CircSMAD3 represses VSMC phenotype switching and neointima formation via promoting hnRNPA1 ubiquitination degradation

Aims Circular RNAs (circRNAs) are novel regulatory RNAs with high evolutionary conservation and stability, making them attractive therapeutic agents for various vascular diseases. SMAD family is a downstream mediator of the canonical TGFβ signalling pathway and has been considered a critical regulator in vascular injury. However, the role of circRNAs derived from the SMAD family members in vascular physiology remains unclear. Therefore, this study aimed to identify a functional circRNA derived from the SMAD family and elucidate its potential as an effective therapeutic agent for vascular proliferative diseases. Methods and Results We initially identified potential functional circRNAs originating from the SMAD family using integrated transcriptome screening. circSMAD3, derived from the SMAD3 gene, was identified to be significantly downregulated in vascular injury and atherosclerosis. Transcriptome analysis was conducted to comprehensively illustrate the pathways modulated by circRNAs. Functionally, circSMAD3 repressed VSMC proliferation and phenotype switching in vitro evidenced by morphological assays and ameliorated arterial injury-induced neointima formation in vivo . Mechanistically, circSMAD3 interacted with heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) within the nucleus, enhanced its interaction with E3 ligase WD repeat domain 76 (WDR76) to promote hnRNPA1 ubiquitination degradation, facilitated p53 pre-RNA splicing, activated p53γ signalling pathway, and finally suppressed VSMC proliferation and phenotype switching. Conclusion Our study identifies circSMAD3 as a novel epigenetic regulator that suppresses VSMC proliferation and phenotype switching, thereby attenuating vascular remodelling and providing a new circRNA-based therapeutic strategy for cardiovascular diseases. ### Competing Interest Statement The authors have declared no competing interest.