BBA - Molecular and Cell Biology of Lipids (v.1781, #9)

Ceramidases catalyze hydrolysis of ceramides to generate sphingosine (SPH), which is phosphorylated to form sphingosine-1-phosphate (S1P). Ceramide, SPH, and S1P are bioactive lipids that mediate cell proliferation, differentiation, apoptosis, adhesion, and migration. Presently, 5 human ceramidases encoded by 5 distinct genes have been cloned: acid ceramidase (AC), neutral ceramidase (NC), alkaline ceramidase 1 (ACER1), alkaline ceramidase 2 (ACER2), and alkaline ceramidase 3 (ACER3). Each human ceramidase has a mouse counterpart. AC, NC, and ACER1–3 have maximal activities in acidic, neutral, and alkaline environments, respectively. ACER1–3 have similar protein sequences but no homology to AC and NC. AC and NC also have distinct protein sequences. The human AC (hAC) was implicated in Farber disease, and hAC may be important for cell survival. The mouse AC (mAC) is needed for early embryo survival. NC is protective against inflammatory cytokines, and the mouse NC (mNC) is required for the catabolism of ceramides in the digestive tract. ACER1 is critical in mediating cell differentiation by controlling the generation of SPH and S1P and that ACER2's role in cell proliferation and survival depends on its expression or the cell type in which it is found. Here, we discuss the role of each ceramidase in regulating cellular responses mediated by ceramides, SPH, and S1P.
Keywords: Apoptosis; Bioactive lipid; Cell adhesion; Differentiation; Growth arrest; Proliferation;

Sphingosine-1-phosphate regulation of mammalian development by Mari Kono; Maria Laura Allende; Richard L. Proia (435-441).
Sphingosine-1-phosphate (S1P) was first identified as a lysophospholipid metabolite whose formation is required for the irreversible degradation of sphingolipids. Years later, it was discovered that S1P is a bioactive lipid that provokes varied cell responses by acting through cell-surface receptors to drive cell signaling. More recent findings in model organisms have now established that S1P metabolism and signaling are integrated into many physiological systems. We describe here the surprising breadth of function of S1P in mammalian development and the underlying biologic processes that S1P regulates.
Keywords: Lysophospholipid; S1P; Development; Vascular; Neural; Maternal:fetal interface; Decidualization;

The role of sphingosine kinase 1 in cancer: Oncogene or non-oncogene addiction? by Mathew Vadas; Pu Xia; Geoff McCaughan; Jennifer Gamble (442-447).
Sphingosine kinase 1 (SphK1) is a lipid kinase that catalyses the phosphorylation of sphingosine to sphingosine-1-phosphate. There is strong evidence from cellular or animal systems that SphK1 is involved in the major mechanisms underpinning oncogenesis, namely, the promotion of cellular survival, proliferation and transformation, the prevention of apoptosis and the stimulation of angiogenesis. Furthermore there is also good evidence from clinical samples that SphK1 is overexpressed in many, if not most tumor types examined and that many inhibitors of SphK1 render tumors sensitive to chemotherapeutic agents. A major question that remains concerns the exact mechanism of action of SphK1 in cancer. The tools available to probe SphK1 function perturb a set of cellular functions, and it is possible that several of these are involved in driving its oncogenic role. Furthermore, the importance of SphK1 functions in normal physiology and the lack of mutations of SphK1 in cancer, suggest that the mechanism in cancer might be an over reliance on this system of cellular signaling; an example of non-oncogene addiction.
Keywords: Sphingosine kinase; Cancer; Oncogene; Sphingosine-1-phosphate;

Sphingosine-1-phosphate lyase (SPL) is a highly conserved enzyme that catalyses the final step of sphingolipid degradation, namely the irreversible cleavage of the carbon chain at positions 2–3 of a long-chain base phosphate (LCBP), thereby yielding a long-chain aldehyde and phosphoethanolamine. LCBPs are potent signaling molecules involved in cell proliferation, survival, migration, cell–cell interactions and cell stress responses. Therefore, tight regulation of LCBP signaling is required for proper cell function, and perturbations of this system can lead to alterations in biological processes including development, reproduction and physiology. SPL is a key enzyme in regulating the intracellular and circulating levels of LCBPs and is, therefore, gaining attention as a putative target for pharmacological intervention. This review provides an overview of our current understanding of SPL structure and function, mechanisms involved in SPL regulation and the role of SPL in development and disease.
Keywords: Sphingosine-1-phosphate lyase; S1P lyase; Long-chain base; Long-chain phosphorylated base; Sphingolipid; Sphingosine; Dihydrosphingosine;

Regulation and functions of sphingosine kinases in the brain by Lauren Bryan; Tomasz Kordula; Sarah Spiegel; Sheldon Milstien (459-466).
It has long been known that sphingolipids, especially sphingomyelin, a principal component of myelin, are highly enriched in the central nervous system and are structural components of all eukaryotic cell membranes. In the last few years, substantial evidence has accumulated from studies of many types of cells demonstrating that in addition to their structural roles, their breakdown products form a new class of signaling molecules with potent and myriad regulatory effects on essentially every cell in the body. While the sphingolipid metabolites sphingosine and its precursor ceramide have been associated with cell growth arrest and apoptosis, sphingosine-1-phosphate (S1P) enhances proliferation, differentiation, and cell survival as well as regulates many physiological and pathological processes. The relative levels of these three interconvertible sphingolipid metabolites, and thus cell fate, are strongly influenced by the activity of sphingosine kinases, of which there are two isoforms, designated SphK1 and SphK2, the enzymes that phosphorylate sphingosine to produce S1P. Not much is yet known of the importance of S1P in the central nervous system. Therefore, this review is focused on current knowledge of regulation of SphK1 and SphK2 on both transcriptional and post-translational levels and the functions of these isozymes and their product S1P and its receptors in the central nervous system.
Keywords: Sphingosine kinase; Sphingsosine-1-phosphate; Phosphorylation; Transcription; Post-translational modifications; Central nervous system;

Sphingosine 1 phosphate (S1P) and lysophosphatidic acid (LPA) are bioactive lipid phosphates that bind to cell surface G-protein coupled receptors (GPCR) and, in addition, exhibit intracellular actions. We have summarised herein, an important functional interaction between lipid phosphate GPCR and receptor tyrosine kinases (RTK) that enables growth factors to spatially regulate effectors, thereby governing the nature of the biological response. For instance, we describe how the formation of functional complexes between the S1P1 receptor and PDGFβ receptor may effectively re-programme platelet-derived growth factor from a mitogenic to a migratory stimulus. This is achieved by integration of RTK- and GPCR-specific signals that results in spatial regulation of a cytoplasmic retained pool of extracellular signal regulated kinase-1/2 linked to myosin light chain kinase, myosin light chain phosphorylation and migration. We therefore suggest that the lipid phosphate receptor is a major determinant in regulating growth factor-dependent biology. Growth factors can also increase S1P inside cells, and we discuss the concept of spatial/temporal aspects of compartmentalised intracellular signaling of S1P in relation to defined interactions between, for instance, sphingosine kinase, phospholipase D1 and lipid phosphate phosphatases and regulation of cell survival.
Keywords: Sphingosine 1-phosphate; Lysophospatidic acid; PDGF; NGF; Growth factor; Lipid phosphate phosphatase; Sphingosine kinase; Phospholipase D; Integrative signalling;

The vascular S1P gradient—Cellular sources and biological significance by Timothy Hla; Krishnan Venkataraman; Jason Michaud (477-482).
Sphingosine 1-phosphate (S1P), a product of sphingomyelin metabolism, is enriched in the circulatory system whereas it is estimated to be much lower in interstitial fluids of tissues. This concentration gradient, termed the vascular S1P gradient appears to form as a result of substrate availability and the action of metabolic enzymes. S1P levels in blood and lymph are estimated to be in the μM range. In the immune system, the S1P gradient is needed as a spatial cue for lymphocyte and hematopoietic cell trafficking. During inflammatory reactions in which enhanced vascular permeability occurs, a burst of S1P becomes available to its receptors in the extravascular compartment, which likely contributes to the tissue reactions. Thus, the presence of the vascular S1P gradient is thought to contribute to physiological and pathological conditions. From an evolutionary perspective, S1P receptors may have co-evolved with the advent of a closed vascular system and the trafficking paradigms for hematopoietic cells to navigate in and out of the vascular system.
Keywords: Endothelium; Sphingosine 1-phosphate; Vascular biology;

Sphingosine-1-phosphate signaling and biological activities in the cardiovascular system by Yoh Takuwa; Yasuo Okamoto; Kazuaki Yoshioka; Noriko Takuwa (483-488).
The plasma lysophospholipid mediator sphingosine-1-phosphate (S1P) is produced exclusively by sphingosine kinase (SPHK) 1 and SPHK2 in vivo, and plays diverse biological and pathophysiological roles by acting largely through three members of the G protein-coupled S1P receptors, S1P1, S1P2 and S1P3. S1P1 expressed on endothelial cells mediates embryonic vascular maturation and maintains vascular integrity by contributing to eNOS activation, inhibiting vascular permeability and inducing endothelial cell chemotaxis via Gi-coupled mechanisms. By contrast, S1P2, is expressed in high levels on vascular smooth muscle cells (VSMCs) and certain types of tumor cells, inhibiting Rac and cell migration via a G12/13-and Rho-dependent mechanism. In rat neointimal VSMCs, S1P1 is upregulated to mediate local production of platelet-derived growth factor, which is a key player in vascular remodeling. S1P3 expressed on endothelial cells also mediates chemotaxis toward S1P and vasorelaxation via NO production in certain vascular bed, playing protective roles for vascular integrity. S1P3 expressed on VSMCs and cardiac sinoatrial node cells mediates vasopressor and negative chronotropic effect, respectively. In addition, S1P3, together with S1P2 and SPHK1, is suggested to play a protective role against acute myocardial ischemia. However, our recent work indicates that overexpressed SPHK1 is involved in cardiomyocyte degeneration and fibrosis in vivo, in part through S1P activation of the S1P3 signaling. We also demonstrated that exogenously administered S1P accelerates neovascularization and blood flow recovery in ischemic limbs, suggesting its usefulness for angiogenic therapy. These results provide evidence for S1P receptor subtype-specific pharmacological intervention as a novel therapeutic approach to cardiovascular diseases and cancer.
Keywords: Sphingosine-1-phosphate; Sphingosine kinase; S1P Receptor; Signaling; Endothelial cell; Smooth muscle; Cardiomyocyte; Migration; Angiogenesis; Cardiac remodeling;

S1P and eNOS regulation by Junsuke Igarashi; Thomas Michel (489-495).
In the mammalian cardiovascular system, nitric oxide (NO), a small diffusible gaseous signal mediator, plays pivotal roles in the maintenance of vascular homeostasis. The endothelial isoform of nitric oxide synthase (eNOS) is activated by diverse agonist-modulated cell surface receptors, and eNOS-derived NO is a key determinant of blood pressure, platelet activation, angiogenesis and other fundamental responses in the vascular wall. Sphingosine 1-phosphate (S1P) has recently been identified as an important activator of eNOS. This review summarizes the roles of sphingosine 1-phosphate and S1P receptors in eNOS activation, and analyzes the eNOS regulatory processes evoked by S1P. The implications of S1P activation of eNOS in cardiovascular (patho)physiology will be also discussed.
Keywords: eNOS; Caveolae; G-protein coupled receptors; Vascular signaling; Sphingosine 1-phosphate; VEGF;

The bioactive lipid molecule sphingosine 1-phosphate (S1P) binds to specific cell surface receptors and regulates several cellular processes. S1P is abundant in plasma, and physiologically its most important target cells are lymphocytes and vascular endothelial cells. S1P plays a pivotal role in the immune system by regulating lymphocyte egress from the thymus and secondary lymphoid organs. The immunomodulator FTY720 impairs this egress, causing lymphopenia. Platelets had long been considered to be the major source of plasma S1P, however recent studies revealed the importance of erythrocytes as a major supply. The sphingosine analog FTY720 is a prodrug, and FTY720 phosphate (FTY720-P) its functional form. Although both erythrocytes and platelets can produce S1P, only platelets synthesize and release FTY720-P. This review will focus on the recent advances in our understanding of the metabolism and release of S1P and FTY720-P, especially in platelets and erythrocytes.
Keywords: Sphingosine 1-phosphate; FTY720; Erythrocyte; Platelet; Immunomodulator; Sphingolipid;

The lipid mediator sphingosine 1-phosphate (S1P) and its type 1 G protein-coupled receptor (S1P1) affect mammalian immunity through alterations in thymocyte emigration, differentiation of T cell subsets, lymphocyte trafficking in lymphoid organs and other tissues, T cell-dendritic cell and T cell-B cell interactions, and cytokine generation. Recent attention to effects of the S1P-S1P1 axis on non-migration functions of lymphocytes includes delineation of a role in terminal differentiation and survival of Th17 effector cells and adaptive Treg cells of the CD4 T cell constellation, and a greater understanding of interactions of the S1P–S1P1 axis with immune cytokines in lymphocyte survival and activities. This breadth of involvement of the S1P–S1P1 axis in immune responses that often are altered in immunological diseases has provided many opportunities for novel therapeutic interventions. A spectrum of pharmacological and immunochemical agents is available that alter immunity by affecting either tissue and fluid concentrations of S1P or levels of expression and signaling activities of S1P1. Such agents have so far been beneficial in the settings of autoimmunity and rejection of transplanted organs, and are likely to become valuable constituents of combined drug programs.
Keywords: Lipid mediator; Immunoregulation; Inflammation; Lymphocyte migration; Cytokine; Regulatory T cell;

Sphingosine 1-phosphate chemical biology by Kevin R. Lynch; Timothy L. Macdonald (508-512).
A dozen years ago, the term ‘S1P’ (sphingosine 1-phosphate) was not in the lexicons of scientific literature databases. By early 2008, this query term retrieved well over 1000 citations from PubMed — about 225 of these appeared in 2007. Indeed, S1P is arguably the most heavily studied lipid molecule at present. What happened to distinguish S1P among many other signaling lipids? We believe that the seminal event was the linking of the investigational drug, FTY720 (fingolimod), to S1P signaling. This realization profoundly altered understanding of S1P biology, revealing both that S1P is prominent in lymphocyte trafficking and that mimicking S1P signaling with an agonist drug can modulate the immune system to considerable therapeutic benefit. Neither fact was known prior to FTY720; indeed, this molecule is testament to the power of chemical biology. In this communication, we attempt to summarize progress to date in S1P chemical biology.
Keywords: Sphingosine 1-phosphate; S1P; Sphingosine kinase; SPHK; S1P receptor; FTY720; Fingolimod;

Two pathways for lysophosphatidic acid production by Junken Aoki; Asuka Inoue; Shinichi Okudaira (513-518).
Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) is a simple phospholipid but displays an intriguing cell biology that is mediated via interactions with G protein-coupled seven transmembrane receptors (GPCRs). So far, five GPCRs, designated LPA1–5, and, more recently, two additional GPCRs, GPR87 and P2Y5, have been identified as receptors for LPA. These LPA receptors can be classified into two families, the EDG and P2Y families, depending on their primary structures. Recent studies on gene targeting mice and family diseases of these receptors revealed that LPA is involved in both pathological and physiological states including brain development (LPA1), neuropathy pain (LPA1), lung fibrosis (LPA1), renal fibrosis (LPA1) protection against radiation-induced intestinal injury (LPA2), implantation (LPA3) and hair growth (P2Y5). LPA is produced both in cells and biological fluids, where multiple synthetic reactions occur. There are at least two pathways for LPA production. In serum or plasma, LPA is predominantly produced by a plasma enzyme called autotaxin (ATX). ATX is a multifunctional ectoenzyme and is involved in many patho-physiological conditions such as cancer, neuropathy pain, lymphocyte tracking in lymph nodes, obesity, diabetes and embryonic blood vessel formation. LPA is also produced from phosphatidic acid (PA) by its deacylation catalyzed by phospholipase A (PLA)-type enzymes. However, the physiological roles of this pathway as well as the enzymes involved remained to be solved. A number of phospholipase A1 and A2 isozymes could be involved in this pathway. One PA-selective PLA1 called mPA-PLA1α/LIPH is specifically expressed in hair follicles, where it has a critical role in hair growth by producing LPA through a novel LPA receptor called P2Y5.
Keywords: Lysophosphatidic acid; LPA; LPA receptor; G protein-coupled receptor; Autotaxin; mPA-PLA1α/LIPH; P2Y5;

Cyclic phosphatidic acid (CPA) is a naturally occurring analog of the growth factor-like phospholipid mediator, lysophosphatidic acid (LPA). The sn-2 hydroxy group of CPA forms a 5-membered ring with the sn-3 phosphate. CPA affects numerous cellular functions, including anti-mitogenic regulation of the cell cycle, induction of stress fiber formation, inhibition of tumor cell invasion and metastasis, and regulation of differentiation and survival of neuronal cells. Interestingly, many of these cellular responses caused by CPA oppose those of LPA despite the activation of apparently overlapping receptor populations. Since the early 1990s, studies on CPA actions gradually developed, and we are now beginning to understand the importance of this lipid. In this review, we focus on the current knowledge about CPA, including enzymatic formation of CPA, unique biological activities and biological targets of CPA, and we also explore metabolically stabilized CPA analogs.
Keywords: Cyclic phosphatidic acid; Transphosphatidylation; Cancer cell invasion; Tumor metastasis; ATX inhibitor; Anti-cancer drug;

Recent studies have established that autotaxin (ATX), also known as phosphodiesterase Iα/autotaxin (PD-Iα/ATX) or (ecto)nucleotide pyrophosphatase/phosphodiesterase 2 [(E)NPP2], represents a multi-functional and multi-modular protein. ATX was initially thought to function exclusively as a phosphodiesterase/pyrophosphatase. However, it has become apparent that this enzymatically active site, which is ultimately responsible for ATX's originally discovered property of tumor cell motility stimulation, mediates the conversion of lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA). In addition, a separate functionally active domain, here referred to as the Modulator of Oligodendrocyte Remodeling and Focal adhesion Organization (MORFO) domain, was discovered in studies analyzing the role of ATX during the differentiation of myelinating cells of the central nervous system (CNS), namely oligodendrocytes. This novel domain was found to mediate anti-adhesive, i.e. matricellular, properties and to promote morphological maturation of oligodendrocytes. In this review, we summarize our current understanding of ATX's structure–function domains and discuss their contribution to the presently known main functional roles of ATX.
Keywords: Autotaxin; LysoPLD; Phosphodiesterase-Iα; Matricellular; Tumor progression; Vascular development; Oligodendrocyte development;

Biological roles of lysophospholipid receptors revealed by genetic null mice: An update by Ji Woong Choi; Chang-Wook Lee; Jerold Chun (531-539).
Two lysophospholipids (LPs), lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), are known to affect various cellular events. Their actions are mediated by binding to at least ten bona fide high-affinity G protein-coupled receptors referred to as LPA1–5 and S1P1–5. These LPs are expressed throughout the body and are involved in a range of biological activities including normal development, as well as functioning in most organ systems. A growing number of biological functions have been uncovered in vivo using single- or multiple-null mice for each LP receptor. This review will focus on findings from in vivo as well as in vitro studies using genetic null mice for the LP receptors, LPA1,2,3 and S1P1,2,3,5, and for the LP producing enzymes, autotaxin and sphingosine kinase 1/2.
Keywords: LPA; S1P; Sphingosine; Lysophosphatidic acid; Phospholipid; Lysophospholipid;

Bioactive lysophospholipids include lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), cyclic-phosphatidic acid (CPA) and alkyl glycerolphosphate (AGP). These lipid mediators stimulate a variety of responses that include cell survival, proliferation, migration, invasion, wound healing, and angiogenesis. Responses to lysophospholipids depend upon interactions with biomolecular targets in the G protein-coupled receptor (GPCR) and nuclear receptor families, as well as enzymes. Our current understanding of lysophospholipid interactions with these targets is based on a combination of lysophospholipid analog structure activity relationship studies as well as more direct structural characterization techniques such as X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, and experimentally-validated molecular modeling. The direct structural characterization studies are the focus of this review, and provide the insight necessary to stimulate structure-based therapeutic lead discovery efforts in the future.
Keywords: Phospholipid; G protein-coupled receptor; Lysophosphatidic acid; Sphingosine 1-phosphate; Autotaxin; PPAR;

Since the molecular cloning of the vzg-1/Edg-2/LPA1 gene, studies have attempted to characterize LPA1 receptor functionality into a single categorical role, different from the other Edg-family LPA receptors. The desire to categorize LPA1 function has highlighted its complexity and demonstrated that the LPA1 receptor does not have one absolute function throughout every system. The central nervous system is highly enriched in the LPA1 receptor, suggesting an integral role in neuronal processes. Metastatic and invasive breast cancer also appears to have LPA-mediated LPA1 receptor functions that enhance phenotypes associated with tumorigenesis. LPA1 possesses a number of motifs conserved among G protein-coupled receptors (GPCRs): a DRY-like motif, a PDZ domain, Ser/Thr predicted sites of phosphorylation, a di-leucine motif, double cysteines in the tail and conserved residues that stabilize structure and determine ligand binding. The third intracellular loop of the LPA1 receptor may be the crux of receptor signaling and attenuation with phosphorylation of Thr-236 potentially a key determinant of basal LPA1 signaling. Mutagenesis data supports the notion that Thr-236 regulates this process since mutating Thr-236 to Ala-236 increased basal and LPA-mediated serum response factor (SRF) signaling activity and Lys-236 further increased this basal signaling. Here we describe progress on defining the major functions of the LPA1 receptor, discuss a context dependent dualistic role as both a negative regulator in cancer and a proto-oncogene, outline its structural components at the molecular amino acid level and present mutagenesis data on the third intracellular loop of the receptor.
Keywords: LPA1 receptor; LPA; AKT; Mutagenesis; Ovarian cancer; Breast cancer; ICL3;

While it is well known that lysophosphatidic acid (LPA) mediates diverse physiological and pathophysiological responses through the activation of G protein-coupled LPA receptors, the specificity and molecular mechanisms by which different LPA receptors mediate these biological responses remain largely unknown. Recent identification of several PDZ proteins and zinc finger proteins that interact with the carboxyl-terminal tail of the LPA2 receptor provides a considerable progress towards the understanding of the mechanisms how the LPA2 receptor specifically mediates LPA signaling pathways. These findings have led to the proposal that there are at least two distinct protein interaction motifs present in the carboxyl-terminus of the LPA2 receptor. Together, these data provide a new concept that the efficiency and specificity of the LPA2 receptor-mediated signal transduction can be achieved through the cross-regulation between the classical G protein-activated signaling cascades and the interacting partner-mediated signaling pathways.
Keywords: LPA; LPA2 receptor; PDZ; LIM; Zinc finger; Protein–protein interactions;

Roles of lysophosphatidic acid in cardiovascular physiology and disease by Susan S. Smyth; Hsin-Yuan Cheng; Sumitra Miriyala; Manikandan Panchatcharam; Andrew J. Morris (563-570).
The bioactive lipid mediator lysophosphatidic acid (LPA) exerts a range of effects on the cardiovasculature that suggest a role in a variety of critical cardiovascular functions and clinically important cardiovascular diseases. LPA is an activator of platelets from a majority of human donors identifying a possible role as a regulator of acute thrombosis and platelet function in atherogenesis and vascular injury responses. Of particular interest in this context, LPA is an effective phenotypic modulator of vascular smooth muscle cells promoting the de-differentiation, proliferation and migration of these cells that are required for the development of intimal hyperplasia. Exogenous administration of LPA results in acute and systemic changes in blood pressure in different animal species, suggesting a role for LPA in both normal blood pressure regulation and hypertension. Advances in our understanding of the molecular machinery responsible for the synthesis, actions and inactivation of LPA now promise to provide the tools required to define the role of LPA in cardiovascular physiology and disease. In this review we discuss aspects of LPA signaling in the cardiovasculature focusing on recent advances and attempting to highlight presently unresolved issues and promising avenues for further investigation.
Keywords: Lysophosphatidic acid Cardiovascular disease;

The early- and late stages in phenotypic modulation of vascular smooth muscle cells: Differential roles for lysophosphatidic acid by Huazhang Guo; Natalia Makarova; Yunhui Cheng; Shuyu E; Rui-Rui Ji; Chunxiang Zhang; Patricia Farrar; Gabor Tigyi (571-581).
Lysophosphatidic acid (LPA) has been implicated as causative in phenotypic modulation (PM) of cultured vascular smooth muscle cells (VSMC) in their transition to the dedifferentiated phenotype. We evaluated the contribution of the three major LPA receptors, LPA1 and LPA2 GPCR and PPARγ, on PM of VSMC. Expression of differentiated VSMC-specific marker genes, including smooth muscle α-actin, smooth muscle myosin heavy chain, calponin, SM-22α, and h-caldesmon, was measured by quantitative real-time PCR in VSMC cultures and aortic rings kept in serum-free chemically defined medium or serum- or LPA-containing medium using wild-type C57BL/6, LPA1, LPA2, and LPA1&2 receptor knockout mice. Within hours after cells were deprived of physiological cues, the expression of VSMC marker genes, regardless of genotype, rapidly decreased. This early PM was neither prevented by IGF-I, inhibitors of p38, ERK1/2, or PPARγ nor significantly accelerated by LPA or serum. To elucidate the mechanism of PM in vivo, carotid artery ligation with/without replacement of blood with Krebs solution was used to evaluate contributions of blood flow and pressure. Early PM in the common carotid was induced by depressurization regardless of the presence/absence of blood, but eliminating blood flow while maintaining blood pressure or after sham surgery elicited no early PM. The present results indicate that LPA, serum, dissociation of VSMC, IGF-I, p38, ERK1/2, LPA1, and LPA2 are not causative factors of early PM of VSMC. Tensile stress generated by blood pressure may be the fundamental signal maintaining the fully differentiated phenotype of VSMC.
Keywords: LPA; Dedifferentiation; Vascular smooth muscle cell; Aortic ring; Blood pressure; Common carotid artery;

Lysophosphatidic acid and renal fibrosis by Jean-Philippe Pradère; Julien Gonzalez; Julie Klein; Philippe Valet; Sandra Grès; David Salant; Jean-Loup Bascands; Jean-Sébastien Saulnier-Blache; Joost P. Schanstra (582-587).
The development of fibrosis involves a multitude of events and molecules. Until now the majority of these molecules were found to be proteins or peptides. But recent data show significant involvement of the phospholipid lysophosphatidic acid (LPA) in the development of pulmonary, liver and renal fibrosis. The latest data on the role of LPA and the G-protein-coupled LPA1 receptor in the development of renal fibrosis will be discussed. LPA1-receptor activation was found to be associated with increased vascular leakage and increased fibroblast recruitment in pulmonary fibrosis. Furthermore, in renal fibrosis LPA1-receptor activation stimulates macrophage recruitment and connective tissue growth factor expression. The observations make this receptor an interesting alternative and new therapeutic target in fibrotic diseases.
Keywords: Kidney; Fibrosis; Lysophosphatidic acid; Receptor;

Phosphatase-resistant analogues of lysophosphatidic acid: Agonists promote healing, antagonists and autotaxin inhibitors treat cancer by Glenn D. Prestwich; Joanna Gajewiak; Honglu Zhang; Xiaoyu Xu; Guanghui Yang; Monica Serban (588-594).
Isoform-selective agonists and antagonists of the lysophosphatidic acid (LPA) G protein-coupled receptors (GPCRs) have important potential applications in cell biology and therapy. LPA GPCRs regulate cancer cell proliferation, invasion, angiogenesis, and also biochemical resistance to chemotherapy- and radiotherapy-induced apoptosis. LPA and its analogues also are feedback inhibitors of the enzyme lysophospholipase D (lysoPLD, a.k.a., autotaxin, ATX), a central regulator of invasion and metastasis. For cancer therapy, the optimal therapeutic profile would be a metabolically-stabilized, pan-LPA receptor antagonist that also inhibited lysoPLD. For protection of gastrointestinal mucosa and lymphocytes, LPA agonists would be desirable to minimize or reverse radiation or chemical-induced injury. Analogues of lysophosphatidic acid (LPA) that are chemically modified to be less susceptible to phospholipases and phosphatases show activity as long-lived receptor-specific agonists and antagonists for LPA receptors, as well as inhibitors for the lysoPLD activity of ATX.
Keywords: Phosphorothioate; Methylene phosphonate; Aminooxy; Autotaxin; Lysophospholipase D inhibitor; Receptor isoform selectivity; GPCR antagonist; Tumor regression;

Recently, a set of five brain-specifically expressed membrane proteins, which define a novel subclass of the lipid phosphate phosphatases (LPP-)superfamily, has been identified, namely plasticity-related genes (PRGs/LRPs). The primary known significance of these genes is their involvement in regeneration processes and attenuation of effects induced by lysophosphatidic acid (LPA). LPA is key player in lysophospholipids, a hydrophilic group of lipids that have been recognized as important signaling molecules. It is a lipid mediator with a wide variety of biological actions, such as cell proliferation, migration and survival. Its extracellular effects are mediated through five distinct G-protein-coupled receptors (LPA1–5) and LPA therefore activates multiple signal transduction pathways. LPA signaling has been implicated in diverse processes, such as wound healing, brain development, vascular remodeling and tumor progression. LPA levels are controlled by enzymes that synthesize or degrade LPA and, thus, these enzymes also regulate many aspects of signaling transduction. Three LPPs and a splice variant have been demonstrated as deactivating LPA. Studies of PRGs indicate that this group of proteins may in fact serve as controllers of LPA and therefore opening the door to new therapeutic approaches.
Keywords: PRG/LRP; LPA; CNS; Regeneration;