Lysophosphatidic acid stimulates two ion currents in cultured human retinal pigment epithelial cells

A low level of lysophosphatidic acid in human gingival crevicular fluid from patients with periodontitis due to high soluble lysophospholipase activity: Its potential protective role on alveolar bone loss by periodontitis

We previously detected a submicromolar concentration of lysophosphatidic acid (LPA) in human saliva. Here, we compare LPA concentrations in human gingival crevicular fluid (GCF) from patients with periodontitis and healthy controls, and examine how the local LPA levels are regulated enzymatically. The concentrations of LPA and its precursor lysophospholipids in GCF was measured by liquid chromatography-tandem mass spectrometry. The LPA-producing and LPA-degrading enzymatic activities were measured by quantifying the liberated choline and free fatty acid, respectively. The concentration of LPA in GCF of periodontitis patients was lower than that of healthy controls, due to higher soluble lysophospholipase activity toward LPA. LPA was found to prevent survival of Sa3, a human gingival epithelium-derived tumor cell line, activate Sa3 through Ca²⁺ mobilization, and release interleukin 6 from Sa3 in vitro. Furthermore, local injection of LPA into the gingiva attenuated ligature-induced experimental alveolar bone loss induced by oral bacteria inoculation in a rat model of periodontitis in vivo. A high concentration of LPA in human GCF is necessary to maintain normal gingival epithelial integrity and function, protecting the progression of periodontitis.

Lysophosphatidic acid regulates adhesion molecules and enhances migration of human oral keratinocytes

Oral keratinocytes are connected via cell-to-cell adhesions to protect underlying tissues from physical and bacterial damage. Lysophosphatidic acids (LPAs) are a family of phospholipid mediators that have the ability to regulate gene expression, cytoskeletal rearrangement, and cytokine/chemokine secretion, which mediate proliferation, migration, and differentiation. Several forms of LPA are found in saliva and gingival crevicular fluid, but it is unknown how they affect human oral keratinocytes (HOK). The aim of the present study was therefore to examine how different LPA forms affect the expression of adhesion molecules and the migration and proliferation of HOK. Keratinocytes were isolated from gingival biopsies obtained from healthy donors and challenged with different forms of LPA. Quantitative real-time RT-PCR, immunocytochemistry, and flow cytometry were used to analyze the expression of adhesion molecules. Migration and proliferation assays were performed. Lysophosphatidic acids strongly promoted expression of E-cadherin and occludin mRNAs and translocation of E-cadherin protein from the cytoplasm to the membrane. Occludin and claudin-1 proteins were up-regulated by LPA. Migration of HOK in culture was increased, but proliferation was reduced, by the addition of LPA. This indicates that LPA can have a role in the regulation of the oral epithelial barrier by increasing the expression of adhesion molecules of HOK, by promotion of migration and by inhibition of proliferation.

Genetics and cell biology of lysophosphatidic acid receptor-mediated signaling during cortical neurogenesis

Lysophosphatidic acid (LPA) is a small lysophospholipid that signals through G-protein coupled receptors (GPCRs) to mediate diverse cellular responses. Two LPA receptors, LPA(1) and LPA(2), show gene expression profiles in mouse embryonic cerebral cortex, suggesting roles for LPA signaling in cerebral cortical development. Here, we review loss-of-function and gain-of-function models that have been used to examine LPA signaling. Genetic deletion of lpa(1) or both lpa(1) and lpa(2) in mice results in 50-65% neonatal lethality, but not obvious cortical phenotypes in survivors, suggesting that compensatory signaling systems exist for regulating cortical development. A gain-of-function model, approached by increasing receptor activation through exogenous delivery of LPA, shows that LPA signaling regulates cerebral cortical growth and anatomy by affecting proliferation, differentiation and cell survival during embryonic development.

Lysophosphatidic acid in neural signaling

The physiological and pathological importance of lysophosphatidic acid (LPA) in the nervous system is underscored by its presence, as well as the expression of its receptors in neural tissues. In fact, LPA produces responses in a broad range of cell types related to the function of the nervous system. These cell types include neural cell lines, neural progenitors, primary neurons, oligodendrocytes, Schwann cells, astrocytes, microglia, and brain endothelial cells. LPA-induced cell type-specific effects include changes in cell morphology, promotion of cell proliferation and cell survival, induction of cell death, changes in ion conductance and Ca2+ mobilization, induction of pain transmission, and stimulation of vasoconstriction. These effects are mediated through a number of G protein-coupled LPA receptors that activate various downstream signaling cascades. This review provides a current summary of LPA-induced effects in neural cells in vitro or in vivo in combination with our current understanding of the signaling pathways responsible for these effects.

Neurobiology of lysophosphatidic acid signaling

Lysophosphatidic acid (LPA), a growth factor-like lysophospholipid, induces diverse cellular responses. The identification of the first LPA receptor gene, through studies of neuroproliferative regions within the embryonic cerebral cortex, has led to the classification of a family of at least eight lysophospholipid receptors with diverse roles in organismal development and function. A growing body of literature has identified roles for LPA signaling under physiological and pathological conditions, particularly within the developing nervous system. Here the authors review features of the LPA receptor family and cellular responses of nervous system-derived cells, and discuss developmental and pathological roles for LPA signaling in the nervous system.

Activation of a nonspecific cation current in rat cultured retinal pigment epithelial cells: involvement of a G(alpha i) subunit protein and the mitogen-activated protein kinase signalling pathway

1. Whole-cell patch-clamp recording techniques were used to investigate the G protein subtype and related signalling molecules involved in activation of a nonspecific cation (NSC) current in rat cultured retinal pigment epithelial (RPE) cells. 2. Under control conditions, in 130 mM NaCl with K+ aspartate in the pipette, cytosolic dialysis with guanosine-5'-O-(3-triphosphate) (GTPgammaS, 0.1 mM) activated a large non-inactivating NSC current in 80% of the cells recorded from. 3. Loading RPE cells with antibodies (10 microg-ml(-1)) against the alpha subunit of all PTX-sensitive G proteins (G(alpha i/o/t/z)) reduced NSC current activation to 11%, while loading RPE cells with antibodies directed specifically against the alpha subunits of the Gi subclass (G(alpha i-3)) completely abolished current activation. In RPE cells loaded with anti-G(alpha s) activation of the NSC current was unaffected. 4. Investigation of the potential downstream mediators in the G(alpha i) NSC channel pathway revealed that activation of the cation conductance was unaffected by treatment of RPE cells with the selective protein kinase C inhibitor GF 109203X (3 microM) or the selective CaM kinase II inhibitor KN-93 (50 microM). However, NSC current activation was delayed and the current amplitude reduced in the presence of the nonselective kinase inhibitor H-7 (100 microM) or the selective inhibitor of MAPKK (MEK) activation, PD 98059 (50 microM). 5. In the absence of GTPgammaS, the NSC current was not activated by superfusion of the cells with the cyclic GMP kinase activator dibutyryl-cyclic GMP or with the adenylate cyclase activator forskolin. 6. These results support the involvement of a G protein of the G(alpha i) subclass in the activation of a NSC current in rat RPE cells, and suggest a potential modulatory role for MAP kinase-dependent phosphorylation in current regulation.