Differentiation defect in neural crest-derived smooth muscle cells in patients with aortopathy associated with bicuspid aortic valves

Distal aortic progression following acute type A aortic dissection repair among patients with bicuspid and tricuspid aortic valves

OBJECTIVE

The study objective was to analyze long-term growth and outcomes of the distal aorta after open acute type A aortic dissection repair in patients with bicuspid aortic valves or tricuspid aortic valves without connective tissue disease.

METHODS

From 1996 to 2021, 60 patients with bicuspid aortic valves and 655 patients with tricuspid aortic valves without connective tissue disease underwent open repair for acute type A aortic dissection. Data were collected from the local Society of Thoracic Surgeons database, medical record review, surveys, and the National Death Index and Michigan Death Index (December 12, 2021).

RESULTS

Compared with the tricuspid aortic valve group, the bicuspid aortic valve group was significantly younger, had more severe aortic insufficiency (33% vs 22%, P = .05), and had less hypertension (67% vs 78%, P = .05). Intraoperatively, patients with bicuspid aortic valves received more aortic root replacements (70% vs 26%, P < .001), less zone 2 aortic arch replacement (8.3% vs 20%, P = .03), and longer median cardiopulmonary bypass (233 vs 214 minutes, P = .05) and aortic crossclamp (184 vs 141 minutes, P < .001) times. The average annual aortic arch growth rate (0.23 mm/year vs 0.39 mm/year, P = .52) and descending aorta growth rate (0.61 mm/year vs 0.79 mm/year, P = .39) were similar between the bicuspid aortic valve and tricuspid aortic valve groups. The bicuspid aortic valve group had lower annual abdominal aorta growth (0.51 mm/year vs 0.68 mm/year, P = .03). The cumulative incidence of reoperation for the distal aorta (9.7% vs 16.0%, P = .77) was similar between the bicuspid aortic valve and tricuspid aortic valve groups. The 10-year survival was higher in the bicuspid aortic valve group (75.4% vs 66.0%, P = .03).

CONCLUSIONS

Patients with bicuspid aortic valves could be treated similarly as patients with tricuspid aortic valves without connective tissue disease in the setting of open acute type A aortic dissection repair.

Site-specific genetic and functional signatures of aortic endothelial cells at aneurysm predilection sites in healthy and AngII ApoE-/- mice

Aortic aneurysm is characterized by a pathological dilation at specific predilection sites of the vessel and potentially results in life-threatening vascular rupture. Herein, we established a modified "Häutchen method" for the local isolation of endothelial cells (ECs) from mouse aorta to analyze their spatial heterogeneity and potential role in site-specific disease development. When we compared ECs from aneurysm predilection sites of healthy mice with adjacent control segments we found regulation of genes related to extracellular matrix remodeling, angiogenesis and inflammation, all pathways playing a critical role in aneurysm development. We also detected enhanced cortical stiffness of the endothelium at these sites. Gene expression of ECs from aneurysms of the AngII ApoE-/- model when compared to sham animals mimicked expression patterns from predilection sites of healthy animals. Thus, this work highlights a striking genetic and functional regional heterogeneity in aortic ECs of healthy mice, which defines the location of aortic aneurysm formation in disease.

Smooth muscle cell phenotypic switching occurs independent of aortic dilation in bicuspid aortic valve-associated ascending aortas

BACKGROUND

Bicuspid aortic valves (BAV) are frequently associated with ascending aortic aneurysms. The etiology is incompletely understood, but genetic factors, in addition to flow perturbations, are likely involved. Since loss of contractility and elaboration of extracellular matrix in the vessel wall are features of BAV-associated aortopathy, phenotypic modulation of smooth muscle cells (SMCs) may play a role.

METHODS

Ascending aortic tissue was collected intra-operatively from 25 individuals with normal (i.e., tricuspid) aortic valves (TAV) and from 25 individuals with BAVs. For both TAV and BAV, 10 patients had non-dilated (ND) and 15 patients had dilated (D) aortas. SMCs were isolated and cultured from a subset of patients from each group. Aortic tissue and SMCs were fluorescently immunolabeled for SMC phenotypic markers (i.e., alpha-smooth muscle actin (ASMA, contractile), vimentin (synthetic) and p16INK4a and p21Cip1 (senescence). SMCs were also analyzed for replicative senescence in culture.

RESULTS

In normal-sized and dilated BAV aortas, SMCs switched from the contractile state to either synthetic or senescent phenotypes, as observed by loss of ASMA (ND: P = 0.001, D: P = 0.002) and associated increases in vimentin (ND: P = 0.03, D: P = 0.004) or p16/p21 (ND: P = 0.03, D: P<0.0001) compared to TAV. Dilatation of the aorta exacerbated SMC phenotypic switching in both BAV and TAV aortas (all P<0.05). In SMCs cultured from normal and dilated aortas, those isolated from BAV reached replicative senescence faster than those from TAV aortas (all P = 0.02). Furthermore, there was a stark inverse correlation between ASMA and cell passage number in BAV SMCs (ND: P = 0.0006, D: P = 0.01), but not in TAV SMCs (ND: P = 0.93, D: P = 0.20).

CONCLUSIONS

The findings of this study provide direct evidence from cell culture studies implying that SMCs switch from the contractile state to either synthetic or senescent phenotypes in the non-dilated BAV aorta. In cultured SMCs from both non-dilated and dilated aortas, we found that this process may precede dilatation and accompany aneurysm development in BAV. Our findings suggest that therapeutically targeting SMC phenotypic modulation in BAV patients may be a viable option to prevent or delay ascending aortic aneurysm formation.

Use of iPSC-Derived Smooth Muscle Cells to Model Physiology and Pathology

The implementation of human induced pluripotent stem cell (hiPSC) models has introduced an additional tool for identifying molecular mechanisms of disease that complement animal models. Patient-derived or CRISPR/Cas9-edited induced pluripotent stem cells differentiated into smooth muscle cells (SMCs) have been leveraged to discover novel mechanisms, screen potential therapeutic strategies, and model in vivo development. The field has evolved over almost 15 years of research using hiPSC-SMCs and has made significant strides toward overcoming initial challenges such as the lineage specificity of SMC phenotypes. However, challenges both specific (eg, the lack of specific markers to thoroughly validate hiPSC-SMCs) and general (eg, a lack of transparency and consensus around methodology in the field) remain. In this review, we highlight the recent successes and remaining challenges of the hiPSC-SMC model.

Applications, challenges, and prospects of induced pluripotent stem cells for vascular disease

Vascular disease, including heart disease, stroke, and peripheral arterial disease, is one of the leading causes of death and disability and represents a significant global health issue. Since the development of human induced pluripotent stem cells (hiPSCs) in 2007, hiPSCs have provided unique and tremendous opportunities for studying human pathophysiology, disease modeling, and drug discovery in the field of regenerative medicine. In this review, we discuss vascular physiology and related diseases, the current methods for generating vascular cells (eg, endothelial cells, smooth muscle cells, and pericytes) from hiPSCs, and describe the opportunities and challenges to the clinical applications of vascular organoids, tissue-engineered blood vessels, and vessels-on-a-chip. We then explore how hiPSCs can be used to study and treat inherited vascular diseases and discuss the current challenges and future prospects. In the future, it will be essential to develop vascularized organoids or tissues that can simultaneously undergo shear stress and cyclic stretching. This development will not only increase their maturity and function but also enable effective and innovative disease modeling and drug discovery.

Treatment strategies and outcomes following acute type A aortic dissection repair in patients with bicuspid and tricuspid aortic valves: A meta-analysis

Background

There is no consensus regarding the strategies for repairing acute type A aortic dissection (ATAAD) in patients with bicuspid aortic valve (BAV). This meta-analysis aimed to compare the treatment strategies and outcomes of ATAAD repair between patients with BAV and those with tricuspid aortic valve (TAV).

Methods

A systematic review of databases were performed from inception through March 2023. The primary outcome of interest was all-cause mortality, with a minimum follow-up of 1 year. The secondary outcomes of interest included ratios of performed procedures and rate of distal aortic reoperation. Data were extracted, and pooled analysis was performed using a random-effects model.

Results

Eight observational studies including a total of 3701 patients (BAV, n = 349; TAV, n = 3352) were selected for a meta-analysis. Concerning proximal aortic procedures, BAV patients exhibited a higher incidence of necessary root replacement (odds ratio [OR], 6.53; 95% confidence interval [CI], 3.84 to 11.09; P < .01). Regarding distal aortic procedures, extended arch replacement was performed less frequently in BAV patients (OR, 0.69; 95% CI, 0.49 to 0.99; P = .04), whereas hemiarch procedure rates were comparable in the 2 groups. All-cause mortality was lower in the BAV group (hazard ratio, 0.68; 95% CI, 0.50 to 0.92; P = .01). Distal aortic reoperation rates were comparable in the 2 groups.

Conclusions

This study highlights distinct procedural patterns in ATAAD patients with BAV and TAV. Despite differing baseline characteristics, BAV patients exhibited superior survival compared to TAV patients, with comparable distal aortic reoperation rates. These findings may be useful for decision making regarding limited versus extended aortic arch repair.

Heritable thoracic aortic disease: a literature review on genetic aortopathies and current surgical management

Heritable thoracic aortic disease puts patients at risk for aortic aneurysms, rupture, and dissections. The diagnosis and management of this heterogenous patient population continues to evolve. Last year, the American Heart Association/American College of Cardiology Joint Committee published diagnosis and management guidelines for aortic disease, which included those with genetic aortopathies. Additionally, evolving research studying the implications of underlying genetic aberrations with new genetic testing continues to become available. In this review, we evaluate the current literature surrounding the diagnosis and management of heritable thoracic aortic disease, as well as novel therapeutic approaches and future directions of research.

Systematic review of cardiovascular neurocristopathy-contemporary insights and future perspectives

Introduction

Neural crest cells (NCCs) are multipotent and are attributed to the combination of complex multimodal gene regulatory mechanisms. Cardiac neural crest (CNC) cells, originating from the dorsal neural tube, are pivotal architects of the cardio-neuro-vascular domain, which orchestrates the embryogenesis of critical cardiac and vascular structures. Remarkably, while the scientific community compiled a comprehensive inventory of neural crest derivatives by the early 1980s, our understanding of the CNC's role in various cardiovascular disease processes still needs to be explored. This review delves into the differentiation of NCC, specifically the CNC cells, and explores the diverse facets of non-syndromic cardiovascular neurocristopathies.

Methods

A systematic review was conducted as per the PRISMA Statement. Three prominent databases, PubMed, Scopus, and Embase, were searched, which yielded 1,840 studies. We excluded 1,796 studies, and the final selection of 44 studies formed the basis of this comprehensive review.

Results

Neurocristopathies are a group of genetic disorders that affect the development of cells derived from the NC. Cardiovascular neurocristopathy, i.e., cardiopathy and vasculopathy, associated with the NCC could occur in the form of (1) cardiac septation disorders, mainly the aortico-pulmonary septum; (2) great vessels and vascular disorders; (3) myocardial dysfunction; and (4) a combination of all three phenotypes. This could result from abnormalities in NCC migration, differentiation, or proliferation leading to structural abnormalities and are attributed to genetic, familial, sporadic or acquired causes.

Discussion

Phenotypic characteristics of cardiovascular neurocristopathies, such as bicuspid aortic valve and thoracic aortic aneurysm, share a common embryonic origin and are surprisingly prevalent in the general population, necessitating further research to identify the underlying pathogenic and genetic factors responsible for these cardiac anomalies. Such discoveries are essential for enhancing diagnostic screening and refining therapeutic interventions, ultimately improving the lives of individuals affected by these conditions.

Differentiation of Pluripotent Stem Cells for Disease Modeling: Learning from Heart Development

Heart disease is a pressing public health problem and the leading cause of death worldwide. The heart is the first organ to gain function during embryogenesis in mammals. Heart development involves cell determination, expansion, migration, and crosstalk, which are orchestrated by numerous signaling pathways, such as the Wnt, TGF-β, IGF, and Retinoic acid signaling pathways. Human-induced pluripotent stem cell-based platforms are emerging as promising approaches for modeling heart disease in vitro. Understanding the signaling pathways that are essential for cardiac development has shed light on the molecular mechanisms of congenital heart defects and postnatal heart diseases, significantly advancing stem cell-based platforms to model heart diseases. This review summarizes signaling pathways that are crucial for heart development and discusses how these findings improve the strategies for modeling human heart disease in vitro.

Understanding genomic medicine for thoracic aortic disease through the lens of induced pluripotent stem cells

Thoracic aortic disease (TAD) is often silent until a life-threatening complication occurs. However, genetic information can inform both identification and treatment at an early stage. Indeed, a diagnosis is important for personalised surveillance and intervention plans, as well as cascade screening of family members. Currently, only 20% of heritable TAD patients have a causative mutation identified and, consequently, further advances in genetic coverage are required to define the remaining molecular landscape. The rapid expansion of next generation sequencing technologies is providing a huge resource of genetic data, but a critical issue remains in functionally validating these findings. Induced pluripotent stem cells (iPSCs) are patient-derived, reprogrammed cell lines which allow mechanistic insights, complex modelling of genetic disease and a platform to study aortic genetic variants. This review will address the need for iPSCs as a frontline diagnostic tool to evaluate variants identified by genomic discovery studies and explore their evolving role in biological insight through to drug discovery.

Using Genomics to Identify Novel Therapeutic Targets for Aortic Disease

Aortic disease, including dissection, aneurysm, and rupture, carries significant morbidity and mortality and is a notable cause of sudden cardiac death. Much of our knowledge regarding the genetic basis of aortic disease has relied on the study of individuals with Mendelian aortopathies and, until recently, the genetic determinants of population-level variance in aortic phenotypes remained unclear. However, the application of machine learning methodologies to large imaging datasets has enabled researchers to rapidly define aortic traits and mine dozens of novel genetic associations for phenotypes such as aortic diameter and distensibility. In this review, we highlight the emerging potential of genomics for identifying causal genes and candidate drug targets for aortic disease. We describe how deep learning technologies have accelerated the pace of genetic discovery in this field. We then provide a blueprint for translating genetic associations to biological insights, reviewing techniques for locus and cell type prioritization, high-throughput functional screening, and disease modeling using cellular and animal models of aortic disease.

Deciphering Congenital Heart Disease Using Human Induced Pluripotent Stem Cells

Congenital heart disease (CHD) is a leading cause of birth defect-related death. Despite significant advances, the mechanisms underlying the development of CHD are complex and remain elusive due to a lack of efficient, reproducible, and translational model systems. Investigations relied on animal models have inherent limitations due to interspecies differences. Human induced pluripotent stem cells (iPSCs) have emerged as an effective platform for disease modeling. iPSCs allow for the production of a limitless supply of patient-specific somatic cells that enable advancement in cardiovascular precision medicine. Over the past decade, researchers have developed protocols to differentiate iPSCs to multiple cardiovascular lineages, as well as to enhance the maturity and functionality of these cells. With the development of physiologic three-dimensional cardiac organoids, iPSCs represent a powerful platform to mechanistically dissect CHD and serve as a foundation for future translational research.

Can transforming growth factor beta and downstream signalers distinguish bicuspid aortic valve patients susceptible for future aortic complications?

Patients with a bicuspid aortic valve have an extreme high risk to develop a thoracic aortic aneurysm and dissection (TAAD). TAADs form a leading cause of death worldwide, with the majority of deaths being preventable if individuals at risk are identified and properly managed. Risk stratification for TAADs in bicuspidy is so far solely based on the aortic diameter. Exclusive use of aortic wall dimension, as in the current guidelines, is however not sufficient in selecting patients vulnerable for future aortic wall complications. Moreover, there are no effective medical treatments for TAADs to retain progressive aortic dilatation and thus prevent or delay aortic complications. Only surgical replacement of the aorta increases life expectancy in patients with a risk for a TAAD. Therefore, the next major challenge in the management of TAADs is the development of a personalized patient-tailored risk stratification for early detection of patients with an increased risk for TAADs, who will benefit from surgical resection of the aorta. Several signaling pathways have been studied in recent times to develop a patient specific risk stratification model. In this paper we discuss TGF-β signaling and downstream signalers as potential markers for future aortic complications in bicuspid aortic valve patients.

Structural abnormalities in the non-dilated ascending aortic wall of bicuspid aortic valve patients

BACKGROUND

A bicuspid aortic valve (BAV) is the most common congenital cardiac malformation. The development of the aortic valve is closely related to the development of the ascending aorta, associated with structural differences in the bicuspid aorta. Here we describe the non-dilated ascending aortic wall in bicuspid aortic valve patients.

METHODS

BAV (n=41) and tricuspid aortic valve (TAV) (n=18) non-dilated ascending aortic wall samples were studied. We investigated the following features of the aortic wall: vessel wall thickness, endothelial cell morphology, atherosclerosis, and elastic lamellae organization. Medial pathologic features encompassing elastic fiber thinning, fragmentation and degeneration, overall medial degeneration, mucoid extracellular matrix accumulation, and smooth muscle cell nuclei loss were studied. Furthermore, we included apoptosis, periaortic inflammation, and the level of expression of differentiated vascular smooth muscle cells.

RESULTS

The non-dilated BAV ascending aortic wall is characterized by a significantly thinner intimal layer, without features of atherosclerosis (P<.001). The medial layer is significantly thicker (P<.001) with more mucoid extracellular matrix accumulation (P<.001). All other medial pathologic features were more prominent in the TAV (P<.001). The media has significantly less differentiated vascular smooth muscle cells (P<.001) between the neatly regulated elastic lamellae which are thinner in the BAV as compared to the TAV (P<.0001).

CONCLUSIONS

The BAV ascending aorta without dilatation is characterized by a differentiation defect of vascular smooth muscle cells in the media and a significantly thinner intimal layer without overt pathologic features.

Short-term rapamycin treatment increases life span and attenuates aortic aneurysm in a murine model of Marfan-Syndrome

BACKGROUND

Marfan syndrome (MFS) is a genetic disorder leading to medial aortic degeneration and life-limiting dissections. To date, there is no causal prevention or therapy. Rapamycin is a potent and selective inhibitor of the mechanistic target of rapamycin (mTOR) protein kinase, regulating cell growth and metabolism. The mgR/mgR mice represent an accepted MFS model for studying aortic pathologies to understand the underlying molecular pathomechanisms. This study investigated whether rapamycin inhibits the development of thoracic aortic aneurysms and dissections in mgR/mgR mice.

METHODS

Isolated primary aortic smooth muscle cells (mAoSMCs) from mgR/mgR mice were used for in vitro studies. Two mg kg/BW rapamycin was injected intraperitoneally daily for two weeks, beginning at 7-8 weeks of age. Mice were sacrificed 30 days post-treatment. Histopathological and immunofluorescence analyses were performed using adequate tissue specimens and techniques. Animal survival was evaluated accompanied by periodic echocardiographic examinations of the aorta.

RESULTS

The protein level of the phosphorylated ribosomal protein S6 (p-RPS6), a downstream target of mTOR, was significantly increased in the aortic tissue of mgR/mgR mice. In mAoSMCs isolated from these animals, expression of mTOR, p-RPS6, tumour necrosis factor α, matrix metalloproteinase-2 and -9 was significantly suppressed by rapamycin, demonstrating its anti-inflammatory capacity. Short-term rapamycin treatment of Marfan mice was associated with delayed aneurysm formation, medial aortic elastolysis and improved survival.

CONCLUSIONS

Short-term rapamycin-mediated mTOR inhibition significantly reduces aortic aneurysm formation and thus increases survival in mgR/mgR mice. Our results may offer the first causal treatment option to prevent aortic complications in MFS patients.

Experimental evidence of the genetic hypothesis on the etiology of bicuspid aortic valve aortopathy in the hamster model

Bicuspid aortopathy occurs in approximately 50% of patients with bicuspid aortic valve (BAV), the most prevalent congenital cardiac malformation. Although different molecular players and etiological factors (genetic and hemodynamic) have been suggested to be involved in aortopathy predisposition and progression, clear etiophysiopathological mechanisms of disease are still missing. The isogenic (genetically uniform) hamster (T) strain shows 40% incidence of BAV, but aortic dilatations have not been detected in this model. We have performed comparative anatomical, histological and molecular analyses of the ascending aorta of animals with tricuspid aortic valve (TAV) and BAV from the T strain (TTAV and TBAV, respectively) and with TAV from a control strain (HTAV). Aortic diameter, smooth muscle apoptosis, elastic waviness, and Tgf-β and Fbn-2 expression were significantly increased in T strain animals, regardless of the valve morphology. Strain and aortic valve morphology did not affect Mmp-9 expression, whereas Mmp-2 transcripts were reduced in BAV animals. eNOS protein amount decreased in both TBAV and TTAV compared to HTAV animals. Thus, histomorphological and molecular alterations of the ascending aorta appear in a genetically uniform spontaneous hamster model irrespective of the aortic valve morphology. This is a direct experimental evidence supporting the genetic association between BAV and aortic dilatation. This model may represent a population of patients with predisposition to BAV aortopathy, in which increased expression of Tgf-β and Fbn-2 alters elastic lamellae structure and induces cell apoptosis mediated by eNOS. Patients either with TAV or BAV with the same genetic defect may show the same risk to develop bicuspid aortopathy.

Patient-derived microphysiological model identifies the therapeutic potential of metformin for thoracic aortic aneurysm

Background

Thoracic aortic aneurysm (TAA) is the permanent dilation of the thoracic aortic wall that predisposes patients to lethal events such as aortic dissection or rupture, for which effective medical therapy remains scarce. Human-relevant microphysiological models serve as a promising tool in drug screening and discovery.

Methods

We developed a dynamic, rhythmically stretching, three-dimensional microphysiological model. Using patient-derived human aortic smooth muscle cells (HAoSMCs), we tested the biological features of the model and compared them with native aortic tissues. Drug testing was performed on the individualized TAA models, and the potentially effective drug was further tested using β-aminopropionitrile-treated mice and retrospective clinical data.

Findings

The HAoSMCs on the model recapitulated the expressions of many TAA-related genes in tissue. Phenotypic switching and mitochondrial dysfunction, two disease hallmarks of TAA, were highlighted on the microphysiological model: the TAA-derived HAoSMCs exhibited lower alpha-smooth muscle actin expression, lower mitochondrial membrane potential, lower oxygen consumption rate and higher superoxide accumulation than control cells, while these differences were not evidently reflected in two-dimensional culture flasks. Model-based drug testing demonstrated that metformin partially recovered contractile phenotype and mitochondrial function in TAA patients’ cells. Mouse experiment and clinical investigations also demonstrated better preserved aortic microstructure, higher nicotinamide adenine dinucleotide level and lower aortic diameter with metformin treatment.

Interpretation

These findings support the application of this human-relevant microphysiological model in studying personalized disease characteristics and facilitating drug discovery for TAA. Metformin may regulate contractile phenotypes and metabolic dysfunctions in diseased HAoSMCs and limit aortic dilation.

Funding

This work was supported by grants from National Key R&D Program of China (2018YFC1005002), National Natural Science Foundation of China (82070482, 81771971, 81772007, 51927805, and 21734003), the Science and Technology Commission of Shanghai Municipality (20ZR1411700, 18ZR1407000, 17JC1400200, and 20YF1406900), Shanghai Municipal Science and Technology Major Project (2017SHZDZX01), and Shanghai Municipal Education Commission (Innovation Program 2017-01-07-00-07-E00027). Y.S.Z. was not supported by any of these funds; instead, the Brigham Research Institute is acknowledged.

Plasma Exosomal Mir-423-5p Is Involved in the Occurrence and Development of Bicuspid Aortopathy via TGF-β/SMAD2 Pathway

OBJECTIVES

Patients with bicuspid aortic valve (BAV) are at increased risk for ascending aortic dilation (AAD). Our study was aimed at systemically analyzing the expression profile and mechanism of circulating plasma exosomal microRNAs (miRNAs) related to BAV and AAD.

METHODS

We isolated plasma exosomes from BAV patients (n=19), BAV patients with AAD (BAVAD, n=26), and healthy tricuspid aortic valve individuals with low cardiovascular risk (TAVnon, n=16). We applied a small RNA sequencing approach to identify the specific plasma exosomal miRNAs associated with BAV (n=8) and BAVAD (n=10) patients compared with healthy TAVnon (n=6) individuals. The candidate differentially expressed (DE) miRNAs were selected and validated by RT-qPCR in the remaining samples. GO and KEGG pathway enrichment analyses were performed to illustrate the functions of target genes. Western blot analysis and luciferase reporter assay were conducted in human aortic vascular smooth muscle cells (VSMCs) to verify the results of target gene prediction in vitro. Results: The expression levels of three up-regulated (miR-151a-3p, miR-423-5p, and miR-361-3p) and two down-regulated (miR-16-5p and miR-15a-5p) exosomal miRNAs were significantly altered in BAV disease. Additionally, miR-423-5p could be functionally involved in the occurrence and development of BAV and its complication BAVAD by regulating TGF-β signaling. miR-423-5p could target to SMAD2 and decreased the protein levels of SMAD2 and P-SMAD2.

CONCLUSION

Plasma exosomal miR-423-5p regulated TGF-β signaling by targeting SMAD2, thus exerting functions in the occurrence and development of BAV disease and its complication bicuspid aortopathy.

Residual root fate after aortic surgery in bicuspid aortic valve with right-to-left fusion: A comparative risk analysis

BACKGROUND AND AIM

Although bicuspid aortic valve (BAV) anatomy might influence aortic aneurysm development, BAV-related root involvement still lacks standardized surgical management. We aimed to evaluate late clinical outcomes and risk factors for root dilation after proximal aortic replacement in patients with BAV and right-left fusion (RL-BAV).

METHODS

Clinical and echocardiographic data of all patients with intraoperative RL-BAV who underwent ascending aortic replacement with or without noncoronary sinus (NCS) replacement (Groups 1 and 2, respectively) between 1999 and 2017, were retrospectively revised. A multivariable analysis assessed hazard factors for root dilation during follow-up (FU).

RESULTS

Of 206 surgeries performed (M 81%; age: 57 ± 13 years, EuroSCORE II: 2.7 ± 1.9%), 79 (38%) required NCS replacement. One hundred fifty-seven patients (76%) underwent aortic valve replacement (with aortic regurgitation predominating in Group 1, p = .04). The preoperative aortic root was larger in patients requiring NCS replacement (43.3 ± 5.1 vs. 39.2 ± 4.8 mm, p < .001). At a median FU time of 7 years (interquartile range: 4-10), no residual root dissections occurred, and only two patients (belonging to Group 2) required redo root surgery. Preoperative mild aortic regurgitation and aortic root diameter >35 mm at discharge were risk factors for root dilation >40 mm at FU (p = .02). Aortic root did not dilate over time, irrespective of NCS replacement (p = .06).

CONCLUSIONS

Aortic root in patients with RL-BAV undergoing ascending aortic replacement (±NCS replacement) does not significantly dilate over time, even if patients with preoperative aortic regurgitation and postoperative root more than 35 mm might require more surveillance.

Generation of Vascular Smooth Muscle Cells From Induced Pluripotent Stem Cells: Methods, Applications, and Considerations

The developmental origin of vascular smooth muscle cells (VSMCs) has been increasingly recognized as a major determinant for regional susceptibility or resistance to vascular diseases. As a human material-based complement to animal models and human primary cultures, patient induced pluripotent stem cell iPSC-derived VSMCs have been leveraged to conduct basic research and develop therapeutic applications in vascular diseases. However, iPSC-VSMCs (induced pluripotent stem cell VSMCs) derived by most existing induction protocols are heterogeneous in developmental origins. In this review, we summarize signaling networks that govern in vivo cell fate decisions and in vitro derivation of distinct VSMC progenitors, as well as key regulators that terminally specify lineage-specific VSMCs. We then highlight the significance of leveraging patient-derived iPSC-VSMCs for vascular disease modeling, drug discovery, and vascular tissue engineering and discuss several obstacles that need to be circumvented to fully unleash the potential of induced pluripotent stem cells for precision vascular medicine.

Neural crest-like stem cells for tissue regeneration

Neural crest stem cells (NCSCs) are a transient population of cells that arise during early vertebrate development and harbor stem cell properties, such as self‐renewal and multipotency. These cells form at the interface of non‐neuronal ectoderm and neural tube and undergo extensive migration whereupon they contribute to a diverse array of cell and tissue derivatives, ranging from craniofacial tissues to cells of the peripheral nervous system. Neural crest‐like stem cells (NCLSCs) can be derived from pluripotent stem cells, placental tissues, adult tissues, and somatic cell reprogramming. NCLSCs have a differentiation capability similar to NCSCs, and possess great potential for regenerative medicine applications. In this review, we present recent developments on the various approaches to derive NCLSCs and the therapeutic application of these cells for tissue regeneration.

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.

Modeling aortic diseases using induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) offer an effective platform for studies of human physiology and have revealed new possibilities for disease modeling at the cellular level. These cells also have the potential to be leveraged in the practice of precision medicine, including personalized drug testing. Aortic diseases result in significant morbidity and mortality and pose a global burden to healthcare. Their pathogenesis is mostly associated with functional alterations of vascular components, such as endothelial cells and vascular smooth muscle cells. Drugs that have been proven to be effective in animal models often fail to protect patients from adverse aortic events in clinical studies, provoking researchers to develop reliable in vitro models using human cells. In this review, we summarize the patient iPSC-derived aortic cells that have been utilized to model aortic diseases in vitro. In advanced models, hemodynamic factors, such as blood flow-induced shear stress and cyclic strain, have been added to the systems to replicate cellular microenvironments in the aortic wall. Examples of the utility of such factors in modeling various aortopathies, such as Marfan syndrome, Loeys-Dietz syndrome, and bicuspid aortic valve-related aortopathy, are also described. Overall, the iPSC-based in vitro cell models have shown the potential to promote the development and practice of precision medicine in the treatment of aortic diseases.

Aortic "Disease-in-a-Dish": Mechanistic Insights and Drug Development Using iPSC-Based Disease Modeling

Thoracic aortic diseases, whether sporadic or due to a genetic disorder such as Marfan syndrome, lack effective medical therapies, with limited translation of treatments that are highly successful in mouse models into the clinic. Patient-derived induced pluripotent stem cells (iPSCs) offer the opportunity to establish new human models of aortic diseases. Here we review the power and potential of these systems to identify cellular and molecular mechanisms underlying disease and discuss recent advances, such as gene editing, and smooth muscle cell embryonic lineage. In particular, we discuss the practical aspects of vascular smooth muscle cell derivation and characterization, and provide our personal insights into the challenges and limitations of this approach. Future applications, such as genotype-phenotype association, drug screening, and precision medicine are discussed. We propose that iPSC-derived aortic disease models could guide future clinical trials via “clinical-trials-in-a-dish”, thus paving the way for new and improved therapies for patients.

Vascular Smooth Muscle Cell Derived from IPS Cell of Moyamoya Disease - Comparative Characterization with Endothelial Cell Transcriptome

BACKGROUND

Moyamoya disease (MMD) is an occlusive cerebrovascular disease, causing stroke in children and young adults with unknown etiology. The fundamental pathology is fibrocellular intimal thickening of cerebral arteries, in which vascular smooth muscle cells (VSMCs) are observed as one of the major cell types. Although the characteristics of circulating smooth muscle progenitor cells have been previously reported, the VSMCs are poorly characterized in MMD. We aimed to characterize VSMCs in MMD using induced pluripotent stem cell (iPSC)-technology.

METHODS

We differentiated VSMCs from neural crest stem cells (NCSCs) using peripheral blood mononuclear cell-derived iPSCs and compared biological and transcriptome features under naïve culture conditions between three independent healthy control (HC) subjects and three MMD patients. VSMC transcriptome profiles were also compared to those of endothelial cells (ECs) differentiated from the same iPSCs.

RESULTS

Homogeneous spindle-shaped cells differentiated from iPSCs exhibited smooth muscle cell marker expressions, including α-smooth muscle actin (αSMA, 82.3 ± 6.7% and 81.0 ± 6.7%); calponin (91.3 ± 2.1% and 90.9 ± 1.3%); myosin heavy chain-11 (MYH11, 96.9 ± 0.7% and 97.1 ± 0.3%) without significance of differences between the two groups. Real-time PCR showed few PECAM1 and CD34 gene expressions in both groups, indicating features of differentiated VSMCs. There were no significant differences in cellular proliferation (p = 0.45), migration (p = 0.60), and contractile abilities (p = 0.96) between the two groups. Transcriptome analysis demonstrated similar gene expression profiles of VSMCs in HC subjects and MMD patients with six differentially expressed genes (DEGs); while ECs showed a distinct transcriptome profile in MMD patients with 120 DEGs. The Wnt-signaling pathway was a significant pathway in VSMCs.

CONCLUSIONS

This is the first study that established VSMCs from NCSCs using MMD patient-derived iPSCs and demonstrated similar biological function and transcriptome profile of iPSC-derived VMSCs in MMD patients and HC subjects under naïve single culture condition. Comparative transcriptome features between iPSC-derived VSMCs and ECs, displaying distinct transcriptome in the ECs, suggested that pathological traits can be driven by naïve ECs predominantly and VSMCs may require specific environmental factors in MMD, which provides novel insight into the pathophysiology of MMD. Our iPSC derived VSMC model can contribute to further investigations of diagnostic and therapeutic target of MMD in addition to the current iPSC derived EC model.

Human Cell Modeling for Cardiovascular Diseases

The availability of appropriate and reliable in vitro cell models recapitulating human cardiovascular diseases has been the aim of numerous researchers, in order to retrace pathologic phenotypes, elucidate molecular mechanisms, and discover therapies using simple and reproducible techniques. In the past years, several human cell types have been utilized for these goals, including heterologous systems, cardiovascular and non-cardiovascular primary cells, and embryonic stem cells. The introduction of induced pluripotent stem cells and their differentiation potential brought new prospects for large-scale cardiovascular experiments, bypassing ethical concerns of embryonic stem cells and providing an advanced tool for disease modeling, diagnosis, and therapy. Each model has its advantages and disadvantages in terms of accessibility, maintenance, throughput, physiological relevance, recapitulation of the disease. A higher level of complexity in diseases modeling has been achieved with multicellular co-cultures. Furthermore, the important progresses reached by bioengineering during the last years, together with the opportunities given by pluripotent stem cells, have allowed the generation of increasingly advanced in vitro three-dimensional tissue-like constructs mimicking in vivo physiology. This review provides an overview of the main cell models used in cardiovascular research, highlighting the pros and cons of each, and describing examples of practical applications in disease modeling.

The science of BAV aortopathy

The aortopathy associated with bicuspid aortic valve (BAV) is an epidemiologically relevant source of chronic and acute aortic disease (aneurysm and dissection). However, its pathogenesis is still the object of scientific uncertainties and debates. Indeed, the mechanisms determining the diseases of the ascending aorta in BAV patients are most likely complex and multifactorial, i.e. resulting from variable modes of interplay between genetic and hemodynamic factors. Although few scientific studies have so far taken into adequate account this complexity, leaving the precise sequence of pathogenetic events still undiscovered, the accumulated evidence from previous research approaches have at least brought about important insights. While genetic studies have so far identified variants relevant to either valve malformation or aortic complications (including those in the genes NOTCH1, TGFBR2, ACTA2, GATA5, NKX2.5, SMAD6, ROBO4), however each explaining not more than 5% of the study population, other investigations have thoroughly described both the flow features, with consequent forces acting on the arterial wall (including skewed flow jet direction, rotational flow, wall shear stress), and the main changes in the molecular and cellular wall structure (including extracellular matrix degradation, smooth muscle cell changes, oxidative stress, unbalance of TGF-β signaling, aberrant endothelial-to-mesenchymal transition). All of this evidence, together with the recognition of the diverse phenotypes that the aortopathy can assume in BAV patients, holding possible prognostic significance, is reviewed in this chapter. The complex and multifaceted body of knowledge resulting from clinical and basic science studies on BAV aortopathy has the potential to importantly influence modes of clinical management of this disease in the near future.

In Vitro Lineage-Specific Differentiation of Vascular Smooth Muscle Cells in Response to SMAD3 Deficiency: Implications for SMAD3-Related Thoracic Aortic Aneurysm

OBJECTIVE

SMAD3 pathogenic variants are associated with the development of thoracic aortic aneurysms. We sought to determine the role of SMAD3 in lineage-specific vascular smooth muscle cells (VSMCs) differentiation and function. Approach and Results: SMAD3 c.652delA, a frameshift mutation and nonsense-mediated decay, was introduced in human-induced pluripotent stem cells using CRISPR-Cas9. The wild-type and SMAD3^-/- (c.652delA) human-induced pluripotent stem cells were differentiated into cardiovascular progenitor cells or neural crest stem cells and then to lineage-specific VSMCs. Differentiation, contractility, extracellular matrix synthesis, and TGF-β (transforming growth factor-β) signaling of the differentiated VSMCs were analyzed. The homozygous frameshift mutation resulted in SMAD3 deficiency and was confirmed in human-induced pluripotent stem cells by Sanger sequencing and immunoblot analysis. In cardiovascular progenitor cell-VSMCs, SMAD3 deletion significantly disrupted canonical TGF-β signaling and decreased gene expression of VSMC markers, including SM α-actin, myosin heavy chain 11, calponin-1, SM22α, and key controlling factors, SRF and myocardin, but increased collagen expression. The loss of SMAD3 significantly decreased VSMC contractility. In neural crest stem cells-VSMCs, SMAD3 deficiency did not significantly affect the VSMC differentiation but decreased ELN (elastin) expression and increased phosphorylated SMAD2. Expression of mir-29 was increased in SMAD3^-/- VSMCs, and inhibition of mir-29 partially rescued ELN expression.

CONCLUSIONS

SMAD3-dependent TGF-β signaling was essential for the differentiation of cardiovascular progenitor cell-VSMCs but not for the differentiation of neural crest stem cell-VSMCs. The lineage-specific TGF-β responses in human VSMCs may potentially contribute to the development of aortic root aneurysms in patients with SMAD3 mutations.

Cardiac Neural Crest Cells: Their Rhombomeric Specification, Migration, and Association with Heart and Great Vessel Anomalies

Outflow tract abnormalities are the most frequent congenital heart defects. These are due to the absence or dysfunction of the two main cell types, i.e., neural crest cells and secondary heart field cells that migrate in opposite directions at the same stage of development. These cells directly govern aortic arch patterning and development, ascending aorta dilatation, semi-valvular and coronary artery development, aortopulmonary septation abnormalities, persistence of the ductus arteriosus, trunk and proximal pulmonary arteries, sub-valvular conal ventricular septal/rotational defects, and non-compaction of the left ventricle. In some cases, depending on the functional defects of these cells, additional malformations are found in the expected spatial migratory area of the cells, namely in the pharyngeal arch derivatives and cervico-facial structures. Associated non-cardiovascular anomalies are often underestimated, since the multipotency and functional alteration of these cells can result in the modification of multiple neural, epidermal, and cervical structures at different levels. In most cases, patients do not display the full phenotype of abnormalities, but congenital cardiac defects involving the ventricular outflow tract, ascending aorta, aortic arch and supra-aortic trunks should be considered as markers for possible impaired function of these cells. Neural crest cells should not be considered as a unique cell population but on the basis of their cervical rhombomere origins R3-R5 or R6-R7-R8 and specific migration patterns: R3-R4 towards arch II, R5-R6 arch III and R7-R8 arch IV and VI. A better understanding of their development may lead to the discovery of unknown associated abnormalities, thereby enabling potential improvements to be made to the therapeutic approach.

Therapeutic Effect of Rapamycin on Aortic Dissection in Mice

Aortic dissection (AD) is a serious clinical condition that is unpredictable and frequently results in fatal outcome. Although rapamycin, an inhibitor of mechanistic target of rapamycin (mTOR), has been reported to be effective in preventing aortopathies in mouse models, its mode of action has yet to be clarified. A mouse AD model that was created by the simultaneous administration of β-aminopropionitrile (BAPN) and angiotensin II (AngII) for 14 days. Rapamycin treatment was started either at day 1 or at day 7 of BAPN+AngII challenge, and continued throughout the observational period. Rapamycin was effective both in preventing AD development and in suppressing AD progression. On the other hand, gefitinib, an inhibitor of growth factor signaling, did not show such a beneficial effect, even though both rapamycin and gefitinib suppressed cell cycle activation in AD. Rapamycin suppressed cell cycle-related genes and induced muscle development-related genes in an AD-related gene expression network without a major impact on inflammation-related genes. Rapamycin augmented the activation of Akt1, Akt2, and Stat3, and maintained the contractile phenotype of aortic smooth muscle cells. These findings indicate that rapamycin was effective both in preventing the development and in suppressing the progression of AD, indicating the importance of the mTOR pathway in AD pathogenesis.

Functional characterization and circulating expression profile of dysregulated microRNAs in BAV-associated aortopathy

Compelling evidence has shown that microRNAs (miRs) are involved in the pathophysiology of BAV-associated aortopathy. The purpose of this study was to assess the biological role as well as the circulating expression of two miRs (miR-424-3p and miR-3688-3p) that have been previously identified as significantly dysregulated in thoracic aortic aneurysm specimens of BAV patients. Bioinformatic tools were used to predict miR gene targets followed by functional validation transfecting synthetic miR mimics and negative controls into human aortic smooth muscle cells (HASMCs). Levels of miRs and target genes were evaluated by qRT-PCR. The circulating miR expression profile analysis was assessed on plasma samples collected from a cohort of 72 patients with aortopathy including 39 BAV (33 males; 58 ± 13 years) and 33 TAV patients (26 males; 67 ± 9 years). Computational analysis revealed that SMAD7 and YAP1 were potential targets of miR-424-3p and miR-3688-3p, respectively. Transfection with mimics confirmed a significantly decreased gene expression of SMAD7 and YAP1 compared to mimic negative control (p = 0.04 and p = 0.0005, respectively) or blank control (p = 0.01 and p = 0.0007, respectively). Overexpression of miR-3688-3p also significantly upregulated pro-apoptotic caspase-3 gene expression compared to mimic negative control (p = 0.02) or blank control (p = 0.01). Furthermore, a significant down-regulation of the circulating miR-424-3p was observed in BAV compared to TAV patients (p = 0.001). In multiple linear regression analysis, the aortic valve morphology (β = - 0.29, p = 0.04) and the presence of aortic stenosis (β = - 0.28, p = 0.03) had a significant effect on the miR-424-3p expression. In conclusion, our study demonstrated that miR-424-3p and miR-3688-3p directly targeted SMAD7 and YAP1 in HASMCs, pivotal genes of the TGF-β and Hippo-signaling pathways. Circulating miR-424-3p was also found to be significantly decreased in BAV patients when compared to TAV patients, especially in patients with aortic stenosis. Further large studies of well-characterized BAV patient cohorts are needed to define the clinical significance of the miR-424-3p.

Induced pluripotent stem cell-derived vascular smooth muscle cells

The reproducible generation of human-induced pluripotent stem cell (hiPSC)-derived vascular smooth muscle cells (vSMCs) in vitro has been critical to overcoming many limitations of animal and primary cell models of vascular biology and disease. Since this initial advance, research in the field has turned toward recapitulating the naturally occurring subtype specificity found in vSMCs throughout the body, and honing functional models of vascular disease. In this review, we summarize vSMC derivation approaches, including current phenotype and developmental origin-specific methods, and applications of vSMCs in functional disease models and engineered tissues. Further, we discuss the challenges of heterogeneity in hiPSC-derived tissues and propose approaches to identify and isolate vSMC subtype populations.

Direct Reprogramming of Fibroblasts Into Smooth Muscle-Like Cells With Defined Transcription Factors-Brief Report

Objective- To identify the transcription factors that could contribute to direct reprogramming of fibroblasts toward smooth muscle cell fate. Approach and Results- We screened various combinations of transcription factors, including Myocd (myocardin), Mef2C (myocyte enhancer factor 2C), Mef2B (myocyte enhancer factor 2B), Mkl1 (MKL [megakaryoblastic leukemia]/Myocd-like 1), Gata4 (GATA-binding protein 4), Gata5 (GATA-binding protein 5), Gata6 (GATA-binding protein 6), Ets1 (E26 avian leukemia oncogene 1, 5' domain), and their corresponding carboxyterminal fusions to the transactivation domain of MyoD (myogenic differentiation 1)-indicated by *-for their effects on reprogramming mouse embryonic fibroblasts and human adult dermal fibroblasts to the smooth muscle cell fate as determined by the expression of specific markers. The combination of 3 transcription factors, Myocd (or Myocd*) with Mef2C (or Mef2C*) and Gata6, was the most efficient in enhancing the expression of smooth muscle marker genes and decreasing fibroblast gene expression. Additionally, the derived induced smooth muscle-like cells showed a contractile phenotype in response to carbachol. Conclusions- Combination of Myocd and Gata6 with Mef2C* (MG2*) could sufficiently and efficiently direct differentiation of mouse embryonic and human dermal fibroblasts into induced smooth muscle-like cells, thus opening new opportunities for disease modeling, tissue engineering, and personalized medicine.

The Application of Induced Pluripotent Stem Cells in Pathogenesis Study and Gene Therapy for Vascular Disorders: Current Progress and Future Challenges

Vascular disorders are complex diseases with high morbidity and mortality. Among them, the dilated macrovascular diseases (MVD), such as aortic aneurysm and aortic dissection, have presented a huge threat to human health. The pathogenesis of vascular diseases is mostly associated with property alteration of vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). Studies have confirmed that induced pluripotent stem cells (iPSCs) can be proliferated and differentiated into other somatic cells, such as VECs and VSMCs. And patient-specific cells could provide detailed human-associated information in regard to pathogenesis or drug responses. In addition, differentiated ECs from iPSC have been widely used in disease modeling as a cell therapy. In this review, we mainly discussed the application of hiPSCs in investigating the pathological mechanism of different inherited vascular diseases and provide a comprehensive understanding of hiPSCs in the field of clinical diagnosis and gene therapy.

HiPS-Cardiac Trilineage Cell Generation and Transplantation: a Novel Therapy for Myocardial Infarction

Despite primary percutaneous coronary intervention (PPCI) and the availability of optimal medications, including dual antiplatelet therapy (DAPT), most patients still experience major adverse cardiovascular events (MACEs) due to frequent recurrence of thrombotic complications and myocardial infarction (MI). MI occurs secondary to a massive loss of endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and cardiomyocytes (CMs). The adult cardiovascular system gradually loses the ability to spontaneously and regularly regenerate ECs, VSMCs, and CMs. However, human cells can be induced by cytokines and growth factors to regenerate human-induced pluripotent stem cells (hiPSCs), which progress to produce cardiac trilineage cells (CTCs) such as ECs, VSMCs, and CMs, replacing lost cells and inducing myocardial repair. Nevertheless, the processes and pathways involved in hiPSC-CTC generation and their potential therapeutic effects remain unknown. Herein, we provide evidence of in vitro CTC generation, the pathways involved, in vivo transplantation, and its therapeutic effect, which may provide novel targets in regenerative medicine for the treatment of cardiovascular diseases (CVDs).

Seno-destructive smooth muscle cells in the ascending aorta of patients with bicuspid aortic valve disease

Background

Ascending aortic aneurysms constitute an important hazard for individuals with a bicuspid aortic valve (BAV). However, the processes that degrade the aortic wall in BAV disease remain poorly understood.

Methods

We undertook in situ analysis of ascending aortas from 68 patients, seeking potentially damaging cellular senescence cascades. Aortas were assessed for senescence-associated-ß-galactosidase activity, p16^Ink4a and p21 expression, and double-strand DNA breaks. The senescence-associated secretory phenotype (SASP) of cultured-aged BAV aortic smooth muscle cells (SMCs) was evaluated by transcript profiling and consequences probed by combined immunofluorescence and circular polarization microscopy. The contribution of p38 MAPK signaling was assessed by immunostaining and blocking strategies.

Findings

We uncovered SMCs at varying depths of cellular senescence within BAV- and tricuspid aortic valve (TAV)-associated aortic aneurysms. Senescent SMCs were also abundant in non-aneurysmal BAV aortas but not in non-aneurysmal TAV aortas. Multivariable analysis revealed that BAV disease independently associated with SMC senescence. Furthermre, SMC senescence was heightened at the convexity of aortas associated with right-left coronary cusp fusion. Aged BAV SMCs had a pronounced collagenolytic SASP. Moreover, senescent SMCs in the aortic wall were enriched with surface-localized MMP1 and surrounded by weakly birefringent collagen fibrils. The senescent-collagenolytic SMC phenotype depended on p38 MAPK signaling, which was chronically activated in BAV aortas.

Interpretation

We have identified a cellular senescence-collagen destruction axis in at-risk ascending aortas. This novel “seno-destructive” SMC phenotype could open new opportunities for managing BAV aortopathy.

Fund

Canadian Institutes of Health Research, Lawson Health Research Institute, Heart and Stroke Foundation of Ontario/Barnett-Ivey Chair.

Human Pluripotent Stem Cell-Derived Neural Crest Cells for Tissue Regeneration and Disease Modeling

Neural crest cells (NCCs) are a multipotent and migratory cell population in the developing embryo that contribute to the formation of a wide range of tissues. Defects in the development, differentiation and migration of NCCs give rise to a class of syndromes and diseases that are known as neurocristopathies. NCC development has historically been studied in a variety of animal models, including xenopus, chick and mouse. In the recent years, there have been efforts to study NCC development and disease in human specific models, with protocols being established to derive NCCs from human pluripotent stem cells (hPSCs), and to further differentiate these NCCs to neural, mesenchymal and other lineages. These in vitro differentiation platforms are a valuable tool to gain a better understanding of the molecular mechanisms involved in human neural crest development. The use of induced pluripotent stem cells (iPSCs) derived from patients afflicted with neurocristopathies has also enabled the study of defective human NCC development using these in vitro platforms. Here, we review the various in vitro strategies that have been used to derive NCCs from hPSCs and to specify NCCs into cranial, trunk, and vagal subpopulations and their derivatives. We will also discuss the potential applications of these human specific NCC platforms, including the use of iPSCs for disease modeling and the potential of NCCs for future regenerative applications.

Histologic differences between the ascending and descending aortas in young adults with fibrillin-1 mutations

OBJECTIVES

This study aimed to review the clinical results of young adult patients with aortic disease associated with mutations in the fibrillin-1 gene (FBN1) and disclose the histologic differences between the ascending and descending aortas.

METHODS

Between 2012 and 2015, 94 patients aged less than 50 years underwent surgery for thoracic aortic diseases. Forty-two patients (44.7%) had FBN-1 mutations. Of these, 40 patients (42.5%) with surgical specimens for histologic evaluation were included in the study. With the histologic results including the specimen sampled at their previous operations, cystic medial necrosis was classified into 3 grades according to the degree of the cystic area.

RESULTS

Thirty-nine patients (97.5%) had aortic root dilatation (Z ≥2), and 13 patients (32.5%) had ectopia lentis. Thirty-nine patients (97.5%) fulfilled the diagnostic criteria for Marfan syndrome. There were no in-hospital deaths. The majority (27/29: 93.1%) of the specimens of the ascending aorta revealed cystic medial necrosis pattern. With grade III being the most severe condition, these cases were classified into grade I (n = 2), grade II (n = 5), and grade III (n = 20). In contrast, only 6 specimens (6/17: 35.3%) of the descending aorta showed a cystic medial necrosis pattern that was classified into grade I (n = 2) and grade III (n = 4), (P < .00001).

CONCLUSIONS

Fewer specimens of the descending aorta revealed cystic medial necrosis compared with those of the ascending aorta. This difference might influence the characteristic aortic disease in Marfan syndrome associated with FBN-1 mutations.

Activation of the AKT Pathway in the Ascending Aorta With Bicuspid Aortic Valve

BACKGROUND

Dilatation of the ascending aorta affects those patients with bicuspid aortic valve (BAV), even after valvular surgery, possibly due to tissue fragility. The goal of the study was the molecular characterization of aorta with BAV compared to that with normal tricuspid aortic valve (TAV). Methods and Results: The subjects were patients who underwent surgery for aortic valve stenosis in 2013 and 2014. Nine patients with BAV and 13 with TAV were examined. There was no difference in the clinical characteristics or grade of aortic valve stenosis, but the diameters of the ascending aorta were significantly higher in the BAV group. The ascending aortic specimens were subjected to transcriptome analyses, which revealed the changes in receptor tyrosine kinase (RTK) pathway-related genes between TAV and BAV samples. Immunohistochemical study revealed higher staining of phosphorylated AKT (pAKT) in the media of the ascending aorta in the BAV group, regardless of the size of ascending aorta, whereas total AKT did not show such a difference. Immunofluorescence staining revealed the AKT activation was mainly in the medial vascular smooth muscle cells.

CONCLUSIONS

The results showed that the RTK-AKT pathway in the medial layer of the ascending aorta is activated in aortae with BAV. Activation of this pathway may be associated with fragility and dilatation of the ascending aorta with BAV.

Induced pluripotent stem cells with NOTCH1 gene mutation show impaired differentiation into smooth muscle and endothelial cells: Implications for bicuspid aortic valve-related aortopathy

OBJECTIVE

The NOTCH1 gene mutation has been identified in bicuspid aortic valve patients. We developed an in vitro model with human induced pluripotent stem cells (iPSCs) to evaluate the role of NOTCH1 in smooth muscle and endothelial cell (EC) differentiation.

METHODS

The iPSCs were derived from a patient with a normal tricuspid aortic valve and aorta. The NOTCH1 gene was targeted in iPSCs with the Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9 nuclease (Cas9) system. The NOTCH1^-/- (NOTCH1 homozygous knockout) and isogenic control iPSCs (wild type) were differentiated into neural crest stem cells (NCSCs) and into cardiovascular progenitor cells (CVPCs). The NCSCs were differentiated into smooth muscle cells (SMCs). The CVPCs were differentiated into ECs. The differentiations of SMCs and ECs were compared between NOTCH1^-/- and wild type cells.

RESULTS

The expression of NCSC markers (SRY-related HMG-box 10 and transcription factor AP-2 alpha) was significantly lower in NOTCH1^-/-NCSCs than in wild type NCSCs. The SMCs derived from NOTCH1^-/- NCSCs showed immature morphology with smaller size and decreased expression of all SMC-specific contractile proteins. In NOTCH1^-/-CVPCs, the expression of ISL1, NKX2.5, and MYOCD was significantly lower than that in isogenic control CVPCs, indicating impaired differentiation from iPSCs to CVPCs. The NOTCH1^-/-ECs derived from CVPCs showed significantly lower expression of cluster of differentiation 105 and cluster of differentiation 31 mRNA and protein, indicating a defective differentiation process.

CONCLUSIONS

NOTCH1 is critical in SMC and EC differentiation of iPSCs through NCSCs and CVPCs, respectively. NOTCH1 gene mutations might potentially contribute to the development of thoracic aortic aneurysms by affecting SMC differentiation in some patients with bicuspid aortic valve.

Non-coding RNAs in aneurysmal aortopathy

Aortic aneurysms represent a major public health burden, and currently have no medical treatment options. The pathophysiology behind these aneurysms is complex and variable, depending on location and underlying cause, and generally involves progressive dysfunction of all elements of the aortic wall. Changes in smooth muscle behavior, endothelial signaling, extracellular matrix remodeling, and to a variable extent inflammatory signaling and cells, all contribute to the dilation of the aorta, ultimately resulting in high mortality and morbidity events including dissection and rupture. A large number of researchers have identified non-coding RNAs as crucial regulators of aortic aneurysm development, both in humans and in animal models. While most work to-date has focused on microRNAs, intriguing information has also begun to emerge regarding the role of long-non-coding RNAs. This review summarizes the currently available data regarding the involvement of non-coding RNAs in aneurysmal aortopathies. Going forward, these represent key potential therapeutic targets that might be leveraged in the future to slow or prevent aortic aneurysm formation, progression and rupture.

Aortic valve-mediated wall shear stress is heterogeneous and predicts regional aortic elastic fiber thinning in bicuspid aortic valve-associated aortopathy

OBJECTIVES

The objectives of this study were to investigate an association between the magnitude of flow-mediated aortic wall shear stress (WSS) and medial wall histopathology in patients with bicuspid aortic valve (BAV) with aortopathy.

METHODS

Patients with BAV (n = 27; 52 ± 15 years; 3 women; proximal thoracic aorta diameter = 4.4 ± 0.7 and 4.6 ± 0.5 cm) who underwent prophylactic aortic resection received preoperative 3-dimensional time-resolved phase-contrast magnetic resonance imaging with 3-dimensional velocity encoding to quantify WSS relative to a population of healthy age- and sex-matched tricuspid aortic valve control participants (n = 20). Quantitative histopathology was conducted on BAV aorta tissue samples resected at surgery (n = 93), and correlation was performed between elastic fiber thickness and in vivo aortic WSS as continuous variables. Validation of elastic fiber thickness was achieved by correlation relative to tissue stiffness determined using biaxial biomechanical testing (n = 22 samples).

RESULTS

Elastic fibers were thinner and WSS was higher along the greater curvature compared with other circumferential regions (vs anterior wall: P = .003 and P = .0001, respectively; lesser curvature: both P = .001). Increased regional WSS was associated with decreased elastic fiber thickness (r = -0.25; P = .02). Patient stratification with subanalysis showed an increase in the correlation between WSS and histopathology with aortic valve stenosis (r = -0.36; P = .002) and smaller aortic diameters (<4.5 cm: r = -0.39; P = .03). Elastic fiber thinning was associated with circumferential stiffness (r = -0.41; P = .06).

CONCLUSIONS

For patients with BAV, increased aortic valve-mediated WSS is significantly associated with elastic fiber thinning, particularly with aortic valve stenosis and in earlier stages of aortopathy. Elastic fiber thinning correlates with impaired tissue biomechanics. These novel findings further implicate valve-mediated hemodynamics in the progression of BAV aortopathy.

Enlightening the Association between Bicuspid Aortic Valve and Aortopathy

Bicuspid aortic valve (BAV) patients have an increased incidence of developing aortic dilation. Despite its importance, the pathogenesis of aortopathy in BAV is still largely undetermined. Nowadays, intense focus falls both on BAV morphology and progression of valvular dysfunction and on the development of aortic dilation. However, less is known about the relationship between aortic valve morphology and aortic dilation. A better understanding of the molecular pathways involved in the homeostasis of the aortic wall, including the extracellular matrix, the plasticity of the vascular smooth cells, TGFβ signaling, and epigenetic dysregulation, is key to enlighten the mechanisms underpinning BAV-aortopathy development and progression. To date, there are two main theories on this subject, i.e., the genetic and the hemodynamic theory, with an ongoing debate over the pathogenesis of BAV-aortopathy. Furthermore, the lack of early detection biomarkers leads to challenges in the management of patients affected by BAV-aortopathy. Here, we critically review the current knowledge on the driving mechanisms of BAV-aortopathy together with the current clinical management and lack of available biomarkers allowing for early detection and better treatment optimization.

iPSCs-based generation of vascular cells: reprogramming approaches and applications

Recent advances in the field of induced pluripotent stem cells (iPSCs) research have opened a new avenue for stem cell-based generation of vascular cells. Based on their growth and differentiation potential, human iPSCs constitute a well-characterized, generally unlimited cell source for the mass generation of lineage- and patient-specific vascular cells without any ethical concerns. Human iPSCs-derived vascular cells are perfectly suited for vascular disease modeling studies because patient-derived iPSCs possess the disease-causing mutation, which might be decisive for full expression of the disease phenotype. The application of vascular cells for autologous cell replacement therapy or vascular engineering derived from immune-compatible iPSCs possesses huge clinical potential, but the large-scale production of vascular-specific lineages for regenerative cell therapies depends on well-defined, highly reproducible culture and differentiation conditions. This review will focus on the different strategies to derive vascular cells from human iPSCs and their applications in regenerative therapy, disease modeling and drug discovery approaches.

New models to study vascular mural cell embryonic origin: implications in vascular diseases

A key question in vascular biology is how the diversity of origin of vascular mural cells, namely smooth muscle cells (SMCs) and pericytes influences vessel properties, in particular the regional propensity to vascular diseases. This review therefore first describes the role and regulation of mural cells during vascular formation, with a focus on embryonic origin. We then consider the evidence that connects heterogeneities in SMC and pericyte origins with disease. Since this idea has major implications for understanding and modelling human disease, then there is a pressing need for new model systems to investigate mural cell development and the consequences of heterogeneity. Recent advances arising from in vitro strategies for deriving mural cells from human pluripotent stem cells as well as from the zebrafish model will be discussed and the medical relevance of these discoveries will be highlighted.