LPA in neural cell development

Schwann cell stimulation induces functional and structural changes in peripheral nerves

Signal propagation is the essential function of nerves. Lysophosphatidic acid 18:1 (LPA) allows the selective stimulation of calcium signaling in Schwann cells but not neurons. Here, the time course of slowing and amplitude reduction on compound action potentials due to LPA exposure was observed in myelinated and unmyelinated fibers of the mouse, indicating a clear change of axonal function. Teased nerve fiber imaging showed that Schwann cell activation is also present in axon-attached Schwann cells in freshly isolated peripheral rat nerves. The LPA receptor 1 was primarily localized at the cell extensions in isolated rat Schwann cells, suggesting a role in cell migration. Structural investigation of rat C-fibers demonstrated that LPA leads to an evagination of the axons from their Schwann cells. In A-fibers, the nodes of Ranvier appeared unchanged, but the Schmidt-Lanterman incisures were shortened and myelination reduced. The latter might increase leak current, reducing the potential spread to the next node of Ranvier and explain the changes in conduction velocity. The observed structural changes provide a plausible explanation for the functional changes in myelinated and unmyelinated axons of peripheral nerves and the reported sensory sensations such as itch and pain.

The lysophosphatidic acid axis in fibrosis: Implications for glaucoma

Glaucoma is a common progressive optic neuropathy that results in visual field defects and can lead to irreversible blindness. The pathophysiology of glaucoma involves dysregulated extracellular matrix remodelling in both the trabecular meshwork in the anterior chamber and in the lamina cribrosa of the optic nerve head. Fibrosis in these regions leads to raised intraocular pressure and retinal ganglion cell degeneration, respectively. Lysophosphatidic acid (LPA) is a bioactive lipid mediator which acts via six G-protein coupled receptors on the cell surface to activate intracellular pathways that promote cell proliferation, transcription and survival. LPA signalling has been implicated in both normal wound healing and pathological fibrosis. LPA enhances fibroblast proliferation, migration and contraction, and induces expression of pro-fibrotic mediators such as connective tissue growth factor. The LPA axis plays a major role in diseases such as idiopathic pulmonary fibrosis, where it has been identified as an important pharmacological target. In glaucoma, LPA is present in high levels in the aqueous humour, and its signalling has been found to increase resistance to aqueous humour outflow through altered trabecular meshwork cellular contraction and extracellular matrix deposition. LPA signalling may, therefore, also represent an attractive target for treatment of glaucoma. In this review we wish to describe the role of LPA and its related proteins in tissue fibrosis and glaucoma.

A novel methylation signature predicts radiotherapy sensitivity in glioma

Glioblastoma (GBM) is the most common and malignant cancer of the central nervous system, and radiotherapy is widely applied in GBM treatment; however, the sensitivity to radiotherapy varies in different patients. To solve this clinical dilemma, a radiosensitivity prediction signature was constructed in the present study based on genomic methylation. In total, 1044 primary GBM samples with clinical and methylation microarray data were involved in this study. LASSO-COX, GSVA, Kaplan–Meier survival curve analysis, and COX regression were performed for the construction and verification of predictive models. The R programming language was used as the main tool for statistical analysis and graphical work. Via the integration analysis of methylation and the survival data of primary GBM, a novel prognostic and radiosensitivity prediction signature was constructed. This signature was found to be stable in prognosis prediction in the TCGA and CGGA databases. The possible mechanism was also explored, and it was found that this signature is closely related to DNA repair functions. Most importantly, this signature could predict whether GBM patients could benefit from radiotherapy. In summary, a radiosensitivity prediction signature for GBM patients based on five methylated probes was constructed, and presents great potential for clinical application.

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.

Lysophosphatidic Acid and Glutamatergic Transmission

Signaling through bioactive lipids regulates nervous system development and functions. Lysophosphatidic acid (LPA), a membrane-derived lipid mediator particularly enriched in brain, is able to induce many responses in neurons and glial cells by affecting key processes like synaptic plasticity, neurogenesis, differentiation and proliferation. Early studies noted sustained elevations of neuronal intracellular calcium, a primary response to LPA exposure, suggesting functional modifications of NMDA and AMPA glutamate receptors. However, the crosstalk between LPA signaling and glutamatergic transmission has only recently been shown. For example, stimulation of presynaptic LPA receptors in hippocampal neurons regulates glutamate release from the presynaptic terminal, and excess of LPA induce seizures. Further evidence indicating a role of LPA in the modulation of neuronal transmission has been inferred from animal models with deficits on LPA receptors, mainly LPA₁ which is the most prevalent receptor in human and mouse brain tissue. LPA₁ null-mice exhibit cognitive and attention deficits characteristic of schizophrenia which are related with altered glutamatergic transmission and reduced neuropathic pain. Furthermore, silencing of LPA₁ receptor in mice induced a severe down-regulation of the main glutaminase isoform (GLS) in cerebral cortex and hippocampus, along with a parallel sharp decrease on active matrix-metalloproteinase 9. The downregulation of both enzymes correlated with an altered morphology of glutamatergic pyramidal cells dendritic spines towards a less mature phenotype, indicating important implications of LPA in synaptic excitatory plasticity which may contribute to the cognitive and memory deficits shown by LPA₁-deficient mice. In this review, we present an updated account of current evidence pointing to important implications of LPA in the modulation of synaptic excitatory transmission.

Inhibition of autotaxin alleviates inflammation and increases the expression of sodium-dependent glucose cotransporter 1 and Na+/H+ exchanger 3 in SAMP1/Fc mice

Crohn's disease (CD) is a chronic, relapsing, inflammatory disease that is often associated with malnutrition because of inflammation in the small intestine. Autotaxin (ATX) is a secreted enzyme that produces extracellular lysophosphatidic acid. Increasing evidence suggests that ATX is upregulated during inflammation, and inhibition of ATX has been effective in attenuating chronic inflammatory conditions, such as arthritis and pulmonary fibrosis. This study aims to determine whether inhibition of ATX alleviates CD-associated inflammation and malnutrition by using SAMP1/Fc mice, a model of CD-like ileitis. SAMP1/Fc mice were treated the ATX inhibitor PF-8380 for 4 wk. Inhibition of ATX led to increased weight gain in SAMP1/Fc mice, decreased T helper 2 cytokine expression, including IL-4, IL-5, and IL-13, and attenuated immune cell migration. SAMP1/Fc mice have low expression of Na⁺-dependent glucose transporter 1 (SGLT1), suggesting impaired nutrient absorption associated with ileitis. PF-8380 treatment significantly enhanced SGLT1 expression in SAMP1/Fc mice, which could reflect the increased weight changes. However, IL-4 or IL-13 did not alter SGLT1 expression in Caco-2 cells, ruling out their direct effects on SGLT1 expression. Immunofluorescence analysis showed that the expression of sucrase-isomaltase, a marker for intestinal epithelial cell (IEC) differentiation, was decreased in inflamed regions of SAMP1/Fc mice, which was partially restored by PF-8380. Moreover, expression of Na⁺/H⁺ exchanger 3 was also improved by PF-8380, suggesting that suppression of inflammation by PF-8380 enhanced IEC differentiation. Our study therefore suggests that ATX is a potential target for treating intestinal inflammation and restoration of the absorptive function of the intestine. NEW & NOTEWORTHY This study is the first, to our knowledge, to determine whether autotoxin (ATX) inhibition improves inflammation and body weights in SAMP1/Fc mice, a mouse model of ileitis. ATX inhibition increased body weights of SAMP1/Fc mice and increased Na⁺-dependent glucose transporter 1 (SGLT1) expression. Increased SGLT1 expression in the inflamed regions was not a direct effect of cytokines but an indirect effect of increased epithelial cell differentiation upon ATX inhibition.

Lysophosphatidic acid provides a missing link between osteoarthritis and joint neuropathic pain

OBJECTIVE

Emerging evidence suggests that osteoarthritis (OA) has a neuropathic component; however, the identity of the molecules responsible for this peripheral neuropathy is unknown. The aim of this study was to determine the contribution of the bioactive lipid lysophosphatidic acid (LPA) to joint neuropathy and pain.

DESIGN

Male Lewis rats received an intra-articular injection of 50 μg of LPA into the knee and allowed to recover for up to 21 days. Saphenous nerve myelination was assessed by g-ratio calculation from electron micrographs and afferent nerve damage visualised by activation transcription factor-3 (ATF-3) expression. Nerve conduction velocity was measured electrophysiologically and joint pain was determined by hindlimb incapacitance. The effect of the LPA antagonist Ki-16425 was also evaluated. Experiments were repeated in the sodium monoiodoacetate (MIA) model of OA.

RESULTS

LPA caused joint nerve demyelination which resulted in a drop in nerve conduction velocity. Sensory neurones were ATF-3 positive and animals exhibited joint pain and knee joint damage. MIA-treated rats also showed signs of demyelination and joint neuropathy with concomitant pain. Nerve damage and pain could be ameliorated by Ki-16425 pre-treatment.

CONCLUSION

Intra-articular injection of LPA caused knee joint neuropathy, joint damage and pain. Pharmacological blockade of LPA receptors inhibited joint nerve damage and hindlimb incapacitance. Thus, LPA is a candidate molecule for the development of OA nerve damage and the origin of joint neuropathic pain.

Effects of gintonin-enriched fraction on hippocampal cell proliferation in wild-type mice and an APPswe/PSEN-1 double Tg mouse model of Alzheimer's disease

We previously showed that gintonin, an exogenous lysophosphatidic acid (LPA) receptor ligand, attenuated β-amyloid plaque formation in the cortex and hippocampus, and restored β-amyloid-induced memory dysfunction. Both endogenous LPA and LPA receptors play a key role in embryonic brain development. However, little is known about whether gintonin can induce hippocampal cell proliferation in adult wild-type mice and an APPswe/PSEN-1 double Tg mouse model of Alzheimer's disease (AD). In the present study, we examined the effects of gintonin on the proliferation of hippocampal neural progenitor cells (NPCs) in vitro and its effects on the hippocampal cell proliferation in wild-type mice and a transgenic AD mouse model. Gintonin treatment increased 5-bromo-2'-deoxyuridine (BrdU) incorporation in hippocampal NPCs in a dose- and time-dependent manner. Gintonin (0.3 μg/ml) increased the immunostaining of glial fibrillary acidic protein, NeuN, and LPA1 receptor in hippocampal NPCs. However, the gintonin-induced increase in BrdU incorporation and immunostaining of biomarkers was blocked by an LPA1/3 receptor antagonist and Ca²⁺ chelator. Oral administration of the gintonin-enriched fraction (50 and 100 mg/kg) increased hippocampal BrdU incorporation and LPA1/3 receptor expression in adult wild-type and transgenic AD mice. The present study showed that gintonin could increase the number of hippocampal neurons in adult wild-type mice and a transgenic AD mouse model. Our results indicate that gintonin-mediated hippocampal cell proliferation contributes to the gintonin-mediated restorative effect against β-amyloid-induced hippocampal dysfunction. These results support the use of gintonin for the prevention or treatment of neurodegenerative diseases such as AD via promotion of hippocampal neurogenesis.

Modulation of Nav1.8 by Lysophosphatidic Acid in the Induction of Bone Cancer Pain

Given that lysophosphatidic acid (LPA) and the tetrodotoxin-resistant sodium channel Nav1.8 are both involved in bone cancer pain, the present study was designed to investigate whether crosstalk between the LPA receptor LPA1 (also known as EDG2) and Nav1.8 in the dorsal root ganglion (DRG) contributes to the induction of bone cancer pain. We showed that the EDG2 antagonist Ki16198 blocked the mechanical allodynia induced by intrathecal LPA in naïve rats and attenuated mechanical allodynia in a rat model of bone cancer. EDG2 and Nav1.8 expression in L4-6 DRGs was upregulated following intrathecal or hindpaw injection of LPA. EDG2 and Nav1.8 expression in ipsilateral L4-6 DRGs increased with the development of bone cancer. Furthermore, we showed that EDG2 co-localized with Nav1.8 and LPA remarkably enhanced Nav1.8 currents in DRG neurons, and this was blocked by either a protein kinase C (PKC) inhibitor or a PKCε inhibitor. Overall, we demonstrated the modulation of Nav1.8 by LPA in DRG neurons, and that this probably underlies the peripheral mechanism by which bone cancer pain is induced.

In vitro models of axon regeneration

A variety of in vitro models have been developed to understand the mechanisms underlying the regenerative failure of central nervous system (CNS) axons, and to guide pre-clinical development of regeneration-promoting therapeutics. These range from single-cell based assays that typically focus on molecular mechanisms to organotypic assays that aim to recapitulate in vivo behavior. By utilizing a combination of models, researchers can balance the speed, convenience, and mechanistic resolution of simpler models with the biological relevance of more complex models. This review will discuss a number of models that have been used to build our understanding of the molecular mechanisms of CNS axon regeneration.

Anatomical location of LPA1 activation and LPA phospholipid precursors in rodent and human brain

Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors: LPA1 -LPA6 . LPA evokes several responses in the CNS, including cortical development and folding, growth of the axonal cone and its retraction process. Those cell processes involve survival, migration, adhesion proliferation, differentiation, and myelination. The anatomical localization of LPA1 is incompletely understood, particularly with regard to LPA binding. Therefore, we have used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 binding sites in adult rodent and human brain. The greatest activity was observed in myelinated areas of the white matter such as corpus callosum, internal capsule and cerebellum. MaLPA1 -null mice (a variant of LPA1 -null) lack [(35) S]GTPγS basal binding in white matter areas, where the LPA1 receptor is expressed at high levels, suggesting a relevant role of the activity of this receptor in the most myelinated brain areas. In addition, phospholipid precursors of LPA were localized by MALDI-IMS in both rodent and human brain slices identifying numerous species of phosphatides and phosphatidylcholines. Both phosphatides and phosphatidylcholines species represent potential LPA precursors. The anatomical distribution of these precursors in rodent and human brain may indicate a metabolic relationship between LPA and LPA1 receptors. Lysophosphatidic acid (LPA) is a signaling molecule that binds to six known G protein-coupled receptors (GPCR), LPA1 to LPA6 . LPA evokes several responses in the central nervous system (CNS), including cortical development and folding, growth of the axonal cone and its retraction process. We used functional [(35) S]GTPγS autoradiography to verify the anatomical distribution of LPA1 -binding sites in adult rodent and human brain. The distribution of LPA1 receptors in rat, mouse and human brains show the highest activity in white matter myelinated areas. The basal and LPA-evoked activities are abolished in MaLPA1 -null mice. The phospholipid precursors of LPA are localized by MALDI-IMS. The anatomical distribution of LPA precursors in rodent and human brain suggests a relationship with functional LPA1 receptors.

Non-cell autonomous and non-catalytic activities of ATX in the developing brain

The intricate formation of the cerebral cortex requires a well-coordinated series of events, which are regulated at the level of cell-autonomous and non-cell autonomous mechanisms. Whereas cell-autonomous mechanisms that regulate cortical development are well-studied, the non-cell autonomous mechanisms remain poorly understood. A non-biased screen allowed us to identify Autotaxin (ATX) as a non-cell autonomous regulator of neural stem cells. ATX (also known as ENPP2) is best known to catalyze lysophosphatidic acid (LPA) production. Our results demonstrate that ATX affects the localization and adhesion of neuronal progenitors in a cell autonomous and non-cell autonomous manner, and strikingly, this activity is independent from its catalytic activity in producing LPA.

K(+) channels: function-structural overview

Potassium channels are particularly important in determining the shape and duration of the action potential, controlling the membrane potential, modulating hormone secretion, epithelial function and, in the case of those K(+) channels activated by Ca(2+), damping excitatory signals. The multiplicity of roles played by K(+) channels is only possible to their mammoth diversity that includes at present 70 K(+) channels encoding genes in mammals. Today, thanks to the use of cloning, mutagenesis, and the more recent structural studies using x-ray crystallography, we are in a unique position to understand the origins of the enormous diversity of this superfamily of ion channels, the roles they play in different cell types, and the relations that exist between structure and function. With the exception of two-pore K(+) channels that are dimers, voltage-dependent K(+) channels are tetrameric assemblies and share an extremely well conserved pore region, in which the ion-selectivity filter resides. In the present overview, we discuss in the function, localization, and the relations between function and structure of the five different subfamilies of K(+) channels: (a) inward rectifiers, Kir; (b) four transmembrane segments-2 pores, K2P; (c) voltage-gated, Kv; (d) the Slo family; and (e) Ca(2+)-activated SK family, SKCa.

Rho/ROCK pathway is essential to the expansion, differentiation, and morphological rearrangements of human neural stem/progenitor cells induced by lysophosphatidic acid

We previously reported that lysophosphatidic acid (LPA) inhibits the neuronal differentiation of human embryonic stem cells (hESC). We extended these studies by analyzing LPA's effects on the expansion of neural stem/progenitor cells (NS/PC) derived from hESCs and human induced pluripotent stem cells (iPSC), and we assessed whether data obtained on the neural differentiation of hESCs were relevant to iPSCs. We showed that hESCs and iPSCs exhibited comparable mRNA expression profiles of LPA receptors and producing enzymes upon neural differentiation. We demonstrated that LPA inhibited the expansion of NS/PCs of both origins, mainly by increased apoptosis in a Rho/Rho-associated kinase (ROCK)-dependent mechanism. Furthermore, LPA inhibited the neuronal differentiation of iPSCs. Lastly, LPA induced neurite retraction of NS/PC-derived early neurons through Rho/ROCK, which was accompanied by myosin light chain (MLC) phosphorylation. Our data demonstrate the consistency of LPA effects across various sources of human NS/PCs, rendering hESCs and iPSCs valuable models for studying lysophospholipid signaling in human neural cells. Our data also highlight the importance of the Rho/ROCK pathway in human NS/PCs. As LPA levels are increased in the central nervous system (CNS) following injury, LPA-mediated effects on NS/PCs and early neurons could contribute to the poor neurogenesis observed in the CNS following injury.

Phospholipases of mineralization competent cells and matrix vesicles: roles in physiological and pathological mineralizations

The present review aims to systematically and critically analyze the current knowledge on phospholipases and their role in physiological and pathological mineralization undertaken by mineralization competent cells. Cellular lipid metabolism plays an important role in biological mineralization. The physiological mechanisms of mineralization are likely to take place in tissues other than in bones and teeth under specific pathological conditions. For instance, vascular calcification in arteries of patients with renal failure, diabetes mellitus or atherosclerosis recapitulates the mechanisms of bone formation. Osteoporosis—a bone resorbing disease—and rheumatoid arthritis originating from the inflammation in the synovium are also affected by cellular lipid metabolism. The focus is on the lipid metabolism due to the effects of dietary lipids on bone health. These and other phenomena indicate that phospholipases may participate in bone remodelling as evidenced by their expression in smooth muscle cells, in bone forming osteoblasts, chondrocytes and in bone resorbing osteoclasts. Among various enzymes involved, phospholipases A₁ or A₂, phospholipase C, phospholipase D, autotaxin and sphingomyelinase are engaged in membrane lipid remodelling during early stages of mineralization and cell maturation in mineralization-competent cells. Numerous experimental evidences suggested that phospholipases exert their action at various stages of mineralization by affecting intracellular signaling and cell differentiation. The lipid metabolites—such as arachidonic acid, lysophospholipids, and sphingosine-1-phosphate are involved in cell signaling and inflammation reactions. Phospholipases are also important members of the cellular machinery engaged in matrix vesicle (MV) biogenesis and exocytosis. They may favour mineral formation inside MVs, may catalyse MV membrane breakdown necessary for the release of mineral deposits into extracellular matrix (ECM), or participate in hydrolysis of ECM. The biological functions of phospholipases are discussed from the perspective of animal and cellular knockout models, as well as disease implications, development of potent inhibitors and therapeutic interventions.

Lack of lipid phosphate phosphatase-3 in embryonic stem cells compromises neuronal differentiation and neurite outgrowth

BACKGROUND

Bioactive lipids such as lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) have been recently described as important regulators of pluripotency and differentiation of embryonic stem (ES) cells and neural progenitors. Due to the early lethality of LPP3, an enzyme that regulates the levels and biological activities of the aforementioned lipids, it has been difficult to assess its participation in early neural differentiation and neuritogenesis.

RESULTS

We find that Ppap2b(-/-) (Lpp3(-/-) ) ES cells differentiated in vitro into spinal neurons show a considerable reduction in the amount of neural precursors and young neurons formed. In addition, differentiated Lpp3(-/-) neurons exhibit impaired neurite outgrowth. Surprisingly, when Lpp3(-/-) ES cells were differentiated, an unexpected appearance of smooth muscle actin-positive cells was observed, an event that was partially dependent upon phosphorylated sphingosines.

CONCLUSIONS

Our data show that LPP3 plays a fundamental role during spinal neuron differentiation from ES and that it also participates in regulating neurite and axon outgrowth.

Blockage of lysophosphatidic acid signaling improves spinal cord injury outcomes

Evidence suggests a proinflammatory role of lysophosphatidic acid (LPA) in various pathologic abnormalities, including in the central nervous system. Herein, we describe LPA as an important mediator of inflammation after spinal cord injury (SCI) in zebrafish and mice. Furthermore, we describe a novel monoclonal blocking antibody raised against LPA that potently inhibits LPA's effect in vitro and in vivo. This antibody, B3, specifically binds LPA, prevents it from interacting with its complement of receptors, and blocks LPA's effects on the neuronal differentiation of human neural stem/progenitor cells, demonstrating its specificity toward LPA signaling. When administered systemically to mice subjected to SCI, B3 substantially reduced glial inflammation and neuronal death. B3-treated animals demonstrated significantly more neuronal survival upstream of the lesion site, with some functional improvement. This study describes the use of anti-LPA monoclonal antibody as a novel therapeutic approach for the treatment of SCI.

Lysophosphatidic acid induces neurite branch formation through LPA3

Although neurite branching is crucial for neuronal network formation after birth, its underlying mechanisms remain unclear. Here, we demonstrate that lysophosphatidic acid (LPA) stimulates neurite branching through a novel signaling pathway. Treatment of neuronal cell lines with LPA resulted in neurite branch formation when LPA(3) receptor was introduced. The effects of LPA were blocked by inhibition of G(q) signaling. Furthermore, expression of inhibitory mutants of the small GTPase Rnd2/Rho7 or an Rnd2 effector rapostlin abolished LPA(3)-mediated neurite branching. The LPA(3) agonist 2(S)-OMPT or LPA also induced axonal branch formation in hippocampal neurons, which was blocked by G(q) and Rnd2 pathway inhibition or LPA(3) knockdown. These findings suggest that the novel signaling pathway involving LPA(3), G(q), and Rnd2 may play an important role in neuronal network formation.

Lpa2 is a negative regulator of both dendritic cell activation and murine models of allergic lung inflammation

Negative regulation of innate immune responses is essential to prevent excess inflammation and tissue injury and promote homeostasis. Lysophosphatidic acid (LPA) is a pleiotropic lipid that regulates cell growth, migration, and activation and is constitutively produced at low levels in tissues and in serum. Extracellular LPA binds to specific G protein-coupled receptors, whose function in regulating innate or adaptive immune responses remains poorly understood. Of the classical LPA receptors belonging to the Edg family, lpa2 (edg4) is expressed by dendritic cells (DC) and other innate immune cells. In this article, we show that DC from lpa2(-/-) mice are hyperactive compared with their wild-type counterparts and are less susceptible to inhibition by different LPA species. In transient-transfection assays, we found that lpa2 overexpression inhibits NF-κB-driven gene transcription. Using an adoptive-transfer approach, we found that allergen-pulsed lpa2(-/-) DC induced substantially more lung inflammation than did wild-type DC after inhaled allergen challenge. Finally, lpa2(-/-) mice develop greater allergen-driven lung inflammation than do their wild-type counterparts in models of allergic asthma involving both systemic and mucosal sensitization. Taken together, these findings identify LPA acting via lpa2 as a novel negative regulatory pathway that inhibits DC activation and allergic airway inflammation.

Abnormalities in α/β-CaMKII and related mechanisms suggest synaptic dysfunction in hippocampus of LPA1 receptor knockout mice

Lysophosphatidic acid (LPA) is a natural lysophospholipid that regulates neuronal maturation. In mice, the deletion of the LPA1 receptor causes some phenotypic defects partly overlapping with those found in schizophrenia. In this study, we identified molecular abnormalities in hippocampal synaptic mechanisms involved in glutamatergic neurotransmission, which allow further characterization of synaptic aberrations in LPA1 knockout (KO) mice. At the synaptic level, we found dysregulation of Ca2+/calmodulin (CaM)-dependent kinase II (CaMKII) activity and phosphorylation, with markedly higher Ca2+-dependent kinase activity, probably related to increased expression levels of the β isoform of CaMKII. Conversely, although the synaptic Ca2+-independent activity of the enzyme was unchanged, autophosphorylation levels of both α and β isoforms were significantly increased in LPA1 KO mice. Moreover, in LPA1 KO mice the α/β isoform ratio of CaMKII, which plays a key role in neuronal maturation during development, was markedly decreased, as found previously in schizophrenia patients. At post-synaptic level, LPA1 KO mice showed changes in expression, phosphorylation and interactions of NMDA and AMPA receptor subunits that are consistent with basal strengthening of glutamatergic synapses. However, we measured a reduction of nuclear cAMP responsive element-binding protein phosphorylation, suggesting that activation of the NMDA receptor does not occur at the intracellular signalling level. At the presynaptic level, in line with previous evidence from schizophrenia patients and animal models of pathology, LPA1 KO mice showed accumulation of SNARE protein complexes. This study shows that CaMKII and related synaptic mechanisms at glutamatergic synapses are strongly dysregulated in LPA1 KO mice.

Coordinated interactions between actin and microtubules through crosslinkers in neurite retraction induced by lysophosphatidic acid

Neurite development requires rearrangement of cytoskeletal elements, which are mechanically and functionally integrated with each other. Although the process of how an extracellular signal induces rearrangement of a single element has been closely examined, the mechanisms by which the signal regulates cytoskeletal integration during cell shape changes are poorly understood. We previously reported that lysophosphatidic acid (LPA) induces actin polymerization-dependent microtubule (MT) rearrangement, leading to neurite retraction in cultured neurons. Here we examined whether the crosslinker proteins were involved in LPA-induced neurite retraction using immortalized mouse neuroblast TR cells. When the MT-binding domains of MACF (MT actin-crosslinking factor) were exogenously expressed in TR cells, MTs were found to be stabilized and become resistant to exposure to LPA. On the other hand, expression of MT-associated protein 2c showed no effect on LPA-induced neurite retraction. These findings suggest that MACF is involved in actin-dependent MT rearrangement during LPA-induced neurite retraction.

Mechanism of sphingosine 1-phosphate- and lysophosphatidic acid-induced up-regulation of adhesion molecules and eosinophil chemoattractant in nerve cells

The lysophospholipids sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) act via G-protein coupled receptors S1P(1-5) and LPA(1-3) respectively, and are implicated in allergy. Eosinophils accumulate at innervating cholinergic nerves in asthma and adhere to nerve cells via intercellular adhesion molecule-1 (ICAM-1). IMR-32 neuroblastoma cells were used as an in vitro cholinergic nerve cell model. The G(i) coupled receptors S1P(1), S1P(3), LPA(1), LPA(2) and LPA(3) were expressed on IMR-32 cells. Both S1P and LPA induced ERK phosphorylation and ERK- and G(i)-dependent up-regulation of ICAM-1 expression, with differing time courses. LPA also induced ERK- and G(i)-dependent up-regulation of the eosinophil chemoattractant, CCL-26. The eosinophil granule protein eosinophil peroxidase (EPO) induced ERK-dependent up-regulation of transcription of S1P(1), LPA(1), LPA(2) and LPA(3), providing the situation whereby eosinophil granule proteins may enhance S1P- and/or LPA- induced eosinophil accumulation at nerve cells in allergic conditions.

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.

Lysophosphatidic acid is a lipid mediator with wide range of biological activities. Biosynthetic pathways and mechanism of action

Lysophosphatidic acid (LPA) is a lipid mediator required for maintaining homeostasis of numerous physiological functions and also involved in development of some pathological processes through interactions with G protein-coupled receptors. Recently many data have appeared about the role of this phospholipid in humans, but pathways of LPA biosynthesis and mechanisms of its action remain unclear. This review presents modern concepts about biosynthesis, reception, and biological activity of LPA in humans. Natural and synthetic LPA analogs are considered in the view of their possible use in pharmacology as agonists and/or antagonists of G protein-coupled receptors of LPA.

Fasudil protects cultured N1E-115 cells against lysophosphatidic acid-induced neurite retraction through inhibition of Rho-kinase

The aim of this study was to investigate the possible effects of the Rho-kinase inhibitor, fasudil, on the lysophosphatidic acid (LPA)-induced neurite retraction in N1E-115 cells. In cultured N1E-115 cells, LPA produced a marked increase in the population of rounded cells. Fasudil or hydroxyfasudil, an active metabolite of fasudil, blocked cell rounding in a concentration-dependent manner at levels between 1 and 10 μM, with IC₅₀ values of 1.7 or 1.6 μM, respectively. Fasudil or hydroxyfasudil concentration-dependently inhibited phosphorylation of the myosin binding subunit of myosin phosphatase in N1E-115 cells. These results indicate that Rho-kinase is essential for LPA-induced neurite retraction in N1E-115 cells and that inactivation of Rho-kinase by a Rho-kinase inhibitor, such as fasudil, eliminates cell rounding and promotes neurite outgrowth, thus improving neurological function in the brain damage.

ATX expression and LPA signalling are vital for the development of the nervous system

Autotaxin (ATX) is a secreted glycoprotein widely present in biological fluids, originally isolated from the supernatant of melanoma cells as an autocrine motility stimulation factor. Its enzymatic product, lysophosphatidic acid (LPA), is a phospholipid mediator that evokes growth-factor-like responses in almost all cell types through G-protein coupled receptors. To assess the role of ATX and LPA signalling in pathophysiology, a conditional knockout mouse was created. Ubiquitous, obligatory deletion resulted to embryonic lethality most likely due to aberrant vascular branching morphogenesis and chorio-allantoic fusion. Moreover, the observed phenotype was shown to be entirely depended on embryonic, but not extraembryonic or maternal ATX expression. In addition, E9.5 ATX null mutants exhibited a failure of neural tube closure, most likely independent of the circulatory failure, which correlated with decreased cell proliferation and increased cell death. More importantly, neurite outgrowth in embryo explants was severely compromised in mutant embryos but could be rescued upon the addition of LPA, thus confirming a role for ATX and LPA signalling in the development of the nervous system. Finally, expression profiling of mutant embryos revealed attenuated embryonic expression of HIF-1a in the absence of ATX, suggesting a novel effector pathway of ATX/LPA.

Human neural progenitors express functional lysophospholipid receptors that regulate cell growth and morphology

Background

Lysophospholipids regulate the morphology and growth of neurons, neural cell lines, and neural progenitors. A stable human neural progenitor cell line is not currently available in which to study the role of lysophospholipids in human neural development. We recently established a stable, adherent human embryonic stem cell-derived neuroepithelial (hES-NEP) cell line which recapitulates morphological and phenotypic features of neural progenitor cells isolated from fetal tissue. The goal of this study was to determine if hES-NEP cells express functional lysophospholipid receptors, and if activation of these receptors mediates cellular responses critical for neural development.

Results

Our results demonstrate that Lysophosphatidic Acid (LPA) and Sphingosine-1-phosphate (S1P) receptors are functionally expressed in hES-NEP cells and are coupled to multiple cellular signaling pathways. We have shown that transcript levels for S1P1 receptor increased significantly in the transition from embryonic stem cell to hES-NEP. hES-NEP cells express LPA and S1P receptors coupled to G_i/o G-proteins that inhibit adenylyl cyclase and to G_q-like phospholipase C activity. LPA and S1P also induce p44/42 ERK MAP kinase phosphorylation in these cells and stimulate cell proliferation via G_i/o coupled receptors in an Epidermal Growth Factor Receptor (EGFR)- and ERK-dependent pathway. In contrast, LPA and S1P stimulate transient cell rounding and aggregation that is independent of EGFR and ERK, but dependent on the Rho effector p160 ROCK.

Conclusion

Thus, lysophospholipids regulate neural progenitor growth and morphology through distinct mechanisms. These findings establish human ES cell-derived NEP cells as a model system for studying the role of lysophospholipids in neural progenitors.

Antagonistic regulation of neurite morphology through Gq/G11 and G12/G13

The induction of neurite retraction and growth cone collapse via G-protein-coupled receptors is involved in developmental as well as regenerative processes. The role of individual G-protein-mediated signaling processes in the regulation of neurite morphology is still incompletely understood. Using primary neurons from brains lacking Galpha(q)/Galpha(11) or Galpha(12)/Galpha(13), we show here that G(12)/G(13)-mediated signaling is absolutely required for neurite retraction and growth cone collapse induced by the blood-borne factors lysophosphatidic acid and thrombin. Interestingly, the effects of lysophosphatidic acid were mediated mainly by G(13), whereas thrombin effects required G(12). Surprisingly, lack of Galpha(q)/Galpha(11) resulted in overshooting responses to both stimuli, indicating that G(q)/G(11)-mediated signaling most likely via activation of Rac antagonizes the effects of G(12)/G(13).

Autotaxin (ATX): a multi-functional and multi-modular protein possessing enzymatic lysoPLD activity and matricellular properties

Recent studies have established that autotaxin (ATX), also known as phosphodiesterase Ialpha/autotaxin (PD-Ialpha/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.

Deletion of lysophosphatidic acid receptor LPA1 reduces neurogenesis in the mouse dentate gyrus

Neurogenesis persists in certain regions of the adult brain including the subgranular zone of the hippocampal dentate gyrus wherein its regulation is essential, particularly in relation to learning, stress and modulation of mood. Lysophosphatidic acid (LPA) is an extracellular signaling phospholipid with important neural regulatory properties mediated by specific G protein-coupled receptors, LPA(1-5). LPA(1) is highly expressed in the developing neurogenic ventricular zone wherein it is required for normal embryonic neurogenesis, and, by extension may play a role in adult neurogenesis as well. By means of the analyses of a variant of the original LPA(1)-null mutant mouse, termed the Malaga variant or "maLPA(1)-null," which has recently been reported to have defective neurogenesis within the embryonic cerebral cortex, we report here a role for LPA(1) in adult hippocampal neurogenesis. Proliferation, differentiation and survival of newly formed neurons are defective in the absence of LPA(1) under normal conditions and following exposure to enriched environment and voluntary exercise. Furthermore, analysis of trophic factors in maLPA(1)-null mice demonstrated alterations in brain-derived neurotrophic factor and insulin growth factor 1 levels after enrichment and exercise. Morphological analyses of doublecortin positive cells revealed the anomalous prevalence of bipolar cells in the subgranular zone, supporting the operation of LPA(1) signaling pathways in normal proliferation, maturation and differentiation of neuronal precursors.

Propofol causes neurite retraction in neurones

BACKGROUND

The mechanism by which anaesthetic agents produce general anaesthesia is not yet fully understood. Retraction of neurites is an important function of individual neurones and neural plexuses during normal and pathological conditions, and it has been shown that such a retraction pathway exists in developing and mature neurones. We hypothesized that propofol decreases neuronal activity by causing retraction of neuronal neurites.

METHODS

Primary cultures of rat cortical neurones were exposed in concentration- and time-response experiments to 0.02, 0.2, 2, and 20 microM propofol or lipid vehicle. Neurones were pretreated with the GABA(A) receptor (GABA(A)R) antagonist, bicuculline, the myosin II ATPase activity inhibitor, blebbistatin, and the F-actin stabilizing agent, phalloidin, followed by administration of propofol (20 microM). Changes in neurite retraction were evaluated using time-lapse light microscopy.

RESULTS

Propofol caused a concentration- and time-dependent reversible retraction of cultured cortical neurone neurites. Bicuculline, blebbistatin, and phalloidin completely inhibited propofol-induced neurite retraction. Images of retracted neurites were characterized by a retraction bulb and a thin trailing membrane remnant.

CONCLUSIONS

Cultured cortical rat neurones retract their neurites after exposure to propofol in a concentration- and time-dependent manner. This retraction is GABA(A)R mediated, reversible, and dependent on actin and myosin II. Furthermore, the concentrations and times to full retraction and recovery correspond to those observed during propofol anaesthesia.

A role for S1P signalling in axon guidance in the Xenopus visual system

Sphingosine 1-phosphate (S1P), a lysophospholipid, plays an important chemotactic role in the migration of lymphocytes and germ cells, and is known to regulate aspects of central nervous system development such as neurogenesis and neuronal migration. Its role in axon guidance, however, has not been examined. We show that sphingosine kinase 1, an enzyme that generates S1P, is expressed in areas surrounding the Xenopus retinal axon pathway, and that gain or loss of S1P function in vivo causes errors in axon navigation. Chemotropic assays reveal that S1P elicits fast repulsive responses in retinal growth cones. These responses require heparan sulfate, are sensitive to inhibitors of proteasomal degradation, and involve RhoA and LIM kinase activation. Together, the data identify downstream components that mediate S1P-induced growth cone responses and implicate S1P signalling in axon guidance.

Lysophosphatidic acid-LPA1 receptor-Rho-Rho kinase-induced up-regulation of Nav1.7 sodium channel mRNA and protein in adrenal chromaffin cells: enhancement of 22Na+ influx, 45Ca2+ influx and catecholamine secretion

In cultured bovine adrenal chromaffin cells, chronic (> or = 24 h) treatment with lysophosphatidic acid (LPA) augmented veratridine-induced 22Na+ influx via Na(v)1.7 by approximately 22% (EC(50) = 1 nmol/L), without changing nicotine-induced 22Na+ influx via nicotinic receptor-associated channel. LPA enhanced veratridine (but not nicotine)-induced 45Ca2+ influx via voltage-dependent calcium channel and catecholamine secretion. LPA shifted concentration-response curve of veratridine for 22Na+ influx upward, without altering the EC(50) of veratridine. Ptychodiscus brevis toxin-3 allosterically enhanced veratridine-induced 22Na+ influx by twofold in non-treated and LPA-treated cells. Whole-cell patch-clamp analysis showed that peak Na+ current amplitude was greater by 39% in LPA (100 nmol/L for 36 h)-treated cells; however, I-V curve and steady-state inactivation/activation curves were comparable between non-treated and LPA-treated cells. LPA treatment (> or = 24 h) increased cell surface [3H]saxitoxin binding by approximately 28%, without altering the K(d) value; the increase was prevented by cycloheximide, actinomycin D, or Ki16425, dioctylglycerol pyrophosphate 8:0 (two inhibitors of LPA(1) and LPA3 receptors), or botulinum toxin C3 (Rho inhibitor), Y27632 (Rho kinase inhibitor), consistent with LPA(1) receptor expression in adrenal chromaffin cells. LPA raised Nav1.7 mRNA level by approximately 37%. Thus, LPA-LPA(1) receptor-Rho/Rho kinase pathway up-regulated cell surface Nav1.7 and Nav1.7 mRNA levels, enhancing veratridine-induced Ca2+ influx and catecholamine secretion.

Stem cell regulation by lysophospholipids

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) regulate a diverse range of mammalian cell processes, largely through engaging multiple G protein-coupled receptors specific for these lysophospholipids. LPA and S1P have been clearly identified to have widespread physiological and pathophysiological actions, controlling events within the reproductive, gastrointestinal, vascular, nervous and immune systems, and also having a prominent role in cancer. Here we review the recent literature showing the additional emerging role for LPA and S1P in the regulation of stem cells and their progenitors. We discuss the role of these lysophospholipids in regulating the proliferation, survival, differentiation and migration of a range of adult and embryonic stem cells and progenitors, and thus are likely to play a substantial role in the maintenance, generation, mobilisation and homing of stem cell and progenitor populations in the body.

Absence of LPA1 signaling results in defective cortical development

Lysophosphatidic acid (LPA) is a simple phospholipid with extracellular signaling properties mediated by specific G protein-coupled receptors. At least 2 LPA receptors, LPA(1) and LPA(2), are expressed in the developing brain, the former enriched in the neurogenic ventricular zone (VZ), suggesting a normal role in neurogenesis. Despite numerous studies reporting the effects of exogenous LPA using in vitro neural models, the first LPA(1) loss-of-function mutants reported did not show gross cerebral cortical defects in the 50% that survived perinatal demise. Here, we report a role for LPA(1) in cortical neural precursors resulting from analysis of a variant of a previously characterized LPA(1)-null mutant that arose spontaneously during colony expansion. These LPA(1)-null mice, termed maLPA(1), exhibit almost complete perinatal viability and show a reduced VZ, altered neuronal markers, and increased cortical cell death that results in a loss of cortical layer cellularity in adults. These data support LPA(1) function in normal cortical development and suggest that the presence of genetic modifiers of LPA(1) influences cerebral cortical development.

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

Lysophosphatidic acid (LPA) is a potent lipid mediator that evokes a variety of biological responses in many cell types via its specific G protein-coupled receptors. In particular, LPA affects cell morphology, cell survival, and cell cycle progression in neuronal cells. Recently, we identified p2y(9)/GPR23 as a novel fourth LPA receptor, LPA(4) (Noguchi, K., Ishii, S., and Shimizu, T. (2003) J. Biol. Chem. 278, 25600-25606). To assess the functions of LPA(4) in neuronal cells, we used rat neuroblastoma B103 cells that lack endogenous responses to LPA. In B103 cells stably expressing LPA(4), we observed G(q/11)-dependent calcium mobilization, but LPA did not affect adenylyl cyclase activity. In LPA(4) transfectants, LPA induced dramatic morphological changes, i.e. neurite retraction, cell aggregation, and cadherin-dependent cell adhesion, which involved Rho-mediated signaling pathways. Thus, our results demonstrated that LPA(4) as well as LPA(1) couple to G(q/11) and G(12/13), whereas LPA(4) differs from LPA(1) in that it does not couple to G(i/o). Through neurite retraction and cell aggregation, LPA(4) may play a role in neuronal development such as neurogenesis and neuronal migration.

Synthesis of Cyclic Phosphonate Analogues of (Lyso)phosphatidic Acid Using a Ring-Closing Metathesis Reaction

We describe a versatile and efficient method for the preparation of acyloxy-substituted six-membered cyclic phosphonates using the ring-closing metathesis. After closure, the key cyclic phosphonate intermediate was dihydroxylated and converted to a new class of conformationally constrained PA and LPA analogues. The oleoyloxy-substituted cyclic phosphonate 4 had unique receptor-selective properties as a ligand, showing partial activation of the LPA2 GPCR and weak antagonism of the LPA1 GPCR.

Actomyosin-dependent microtubule rearrangement in lysophosphatidic acid-induced neurite remodeling of young cortical neurons

It has been shown that lysophosphatidic acid (LPA), a signaling phospholipid, induces neurite retraction and the formation of retraction fibers in young cortical neurons by actin rearrangement. This study examined the rearrangement of microtubules (MTs) during LPA-induced neurite remodeling by immunostaining with antibodies against several types of tubulin. The results showed that alpha-tubulin was present in growing neurites as well as in cell bodies with various localization profiles. Exposure of neurons to LPA resulted in neurite retraction, accompanied by the rearrangement of MTs in neurites and the accumulation of MTs in cell bodies, without significant changes in the total amount of MTs in the cytoskeletal fraction of cultured neurons. Similar findings were obtained when young neurons were stained for other types of tubulin, including beta-tubulin type III and posttranslationally acetylated and tyrosinated tubulin. LPA-induced MT rearrangement was accompanied by accumulation of myosin IIB and polymerized actin at the base of retraction fibers. These effects of LPA on MTs and myosin IIB were blocked by pretreatment with inhibitors of the actomyosin and Rho pathways (cytochalasin D, blebbistatin, and Y27632), but not by an MT stabilizer (taxol), whereas taxol inhibited neurite retraction and MT depolymerization induced by nocodazole. Furthermore, neurofilaments also showed rearrangement in response to LPA, which was blocked by cytochalasin D and Y27632, but not taxol. Taken together, these results suggested that LPA did not induce MT depolymerization and that LPA-induced actomyosin activation produced MT and neurofilament rearrangement, leading to neurite remodeling.

Phosphodiesterase-Ialpha/autotaxin (PD-Ialpha/ATX): a multifunctional protein involved in central nervous system development and disease

Phosphodiesterase-Ialpha/autotaxin (PD-Ialpha/ATX) was originally identified as a cell-motility-stimulating factor secreted by a variety of tumor cells. Thus, studies related to its potential functional roles have traditionally focused on tumorigenesis. PD-Ialpha/ATX's catalytic activity, initially defined as nucleotide pyrophosphatase/phosphodiesterase, was soon recognized as being necessary for its tumor cell-motility-stimulating activity. However, only the discovery of PD-Ialpha/ATX's identity with lysophospholipase D, an extracellular enzyme that converts lysophosphatidylcholine into lysophosphatidic acid (LPA) and potentially sphingosylphosphoryl choline into sphingosine 1-phosphate (S1P), revealed the actual effectors responsible for PD-Ialpha/ATX's ascribed motogenic functions, i.e., its catalytic products. PD-Ialpha/ATX has also been detected during normal development in a number of tissues, in particular, the central nervous system (CNS), where expression levels are high. Similar to tumor cells, PD-Ialpha/ATX-expressing CNS cells secrete catalytically active PD-Ialpha/ATX into the extracellular environment. Thus, it appears reasonable to assume that PD-Ialpha/ATX's CNS-related functions are mediated via lysophospholipid, LPA and potentially S1P, signaling. However, recent studies identified PD-Ialpha/ATX as a matricellular protein involved in the modulation of oligodendrocyte-extracellular matrix interactions and oligodendrocyte remodeling. This property of PD-Ialpha/ATX was found to be independent of its catalytic activity and to be mediated by a novel functionally active domain. These findings, therefore, uncover PD-Ialpha/ATX, at least in the CNS, as a multifunctional protein able to induce complex signaling cascades via distinct structure-function domains. This Mini-Review describes PD-Ialpha/ATX's multifunctional roles in the CNS and discusses their potential contributions to CNS development and pathology.

NPP-type ectophosphodiesterases: unity in diversity

Nucleotide pyrophosphatase/phosphodiesterase (NPP)-type ectophosphodiesterases are found at the cell surface as type-I or type-II transmembrane proteins, but are also found extracellularly as secreted or shedded enzymes. They hydrolyze pyrophosphate or phosphodiester bonds in a variety of extracellular compounds including nucleotides, (lyso)phospholipids and choline phosphate esters. Despite their structurally related catalytic domain, each enzyme has well-defined substrate specificity. Catalysis by NPPs affects processes as diverse as cell proliferation and motility, angiogenesis, bone mineralization and digestion. In addition, there is emerging evidence for non-catalytic functions of NPPs in cell signaling. NPP-type ectophosphodiesterases are also implicated in the pathophysiology of cancer, insulin resistance and calcification diseases, and they hold great promise as easily accessible therapeutic targets.