Introduction: Pathogenic transformation of vascular smooth muscle cells (VSMCs) into osteochondrogenic phenotypes is a key feature of advanced atherosclerotic cardiovascular disease and is driven by transcription factors, like SOX9 and RUNX2. Here, we explore the previously uncharacterized role of SMYD2, a histone lysine methyltransferase, in VSMC phenotypic switching during atherosclerotic plaque formation.

Methods: C3H/10T1/2 (10T1/2) cells, wildtype (WT) and Smyd2-depleted (Smyd2KO), were cultured and treated with 5 mmol/L inorganic phosphate (Pi) for 24 or 72 hours, followed by Western blot (WB) analysis. For RUNX2 inhibition, 10T1/2 cells were treated with CADD522 and 5 mmol/L Pi for 8, 24, 48, or 72 hours, with protein expression analyzed by WB. Co-immunoprecipitation (Co-IP) was performed on WT or Smyd2 KO 10T1/2 cells. Immunoprecipitation was conducted using an antibody against RUNX2, followed by immunoblotting with a SUMO-2/3 antibody to assess RUNX2 SUMOylation. For SUMO inhibition, 10T1/2 cells were treated with ginkgolic acid and 5 mmol/L Pi for 24 hours, with protein expression analyzed by WB.

Results: Western blotting revealed lower RUNX2 protein levels in Smyd2KO 10T1/2 cells. Co-IP demonstrated increased SUMOylation of RUNX2 in Smyd2KO cells compared to wild-type cells. RUNX2 inhibition with CADD522 reduced SMYD2, while SUMOylation inhibition with ginkgolic acid had no effect on SMYD2 and RUNX2 expression.

Conclusion: Smyd2 promotes atherosclerotic plaque formation by regulating SUMOylation of essential transcription factors involved in VSMC osteochondrogenic phenotypic switching. Targeting SMC-specific Smyd2 and SUMOylation pathways may offer a novel therapeutic strategy in preventing vascular calcification in atherosclerosis.