Genetically engineered resistance for MMP collagenases promotes abdominal aortic aneurysm formation in mice infused with angiotensin II

Homeostatic, Non-Canonical Role of Macrophage Elastase in Vascular Integrity

BACKGROUND

Matrix metalloproteinase (MMP)-12 is highly expressed in abdominal aortic aneurysms and its elastolytic function has been implicated in the pathogenesis. This concept is challenged, however, by conflicting data. Here, we sought to revisit the role of MMP-12 in abdominal aortic aneurysm.

METHODS

Apoe^-/- and Mmp12^-/-/Apoe^-/- mice were infused with Ang II (angiotensin). Expression of neutrophil extracellular traps (NETs) markers and complement component 3 (C3) levels were evaluated by immunostaining in aortas of surviving animals. Plasma complement components were analyzed by immunoassay. The effects of a complement inhibitor, IgG-FH_1-5 (factor H-immunoglobulin G), and macrophage-specific MMP-12 deficiency on adverse aortic remodeling and death from rupture in Ang II-infused mice were determined.

RESULTS

Unexpectedly, death from aortic rupture was significantly higher in Mmp12^-/-/Apoe^-/- mice. This associated with more neutrophils, citrullinated histone H3 and neutrophil elastase, markers of NETs, and C3 levels in Mmp12^-/- aortas. These findings were recapitulated in additional models of abdominal aortic aneurysm. MMP-12 deficiency also led to more pronounced elastic laminae degradation and reduced collagen integrity. Higher plasma C5a in Mmp12^-/- mice pointed to complement overactivation. Treatment with IgG-FH_1-5 decreased aortic wall NETosis and reduced adverse aortic remodeling and death from rupture in Ang II-infused Mmp12^-/- mice. Finally, macrophage-specific MMP-12 deficiency recapitulated the effects of global MMP-12 deficiency on complement deposition and NETosis, as well as adverse aortic remodeling and death from rupture in Ang II-infused mice.

CONCLUSIONS

An MMP-12 deficiency/complement activation/NETosis pathway compromises aortic integrity, which predisposes to adverse vascular remodeling and abdominal aortic aneurysm rupture. Considering these new findings, the role of macrophage MMP-12 in vascular homeostasis demands re-evaluation of MMP-12 function in diverse settings.

A common Matrix metalloproteinase 8 promoter haplotype enhances the risk for hypertension via diminished interactions with nuclear factor kappa B

OBJECTIVES

Matrix metalloproteinase 8 (MMP8) has a prominent role in collagen turnover in blood vessels and vascular remodeling. The contribution of regulatory single nucleotide polymorphisms in MMP8 to cardiovascular diseases is unclear. We aimed to delineate the influence of MMP8 promoter variations on hypertension.

METHODS

A case-control study in unrelated individuals ( n  = 2565) was carried out. Resequencing of the MMP8 proximal promoter, linkage disequilibrium analysis, genotyping of variants and regression analyses were performed. MMP8 promoter-reporter constructs were generated and expressed in human vascular endothelial cells under various conditions.

RESULTS

We identified four single nucleotide polymorphisms (SNPs) in the promoter region of MMP8 : -1089A/G (rs17099452), -815G/T (rs17099451), -795C/T (rs11225395), -763A/T (rs35308160); these SNPs form three major haplotypes. Hap3 (viz., GTTT haplotype) carriers showed significant associations with hypertension in two geographically distinct human populations (e.g., Chennai: odds ratio [OR] = 1.47, 95% confidence interval [CI] = 1.16-1.86, P  = 2 × 10 -3 ; Chandigarh: OR = 1.85, 95% CI = 1.21-2.81, P  = 4 × 10 -3 ). Hap3 carriers also displayed elevated systolic blood pressure, diastolic blood pressure and mean arterial pressure levels. Hap3 promoter-reporter construct showed lower promoter activity than the wild-type (Hap1) construct. In silico analysis and molecular dynamics studies predicted diminished binding of the transcription factor nuclear factor kappa B (NF-κB) to the functional -815T allele of Hap3 compared to the -815G wild-type allele; this prediction was validated by in-vitro experiments. Hap3 displayed impaired response to tumor necrosis factor-alpha treatment, possibly due to weaker binding of NF-κB. Notably, MMP8 promoter haplotypes were identified as independent predictors of plasma MMP8 and endothelial dysfunction markers (von Willebrand factor and endothelin-1) levels.

CONCLUSION

MMP8 promoter GTTT haplotype has a functional role in reducing MMP8 expression during inflammation via diminished interaction with NF-κB and in enhancing the risk of hypertension.

RUNX3 is up-regulated in abdominal aortic aneurysm and regulates the function of vascular smooth muscle cells by regulating TGF-β1

Abdominal aortic aneurysm (AAA) has been associated with the dysfunction of vascular smooth muscle cells (VSMCs) and extracellular matrix (ECM) remodelling. Runt-related transcription factor 3 (RUNX3) has been reported to be up-regulated in aneurysmal aorta samples compared with normal aorta. However, its function in VSMCs and the mechanism of function remains unknown. Therefore, our study aimed to investigate the role of RUNX3 in ECM remodelling and VSMC function, and further explore the underlying mechanism. Our results verified that RUNX3 was increased in aortic samples of AAA compared with healthy controls. Overexpression vectors of RUNX3 (ov-RUNX3) and siRNA of RUNX3 (si-RUNX3) were transfected into Human aortic smooth muscle cells (HAoSMCs). The results indicated that ov-RUNX3 promoted cell proliferation, migration, and MMP-2/3/9 secretion, and suppressed TIMP-1, collagen I/III, SM22, MYH11 and CNN1 expression in HAoSMCs. The silencing of RUNX3 has the opposite effect. Furthermore, we found that RUNX3 targets TGF-β1 and suppressed its transcription. The silencing of TGF-β1 increased cell proliferation, migration and MMP-2/3/9 expression, and inhibited TIMP-1, Collagen I/III, SM22, MYH11 and CNN1 expression. In addition, TGF-β1 reversed the effect of RUNX3 overexpression on HAoSMCs. Hence, our study indicated that RUNX3 promotes cell proliferation, migration, and ECM remodelling through suppressing TGF-β1.

Transglutaminase 2 moderates the expansion of mouse abdominal aortic aneurysms

Objective

Previously published work has indicated that transcripts encoding transglutaminase 2 (TG2) increase markedly in a rat model of abdominal aortic aneurysm. This study determines whether TG2 and the related TG, factor XIII-A (FXIII-A), protect against aortic aneurysm development in mice.

Methods

C57BL/6J wild-type, Tgm2 ^-/- knockout, F13a1 ^-/- knockout, and Tgm2 ^-/- /F13a1 ^-/- double knockout mice were subjected to laparotomy and periaortic application of CaCl₂.

Results

Tgm2 ^-/- mice showed slightly greater aortic dilatation at 6 weeks after treatment when compared with wild type. However, vessels from Tgm2 ^-/- mice, but not wild-type mice, continued to dilate up to 6 months after injury and by 24 weeks, a greater number of Tgm2 ^-/- mice had developed aneurysms (16/17 vs 10/19; P = .008). Laparotomy resulted in a high death rate in F13a1 ^-/- knockout mice, more frequently from cardiac complications than from hemorrhage, but among F13a1 ^-/- mice that survived for 6 weeks after CaCl₂ treatment, abdominal aortic aneurysm diameter was unaltered relative to wild-type mice. Laparotomy resulted in a higher death rate among Tgm2 ^-/- /F13a1 ^-/- double knockout mice, owing to an increased frequency of delayed bleeding. Surprisingly, Tgm2 ^-/- /F13a1 ^-/- double knockout mice showed a trend toward decreased dilatation of the aorta 6 weeks after injury, and this finding was replicated in Tgm2 ^-/- /F13a1 ^-/- mice subjected to carotid artery injury. Levels of transcripts encoding TG2 were not increased in the aortas of injured wild-type or F13a1 ^-/- knockout mice relative to uninjured mice, although changes in the levels of other transcripts accorded with previous descriptions of the CaCl₂ aneurysm model in mice.

Conclusions

Knockout of Tgm2, but not F13a1 exacerbates aortic dilatation, suggesting that TG2 confers protection. However, levels of TG2 messenger RNA are not acutely elevated after injury. FXIII-A plays a role in preventing postoperative damage after laparotomy, confirming previous reports that it prevents distal organ damage after trauma. TG2 promotes wound healing after surgery and, in its absence, the bleeding diathesis associated with FXIII-A deficiency is further exposed.

Evidence of enteric angiopathy and neuromuscular hypoxia in patients with mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive disease caused by thymidine phosphorylase (TP) enzyme defect. As gastrointestinal changes do not revert in patients undergone TP replacement therapy, one can postulate that other unexplored mechanisms contribute to MNGIE pathophysiology. Hence, we focused on the local TP angiogenic potential that has never been considered in MNGIE. In this study, we investigated the enteric submucosal microvasculature and the effect of hypoxia on fibrosis and enteric neurons density in jejunal full-thickness biopsies collected from patients with MNGIE. Orcein staining was used to count blood vessels based on their size. Fibrosis was assessed using the Sirius Red and Fast Green method. Hypoxia and neoangiogenesis were determined via hypoxia-inducible-factor-1α (HIF-1α) and vascular endothelial cell growth factor (VEGF) protein expression, respectively. Neuron-specific enolase was used to label enteric neurons. Compared with controls, patients with MNGIE showed a decreased area of vascular tissue, but a twofold increase of submucosal vessels/mm² with increased small size and decreased medium and large size vessels. VEGF positive vessels, fibrosis index, and HIF-1α protein expression were increased, whereas there was a diminished thickness of the longitudinal muscle layer with an increased interganglionic distance and reduced number of myenteric neurons. We demonstrated the occurrence of an angiopathy in the GI tract of patients with MNGIE. Neoangiogenetic changes, as detected by the abundance of small size vessels in the jejunal submucosa, along with hypoxia provide a morphological basis to explain neuromuscular alterations, vasculature breakdown, and ischemic abnormalities in MNGIE.NEW & NOTEWORTHY Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is characterized by a genetically driven defect of thymidine phosphorylase, a multitask enzyme playing a role also in angiogenesis. Indeed, major gastrointestinal bleedings are life-threatening complications of MNGIE. Thus, we focused on jejunal submucosal vasculature and showed intestinal microangiopathy as a novel feature occurring in this disease. Notably, vascular changes were associated with neuromuscular abnormalities, which may explain gut dysfunction and help to develop future therapeutic approaches in MNGIE.

Hypercholesterolemia Accelerates Both the Initiation and Progression of Angiotensin II-induced Abdominal Aortic Aneurysms

OBJECTIVE

This study determined whether hypercholesterolemia would contribute to both the initiation and progression of angiotensin (Ang)II-induced abdominal aortic aneurysms (AAAs) in mice.

METHODS AND RESULTS

To determine whether hypercholesterolemia accelerates the initiation of AAAs, male low-density lipoprotein (LDL) receptor -/- mice were either fed one week of Western diet prior to starting AngII infusion or initiated Western diet one week after starting AngII infusion. During the first week of AngII infusion, mice fed normal diet had less luminal expansion of the suprarenal aorta compared to those initiated Western diet after the first week of AngII infusion. The two groups achieved comparable luminal dilation on week 2 through week 6 of AngII infusion as monitored by ultrasound. To determine whether hypercholesterolemia contributed to the progression of established AAAs, male LDL receptor -/- mice were fed Western diet and infused with AngII for 4 weeks. Mice with established AAAs were then stratified into two groups based on luminal diameters measured by ultrasound. While AngII infusion was continued for another 8 weeks in both groups, mice in one group were continuously fed Western diet, but diet in the other group was switched to normal laboratory diet. In the latter group, plasma cholesterol concentrations were reduced rapidly to approximately 500 mg/dl within one week after the diet was switched from Western diet to normal laboratory diet. Luminal expansion progressed constantly in mice continuously fed Western diet, whereas no continuous expansion was detected in mice that were switched to normal laboratory diet.

CONCLUSION

Hypercholesterolemia accelerates both the initiation of AAAs and progression of established AAAs in AngII-infused male LDL receptor -/- mice.

CLINICAL RELEVANCE

Hypercholesterolemia is modestly associated with AAAs in observational or retrospective clinical studies. It is not feasible to study whether hypercholesterolemia contributes to the initiation of AAAs or progression of established AAAs in human. This study using AngII-induced AAA mouse model provides solid evidence that hypercholesterolemia contributes to both the initiation and progression of AAAs, supporting that statin therapy at any stage of AAA development may be beneficial to hypercholesterolemic patients with AAAs.

Diabetes and aortic aneurysm: current state of the art

Aortic aneurysm is a life-threatening disease due to the risk of aortic rupture. The only curative treatment available relies on surgical approaches; drug-based therapies are lacking, highlighting an unmet need for clinical practice. Abdominal aortic aneurysm (AAA) is frequently associated with atherosclerosis and cardiovascular risk factors including male sex, age, smoking, hypertension, and dyslipidaemia. Thoracic aortic aneurysm (TAA) is more often linked to genetic disorders of the extracellular matrix and the contractile apparatus but also share similar cardiovascular risk factors. Intriguingly, a large body of evidence points to an inverse association between diabetes and both AAA and TAA. A better understanding of the mechanisms underlying the negative association between diabetes and aortic aneurysm could help the development of innovative diagnostic and therapeutic approaches to tackle the disease. Here, we summarize current knowledge on the relationship between glycaemic parameters, diabetes, and the development of aortic aneurysm. Cellular and molecular pathways that underlie the protective effect of diabetes itself and its treatment are reviewed and discussed, along with their potential implications for clinical translation.

X-ray scanning microscopies of microcalcifications in abdominal aortic and popliteal artery aneurysms

Abdominal aortic and popliteal artery aneurysms are vascular diseases which show massive degeneration, weakening of the vascular wall and loss of the vascular tissue functionality. They are driven by inflammatory, hemodynamical factors and biological alterations that may lead, in the case of an abdominal aortic aneurysm, to sudden and dangerous ruptures of the arteries. Here, human aortic and popliteal aneurysm tissues were obtained during surgical repair, and studied by synchrotron radiation X-ray scanning microdiffraction and small-angle scattering, to investigate the microcalcifications present in the tissues. Data collected during the experiments were transformed into quantitative microscopy images through the combination of statistical approaches and crystallographic methods. As a result of this multi-step analysis, microcalcifications, which are markers of the pathology, were classified in terms of chemical and structural content. This analysis helped to identify the presence of nanocrystalline hy-droxy-apatite and microcrystalline cholesterol, embedded in myofilament, and elastin-containing tissue with low collagen content in predominantly nanocrystalline areas. The generality of the approach allows it to be transferred to other types of tissue and other pathologies affected by microcalcifications, such as thyroid carcinoma, breast cancer, testicular microli-thia-sis or glioblastoma.

The protective effect of puerarin on angiotensin II-induced aortic aneurysm formation by the inhibition of NADPH oxidase activation and oxidative stress-triggered AP-1 signaling pathways

Puerarin, an active ingredient of Pueraria lobata, has a range of pharmacological effects and excellent pharmacodynamic properties. In the present study, the effect of puerarin on angiotensin II-induced aortic aneurysm formation and the potential underlying molecular mechanisms were examined. The results revealed that puerarin significantly suppressed the viability, and induced the apoptosis, of aneurysm-inducing cells in a time- and dose-dependent manner. Furthermore, treatment with puerarin significantly suppressed the production of reactive oxygen species (ROS) and the expression of matrix metalloproteinase-2 (MMP-2) protein in aneurysm cells. Puerarin treatment significantly increased caspase-9 and -3 activity, induced the protein expression of phosphorylated (p)-Jun and inhibited the protein expression of activator protein 1 (AP-1) in aneurysm cells. It was also demonstrated that Puerarin significantly suppressed the reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase activity in aneurysm cells. Therefore, it was demonstrated that puerarin on suppressed the cell growth of angiotensin II-induced aortic aneurysm formation by affecting the rate of apoptosis, the generation of ROS, MMP-2, AP-1 and p-Jun protein expression and NADPH oxidase.

Relaxin and Matrix Metalloproteinase-9 in Angiotensin II-Induced Abdominal Aortic Aneurysms

BACKGROUND

This study determined whether relaxin or matrix metalloproteinase (MMP)-9 influences angiotensin II (AngII)-induced abdominal aortic aneurysms (AAA).Methods and Results:Male C57BL/6 or apolipoprotein E^-/-mice were infused with AngII with or without relaxin. Relaxin did not influence AngII-induced AAA in either mouse strain. Infusion of AngII reduced, but relaxin increased, MMP-9 mRNA in macrophages. We then determined the effects of MMP-9 deficiency on AAA in apolipoprotein E^-/-mice. MMP-9 deficiency led to AAA formation in the absence of AngII, and augmented AngII-induced aortic rupture and AAA incidence.

CONCLUSIONS

MMP-9 deficiency augmented AngII-induced AAA.

Incidence, severity, mortality, and confounding factors for dissecting AAA detection in angiotensin II-infused mice: a meta-analysis

AIMS

While angiotensin II-infused mice are the most popular model for preclinical aneurysm research, representative data on incidence, severity, and mortality of dissecting abdominal aortic aneurysms (AAAs) have never been established, and the influence of confounding factors is unknown.

METHODS AND RESULTS

We performed a meta-analysis including 194 manuscripts representing 1679 saline-infused, 4729 non-treated angiotensin II-infused, and 4057 treated angiotensin II-infused mice. Incidence (60%) and mortality (20%) rates are reported overall as well as for grade I (22%), grade II (26%), grade III (29%), and grade IV (24%) aneurysms. Dissecting AAA incidence was significantly (P < 0.05) influenced by sex, age, genetic background, infusion time, and dose of angiotensin II. Mortality was influenced by sex, genetic background, and dose, but not by age or infusion time. Surprisingly, both incidence and mortality were significantly different (P < 0.05) when comparing angiotensin II-infused mice in descriptive studies (56% incidence and 19% mortality) with angiotensin II-infused mice that served as control animals in treatment studies designed to either enhance (35% incidence and 13% mortality) or reduce (73% incidence and 25% mortality) dissecting AAA formation. After stratification to account for confounding factors (selection bias), the observed effect was still present for incidence, but not for mortality. Possible underlying causes are detection bias (non-uniform definition for detection and quantification of dissecting AAA in mice) or publication bias (studies with negative results, related to incidence in the control group, not being published).

CONCLUSIONS

Our data provide a new meta-analysis-based reference for incidence and mortality of dissecting AAA in angiotensin II-infused mice, and indicate that treatment studies using this mouse model should be interpreted with caution.

SMAD3 deficiency promotes vessel wall remodeling, collagen fiber reorganization and leukocyte infiltration in an inflammatory abdominal aortic aneurysm mouse model

TGF-β signaling plays critical roles in the pathogenesis of aneurysms; however, it is still unclear whether its role is protective or destructive. In this study, we investigate the role of SMAD3 in the pathogenesis of calcium chloride (CaCl₂)-induced abdominal aortic aneurysms (AAA) in Smad3^−/−, Smad3^+/− and Smad3^+/+ mice. We find that loss of SMAD3 drastically increases wall thickening of the abdominal aorta. Histological analyses show significant vessel wall remodeling with elastic fiber fragmentation. Remarkably, under polarized light, collagen fibers in the hyperplastic adventitia of Smad3^−/− mice show extensive reorganization accompanied by loosely packed thin and radial collagen fibers. The expressions of matrix metalloproteinases including MMP2, MMP9, and MMP12 and infiltration of macrophage/T cells are drastically enhanced in the vascular wall of Smad3^−/− mice. We also observe marked increase of NF-κB and ERK1/2 signaling as well as the expression of nuclear Smad2, Smad4 and TGF-β1 in the vessel wall of Smad3^−/− mice. In addition, we find that SMAD3 expression is reduced in the dedifferentiated medial smooth muscle-like cells of human AAA patients. These findings provide direct in vivo evidence to support the essential roles of SMAD3 in protecting vessel wall integrity and suppressing inflammation in the pathogenesis of AAAs.

Thrombospondin-1 (TSP1) contributes to the development of vascular inflammation by regulating monocytic cell motility in mouse models of abdominal aortic aneurysm

RATIONALE

Histological examination of abdominal aortic aneurysm (AAA) tissues demonstrates extracellular matrix destruction and infiltration of inflammatory cells. Previous work with mouse models of AAA has shown that anti-inflammatory strategies can effectively attenuate aneurysm formation. Thrombospondin-1 is a matricellular protein involved in the maintenance of vascular structure and homeostasis through the regulation of biological functions, such as cell proliferation, apoptosis, and adhesion. Expression levels of thrombospondin-1 correlate with vascular disease conditions.

OBJECTIVE

To use thrombospondin-1-deficient (Thbs1(-/-)) mice to test the hypothesis that thrombospondin-1 contributes to pathogenesis of AAAs.

METHODS AND RESULTS

Mouse experimental AAA was induced through perivascular treatment with calcium phosphate, intraluminal perfusion with porcine elastase, or systemic administration of angiotensin II. Induction of AAA increased thrombospondin-1 expression in aortas of C57BL/6 or apoE-/- mice. Compared with Thbs1(+/+) mice, Thbs1(-/-) mice developed significantly smaller aortic expansion when subjected to AAA inductions, which was associated with diminished infiltration of macrophages. Thbs1(-/-) monocytic cells had reduced adhesion and migratory capacity in vitro compared with wild-type counterparts. Adoptive transfer of Thbs1(+/+) monocytic cells or bone marrow reconstitution rescued aneurysm development in Thbs1(-/-) mice.

CONCLUSIONS

Thrombospondin-1 expression plays a significant role in regulation of migration and adhesion of mononuclear cells, contributing to vascular inflammation during AAA development.

Structural analysis of adventitial collagen to feature aging and aneurysm formation in human aorta

OBJECTIVE

Adventitial collagen structure provides the aorta with tensile strength. Like other collagen-rich tissues, it can be affected by internal factors including aging and location. We determined whether the structural characteristics of human aortic adventitial collagen change with aging, location, and aneurysm formation.

METHODS

Nonatherosclerotic nonaneurysmal (NANA) human abdominal aortas were collected from 15 individuals who had died of noncardiovascular diseases (<40 years old, NANA young, n = 5; >60 years old, NANA old, n = 5). The architecture of adventitial collagen in the aortas was assessed by scanning electron microscopy, and fiber orientation was assessed by polarized microscopy with two-dimensional fast Fourier transform. We then analyzed retardation as an anisotropic property of adventitial collagen by polarized light microscopy. The orientation and retardation of NANA aortas were compared with those of abdominal aortic specimens from patients who were surgically treated for abdominal aortic aneurysm (AAA) (>60 years old, n = 11).

RESULTS

Adventitial collagen of the abdominal aortas on scanning electron microscopy images appeared as wavy, ropy fibers in aortas from young individuals (NANA young, n = 5) and were essentially flattened in those from older patents (NANA old, n = 5) and from those with AAA. Collagen fibers were thicker but sparser in the adventitia of aortas with AAA. Orientation maintained in the collagen fibers of NANA aortas (n = 15) on two-dimensional fast Fourier transform analysis was unrelated to either location or age and did not differ between NANA aortas and those with AAA. However, collagen fibrils in NANA aortas (n = 15) were significantly less retarded only at the level of the inferior mesenteric artery compared with other aortic locations. In addition, retardation was significantly reduced in abdominal aortas with AAA at the level of the inferior mesenteric artery.

CONCLUSIONS

The basic structure of adventitial collagen fiber was maintained in abdominal aortas regardless of location or age. Because the molecular structure at the subfibril level changed at abdominal aorta and enhanced in aortas with AAA, alterations in the molecular structure of adventitial collagen might be associated with aneurysmal formation.

Vascular wall extracellular matrix proteins and vascular diseases

Extracellular matrix proteins form the basic structure of blood vessels. Along with providing basic structural support to blood vessels, matrix proteins interact with different sets of vascular cells via cell surface integrin or non-integrin receptors. Such interactions induce vascular cell de novo synthesis of new matrix proteins during blood vessel development or remodeling. Under pathological conditions, vascular matrix proteins undergo proteolytic processing, yielding bioactive fragments to influence vascular wall matrix remodeling. Vascular cells also produce alternatively spliced variants that induce vascular cell production of different matrix proteins to interrupt matrix homeostasis, leading to increased blood vessel stiffness; vascular cell migration, proliferation, or death; or vascular wall leakage and rupture. Destruction of vascular matrix proteins leads to vascular cell or blood-borne leukocyte accumulation, proliferation, and neointima formation within the vascular wall; blood vessels prone to uncontrolled enlargement during blood flow diastole; tortuous vein development; and neovascularization from existing pathological tissue microvessels. Here we summarize discoveries related to blood vessel matrix proteins within the past decade from basic and clinical studies in humans and animals - from expression to cross-linking, assembly, and degradation under physiological and vascular pathological conditions, including atherosclerosis, aortic aneurysms, varicose veins, and hypertension.

Analysis of oxidative stress enzymes and structural and functional proteins on human aortic tissue from different aortopathies

The role of oxidative stress in different aortopathies is evaluated. Thirty-two tissue samples from 18 men and 14 women were divided into: 4 control (C) subjects, 11 patients with systemic arterial hypertension (SAH), 4 with variants of Marfan's syndrome (MV), 9 with Marfan's syndrome (M), 2 with Turner's syndrome, and 2 with Takayasu's arteritis (TA). Aorta fragments were homogenized. Lipoperoxidation (LPO), copper-zinc and manganese superoxide dismutase (Mn and Cu-Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), endothelial nitric oxide synthase (eNOS), nitrates and nitrites (NO3(-)/NO2(-)), and type IV collagen, and laminin were evaluated. There was an increase in Mn- and Cu-Zn-SOD activity in SAH, MV, M, and Turner's syndrome. There was also an increase in CAT activity in M and Turner' syndrome. GPx and GST activity decreased and LPO increased in all groups. eNOS was decreased in SAH, MV, and M and NO3 (-)/NO2 (-) were increased in SAH and TA. Type IV collagen was decreased in Turner's syndrome and TA. Laminin γ-1 was decreased in MV and increased in M. In conclusion, similarities and differences in oxidative stress in the different aortopathies studied including pathologies with aneurysms were found with alterations in SOD, CAT, GPx, GST, and eNOS activity that modify subendothelial basement membrane proteins.

Identification of 5' AMP-activated kinase as a target of reactive aldehydes during chronic ingestion of high concentrations of ethanol

The production of reactive aldehydes including 4-hydroxy-2-nonenal (4-HNE) is a key component of the pathogenesis in a spectrum of chronic inflammatory hepatic diseases including alcoholic liver disease (ALD). One consequence of ALD is increased oxidative stress and altered β-oxidation in hepatocytes. A major regulator of β-oxidation is 5' AMP protein kinase (AMPK). In an in vitro cellular model, we identified AMPK as a direct target of 4-HNE adduction resulting in inhibition of both H2O2 and 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR)-induced downstream signaling. By employing biotin hydrazide capture, it was confirmed that 4-HNE treatment of cells resulted in carbonylation of AMPKα/β, which was not observed in untreated cells. Using a murine model of alcoholic liver disease, treatment with high concentrations of ethanol resulted in an increase in phosphorylated as well as carbonylated AMPKα. Despite increased AMPK phosphorylation, there was no significant change in phosphorylation of acetyl CoA carboxylase. Mass spectrometry identified Michael addition adducts of 4-HNE on Cys(130), Cys(174), Cys(227), and Cys(304) on recombinant AMPKα and Cys(225) on recombinant AMPKβ. Molecular modeling analysis of identified 4-HNE adducts on AMPKα suggest that inhibition of AMPK occurs by steric hindrance of the active site pocket and by inhibition of hydrogen peroxide induced oxidation. The observed inhibition of AMPK by 4-HNE provides a novel mechanism for altered β-oxidation in ALD, and these data demonstrate for the first time that AMPK is subject to regulation by reactive aldehydes in vivo.

Disparate Changes in the Mechanical Properties of Murine Carotid Arteries and Aorta in Response to Chronic Infusion of Angiotensin-II

Chronic infusion of angiotensin-II has proved useful for generating dissecting aortic aneurysms in atheroprone mice. These lesions preferentially form in the suprarenal abdominal aorta and sometimes in the ascending aorta, but reasons for such localization remain unknown. This study focused on why these lesions do not form in other large (central) arteries. Toward this end, we quantified and compared the geometry, composition, and biaxial material behavior (using a nonlinear constitutive relation) of common carotid arteries from three groups of mice: non-treated controls as well as mice receiving a subcutaneous infusion of angiotensin-II for 28 days that either did or did not lead to the development of a dissecting aortic aneurysm. Consistent with the mild hypertension induced by the angiotensin-II, the carotid wall thickened as expected and remodeled modestly. There was no evidence, however, of a marked loss of elastic fibers or smooth muscle cells, each of which appear to be initiating events for the development of aneurysms, and there was no evidence of intramural discontinuities that might give rise to dissections.

Role of the renin-angiotensin system on abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex degenerative disease, which leads to morbidity and mortality in a large portion of the elderly population. Current treatment options for AAA are quite limited as there is no proven indication for pharmacological therapy and surgery is recommended for AAA larger than 5·5 cm in luminal diameter. Thus, there is a great need to elucidate the underlying pathophysiological cellular and molecular mechanisms to develop effective therapies. In this narrative review, we will discuss recent findings concerning some potential molecular and clinical aspects of the renin-angiotensin system (RAS) in AAA pathophysiology.

MATERIALS AND METHODS

This narrative review is based on the material found on MEDLINE and PubMed up to April 2013. We looked for the terms 'angiotensin, AT1 receptor, ACE inhibitors' in combination with 'abdominal aortic aneurysm, pathophysiology, pathways'.

RESULTS

Several basic research and clinical studies have recently investigated the role of the RAS in AAA. In particular, the subcutaneous infusion of Angiotensin II has been shown to induce AAA in Apo56 knockout mice. On the other hand, the pharmacological treatments targeting this system have been shown as beneficial in AAA patients.

CONCLUSIONS

Emerging evidence suggests that RAS may act as a molecular and therapeutic target for treating AAA. However, several issues on the role of RAS and the protective activities of angiotensin-converting enzyme (ACE) inhibitors and Angiotensin 1 receptors blockers against AAA require further clarifications.

Bortezomib, a proteasome inhibitor, attenuates angiotensin II-induced hypertension and aortic remodeling in rats

Background

Hypertension is a highly prevalent disorder and a major risk factor for cardiovascular diseases. Hypertensive vascular remodeling is the pathological mal-adaption of blood vessels to the hypertensive condition that contributes to further development of high blood pressure and end-organ damage. Hypertensive remodeling involves, at least in part, changes in protein turnover. The ubiquitin proteasome system (UPS) is a major protein quality and quantity control system. This study tested the hypothesis that the proteasome inhibitor, bortezomib, would attenuate AngII-induced hypertension and its sequelae such as aortic remodeling in rats.

Methodology/Principal Findings

Male Sprague Dawley rats were subjected to AngII infusion for two weeks in the absence or presence of bortezomib. Mean arterial pressure was measured in conscious rats. Aortic tissue was collected for estimation of wall area, collagen deposition and expression of tissue inhibitors of matrix metalloproteases (TIMP), Ki67 (a marker of proliferation), reactive oxygen species (ROS) and VCAM-1 (a marker of inflammation). AngII infusion increased arterial pressure significantly (160±4 mmHg vs. vehicle treatment 133±2 mmHg). This hypertensive response was attenuated by bortezomib (138±5 mmHg). AngII hypertension was associated with significant increases in aortic wall to lumen ratio (∼29%), collagen deposition (∼14%) and expression of TIMP1 and TIMP2. AngII also increased MMP2 activity, proteasomal chymotrypsin-like activity, Ki67 staining, ROS generation and VCAM-1 immunoreactivity. Co-treatment of AngII-infused rats with bortezomib attenuated these AngII-induced responses.

Conclusions

Collectively, these data support the idea that proteasome activity contributes to AngII-induced hypertension and hypertensive aortic vascular remodeling at least in part by modulating TIMP1/2 and MMP2 function. Preliminary observations are consistent with a role for ROS, inflammatory and proliferative mechanisms in this effect. Further understanding of the mechanisms by which the proteasome is involved in hypertension and vascular structural remodeling may reveal novel targets for pharmacological treatment of hypertension, hypertensive remodeling or both.

Collagenases and cracks in the plaque

The core of an atheromatous plaque contains lipids, macrophages, and cellular debris, typically covered by a fibrous cap that separates the thrombogenic core from the blood. Rupture of the fibrous cap causes most fatal myocardial infarctions. Interstitial collagen confers tensile strength on the cap, as it does in skin and tendons. In 1994, Peter Libby and colleagues demonstrated overexpression of collagenolytic enzymes in atheromatous plaques and implicated MMPs in the destabilization of these lesions.

Progressive alterations in microstructural organization and biomechanical response in the ApoE mouse model of aneurysm

AAA is a complex disease that leads to a localized dilation of the infrarenal aorta that develops over years. Longitudinal information in humans has been difficult to obtain for this disease, therefore mouse models have become increasingly used to study the development of AAAs. The objective of this study was to determine any changes that occur in the biomechanical response and fiber microstructure in the ApoE^−/− AngII mouse model of aneurysm during disease progression. Adult ApoE^−/− AngII infused mice along with wild-type controls were taken at 14 and 28 d. Aortas were excised and tested simultaneously for biaxial mechanical response and ECM organization. Data sets were fit to a Fung-type constitutive model to give peak strains and stiffness values. Images from two photon microscopy were quantified in order to assess the preferred fiber alignment and degree of fiber orientation. Biomechanical results found significant differences that were present at 14 d had returned to normal by 28 d along with significant changes in fiber orientation and dispersion indicating remodeling occurring within the aneurysmal wall. This return of some of the normal biomechanical function, in addition the continuing changes that occur in the microstructure suggest a restorative response that occurs in the ApoE^−/− AngII infused model after the initial aneurysm formation.

Involvement of the renin-angiotensin system in abdominal and thoracic aortic aneurysms

Aortic aneurysms are relatively common maladies that may lead to the devastating consequence of aortic rupture. AAAs (abdominal aortic aneurysms) and TAAs (thoracic aortic aneurysms) are two common forms of aneurysmal diseases in humans that appear to have distinct pathologies and mechanisms. Despite this divergence, there are numerous and consistent demonstrations that overactivation of the RAS (renin-angiotensin system) promotes both AAAs and TAAs in animal models. For example, in mice, both AAAs and TAAs are formed during infusion of AngII (angiotensin II), the major bioactive peptide in the RAS. There are many proposed mechanisms by which the RAS initiates and perpetuates aortic aneurysms, including effects of AngII on a diverse array of cell types and mediators. These experimental findings are complemented in humans by genetic association studies and retrospective analyses of clinical data that generally support a role of the RAS in both AAAs and TAAs. Given the lack of a validated pharmacological therapy for any form of aortic aneurysm, there is a pressing need to determine whether the consistent findings on the role of the RAS in animal models are translatable to humans afflicted with these diseases. The present review compiles the recent literature that has shown the RAS as a critical component in the pathogenesis of aortic aneurysms.

Hyperhomocysteinemia exaggerates adventitial inflammation and angiotensin II-induced abdominal aortic aneurysm in mice

RATIONALE

A number of epidemiological studies have suggested an association of hyperhomocysteinemia (HHcy) and abdominal aortic aneurysm (AAA), but discrepancies exist. In addition, we lack direct evidence supporting a causal role.

OBJECTIVE

We determined the association and contribution of HHcy to AAA formation.

METHODS AND RESULTS

We first performed a meta-analysis of studies involving 1489 subjects and found a strong association of HHcy and AAA (odds ratio, 7.39). Next, we used angiotensin II-infused male apolipoprotein E-deficient mice and tested whether HHcy contributes to AAA pathogenesis. Homocysteine (Hcy) supplement (1.8 g/L) in drinking water resulted in mild HHcy. Intriguingly, HHcy greatly increased the incidence of angiotensin II-induced AAA and aortic dissection in apolipoprotein E-deficient mice (vehicle versus Hcy: 50% versus 100%; P<0.05). Histology indicated HHcy markedly exaggerated aortic adventitial inflammation. Increased levels of proinflammatory interleukin-6 and monocyte chemoattractant protein-1 were preferentially colocalized within adventitial fibroblasts in HHcy plus angiotensin II mice, which suggested the importance of adventitial fibroblasts activation in Hcy-aggravated AAA. Hcy sequentially stimulated adventitial fibroblasts transformation into myofibroblasts, secretion of interleukin-6 and monocyte chemoattractant protein-1, and consequent recruitment of monocytes/macrophages to adventitial fibroblasts, which was abolished by the NADPH oxidase inhibitor diphenyliodonium. NADPH oxidase 4, but not other homologs of NADPH oxidase, was significantly upregulated by Hcy in adventitial fibroblasts, whereas NADPH oxidase 4 small interfering RNA silencing diminished Hcy-induced adventitial fibroblasts activation. Finally, folic acid supplement (0.071 μg/g per day) markedly reduced HHcy-aggravated angiotensin II-induced AAA formation in apolipoprotein E-deficient mice.

CONCLUSIONS

HHcy may aggravate AAA formation at least partially via activating adventitial fibroblast NADPH oxidase 4.

Selective inhibition of matrix metalloproteinase-13 increases collagen content of established mouse atherosclerosis

OBJECTIVE

Evidence has linked collagen loss with the onset of acute coronary events. This study tested the hypothesis that selective matrix metalloproteinase-13 (MMP-13) collagenase inhibition increases collagen content in already established and nascent mouse atheromas.

METHODS AND RESULTS

In vitro and in situ experiments documented the selectivity and efficacy of an orally available MMP-13 inhibitor (MMP13i-A). In vivo observations monitored macrophage accumulation and MMP-13 activity using molecular imaging. After 10 weeks of MMP13i-A treatment, apolipoprotein E-deficient mice with evolving or established lesions exhibited reduced MMP-13 activity without affecting macrophage content, measured either by intravital microscopy or fluorescence reflectance imaging. Histological analysis indicated that MMP13-iA did not affect plaque size or macrophage or smooth muscle cell accumulation. Administration of MMP13i-A to mice with evolving or established atheromas substantially increased plaque interstitial collagen content in the intima and locally in the fibrous cap, compared with vehicle-treated controls. Analysis of collagen revealed thicker collagen fibers within the plaques of treated groups.

CONCLUSION

Pharmacological MMP-13 inhibition yields collagen accumulation in plaques (a feature associated in humans with resistance to rupture), even in established plaques. This study, of considerable clinical relevance, furnishes new mechanistic insight into regulation of the plaque's extracellular matrix and validates molecular imaging for studying plaque biology.

Analysis of the molecular mobility of collagen and elastin in safe, atheromatous and aneurysmal aortas

AIM OF THE STUDY

In this study, we propose to use a thermal technique, Differential Scanning Calorimetry (DSC) to follow the evolution of elastin and collagen in safe and pathological cardiovascular tissues.

PATIENTS AND METHODS

The first part of this study deals with the analysis of the elastin network and associated proteins during ageing (from children to old persons) in aortic walls. The second part is devoted to the characterization of the collagenic phase in aneurysms. In both cases, physical data are correlated with biochemical analyses.

RESULTS AND CONCLUSION

For old persons aortas with atheromatous stades, elastin and associated proteins are found to interpenetrate to form a homogenous phase. Abdominal aortic aneurysms (AAA) are characterized by structural alterations of the aortic wall resulting from the degradation of elastic fibers and an increase of collagen/elastin ratio. Notable modifications are evidenced between collagen from control tissue and collagen from AAA, particularly concerning the thermal denaturation. Biochemical and thermal results are compatible with the increase of new collagen deposition and/or impairment of the collagen phase stability in the extracellular matrix of AAAs.

Urokinase-type plasminogen activator deficiency in bone marrow-derived cells augments rupture of angiotensin II-induced abdominal aortic aneurysms

OBJECTIVE

Abdominal aortic aneurysms (AAAs) are associated with fragmentation of extracellular matrix during development of aortic dilation and rupture. Therefore, it is important to identify specific protease systems involved in extracellular matrix degradation during AAA formation. The present study determined the contribution of the urokinase system to AAA formation and rupture.

METHODS AND RESULTS

Angiotensin II (Ang II)-induced AAAs were associated with increased aortic abundance of both urokinase-type plasminogen activator receptor (uPAR) and urokinase-type plasminogen activator (uPA) proteins. However, this increased presence was unrelated to AAA formation because deficiencies of either uPAR or uPA had no effect on either the incidence or size of Ang II-induced AAAs in both normolipidemic mice and low-density lipoprotein receptor-/- mice fed a saturated fat-enriched diet. Although uPA deficiency did not affect development of AAAs, there was an effect of increasing mortality rate from AAA rupture in hypercholesterolemic mice. Bone marrow transplantation demonstrated that enhanced aneurysmal rupture was attributable to deficiency of uPA in leukocytes. uPA deficiency led to an increased propensity for impaired resolution of the thrombotic material within the aneurysmal tissue. Neither uPAR nor uPA deficiency had any effect on Ang II-induced atherosclerosis in low-density lipoprotein receptor-/- mice.

CONCLUSIONS

The uPA-uPAR axis has no effect on the formation of Ang II-induced AAAs, but uPA deficiency promotes aneurysmal rupture.

Type I collagen cleavage is essential for effective fibrotic repair after myocardial infarction

Efficient deposition of type I collagen is fundamental to healing after myocardial infarction. Whether there is also a role for cleavage of type I collagen in infarct healing is unknown. To test this, we undertook coronary artery occlusion in mice with a targeted mutation (Col1a1(r/r)) that yields collagenase-resistant type I collagen. Eleven days after infarction, Col1a1(r/r) mice had a lower mean arterial pressure and peak left ventricular systolic pressure, reduced ventricular systolic function, and worse diastolic function, compared with wild-type littermates. Infarcted Col1a1(r/r) mice also had greater 30-day mortality, larger left ventricular lumens, and thinner infarct walls. Interestingly, the collagen fibril content within infarcts of mutant mice was not increased. However, circular polarization microscopy revealed impaired collagen fibril organization and mechanical testing indicated a predisposition to scar microdisruption. Three-dimensional lattices of collagenase-resistant fibrils underwent cell-mediated contraction, but the fibrils did not organize into birefringent collagen bundles. In addition, time-lapse microscopy revealed that, although cells migrated smoothly on wild-type collagen fibrils, crawling and repositioning on collagenase-resistant collagen was impaired. We conclude that type I collagen cleavage is required for efficient healing of myocardial infarcts and is critical for both dynamic positioning of collagen-producing cells and hierarchical assembly of collagen fibrils. This seemingly paradoxical requirement for collagen cleavage in fibrotic repair should be considered when designing potential strategies to inhibit matrix degradation in cardiac disease.

Mechanical properties of suprarenal and infrarenal abdominal aorta: implications for mouse models of aneurysms

Multiple mouse models have been developed to increase our understanding of the natural history of abdominal aortic aneurysms. An advantage of such models is that one can quantify the time course of changes in geometry, histology, cell biology, and mechanics as a lesion develops. One of the most commonly used mouse models yields lesions in the suprarenal abdominal aorta whereas most other models target the infrarenal abdominal aorta, consistent with the clinical observation that nearly all abdominal aneurysms in humans occur in the infrarenal aorta. Understanding reasons for similarities and differences between diverse mouse models and human lesions may provide increased insight that would not be possible studying a single situation alone. Toward this end, however, we must first compare directly the native structure and properties of these two portions of the abdominal aorta in the mouse. In this paper, we present the first biaxial mechanical data and nonlinear constitutive descriptors for the suprarenal and infrarenal aorta in mice, which reveals only subtle mechanical differences despite marked morphological and histological differences. Such data promise to increase our ability to understand and model the natural history of these deadly lesions.

Animal models of cardiovascular diseases

Cardiovascular diseases are the first leading cause of death and morbidity in developed countries. The use of animal models have contributed to increase our knowledge, providing new approaches focused to improve the diagnostic and the treatment of these pathologies. Several models have been developed to address cardiovascular complications, including atherothrombotic and cardiac diseases, and the same pathology have been successfully recreated in different species, including small and big animal models of disease. However, genetic and environmental factors play a significant role in cardiovascular pathophysiology, making difficult to match a particular disease, with a single experimental model. Therefore, no exclusive method perfectly recreates the human complication, and depending on the model, additional considerations of cost, infrastructure, and the requirement for specialized personnel, should also have in mind. Considering all these facts, and depending on the budgets available, models should be selected that best reproduce the disease being investigated. Here we will describe models of atherothrombotic diseases, including expanding and occlusive animal models, as well as models of heart failure. Given the wide range of models available, today it is possible to devise the best strategy, which may help us to find more efficient and reliable solutions against human cardiovascular diseases.

Analysis of positional candidate genes in the AAA1 susceptibility locus for abdominal aortic aneurysms on chromosome 19

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex disorder with multiple genetic risk factors. Using affected relative pair linkage analysis, we previously identified an AAA susceptibility locus on chromosome 19q13. This locus has been designated as the AAA1 susceptibility locus in the Online Mendelian Inheritance in Man (OMIM) database.

METHODS

Nine candidate genes were selected from the AAA1 locus based on their function, as well as mRNA expression levels in the aorta. A sample of 394 cases and 419 controls was genotyped for 41 SNPs located in or around the selected nine candidate genes using the Illumina GoldenGate platform. Single marker and haplotype analyses were performed. Three genes (CEBPG, PEPD and CD22) were selected for DNA sequencing based on the association study results, and exonic regions were analyzed. Immunohistochemical staining of aortic tissue sections from AAA and control individuals was carried out for the CD22 and PEPD proteins with specific antibodies.

RESULTS

Several SNPs were nominally associated with AAA (p < 0.05). The SNPs with most significant p-values were located near the CCAAT enhancer binding protein (CEBPG), peptidase D (PEPD), and CD22. Haplotype analysis found a nominally associated 5-SNP haplotype in the CEBPG/PEPD locus, as well as a nominally associated 2-SNP haplotype in the CD22 locus. DNA sequencing of the coding regions revealed no variation in CEBPG. Seven sequence variants were identified in PEPD, including three not present in the NCBI SNP (dbSNP) database. Sequencing of all 14 exons of CD22 identified 20 sequence variants, five of which were in the coding region and six were in the 3'-untranslated region. Five variants were not present in dbSNP. Immunohistochemical staining for CD22 revealed protein expression in lymphocytes present in the aneurysmal aortic wall only and no detectable expression in control aorta. PEPD protein was expressed in fibroblasts and myofibroblasts in the media-adventitia border in both aneurysmal and non-aneurysmal tissue samples.

CONCLUSIONS

Association testing of the functional positional candidate genes on the AAA1 locus on chromosome 19q13 demonstrated nominal association in three genes. PEPD and CD22 were considered the most promising candidate genes for altering AAA risk, based on gene function, association evidence, gene expression, and protein expression.

Integrins as "functional hubs" in the regulation of pathological angiogenesis

It is well accepted that complex biological processes such as angiogenesis are not controlled by a single family of molecules or individually isolated signaling pathways. In this regard, new insight into the interconnected mechanisms that regulate angiogenesis might be gained by examining this process from a more global network perspective. The coordination of signaling cues from both outside and inside many different cell types is required for the successful completion of angiogenesis. Evidence is accumulating that the multifunctional integrin family of cell adhesion receptors represent an important group of molecules that play active roles in sensing, integrating, and distributing a diverse set of signals that regulate many cellular events required for angiogenesis. Given the ability of integrins to bind numerous extracellular ligands and transmit signals in a bi-directional fashion, we will discuss the multiple ways by which integrins may serve as a functional hub during pathological angiogenesis. In addition, we will highlight potential imaging and therapeutic strategies based on the expanding new insight into integrin function.