Exogenous sphingosine 1-phosphate and sphingosine kinase activated by endothelin-1 induced myometrial contraction through differential mechanisms

Association between Maternal Serum Lipids and Intrapartum Oxytocin Requirements during Labor Induction and Augmentation

OBJECTIVE

This study aimed to investigate the relationship between maternal serum lipid parameters and oxytocin requirements among women with term vaginal deliveries.

STUDY DESIGN

In this secondary analysis of a prospective cohort study, women who presented for delivery at ≥37 weeks' gestation and received oxytocin during their labor were included. Maternal serum was collected intrapartum. The cohort was stratified into two groups based on maximum oxytocin infusion dose during labor. Primary outcomes were maternal total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride levels. Generalized linear regression models were used to assess the association between lipid parameters and maximum oxytocin dose requirements while controlling for potential confounders. For secondary analyses, the cohort was stratified by HDL-C into two groups. Multivariable logistic regression was used to evaluate the relationship between low maternal HDL-C and additional intrapartum oxytocin parameters.

RESULTS

There were no differences in maternal total cholesterol, LDL-C, or triglyceride values between high and low maximum oxytocin groups. Median serum HDL-C was significantly lower among women in the high oxytocin group compared with those in the low oxytocin group (56 vs. 62 mg/dL, p < 0.01). For every 0.26 mg/dL lower HDL-C, women had 1 mU/min higher maximum oxytocin infusion dose during labor. Women with low serum HDL-C were also more likely to require maximum oxytocin doses above the 75th percentile (adjusted odds ratio [aOR]: 1.99, 95% confidence interval [CI]: 1.06-3.75) and above the 90th percentile (aOR: 2.47, 95% CI: 1.10-5.54). Among women undergoing induction of labor, low serum HDL-C was also associated with longer duration of oxytocin infusion (aOR: 2.07, 95% CI: 1.02-4.20).

CONCLUSION

Low maternal HDL-C levels at term are associated with higher maximum oxytocin infusion doses among women undergoing labor induction or augmentation. Given the growing prevalence of metabolic syndrome in the United States and persistently high rates of cesarean delivery, HDL-C or its components may present a new target for predicting and improving labor outcomes.

KEY POINTS

· Serum HDL-C at term is inversely correlated with oxytocin infusion doses at term.. · Low maternal serum HDL-C is associated with higher oxytocin requirements during labor induction or augmentation.. · No association between maternal serum total cholesterol, LDL-C, or triglyceride levels and oxytocin requirements in labor..

Stromal cells-specific retinoic acid determines parturition timing at single-cell and spatial-temporal resolution

The underlying mechanisms governing parturition remain largely elusive due to limited knowledge of parturition preparation and initiation. Accumulated evidences indicate that maternal decidua plays a critical role in parturition initiation. To comprehensively decrypt the cell heterogeneity in decidua approaching parturition, we investigate the roles of various cell types in mouse decidua process and reveal previously unappreciated insights in parturition initiation utilizing single-cell RNA sequencing (scRNA-seq). We enumerate the cell types in decidua and identity five different stromal cells populations and one decidualized stromal cells. Furthermore, our study unravels that stromal cells prepare for parturition by regulating local retinol acid (RA) synthesis. RA supplement decreases expression of extracellular matrix-related genes in vitro and accelerates the timing of parturition in vivo. Collectively, the discovery of contribution of stromal cells in parturition expands current knowledge about parturition and opens up avenues for the intervention of preterm birth (PTB).

Sphingosine 1-Phosphate Activates S1PR3 to Induce a Proinflammatory Phenotype in Human Myometrial Cells

One of the common mechanisms responsible for obstetric complications, affecting millions of women every year, is abnormal uterine contractility. Despite the critical importance of this process for women's health, the mechanisms of uterine contraction regulation remain poorly understood. The initiation of uterine smooth muscle (myometrial) contraction is an inflammatory process, accompanied by upregulation of proinflammatory genes and cytokine release. In this study, we show that sphingolipid metabolism is activated during human labor and that sphingosine 1-phosphate (S1P), the main bioactive sphingolipid, may modify the myometrial proinflammatory phenotype. Our data in both primary and immortalized human myometrial cells show that exogenous S1P induces a proinflammatory gene signature and upregulates the expression of known inflammatory markers of parturition, such as IL8 and COX2. Using expression of IL8 as a readout for S1P activity in myometrial cells, we established that these S1P effects are mediated through the activation of S1P receptor 3 (S1PR3) and downstream activation of ERK1/2 pathways. Inhibition of S1PR3 in human myometrial cells attenuates upregulation of IL8, COX2, and JUNB both at the mRNA and protein levels. Furthermore, activation of S1PR3 with a receptor-specific agonist recapitulated the effects seen after treatment with exogenous S1P. Collectively, these results suggest a signaling pathway activated by S1P in human myometrium during parturition and propose new targets for development of novel therapeutics to alter uterine contractility during management of preterm labor or labor dystocia.

Endothelins and their receptors in embryo implantation

As a critical stage of pregnancy, the implantation of blastocysts into the endometrium is a progressive, excessively regulated local tissue remodeling step involving a complex sequence of genetic and cellular interplay executed within an optimal time frame. For better understanding the causes of infertility and, more importantly, for developing powerful strategies for successful implantations and combating infertility, an increasing number of recent studies have been focused on the identification and study of newly described substances in the reproductive tree. The endothelins (ET), a 21-aminoacidic family of genes, have been reported to be responsible for the contraction of vascular and nonvascular smooth muscles, including the smooth muscles of the uterus. Therefore, this review aims to comprehensively discuss the physiological role of endothelins and signaling through their receptors, as well as their probable involvement in the implantation process.

The effect of sphingosine-1-phosphate on colonic smooth muscle contractility: Modulation by TNBS-induced colitis

Aim

Increased levels of circulating sphingosine-1-phosphate (S1P) have been reported in ulcerative colitis. The objective of this study was to examine the effect of S1P on colonic smooth muscle contractility and how is it affected by colitis.

Methods

Colonic inflammation was induced by intrarectal administration of trinitrobenzene sulfonic acid. Five days later colon segments were isolated and used for contractility experiments and immunoblotting.

Results

S1P contracted control and inflamed colon segments and the contraction was significantly greater in inflamed colon segments. S1P-induced contraction was mediated by S1PR1 and S1PR2 in control and S1PR2 in inflamed colon segments. S1PR3 did not play a significant role in S1P-induced contractions in control or inflamed colon. S1PR1, S1PR2 and S1PR3 proteins were expressed in colon segments from both groups. The expression of S1PR1 and S1PR2 was significantly enhanced in control and inflamed colon segments, respectively. S1PR3 levels however were not significantly different between the two groups. Nifedipine significantly reduced S1P-induced contraction in control but not inflamed colon segments. Thapsigargin significantly reduced S1P-induced contraction of the inflamed colon. GF 109203X and Y-27632, alone abolished S1P-induced contraction of the control but not inflamed colon segments. Combination of GF 109203X, Y-27632 and thapsigargin abolished S1P-induced contraction of inflamed colon segments.

Conclusion

S1P contracted control colon via S1PR1 and S1PR2 and inflamed colon exclusively via S1PR2. Calcium influx (control) or release (inflamed) and calcium sensitization are involved in S1P-induced contraction. Exacerbated response to S1P in colitic colon segments may explain altered colonic motility reported in patients and experimental models of inflammatory bowel disease.

Elevated adenosine signaling via adenosine A2B receptor induces normal and sickle erythrocyte sphingosine kinase 1 activity

Erythrocyte possesses high sphingosine kinase 1 (SphK1) activity and is the major cell type supplying plasma sphingosine-1-phosphate, a signaling lipid regulating multiple physiological and pathological functions. Recent studies revealed that erythrocyte SphK1 activity is upregulated in sickle cell disease (SCD) and contributes to sickling and disease progression. However, how erythrocyte SphK1 activity is regulated remains unknown. Here we report that adenosine induces SphK1 activity in human and mouse sickle and normal erythrocytes in vitro. Next, using 4 adenosine receptor-deficient mice and pharmacological approaches, we determined that the A2B adenosine receptor (ADORA2B) is essential for adenosine-induced SphK1 activity in human and mouse normal and sickle erythrocytes in vitro. Subsequently, we provide in vivo genetic evidence that adenosine deaminase (ADA) deficiency leads to excess plasma adenosine and elevated erythrocyte SphK1 activity. Lowering adenosine by ADA enzyme therapy or genetic deletion of ADORA2B significantly reduced excess adenosine-induced erythrocyte SphK1 activity in ADA-deficient mice. Finally, we revealed that protein kinase A-mediated extracellular signal-regulated kinase 1/2 activation functioning downstream of ADORA2B underlies adenosine-induced erythrocyte SphK1 activity. Overall, our findings reveal a novel signaling network regulating erythrocyte SphK1 and highlight innovative mechanisms regulating SphK1 activity in normal and SCD.

Inhibition of sphingosine kinase prevents lipopolysaccharide-induced preterm birth and suppresses proinflammatory responses in a murine model

Premature delivery occurs in 12% of all births, and accounts for nearly half of long-term neurological morbidity, and 60% to 80% of perinatal mortality. Despite advances in obstetrics and neonatology, the rate of premature delivery has increased approximately 12% since 1990. The single most common cause of spontaneous preterm birth is infection. Several lines of evidence have demonstrated the role of endothelin-1 as both a constrictor of uterine myometrial smooth muscle and a proinflammatory mediator. Endothelin-1 activates the phospholipase C pathway, leading to activation of protein kinase C and, in turn, sphingosine kinase (SphK). The inhibition of SphK has been recently shown to control the proinflammatory response associated with sepsis. We show herein, for the first time, that SphK inhibition prevents inflammation-associated preterm birth in a murine model. Rescue of pups from premature abortion with an SphK inhibitor occurs by suppression of the proinflammatory cytokines tumor necrosis factor α, Il-1β, and Il-6 and attenuation of polymorphonuclear inflammatory cells into the placental labyrinth. Moreover, we postulate that inhibition of SphK leads to suppression of endothelin-converting enzyme-1 expression, indicating the presence of an endothelin-converting enzyme 1/endothelin 1-SphK positive feedback loop. This work introduces a novel approach for the control of infection-triggered preterm labor, a condition for which there is no effective treatment.

Sphingosine kinase: a novel putative target for the prevention of infection-triggered preterm birth

Preterm birth is defined as any delivery before 37 complete weeks of gestation. It is a universal challenge in the field of obstetrics owing to its high rate of mortality, long-term morbidity, associated human suffering and economic burden. In the United States, about 12.18% deliveries in 2009 were preterm, producing an exorbitant cost of $5.8 billion. Infection-associated premature rupture of membranes (PROM) accounts for 40% of extremely preterm births (<28 weeks of gestation). Major research efforts are directed towards improving the understanding of the pathophysiology of preterm birth and ways to prevent or at least postpone delivery. Endothelin-1 (ET-1) is a potent vasoconstrictor that plays a significant role in infection-triggered preterm birth. Its involvement in a number of pathological mechanisms and its elevation in preterm delivered amniotic fluid samples implicate it in preterm birth. Sphingosine kinase (SphK) is a ubiquitous enzyme responsible for the production of sphingosine-1-phosphate (S1P). S1P acts as second messenger in a number of cell proliferation and survival pathways. SphK is found to play a key role in ET-1 mediated myometrial contraction. This review highlights SphK as a prospective target with great potential to prevent preterm birth.

Increased expression of sphingosine kinase in the amnion during labor

INTRODUCTION

Sphingosine-1-phosphate (S1P), a bioactive lipid, has been reported to regulate inflammation processes. The onset of labor is thought to be related to inflammation. We therefore hypothesized that S1P might be involved in the onset of labor.

METHODS

The expression of sphingosine kinase (SPHK)-1, which produces S1P, and S1P lyase (SPL)-1, which irreversibly inactivates S1P, were examined in the fetal membranes. The expression levels were compared between amnions from cases of elective Caesarean deliveries (pre-labor) and those from vaginal deliveries (post-labor). In primary cultured human amnion cells, the expression levels of prostaglandin-endoperoxide synthase (PTGS)-2 were examined in the presence or absence of S1P treatment.

RESULTS

SPHK-1 and SPL-1 were both expressed in the amnion. The expression of SPHK-1 in the post-labor amnions increased compared with that in the pre-labor amnions. The expression of PTGS-2, a key regulator of labor, also increased in the post-labor amnion. However, the SPL-1 expression in the pre-labor amnion was not significantly different from that in the post-labor amnion. S1P1-3 and 5, which were coupled with Gi protein, were consistently found in the amnion cells. The treatment with S1P increased the expression of PTGS-2, and this was completely suppressed by a Gi inhibitor in the amnion cells.

DISCUSSION

We are herein provide the first evidence of increased SPHK-1 expression in post-labor amnions, and that S1P increases the PTGS-2 expression in amnion cells.

CONCLUSIONS

Our results suggest that S1P might play a role in the onset of labor via the induction of PTGS-2.

The endothelin axis in uterine leiomyomas: new insights

The endothelin axis, comprising endothelin-1 (ET-1) and its receptors (ETA and ETB), is involved in the pathophysiology of different human tumors. Here we review conventional approaches and gene expression profiling indicating the association of ET-1 and its cognate receptors with human and rat leiomyomas, the most common benign tumors of myometrium. Specifically, ET-1/ETA interactions affect human and rat leiomyoma cell proliferation through protein kinase C and mitogen-activated protein kinase-dependent signaling pathways. Recent experiments demonstrate that the ET-1 axis exerts a potent antiapoptotic effect involving sphingolipid metabolism and prostaglandin-endoperoxide synthase 2/prostaglandin system in the rat Eker leiomyoma tumor-derived ELT3 cell line. Evidence supports that steroid hormones, growth factors, and extracellular matrix are key regulators of the leiomyoma growth. Interestingly, the ET-1 axis is under steroid hormones and can cooperate with these growth factors. Therefore, ET-1 alone or in association with these factors could contribute to the complex regulation of uterine tumor growth, such as proliferation, survival, and extracellular matrix production. This review summarizes current knowledge and emerging data on ET-1 in uterine leiomyoma pathology.

Maternal serum proteome changes between the first and third trimester of pregnancy in rural southern Nepal

Characterization of normal changes in the serum proteome during pregnancy may enhance understanding of maternal physiology and lead to the development of new gestational biomarkers. In 23 Nepalese pregnant women who delivered at term, two-dimensional difference in-gel electrophoresis (DIGE) was used to assess changes in relative protein abundance between paired serum samples collected in the first and third trimesters. One-hundred and forty-five of over 700 protein spots in DIGE gels (pI 4.2-6.8) exhibited nominally significant (p < 0.05) differences in abundance across trimesters. Additional filtering using a Bonferroni correction reduced the number of significant (p < 0.00019) spots to 61. Mass spectrometric analysis detected 38 proteins associated with gestational age, cytoskeletal remodeling, blood pressure regulation, lipid and nutrient transport, and inflammation. One new protein, pregnancy-specific β-glycoprotein 4 was detected. A follow-up isotope tagging for relative and absolute quantitation (iTRAQ) experiment of six mothers from the DIGE study revealed 111 proteins, of which 11 exhibited significant (p < 0.05) differences between trimesters. Four of these proteins: gelsolin, complement C1r subcomponent, α-1-acid glycoprotein, and α-1B-glycoprotein also changed in the DIGE analysis. Although not previously associated with normal pregnancy, gelsolin decreased in abundance by the third trimester (p < 0.01) in DIGE, iTRAQ and Western analyses. Changes in abundance of proteins in serum that are associated with syncytiotrophoblasts (gelsolin, pregnancy-specific β-1 glycoprotein 1 and β-2-glycoprotein I) probably reflect dynamics of a placental proteome shed into maternal circulation during pregnancy. Measurement of changes in the maternal serum proteome, when linked with birth outcomes, may yield biomarkers for tracking reproductive health in resource poor settings in future studies.

ATP-binding cassette ABCC1 is involved in the release of sphingosine 1-phosphate from rat uterine leiomyoma ELT3 cells and late pregnant rat myometrium

Sphingosine 1-phosphate (S1P), a bioactive lipid generated by sphingosine kinases (SphK1/2), initiates different signalling pathways involved in physiological and pathological processes. We previously demonstrated that in rat myometrium at late (day 19) gestation, SphK1 increases the expression of COX2 via S1P generation and release. In rat uterine leiomyoma cells (ELT3), SphK1/S1P axis controls survival and proliferation. In the present study we demonstrate that PDBu activates SphK1 but not SphK2. SphK1 activation requires PKC and MAPK ERK1/2. S1P produced by PDBu is released in the medium. PDBu-induced S1P export is abolished by Ro-318220 and BIM (PKC inhibitors), by U0126 and PD98059 (MEK inhibitors), SKI-II (SphKI/2 inhibitor) and SphK1-siRNA, suggesting the involvement of PKC, ERK and SphK1 respectively. The release of S1P is insensitive to inhibitors of ATP Binding Cassette (ABC)A1 and ABCB1 transporters, but is abolished when ABCC1 transporters are inhibited by MK571 or down-regulated by ABCC1-siRNA. PDBu increases COX2 expression that is blocked by the inhibition of PKC, ERK1/2, SphK1, and when cells are treated with MK571 or transfected with ABCC1-siRNA. The induction of COX2 by the S1P release due to PDBu or by exogenous S1P involves S1P2 receptors coupled to Gi. In myometrium from rat at late gestation, the release of S1P is also strongly reduced when SphK and ABCC1 are inhibited. The data reveal that in rat leiomyoma cells and late pregnant rat myometrium, the release of S1P involves a similar signalling pathway and occurs through ABCC1.

Endothelin-1: physiological and pathological roles in myometrium

Endothelin-1 (ET-1), a member of endothelin peptide family is released by many different tissues including uterine smooth muscle. ET-1 acts through ETA and ETB receptors and is implicated in a wide range of biological and pathological functions that explain the great attention of the pharmacological industry for ET-1 receptors as potential therapeutic targets in vascular pathologies and cancers. It is now well established that ET-1 is also able to regulate myometrial functions. In the present review, we focused on ET axis and related signaling pathways involved in the regulation of myometrial contraction, as well as cell proliferation and survival. Such ET-1-mediated cellular functions play a critical role in normal pregnancy, preterm birth and uterine leiomyoma.

Vessel-specific role of sphingosine kinase 1 in the vasoconstriction of isolated basilar arteries

Sphingosine-1-phosphate (S1P) constricts cerebral arteries through S1P(3) receptor stimulation. Because the activity of the key S1P-synthesizing enzyme, sphingosine kinase (SPK), can be stimulated by agonists of various G protein-coupled receptors, it is likely that S1P also acts as a second messenger for other vasoconstrictors. We investigated the effect of SPK inhibitors and SPK gene deletion on the contractile responses of isolated vessels to vasoactive agonists and KCl-induced depolarization. Basilar and femoral arteries of rat, mounted in a wire myograph, were incubated with dimethylsphingosine (DMS), 2-(p-hydroxyanilino)-4-(p-chlorophenyl) thiazole (Compound 2) or FTY720, and exposed to KCl, 5-hydroxytryptamine (5-HT), S1P or phenylephrine (PE). Vasomotor responses in basilar artery were decreased by DMS, Compound 2 and FTY720, while they were not affected in femoral artery. Basilar arteries from SPK1(-/-) mice exhibited weaker vasoconstriction to both KCl and agonists (S1P and the prostanoid U46619) when compared to either wild type (WT) or SPK2(-/-). In contrast, in mesenteric resistance arteries, neither the contraction to KCl nor the maximum contraction to PE and S1P significantly differed among WT, SPK1(-/-) and SPK2(-/-). Quantitative analysis of SPK mRNA (reverse transcription and real time polymerase chain reaction) in mouse arteries showed 40-80-fold higher SPK1 expression in cerebral arteries than in aorta or mesenteric arteries. SPK1 critically modulates the reactivity of cerebral vasculature to vasoconstrictors. S1P plays a specific role as modulator of cerebral blood flow, potentially acting either directly outside vascular smooth muscle cells on S1P(3) receptors, or indirectly after being generated inside the cell in response to vasoconstrictors.

Sphingolipids and the orchestration of endothelium-derived vasoactive factors: when endothelial function demands greasing

Vasomotor tone is regulated by a complex interplay of a variety of extrinsic neurohumoral and intrinsic factors. It is the endothelium that has a major influence on smooth muscle cell tone via the release of intrinsic vasoactive factors and is therefore an important regulator of vasomotor tone. Sphingolipids are an emerging class of lipid mediators with important physiological properties. In the last two decades it has not only become increasingly clear that sphingolipid signaling plays a pivotal role in immune function, but also its role in the vascular system is now becoming more recognized. In this mini-review we will highlight the possible cross-talk between sphingolipids and intrinsic vasoactive factors released by the endothelium. Via this cross-talk sphingolipids can orchestrate vasomotor tone and may therefore also be involved in the pathophysiology of disease states associated with endothelial dysfunction.

Regulation of smooth muscle contraction by small GTPases

Next to changes in cytosolic [Ca(2+)], members of the Rho subfamily of small GTPases, in particular Rho and its effector Rho kinase, also known as ROK or ROCK, emerged as key regulators of smooth muscle function in health and disease. In this review, we will focus on the regulation of the contractile machinery by Rho/ROK signaling and its interaction with PKC and cyclic nucleotide signaling. We will briefly discuss the emerging evidence that remodeling of cortical actin is necessary for contraction.

Increased expression of enzymes for sphingosine 1-phosphate turnover and signaling in human decidua during late pregnancy

An appropriate balance between uterine quiescence and activation during pregnancy is essential for a successful outcome. Sphingosine 1-phosphate (S1P), a bioactive lipid, increases cell survival, proliferation, and angiogenesis, all important to maintain the pregnancy. Indeed progesterone increases sphingosine kinase 1 (SPHK1) mRNA, which produces S1P. In contrast, induction of prostaglandin endoperoxide synthase 2 by S1P and stimulation of SPHK1 by estradiol and cytokines suggests a role for S1P in the termination of pregnancy. Human decidua is important for regulating the maintenance and termination of pregnancy with production of progesterone receptors, cytokines, and prostaglandins. We hypothesized that S1P is produced by and acts on the decidua to stimulate production of mediators that induce labor. Our objective was to investigate the metabolism of S1P and its receptors in human decidua during pregnancy. We found that SPHK1 protein and activity positively correlated with increasing gestational age in human decidua parietalis. This was accompanied at term by increased expression of the S1P lyase, which irreversibly degrades S1P. This implies increased S1P turnover in the decidua at term. Although the mRNA level of phosphatidic acid phosphatase type 2A and 2B (PPAP2A,B), which dephosphorylate extracellular S1P, were increased at term, PPAP2 activity did not change. Sphingosine 1-phosphate receptor 3 protein expression also increased at term, indicating increased signaling by S1P in the decidua. There were no differences in any parameter tested in decidua from women in labor compared to those who were not. This work provides the first evidence of increased S1P synthesis, degradation, and signaling in human decidua during gestation.

Cdc42GAP, reactive oxygen species, and the vimentin network

Cdc42GAP (GTPase-activating protein) has been implicated in the regulation of cell motility, adhesion, proliferation, and apoptosis. In this study, Cdc42GAP was cloned from smooth muscle tissues. Cdc42GAP, but not inactive R282A Cdc42GAP (alanine substitution at arginine-282), enhanced the GTP hydrolysis of Cdc42 in an in vitro assay. Furthermore, we developed an assay to evaluate the activity of Cdc42GAP in vivo. Stimulation of smooth muscle cells with 5-hydroxytryptamine (5-HT) resulted in the decrease in Cdc42GAP activity. The agonist-induced GAP suppression was reversed by reactive oxygen species inhibitors. Treatment with hydrogen peroxide also inhibited GAP activity in smooth muscle cells. Because the vimentin cytoskeleton undergoes dynamic changes in response to contractile activation, we evaluated the role of Cdc42GAP in regulating vimentin filaments. Smooth muscle cells were infected with retroviruses encoding wild-type Cdc42GAP or its R282A mutant. Expression of wild-type Cdc42GAP, but not mutant R282A GAP, inhibited the increase in the activation of Cdc42 upon agonist stimulation. Phosphorylation of p21-activated kinase (PAK) at Thr-423 (an indication of PAK activation), vimentin phosphorylation (Ser-56), partial disassembly and spatial remodeling, and contraction were also attenuated in smooth muscle cells expressing Cdc42GAP. Our results suggest that the activity of Cdc42GAP is regulated upon contractile activation, which is mediated by intracellular ROS. Cdc42GAP regulates the vimentin network through the Cdc42-PAK pathway in smooth muscle cells during 5-HT stimulation.

Lysophospholipid signaling in the function and pathology of the reproductive system

BACKGROUND

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two prominent signaling lysophospholipids (LPs) exerting their functions through a group of G protein-coupled receptors (GPCRs). This review covers current knowledge of the LP signaling in the function and pathology of the reproductive system.

METHODS

PubMed was searched up to May 2008 for papers on lysophospholipids/LPA/S1P/LPC/SPC in combination with each part of the reproductive system, such as testis/ovary/uterus.

RESULTS

LPA and SIP are found in significant amounts in serum and other biological fluids. To date, 10 LP receptors have been identified, including LPA(1-5) and S1P(1-5). In vitro and in vivo studies from the past three decades have demonstrated or suggested the physiological functions of LP signaling in reproduction, such as spermatogenesis, male sexual function, ovarian function, fertilization, early embryo development, embryo spacing, implantation, decidualization, pregnancy maintenance and parturition, as well as pathological roles in ovary, cervix, mammary gland and prostate cancers.

CONCLUSIONS

Receptor knock-out and other studies indicate tissue-specific and receptor-specific functions of LP signaling in reproduction. More comprehensive studies are required to define mechanisms of LP signaling and explore the potential use as a therapeutic target.

Intermediate filaments in smooth muscle

The intermediate filament (IF) network is one of the three cytoskeletal systems in smooth muscle. The type III IF proteins vimentin and desmin are major constituents of the network in smooth muscle cells and tissues. Lack of vimentin or desmin impairs contractile ability of various smooth muscle preparations, implying their important role for smooth muscle force development. The IF framework has long been viewed as a fixed cytostructure that solely provides mechanical integrity for the cell. However, recent studies suggest that the IF cytoskeleton is dynamic in mammalian cells in response to various external stimulation. In this review, the structure and biological properties of IF proteins in smooth muscle are summarized. The role of IF proteins in the modulation of smooth muscle force development and redistribution/translocation of signaling partners (such as p130 Crk-associated substrate, CAS) is depicted. This review also summarizes our latest understanding on how the IF network may be regulated in smooth muscle.

Analysis of sphingosine 1-phosphate receptors involved in constriction of isolated cerebral arteries with receptor null mice and pharmacological tools

BACKGROUND AND PURPOSE

Sphingosine 1-phosphate (S1P) selectively and potently constricts isolated cerebral arteries, but this response has not been pharmacologically characterized.

EXPERIMENTAL APPROACH

The receptor subtype(s) involved in S1P-induced cerebrovascular constriction were characterized using genetic (S1P(2) and S1P(3) receptor null mice) and pharmacological tools (phospho-FTY720, a S1P(1/3/4/5) receptor agonist; SEW2871, a S1P(1) receptor agonist, JTE-013, a S1P(2) receptor antagonist, VPC23019, a S1P(1/3) receptor antagonist). Isolated basilar or peripheral (femoral, mesenteric resistance) arteries, from either rat or mouse, were studied in a wire myograph.

KEY RESULTS

S1P concentration-dependently constricted basilar artery in rat, wild-type (WT) and S1P(2) null mice, but barely affected vascular tone in S1P(3) null mice. Vasoconstriction to U46619 (a thromboxane analogue) or to endothelin-1 did not differ between WT, S1P(2) and S1P(3) null mice. JTE-013 inhibited not only S1P-induced vasoconstriction, but also KCl-, U46619- and endothelin-1-induced constriction. This effect was observed in WT as well as in S1P(2) null mice. VPC23019 increased the concentration-dependent vasoconstriction to S1P in both rat and mouse basilar arteries with intact endothelium, but not in rat basilar artery without endothelium. Phospho-FTY720 concentration-dependently constricted rat basilar arteries, but not femoral or mesenteric resistance arteries, while SEW2871 did not induce any response in the same arteries.

CONCLUSIONS AND IMPLICATIONS

S1P constricts cerebral arteries through S1P(3) receptors. The purported S1P(2) receptor antagonist JTE-013 does not appear to be selective, at least in rodents. Enhancement of S1P-induced contraction by VPC23019 might be related to blockade of S1P(1) receptors and NO generation.

Role of lysophosphatidic acid in the regulation of uterine leiomyoma cell proliferation by phospholipase D and autotaxin

Phospholipase D (PLD) hydrolyzes phosphatidylcholine into phosphatidic acid (PA), a lipidic mediator that may act directly on cellular proteins or may be metabolized into lysophosphatidic acid (LPA). We previously showed that PLD contributed to the mitogenic effect of endothelin-1 (ET-1) in a leiomyoma cell line (ELT3 cells). In this work, we tested the ability of exogenous PA and PLD from Streptomyces chromofuscus (scPLD) to reproduce the effect of endogenous PLD in ELT3 cells and the possibility that these agents acted through LPA formation. We found that PA, scPLD, and LPA stimulated thymidine incorporation. LPA and scPLD induced extracellular signal-regulated kinase (ERK(1/2)) mitogen-activated protein kinase activation. Using Ki16425, an LPA(1)/LPA(3) receptor antagonist and small interfering RNA targeting LPA(1) receptor, we demonstrated that scPLD acted through LPA production and LPA(1) receptor activation. We found that scPLD induced LPA production by hydrolyzing lysophosphatidylcholine through its lysophospholipase D (lysoPLD) activity. Autotaxin (ATX), a naturally occurring lysoPLD, reproduced the effects of scPLD. By contrast, endogenous PLD stimulated by ET-1 failed to produce LPA. These results demonstrate that scPLD stimulated ELT3 cell proliferation by an LPA-dependent mechanism, different from that triggered by endogenous PLD. These data suggest that in vivo, an extracellular lysoPLD such as ATX may participate in leiomyoma growth through local LPA formation.

Autocrine and paracrine roles of sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite that has been implicated in many biological processes, including cell migration, survival, proliferation, angiogenesis and immune and allergic responses. S1P levels inside cells are regulated tightly by the balance between its synthesis by sphingosine kinases and degradation by S1P lyases and S1P phosphatases. Activation of sphingosine kinase by any of a variety of agonists increases S1P levels, which in turn can function intracellularly as a second messenger or in an autocrine and/or paracrine fashion to activate and signal through S1P receptors present on the surface of the cell. This review summarizes recent findings on the roles of S1P as a mediator of the actions of cytokines, growth factors and hormones.

Sphingosine 1-phosphate receptors in health and disease: mechanistic insights from gene deletion studies and reverse pharmacology

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that is critically involved in the embryonic development of the cardiovascular and central nervous systems. In the adult, S1P can produce cytoskeletal re-arrangements in many cell types to regulate immune cell trafficking, vascular homeostasis and cell communication in the central nervous system. S1P is contained in body fluids and tissues at different concentrations, and excessive production of the pleiotropic mediator at inflammatory sites may participate in various pathological conditions. Gene deletion studies and reverse pharmacology (techniques aiming to identify both ligands and function of receptors) provided evidence that many effects of S1P are mediated via five G-protein-coupled S1P receptor subtypes, and novel therapeutic strategies based on interaction with these receptors are being initiated. The prototype S1P receptor modulator, FTY720 (fingolimod), targets four of the five S1P receptor subtypes and may act at several levels to modulate lymphocyte trafficking via lymphocytic and endothelial S1P1 and, perhaps, other inflammatory processes through additional S1P receptor subtypes. A recently completed Phase II clinical trial suggested that the drug may provide an effective treatment of relapsing-remitting multiple sclerosis. FTY720 is currently being evaluated in larger-scale, longer-term, Phase III studies. This review provides an overview on S1P activities and S1P receptor function in health and disease, and summarizes the clinical experience with FTY720 in transplantation and multiple sclerosis.

Hormonal signaling and signal pathway crosstalk in the control of myometrial calcium dynamics

Understanding the basis for the control of myometrial contractant and relaxant signaling pathways is important to understanding how to manage myometrial contractions. Signaling pathways are influenced by the level of expression of the signals and signal pathway components, the location of these components in the appropriate subcellular environment, and covalent modification. Crosstalk between these pathways regulates the effectiveness of signal transduction and represents an important way by which hormones can regulate phenotype. This review deals primarily with signaling pathways that control Ca2+ entry and intracellular release, as well as the interplay between these pathways.