Abstract Body: Background: Elastic fibers are crucial for aortic wall integrity and are severely disrupted in aortic dissection (AD). We demonstrated previously that new elastic fibers are generated in the false lumen wall of AD in humans and mice after long-term β-aminopropionitrile (BAPN) administration. The false lumen wall was predominantly populated by cells expressing smooth muscle cell (SMC) markers. However, the mechanisms by which these elastogenic cells emerge and expand after AD remain unclear.

Methods and Results: To explore the molecular basis underlying the expansion of elastogenic cells following AD, we first performed bulk RNA sequencing in normal aortas of control mice and AD samples of mice administered BAPN for 12 weeks. Transcriptomic analyses revealed upregulation of genes implicated in SMC differentiation, along with increased expression of elastic fiber-component genes. Genes associated with TGFβ signaling, including Tgfb1, Tgfbr2, and Smad3, as well as Notch signaling-related genes, such as Notch3, Jag1, and Hey1, were increased in AD samples. In addition, retinoic acid (RA) signaling-related genes, including Aldh1a1, Rara, and Cyp26a1, were upregulated. These data indicated active SMC differentiation accompanied by de novo elastic fiber synthesis in AD. Next, spatial transcriptome was performed to determine the molecular features of elastogenic cells. Although cells composing the false lumen wall were enriched for SMC marker genes, Acta2 and Myh11, their abundance was lower than that observed in resident SMCs. Instead, immature and progenitor cell signatures, such as Cd34 and Thy1, were prominent in the false lumen wall. Consistent with the bulk RNA sequencing, RA signaling-related genes, Aldh1a1 and Rbp1, were highly abundant in cells composed of the false lumen. Interestingly, lineage tracing studies found that elastogenic cells did not originate from the resident SMC lineage, supporting differentiation from a non-SMC lineage after AD. Immunostaining revealed that these cells were positive for stem cell antigen 1, markers for adventitial progenitor cells of the aorta. In vitro experiments demonstrated that adventitial progenitor cells spontaneously initiated expression of SMC markers and Eln mRNA. RA stimulation enhanced SMC marker expression and elastic fiber synthesis in cultured progenitor cells.

Conclusion: RA mediates the differentiation of adventitial progenitor cells into SMC-like cells and de novo elastic fiber synthesis following AD.