Abstract 4363062: BRCC3 inhibition of EndoMT via deubiquitination of Smad7: Implication in Atherosclerosis

Background: Endothelial-to-mesenchymal transition (EndoMT), driven by the TGF-β/Smad2/3 signaling, contributes to endothelial dysfunction and atherosclerosis. BRCC3 is a K63-dependent deubiquitinase know to downregulate Smad pathways, but its role in EndoMT and atherosclerosis remains unclear. Objective: To investigate the mechanism by which BRCC3 mitigates EndoMT via downregulating TGF pathway and its implication in atherosclerosis. Method: Cultured vascular endothelial cells (ECs), co-immunoprecipitation, and immuostaining were used to study EndoMT, BRCC3–Smad7 interactions, and Smad7 deubiquitination sites. In vivo , mice with EC-specific ablation or overexpression of BRCC3 were used to study atherosclerosis. EndoMT and plaque burden were assessed via lineage tracing and immunostaining. Results: BRCC3 was significantly downregulated in human and murine atherosclerotic lesions. In cultured ECs, BRCC3overexpression reduced levels of mesenchymal but increased those of EC markers. Mechanistically, BRCC3 deubiquitinated Smad7 at Lys-343, which stabilized Smad7 and inhibited Smad2 nuclear translocation. Mice with EC-specific ablation of BRCC3 showed exacerbated plaque burden. In C57BL6 mice, liraglutide activation of BRCC3attenuated EndoMT in vivo . Conclusion: Our findings demonstrate that BRCC3 is a key regulator of EndoMT through its deubiquitination and thus stabilization of Smad7, which suppresses TGF-β/Smad2/3 signaling. BRCC3 loss promotes EndoMT and exacerbates atherosclerosis. By contrast, genetic or pharmacological elevation of BRCC3 maintains functional endothelium. These results reveal a novel mechanism highlighting the athero-protective role of BRCC3.