Angiotensinogen as a Therapeutic Target for Cardiovascular and Metabolic Diseases.

AGT (angiotensinogen) is the unique precursor for the generation of all the peptides of the renin-angiotensin system, but it has received relatively scant attention compared to many other renin-angiotensin system components. Focus on AGT has increased recently, particularly with the evolution of drugs to target the synthesis of the protein. AGT is a noninhibitory serpin that has several conserved domains in addition to the angiotensin II sequences at the N terminus. Increased study is needed on the structure-function relationship to resolve many unknowns regarding AGT metabolism. Constitutive whole-body genetic deletion of Agt in mice leads to multiple developmental defects creating a challenge to use these mice for mechanistic studies. This has been overcome by creating Agt-floxed mice to enable the development of cell-specific deficiencies that have provided considerable insight into a range of cardiovascular and associated diseases. This has been augmented by the recent development of pharmacological approaches targeting hepatocytes in humans to promote protracted inhibition of AGT synthesis. Genetic deletion or pharmacological inhibition of Agt has been demonstrated to be beneficial in a spectrum of diseases experimentally, including hypertension, atherosclerosis, aortic and superior mesenteric artery aneurysms, myocardial dysfunction, and hepatic steatosis. This review summarizes the findings of recent studies utilizing AGT manipulation as a therapeutic approach.

Deletion of AT1a (Angiotensin II Type 1a) Receptor or Inhibition of Angiotensinogen Synthesis Attenuates Thoracic Aortopathies in Fibrillin1C1041G/+ Mice.

Objective: A cardinal feature of Marfan syndrome is thoracic aortic aneurysm. The contribution of the renin-angiotensin system via AT1aR (Ang II [angiotensin II] receptor type 1a) to thoracic aortic aneurysm progression remains controversial because the beneficial effects of angiotensin receptor blockers have been ascribed to off-target effects. This study used genetic and pharmacological modes of attenuating angiotensin receptor and ligand, respectively, to determine their roles on thoracic aortic aneurysm in mice with fibrillin-1 haploinsufficiency (Fbn1C1041G/+). Approach and Results: Thoracic aortic aneurysm in Fbn1C1041G/+ mice was found to be strikingly sexual dimorphic. Males displayed aortic dilation over 12 months while aortic dilation in Fbn1C1041G/+ females did not differ significantly from wild-type mice. To determine the role of AT1aR, Fbn1C1041G/+ mice that were either +/+ or -/- for AT1aR were generated. AT1aR deletion reduced expansion of ascending aorta and aortic root diameter from 1 to 12 months of age in males. Medial thickening and elastin fragmentation were attenuated. An antisense oligonucleotide against angiotensinogen was administered to male Fbn1C1041G/+ mice to determine the effects of Ang II depletion. Antisense oligonucleotide against angiotensinogen administration attenuated dilation of the ascending aorta and aortic root and reduced extracellular remodeling. Aortic transcriptome analyses identified potential targets by which inhibition of the renin-angiotensin system reduced aortic dilation in Fbn1C1041G/+ mice. Conclusions: Deletion of AT1aR or inhibition of Ang II production exerted similar effects in attenuating pathologies in the proximal thoracic aorta of male Fbn1C1041G/+ mice. Inhibition of the renin-angiotensin system attenuated dysregulation of genes within the aorta related to pathology of Fbn1C1041G/+ mice.

Spontaneous Rupture of Mesenteric Vasculature Associated with Fibromuscular Dysplasia in a 28-Year-Old Male.

Spontaneous rupture of mesenteric vasculature associated with fibromuscular dysplasia is an unreported phenomenon. We describe a case in a 28-year-old male with a history of chronic abdominal pain who presented to our facility in hemorrhagic shock secondary to a ruptured transverse mesocolon middle colic aneurysm status postemergent transverse colectomy. He was found to have chronic vertebral, renovisceral, and iliac aneurysms as well as acute superior and inferior mesenteric artery dissection and chronic bilateral vertebral artery dissections. He subsequently developed disseminated intravascular coagulopathy, resulting in saddle pulmonary embolus as well as right renal artery and splenic artery thrombosis. Ultimately, the patient expired.

Assessment of gait mechanics and muscle strength in hypermobile Ehlers Danlos Syndrome.

BACKGROUND: Hypermobile Ehlers Danlos Syndrome, a heritable connective tissue disorder, is associated with muscle dysfunction, joint subluxations and pain. The impact of hypermobile Ehlers Danlos Syndrome on musculoskeletal mechanics is understudied. Therefore, the aim of this study was to assess the effects of hypermobile Ehlers Danlos Syndrome on lower extremity gait mechanics and muscle strength. METHODS: Eleven people with hypermobile Ehlers Danlos Syndrome and 11 asymptomatic controls underwent a 3D gait analysis and isometric hip and knee muscle strength assessment. Joint subluxations were self-reported by the hypermobile Ehlers Danlos syndrome group. Independent t-tests and Mann Whitney U tests were used to analyze joint mechanics, muscle strength, and patient report outcomes (p < 0.05). FINDINGS: Both groups exhibited similar walking speeds as well as similar hip, knee, and ankle joint kinematics. The hypermobile Ehlers Danlos Syndrome group walked with a lower peak hip extensor moment (hypermobile Ehlers Danlos Syndrome: -0.52 ± 0.28 Nmˑkg-1, Control: -0.83 ± 0.26 Nmˑkg-1, p = 0.01) yet similar knee and ankle joint moments. The hypermobile Ehlers Danlos Syndrome group exhibited a 40% deficit in peak hip extensor strength (hypermobile Ehlers Danlos Syndrome:1.07 ± 0.53 Nmˑkg-1, Control: 1.77 ± 0.79 Nmˑkg-1, p = 0.04). Approximately 73%, 55% and 45% of the hypermobile Ehlers Danlos Syndrome cohort self-reported hip, knee/patella and ankle joint subluxations, respectively, at least once a week. INTERPRETATION: Patients with hypermobile Ehlers Danlos Syndrome ambulated with altered hip extensor moments and exhibit hip extensor weakness. Future work should investigate the underlying mechanisms of hip extensor weakness and corresponding effects on joint health in people with hypermobile Ehlers Danlos Syndrome.

Novel Insights into the Aortic Mechanical Properties of Mice Modeling Hereditary Aortic Diseases.

OBJECTIVE: Hereditary aortic diseases (hADs) increase the risk of aortic dissections and ruptures. Recently, we have established an objective approach to measure the rupture force of the murine aorta, thereby explaining the outcomes of clinical studies and assessing the added value of approved drugs in vascular Ehlers-Danlos syndrome (vEDS). Here, we applied our approach to six additional mouse hAD models. MATERIAL AND METHODS: We used two mouse models (Fbn1C1041G and Fbn1mgR ) of Marfan syndrome (MFS) as well as one smooth-muscle-cell-specific knockout (SMKO) of Efemp2 and three CRISPR/Cas9-engineered knock-in models (Ltbp1, Mfap4, and Timp1). One of the two MFS models was subjected to 4-week-long losartan treatment. Per mouse, three rings of the thoracic aorta were prepared, mounted on a tissue puller, and uniaxially stretched until rupture. RESULTS: The aortic rupture force of the SMKO and both MFS models was significantly lower compared with wild-type mice but in both MFS models higher than in mice modeling vEDS. In contrast, the Ltbp1, Mfap4, and Timp1 knock-in models presented no impaired aortic integrity. As expected, losartan treatment reduced aneurysm formation but surprisingly had no impact on the aortic rupture force of our MFS mice. CONCLUSION: Our read-out system can characterize the aortic biomechanical integrity of mice modeling not only vEDS but also related hADs, allowing the aortic-rupture-force-focused comparison of mouse models. Furthermore, aneurysm progression alone may not be a sufficient read-out for aortic rupture, as antihypertensive drugs reducing aortic dilatation might not strengthen the weakened aortic wall. Our results may enable identification of improved medical therapies of hADs.

Novel SMAD3 variant identified in a patient with familial aortopathy modeled using a zebrafish embryo assay.

In human, pathogenic variants in smad3 are one cause of familial aortopathy. We describe a novel SMAD3 variant of unknown significance (VUS), V244F, in a patient who presented with aortic root dilation, right coronary artery ectasia, abdominal aortic aneurysm, right vertebral artery atresia, and cavernoma. Determination of variant pathogenicity impacted multiple aspects of the patient's care, including the most appropriate surgical threshold for which to recommend a valve-sparing aortic root replacement. To determine whether the newly identified SMAD3 variant, and whether SMAD3 induced aortopathy in general, can be assayed in a zebrafish embryo model, we injected smad3a mRNA into Tg[kdrl:mCherry] zebrafish embryos. By measuring the size of the dorsal aorta at 48hpf we found a correlation between pathogenic SMAD3 variants and increased dorsal aortic diameter. The newly identified V244F variant increased dorsal aortic diameter (p < 0.0001) similar to that of the pathogenic control variant T261I (p < 0.0084). In addition, we examined several previously identified variants of uncertain significance and found P124T (p < 0.0467), L296P (p < 0.0025) and A349P (p < 0.0056) to behave like T261I. These results demonstrate that the zebrafish embryo assay was successful in validating known pathogenic variants, classifying our newly identified variant V244F as likely pathogenic, and classifying previously identified variants P124T, L296P, and A349P as likely pathogenic. Overall, our findings identify a novel SMAD3 variant that is likely pathogenic as well as offer a new mechanism to model SMAD3 VUSs in vivo.

A Comprehensive Research Schema for the Characterization of Aortic Aneurysms.

A robust, accurate, and standardized approach to measurement of the aorta is critical to improve the predictive accuracy of these aortic measurements, and to investigate other aortic imaging biomarkers. Developing a comprehensive and generic schema for characterization of the aorta to enable investigators to standardize data that are collected across all aorta research. A systematic review of the literature was conducted to identify and assess schemata of aortic measurement and description. The schemata were reported and discussed to guide the synthesis of a comprehensive schema. We propose the International College of Angiology Aortic Research Schema as a comprehensive design that fills the gaps left behind by previously reported schemata. It is intended to be applicable for all clinically relevant purposes, including endograft development for aneurysm repair and for the accurate characterization of the aortic anatomy. This schema divides the aorta into 14 segments and 2 sections (thoracic and abdominal aortas). The segmentation proposed can be used in addition to specific measurements taken for any aneurysm including the neck, and maximal and minimal diameters of the aneurysm.

Sports Participation and Physical Activity in Individuals with Heritable Thoracic Aortic Disease and Aortopathy Conditions.

The evaluation and management of athletes with HTAD and aortopathy conditions requires shared decision-making encompassing the underlying condition, family history, aortic diameter, and type and intensity of sports and exercise. Mouse models of thoracic aortic disease show that low-to-moderate-level aerobic exercise can maintain aortic architecture and attenuate pathologic aortic root dilation. Although controlled trials in human are lacking, recreational physical activities performed at a low-to-moderate aerobic pace are generally low risk for most individuals with aortopathy conditions. High-intensity, competitive, and contact sports or physical activities are generally prohibited in individuals with aortopathy conditions.

Hybrid Repair of Type B Aortic Dissection With Thoracoabdominal Aortic Aneurysmal Degeneration in the Setting of Marfan Syndrome.

Aneurysmal degeneration of the thoracoabdominal aorta after aortic dissection is a well-documented sequela of Marfan syndrome (MFS). Hybrid technique (HT), an emerging treatment modality for complex aortic pathologies, decreases morbidity and mortality relative to open surgery. However, outcome data regarding HT in genetic aortopathies such as MFS is limited. We describe a case of a young male with hypertension and type B aortic dissection (AD) complicated by a symptomatic thoracoabdominal aortic aneurysm (TAAA). He underwent staged HT comprised of carotid-carotid transposition followed by zone 1 thoracic endovascular aortic repair and concurrent retrograde left subclavian stent graft placement. Genetic analysis was consistent with Marfan syndrome. Subsequent growth of his TAAA warranted open extent type IV TAAA repair with individual renovisceral and iliac bypasses. The patient recovered from the second surgery without further progression of disease or late complication.

Aortic Strain Correlates with Elastin Fragmentation in Fibrillin-1 Hypomorphic Mice.

BACKGROUND: High frequency ultrasound has facilitated in vivo measurements of murine ascending aortas, allowing aortic strains to be gleaned from two-dimensional images. Thoracic aortic aneurysms associated with mutations in fibrillin-1 (FBN1) display elastin fragmentation, which may impact aortic strain. In this study, we determined the relationship between elastin fragmentation and aortic circumferential strain in wild type and fibrillin-1 hypomorphic (FBN1 mgR/mgR) mice. METHODS AND RESULTS: Luminal diameters of the ascending aorta from wild type and FBN1 hypomorphic (FBN1 mgR/mgR) mice were measured in systole and diastole. Expansion of the ascending aorta during systole in male and female wild type mice was 0.21±0.02 mm (16.3%) and 0.21±0.01 mm (17.0%) respectively, while expansion in male and female FBN1 mgR/mgR mice was 0.11±0.04 mm (4.9%) and 0.07±0.02 mm (4.5%) respectively. Reduced circumferential strain was observed in FBN1 mgR/mgR mice compared to wild type littermates. Elastin fragmentation was inversely correlated to circumferential strain (R^2 = 0.628 p = 0.004) and significantly correlated with aortic diameter. (R^2 = 0.397, p = 0.038 in systole and R^2 = 0.515, p =0.013 in diastole). CONCLUSIONS: FBN1 mgR/mgR mice had increased aortic diameters, reduced circumferential strain, and increased elastin fragmentation. Elastin fragmentation in FBN1 mgR/mgR and their wild type littermates was correlated with reduced circumferential strain.