Smooth Muscle Cell Depletion Research Articles

Gasdermin D Inhibitor Necrosulfonamide Alleviates Angiotensin II-Induced Abdominal Aortic Aneurysms in Apolipoprotein E-Deficient Mice.

Abdominal aortic aneurysm (AAA) is a chronic aortic disease that lacks effective pharmacological therapies. This study was performed to determine the influence of treatment with the gasdermin D inhibitor necrosulfonamide on experimental AAAs. AAAs were induced in male apolipoprotein E-deficient mice by subcutaneous angiotensin II infusion (1000 ng/kg body weight/min), with daily administration of necrosulfonamide (5 mg/kg body weight) or vehicle starting 3 days prior to angiotensin II infusion for 30 days. Necrosulfonamide treatment remarkably suppressed AAA enlargement, as indicated by reduced suprarenal maximal external diameter and surface area, and lowered the incidence and reduced the severity of experimental AAAs. Histologically, necrosulfonamide treatment attenuated medial elastin breaks, smooth muscle cell depletion, and aortic wall collagen deposition. Macrophages, CD4+ T cells, CD8+ T cells, and neovessels were reduced in the aneurysmal aortas of necrosulfonamide- as compared to vehicle-treated angiotensin II-infused mice. Atherosclerosis and intimal macrophages were also substantially reduced in suprarenal aortas from angiotensin II-infused mice following necrosulfonamide treatment. Additionally, the levels of serum interleukin-1β and interleukin-18 were significantly lower in necrosulfonamide- than in vehicle-treated mice without affecting body weight gain, lipid levels, or blood pressure. Our findings indicate that necrosulfonamide reduced experimental AAAs by preserving aortic structural integrity as well as reducing mural leukocyte accumulation, neovessel formation, and systemic levels of interleukin-1β and interleukin-18. Thus, pharmacologically inhibiting gasdermin D activity may lead to the establishment of nonsurgical therapies for clinical AAA disease.

Abstract 3013: Indoleamine 2,3-dioxygenase-mediated Tryptophan Catabolism Limits Experimental Abdominal Aortic Aneurysms

Background: Indoleamine 2,3-dioxygenase (IDO) promotes immunosuppression. Genetic IDO deficiency limits angiotensin II-induced abdominal aortic aneurysms (AAAs) in hyperlipidemic mice. We investigated the influence of IDO inhibition or IDO-catabolized tryptophan catabolite on elastase-induced AAAs in normolipidemic mice. Methods: AAAs were induced in male C57B/6J mice via intra-aortic porcine pancreatic elastase (PPE) infusion. Mice were treated with IDO inhibitor 1-methyl-DL-tryptophan (MT, 2 mg/ml in drinking water), tryptophan metabolite 3-hydroxyanthranilic acid (HAA, 200 mg/kg, oral gavage), or vehicle, starting 3 days prior to PPE infusion for 17 days. AAAs were assessed via ultrasonography and histopathology at sacrifice. Results: The Figure summarizes aortic diameters and histopathology in differentially treated PPE-infused mice. Rapid aortic enlargement was noted in MT-, as compared to vehicle-treated mice following PPE infusion. AAA rupture, unusual for this model, was noted in MT-treated AAA mice. No difference was noted between groups in medial elastin degradation, smooth muscle cell depletion, or macrophage accumulation. However, mural neoangiogenesis and lymphocyte accumulation were remarkably augmented in MT-treated mice. HAA Treatment attenuated aortic enlargement in conjunction with improved medial elastin and smooth muscle cell retention and reduced aortic leukocyte accumulation and neovessels. Conclusion: IDO activity and its tryptophan metabolite HAA limit experimental AAA progression in the PPE model. These results provide further support for investigating tryptophan metabolites in clinical AAA disease suppression.

Treatment With Small Molecule Inhibitors of Advanced Glycation End-Products Formation and Advanced Glycation End-Products-Mediated Collagen Cross-Linking Promotes Experimental Aortic Aneurysm Progression in Diabetic Mice.

Background Although diabetes attenuates abdominal aortic aneurysms (AAAs), the mechanisms by which diabetes suppresses AAAs remain incompletely understood. Accumulation of advanced glycation end- (AGEs) reduces extracellular matrix (ECM) degradation in diabetes. Because ECM degradation is critical for AAA pathogenesis, we investigated whether AGEs mediate experimental AAA suppression in diabetes by blocking AGE formation or disrupting AGE-ECM cross-linking using small molecule inhibitors. Methods and Results Male C57BL/6J mice were treated with streptozotocin and intra-aortic elastase infusion to induce diabetes and experimental AAAs, respectively. Aminoguanidine (AGE formation inhibitor, 200 mg/kg), alagebrium (AGE-ECM cross-linking disrupter, 20 mg/kg), or vehicle was administered daily to mice from the last day following streptozotocin injection. AAAs were assessed via serial aortic diameter measurements, histopathology, and in vitro medial elastolysis assays. Treatment with aminoguanidine, not alagebrium, diminished AGEs in diabetic AAAs. Treatment with both inhibitors enhanced aortic enlargement in diabetic mice as compared with vehicle treatment. Neither enhanced AAA enlargement in nondiabetic mice. AAA enhancement in diabetic mice by aminoguanidine or alagebrium treatment promoted elastin degradation, smooth muscle cell depletion, mural macrophage accumulation, and neoangiogenesis without affecting matrix metalloproteinases, C-C motif chemokine ligand 2, or serum glucose concentration. Additionally, treatment with both inhibitors reversed suppression of diabetic aortic medial elastolysis by porcine pancreatic elastase in vitro. Conclusions Inhibiting AGE formation or AGE-ECM cross-linking enhances experimental AAAs in diabetes. These findings support the hypothesis that AGEs attenuate experimental AAAs in diabetes. These findings underscore the potential translational value of enhanced ECM cross-linking as an inhibitory strategy for early AAA disease.

Genetic deficiency of protein inhibitor of activated STAT3 suppresses experimental abdominal aortic aneurysms.

Signal transducer and activator of transcription (STAT) signaling is critical for the pathogenesis of abdominal aortic aneurysms (AAAs). Though protein inhibitor of activated STAT3 (PIAS3) negatively modulates STAT3 activity, but its role in AAA disease remains undefined. AAAs were induced in PIAS3 deficient (PIAS3-/-) and wild type (PIAS3+/+) male mice via transient intra-aortic elastase infusion. AAAs were assessed by in situ measurements of infrarenal aortic external diameters prior to (day 0) and 14 days after elastase infusion. Characteristic aneurysmal pathologies were evaluated by histopathology. Fourteen days following elastase infusion, aneurysmal aortic diameter was reduced by an approximately 50% in PIAS3-/- as compared to PIAS3+/+ mice. On histological analyses, PIAS3-/- mice showed less medial elastin degradation (media score: 2.5) and smooth muscle cell loss (media score: 3.0) than those in PIAS3+/+ mice (media score: 4 for both elastin and SMC destruction). Aortic wall leukocyte accumulation including macrophages, CD4+ T cells, CD8+ T cells and B cells as well as mural neovessel formation were significantly reduced in PIAS3-/- as compared to PIAS3+/+ mice. Additionally, PIAS3 deficiency also downregulated the expression levels of matrix metalloproteinases 2 and 9 by 61% and 70%, respectively, in aneurysmal lesion. PIAS3 deficiency ameliorated experimental AAAs in conjunction with reduced medial elastin degradation and smooth muscle cell depletion, mural leukocyte accumulation and angiogenesis.

Type I Interferon Receptor Subunit 1 Deletion Attenuates Experimental Abdominal Aortic Aneurysm Formation.

Objective: Type I interferon receptor signaling contributes to several autoimmune and vascular diseases such as lupus, atherosclerosis and stroke. The purpose of this study was to assess the influence of type I interferon receptor deficiency on the formation and progression of experimental abdominal aortic aneurysms (AAAs). Methods: AAAs were induced in type I interferon receptor subunit 1 (IFNAR1)-deficient and wild type control male mice via intra-infrarenal aortic infusion of porcine pancreatic elastase. Immunostaining for IFNAR1 was evaluated in experimental and clinical aneurysmal abdominal aortae. The initiation and progression of experimental AAAs were assessed via ultrasound imaging prior to (day 0) and days 3, 7 and 14 following elastase infusion. Aneurysmal histopathology was analyzed at sacrifice. Results: Increased aortic medial and adventitial IFNAR1 expression was present in both clinical AAAs harvested at surgery and experimental AAAs. Following AAA induction, wild type mice experienced progressive, time-dependent infrarenal aortic enlargement. This progression was substantially attenuated in IFNAR1-deficient mice. On histological analyses, medial elastin degradation, smooth muscle cell depletion, leukocyte accumulation and neoangiogenesis were markedly diminished in IFNAR1-deficient mice in comparison to wild type mice. Conclusion: IFNAR1 deficiency limited experimental AAA progression in response to intra-aortic elastase infusion. Combined with clinical observations, these results suggest an important role for IFNAR1 activity in AAA pathogenesis.

Abstract 345: Natural Vascular Scaffolding Suppresses Experimental Abdominal Aortic Aneurysms

Objective: Proteolytic destruction of aortic extracellular matrix (ECM) is central to abdominal aortic aneurysm (AAA) pathogenesis. Matrix metalloproteinase inhibition with doxycycline failed to limit AAA progression. However, photochemical modification of collagen and elastin fibers may provide an alternative approach to ECM stabilization. We investigated the effectiveness of this treatment in limiting experimental AAA progression. Methods: AAAs were created in 8-10 weeks old male C57BL/6J mice via intra-aortic elastase infusion. Natural vascular scaffolding (NVS) (2 mg/ml, Alucent Biomedical) or vehicle solution was applied to the abluminal aortic wall immediately following elastase infusion and aortotomy closure and exposed to laser light activation. AAA progression was assessed via serial ultrasound aortic diameter measurements and histopathologic analysis at sacrifice. Results: Ultrasonography confirmed progressive aortic enlargement and AAA formation in all vehicle-treated mice within 14 days following elastase infusion. NVS treatment substantially attenuated AAA development and progression with reduced medial elastin degradation and smooth muscle cell depletion, as well as mural neovessel development. No difference was seen in aortic CD4 or CD8 T accumulation between the two treatment groups. Conclusion: Photochemical linking of extracellular matrix proteins attenuated experimental AAA progression, suggesting a potential translational application for this approach in clinical disease management.

Temporal and Quantitative Analysis of Aortic Immunopathologies in Elastase-Induced Mouse Abdominal Aortic Aneurysms.

Objective Elastase-induced abdominal aortic aneurysm (AAA) model is widely used for aneurysmal pathogenesis and translational research. However, temporal alternations in aneurysmal histologies remain unknown. This study is aimed at analyzing temporal immunopathologies of aneurysmal aorta following experimental AAA induction. Methods Male C57BL/6J mice at the age of 10-14 weeks received intra-aortic infusion of elastase to induce AAAs. Aortic diameters at the baseline and indicated days after AAA induction were measured, and aortae were collected for histopathological analysis. Results Aorta diameters increased from 0.52 mm at the baseline levels to 0.99 mm, 1.34 mm, and 1.41 mm at days 7, 14, and 28, respectively, corresponding 90%, 158%, and 171% increases over the baseline level. Average aortic diameters did not differ between days 14 and 28. Severe elastin degradation and smooth muscle cell depletion were found at days 14 and 28 as compared to the baseline and day 7. No difference in the scores of medial elastin and SMC destruction was noted between days 14 and 28. Consistent results were found for leukocyte accumulation, neoangiogenesis, and matrix metalloproteinase expression. Twenty-eight days after AAA induction, all aneurysmal pathologies showed an attenuated trend, although most histopathological parameters did no differ between days 14 and 28. Conclusion Our data suggest that almost aneurysmal immunohistopathologies reach maximal 14 days following AAA induction. Analysis of day 14 histologies is sufficient for AAA pathogenesis and translational studies in elastase-induced mouse experimental AAAs.

No Effect of Hypercholesterolemia on Elastase-Induced Experimental Abdominal Aortic Aneurysm Progression.

Objective: Epidemiological studies link hyperlipidemia with increased risk for abdominal aortic aneurysms (AAAs). However, the influence of lipid-lowering drugs statins on prevalence and progression of clinical and experimental AAAs varies between reports, engendering controversy on the association of hyperlipidemia with AAA disease. This study investigated the impact of hypercholesterolemia on elastase-induced experimental AAAs in mice. Methods: Both spontaneous (targeted deletion of apolipoprotein E) and induced mouse hypercholesterolemia models were employed. In male wild type (WT) C57BL/6J mice, hypercholesterolemia was induced via intraperitoneal injection of an adeno-associated virus (AAV) encoding a gain-of-function proprotein convertase subtilisin/kexin type 9 mutation (PCSK9) followed by the administration of a high-fat diet (HFD) (PCSK9+HFD) for two weeks. As normocholesterolemic controls for PCSK9+HFD mice, WT mice were infected with PCSK9 AAV and fed normal chow, or injected with phosphate-buffered saline alone and fed HFD chow. AAAs were induced in all mice by intra-aortic infusion of porcine pancreatic elastase and assessed by ultrasonography and histopathology. Results: In spontaneous hyper- and normo-cholesterolemic male mice, the aortic diameter enlarged at a constant rate from day 3 through day 14 following elastase infusion. AAAs, defined as a more than 50% diameter increase over baseline measurements, formed in all mice. AAA progression was more pronounced in male mice, with or without spontaneous hyperlipidemia. The extent of elastin degradation and smooth muscle cell depletion were similar in spontaneous hyper- (score 3.5 for elastin and 4.0 for smooth muscle) and normo- (both scores 4.0) cholesterolemic male mice. Aortic mural macrophage accumulation was also equivalent between the two groups. No differences were observed in aortic accumulation of CD4+ or CD8+ T cells, B cells, or mural angiogenesis between male spontaneous hyper- and normocholesterolemic mice. Similarly, no influence of spontaneous hypercholesterolemia on characteristic aneurysmal histopathology was noted in female mice. In confirmatory experiments, induced hypercholesterolemia also exerted no appreciable effect on AAA progression and histopathologies. Conclusion: This study demonstrated no recognizable impact of hypercholesterolemia on elastase-induced experimental AAA progression in both spontaneous and induced hypercholesterolemia mouse models. These results add further uncertainty to the controversy surrounding the efficacy of statin therapy in clinical AAA disease.

Single-Cell RNA Sequencing Reveals Heterogeneity of Vascular Cells in Early Stage Murine Abdominal Aortic Aneurysm-Brief Report.

Abdominal aortic aneurysm (AAA) is a life-threatening vascular disease characterized by smooth muscle cell depletion, ECM (extracellular matrix) degradation, and infiltration of immune cells. The cellular and molecular profiles that govern the heterogeneity of the AAA aorta are yet to be elucidated. Approach and Results: We performed single-cell RNA sequencing on mouse AAA tissues. AAA was induced in C57BL/6J mice by perivascular application of CaCl2. Unbiased clustering identified 12 distinct populations of 8 cell types. Percentages of each population and gene expression were compared between sham and AAA tissue. Furthermore, we characterized the transcriptional profiles and potential functional features of populations in smooth muscle cells, fibroblasts, and macrophages and revealed the unique regulons in each cell type. Together, these data provide high-resolution insight into the complexity and heterogeneity of mouse AAA and indicate that populations within major cell types such as smooth muscle cells, fibroblasts, and macrophages may contribute differently to AAA pathogenesis. Graphic Abstract: A graphic abstract is available for this article.

Inhibition of miR-188-5p Suppresses Progression of Experimental Abdominal Aortic Aneurysms.

Abdominal aortic aneurysm (AAA) is an aging-related degenerative disease. miR-188-5p was reported to induce cell senescence and play a key role in aging-related disease. Therefore, in this study, we investigated miR-188-5p expression during progression in experimental AAAs. Furthermore, we investigated whether inhibition of miR-188-5p could suppress AAA progression. Experimental AAAs were created in 9-12-week-old male C57BL/6J mice by transient intra-aortic infusion of porcine pancreatic elastase. Expression of miR-188-5p levels were assessed in aneurysmal and control aortae during the progression of aneurysm. For inhibition experiment, miR-188 inhibiting group mice were injected with AAV2-miR188-5p sponge through tail vein and control group mice were injected with AAV2-CMV-GFP. Influences on experimental AAA progression were assessed by measurements of aortic diameter and histopathologic analysis at sacrifice. Meanwhile, immunohistochemistry and fluorescence in situ hybridization were used to determine the inflammatory cells infiltration and colocalization of miR-188-5p in aortic sections. Expression of miR-188-5p is upregulated during progression of AAA. Importantly, miR-188-5p inhibition treatment prevented enlargement of experimental aneurysms. Meanwhile, miR-188-5p inhibition regimens attenuated medial elastin degradation, smooth muscle cell depletion, and mural angiogenesis and the accumulation of macrophages, T cells, and angiogenesis. Furthermore, colocalization of miR188-5p with CD68 and CD3 was observed, which suggest miR-188-5p was expressed mainly in infiltrated macrophages and T cells. Expression of miR-188-5p is increased in experimental AAAs. Treatment with miR-188-5p inhibition limits experimental AAA progression, with histologic evidence of reduced neovessels and attenuated mural leukocyte infiltration. These findings underscore the potential significance of miR-188-5p in aneurysm pathogenesis and as a target for suppression of AAA disease.

Vinpocetine protects against the development of experimental abdominal aortic aneurysms.

Abdominal aortic aneurysm (AAA), commonly occurring in the aged population, is a degenerative disease that dilate and weaken infrarenal aorta due to progressive degeneration of aortic wall integrity. Vinpocetine, a derivative of alkaloid vincamine, has long been used for cerebrovascular disorders and cognitive impairment in the aged population. Recent studies have indicated that vinpocetine antagonizes occlusive vascular disorders such as intimal hyperplasia and atherosclerosis. However, its role in vascular degenerative disease AAA remains unexplored. Herein, we determined the effect of vinpocetine on the formation of AAA as well as the intervention of pre-existing moderate AAA. AAA was induced by periaortic elastase application in C57BL/6J mice. Systemic vinpocetine treatment was applied daily via intraperitoneal injection. We showed that vinpocetine pre-treatment remarkably attenuated aneurysmal dilation assessed by diameter and volume. More importantly, vinpocetine also significantly suppressed the progression of pre-existing moderate AAA in a post-intervention model. Vinpocetine improved multiple cellular and molecular changes associated with AAA, such as elastin degradation, media smooth muscle cell depletion, collagen fibers remodeling and macrophage infiltration in aneurysmal tissues. Vinpocetine potently suppressed tumor necrosis factor-α-induced nuclear factor kappa-light-chain-enhancer of activated B cells activation and proinflammatory mediator expression in primary cultured macrophages in vitro, as well as in the aorta wall in vivo, suggesting vinpocetine conferred anti-AAA effect at least partially via the inhibition of inflammation. Taken together, our findings reveal a novel role of vinpocetine in AAA formation, development and progression. Given the excellent safety profile of vinpocetine, the present study suggests vinpocetine may be a novel therapeutic agent for AAA prevention and treatment.

Premature Vascular Aging with Features of Plaque Vulnerability in an Atheroprone Mouse Model of Hutchinson-Gilford Progeria Syndrome with Ldlr Deficiency.

Hutchinson–Gilford progeria syndrome (HGPS) is among the most devastating of the laminopathies, rare genetic diseases caused by mutations in genes encoding nuclear lamina proteins. HGPS patients age prematurely and die in adolescence, typically of atherosclerosis-associated complications. The mechanisms of HGPS-related atherosclerosis are not fully understood due to the scarcity of patient-derived samples and the availability of only one atheroprone mouse model of the disease. Here, we generated a new atherosusceptible model of HGPS by crossing progeroid LmnaG609G/G609G mice, which carry a disease-causing mutation in the Lmna gene, with Ldlr−/− mice, a commonly used preclinical atherosclerosis model. Ldlr−/−LmnaG609G/G609G mice aged prematurely and had reduced body weight and survival. Compared with control mice, Ldlr−/−LmnaG609G/G609G mouse aortas showed a higher atherosclerosis burden and structural abnormalities typical of HGPS patients, including vascular smooth muscle cell depletion in the media, adventitial thickening, and elastin structure alterations. Atheromas of Ldlr−/−LmnaG609G/G609G mice had features of unstable plaques, including the presence of erythrocytes and iron deposits and reduced smooth muscle cell and collagen content. Ldlr−/−LmnaG609G/G609G mice faithfully recapitulate vascular features found in patients and thus provide a new tool for studying the mechanisms of HGPS-related atherosclerosis and for testing therapies.

Identification of a novel class of RIP1/RIP3 dual inhibitors that impede cell death and inflammation in mouse abdominal aortic aneurysm models

Receptor interacting protein kinase-1 and -3 (RIP1 and RIP3) are essential mediators of cell death processes and participate in inflammatory responses. Our group recently demonstrated that gene deletion of Rip3 or pharmacological inhibition of RIP1 attenuated pathogenesis of abdominal aortic aneurysm (AAA), a life-threatening degenerative vascular disease characterized by depletion of smooth muscle cells (SMCs), inflammation, negative extracellular matrix remodeling, and progressive expansion of aorta. The goal of this study was to develop drug candidates for AAA and other disease conditions involving cell death and inflammation. We screened 1141 kinase inhibitors for their ability to block necroptosis using the RIP1 inhibitor Necrostatin-1s (Nec-1s) as a selection baseline. Positive compounds were further screened for cytotoxicity and virtual binding to RIP3. A cluster of top hits, represented by GSK2593074A (GSK’074), displayed structural similarity to the established RIP3 inhibitor GSK’843. In multiple cell types including mouse SMCs, fibroblasts (L929), bone marrow derived macrophages (BMDM), and human colon epithelial cells (HT29), GSK’074 inhibited necroptosis with an IC50 of ~3 nM. Furthermore, GSK’074, but not Nec-1s, blocked cytokine production by SMCs. Biochemical analyses identified both RIP1 and RIP3 as the biological targets of GSK’074. Unlike GSK’843 which causes profound apoptosis at high doses (>3 µM), GSK’074 showed no detectable cytotoxicity even at 20 µM. Daily intraperitoneal injection of GSK’074 at 0.93 mg/kg significantly attenuated aortic expansion in two mouse models of AAA (calcium phosphate: DMSO 66.06 ± 9.17% vs GSK’074 27.36 ± 8.25%, P < 0.05; Angiotensin II: DMSO 85.39 ± 15.76% vs GSK’074 36.28 ± 5.76%, P < 0.05). Histologically, GSK’074 treatment diminished cell death and macrophage infiltration in aneurysm-prone aortae. Together, our data suggest that GSK’074 represents a new class of necroptosis inhibitors with dual targeting ability to both RIP1 and RIP3. The high potency and minimum cytotoxicity make GSK’074 a desirable drug candidate of pharmacological therapies to attenuate AAA progression and other necroptosis related diseases.

A novel swine model of abdominal aortic aneurysm

ObjectiveFew large-animal models exist for the study of aortic aneurysms. β-Aminopropionitrile (BAPN) is a compound known to cause aortic aneurysms by inhibiting lysyl oxidase, a collagen cross-linking enzyme. It is hypothesized that BAPN plus aneurysm induction surgery would result in significant aneurysm formation in swine with biologic properties similar to human disease. MethodsInitial experiments were performed in uncastrated male swine not treated with BAPN (surgery alone). Subsequently, uncastrated male swine were fed BAPN (0.15 g/kg) for 7 days before undergoing surgery; the infrarenal aorta was circumferentially dissected and measured, balloon dilated, and perfused with elastase (500 units) and type I collagenase (8000 units), with extraluminal elastase application. In the BAPN groups, daily BAPN feedings continued until swine harvest at postoperative days 7, 14, and 28. ResultsSwine undergoing surgery alone (n = 12) had significantly less dilation at 28 days compared with BAPN + surgery swine (51.9% ± 29.2% [0%-100%] vs 113.5% ± 30.2% [52.9%-146.2%]; P < .0003). Mean aortic dilation in animals undergoing treatment with surgery and BAPN was 86.9% ± 47.4% (range, 55.6%-157.1%), 105.4% ± 58.1% (50%-133.3%), and 113.5% ± 30.2% (52.9%-146.2%) at 7, 14, and 28 days, respectively. In the BAPN + surgery group, significant elastolysis was present at all time points, whereas aortic wall collagen content was not significantly different. Smooth muscle cells were significantly depleted at 14 and 28 days, and M1 macrophages were increased at 14 and 28 days (P < .05, all). Matrix metalloproteinase 2 was elevated at 7 days (P < .05). Multiple proinflammatory cytokines were elevated within the aortic wall of BAPN + surgery swine. ConclusionsBAPN plus surgery resulted in significantly larger aortic aneurysms than surgery alone and was critical to aneurysm formation in this novel swine model. Hallmarks of human disease, such as elastin fragmentation, smooth muscle cell depletion, macrophage infiltration, matrix metalloproteinase activation, and proinflammatory cytokine expression, were observed in BAPN-treated swine. This model better parallels many of the characteristics of human AAAs and may be suitable for prehuman drug trials.

Abstract 058: Efficacy and Mechanisms of Metformin Therapy in Established Experimental Abdominal Aortic Aneurysms

Objective: Diabetes reduces the risk for abdominal aortic aneurysm (AAA) disease. In prior work in rodent models, pre-treatment with metformin was protective against experimental AAA initiation and progression. This study examined the influence of metformin therapy on progression of existing experimental AAAs. Methods: AAAs were created in 10-12 week old male C57BL/6J mice via transient intra-aortic infusion of porcine pancreatic elastase (PPE). Mice were treated with metformin (250 mg/kg via oral gavage), metformin plus AMPK inhibitor Compound C (the later via 10 mg/kg intraperitoneal injection) or vehicle alone for 10 days starting on day 4 following AAA creation. Outcomes were assessed by serial transabdominal ultrasonographic assessment of aortic diameter during treatment, as well as histological examination at sacrifice. Results: The principal findings are summarized in the Figure. Vehicle-treated mice experienced progressive, time-dependent aortic enlargement from day 3 to 14 following PPE infusion. Metformin treatment substantially attenuated further enlargement of existing AAAs. Treatment with Compound C partially rescued the AAA phenotype in metformin-treated mice. Histologically, characteristic aneurysmal pathologic changes, including medial elastin degradation, smooth muscle cell (SMC) depletion, mural leukocyte accumulation and neoangiogenesis (assessed by CD31 staining), present in PPE-infused, vehicle-treated mice, were substantially attenuated with metformin treatment. Co-treatment with Compound C abrogated the effects of metformin on media elastin degradation, SMC depletion and mural macrophage infiltration, with less influence on mural angiogenesis. Conclusion: Metformin therapy suppresses further expansion of existing experimental AAAs. This effect is abrogated by co-treatment with Compound C. These findings further justify performance of a clinical trial of metformin for medical management of AAA disease.

Abstract 713: Angiotensin 1-7 Suppresses Experimental Abdominal Aortic Aneurysms

Objectives: Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease, the pathogenesis of which remains incompletely defined. We and others have demonstrated the critical role of angiotensin (Ang) II and its receptor AT1 in experimental AAAs. Although Ang 1-7 and its receptor Mas counteract many AT1 functions, the role of the Ang 1-7/Mas pathway has not been studied in AAAs. This study evaluated the influences of Ang 1-7 and Mas on experimental AAAs. Methods: AAAs were created in male C57BL/6J mice via porcine pancreatic elastase (PPE) infusion. Mice were treated with Ang 1-7 (0.5 mg/kg/day via s.c) or vehicle starting immediately prior to, or 4 days following, PPE infusion. Additional mice were co-treated with Ang 1-7 and the Mas receptor antagonist A779 (0.5 mg/kg/day) beginning immediately prior to PPE infusion. Influences on AAAs were evaluated by serial ultrasound imaging and histology. Results: Figure summarizes major results. In ultrasound imaging, at 14 days Ang 1-7 treatment initiated immediately following aneurysm creation substantially suppressed aortic enlargement as compared to vehicle treatment. Histologically, Ang 1-7 treatment was associated with attenuation of aortic medial elastin and smooth muscle cell depletion, mural macrophage, CD4 + , CD8 + T and B cell density and neoangiogenesis. Co-treatment with Ang 1-7 receptor Mas antagonist A779 “rescued” the aneurysm phenotype. Additionally, Ang 1-7 treatment initiated even 4 days following AAA creation was still effective in limiting further aneurysmal enlargement and pathologic evolution. Conclusions: Ang 1-7 treatment, initiated either at, or up to 4 days following, AAA initiation limits further progression of experimental AAAs. This inhibitory effect seems likely related to activation of the Mas receptor. These results suggest that either Ang 1-7 or alternative Mas receptor agonists may have clinical utility in suppressing progression of early AAA disease.

Discovery of a new class of RIP1/RIP3 dual inhibitors with anti‐cell death and anti‐inflammatory properties

BackgroundReceptor interacting protein kinase‐1 and ‐3 (RIP1 and RIP3) are essential mediators of cell death processes and participate in inflammatory responses. Our group recently demonstrated that gene deletion of Rip3 or pharmacological inhibition of RIP1 attenuate the pathogenesis of abdominal aortic aneurysm (AAA), a life‐threatening, degenerative vascular disease characterized by depletion of smooth muscle cells, inflammation, negative extracellular matrix remodeling, and progressive expansion of the aorta. The goal of this study is to develop a potent RIP1/RIP3 inhibitor applicable to treating disease conditions such as AAA that involve cell necrosis and inflammation.Methods and ResultsWe screened 1,141 kinase inhibitors available in the Small Molecule Screening Facility at UW‐Madison. The compounds were selected for their ability to block necroptosis more potently than Necrostatin‐1s (Nec‐1s, 20 μM, a widely used RIP1 inhibitor), followed by cytotoxicity tests and a virtual screen for RIP3 binding affinity. Among the top hits, compound C9 displayed structural similarity to the established RIP3 inhibitor GSK’843. In multiple cell types including mouse smooth muscle cells, fibroblast cells (L929), and human colon cancer cells (HT29), C9 inhibited necroptosis with an IC50 of 3 nM, which was significantly lower than Nec‐1s (802 nM) and GSK’843 (993 nM). Furthermore, C9, but not Nec‐1s, blocked cytokine production by smooth muscle cells. Biochemical studies and molecular docking revealed that C9 directly targeted RIP1 and RIP3 as a type II kinase inhibitor. C9 inhibited necroptosis signaling including necrosome formation and downstream activation of mixed lineage kinase domain like (MLKL). Unlike GSK’843 which caused apoptosis at high doses (&gt;3 μM), C9 showed no cytotoxicity at even 20 μM. Of note, C9 did not rescue the apoptotic response induced by GSK’843 or ER stress. Encouraged by the minimum cytotoxicity and relative high stability (half‐life in liver microsome ~1 hour), we tested C9 in mice using two AAA models: the calcium phosphate model and angiotensin II (AngII) model. Daily intraperitoneal injection of C9 at 2 μmol/kg significantly blocked aortic expansion in both models (aortic expansion in calcium phosphate model: DMSO 66.06±9.17% vs C9 27.36±8.25%, P&lt;0.05; AngII model: DMSO 85.39±15.76% vs C9 36.28±5.76%, P&lt;0.05). Histologically, C9 treatment diminished necrosis and macrophage infiltration in aneurysm‐prone aortae.ConclusionTogether, our data suggests that C9 is a new class of type II kinase inhibitor with dual targeting ability to both RIP1 and RIP3. Its high potency and minimum cytotoxicity make C9 a desirable drug candidate for pharmacological attenuation of aneurysm progression and other necroptosis related pathologies.Support or Funding InformationThis study was supported by NIH R01HL088447 (Bo Liu), American Heart Associationpostdoctoral fellowship 17POST33680095 (Ting Zhou).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hypoxia-inducible factor 1 in clinical and experimental aortic aneurysm disease

ObjectiveMural angiogenesis and macrophage accumulation are two pathologic hallmarks of abdominal aortic aneurysm (AAA) disease. The heterodimeric transcription factor hypoxia-inducible factor 1 (HIF-1) is an essential regulator of angiogenesis and macrophage function. In this study, we investigated HIF-1 expression and activity in clinical and experimental AAA disease. MethodsHuman aortic samples were obtained from 24 AAA patients and six organ donors during open abdominal surgery. Experimental AAAs were created in 10-week-old male C57BL/6J mice by transient intra-aortic infusion of porcine pancreatic elastase (PPE). Expression of HIF-1α and its target gene messenger RNA (mRNA) levels were assessed in aneurysmal and control aortae. The HIF-1α inhibitors 2-methoxyestradiol and digoxin, the prolyl hydroxylase domain-containing protein (PHD) inhibitors cobalt chloride and JNJ-42041935, and the vehicle alone as control were administered daily to mice at varying time points beginning before or after PPE infusion. Influences on experimental AAA formation and progression were assessed by serial transabdominal ultrasound measurements of aortic diameter and histopathologic analysis at sacrifice. ResultsThe mRNA levels for HIF-1α, vascular endothelial growth factor A, glucose transporter 1, and matrix metalloproteinase 2 were significantly increased in both human and experimental aneurysm tissue. Tissue immunostaining detected more HIF-1α protein in both human and experimental aneurysmal aortae compared with respective control aortae. Treatment with either HIF-1α inhibitor, beginning before or after PPE infusion, prevented enlargement of experimental aneurysms. Both HIF-1α inhibition regimens attenuated medial elastin degradation, smooth muscle cell depletion, and mural angiogenesis and the accumulation of macrophages, T cells, and B cells. Whereas mRNA levels for PHD1 and PHD2 were elevated in experimental aneurysmal aortae, pharmacologic inhibition of PHDs had limited effect on experimental aneurysm progression. ConclusionsExpression of HIF-1α and its target genes is increased in human and experimental AAAs. Treatment with HIF-1α inhibitors limits experimental AAA progression, with histologic evidence of attenuated mural leukocyte infiltration and angiogenesis. These findings underscore the potential significance of HIF-1α in aneurysm pathogenesis and as a target for pharmacologic suppression of AAA disease.

Abdominal aortic aneurysm: novel mechanisms and therapies.

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

Abstract 665: Conditional Deficiency of Myeloid Cell Hif-2α Activity Promotes Aneurysmal Aortic Degeneration

Abdominal aortic aneurysm (AAA) is a chronic degenerative disease mediated by myeloid cells, particularly macrophages. The transcription factor hypoxia inducible factor (HIF)-2α is a potent modulator of macrophage activation/ polarization. A potential role for HIF-2α in aneurysm pathogenesis has yet to be demonstrated. To consider this role, we created experimental AAA in conditional, myeloid cell-specific HIF-2α deficient mice (CKO) by intra-aortic infusion of porcine pancreatic elastase (PPE). Following PPE infusion, serial ultrasound imaging demonstrated progressively larger aneurysms in HIF-2α CKO mice, characterized by increased aortic medial elastin fragmentation and smooth muscle cell depletion, compared to WT controls. Aortic accumulation of CD68+ macrophages and CD4+ T cells, as well as aortic mural CD31+ neovessel formation were also augmented in HIF-2α CKO mice. These observations suggest that myeloid cell-derived HIF-2α activity may limit aneurysm pathogenesis and influence progression of AAA disease.