Abstract 13284: New Elastic Fiber Formation by Non-Smooth Muscle Lineage Cells During the Progression of Aortic Dissections

Abstract

Introduction: Aortic dissection (AD) is a life-threatening vascular disease displaying the disruption of the extracellular matrix (ECM). Elastic fibers are a major component of ECM and confer structural integrity to the aortic wall. Normally, elastic fibers are minimally synthesized in adulthood. However, it remains unknown whether and how elastic fibers are synthesized following ADs. Methods and Results: AD was induced by administration of β-aminopropionitrile (BAPN, 0.5% wt/vol) to male C57BL/6J mice at 4 weeks of age. Thoracic aortas were collected after 4 or 12 weeks of BAPN administration. False lumen formation with fresh hematomas was observed at 4 weeks of BAPN administration, indicating development of acute ADs. The false lumen developed striking remodeling at 12 weeks, suggesting progression to the chronic phase. RT-qPCR revealed that mRNA abundance of tropoelastin, a precursor of elastic fibers, was increased significantly at the chronic phase of ADs, but not at the acute phase. Tropoelastin mRNA was observed primarily in the vascular wall of the false lumen, as evidenced by in situ hybridization. Of interest, elastic fibers were formed in the wall of the false lumen in chronic ADs. These data suggest that elastic fibers were newly synthesized during the progression of ADs. Immunostaining revealed that the walls of true and false lumens of chronic ADs were mainly composed of cells expressing both αSMA (encoding by Acta2 ) and MYH11, common markers for smooth muscle cells (SMCs). However, in a lineage tracing study, the walls of the false lumen of chronic ADs were negative for the Acta2 lineage, suggesting that cells in the wall of the false lumen were derived from a non-SMC lineage but acquired SMC properties during AD progression. Bulk RNA sequencing identified the increased abundance of 2,799 genes in chronic ADs and 102 transcription factors were predicted to regulate these genes. Among them, JunB was the most abundant molecule that can be aligned in the promotor region of tropoelastin. Of note, JunB was expressed adjacent to both αSMA-positive cells and new elastic fibers in the dissected aortas. Conclusion: ADs exhibit vascular remodeling with newly elastic fiber formation by non-SMC lineage cells during the disease progression.