Sphingosine-1-phosphate (S1P) in ovarian physiology and disease.

Sphingosine-1-phoshate (S1P) is a membrane sphingolipid involved in several physiological processes, including cell proliferation, tissue growth, cell survival and migration, inflammation, vasculogenesis, and angiogenesis. Herein, we review the most critical effects of S1P on ovarian function, including its physiological and pathophysiological effects. Based on the available evidence, S1P plays an important role in ovarian physiology, participating as an essential stimulator of follicular development in both the preantral and antral phases, as well as in ovulation and corpus luteum development. Moreover, S1P may be a good cytoprotective agent against cancer treatment side-effects (chemotherapy with or without radiation therapy). In the future, this compound may be given for fertility preservation to women undergoing cancer treatment. However, further studies are required to confirm its efficacy in ovarian protection and also its safety in terms of cancer prognosis, given the biological action of the compound. Under- or over-production of S1P may be related to ovarian pathologies.

Identification and electrophysiological properties of a sphingosine-dependent plasma membrane Ca2+ channel in Trypanosoma cruzi.

Trypanosoma cruzi is the causative agent of Chagas disease. The only two drugs accepted for the treatment of this infection are benznidazole and nifurtimox, which are of limited use in the predominant chronic phase. On the search for new drugs, the intracellular Ca2+ regulation has been postulated as a possible target, due to differences found between host cells and the parasite. The mechanisms involved in the intracellular Ca2+ regulation of T. cruzi have been partially elucidated. However, nothing is known about a putative channel responsible for the Ca2+ entry into this parasite. In contrast, in Leishmania spp., a closely related hemoflagelate, a sphingosine-activated plasma membrane Ca2+ channel has been recently described. The latter resembles the L-type voltage-gated Ca2+ channel present in humans, but with distinct characteristics. This channel is one of the main targets concerning the mechanism of action of miltefosine, the unique oral drug approved against leishmaniasis. In the present work, we describe for the first time, the electrophysiological characterization of a sphingosine-activated Ca2+ channel of T. cruzi by reconstituting plasma membrane vesicles into giant liposomes and patch clamp. This channel shares some characteristic as activation by Bay K8644 and inhibition by channel blockers such as nifedipine. However, the T. cruzi channel differs from the L-type VGCC in its activation by sphingosine and/or miltefosine. Albeit the conductance for each, Ba2+ , Ca2+ and Sr2+ was similar, the parasite channel appears not to be voltage dependent. A gene that presents homology in critical amino acids with its human ortholog Ca2+ channel was identified.

Esfingosina-1-fosfato y cánceres urológicos: identificando potenciales blancos terapéuticos en su etabolismo y señalización / Sphingosine-1-phosphate and urological cancers: identifying potential therapeutic targets in its metabolism and signalling

Los lípidos no sólo son moléculas estructurales de las membranas. Hay numerosos ejemplos de lípidos que median acciones fisiológicas dentro de las células. Específicamente, esfingolípidos como ceramida, esfingosina y esfingosina-1-fosfato (S1P) han sido involucrados en el control del crecimiento celular, la proliferación y la migración, todo lo cual se ha relacionado con el cáncer.Los efectos pro-apoptóticos de la ceramida y la esfingosina son revertidos por S1P. Por lo tanto, el destino de la célula puede ser modulada mediante el cambio de la proporción de estos esfingolípidos (el modelo reóstato). S1P promueve la proliferación celular, el crecimiento, la supervivencia, la migración, invasión y resistencia fármacos y radiación, en parte a través de receptores de membrana (S1PR1-5). La sobreexpresión de enzimas productoras de S1P y el aumento de los niveles de S1P se ha descrito en muchos tipos de cáncer, incluyendo cánceres urológicos. Por lo tanto, se pueden identificar posibles objetivos terapéuticos en el metabolismo y las vías de señalización de los esfingolípidos, cuya relevancia clínica debe ser determinada en futuros estudios.

Lipids are not only structural molecules of the membranes. There are numerous examples of lipids mediating physiologic actions within the cells. Specifically, sphingolipids like ceramide, sphingosine and sphingosine-1-phosphate (S1P) have been described to be involved in the control of cell growth, proliferation and migration, all of which has been linked to cancer. The pro-apoptotic effects of ceramide and sphingosine are opposed by S1P. Therefore, the fate of the cell can be modulated by changing the ratio of these sphingolipids (the rheostat model). S1P promotes cell proliferation, growth, survival, migration, invasion and resistance to drugs and radiation, in part mediated by S1P membrane receptors (S1PR1-5). Overexpression of S1P producing enzymes and increased S1P levels has been described in many cancers, including urological cancers. Therefore, potential therapeutic targets can be recognized in the metabolism and signaling pathways of sphingolipids and their clinical relevance have to be determined in future studies.

[Ca2+ and sphingolipids as modulators for apoptosis and cancer]. / El Ca2+ y los esfingolipidos como moduladores de la apoptosis y el cáncer.

Ca2+ is a second messenger which regulates many functions directly related with cancer such as proliferation, differentiation and apoptosis. The intracellular Ca2+ concentration ([Ca2+],) is finely regulated by several mechanisms, among them ionic channels, the endoplasmic reticulum Ca2+-ATPase (SERCA), the plasma membrane calcium pump (PMCA) and the mitochondrial Ca2+ transport. In cancer, the tumour cell proliferates without control since the capacity to recognize apoptotic signals has been lost. The apoptosis is regulated by changes in several proteins, as caspases and the Bcl-2 family members, among others. Additionally, the "reticulum stress", promoted by the accumulation and aggregation of unfolded proteins in the interior of the endoplasmic reticulum (ER), ussually leads to apoptosis. The "reticulum stress" can be induced by several agents, remarkably with thapsigargin, a selective inhibitor of the SERCA, which in turn induces a large increment in [Ca2+],, leading to apoptosis. As a consequence, currently, derivatives of thapsigargin are successfully been assayed as anti-neoplastic agents. Ca2+ is then transferred to the mitochondria, where it is known to constitute a main apoptotic signal. On the other hand, several sphingolipids, such as ceramide and sphingosine, and their phosphorylated derivatives ceramide-1-phosphate and sphingosine-1-phosphate, directly involved in the [Ca2+]1 regulation, are also recognized as signal messengers related with cancer processes. In this review we discuss new evidences on the effect of several sphingolipids in the intracellular Ca2+ homeostasis and its relationship with apoptosis and cancer.

El Ca2+ y los esfingolípidos como moduladores de la apoptosis y el cáncer / Ca2+ and sphingolipids as modulators for apoptosis and cancer

El Ca2+ es un segundo mensajero que regula funciones directamente relacionadas con el cáncer como la proliferación, diferenciación y la apoptosis. La concentración intracelular de Ca2+ ([Ca2+]i) está altamente regulada por diversos mecanismos entre los que destacan canales iónicos, la Ca2+-ATPasa del retículo endoplasmático (SERCA) y de la membrana plasmática (PMCA), y el transporte de Ca2+ mitocondrial. En el cáncer, la célula tumoral prolifera sin control tras su incapacidad de reconocer señales apoptóticas. La apoptosis es mediada a través de cambios en la actividad de ciertas proteínas como las caspasas y miembros de la familia Bcl-2. Adicionalmente, el “estrés del retículo”, promovido por la acumulación y agregación de proteínas mal plegadas en el interior del retículo endoplasmático (RE), puede desencadenar la apoptosis. El “estrés del retículo” es inducido por una variedad de agentes, entre los que destaca la tapsigargina, inhibidor específico de la SERCA, la cual promueve un notable aumento en la [Ca2+]i, induciendo además apoptosis. En consecuencia, actualmente se están ensayando exitosamente derivados de la tapsigargina como agentes antineoplásicos. El Ca2+ es transferido a la mitocondria desencadenando señales apoptóticas. Por otra parte, los esfingolípidos, como la ceramida y la esfingosina, y sus derivados fosforilados, la ceramida-1-fosfato y la esfingosina-1-fosfato, los cuales regulan la [Ca2+]i, también están estrechamente vinculados con la señalización intracelular en procesos relacionados con el cáncer. Esta revisión discute nuevas evidencias sobre el efecto de estos esfingolípidos en la homeostasis de Ca+2 intracelular y su conexión con la apoptosis y el cáncer.

Ca2+ is a second messenger which regulates many functions directly related with cancer such as proliferation, differentiation and apoptosis. The intracellular Ca2+ concentration ([Ca2+]i) is finely regulated by several mechanisms, among them ionic channels, the endoplasmic reticulum Ca2+-ATPase (SERCA), the plasma membrane calcium pump (PMCA) and the mitochondrial Ca2+ transport. In cancer, the tumour cell proliferates without control since the capacity to recognize apoptotic signals has been lost. The apoptosis is regulated by changes in several proteins, as caspases and the Bcl-2 family members, among others. Additionally, the “reticulum stress”, promoted by the accumulation and aggregation of unfolded proteins in the interior of the endoplasmic reticulum (ER), ussually leads to apoptosis. The “reticulum stress” can be induced by several agents, remarkably with thapsigargin, a selective inhibitor of the SERCA, which in turn induces a large increment in [Ca2+]I, leading to apoptosis. As a consequence, currently, derivatives of thapsigargin are successfully been assayed as anti-neoplastic agents. Ca2+ is then transferred to the mitochondria, where it is known to constitute a main apoptotic signal. On the other hand, several sphingolipids, such as ceramide and sphingosine, and their phosphorylated derivatives ceramide-1-phosphate and sphingosine-1-phosphate, directly involved in the [Ca2+]I regulation, are also recognized as signal messengers related with cancer processes. In this review we discuss new evidences on the effect of several sphingolipids in the intracellular Ca2+ homeostasis and its relationship with apoptosis and cancer.

Synthesis of sphingosine is essential for oxidative stress-induced apoptosis of photoreceptors.

PURPOSE: Oxidative stress is involved in inducing apoptosis of photoreceptors in many retinal neurodegenerative diseases. It has been shown that oxidative stress increases in photoreceptors the synthesis of ceramide, a sphingolipid precursor that then activates apoptosis. In several cell types, ceramide is converted by ceramidases to sphingosine (Sph), another apoptosis mediator; hence, this study was undertaken to determine whether Sph participates in triggering photoreceptor apoptosis. METHODS: Rat retina neurons were incubated with [(3)H]palmitic acid and treated with the oxidant paraquat (PQ) to evaluate Sph synthesis. Sph was added to cultures with or without docosahexaenoic acid (DHA), the major retina polyunsaturated fatty acid and a photoreceptor survival factor, to evaluate apoptosis. Synthesis of Sph and sphingosine-1-phosphate (S1P), a prosurvival signal, were inhibited with alkaline ceramidase or sphingosine kinase inhibitors, respectively, before adding PQ, C(2)-ceramide, or Sph. Apoptosis, mitochondrial membrane polarization, cytochrome c localization, and reactive oxygen species (ROS) production were determined. RESULTS: PQ increased [(3)H]Sph synthesis in photoreceptors and blocking this synthesis by inhibiting alkaline ceramidase decreased PQ-induced apoptosis. Addition of Sph induced photoreceptor apoptosis, increased ROS production, and promoted cytochrome c release from mitochondria. Although DHA prevented this apoptosis, inhibiting Sph conversion to S1P blocked DHA protection. CONCLUSIONS: These results suggest that oxidative stress enhances formation of ceramide and its subsequent breakdown to Sph; ceramide and/or Sph would then trigger photoreceptor apoptosis. Preventing Sph synthesis or promoting its phosphorylation to S1P rescued photoreceptors, suggesting that Sph is a mediator of their apoptosis and modulation of Sph metabolism may be crucial for promoting photoreceptor survival.

[Sphingolipids in embryonic implantation]. / Los esfingolípidos en la implantación embrionaria.

Embryonic implantation is a complex series of processes that establishes the connection between maternal and embryonic tissues and requires an intricate program of uterine preparation. During early gestation in invasively implanting species, the uterine stromal compartment undergoes dramatic remodeling, defined by the differentiation of stromal fibroblast cells into decidual cells. Lipid signaling molecules from a number of pathways are well-established functional components of this decidualization reaction. The decidua provides a vascular network for nutrition and gas exchange for the developing embryo before a functional placenta is established. Because of a correlation in the events that transpire in the uterus during early implantation with known functions of bioactive sphingolipid metabolites established from studies in other organ systems, we hypothesized that uterine sphingolipid metabolism would change during implantation Thus, sphingolipid metabolism regulates proper uterine decidualization and blood vessel stability. The findings also suggest that disturbance in sphingolipid metabolism may be considered as a cause of pregnancy loss in humans.

Sphingosine-1-phosphate is a key regulator of proliferation and differentiation in retina photoreceptors.

PURPOSE: Identifying the cues required for the survival and development of photoreceptors is essential for treating retinal neurodegeneration. The authors previously established that glial-derived neurotrophic factor (GDNF) stimulates proliferation and that docosahexaenoic acid (DHA) promotes photoreceptor survival and differentiation. Later findings that ceramide triggers photoreceptor apoptosis suggested sphingolipids might also control photoreceptor development. The present study investigated whether sphingosine-1-phophate (S1P), which promotes survival and differentiation in several cell types, regulates photoreceptor proliferation and differentiation and whether it is a mediator in GDNF and DHA effects. METHODS: Rat retina neuronal cultures were supplemented at day 0 or 1 with S1P, GDNF, or DHA and were treated with DL-threo-dihydrosphingosine to inhibit S1P synthesis or with brefeldin A (BFA) to block intracellular trafficking. Proliferation was quantified to determine bromodeoxyuridine uptake and number of mitotic figures. Opsin, peripherin, and sphingosine kinase (SphK), the enzyme required for S1P synthesis, were quantified by immunocytochemistry and Western blot analysis. RESULTS: S1P increased the proliferation of photoreceptor progenitors. It also stimulated the formation of apical processes, enhanced opsin and peripherin expression, and promoted their localization in these processes; DHA had similar effects. BFA prevented S1P and DHA enhancement of apical process formation without affecting opsin expression. GDNF and DHA enhanced SphK expression in photoreceptors, while inhibiting S1P synthesis blocked GDNF mitogenic effects and DHA effects on differentiation. CONCLUSIONS: The authors propose S1P as a key regulator in photoreceptor development. GDNF and DHA might upregulate SphK levels to promote S1P synthesis, which would initially promote proliferation and then advance photoreceptor differentiation.

Involvement of lysophosphatidic acid, sphingosine 1-phosphate and ceramide 1-phosphate in the metabolization of phosphatidic acid by lipid phosphate phosphatases in bovine rod outer segments.

The aim of the present research was to evaluate the generation of [2-3H]diacylglycerol ([2-3H]DAG) from [2-3H]-Phosphatidic acid ([2-3H]PA) by lipid phosphate phosphatases (LPPs) at different concentrations of lysophosphatidic acid (LPA), sphingosine 1-phosphate (S1P), and ceramide 1-phosphate (C1P) in purified ROS obtained from dark-adapted retinas (DROS) or light-adapted retinas (BLROS) as well as in ROS membrane preparations depleted of soluble and peripheral proteins. Western blot analysis revealed the presence of LPP3 exclusively in all membrane preparations. Immunoblots of entire ROS and depleted ROS did not show dark-light differences in LPP3 levels. LPPs activities were diminished by 53% in BLROS with respect to DROS. The major competitive effect on PA hydrolysis was exerted by LPA and S1P in DROS and by C1P in BLROS. LPPs activities in depleted ROS were similar to the activity observed in entire DROS and BLROS, respectively. LPA, S1P and C1P competed at different extent in depleted DROS and BLROS. Sphingosine and ceramide inhibited LPPs activities in entire and depleted DROS. Ceramide also inhibited LPPs activities in entire and in depleted BLROS. Our findings are indicative of a different degree of competition between PA and LPA, S1P and C1P by LPPs depending on the illumination state of the retina.

Ceramide mimics tumour necrosis factor-alpha in the induction of cell cycle arrest in endothelial cells. Induction of the tumour suppressor p53 with decrease in retinoblastoma/protein levels.

Tumour necrosis factor (TNF)-alpha induces a transient increase in N-octanoylsphingosine (C8-ceramide) which has been postulated as an intracellular mediator in TNF-alpha signalling. We tested the ability of C8-ceramide to reproduce the TNF-alpha-mediated interference with endothelial cell proliferation and DNA synthesis. TNF-alpha (10 ng.mL-1) and C8-ceramide (20 microM) inhibited the incorporation of [3H]thymidine into DNA and led to an accumulation of cells in the G1 phase of the cell cycle. When the responses of the tumour suppressors p53 and RB were analysed, it was found that TNF-alpha and C8-ceramide induced increased expression of p53. Treatment with TNF-alpha or C8-ceramide lead to a significant decrease in total retinoblastoma protein (RB) content that correlated with high levels of p53. These results suggest that p53 and RB may complement each other in their contribution to cell cycle arrest. TNF-alpha prevented RB phosphorylation whereas C8-ceramide did not interfere with this process, suggesting that it follows a ceramide-independent pathway.