Mfsd2b is essential for the sphingosine-1-phosphate export in erythrocytes and platelets

Abstract

Sphingosine-1-phosphate (S1P), a potent signalling lipid secreted by red blood cells and platelets, plays numerous biologically significant roles. However, the identity of its long-sought exporter is enigmatic. Here we show that the major facilitator superfamily transporter 2b (Mfsd2b), an orphan transporter, is essential for S1P export from red blood cells and platelets. Comprehensive lipidomic analysis indicates a dramatic and specific accumulation of S1P species in Mfsd2b knockout red blood cells and platelets compared with that of wild-type controls. Consistently, biochemical assays from knockout red blood cells, platelets, and cell lines overexpressing human and mouse Mfsd2b proteins demonstrate that Mfsd2b actively exports S1P. Plasma S1P level in knockout mice is significantly reduced by 42-54% of that of wild-type level, indicating that Mfsd2b pathway contributes approximately half of the plasma S1P pool. The reduction of plasma S1P in knockout mice is insufficient to cause blood vessel leakiness, but it does render the mice more sensitive to anaphylactic shock. Stress-induced erythropoiesis significantly increased plasma S1P levels and knockout mice were sensitive to these treatments. Surprisingly, knockout mice exhibited haemolysis associated with red blood cell stomatocytes, and the haemolytic phenotype was severely increased with signs of membrane fragility under stress erythropoiesis. We show that S1P secretion by Mfsd2b is critical for red blood cell morphology. Our data reveal an unexpected physiological role of red blood cells in sphingolipid metabolism in circulation. These findings open new avenues for investigating the signalling roles of S1P derived from red blood cells and platelets.

The signalling roles of sphingosine‐1‐phosphate derived from red blood cells and platelets

“…identified Mfsd2b, an orphan transporter that is expressed in erythrocytes and platelets. This transporter provides approximately 50% of the S1P in plasma as observed in Mfsd2b −/− mice (Vu et al ., ). This corroborates well with previous determinations of S1P sources from haematopoietic cells (Gazit et al ., ).…”

“…This corroborates well with previous determinations of S1P sources from haematopoietic cells (Gazit et al ., ). Mfsd2b −/− mice exhibited phenotypes that are linked to abnormal S1P signalling, such as low circulating lymphocytes and sensitivity to vascular stress (Vu et al ., ).…”

“…Mfsd2b is also highly expressed in platelets, and this transporter is required for S1P release from resting and activated platelets (Vu et al ., ). In the study by Vu et al, () Mfsd2b was shown to be expressed in cell membranes and intracellular membrane structures. However, the expression pattern of Mfsd2b in resting platelets is not known.…”

Survival benefit of sphingosin‐1‐phosphate and receptors expressions in breast cancer patients

“…Recent studies indicated spinster homolog 2 (Spns2) expressed on endothelial cells (ECs) function as S1P transporter 9, 10. In addition, studies showed that red blood cells and platelets requires the major facilitator superfamily transporter 2b (Mfsd2b) to export S1P 11, 12 and maintained S1P level in blood stream. The function of S1P is go through its receptors S1PRs (S1PR1‐5) which belongs to the G‐protein coupled receptor (GPCR) family 2 and each receptor, respectively, involved in cell growth, apoptosis, proliferation, angiogenesis, chemo resistance, or vascular stability 5, 13, 14, 15.…”

Arteriovenous Sphingosine-1-Phosphate Differences Across Selected Organs of the Rat

“…S1P is produced in all cells by sphingosine kinase (SphK)-mediated phosphorylation of sphingosine (a catabolite of ceramide), and may be subsequently released to the extracellular milieu with the help of spinster homolog 2 (SPNS2), ATP-binding cassette transporter C1, and major facilitator superfamily transporter 2b [2-4]. In addition to sphingosine, SphK is also able to phosphorylate sphinganine (an intermediate of ceramide de novo synthesis pathway) to form sphinganine-1-phosphate (SA1P) [5].…”