Sphingosine kinase 1 (Sphk1) negatively regulates platelet activation and thrombus formation

Abstract

Sphingosine 1-phosphate (S1P) is a powerful regulator of platelet formation. Enzymes generating S1P include sphingosine kinase 1. The present study thus explored the role of sphingosine kinase 1 in platelet formation and function. Activation-dependent platelet integrin αIIbβ3 activation and secretion of platelets lacking functional sphingosine kinase 1 (sphk1(-/-)) and of wild-type platelets (sphk1(+/+)) were determined utilizing flow cytometry and chronolume luciferin assay. Cytosolic Ca(2+) activity ([Ca(2+)]i) and aggregation were measured using fura-2 fluorescence and aggregometry, respectively. In vitro platelet adhesion and thrombus formation were evaluated using a flow chamber with shear rates of 1,700 s(-1). Activation-dependent increase of [Ca(2+)]i, degranulation (release of alpha and dense granules), integrin αIIbβ3 activation, and aggregation were all significantly increased in sphk1(-/-) platelets compared with sphk1(+/+) platelets. Moreover, while platelet adhesion and thrombus formation under arterial shear rates were significantly augmented in Sphk1-deficient platelets, bleeding time and blood count were unaffected in sphk1(-/-) mice. In conclusion, sphingosine kinase 1 is a powerful negative regulator of platelet function counteracting degranulation, aggregation, and thrombus formation.

Sphingosine 1-Phosphate Produced by Sphingosine Kinase 2 Intrinsically Controls Platelet Aggregation In Vitro and In Vivo

“…Hence, platelet S1P facilitates rather than inhibits platelet activation, explaining the increased aggregation reported in Sphk1-deficient platelets. 42 We show that S1P mainly induces a dose-dependent aggregation response via the S1PR 1 in whole blood. A recent study showed that aggregation of washed human platelets was reduced not only by inhibition of S1PR 1 , but also in the presence of the S1PR 2 antagonist JTE-013 40 .…”

“…In our present study, we performed whole blood aggregation assays to mimic physiological conditions as closely as possible. Münzer et al 42 recently reported that Sphk1-deficient platelets show elevated degranulation (release of alpha and dense granules) and aggregation in response to low-dose agonist stimulation. Based on their findings, the authors speculated that this was because of reduced levels of intracellular platelet S1P and proposed that platelet S1P acts as a negative regulator of platelet aggregation.…”

“Beet-ing” the Mountain: A Review of the Physiological and Performance Effects of Dietary Nitrate Supplementation at Simulated and Terrestrial Altitude

“… was ~4% lower during cycle ergometry exercise at 45% peak O 2 uptake () in extreme normobaric hypoxia (F I O 2 11%, ~5000 m). Subsequent studies have reported reductions of 4–10% (similar magnitudes to those reported in normoxia) during cycle ergometry [29, 30, 36] and treadmill running exercise [64] across a range of simulated altitudes (F I O 2 11–15.4%, ~2500–5000 m). Interestingly, one study reported lower steady-state in normobaric hypoxia (F I O 2 13.1%, ~3500 m) but not normoxia [36] following NO 3 − supplementation.…”

“…This reaction is catalyzed by the NO synthase (NOS) enzymes and requires O 2 as a co-substrate. In vitro evidence suggests that NO generated via the l -arginine NOS pathway is suppressed in hypoxia [33], although in vivo evidence is less clear [34–36]. Alternatively, NO can be generated via the reduction of nitrate (NO 3 − ) and nitrite (NO 2 − ) through the recently elucidated NO 3 − –NO 2 − –NO pathway [37].…”

Exploration of the Sphingolipid Metabolite, Sphingosine-1-phosphate and Sphingosine, as Novel Biomarkers for Aspirin-exacerbated Respiratory Disease

“…After platelet activation, intracellular S1P is released into the environment3738. In vitro studies have found that arachidonic acid could stimulate platelets to secrete S1P through the activation of the thromboxane receptor38.…”