline-rich tyrosine kinase2 (PYK2), and factors associated with apoptosis, including B-cell lymphoma-2 (Bcl-2), Bcl-2 associated protein X (Bax), caspase 3 and cleaved-caspase 3. The results found that capillaries and vascular smooth muscle cell content reduced, and NgBR and ICAM-1 were elevated in rats with diabetic ED. si-NgBR relieved ED by decreasing penile corpus cavernosum smooth muscle systolic percentage and increasing erectile time and rate, intracavernous pressure (ICP)/mean arterial pressure (MAP) and diastolic percentage, improving the pathological changes and inhibiting cavernosum cell apoptosis. si-NgBR also resulted in the down-regulation of ICAM-1 and downstream SRC and PYK2 and promoted α-SMA expression. In conclusion, si-NgBR can provide a potential therapy for diabetic ED in rats by down-regulating ICAM-1, SRC and PYK2, making it a potential therapeutic option for diabetic ED.

Aldehyde dehydrogenase 2 deficiency promotes atherosclerotic plaque instability through accelerating mitochondrial ROS-mediated vascular smooth muscle cell senescence

Previous evidence has indicated a beneficial role for aldehyde dehydrogenase 2 (ALDH2) in suppressing atherosclerotic plaque progression and instability. However, the underlying mechanism remains somewhat elusive. This study was designed to examine the effect of ALDH2 deficiency on high-cholesterol diet-induced atherosclerotic plaque progression and plaque vulnerability in atherosclerosis-prone ApoE knockout (ApoE−/−) mice with a focus on foam cell formation in macrophages and senescence of vascular smooth muscle cells (VSMCs). Serum lipid profile, plaque progression, and plaque vulnerability were examined in ApoE−/− and ALDH2/ApoE double knockout (ALDH2−/−ApoE−/−) mice after high-cholesterol diet intake for 8 weeks. ALDH2 deficiency increased the serum levels of triglycerides while it decreased levels of total cholesterol and high-density lipoprotein cholesterol. Unexpectedly, ALDH2 deficiency reduced the plaque area by 58.9% and 37.5% in aorta and aortic sinus, respectively. Plaque instability was aggravated by ALDH2 deficiency along with the increased necrotic core size, decreased collagen content, thinner fibrous cap area, decreased VSMC content, and increased macrophage content. In atherosclerotic lesions, ALDH2 protein was located in both macrophages and VSMCs. Further results revealed downregulated ALDH2 expression in aorta of aged ApoE−/− mice compared with young mice. However, in vitro study suggested that ALDH2 expression was upregulated in bone marrow-derived macrophages (BMDMs) with an opposite effect in VSMCs following 80 μg/ml oxidized low-density lipoprotein (oxLDL) treatment. Interestingly, ALDH2 deficiency displayed little effect in oxLDL-induced foam cell formation from BMDMs, while ALDH2 knockdown by siRNA and ALDH2 overexpression by lentivirus infection promoted and retarded oxLDL-induced VSMC senescence, respectively. Mechanistically, ALDH2 mitigated oxLDL-induced overproduction of mitochondrial reactive oxygen species (mROS) and activation of downstream p53/p21/p16 pathway. Clearance of mROS by mitoTEMPO significantly reversed the promotive effect of ALDH2 knockdown on VSMC senescence. Taken together, our data revealed that ALDH2 deficiency suppressed atherosclerotic plaque area while facilitating plaque instability possibly through accelerating mROS-mediated VSMC senescence.This article is part of a Special Issue entitled: Genetic and epigenetic regulation of aging and longevity edited by Jun Ren & Megan Yingmei Zhang.

MicroRNA-124-3p inhibits collagen synthesis in atherosclerotic plaques by targeting prolyl 4-hydroxylase subunit alpha-1 (P4HA1) in vascular smooth muscle cells

Background and aimsCollagen synthesis in vascular smooth muscle cells (VSMCs) is very important in atherosclerosis, as it affects plaque stability. In this study, we aim to assess whether miR-124-3p is involved in the collagen synthesis process in VSMCs and the role it might play in atherosclerotic development. MethodsWe modulated the miR-124-3p expression in the aortic root plaques of high-fat-diet fed ApoE−/− mice by lentivirus injection. To determine plaque size and the content of plaque-stability-related cells or molecules, stainings, including hematoxylin and eosin, Oil red O, Sirius Red and immunohistochemical staining, were performed. Fluorescence in situ hybridization (FISH) was used to locate miR-124-3p in atherosclerotic plaques. Western blotting and RT-qPCR were carried out to determine the level of P4HA1 as well as type I and type III collagen protein and mRNA expression. ResultsResults showed that collagen and VSMC content of plaques was inversely correlated with miR-124-3p levels. By FISH, we identified that miR-124-3p was primarily expressed by VSMCs. We also found that protein levels of type I and type III collagen in aortas and atherosclerotic plaques were decreased by miR-124-3p. We modulated miR-124-3p level in vitro and found it could inhibit collagen expression in HASMCs. This might be caused by the downregulation of P4HA1. P4HA1 was predicted as miR-124-3p's direct target, which was verified with a dual luciferase reporter assay and RIP test. ConclusionsThe results presented here provide evidence that miR-124-3p inhibits VSMC collagen synthesis by directly targeting P4HA1, which might decrease atherosclerotic plaque stability.

Abstract 450: Vascular Smooth Muscle Cell-expressed Tie2 Controls Atherosclerosis Progression

Angiopoietin (Angpt)/Tie signaling in microvascular endothelial cells (EC) controls vascular development, remodeling and maturation. Biomarker studies also imply a role of macrovascular Angpt/Tie signaling. The model of Angpt1/stimulation versus Angpt2/destabilization would imply an anti-atherosclerotic function of Angpt1 and a pro-atherosclerotic function of Angpt2. Yet, experimental studies on the role of the Angpt ligands and the Tie receptors in atherosclerosis have yielded conflicting results suggesting spatiotemporally context-dependent pro- and anti-atherosclerotic functions in different experimental settings. The endotheliocentric view of Angpt/Tie signaling is not sufficient to mechanistically explain the divergent roles of Angpt/Tie signaling during atherosclerosis. We hypothesized that vascular smooth muscle cell (VSMC)-expressed Tie2 may contribute to the pathogenesis of atherosclerosis. Employing genetic models, the present study was aimed at elucidating the role of VSMC-expressed Tie2 during atherosclerosis. Compared to EC, VSMC express lower, but consistently detectable levels of functional Tie2. We therefore generated VSMC-specific Tie2 - deficient mice ( Tie2 SMC-KO ), using a mural cell-specific Sm22α-Cre driver line. These were crossed with atherosclerosis-prone ApoE- deficient mice ( ApoE KO Tie2 SMC-KO ). ApoE KO Tie2 SMC-KO mice, fed a Western-type diet for 14 weeks, showed significantly reduced atherosclerotic lesion progression with less VSMC content. Transcriptionally, Tie2 controlled the phenotypic switch of VSMC with increased contractile and reduced synthetic phenotype-specific gene expression in isolated Tie2-deficient VSMC. Correspondingly, migration and proliferation was significantly reduced in Tie2-deficient cultured VSMC. Serum Angpt2 as well as the Angpt2/Angpt1 ratio were significantly increased in ApoE KO Tie2 SMC-KO mice. Collectively, the data expand and revise the endotheliocentric Tie2 signaling concept to show that mural cell-expressed Tie2 is involved in regulating macrovascular functions related to atherosclerosis. VSMC-expressed Tie2 acts pro-atherosclerotic to control the phenotypic switch towards a proliferative and migratory synthetic VSMC phenotype.

Potential role of insulin receptor isoforms and IGF receptors in plaque instability of human and experimental atherosclerosis

BackgroundClinical complications associated with atherosclerotic plaques arise from luminal obstruction due to plaque growth or destabilization leading to rupture. We previously demonstrated that overexpression of insulin receptor isoform A (IRA) and insulin-like growth factor-I receptor (IGF-IR) confers a proliferative and migratory advantage to vascular smooth muscle cells (VSMCs) promoting plaque growth in early stages of atherosclerosis. However, the role of insulin receptor (IR) isoforms, IGF-IR or insulin-like growth factor-II receptor (IGF-IIR) in VSMCs apoptosis during advanced atherosclerosis remains unclear.MethodsWe evaluated IR isoforms expression in human carotid atherosclerotic plaques by consecutive immunoprecipitations of insulin receptor isoform B (IRB) and IRA. Western blot analysis was performed to measure IGF-IR, IGF-IIR, and α-smooth muscle actin (α-SMA) expression in human plaques. The expression of those proteins, as well as the presence of apoptotic cells, was analyzed by immunohistochemistry in experimental atherosclerosis using BATIRKO; ApoE−/− mice, a model showing more aggravated vascular damage than ApoE−/− mice. Finally, apoptosis of VSMCs bearing IR (IRLoxP+/+ VSMCs), or not (IR−/− VSMCs), expressing IRA (IRA VSMCs) or expressing IRB (IRB VSMCs), was assessed by Western blot against cleaved caspase 3.ResultsWe observed a significant decrease of IRA/IRB ratio in human complicated plaques as compared to non-complicated regions. Moreover, complicated plaques showed a reduced IGF-IR expression, an increased IGF-IIR expression, and lower levels of α-SMA indicating a loss of VSMCs. In experimental atherosclerosis, we found a significant decrease of IRA with an increased IRB expression in aorta from 24-week-old BATIRKO; ApoE−/− mice. Furthermore, atherosclerotic plaques from BATIRKO; ApoE−/− mice had less VSMCs content and higher number of apoptotic cells. In vitro experiments showed that IGF-IR inhibition by picropodophyllin induced apoptosis in VSMCs. Apoptosis induced by thapsigargin was lower in IR−/− VSMCs expressing higher IGF-IR levels as compared to IRLoxP+/+ VSMCs. Finally, IRB VSMCs are more prone to thapsigargin-induced apoptosis than IRA or IRLoxP+/+ VSMCs.ConclusionsIn advanced human atherosclerosis, a reduction of IRA/IRB ratio, decreased IGF-IR expression, or increased IGF-IIR may contribute to VSMCs apoptosis, promoting plaque instability and increasing the risk of plaque rupture and its clinical consequences.

4-phenylbutyrate and valproate treatment attenuates the progression of atherosclerosis and stabilizes existing plaques

Background and aimsRecent evidence suggests that endoplasmic reticulum (ER) stress signaling through glycogen synthase kinase (GSK)-3α/β is involved in the activation of pro-atherosclerotic processes. In this study, we examined the effects of small molecules that interfere with ER stress-GSK3α/β signaling on the progression and regression of atherosclerosis in a mouse model. MethodsTo examine atherosclerotic progression, low-density lipoprotein receptor deficient (Ldlr−/−) mice were placed on a high-fat diet (HFD) and treated with the chemical chaperone, 4-phenylbutyrate (4PBA, 3.8 g/L drinking water), or the GSK3α/β inhibitor, valproate (VPA, 625 mg VPA/kg diet), for 10 weeks. To examine potential effects on atherosclerotic regression, 4 week old Ldlr−/− mice were placed on a HFD for 16 weeks. Subsets of mice were harvested at this time or switched to a chow (low fat) diet, or a chow diet with 4PBA or VPA treatment for 4 weeks. ResultsIn the progression model, the 4PBA- and VPA-treated mice had significantly reduced lesion and necrotic core size. Treatments had no effect on metabolic parameters, including plasma and hepatic lipid levels, or plaque composition. In the regression model, mice with 4PBA or VPA treatment showed no alterations in lesion size, but the lesions had significantly smaller necrotic cores, increased vascular smooth muscle cell content, and increased collagen content. These features are consistent with more stable plaques. ConclusionsThe pharmacological attenuation of ER stress or inhibition of GSK3α/β impedes the development of atherosclerosis in Ldlr−/− mice and appears to promote the stabilization of existing lesions.

Deficiency of TLR4 homologue RP105 aggravates outward remodeling in a murine model of arteriovenous fistula failure

Arteriovenous access dysfunction is a major cause of morbidity for hemodialysis patients. The pathophysiology of arteriovenous fistula (AVF) maturation failure is associated with inflammation, impaired outward remodeling (OR) and intimal hyperplasia. RP105 is a critical physiologic regulator of TLR4 signaling in numerous cell types. In the present study, we investigated the impact of RP105 on AVF maturation, and defined cell-specific effects of RP105 on macrophages and vascular smooth muscle cells (VSMCs). Overall, RP105−/− mice displayed a 26% decrease in venous OR. The inflammatory response in RP105−/− mice was characterized by accumulation of anti-inflammatory macrophages, a 76% decrease in pro- inflammatory macrophages, a 70% reduction in T-cells and a 50% decrease in MMP-activity. In vitro, anti-inflammatory macrophages from RP105−/− mice displayed increased IL10 production, while MCP1 and IL6 levels secreted by pro-inflammatory macrophages were elevated. VSMC content in RP105−/− AVFs was markedly decreased. In vitro, RP105−/− venous VSMCs proliferation was 50% lower, whereas arterial VSMCs displayed a 50% decrease in migration, relative to WT. In conclusion, the impaired venous OR in RP105−/− mice could result from of a shift in both macrophages and VSMCs towards a regenerative phenotype, identifying a novel relationship between inflammation and VSMC function in AVF maturation.

Abstract 654: Loss of SPRR3 In ApoE -/- Mice Leads to Increased Atheroma Vulnerability and Evidence of Plaque Rupture and Cardiac Infarcts

Atheroma rupture is the leading cause of myocardial infarction. While studies have examined inflammatory cell-mediated effects on plaque vulnerability, less is known about the role of vascular smooth muscle cells (VSMCs) or specific molecular players in the maintenance of atheroma stability. We reported that loss of small proline-rich repeat protein 3 (SPRR3), enriched in atheroma VSMCs, leads to increased VSMC death and significantly accelerates atherosclerosis progression in ApoE -/- mice. Here, we show that loss of SPRR3 promotes features in plaques of brachiocephalic arteries common to unstable lesions, such as increased necrotic core size, reduced cap collagen content, and reduced VSMC content. Moreover, ApoE -/- mice lacking SPRR3 develop coronary artery lesions with advanced features, including intraplaque hemorrhage. In addition, Sprr3 -/- ApoE -/- mice fed a high-fat diet for 6 months develop spontaneous myocardial infarction. In vitro , SPRR3 deficient VSMCs show reduced expression of procollagen type I, an event associated with Akt activation. SPRR3-deficient VSMCs also show increased expression of MMP2 transcripts, and aortic root lesions of Sprr3 -/- ApoE -/- mice have increased gelatinase activity consistent with MMP2 activation. Our data demonstrate that SPRR3 loss in ApoE -/- mice decreases VSMC survival and collagen I synthesis while increasing MMP2 synthesis and activity, resulting in atheroma instability with evidence of downstream myocardial infarction. Taken together the results present the Sprr3 -/- ApoE -/- mouse as an experimental model of plaque rupture. This model will be used for additional experimental studies including in vivo genetic modulation of the Akt pathway as well as in vitro studies to determine phenotypic outcome, i.e. coronary arterial lesions, myocardial infarction, VSMC survival and collagen synthesis. We hope to establish a mechanistic link between altered Akt signaling and matrix integrity in the context of atheroma rupture, as well as potentially use SPRR3 as a molecular marker which could lead to detection of plaque instability as well as therapeutic intervention methodologies.

Caspase-3 Deletion Promotes Necrosis in Atherosclerotic Plaques of ApoE Knockout Mice.

Apoptosis of macrophages and vascular smooth muscle cells (VSMCs) in advanced atherosclerotic plaques contributes to plaque progression and instability. Caspase-3, a key executioner protease in the apoptotic pathway, has been identified in human and mouse atherosclerotic plaques but its role in atherogenesis is not fully explored. We therefore investigated the impact of caspase-3 deletion on atherosclerosis by crossbreeding caspase-3 knockout (Casp3−/−) mice with apolipoprotein E knockout (ApoE−/−) mice. Bone marrow-derived macrophages and VSMCs isolated from Casp3−/−ApoE−/− mice were resistant to apoptosis but showed increased susceptibility to necrosis. However, caspase-3 deficiency did not sensitize cells to undergo RIP1-dependent necroptosis. To study the effect on atherosclerotic plaque development, Casp3+/+ApoE−/− and Casp3−/−ApoE−/− mice were fed a western-type diet for 16 weeks. Though total plasma cholesterol, triglycerides, and LDL cholesterol levels were not altered, both the plaque size and percentage necrosis were significantly increased in the aortic root of Casp3−/−ApoE−/− mice as compared to Casp3+/+ApoE−/− mice. Macrophage content was significantly decreased in plaques of Casp3−/−ApoE−/− mice as compared to controls, while collagen content and VSMC content were not changed. To conclude, deletion of caspase-3 promotes plaque growth and plaque necrosis in ApoE−/− mice, indicating that this antiapoptotic strategy is unfavorable to improve atherosclerotic plaque stability.

Differential effects of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 on atherosclerosis and monocyte/macrophage invasion.

AimsMMPs contribute to atherosclerotic plaque progression and instability, but the relative potency of their endogenous tissue inhibitors of metalloproteinases (TIMPs) as protective factors has not been defined. We therefore investigated the impact of TIMP-1 and TIMP-2 knockout on atherosclerotic plaque burden and composition in apolipoprotein E-knockout (Apoe−/−) mice and studied the underlying effects on monocyte/macrophage behaviour.Methods and resultsAnalysis of brachiocephalic artery plaques revealed comparable atherosclerotic lesion areas between TIMP-1−/− Apoe−/− or TIMP-2−/− Apoe−/− double deficient mice and relevant age-matched, strain-matched Apoe−/− controls after 8 weeks of high-fat feeding. However, lesions from TIMP-2−/− Apoe−/− mice had higher levels of markers associated with plaque vulnerability, including increased macrophage: vascular smooth muscle cell ratios, larger necrotic core areas, reduced collagen contents, increased macrophage proliferation, and apoptosis frequencies, compared with TIMP-1−/−Apoe−/− and controls. In contrast, TIMP-1−/− Apoe−/− animals only had a significant reduction in vascular smooth muscle cell content compared with Apoe−/− controls. In vitro and in vivo findings implicated heightened monocyte/macrophage invasion in the detrimental effects observed on atherosclerotic plaque composition in TIMP-2−/− Apoe−/− mice. Moreover, TIMP-2 specifically decreased MMP-14-dependent monocyte/macrophage infiltration into sites of experimentally induced inflammation and established atherosclerotic lesions.ConclusionOur data demonstrate that TIMP-2 plays a greater protective role than TIMP-1 during the pathogenesis of atherosclerosis, in part by suppressing MMP-14-dependent monocyte/macrophage accumulation into plaques.

Ablation of CD8α(+) dendritic cell mediated cross-presentation does not impact atherosclerosis in hyperlipidemic mice.

Clinical complications of atherosclerosis are almost exclusively linked to destabilization of the atherosclerotic plaque. Batf3-dependent dendritic cells specialize in cross-presentation of necrotic tissue-derived epitopes to directly activate cytolytic CD8 Tcells. The mature plaque (necrotic, containing dendritic cells and CD8 Tcells) could offer the ideal environment for cross-presentation, resulting in cytotoxic immunity and plaque destabilization. Ldlr−/− mice were transplanted with batf3−/− or wt bone marrow and put on a western type diet. Hematopoietic batf3 deficiency sharply decreased CD8α+ DC numbers in spleen and lymph nodes (>80%; P < 0,001). Concordantly, batf3−/− chimeras had a 75% reduction in OT-I cross-priming capacity in vivo. Batf3−/− chimeric mice did not show lower Tcell or other leukocyte subset numbers. Despite dampened cross-presentation capacity, batf3−/− chimeras had equal atherosclerosis burden in aortic arch and root. Likewise, batf3−/− chimeras and wt mice revealed no differences in parameters of plaque stability: plaque Tcell infiltration, cell death, collagen composition, and macrophage and vascular smooth muscle cell content were unchanged. These results show that CD8α+ DC loss in hyperlipidemic mice profoundly reduces cross-priming ability, nevertheless it does not influence lesion development. Taken together, we clearly demonstrate that CD8α+ DC-mediated cross-presentation does not significantly contribute to atherosclerotic plaque formation and stability.

Hepatic Overexpression of Soluble Urokinase Receptor (uPAR) Suppresses Diet-Induced Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient (LDLR-/-) Mice.

ObjectiveAtherosclerosis, a chronic inflammatory disease, arises from metabolic disorders and is driven by inappropriate recruitment and proliferation of monocytes / macrophages and vascular smooth-muscle-cells. The receptor for the urokinase-type plasminogen activator (uPAR, Plaur) regulates the proteolytic activation of plasminogen. It is also a coactivator of integrins and facilitates leukocyte-endothelial interactions and vascular smooth-muscle-cell migration. The role of uPAR in atherogenesis remains elusive.Methods and ResultsWe generated C57Bl6/J low-density lipoprotein receptor (LDL) and uPAR double knockout (uPAR-/-/LDLR-/-) mice to test the role of uPAR in two distinct atherosclerosis models. In LDLR-/- mice, hepatic overexpression following hydrodynamic transfection of soluble uPAR that competes with endogenous membrane-bound uPAR was performed as an interventional strategy. Aortic root atherosclerotic lesions induced by feeding a high-fat diet were smaller and comprised less macrophages and vascular smooth-muscle-cells in double knockout mice and animals overexpressing soluble uPAR when compared to controls. In contrast, lesion size, lipid-, macrophage-, and vascular smooth muscle cell content of guide-wire-induced intima lesions in the carotid artery were not affected by uPAR deficiency. Adhesion of uPAR-/--macrophages to TNFα-stimulated endothelial cells was decreased in vitro accompanied by reduced VCAM-1 expression on primary endothelial cells. Hepatic overexpression of soluble full-length murine uPAR in LDLR-/- mice led to a reduction of diet-induced atherosclerotic lesion formation and monocyte recruitment into plaques. Ex vivo incubation with soluble uPAR protein also inhibited adhesion of macrophages to TNFα-stimulated endothelial cells in vitro.ConclusionuPAR-deficiency as well as competitive soluble uPAR reduced diet-promoted but not guide-wire induced atherosclerotic lesions in mice by preventing monocyte recruitment and vascular smooth-muscle-cell infiltration. Soluble uPAR may represent a therapeutic tool for the modulation of hyperlipidemia-associated atherosclerotic lesion formation.

Abstract 555: The Atypical Cadherin Fat1 Interacts With the Intermediate Filament Vimentin in Vascular Smooth Muscle Cells and Limits Atherosclerosis

Fat1 controls vascular smooth muscle cell (VSMC) growth and migration. In recent studies, we found that Fat1 expression colocalizes with VSMCs in atherosclerotic lesions from apoE -/- mice, and also identified the intermediate filament protein vimentin as a novel Fat1 interactor. Like Fat1, vimentin is expressed in VSMCs in atherosclerotic lesions and affects cell growth. We hypothesized that Fat1 regulation of VSMC activities limits atherosclerosis, and that the Fat1-vimentin interaction contributes to this regulation. To test this idea, we generated fat1 VSMC-KO ; apoE double knockout (DKO) mice and assessed atherosclerosis after 24 weeks on a high fat diet, analyzing aortic roots and brachiocephalic arteries (BCA) for lesion area and immunohistochemical features. DKO mice (N=10) exhibited larger lesions (p&lt;0.05) at the aortic root (80837.0±7942.4μm 2 ) and BCA (36017.2±10496.4) compared to control (64190.2±6539.1 and 19462.9±5246.3, respectively). These lesions displayed significantly thicker fibrous caps (+54%, N=7, p&lt;0.05) and larger necrotic cores (+40%, N=8) compared to control, with a trend towards increased cellularity in the DKO group (+24%, p=0.0573, N=7). To evaluate lesional macrophage and VSMC content, we stained for Mac-2 and SM22α, respectively. We found no difference in macrophage number, but greater SM22α-positive lesion area in DKO lesions (1.15±0.25μm 2 , vs. control, 0.37±0.08, p&lt;0.01, N=9). Proliferation in plaques, assessed by phospho-histone H3 staining, was also higher (DKO, 52.6±13.3 cells/field vs. control, 31.4±10.1, p&lt;0.05, N=7). Fat1 and vimentin expression colocalized within fibrous caps, and their physical interaction was validated by co-immunoprecipitation. In addition, Fat1-deficient VSMCs and lesions exhibited increased vimentin levels (&gt;3-fold, p&lt;0.05 by immunoblotting). Thus Fat1 interacts with vimentin and controls its abundance in VSMCs; preliminary knockdown studies suggest that the increased proliferation seen in Fat1-deficient VSMCs depends on vimentin. In summary, our in vivo data support a role for Fat1 in the regulation of VSMCs during atherogenesis, and suggest that the Fat1-vimentin interaction is important for this regulation.

Abstract 554: Vascular Lesion Formation is Attenuated by Genetic Deletion of Hyaluronan Synthase 3

An extensive accumulation of the matrix component hyaluronan (HA) has been observed in vascular lesions. HA is thought to confer immunomodulatory actions and to regulate cell proliferation and migration in diseased vessels. HA is extruded into the extracellular space by three transmembrane HA-synthase isoenzymes (HAS1, -2, -3). Objective of the current study was to assess specifically the role of HAS3 in vascular pathologies such as restenosis and atherosclerosis. In HAS3 deficient mice (HAS3-/-) and wildtype controls (WT) neointimal hyperplasia was induced using a carotid artery ligation model. Morphometric analysis of carotid arteries harvested 28 days after ligation revealed that lack of HAS3 mitigates neointimal lesion formation as indicated by a decrease in intimal area (AUC: HAS3-/-, 1.53 x107 ± 0.23 x107 μm3 vs. WT, 2.59 x 107 ± 0.34 107 μm3, n = 9, p &lt; 0.05) and reduced intima/media ratio (HAS3-/-, 0.94 ± 0.13 vs. WT, 1.39 ± 0.13, n = 9, p &lt; 0.05). Supportive in vitro studies suggest that blunted neointimal hyperplasia is mainly due to a reduced migration and to a lesser extent reduced proliferation of vascular smooth muscle cell (VSMC). Next atherosclerosis-prone apolipoprotein E/HAS3 double-deficient (apoE-/-/HAS3-/-) mice were generated and fed with a cholesterol-rich Western type diet for 15 weeks. Analysis of aortic en face preparations stained with Oil Red O revealed reduced plaque burden compared to apoE-/- controls (apoE-/-/HAS3-/-, 6.95 ± 2.66, n = 10 vs. apoE-/-, 11.43 ± 4.06, n = 13, p &lt; 0.05). Plasma lipids (total cholesterol, LDL/VLDL, HDL cholesterol) did not differ between the groups. Plaque composition at the aortic root showed decreased collagen content (Picro Sirius Red staining) but no differences in cell density, VSMC content (alpha Actin staining) and macrophage count (Mac2 staining). In contrast, flow cytometry data point to a reduction in circulating T cells (apoE-/-/HAS3-/-, 28.4 ± 1.2 %, n = 5 vs. control, 41.7 ± 5.1 %, n = 6). Collectively, these findings suggest a role for HAS3 in vascular lesion formation. In neointimal hyperplasia HAS3-dependent HA synthesis may support mainly VSMC migration whereas in atherogenesis additional immunomodulatory actions are proposed.