Renal cystic disease in the Fbn1C1039G/+ Marfan mouse is associated with enhanced aortic aneurysm formation

Extracellular matrix and vascular dynamics in the kidney of a murine model for Marfan syndrome

Fibrillin-1 is a pivotal structural component of the kidney's glomerulus and peritubular tissue. Mutations in the fibrillin-1 gene result in Marfan syndrome (MFS), an autosomal dominant disease of the connective tissue. Although the kidney is not considered a classically affected organ in MFS, several case reports describe glomerular disease in patients. Therefore, this study aimed to characterize the kidney in the mgΔlpn-mouse model of MFS. Affected animals presented a significant reduction of glomerulus, glomerulus-capillary, and urinary space, and a significant reduction of fibrillin-1 and fibronectin in the glomerulus. Transmission electron microscopy and 3D-ultrastructure analysis revealed decreased amounts of microfibrils which also appeared fragmented in the MFS mice. Increased collagen fibers types I and III, MMP-9, and α-actin were also observed in affected animals, suggesting a tissue-remodeling process in the kidney. Video microscopy analysis showed an increase of microvessel distribution coupled with reduction of blood-flow velocity, while ultrasound flow analysis revealed significantly lower blood flow in the kidney artery and vein of the MFS mice. The structural and hemodynamic changes of the kidney indicate the presence of kidney remodeling and vascular resistance in this MFS model. Both processes are associated with hypertension which is expected to worsen the cardiovascular phenotype in MFS.

Treatment With Methotrexate Associated With Lipid Core Nanoparticles Prevents Aortic Dilation in a Murine Model of Marfan Syndrome

In Marfan syndrome (MFS), dilation, dissection, and rupture of the aorta occur. Inflammation can be involved in the pathogenicity of aortic defects and can thus be a therapeutic target for MFS. Previously, we showed that the formulation of methotrexate (MTX) associated with lipid nanoparticles (LDE) has potent anti-inflammatory effects without toxicity. To investigate whether LDEMTX treatment can prevent the development of aortic lesions in the MFS murine model. MgΔloxPneo MFS (n = 40) and wild-type (WT, n = 60) mice were allocated to 6 groups weekly injected with IP solutions of: (1) only LDE; (2) commercial MTX; (3) LDEMTX (dose = 1mg/kg) between 3rd and 6th months of life. After 12 weeks of treatments, animals were examined by echocardiography and euthanatized for morphometric and molecular studies. MFS mice treated with LDEMTX showed narrower lumens in the aortic arch, as well as in the ascending and descending aorta. LDEMTX reduced fibrosis and the number of dissections in MFS but not the number of elastic fiber disruptions. In MFS mice, LDEMTX treatment lowered protein expression of pro-inflammatory factors macrophages (CD68), T-lymphocytes (CD3), tumor necrosis factor-α (TNF-α), apoptotic factor cleaved-caspase 3, and type 1 collagen and lowered the protein expression of the transforming growth factor-β (TGF-β), extracellular signal-regulated kinases ½ (ERK1/2), and SMAD3. Protein expression of CD68 and CD3 had a positive correlation with an area of aortic lumen (r² = 0.36; p < 0.001), suggesting the importance of inflammation in the causative mechanisms of aortic dilation. Enhanced adenosine availability by LDEMTX was suggested by higher aortic expression of an anti-adenosine A2a receptor (A2a) and lower adenosine deaminase expression. Commercial MTX had negligible effects. LDEMTX prevented the development of MFS-associated aortic defects and can thus be a candidate for testing in clinical studies.

CRISPR/Cas9 in zebrafish: An attractive model for FBN1 genetic defects in humans

Background

Mutations in the fibrillin‐1 gene (FBN1) are associated with various heritable connective tissue disorders (HCTD). The most studied HCTD is Marfan syndrome. Ninety percent of Marfan syndrome is caused by mutations in the FBN1 gene. The zebrafish share high genetic similarity to humans, representing an ideal model for genetic research of human diseases. This study aimed to generate and characterize fbn1^+/− mutant zebrafish using the CRISPR/Cas9 gene‐editing technology.

Methods

CRISPR/Cas9 was applied to generate an fbn1 frameshift mutation (fbn1^+/−) in zebrafish. F1 fbn1^+/− heterozygotes were crossed with transgenic fluorescent zebrafish to obtain F2 fbn1^+/− zebrafish. Morphological abnormalities were assessed in F2 fbn1^+/− zebrafish by comparing with the Tuebingen (TU) wild‐type controls at different development stages.

Results

We successfully generated a transgenic line of fbn1^+/− zebrafish. Compared with TU wild‐type zebrafish, F2 fbn1^+/− zebrafish exhibited noticeably decreased pigmentation, increased lengths, slender body shape, and abnormal cardiac blood flow from atrium to ventricle.

Conclusion

We generated the first fbn1^+/− zebrafish model using CRISPR/Cas9 gene‐editing approach to mimic FBN1 genetic defects in humans, providing an attractive model of Marfan syndrome and a method to determine the pathogenicity of gene mutation sites.

The Role of Inflammation and Myeloperoxidase-Related Oxidative Stress in the Pathogenesis of Genetically Triggered Thoracic Aortic Aneurysms

Genetically triggered thoracic aortic aneurysms (TAAs) are usually considered to exhibit minimal levels of inflammation. However, emerging data demonstrate that specific features of an inflammatory response can be observed in TAA, and that the extent of the inflammatory response can be correlated with the severity, in both mouse models and in human studies. Myeloperoxidase (MPO) is a key mediator of the inflammatory response, via production of specific oxidative species, e.g., the hypohalous acids. Specific tissue modifications, mediated by hypohalous acids, have been documented in multiple cardiovascular pathologies, including atherosclerosis associated with coronary artery disease, abdominal aortic, and cerebral aneurysms. Similarly, data are now emerging that show the capacity of MPO-derived oxidative species to regulate mechanisms important in TAA pathogenesis, including alterations in extracellular matrix homeostasis, activation of matrix metalloproteinases, induction of endothelial dysfunction and vascular smooth muscle cell phenotypic switching, and activation of ERK1/2 signaling. The weight of evidence supports a role for inflammation in exacerbating the severity of TAA progression, expanding our understanding of the pathogenesis of TAA, identifying potential biomarkers for early detection of TAA, monitoring severity and progression, and for defining potential novel therapeutic targets.

Inflammation in thoracic aortic aneurysms

Mutations in extracellular matrix and smooth muscle cell contractile proteins predispose to thoracic aortic aneurysms in Marfan syndrome (MFS) and related disorders. These genetic alterations lead to a compromised extracellular matrix-smooth muscle cell contractile unit. The abnormal aortic tissue responds with defective mechanosensing under hemodynamic stress. Aberrant mechanosensing is associated with transforming growth factor-beta (TGF-β) hyperactivity, enhanced angiotensin-II (Ang-II) signaling, and perturbation of other cellular signaling pathways. The downstream consequences include enhanced proteolytic activity, expression of inflammatory cytokines and chemokines, infiltration of inflammatory cells in the aortic wall, vascular smooth muscle cell apoptosis, and medial degeneration. Mouse models highlight aortic inflammation as a contributing factor in the development of aortic aneurysms. Anti-inflammatory drugs and antioxidants can reduce aortic oxidative stress that prevents aggravation of aortic disease in MFS mice. Targeting TGF-β and Ang-II downstream signaling pathways such as ERK1/2, mTOR, PI3/Akt, P38/MAPK, and Rho kinase signaling attenuates disease pathogenesis. Aortic extracellular matrix degradation and medial degeneration were reduced upon inhibition of inflammatory cytokines and matrix metalloproteinases, but the latter lack specificity. Treating inflammation associated with aortic aneurysms in MFS and related disorders could prove to be beneficial in limiting disease pathogenesis.

MiR-574-5p: A Circulating Marker of Thoracic Aortic Aneurysm

Thoracic aortic aneurysm (TAA) can lead to fatal complications such as aortic dissection. Since aneurysm dimension poorly predicts dissection risk, microRNAs (miRNAs) may be useful to diagnose or risk stratify TAA patients. We aim to identify miRNAs associated with TAA pathogenesis and that are possibly able to improve TAA diagnosis. MiRNA microarray experiments of aortic media tissue samples from 19 TAA patients and 19 controls allowed identifying 232 differentially expressed miRNAs. Using interaction networks between these miRNAs and 690 genes associated with TAA, we identified miR-574-5p as a potential contributor of TAA pathogenesis. Interestingly, miR-574-5p was significantly down-regulated in the TAA tissue compared to the controls, but was up-regulated in serum samples from a separate group of 28 TAA patients compared to 20 controls (p < 0.001). MiR-574-5p serum levels discriminated TAA patients from controls with an area under the receiver operating characteristic curve of 0.87. In the Fbn1^C1041G/+ mouse model, miR-574-5p was down-regulated in aortic tissue compared to wild-type (p < 0.05), and up-regulated in plasma extracellular vesicles from Fbn1^C1041G/+ mice compared to wild-type mice (p < 0.05). Furthermore, in vascular smooth muscle cells, angiotensin II appears to induce miR-574-5p secretion in extracellular vesicles. In conclusion, miR-574-5p is associated with TAA pathogenesis and may help in diagnosing this disease.