Epigenetic and O-glycosylation regulation of p66Shc mitigates mitochondrial oxidative stress in aortic dissection

<b>Background:</b> Aortic dissection (AD) is a life-threatening vascular emergency with limited effective pharmacological treatments. Recent studies have identified Src homology 2 domain-containing transforming protein C1 (p66Shc) as a crucial mediator of oxidative stress, apoptosis, and inflammation in aortic cells, thereby contributing to cellular dysfunction and vascular remodeling implicated in AD development and progression. Despite its established role in promoting vascular dysfunction and remodeling, the protective potential of targeting p66Shc in AD remains unclear. <b>Methods:</b> We quantified activated protein C (aPC) levels in clinical plasma samples from control subjects and AD patients using enzyme-linked immunosorbent assay (ELISA). To evaluate changes in p66Shc expression, we analyzed aortic tissues by Western blotting (WB), immunohistochemistry (IHC), and immunofluorescence (IF) staining. An <i>in vivo</i> AD model was established in thrombomodulin (TM)-mutant ApoE^-/- mice, which display impaired TM-dependent PC activation, and exogenous PC was administered to evaluate its therapeutic effect. In parallel, mechanistic studies were performed in human endothelial cells using WB, co-immunoprecipitation (Co-IP), dual-label IF staining, chromatin immunoprecipitation (ChIP), luciferase reporter assays, and mitochondrial functional analyses. <b>Results:</b> In this study, we demonstrate that aPC, a coagulation protease with known cytoprotective properties, downregulates <i>p66Shc</i> expression through epigenetic modifications. Additionally, aPC can modulate the expression of a cold shock protein Y-box-binding protein 1 (YB1), which acts as a transcription factor, leading to elevated O-linked N-acetylglucosamine transferase (OGT) levels. This upregulation enhances the O-glycosylation of p66Shc on its 29th tyrosine residue, preventing its mitochondrial translocation, preserving mitochondrial membrane potential, and reducing reactive oxygen species (ROS) production. Consequently, these molecular mechanisms inhibit the onset and progression of AD. <b>Conclusions:</b> aPC epigenetically represses p66Shc transcription and promotes its O-glycosylation at Thr29 <i>via</i> the YB-1/OGT axis, thereby inhibiting mitochondrial ROS production and preventing vascular injury.