Pharmacological characterization of lysophospholipid receptor signal transduction pathways in rat cerebrocortical astrocytes.
Lysophosphatidic acid (1-acyl-2-lyso-sn-glycero-3-phosphate; LPA) and sphingosine-1-phosphate (S1P) are bioactive phospholipids which respectively act as agonists for the G-protein-coupled lpA receptors (LPA1, LPA2, and LPA3) and s1p receptors (S1P1, S1P2, S1P3, S1P4, and S1P5), collectively referred to as lysophospholipid receptors (lpR). Since astrocytes are responsive to LPA and S1P, we examined mechanisms of lpR signaling in rat cortical secondary astrocytes. Rat cortical astrocyte mRNA expression by quantitative TaqMan polymerase chain reaction (PCR) analysis revealed the following order of relative expression of lpR mRNAs: s1p3>s1p1>lpa1>s1p2=lpa3>>s1p5. Activation of lpRs by LPA or S1P led to multiple pharmacological effects, including the influx of calcium, phosphoinositide (PI) hydrolysis, phosphorylation of extracellular receptor regulated kinase (ERK) and release of [3H]-arachidonic acid (AA). These signalling events downstream of lpR activation were inhibited to varying degrees by pertussis toxin (PTX) pretreatment or by the inhibition of sphingosine kinase (SK), a rate-limiting enzyme in the biosynthesis of S1P from sphingosine. These results suggest that astrocyte lpR signalling mechanisms likely involve both Gi- and Gq-coupled GPCRs and that receptor-mediated activation of SK leads to intracellular generation of S1P, which in turn amplifies the lpR signalling in a paracrine/autocrine manner.
Rao
Tadimeti S
TS
Merck Research Laboratories, 3535 General Atomics Court, Building 1, San Diego, CA 92121, USA. trao@kalypsys.com
Lariosa-Willingham
Karen D
KD
Lin
Fen-Fen
FF
Palfreyman
Emma L
EL
Yu
Naichen
N
Chun
Jerold
J
Webb
Michael
M
D000199:Actins / Q000096:biosynthesis / Q000235:genetics; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D015153:Blotting, Western; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003001:Cloning, Molecular; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D007295:Inositol Phosphates / Q000378:metabolism; D008246:Lysophospholipids / Q000378:metabolism* / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020239:Receptor Cross-Talk / Q000187:drug effects; D018110:Receptors, Lipoprotein / Q000096:biosynthesis / Q000187:drug effects*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000099157:Sphingosine Kinase
D000199:Actins; D016718:Arachidonic Acid; D007295:Inositol Phosphates; D008246:Lysophospholipids; D019950:Mitogen-Activated Protein Kinase 1; D017853:Phosphotransferases (Alcohol Group Acceptor); D012333:RNA, Messenger; D018110:Receptors, Lipoprotein; D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate