DHCR24 Alleviates DNA Damage in Senescent Vascular Endothelial Cells via ENKUR/Ca²⁺ Signaling

DNA damage is considered one of the major contributors to aging. DHCR24, a multifunctional enzyme located within the endoplasmic reticulum (ER), is closely related to DNA damage. Our previous study showed that DHCR24 could delay vascular endothelial cells (ECs) senescence. The relationship between DHCR24 and DNA damage during ECs senescence requires further investigation. Here, we demonstrate that aging activates ATM-mediated DNA damage response (DDR) in human umbilical vein endothelial cells (HUVECs) and mouse pulmonary microvascular endothelial cells (PMVECs), and DHCR24 expression is downregulated. Knocking down DHCR24 in young HUVECs induces the activation of ATM-mediated DDR, which has been confirmed in PMVECs of DHCR24 endothelial-specific knockout mice. Consistently, RNAseq indicated that DHCR24 was essential for cell cycle regulation. Further investigations revealed that both replicatively senescent HUVECs and young HUVECs with DHCR24 knockout exhibited ER stress and mitochondrial dysfunction, which might be attributable to calcium overload resulting from DHCR24 deficiency. In this pathological process, the DHCR24-deficiency-induced upregulation of ENKUR markedly exacerbates calcium overload. Conversely, ENKUR knockdown not only alleviates the ER stress and mitochondrial dysfunction caused by DHCR24 inhibition, but also suppresses the ATM-mediated DDR. Moreover, DHCR24 overexpression reduces the elevated ENKUR levels and simultaneously mitigates DOX-induced calcium overload in HUVECs. Collectively, these findings identify DHCR24-ENKUR-dependent Ca²⁺ signaling as a mechanism linking ER-mitochondrial homeostasis to endothelial DNA damage and senescence. Accordingly, restoring DHCR24 function or regulating calcium signal transduction through this pathway may hold therapeutic potential for delaying vascular ECs senescence and preventing age-related diseases.