Erythrocytes efficiently utilize exogenous sphingosines for S1P synthesis and export via Mfsd2b

Area of Science:

• Lipid mediator signaling
• Erythrocyte biology
• Membrane transport mechanisms

Background:

• Sphingosine-1-phosphate (S1P) is a key lipid mediator activating S1P receptors (S1P1-5).
• S1P is synthesized by sphingosine kinases (SphK1/2) and requires export for extracellular signaling.
• Mfsd2b was identified as the S1P transporter in the hematopoietic system, but its role in erythrocytes was unclear.

Purpose of the Study:

• To investigate sphingosine sources and S1P synthesis in erythrocytes.
• To elucidate the transport mechanism of Mfsd2b in erythrocytes.
• To identify potential inhibitors of S1P export.

Main Methods:

• Analysis of sphingosine uptake and de novo synthesis in erythrocytes.
• Investigating the role of SphK1 in sphingosine influx.
• Characterizing Mfsd2b transport activity using site-directed mutagenesis and proton gradient assays.
• Screening for S1P export inhibitors.

Main Results:

• Erythrocytes efficiently uptake exogenous sphingosine, partly supplied by de novo synthesis.
• SphK1 activity enhances sphingosine influx, creating an irreversible S1P synthesis pathway.
• Mfsd2b utilizes a proton gradient for S1P release, with key residues D95 and T157 being essential.
• An S1P analog was identified that inhibits S1P export from erythrocytes.

Conclusions:

• Erythrocytes are significant sites for sphingosine uptake and S1P production.
• Mfsd2b-mediated S1P export is critical in erythrocytes and depends on a proton gradient.
• Sphingosine analogs represent a potential therapeutic strategy to modulate S1P export.