Matrix Metalloproteinase and Aortic Aneurysm: A Two-sample Mendelian Randomization Study.

BACKGROUND: Studies have linked matrix metalloproteinases (MMPs) to both thoracic aortic aneurysm and abdominal aortic aneurysm (TAA and AAA). The precise MMPs entailed in this procedure, however, were still unknown. This study used a two-sample Mendelian randomization (MR) analysis to look into the causal relationship between MMPs and the risk of TAA and AAA. METHODS: Eight MMPs, including MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, MMP-10, MMP-12, and MMP-13, were found among people of European ancestry with accessible Genome-Wide Association Studies (GWAS). We employed the findings from Genome-Wide Association Studies (GWAS) for 8 MMPs, and TAA and AAA from the FinnGen consortiums (3,201 cases and 317,899 controls, respectively) were used in a two-sample MR analysis. The primary method of analysis for MR was the inverse variance weighted (IVW) method, along with analyses of heterogeneity and horizontal pleiotropy. 31 single-nucleotide polymorphisms connected to MMP were retrieved. RESULTS: IVW demonstrated a negative causal association between TAA and AAA and serum MMP-12 levels. The incidence of TAA decreased by 1.031% for every 1 ng/mL increase in serum MMP-12 [odds ratio (OR) = 0.897, 95% confidence interval (CI): 0.831-0.968, P = 0.005]. The incidence of AAA fell by 1.653% (OR = 0.835, 95% CI: 0.752-0.926, P = 0.001) for every 1 ng/mL increase in serum MMP-12. There was no horizontal pleiotropy or heterogeneity in the MR data (P > 0.05). CONCLUSIONS: The levels of TAA and AAA and serum MMP-12 are causally related. MMP-12 is a factor that reduces the risk of AAA and TTA. Our study suggested that MMP-12 level is causally associated with a decreased risk of TAA and AAA.

Allosteric activation of PP2A inhibits experimental abdominal aortic aneurysm.

Although extremely important, the molecular mechanisms that govern aortic aneurysm (AA) formation and progression are still poorly understood. This deficit represents a critical roadblock toward the development of effective pharmaceutical therapies for the treatment of AA. While dysregulation of protein phosphatase 2A (PP2A) is thought to play a role in cardiovascular disease, its role in aortic aneurysm is unknown. The objective of the present study is to test the hypothesis that PP2A regulates abdominal aortic aneurysm (AAA) progression in a murine model. In an angiotensin II-induced AAA murine model, the PP2A inhibitor, LB-100, markedly accelerated AAA progression as demonstrated by increased abdominal aortic dilation and mortality. AAA progression was associated with elevated inflammation and extracellular matrix fragmentation, concomitant with increases in both metalloproteinase activity and reactive oxygen species production. Conversely, administration of a novel class of small molecule activators of PP2A (SMAPs) resulted in an antithetical effect. SMAPs effectively reduced AAA incidence along with the corresponding pathologies that were increased with LB-100 treatment. Mechanistically, modulation of PP2A activities in vivo functioned in part via alteration of the ERK1/2 and NFκB signaling pathways, known regulators of AAA progression. These studies, for the first time, demonstrate a role of PP2A in AAA etiology and demonstrate that PP2A activation may represent a novel strategy for the treatment of abdominal aortic aneurysms.

PKM2 Activator TEPP-46 Attenuates Thoracic Aortic Aneurysm and Dissection by Inhibiting NLRP3 Inflammasome-Mediated IL-1ß Secretion.

BACKGROUND: The development of thoracic aortic aneurysm and dissection (TAAD) is mediated by inflammasome activation, which exacerbates the secretion of pro-inflammatory cytokines, chemokines, matrix metalloproteinases (MMPs), and reactive oxygen species (ROS). The glycolytic enzyme pyruvate kinase M2 (PKM2) has shown a protective role against various disorders with an inflammatory basis, such as sepsis, tumorigenesis, and diabetic nephropathy. However, its potential role in TAAD has not been investigated so far. APPROACH AND RESULTS: We analyzed aortic tissues from TAAD patients and the ß-aminopropionitrile fumarate (BAPN)-induced mouse model of TAAD and observed elevated levels of PKM2 in the aortic lesions of both. Treatment with the PKM2 activator TEPP-46 markedly attenuated the progression of TAAD in the mouse model as demonstrated by decreased morbidity and luminal diameter of the aorta. In addition, the thoracic aortas of the BAPN-induced mice showed reduced monocytes and macrophages infiltration and lower levels of IL-1ß, MMPs, and ROS when treated with TEPP-46. Furthermore, TEPP-46 treatment also suppressed the activation of the NOD-like receptor (NLR) family and pyrin domain-containing protein 3 (NLRP3) inflammasome by downregulating p-STAT3 and HIF1-α. CONCLUSION: Pyruvate kinase M2 plays a protective role in TAAD development, and its activation is a promising therapeutic strategy against the progression of TAAD.

Long Noncoding RNA XIST/miR-17/PTEN Axis Modulates the Proliferation and Apoptosis of Vascular Smooth Muscle Cells to Affect Stanford Type A Aortic Dissection.

Stanford type A aortic dissection (TAAD) is one of the most lethal cardiovascular diseases with an extremely high morbidity and mortality rate. LncRNA X-inactive specific transcript (XIST) is abundantly expressed in human thoracic aortic dissection, indicating it may play important roles in TAAD progression. However, the molecular mechanism of lncRNA XIST in TAAD is still in its infancy. Quantitative real-time PCR (qRT-PCR) was performed to detect the expression of XIST and miR-17 in the aortic wall tissues of TAAD patients and age-matched healthy volunteers. The relationships between XIST, miR-17, and PTEN were evaluated using dual-luciferase reporter, western blot, and qRT-PCR assays. The biological functions of XIST in rat aortic vascular smooth muscle cells (VSMCs) were explored with Cell Counting Kit 8 (CCK-8), qRT-PCR, and western blot assays. Results found that XIST was upregulated in aortic wall tissues of patients with TAAD and associated with the prognosis of patients with TAAD. Silence XIST facilitated VSMC proliferation and inhibited VSMC apoptosis, whereas restoration XIST displayed opposite effects. Moreover, mechanistic studies revealed that XIST contained binding sites for miR-17 and miR-17 downregulation reversed the elevation of cell proliferation and attenuation of cell apoptosis, which was induced by silence XIST. Further study revealed that XIST positively regulated PTEN expression through its competitive target miR-17. In conclusion, knockdown of lncRNA XIST might attenuate the progression of TAAD by sponging miR-17 and regulating the following downstream PTEN, which suggested a novel therapeutic target for TAAD treatment.

Chronic mTOR activation induces a degradative smooth muscle cell phenotype.

Smooth muscle cell (SMC) proliferation has been thought to limit the progression of thoracic aortic aneurysm and dissection (TAAD) because loss of medial cells associates with advanced disease. We investigated effects of SMC proliferation in the aortic media by conditional disruption of Tsc1, which hyperactivates mTOR complex 1. Consequent SMC hyperplasia led to progressive medial degeneration and TAAD. In addition to diminished contractile and synthetic functions, fate-mapped SMCs displayed increased proteolysis, endocytosis, phagocytosis, and lysosomal clearance of extracellular matrix and apoptotic cells. SMCs acquired a limited repertoire of macrophage markers and functions via biogenesis of degradative organelles through an mTOR/ß-catenin/MITF-dependent pathway, but were distinguishable from conventional macrophages by an absence of hematopoietic lineage markers and certain immune effectors even in the context of hyperlipidemia. Similar mTOR activation and induction of a degradative SMC phenotype in a model of mild TAAD due to Fbn1 mutation greatly worsened disease with near-uniform lethality. The finding of increased lysosomal markers in medial SMCs from clinical TAAD specimens with hyperplasia and matrix degradation further supports the concept that proliferation of degradative SMCs within the media causes aortic disease, thus identifying mTOR-dependent phenotypic modulation as a therapeutic target for combating TAAD.

Effect of miR-21 on rat thoracic aortic aneurysm model by regulating the expressions of MMP-2 and MMP-9.

OBJECTIVE: To explore the mechanism underlying micro ribonucleic acid (miR)-21 in the invasion of rat aortic aneurysm cells in vitro by regulating matrix metalloproteinase (MMP)-2 and MMP-9. MATERIALS AND METHODS: Rats were randomly divided into three groups: control group, model group, and miR-21 group. Real Time fluorescence quantitative Polymerase Chain Reaction (qRT-PCR) was adopted to detect the levels of miR-21 in each group of cells, transwell assay was performed to measure the effect of miR-21 on the invasion of aortic aneurysm cells. Western blotting was used to examine the expression of PTEN, which is the predicted target of miR-21 in aortic aneurysm cells, as well as the expressions of invasion-related proteases, MMP-2 and MMP-9. RESULTS: The expression level of miR-21 in thoracic aortic aneurysm cells in model group was significantly higher than that in normal group (p<0.05), and that in miR-21 group was remarkably higher than that in model group (p<0.05). MiR-21 group had evidently more aortic aneurysm cells and stronger cell invasion ability than normal group and model group (p<0.05). In addition, the expression level of PTEN in model group was significantly higher than that in normal group (p<0.05), while that in miR-21 group notably declined compared to model group, (p<0.05). Compared with normal group and model group, the expressions of MMP-2 and MMP-9 were markedly increased in miR-21 group (p<0.05). CONCLUSIONS: In aortic aneurysm cells of rats, miR-21 could suppress the expression of PTEN and activate MMP-2 and MMP-9 signals to promote the proliferation and migration of aortic aneurysm cells.

The natural history of type B aortic dissection in patients with PRKG1 mutation c.530G>A (p.Arg177Gln).

OBJECTIVE: The c.530G>A (p.Arg177Gln) mutation in PRKG1 has been shown to be associated with thoracic aortic aneurysms and dissections. This rare mutation accounts for an estimated 1% of nonsyndromic heritable thoracic aortic disease. We sought to describe the clinical presentation of type B aortic dissection (TBAD), management, and outcomes in patients with this mutation. METHODS: This is a descriptive multi-institutional retrospective study of patients from six families with the PRKG1 mutation. Patients with TBAD were selected for analysis. Demographics, family histories, TBAD management, and outcomes were reviewed. RESULTS: Of the 29 individuals diagnosed with the PRKG1 mutation, 12 (41.3%) had TBAD (50% male, TBAD median age: 31 years [range, 16-58 years], median follow-up: 6 years [range, 3-15 years] after TBAD). All had a family history of aortic dissections and none had features of Marfan syndrome. The median size of the descending thoracic aorta (DTA) at TBAD was 4.1 cm (range, 3.8-5 cm). Most cases (9 acute TBAD, 1 incidental TBAD diagnosis during screening) were managed medically. One case had open DTA repair the acute phase. Repair for dissection-related aneurysmal degeneration was performed in seven cases (58.3%) in the chronic phase at a median of 2 years (range, 1-8 years) after TBAD. In four cases (33.3%), the DTA remained stable in size over a range of 1 to 7 years after TBAD. Type A aortic dissection subsequent to TBAD occurred in three cases (25%). There were four (33.3%) deaths in the series, all aortic related at a median age of 24 years (range, 19-43 years). CONCLUSIONS: The PRKG1 (p.Arg177Gln) mutation although rare is associated with nonsyndromic TBAD in young and middle-aged patients. Workup for this gene mutation should be included as part of the workup for TBAD etiology in relatively young patients and those with familial history of aortic dissections. Once diagnosed, testing of first-degree family members is warranted. In all individuals with a PRKG1 mutation, close follow-up for aortic root dilatation and hypertension control is essential to reduce the risk of type A or type B aortic dissection, and in cases of TBAD, to decrease the risk of dissection-related aneurysmal degeneration.

Rapamycin prevents thoracic aortic aneurysm and dissection in mice.

OBJECTIVE: The purpose of this study was to investigate whether rapamycin inhibits the development of thoracic aortic aneurysm and dissection (TAAD) in mice. METHODS: Three-week-old C57BL/6J male mice were fed a normal diet and randomized into a control group (n = 6), ß-aminopropionitrile fumarate (BAPN) group (Gp A; n = 15), BAPN plus rapamycin (5 mg) group (Gp B; n = 8), and BAPN plus rapamycin (10 mg) group (Gp C; n = 8). Gp A, Gp B, and Gp C were administered BAPN (1 g/kg/d) for 4 weeks. One week after BAPN administration, Gp B and Gp C were treated with rapamycin (5 mg/kg/d or 10 mg/kg/d) through gavage for 21 days. Thoracic aortas were harvested for Western blot and immunofluorescence staining at day 14 and for morphologic and histologic analyses at day 28. RESULTS: BAPN treatment induced TAAD formation in mice. The incidence of TAAD in control, Gp A, Gp B, and Gp C mice was 0%, 80%, 25%, and 37.5%, respectively. Smaller thoracic aortic diameters (ascending aorta and arch) were observed in Gp B and Gp C mice than in Gp A mice (Gp B vs Gp A: ascending aorta, ex vivo, 1.07 ± 0.21 mm vs 1.80 ± 0.67 mm [P < .05]; aortic arch, ex vivo, 1.51 ± 0.40 mm vs 2.70 ± 1.06 mm [P < .05]; Gp C vs Gp A: ascending aortas, ex vivo, 1.10 ± 0.33 mm vs 1.80 ± 0.67 mm [P < .05]; aortic arch, ex vivo, 1.55 ± 0.56 mm vs 2.70 ± 1.06 mm [P < .05]). TAAD mice exhibited elastin fragmentation, abundant inflammatory cell infiltration, and significantly increased matrix metalloproteinase production in the aorta, and rapamycin treatment alleviated these changes. The protein levels of p-S6K and p-S6 in TAAD aortic tissues increased significantly, whereas they were suppressed by rapamycin. CONCLUSIONS: Rapamycin suppressed TAAD formation, probably by inhibition of mechanistic target of rapamycin signaling and reduction of inflammatory cell infiltration and matrix metalloproteinase 9 production. Targeting of the mechanistic target of rapamycin signaling pathway using rapamycin may be a favorable modulation for the clinical treatment of TAAD.

Role of ADAMTS-5 in Aortic Dilatation and Extracellular Matrix Remodeling.

OBJECTIVE: Thoracic aortic aneurysm (TAA), a degenerative disease of the aortic wall, is accompanied by changes in the structure and composition of the aortic ECM (extracellular matrix). The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family of proteases has recently been implicated in TAA formation. This study aimed to investigate the contribution of ADAMTS-5 to TAA development. APPROACH AND RESULTS: A model of aortic dilatation by AngII (angiotensin II) infusion was adopted in mice lacking the catalytic domain of ADAMTS-5 (Adamts5Δcat). Adamts5Δcat mice showed an attenuated rise in blood pressure while displaying increased dilatation of the ascending aorta (AsAo). Interestingly, a proteomic comparison of the aortic ECM from AngII-treated wild-type and Adamts5Δcat mice revealed versican as the most upregulated ECM protein in Adamts5Δcat mice. This was accompanied by a marked reduction of ADAMTS-specific versican cleavage products (versikine) and a decrease of LRP1 (low-density lipoprotein-related protein 1). Silencing LRP1 expression in human aortic smooth muscle cells reduced the expression of ADAMTS5, attenuated the generation of versikine, but increased soluble ADAMTS-1. A similar increase in ADAMTS-1 was observed in aortas of AngII-treated Adamts5Δcat mice but was not sufficient to maintain versican processing and prevent aortic dilatation. CONCLUSIONS: Our results support the emerging role of ADAMTS proteases in TAA. ADAMTS-5 rather than ADAMTS-1 is the key protease for versican regulation in murine aortas. Further studies are needed to define the ECM substrates of the different ADAMTS proteases and their contribution to TAA formation.

Interleukin-3 stimulates matrix metalloproteinase 12 production from macrophages promoting thoracic aortic aneurysm/dissection.

Thoracic aortic aneurysm and dissection (TAAD) is due to degeneration of the aorta and causes a high mortality rate, while molecular mechanisms for the development of TAAD are still not completely understood. In the present study, 3-aminopropionitrile (BAPN) treatment was used to induce TAAD mouse model. Through transcriptome analysis, we found the expression levels of genes associated with interleukin-3 (IL-3) signaling pathway were up-regulated during TAAD development in mouse, which were validated by real-time PCR. IL-3 positive cells were increased in TAAD mouse aortas, especially for smooth muscle cells (SMCs). IL-3 deficiency reduced BAPN-induced TAAD formation. We then examined the matrix metalloproteinases (MMPs) expression during TAAD formation in both wild-type and IL-3 deficient mice, showing that MMP12 were significantly down-regulated in IL-3 deficient aortas. Mechanistically, we found recombinant IL-3 could increase MMP12 production and activity from macrophages in vitro Silencing of IL-3 receptor ß, which was mainly expressed in macrophages but not SMCs, diminished the activation of c-Jun N terminal kinase (JNK)/extracellular-regulated protein kinases 1/2 (ERK1/2)/AP-1 signals, and decreased MMP12 expression in IL-3 stimulated macrophages. Moreover, both circulating and aortic inflammation were decreased in IL-3 deficient aortas. Taken together, our results demonstrated that IL-3 stimulated the production of MMP12 from macrophages by a JNK- and ERK1/2-dependent AP-1 pathway, contributing to TAAD formation. Thus, the IL-3/IL-3Rß/MMP12 signals activation may be an important pathological mechanism for progression of TAAD.

Multiple sites of vascular dilation or aneurysmal disease and matrix metalloproteinase genetic variants in patients with abdominal aortic aneurysm.

OBJECTIVE: The objective of this study was to assess whether functional genetic polymorphisms of matrix metalloproteinases (MMPs) 1, 3, 9, and 12 are associated with arterial enlargements or aneurysms of the thoracic aorta or popliteal arteries in patients with abdominal aortic aneurysm (AAA). METHODS: The associations between MMP1 (-1607 G in/del, rs1799750), MMP3 (-1171 A in/del rs35068180), MMP9 (13-26 CA repeats around -90, rs2234681, rs917576, rs917577), and MMP12 (G/T missense variation, rs652438) polymorphisms and enlargements or aneurysms of the thoracic aorta and popliteal arteries were tested in 169 consecutive AAA patients. RESULTS: Thoracic aorta enlargement or aneurysm (TE/A; maximum diameter, >35 mm) was detected in 34 patients (20.1% prevalence). MMP9 rs2234681 microsatellite was the only genetic determinant of TE/A in AAA patients (P = .003), followed by hypercholesterolemia and antiplatelet use. Carriers of both alleles with ≥22 CA repeats had a 5.9 (95% confidence interval, 1.9-18.6; P < .0001) increased odds of TE/A, and a score considering all three variables showed 98% negative predictive value and 30% positive predictive value for thoracic aortic aneurysm detection. Eighty-two popliteal artery enlargements or aneurysms (diameter >10 mm) occurred in 55 patients (33.1% prevalence). Carriers of MMP12 rs652438 C allele showed an 18% (P = .006) increased diameter in popliteal arteries and a 2.8 (95% confidence interval, 1.3-6; P = .008) increased odds of popliteal artery enlargement or aneurysm compared with TT genotype. CONCLUSIONS: Among patients with AAA, carriers of homozygous ≥22 CA repeats in MMP9 rs12234681 and of C allele in MMP12 rs652438 have a substantial risk of carrying thoracic and popliteal enlargements, respectively.

Regulation of membrane type-1 matrix metalloproteinase activity and intracellular localization in clinical thoracic aortic aneurysms.

OBJECTIVE: Membrane type-1 matrix metalloproteinase (MT1-MMP) is elevated during thoracic aortic aneurysm (TAA) development in mouse models, and plays an important role in the activation of matrix metalloproteinase (MMP)-2 and the release of matrix- bound transforming growth factor-ß. In this study, we tested the hypothesis that MT1-MMP is subject to protein kinase C (PKC)-mediated regulation, which alters intracellular trafficking and activity with TAAs. METHODS: Levels of MMP-2, native and phosphorylated MT1-MMP, and PKC-δ were measured in aortic tissue from patients with small TAAs (<5 cm; n = 8) and large TAAs (>6.5 cm; n = 8), and compared with values measured in normal controls (n = 8). Cellular localization of green fluorescent protein (GFP)-tagged MT1-MMP was assessed in aortic fibroblasts isolated from control and 4-week TAA mice. The effects of PKC-mediated phosphorylation on MT1-MMP cellular localization and function (active MMP-2 vs phospo-Smad2 abundance) were assessed after treatment with a PKC activator (phorbol-12-myristate-13-acetate [PMA], 100 nM) with and without a PKC-δ-specific inhibitor (röttlerin, 3 µM). RESULTS: Compared with controls, MT1-MMP abundance was increased in aortas from both TAA groups. Active MMP-2 was increased only in the large TAA group. The abundances of phosphorylated MT1-MMP and activated PKC-δ were enhanced in the small TAA group compared with the large TAA group. MT1-MMP was localized on the plasma membrane in aortic fibroblasts from control mice and in endosomes from TAA mice. Treatment with PMA induced MT1-MMP-GFP internalization, enhanced phospho-Smad2, and reduced MMP-2 activation, whereas röttlerin pretreatment inhibited these effects. CONCLUSIONS: Phosphorylation of MT1-MMP mediates its activity through directing cellular localization, shifting its role from MMP-2 activation to intracellular signaling. Thus, targeted inhibition of MT1-MMP may have therapeutic relevance as an approach to attenuating TAA development.

Impaired mechanics and matrix metalloproteinases/inhibitors expression in female ascending thoracic aortic aneurysms.

We hypothesized that female gender may have a specific negative impact on the mechanical characteristics, composition, and expression of matrix metalloproteinases/tissue inhibitors (MMPs/TIMPs) in the wall of ascending thoracic aortic aneurysms (ATAAs). Degenerative ATAAs were resected from 35 patients (age: 67±2 years, male: 20, ATAA diameter: 5.5±0.1cm) undergoing elective surgery. Tissue specimens were grouped by gender, region, and direction and submitted to immunohistochemistry for semi-quantitative assessment of MMP-2, MMP-9, TIMP-1, and TIMP-2 expressions, i.e. of staining intensity in extracellular matrix and immunoreactivity in vascular cells, as well as to histology for quantitation of elastin/collagen contents. Biomechanical characterization by the Fung-type model and examination of failure properties was performed. Gender differences in patient age, ATAA diameter, and ATAA diameter/body-surface area were non-significant. Increased MMP-2 and MMP-9, and decreased TIMP-1 and TIMP-2 expressions were observed in females. Elastin/collagen contents were higher in males than females, as was failure stress in circumferential but not longitudinal specimens. In both directions, failure stretch was invariant, while the Fung-type model parameters and elastic moduli calculated at physiologic stress levels were higher in females, suggestive of increased wall stiffness compared to males. MMP and TIMP expressions did not differ with region, unlike failure stress longitudinally that was greater posteriorly than anteriorly. The female gender is associated with impaired ATAA strength and increased stiffness, relating to the more extensive extracellular matrix breakdown and significantly higher ratio of MMP/TIMP expression witnessed in females. The present data may aid to identify the underlying pathophysiology accountable for the higher rupture risk, documented by epidemiologic studies in females.

Association of the polymorphisms of MMP-9 and TIMP-3 genes with thoracic aortic dissection in Chinese Han population.

AIM: Thoracic aortic dissection (TAD) is the most common life-threatening disorder, and a shifted balance of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) is involved in TAD pathogenesis. The aim of this study was to evaluate the association of 4 single-nucleotide polymorphisms (SNPs) in MMP-9 and TIMP-3 genes with TAD risk in Chinese Han population. METHODS: A total of 206 Chinese patients with TAD and 180 controls were included in this study. Four SNPs (rs3918249, rs2274756, rs9609643 and rs8136803) were genotyped using high-throughput MALDI-TOF mass spectrometry. Allele and genotype association analyses were conducted using PLINK. RESULTS: All the 4 SNPs resulted in Hardy-Weinberg equilibrium in patients and controls. The G allele frequency for the MMP-9 SNP rs2274756 was significantly higher in female TAD patients than in female controls (P=0.0099). Moreover, after adjusting for traditional cardiovascular risk factors (sex, age, hypertension, dyslipidemia, diabetes and smoking habit), the rs2274756 polymorphism (odds ratio: 0.30; 95% confidence interval: 0.11 to 0.79, P=0.015) resulted in an independent susceptibility factor for TAD in females. No associations were found between the other SNPs and TAD. CONCLUSION: The results provide strong evidence for an association between MMP-9 SNP rs2274756 and female TAD risk in Chinese Han population.

AKT2 confers protection against aortic aneurysms and dissections.

RATIONALE: Aortic aneurysm and dissection (AAD) are major diseases of the adult aorta caused by progressive medial degeneration of the aortic wall. Although the overproduction of destructive factors promotes tissue damage and disease progression, the role of protective pathways is unknown. OBJECTIVE: In this study, we examined the role of AKT2 in protecting the aorta from developing AAD. METHODS AND RESULTS: AKT2 and phospho-AKT levels were significantly downregulated in human thoracic AAD tissues, especially within the degenerative medial layer. Akt2-deficient mice showed abnormal elastic fibers and reduced medial thickness in the aortic wall. When challenged with angiotensin II, these mice developed aortic aneurysm, dissection, and rupture with features similar to those in humans, in both thoracic and abdominal segments. Aortas from Akt2-deficient mice displayed profound tissue destruction, apoptotic cell death, and inflammatory cell infiltration that were not observed in aortas from wild-type mice. In addition, angiotensin II-infused Akt2-deficient mice showed significantly elevated expression of matrix metalloproteinase-9 (MMP-9) and reduced expression of tissue inhibitor of metalloproteinase-1 (TIMP-1). In cultured human aortic vascular smooth muscle cells, AKT2 inhibited the expression of MMP-9 and stimulated the expression of TIMP-1 by preventing the binding of transcription factor forkhead box protein O1 to the MMP-9 and TIMP-1 promoters. CONCLUSIONS: Impaired AKT2 signaling may contribute to increased susceptibility to the development of AAD. Our findings provide evidence of a mechanism that underlies the protective effects of AKT2 on the aortic wall and that may serve as a therapeutic target in the prevention of AAD.

A particular phenotype of ascending aorta aneurysms as precursor of type A aortic dissection.

OBJECTIVES: We aimed to identify a phenotype of ascending thoracic aortic aneurysm (TAA), which, more than others, evolves into type A dissection (TAD). METHODS: Aortic specimens were obtained from patients undergoing surgical repair of TAA and TAD (108 and 26, respectively). Histopathological and immunohistochemical analyses were performed by using adequate tissue specimens, appropriate techniques and criteria. RESULTS: We identified the three following TAA phenotypes: phenotype I (cystic medial degeneration balanced by a substitutive fibrosis, in absence of medial apoptosis and with a faint collagenase concentration), phenotype II (cystic medial degeneration of higher grade, respectively, than substitutive fibrosis, with focal medial apoptosis and moderate collagenase concentration), and phenotype III (elevated cystic medial degeneration without substitutive fibrosis, with plurifocal medial apoptosis and severe collagenase concentration). The same medial degenerative lesions of TAA phenotype III were observed in TAD tissue samples. CONCLUSIONS: The morphological identity of medial lesions observed in both the TAA phenotype III and in TAD aortas might be assumed to be the precursor-and consequently the optimal biomarker- of dissection, independently of aneurysm diameter or valvular disorder. Identification of genetic risk factors, useful both in diagnostics and in developing more targeted treatment for individual patients, might also be needed.

Matrix metalloproteinases and descending aortic aneurysms: parity, disparity, and switch.

Central to the pathologic changes in developing aortic aneurysms are alterations in the abundance and activity of proteases, of which the most important for aneurysm production comprise the matrix metalloproteinase (MMP) family. In this review, literature demonstrating the role of MMPs in the development of aortic aneurysms is presented, with emphasis on the parity and disparity between the thoracic and abdominal aorta. Furthermore, the role of embryologic cellular origins and evidence of phenotypic switch will be addressed in terms of how this process alters MMP production during aneurysm development.

A microRNA profile comparison between thoracic aortic dissection and normal thoracic aorta indicates the potential role of microRNAs in contributing to thoracic aortic dissection pathogenesis.

OBJECTIVES: Our aim was to identify important microRNAs (miRNAs) that might play an important role in contributing to aortic dissection by conducting a miRNA profile comparison between thoracic aortic dissection (TAD) and normal thoracic aorta. METHODS: The differentially expressed miRNA profiles of the aortic tissue between TAD patients (n = 6) and age-matched donors without aortic diseases (NA; n = 6) were analyzed by miRNA microarray. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was further performed to verify the expression of 12 selected miRNAs with an increased number of samples (TAD n = 12; NA n = 8). The potential targets of the differentially expressed miRNAs were predicted using computational searches. Bioinformatic analyses of the predicted target genes (gene ontology, pathway and network analysis) were done for further research. Additionally, Western blotting was performed to confirm the bioinformatics findings. RESULTS: The miRNA microarray revealed differentially expressed miRNAs between the TAD and NA groups. In the TAD group, 18 miRNAs were upregulated and 56 were downregulated (fold change >2, P < .01). qRT-PCR verified statistically consistent expression of seven selected miRNAs with microarray analysis. Combined with our previous proteomics study, target gene prediction revealed that some miRNAs reciprocally expressed with their targeted proteins. Target gene-related pathway analysis showed a significant change in five pathways in the TAD group compared with the NA group, especially the focal adhesion and the mitogen-activated protein kinase (MAPK) signaling pathways. By further conducting miRNA gene network analysis, we found that the mir-29 and mir-30 families are likely to play a role in the regulation of these two pathways, respectively. CONCLUSIONS: Our results indicate that miRNAs expression profiles in aortic media from TAD were significantly changed. These results may provide important insights into TAD disease mechanisms. This study also suggests that the focal adhesion and MAPK signaling pathways might play important roles in the pathogenesis of TAD.

Protective effects of angiotensin-converting enzyme I/I and matrix metalloproteinase-3 6A/6A polymorphisms on dilatative pathology within the ascending thoracic aorta.

OBJECTIVE: Activation of matrix metalloproteinases and the renin/angiotensin signaling pathways is under investigation with regard to their potential pathogenesis in dilatative pathology of the aorta. The purpose of this study was to explore matrix metalloproteinase-3 5A/6A and angiotensin-converting enzyme I/D polymorphisms as predisposing factors to dilatative pathology of the aorta. METHODS: We studied 107 patients who underwent aortic reconstruction surgery due to dilatative pathology of ascending thoracic aorta and a random sample of the population (n = 773), all from Lithuania. The insertion/deletion (-1171 5A/6A) polymorphism in the promoter region of matrix metalloproteinase-3 studied by real-time polymerase-chain-reaction amplification and the D and I alleles were identified on the basis of standard polymerase-chain-reaction amplification of the respective fragments from intron 16 of the angiotensin-converting enzyme gene. RESULTS: The frequency of the angiotensin-converting enzyme D allele was significantly higher in dilatative pathology of ascending thoracic aorta patients than in the reference group subjects (0.55 vs 0.48, respectively). The latter group had a significantly higher frequency of the angiotensin-converting enzyme I/I genotype than in dilatative pathology of ascending thoracic aorta patients (27.4% vs 16.5%, respectively). In the reference group, the frequency of combined angiotensin-converting enzyme I/I and matrix metalloproteinase-3 6A/6A genotypes was 7.5%, while in the dilatative pathology of ascending thoracic aorta patient group, there was no one carrying that combined genotype (p = 0.001). CONCLUSIONS: The present study showing a role of angiotensin-converting enzyme and matrix metalloproteinase-3 in the development of dilatative pathology of ascending thoracic aorta permits us to entertain a possible protective mechanism for the combined effects of the angiotensin-converting enzyme I/I and the matrix metalloproteinase-3 6A/6A genotypes.