Abstract 301: Inhibition Of Tlr-7 Signaling Attenuates TAAD Formation

The critical role for chronic inflammation in the development of thoracic aortic aneurysms and dissections (TAADs) has been recognized in both experimental and clinical settings. However, challenges remain on translating this knowledge to clinical applications. In this study, we tested the hypothesis that TLR-7 signaling triggered by self-RNAs substantiates chronic inflammation, promoting TAAD formation. A mouse TAAD model induced by SMC-specific deletion of Tgfbr1 ( Tgfbr1 iko ) was used. In this model, the expression of TLR-7 was progressively upregulated during the early stages, resulting in a two-fold differential at two weeks compared to control aortas ( P =0.003). RNAScope assays showed that cells located in the media and adventitia were responsible for the upregulation. Additionally, immunofluorescence (IF) staining showed that TLR-7 is induced in human TAADs. Treatment with hydroxychloroquine, which inhibits TLR-7 receptor function, significantly reduced the number of intimal/medial tears ( P =0.026) and mitigated intramural hemorrhage ( P =0.007) compared with vehicle controls (n=7/group). Further assays with bone marrow derived dendritic cells demonstrated that RNAs, particularly small RNAs, extracted from TAADs induced significantly higher IFNα/β levels compared with normal aortas ( P =0.025). Similarly, RNAs extracted from Tgfbr1 iko SMCs induced higher levels of IFNα, IP-10, and MCP1 compared with those harvested from wild type SMCs. Necroptosis (labeled with RIPK3 and pMLKL) and RNA-oxidation (labeled with 8-OHG) were evident in the media of TAADs, and might serve as the source for the endogenous TLR-7 ligand. Finally, treatment with the TLR-7 specific inhibitor, M5049, at a dose of 1.0 or 5.0 mg/kg/day via oral gavage prevented dilation of TAADs at four weeks compared with vehicle controls (9% vs. 8% vs. 23%, P<0.001). In conclusion, self-RNAs released from stressed and dying cells is associated with chronically inflamed aortic tissue and promotes TAAD development via triggering TLR-7 signaling. Blocking TLR-7 signaling may represent a novel strategy to treat human TAADs.