Lysophospholipid receptors: implications for neural signaling.

Lysophospholipids (LPs) such as lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) represent quantitatively minor phospholipid species that nonetheless are capable of acting as extracellular signals. As an organ system dominated by lipids, the nervous system would seem a likely benefactor of this form of intercellular signaling. A major difficulty in determining the neurobiological importance of these lipids, however, has been a lack of cloned receptors. The unavailability, indeed, uncertain existence, of these receptors has been particularly problematic because of the absence of specific, competitive antagonists to block function. Further, these lipids have detergent-like chemical structures, raising the explanation that any observed effects of exogenously applied lysophospholipids could be due to nonspecific membrane perturbations. During studies of G-protein coupled receptor (GPCR) genes involved with cerebral cortical neurogenesis, the first lysophospholipid receptor gene (lpA1/vzg-1) was isolated (Hecht et al., J. Cell Biol., 135, 1071, 1996), implicating receptor-mediated lysophospholipid signaling as potentially important components of nervous system development and function. Expression studies indicated roles in neurogenesis, cortical development, and effects on glia, particularly oligodendrocyte and Schwann cell development. Reviewed here are the molecular biology of LP receptors, relevant aspects of intracellular signaling, and their possible roles in the nervous system.