Abstract 17364: Lysyl Oxidase Inhibition Induces Acute Aortic Dissection Through Activation of Focal Adhesions and Mammalian Target of Rapamycin Signaling in Mice

Introduction: Defective genes that predispose to acute aortic dissections (AADs) suggest that maintenance of aortic integrity requires mature extracellular matrix (ECM) and intracellular homeostatic contraction of smooth muscle cells (SMCs). Focal adhesions (FAs) link the ECM to SMC contractile units, and we sought to determine the role of SMC FA signaling in a mouse model in which AADs are induced by disrupting ECM with a lysyl oxidase inhibitor, β-aminopropionitrile (BAPN).

Methods: C57BL/6J wild-type mice at postnatal day 21 (P21) were exposed to BAPN to induce AADs. All aortas were visually inspected at necropsy or tissue harvest. Proximal aortas were harvested for single-cell RNA sequencing (scRNAseq) at P35 and for immunoblot analyses at P24 and P35. Echocardiography, tail-cuff blood pressure, and histopathology analyses were performed on surviving mice at P49.

Results: MELD analysis of scRNAseq data identified SMC clusters as the top altered cell type in BAPN-treated aortas. KEGG pathway analysis identified activated FA, along with Rho/ROCK and mTOR signaling, in the BAPN-treated SMC cluster. Immunoblots confirmed increased phosphorylation of FAK, MYPT1, mTOR, p70S6K, and S6RP in BAPN-treated aortas, and FAK inhibition blocked Rho/ROCK and mTOR pathways. Pharmacological inhibition of mTOR with rapamycin significantly rescued BAPN-induced AAD deaths (9% vs. 50%, p=0.001) without altering blood pressure, aortic enlargement, or aortic medial elastic fiber degeneration. Immunoblot analyses confirmed dramatic decrease of mTOR, p70S6K, and S6RP phosphorylation levels in BAPN aortas with rapamycin treatment. Administration of a ROCK inhibitor, Y-27632, significantly augmented type A AAD incidence (p=0.04) without altering blood pressure in BAPN mice, and immunoblot analyses identified increased mTOR signaling as early as P24 in BAPN plus Y-27632-treated aortas compare with BAPN group.

Conclusions: Activation of FA and downstream mTOR signaling triggers AAD when the ECM is disrupted by BAPN, and mTOR inhibition significantly attenuates these deaths. FAs also activate Rho/ROCK, which is protective. These findings support that preventing mTOR signaling or augmenting Rho/ROCK signaling are therapeutic targets to prevent AADs.