Longitudinal sphingolipidomics reveals sphingosine-1-phosphate as an indicator of impending aneurysm rupture or repair

Background Aortic aneurysm (AA) dissection and rupture are catastrophic complications of aortic disease and major causes of cardiovascular mortality, with no pharmacological therapy to prevent progression. The bioactive lipid sphingosine-1-phosphate (S1P) regulates vascular homeostasis by modulating endothelial integrity and smooth muscle contractility via five G protein-coupled receptors (S1PR1-5). Although dysregulated S1P signaling is implicated in cardiovascular disorders, its role in aneurysm formation and rupture remains unclear. Methods Plasma and aneurysmal tissue were obtained from patients undergoing elective repair of abdominal aneurysms (n=60) and compared with healthy controls (n=40). An independent longitudinal cohort of 120 AA patients from the MA³RS study (University of Edinburgh, UK) provided serial plasma samples at baseline and every 6 months for up to 2 years, before and after repair, rupture, or continued surveillance. Sphingolipids were quantified by LC-MS/MS. Experimental aneurysms were induced in ApoE-deficient mice by Angiotensin II (1000ng/kg/min; 28 days) with or without the S1P lyase inhibitor 4′-deoxypyridoxine (DOP, 4.5mg/kg/day). AA morphology, molecular signatures, and vascular biomechanics were analysed; ApoE/S1PR3-deficient mice defined receptor-specific effects. Results Targeted sphingolipidomics revealed marked alterations in plasma and aneurysmal tissue, clearly separating AA patients from controls by principal component analysis. Among all detected species, S1P was the most upregulated lipid and strongest discriminator (AUC 0.90, 95% CI 0.81-0.96), with 2-fold higher plasma and 3-fold higher tissue levels in aneurysmal versus control aortae. The pathophysiological relevance of S1P was supported by longitudinal analyses in the MA³RS cohort. Plasma S1P inversely correlated with time to rupture or surgical repair, rising as events approached and declining after intervention, independent of aneurysm diameter. Adding plasma S1P (HR 1.345; 95% CI 1.01-1.79) to aneurysm diameter in a multivariable model significantly improved prediction of rupture/repair (likelihood ratio χ² = 4.06, P = 0.04). Although AA patients generally exhibited elevated S1P levels compared with controls, intra-cohort stratification showed that those with the highest circulating S1P concentrations had the greatest rupture/repair risk. Mechanistically, pharmacological S1P elevation in mice (DOP) increased rupture-related mortality (70% vs. 25%; p<0.05), increased aortic stiffness, and suppressed contractile gene expression via S1P/S1PR3 signaling. ApoE/S1PR3-deficient mice were protected, preserving aortic integrity and contractile phenotype despite elevated S1P. Conclusion S1P dynamically tracks aneurysm instability in humans and promotes rupture through S1PR3-dependent VSMC reprogramming, identifying the S1P/S1PR3 axis as a size-independent determinant of aneurysm progression and a potential therapeutic target.