Inhibition of Notch1 signaling reduces abdominal aortic aneurysm in mice by attenuating macrophage-mediated inflammation

Nuclear mechanosensing of the aortic endothelium in health and disease

The endothelium, the monolayer of endothelial cells that line blood vessels, is exposed to a number of mechanical forces, including frictional shear flow, pulsatile stretching and changes in stiffness influenced by extracellular matrix composition. These forces are sensed by mechanosensors that facilitate their transduction to drive appropriate adaptation of the endothelium to maintain vascular homeostasis. In the aorta, the unique architecture of the vessel gives rise to changes in the fluid dynamics, which, in turn, shape cellular morphology, nuclear architecture, chromatin dynamics and gene regulation. In this Review, we discuss recent work focusing on how differential mechanical forces exerted on endothelial cells are sensed and transduced to influence their form and function in giving rise to spatial variation to the endothelium of the aorta. We will also discuss recent developments in understanding how nuclear mechanosensing is implicated in diseases of the aorta.

Deficiency of cystathionine gamma-lyase promotes aortic elastolysis and medial degeneration in aged mice

Enzymatic degradation of elastin by matrix metalloproteinases (MMPs) leads to the permanent dilation of aortic wall and constitutes the most prominent characters of aortic aneurysm and aging-related medial degeneration. Hydrogen sulfide (H₂S) as a gasotransmitter exhibits a wide variety of cardio-protective functions through its anti-inflammatory and anti-oxidative actions. Cystathionine gamma-lyase (CSE) is a main H₂S-generating enzyme in cardiovascular system. The regulatory roles of CSE/H₂S system on elastin homeostasis and blood vessel degeneration have not yet been explored. Here we found that aged CSE knockout mice had severe aortic dilation and elastic degradation in abdominal aorta and were more sensitive to angiotensin II-induced aortic elastolysis and medial degeneration. Administration of NaHS would protect the mice from angiotensin II-induced inflammation, gelatinolytic activity, elastin fragmentation, and aortic dilation. In addition, human aortic aneurysm samples had higher inflammatory infiltration and lower expression of CSE. In cultured smooth muscle cells (SMCs), TNFα-induced MMP2/9 hyperactivity and elastolysis could be attenuated by exogenously applied NaHS or CSE overexpression while further deteriorated by complete knockout of CSE. It was further found that H₂S inhibited MMP2 transcription by posttranslational modification of Sp1 via S-sulfhydration. H₂S also directly suppressed MMP hyperactivity by S-sulfhydrating the cysteine switch motif. Taken together, this study revealed the involvement of CSE/H₂S system in the pathogenesis of aortic elastolysis and medial degeneration by maintaining the inactive form of MMPs, suggesting that CSE/H₂S system can be a target for the prevention of age-related medial degeneration and treatment of aortic aneurysm.

Adventitial Fibroblasts in Aortic Aneurysm: Unraveling Pathogenic Contributions to Vascular Disease

Aortic aneurysm (AA) is a degenerative vascular disease that involves aortic dilatation, and, if untreated, it can lead to rupture. Despite its significant impact on the healthcare system, its multifactorial nature and elusive pathophysiology contribute to limited therapeutic interventions that prevent the progression of AA. Thus, further research into the mechanisms underlying AA is paramount. Adventitial fibroblasts are one of the key constituents of the aortic wall, and they play an essential role in maintaining vessel structure and function. However, adventitial fibroblasts remain understudied when compared with endothelial cells and smooth muscle cells. Adventitial fibroblasts facilitate the production of extracellular matrix (ECM), providing structural integrity. However, during biomechanical stress and/or injury, adventitial fibroblasts can be activated into myofibroblasts, which move to the site of injury and secrete collagen and cytokines, thereby enhancing the inflammatory response. The overactivation or persistence of myofibroblasts has been shown to initiate pathological vascular remodeling. Therefore, understanding the underlying mechanisms involved in the activation of fibroblasts and in regulating myofibroblast activation may provide a potential therapeutic target to prevent or delay the progression of AA. This review discusses mechanistic insights into myofibroblast activation and associated vascular remodeling, thus illustrating the contribution of fibroblasts to the pathogenesis of AA.

Age as a risk factor in vasculitis

Two vasculitides, giant cell arteritis (GCA) and Takayasu arteritis (TAK), are recognized as autoimmune and autoinflammatory diseases that manifest exclusively within the aorta and its large branches. In both entities, the age of the affected host is a critical risk factor. TAK manifests during the 2nd-4th decade of life, occurring while the immune system is at its height of performance. GCA is a disease of older individuals, with infrequent cases during the 6th decade and peak incidence during the 8th decade of life. In both vasculitides, macrophages and T cells infiltrate into the adventitia and media of affected vessels, induce granulomatous inflammation, cause vessel wall destruction, and reprogram vascular cells to drive adventitial and neointimal expansion. In GCA, abnormal immunity originates in an aged immune system and evolves within the aged vascular microenvironment. One hallmark of the aging immune system is the preferential loss of CD8⁺ T cell function. Accordingly, in GCA but not in TAK, CD8⁺ effector T cells play a negligible role and anti-inflammatory CD8⁺ T regulatory cells are selectively impaired. Here, we review current evidence of how the process of immunosenescence impacts the risk for GCA and how fundamental differences in the age of the immune system translate into differences in the granulomatous immunopathology of TAK versus GCA.

Combined Detection of Plasma Tumor Necrosis Factor-α Converting Enzyme and Notch1 is Valuable in Screening Endoleak After Endovascular Abdominal Aortic Aneurysms Repair

OBJECTIVES

Endoleaks may be present in up to 25% of patients after endovascular abdominal aortic aneurysm repair (EVAR) and there is no clear consensus on valuable biomarkers to determine endoleak presence. The aim of this study was to examine the potential value of plasma tumor necrosis factor-α converting enzyme (TACE) and Notch1 concentrations in determining endoleak presence after EVAR.

METHODS

A total of 110 patients with abdominal aortic aneurysm who underwent EVAR were enrolled in our study, and plasma TACE and Notch1 concentrations were measured prior to and 6 months after EVAR. Logistic regression was performed to assess the association of postoperative plasma TACE and Notch1 concentrations with endoleak after adjusting for potential confounders. The ability of plasma TACE and Notch1 concentrations to determine endoleak presence was assessed using receiver operating characteristic curves and area under the curve (AUC).

RESULTS

Twenty-four patients developed endoleaks 6 months after EVAR. Both postoperative plasma TACE and Notch1 concentrations were higher in patients with endoleak than in those without endoleak (2376.4 ± 28.1 pg/ml vs. 2094.1 ± 27.3 pg/ml, P < 0.01; 218.6 ± 1.9 pg/ml vs. 195.0 ± 2.1 pg/ml, P < 0.01, respectively). The AUCs from receiver operating characteristic curve analysis of plasma TACE and Notch1 concentrations in determining endoleak presence were 0.844 (95% CI 0.771 to 0.918, P < 0.01) and 0.860 (95% CI 0.791 to 0.930, P < 0.01), respectively. Combining the detection of plasma Notch1 and TACE concentrations could improve the accuracy in determining endoleak presence (AUC 0.930, 95% CI 0.883 to 0.978, P < 0.01). The predicted probability cutoff of 0.22 yielded a sensitivity of 95.8% and a specificity of 82.6% for endoleak presence.

CONCLUSIONS

Plasma TACE and Notch1 levels can discriminate patients with and without endoleak 6 months after EVAR, and have a potential role in screening patients requiring computed tomography angiography.

Mineralocorticoid Receptor in Myeloid Cells Mediates Angiotensin II-Induced Vascular Dysfunction in Female Mice

Enhanced mineralocorticoid receptor (MR) signaling is critical to the development of endothelial dysfunction and arterial stiffening. However, there is a lack of knowledge about the role of MR-induced adipose tissue inflammation in the genesis of vascular dysfunction in women. In this study, we hypothesize that MR activation in myeloid cells contributes to angiotensin II (Ang II)-induced aortic stiffening and endothelial dysfunction in females via increased pro-inflammatory (M1) macrophage polarization. Female mice lacking MR in myeloid cells (MyMRKO) were infused with Ang II (500 ng/kg/min) for 4 weeks. This was followed by determinations of aortic stiffness and vasomotor responses, as well as measurements of markers of inflammation and macrophage infiltration/polarization in different adipose tissue compartments. MyMRKO mice were protected against Ang II-induced aortic endothelial stiffening, as assessed via atomic force microscopy in aortic explants, and vasorelaxation dysfunction, as measured by aortic wire myography. In alignment, MyMRKO mice were protected against Ang II-induced macrophage infiltration and M1 polarization in visceral adipose tissue (VAT) and thoracic perivascular adipose tissue (tPVAT). Collectively, this study demonstrates a critical role of MR activation in myeloid cells in the pathogenesis of vascular dysfunction in females associated with pro-inflammatory macrophage polarization in VAT and tPVAT. Our data have potential clinical implications for the prevention and management of cardiovascular disease in women, who are disproportionally at higher risk for poor outcomes.

Effect of endovascular therapy on the expression levels of serum T lymphocyte subsets, Notch1 and TACE proteins in patients with abdominal aortic aneurysm

To investigate the effect of endovascular therapy on the expression levels of serum T lymphocyte subsets, Notch1 and TACE proteins in patients with abdominal aortic aneurysm (AAA). A total of 84 AAA patients treated in the General Hospital of Northern Theater Command of Chinese PLA from January 2018 to October 2019 were equally divided into the control group and research group according to different surgical methods. The control group underwent laparotomy and the research group received endoluminal repair. The expression levels of serum T-cell subsets, plasma Notch1 and TACE proteins were compared before and 1 week after surgery between the two groups; the expression levels of plasma Notch1 and TACE proteins in patients with different tumor diameters in the research group were compared; the comparison of the surgical indexes and the incidence of complications was conducted. After treatment, the molecular level of CD3⁺ and CD4⁺ in the research group was significantly higher than that in the control group, whereas the molecular level of CD8⁺, and the expression levels of Notch1 and TACE proteins in the plasma were significantly lower than that in the control group (P < 0.05). In the research group, the expression levels of plasma Notch1 and TACE proteins were in direct proportion with tumor diameter (P < 0.05). The intraoperative blood loss in the research group was significantly less than that in the control group, the operation time, postoperative fasting time and postoperative hospital stay were significantly shorter than that in the control group, and the total incidence of complications (11.90%) was significantly lower than that in the control group (38.09%) (P < 0.05). At 12 months after operation, there was no statistically significant difference in the incidence of complications and mortality between the two groups. Endovascular therapy fro AAA can greatly improve the expression levels of T-lymphocyte subsets, Notch1 and TACE proteins, and markedly reduce the incidence of complications.

Interleukin 12p40 Deficiency Promotes Abdominal Aortic Aneurysm by Activating CCN2/MMP2 Pathways

Background Development of abdominal aortic aneurysm (AAA) is associated with proinflammatory cytokines including interleukin-12 (IL12). Deficiency of interleukin 12p40 (IL12p40) increases localized fibrotic events by promoting TGFβ2 (transforming growth factor β)-dependent anti-inflammatory response. Here, we determined whether IL12p40 deficiency in apolipoprotein E-/- mice attenuates the development of AAA by antagonizing proinflammatory response. Methods and Results Double knockout (DKO) mice were generated by crossbreeding IL12p40-/- mice with apolipoprotein E-/- mice (n=12). Aneurysmal studies were performed using angiotensin II (1 µg/kg/min; subcutaneous). Surprisingly, DKO mice did not prevent the development of AAA with angiotensin II infusion. Immunohistological analysis, however, showed distinct pathological features between apolipoprotein E-/- and DKO mice. Polymerase chain reaction (7 day) and cytokine arrays (28 day) of the aortic tissues from DKO mice showed significantly increased expression of cytokines related to anti-inflammatory response (interleukin 5 and interleukin 13), synthetic vascular smooth muscle cell phenotype (Activin receptor-like kinase-1 (ALK-1), artemin, and betacellulin) and T helper 17-associated response (4-1BB, interleukin-17e (Il17e) and Cd40 ligand (Cd-40L)). Indeed, DKO mice exhibited increased expression of the fibro-proteolytic pathway in the medial layer of aortae induced by cellular communication network factor 2 (CCN2) and Cd3+IL17+ cells compared with apolipoprotein E-/- mice. Laser capture microdissection showed predominant expression of CCN2/TGFβ2 in the medial layer of human AAA. Finally, Ccn2 haploinsufficiency in the mice showed decreased AAA incidence in response to elastase infusion, associated with decreased matrix metalloproteinase-2 expression. Conclusions Our study reveals novel roles for IL12p40 deficiency in inducing fibro-proteolytic activities in the aneurysmal mouse model. Mechanistically, these effects of IL12p40 deficiency are mediated by CCN2/matrix metalloproteinase-2 crosstalk in the medial layer of aneurysmal aortae.

Dibenzazepine combats acute liver injury in rats via amendments of Notch signaling and activation of autophagy

Paracetamol is a commonly used over-the-counter analgesic and antipyretic drug. Nevertheless, an overdose of paracetamol leads to hepatic necrosis that can be lethal. This study aimed to assess the potential hepatoprotective effects of dibenzazepine, a Notch inhibitor, against acute liver injury in rats via interfering with oxidative stress, inflammation, apoptosis, autophagy, and Notch signaling. Silymarin (200 mg/kg, p.o.) or dibenzazepine (2 mg/kg, i.p.) were administered to rats for 5 days before a single hepatotoxic dose of paracetamol (800 mg/kg, i.p.). Pretreatment with silymarin and dibenzazepine significantly mitigated oxidative stress, inflammatory and apoptotic markers induced by paracetamol hepatotoxicity where dibenzazepine showed greater repression of inflammation. Furthermore, dibenzazepine was found to be significantly more efficacious than silymarin in inhibiting Notch signaling as represented by expression of Notch-1 and Hes-1. A significantly greater response was also demonstrated with dibenzazepine pretreatment with regard to the expression of autophagic proteins, Beclin-1 and LC-3. The aforementioned biochemical results were confirmed by histopathological examination. Autophagy and Notch signaling seem to play a significant role in protection provided by dibenzazepine for paracetamol-induced hepatotoxicity in rats, which could explain its superior results relative to silymarin. Graphical abstract.

Insights on the Pathogenesis of Aneurysm through the Study of Hereditary Aortopathies

Thoracic aortic aneurysms (TAA) are permanent and localized dilations of the aorta that predispose patients to a life-threatening risk of aortic dissection or rupture. The identification of pathogenic variants that cause hereditary forms of TAA has delineated fundamental molecular processes required to maintain aortic homeostasis. Vascular smooth muscle cells (VSMCs) elaborate and remodel the extracellular matrix (ECM) in response to mechanical and biochemical cues from their environment. Causal variants for hereditary forms of aneurysm compromise the function of gene products involved in the transmission or interpretation of these signals, initiating processes that eventually lead to degeneration and mechanical failure of the vessel. These include mutations that interfere with transduction of stimuli from the matrix to the actin-myosin cytoskeleton through integrins, and those that impair signaling pathways activated by transforming growth factor-β (TGF-β). In this review, we summarize the features of the healthy aortic wall, the major pathways involved in the modulation of VSMC phenotypes, and the basic molecular functions impaired by TAA-associated mutations. We also discuss how the heterogeneity and balance of adaptive and maladaptive responses to the initial genetic insult might contribute to disease.

Dibenzazepine Attenuates Against Cisplatin-Induced Nephrotoxicity in Rats: Involvement of NOTCH Pathway

Cisplatin is one of the standard anti-cancer agents that are used to treat variety of solid tumors. Nevertheless, due to the accumulation of cisplatin in the renal epithelial cells, nephrotoxicity was found to be the main side effect that limits its clinical use. The current study was conducted to assess the potential nephroprotective effect of dibenzazepine, a Notch inhibitor, against cisplatin-induced nephrotoxicity in rats as well as the possible mechanisms underlying this nephroprotection. The rats were pre-treated with 2 mg/kg dibenzazepine for 7 days before giving a single nephrotoxic dose of cisplatin (7 mg/kg). Cisplatin induced acute nephrotoxicity, where blood urea nitrogen and serum creatinine levels were significantly increased. Besides, lipid peroxidation was markedly elevated and the levels of reduced glutathione and catalase were significantly reduced. Also, the tissue levels of the pro-inflammatory mediators; IL-1β, TNF-α, and NF-kB, were significantly increased in the cisplatin group. The pre-treatment with dibenzazepine significantly mitigated the nephrotoxic effects of cisplatin, the oxidative stress and inflammatory status as well as decreased caspase-3 expression, as compared to the cisplatin group. Furthermore, the up-regulation of Notch-1 and Hes-1 was found to be involved in cisplatin-induced nephrotoxicity and their expression was significantly reduced by dibenzazepine. The nephroprotective effect of dibenzazepine was further confirmed by the histopathological assessment. Moreover, dibenzazepine pre-treatment of hela and PC3 cells in vitro did not antagonize the cisplatin anti-cancer activity. In conclusion, these findings show that dibenzazepine provides protection against cisplatin-induced nephrotoxicity. Moreover, the up-regulation of the Notch pathway was shown to play a role in the pathogenesis of cisplatin-induced renal injury.

DAPT, a potent Notch inhibitor regresses actively growing abdominal aortic aneurysm via divergent pathways

Abdominal aortic aneurysm (AAA) is a localized pathological dilation of the aorta exceeding the normal diameter (∼20 mm) by more than 50% of its original size (≥30 mm), accounting for approximately 150000-200000 deaths worldwide per year. We previously reported that Notch inhibition does not decrease the size of pre-established AAA at late stage of the disease. Here, we examined whether a potent pharmacologic inhibitor of Notch signaling (DAPT (N-[N-(3,5-Difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester)), regresses an actively growing AAA. In a mouse model of an aneurysm (Apoe-/- mice; n=44); DAPT (n=17) or vehicle (n=17) was randomly administered at day 14 of angiotensin II (AngII; 1 µg/min/kg), three times a week and mice were killed on day 42. Progressive increase in aortic stiffness and maximal intraluminal diameter (MILD) was observed in the AngII + vehicle group, which was significantly prevented by DAPT (P<0.01). The regression of aneurysm with DAPT was associated with reduced F4/80+Cd68+ (cluster of differentiation 68) inflammatory macrophages. DAPT improved structural integrity of aorta by reducing collagen fibrils abnormality and restoring their diameter. Mechanistically, C-C chemokine receptor type 7 (Ccr7)+F4/80- dendritic cells (DCs), implicated in the regression of aneurysm, were increased in the aorta of DAPT-treated mice. In the macrophages stimulated with AngII or lipopolysaccharide (LPS), DAPT reverted the expression of pro-inflammatory genes Il6 and Il12 back to baseline within 6 h compared with vehicle (P<0.05). DAPT also significantly increased the expression of anti-inflammatory genes, including c-Myc, Egr2, and Arg1 at 12-24 h in the LPS-stimulated macrophages (P<0.05). Overall, these regressive effects of Notch signaling inhibitor emphasize its therapeutic implications to prevent the progression of active AAAs.

Angiotensin II and leukocyte trafficking: New insights for an old vascular mediator. Role of redox-signaling pathways

Inflammation and activation of the immune system are key molecular and cellular events in the pathogenesis of cardiovascular diseases, including atherosclerosis, hypertension-induced target-organ damage, and abdominal aortic aneurysm. Angiotensin II (Ang-II) is the main effector peptide hormone of the renin-angiotensin system. Beyond its role as a potent vasoconstrictor and regulator of blood pressure and fluid homeostasis, Ang-II is intimately involved in the development of vascular lesions in cardiovascular diseases through the activation of different immune cells. The migration of leukocytes from circulation to the arterial subendothelial space is a crucial immune response in lesion development that is mediated through a sequential and coordinated cascade of leukocyte-endothelial cell adhesive interactions involving an array of cell adhesion molecules present on target leukocytes and endothelial cells and the generation and release of chemoattractants that activate and guide leukocytes to sites of emigration. In this review, we outline the key events of Ang-II participation in the leukocyte recruitment cascade, the underlying mechanisms implicated, and the corresponding redox-signaling pathways. We also address the use of inhibitor drugs targeting the effects of Ang-II in the context of leukocyte infiltration in these cardiovascular pathologies, and examine the clinical data supporting the relevance of blocking Ang-II-induced vascular inflammation.

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.

Collagen fibril abnormalities in human and mice abdominal aortic aneurysm

Vascular diseases like abdominal aortic aneurysms (AAA) are characterized by a drastic remodeling of the vessel wall, accompanied with changes in the elastin and collagen content. At the macromolecular level, the elastin fibers in AAA have been reported to undergo significant structural alterations. While the undulations (waviness) of the collagen fibers is also reduced in AAA, very little is understood about changes in the collagen fibril at the sub-fiber level in AAA as well as in other vascular pathologies. In this study we investigated structural changes in collagen fibrils in human AAA tissue extracted at the time of vascular surgery and in aorta extracted from angiotensin II (AngII) infused ApoE^-/- mouse model of AAA. Collagen fibril structure was examined using transmission electron microscopy and atomic force microscopy. Images were analyzed to ascertain length and depth of D-periodicity, fibril diameter and fibril curvature. Abnormal collagen fibrils with compromised D-periodic banding were observed in the excised human tissue and in remodeled regions of AAA in AngII infused mice. These abnormal fibrils were characterized by statistically significant reduction in depths of D-periods and an increased curvature of collagen fibrils. These features were more pronounced in human AAA as compared to murine samples. Thoracic aorta from Ang II-infused mice, abdominal aorta from saline-infused mice, and abdominal aorta from non-AAA human controls did not contain abnormal collagen fibrils. The structural alterations in abnormal collagen fibrils appear similar to those reported for collagen fibrils subjected to mechanical overload or chronic inflammation in other tissues. Detection of abnormal collagen could be utilized to better understand the functional properties of the underlying extracellular matrix in vascular as well as other pathologies. STATEMENT OF SIGNIFICANCE: Several vascular diseases including abdominal aortic aneurysm (AAA) are characterized by extensive remodeling in the vessel wall. Although structural alterations in elastin fibers are well characterized in vascular diseases, very little is known about the collagen fibril structure in these diseases. We report here a comprehensive ultrastructural evaluation of the collagen fibrils in AAA, using high-resolution microscopy techniques like transmission electron microscopy (TEM) and atomic force microscopy (AFM). We elucidate how abnormal collagen fibrils with compromised D-periodicity and increased fibril curvature are present in the vascular tissue in both clinical AAA as well as in murine models. We discuss how these abnormal collagen fibrils are likely a consequence of mechanical overload accompanying AAA and could impact the functional properties of the underlying tissue.

AT2R agonist NP-6A4 mitigates aortic stiffness and proteolytic activity in mouse model of aneurysm

Clinical and experimental studies show that angiotensin II (AngII) promotes vascular pathology via activation of AngII type 1 receptors (AT1Rs). We recently reported that NP-6A4, a selective peptide agonist for AngII type 2 receptor (AT2R), exerts protective effects on human vascular cells subjected to serum starvation or doxorubicin exposure. In this study, we investigated whether NP-6A4-induced AT2R activation could mitigate AngII-induced abdominal aortic aneurism (AAA) using AngII-treated Apoe^-/- mice. Male Apoe^-/- mice were infused with AngII (1 µg/kg/min) by implanting osmotic pumps subcutaneously for 28 days. A subset of mice was pre-treated subcutaneously with NP-6A4 (2.5 mg/kg/day) or vehicle for 14 days prior to AngII, and treatments were continued for 28 days. NP-6A4 significantly reduced aortic stiffness of the abdominal aorta induced by AngII as determined by ultrasound functional analyses and histochemical analyses. NP-6A4 also increased nitric oxide bioavailability in aortic tissues and suppressed AngII-induced increases in monocyte chemotactic protein-1, osteopontin and proteolytic activity of the aorta. However, NP-6A4 did not affect maximal intraluminal aortic diameter or AAA incidences significantly. These data suggest that the effects of AT2R agonist on vascular pathologies are selective, affecting the aortic stiffness and proteolytic activity without affecting the size of AAA.

The Role of a Selective P2Y6 Receptor Antagonist, MRS2578, on the Formation of Angiotensin II-Induced Abdominal Aortic Aneurysms

Objective

The P2Y₆ receptor has been shown to be involved in many cardiovascular diseases, including hypertension and atherosclerosis. The study is aimed at exploring the role of the P2Y₆ receptor in Ang II-induced abdominal aortic aneurysm (AAA) formation in apolipoprotein E-deficient (apoE^−/−) mice by using its selective antagonist.

Methods

Male apoE^−/− mice were fed with high-fat diet and infused with angiotensin (Ang) II (1000 ng/kg/min) for 4 weeks to induce AAA or saline as controls. Mice were divided into four groups: normal saline (NS, placebo control) group (n = 8), Ang II+vehicle (Ang II) group (n = 14), Ang II-low dose MRS2578 (Ang II+MRS-16 mg) group (n = 14), and Ang II-high dose MRS2578 (Ang II+MRS-32 mg) group (n = 14). Daily intraperitoneal injection with vehicle or MRS2578 was pretreated one week before Ang II infusion. On postoperative day 10, aorta imaging of each group was taken by ultrasonography. After 4 weeks of Ang II infusion, the excised aortas were processed for diameter measurement and quantification of aneurysm severity and tissue characteristics; the blood samples were collected for measurement of the lipid profile and levels of cytokines. Verhoeff's Van Gieson (EVG) staining and immunochemistry staining were performed to evaluate disruption of the extracellular matrix (ECM) and infiltration of macrophages. Expression and activity of matrix metalloproteinases (MMPs) was measured by gelatin zymography.

Results

Treatment with MRS2578 made no significant difference in AAA formation, and maximal aortic diameter yet caused higher AAA rupture-induced mortality from 7% (Ang II) to 21.4% (Ang II+MRS-16 mg) or 42.9% (Ang II+MRS-32 mg), respectively (p < 0.05). Consistently, the severity of aneurysm tended to be more deteriorated in MRS2578-treated groups, especially the high-dosage group. The ratios of type III and IV aneurysm were much higher in the MRS2578-coadministered groups (p < 0.05). Furthermore, histological analyses showed that administration of MRS2578 significantly increased infiltration of macrophages, expression of monocyte chemotactic protein 1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1), and activities of MMP-2 and MMP-9 followed by aggravating degradation elastin in vivo (p < 0.05). However, the multiple effects of MRS2578 on the development of AAA are independent of changes in systolic blood pressure and lipid profiles.

Conclusions

The present study demonstrated that administration of MRS2578 exacerbated the progression and rupture of experimental AAA through promoting proinflammatory response and MMP expression and activity, which indicated a crucial role of the P2Y₆ receptor in AAA development. Clinical Relevance. Purinergic P2Y receptors have attracted much attention since the P2Y₁₂ receptor antagonist had been successfully applied in clinical practice. Elucidating the underlying mechanisms of AAA and exploring potential therapeutic strategies are essential to prevent its progression and reduce the mortality rate.

Insight into the expression of toll-like receptors 2 and 4 in patients with abdominal aortic aneurysm

An abdominal aortic aneurysm (AAA) is a relatively common, life-threatening disease prevalent in persons over the age of 65. In recent years, an increasing number of studies have suggested that pattern-recognition receptors (PRRs), including Toll-like receptors (TLRs), may serve as important regulators in the development of AAAs. In this study, we evaluated the TLR2 and TLR4 expression in the aortic wall and blood of patients with AAA. The TLR2 and TLR4 mRNA expression were significantly higher in the blood of patients with AAA than in the blood of healthy volunteers (p = 0.009 and p = 0.010, respectively). The expression of TLR2 and TLR4 transcripts was also higher in the blood compared with the aortic wall tissue of AAA patients (p = 0.001 for both). Higher TLR2 protein expression was observed in the aortic wall of AAA patients compared with the blood (p = 0.026). A significantly higher concentration of TNF-α and IL-4 in patients with AAA than in healthy volunteers (p < 0.001 for both) was noticed. This study suggests that TLR2 may play a role in the inflammatory response in the aorta, both locally and systemically, in patients with AAA.

Measurement of Pulse Propagation Velocity, Distensibility and Strain in an Abdominal Aortic Aneurysm Mouse Model

An abdominal aortic aneurysm (AAA) is defined as a localized dilation of the abdominal aorta that exceeds the maximal intraluminal diameter (MILD) by 1.5 times of its original size. Clinical and experimental studies have shown that small aneurysms may rupture, while a subpopulation of large aneurysms may remain stable. Thus, in addition to the measurement of intraluminal diameter of the aorta, knowledge of structural traits of the vessel wall may provide important information to assess the stability of the AAA. Aortic stiffening has recently emerged as a reliable tool to determine early changes in the vascular wall. Pulse propagation velocity (PPV) along with the distensibility and radial strain are highly useful ultrasound-based methods relevant for assessing aortic stiffness. The primary purpose of this protocol is to provide a comprehensive technique for the use of ultrasound imaging system to acquire images and analyze the structural and functional properties of the aorta as determined by MILD, PPV, distensibility and radial strain.

Cellular signaling in Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAAs) are highly lethal cardiovascular diseases without effective medications. However, the molecular and signaling mechanisms remain unclear. A series of pathological cellular processes have been shown to contribute to AAA formation, including vascular extracellular matrix remodeling, inflammatory and immune responses, oxidative stress, and dysfunction of vascular smooth muscle cells. Each cellular process involves complex cellular signaling, such as NF-κB, MAPK, TGFβ, Notch and inflammasome signaling. In this review, we discuss how cellular signaling networks function in various cellular processes during the pathogenesis and progression of AAA. Understanding the interaction of cellular signaling networks with AAA pathogenesis as well as the crosstalk of different signaling pathways is essential for the development of novel therapeutic approaches to and personalized treatments of AAA diseases.

Deficiency of IL12p40 (Interleukin 12 p40) Promotes Ang II (Angiotensin II)-Induced Abdominal Aortic Aneurysm

Objective- Abdominal aortic aneurysm is caused by the accumulation of inflammatory cells in the aortic wall. Our recent studies demonstrated that inhibition of Notch signaling attenuates abdominal aortic aneurysm formation by shifting the macrophage balance towards anti-inflammatory (M2) phenotype. Using IL12p40^-/- (interleukin 12 p40) mice, we investigated the effects of M2-predominant macrophages on the development of abdominal aortic aneurysm. Approach and Results- Male (8-10 week-old) wild-type and IL12p40^-/- mice (n=15) on C57BL/6 background were infused with Ang II (angiotensin II, 1000 ng/kg per minute) by implanting osmotic pumps subcutaneously for 28 days. In the IL12p40^-/- mice, Ang II significantly increased the maximal intraluminal diameter (9/15) as determined by transabdominal ultrasound imaging. In addition, IL12p40-deletion significantly increased aortic stiffness in response to Ang II as measured by pulse wave velocity and atomic force microscopy. Histologically, IL12p40^-/- mice exhibited increased maximal external diameter of aorta and aortic lesions associated with collagen deposition and increased elastin fragmentation compared with wild-type mice infused with Ang II. Mechanistically, IL12p40 deficiency by siRNA (small interfering RNA) augmented the Tgfβ2-mediated Mmp2 expression in wild-type bone marrow-derived macrophages without affecting the expression of Mmp9. No such effects of IL12p40 deficiency on MMP2/MMP9 was observed in human aortic smooth muscle cells or fibroblasts. Depletion of macrophages in IL12p40^-/- mice by clodronate liposomes significantly decreased the maximal external diameter of aorta and aortic stiffness in response to Ang II as determined by imaging and atomic force microscopy. Conclusions- IL12p40 depletion promotes the development of abdominal aortic aneurysm, in part, by facilitating recruitment of M2-like macrophages and potentiating aortic stiffness and fibrosis mediated by Tgfβ2.

Pharmacological inhibition of Notch signaling regresses pre-established abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is characterized by transmural infiltration of myeloid cells at the vascular injury site. Previously, we reported preventive effects of Notch deficiency on the development of AAA by reduction of infiltrating myeloid cells. In this study, we examined if Notch inhibition attenuates the progression of pre-established AAA and potential implications. Pharmacological Notch inhibitor (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-(S)-phenylglycine t-butyl ester; DAPT) was administered subcutaneously three times a week starting at day 28 of angiotensin II (AngII) infusion. Progressive increase in pulse wave velocity (PWV), maximal intra-luminal diameter (MILD) and maximal external aortic diameter (MEAD) were observed at day 56 of the AngII. DAPT prevented such increase in MILD, PWV and MEAD (P < 0.01). Histologically, the aortae of DAPT-treated Apoe-/- mice had significant reduction in inflammatory response and elastin fragmentation. Naked collagen microfibrils and weaker banded structure observed in the aortae of Apoe-/- mice in response to AngII, were substantially diminished by DAPT. A significant decrease in the proteolytic activity in the aneurysmal tissues and vascular smooth muscle cells (vSMCs) was observed with DAPT (P < 0.01). In human and mouse AAA tissues, increased immunoreactivity of activated Notch signaling correlated strongly with CD38 expression (R2 = 0.61). Collectively, we propose inhibition of Notch signaling as a potential therapeutic target for AAA progression.

Transcriptomics Analysis Reveals New Insights into the Roles of Notch1 Signaling on Macrophage Polarization

Naïve macrophages (Mφ) polarize in response to various environmental cues to a spectrum of cells that have distinct biological functions. The extreme ends of the spectrum are classified as M1 and M2 macrophages. Previously, we demonstrated that Notch1 deficiency promotes Tgf-β2 dependent M2-polarization in a mouse model of abdominal aortic aneurysm. The present studies aimed to characterize the unique set of genes regulated by Notch1 signaling in macrophage polarization. Bone marrow derived macrophages isolated from WT or Notch1+/- mice (n = 12) were differentiated to Mφ, M1 or M2-phenotypes by 24 h exposure to vehicle, LPS/IFN-γ or IL4/IL13 respectively and total RNA was subjected to RNA-Sequencing (n = 3). Bioinformatics analyses demonstrated that Notch1 haploinsufficiency downregulated the expression of 262 genes at baseline level, 307 genes with LPS/IFN-γ and 254 genes with IL4/IL13 treatment. Among these, the most unique genes downregulated by Notch1 haploinsufficiency included fibromodulin (Fmod), caspase-4, Has1, Col1a1, Alpl and Igf. Pathway analysis demonstrated that extracellular matrix, macrophage polarization and osteogenesis were the major pathways affected by Notch1 haploinsufficiency. Gain and loss-of-function studies established a strong correlation between Notch1 haploinsufficiency and Fmod in regulating Tgf-β signaling. Collectively, our studies suggest that Notch1 haploinsufficiency increases M2 polarization through these newly identified genes.

An overview of the molecular mechanisms underlying development and progression of bicuspid aortic valve disease

Bicuspid aortic valve (BAV) is a common congenital heart malformation frequently associated with the development of aortic valve diseases and severe aortopathy, such as aortic dilatation, aneurysm and dissection. To date, different genetic loci have been identified in syndromic and non- syndromic forms of BAV. Among these, genes involved in the regulation of extracellular matrix remodelling, epithelial to mesenchymal transition and nitric oxide metabolism appear to be the main contributors to BAV pathogenesis. However, no- single gene model explains BAV inheritance, suggesting that more factors are simultaneously involved. In this regard, characteristic epigenetic and immunological profiles have been documented to contradistinguish BAV individuals. In this review, we provide a comprehensive overview addressing molecular mechanisms involved in BAV development and progression.

Development and growth trends in angiotensin II-induced murine dissecting abdominal aortic aneurysms

Abdominal aortic aneurysms are pathological dilations that can suddenly rupture, causing more than 15,000 deaths in the U.S. annually. Current treatment focuses on observation until an aneurysm's size warrants surgical intervention. Thus, there is a need for therapeutic intervention to inhibit growth of smaller aneurysms. An experimental aneurysm model that infuses angiotensin II into apolipoprotein E‐deficient mice is widely used to investigate underlying pathological mechanisms and potential therapeutics, but this model has two caveats: (1) aneurysms do not always form, and (2) aneurysm severity and growth is inconsistent among animals. Here we use high‐frequency ultrasound to collect data from angiotensin II‐induced aneurysms to develop prediction models of both aneurysm formation and growth. Baseline measurements of aortic diameter, volume/length, and strain were used with animal mass and age in a quadratic discriminant analysis and logistic regression to build two statistical models to predict disease status. Longitudinal ultrasound data were also acquired from mice with aneurysms to quantify aneurysm diameter, circumferential strain, blood flow velocity, aneurysm volume/length, and thrombus and open‐false lumen volumes over 28 days. Measurements taken at aneurysm diagnosis were used with branching artery information to produce a multiple linear regression model to predict final aneurysm volume/length. All three statistical models could be useful in future aneurysm therapeutic studies to better delineate the effects of preventative and suppressive treatments from normal variations in the angiotensin II aneurysm model.

Potential Medication Treatment According to Pathological Mechanisms in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a vascular disease with high mortality. Because of the lack of effective medications to stop or reverse the progression of AAA, surgical operation has become the most predominant recommendation of treatment for patients. There are many potential mechanisms, including inflammation, smooth muscle cell apoptosis, extracellular matrix degradation, oxidative stress, and so on, involving in AAA pathogenesis. According to those mechanisms, some potential therapeutic drugs have been proposed and tested in animal models and even in clinical trials. This review focuses on recent advances in both pathogenic mechanisms and potential pharmacologic therapies of AAA.

Diverse roles of macrophage polarization in aortic aneurysm: destruction and repair

Aortic aneurysm (AA) is defined as an enlargement of the aorta greater than 1.5 times its normal size. Early diagnosis of AA is challenging and mortality of AA is high. Curative pharmacological treatments for AA are still lacking, highlighting the need for better understanding of the underlying mechanisms of AA progression. Accumulating studies have proven that the polarization state of circulating monocyte-derived macrophages plays a crucial role in regulating the development of AA. Distinct macrophage subtypes display different functions. Several studies targeting macrophage polarization during AA formation and progression showed potential treatment effects. In this review, we focus on the recent advances of research on macrophage polarization in the progression of AA and propose that targeting macrophage polarization could hold great promise for preventing and treating AA.

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.

Deregulation of Notch1 pathway and circulating endothelial progenitor cell (EPC) number in patients with bicuspid aortic valve with and without ascending aorta aneurysm

Bicuspid aortic valve (BAV) is frequently associated with the development of ascending aortic aneurysm, even if the underlying mechanisms remain to be clarified. Here, we investigated if a deregulation of Notch1 signaling pathway and endothelial progenitor cells (EPCs) number is associated with BAV disease and an early ascending aortic aneurysm (AAA) onset. For this purpose, 70 subjects with BAV (M/F 50/20; mean age: 58.8 ± 14.8 years) and 70 subjects with tricuspid aortic valve (TAV) (M/F 35/35; mean age: 69.1 ± 12.8 years) and AAA complicated or not, were included. Interestingly, patients with AAA showed a significant increase in circulating Notch1 levels and EPC number than subjects without AAA. However, circulating Notch1 levels and EPC number were significantly lower in BAV subjects than TAV patients either in the presence or absence of AAA. Finally, Notch pathway was activated to a greater extent in aortic aneurysmatic portions with respect to healthy aortic fragments in both BAV and TAV patients. However, the expression of genes encoding components and ligands of Notch pathway in aortic tissues was significantly lower in BAV than TAV subjects. Our study demonstrates that BAV subjects are characterized by a significant decrease in both tissue and circulating levels of Notch pathway, and in blood EPC number than TAV patients, either in presence or absence of AAA disease.

Shear stress, arterial identity and atherosclerosis

In the developing embryo, the vasculature first takes the form of a web-like network called the vascular plexus. Arterial and venous differentiation is subsequently guided by the specific expression of genes in the endothelial cells that provide spatial and temporal cues for development. Notch1/4, Notch ligand delta-like 4 (Dll4), and Notch downstream effectors are typically expressed in arterial cells along with EphrinB2, whereas chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) and EphB4 characterise vein endothelial cells. Haemodynamic forces (blood pressure and blood flow) also contribute importantly to vascular remodelling. Early arteriovenous differentiation and local blood flow may hold the key to future inflammatory diseases. Indeed, despite the fact that atherosclerosis risk factors such as smoking, hypertension, hypercholesterolaemia, and diabetes all induce endothelial cell dysfunction throughout the vasculature, plaques develop only in arteries, and they localise essentially in vessel branch points, curvatures and bifurcations, where blood flow (and consequently shear stress) is low or oscillatory. Arterial segments exposed to high blood flow (and high laminar shear stress) tend to remain plaque-free. These observations have led many to investigate what particular properties of arterial or venous endothelial cells confer susceptibility or protection from plaque formation, and how that might interact with a particular shear stress environment.

Mouse macrophage specific knockout of SIRT1 influences macrophage polarization and promotes angiotensin II-induced abdominal aortic aneurysm formation

Abdominal aortic aneurysm (AAA) is a vascular degenerative disease. Macrophage polarization and the balance between classically activated macrophages (M1) and alternatively activated macrophages (M2) are crucial for AAA pathogenesis. The present study aims to investigate the roles of macrophage SIRT1 in AAA formation and macrophage polarization. We found that in mouse peritoneal macrophages, SIRT1 expression was decreased after M1 stimulation, but was enhanced after M2 stimulation. Results from SIRT1^flox/flox mice and macrophage specific SIRT1 knockout mice with treatment of angiotensin II (Ang II) for 4 weeks showed that macrophage specific deficiency of SIRT1 increased the incidence of AAA and exacerbated the severity, including more severe aneurysm types, enlarged diameter of the aneurysm and increased degradation of elastin. In mouse aortas, SIRT1 deficiency increased the pro-inflammatory M1 molecule inducible nitric oxide synthase (iNOS), and decreased M2 molecules such as arginase 1 (Arg1) and mannose receptor (MR). Furthermore, in peritoneal macrophages, SIRT1 deficiency increased the expression of M1 inflammatory molecules, but decreased the expression of M2 molecules. Overexpression of SIRT1 had the opposite effects. Thus, macrophage specific knockout of SIRT1 influences macrophage polarization and accelerates Ang II-induced AAA formation.

Thoracic Aortic Aneurysm Development in Patients with Bicuspid Aortic Valve: What Is the Role of Endothelial Cells?

Bicuspid aortic valve (BAV) is the most common type of congenital cardiac malformation. Patients with a BAV have a predisposition for the development of thoracic aortic aneurysm (TAA). This pathological aortic dilation may result in aortic rupture, which is fatal in most cases. The abnormal aortic morphology of TAAs results from a complex series of events that alter the cellular structure and extracellular matrix (ECM) composition of the aortic wall. Because the major degeneration is located in the media of the aorta, most studies aim to unravel impaired smooth muscle cell (SMC) function in BAV TAA. However, recent studies suggest that endothelial cells play a key role in both the initiation and progression of TAAs by influencing the medial layer. Aortic endothelial cells are activated in BAV mediated TAAs and have a substantial influence on ECM composition and SMC phenotype, by secreting several key growth factors and matrix modulating enzymes. In recent years there have been significant advances in the genetic and molecular understanding of endothelial cells in BAV associated TAAs. In this review, the involvement of the endothelial cells in BAV TAA pathogenesis is discussed. Endothelial cell functioning in vessel homeostasis, flow response and signaling will be highlighted to give an overview of the importance and the under investigated potential of endothelial cells in BAV-associated TAA.

Smooth muscle cell-specific Notch1 haploinsufficiency restricts the progression of abdominal aortic aneurysm by modulating CTGF expression

Aims

Infiltration of macrophages and apoptosis of vascular smooth muscle cells (VSMCs) promote the development of abdominal aortic aneurysm (AAA). Previously, we demonstrated that global Notch1 deficiency prevents the formation of AAA in a mouse model. Herein, we sought to explore the cell-specific roles of Notch1 in AAA development.

Methods and results

Cell-specific Notch1 haploinsufficient mice, generated on Apoe^-/- background using Cre-lox technology, were infused with angiotensin II (1000 ng/min/kg) for 28 days. Notch1 haploinsufficiency in myeloid cells (n = 9) prevented the formation of AAA attributed to decreased inflammation. Haploinsufficiency of Notch1 in SMCs (n = 14) per se did not prevent AAA formation, but histoarchitectural traits of AAA including elastin degradation and aortic remodeling, were minimal in SMC-Notch1^+/-;Apoe^-/- mice compared to Apoe^-/- mice (n = 33). Increased immunostaining of the contractile SMC-phenotype markers and concomitant decreased expression of synthetic SMC-phenotype markers were observed in the aortae of SMC-Notch1^+/-;Apoe^-/- mice. Expression of connective tissue growth factor (CTGF), a matrix-associated protein that modulates the synthetic VSMC phenotype, increased in the abdominal aorta of Apoe^-/- mice and in the adventitial region of the abdominal aorta in human AAA. Notch1 haploinsufficiency decreased the expression of Ctgf in the aorta and in vitro cell culture system. In vitro studies on SMCs using the Notch1 intracellular domain (NICD) plasmid, dominant negative mastermind-like (dnMAML), or specific siRNA suggest that Notch1, not Notch3, directly modulates the expression of CTGF.

Conclusions

Our data suggest that lack of Notch1 in SMCs limits dilation of the abdominal aorta by maintaining contractile SMC-phenotype and preventing matrix-remodeling.

AT1 receptor signaling pathways in the cardiovascular system

The importance of the renin angiotensin aldosterone system in cardiovascular physiology and pathophysiology has been well described whereas the detailed molecular mechanisms remain elusive. The angiotensin II type 1 receptor (AT1 receptor) is one of the key players in the renin angiotensin aldosterone system. The AT1 receptor promotes various intracellular signaling pathways resulting in hypertension, endothelial dysfunction, vascular remodeling and end organ damage. Accumulating evidence shows the complex picture of AT1 receptor-mediated signaling; AT1 receptor-mediated heterotrimeric G protein-dependent signaling, transactivation of growth factor receptors, NADPH oxidase and ROS signaling, G protein-independent signaling, including the β-arrestin signals and interaction with several AT1 receptor interacting proteins. In addition, there is functional cross-talk between the AT1 receptor signaling pathway and other signaling pathways. In this review, we will summarize an up to date overview of essential AT1 receptor signaling events and their functional significances in the cardiovascular system.

Notch signaling mediated by TGF-β/Smad pathway in concanavalin A-induced liver fibrosis in rats

AIM

To explore the exact interaction between Notch and transforming growth factor (TGF)-β signaling in liver fibrosis.

METHODS

We established a rat model of liver fibrosis induced by concanavalin A. Peripheral blood mononuclear cells (PBMCs) were isolated from the modeled rats, and cultured with γ-secretase inhibitor DAPT and TGF-β inhibitor for 24 h. The mRNA levels of Notch and TGF-β signaling were detected by quantitative real-time polymerase chain reaction. Expression of Notch and TGF-β proteins was analyzed by western blotting.

RESULTS

Compared to control rats, Notch and TGF-β signaling was activated in PBMCs of model rats. Administration of DAPT and TGF-β inhibitor suppressed Notch and TGF-β signal transducer in PBMCs of model rats. DAPT reduced mRNA and protein expression of TGF-β signaling, such as TGF-β1 and Smad3. TGF-β inhibitor also downregulated Notch1, Hes1 and Hes5, and mRNA and protein expression of the Notch signaling pathway.

CONCLUSION

Notch and TGF-β signaling play a role in liver fibrosis. TGF-β signaling upregulates Notch signaling, which promotes TGF-β signaling.

Pathophysiology of aortic aneurysm: insights from human genetics and mouse models

Aneurysms are local dilations of an artery that predispose the vessel to sudden rupture. They are often asymptomatic and undiagnosed, resulting in a high mortality rate. The predisposition to develop thoracic aortic aneurysms is often genetically inherited and associated with syndromes affecting connective tissue homeostasis. This review discusses how elucidation of the genetic causes of syndromic forms of thoracic aortic aneurysm has helped identify pathways that contribute to disease progression, including those activated by TGF-β, angiotensin II and Notch ligands. We also discuss how pharmacological manipulation of these signaling pathways has provided further insight into the mechanism of disease and identified compounds with therapeutic potential in these and related disorders.

Abdominal aortic aneurysm: novel mechanisms and therapies

PURPOSE OF REVIEW

Abdominal aortic aneurysm (AAA) is a pathological condition of permanent dilation that portends the potentially fatal consequence of aortic rupture. This review emphasizes recent advances in mechanistic insight into aneurysm pathogenesis and potential pharmacologic therapies that are on the horizon for AAAs.

RECENT FINDINGS

An increasing body of evidence demonstrates that genetic factors, including 3p12.3, DAB2IP, LDLr, LRP1, matrix metalloproteinase (MMP)-3, TGFBR2, and SORT1 loci, are associated with AAA development. Current human studies and animal models have shown that many leukocytes and inflammatory mediators, such as IL-1, IL-17, TGF-β, and angiotensin II, are involved in the pathogenesis of AAAs. Leukocytic infiltration into aortic media leads to smooth muscle cell depletion, generation of reactive oxygen species, and extracellular matrix fragmentation. Preclinical investigations into pharmacological therapies for AAAs have provided intriguing insight into the roles of microRNAs in regulating many pathological pathways in AAA development. Several large clinical trials are ongoing, seeking to translate preclinical findings into therapeutic options.

SUMMARY

Recent studies have identified many potential mechanisms involved in AAA pathogenesis that provide insight into the development of a medical treatment for this disease.

Impact of aortic root size on left ventricular afterload and stroke volume

PURPOSE

The left ventricle (LV) ejects blood into the proximal aorta. Age and hypertension are associated with stiffening and dilation of the aortic root, typically viewed as indicative of adverse remodeling. Based on analytical considerations, we hypothesized that a larger aortic root should be associated with lower global afterload (effective arterial elastance, EA) and larger stroke volume (SV). Moreover, as antihypertensive drugs differ in their effect on central blood pressure, we examined the role of antihypertensive drugs for the relation between aortic root size and afterload.

METHODS

We studied a large group of patients (n = 1250; 61 ± 12 years; 78 % males; 64 % hypertensives) from a single-center registry with known or suspected coronary artery disease. Aortic root size was measured by echocardiography as the diameter of the tubular portion of the ascending aorta. LV outflow tract Doppler was used to record SV.

RESULTS

In the population as a whole, after adjusting for key covariates in separate regression models, aortic root size was an independent determinant of both SV and EA. This association was found to be heterogeneous and stronger in patients taking a calcium channel blocker (CCB; 10.6 % of entire population; aortic root size accounted for 8 % of the explained variance of EA).

CONCLUSION

Larger aortic root size is an independent determinant of EA and SV. This association was heterogeneous and stronger in patients on CCB therapy.

Notch1 inhibition reduces low shear stress-induced plaque formation

Low shear stress (LSS) contributes to the pathogenesis of inflammatory diseases, such as atherosclerosis. Notch1 is a type I transmembrane receptor that critically determines the growth, differentiation, and survival of various cell types, but its role and mechanism in LSS-induced inflammatory response remains undetermined. Apolipoprotein E-deficient (ApoE(-/-)) mice were fed with high fat diet and administered intraperitoneally with DAPT (a γ-secretase inhibitor). Perivascular shear stress modifiers were placed around the right carotid arteries to induce LSS. The left carotid arteries with undisturbed shear stress (USS) were used as the control. LSS increased Delta-like 1 (DLL-1) protein expression and the expression of Notch1 and NICD, while DAPT administration reduced NICD expression. Compared with the LSS group, DAPT reduced LSS-induced plaque formation and intercellular adhesion molecule 1 (ICAM-1) expression. Human umbilical vein endothelial cells (HUVECs) were exposure to undisturbed shear stress (USS, 1Pa) or LSS (0.4Pa). Notch1 was inhibited by siRNA or DAPT. RT-PCR and western blotting analysis showed that LSS upregulated the expression of Notch1 in a time-dependent manner. Caveolin-1 (CAV1) inhibition by siRNA could reduce Notch1 and NICD expression. Compared with USS, LSS increased inflammatory response, including IL-1β and IL-6 secretion, ICAM-1 and inducible nitric oxide synthase (iNOS) expression, and THP-1 cells adhesion. Notch1 inhibition by siRNA or DAPT could reduce these inflammatory responses by reduction of NF-κB phosphorylation, upregulation of IkBα expression, and inhibition of nuclear translocation of NF-κB, while Notch1 activation by DLL-4 had an adverse effect. The Notch signaling system is therefore a potential target for modulating LSS-induced inflammation response during atherosclerosis.

The potential role of DNA methylation in abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a complex disorder that has a significant impact on the aging population. While both genetic and environmental risk factors have been implicated in AAA formation, the precise genetic markers involved and the factors influencing their expression remain an area of ongoing investigation. DNA methylation has been previously used to study gene silencing in other inflammatory disorders and since AAA has an extensive inflammatory component, we sought to examine the genome-wide DNA methylation profiles in mononuclear blood cells of AAA cases and matched non-AAA controls. To this end, we collected blood samples and isolated mononuclear cells for DNA and RNA extraction from four all male groups: AAA smokers (n = 11), AAA non-smokers (n = 9), control smokers (n = 10) and control non-smokers (n = 11). Methylation data were obtained using the Illumina 450k Human Methylation Bead Chip and analyzed using the R language and multiple Bioconductor packages. Principal component analysis and linear analysis of CpG island subsets identified four regions with significant differences in methylation with respect to AAA: kelch-like family member 35 (KLHL35), calponin 2 (CNN2), serpin peptidase inhibitor clade B (ovalbumin) member 9 (SERPINB9), and adenylate cyclase 10 pseudogene 1 (ADCY10P1). Follow-up studies included RT-PCR and immunostaining for CNN2 and SERPINB9. These findings are novel and suggest DNA methylation may play a role in AAA pathobiology.

Macrophages in vascular inflammation--From atherosclerosis to vasculitis

The spectrum of vascular inflammatory disease ranges from atherosclerosis and hypertension, widespread conditions affecting large proportions of the population, to the vasculitides, rare syndromes leading to fast and irreversible organ failure. Atherosclerosis progresses over decades, inevitably proceeding through multiple phases of disease and causes its major complications when the vessel wall lesion ruptures, giving rise to lumen-occlusive atherothrombosis. Vasculitides of medium and large arteries progress rapidly, causing tissue ischemia through lumen-occlusive intimal hyperplasia. In both disease entities, macrophages play a decisive role in pathogenesis, but function in the context of other immune cells that direct their differentiation and their functional commitments. In atherosclerosis, macrophages are involved in the removal of lipids and tissue debris and make a critical contribution to tissue damage and wall remodeling. In several of the vasculitides, macrophages contribute to granuloma formation, a microstructural platform optimizing macrophage-T-cell interactions, antigen containment and inflammatory amplification. By virtue of their versatility and plasticity, macrophages are able to promote a series of pathogenic functions, ranging from the release of cytokines and enzymes, the production of reactive oxygen species, presentation of antigen and secretion of tissue remodeling factors. However, as short-lived cells that lack memory, macrophages are also amendable to reprogramming, making them promising targets for anti-inflammatory interventions.

Combining detection of Notch1 and tumor necrosis factor-α converting enzyme is a reliable biomarker for the diagnosis of abdominal aortic aneurysms

AIMS

Although many markers were associated with abdominal aortic aneurysm (AAA), there is no clear consensus on which marker is of the most value. Studies have implicated the role of Notch signaling in the pathogenesis of AAA. We investigate the value of plasma Jagged1, Notch receptors and tumor necrosis factor-α converting enzyme (TACE) in identifying AAA.

MAIN METHODS

42 patients with AAA and 36 controls were enrolled in our study. The concentrations of plasma Jagged1, Notch receptors and TACE were measured by enzyme-linked immunosorbent assay (ELISA). The diagnostic value of plasma Notch1 and TACE was assessed by logistic regression and receiver operator characteristic (ROC) curve. Double immunofluorescence staining was used to investigate the distribution of Notch1 and TACE in AAA tissue specimens.

KEY FINDINGS

The concentrations of plasma Notch1 and TACE were significantly higher in AAA than in the controls, respectively (Notch1: P < 0.001; TACE: P = 0.0001). The area under the curve (AUC) from ROC curve of plasma Notch1 and TACE in determining the presence of AAA was 0.878 and 0.804, respectively. Combining detection of plasma Notch1 and TACE could improve the accuracy in detecting AAA (AUC 0.984, P < 0.0001). The predicted probability cutoff of 0.70 gave a sensitivity of 90.5% and a specificity of 100% for combining detection of plasma Notch1 and TACE in predicting AAA.

SIGNIFICANCE

This is the first report revealing that plasma Notch1 and TACE are highly expressed in AAA. Combining detection of plasma Notch1 and TACE may be reliable for identifying the presence of AAA.

Identification and characterization of CD4(+)AT2(+) T lymphocyte population in human thoracic aortic aneurysm

Thoracic aortic aneurysm (TAA) is progressive fatal aortic pathological dilation. However, the underlying molecular mechanisms are still largely unknown. Evidences suggest that endothelial cells and renin-angiotensin system may participate in the pathogenesis of TAA. This study aimed to investigate whether angiotensin II type 2 receptor (AT2) positive cells are involved in TAA formation. The mRNA level of AT2 is dramatically elevated in TAA compared with in controls. CD4(+)AT2(+) cells increased in both aortic wall and circulation of TAA patients. The levels of IL-1β and IL-17B in CD4(+)AT2(+) cells were lower than those in CD4(+)AT2(-) cells. When compared with endothelial cells (ECs) cultured alone, CD4(+)AT2(+) cells showed an inhibitory effect on proliferation and MMP2 expression in ECs, but CD4(+)AT2(-) cells promoted proliferation and MMP2 expression in ECs. Both CD4(+)AT2(+) and CD4(+)AT2(-) cells suppressed apoptosis of ECs. In conclusion, we have identified a novel population of CD4(+)AT2(+) T lymphocytes that show protective effect in TAA through inhibition of growth, apoptosis, and MMP2 expression in ECs.

Cross Talk between NOTCH Signaling and Biomechanics in Human Aortic Valve Disease Pathogenesis

Aortic valve disease is a burgeoning public health problem associated with significant mortality. Loss of function mutations in NOTCH1 cause bicuspid aortic valve (BAV) and calcific aortic valve disease. Because calcific nodules manifest on the fibrosa side of the cusp in low fluidic oscillatory shear stress (OSS), elucidating pathogenesis requires approaches that consider both molecular and mechanical factors. Therefore, we examined the relationship between NOTCH loss of function (LOF) and biomechanical indices in healthy and diseased human aortic valve interstitial cells (AVICs). An orbital shaker system was used to apply cyclic OSS, which mimics the cardiac cycle and hemodynamics experienced by AVICs in vivo. NOTCH LOF blocked OSS-induced cell alignment in human umbilical vein endothelial cells (HUVECs), whereas AVICs did not align when subjected to OSS under any conditions. In healthy AVICs, OSS resulted in decreased elastin (ELN) and α-SMA (ACTA2). NOTCH LOF was associated with similar changes, but in diseased AVICs, NOTCH LOF combined with OSS was associated with increased α-SMA expression. Interestingly, AVICs showed relatively higher expression of NOTCH2 compared to NOTCH1. Biomechanical interactions between endothelial and interstitial cells involve complex NOTCH signaling that contributes to matrix homeostasis in health and disorganization in disease.

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.

The Notch γ-secretase inhibitor ameliorates kidney fibrosis via inhibition of TGF-β/Smad2/3 signaling pathway activation

Kidney fibrosis is a common feature of chronic kidney disease (CKD). A recent study suggests that abnormal Notch signaling activation contributes to the development of renal fibrosis. However, the molecular mechanism that regulates this process remains unexplored. Unilateral ureteral obstruction (UUO) or sham-operated C57BL6 mice (aged 10 weeks) were randomly assigned to receive dibenzazepine (DBZ, 250 μg/100g/d) or vehicle for 7 days. Histologic examinations were performed on the kidneys using Masson's trichrome staining and immunohistochemistry. Real-time PCR and western blot analysis were used for detection of mRNA expression and protein phosphorylation. The expression of Notch 1, 3, and 4, Notch intracellular domain (NICD), and its target genes Hes1 and HeyL were upregulated in UUO mice, while the increase in NICD protein was significantly attenuated by DBZ. After 7 days, the severity of renal fibrosis and expression of fibrotic markers, including collagen 1α1/3α1, fibronectin, and α-smooth muscle actin, were markedly increased in UUO compared with sham mice. In contrast, administration of DBZ markedly attenuated these effects. Furthermore, DBZ significantly inhibited UUO-induced expression of transforming growth factor (TGF)-β, phosphorylated Smad 2, and Smad 3. Mechanistically, Notch signaling activation in tubular epithelial cells enhanced fibroblast proliferation and activation in a coculture experiment. Our study provides evidence that Notch signaling is implicated in renal fibrogenesis. The Notch inhibitor DBZ can ameliorate this process via inhibition of the TGF-β/Smad2/3 signaling pathway, and might be a novel drug for preventing chronic kidney disease.