Arachnoid membrane as a source of sphingosine-1-phosphate that regulates mouse middle cerebral artery tone

Growing evidence indicates that perivascular tissue is critical to modulate vessel function. We hypothesized that the arachnoid membrane surrounding middle cerebral artery (MCA) regulates its function via sphingosine-1-phosphate (S1P)-induced vasoconstriction. The MCA from 3- to 9-month-old male and female wild-type (Oncine France 1 and C57BL/6) mice and sphingosine kinase 2 knockout (SphK2-/-) mice in the C57BL/6 background was mounted in pressure myographs with and without arachnoid membrane. Raman microspectroscopy and imaging were used for in situ detection of S1P. The presence of arachnoid tissue was associated with reduced external and lumen MCA diameters, and with an increase in basal tone regardless of sex and strain background. Strong S1P-positive signals were detected in the arachnoid surrounding the MCA wall in both mice models, as well as in a human post-mortem specimen. Selective S1P receptor 3 antagonist TY 52156 markedly reduced both MCA vasoconstriction induced by exogenous S1P and arachnoid-dependent basal tone increase. Compared to 3-month-old mice, the arachnoid-mediated contractile influence persisted in 9-month-old mice despite a decline in arachnoid S1P deposits. Genetic deletion of SphK2 decreased arachnoid S1P content and vasoconstriction. This is the first experimental evidence that arachnoid membrane regulates the MCA tone mediated by S1P.