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 slp receptors (SlP1, SlP2, SlP3, SlP4, and SlP5), 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: slp3>slp1>lpa1>slp2=l-lpa3much greater thanslp5. Activation of lpRs by LPA or SIP led to multiple pharmacological effects, including the influx of calcium, phosphoinositide (PI) hydrolysis, phosphorylation of extracellular receptor regulated kinase (ERK) and release of [H-3]-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 SIP 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 SIP, which in turn amplifies the lpR signalling in a paracrine/autocrine manner. (C) 2003 Elsevier B.V. All rights reserved.