The connection between DNA damage and aging is one of the most intensively studied themes in modern biology, and the new findings place endothelial cells squarely within that framework. As blood vessels age, oxidative stress, chronic inflammation, metabolic imbalance and epigenetic disruption converge to impair endothelial function. DNA damage is increasingly recognized as a key driver of this decline. When DNA strands break or bases are oxidized, the cell mounts a DNA damage response, or DDR, characterized by the recruitment of the kinase ATM to sites of injury and the phosphorylation of histone H2AX at serine 139, producing the well-known γH2AX marker. γH2AX in turn promotes activation of the transducer kinases Chk1 and Chk2, which converge on the p53/p21 axis to arrest the cell cycle and push the cell into senescence, a state of permanent growth arrest that secretes inflammatory signals harmful to surrounding tissue.

To explore how this process unfolds in blood vessels, the researchers used several complementary senescence models. They studied human umbilical vein endothelial cells at early passage, around passage 5, and compared them with late-passage, replicatively senescent cells at passage 13, in which proliferation has nearly ceased. They also isolated pulmonary microvascular endothelial cells from young, 3-month-old mice and naturally aged, 14-month-old mice. Western blotting for γH2AX, immunofluorescent staining for 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage, and analysis of aortic tissue all confirmed that DNA damage accumulates robustly with endothelial aging. Critically, ATM was activated in parallel, and DHCR24 expression fell consistently as the DNA damage response intensified, suggesting that the loss of this enzyme might be permissive for vascular aging.

To forge a direct causal link, the team turned to doxorubicin, a chemotherapy drug well known for inducing DNA damage and cardiac toxicity. Treating endothelial cells with a low dose of 0.05 micromolar doxorubicin for 48 hours, followed by three days of recovery, produced a reproducible model of premature senescence: SIRT1 declined, p16 rose, senescence-associated beta-galactosidase staining increased, proliferation fell, and ATM-mediated DNA damage signaling was engaged. In this model, DHCR24 was again downregulated. Conversely, when the researchers silenced DHCR24 with siRNA in young cells, γH2AX and phosphorylated ATM rose markedly, and the effect was mirrored in pulmonary endothelial cells taken from mice engineered to lack DHCR24 specifically in the vascular endothelium, generated by crossing mice carrying a floxed DHCR24 allele with Tie2-Cre mice. En face staining of aortas from these knockout animals showed strikingly elevated γH2AX along the vessel wall.

Restoring DHCR24, by contrast, proved protective. The team delivered the enzyme into senescent and doxorubicin-treated cells using a lentiviral vector, and the results were unambiguous: overexpression of DHCR24 reduced γH2AX and ATM phosphorylation, lowered phosphorylated p53, decreased senescence-associated beta-galactosidase positivity, restored proliferative capacity measured by EdU incorporation, and reduced the excessive intracellular reactive oxygen species generated by doxorubicin exposure. Flow cytometry revealed that doxorubicin pushed cells into a G2-phase arrest, accompanied by declines in CDK1, Cyclin A2 and Cyclin B1, the kinase and cyclin partners that govern the G2/M transition. DHCR24 overexpression reversed these changes, restoring cell cycle progression. RNA sequencing and KEGG pathway analysis independently reinforced the conclusion that DHCR24’s biological functions cluster around cell cycle regulation.

The question then became mechanistic: how does a cholesterol-biosynthesis enzyme in the endoplasmic reticulum protect the genome? The researchers suspected calcium might be the link. Calcium is a universal intracellular second messenger, and the endoplasmic reticulum is the cell’s principal calcium reservoir. When ER calcium is depleted, store-operated calcium entry, or SOCE, allows extracellular calcium to flood in and replenish stores, but excessive ER calcium accumulation triggers ER stress, activates the unfolded protein response sensor IRE1, and drives reactive oxygen species overproduction. Calcium released from the ER at mitochondria-associated membranes passes through the voltage-dependent anion channel VDAC and the mitochondrial calcium uniporter MCU into the mitochondrial matrix, where overload disrupts the electron transport chain, depolarizes the mitochondrial membrane potential and further amplifies ROS generation. This ROS, in turn, attacks DNA.

The experimental data fit this framework precisely. In replicatively senescent cells, in doxorubicin-treated cells, and in cells with DHCR24 knocked down, the team measured elevated total cellular calcium using the Fluo4-AM fluorescent probe, elevated ER-releasable calcium revealed by thapsigargin challenge, activated store-operated calcium entry, increased IRE1 phosphorylation, and upregulated VDAC and MCU alongside reduced OPA1, a marker of mitochondrial dynamics. Transmission electron microscopy showed the structural consequences directly: in DHCR24-deficient cells and in the aortas of endothelial-specific knockout mice, mitochondria were shrunken, swollen and had ruptured cristae, while the ER showed vesicle dilatation and degeneration. JC-1 staining confirmed loss of mitochondrial membrane potential, and MitoSOX Red fluorescence documented surging mitochondrial ROS. ATP content, measured by luminescent assay and normalized to protein, fell in parallel.

The most novel discovery emerged from the transcriptome. RNA sequencing of DHCR24-silenced cells identified 384 upregulated genes, among which ENKUR, located on chromosome 10p12.1, stood out. ENKUR encodes enkurin, a protein discovered through yeast two-hybrid screening as an interactor of TRPC calcium channels, where it serves as an adaptor that localizes calcium-signaling machinery to channels and mediates calcium influx. Prior studies had implicated ENKUR in tumor suppression and in calcium homeostasis disorders of myeloproliferative neoplasms, but its role in senescence had not been defined. When the researchers performed double knockdowns of DHCR24 and ENKUR, the calcium overload, IRE1 activation, VDAC and MCU upregulation, γH2AX elevation and ATM phosphorylation caused by DHCR24 loss were all substantially reversed. Knocking down ENKUR alone also alleviated calcium overload in senescent cells.

Notably, the regulation appeared to operate at the level of messenger RNA stability. Using actinomycin D chase assays to block new transcription, the team found that ENKUR mRNA degraded far more slowly in DHCR24-deficient cells than in controls, meaning DHCR24 normally promotes the degradation of ENKUR transcripts. When DHCR24 is lost, ENKUR mRNA persists, enkurin protein accumulates, calcium channels remain engaged, ER calcium overloads, and the cascade of ER stress, mitochondrial dysfunction, ROS production and DNA damage follows. Restoring DHCR24 in doxorubicin-treated cells lowered ENKUR expression and broke this chain. The authors therefore propose a DHCR24–ENKUR–Ca2+ axis as the mechanistic link between ER–mitochondrial stress and endothelial senescence.

The findings carry several caveats that the authors themselves acknowledge. The mechanistic experiments were confined to endothelial models—HUVECs, pulmonary microvascular endothelial cells and endothelial-specific knockout mice—so it remains unknown whether the DHCR24–ENKUR pathway operates in other senescing cell types such as fibroblasts. The team also notes that the effects of DHCR24 overexpression on ER and mitochondrial function in doxorubicin-treated cells were not directly validated with ultrastructural imaging. Nevertheless, the study significantly expands the known portfolio of DHCR24, which earlier work from the same group had shown to delay endothelial senescence by inhibiting ROS generation through the Caveolin-1/ERK signaling axis and by relieving ER stress. With the new findings, DHCR24 emerges as a central node coordinating cholesterol metabolism, calcium homeostasis, mitochondrial health and genomic stability in the aging vasculature.

For the broader field of vascular aging research, the work offers a compelling conceptual advance: calcium signaling, long recognized as a marker of cellular aging, is positioned here as an actionable upstream regulator of the DNA damage response in endothelial cells. Because age-related endothelial dysfunction underlies hypertension, atherosclerosis and heart failure, interventions that stabilize the DHCR24–ENKUR–Ca2+ axis—whether by promoting ENKUR mRNA degradation, buffering ER calcium stores or shielding mitochondria from calcium-driven ROS—could in principle slow the vascular component of aging. Translating that insight into therapies will require much additional work, but the identification of a single, druggable signaling axis connecting organelle stress to genome protection in blood vessels gives researchers a concrete molecular target in the fight against cardiovascular aging.

Endothelial cells are far more than a passive lining. They regulate vascular tone, control the traffic of immune cells and molecules between blood and tissue, and maintain the anti-inflammatory, anti-clotting properties of the vessel wall. When these cells enter senescence, a state of irreversible growth arrest accompanied by dysfunction and the secretion of inflammatory factors, arteries stiffen, blood pressure rises, and the risk of heart attack, stroke and other age-related cardiovascular conditions climbs sharply. Understanding what pushes endothelial cells into senescence has therefore become a central goal of geroscience, the field that seeks to target aging itself as a treatable process.

The research team, led by Wukaiyang Liang and Jinhua Yan of Tongji Hospital at Huazhong University of Science and Technology in Wuhan, working with senior authors Zhen Yang and Cuntai Zhang, focused on DHCR24, an enzyme that catalyzes the final step of cholesterol biosynthesis by converting the sterol intermediate desmosterol into cholesterol. Earlier work from the same laboratory had shown that insufficient DHCR24 promotes endothelial senescence and vascular dysfunction by suppressing caveolin-1/ERK signaling. What remained unclear was how a gene best known for lipid metabolism communicates with the cellular machinery of aging. The new study supplies the missing link: the SPHK2/SPNS2-S1P axis.

To dissect this connection, the researchers used two complementary experimental systems. The first was a mouse model in which DHCR24 was deleted specifically in endothelial cells, allowing the team to examine the consequences of losing the gene in the vasculature without confounding effects elsewhere in the body. The second was a culture system of human umbilical vein endothelial cells driven into replicative senescence, the form of cellular aging that accumulates as cells divide repeatedly over time. Across both systems, a consistent pattern emerged: when DHCR24 was depleted, intracellular levels of sphingosine-1-phosphate fell significantly.

S1P is not an obscure molecule. It is one of the most studied bioactive sphingolipids, orchestrating processes ranging from immune cell trafficking to vascular barrier integrity and endothelial cell survival. Its intracellular concentration reflects a tug-of-war between synthesis and export, and it is precisely at these two points that DHCR24 exerts its influence. The team found that loss of DHCR24 downregulated sphingosine kinase 2, or SPHK2, the enzyme responsible for phosphorylating sphingosine to generate S1P. At the same time, DHCR24 loss upregulated SPNS2, a transporter that pumps S1P out of the cell. The combined effect was a double blow: less S1P was being made, and what little remained was being exported faster, draining the intracellular pool of this survival-promoting lipid.

The mechanistic architecture of this axis became clear through a series of gain- and loss-of-function experiments. When the researchers overexpressed SPHK2 in DHCR24-deficient endothelial cells, the senescence phenotypes were rescued, demonstrating that restoring S1P synthesis alone is sufficient to counteract the aging program triggered by DHCR24 loss. Conversely, knocking down SPHK2 in otherwise healthy cells reproduced the damage, inducing senescence markers and, notably, driving up SPNS2 expression, mirroring what happens when DHCR24 is absent. This showed that SPHK2 sits upstream of SPNS2 in the pathway and that reduced S1P production itself promotes the transporter upregulation that further depletes the cell.

Perhaps most striking from a therapeutic standpoint, the team showed that pharmacological inhibition of SPNS2 with a compound known as 16d could block the senescence cascade even when SPHK2 was knocked down. Treatment with 16d attenuated the increases in p16 and p21, two canonical senescence-driving cell cycle inhibitors, and reduced senescence-associated beta-galactosidase activity, a classic histochemical marker of senescent cells. Crucially, the drug also restored expression of endothelial nitric oxide synthase, or eNOS, and returned nitric oxide production to healthier levels. Nitric oxide is the master relaxing factor of blood vessels; its loss is a hallmark of endothelial dysfunction and a key contributor to hypertension and atherosclerosis. The finding that blocking a lipid transporter can revive NO output in senescing cells suggests a concrete pharmaceutical entry point into the aging vasculature.

The animal experiments added an in vivo dimension to the story. Endothelial-specific DHCR24 knockout mice displayed elevated levels of circulating S1P, consistent with the increased export of intracellular S1P through upregulated SPNS2. This observation transforms S1P from a purely intracellular variable into a measurable biomarker detectable in blood plasma. The team went further, examining the human relevance of the finding. In human subjects, plasma S1P levels were positively correlated with pulse wave velocity, a clinical measure of arterial stiffness and one of the most robust indicators of vascular aging. Elevated pulse wave velocity predicts cardiovascular events independently of traditional risk factors, and the correlation between plasma S1P and arterial stiffening suggests that the mechanism uncovered in mice and cultured cells may operate in living humans.

The significance of this work lies partly in its unification of two fields that have often been studied in isolation. Cholesterol metabolism has long been central to cardiovascular medicine, most famously through statin drugs that lower LDL cholesterol. Sphingolipid signaling, meanwhile, has generated its own pharmacological success stories, most visibly in fingolimod, a drug that acts on S1P receptors and is used to treat multiple sclerosis. By demonstrating that a cholesterol synthesis enzyme controls the synthesis and export of a sphingolipid messenger in endothelial cells, the study reveals a regulatory bridge between sterol and sphingolipid metabolism with direct consequences for cellular aging. It adds to a growing recognition that lipids are not merely structural components or energy stores but active regulators of the senescence program, and that manipulating lipid flux may offer new ways to keep tissues young.

There are also important nuances. S1P is a molecule with context-dependent effects: inside the cell it tends to promote survival and stress resistance, in part through interactions with telomerase and histone acetylation machinery, whereas extracellular S1P engages five distinct G-protein-coupled receptors with sometimes opposing vascular effects. The finding that DHCR24 knockout raises circulating S1P while depleting intracellular S1P underscores this spatial complexity, and it cautions against naive interpretations of plasma S1P measurements. The positive correlation between plasma S1P and pulse wave velocity may reflect a compensatory export of S1P from stressed, senescing endothelium rather than a direct role for extracellular S1P in stiffening arteries, a question that will require further investigation.

The study also situates DHCR24 within a broader emerging picture of vascular aging biology. Other recent work has shown that SPNS2 deficiency itself can drive endothelial senescence through mitochondrial dysfunction, and that age-related insufficiency of vascular growth factors such as VEGF contributes to systemic aging. The new findings weave DHCR24 into this network, positioning the SPHK2/SPNS2-S1P axis as a conduit through which sterol metabolism, sphingolipid signaling and the endothelial senescence program converge. For the geroscience community, this kind of mechanistic convergence is valuable because it identifies nodes where a single intervention might affect multiple upstream drivers of aging.

Translational implications are already visible on the horizon. If the pathway holds up in further studies, SPNS2 inhibitors such as 16d, which were originally developed as research tools and are known to be active in vivo, could be repurposed or refined as senotherapeutic agents aimed at preserving endothelial function in aging arteries. Alternatively, strategies to boost SPHK2 activity or intracellular S1P production might achieve similar protection. Plasma S1P, meanwhile, could be developed as a biomarker of endothelial senescence burden, potentially enabling earlier identification of patients whose arteries are aging faster than their chronological years.

The authors emphasize that the work was supported by the National Natural Science Foundation of China and involved collaboration across the Department of Geriatrics and the Key Laboratory of Vascular Aging at Tongji Hospital. As populations worldwide grow older, the burden of vascular aging, manifested as hypertension, atherosclerosis, heart failure and cognitive decline linked to poor brain blood flow, is set to intensify. Pathways like the DHCR24-SPHK2/SPNS2-S1P axis offer something the field has long sought: a specific, druggable molecular mechanism that connects measurable metabolic states to the cellular aging of the vessel wall. The road from mouse models and cultured cells to human therapies is long, but this study provides both a target and a biomarker, and in doing so it brings the goal of keeping aging arteries functionally young a measurable step closer.