The Histone Methyltransferase Setdb2 Modulates Macrophage TIMP-MMP Activity During Abdominal Aortic Aneurysm Development

Introduction: Abdominal aortic aneurysms (AAA) are characterized by aortic wall degradation leading to the fatal consequence of aortic rupture. Aortic remodeling is driven by an inflammatory macrophage (MΦ) phenotype and imbalance of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs). The epigenetic enzyme, SETDB2, plays a critical role in establishing MΦ phenotype and regulating gene expression. We examine the impact of SETDB2 on AAA development and establish SETDB2 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) or saline. AAA maximum diameters were quantified and MΦs were sorted. Setdb and Timp1-3 gene expression was examined. Chromatin immunoprecipitation (ChIP) was used to evaluate histone 3 lysine 9 trimethylation (H3K9me3). Results: Using single-cell RNA sequencing, we identified SETDB2 was profoundly upregulated in human aortic MΦs and two murine AAA models. Mechanistically, interferon-β regulates Setdb2 expression via JAK/STAT signaling which trimethylates histone 3 lysine 9 (H3K9) at NF-κB binding sites on the TIMP1-3 gene promoters thereby suppressing Timp1-3 transcription and leading to unregulated MMP activity. In vivo MΦ-specific knockout of SETDB2 ( Setdb2 f/f Lyz2 Cre+ ) inhibited AAA formation with significant suppression of vascular inflammation, MΦ infiltration, and elastin fragmentation. Gene expression and ChIP analysis demonstrated genetic depletion of SETDB2 prevented AAA development with removal of the repressive H3K9 trimethylation epigenetic mark on the Timp1-3 promoter resulting in increased Timp expression and preserved aortic architecture. Lastly, pharmacological inhibition of the JAK/STAT pathway with a FDA approved inhibitor, Tofacitinib, limited Setdb2 expression and inhibited AAA development. Conclusions: Taken together, our results identify SETDB2 as a critical regulator of MΦ-mediated inflammation and protease production in AAAs and suggest SETDB2 as a mechanistic target for the management of AAAs.