Synaptic PRG-1 modulates excitatory transmission via lipid phosphate-mediated signaling

Plasticity related gene-1 (PRG-1) is a brain-specific membrane protein related to lipid phosphate phosphatases, which acts in the hippocampus specifically at the excitatory synapse terminating on glutamatergic neurons. Deletion of prg-1 in mice leads to epileptic seizures and augmentation of EPSCs, but not IPSCs. In utero electroporation of PRG-1 into deficient animals revealed that PRG-1 modulates excitation at the synaptic junction. Mutation of the extracellular domain of PRG-1 crucial for its interaction with lysophosphatidic acid (LPA) abolished the ability to prevent hyperexcitability. As LPA application in vitro induced hyperexcitability in wild-type but not in LPA(2) receptor-deficient animals, and uptake of phospholipids is reduced in PRG-1-deficient neurons, we assessed PRG-1/LPA(2) receptor-deficient animals, and found that the pathophysiology observed in the PRG-1-deficient mice was fully reverted. Thus, we propose PRG-1 as an important player in the modulatory control of hippocampal excitability dependent on presynaptic LPA(2) receptor signaling.

S1P3-mediated cardiac fibrosis in sphingosine kinase 1 transgenic mice involves reactive oxygen species

AIMS

Sphingosine kinase 1 (SPHK1), its product sphingosine-1-phosphate (S1P), and S1P receptor subtypes have been suggested to play protective roles for cardiomyocytes in animal models of ischaemic preconditioning and cardiac ischaemia/reperfusion injury. To get more insight into roles for SPHK1 in vivo, we have generated SPHK1-transgenic (TG) mice and analysed the cardiac phenotype.

METHODS AND RESULTS

SPHK1-TG mice overexpressed SPHK1 in diverse tissues, with a nearly 20-fold increase in enzymatic activity. The TG mice grew normally with normal blood chemistry, cell counts, heart rate, and blood pressure. Unexpectedly, TG mice with high but not low expression levels of SPHK1 developed progressive myocardial degeneration and fibrosis, with upregulation of embryonic genes, elevated RhoA and Rac1 activity, stimulation of Smad3 phosphorylation, and increased levels of oxidative stress markers. Treatment of juvenile TG mice with pitavastatin, an established inhibitor of the Rho family G proteins, or deletion of S1P3, a major myocardial S1P receptor subtype that couples to Rho GTPases and transactivates Smad signalling, both inhibited cardiac fibrosis with concomitant inhibition of SPHK1-dependent Smad-3 phosphorylation. In addition, the anti-oxidant N-2-mercaptopropyonylglycine, which reduces reactive oxygen species (ROS), also inhibited cardiac fibrosis. In in vivo ischaemia/reperfusion injury, the size of myocardial infarct was 30% decreased in SPHK1-TG mice compared with wild-type mice.

CONCLUSION

These results suggest that chronic activation of SPHK1-S1P signalling results in both pathological cardiac remodelling through ROS mediated by S1P3 and favourable cardioprotective effects.

A reevaluation of tetraploidy in the Alzheimer's disease brain

Alzheimer's disease (AD) is characterized by extensive neuronal death in distinct brain regions, including the frontal cortex and hippocampus, although the specific mechanisms of neuronal degeneration in AD remain a topic of intense scientific pursuit. One model for cell death in AD postulates that abortive cell cycle events in neurons, including tetraploidy, precede neuronal death, and novel therapeutics based on suppressing cell cycle re-entry are being pursued. Using DNA content fluorescence-activated cell sorting combined with fluorescence in situ hybridization and immunostaining, we analyzed neuronal nuclei from postmortem human brain samples from the frontal cortex and hippocampus of nondiseased and AD patients for evidence of tetraploidy. Here, we show that tetraploid nuclei are similarly prevalent in AD and control brains and are exclusively non-neuronal, contrasting with an absence of tetraploid neurons. Our findings demonstrate that neuronal tetraploidy is nonexistent in the AD brain and intimate a reevaluation of neuronal cell cycle re-entry as a therapeutic target for AD.

Identification of neural programmed cell death through the detection of DNA fragmentation in situ and by PCR

Programmed cell death is a fundamental process for the development and somatic maintenance of organisms. This unit describes methods for visualizing both dying cells in situ and for detection of nucleosomal ladders. A description of various current detection strategies is provided, as well as support protocols for preparing positive and negative controls and for preparing genomic DNA.

Behavioral phenotype of maLPA1-null mice: increased anxiety-like behavior and spatial memory deficits

Lysophosphatidic acid (LPA) has emerged as a new regulatory molecule in the brain. Recently, some studies have shown a role for this molecule and its LPA(1) receptor in the regulation of plasticity and neurogenesis in the adult brain. However, no systematic studies have been conducted to investigate whether the LPA(1) receptor is involved in behavior. In this study, we studied the phenotype of maLPA(1)-null mice, which bear a targeted deletion at the lpa(1) locus, in a battery of tests examining neurologic performance, habituation in exploratory behavior in response to low and mild anxiety environments and spatial memory. MaLPA(1)-null mutants showed deficits in both olfaction and somesthesis, but not in retinal or auditory functions. Sensorimotor co-ordination was impaired only in the equilibrium and grasping reflexes. The mice also showed impairments in neuromuscular strength and analgesic response. No additional differences were observed in the rest of the tests used to study sensoriomotor orientation, limb reflexes and co-ordinated limb use. At behavioral level, maLPA(1)-null mice showed an impaired exploration in the open field and increased anxiety-like response when exposed to the elevated plus maze. Furthermore, the mice exhibit impaired spatial memory retention and reduced use of spatial strategies in the Morris water maze. We propose that the LPA(1) receptor may play a major role in both spatial memory and response to anxiety-like conditions.

Mathematical modeling supports substantial mouse neural progenitor cell death

Background

Existing quantitative models of mouse cerebral cortical development are not fully constrained by experimental data.

Results

Here, we use simple difference equations to model neural progenitor cell fate decisions, incorporating intermediate progenitor cells and initially low rates of neural progenitor cell death. Also, we conduct a sensitivity analysis to investigate possible uncertainty in the fraction of cells that divide, differentiate, and die at each cell cycle.

Conclusion

We demonstrate that uniformly low-level neural progenitor cell death, as concluded in previous models, is incompatible with normal mouse cortical development. Levels of neural progenitor cell death up to and exceeding 50% are compatible with normal cortical development and may operate to prevent forebrain overgrowth as observed following cell death attenuation, as occurs in caspase 3-null mutant mice.

The absence of LPA2 attenuates tumor formation in an experimental model of colitis-associated cancer

BACKGROUND & AIMS

Chronic inflammation is a risk factor for colon cancer (CC). Lysophosphatidic acid (LPA), a naturally produced phospholipid, mediates multiple effects that are vital to disease process, including inflammation and cancer. The expression of LPA receptor 2 (LPA2) is up-regulated in several types of cancer, including ovarian and colon cancer, but the importance of LPA and LPA2 in the development and progression of CC is unclear. In this study, we sought to determine whether LPA and LPA2 regulate the progression of CC in vivo.

METHODS

We examined the potential role of LPA in CC progression by administering LPA to mice heterozygous for the adenomatous polyposis coli (Apc) allele. We determined the loss of LPA2 function in tumorigenesis in the colon by treating mice with genetic deletion of LPA2 (LPA2-/-) with azoxymethane and dextran sulfate sodium.

RESULTS

We found that LPA increased tumor incidence in Apc(min/+) mice. LPA2-/- mice showed reduced mucosal damage and fewer tumors than wild-type (WT) mice. Reduced epithelial cell proliferation and decreases in beta-catenin, Krüppel-like factor 5, and cyclooxygenase-2 expression were observed in LPA2-/- mice. Unlike WT mice, induction of monocyte chemoattractant protein-1 and macrophage migration inhibitory factor was significantly attenuated in LPA2-/- mice with reduced infiltration by macrophages.

CONCLUSIONS

These results show that LPA is capable of promoting tumorigenesis in the colon. The absence of LPA2 attenuates several effects that contribute to cancer progression in vivo, and, hence, the current study identifies LPA2 as an important modulator of CC.

Involvement of the ABC-transporter ABCC1 and the sphingosine 1-phosphate receptor subtype S1P(3) in the cytoprotection of human fibroblasts by the glucocorticoid dexamethasone

Glucocorticoids (GC) represent the most commonly used drugs for the treatment of acute and chronic inflammatory skin diseases. However, the topical long-term therapy of GC is limited by the occurrence of skin atrophy. Most interestingly, although GC inhibit proliferation of human fibroblasts, they exert a pronounced anti-apoptopic action. In the present study, we further elucidated the molecular mechanism of the GC dexamethasone (Dex) to protect human fibroblasts from programmed cell death. Dex not only significantly alters the expression of the cytosolic isoenzyme sphingosine kinase 1 but also initiated an enhanced intracellular formation of the sphingolipid sphingosine 1-phosphate (S1P). Investigations using S1P (3) ((-/-)) -fibroblasts revealed that this S1P-receptor subtype is essential for the Dex-induced cytoprotection. Moreover, we demonstrate that the ATP-binding cassette (ABC)-transporter ABCC1 is upregulated by Dex and may represent a crucial carrier to transport S1P from the cytosol to the S1P(3)-receptor subtype.

Lysophosphatidic acid (LPA) receptors: signaling properties and disease relevance

Lysophosphatidic acid (LPA), a water-soluble phospholipid, has gained significant attention in recent years since the discovery that it acts as a potent signaling molecule with wide-ranging effects on many different target tissues. There are currently five identified G protein-coupled receptors for LPA and more are undergoing validation. The complexity of the expression pattern and signaling properties of LPA receptors results in multiple influences on developmental, physiological, and pathological processes. This review provides a summary of LPA receptor signaling and current views on the potential involvement of this pathway in human diseases that include cardiovascular, cancer, neuropathic pain, neuropsychiatric disorders, reproductive disorders, and fibrosis. The involvement of LPA signaling in these processes implicates multiple, potential drug targets including LPA receptor subtypes and LPA metabolizing enzymes. Modulation of LPA signaling may thus provide therapeutic inroads for the treatment of human disease.

Assessment of breast cancer risk prediction models in a high-risk population

Abstract #4074

Background: A variety of risk assessment models have been developed to quantify a woman's risk for developing breast cancer. Although the Gail model (GM) is the most widely utilized model, there are limitations. The Tyrer-Cuzick model (TCM), which has been validated in the United Kingdom (UK), addresses these limitations but its performance in other populations is unclear. The purpose of this study was to evaluate the predictive ability of the TCM in a cohort of high-risk women from the New York metropolitan area and compare the results to the GM.
 Methods: The Women At Risk (WAR) Registry provided the study population. Due to the age limitation of the Gail model, we excluded women who were under 35 and over 80 years of age. Calculation of lifetime Gail scores included the following: age, race, age at first menses, age at first live birth, number of first degree relatives with breast cancer, number of previous breast biopsies, and atypical hyperplasia. These variables were also included in the lifetime Tyrer-Cuzick scores as well as information on menopausal status, use of hormone replacement therapy, LCIS, and age at diagnosis for relatives with ovarian and breast cancer. The Receiver Operating Characteristic (ROC) and estimated area under the ROC curve (AUC) with 95% confidence intervals (CI) were used to assess prediction accuracy of both models.
 Results: Out of a total study population of 1523 women, 82 (5%) developed breast cancer during a median follow-up of 56 months. The median age of women without breast cancer was 49 years, and the median age of women who developed breast cancer was 54 years. The AUC and 95% CI for the Gail model was 0.547 (0.479 to 0.615) and 0.501 (0.433 to 0.569) for the Tyrer-Cuzick model. Our results indicate poor discriminatory accuracy for both models, which performed no better than pure chance (0.5).
 
 Discussion: Quantitative breast cancer risk assessment models are critically important in developing effective risk management strategies. Although the TCM addresses some limitations of the GM, it is unclear how well it performs in populations outside the UK due to the wide variation in international breast cancer rates. In addition, the TCM excludes more recently identified risk factors such as breast density. Bayesian techniques may ultimately lead to a better risk assessment tool as they allow continual modification of the model as new risk factors are identified. Accurate breast cancer risk prediction is a complex undertaking and further studies are warranted in order to achieve truly comprehensive and widely applicable models.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4074.

Lysophosphatidic acid (LPA) and its receptors

Lysophosphatidic acid (LPA), a bioactive phospholipid, and its family of cognate G protein-coupled receptors have demonstrated roles in many biological functions in the nervous system. To date, five LPA receptors have been identified, and additional receptors may exist. Most of these receptors have been genetically deleted in mice toward identifying biological and medically relevant roles. In addition, small molecule agonists and antagonists have been reported. Here we review recent data on the nervous system functions of LPA signaling, and summarize data on reported agonists and antagonists of LPA receptors.

Sphingosine 1-phosphate regulates regeneration and fibrosis after liver injury via sphingosine 1-phosphate receptor 2

Sphingosine 1-phosphate (S1P), a bioactive lipid mediator, stimulates proliferation and contractility in hepatic stellate cells, the principal matrix-producing cells in the liver, and inhibits proliferation via S1P receptor 2 (S1P(2)) in hepatocytes in rats in vitro. A potential role of S1P and S1P(2) in liver regeneration and fibrosis was examined in S1P(2)-deficient mice. Nuclear 5-bromo-2'-deoxy-uridine labeling, proliferating cell nuclear antigen (PCNA) staining in hepatocytes, and the ratio of liver weight to body weight were enhanced at 48 h in S1P(2)-deficient mice after a single carbon tetrachloride (CCl(4)) injection. After dimethylnitrosamine (DMN) administration with a lethal dose, PCNA staining in hepatocytes was enhanced at 48 h and survival rate was higher in S1P(2)-deficient mice. Serum aminotransferase level was unaltered in those mice compared with wild-type mice in both CCl(4)- and DMN-induced liver injury, suggesting that S1P(2) inactivation accelerated regeneration not as a response to enhanced liver damage. After chronic CCl(4) administration, fibrosis was less apparent, with reduced expression of smooth-muscle alpha-actin-positive cells in the livers of S1P(2)-deficient mice, suggesting that S1P(2) inactivation ameliorated CCl(4)-induced fibrosis due to the decreased accumulation of hepatic stellate cells. Thus, S1P plays a significant role in regeneration and fibrosis after liver injury via S1P(2).

Lysophosphatidic acid-induced c-fos up-regulation involves cyclic AMP response element-binding protein activated by mitogen- and stress-activated protein kinase-1

Lysophosphatidic acid (LPA) is a lipid growth factor that exerts diverse biological effects through its cognate receptor-mediated signaling cascades. Recently, we reported that LPA stimulates cAMP response element-binding protein (CREB) through mitogen- and stress-activated protein kinase-1 (MSK1). Previously, LPA has been shown to stimulate c-fos mRNA expression in Rat-2 fibroblast cells via a serum response element binding protein (SRF). However, involvement of CREB in LPA-stimulated c-fos gene expression is not elucidated yet. To investigate the CREB-mediated c-fos activation by LPA, various c-fos promoter-reporter constructs containing wild-type and mutated SRE and CRE were tested for their inducibility by LPA in transient transfection assays. LPA-stimulated c-fos promoter activation was markedly decreased when SRE and CRE were mutated. A dominant negative CREB significantly down-regulated the LPA-stimulated c-fos promoter activation. Chromatin immunoprecipitation assay revealed that LPA induced an increased binding of phosphorylated CREB and CREB-binding protein (CBP) to the CRE region of the endogenous c-fos promoter. Immunoblot analyses with various pharmacological inhibitors further showed that LPA induces up-regulation of c-fos mRNA level by activation of ERK, p38 MAPK, and MSK1. Taken together, our results suggest that CREB plays an important role in up-regulation of c-fos mRNA level in LPA-stimulated Rat-2 fibroblast cells.

Biological roles of lysophospholipid receptors revealed by genetic null mice: an update

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.

Lysophosphatidic acid receptors 1 and 2 play roles in regulation of vascular injury responses but not blood pressure

Phenotypic modulation of vascular smooth muscle cells (SMCs) is essential for the development of intimal hyperplasia. Lysophosphatidic acid (LPA) is a serum component that can promote phenotypic modulation of cultured SMCs, but an endogenous role for this bioactive lipid as a regulator of SMC function in vivo has not been established. Ligation injury of the carotid artery in mice increased levels in the vessel of both autotaxin, the lysophospholipase D enzyme responsible for generation of extracellular LPA, and 2 LPA responsive G protein-coupled receptors 1 (LPA1) and 2 (LPA2). LPA1(-/-)2(-/-) mice were partially protected from the development of injury-induced neointimal hyperplasia, whereas LPA1(-/-) mice developed larger neointimal lesions after injury. Growth in serum, LPA-induced extracellular signal-regulated protein kinase activation, and migration to LPA and serum were all attenuated in SMCs isolated from LPA1(-/-)2(-/-) mice. In contrast, LPA1(-/-) SMCs exhibited enhanced migration resulting from an upregulation of LPA3. However, despite their involvement in intimal hyperplasia, neither LPA1 nor LPA2 was required for dedifferentiation of SMCs following vascular injury or dedifferentiation of isolated SMCs in response to LPA or serum in vitro. Similarly, neither LPA1 nor LPA2 was required for LPA to elicit a transient increase in blood pressure following intravenous administration of LPA to mice. These results identify a role for LPA1 and LPA2 in regulating SMC migratory responses in the context of vascular injury but suggest that additional LPA receptor subtypes are required for other LPA-mediated effects in the vasculature.

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.