Circulating sphingosine-1-phosphate depletion is associated with endothelial activation and altered brain-endothelial...

Ischemic stroke remains a leading cause of disability and mortality worldwide, with limited acute therapeutic options. Sphingosine-1-phosphate (S1P) is a bioactive lipid that regulates endothelial function, vascular integrity, and immune responses, and reduced circulating S1P levels have been reported in ischemic stroke. Whether plasma S1P depletion parallels alterations in brain-endothelial S1P metabolism, receptor expression, and endothelial activation, however, remains unclear. Here, we characterized circulating S1P levels together with stroke-associated changes in brain-endothelial S1P pathway expression, markers related to endothelial activation, and blood-brain barrier (BBB) integrity.

We quantified plasma S1P concentrations in patients with acute ischemic stroke (n = 50) and age- and sex-matched controls (n = 47), with follow-up assessments at 90 days. Complementary experimental stroke studies were performed using transient and permanent middle cerebral artery occlusion (MCAo) in wild-type mice and in endothelial-specific RiboTag mice (Cdh5^Cre-ER(T)) that enable selective isolation of endothelial mRNA. In parallel, human brain microvascular endothelial cells were exposed to oxygen-glucose deprivation in vitro. Endothelial activation-related markers, expression of S1P-metabolizing enzymes and S1P receptors, BBB integrity, and circulating P-selectin levels were assessed by qPCR, Western blotting, immunohistochemistry, and ELISA-based approaches.

Plasma S1P levels were significantly reduced in patients with acute ischemic stroke compared with controls and recovered at follow-up, consistent with findings in experimental stroke. Endothelial-specific transcriptomic profiling revealed reduced expression of sphingosine kinases, S1P-degrading enzymes, and S1P receptors (S1pr1, S1pr3, and S1pr4) in the ischemic brain endothelium. Lower vascular S1PR1 protein expression was associated with increased BBB disruption, and sphingosine kinase 2 protein abundance was reduced in small cerebral vessel endothelial cells of the lesioned compared to the contralateral hemisphere. These alterations were accompanied by acute changes in endothelial barrier- and activation-related markers, together with model-dependent changes in plasma P-selectin in mice. In patients, plasma P-selectin levels were not elevated acutely but showed an inverse association with plasma S1P concentrations.

Ischemic stroke associates with acute plasma S1P depletion that parallels altered brain-endothelial S1P pathway expression, signs of endothelial activation, and BBB disruption. These findings support plasma S1P as a candidate circulating marker associated with cerebrovascular injury after stroke.