Sphingosine 1‐phosphate receptors regulate TLR4‐induced CXCL5 release from astrocytes and microglia

• Published in: Journal of neurochemistry 2018-03, Vol.144 (6), p.736-747
• Main Authors: O'Sullivan, Sinead A., O'Sullivan, Catherine, Healy, Luke M., Dev, Kumlesh K., Sheridan, Graham K.
• Format: Article
• Language: English
• Subjects: Animals; astrocyte; Astrocytes; Astrocytes - drug effects; Astrocytes - metabolism; Attenuation; chemokine; Chemokine CXCL5 - metabolism; Chemokines; CXC chemokines; CXCL10 protein; CXCL5; Egress; Female; Fingolimod Hydrochloride - administration & dosage; FTY720; Glial cells; Humans; Immune response; Inflammation; Inflammation - metabolism; Inflammation Mediators - metabolism; Interferon; Internalization; Kinases; Lipopolysaccharides; Lipopolysaccharides - administration & dosage; Lymph nodes; Lymphocytes; Male; Mice, Inbred C57BL; Microglia; Microglia - drug effects; Microglia - metabolism; Monocyte chemoattractant protein; Monocyte chemoattractant protein 1; Multiple sclerosis; Neuronal-glial interactions; Phosphates; Proteins; Rats, Wistar; Receptors; Receptors, Lysosphingolipid - agonists; Receptors, Lysosphingolipid - metabolism; RNA, Messenger - metabolism; Signal Transduction; Signaling; sphingosine 1‐phosphate; Sphingosine kinase; TLR4 protein; Toll-Like Receptor 4 - metabolism; Toll-like receptors; toll‐like receptor 4; Transcription
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/jnc.14313

Sphingosine 1‐phosphate receptors (S1PR) are G protein‐coupled and compose a family with five subtypes, S1P1R–S1P5R. The drug Gilenya® (Novartis, Basel, Switzerland) (Fingolimod; FTY720) targets S1PRs and was the first oral therapy for patients with relapsing‐remitting multiple sclerosis (MS). The phosphorylated form of FTY720 (pFTY720) binds S1PRs causing initial agonism, then subsequent receptor internalization and functional antagonism. Internalization of S1P1R attenuates sphingosine 1‐phosphate (S1P)‐mediated egress of lymphocytes from lymph nodes, limiting aberrant immune function in MS. pFTY720 also exerts direct actions on neurons and glial cells which express S1PRs. In this study, we investigated the regulation of pro‐inflammatory chemokine release by S1PRs in enriched astrocytes and microglial cultures. Astrocytes and microglia were stimulated with lipopolysaccharide (LPS) and increases in C‐X‐C motif chemokine 5 (CXCL5), also known as LIX (lipopolysaccharide‐induced CXC chemokine) expression were quantified. Results showed that pFTY720 attenuated LPS‐induced CXCL5 (LIX) protein release from astrocytes, as did the S1P1R selective agonist, SEW2871. In addition, pFTY720 blocked messenger ribonucleic acid (mRNA) transcription of the chemokines, (i) CXCL5/LIX, (ii) C‐X‐C motif chemokine 10 (CXCL10) also known as interferon gamma‐induced protein 10 (IP10) and (iii) chemokine (C‐C motif) ligand 2 (CCL2) also known as monocyte chemoattractant protein 1 (MCP1). Interestingly, inhibition of sphingosine kinase attenuated LPS‐induced increases in mRNA levels of all three chemokines, suggesting that LPS‐TLR4 (Toll‐like receptor 4) signalling may enhance chemokine expression via S1P‐S1PR transactivation. Lastly, these observations were not limited to astrocytes since we also found that pFTY720 attenuated LPS‐induced release of CXCL5 from microglia. These data highlight a role for S1PR signalling in regulating the levels of chemokines in glial cells and support the notion that pFTY720 efficacy in multiple sclerosis may involve the direct modulation of astrocytes and microglia. In addition to its immunomodulatory actions, the multiple sclerosis (MS) drug FTY720 binds to membrane sphingosine 1‐phosphate (S1P) receptors and regulates the release of inflammatory mediators from glial cells in the central nervous system. In this study, we found that lipopolysaccharide (LPS) induced the release of chemokines, in particular C‐X‐C motif chemokine 5 (CXCL5), from astrocy