DHCR24 regulates endothelial senescence through the SPHK2/SPNS2-S1P axis.

Vascular endothelial senescence is a pivotal driver of age-related pathologies. Metabolism plays a critical regulatory role in endothelial cell senescence. Our previous studies have shown that deficiency of DHCR24, a gene involved in lipid metabolism, promotes endothelial cell senescence. However, how DHCR24 participates in endothelial cell senescence through lipid metabolism remains unclear. Using endothelial-specific DHCR24 knockout mice and replicative senescent human umbilical vein endothelial cells, we demonstrate that DHCR24 depletion significantly reduced intracellular sphingosine-1-phosphate (S1P) levels. Mechanistically, DHCR24 loss downregulated sphingosine kinase 2 (SPHK2), impairing S1P synthesis, while concurrently upregulating the S1P transporter (SPNS2), enhancing S1P export. Critically, SPHK2 overexpression rescued senescence phenotypes in DHCR24-deficient cells. SPHK2 knockdown recapitulated SPNS2 upregulation and endothelial senescence, whereas pharmacological inhibition of SPNS2 with 16d attenuated SPHK2 knockdown-induced increases in p16, p21 and SA-β-gal activity, and restored eNOS expression and nitric oxide (NO) production. In vivo, endothelial-specific DHCR24 knockout increased circulating S1P levels, and plasma S1P was positively correlated with pulse wave velocity in humans. Collectively, these findings suggest the DHCR24-SPHK2/SPNS2-S1P axis as an important pathway involved in endothelial senescence.