The genetics and biomechanics of thoracic aortic diseases

Investigation of Strategies to Block Downstream Effectors of AT1R-Mediated Signalling to Prevent Aneurysm Formation in Marfan Syndrome

Cardiovascular outcome in Marfan syndrome (MFS) patients most prominently depends on aortic aneurysm progression with subsequent aortic dissection. Angiotensin II receptor blockers (ARBs) prevent aneurysm formation in MFS mouse models. In patients, ARBs only slow down aortic dilation. Downstream signalling from the angiotensin II type 1 receptor (AT1R) is mediated by G proteins and β-arrestin recruitment. AT1R also interacts with the monocyte chemoattractant protein-1 (MCP-1) receptor, resulting in inflammation. In this study, we explore the targeting of β-arrestin signalling in MFS mice by administering TRV027. Furthermore, because high doses of the ARB losartan, which has been proven beneficial in MFS, cannot be achieved in humans, we investigate a potential additive effect by combining lower concentrations of losartan (25 mg/kg/day and 5 mg/kg/day) with barbadin, a β-arrestin blocker, and DMX20, a C-C chemokine receptor type 2 (CCR2) blocker. A high dose of losartan (50 mg/kg/day) slowed down aneurysm progression compared to untreated MFS mice (1.73 ± 0.12 vs. 1.96 ± 0.08 mm, p = 0.0033). TRV027, the combination of barbadin with losartan (25 mg/kg/day), and DMX-200 (90 mg/kg/day) with a low dose of losartan (5 mg/kg/day) did not show a significant beneficial effect. Our results confirm that while losartan effectively halts aneurysm formation in Fbn1C1041G/+ MFS mice, neither TRV027 alone nor any of the other compounds combined with lower doses of losartan demonstrate a notable impact on aneurysm advancement. It appears that complete blockade of AT1R function, achieved by administrating a high dosage of losartan, may be necessary for inhibiting aneurysm progression in MFS.

Statistical shape representation of the thoracic aorta: accounting for major branches of the aortic arch

Statistical shape modeling (SSM) is an emerging tool for risk assessment of thoracic aortic aneurysm. However, the head branches of the aortic arch are often excluded in SSM. We introduced an SSM strategy based on principal component analysis that accounts for aortic branches and applied it to a set of patient scans. Computational fluid dynamics were performed on the reconstructed geometries to identify the extent to which branch model accuracy affects the calculated wall shear stress (WSS) and pressure. Surface-averaged and location-specific values of pressure did not change significantly, but local WSS error was high near branches when inaccurately modeled.

Evidence for a protective role of Protein Disulfide Isomerase-A1 against aortic dissection

BACKGROUND AND AIMS

Redox signaling is involved in the pathophysiology of aortic aneurysm/dissection. Protein Disulfide Isomerases and its prototype PDIA1 are thiol redox chaperones mainly from endoplasmic reticulum (ER), while PDIA1 cell surface pool redox-regulates thrombosis, cytoskeleton remodeling and integrin activation, which are mechanisms involved in aortic disease. Here we investigate the roles of PDIA1 in aortic dissection.

METHODS

Initially, we assessed the outcome of aortic aneurysm/dissection in transgenic PDIA1-overexpressing FVB mice using a model of 28-day exposure to lysyl oxidase inhibitor BAPN plus angiotensin-II infusion. In a second protocol, we assessed the effects of PDIA1 inhibitor isoquercetin (IQ) against aortic dissection in C57BL/6 mice exposed to BAPN for 28 days.

RESULTS

Transgenic PDIA1 overexpression associated with ca. 50% (p = 0.022) decrease (vs.wild-type) in mortality due to abdominal aortic rupture and protected against elastic fiber breaks in thoracic aorta. Conversely, exposure of mice to IQ increased thoracic aorta dissection-related mortality rates, from ca. 18%-50% within 28-days (p = 0.019); elastic fiber disruption and collagen deposition were also enhanced. The structurally-related compound diosmetin, which does not inhibit PDI, had negligible effects. In parallel, stretch-tension curves indicated that IQ amplified a ductile-type of biomechanical failure vs. control or BAPN-exposed mice aortas. IQ-induced effects seemed unassociated with nonspecific antioxidant effects or ER stress. In both models, echocardiographic analysis of surviving mice suggested that aortic rupture was dissociated from progressive dilatation.

CONCLUSIONS

Our data indicate a protective role of PDIA1 against aortic dissection/rupture and potentially uncovers a novel integrative mechanism coupling redox and biomechanical homeostasis in vascular remodeling.

A review on the biomechanical behaviour of the aorta

Large aortic aneurysm and acute and chronic aortic dissection are pathologies of the aorta requiring surgery. Recent advances in medical intervention have improved patient outcomes; however, a clear understanding of the mechanisms leading to aortic failure and, hence, a better understanding of failure risk, is still missing. Biomechanical analysis of the aorta could provide insights into the development and progression of aortic abnormalities, giving clinicians a powerful tool in risk stratification. The complexity of the aortic system presents significant challenges for a biomechanical study and requires various approaches to analyse the aorta. To address this, here we present a holistic review of the biomechanical studies of the aorta by categorising articles into four broad approaches, namely theoretical, in vivo, experimental and combined investigations. Experimental studies that focus on identifying mechanical properties of the aortic tissue are also included. By reviewing the literature and discussing drawbacks, limitations and future challenges in each area, we hope to present a more complete picture of the state-of-the-art of aortic biomechanics to stimulate research on critical topics. Combining experimental modalities and computational approaches could lead to more comprehensive results in risk prediction for the aortic system.

Impacts of Telomeric Length, Chronic Hypoxia, Senescence, and Senescence-Associated Secretory Phenotype on the Development of Thoracic Aortic Aneurysm

Thoracic aortic aneurysm (TAA) is an age-related and life-threatening vascular disease. Telomere shortening is a predictor of age-related diseases, and its progression is associated with premature vascular disease. The aim of the present work was to investigate the impacts of chronic hypoxia and telomeric DNA damage on cellular homeostasis and vascular degeneration of TAA. We analyzed healthy and aortic aneurysm specimens (215 samples) for telomere length (TL), chronic DNA damage, and resulting changes in cellular homeostasis, focusing on senescence and apoptosis. Compared with healthy thoracic aorta (HTA), patients with tricuspid aortic valve (TAV) showed telomere shortening with increasing TAA size, in contrast to genetically predisposed bicuspid aortic valve (BAV). In addition, TL was associated with chronic hypoxia and telomeric DNA damage and with the induction of senescence-associated secretory phenotype (SASP). TAA-TAV specimens showed a significant difference in SASP-marker expression of IL-6, NF-κB, mTOR, and cell-cycle regulators (γH2AX, Rb, p53, p21), compared to HTA and TAA-BAV. Furthermore, we observed an increase in CD163⁺ macrophages and a correlation between hypoxic DNA damage and the number of aortic telocytes. We conclude that chronic hypoxia is associated with telomeric DNA damage and the induction of SASP in a diseased aortic wall, promising a new therapeutic target.

Current Understanding of Aortic Dissection

The aorta is the largest artery in the body, delivering oxygenated blood from the left ventricle to all organs. Dissection of the aorta is a lethal condition caused by a tear in the intimal layer of the aorta, followed by blood loss within the aortic wall and separation of the layers to full dissection. The aorta can be affected by a wide range of causes including acute conditions such as trauma and mechanical damage; and genetic conditions such as arterial hypertension, dyslipidaemia, and connective tissue disorders; all increasing the risk of dissection. Both rapid diagnostic recognition and advanced multidisciplinary treatment are critical in managing aortic dissection patients. The treatment depends on the severity and location of the dissection. Open surgical repair is the gold standard of treatment for dissections located to the proximal part of the aorta and the arch, while endovascular interventions are recommended for most distal or type B aortic dissections. In this review article, we examine the epidemiology, pathophysiology, contemporary diagnoses, and management of aortic dissection.

Aortic local biomechanical properties in ascending aortic aneurysms

Ascending aortic aneurysm (AsAA) is a high-risk cardiovascular disease with an increased incidence over years. In this study, we compare different risk factors based on the pre-failure behavior (from a biomechanical point of view) obtained ex-vivo from an equi-biaxial tensile test. A total of 100 patients (63 ± 12 years, 72 males) with AsAA replacement, were recruited. Equi-biaxial tensile tests of AsAA walls were performed on freshly sampled aortic wall tissue after ascending aortic replacement. The aneurysmal aortic walls were divided into four quadrants (medial, anterior, lateral, and posterior) and two directions (longitudinal and circumferential) were considered. The stiffness was represented by the maximum Young Modulus (MYM). Based on patient information, the following subgroups were considered: age, gender, hypertension, obesity, dyslipidemia, diabetes, smoking history, aortic insufficiency, aortic stenosis, coronary artery disease, aortic diameter and aortic valve type. In general, when the aortic diameter increased, the aortic wall became thicker. In terms of the MYM, the longitudinal direction was significantly higher than that in the circumferential direction. In the multivariant analysis, the impact factors of age (p = 0.07), smoking (p = 0.05), diabetes (p = 0.03), aortic stenosis (p = 0.02), coronary artery disease (p < 10^-3), and aortic diameters (p = 0.02) were significantly influencing the MYM. There was no significant MYM difference when the patients presented arterial hypertension, dyslipidemia, obesity, or bicuspid aortic valve. To conclude, the pre-failure aortic stiffness is multi-factorial, according to our population of 100 patients with AsAA. STATEMENT OF SIGNIFICANCE: : Our research on the topic of "Aortic local biomechanical properties in case of ascending aortic aneurysms" is about the biomechanical properties on one hundred aortic samples according to the aortic wall quadrants and the direction. More than ten factors and risks which may impact ascending aortic aneurysms have been studied. According to our knowledge, so far, this article involved the largest population on this topic. It will be our pleasure to share this information with all the readers.

Genomic insights in ascending aortic size and distensibility

Background

Alterations in the anatomic and biomechanical properties of the ascending aorta (AAo) can give rise to various vascular pathologies. The aim of the current study is to gain additional insights in the biology of the AAo size and function.

Methods

We developed an AI based analysis pipeline for the segmentation of the AAo, and the extraction of AAO parameters. We then performed genome-wide association studies of AAo maximum area, AAo minimum area and AAo distensibility in up to 37,910 individuals from the UK Biobank. Variants that were significantly associated with AAo phenotypes were used as instrumental variables in Mendelian randomization analyses to investigate potential causal relationships with coronary artery disease, myocardial infarction, stroke and aneurysms.

Findings

Genome-wide association studies revealed a total of 107 SNPs in 78 loci. We annotated 101 candidate genes involved in various biological processes, including connective tissue development (THSD4 and COL6A3). Mendelian randomization analyses showed a causal association with aneurysm development, but not with other vascular diseases.

Interpretation

We identified 78 loci that provide insights into mechanisms underlying AAo size and function in the general population and provide genetic evidence for their role in aortic aneurysm development.

Case report: Diagnosis and emergency surgery on a young patient with extensive aortic dissection without any risk factors

Background

Type A aortic dissection is a very dangerous, fatal, and emergency condition for surgery. Acute aortic dissection is a rare condition, such that many patients will not survive without reconstructive surgery.

Case presentation

We present a case 24-year-old male who came with symptoms of shortness of breath and cough. The patient underwent ECG, chest radiology, and ultrasound, where the patient was found to have right pleural effusion while his ECG was normal. In the history taken from the patient, he had no underlying disease, no history of heart diseases in his family. For a better diagnosis, ETT and aortic CT angiography was performed on the patient which confirmed the evidence of dissection. Immediately after the diagnosis, necessary arrangements were made for open heart surgery and the patient was prepared for surgery. The patient was admitted in the cardiac surgery ICU for 5 days and his medication was carefully administered. After the conditions were stabilized, the patient was transferred to the post-cardiac surgery ICU ward. The patient was discharged from the hospital one week after the surgery and returned to the office as an OPD one week after his discharge.

Conclusion

Various risk factors can play a role in creating aortic dissection. Therefore, it is necessary to pay attention to patients’ history for achieving a quick and definitive diagnosis. Therefore, to control the complications of placing the cannula as well as the duration of the surgery, it is very important to reduce the duration of pumping on the patient and to be very careful during the cannula placement.

Bio-chemo-mechanics of the thoracic aorta

The pathophysiology of thoracic aortic aneurysm and dissection is poorly understood, despite high mortality. An evidence review was conducted to examine the biomechanical, chemical and genetic factors involved in thoracic aortic pathology. The composition of connective tissue and smooth muscle cells can mediate important mechanical properties that allow the thoracic aorta to withstand and transmit pressures. Genetic syndromes can affect connective tissue and signalling proteins that interrupt smooth muscle function, leading to tissue failure. There are complex interplaying factors that maintain thoracic aortic function in health and are disrupted in disease, signifying an area for extensive research.

The Role of Thoracic Endovascular Aortic Repair (TEVAR) of Thoracic Aortic Diseases in Patients with Connective Tissue Disorders - A Literature Review

OBJECTIVE

To review the currently available literature to define the role of thoracic endovascular aortic repair (TEVAR) in patients with connective tissue disorders (CTD).

METHODS

A comprehensive electronic database search was performed in PubMed, SCOPUS, Embase, Google scholar, and OVID to identify all the articles that reported on outcomes of utilizing TEVAR in patients with CTD during elective and emergency settings. The search was not limited to time or language of the published study.

RESULTS

All the relevant studies have been summarized in its correspondence section. The outcomes were analyzed in narrative format. The role of TEVAR has been elaborated as per each study. Currently, there is limited large cohort size studies outlining the use of TEVAR in patients with CTD. The use of endovascular repair in patients with CTD is limited due to progressive aortic dilatations and high possibility of further reinterventions at later stage of life.

CONCLUSION

Open repair remains the gold standard method of intervention in young patients with progressive CTD, especially in the setting of acute type A aortic dissection. However, TEVAR can be sought as a reliable alternative in emergency setting of diseases involving the descending thoracic aorta; yet the long-term data needs to be published to support such practice.