Pathophysiology of aortic aneurysm: insights from human genetics and mouse models

Coding and Non-Coding Transcriptomic Landscape of Aortic Complications in Marfan Syndrome

Marfan syndrome (MFS) is a rare congenital disorder of the connective tissue, leading to thoracic aortic aneurysms (TAA) and dissection, among other complications. Currently, the most efficient strategy to prevent life-threatening dissection is preventive surgery. Periodic imaging applying complex techniques is required to monitor TAA progression and to guide the timing of surgical intervention. Thus, there is an acute demand for non-invasive biomarkers for diagnosis and prognosis, as well as for innovative therapeutic targets of MFS. Unraveling the intricate pathomolecular mechanisms underlying the syndrome is vital to address these needs. High-throughput platforms are particularly well-suited for this purpose, as they enable the integration of different datasets, such as transcriptomic and epigenetic profiles. In this narrative review, we summarize relevant studies investigating changes in both the coding and non-coding transcriptome and epigenome in MFS-induced TAA. The collective findings highlight the implicated pathways, such as TGF-β signaling, extracellular matrix structure, inflammation, and mitochondrial dysfunction. Potential candidates as biomarkers, such as miR-200c, as well as therapeutic targets emerged, like Tfam, associated with mitochondrial respiration, or miR-632, stimulating endothelial-to-mesenchymal transition. While these discoveries are promising, rigorous and extensive validation in large patient cohorts is indispensable to confirm their clinical relevance and therapeutic potential.

Innovation in pathogenesis and management of aortic aneurysm

Aortic aneurysm (AA) refers to the persistent dilatation of the aorta, exceeding three centimeters. Investigating the pathophysiology of this condition is important for its prevention and management, given its responsibility for more than 25000 deaths in the United States. AAs are classified based on their location or morphology. various pathophysiologic pathways including inflammation, the immune system and atherosclerosis have been implicated in its development. Inflammatory markers such as transforming growth factor β, interleukin-1β, tumor necrosis factor-α, matrix metalloproteinase-2 and many more may contribute to this phenomenon. Several genetic disorders such as Marfan syndrome, Ehler-Danlos syndrome and Loeys-Dietz syndrome have also been associated with this disease. Recent years has seen the investigation of novel management of AA, exploring the implication of different immune suppressors, the role of radiation in shrinkage and prevention, as well as minimally invasive and newly hypothesized surgical methods. In this narrative review, we aim to present the new contributing factors involved in pathophysiology of AA. We also highlighted the novel management methods that have demonstrated promising benefits in clinical outcomes of the AA.

Angiotensin AT2 receptors reduce inflammation and fibrosis in cardiovascular remodeling

The angiotensin AT2 receptor (AT2R), an important member of the "protective arm" of the renin-angiotensin system (RAS), has been recently defined as a therapeutic target in different pathological conditions. The AT2R activates complex signalling pathways linked to cellular proliferation, differentiation, anti-inflammation, antifibrosis, and induction or inhibition of apoptosis. The anti-inflammatory effect of AT2R activation is commonly associated with reduced fibrosis in different models. Current discoveries demonstrated a direct impact of AT2Rs on the regulation of cytokines, transforming growth factor beta1 (TGF-beta1), matrix metalloproteases (MMPs), and synthesis of the extracellular matrix components. This review article summarizes current knowledge on the AT2R in regard to immunity, inflammation and fibrosis in the heart and blood vessels. In particular, the differential influence of the AT2R on cardiovascular remodeling in preclinical models of myocardial infarction, heart failure and aneurysm formation are discussed. Overall, these studies demonstrate that AT2R stimulation represents a promising therapeutic approach to counteract myocardial and aortic damage in cardiovascular diseases.

Platelet TGF-β1 inhibits the migration and proliferation of smooth muscle cells in aneurysms

BACKGROUND

The study explored the role of platelet TGF-β1 from the perspective of inhibiting the excessive proliferation, migration and invasion of murine aortic vascular smooth muscle cells (MASMCs).

METHOD

The platelets were first extracted from C57BL/6 mice, and the TGF-β1 protein was obtained after the purification of protein. In vitro, the concentrations of angiotensin Ⅱ (Ang Ⅱ) and TGF-β1 for intervention were screened by testing the viability of MASMCs, followed by the analysis concerning the effects of platelets, Ang Ⅱ and TGF-β1 on the proliferation, migration, invasion, and the expressions of pathway-related proteins in MASMCs. In vivo, an Ang Ⅱ-induced mouse model was established. TGF-β1 was injected into the tail of mice as a therapeutic agent, and its action mechanism was further verified by the treatment of inhibitor SB505124. The results of the cell experiment were validated by evaluating the maximum diameter of abdominal aorta, the proportion of total weight, the changes of both pathology and the expressions of pathway-related proteins in the mice.

RESULT

0.5 ng/mL Ang Ⅱ and 15 ng/mL TGF-β1 were chosen for treatment. The following results of cell functional experiments and Western blot assay demonstrated that Ang Ⅱ promoted the proliferation, migration and invasion of MASMCs via regulating related pathways, the effects of which were evidently reversed by TGF-β1 and platelets. Consistent results were also observed in the animal experiments, where TGF-β1 effectively alleviated Ang Ⅱ-induced abdominal aortic injury in mice.

CONCLUSION

TGF-β1 in platelets inhibits Ang Ⅱ-induced proliferation, migration and invasion of MASMCs.

The Histopathological Correlate of Peri-Vascular Adipose Tissue Attenuation on Computed Tomography in Surgical Ascending Aorta Aneurysms: Is This a Measure of Tissue Inflammation?

On computed tomography (CT) imaging, a peri-vascular adipose tissue attenuation (pVAT) measure has been proposed as a non-invasive correlate of inflammation in the coronary artery vessels, and a single research group provided histopathological demonstration of this radiological/pathological correspondence. Our group has shown that patients with surgical-grade ascending aorta (AA) aneurysm display higher pVAT compared with patients with smaller aneurysms or normal AA. Based on histopathological studies on coronary arteries, we speculated that this correlation may be related to a non-otherwise specified aortic inflammatory process. However, since adipose tissue around the AA is often scant, and there are no histopathological studies confirming such hypothesized association between higher pVAT and inflammation around the AA, we cannot exclude that this pVAT change is secondary to different mechanisms, unrelated to the actual presence of peri-vascular inflammation. We performed a retrospective clinical/radiological/pathological study in 78 patients who underwent AA surgery with the aim to correlate pre-operatory pVAT on CT with histopathological findings from the surgical specimens. Histopathological review and immunohistochemistry were performed on the surgical aortic samples. The AA adventitial/periadventitial adipose tissue had higher pVAT by an increasing collagen fiber deposition, which progressively makes the fat hypotrophic and, in the late stages of this process, it replaces the normal soft tissue composition in this location. In the ascending aorta, pVAT on CT imaging is probably not a proxy for the presence of current vascular inflammation, although it may track changes involving the progressive substitution of perivascular adipose cells by higher-pVAT tissues, mainly fibrotic replacement.

A novel intramural TGF β 1 hydrogel delivery method to decrease murine abdominal aortic aneurysm and rat aortic pseudoaneurysm formation and progression

OBJECTIVES

Aneurysms are generally the result of dilation of all 3 layers of the vessel wall, and pseudoaneurysms are the result of localized extravasation of blood that is contained by surrounding tissue. Since there is still no recommended protocol to decrease aneurysm formation and progression, we hypothesised that intramural delivery of TGF β1 hydrogel can decrease aneurysm and pseudoaneurysm formation and progression.

MATERIALS

Male C57BL/6 J mice (12-14 wk), SD rats (200 g) and pig abdominal aortas were used, and hydrogels were fabricated by the interaction of sodium alginate (SA), hyaluronic acid (HA) and CaCO3.

METHODS

A CaCl2 adventitial incubation model in mice and a decellularized human great saphenous vein patch angioplasty model in rats were used. TGF β1 hydrogel was intramurally delivered after CaCl2 incubation in mice; at day 7, the abdomen in some mice was reopened, and TGF β1 hydrogel was injected intramurally into the aorta. In rats, TGF β1 hydrogel was delivered intramurally after patch angioplasty completion. Tissues were harvested at day 14 and analysed by histology and immunohistochemistry staining. The pig aorta was also intramurally injected with hydrogel.

RESULTS

In mice, rhodamine hydrogel was still found between the medium and adventitia at day 14. In the mouse aneurysm model, there was a thicker wall and smaller amount of elastin breaks in the TGF β1 hydrogel-delivered groups both at day 0 and day 7 after CaCl2 incubation, and there were larger numbers of p-smad2- and TAK1-positive cells in the TGF β1 hydrogel-injected groups. In the rat decellularized human saphenous vein patch pseudoaneurysm model, there was a higher incidence of pseudoaneurysm formation when the patch was decellularized using 3% SDS, and delivery of TGF β1 hydrogel could effectively decrease the formation of pseudoaneurysm formation and increase p-smad2 and TAK1 expression. In pig aortas, hydrogels can be delivered between the medium and adventitia easily and successfully.

CONCLUSIONS

Intramural delivery of TGF β1 hydrogel can effectively decease aneurysm and pseudoaneurysm formation and progression in both mice and rats, and pig aortas can also be successfully intramurally injected with hydrogel. This technique may be a promising drug delivery method and therapeutic choice to decrease aneurysm and pseudoaneurysm formation and progression in the clinic.

Targetable cellular signaling events mediate vascular pathology in vascular Ehlers-Danlos syndrome

Vascular Ehlers-Danlos syndrome (vEDS) is an autosomal-dominant connective tissue disorder caused by heterozygous mutations in the COL3A1 gene, which encodes the pro-α 1 chain of collagen III. Loss of structural integrity of the extracellular matrix is believed to drive the signs and symptoms of this condition, including spontaneous arterial dissection and/or rupture, the major cause of mortality. We created 2 mouse models of vEDS that carry heterozygous mutations in Col3a1 that encode glycine substitutions analogous to those found in patients, and we showed that signaling abnormalities in the PLC/IP3/PKC/ERK pathway (phospholipase C/inositol 1,4,5-triphosphate/protein kinase C/extracellular signal-regulated kinase) are major mediators of vascular pathology. Treatment with pharmacologic inhibitors of ERK1/2 or PKCβ prevented death due to spontaneous aortic rupture. Additionally, we found that pregnancy- and puberty-associated accentuation of vascular risk, also seen in vEDS patients, was rescued by attenuation of oxytocin and androgen signaling, respectively. Taken together, our results provide evidence that targetable signaling abnormalities contribute to the pathogenesis of vEDS, highlighting unanticipated therapeutic opportunities.

Diabetes and aortic aneurysm: current state of the art

Aortic aneurysm is a life-threatening disease due to the risk of aortic rupture. The only curative treatment available relies on surgical approaches; drug-based therapies are lacking, highlighting an unmet need for clinical practice. Abdominal aortic aneurysm (AAA) is frequently associated with atherosclerosis and cardiovascular risk factors including male sex, age, smoking, hypertension, and dyslipidaemia. Thoracic aortic aneurysm (TAA) is more often linked to genetic disorders of the extracellular matrix and the contractile apparatus but also share similar cardiovascular risk factors. Intriguingly, a large body of evidence points to an inverse association between diabetes and both AAA and TAA. A better understanding of the mechanisms underlying the negative association between diabetes and aortic aneurysm could help the development of innovative diagnostic and therapeutic approaches to tackle the disease. Here, we summarize current knowledge on the relationship between glycaemic parameters, diabetes, and the development of aortic aneurysm. Cellular and molecular pathways that underlie the protective effect of diabetes itself and its treatment are reviewed and discussed, along with their potential implications for clinical translation.

Intracranial vascular pathology in two further patients with Floating-Harbor syndrome: Proposals for cerebrovascular disease risk management

Floating-Harbor syndrome (FHS) is a rare, heritable disorder caused by variants in the SRCAP gene. Most individuals with FHS have characteristic facial features, short stature, and speech and language impairment. Although FHS has been likely under-diagnosed due to a combination of lack of recognition of the clinical phenotype and limited access to genomic testing, it is a rare condition with around 100 individuals reported in the medical literature. Case series have been biased towards younger individuals (vast majority <20 years of age) meaning that it has been challenging to provide accurate medical advice for affected individuals in adulthood. We report two young adults with FHS who presented with intracranial haemorrhage likely secondary to cerebrovascular aneurysms, with devastating consequences, making a total of four FHS patients reported with significant cerebrovascular abnormalities. Three of four patients had hypertension, at least one in conjunction with normal renal structure. We consider possible relationships between hypertension, renal pathology and aneurysms in the context of FHS, and consider mechanisms through which disruption of the SRCAP protein may lead to vascular pathology. We recommend that clinicians should have a low threshold to investigate symptoms suggestive of cerebrovascular disease in FHS. We advise that patients with FHS should have annual blood pressure monitoring from adolescence, renal ultrasound at diagnosis repeated in adulthood, and timely investigation of any neurological symptoms. For patients with FHS, particularly with hypertension, we advise that clinicians should consider at least one MRA (Magnetic Resonance Imaging with Angiography) to check for cerebral aneurysms.

Ultrasound Imaging of the Thoracic and Abdominal Aorta in Mice to Determine Aneurysm Dimensions

Contemporary high-resolution ultrasound instruments have sufficient resolution to facilitate the measurement of mouse aortas. These instruments have been widely used to measure aortic dimensions in mouse models of aortic aneurysms. Aortic aneurysms are defined as permanent dilations of the aorta, which occur most frequently in the ascending and abdominal regions. Sequential measurements of aortic dimensions by ultrasound are the principal approach for assessing the development and progression of aortic aneurysms in vivo. Although many reported studies used ultrasound imaging to measure aortic diameters as a primary endpoint, there are confounding factors, such as probe position and cardiac cycle, that may impact the accuracy of data acquisition, analysis, and interpretation. The purpose of this protocol is to provide a practical guide on the use of ultrasound to measure the aortic diameter in a reliable and reproducible manner. This protocol introduces the preparation of mice and instruments, the acquisition of appropriate ultrasound images, and data analysis.