Loss of Timp3 gene leads to abdominal aortic aneurysm formation in response to angiotensin II

Pharmacological Inhibition of MMP-12 Exerts Protective Effects on Angiotensin II-Induced Abdominal Aortic Aneurysms in Apolipoprotein E-Deficient Mice

Human abdominal aortic aneurysms (AAAs) are characterized by increased activity of matrix metalloproteinases (MMP), including MMP-12, alongside macrophage accumulation and elastin degradation, in conjunction with superimposed atherosclerosis. Previous genetic ablation studies have proposed contradictory roles for MMP-12 in AAA development. In this study, we aimed to elucidate if pharmacological inhibition of MMP-12 activity with a phosphinic peptide inhibitor protects from AAA formation and progression in angiotensin (Ang) II-infused Apoe-/- mice. Complimentary studies were conducted in a human ex vivo model of early aneurysm development. Administration of an MMP-12 inhibitor (RXP470.1) protected hypercholesterolemia Apoe-/- mice from Ang II-induced AAA formation and rupture-related death, associated with diminished medial thinning and elastin fragmentation alongside increased collagen deposition. Proteomic analyses confirmed a beneficial effect of MMP-12 inhibition on extracellular matrix remodeling proteins combined with inflammatory pathways. Furthermore, RXP470.1 treatment of mice with pre-existing AAAs exerted beneficial effects as observed through suppressed aortic dilation and rupture, medial thinning, and elastin destruction. Our findings indicate that pharmacological inhibition of MMP-12 activity retards AAA progression and improves survival in mice providing proof-of-concept evidence to motivate translational work for MMP-12 inhibitor therapy in humans.

Loss of TIMP3, but not TIMP4, exacerbates thoracic and abdominal aortic aneurysm

AIMS

Aorta exhibits regional heterogeneity (structural and functional), while different etiologies for thoracic and abdominal aortic aneurysm (TAA, AAA) are recognized. Tissue inhibitor of metalloproteinases (TIMPs) regulate vascular remodeling through different mechanisms. Region-dependent functions have been reported for TIMP3 and TIMP4 in vascular pathologies. We investigated the region-specific function of these TIMPs in development of TAA versus AAA.

METHODS & RESULTS

TAA or AAA was induced in male and female mice lacking TIMP3 (Timp3-/-), TIMP4 (Timp4-/-) or in wildtype (WT) mice by peri-adventitial elastase application. Loss of TIMP3 exacerbated TAA and AAA severity in males and females, with a greater increase in proteinase activity, smooth muscle cell phenotypic switching post-AAA and -TAA, while increased inflammation was detected in the media post-AAA, but in the adventitia post-TAA. Timp3-/- mice showed impaired intimal barrier integrity post-AAA, but a greater adventitial vasa-vasorum branching post-TAA, which could explain the site of inflammation in AAA versus TAA. Severity of TAA and AAA in Timp4-/- mice was similar to WT mice. In vitro, Timp3 knockdown more severely compromised the permeability of human aortic EC monolayer compared to Timp4 knockdown or the control group. In aneurysmal aorta specimens from patients, TIMP3 expression decreased in the media in AAA, and in adventitial in TAA specimens, consistent with the impact of its loss in AAA versus TAA in mice.

CONCLUSION

TIMP3 loss exacerbates inflammation, adverse remodeling and aortic dilation, but triggers different patterns of remodeling in AAA versus TAA, and through different mechanisms.

The contribution of matrix metalloproteinases and their inhibitors to the development, progression, and rupture of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) account for up to 8% of deaths in men aged 65 years and over and 2.2% of women. Patients with AAAs often have atherosclerosis, and intimal atherosclerosis is generally present in AAAs. Accordingly, AAAs are considered a form of atherosclerosis and are frequently referred to as atherosclerotic aneurysms. Pathological observations advocate inflammatory cell infiltration alongside adverse extracellular matrix degradation as key contributing factors to the formation of human atherosclerotic AAAs. Therefore, macrophage production of proteolytic enzymes is deemed responsible for the damaging loss of ECM proteins, especially elastin and fibrillar collagens, which characterise AAA progression and rupture. Matrix metalloproteinases (MMPs) and their regulation by tissue inhibitors metalloproteinases (TIMPs) can orchestrate not only ECM remodelling, but also moderate the proliferation, migration, and apoptosis of resident aortic cells, alongside the recruitment and subsequent behaviour of inflammatory cells. Accordingly, MMPs are thought to play a central regulatory role in the development, progression, and eventual rupture of abdominal aortic aneurysms (AAAs). Together, clinical and animal studies have shed light on the complex and often diverse effects MMPs and TIMPs impart during the development of AAAs. This dichotomy is underlined from evidence utilising broad-spectrum MMP inhibition in animal models and clinical trials which have failed to provide consistent protection from AAA progression, although more encouraging results have been observed through deployment of selective inhibitors. This review provides a summary of the supporting evidence connecting the contribution of individual MMPs to AAA development, progression, and eventual rupture. Topics discussed include structural, functional, and cell-specific diversity of MMP members; evidence from animal models of AAA and comparisons with findings in humans; the dual role of MMPs and the requirement to selectively target individual MMPs; and the advances in identifying aberrant MMP activity. As evidenced, our developing understanding of the multifaceted roles individual MMPs perform during the progression and rupture of AAAs, should motivate clinical trials assessing the therapeutic potential of selective MMP inhibitors, which could restrict AAA-related morbidity and mortality worldwide.

Attenuation of Smooth Muscle Cell Phenotypic Switching by Angiotensin 1-7 Protects against Thoracic Aortic Aneurysm

Thoracic aortic aneurysm (TAA) involves extracellular matrix (ECM) remodeling of the aortic wall, leading to reduced biomechanical support with risk of aortic dissection and rupture. Activation of the renin-angiotensin system, and resultant angiotensin (Ang) II synthesis, is critically involved in the onset and progression of TAA. The current study investigated the effects of angiotensin (Ang) 1-7 on a murine model of TAA. Male 8-10-week-old ApoEKO mice were infused with Ang II (1.44 mg/kg/day) and treated with Ang 1-7 (0.576 mg/kg/day). ApoEKO mice developed advanced TAA in response to four weeks of Ang II infusion. Echocardiographic and histological analyses demonstrated increased aortic dilatation, excessive structural remodelling, perivascular fibrosis, and inflammation in the thoracic aorta. Ang 1-7 infusion led to attenuation of pathological phenotypic alterations associated with Ang II-induced TAA. Smooth muscle cells (SMCs) isolated from adult murine thoracic aorta exhibited excessive mitochondrial fission, oxidative stress, and hyperproliferation in response to Ang II. Treatment with Ang 1-7 resulted in inhibition of mitochondrial fragmentation, ROS generation, and hyperproliferation. Gene expression profiling used for characterization of the contractile and synthetic phenotypes of thoracic aortic SMCs revealed preservation of the contractile phenotype with Ang 1-7 treatment. In conclusion, Ang 1-7 prevented Ang II-induced vascular remodeling and the development of TAA. Enhancing Ang 1-7 actions may provide a novel therapeutic strategy to prevent or delay the progression of TAA.

The Role of ADAM17 in Inflammation-Related Atherosclerosis

Atherosclerosis is a chronic inflammatory disease that poses a huge economic burden due to its extremely poor prognosis. Therefore, it is necessary to explore potential mechanisms to improve the prevention and treatment of atherosclerosis. A disintegrin and metalloprotease 17 (ADAM17) is a cell membrane-bound protein that performs a range of functions through membrane protein shedding and intracellular signaling. ADAM17-mediated inflammation has been identified to be an important contributor to atherosclerosis; however, the specific relationship between its multiple regulatory roles and the pathogenesis of atherosclerosis remains unclear. Here, we reviewed the activation, function, and regulation of ADAM17, described in detail the role of ADAM17-mediated inflammatory damage in atherosclerosis, and discussed several controversial points. We hope that these insights into ADAM17 biology will lead to rational management of atherosclerosis. ADAM17 promotes vascular inflammation in endothelial cells, smooth muscle cells, and macrophages, and regulates the occurrence and development of atherosclerosis.

Protective Effects of Circulating TIMP3 on Coronary Artery Disease and Myocardial Infarction: A Mendelian Randomization Study

Tissue inhibitor of metalloproteinase 3 (TIMP3) is a protease with high expression levels in the heart and plays an essential role in extracellular matrix turnover by maintaining equilibrium with matrix metalloproteinases. Considerable data in experimental models have demonstrated a protective role of TIMP3 in coronary artery disease (CAD) and myocardial infarction (MI). However, causality remains unexplored in population studies. Here, we sought to decipher the potential causality between TIMP3 and CAD/MI using the Mendelian randomization (MR) method. We extracted summary−level datasets for TIMP3 and CAD/MI from the genome−wide association studies performed in the KORA study and CARDIoGRAMplusC4D consortium, respectively. Seven independent SNPs were obtained as instrumental variables for TIMP3. The MR analyses were replicated using FinnGen datasets, and the main results were combined in meta−analyses. Elevated genetically predicted serum TIMP3 levels were causally associated with a lower risk of CAD [odds ratio (OR), 0.97; 95% confidence interval (CI), 0.95, 0.98; p = 5.29 × 10⁻⁵] and MI (OR, 0.96; 95% CI, 0.95, 0.98; p = 3.85 × 10⁻⁵). The association patterns persisted in the meta−analyses combining the different datasets (CAD: OR, 0.97; 95% CI, 0.96, 0.99; p = 4.37 × 10⁻⁵; MI: OR, 0.97; 95% CI, 0.96, 0.99; p = 9.96 × 10⁻⁵) and was broadly consistent across a set of complementary analyses. Evidence of heterogeneity and horizontal pleiotropy was limited for all associations considered. In conclusion, this MR study supports inverse causal associations between serum TIMP3 and the risk of CAD and MI. Strategies for raising TIMP3 levels may offer new avenues for the prevention strategies of atherosclerotic cardiovascular diseases.

Altered TIMP-3 Levels in the Cerebrospinal Fluid and Plasma of Patients with Alzheimer’s Disease

Tissue inhibitor of metalloproteinase-3 (TIMP-3) is a component of the extracellular environment and is suggested to play an indirect role in regulating Aβ production and the pathophysiology of Aβ deposition in brains. However, studies on the amount of TIMP-3 in bodily fluids of Alzheimer’s disease (AD) patients have not been conducted. Here, we investigated the relationship between fluid TIMP-3 levels and AD pathology. We first showed that the fluid levels of TIMP-3 were lower in AD dementia patients compared with in non-AD patients. ELISA results revealed that plasma levels of TIMP-3 in 65 patients with AD were significantly lower than those in 115 healthy control subjects and 71 mild cognitive impairment (MCI) subjects. Furthermore, we found that cerebrospinal fluid (CSF) level of TIMP-3 was decreased in AD compared with that in healthy control. These data suggest that fluid TIMP-3 levels negatively correlated with progress of cognitive decline. Collectively, our study suggests that alterations of fluid TIMP-3 levels might be associated with AD pathology.

Disintegrin and Metalloproteinases (ADAMs [A Disintegrin and Metalloproteinase] and ADAMTSs [ADAMs With a Thrombospondin Motif]) in Aortic Aneurysm

Aortic aneurysm is a complex pathology that can be lethal if not detected in time. Although several molecular mechanisms and pathways have been identified to be involved in aortic aneurysm development and growth, the current lack of an effective pharmacological treatment highlights the need for a more thorough understanding of the factors that regulate the remodeling of the aortic wall in response to triggers that lead to aneurysm formation. This task is further complicated by the regional heterogeneity of the aorta and that thoracic and abdominal aortic aneurysm are distinct pathologies with different risk factors and distinct course of progression. ADAMs (a disintegrin and metalloproteinases) and ADAMTS (ADAMs with a thrombospondin motif) are proteinases that share similarities with other proteinases but possess unique and diverse properties that place them in a category of their own. In this review, we discuss what is known on how ADAMs and ADAMTSs are altered in abdominal aortic aneurysm and thoracic aortic aneurysm in patients, in different animal models, and their role in regulating the function of different vascular and inflammatory cell types. A full understanding of the role of ADAMs and ADAMTSs in aortic aneurysm will help reveal a more complete understanding of the underlying mechanism driving aneurysm formation, which will help towards developing an effective treatment in preventing or limiting the growth of aortic aneurysm.

Tissue Inhibitor of Metalloproteases 3 (TIMP-3): In Vivo Analysis Underpins Its Role as a Master Regulator of Ectodomain Shedding

The proteolytical cleavage of transmembrane proteins with subsequent release of their extracellular domain, so-called ectodomain shedding, is a post-translational modification that plays an essential role in several biological processes, such as cell communication, adhesion and migration. Metalloproteases are major proteases in ectodomain shedding, especially the disintegrin metalloproteases (ADAMs) and the membrane-type matrix metalloproteases (MT-MMPs), which are considered to be canonical sheddases for their membrane-anchored topology and for the large number of proteins that they can release. The unique ability of TIMP-3 to inhibit different families of metalloproteases, including the canonical sheddases (ADAMs and MT-MMPs), renders it a master regulator of ectodomain shedding. This review provides an overview of the different functions of TIMP-3 in health and disease, with a major focus on the functional consequences in vivo related to its ability to control ectodomain shedding. Furthermore, herein we describe a collection of mass spectrometry-based approaches that have been used in recent years to identify new functions of sheddases and TIMP-3. These methods may be used in the future to elucidate the pathological mechanisms triggered by the Sorsby’s fundus dystrophy variants of TIMP-3 or to identify proteins released by less well characterized TIMP-3 target sheddases whose substrate repertoire is still limited, thus providing novel insights into the physiological and pathological functions of the inhibitor.

Transcriptional analysis of gasoline engine exhaust particulate matter 2.5-exposed human umbilical vein endothelial cells reveals the different gene expression patterns related to the cardiovascular diseases

Particulate matter (PM) causes several diseases, including cardiovascular diseases (CVDs). Previous studies compared the gene expression patterns in airway epithelial cells and keratinocytes exposed to PM. However, analysis of differentially expressed gene (DEGs) in endothelial cells exposed to PM2.5 (diameter less than 2.5 μm) from fossil fuel combustion has been limited. Here, we exposed human umbilical vein endothelial cells (HUVECs) to PM2.5 from combustion of gasoline, performed RNA-seq analysis, and identified DEGs. Exposure to the IC50 concentrations of gasoline engine exhaust PM2.5 (GPM) for 24 h yielded 1081 (up-regulation: 446, down-regulation: 635) DEGs. The most highly up-regulated gene is NGFR followed by ADM2 and NUPR1. The most highly down-regulated gene is TNFSF10 followed by GDF3 and EDN1. Gene Ontology enrichment analysis revealed that GPM regulated genes involved in cardiovascular system development, tube development and circulatory system development. Kyoto Encyclopedia of Genes and Genomes and Reactome pathway analyses showed that genes related to cytokine–cytokine receptor interactions and cytokine signaling in the immune system were significantly affected by GPM. We confirmed the RNA-seq data of some highly altered genes by qRT-PCR and showed the induction of NGFR, ADM2 and IL-11 at a protein level, indicating that the observed gene expression patterns were reliable. Given the adverse effects of PM2.5 on CVDs, our findings provide new insight into the importance of several DEGs and pathways in GPM-induced CVDs.

Neutrophils as Regulators and Biomarkers of Cardiovascular Inflammation in the Context of Abdominal Aortic Aneurysms

Neutrophils represent up to 70% of circulating leukocytes in healthy humans and combat infection mostly by phagocytosis, degranulation and NETosis. It has been reported that neutrophils are centrally involved in abdominal aortic aneurysm (AAA) pathogenesis. The natural course of AAA is growth and rupture, if left undiagnosed or untreated. The rupture of AAA has a very high mortality and is currently among the leading causes of death worldwide. The use of noninvasive cardiovascular imaging techniques for patient screening, surveillance and postoperative follow-up is well established and recommended by the current guidelines. Neutrophil-derived biomarkers may offer clinical value to the monitoring and prognosis of AAA patients, allowing for potential early therapeutic intervention. Numerous promising biomarkers have been studied. In this review, we discuss neutrophils and neutrophil-derived molecules as regulators and biomarkers of AAA, and our aim was to specifically highlight diagnostic and prognostic markers. Neutrophil-derived biomarkers may potentially, in the future, assist in determining AAA presence, predict size, expansion rate, rupture risk, and postoperative outcome once validated in highly warranted future prospective clinical studies.

Loss of TIMP4 (Tissue Inhibitor of Metalloproteinase 4) Promotes Atherosclerotic Plaque Deposition in the Abdominal Aorta Despite Suppressed Plasma Cholesterol Levels

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Selected conditions associated with an increased incidence of incisional hernia: A review of molecular biology

BACKGROUND

Incisional hernias (IH) following a laparotomy, on average, occur in 10-20% of patients, however, little is known about its molecular basis. Thus, a better understanding of the molecular mechanisms could lead to the identification of key target(s) to intervene pre-and post-operatively.

METHODS

We examined the current literature describing the molecular mechanisms of IH and overlap these factors with smoking, abdominal aortic aneurysm, obesity, diabetes mellitus, and diverticulitis.

RESULTS

The expression levels of collagen I and III, matrix metalloproteinases, and tissue inhibitors of metalloproteases are abnormal in the extracellular matrix (ECM) of IH patients and ECM disorganization has an overlap with these comorbid conditions.

CONCLUSION

Understanding the pathophysiology of IH development and associated risk factors will allow physicians to identify patients that may be at increased risk for IH and to possibly act preemptively to decrease the incidence of IH.

Genetic and Epigenetic Mechanisms Underlying Vascular Smooth Muscle Cell Phenotypic Modulation in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) refers to the localized dilatation of the infra-renal aorta, in which the diameter exceeds 3.0 cm. Loss of vascular smooth muscle cells, degradation of the extracellular matrix (ECM), vascular inflammation, and oxidative stress are hallmarks of AAA pathogenesis and contribute to the progressive thinning of the media and adventitia of the aortic wall. With increasing AAA diameter, and left untreated, aortic rupture ensues with high mortality. Collective evidence of recent genetic and epigenetic studies has shown that phenotypic modulation of smooth muscle cells (SMCs) towards dedifferentiation and proliferative state, which associate with the ECM remodeling of the vascular wall and accompanied with increased cell senescence and inflammation, is seen in in vitro and in vivo models of the disease. This review critically analyses existing publications on the genetic and epigenetic mechanisms implicated in the complex role of SMCs within the aortic wall in AAA formation and reflects the importance of SMCs plasticity in AAA formation. Although evidence from the wide variety of mouse models is convincing, how this knowledge is applied to human biology needs to be addressed urgently leveraging modern in vitro and in vivo experimental technology.

GSK2593074A blocks progression of existing abdominal aortic dilation

Objective

Receptor interacting proteins kinase 1 and 3 (RIPK1 and RIPK3) have been shown to play essential roles in the pathogenesis of abdominal aortic aneurysms (AAAs) by mediating necroptosis and inflammation. We previously discovered a small molecular inhibitor GSK2593074A (GSK’074) that binds to both RIPK1 and RIPK3 with high affinity and prevents AAA formation in mice. In this study, we evaluated whether GSK’074 can attenuate progression of existing AAA in the calcium phosphate model.

Methods

C57BL6/J mice were subjected to the calcium phosphate model of aortic aneurysm generation. Mice were treated with either GSK’074 (4.65 mg/kg/day) or dimethylsulfoxide (DMSO) controls starting 7 days after aneurysm induction. Aneurysm growth was monitored via ultrasound imaging every 7 days until harvest on day 28. Harvested aortas were examined via immunohistochemistry. The impact of GSK’074 on vascular smooth muscle cells and macrophages were evaluated via flow cytometry and transwell migration assay.

Results

At the onset of treatment, mice in both the control (DMSO) and GSK’074 groups showed similar degree of aneurysmal expansion. The weekly ultrasound imaging showed a steady aneurysm growth in DMSO-treated mice. The aneurysm growth was attenuated by GSK’074 treatment. At humane killing, GSK’074-treated mice had significantly reduced progression in aortic diameter from baseline as compared with the DMSO-treated mice (83.2% ± 13.1% [standard error of the mean] vs 157.2% ± 32.0% [standard error of the mean]; P < .01). In addition, the GSK’074-treated group demonstrated reduced macrophages (F4/80, CD206, MHCII), less gelatinase activity, a higher level of smooth muscle cell-specific myosin heavy chain, and better organized elastin fibers within the aortic walls compared with DMSO controls. In vitro, GSK’074 inhibited necroptosis in mouse aortic smooth muscle cells; whereas, it was able to prevent macrophage migration without affecting Il1b and Tnf expression.

Conclusions

GSK’074 is able to attenuate aneurysm progression in the calcium phosphate model. The ability to inhibit both vascular smooth muscle cell necroptosis and macrophage migration makes GSK’074 an attractive drug candidate for pharmaceutical treatment of aortic aneurysms.

Previous clinical trials evaluating pharmaceutical treatments in blocking aneurysm progression have failed. However, most agents used in those trials focused on inhibiting only one mechanism that contributes to aneurysm pathogenesis. In this study, we found GSK’074 is able to attenuate aneurysm progression in the calcium phosphate model by inhibiting both vascular smooth muscle cell necroptosis and macrophage migration, which are both key processes in the pathogenesis of aneurysm progression. The ability of GSK’0474 to inhibit multiple key pathologic mechanisms makes it an attractive therapeutic candidate for aneurysm progression.

Biology of Tissue Inhibitor of Metalloproteinase 3 (TIMP3), and Its Therapeutic Implications in Cardiovascular Pathology

Tissue inhibitor of metalloproteinase 3 (TIMP3) is unique among the four TIMPs due to its extracellular matrix (ECM)-binding property and broad range of inhibitory substrates that includes matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAM with thrombospondin motifs (ADAMTSs). In addition to its metalloproteinase-inhibitory function, TIMP3 can interact with proteins in the extracellular space resulting in its multifarious functions. TIMP3 mRNA has a long 3' untranslated region (UTR) which is a target for numerous microRNAs. TIMP3 levels are reduced in various cardiovascular diseases, and studies have shown that TIMP3 replenishment ameliorates the disease, suggesting a therapeutic potential for TIMP3 in cardiovascular diseases. While significant efforts have been made in identifying the effector targets of TIMP3, the regulatory mechanism for the expression of this multi-functional TIMP has been less explored. Here, we provide an overview of TIMP3 gene structure, transcriptional and post-transcriptional regulators (transcription factors and microRNAs), protein structure and partners, its role in cardiovascular pathology and its application as therapy, while also drawing reference from TIMP3 function in other diseases.

ADAM (a Disintegrin and Metalloproteinase) 15 Deficiency Exacerbates Ang II (Angiotensin II)-Induced Aortic Remodeling Leading to Abdominal Aortic Aneurysm

Supplemental Digital Content is available in the text.

Objective:

ADAM (a disintegrin and metalloproteinase) 15—a membrane-bound metalloprotease from the ADAM (disintegrin and metalloproteinase) family—has been linked to endothelial permeability, inflammation, and metastasis. However, its function in aortic aneurysm has not been explored. We aimed to determine the function of ADAM15 in the pathogenesis of aortic remodeling and aneurysm formation.

Approach and Results:

Male Adam15-deficient and WT (wild type) mice (10 weeks old), on standard laboratory diet, received Ang II (angiotensin II; 1.5 mg/kg per day) or saline (Alzet pump) for 2 or 4 weeks. Ang II increased ADAM15 in WT aorta, while Adam15-deficiency resulted in abdominal aortic aneurysm characterized by loss of medial smooth muscle cells (SMCs), elastin fragmentation, inflammation, but unaltered Ang II–mediated hypertension. In the abdominal aortic tissue and primary aortic SMCs culture, Adam15 deficiency decreased SMC proliferation, increased apoptosis, and reduced contractile properties along with F-actin depolymerization to G-actin. Ang II triggered a markedly greater increase in THBS (thrombospondin) 1 in Adam15-deficient aorta, primarily the medial layer in vivo, and in aortic SMC in vitro; increased SSH1 (slingshot homolog 1) phosphatase activity and cofilin dephosphorylation that promoted F-actin depolymerization and G-actin accumulation. rhTHBS1 (recombinant THBS1) alone was sufficient to activate the cofilin pathway, increase G-actin, and induce apoptosis of aortic SMCs, confirming the key role of THBS1 in this process. Further, in human abdominal aortic aneurysm specimens, decreased ADAM15 was associated with increased THBS1 levels and loss of medial SMCs.

Conclusions:

This study is the first to demonstrate a key role for ADAM15 in abdominal aortic aneurysm through regulating the SMC function, thereby placing ADAM15 in a critical position as a potential therapeutic target for abdominal aortic aneurysm.

Cyclodextrin Prevents Abdominal Aortic Aneurysm via Activation of Vascular Smooth Muscle Cell Transcription Factor EB

BACKGROUND

Abdominal aortic aneurysm (AAA) is a severe aortic disease with a high mortality rate in the event of rupture. Pharmacological therapy is needed to inhibit AAA expansion and prevent aneurysm rupture. Transcription factor EB (TFEB), a master regulator of autophagy and lysosome biogenesis, is critical to maintain cell homeostasis. In this study, we aim to investigate the role of vascular smooth muscle cell (VSMC) TFEB in the development of AAA and establish TFEB as a novel target to treat AAA.

METHODS

The expression of TFEB was measured in human and mouse aortic aneurysm samples. We used loss/gain-of-function approaches to understand the role of TFEB in VSMC survival and explored the underlying mechanisms through transcriptome and functional studies. Using VSMC-selective Tfeb knockout mice and different mouse AAA models, we determined the role of VSMC TFEB and a TFEB activator in AAA in vivo.

RESULTS

We found that TFEB is downregulated in both human and mouse aortic aneurysm lesions. TFEB potently inhibits apoptosis in VSMCs, and transcriptome analysis revealed that TFEB regulates apoptotic signaling pathways, especially apoptosis inhibitor B-cell lymphoma 2. B-cell lymphoma 2 is significantly upregulated by TFEB and is required for TFEB to inhibit VSMC apoptosis. We consistently observed that TFEB deficiency increases VSMC apoptosis and promotes AAA formation in different mouse AAA models. Furthermore, we demonstrated that 2-hydroxypropyl-β-cyclodextrin, a clinical agent used to enhance the solubility of drugs, activates TFEB and inhibits AAA formation and progression in mice. Last, we found that 2-hydroxypropyl-β-cyclodextrin inhibits AAA in a VSMC TFEB-dependent manner in mouse models.

CONCLUSIONS

Our study demonstrated that TFEB protects against VSMC apoptosis and AAA. TFEB activation by 2-hydroxypropyl-β-cyclodextrin may be a promising therapeutic strategy for the prevention and treatment of AAA.

Novel molecular cues for dental defects in hypophosphatasia

Mineralization disorders with a broad range of etiological factors represent a huge challenge in dental diagnosis and therapy. Hypophosphatasia (HPP) belongs to the rare diseases affecting predominantly mineralized tissues, bones and teeth, and occurs due to mutations in the ALPL gene, which encodes tissue-nonspecific alkaline phosphatase (TNAP). Here we analyzed stem cells from bone marrow (BMSCs), dental pulp (DPSCs) and periodontal ligament (PDLSCs) in the absence and presence of efficient TNAP inhibitors. The differentiation capacity, expression of surface markers, and gene expression patterns of donor-matched dental cells were compared during this in vitro study. Differentiation assays showed efficient osteogenic but low adipogenic differentiation (aD) capacity of PDLSCs and DPSCs. TNAP inhibitor treatment completely abolished the mineralization process during osteogenic differentiation (oD). RNA-seq analysis in PDLSCs, comparing oD with and without TNAP inhibitor levamisole, showed clustered regulation of candidate molecular mechanisms that putatively impaired osteogenesis and mineralization, disequilibrated ECM production and turnover, and propagated inflammation. Combined alteration of cementum formation, mineralization, and elastic attachment of teeth to cementum via elastic fibers may explain dental key problems in HPP. Using this in vitro model of TNAP deficiency in DPSCs and PDLSCs, we provide novel putative target areas for research on molecular cues for specific dental problems in HPP.

Pathogenic mechanisms and the potential of drug therapies for aortic aneurysm

Aortic aneurysm is a permanent focal dilation of the aorta. It is usually an asymptomatic disease but can lead to sudden death due to aortic rupture. Aortic aneurysm-related mortalities are estimated at ∼200,000 deaths per year worldwide. Because no pharmacological treatment has been found to be effective so far, surgical repair remains the only treatment for aortic aneurysm. Aortic aneurysm results from changes in the aortic wall structure due to loss of smooth muscle cells and degradation of the extracellular matrix and can form in different regions of the aorta. Research over the past decade has identified novel contributors to aneurysm formation and progression. The present review provides an overview of cellular and noncellular factors as well as enzymes that process extracellular matrix and regulate cellular functions (e.g., matrix metalloproteinases, granzymes, and cathepsins) in the context of aneurysm pathogenesis. An update of clinical trials focusing on therapeutic strategies to slow abdominal aortic aneurysm growth and efforts underway to develop effective pharmacological treatments is also provided.

Extracellular matrix, regional heterogeneity of the aorta, and aortic aneurysm

Aortic aneurysm is an asymptomatic disease with dire outcomes if undiagnosed. Aortic aneurysm rupture is a significant cause of death worldwide. To date, surgical repair or endovascular repair (EVAR) is the only effective treatment for aortic aneurysm, as no pharmacological treatment has been found effective. Aortic aneurysm, a focal dilation of the aorta, can be formed in the thoracic (TAA) or the abdominal (AAA) region; however, our understanding as to what determines the site of aneurysm formation remains quite limited. The extracellular matrix (ECM) is the noncellular component of the aortic wall, that in addition to providing structural support, regulates bioavailability of an array of growth factors and cytokines, thereby influencing cell function and behavior that ultimately determine physiological or pathological remodeling of the aortic wall. Here, we provide an overview of the ECM proteins that have been reported to be involved in aortic aneurysm formation in humans or animal models, and the experimental models for TAA and AAA and the link to ECM manipulations. We also provide a comparative analysis, where data available, between TAA and AAA, and how aberrant ECM proteolysis versus disrupted synthesis may determine the site of aneurysm formation.

A review of aneurysm formation, swelling in blood vessel, in the aorta, examines distinctions between two forms of the condition and the role of proteins in the extracellular matrix which surrounds cells of the arterial wall. Rupture of aneurysms in the aorta, the body’s main artery, is a major cause of death. Researchers led by Zamaneh Kassiri at the University of Alberta, Edmonton, Canada, emphasize that aneurysms in the thoracic and abdominal regions of the aorta are distinct conditions with crucial differences in their causes. Disrupted production and assembly of the extracellular matrix and its proteins may underlie thoracic aneurysm formation. Factors triggering the degradation of extracellular matrix proteins may be more significant in abdominal aneurysms. Understanding the differing molecular mechanisms involved could help address the current lack of effective drug treatments for these dangerous conditions.

Matrix Metalloproteinase in Abdominal Aortic Aneurysm and Aortic Dissection

Abdominal Aortic Aneurysm (AAA) affects 4–5% of men over 65, and Aortic Dissection (AD) is a life-threatening aortic pathology associated with high morbidity and mortality. Initiators of AAA and AD include smoking and arterial hypertension, whilst key pathophysiological features of AAA and AD include chronic inflammation, hypoxia, and large modifications to the extra cellular matrix (ECM). As it stands, only surgical methods are available for preventing aortic rupture in patients, which often presents difficulties for recovery. No pharmacological treatment is available, as such researchers are attempting to understand the cellular and molecular pathophysiology of AAA and AD. Upregulation of matrix metalloproteinase (MMPs), particularly MMP-2 and MMP-9, has been identified as a key event occurring during aneurysmal growth. As such, several animal models of AAA and AD have been used to investigate the therapeutic potential of suppressing MMP-2 and MMP-9 activity as well as modulating the activity of other MMPs, and TIMPs involved in the pathology. Whilst several studies have offered promising results, targeted delivery of MMP inhibition still needs to be developed in order to avoid surgery in high risk patients.

Apelin protects against abdominal aortic aneurysm and the therapeutic role of neutral endopeptidase resistant apelin analogs

Abdominal aortic aneurysm (AAA) remains the second most frequent vascular disease with high mortality but has no approved medical therapy. We investigated the direct role of apelin (APLN) in AAA and identified a unique approach to enhance APLN action as a therapeutic intervention for this disease. Loss of APLN potentiated angiotensin II (Ang II)-induced AAA formation, aortic rupture, and reduced survival. Formation of AAA was driven by increased smooth muscle cell (SMC) apoptosis and oxidative stress in Apln ^-/y aorta and in APLN-deficient cultured murine and human aortic SMCs. Ang II-induced myogenic response and hypertension were greater in Apln ^-/y mice, however, an equivalent hypertension induced by phenylephrine, an α-adrenergic agonist, did not cause AAA or rupture in Apln ^-/y mice. We further identified Ang converting enzyme 2 (ACE2), the major negative regulator of the renin-Ang system (RAS), as an important target of APLN action in the vasculature. Using a combination of genetic, pharmacological, and modeling approaches, we identified neutral endopeptidase (NEP) that is up-regulated in human AAA tissue as a major enzyme that metabolizes and inactivates APLN-17 peptide. We designed and synthesized a potent APLN-17 analog, APLN-NMeLeu9-A2, that is resistant to NEP cleavage. This stable APLN analog ameliorated Ang II-mediated adverse aortic remodeling and AAA formation in an established model of AAA, high-fat diet (HFD) in Ldlr ^-/- mice. Our findings define a critical role of APLN in AAA formation through induction of ACE2 and protection of vascular SMCs, whereas stable APLN analogs provide an effective therapy for vascular diseases.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

I-κB kinase-ε knockout protects against angiotensin II induced aortic valve thickening in apolipoprotein E deficient mice

Aortic stenosis (AS) is considered to be an actively regulated progress that involves similar pathophysiological processes as atherosclerosis. I-κB kinase-ε (IKKε) is a proinflammatory molecule involved in atherosclerosis. The objective of the present study was to define the role of IKKε in pathological valvular remodeling. Aortic valves (AVs) from 52 patients undergoing AV replacement (AS) and 13 patients undergoing heart transplant (Control) were analyzed. ApoE^-/- mice (AK, n = 20) and ApoE^-/-IKKε^-/- mice (DK, n = 20) were generated and infused with saline or Ang II for 4 weeks. We found an upregulation of IKKε in human stenotic aortic valves compared to that in control AVs. Our results demonstrated that AK mice receiving AngII exhibited more advanced valvular remodeling and markedly increased IKKε expression. Conversely, loss of IKKε reduced adverse aortic valve thickening in response to Ang II, as measured by histological analyses. Furthermore, according to immunofluorescence analysis, Ang II resulted in obvious increases in the expression of α-SMA, TGF-β and NF-κB pathway components in the AK group, especially in the thickened area, while these increases were blocked in the DK group. Moreover, IKKε was co-expressed with α-SMA in valvular interstitial cells in ApoE^-/- mice after an AngII infusion. These data provide evidence that IKKε plays a key role in the development of valvular remodeling and that it may be a novel target for the treatment of AS.

Cell-Specific Functions of ADAM17 Regulate the Progression of Thoracic Aortic Aneurysm

RATIONALE

ADAM17 (a disintegrin and metalloproteinase-17) is a membrane-bound enzyme that regulates bioavailability of multiple transmembrane proteins by proteolytic processing. ADAM17 has been linked to several pathologies, but its role in thoracic aortic aneurysm (TAA) has not been determined.

OBJECTIVE

The objective of this study was to explore the cell-specific functions of vascular ADAM17 in the pathogenesis and progression of TAA.

METHODS AND RESULTS

In aneurysmal thoracic aorta from patients, ADAM17 was increased in tunica media and intima. To determine the function of ADAM17 in the major cells types within these regions, we generated mice lacking ADAM17 in smooth muscle cells (SMC; Adam17^f/f/Sm22^Cre/+ ) or endothelial cells (Adam17^f/f/Tie2^Cre/+ ). ADAM17 deficiency in either cell type was sufficient to suppress TAA dilation markedly and adverse remodeling in males and females (in vivo) although through different mechanisms. ADAM17 deficiency in SMCs prevented the contractile-to-synthetic phenotypic switching in these cells after TAA induction, preventing perivascular fibrosis, inflammation, and adverse aortic remodeling. Loss of ADAM17 in endothelial cells protected the integrity of the intimal barrier by preserving the adherens junction (vascular endothelial-cadherin) and tight junctions (junctional adhesion molecule-A and claudin). In vitro studies on primary mouse thoracic SMCs and human primary aortic SMCs and endothelial cells (±ADAM17 small interfering RNA) confirmed the cell-specific functions of ADAM17 and demonstrated the cross-species validity of these findings. To determine the impact of ADAM17 inhibition in treating TAA, we used an ADAM17-selective inhibitor (PF-548) before or 3 days after TAA induction. In both cases, ADAM17 inhibition prevented progression of aneurysmal growth.

CONCLUSIONS

We have identified distinct cell-specific functions of ADAM17 in TAA progression, promoting pathological remodeling of SMC and impairing integrity of the intimal endothelial cell barrier. The dual impact of ADAM17 deficiency (or inhibition) in protecting 2 major cell types in the aortic wall highlights the unique position of this proteinase as a critical treatment target for TAA.

Deletion of BMAL1 in Smooth Muscle Cells Protects Mice From Abdominal Aortic Aneurysms

OBJECTIVE

Abdominal aortic aneurysm (AAA) has high mortality rate when ruptured, but currently, there is no proven pharmacological therapy for AAA because of our poor understanding of its pathogenesis. The current study explored a novel role of smooth muscle cell (SMC) BMAL1 (brain and muscle Arnt-like protein-1)-a transcription factor known to regulate circadian rhythm-in AAA development.

APPROACH AND RESULTS

SMC-selective deletion of BMAL1 potently protected mice from AAA induced by (1) MR (mineralocorticoid receptor) agonist deoxycorticosterone acetate or aldosterone plus high salt intake and (2) angiotensin II infusion in hypercholesterolemia mice. Aortic BMAL1 was upregulated by deoxycorticosterone acetate-salt, and deletion of BMAL1 in SMCs selectively upregulated TIMP4 (tissue inhibitor of metalloproteinase 4) and suppressed deoxycorticosterone acetate-salt-induced MMP (matrix metalloproteinase) activation and elastin breakages. Moreover, BMAL1 bound to the Timp4 promoter and suppressed Timp4 transcription.

CONCLUSIONS

These results reveal an important, but previously unexplored, role of SMC BMAL1 in AAA. Moreover, these results identify TIMP4 as a novel target of BMAL1, which may mediate the AAA protective effect of SMC BMAL1 deletion.

Loss of vascular smooth muscle cell autophagy exacerbates angiotensin II-associated aortic remodeling

OBJECTIVE

The pathophysiologic processes of abdominal aortic aneurysms (AAAs) and atherosclerosis often intersect. Given that anomalies in vascular smooth muscle cell (SMC) autophagy have been noted in models of atherosclerosis, we sought to evaluate the potential role that SMC autophagy may play in the initiation and progression of AAAs.

METHODS

Studies were conducted in ATG7^flx/flxSM22α-Cre^tg/+ (SMC ATG7 knockout [SMC-ATG7-KO]) and ATG7^WT/WT; SM22α-Cre^tg/+ (SMC ATG7 wild-type [SMC-ATG7-WT]) littermates that were continuously infused with angiotensin II (Ang II; 1.5 mg/kg/d) for up to 12 weeks. Mortality, morbidity, hemodynamics, and aortic remodeling were documented.

RESULTS

During the 12-week observation window, all of the Ang II-treated SMC-ATG-WT mice (n = 6) survived, whereas 10 of the 19 Ang II-treated SMC-ATG-KO mice had died by week 7 (log-rank test, P < .001). Mean arterial pressure (128.07 ± 3.4 mm Hg for Ang II-treated SMC-ATG-KO vs 138.5 ± 5.87 mm Hg for Ang II-treated SMC-ATG-WT mice) and diastolic arterial pressure (109.7 ± 2.55 mm Hg for Ang II-treated SMC-ATG7-KO vs 119.4 ± 2.12 mm Hg for Ang II-treated SMC-ATG7-WT mice) were significantly different between the two groups (P < .01). Cardiac rupture, myocardial infarct, end-organ damage, pleural effusion, and venous distention were noted in Ang II-treated SMC-ATG7-KO but not in Ang II-treated SMC-ATG7-WT mice. Although the suprarenal aortic diameters of the Ang II-treated SMC-ATG7-KO group demonstrated a trending increase (at week 4, 1.26 ± 0.06 mm [n = 14] for Ang II-treated SMC-ATG-KO mice vs 1.09 ± 0.02 mm [n = 5] for Ang II-treated SMC-ATG-WT mice; P < .05), only 2 of the 19 developed abdominal aortic dissections.

CONCLUSIONS

Mice with SMC ATG7 deficiency that are chronically infused with Ang II do not tend to develop dissecting AAA but do exhibit adverse aortic remodeling and appreciable cardiac failure-associated mortality.

Deletion of hypoxia-inducible factor-1α in myeloid lineage exaggerates angiotensin II-induced formation of abdominal aortic aneurysm

Hypoxia-inducible factor (HIF)-1α is a transcription factor that regulates various genes responding to hypoxic conditions. We previously reported that myeloid-specific activation of HIF-1α had protective effects on hypertensive cardiovascular remodelling in mice. However the role of myeloid lineage HIF-1α in the development of abdominal aortic aneurysm (AAA) has not been determined. Myeloid-specific HIF-1α knockout (HIF-1KO) mice were created using a Cre-lox recombination system in the background of apolipoprotein E-deficient (ApoE^-/-) mice. HIF-1KO and control mice were fed high-fat diet (HFD) and infused with angiotensin II (Ang II, 1800 ng/kg/min) by an osmotic mini pump for 4 weeks to induce AAA formation. Deletion of HIF-1α increased aortic external diameter (2.47±0.21 mm versus 1.80±0.28 mm in control, P=0.035). AAA formation rate (94.4% in HIF-1KO versus 81.8% in control) was not statistically significant. Elastic lamina degradation grade determined by Elastica van Gieson (EVG) staining was deteriorated in HIF-1KO mice (3.91±0.08 versus 3.25±0.31 in control, P=0.013). The number of infiltrated macrophages into the abdominal aorta was increased in HIF-1KO mice. Expression of tissue inhibitors of metalloproteinases (TIMPs) was suppressed in the aorta and peritoneal macrophages (PMs) from HIF-1KO mice compared with control mice. HIF-1α in myeloid lineage cells may have a protective role against AAA formation induced by Ang II and HFD in ApoE^-/- mice.

A Disintegrin and Metalloprotease 17 in the Cardiovascular and Central Nervous Systems

ADAM17 is a metalloprotease and disintegrin that lodges in the plasmatic membrane of several cell types and is able to cleave a wide variety of cell surface proteins. It is somatically expressed in mammalian organisms and its proteolytic action influences several physiological and pathological processes. This review focuses on the structure of ADAM17, its signaling in the cardiovascular system and its participation in certain disorders involving the heart, blood vessels, and neural regulation of autonomic and cardiovascular modulation.

MicroRNA-181b Controls Atherosclerosis and Aneurysms Through Regulation of TIMP-3 and Elastin

Supplemental Digital Content is available in the text.

Rationale:

Atherosclerosis and aneurysms are leading causes of mortality worldwide. MicroRNAs (miRs) are key determinants of gene and protein expression, and atypical miR expression has been associated with many cardiovascular diseases; although their contributory role to atherosclerotic plaque and abdominal aortic aneurysm stability are poorly understood.

Objective:

To investigate whether miR-181b regulates tissue inhibitor of metalloproteinase-3 expression and affects atherosclerosis and aneurysms.

Methods and Results:

Here, we demonstrate that miR-181b was overexpressed in symptomatic human atherosclerotic plaques and abdominal aortic aneurysms and correlated with decreased expression of predicted miR-181b targets, tissue inhibitor of metalloproteinase-3, and elastin. Using the well-characterized mouse atherosclerosis models of Apoe^−/− and Ldlr^−/−, we observed that in vivo administration of locked nucleic acid anti-miR-181b retarded both the development and the progression of atherosclerotic plaques. Systemic delivery of anti-miR-181b in angiotensin II–infused Apoe^−/− and Ldlr^−/− mice attenuated aneurysm formation and progression within the ascending, thoracic, and abdominal aorta. Moreover, miR-181b inhibition greatly increased elastin and collagen expression, promoting a fibrotic response and subsequent stabilization of existing plaques and aneurysms. We determined that miR-181b negatively regulates macrophage tissue inhibitor of metalloproteinase-3 expression and vascular smooth muscle cell elastin production, both important factors in maintaining atherosclerotic plaque and aneurysm stability. Validation studies in Timp3^−/− mice confirmed that the beneficial effects afforded by miR-181b inhibition are largely tissue inhibitor of metalloproteinase-3 dependent, while also revealing an additional protective effect through elevating elastin synthesis.

Conclusions:

Our findings suggest that the management of miR-181b and its target genes provides therapeutic potential for limiting the progression of atherosclerosis and aneurysms and protecting them from rupture.

Hypoxia-Inducible Factor-1α in Smooth Muscle Cells Protects Against Aortic Aneurysms-Brief Report

OBJECTIVE

The purpose of this study was to determine the role of smooth muscle cell-derived hypoxia-inducible factor-1α (Hif-1α) in the pathogenesis of aortic aneurysms.

APPROACH AND RESULTS

Control mice and smooth muscle cell-specific hypoxia-inducible factor-1α-deficient mice were infused with β-aminopropionitrile for 2 weeks and angiotensin II for 6 weeks to induce aortic aneurysm formation. Mutant mice experienced increased levels of aneurysm formation of the thoracic or abdominal aorta with more severe elastin disruption, compared with control mice. Smooth muscle cell-specific hypoxia-inducible factor-1α deficiency did not affect matrix metalloproteinase-2 activity; however, the activity of lysyl oxidase and the levels of tropoelastin mRNA in the angiotensin II- and β-aminopropionitrile-treated aortae, associated with elastin fiber formation, were suppressed. Furthermore, we observed reduced volumes of mature cross-linked elastin in the thoracoabdominal aorta after treatment with angiotensin II and β-aminopropionitrile.

CONCLUSIONS

Deficiency of smooth muscle cell-derived hypoxia-inducible factor-1α augments aortic aneurysms, accompanied by disruption of elastin fiber formation, but not changes of elastin fiber degradation.

Reducing Timp3 or vitronectin ameliorates disease manifestations in CADASIL mice

OBJECTIVE

CADASIL is a genetic paradigm of cerebral small vessel disease caused by NOTCH3 mutations that stereotypically lead to the extracellular deposition of NOTCH3 ectodomain (Notch3(ECD) ) on the vessels. TIMP3 and vitronectin are 2 extracellular matrix proteins that abnormally accumulate in Notch3(ECD) -containing deposits on brain vessels of mice and patients with CADASIL. Herein, we investigated whether increased levels of TIMP3 and vitronectin are responsible for aspects of CADASIL disease phenotypes.

METHODS

Timp3 and vitronectin expression were genetically reduced in TgNotch3(R169C) mice, a well-established preclinical model of CADASIL. A mouse overexpressing human TIMP3 (TgBAC-TIMP3) was developed. Disease-related phenotypes, including cerebral blood flow (CBF) deficits, white matter lesions, and Notch3(ECD) deposition, were evaluated between 6 and 20 months of age.

RESULTS

CBF responses to neural activity (functional hyperemia), topical application of vasodilators, and decreases in blood pressure (CBF autoregulation) were similarly reduced in TgNotch3(R169C) and TgBAC-TIMP3 mice, and myogenic responses of brain arteries were likewise attenuated. These defects were rescued in TgNotch3(R169C) mice by haploinsufficiency of Timp3, although the number of white matter lesions was unaffected. In contrast, haploinsufficiency or loss of vitronectin in TgNotch3(R169C) mice ameliorated white matter lesions, although CBF responses were unchanged. Amelioration of cerebrovascular reactivity or white matter lesions in these mice was not associated with reduced Notch3(ECD) deposition in brain vessels.

INTERPRETATION

Elevated levels of TIMP3 and vitronectin, acting downstream of Notch3(ECD) deposition, play a role in CADASIL, producing divergent influences on early CBF deficits and later white matter lesions.

The pseudogene TUSC2P promotes TUSC2 function by binding multiple microRNAs

Various non-coding regions of the genome, once presumed to be ‘junk’ DNA, have recently been found to be transcriptionally active. In particular, pseudogenes are now known to have important biological roles. Here we report that transcripts of the two tumour suppressor candidate-2 pseudogenes (TUSC2P), found on chromosomes X and Y, are homologous to the 3′-UTR of their corresponding protein coding transcript, TUSC2. TUSC2P and the TUSC2 3′-UTR share many common miRNA-binding sites, including miR-17, miR-93, miR-299-3p, miR-520a, miR-608 and miR-661. We find that ectopic expression of TUSC2P and the TUSC2 3′-UTR inhibits cell proliferation, survival, migration, invasion and colony formation, and increases tumour cell death. By interacting with endogenous miRNAs, TUSC2P and TUSC2 3′-UTR arrest the functions of these miRNAs, resulting in increased translation of TUSC2. The TUSC2P and TUSC2 3′-UTR could thus be used as combinatorial miRNA inhibitors and might have clinical applications.

Non-coding RNAs have recently emerged as crucial regulators of gene expression. Here Rutnam et al. identify a pseudogene complementary to the 3′-UTR of the TUSC2 tumour suppressor that regulates TUSC2 levels by acting as a decoy for endogenous microRNAs and thereby inhibits tumorigenesis.

Platelet Inhibitors Reduce Rupture in a Mouse Model of Established Abdominal Aortic Aneurysm

OBJECTIVE

Rupture of abdominal aortic aneurysms causes a high morbidity and mortality in the elderly population. Platelet-rich thrombi form on the surface of aneurysms and may contribute to disease progression. In this study, we used a pharmacological approach to examine a role of platelets in established aneurysms induced by angiotensin II infusion into hypercholesterolemic mice.

APPROACH AND RESULTS

Administration of the platelet inhibitors aspirin or clopidogrel bisulfate to established abdominal aortic aneurysms dramatically reduced rupture. These platelet inhibitors reduced abdominal aortic platelet and macrophage recruitment resulting in decreased active matrix metalloproteinase-2 and matrix metalloproteinase-9. Platelet inhibitors also resulted in reduced plasma concentrations of platelet factor 4, cytokines, and components of the plasminogen activation system in mice. To determine the validity of these findings in human subjects, a cohort of aneurysm patients were retrospectively analyzed using developed and validated algorithms in the electronic medical record database at Vanderbilt University. Similar to mice, administration of aspirin or P2Y12 inhibitors was associated with reduced death among patients with abdominal aortic aneurysm.

CONCLUSIONS

These results suggest that platelets contribute to abdominal aortic aneurysm progression and rupture.

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.

TIMP3 interplays with apelin to regulate cardiovascular metabolism in hypercholesterolemic mice

OBJECTIVE

Tissue inhibitor of metalloproteinase 3 (TIMP3) is an extracellular matrix (ECM) bound protein, which has been shown to be downregulated in human subjects and experimental models with cardiometabolic disorders, including type 2 diabetes mellitus, hypertension and atherosclerosis. The aim of this study was to investigate the effects of TIMP3 on cardiac energy homeostasis during increased metabolic stress conditions.

METHODS

ApoE(-/-)TIMP3(-/-) and ApoE(-/-) mice on a C57BL/6 background were subjected to telemetric ECG analysis and experimental myocardial infarction as models of cardiac stress induction. We used Western blot, qRT-PCR, histology, metabolomics, RNA-sequencing and in vivo phenotypical analysis to investigate the molecular mechanisms of altered cardiac energy metabolism.

RESULTS

ApoE(-/-)TIMP3(-/-) revealed decreased lifespan. Telemetric ECG analysis showed increased arrhythmic episodes, and experimental myocardial infarction by left anterior descending artery (LAD) ligation resulted in increased peri-operative mortality together with increased scar formation, ventricular dilatation and a reduction of cardiac function after 4 weeks in the few survivors. Hearts of ApoE(-/-)TIMP3(-/-) exhibited accumulation of neutral lipids when fed a chow diet, which was exacerbated by a high fat, high cholesterol diet. Metabolomics analysis revealed an increase in circulating markers of oxidative stress with a reduction in long chain fatty acids. Using whole heart mRNA sequencing, we identified apelin as a putative modulator of these metabolic defects. Apelin is a regulator of fatty acid oxidation, and we found a reduction in the levels of enzymes involved in fatty acid oxidation in the left ventricle of ApoE(-/-)TIMP3(-/-) mice. Injection of apelin restored the hitherto identified metabolic defects of lipid oxidation.

CONCLUSION

TIMP3 regulates lipid metabolism as well as oxidative stress response via apelin. These findings therefore suggest that TIMP3 maintains metabolic flexibility in the heart, particularly during episodes of increased cardiac stress.

Performance comparison of ultrasound-based methods to assess aortic diameter and stiffness in normal and aneurysmal mice

OBJECTIVE

Several ultrasound-based methods are currently used to assess aortic diameter, circumferential strain and stiffness in mice, but none of them is flawless and a gold standard is lacking. We aimed to assess the validity and sensitivity of these methods in control animals and animals developing dissecting abdominal aortic aneurysm.

METHODS AND RESULTS

We first compared systolic and diastolic diameters as well as local circumferential strains obtained in 47 Angiotensin II-infused ApoE(-/-) mice with three different techniques (BMode, short axis MMode, long axis MMode), at two different abdominal aortic locations (supraceliac and paravisceral), and at three different time points of abdominal aneurysm formation (baseline, 14 days and 28 days). We found that short axis BMode was preferred to assess diameters, but should be avoided for strains. Short axis MMode gave good results for diameters but high standard deviations for strains. Long axis MMode should be avoided for diameters, and was comparable to short axis MMode for strains. We then compared pulse wave velocity measurements using global, ultrasound-based transit time or regional, pressure-based transit time in 10 control and 20 angiotensin II-infused, anti-TGF-Beta injected C57BL/6 mice. Both transit-time methods poorly correlated and were not able to detect a significant difference in PWV between controls and aneurysms. However, a combination of invasive pressure and MMode diameter, based on radio-frequency data, detected a highly significant difference in local aortic stiffness between controls and aneurysms, with low standard deviation.

CONCLUSIONS

In small animal ultrasound the short axis view is preferred over the long axis view to measure aortic diameters, local methods are preferred over transit-time methods to measure aortic stiffness, invasive pressure-diameter data are preferred over non-invasive strains to measure local aortic stiffness, and the use of radiofrequency data improves the accuracy of diameter, strain as well as stiffness measurements.

Compartment-specific expression of collagens and their processing enzymes in intrapulmonary arteries of IPAH patients

Alterations in extracellular matrix (ECM) have been implicated in the pathophysiology of pulmonary hypertension. Here, we have undertaken a compartment-specific study to elucidate the expression profile of collagens and their processing enzymes in donor and idiopathic pulmonary arterial hypertension (IPAH) pulmonary arteries. Predominant intimal, but also medial and perivascular, remodeling and reduced lumen diameter were detected in IPAH pulmonary arteries. Two-photon microscopy demonstrated accumulation of collagen fibers. Quantification of collagen in pulmonary arteries revealed collagen accumulation mainly in the intima of IPAH pulmonary arteries compared with donors. Laser capture-microdissected pulmonary artery profiles (intima+media and perivascular tissue) were analyzed by real-time PCR for ECM gene expression. In the intima+media of IPAH vessels, collagens (COL4A5, COL14A1, and COL18A1), matrix metalloproteinase (MMP) 19, and a disintegrin and metalloprotease (ADAM) 33 were higher expressed, whereas MMP10, ADAM17, TIMP1, and TIMP3 were less abundant. Localization of COLXVIII, its cleavage product endostatin, and MMP10, ADAM33, and TIMP1 was confirmed in pulmonary arteries by immunohistochemistry. ELISA for collagen XVIII/endostatin demonstrated significantly elevated plasma levels in IPAH patients compared with donors, whereas circulating MMP10, ADAM33, and TIMP1 levels were similar between the two groups. Endostatin levels were correlated with pulmonary arterial wedge pressure, and established prognostic markers of IPAH, right atrial pressure, cardiac index, 6-min walking distance, NH2-terminal pro-brain natriuretic peptide, and uric acid. Expression of unstudied collagens, MMPs, ADAMs, and TIMPs were found to be significantly altered in IPAH intima+media. Elevated levels of circulating collagen XVIII/endostatin are associated with markers of a poor prognosis.

Divergent Roles of Matrix Metalloproteinase 2 in Pathogenesis of Thoracic Aortic Aneurysm

Objective—

Aortic aneurysm, focal dilation of the aorta, results from impaired integrity of aortic extracellular matrix (ECM). Matrix metalloproteinases (MMPs) are traditionally known as ECM-degrading enzymes. MMP2 has been associated with aneurysm in patients and in animal models. We investigated the role of MMP2 in thoracic aortic aneurysm using 2 models of aortic remodeling and aneurysm.

Approach and Results—

Male 10-week-old MMP2-deficient (MMP2 −/− ) and wild-type mice received angiotensin II (Ang II, 1.5 mg/kg/day) or saline (Alzet pump) for 4 weeks. Although both genotypes exhibited dilation of the ascending aorta after Ang II infusion, MMP2 −/− mice showed more severe dilation of the thoracic aorta and thoracic aortic aneurysm. The Ang II–induced increase in elastin and collagen (mRNA and protein) was markedly suppressed in MMP2 −/− thoracic aorta and smooth muscle cells, whereas only mRNA levels were reduced in MMP2 −/− -Ang II abdominal aorta. Consistent with the absence of MMP2, proteolytic activities were lower in MMP2 −/− -Ang II compared with wild-type-Ang II thoracic and abdominal aorta. MMP2-deficiency suppressed the activation of latent transforming growth factor-β and the Smad2/3 pathway in vivo and in vitro. Intriguingly, MMP2 −/− mice were protected against CaCl 2 -induced thoracic aortic aneurysm, which triggered ECM degradation but not synthesis.

Conclusions—

This study reveals the dual role of MMP2 in ECM degradation, as well as ECM synthesis. Moreover, the greater susceptibility of the thoracic aorta to impaired ECM synthesis, compared with vulnerability of the abdominal aorta to aberrant ECM degradation, provides an insight into the regional susceptibility of the aorta to aneurysm development.

Pharmacological inhibitor of notch signaling stabilizes the progression of small abdominal aortic aneurysm in a mouse model

Background

The progression of abdominal aortic aneurysm (AAA) involves a sustained influx of proinflammatory macrophages, which exacerbate tissue injury by releasing cytokines, chemokines, and matrix metalloproteinases. Previously, we showed that Notch deficiency reduces the development of AAA in the angiotensin II–induced mouse model by preventing infiltration of macrophages. Here, we examined whether Notch inhibition in this mouse model prevents progression of small AAA and whether these effects are associated with altered macrophage differentiation.

Methods and Results

Treatment with pharmacological Notch inhibitor (DAPT [N‐(N‐[3,5‐difluorophenacetyl]‐L‐alanyl)‐S‐phenylglycine t‐butyl ester]) at day 3 or 8 of angiotensin II infusion arrested the progression of AAA in Apoe^−/− mice, as demonstrated by a decreased luminal diameter and aortic width. The abdominal aortas of Apoe^−/− mice treated with DAPT showed decreased expression of matrix metalloproteinases and presence of elastin precursors including tropoelastin and hyaluronic acid. Marginal adventitial thickening observed in the aorta of DAPT‐treated Apoe^−/− mice was not associated with increased macrophage content, as observed in the mice treated with angiotensin II alone. Instead, DAPT‐treated abdominal aortas showed increased expression of Cd206‐positive M2 macrophages and decreased expression of Il12‐positive M1 macrophages. Notch1 deficiency promoted M2 differentiation of macrophages by upregulating transforming growth factor β2 in bone marrow–derived macrophages at basal levels and in response to IL4. Protein expression of transforming growth factor β2 and its downstream effector pSmad2 also increased in DAPT‐treated Apoe^−/− mice, indicating a potential link between Notch and transforming growth factor β2 signaling in the M2 differentiation of macrophages.

Conclusions

Pharmacological inhibitor of Notch signaling prevents the progression of AAA by macrophage differentiation–dependent mechanisms. The study also provides insights for novel therapeutic strategies to prevent the progression of small AAA.

Proteomic study of the microdissected aortic media in human thoracic aortic aneurysms

Aortic aneurysm is a complex multifactorial disease, and its molecular mechanism is not understood. In thoracic aortic aneurysm (TAA), the expansion of the aortic wall is lead by extracellular matrix (ECM) degeneration in the medial layer, which leads to weakening of the aortic wall. This dilatation may end in rupture and-if untreated-death. The aortic media is composed of vascular smooth muscle cells (VSMCs) and proteins involved in aortic elasticity and distensibility. Delineating their functional and quantitative decrease is critical in elucidating the disease causing mechanisms as well as the development of new preventive therapies. Laser microdissection (LMD) is an advanced technology that enables the isolation of the desired portion of tissue or cells for proteomics analysis, while preserving their integrity. In our study, the aortic media layers of 36 TAA patients and 8 controls were dissected using LMD technology. The proteins isolated from these tissue samples were subjected to comparative proteomic analysis by nano-LC-MS/MS, which enabled the identification of 352 proteins in aortic media. Among these, 41 proteins were differentially expressed in the TAA group with respect to control group, and all were downregulated in the patients. Of these medial proteins, 25 are novel, and their association with TAA is reported for the first time in our study. Subsequent analysis of the data by ingenuity pathway analysis (IPA) shows that the majority of differentially expressed proteins were found to be cytoskeletal-associated proteins and components of the ECM which are critical in maintaining aortic integrity. Our results indicate that the protein expression profile in the aortic media from TAA patients differs significantly from controls. Further analysis of the mechanism points to markers of pathological ECM remodeling, which, in turn, affect VSMC cytosolic structure and architecture. In the future, the detailed investigation of the differentially expressed proteins may provide insight into the elucidation of the pathological processes underlying aneurysms.

Matrix metalloproteinases are involved in cardiovascular diseases

This MiniReview describes the essential biochemical and molecular aspects of matrix metalloproteinases (MMPs) and briefly discusses how they engage in different diseases, with particular emphasis on cardiovascular diseases. There is compelling scientific evidence that many MMPs, especially MMP-2, play important roles in the development of cardiovascular diseases; inhibition of these enzymes is beneficial to many cardiovascular conditions, sometimes precluding or postponing end-organ damage and fatal outcomes. Conducting comprehensive discussions and further studies on how MMPs participate in cardiovascular diseases is important, because inhibition of these enzymes may be an alternative or an adjuvant for current cardiovascular disease therapy.

Myocardial recovery from ischemia-reperfusion is compromised in the absence of tissue inhibitor of metalloproteinase 4

BACKGROUND

Myocardial reperfusion after ischemia (I/R), although an effective approach in rescuing the ischemic myocardium, can itself trigger several adverse effects including aberrant remodeling of the myocardium and its extracellular matrix. Tissue inhibitor of metalloproteinases (TIMPs) protect the extracellular matrix against excess degradation by matrix metalloproteinases (MMPs). TIMP4 levels are reduced in myocardial infarction; however, its causal role in progression of post-I/R injury has not been explored.

METHODS AND RESULTS

In vivo I/R (20-minute ischemia, 1-week reperfusion) resulted in more severe systolic and diastolic dysfunction in TIMP4(-/-) mice with enhanced inflammation, oxidative stress (1 day post-I/R), hypertrophy, and interstitial fibrosis (1 week). After an initial increase in TIMP4 (1 day post-I/R), TIMP4 mRNA and protein decreased in the ischemic myocardium from wild-type mice by 1 week post-I/R and in tissue samples from patients with myocardial infarction, which correlated with enhanced activity of membrane-bound MMP, membrane-type 1 MMP. By 4 weeks post-I/R, wild-type mice showed no cardiac dysfunction, elevated TIMP4 levels (to baseline), and normalized membrane-type 1 MMP activity. TIMP4-deficient mice, however, showed exacerbated diastolic dysfunction, sustained elevation of membrane-type 1 MMP activity, and worsened myocardial hypertrophy and fibrosis. Ex vivo I/R (20- or 30-minute ischemia, 45-minute reperfusion) resulted in comparable cardiac dysfunction in wild-type and TIMP4(-/-) mice.

CONCLUSIONS

TIMP4 is essential for recovery from myocardial I/R in vivo, primarily because of its membrane-type 1 MMP inhibitory function. TIMP4 deficiency does not increase susceptibility to ex vivo I/R injury. Replenishment of myocardial TIMP4 could serve as an effective therapy in post-I/R recovery for patients with reduced TIMP4.

Loss of NOX2 (gp91phox) prevents oxidative stress and progression to advanced heart failure

Oxidative stress plays a key pathogenic role in experimental and human heart failure. However, the source of ROS (reactive oxygen species) is a key determinant of the cardiac adaptation to pathological stressors. In the present study, we have shown that human dilated cardiomyopathy is associated with increased NOX2 (NADPH oxidase 2) levels, increased oxidative stress with adverse myocardial remodelling and activation of MAPKs (mitogen-activated protein kinases). Advanced heart failure in mice was also associated with increased NOX2 levels. Furthermore, we have utilized the pressure-overload model to examine the role of NOX2 in advanced heart failure. Increased cardiomyocyte hypertrophy and myocardial fibrosis in response to pressure overload correlated with increased oxidative stress, and loss of NOX2 prevented the increase in oxidative stress, development of cardiomyocyte hypertrophy, myocardial fibrosis and increased myocardial MMP (matrix metalloproteinase) activity in response to pressure overload. Consistent with these findings, expression of disease markers revealed a marked suppression of atrial natriuretic factor, β-myosin heavy chain, B-type natriuretic peptide and α-skeletal actin expression in pressure-overloaded hearts from NOX2-deficient mice. Activation of MAPK signalling, a well-known mediator of pathological remodelling, was lowered in hearts from NOX2-deficient mice in response to pressure overload. Functional assessment using transthoracic echocardiography and invasive pressure-volume loop analysis showed a marked protection in diastolic and systolic dysfunction in pressure-overloaded hearts from NOX2-deficient mice. Loss of NOX2 prevented oxidative stress in heart disease and resulted in sustained protection from the progression to advanced heart failure. Our results support a key pathogenic role of NOX2 in murine and human heart failure, and specific therapy antagonizing NOX2 activity may have therapeutic effects in advanced heart failure.