Introduction: Defective genes that predispose to acute aortic dissections (AADs) suggest that maintenance of aortic integrity requires mature extracellular matrix (ECM) and intracellular homeostatic contraction of smooth muscle cells (SMCs). Focal adhesions (FAs) link the ECM to SMC contractile units, and we sought to determine the role of SMC FA signaling in a mouse model in which AADs are induced by disrupting ECM with a lysyl oxidase inhibitor, β-aminopropionitrile (BAPN). Methods: C57BL/6J wild-type mice at postnatal day 21 (P21) were exposed to BAPN to induce AADs. All aortas were visually inspected at necropsy or tissue harvest. Proximal aortas were harvested for single-cell RNA sequencing (scRNAseq) at P35 and for immunoblot analyses at P24 and P35. Echocardiography, tail-cuff blood pressure, and histopathology analyses were performed on surviving mice at P49. Results: MELD analysis of scRNAseq data identified SMC clusters as the top altered cell type in BAPN-treated aortas. KEGG pathway analysis identified activated FA, along with Rho/ROCK and mTOR signaling, in the BAPN-treated SMC cluster. Immunoblots confirmed increased phosphorylation of FAK, MYPT1, mTOR, p70S6K, and S6RP in BAPN-treated aortas, and FAK inhibition blocked Rho/ROCK and mTOR pathways. Pharmacological inhibition of mTOR with rapamycin significantly rescued BAPN-induced AAD deaths (9% vs. 50%, p=0.001) without altering blood pressure, aortic enlargement, or aortic medial elastic fiber degeneration. Immunoblot analyses confirmed dramatic decrease of mTOR, p70S6K, and S6RP phosphorylation levels in BAPN aortas with rapamycin treatment. Administration of a ROCK inhibitor, Y-27632, significantly augmented type A AAD incidence (p=0.04) without altering blood pressure in BAPN mice, and immunoblot analyses identified increased mTOR signaling as early as P24 in BAPN plus Y-27632-treated aortas compare with BAPN group. Conclusions: Activation of FA and downstream mTOR signaling triggers AAD when the ECM is disrupted by BAPN, and mTOR inhibition significantly attenuates these deaths. FAs also activate Rho/ROCK, which is protective. These findings support that preventing mTOR signaling or augmenting Rho/ROCK signaling are therapeutic targets to prevent AADs.
Background —Aneurysms and dissections affecting the ascending aorta are associated primarily with degeneration of the aortic media, called medial necrosis. Families identified with dominant inheritance of thoracic aortic aneurysms and dissections (TAA/dissections) indicate that single gene mutations can cause medial necrosis in the absence of an associated syndrome. Methods and Results —Fifteen families were identified with multiple members with TAAs/dissections. DNA from affected members from 2 of the families was used for a genome-wide search for the location of the defective gene by use of random polymorphic markers. The data were analyzed by the affected-pedigree-member method of linkage analysis. This analysis revealed 3 chromosomal loci with multiple markers demonstrating evidence of linkage to the phenotype. Linkage analysis using further markers in these regions and DNA from 15 families confirmed linkage of some of the families to 5q13-14. Genetic heterogeneity for the condition was confirmed by a heterogeneity test. Data from 9 families with the highest conditional probability of being linked to 5q were used to calculate the pairwise and multipoint logarithm of the odds (LOD) scores, with a maximum LOD of 4.74, with no recombination being obtained for the marker D5S2029 . In 6 families, the phenotype was not linked to the 5q locus. Conclusions —A major locus for familial TAAs and dissections maps to 5q13-14, with the majority (9 of 15) of the families identified demonstrating evidence of linkage to this locus. The condition is genetically heterogeneous, with 6 families not demonstrating evidence of linkage to any loci previously associated with aneurysm formation.
Aortic aneurysms and dissections are the most common disorders affecting the aorta, and are a major cause of morbidity and mortality in the United States. Familial thoracic aortic aneurysms and dissections (FTAAD) are inherited in an autosomal dominant manner with variable expression and decreased penetrance. The disorder is genetically heterogeneous with four loci and three genes identified. Mutations in either TGFBR2 , encoding the transforming growth factor β (TGF-β) type II receptor, or MYH11 , encoding the smooth muscle cell (SMC)-specific β-myosin heavy chain, were previously found to cause FTAAD. Recently, positional cloning identified smooth muscle α-actin ( ACTA2 ) mutations as a novel cause in 10% of FTAAD. Mutations in ACTC and MYH7 cause hypertrophic cardiomyopathy (HCM), characterized by myocyte disarray and upregulation of mitotic and trophic factors. Histologic examination of aortic tissue from patients with ACTA2 (n = 6) and MYH11 (n = 2) mutations revealed SMC disarray in the aortic media similar to that seen in HCM. Furthermore, we hypothesized that mutations in ACTA2 and MYH11 cause a similar increase of mitotic and trophic factors in SMCs. The expression of two factors known to be increased in HCM, TGF-β1 and insulin-like growth factor 1 (IGF-1), were analyzed in patients’ aortic SMCs and dermal myofibroblasts. No changes in TGF-β1 were found; however, both mRNA, as measured by Q-PCR (p<0.05), and protein levels, as assessed by immunostaining, of IGF-1 were markedly increased in MYH11 and two ACTA2 mutant SMCs and aortic tissue compared with control SMCs and tissue. Differentiation of dermal fibroblasts into myofibroblasts was accomplished using TGF-β1 treatment; myofibroblast differentiation was confirmed by assessing α-actin mRNA and protein levels in untreated vs. TGF-β1-treated fibroblasts. Upon differentiation, patients’ myofibroblasts (n = 3) demonstrated increased IGF-1 expression compared with controls (p<0.05), similar to the increased IGF-1 expression by SMCs. In conclusion, IGF-1 secretion is increased in response to defects in SMC contractile proteins in SMCs and myofibroblasts. Future studies will clarify the role of IGF-1 in FTAAD and identify the pathways leading to increased IGF-1 expression.
Introduction: Pathogenic (P) or likely pathogenic (LP) aortopathy gene variants cause hereditary thoracic aortic aneurysm and dissection, but P/LP variants only explain approximately 20% of cases of thoracic aortic disease. Variants of unknown significance (VUS) are frequently identified among individuals undergoing genetic testing for thoracic aortic disease, however managing patients with VUSs remains clinically challenging. Hypothesis: Bioinformatic tools can be used to determine thresholds above which VUSs may be considered “high-risk.” Methods: Primary analyses were performed in the Penn Medicine Biobank (PMBB) which is composed of 43,731 participants who volunteered to have clinical information linked to biospecimen data including DNA which has undergone whole exome sequencing. PMBB participants were screened for VUSs in one of 11 aortopathy genes. VUS REVEL, AlphaMissense and minor allele frequency (MAF) high-risk thresholds were derived using cutpointR, a statistical package to optimize continuous variable thresholds based on binary outcomes. These thresholds were applied to VUS carriers in the PMBB and two independent validation cohorts. Logistic regression analysis was performed to test the association of high-risk VUSs with prevalent thoracic aortic disease. Results: There were 11,925 individuals in PMBB who carried at least one missense VUS. Carrying a VUS was associated with a modest increased risk of thoracic aortic aneurysm (TAA: OR=1.14, 95% confidence interval [CI] 1.01 to 1.29, P =0.034) but no increased risk of thoracic aortic dissection (OR=1.04, 95%CI 0.55 to 2.00, P =0.896). As VUS REVEL or AlphaMissense increased, or MAF decreased, the association between VUSs and thoracic aortic disease became statistically significant. Using cutpointR, we derived REVEL (>0.649), AlphaMissense (>0.2543), and MAF (<8.16x10 -6 ) thresholds that together identified 435 high-risk VUSs robustly associated with prevalent dissection (OR=7.85, 95%CI 4.73 to 13.03, P <0.001), though the association with TAA was attenuated (OR=2.35, 95%CI 1.62 to 3.42, P <0.001). Similar results were observed in the UK Biobank (UKB) and Early Onset Sporadic Thoracic Aortic Dissection (ESTAD) cohorts. Conclusions: VUSs that met high-risk bioinformatic thresholds were strongly associated with prevalent aortic dissection in the PMBB, UKB and ESTAD. Future investigation is warranted to determine if these thresholds can instruct clinical care of individuals carrying aortopathy gene VUSs.
Introduction: Bicuspid Aortic Valve (BAV), the most common adult congenital heart defect, is a major cause of aortic insufficiency or stenosis requiring valve replacement and thoracic aortic aneurysms predisposing to acute aortic dissections. The spectrum of BAV ranges from early onset valve and aortic complications to sporadic late onset disease. We determined the frequency and gene content of rare genomic copy number variants (CNVs) in isolated BAV cases. Methods: We performed genome-wide SNP microarray analysis of familial BAV cases with early onset complications in the UTHealth BAV Research Registry (EBAV, n=394) and elderly probands from the International BAV Consortium (BAVCON, n=4216). CNVs were detected in Illumina genotypes using the PennCNV, QuantiSNP and cnvPartition algorithms. BAV cases were compared to 16,576 controls without known cardiovascular disease from the Database of Genotypes and Phenotypes. Only CNV calls with >6 consecutive variants, >20 kb in length, identified by at least two algorithms and intersected with known genes were included. For comparison, we assessed a cohort with left ventricular outflow tract obstructive lesions including BAV (LVOTO, n=1561) using identical methods. CNV burden and associations were tested using PLINK. Results: We identified 84 large recurrent CNVs in BAV cases that are absent or rare (<0.1%) in controls. 34 rare CNVs overlap between BAV and LVOTO cases and involve candidate genes that interact with each other during heart development. The largest and most prevalent of the recurrent CNVs are 8p23 duplications involving GATA4 (OR 340, CI: 42-2700). CNVs of genes that cause BAV when mutated were significantly enriched in cases (n=135, P =1x10 -27 ). The overall burden of rare genic CNVs, specifically large deletions, was also increased in BAV cases (empiric P < 1x10 -5 ) and was higher in younger EBAV cases than in older BAVCON cases. Conclusion: We identified likely pathogenic CNVs in more than 10% of BAV cases, implicating alterations of candidate genes at these loci in the pathogenesis of BAV.
Background —Aortic aneurysms cause significant mortality, and >20% relate to hereditary disorders. Familial aortic aneurysm (FAA) has been described in such conditions as the Marfan and Ehlers-Danlos type IV syndromes, due to defects in the fibrillin-1 and type III procollagen genes, respectively. Other gene defects that cause isolated aneurysms, however, have not thus far been described. Methods and Results —We studied 3 families affected by FAA. No family met the diagnostic criteria for either Marfan or Ehlers-Danlos syndrome. Echocardiography defined involvement of both the thoracic and abdominal aorta. In family ANA, candidate gene analysis excluded linkage to loci associated with aneurysm formation, including fibrillin-1 , fibrillin-2 , and type III procollagen , and chromosome 3p24.2-p25. Genome-wide linkage analysis identified a 2.3-cM FAA locus ( FAA1 ) on chromosome 11q23.3-q24 with a maximum multipoint logarithm of the odds score of 4.4. In family ANB, FAA was linked to fibrillin-1 . In family ANF, however, FAA was not linked to any locus previously associated with aneurysm formation, including fibrillin-1 and FAA1 . Conclusions —FAA disease is genetically heterogeneous. We have identified a novel FAA locus at chromosome 11q23.3-q24, a critical step toward elucidating 1 gene defect responsible for aortic dilatation. Future characterization of the FAA1 gene will enhance our ability to achieve presymptomatic diagnosis of aortic aneurysms and will define molecular mechanisms to target therapeutics.
Abstract Bicuspid aortic valve (BAV), the most common congenital heart defect, is a major cause of aortic valve disease requiring valve interventions and thoracic aortic aneurysms predisposing to acute aortic dissections. The spectrum of BAV ranges from early onset valve and aortic complications (EBAV) to sporadic late onset disease. Rare genomic copy number variants (CNVs) have previously been implicated in the development of BAV and thoracic aortic aneurysms. We determined the frequency and gene content of rare CNVs in EBAV probands (n = 272) using genome-wide SNP microarray analysis and three complementary CNV detection algorithms (cnvPartition, PennCNV, and QuantiSNP). Unselected control genotypes from the Database of Genotypes and Phenotypes were analyzed using identical methods. We filtered the data to select large genic CNVs that were detected by multiple algorithms. Findings were replicated in cohorts with late onset sporadic disease (n = 5040). We identified 34 large and rare (< 1:1000 in controls) CNVs in EBAV probands. The burden of CNVs intersecting with genes known to cause BAV when mutated was increased in case-control analysis. CNVs intersecting with GATA4 and DSCAM were enriched in cases, recurrent in other datasets, and segregated with disease in families. In total, we identified potentially pathogenic CNVs in 8% of EBAV cases, implicating alterations of candidate genes at these loci in the pathogenesis of BAV. Author Summary Bicuspid aortic valve (BAV) is the most common form of congenital heart disease and can lead to long-term complications such as aortic stenosis, aortic regurgitation, or thoracic aortic aneurysms. Most BAV-related complications arise in late adulthood, but 10-15% of individuals with BAV develop early onset complications before age 30. Copy number variants (CNVs) are genomic structural variations that have been previously implicated in some types of congenital heart disease, including BAV. Here we demonstrate that individuals with early onset complications of BAV are enriched for specific rare CNVs compared to individuals with late-onset BAV disease. We also describe novel CNVs involving DSCAM , a gene on chromosome 21 that has not previously been associated with the development of BAV. These results may lead to improved risk stratification and targeted therapies for BAV patients.
