Hypoxia has been previously shown to inhibit the
dihydroceramide (DHC) desaturase, leading to the accumulation of DHC. In this study, we used metabolic labeling with [3H]-
palmitate, HPLC/MS/MS analysis, and specific inhibitors to show numerous
sphingolipid changes after
oxygen deprivation in cerebral microendothelial cells. The increased DHC, particularly long-chain forms, was observed in both whole cells and
detergent-resistant membranes. This was reversed by reoxygenation and blocked by the de novo
sphingolipid synthesis inhibitor
myriocin, but not by the neutral
sphingomyelinase inhibitor
GW-4869. Furthermore,
oxygen deprivation of microendothelial cells increased levels of dihydro-
sphingosine (DH-Sph), DH-sphingosine1-phosphate (DH-S1P), DH-
sphingomyelin (DH-SM), DH-
glucosylceramide (DH-GlcCer), and S1P levels. In vitro assays revealed no changes in the activity of sphingomyelinases or
sphingomyelin synthase, but resulted in reduced S1P
lyase activity and 40% increase in
glucosylceramide synthase (GCS) activity, which was reversed by reoxygenation. Inhibition of the de novo
sphingolipid pathway (
myriocin) or GCS (EtPoD4) induced endothelial barrier dysfunction and increased
caspase 3-mediated cell death in response to
hypoxia. Our findings suggest that
hypoxia induces synthesis of S1P and multiple dihydro-
sphingolipids, including DHC, DH-SM, DH-GlcCer, DH-Sph and DH-S1P, which may be involved in ameliorating the effects of
stroke . Progressive
hypoxia leads to the accumulation of several dihydrosphingolipids in cerebral microendothelial cells.
Hypoxia also increases
sphingosine-1-phosphate and the activity of
glucosylceramide (Glc-Cer) synthase. These changes reverse by inhibiting the de novo
sphingolipid synthesis, which worsens
hypoxia-induced endothelial barrier dysfunction and apoptosis, suggesting that the identified
sphingolipids may be vasculoprotective.