Abstract 12885: Pathological Perk/Atf4 Activation in Abdominal Aortic Aneurysm Formation

Abstract

Introduction: Abdominal aortic aneurysms (AAA) are characterized by vascular smooth muscle cell (VSMC) apoptosis leading to pathological aortic remodeling. Activation of the endoplasmic reticulum (ER) stress response has been linked to VSMC dysfunction but the driving factors behind ER stress activation and its role on AAA development remains poorly defined. The epigenetic enzyme, MLL1, plays a critical role in establishing cellular phenotype and regulating gene expression. We examine the MLL-mediated epigenetic regulation of the ER stress response in VSMCs during AAA development and establish the ER stress pathways as a novel target in the treatment AAAs. Methods: Single-cell sequencing was conducted on human AAA and control tissue samples. For our murine model, C57BL/6 mice were injected with an AAV encoding a PCSK9 gain-of-function mutation and then fed a saturated fat-enriched diet and infused with AngII (1 μg/kg/min) with or without 4-PBA (20mg/kg/day). The elastase induced AAA model was used as a secondary murine model. AAA maximum diameters were quantified and VSCMs were isolated. Eif2a, Atf4 , and Chop gene expression was examined. Apoptosis was quantified by Annexin V staining. Results: Using single-cell RNA sequencing of human aortic tissue, we identified EIF2A, ATF4 , and CHOP were profoundly upregulated in aneurysmal VSMCs as well as two murine AAA models. Mechanistically, TNFα signaling in VSMCs leads to activation of MLL1 which trimethylates histone 3 lysine 4 (H3K4me3) at NF-κB binding sites on the EIF2A and ATF4 gene promoters thereby upregulating the ER stress response and driving VSMC apoptosis. In vivo pharmacological inhibition of the eIF2A/ATF4 ER stress response via 4-PBA injection inhibited AAA formation in both the AngII-induced and elastase-induced AAA model resulting with in significant reduction in VSMC apoptosis, elastin fragmentation, and inflammatory cytokine infiltration. Conclusions: Taken together, our results identify MLL1-mediated activation of the eIF2A/ATF4 ER stress response as a critical regulator of VSMC apoptosis in AAA formation and suggest inhibition of ER stress response as a mechanistic target for the management of AAAs.