MyD88-dependent, superoxide-initiated inflammation is necessary for flow-mediated inward remodeling of conduit arteries

Tie2-Cre-Induced Inactivation of Non-Nuclear Estrogen Receptor-α Signaling Abrogates Estrogen Protection Against Vascular Injury

Using the Cre-loxP system, we generated the first mouse model in which estrogen receptor-α non-nuclear signaling was inactivated in endothelial cells. Estrogen protection against mechanical vascular injury was impaired in this model. This result indicates the pivotal role of endothelial estrogen receptor-α non-nuclear signaling in the vasculoprotective effects of estrogen.

Detection of superoxide radical in all biological systems by Thin Layer Chromatography

The study presents a new method that detects O₂^•-, via quantification of 2-hydroxyethidium (2-ΟΗ-Ε⁺) as low as ∼30 fmoles by High-Performance Thin Layer Chromatography (HPTLC). The method isolates 2-ΟΗ-Ε⁺ after its extraction by the anionic detergent SDS (at 18-fold higher than its CMC) together with certain organic/inorganic reagents, and its HPTLC-separation from di-ethidium (di-Ε⁺) and ethidium (Ε⁺). Quantification of 2-OH-E⁺ is based on its ex/em maxima at 290/540 nm, and of di-E⁺ and E⁺ at 295/545 nm. The major innovations of the present method are the development of protocols for (i) efficient extraction (by SDS) and (ii) sensitive quantification (by HPTLC) for 2-OH-E⁺ (as well as di-E⁺ and E⁺) from most biological systems (animals, plants, cells, subcellular compartments, fluids). The method extracts 2-ΟΗ-Ε⁺ (by neutralizing the strong binding between its quaternary N⁺ and negatively charged sites on phospholipids, DNA etc) together with free HE, while protects both from biological oxidases, and also extracts/quantifies total proteins (hydrophilic and hydrophobic) for expressing O₂^•- levels per protein quantity. The method also uses SDS (at 80-fold lower than its CMC) to extract/remove/wash 2-ΟΗ-Ε⁺ from cell/organelle exterior membrane sites, for more accurate internal content quantification. The new method is applied on indicative biological systems: (1) artificially stressed (mouse organs and liver mitochondria and nuclei, ±exposed to paraquat, a known O₂^•- generator), and (2) physiologically stressed (cauliflower plant, exposed to light/dark).

Excessive adventitial stress drives inflammation-mediated fibrosis in hypertensive aortic remodelling in mice

Hypertension induces significant aortic remodelling, often adaptive but sometimes not. To identify immuno-mechanical mechanisms responsible for differential remodelling, we studied thoracic aortas from 129S6/SvEvTac and C57BL/6 J mice before and after continuous 14-day angiotensin II infusion, which elevated blood pressure similarly in both strains. Histological and biomechanical assessments of excised vessels were similar at baseline, suggesting a common homeostatic set-point for mean wall stress. Histology further revealed near mechano-adaptive remodelling of the hypertensive 129S6/SvEvTac aortas, but a grossly maladaptive remodelling of C57BL/6 J aortas. Bulk RNA sequencing suggested that increased smooth muscle contractile processes promoted mechano-adaptation of 129S6/SvEvTac aortas while immune processes prevented adaptation of C57BL/6 J aortas. Functional studies confirmed an increased vasoconstrictive capacity of the former while immunohistochemistry demonstrated marked increases in inflammatory cells in the latter. We then used multiple computational biomechanical models to test the hypothesis that excessive adventitial wall stress correlates with inflammatory cell infiltration. These models consistently predicted that increased vasoconstriction against an increased pressure coupled with modest deposition of new matrix thickens the wall appropriately, restoring wall stress towards homeostatic consistent with adaptive remodelling. By contrast, insufficient vasoconstriction permits high wall stresses and exuberant inflammation-driven matrix deposition, especially in the adventitia, reflecting compromised homeostasis and gross maladaptation.

Redox-sensitive enzyme SENP3 mediates vascular remodeling via de-SUMOylation of β-catenin and regulation of its stability

Background

Oxidative stress plays critical pathophysiological roles in vascular remodeling-related cardiovascular diseases, including hypertension, atherosclerosis, and restenosis. Previous studies demonstrate that SENP3, a redox-sensitive SUMO2/3-specific protease, is strongly implicated in cancer development and progression. However, the role of SENP3 in vascular remodeling remains unknown.

Methods

We generated three mouse models of vascular remodeling due to low shear stress, hypertension, and atherosclerosis. The expression of SENP3 was determined by western blotting and/or immunofluorescence staining in cultured vascular smooth muscle cells (VSMCs), animal models, and human samples. The biological function of SENP3 in proliferation and migration of VSMC and vascular remodeling was further investigated in vitro and in vivo models.

Findings

SENP3 was highly expressed in VSMCs of remodeled arteries, accompanied by elevated reactive oxygen species (ROS) levels. In cultured VSMCs, SENP3 protein levels were enhanced by oxidized low-density lipoprotein and Angiotensin II in a ROS-dependent manner. SENP3 overexpression significantly promoted and sh-RNA-mediated knockdown markedly inhibited VSMCs proliferation and migration. Immunofluorescence staining showed that SENP3 expression was correlated with intimal area in remodeled arteries. Furthermore, we demonstrated that SENP3 interacted with β-catenin and inhibited its proteasome-dependent degradation via de-SUMOylation of β-catenin. Most importantly, SENP3^+/− mice exhibited alleviated vascular remodeling.

Interpretation

Our results highlight the important function of SENP3 as a redox sensor and mediator in vascular remodeling.

Complementary roles of mechanotransduction and inflammation in vascular homeostasis

Arteries are exposed to relentless pulsatile haemodynamic loads, but via mechanical homeostasis they tend to maintain near optimal structure, properties and function over long periods in maturity in health. Numerous insults can compromise such homeostatic tendencies, however, resulting in maladaptations or disease. Chronic inflammation can be counted among the detrimental insults experienced by arteries, yet inflammation can also play important homeostatic roles. In this paper, we present a new theoretical model of complementary mechanobiological and immunobiological control of vascular geometry and composition, and thus properties and function. We motivate and illustrate the model using data for aortic remodelling in a common mouse model of induced hypertension. Predictions match the available data well, noting a need for increased data for further parameter refinement. The overall approach and conclusions are general, however, and help to unify two previously disparate literatures, thus leading to deeper insight into the separate and overlapping roles of mechanobiology and immunobiology in vascular health and disease.

Mechanisms of Vascular Remodeling in Hypertension

Hypertension is both a cause and a consequence of central artery stiffening, which in turn is an initiator and indicator of myriad disease conditions and thus all-cause mortality. Such stiffening results from a remodeling of the arterial wall that is driven by mechanical stimuli and mediated by inflammatory signals, which together lead to differential gene expression and concomitant changes in extracellular matrix composition and organization. This review focuses on biomechanical mechanisms by which central arteries remodel in hypertension within the context of homeostasis-what promotes it, what prevents it. It is suggested that the vasoactive capacity of the wall and inflammatory burden strongly influence the ability of homeostatic mechanisms to adapt the arterial wall to high blood pressure or not. Maladaptation, often reflected by inflammation-driven adventitial fibrosis, not just excessive intimal-medial thickening, significantly diminishes central artery function and disturbs hemodynamics, ultimately compromising end organ perfusion and thus driving the associated morbidity and mortality. It is thus suggested that there is a need for increased attention to controlling both smooth muscle phenotype and inflammation in hypertensive remodeling of central arteries, with future studies of the often adaptive response of medium-sized muscular arteries promising to provide additional guidance.

Resveratrol and the Interaction between Gut Microbiota and Arterial Remodelling

Arterial remodelling refers to the alteration in the structure of blood vessel that contributes to the progression of hypertension and other cardiovascular complications. Arterial remodelling is orchestrated by the crosstalk between the endothelium and vascular smooth muscle cells (VSMC). Vascular inflammation participates in arterial remodelling. Resveratrol is a natural polyphenol that possesses anti-oxidant and anti-inflammatory properties and has beneficial effects in both the endothelium and VSMC. Resveratrol has been studied for the protective effects in arterial remodelling and gut microbiota, respectively. Gut microbiota plays a critical role in the immune system and inflammatory processes. Gut microbiota may also regulate vascular remodelling in cardiovascular complications via affecting endothelium function and VSMC proliferation. Currently, there is new evidence showing that gut microbiota regulate the proliferation of VSMC and the formation of neointimal hyperplasia in response to injury. The change in population of the gut microbiota, as well as their metabolites (e.g., short-chain fatty acids) could critically contribute to VSMC proliferation, cell cycle progression, and migration. Recent studies have provided strong evidence that correlate the effects of resveratrol in arterial remodelling and gut microbiota. This review aims to summarize recent findings on the resveratrol effects on cardiovascular complications focusing on arterial remodelling and discuss the possible interactions of resveratrol and the gut microbiota that modulate arterial remodelling.

Short AIP1 (ASK1-Interacting Protein-1) Isoform Localizes to the Mitochondria and Promotes Vascular Dysfunction

OBJECTIVE

Vascular endothelial cells (ECs) normally maintain vascular homeostasis and are regulated by proinflammatory cytokines and reactive oxygen species. A human genome-wide association study identified that AIP1 (ASK1 [apoptosis signal-regulating kinase 1]-interacting protein-1; also identified as DAB2IP) gene variants confer susceptibility to cardiovascular disease, but the underlying mechanism is unknown. Approach and Results: We detected a normal AIP1 form (named AIP1A) in the healthy aorta, but a shorter form of AIP1 (named AIP1B) was found in diseased aortae that contained atherosclerotic plaques and graft arteriosclerosis. AIP1B transcription in resting ECs was suppressed through epigenetic inhibition by RIF1 (Rap1 [ras-related protein 1]-interacting factor 1)/H3K9 (histone H3 lysine 9) methyltransferase-mediated H3K9 trimethylation, and this inhibition was released by proinflammatory cytokines. AIP1A, but not AIP1B, was downregulated by proteolytic degradation through a Smurf1 (SMAD [suppressor of mothers against decapentaplegic miscellaneous] ubiquitylation regulatory factor 1)-dependent pathway in ECs under inflammation. Therefore, AIP1B was the major form present during inflammatory conditions. AIP1B, which lacks the N-terminal pleckstrin homology domain of AIP1A, localized to the mitochondria and augmented TNFα (tumor necrosis factor alpha)-induced mitochondrial reactive oxygen species generation and EC activation. AIP1B-ECTG (EC-specific AIP1B transgenic) mice exhibited augmented reactive oxygen species production, EC activation, and neointima formation in vascular remodeling models.

CONCLUSIONS

Our current study suggests that a shift from anti-inflammatory AIP1A to proinflammatory AIP1B during chronic inflammation plays a key role in inflammatory vascular diseases.

Dynamic and diverse changes in the functional properties of vascular smooth muscle cells in pulmonary hypertension

Pulmonary hypertension (PH) is the end result of interaction between pulmonary vascular tone and a complex series of cellular and molecular events termed 'vascular remodelling'. The remodelling process, which can involve the entirety of pulmonary arterial vasculature, almost universally involves medial thickening, driven by increased numbers and hypertrophy of its principal cellular constituent, smooth muscle cells (SMCs). It is noted, however that SMCs comprise heterogeneous populations of cells, which can exhibit markedly different proliferative, inflammatory, and extracellular matrix production changes during remodelling. We further consider that these functional changes in SMCs of different phenotype and their role in PH are dynamic and may undergo significant changes over time (which we will refer to as cellular plasticity); no single property can account for the complexity of the contribution of SMC to pulmonary vascular remodelling. Thus, the approaches used to pharmacologically manipulate PH by targeting the SMC phenotype(s) must take into account processes that underlie dominant phenotypes that drive the disease. We present evidence for time- and location-specific changes in SMC proliferation in various animal models of PH; we highlight the transient nature (rather than continuous) of SMC proliferation, emphasizing that the heterogenic SMC populations that reside in different locations along the pulmonary vascular tree exhibit distinct responses to the stresses associated with the development of PH. We also consider that cells that have often been termed 'SMCs' may arise from many origins, including endothelial cells, fibroblasts and resident or circulating progenitors, and thus may contribute via distinct signalling pathways to the remodelling process. Ultimately, PH is characterized by long-lived, apoptosis-resistant SMC. In line with this key pathogenic characteristic, we address the acquisition of a pro-inflammatory phenotype by SMC that is essential to the development of PH. We present evidence that metabolic alterations akin to those observed in cancer cells (cytoplasmic and mitochondrial) directly contribute to the phenotype of the SM and SM-like cells involved in PH. Finally, we raise the possibility that SMCs transition from a proliferative to a senescent, pro-inflammatory and metabolically active phenotype over time.

Multiorgan Development of Oxidative and Nitrosative Stress in LPS-Induced Endotoxemia in C57Bl/6 Mice: DHE-Based In Vivo Approach

Detection of free radicals in tissues is challenging. Most approaches rely on incubating excised sections or homogenates with reagents, typically at supraphysiologic oxygen tensions, to finally detect surrogate, nonspecific end products. In the present work, we explored the potential of using intravenously (i.v.) injected dihydroethidine (DHE) to detect superoxide radical (O₂ ^∙-) abundance in vivo by quantification of the superoxide-specific DHE oxidation product, 2-hydroxyethidium (2-OH-E⁺), as well as ethidium (E⁺) and DHE in multiple tissues in a murine model of endotoxemia induced by lipopolysaccharide (LPS). LPS was injected intraperitoneally (i.p.), while DHE was delivered via the tail vein one hour before sacrifice. Tissues (kidney, lung, liver, and brain) were harvested and subjected to HPLC/fluorescent analysis of DHE and its monomeric oxidation products. In parallel, electron spin resonance (EPR) spin trapping was used to measure nitric oxide (^∙NO) production in the aorta, lung, and liver isolated from the same mice. Endotoxemic inflammation was validated by analysis of plasma biomarkers. The concentration of 2-OH-E⁺ varied in the liver, lung, and kidney; however, the ratios of 2-OH-E⁺/E⁺ and 2-OH-E⁺/DHE were increased in the liver and kidney but not in the lung or the brain. An LPS-induced robust level of ^∙NO burst was observed in the liver, whereas the lung demonstrated a moderate yet progressive increase in the rate of ^∙NO production. Interestingly, endothelial dysfunction was observed in the aorta, as evidenced by decreased ^∙NO production 6 hours post-LPS injection that coincided with the inflammatory burden of endotoxemia (e.g. elevated serum amyloid A and prostaglandin E₂). Combined, these data demonstrate that systemic delivery of DHE affords the capacity to specifically detect O₂ ^∙- production in vivo. Furthermore, the ratio of 2-OH-E⁺/E⁺ oxidation products in tissues provides a tool for comparative insight into the oxidative environments in various organs. Based on our findings, we demonstrate that the endotoxemic liver is susceptible to both O₂ ^∙--mediated and nonspecific oxidant stress as well as nitrosative stress. Oxidant stress in the lung was detected to a lesser extent, thus underscoring a differential response of liver and lung to endotoxemic injury induced by intraperitoneal LPS injection.

Inflammation, Immunity, and Oxidative Stress in Hypertension-Partners in Crime?

Hypertension is considered as the most common risk factor for cardiovascular disease. Inflammatory processes link hypertension and cardiovascular disease, and participate in their pathophysiology. In recent years, there has been an increase in research focused on unraveling the role of inflammation and immune activation in development and maintenance of hypertension. Although inflammation is known to be associated with hypertension, whether inflammation is a cause or effect of hypertension remains to be elucidated. This review describes the recent studies that link inflammation and hypertension and demonstrate the involvement of oxidative stress and endothelial dysfunction-two of the key processes in the development of hypertension. Etiology of hypertension, including novel immune cell subtypes, cytokines, toll-like receptors, inflammasomes, and gut microbiome, found to be associated with inflammation and hypertension are summarized and discussed. Most recent findings in this field are presented with special emphasis on potential of anti-inflammatory drugs and statins for treatment of hypertension.

Perivascular adipose tissue modulates carotid plaque formation induced by disturbed flow in mice

OBJECTIVE

Emerging evidence shows that perivascular adipose tissue (PVAT) is crucially involved in inflammation and cardiovascular diseases. However, controversial results have been reported regarding the effect of PVAT in atherosclerosis. This study aimed to determine the role of PVAT in disturbed blood flow (d-flow)-induced carotid plaque formation.

METHODS

ApoE^-/- male mice underwent partial carotid ligation (PCL) to induce d-flow in the left carotid artery (LCA) and were fed a high-fat diet for 2 weeks. Oil Red O and hematoxylin and eosin stains were used to determine adipose tissue. Thoracic PVAT from ApoE^-/- or wild-type female mice were transplanted to the LCA of PCL-treated ApoE^-/- mice. Carotid arteries were stained with Sudan IV to detect atherosclerotic lesions. Quantitative real-time reverse transcription polymerase chain reaction and immunofluorescence staining were performed to assess macrophage infiltration.

RESULTS

By 2 weeks of the high-fat diet after PCL surgery, de novo adipose tissue was formed around the ligated LCA, where atherosclerotic plaques were also observed. Quantitative real-time reverse transcription polymerase chain reaction analysis of the newly formed PVAT revealed a similar transcription profile to native PVAT. Treatment with bisphenol A diglycidyl ether, a peroxisome proliferator-activated receptor γ inhibitor, diminished PVAT formation but increased plaque size and macrophage infiltration. Transplantation of thoracic PVAT from wild-type mice (PVAT-T^WT) rather than from ApoE^-/- mice (PVAT-T^ApoE-/-) nearly abrogated LCA plaque macrophage content without affecting plaque size. Mechanistically, PVAT-T^ApoE-/- showed higher messenger RNA levels of inflammatory cytokines compared with PVAT-T^WT.

CONCLUSIONS

Our findings suggest that regulated PVAT formation may confer protection against atherosclerosis-prone shear stress, probably through attenuation of focal inflammation.

Microbiota control acute arterial inflammation and neointimal hyperplasia development after arterial injury

BACKGROUND

The microbiome has a functional role in a number of inflammatory processes and disease states. While neointimal hyperplasia development has been linked to inflammation, a direct role of the microbiota in neointimal hyperplasia has not yet been established. Germ-free (GF) mice are an invaluable model for studying causative links between commensal organisms and the host. We hypothesized that GF mice would exhibit altered neointimal hyperplasia following carotid ligation compared to conventionally raised (CONV-R) mice.

METHODS

Twenty-week-old male C57BL/6 GF mice underwent left carotid ligation under sterile conditions. Maintenance of sterility was assessed by cultivation and 16S rRNA qPCR of stool. Neointimal hyperplasia was assessed by morphometric and histologic analysis of arterial sections after 28 days. Local arterial cell proliferation and inflammation was assessed by immunofluorescence for Ki67 and inflammatory cell markers at five days. Systemic inflammation was assessed by multiplex immunoassays of serum. CONV-R mice treated in the same manner served as the control cohort. GF and CONV-R mice were compared using standard statistical methods.

RESULTS

All GF mice remained sterile during the entire study period. Twenty-eight days after carotid ligation, CONV-R mice had significantly more neointimal hyperplasia development compared to GF mice, as assessed by intima area, media area, intima+media area, and intima area/(intima+media) area. The collagen content of the neointimal lesions appeared qualitatively similar on Masson's trichrome staining. There was significantly reduced Ki67 immunoreactivity in the media and adventitia of GF carotid arteries 5 days after ligation. GF mice also had increased arterial infiltration of anti-inflammatory M2 macrophages compared to CONV-R mouse arteries and a reduced proportion of mature neutrophils. GF mice had significantly reduced serum IFN-γ-inducible protein (IP)-10 and MIP-2 5 days after carotid ligation, suggesting a reduced systemic inflammatory response.

CONCLUSIONS

GF mice have attenuated neointimal hyperplasia development compared to CONV-R mice, which is likely related to altered kinetics of wound healing and acute inflammation. Recognizing the role of commensals in the regulation of arterial remodeling will provide a deeper understanding of the pathophysiology of restenosis and support strategies to treat or reduce restenosis risk by manipulating microbiota.

Lysyl oxidase (LOX) limits VSMC proliferation and neointimal thickening through its extracellular enzymatic activity

Lysyl oxidase (LOX) plays a critical role in extracellular matrix maturation and limits VSMC proliferation and vascular remodeling. We have investigated whether this anti-proliferative effect relies on the extracellular catalytically active LOX or on its biologically active propeptide (LOX-PP). High expression levels of both LOX and LOX-PP were detected in the vascular wall from transgenic mice over-expressing the full-length human LOX cDNA under the control of SM22α promoter (TgLOX), which targets the transgene to VSMC without affecting the expression of mouse LOX isoenzymes. TgLOX VSMC also secrete high amounts of both mature LOX and LOX-PP. Wild-type (WT) mouse VSMC exposed to VSMC supernatants from transgenic animals showed reduced proliferative rates (low [³H]-thymidine uptake and expression of PCNA) than those incubated with conditioned media from WT cells, effect that was abrogated by β-aminopropionitrile (BAPN), an inhibitor of LOX activity. Lentiviral over-expression of LOX, but not LOX-PP, decreased human VSMC proliferation, effect that was also prevented by BAPN. LOX transgenesis neither impacted local nor systemic inflammatory response induced by carotid artery ligation. Interestingly, in this model, BAPN normalized the reduced neointimal thickening observed in TgLOX mice. Therefore, extracellular enzymatically active LOX is required to limit both VSMC proliferation and vascular remodeling.

Detection and Characterization of Reactive Oxygen and Nitrogen Species in Biological Systems by Monitoring Species-Specific Products

SIGNIFICANCE

Since the discovery of the superoxide dismutase enzyme, the generation and fate of short-lived oxidizing, nitrosating, nitrating, and halogenating species in biological systems has been of great interest. Despite the significance of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in numerous diseases and intracellular signaling, the rigorous detection of ROS and RNS has remained a challenge. Recent Advances: Chemical characterization of the reactions of selected ROS and RNS with electron paramagnetic resonance (EPR) spin traps and fluorescent probes led to the establishment of species-specific products, which can be used for specific detection of several forms of ROS and RNS in cell-free systems and in cultured cells in vitro and in animals in vivo. Profiling oxidation products from the ROS and RNS probes provides a rigorous method for detection of those species in biological systems.

CRITICAL ISSUES

Formation and detection of species-specific products from the probes enables accurate characterization of the oxidative environment in cells. Measurement of the total signal (fluorescence, chemiluminescence, etc.) intensity does not allow for identification of the ROS/RNS formed. It is critical to identify the products formed by using chromatographic or other rigorous techniques. Product analyses should be accompanied by monitoring of the intracellular probe level, another factor controlling the yield of the product(s) formed.

FUTURE DIRECTIONS

More work is required to characterize the chemical reactivity of the ROS/RNS probes, and to develop new probes/detection approaches enabling real-time, selective monitoring of the specific products formed from the probes. Antioxid. Redox Signal. 28, 1416-1432.

Endothelial AIP1 Regulates Vascular Remodeling by Suppressing NADPH Oxidase-2

Objective: AIP1 expression is downregulated in human atherosclerotic plaques and global deletion of AIP1 in mice exacerbates atherosclerosis in ApoE-KO mouse models. However, the direct role of AIP1 in endothelium, vascular remodeling and associated vascular diseases has not been determined. Approach and Results: We used endothelial cell (EC)-specific AIP1-deficient (AIP1-ECKO) mice to define the role of AIP1 in vascular remodeling and intima-media thickening in a mouse carotid artery ligation model characterized by both neointimal hyperplasia and inward vessel remodeling. Compared to WT littermates, AIP1-ECKO mice had 2.2-fold larger intima area and 4.4-fold thicker intima as measured by intima/media ratio in arteries with more proliferating vascular smooth muscle cells (VSMCs) at week 2-4 post-injury. Increased reactive oxygen species (ROS) in endothelium at early time points induced inflammation and vessel dysfunction in AIP1-ECKO prior to VSMC accumulations. Moreover, knockdown of AIP1 in human EC enhanced ROS generation which was attenuated by co-silencing of NOX2. Mechanistically, AIP1 via its proline-rich region binds to the SH3 domain of cytosolic subunit p47phox to disrupt formation of an active NOX2 complex, attenuating ROS production. Conclusion: Our study supports that AIP1 regulates vascular remodeling with intima-media thickening by suppressing endothelial NOX2-dependent oxidative stress. Highlights: •In a carotid ligation model, endothelial cell (EC)-specific AIP1-deficient (AIP1-ECKO) mice had much larger media area, thicker vessel wall and augmented neointima formation.•Increased production of reactive oxygen species in vascular EC at early time points concomitant with vessel dysfunction in AIP1-ECKO.•AIP1 via its proline-rich region binds to the SH3 domain of cytosolic subunit p47phox to disrupt formation of an active NOX2 complex, attenuating ROS production.

Vascular remodeling: A redox-modulated mechanism of vessel caliber regulation

Vascular remodeling, i.e. whole-vessel structural reshaping, determines lumen caliber in (patho)physiology. Here we review mechanisms underlying vessel remodeling, with emphasis in redox regulation. First, we discuss confusing terminology and focus on strictu sensu remodeling. Second, we propose a mechanobiological remodeling paradigm based on the concept of tensional homeostasis as a setpoint regulator. We first focus on shear-mediated models as prototypes of remodeling closely dominated by highly redox-sensitive endothelial function. More detailed discussions focus on mechanosensors, integrins, extracellular matrix, cytoskeleton and inflammatory pathways as potential of mechanisms potentially coupling tensional homeostasis to redox regulation. Further discussion of remodeling associated with atherosclerosis and injury repair highlights important aspects of redox vascular responses. While neointima formation has not shown consistent responsiveness to antioxidants, vessel remodeling has been more clearly responsive, indicating that despite the multilevel redox signaling pathways, there is a coordinated response of the whole vessel. Among mechanisms that may orchestrate redox pathways, we discuss roles of superoxide dismutase activity and extracellular protein disulfide isomerase. We then discuss redox modulation of aneurysms, a special case of expansive remodeling. We propose that the redox modulation of vascular remodeling may reflect (1) remodeling pathophysiology is dominated by a particularly redox-sensitive cell type, e.g., endothelial cells (2) redox pathways are temporospatially coordinated at an organ level across distinct cellular and acellular structures or (3) the tensional homeostasis setpoint is closely connected to redox signaling. The mechanobiological/redox model discussed here can be a basis for improved understanding of remodeling and helps clarifying mechanisms underlying prevalent hard-to-treat diseases.

Cathepsin L promotes Vascular Intimal Hyperplasia after Arterial Injury

The inflammatory pathways that drive the development of intimal hyperplasia (IH) following arterial injury are not fully understood. We hypothesized that the lysosomal cysteine protease cathepsin L activates processes leading to IH after arterial injury. Using a mouse model of wire-induced carotid artery injury we showed that cathepsin L activity peaks at day 7 and remains elevated to 28 days. The genetic deletion of cathepsin L prevented IH and monocyte recruitment in the carotid wall. The injury-induced increases in cathepsin L mRNA and activity were mitigated in mice with myeloid-specific deletion of toll like receptor 4 (TLR4) or myeloid differentiation primary response gene 88 (MyD88). We further discovered that a HIV-protease inhibitor saquinavir (SQV), which is known to block recombinant mouse cathepsin L activity in vitro, prevented IH after arterial injury. SQV also suppressed LPS (TLR4 agonist) induced monocyte adhesion to endothelial monolayers. These findings establish cathepsin L as a critical regulator of the inflammation that leads to IH and that the TLR4- MyD88 pathway in myeloid lineages regulates cathepsin L expression in the vessel wall following wire injury. The FDA approved drug, SQV blocks IH though mechanisms that may include the suppression of cathepsin L.

Tumor-associated macrophages drive spheroid formation during early transcoelomic metastasis of ovarian cancer

Tumor-associated macrophages (TAMs) can influence ovarian cancer growth, migration, and metastasis, but the detailed mechanisms underlying ovarian cancer metastasis remain unclear. Here, we have shown a strong correlation between TAM-associated spheroids and the clinical pathology of ovarian cancer. Further, we have determined that TAMs promote spheroid formation and tumor growth at early stages of transcoelomic metastasis in an established mouse model for epithelial ovarian cancer. M2 macrophage-like TAMs were localized in the center of spheroids and secreted EGF, which upregulated αMβ2 integrin on TAMs and ICAM-1 on tumor cells to promote association between tumor cells and TAM. Moreover, EGF secreted by TAMs activated EGFR on tumor cells, which in turn upregulated VEGF/VEGFR signaling in surrounding tumor cells to support tumor cell proliferation and migration. Pharmacological blockade of EGFR or antibody neutralization of ICAM-1 in TAMs blunted spheroid formation and ovarian cancer progression in mouse models. These findings suggest that EGF secreted from TAMs plays a critical role in promoting early transcoelomic metastasis of ovarian cancer. As transcoelomic metastasis is also associated with many other cancers, such as pancreatic and colon cancers, our findings uncover a mechanism for TAM-mediated spheroid formation and provide a potential target for the treatment of ovarian cancer and other transcoelomic metastatic cancers.

Fibroblast growth factor (FGF) signaling regulates transforming growth factor beta (TGFβ)-dependent smooth muscle cell phenotype modulation

Smooth muscle cells (SMCs) in normal blood vessels exist in a highly differentiate state characterized by expression of SMC-specific contractile proteins ("contractile phenotype"). Following blood vessel injury in vivo or when cultured in vitro in the presence of multiple growth factors, SMC undergo a phenotype switch characterized by the loss of contractile markers and appearance of expression of non-muscle proteins ("proliferative phenotype"). While a number of factors have been reported to modulate this process, its regulation remains uncertain. Here we show that induction of SMC FGF signaling inhibits TGFβ signaling and converts contractile SMCs to the proliferative phenotype. Conversely, inhibition of SMC FGF signaling induces TGFβ signaling converting proliferating SMCs to the contractile phenotype, even in the presence of various growth factors in vitro or vascular injury in vivo. The importance of this signaling cross-talk is supported by in vivo data that show that an SMC deletion of a pan-FGF receptor adaptor Frs2α (fibroblast growth factor receptor substrate 2 alpha) in mice profoundly reduces neointima formation and vascular remodelling following carotid artery ligation. These results demonstrate that FGF-TGFβ signaling antagonism is the primary regulator of the SMC phenotype switch. Manipulation of this cross-talk may be an effective strategy for treatment of SMC-proliferation related diseases.

Metabolic reprogramming and inflammation act in concert to control vascular remodeling in hypoxic pulmonary hypertension

Pulmonary hypertension (PH) is a complex, multifactorial syndrome that remains poorly understood despite decades of research. PH is characterized by profound pulmonary artery (PA) remodeling that includes significant fibro-proliferative and inflammatory changes of the PA adventitia. In line with the emerging concept that PH shares key features with cancer, recent work centers on the idea that PH results from a multistep process driven by reprogramming of gene-expression patterns that govern changes in cell metabolism, inflammation, and proliferation. Data demonstrate that in addition to PA endothelial cells and smooth muscle cells, adventitial fibroblasts from animals with experimental hypoxic PH and from humans with PH (hereafter, termed PH-Fibs) exhibit proinflammatory activation, increased proliferation, and apoptosis resistance, all in the context of metabolic reprogramming to aerobic glycolysis. PH-Fibs can also recruit, retain, and activate naïve macrophages (Mϕ) toward a proinflammatory/proremodeling phenotype through secretion of chemokines, cytokines, and glycolytic metabolites, among which IL-6 and lactate play key roles. Furthermore, these fibroblast-activated Mϕ (hereafter, termed FAMϕ) exhibit aerobic glycolysis together with high expression of arginase 1, Vegfa, and I1lb, all of which require hypoxia-inducible factor 1α and STAT3 signaling. Strikingly, in situ, the adventitial Mϕ phenotype in the remodeled PA closely resembles the Mϕ phenotype induced by fibroblasts in vitro (FAMϕ), suggesting that FAMϕ crosstalk involving metabolic and inflammatory signals is a critical, pathogenetic component of vascular remodeling. This review discusses metabolic and inflammatory changes in fibroblasts and Mϕ in PH with the goal of raising ideas about new interventions to abrogate remodeling in hypoxic forms of PH.

Toll-like receptor 4 contributes to vascular remodelling and endothelial dysfunction in angiotensin II-induced hypertension

BACKGROUND AND PURPOSE

Toll-like receptor 4 (TLR4) signalling contributes to inflammatory cardiovascular diseases, but its role in hypertension and the associated vascular damage is not known. We investigated whether TLR4 activation contributed to angiotensin II (AngII)-induced hypertension and the associated vascular structural, mechanical and functional alterations.

EXPERIMENTAL APPROACH

AngII was infused (1.44 mg · kg(-1) · day(-1), s.c.) for 2 weeks in C57BL6 mice, treated with a neutralizing anti-TLR4 antibody or IgG (1 μg · day(-1); systolic BP (SBP) and aortic cytokine levels were measured. Structural, mechanical and contractile properties of aortic and mesenteric arterial segments were measured with myography and histology. RT-PCR and Western blotting were used to analyse these tissues and cultured vascular smooth muscle cells (VSMC) from hypertensive rats (SHR).

KEY RESULTS

Aortic TLR4 mRNA levels were raised by AngII infusion. Anti-TLR4 antibody treatment of AngII-treated mice normalised: (i) increased SBP and TNF-α, IL-6 and CCL2 levels; (ii) vascular structural and mechanical changes; (iii) altered aortic phenylephrine- and ACh-induced responses; (iv) increased NOX-1 mRNA levels, superoxide anion production and NAD(P)H oxidase activity and effects of catalase, apocynin, ML-171 and Mito-TEMPO on vascular responses; and (v) reduced NO release and effects of L-NAME on phenylephrine-induced contraction. In VSMC, the MyD88 inhibitor ST-2825 reduced AngII-induced NAD(P)H oxidase activity. The TLR4 inhibitor CLI-095 reduced AngII-induced increased phospho-JNK1/2 and p65 NF-κB subunit nuclear protein expression.

CONCLUSIONS AND IMPLICATIONS

TLR4 up-regulation by AngII contributed to the inflammation, endothelial dysfunction, vascular remodelling and stiffness associated with hypertension by mechanisms involving oxidative stress. MyD88-dependent activation and JNK/NF-κB signalling pathways participated in these alterations.

Inflammatory and immune responses in the arterial media

Inflammatory arterial diseases differentially affect the compartments of the vessel wall. The intima and adventitia are commonly involved by the disease process, with luminal and microvascular endothelial cells playing a critical role in the recruitment and activation of leukocytes. In contrast, the avascular media is often spared by immune-mediated disorders. Surprisingly, vascular smooth muscle cells (VSMCs), the predominant and often exclusive cell type of the media, are capable of robust proinflammatory responses to diverse stressors. The multiple cytokines and chemokines produced within the media can profoundly affect macrophage and T cell function, thus amplifying and shaping innate and adaptive immune responses. On the other hand, VSMCs and the extracellular matrix that they produce also display significant anti-inflammatory properties. The balance between the pro- and anti-inflammatory effects of VSMCs and their extracellular matrix versus the strength of the inciting immunologic events determines the pattern of medial pathology. Limitations on the extent of medial infiltration and injury, defined as medial immunoprivilege, are typically seen in arteriosclerotic diseases, such as atherosclerosis and transplant vasculopathy. Conversely, breakdown of medial immunoprivilege that manifests as more intense leukocytic infiltrates, loss of VSMCs, and destruction of the extracellular matrix architecture is a general feature of certain aneurysmal diseases and vasculitides. In this review, we consider the inflammatory and immune functions of VSMCs and how they may lead to medial immunoprivilege or medial inflammation in arterial diseases.

A comparative review of the hemodynamics and pathogenesis of cerebral and abdominal aortic aneurysms: lessons to learn from each other

OBJECTIVE

Cerebral aneurysms (CAs) and abdominal aortic aneurysms (AAAs) are degenerative vascular pathologies that manifest as abnormal dilations of the arterial wall. They arise with different morphologies in different types of blood vessels under different hemodynamic conditions. Although treated as different pathologies, we examine common pathways in their hemodynamic pathogenesis in order to elucidate mechanisms of formation.

MATERIALS AND METHODS

A systematic review of the literature was performed. Current concepts on pathogenesis and hemodynamics were collected and compared.

RESULTS

CAs arise as saccular dilations on the cerebral arteries of the circle of Willis under high blood flow, high wall shear stress (WSS), and high wall shear stress gradient (WSSG) conditions. AAAs arise as fusiform dilations on the infrarenal aorta under low blood flow, low, oscillating WSS, and high WSSG conditions. While at opposite ends of the WSS spectrum, they share high WSSG, a critical factor in arterial remodeling. This alone may not be enough to initiate aneurysm formation, but may ignite a cascade of downstream events that leads to aneurysm development. Despite differences in morphology and the structure, CAs and AAAs share many histopathological and biomechanical characteristics. Endothelial cell damage, loss of elastin, and smooth muscle cell loss are universal findings in CAs and AAAs. Increased matrix metalloproteinases and other proteinases, reactive oxygen species, and inflammation also contribute to the pathogenesis of both aneurysms.

CONCLUSION

Our review revealed similar pathways in seemingly different pathologies. We also highlight the need for cross-disciplinary studies to aid in finding similarities between pathologies.

Interleukin-1 receptor antagonist originating from bone marrowderived cells and non-bone marrow-derived cells helps to suppress arterial inflammation and reduce neointimal formation after injury

AIM

Interleukin-1 receptor antagonist (IL-1Ra) negatively regulates IL-1 signaling by blocking the functional receptor. We previously demonstrated that IL-1Ra-deficient (IL-1Ra-/-) mice exhibit marked neointimal formation after injury. IL-1Ra is expressed on bone marrow (BM)-derived cells as well as non-BM intrinsic arterial cells. However, the importance of various cell types as sources of IL-1Ra remains unknown. The aim of this study was to test the hypothesis that IL-1Ra originating from BM-derived cells and non-BM intrinsic cells helps to suppress both inflammation and neointimal formation after vascular injury using a model of BM cell transplantation (BMT).

METHODS

In order to determine the contribution of IL-1Ra-deficient (Ra-/-) and wild-type (WT) BM cells to neointimal formation, we developed four types of BM chimeric mice (BMT(WT→WT) (n=12), BMT(Ra-/-→WT) (n=12), BMT(WT→Ra-/-) (n=12) and BMT(Ra-/-→Ra-/-) (n=12)). At four weeks after BMT, we induced vascular injury by placing a non-occlusive cuff around the femoral artery. Histological analyses were subsequently performed two weeks after injury.

RESULTS

Neointimal formation was decreased in the BMT(WT→Ra-/-) mice compared with that observed in the BMT(Ra-/-→Ra-/-) mice (p＜0.001), but significantly more so in the BMT(Ra-/-→WT) (p＜0.01) and BMT(WT→WT) (p＜0.01) mice. In contrast, the neointimal formation in the BMT(Ra-/-→WT) mice was significantly increased compared with that noted in the BMT(WT→WT) mice (p＜0.05). In addition, immunostaining revealed that Mac3-positive areas were significantly increased in the BMT(Ra-/-→Ra-/-) mice compared with those seen in the other three groups (p＜0.001), with a significantly decreased percentage of alpha-SMA-positive areas in the neointima in the BMT(Ra-/-→Ra-/-) mice compared with that found in the remaining groups (p＜0.001). Furthermore, IL-1Ra staining demonstrated the IL-1Ra expression in several inflammatory cells in the adventitia in the BMT(WT→WT) and BMT(WT→Ra-/-) mice, compared to the neointima in the BMT(WT→WT) and BMT(Ra-/-→WT) mice.

CONCLUSIONS

The IL-1Ra present in BM-derived cells and non-BM cells helps to suppress arterial inflammation, resulting in decreased neointimal formation after injury. These findings shed new light on the mechanisms underlying the development of atherosclerosis and restenosis after angioplasty.

Tgfbr2 disruption in postnatal smooth muscle impairs aortic wall homeostasis

TGF-β is essential for vascular development; however, excess TGF-β signaling promotes thoracic aortic aneurysm and dissection in multiple disorders, including Marfan syndrome. Since the pathology of TGF-β overactivity manifests primarily within the arterial media, it is widely assumed that suppression of TGF-β signaling in vascular smooth muscle cells will ameliorate aortic disease. We tested this hypothesis by conditional inactivation of Tgfbr2, which encodes the TGF-β type II receptor, in smooth muscle cells of postweanling mice. Surprisingly, the thoracic aorta rapidly thickened, dilated, and dissected in these animals. Tgfbr2 disruption predictably decreased canonical Smad signaling, but unexpectedly increased MAPK signaling. Type II receptor-independent effects of TGF-β and pathological responses by nonrecombined smooth muscle cells were excluded by serologic neutralization. Aortic disease was caused by a perturbed contractile apparatus in medial cells and growth factor production by adventitial cells, both of which resulted in maladaptive paracrine interactions between the vessel wall compartments. Treatment with rapamycin restored a quiescent smooth muscle phenotype and prevented dissection. Tgfbr2 disruption in smooth muscle cells also accelerated aneurysm growth in a murine model of Marfan syndrome. Our data indicate that basal TGF-β signaling in smooth muscle promotes postnatal aortic wall homeostasis and impedes disease progression.

The cooperative roles of inflammation and oxidative stress in the pathogenesis of hypertension

SIGNIFICANCE

Innate and adaptive immunity play fundamental roles in the development of hypertension and its complications. As effectors of the cell-mediated immune response, myeloid cells and T lymphocytes protect the host organism from infection by attacking foreign intruders with bursts of reactive oxygen species (ROS).

RECENT ADVANCES

While these ROS may help to preserve the vascular tone and thereby protect against circulatory collapse in the face of overwhelming infection, aberrant elaboration of ROS triggered by immune cells in the absence of a hemodynamic insult can lead to pathologic increases in blood pressure. Conversely, misdirected oxidative stress in cardiovascular control organs, including the vasculature, the kidney, and the nervous system potentiates inflammatory responses, augmenting blood pressure elevation and inciting target organ damage.

CRITICAL ISSUES

Inflammation and oxidative stress thereby act as cooperative and synergistic partners in the pathogenesis of hypertension.

FUTURE DIRECTIONS

Pharmacologic interventions for hypertensive patients will need to exploit this robust bidirectional relationship between ROS generation and immune activation in cardiovascular control organs to maximize therapeutic benefit, while limiting off-target side effects.

Toll-like receptors and damage-associated molecular patterns: novel links between inflammation and hypertension

Low-grade systemic inflammation is a common manifestation of hypertension; however, the exact mechanisms that initiate this pathophysiological response, thereby contributing to further increases in blood pressure, are not well understood. Aberrant vascular inflammation and reactivity via activation of the innate immune system may be the first step in the pathogenesis of hypertension. One of the functions of the innate immune system is to recognize and respond to danger. Danger signals can arise from not only pathogenic stimuli but also endogenous molecules released following cell injury and/or death [damage-associated molecular patterns (DAMPs)]. In the short-term, activation of the innate immune system is beneficial in the vasculature by providing cytoprotective mechanisms and facilitating tissue repair following injury or infection. However, sustained or excessive immune system activation, such as in autoimmune diseases, may be deleterious and can lead to maladaptive, irreversible changes to vascular structure and function. An initial source of DAMPs that enter the circulation to activate the innate immune system could arise from modest elevations in peripheral vascular resistance. These stimuli could subsequently lead to ischemic- or pressure-induced events aggravating further cell injury and/or death, providing more DAMPs for innate immune system activation. This review will address and critically evaluate the current literature on the role of the innate immune system in hypertension pathogenesis. The role of Toll-like receptor activation on somatic cells of the vasculature in response to the release of DAMPs and the consequences of this activation on inflammation, vasoreactivity, and vascular remodeling will be specifically discussed.

Vein graft failure

After the creation of an autogenous lower extremity bypass graft, the vein must undergo a series of dynamic structural changes to stabilize the arterial hemodynamic forces. These changes, which are commonly referred to as remodeling, include an inflammatory response, the development of a neointima, matrix turnover, and cellular proliferation and apoptosis. The sum total of these processes results in dramatic alterations in the physical and biomechanical attributes of the arterialized vein. The most clinically obvious and easily measured of these is lumen remodeling of the graft. However, although somewhat less precise, wall thickness, matrix composition, and endothelial changes can be measured in vivo within the healing vein graft. Recent translational work has demonstrated the clinical relevance of remodeling as it relates to vein graft patency and the systemic factors influencing it. By correlating histologic and molecular changes in the vein, insights into potential therapeutic strategies to prevent bypass failure and areas for future investigation are explored.

The multifunctional Ca²⁺/calmodulin-dependent kinase IIδ (CaMKIIδ) regulates arteriogenesis in a mouse model of flow-mediated remodeling

Objective

Sustained hemodynamic stress mediated by high blood flow promotes arteriogenesis, the outward remodeling of existing arteries. Here, we examined whether Ca²⁺/calmodulin-dependent kinase II (CaMKII) regulates arteriogenesis.

Methods and Results

Ligation of the left common carotid led to an increase in vessel diameter and perimeter of internal and external elastic lamina in the contralateral, right common carotid. Deletion of CaMKIIδ (CaMKIIδ−/−) abolished this outward remodeling. Carotid ligation increased CaMKII expression and was associated with oxidative activation of CaMKII in the adventitia and endothelium. Remodeling was abrogated in a knock-in model in which oxidative activation of CaMKII is abolished. Early after ligation, matrix metalloproteinase 9 (MMP9) was robustly expressed in the adventitia of right carotid arteries of WT but not CaMKIIδ−/− mice. MMP9 mainly colocalized with adventitial macrophages. In contrast, we did not observe an effect of CaMKIIδ deficiency on other proposed mediators of arteriogenesis such as expression of adhesion molecules or smooth muscle proliferation. Transplantation of WT bone marrow into CaMKIIδ−/− mice normalized flow-mediated remodeling.

Conclusion

CaMKIIδ is activated by oxidation under high blood flow conditions and is required for flow-mediated remodeling through a mechanism that includes increased MMP9 expression in bone marrow-derived cells invading the arterial wall.

Targeting the adventitial microenvironment in pulmonary hypertension: A potential approach to therapy that considers epigenetic change

Experimental data indicate that the adventitial compartment of blood vessels, in both the pulmonary and systemic circulations, like the connective tissue stroma in tissues throughout the body, is a critical regulator of vessel wall function in health and disease. It is clear that adventitial cells, and in particular the adventitial fibroblast, are activated early following vascular injury, and play essential roles in regulating vascular wall structure and function through production of chemokines, cytokines, growth factors, and reactive oxygen species (ROS). The recognition of the ability of these cells to generate and maintain inflammatory responses within the vessel wall provides insight into why vascular inflammatory responses, in certain situations, fail to resolve. It is also clear that the activated adventitial fibroblast plays an important role in regulating vasa vasorum growth, which can contribute to ongoing vascular remodeling by acting as a conduit for delivery of inflammatory and progenitor cells. These functions of the fibroblast clearly support the idea that targeting chemokine, cytokine, adhesion molecule, and growth factor production in activated fibroblasts could be helpful in abrogating vascular inflammatory responses and thus in ameliorating vascular disease. Further, the recent observations that fibroblasts in vascular and fibrotic diseases may maintain their activated state through epigenetic alterations in key inflammatory and pro-fibrotic genes suggests that current therapies used to treat pulmonary hypertension may not be sufficient to induce apoptosis or to inhibit key inflammatory signaling pathways in these fibroblasts. New therapies targeted at reversing changes in the acetylation or methylation status of key transcriptional networks may be needed. At present, therapies specifically targeting abnormalities of histone deacytelase (HDAC) activity in fibroblast-like cells appear to hold promise.

Effect of an acute mechanical stimulus on aortic structure in the transverse aortic constriction mouse model

1. Vascular remodelling is an adaptive response to various stimuli, including mechanical forces, inflammatory cytokines and hormones. In the present study, we investigated histological modification of the aorta and the expression of key proteins participating in vascular remodelling under an acute mechanical stimulus using a transverse aortic constriction (TAC) mouse model. 2. The TAC was performed in male C57BL/6 mice aged 10-12 weeks. A Millar conductance catheter was used to measure cardiac haemodynamic parameters 3 and 14 days after TAC. Aortic structural variations were observed by haematoxylin and eosin, Sirius red and Weigert's elastin staining. Protein levels of Type I collagen, F4/80, α-smooth muscle actin (SMA) and SM22α were analysed by immunohistochemistry. 3. Three days after TAC, the medial area proximal to the aortic band (PA-B) was increased, whereas the area distal to the aortic band (DA-B) was unchanged. There was no difference in luminal area between TAC and sham groups. The adventitia displayed the most significant difference 14 days after TAC: adventitial hyperplasia was abundant and collagen was upregulated in the adventitia of the PA-B with a considerable increase in α-SMA and SM22α. Macrophages accumulated in the adventitia of the PA-B 3 days after TAC and infiltrated into the media and intima of the PA-B 14 days after TAC. 4. In conclusion, the aortic structure undergoes considerable remodelling following an acute mechanical stimulus in the TAC model, mainly in the adventitia. Upregulation of α-SMA and extracellular matrix components accompanied by macrophage infiltration may contribute to adventitial modification in the TAC mouse model.

Inhibition of clathrin/dynamin-dependent internalization interferes with LPS-mediated TRAM-TRIF-dependent signaling pathway

Recognition of lipopolysaccharide (LPS) by Toll-like receptor 4 (TLR4) activates two district proinflammatory signaling pathway and initiates LPS internalization. To investigate roles of LPS internalization, a traditionally regarded metabolic pathway for LPS, in regulation of these two pathways, three internalization inhibitors, monodansylcadaverine (MDC, a clathrin inhibitor), dynasore (DS, a dynamin inhibitor) and chloroquine (CQ, an endosome acidifying maturation inhibitor) were applied to induce internalization dysfunction in macrophages. Results showed MDC and DS affected LPS internalization but did not interfere with their colocalization. Additionally, they decreased cytokines and chemokines release and inhibited signaling molecules activation mediated by TRAM-TRIF-dependent pathway as determined by protein array. In contrast, CQ did not inhibit LPS internalization but affected the colocalization. It also suppressed macrophage activation mediated by both MyD88-dependent and TRAM-TRIF-dependent pathways. The above data indicated that LPS internalization was clathrin/dynamin dependent and it was essential for activation of TRAM-TRIF-dependent signaling pathway.

Genetic inactivation of IL-1 signaling enhances atherosclerotic plaque instability and reduces outward vessel remodeling in advanced atherosclerosis in mice

Clinical complications of atherosclerosis arise primarily as a result of luminal obstruction due to atherosclerotic plaque growth, with inadequate outward vessel remodeling and plaque destabilization leading to rupture. IL-1 is a proinflammatory cytokine that promotes atherogenesis in animal models, but its role in plaque destabilization and outward vessel remodeling is unclear. The studies presented herein show that advanced atherosclerotic plaques in mice lacking both IL-1 receptor type I and apolipoprotein E (Il1r1⁻/⁻Apoe⁻/⁻ mice) unexpectedly exhibited multiple features of plaque instability as compared with those of Il1r1⁺/⁺Apoe⁻/⁻ mice. These features included reduced plaque SMC content and coverage, reduced plaque collagen content, and increased intraplaque hemorrhage. In addition, the brachiocephalic arteries of Il1r1⁻/⁻Apoe⁻/⁻ mice exhibited no difference in plaque size, but reduced vessel area and lumen size relative to controls, demonstrating a reduction in outward vessel remodeling. Interestingly, expression of MMP3 was dramatically reduced within the plaque and vessel wall of Il1r1⁻/⁻Apoe⁻/⁻ mice, and Mmp3⁻/⁻Apoe⁻/⁻ mice showed defective outward vessel remodeling compared with controls. In addition, MMP3 was required for IL-1-induced SMC invasion of Matrigel in vitro. Taken together, these results show that IL-1 signaling plays a surprising dual protective role in advanced atherosclerosis by promoting outward vessel remodeling and enhancing features of plaque stability, at least in part through MMP3-dependent mechanisms.

Repeated exposure to Aspergillus fumigatus conidia results in CD4+ T cell-dependent and -independent pulmonary arterial remodeling in a mixed Th1/Th2/Th17 microenvironment that requires interleukin-4 (IL-4) and IL-10

Pulmonary arterial remodeling is a pathological process seen in a number of clinical disease states, driven by inflammatory cells and mediators in the remodeled artery microenvironment. In murine models, Th2 cell-mediated immune responses to inhaled antigens, such as purified Aspergillus allergen, have been reported to induce remodeling of pulmonary arteries. We have previously shown that repeated intranasal exposure of healthy C57BL/6 mice to viable, resting Aspergillus fumigatus conidia leads to the development of chronic pulmonary inflammation and the coevolution of Th1, Th2, and Th17 responses in the lungs. Our objective was to determine whether repeated intranasal exposure to Aspergillus conidia would induce pulmonary arterial remodeling in this mixed Th inflammatory microenvironment. Using weekly intranasal conidial challenges, mice developed robust pulmonary arterial remodeling after eight exposures (but not after two or four). The process was partially mediated by CD4+ T cells and by interleukin-4 (IL-4) production, did not require eosinophils, and was independent of gamma interferon (IFN-γ) and IL-17. Furthermore, remodeling could occur even in the presence of strong Th1 and Th17 responses. Rather than serving an anti-inflammatory function, IL-10 was required for the development of the Th2 response to A. fumigatus conidia. However, in contrast to previous studies of pulmonary arterial remodeling driven by the A. fumigatus allergen, viable conidia also stimulated pulmonary arterial remodeling in the absence of CD4+ T cells. Remodeling was completely abrogated in IL-10-/- mice, suggesting that a second, CD4+ T cell-independent, IL-10-dependent pathway was also driving pulmonary arterial remodeling in response to repeated conidial exposure.

Age-related neointimal hyperplasia is associated with monocyte infiltration after balloon angioplasty

Carotid angioplasty is associated with adverse events in elderly patients; it is unclear whether this is related to an altered inflammatory axis. The carotid arteries of young (6 months) or aged (22-24 months) Fischer 344 rats were balloon injured. Aged rats had reduced lumen area (0.18 ± 0.03 vs 0.24 ± 0.01 mm(2), p = .02) and increased neointimal thickening (0.15 ± 0.04 vs 0.08 ± 0.03 mm(2), p = .006). Aged rats had increased circulating monocytes (96 ± 21 vs. 54 ± 7; p = .002) as well as increased numbers of monocytes at the post-angioplasty site. Aged rats had sustained monocyte chemotactic protein-1 expression after angioplasty but young rats did not. Aged arteries also exhibited defective vasorelaxation and abnormal eNOS localization. Aged (≥80 years) human patients with high-grade carotid stenosis had increased number of monocytes (9.1% ± 0.4%) compared with younger (65-80 years) patients (8.1% ± 0.3%, p = .013). Aged rats develop neointimal hyperplasia after carotid angioplasty with increased numbers of monocytes, and elderly humans with carotid stenosis have increased numbers of circulating monocytes. These preliminary results may suggest a role for monocytes in the response to carotid angioplasty.

The adventitia: a progenitor cell niche for the vessel wall

Recent observations suggest that the adventitial layer of blood vessels exhibits properties resembling a stem/progenitor cell niche. Progenitor cells have been isolated from the adventitia of both murine and human blood vessels with the potential to form endothelial cells, mural cells, osteogenic cells, and adipocytes. These progenitors appear to cluster at or near the border zone between the outer media and inner adventitia. In the mouse, this border zone region corresponds to a localized site of sonic hedgehog signaling in the artery wall. This brief review will discuss the emerging evidence that the tunica adventitia may provide a niche-like signaling environment for resident progenitor cells and will address the role of the adventitia in growth, remodeling, and repair of the artery wall.

Animal, in vitro, and ex vivo models of flow-dependent atherosclerosis: role of oxidative stress

Atherosclerosis is an inflammatory disease preferentially occurring in curved or branched arterial regions, whereas straight parts of the arteries are protected, suggesting a close relationship between flow and atherosclerosis. However, evidence directly linking disturbed flow to atherogenesis is just emerging, thanks to the recent development of suitable animal models. In this article, we review the status of various animal, in vitro, and ex vivo models that have been used to study flow-dependent vascular biology and atherosclerosis. For animal models, naturally flow-disturbed regions such as branched or curved arterial regions as well as surgically created models, including arterio-venous fistulas, vascular grafts, perivascular cuffs, and complete, incomplete, or partial ligation of arteries, are used. Although in vivo models provide the environment needed to mimic the complex pathophysiological processes, in vitro models provide simple conditions that allow the study of isolated factors. Typical in vitro models use cultured endothelial cells exposed to various flow conditions, using devices such as cone-and-plate and parallel-plate chambers. Ex vivo models using isolated vessels have been used to bridge the gap between complex in vivo models and simple in vitro systems. Here, we review these flow models in the context of the role of oxidative stress in flow-dependent inflammation, a critical proatherogenic step, and atherosclerosis.

The adventitia: a dynamic interface containing resident progenitor cells

Conventional views of the tunica adventitia as a poorly organized layer of vessel wall composed of fibroblasts, connective tissue, and perivascular nerves are undergoing revision. Recent studies suggest that the adventitia has properties of a stem/progenitor cell niche in the artery wall that may be poised to respond to arterial injury. It is also a major site of immune surveillance and inflammatory cell trafficking and harbors a dynamic microvasculature, the vasa vasorum, that maintains the medial layer and provides an important gateway for macrophage and leukocyte migration into the intima. In addition, the adventitia is in contact with tissue that surrounds the vessel and may actively participate in exchange of signals and cells between the vessel wall and the tissue in which it resides. This brief review highlights recent advances in our understanding of the adventitia and its resident progenitor cells and discusses progress toward an integrated view of adventitial function in vascular development, repair, and disease.

Transcriptional profiling and network analysis of the murine angiotensin II-induced abdominal aortic aneurysm

We sought to characterize temporal gene expression changes in the murine angiotensin II (ANG II)-ApoE-/- model of abdominal aortic aneurysm (AAA). Aortic ultrasound measurements were obtained over the 28-day time-course. Harvested suprarenal aortic segments were evaluated with whole genome expression profiling at 7, 14, and 28 days using the Agilent Whole Mouse Genome microarray platform and Statistical Analysis of Microarrays at a false discovery rate of <1%. A group of angiotensin-treated mice experienced contained rupture (CR) within 7 days and were analyzed separately. Progressive aortic dilatation occurred throughout the treatment period. However, the numerous early expression differences between ANG II-treated and control were not sustained over time. Ontologic analysis revealed widespread upregulation of inflammatory, immune, and matrix remodeling genes with ANG II treatment, among other pathways such as apoptosis, cell cycling, angiogenesis, and p53 signaling. CR aneurysms displayed significant decreases in TGF-β/BMP-pathway signaling, MAPK signaling, and ErbB signaling genes vs. non-CR/ANG II-treated samples. We also performed literature-based network analysis, extracting numerous highly interconnected genes associated with aneurysm development such as Spp1, Myd88, Adam17 and Lox. 1) ANG II treatment induces extensive early differential expression changes involving abundant signaling pathways in the suprarenal abdominal aorta, particularly wide-ranging increases in inflammatory genes with aneurysm development. 2) These gene expression changes appear to dissipate with time despite continued growth, suggesting that early changes in gene expression influence disease progression in this AAA model, and that the aortic tissue adapts to prolonged ANG II infusion. 3) Network analysis identified nexus genes that may constitute aneurysm biomarkers or therapeutic targets.

Recent aspects of vasculitis and future direction

Vasculitis is pathologically identified as specific cellular inflammation, vessel destruction, and tissue necrosis. Current classifications of vasculitis such as the Chapel Hill Classification (CHCC) and American College of Rheumatology (ACR) guidelines are not sufficiently adequate for clinicians to diagnose vasculitis. The biomarkers that are currently in clinical use such as PR3-ANCA and MPO-ANCA, only help in diagnosing small vessel vasculitis and their sensitivity and specificity are not sufficient. However, recent developments related to the pathogenesis and etiopathogenesis of vasculitis have the potential to contribute to new and improved biomarkers. The determination of diverse roles of ANCA and synergistic effects of infection, genetic, environmental factors and drugs on pathogenesis is quite important. The demonstration of a new autoantibody directed to hLAMP-2 and the resemblance to some microbial structures, in addition to the determination of the possible roles of hepatitis B and C on vasculitis are important findings. These hints may lead to new biomarker developments, providing a better method to diagnose vasculitis. The evidence on T cell immunity as circulatory and lesional will likely contribute to the development of new drugs for vasculitis.

Immune responses regulating the response to vascular injury

PURPOSE OF REVIEW

Immune modulation of neointimal formation after vascular injury has been investigated for several decades but the complexities involved continue to obscure a clearer understanding of the process. The rapidly changing field of immunology makes this knowledge imperative.

RECENT FINDINGS

The review discusses immune factors involved in the response to vascular injury. Although innate immune responses play a predominantly detrimental role, the adaptive immune response is more complex. Mechanisms of T-cell activation, recruitment, as well as possible regulation are highlighted.

SUMMARY

Progress in understanding the role of the immune system in the response to arterial injury has been impressive. However, recent findings underscore the need to unravel the intricacies involved such as the kinetics and specific pathways of activation, specificity of immune cell involvement, and identification of targets for therapy. This is relevant in light of the increasing reports of immune factors involved in vascular disease and intervention in the clinical setting.

CXCR3-dependent accumulation and activation of perivascular macrophages is necessary for homeostatic arterial remodeling to hemodynamic stresses

Sustained changes in blood flow modulate the size of conduit arteries through structural alterations of the vessel wall that are dependent on the transient accumulation and activation of perivascular macrophages. The leukocytic infiltrate appears to be confined to the adventitia, is responsible for medial remodeling, and resolves once hemodynamic stresses have normalized without obvious intimal changes. We report that inward remodeling of the mouse common carotid artery after ligation of the ipsilateral external carotid artery is dependent on the chemokine receptor CXCR3. Wild-type myeloid cells restored flow-mediated vascular remodeling in CXCR3-deficient recipients, adventitia-infiltrating macrophages of Gr1^low resident phenotype expressed CXCR3, the perivascular accumulation of macrophages was dependent on CXCR3 signaling, and the CXCR3 ligand IP-10 was sufficient to recruit monocytes to the adventitia. CXCR3 also contributed to selective features of macrophage activation required for extracellular matrix turnover, such as production of the transglutaminase factor XIII A subunit. Human adventitial macrophages displaying a CD14⁺/CD16⁺ resident phenotype, but not circulating monocytes, expressed CXCR3, and such cells were more frequent at sites of disturbed flow. Our observations reveal a CXCR3-dependent accumulation and activation of perivascular macrophages as a necessary step in homeostatic arterial remodeling triggered by hemodynamic stress in mice and possibly in humans as well.

Inflammation and brain injury: acute cerebral ischaemia, peripheral and central inflammation

Inflammation is a classical host defence response to infection and injury that has many beneficial effects. However, inappropriate (in time, place and magnitude) inflammation is increasingly implicated in diverse disease states, now including cancer, diabetes, obesity, atherosclerosis, heart disease and, most relevant here, CNS disease. A growing literature shows strong correlations between inflammatory status and the risk of cerebral ischaemia (CI, most commonly stroke), as well as with outcome from an ischaemic event. Intervention studies to demonstrate a causal link between inflammation and CI (or its consequences) are limited but are beginning to emerge, while experimental studies of CI have provided direct evidence that key inflammatory mediators (cytokines, chemokines and inflammatory cells) contribute directly to ischaemic brain injury. However, it remains to be determined what the relative importance of systemic (largely peripheral) versus CNS inflammation is in CI. Animal models in which CI is driven by a CNS intervention may not accurately reflect the clinical condition; stroke being typically induced by atherosclerosis or cardiac dysfunction, and hence current experimental paradigms may underestimate the contribution of peripheral inflammation. Experimental studies have already identified a number of potential anti-inflammatory therapeutic interventions that may limit ischaemic brain damage, some of which have been tested in early clinical trials with potentially promising results. However, a greater understanding of the contribution of inflammation to CI is still required, and this review highlights some of the key mechanism that may offer future therapeutic targets.

Soluble epoxide hydrolase deficiency attenuates neointima formation in the femoral cuff model of hyperlipidemic mice

OBJECTIVE

Epoxyeicosatrienoic acids (EETs) have antiinflammatory effects and are required for normal endothelial function. The soluble epoxide hydrolase (sEH) metabolizes EETs to their less active diols. We hypothesized that knockout and inhibition of sEH prevents neointima formation in hyperlipidemic ApoE(-/-) mice.

METHODS AND RESULTS

Inhibition of sEH by 12-(3-adamantan-1-yl-ureido) dodecanoic acid or knockout of the enzyme significantly increased plasma EET levels. sEH activity was detectable in femoral and carotid arteries. sEH knockout or inhibition resulted in a significant reduction of neointima formation in the femoral artery cuff model but not following carotid artery ligation. Although macrophage infiltration occurred abundantly at the site of cuff placement in both sEH(+/+) and sEH(-/-), the expression of proinflammatory genes was significantly reduced in femoral arteries from sEH(-/-) mice. Moreover, an in vivo 5-bromo-2'-deoxyuridine assay revealed that smooth muscle cell proliferation at the site of cuff placement was attenuated in sEH knockout and sEH inhibitor-treated animals.

CONCLUSION

These observations suggest that inhibition of sEH prevents vascular remodeling in an inflammatory model but not in a blood flow-dependent model of neointima formation.

Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.

Hemodynamic influences on abdominal aortic aneurysm disease: Application of biomechanics to aneurysm pathophysiology

"Atherosclerotic" abdominal aortic aneurysms (AAAs) occur with the greatest frequency in the distal aorta. The unique hemodynamic environment of this area predisposes it to site-specific degenerative changes. In this review, we summarize the differential hemodynamic influences present along the length of the abdominal aorta, and demonstrate how alterations in aortic flow and wall shear stress modify AAA progression in experimental models. Improved understanding of aortic hemodynamic risk profiles provides an opportunity to modify patient activity patterns to minimize the risk of aneurysmal degeneration.