LPA4/p2y9/GPR23 mediates rho-dependent morphological changes in a rat neuronal cell line

Temporal Dynamics of Purinergic Receptor Expression in the Lungs of Marek's Disease (MD) Virus-Infected Chickens Resistant or Susceptible to MD

Marek's disease virus (MDV) is an economic concern for the poultry industry due to its poorly understood pathophysiology. Purinergic receptors (PRs) are potential therapeutic targets for viral infections, including herpesviruses, prompting our investigation into their role in MDV pathogenesis. The current study is part of an experimental series analyzing the expression of PRs during MDV infection. To address the early or short-acting P2 PR responses during natural MDV infection, we performed an "exposure" experiment where age-matched chickens were exposed to experimentally infected shedders to initiate natural infection. In addition, select non-PR regulatory gene responses were measured. Two groups of naïve contact chickens (n = 5/breed/time point) from MD-resistant (White Leghorns: WL) and -susceptible (Pure Columbian) chicken lines were housed separately with experimentally infected PC (×PC) and WL (×WL) chickens for 6 or 24 h. Whole lung lavage cells (WLLC) were collected, RNA was extracted, and RT-qPCR assays were used to measure specific PR responses. In addition, other potentially important markers in pathophysiology were measured. Our study revealed that WL chickens exhibited higher P1 PR expression during natural infection. WL chickens also showed higher expression of P1A3 and P2X3 at 6 and 24 h when exposed to PC-infected chickens. P2X5 and P2Y1 showed higher expression at 6 h, while P2Y5 showed higher expression at 6 and 24 h; regardless of the chicken line, PC chickens exhibited higher expression of P2X2, P2Y8, P2Y10, P2Y13, and P2Y14 when exposed to either group of infected chickens. In addition, MDV infection altered the expression of DDX5 in both WL and PC groups exposed to PC-infected birds only. However, irrespective of the source of exposure, BCL2 and ANGPTL4 showed higher expression in both WL and PC. The expression of STAT1A and STAT5A was influenced by time and breed, with major changes observed in STAT5A. CAT and SOD1 expression significantly increased in both WL and PC birds, regardless of the source of infection. GPX1 and GPX2 expression also increased in both WL and PC, although overall lower expression was observed in PC chickens at 24 h compared to 6 h. Our data suggest systemic changes in the host during early infection, indicated by the altered expression of PRs, DDX5, BCL2, ANGPTL4, and other regulatory genes during early MDV infection. The relative expression of these responses in PC and WL chickens suggests they may play a key role in their response to natural MDV infection in the lungs and long-term pathogenesis and survival.

Emerging Roles of Lysophosphatidic Acid in Macrophages and Inflammatory Diseases

Lysophosphatidic acid (LPA) is a bioactive phospholipid that regulates physiological and pathological processes in numerous cell biological functions, including cell migration, apoptosis, and proliferation. Macrophages are found in most human tissues and have multiple physiological and pathological functions. There is growing evidence that LPA signaling plays a significant role in the physiological function of macrophages and accelerates the development of diseases caused by macrophage dysfunction and inflammation, such as inflammation-related diseases, cancer, atherosclerosis, and fibrosis. In this review, we summarize the roles of LPA in macrophages, analyze numerous macrophage- and inflammation-associated diseases triggered by LPA, and discuss LPA-targeting therapeutic strategies.

Lysophosphatidic acid, a simple phospholipid with myriad functions

Lysophosphatidic acid (LPA) is a simple phospholipid consisting of a phosphate group, glycerol moiety, and only one hydrocarbon chain. Despite its simple chemical structure, LPA plays an important role as an essential bioactive signaling molecule via its specific six G protein-coupled receptors, LPA_1-6. Recent studies, especially those using genetic tools, have revealed diverse physiological and pathological roles of LPA and LPA receptors in almost every organ system. Furthermore, many studies are illuminating detailed mechanisms to orchestrate multiple LPA receptor signaling pathways and to facilitate their coordinated function. Importantly, these extensive "bench" works are now translated into the "bedside" as exemplified by approaches targeting LPA₁ signaling to combat fibrotic diseases. In this review, we discuss the physiological and pathological roles of LPA signaling and their implications for clinical application by focusing on findings revealed by in vivo studies utilizing genetic tools targeting LPA receptors.

The C-terminal mutation beyond the catalytic site of brown spider phospholipase D significantly impacts its biological activities

Loxosceles spider envenomation results in dermonecrosis, principally due to phospholipases D (PLDs) present in the venom. These enzymes have a strongly conserved sequence, ₂₇₃ATXXDNPW₂₈₀, in the C-terminal region (SMD-tail) that make contact with β-sheets of the TIM barrel, in which the amino acids Asp277 and Trp280 establish the energetically strongest contacts. The SMD-tail is conserved in PLDs from different species but absent in the non-toxic PLD ancestral glycerophosphodiester phosphodiesterases (GDPDs). This work aims to understand the role of the C-terminal region in the structural stability and/or function of phospholipases D. Through site-directed mutagenesis of the rLiD1 protein (recombinant Loxosceles intermedia dermonecrotic protein 1), we produced two mutants: rLiD1D277A and rLiD1W280A (both with sphingomyelinase activity), in which Asp277 and Trp280 were replaced by alanine. rLiD1D277A showed similar sphingomyelinase activity but at least 2 times more dermonecrotic activity than rLiD1 (wild-type protein). Conversely, while the rLiD1W280A displayed a slight increase in sphingomyelinase activity, its biological activity was similar or lower compared to rLiD1, potentially due to its decreased thermostability and formation of amyloid aggregates. In conclusion, these new findings provide evidence that SMD-tail mutants impact the structure and function of these proteins and point out that residues outside the active site can even increase the function of these enzymes.

Purinergic signaling during Marek's disease in chickens

Purinergic receptors (PRs) have been reported as potential therapeutic targets for many viral infections including herpesviruses, which urges the investigation into their role in Marek's disease (MD), a herpesvirus induced cancer in chickens that is an important pathogen for the poultry industry. MD is caused by MD virus (MDV) that has a similar viral life cycle as human varicella zoster virus in that it is shed from infected epithelial skin cells and enters the host through the respiratory route. In this report, PR responses during natural MDV infection and disease progression was examined in MD-resistant white Leghorns (WL) and MD-susceptible Pure Columbian (PC) chickens during natural infection. Whole lung lavage cells (WLLC) and liver tissue samples were collected from chickens infected but showing no clinical signs of MD (Infected) or presenting with clinical disease (Diseased). RNA was extracted followed by RT-qPCR analysis with gene specific primers against members of the P1, P2X, and P2Y PR families. Differential expression (p < 0.05) was observed in breed and disease conditions. Some PRs showed tissue specific expression (P1A1, P2X1, and P2X6 in WLLC) whereas others responded to MDV infection only in MD-susceptible (PC) chickens (P1A2A, P2X1, P2X5, P2X7). P2Y PRs had differential expression in both chicken lines in response to MDV infection and MD progression. This study is the first to our knowledge to examine PR responses during MDV infection and disease progression. These results suggest PR signaling may an important area of research for MDV replication and MD.

Guanine inhibits the growth of human glioma and melanoma cell lines by interacting with GPR23

Guanine-based purines (GBPs) exert numerous biological effects at the central nervous system through putative membrane receptors, the existence of which is still elusive. To shed light on this question, we screened orphan and poorly characterized G protein-coupled receptors (GPRs), selecting those that showed a high purinoreceptor similarity and were expressed in glioma cells, where GBPs exerted a powerful antiproliferative effect. Of the GPRs chosen, only the silencing of GPR23, also known as lysophosphatidic acid (LPA) 4 receptor, counteracted GBP-induced growth inhibition in U87 cells. Guanine (GUA) was the most potent compound behind the GPR23-mediated effect, acting as the endpoint effector of GBP antiproliferative effects. Accordingly, cells stably expressing GPR23 showed increased sensitivity to GUA. Furthermore, while GPR23 expression was low in a hypoxanthine-guanine phosphoribosyl-transferase (HGPRT)-mutated melanoma cell line showing poor sensitivity to GBPs, and in HGPRT-silenced glioma cells, GPR23-induced expression in both cell types rescued GUA-mediated cell growth inhibition. Finally, binding experiments using [3H]-GUA and U87 cell membranes revealed the existence of a selective GUA binding (KD = 29.44 ± 4.07 nM; Bmax 1.007 ± 0.035 pmol/mg prot) likely to GPR23. Overall, these data suggest GPR23 involvement in modulating responses to GUA in tumor cell lines, although further research needs to verify whether this receptor mediates other GUA effects.

Identification of lysophosphatidic acid in serum as a factor that promotes epithelial apical junctional complex organization

The apical junctional complex (AJC) consists of adherens junctions (AJs) and tight junctions and regulates epithelial integrity and remodeling. However, it is unclear how AJC organization is regulated based on environmental cues. We found here using cultured EpH4 mouse mammary epithelial cells that fetal bovine serum (FBS) in a culture medium showed an activity to promote AJC organization and that FBS showed an activity to promote tight junction formation even in the absence of AJ proteins, such as E-cadherin, αE-catenin, and afadin. Furthermore, we purified the individual factor responsible for these functions from FBS and identified this molecule as lysophosphatidic acid (LPA). In validation experiments, purified LPA elicited the same activity as FBS. In addition, we found that the AJC organization–promoting activity of LPA was mediated through the LPA receptor 1/5 via diacylglycerol–novel PKC and Rho–ROCK pathway activation in a mutually independent, but complementary, manner. We demonstrated that the Rho–ROCK pathway activation–mediated AJC organization was independent of myosin II-induced actomyosin contraction, although this signaling pathway was previously shown to induce myosin II activation. These findings are in contrast to the literature, as previous results suggested an AJC organization–disrupting activity of LPA. The present results indicate that LPA in serum has an AJC organization–promoting activity in a manner dependent on or independent of AJ proteins.

Lysophosphatidic acid stimulates pericyte migration via LPA receptor 1

Lysophosphatidic acid (LPA) is a bioactive compound known to regulate various vascular functions. However, despite the fact that many vascular functions are regulated by peri-vascular cells such as pericytes, the effect of LPA on brain pericytes has not been fully evaluated. Thus, we designed this study to evaluate the effects of LPA on brain pericytes. These experiments revealed that while LPA receptors (LPARs) are expressed in cultured pericytes from mouse brains, LPA treatment does not influence the proliferation of these cells but does have a profound impact on their migration, which is regulated via the expression of LPAR1. LPAR1 expression was also detected in human pericyte culture and LPA treatment of these cells also induced migration. Taken together these findings imply that LPA-LPAR1 signaling is one of the key mechanisms modulating pericyte migration, which may help to control vascular function during development and repair processes.

Role of lysophosphatidic acid and its receptors in health and disease: novel therapeutic strategies

Lysophosphatidic acid (LPA) is an abundant bioactive phospholipid, with multiple functions both in development and in pathological conditions. Here, we review the literature about the differential signaling of LPA through its specific receptors, which makes this lipid a versatile signaling molecule. This differential signaling is important for understanding how this molecule can have such diverse effects during central nervous system development and angiogenesis; and also, how it can act as a powerful mediator of pathological conditions, such as neuropathic pain, neurodegenerative diseases, and cancer progression. Ultimately, we review the preclinical and clinical uses of Autotaxin, LPA, and its receptors as therapeutic targets, approaching the most recent data of promising molecules modulating both LPA production and signaling. This review aims to summarize the most update knowledge about the mechanisms of LPA production and signaling in order to understand its biological functions in the central nervous system both in health and disease.

Lysophosphatidic Acid Signalling in Nervous System Development and Function

One class of molecules that are now coming to be recognized as essential for our understanding of the nervous system are the lysophospholipids. One of the major signaling lysophospholipids is lysophosphatidic acid, also known as LPA. LPA activates a variety of G protein-coupled receptors (GPCRs) leading to a multitude of physiological responses. In this review, I describe our current understanding of the role of LPA and LPA receptor signaling in the development and function of the nervous system, especially the central nervous system (CNS). In addition, I highlight how aberrant LPA receptor signaling may underlie neuropathological conditions, with important clinical application.

Lysophosphatidic Acid Receptors: Biochemical and Clinical Implications in Different Diseases

Lysophosphatidic acid (LPA, 1-acyl-2-hemolytic-sn-glycerol-3-phosphate) extracted from membrane phospholipid is a kind of simple bioactive glycophospholipid, which has many biological functions such as stimulating cell multiplication, cytoskeleton recombination, cell survival, drug-fast, synthesis of DNA and ion transport. Current studies have shown that six G-coupled protein receptors (LPAR1-6) can be activated by LPA. They stimulate a variety of signal transduction pathways through heterotrimeric G-proteins (such as Gα12/13, Gαq/11, Gαi/o and GαS). LPA and its receptors play vital roles in cancers, nervous system diseases, cardiovascular diseases, liver diseases, metabolic diseases, etc. In this article, we discussed the structure of LPA receptors and elucidated their functions in various diseases, in order to better understand them and point out new therapeutic schemes for them.

Dynamic actin remodeling in response to lysophosphatidic acid

Lysophosphatidic acid (LPA) is a multifunctional regulator of actin cytoskeleton that exerts a dramatic impact on the actin cytoskeleton to build a platform for diverse cellular processes including growth cone guidance, neurite retraction and cell motility. It has been implicated in the formation and dissociation of complexes between actin and actin binding proteins, supporting its role in actin remodeling. Several studies point towards its ability to facilitate formation of special cellular structures including focal adhesions and actin stress fibres by phosphoregulation of several actin associated proteins and their multiple regulatory kinases and phosphatases. In addition, multiple levels of crosstalk among the signaling cascades activated by LPA, affect actin cytoskeleton-mediated cell migration and chemotaxis which in turn play a crucial role in cancer metastasis. In the current review, we have attempted to highlight the role of LPA as an actin modulator which functions by controlling activities of specific cellular proteins that underlie mechanisms employed in cytoskeletal and pathophysiological events within the cell. Further studies on the actin affecting/remodeling activity of LPA in different cell types will no doubt throw up many surprises essential to gain a full understanding of its contribution in physiological processes as well as in diseases.Communicated by Ramaswamy H. Sarma.

Targeting Lysophosphatidic Acid in Cancer: The Issues in Moving from Bench to Bedside

Since the clear demonstration of lysophosphatidic acid (LPA)'s pathological roles in cancer in the mid-1990s, more than 1000 papers relating LPA to various types of cancer were published. Through these studies, LPA was established as a target for cancer. Although LPA-related inhibitors entered clinical trials for fibrosis, the concept of targeting LPA is yet to be moved to clinical cancer treatment. The major challenges that we are facing in moving LPA application from bench to bedside include the intrinsic and complicated metabolic, functional, and signaling properties of LPA, as well as technical issues, which are discussed in this review. Potential strategies and perspectives to improve the translational progress are suggested. Despite these challenges, we are optimistic that LPA blockage, particularly in combination with other agents, is on the horizon to be incorporated into clinical applications.

Lysophosphatidic acid-induced YAP/TAZ activation promotes developmental angiogenesis by repressing Notch ligand Dll4

Lysophosphatidic acid (LPA) is a potent lipid mediator with various biological functions mediated through six G protein-coupled receptors (GPCRs), LPA1-6. Previous studies have demonstrated that LPA-Gα12/Gα13 signaling plays an important role in embryonic vascular development. However, the responsible LPA receptors and underlying mechanisms are poorly understood. Here, we show a critical role of LPA4 and LPA6 in developmental angiogenesis. In mice, Lpa4;Lpa6 double knockout (DKO) embryos were lethal due to global vascular deficiencies, and endothelial cell (EC)-specific Lpa4;Lpa6 DKO retinas had impaired sprouting angiogenesis. Mechanistically, LPA activated the transcriptional regulators YAP and TAZ through LPA4/LPA6-mediated Gα12/Gα13-Rho-ROCK signaling in ECs. YAP/TAZ knockdown increased β-catenin- and Notch intracellular domain (NICD)-mediated endothelial expression of the Notch ligand delta-like 4 (DLL4). Fibrin gel sprouting assay revealed that LPA4/LPA6, Gα12/Gα13, or YAP/TAZ knockdown consistently blocked EC sprouting, which was rescued by a Notch inhibitor. Of note, the inhibition of Notch signaling also ameliorated impaired retinal angiogenesis in EC-specific Lpa4;Lpa6 DKO mice. Overall, these results suggest that the Gα12/Gα13-coupled receptors LPA4 and LPA6 synergistically regulate endothelial Dll4 expression through YAP/TAZ activation. This could in part account for the mechanism of YAP/TAZ-mediated developmental angiogenesis. Our findings provide a novel insight into the biology of GPCR-activated YAP/TAZ.

LPA receptor 4 deficiency attenuates experimental atherosclerosis

The widely expressed lysophosphatidic acid (LPA) selective receptor 4 (LPAR4) contributes to vascular development in mice and zebrafish. LPAR4 regulates endothelial permeability, lymphocyte migration, and hematopoiesis, which could contribute to atherosclerosis. We investigated the role of LPAR4 in experimental atherosclerosis elicited by adeno-associated virus expressing PCSK9 to lower LDL receptor levels. After 20 weeks on a Western diet, cholesterol levels and lipoprotein distribution were similar in WT male and Lpar4Y/- mice (P = 0.94). The atherosclerotic lesion area in the proximal aorta and arch was ∼25% smaller in Lpar4Y/- mice (P = 0.009), and less atherosclerosis was detected in Lpar4Y/- mice at any given plasma cholesterol. Neutral lipid accumulation in aortic root sections occupied ∼40% less area in Lpar4Y/- mice (P = 0.001), and CD68 expression was ∼25% lower (P = 0.045). No difference in α-smooth muscle actin staining was observed. Bone marrow-derived macrophages isolated from Lpar4Y/- mice displayed significantly increased upregulation of the M2 marker Arg1 in response to LPA compared with WT cells. In aortic root sections from Lpar4Y/- mice, heightened M2 "repair" macrophage marker expression was detected by CD206 staining (P = 0.03). These results suggest that LPAR4 may regulate the recruitment of specific sets of macrophages or their phenotypic switching in a manner that could influence the development of atherosclerosis.

LPA1 , LPA2 , LPA4 , and LPA6 receptor expression during mouse brain development

Background

LPA is a small bioactive phospholipid that acts as an extracellular signaling molecule and is involved in cellular processes, including cell proliferation, migration, and differentiation. LPA acts by binding and activating at least six known G protein–coupled receptors: LPA_1–6. In recent years, LPA has been suggested to play an important role both in normal neuronal development and under pathological conditions in the nervous system.

Results

We show the expression pattern of LPA receptors during mouse brain development by using qRT‐PCR, in situ hybridization, and immunocytochemistry. Only LPA₁, LPA_2,LPA_4, and LPA₆ mRNA transcripts were detected throughout development stages from embryonic day 16 until postnatal day 30 of hippocampus, neocortex, cerebellum, and bulbus olfactorius in our experiments, while expression of LPA₃ and LPA₅ genes was below detection level. In addition to our qRT‐PCR results, we also analyzed the cellular protein expression of endogenous LPA receptors, with focus on LPA₁ and LPA₂ within postnatal brain slices and primary neuron differentiation with and without cytoskeleton stabilization and destabilization.

Conclusions

The expression of LPA receptors changes depends on the developmental stage in mouse brain and in cultured hippocampal primary neurons. Interestingly, we found that commercially available antibodies for LPA receptors are largely unspecific.

LPA1, ‐2, ‐4, and ‐6 genes are dynamically expressed during postnatal brain development.

LPA1, ‐2, ‐4, and ‐6 genes are differently expressed in the hippocampus, neocortex, cerebellum, and bulbus olfactorius.

LPA1 and ‐2 gene expression alters during neuronal differentiation.

LPA1, ‐2, ‐3, ‐4, and ‐6 genes are expressed in glia cells, but differed in gene expression levels.

The Gα12/13-coupled receptor LPA4 limits proper adipose tissue expansion and remodeling in diet-induced obesity

White adipose tissue (WAT) can dynamically expand and remodel through adipocyte hypertrophy and hyperplasia. The relative contribution of these 2 mechanisms to WAT expansion is a critical determinant of WAT function and dysfunction in obesity. However, little is known about the signaling systems that determine the mechanisms of WAT expansion. Here, we show that the GPCR LPA4 selectively activates Gα12/13 proteins in adipocytes and limits continuous remodeling and healthy expansion of WAT. LPA4-KO mice showed enhanced expression of mitochondrial and adipogenesis genes and reduced levels of inhibitory phosphorylation of PPARγ in WAT, along with increased production of adiponectin. Furthermore, LPA4-KO mice showed metabolically healthy obese phenotypes in a diet-induced obesity model, with continuous WAT expansion, as well as protection from WAT inflammation, hepatosteatosis, and insulin resistance. These findings unravel a potentially new signaling system that underlies WAT plasticity and expandability, providing a promising therapeutic approach for obesity-related metabolic disorders.

Microrna-139-5p inhibits epithelial-mesenchymal transition and fibrosis in post-menopausal women with interstitial cystitis by targeting LPAR4 via the PI3K/Akt signaling pathway

The study explores whether miR-139-5p targeting LPAR4 affects epithelial-mesenchymal transition (EMT) and fibrosis in post-menopausal women with interstitial cystitis (IC) via the PI3K/Akt signaling pathway. Bladder tissues of IC and normal bladder tissues were collected. The pathology of bladder tissues was observed by HE, Masson and Picrosirius red staining. LPAR4 positive expression rate were determined by IHC. ELISA was performed to detect the levels of IL-6, IL-8, IL-10, and TNF-α. Rat IC models were randomized into seven different groups. miR-139-5p, LPAR1, LPAR2, LPAR3, LPAR4, LPAR5, P13K, Akt, E-cadherin, N-cadherin, Vimentin, TGF-β1, and CTGF expression were determined by RT-qPCR and Western blotting. Dual luciferase reporter gene assay verified that LPAR4 is a target gene of miR-139-5p. Fibrosis was a pathological manifestation of IC. The IC group showed higher LPAR4, PI3K, Akt, p-PI3K, p-Akt, N-cadherin, Vimentin, TGF-β1, and CTGF expression but lower miR-139-5p and E-cadherin expression than the normal group. The levels of IL-6, IL-8, IL-10, and TNF-α expression decreased while HB-EGF increased in the IC group in comparison of the normal group. Compared with the blank and NC groups, E-cadherin expression was increased in the miR-139-5p mimic and siRNA-LPAR4 groups, while LPAR4, PI3K, Akt, p-P13K, p-Akt, N-cadherin, Vimentin, TGF-β1, and CTGF expression were decreased. An opposite trend was found in the miR-139-5p inhibitor group. The miR-139-5p decreased in the miR-139-5p inhibitor + siRNA-LPAR4 and miR-139-5p inhibitor + wortmannin groups. Conclusively, miR-139-5p targeting LPAR4 inhibits EMT and fibrosis in post-menopausal IC women through the PI3K/Akt signaling pathway.

A porcine ex vivo model of pigmentary glaucoma

Pigment dispersion can lead to pigmentary glaucoma, a poorly understood condition of younger myopic eyes with fluctuating high intraocular pressure. It has been difficult to investigate its pathogenesis without a model similar to human eyes in size and behavior. Here we present a porcine ex vivo model that recreates several features of pigmentary glaucoma, including intraocular hypertension, accumulation of pigment in the trabecular meshwork, and declining phagocytosis. We found that trabecular meshwork cells regulate outflow, form actin stress fibers, and have a decreased phagocytic activity. Gene expression microarrays and a pathway analysis of TM monolayers as well as ex vivo anterior segment perfusion cultures indicated that RhoA plays a central role in regulating the cytoskeleton, motility, and phagocytosis in the trabecular meshwork, providing new insights and targets to investigate in pigmentary glaucoma.

A new approach to chromosome-wide analysis of X-linked markers identifies new associations in Asian and European case-parent triads of orofacial clefts

Background

GWAS discoveries on the X-chromosome are underrepresented in the literature primarily because the analytical tools that have been applied were originally designed for autosomal markers. Our objective here is to employ a new robust and flexible tool for chromosome-wide analysis of X-linked markers in complex traits. Orofacial clefts are good candidates for such analysis because of the consistently observed excess of females with cleft palate only (CPO) and excess of males with cleft lip with or without cleft palate (CL/P).

Methods

Genotypes for 14,486 X-chromosome SNPs in 1,291 Asian and 1,118 European isolated cleft triads were available from a previously published GWAS. The R-package HAPLIN enables genome-wide–level analyses as well as statistical power simulations for a range of biologic scenarios. We analyzed isolated CL/P and isolated CPO for each ethnicity in HAPLIN, using a sliding-window approach to haplotype analysis and two different statistical models, with and without X-inactivation in females.

Results

There was a larger number of associations in the Asian versus the European sample, and similar to previous reports that have analyzed the same GWAS dataset using different methods, we identified associations with EFNB1/PJA1 and DMD. In addition, new associations were detected with several other genes, among which KLHL4, TBX22, CPXCR1 and BCOR were noteworthy because of their roles in clefting syndromes. A few of the associations were only detected by one particular X-inactivation model, whereas a few others were only detected in one sex.

Discussion/Conclusion

We found new support for the involvement of X-linked variants in isolated clefts. The associations were specific for ethnicity, sex and model parameterization, highlighting the need for flexible tools that are capable of detecting and estimating such effects. Further efforts are needed to verify and elucidate the potential roles of EFNB1/PJA1, KLHL4, TBX22, CPXCR1 and BCOR in isolated clefts.

G-Protein-Coupled Lysophosphatidic Acid Receptors and Their Regulation of AKT Signaling

A hallmark of G-protein-coupled receptors (GPCRs) is their ability to recognize and respond to chemically diverse ligands. Lysophospholipids constitute a relatively recent addition to these ligands and carry out their biological functions by activating G-proteins coupled to a large family of cell-surface receptors. This review aims to highlight salient features of cell signaling by one class of these receptors, known as lysophosphatidic acid (LPA) receptors, in the context of phosphatidylinositol 3-kinase (PI3K)-AKT pathway activation. LPA moieties efficiently activate AKT phosphorylation and activation in a multitude of cell types. The interplay between LPA, its receptors, the associated Gαi/o subunits, PI3K and AKT contributes to the regulation of cell survival, migration, proliferation and confers chemotherapy-resistance in certain cancers. However, detailed information on the regulation of PI3K-AKT signals induced by LPA receptors is missing from the literature. Here, some urgent issues for investigation are highlighted.

Lysophosphatidic acid receptors LPA4 and LPA6 differentially promote lymphocyte transmigration across high endothelial venules in lymph nodes

HEV LPA receptors differentially regulate lymphocyte recirculation

Naive lymphocytes continuously migrate from the blood into lymph nodes (LNs) via high endothelial venules (HEVs). To extravasate from the HEVs, lymphocytes undergo multiple adhesion steps, including tethering, rolling, firm adhesion and transmigration. We previously showed that autotaxin (ATX), an enzyme that generates lysophosphatidic acid (LPA), is highly expressed in HEVs, and that the ATX/LPA axis plays an important role in the lymphocyte transmigration across HEVs. However, the detailed mechanism underlying this axis’s involvement in lymphocyte transmigration has remained ill-defined. Here, we show that two LPA receptors, LPA₄ and LPA₆, are selectively expressed on HEV endothelial cells (ECs) and that LPA₄ plays a major role in the lymphocyte transmigration across HEVs in mice. In the absence of LPA₄ expression, lymphocytes accumulated heavily within the HEV EC layer, compared to wild-type (WT) mice. This accumulation was also observed in the absence of LPA₆ expression, but it was less pronounced. Adoptive transfer experiments using WT lymphocytes revealed that the LPA₄ deficiency in ECs specifically compromised the lymphocyte transmigration process, whereas the effect of LPA₆ deficiency was not significant. These results indicate that the signals evoked in HEV ECs via the LPA₄ and LPA₆ differentially regulate lymphocyte extravasation from HEVs in the peripheral LNs.

Structure of ginseng major latex-like protein 151 and its proposed lysophosphatidic acid-binding mechanism

Lysophosphatidic acid (LPA) is a phospholipid growth factor with myriad effects on biological systems. LPA is usually present bound to animal plasma proteins such as albumin or gelsolin. When LPA complexes with plasma proteins, it binds to its cognate receptors with higher affinity than when it is free. Recently, gintonin from ginseng was found to bind to LPA and to activate mammalian LPA receptors. Gintonin contains two components: ginseng major latex-like protein 151 (GLP) and ginseng ribonuclease-like storage protein. Here, the crystal structure of GLP is reported, which belongs to the plant Bet v 1 superfamily, and a model is proposed for how GLP binds LPA. Amino-acid residues of GLP recognizing LPA were identified using site-directed mutagenesis and isothermal titration calorimetry. The resulting GLP mutants were used to study the activation of LPA receptor-dependent signalling pathways. In contrast to wild-type GLP, the H147A mutant did not bind LPA, elicit intracellular Ca2+transients in neuronal cells or activate Ca2+-dependent Cl−channels inXenopusoocytes. Based on these results, a mechanism by which GLP recognizes LPA and its requirement to activate G protein-coupled LPA receptors to elicit diverse biological responses were proposed.

Lysophosphatidylethanolamine increases intracellular Ca(2+) through LPA(1) in PC-12 neuronal cells

G protein-coupled receptors (GPCRs) have been implicated in lysophosphatidylethanolamine (LPE)-induced increases in intracellular Ca(2+) ([Ca(2+)]i), but in different cell types, this response may be dependent or independent of lysophosphatidic acid (LPA) GPCR. The effects of LPEs from Grifola frondosa on the neuronal differentiation and apoptosis of PC-12 neuronal cells have been previously reported. In the present study, the authors sought to identify the mechanism responsible for the effects of LPEs in PC-12 neuronal cells. LPE increase [Ca(2+)]i concentration-dependently in PC-12 neuronal cells, but this LPE-induced [Ca(2+)]i increase was less than that elicited by LPA. Studies using specific inhibitors showed that LPE-induced Ca(2+) response was mediated via pertussis toxin-sensitive Gi/o proteins, edelfosine-sensitive phospholipase C, and 2-APB-sensitive IP3 receptor and by Ca(2+) influx across the cell membrane, and that this did not involve the conversion of LPE to LPA. Furthermore, LPE- and LPA-induced responses were found to show homologous and heterologous desensitization in PC-12 cells. VPC32183 and Ki16425 (antagonists of LPA1 and LPA3) inhibited LPE-induced [Ca(2+)]i increases. Furthermore, AM-095 (a specific inhibitor of LPA1) inhibited LPE-induced Ca(2+) response completely in PC-12 cells. These findings indicate LPE increases [Ca(2+)]i via a LPA1/Gi/o proteins/phospholipase C/IP3/Ca(2+) rise/Ca(2+) influx pathway in PC-12 neuronal cells.

Attenuation of LPS-induced cyclooxygenase-2 and inducible NO synthase expression by lysophosphatidic acid in macrophages

LPS can activate the inflammatory cascades by inducing various inflammatory mediators, such as prostaglandin E2 (PGE2) resulting from cyclooxygenase-2 (COX-2), and NO produced by inducible NO synthase (iNOS). Lysophosphatidic acid (LPA) has been demonstrated to participate in inflammation. This study aimed to clarify the impact and the involving mechanisms of LPA on LPS-incurred inflammation in macrophages. First, LPA appeared to attenuate LPS-induced protein and mRNA expression of COX-2 and iNOS genes, as well as production of PGE2 and NO. By using selective inhibitors targeting various signaling players, the inhibitory G protein alpha subunit (Gαi) seemed to be involved in the effect of LPA; p38, ERK and NF-κB were involved in the LPS-mediated COX-2/PGE2 pathway; and p38, JNK, phosphoinositide-3-kinase and NF-κB were involved in the LPS-mediated iNOS/NO pathway. LPA was able to diminish LPS-induced phosphorylation of p38 and Akt, as well as NF-κB p65 nuclear translocation. By utilization of inhibitors of COX-2 and iNOS, there appeared to be no modulation between the COX-2/PGE2 and the iNOS/NO signaling pathways. Our findings demonstrate a clear anti-inflammatory role of LPA acting via Gαi in LPS-mediated inflammatory response in macrophages, owing, at least in part, to its suppressive effect on LPS-induced activation of p38, Akt and NF-κB.

G-protein-coupled receptor cell signaling pathways mediating embryonic chick retinal growth cone collapse induced by lysophosphatidic acid and sphingosine-1-phosphate

In the development of the nervous system, one of the critical aspects is the proper navigation of axons to their targets, i.e. the problem of axonal guidance. We used the chick visual system as a model to investigate the role of the lysophospholipids lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) as potential axon guidance cues. We showed that both LPA and S1P cause a specific, dose-dependent growth cone collapse of retinal neurons in vitro in the chick model system, with slight differences compared to the mouse but very similar to observations in Xenopus. Because LPA and S1P receptors are G-protein-coupled receptors, we analyzed the intracellular signaling pathways using pharmacological inhibitors in chick retinal neurons. Blocking rho kinase (ROCK) prevented growth cone collapse by LPA and S1P, while blocking PLC or chelating calcium had no effect on growth cone collapse. Inhibition of Gi/o with pertussis toxin resulted in a partial reduction of growth cone collapse, both with LPA and with S1P. Inhibition of p38 blocked growth cone collapse mediated by LPA but not S1P. Thus, in addition to the involvement of the G12/13-ROCK pathway, LPA- and S1P-induced collapse of chick retinal growth cones has a partial requirement for Gi/o.

Lysophospholipid receptor nomenclature review: IUPHAR Review 8

Lysophospholipids encompass a diverse range of small, membrane-derived phospholipids that act as extracellular signals. The signalling properties are mediated by 7-transmembrane GPCRs, constituent members of which have continued to be identified after their initial discovery in the mid-1990s. Here we briefly review this class of receptors, with a particular emphasis on their protein and gene nomenclatures that reflect their cognate ligands. There are six lysophospholipid receptors that interact with lysophosphatidic acid (LPA): protein names LPA1 - LPA6 and italicized gene names LPAR1-LPAR6 (human) and Lpar1-Lpar6 (non-human). There are five sphingosine 1-phosphate (S1P) receptors: protein names S1P1 -S1P5 and italicized gene names S1PR1-S1PR5 (human) and S1pr1-S1pr5 (non-human). Recent additions to the lysophospholipid receptor family have resulted in the proposed names for a lysophosphatidyl inositol (LPI) receptor - protein name LPI1 and gene name LPIR1 (human) and Lpir1 (non-human) - and three lysophosphatidyl serine receptors - protein names LyPS1 , LyPS2 , LyPS3 and gene names LYPSR1-LYPSR3 (human) and Lypsr1-Lypsr3 (non-human) along with a variant form that does not appear to exist in humans that is provisionally named LyPS2L . This nomenclature incorporates previous recommendations from the International Union of Basic and Clinical Pharmacology, the Human Genome Organization, the Gene Nomenclature Committee, and the Mouse Genome Informatix.

LPA receptor signaling: pharmacology, physiology, and pathophysiology

Lysophosphatidic acid (LPA) is a small ubiquitous lipid found in vertebrate and nonvertebrate organisms that mediates diverse biological actions and demonstrates medicinal relevance. LPA's functional roles are driven by extracellular signaling through at least six 7-transmembrane G protein-coupled receptors. These receptors are named LPA1-6 and signal through numerous effector pathways activated by heterotrimeric G proteins, including Gi/o, G12/13, Gq, and Gs LPA receptor-mediated effects have been described in numerous cell types and model systems, both in vitro and in vivo, through gain- and loss-of-function studies. These studies have revealed physiological and pathophysiological influences on virtually every organ system and developmental stage of an organism. These include the nervous, cardiovascular, reproductive, and pulmonary systems. Disturbances in normal LPA signaling may contribute to a range of diseases, including neurodevelopmental and neuropsychiatric disorders, pain, cardiovascular disease, bone disorders, fibrosis, cancer, infertility, and obesity. These studies underscore the potential of LPA receptor subtypes and related signaling mechanisms to provide novel therapeutic targets.

Rapid and reversible enhancement of blood-brain barrier permeability using lysophosphatidic acid

The present study characterizes the effects of lysophosphatidic acid (LPA) on blood-brain barrier (BBB) permeability focusing specifically on the time of onset, duration, and magnitude of LPA-induced changes in cerebrovascular permeability in the mouse using both magnetic resonance imaging (MRI) and near infrared fluorescence imaging (NIFR). Furthermore, potential application of LPA for enhanced drug delivery to the brain was also examined by measuring the brain accumulation of radiolabeled methotrexate. Exposure of primary cultured brain microvessel endothelial cells (BMECs) to LPA produced concentration-dependent increases in permeability that were completely abolished by clostridium toxin B. Administration of LPA disrupted BBB integrity and enhanced the permeability of small molecular weight marker gadolinium diethylenetriaminepentaacetate (Gd-DTPA) contrast agent, the large molecular weight permeability marker, IRdye800cwPEG, and the P-glycoprotein efflux transporter probe, Rhodamine 800 (R800). The increase in BBB permeability occurred within 3 minutes after LPA injection and barrier integrity was restored within 20 minutes. A decreased response to LPA on large macromolecule BBB permeability was observed after repeated administration. The administration of LPA also resulted in 20-fold enhancement of radiolabeled methotrexate in the brain. These studies indicate that administration of LPA in combination with therapeutic agents may increase drug delivery to the brain.

Lysophosphatidylethanolamine utilizes LPA(1) and CD97 in MDA-MB-231 breast cancer cells

Lysophosphatidylethanolamine (LPE) is a lyso-type metabolite of phosphatidylethanolamine (a plasma membrane component), and its intracellular Ca(2+) ([Ca(2+)]i) increasing actions may be mediated through G-protein-coupled receptor (GPCR). However, GPCRs for lysophosphatidic acid (LPA), a structurally similar representative lipid mediator, have not been implicated in LPE-mediated activities in SK-OV3 or OVCAR-3 ovarian cancer cells or in receptor over-expression systems. In the present study, LPE-induced [Ca(2+)]i increase was observed in MDA-MB-231 cells but not in other breast cancer cell lines. In addition, LPE- and LPA-induced responses showed homologous and heterologous desensitization. Furthermore, VPC32183 and Ki16425 (antagonists of LPA1 and LPA3) inhibited LPE-induced [Ca(2+)]i increases, and knockdown of LPA1 by transfection with LPA1 siRNA completely inhibited LPE-induced [Ca(2+)]i increases. Furthermore, the involvement of CD97 (an adhesion GPCR) in the action of LPA1 in MDA-MB-231 cells was demonstrated by siRNA transfection. Pertussis toxin (a specific inhibitor of Gi/o proteins), edelfosine (an inhibitor of phospholipase C), or 2-APB (an inhibitor of IP3 receptor) completely inhibited LPE-induced [Ca(2+)]i increases, whereas HA130, an inhibitor of autotaxin/lysophospholipase D, did not. Therefore, LPE is supposed to act on LPA1-CD97/Gi/o proteins/phospholipase C/IP3/Ca(2+) rise in MDA-MB-231 breast cancer cells.

Lysophosphatidic acid receptor 4 signaling potentially modulates malignant behavior in human head and neck squamous cell carcinoma cells

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common non-skin cancer worldwide. Despite improvement in therapeutic strategies, the prognosis of advanced HNSCC remains poor. The extacellular lipid mediators known as lysophosphatidic acids (LPAs) have been implicated in tumorigenesis of HNSCC. LPAs activate G-protein-coupled receptors not only in the endothelial differentiation gene (Edg) family (LPA1, LPA2, LPA3) but also in the phylogenetically distant non-Edg family (LPA4, LPA5, LPA6). The distinct roles of these receptor isoforms in HNSCC tumorigenesis have not been clarified. In the present study, we investigated the effect of ectopic expression of LPA4 in SQ-20B, an HNSCC cell line, expressing a trivial level of endogenous LPA4. LPA (18:1) stimulated proliferation of SQ-20B cells, but did not affect proliferation of HEp-2, an SCC cell line expressing higher levels of LPA4, comparable to those of with LPA1. LPA-stimulated proliferation of SQ-20B cells was attenuated by Ki16425 and Rac1 inhibitor, but not by Y-27632. Infection with doxycycline-regulatable adenovirus vector expressing green fluorescent protein-tagged LPA4 (AdvLPA4G) abolished LPA-stimulated proliferation in SQ-20B cells with the accumulation of G2/M-phasic cells. Ectopic LPA4 induction further downregulated proliferation of Ki16425-treated SQ-20B cells, of which downregulation was partially recovered by LPA. Ectopic LPA4 induction also downregulated proliferation of Rac1 inhibitor-treated SQ-20B cells, however, LPA no longer recovered it. Finally, LPA-induced cell motility was suppressed by ectopic LPA4 expression as well as by Ki16425, Rac1 inhibitor or Y-27632. Our data suggest that LPA4 signaling potentially modulates malignant behavior of SQ-20B cells. LPA signaling, which is mediated by both Edg and non-Edg receptors, may be a determinant of malignant behavior of HNSCC and could therefore be a promising therapeutic target.

Altered immune pathway activity under exercise challenge in Gulf War Illness: an exploratory analysis

Though potentially linked to the basic physiology of stress response we still have no clear understanding of Gulf War Illness (GWI), a debilitating illness presenting with a complex constellation of immune, endocrine and neurological symptoms. Here we compared male GWI (n=20) with healthy veterans (n=22) and subjects with chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) (n=7). Blood was drawn during a Graded eXercise Test (GXT) prior to exercise, at peak effort (VO2 max) and 4-h post exercise. Affymetrix HG U133 plus 2.0 microarray gene expression profiling in peripheral blood mononuclear cells (PBMCs) was used to estimate activation of over 500 documented pathways. This was cast against ELISA-based measurement of 16 cytokines in plasma and flow cytometric assessment of lymphocyte populations and cytotoxicity. A 2-way ANOVA corrected for multiple comparisons (q statistic <0.05) indicated significant increases in neuroendocrine-immune signaling and inflammatory activity in GWI, with decreased apoptotic signaling. Conversely, cell cycle progression and immune signaling were broadly subdued in CFS. Partial correlation networks linking pathways with symptom severity via changes in immune cell abundance, function and signaling were constructed. Central to these were changes in IL-10 and CD2+ cell abundance and their link to two pathway clusters. The first consisted of pathways supporting neuronal development and migration whereas the second was related to androgen-mediated activation of NF-κB. These exploratory results suggest an over-expression of known exercise response mechanisms as well as illness-specific changes that may involve an overlapping stress-potentiated neuro-inflammatory response.

Autotaxin in embryonic development

Autotaxin (ATX) is a secreted lysophospholipase D that generates the multifunctional lipid mediator lysophosphatidic acid (LPA). LPA signals through six distinct G protein-coupled receptors, acting alone or in concert to activate multiple effector pathways. The ATX-LPA signaling axis is implicated in a remarkably wide variety of physiological and pathological processes and plays a vital role in embryonic development. Disruption of the ATX-encoding gene (Enpp2) in mice results in intrauterine death due to vascular defects in the extra-embryonic yolk sac and embryo proper. In addition, Enpp2 (-/-) embryos show impaired neural development. The observed angiogenic defects are attributable, at least in part, to loss of LPA signaling through the Gα(12/13)-linked RhoA-ROCK-actin remodeling pathway. Studies in zebrafish also have uncovered a dual role for ATX in both vascular and neural development; furthermore, they point to a key role for ATX-LPA signaling in the regulation of left-right asymmetry. Here we discuss our present understanding of the role of ATX-LPA signaling in vertebrate development. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Current progress in non-Edg family LPA receptor research

Lysophosphatidic acid (LPA) is the simplest phospholipid yet possesses myriad biological functions. Until 2003, the functions of LPA were thought to be elicited exclusively by three subtypes of the endothelial differentiation gene (Edg) family of G protein-coupled receptors - LPA(1), LPA(2), and LPA(3). However, several biological functions of LPA could not be assigned to any of these receptors indicating the existence of one or more additional LPA receptor(s). More recently, the discovery of a second cluster of LPA receptors which includes LPA(4), LPA(5), and LPA(6) has paved the way for new avenues of LPA research. Analyses of these non-Edg family LPA receptors have begun to fill in gaps to understand biological functions of LPA such as platelet aggregation and vascular development that could not be ascribed to classical Edg family LPA receptors and are also unveiling new biological functions. Here we review recent progress in the non-Edg family LPA receptor research, with special emphasis on the pharmacology, signaling, and physiological roles of this family of receptors. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Lysophosphatidic acid signaling may initiate fetal hydrocephalus

Fetal hydrocephalus (FH), characterized by the accumulation of cerebrospinal fluid, an enlarged head, and neurological dysfunction, is one of the most common neurological disorders of newborns. Although the etiology of FH remains unclear, it is associated with intracranial hemorrhage. Here, we report that lysophosphatidic acid (LPA), a blood-borne lipid that activates signaling through heterotrimeric guanosine 5'-triphosphate-binding protein (G protein)-coupled receptors, provides a molecular explanation for FH associated with hemorrhage. A mouse model of intracranial hemorrhage in which the brains of mouse embryos were exposed to blood or LPA resulted in development of FH. FH development was dependent on the expression of the LPA(1) receptor by neural progenitor cells. Administration of an LPA(1) receptor antagonist blocked development of FH. These findings implicate the LPA signaling pathway in the etiology of FH and suggest new potential targets for developing new treatments for FH.

Non-Edg family LPA receptors: the cutting edge of LPA research

Lysophosphatidic acid (LPA) is a bioactive lipid mediator with diverse physiological and pathological actions on many types of cells. Originally, LPA was thought to elicit its biological functions through three subtypes of endothelial differentiation gene (Edg) family G protein-coupled receptors (LPA1, LPA2 and LPA3) until our group identified a fourth subtype, LPA4. The discovery of this receptor, which is structurally distinct from the Edg family LPA receptors, led to the identification of two additional LPA receptors, LPA5 and LPA6, homologous to LPA4. These 'non-Edg family' LPA receptors now provide a new framework for understanding the diverse functions of LPA, including vascular development, platelet activation and hair growth. In this review, we summarize the identification, intracellular signalling and biological functions of this novel cluster of LPA receptors.

Lysophosphatidic acid induces neurite retraction in differentiated neuroblastoma cells via GSK-3β activation

Lysophosphatidic acid (LPA) is a lipid growth factor that exerts diverse biological effects, including rapid neurite retraction and cell migration. Alterations in cell morphology, including neurite retraction, in neurodegenerative disorders such as Alzheimer's disease involve hyperphosphorylation of the cytoskeletal protein tau. Since LPA has been shown to induce neurite retraction in various cultured neural cells and the detailed underlying molecular mechanisms have not yet been elucidated, we investigated whether LPA induced neurite retraction through taumediated signaling pathways in differentiated neuroblastoma cells. When Neuro2a cells differentiated with retinoic acid (RA) were exposed to LPA, cells exhibited neurite retraction in a time-dependent manner. The retraction of neurites was accompanied by the phosphorylation of tau. The LPA-induced neurite retraction and tau phosphorylation in differentiated Neuro2a cells were significantly abolished by the glycogen synthase kinase-3β (GSK-3β) inhibitor lithium chloride. Interestingly, the LPA-stimulated tau phosphorylation and neurite retraction were markedly prevented by the administration of H89, an inhibitor of both cyclic-AMP dependent protein kinase (PKA) and cyclic-AMP response element-binding protein (CREB). Transfection of the dominant-negative CREBs, K-CREB and A-CREB, failed to prevent LPA-induced tau phosphorylation and neurite retraction in differentiated Neuro2a cells. Taken together, these results suggest that GSK-3β and PKA, rather than CREB, play important roles in tau phosphorylation and neurite retraction in LPA-stimulated differentiated Neuro2a cells.

Strategy for the identification of GPR23/LPA4 receptor agonists and inverse agonists

Lysophosphatidic acid (LPA) is a bioactive phospholipid that signals through G-protein-coupled receptors to produce a range of biological responses. A recently reported LPA receptor GPR23 (LPA4 receptor) has a low homology to the LPA(1-3) receptors identified previously. In Chinese hamster ovary cells expressing the human GPR23, LPA induced an increase in cellular cyclic adenosine monophosphate (cAMP) and calcium levels. GPR23-selective agonists or antagonists have not been reported previously. Such ligands, if available, would be valuable tools for studying the functions of this receptor. Here we report the identification of novel GPR23 agonists, inverse agonists, and a negative modulator from 2 high-throughput screens, a beta-lactamase reporter screen, and a [3H]LPA-binding screen. Several screening hits were selected for mechanism of action studies using the beta-lactamase reporter assay and a cAMP assay. An evaluation of their selectivity at the other LPA receptors was also conducted. This study demonstrates a strategy for the identification of GPR23 agonists and inverse agonists. We believe the strategy employed here is applicable to other constitutively active GPCRs.

Pivotal role of actin depolymerization in the regulation of cochlear outer hair cell motility

Cochlear outer hair cells undergo reversible changes in shape when externally stimulated. This response, known as OHC motility, is a central component of the cochlear amplifier, the mechanism responsible for the high sensitivity of mammalian hearing. We report that actin depolymerization, as regulated by activation/inhibition of LIMK/cofilin-mediated pathways, has a pivotal role in OHC motility. LIMK-mediated cofilin phosphorylation, which inhibits the actin depolymerizing activity of this protein, increases both electromotile amplitude and total length of guinea pig OHCs. In contrast, a decrease in cofilin phosphorylation reduces both OHC electromotile amplitude and OHC length. Experiments with acetylcholine and lysophosphatidic acid indicate that the effects of these agents on OHC motility are associated with regulation of cofilin phosphorylation via different signaling cascades. On the other hand, nonlinear capacitance measurements confirmed that all observed changes in OHC motile response were independent of the performance of the motor protein prestin. Altogether, these results strongly support the hypothesis that the cytoskeleton has a major role in the regulation of OHC motility, and identify actin depolymerization as a key process for modulating cochlear amplification.

Pharmacological tools for lysophospholipid GPCRs: development of agonists and antagonists for LPA and S1P receptors

Previous studies on lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) using various approaches have shown that both the molecules can act as intercellular signaling molecules. The discovery of the Edg subfamily of G-protein-coupled receptors (GPCRs) (later renamed LPA(1-3) and S1P(1-5)) for these molecules has opened up a new avenue for pathophysiological research on lysophospholipids. Genetic and molecular studies on lysophospholipid GPCRs have elucidated pathophysiological impacts and roles in cellular signaling pathways. Recently, lysophospholipid GPCR genes have been used to develop receptor subtype-selective agonists and antagonists. The discovery of FTY720, a novel immune modulator, along with other chemical tools, has provided a means of elucidating the functions of each lysophospholipid GPCR on an organ and the whole body level. This communication attempts to retrospectively review the development of agonists and antagonists for lysophospholipid GPCRs, provide integrated information on pharmacological tools for lysophospholipid GPCR signaling, and speculate on future drug development.