A novel genetic mouse model of fatal aortic dissection reveals massive inflammatory cell infiltration in the thoracic aorta

Background: Aortic dissection (AD) is the separation of medial layers of the aorta and is a major cause of death in patients with connective tissue disorders such as Marfan syndrome. However, molecular triggers instigating AD, its temporospatial progression, and how vascular cells in each vessel layer interact and participate in the pathological process remain incompletely understood. To unravel the underlying molecular mechanism of AD, we generated a spontaneous AD mouse model. Methods: We incorporated a novel missense variant (p.G234D) in FBN1, the gene for fibrillin-1, identified in a non-syndromic familial AD patient into mice using CRISPR/Cas9 system. We performed histopathological analyses of the aortic lesions by histology, immunofluorescence staining, electron microscopy, synchrotron-based imaging and single-cell (sc)RNA-sequencing. Biochemical analysis was performed to examine the binding capacity of mutant human FBN1G234D protein to latent Tgfbeta binding proteins (LTBPs), and signaling pathways in the mutant aortic wall were examined by western blot analysis. Results: 50% of the Fbn1G234D/G234D mutant mice died within 5 weeks of age from multiple intimomedial tears that expanded longitudinally and progressed to aortic rupture accompanied by massive immune cell infiltration. scRNA-sequencing, validated by immunostaining, revealed a significant increase in MHC class II-positive pro-inflammatory macrophages and monocytes at the site of intima tears with upregulation of MMP2/9 and marked disruption of elastic lamina. Subendothelial matrices, such as type IV collagen and laminin, expanded into the medial layer, where fibronectin expression was highly upregulated. Fbn1G234D/G234D endothelial cells exhibited altered mechanosensing with loss of parallel alignment to blood flow and upregulation of VCAM-1 and ICAM-1, all of which likely contributed to the infiltration of immune cells. Biochemically, FBN1G234D lost the ability to bind to latent TGFbeta binding protein (LTBP)-1, -2, and -4, resulting in the downregulation of TGFbeta signaling in the aortic wall. Conclusions: We show that dynamic interactions involving endothelial cells (ECs) and macrophages/monocytes in the intima, where the ECM microenvironment is altered with the reduced TGFbeta signaling, contributes to the initiation of AD. Our novel AD mouse model provides a unique opportunity to identify target molecules involved in the intimomedial tears that can be utilized for development of therapeutic strategies. ### Competing Interest Statement The authors have declared no competing interest.