AKT1-dependent phosphorylation of PRMT5 prevents Siah1a-mediated CtBP1/2 ubiquitination to contribute to abdominal aortic aneurysm progression.

AIMS: Abdominal aortic aneurysm (AAA) is a progressive vascular disease characterized by chronic inflammation and extracellular matrix (ECM) degradation. Although C-terminal binding protein 1 and 2 (CtBP1/2)-mediated transcriptional activation has been implicated in AAA progression, the upstream mechanisms regulating CtBP stability remain unclear. MATERIALS AND METHODS: We combined tandem mass tag (TMT)-based proteomics, biochemical assays, and functional analyses in calcium chloride (CaCl₂)- and elastase-induced AAA mouse models and in TNF-α-stimulated primary aortic endothelial cells. Immunoprecipitation, mass spectrometry, mutagenesis, in vitro kinase and methylation assays, and preventive inhibition experiments were used to define the regulatory pathway controlling CtBP1/2. KEY FINDINGS: Proteomic analyses revealed activation of the phosphatidylinositol 3-kinase catalytic subunit alpha (PI3Kα)-protein kinase B (AKT1) pathway accompanied by upregulation of PRMT5 (protein arginine methyltransferase 5) in AAA tissues. AKT1 directly phosphorylated PRMT5 at Thr634, which enhanced PRMT5-mediated arginine methylation of CtBP1 and CtBP2 at R283 and R289, respectively. This methylation prevented Siah1a (seven in absentia homolog 1a)-dependent ubiquitination and proteasomal degradation of CtBP1/2, thereby stabilizing the CtBP1/2 complex. Stabilized CtBP1/2 promoted the expression of matrix metalloproteinases and proinflammatory cytokines, reinforcing ECM destruction and vascular inflammation. Conversely, PRMT5 deficiency enhanced CtBP1/2 destabilization. In vivo, preventive inhibition of PI3Kα, AKT1, or PRMT5 markedly attenuated inflammatory cytokine production, aneurysmal dilation, and histopathological injury during AAA development. SIGNIFICANCE: These findings identify an AKT1-PRMT5-Siah1a-CtBP1/2 signaling axis that links phosphorylation, arginine methylation, and ubiquitin-mediated degradation during AAA development, suggesting that modulation of this pathway may provide a potential preventive strategy for experimental AAA.