Epigenetic Regulation of Trained Immunity in Thoracic Aortic Aneurysms and Dissections

Baylor College Of Medicine, Houston TX

Investigators

Abstract

Profound accumulation of macrophages (MΦs) and persistent inflammation are prominent features in as- cending thoracic aortic aneurysms and dissections (ATAAD), and the underlying mechanisms are poorly under- stood. Recent studies suggest that innate immune cells, including monocytes/MΦs, can differentiate into a pro- inflammatory phenotype and conserve this memory after exposure to stimuli, a process known as trained im- munity, thereby enhancing the subsequent inflammatory response. In our preliminary studies, scRNA-seq analysis revealed several MΦ subpopulations. Importantly, aortic MΦs in sporadic ATAAD patients and in an- giotensin (Ang II)-induced ATAAD mice exhibited pro-inflammatory status with enhanced differentiation to pro- inflammatory MΦs and suppressed differentiation to phagocytic/anti-inflammatory MΦs. Intriguingly, this pro- inflammatory status can be observed in monocytes/MΦs isolated from bone marrow of mice, and the memory can stably last for 5 days in ex vivo culture. Furthermore, scATAC-seq suggested that the training of the mono- cytes/MΦs occurred at the epigenetic level, and several TFs, including IRF3 and surprisingly IRF4 (known as an anti-inflammatory lineage-determining TF), may drive the induction of pro-inflammatory differentiation. In cul- tured cells, DNA from damaged aortic cells induced monocytes/MΦs toward a pro-inflammatory phenotype through cGAMP-STING-IRF3/IRF4 signaling. Finally, Sting-deficient mice showed preservation of phago- cytic/anti-inflammatory MΦs and reduction of pro-inflammatory MΦs. The objective of this project is to under- stand the training of monocytes/MΦs to different functional phenotypes in the aortic wall, and to identify key pathways driving monocytes/MΦs to a pro-inflammatory direction in ATAAD. In Aim 1, we will determine the sites of the immunity training, the epigenetic signatures of the trained monocytes/MΦs, and the duration of the memory in ATAAD by performing integrated omics analyses (scRNA-seq, scATAC-seq, and spatial RNA-seq) of monocytes/MΦs in bone marrow and the aortic wall in mice and will confirm the epigenetic signatures of the trained monocytes/MΦs in circulation and the aortic wall in ATAAD patients. In Aim 2, we will determine the causal role of the STING-IRF3/IRF4 circuitry in training monocytes/MΦs during ATAAD development by per- forming omics and functional analyses of aortic tissues and bone marrow monocytes from MΦ-Sting-/-, MΦ-Irf3- /-, MΦ-Irf4-/-, and WT mice, and dissect the link between dsDNA/cGAMP-STING-IRF3/IRF4, chromatin remodel- ing, gene expression, and MΦ phenotypes in cultured monocytes/MΦs. In Aim 3, we will determine the role of MΦ-specific STING-IRF3/IRF4 in ATAAD development in mice. The impact of this work will be an improved understanding of the molecular mechanisms that cause persistent aortic inflammation and degeneration, provid- ing a new direction for treatment strategies for preventing ATAAD and its fatal sequelae. Elucidating the immunity training of monocytes/MΦs is likely to have broad implications for many other cardiovascular diseases in which persistent inflammation plays a critical role in tissue destruction and disease progression.