Pregnancy-specific enhancement of agonist-stimulated ERK-1/2 signaling in uterine artery endothelial cells increases Ca(2+) sensitivity of endothelial nitric oxide synthase as well as cytosolic phospholipase A(2)

Alphastatin-C a new inhibitor of endothelial cell activation is a pro-arteriogenic agent in vivo and retards B16-F10 melanoma growth in a preclinical model

Most characterized angiogenic modulators are proteolytic fragments of structural plasma and/or matrix components. Herein, we have identified a novel anti-angiogenic peptide generated by the in vitro hydrolysis of the C-terminal moiety of the fibrinogen alpha chain, produced by the snake venom metalloprotease bothropasin (SVMP), a hemorrhagic proteinase in Bothrops jararaca venom. The 14-amino acids peptide (alphastatin-C) is a potent antagonist of basic fibroblast growth factor, induced endothelial cell (HUVEC-CS) proliferation, migration and capillary tube formation in matrigel. It also inhibits cell adhesion to fibronectin. The basis of the antagonism between bFGF and alphastatin-C is elucidated by the inhibition of various bFGF induced signaling pathways and their molecular components modification, whenever the combination of the stimuli is provided, in comparison to the treatment with bFGF only. To corroborate to the potential therapeutic use of alphastatin-C, we have chosen to perform in vivo assays in two distinct angiogenic settings. In chick model, alphastatin-C inhibits chorioallantoic membrane angiogenesis. In mouse, it efficiently reduces tumor number and volume in a melanoma model, due to the impairment of tumor neovascularization in treated mice. In contrast, we show that the alphastatin-C peptide induces arteriogenesis, increasing pial collateral density in neonate mice. alphastatin-C is an efficient new antiangiogenic FGF-associated agent in vitro, it is an inhibitor of embryonic and tumor vascularization in vivo while, it is an arteriogenic agent. The results also suggest that SVMPs can be used as in vitro biochemical tools to process plasma and/or matrix macromolecular components unraveling new angiostatic peptides.

Estrogen Receptors and Estrogen-Induced Uterine Vasodilation in Pregnancy

Normal pregnancy is associated with dramatic increases in uterine blood flow to facilitate the bidirectional maternal–fetal exchanges of respiratory gases and to provide sole nutrient support for fetal growth and survival. The mechanism(s) underlying pregnancy-associated uterine vasodilation remain incompletely understood, but this is associated with elevated estrogens, which stimulate specific estrogen receptor (ER)-dependent vasodilator production in the uterine artery (UA). The classical ERs (ERα and ERβ) and the plasma-bound G protein-coupled ER (GPR30/GPER) are expressed in UA endothelial cells and smooth muscle cells, mediating the vasodilatory effects of estrogens through genomic and/or nongenomic pathways that are likely epigenetically modified. The activation of these three ERs by estrogens enhances the endothelial production of nitric oxide (NO), which has been shown to play a key role in uterine vasodilation during pregnancy. However, the local blockade of NO biosynthesis only partially attenuates estrogen-induced and pregnancy-associated uterine vasodilation, suggesting that mechanisms other than NO exist to mediate uterine vasodilation. In this review, we summarize the literature on the role of NO in ER-mediated mechanisms controlling estrogen-induced and pregnancy-associated uterine vasodilation and our recent work on a “new” UA vasodilator hydrogen sulfide (H₂S) that has dramatically changed our view of how estrogens regulate uterine vasodilation in pregnancy.

The Roles of NO and H2S in Sperm Biology: Recent Advances and New Perspectives

After being historically considered as noxious agents, nitric oxide (NO) and hydrogen sulfide (H2S) are now listed as gasotransmitters, gaseous molecules that play a key role in a variety of cellular functions. Both NO and H2S are endogenously produced, enzymatically or non-enzymatically, and interact with each other in a range of cells and tissues. In spite of the great advances achieved in recent decades in other biological systems, knowledge about H2S function and interactions with NO in sperm biology is in its infancy. Here, we aim to provide an update on the importance of these molecules in the physiology of the male gamete. Special emphasis is given to the most recent advances in the metabolism, mechanisms of action, and effects (both physiological and pathophysiological) of these gasotransmitters. This manuscript also illustrates the physiological implications of NO and H2S observed in other cell types, which might be important for sperm function. The relevance of these gasotransmitters to several signaling pathways within sperm cells highlights their potential use for the improvement and successful application of assisted reproductive technologies.

Pregnancy-adapted uterine artery endothelial cell Ca2+ signaling and its relationship with membrane potential

Pregnancy‐derived uterine artery endothelial cells (P‐UAEC) express P2Y2 receptors and at high cell density show sustained and synchronous [Ca2+]i burst responses in response to ATP. Bursts in turn require coupling of transient receptor potential canonical type3 channel (TRPC3) and inositol 1,4,5‐triphosphate receptor type 2 (IP3R2), which is upregulated in P‐UAEC in a manner dependent on connexin 43 (Cx43) gap junctions. While there is no known direct interaction of TRPC3 with Cx43, early descriptions of TRPC3 function showed it may also be influenced by altered membrane potential (V_m). Herein, we ask if enhanced TRPC3 Ca2+ bursting due to enhanced Cx43 coupling may be coupled via dynamic alterations in V_m in P‐UAEC, as reported in some (HUVEC) but not all endothelial cells. Following basic electrical characterization of UAEC, we employed a high sensitivity cell imaging system to simultaneously monitor cell V_m and [Ca2+]i in real time in continuous monolayers of UAEC. Our findings show that while acute and sustained phase [Ca2+]i bursting occur dose‐dependently in response to ATP, V_m is not coregulated with any periodicity related to [Ca2+]i bursting. Only a small but significant progressive change in V_m is seen, and this is more closely related to overall mobilization of Ca2+. Surprisingly, this is also most apparent in NP‐UAEC > P‐UAEC. In contrast [Ca2+]i bursting is more synchronous in P‐UAEC and even achieves [Ca2+]i waves passing through the P‐UAEC monolayer. The relevance of these findings to mechanisms of pregnancy adaptation and its failure in hypertensive pregnancy are discussed.

Phosphorylation of Ser-279/282 and Tyr-265 positions on Cx43 as possible mediators of VEGF-165 inhibition of pregnancy-adapted Ca2+ burst function in ovine uterine artery endothelial cells

Normal pregnancy requires increased uterine endothelial cell driven vasodilation that is related to increases in sustained Ca2+ signaling via increased connexin 43 (Cx43) gap junction function. Preeclampsia, a hypertensive disorder of pregnancy associated with endothelial dysfunction, is also linked with down regulation of Ca2+ driven vasodilator production and increased levels of vascular endothelial growth factor (VEGF). Cx43 function can be acutely down-regulated by phosphorylation of multiple inhibitory residues and VEGF is known to promote phosphorylation of Cx43. Herein, we show that VEGF-165 promotes Cx43 phosphorylation at Ser-279/282 and Tyr-265 residues and blocks pregnancy-adapted Ca2+ signaling in ovine uterine artery endothelial cells (UAEC). Pharmacological Src and ERK kinase pathway inhibitors (PP2 and U0126) reverse these phosphorylations and rescue Ca2+ signaling. We also report a nutraceutical Src inhibitor, t10,c12 conjugated linoleic acid (10,12 CLA), rescues Ca2+ signaling in UAEC and therefore may have therapeutic potential for preeclampsia.

Altered VEGF-stimulated Ca2+ signaling in part underlies pregnancy-adapted eNOS activity in UAEC

In pregnancy, the uterine vasculature undergoes dramatic vasodilatory adaptations. Previously, vascular endothelial growth factor (VEGF) has been shown to stimulate endothelial nitric oxide synthase (eNOS) in uterine artery endothelial cells (UAECs) derived from pregnant ewes to a greater extent than those from non-pregnant ewes in a manner not fully explained by changes in the phosphorylation of eNOS. In this study, we used Fura-2 Ca(2+) imaging and arginine-to-citrulline conversion eNOS activity assays to assess the importance of VEGF-stimulated Ca(2+) responses in pregnancy-related changes in NO production in UAEC. In this study, we show that pregnancy-induced changes in VEGF-stimulated Ca(2+) responses could account in part for the greater capacity of VEGF to stimulate eNOS in UAECs from pregnant versus non-pregnant animals. VEGF-stimulated Ca(2+) responses in UAECs from pregnant and non-pregnant animals were mediated through VEGF receptor 2 and were detected in roughly 15% of all cells. There were no pregnancy-specific differences in area under the curve or peak height. UAECs from pregnant animals were more consistent in the time to response initiation, had a larger component of extracellular Ca(2+) entry, and were more sensitive to a submaximal dose of VEGF. In UAECs from pregnant and non-pregnant animals Ca(2+) responses and eNOS activation were sensitive to the phospholipase C/inositol 1,4,5-trisphosphate pathway inhibitors 2-aminoethoxydiphenylborane and U73122. Thus, changes in VEGF-stimulated [Ca(2+)]i are necessary for eNOS activation in UAECs, and pregnancy-induced changes in Ca(2+) responses could also in part explain the pregnancy-specific adaptive increase in eNOS activity in UAECs.

eNOS activation and NO function: pregnancy adaptive programming of capacitative entry responses alters nitric oxide (NO) output in vascular endothelium--new insights into eNOS regulation through adaptive cell signaling

In pregnancy, vascular nitric oxide (NO) production is increased in the systemic and more so in the uterine vasculature, thereby supporting maximal perfusion of the uterus. This high level of functionality is matched in the umbilical vein, and in corresponding disease states such as pre-eclampsia, reduced vascular responses are seen in both uterine artery and umbilical vein. In any endothelial cell, NO actually produced by endothelial NO synthase (eNOS) is determined by the maximum capacity of the cell (eNOS expression levels), eNOS phosphorylation state, and the intracellular [Ca(2+)](i) concentration in response to circulating hormones or physical forces. Herein, we discuss how pregnancy-specific reprogramming of NO output is determined as much by pregnancy adaptation of [Ca(2+)](i) signaling responses as it is by eNOS expression and phosphorylation. By examining the changes in [Ca(2+)](i) signaling responses from human hand vein endothelial cells, uterine artery endothelial cells, and human umbilical vein endothelial cells in (where appropriate) nonpregnant, normal pregnant, and pathological pregnant (pre-eclamptic) state, it is clear that pregnancy adaptation of NO output occurs at the level of sustained phase 'capacitative entry' [Ca(2+)](i) response, and the adapted response is lacking in pre-eclamptic pregnancies. Moreover, gap junction function is an essential permissive regulator of the capacitative response and impairment of NO output results from any inhibitor of gap junction function, or capacitative entry using TRPC channels. Identifying these [Ca(2+)](i) signaling mechanisms underlying normal pregnancy adaptation of NO output not only provides novel targets for future treatment of diseases of pregnancy but may also apply to other common forms of hypertension.

[Ca2+]i signaling vs. eNOS expression as determinants of NO output in uterine artery endothelium: relative roles in pregnancy adaptation and reversal by VEGF165

Pregnancy is a time of greatly increased uterine blood flow to meet the needs of the growing fetus. Increased uterine blood flow is also observed in the follicular phase of the ovarian cycle. Simultaneous fura-2 and 4,5-diaminofluoresceine (DAF-2) imaging reveals that cells of the uterine artery endothelium (UA Endo) from follicular phase ewes produce marginally more nitric oxide (NO) in response to ATP than those from luteal phase. However, this is paralleled by changes in NO in response to ionomycin, suggesting this is solely due to higher levels of endothelial nitric oxide synthase (eNOS) protein in the follicular phase. In contrast, UA Endo from pregnant ewes (P-UA Endo) produces substantially more NO (4.62-fold initial maximum rate, 2.56-fold overall NO production) in response to ATP, beyond that attributed to eNOS levels alone (2.07-fold initial maximum rate, 1.93-fold overall with ionomycin). The ATP-stimulated intracellular free calcium concentration ([Ca(2+)](i)) response in individual cells of P-UA Endo comprises an initial peak followed by transient [Ca(2+)](i) bursts that are limited in the luteal phase, not altered in the follicular phase, but are sustained in pregnancy and observed in more cells. Thus pregnancy adaptation of UA Endo NO output occurs beyond the level of eNOS expression and likely through associated [Ca(2+)](i) cell signaling changes. Preeclampsia is a condition of a lack of UA Endo adaptation and poor NO production/vasodilation and is associated with elevated placental VEGF(165). While treatment of luteal NP-UA Endo and P-UA Endo with VEGF(165) acutely stimulates a very modest [Ca(2+)](i) and NO response, subsequent stimulation of the same vessel with ATP results in a blunted [Ca(2+)](i) and an associated NO response, with P-UA Endo reverting to the response of luteal NP-UA Endo. This demonstrates the importance of adaptation of cell signaling over eNOS expression in pregnancy adaptation of uterine endothelial function and further implicates VEGF in the pathophysiology of preeclampsia.

Pregnancy enhances sustained Ca2+ bursts and endothelial nitric oxide synthase activation in ovine uterine artery endothelial cells through increased connexin 43 function

Endothelium-mediated vasodilation is specifically enhanced in uterine circulation during pregnancy, and production of nitric oxide (NO) is increased in response to a wide array of agonists. Uterine artery endothelial cells from nonpregnant (NP-UAECs) or pregnant (P-UAECs) ewes maintained in culture still show a pregnancy-enhanced difference in ATP-stimulated endothelial NO synthase (eNOS; official symbol NOS3) activation, even though NOS3 protein, purinergic receptors, and associated cell signaling proteins are expressed at equal levels. We have also shown that the pregnancy-enhanced endothelial cell NO response to ATP requires an enhanced and sustained capacitative entry phase that is likely mediated via canonical transient receptor potential protein/inositol 1,4,5-trisphosphate receptor type 2 interaction. In this study, we now show by simultaneous video imaging of individual Fura-2-loaded cells that the pregnancy-enhanced capacitative entry phase is not continuous and equal in all cells, but is in fact mediated as a series of periodic [Ca(2+)](i) bursts within individual cells. Not only does pregnancy increase the number of bursts over a longer time period in individual cells, but also a greater proportion of cells exhibit this burst activity, and at high cell density this occurs in a synchronous manner. The mediator of cell synchronization is connexin 43 (Cx43) gap junctions because 1) Cx43 is readily detectable by Western blot analysis in UAECs, whereas Cx40 and Cx37 are weakly detected or absent, and 2) pregnancy-specific enhancement of [Ca(2+)](i) bursts by ATP is blocked by inhibitory loop peptides selective to Cx43 ((43,37)GAP27) but not by a scrambled control peptide or (40)GAP27 or (40,37)GAP26 peptides, which are specific to Cx40 or Cx37. The relationship between Ca(2+) bursts and NOS3 activation is further established by the finding that (43,37)GAP27 inhibits ATP-stimulated NOS3 activation but has no effect on cell mitogenesis. We conclude that it is pregnancy-enhanced gap junction communication between cells that underlies pregnancy enhancement of capacitative entry via TRPC3 and, in turn, NOS3 activation. Such improved gap junction function allows greater and more sustained [Ca(2+)](i) responses to agents such as ATP within a single cell, as well as the additional recruitment of greater numbers of cells to the response in a coordinated and synchronous manner to support enhanced NO production.

Pregnancy and Ovarian Steroid Regulation of Angiotensin II Type 1 and Type 2 Receptor Expression in Ovine Uterine Artery Endothelium and Vascular Smooth Muscle

Although pregnancy is clearly associated with refractoriness to infused angiotensin II (AII) in the uteroplacental unit, there is still dispute over the mechanism by which angiotensin type 1 and type 2 receptors (AT1R and AT2R) may mediate this response in the uterine artery. This is in large part due to incomplete knowledge of levels of AT1R and AT2R expression and function in uterine artery endothelium (UA Endo) in the nonpregnant (NP) and pregnant (P) states, combined with the disagreement on whether AII may act through release of adrenomedullary catecholamines. The authors have previously described an increase in AT1R in UA Endo but not UA vascular smooth muscle (VSM) during pregnancy as compared to the nonpregnant intact ewe. Herein they report that the pregnancy-associated increase in AT(1)R expression in UA Endo is regulated by ovarian steroids. Using a recently developed antibody to AT2R, the authors now show there is no change in AT2R in UA Endo or VSM associated with ovarian function, and although AT2R is not changed in UA Endo by pregnancy, there is a significant decrease observed in UA VSM at that time. The authors also examined changes in receptors in UA Endo and VSM in estrogen (E2beta)-primed ewes in view of the common use of this model as a control for physiologic studies. In contrast to their findings in nonprimed nonpregnant or pregnant animals, the authors observed a significant increase in both AT1R and AT2R in UA Endo in response to the supraphysiologic priming with E2beta. In order to address the possible functionality of AT1R or AT2R in UA Endo, the authors used the uterine artery endothelial cell (UAEC) model of UA endothelial cells maintained in culture to passage 4. Differences in expression of AT1R or AT2R were normalized at passage 4 in P-UAECs and NP-UAECs. Treatment with AII activated phospholipase C (PLC) in both NP- and P-UAECs but signaling through the extracellular signal-regulated kinase (ERK) pathway was dramatically enhanced in P-UAECs compared to NP-UAECs. Surprisingly, both phosphoinositol turnover and ERK2 phosphorylation responses failed to display the expected dose-responses. Inhibition of AII-stimulated ERK2 phosphorylation with antagonists DUP 753 (AT1R, 10 microM) and PD 123319 (AT2R, 10 microM) failed to selectively inhibit ERK2 phosphorylation. The authors conclude that (a) the net effect of pregnancy may be an increase in the AT1R/AT2R ratio in both UA Endo and VSM but through apparently distinct mechanisms, (b) the ovariectomized animal model is similar to the luteal state for AT1R and AT2R expression, while the E2beta-primed model does not resemble the nonpregnant or pregnant state, and (c) there is a real possibility that AII may mediate its effects either through a complex AT1R-AT2R interaction or via an as-yet unidentified non-AT1, non-AT2 receptor.

Vascular endothelial growth factor acts through novel, pregnancy-enhanced receptor signalling pathways to stimulate endothelial nitric oxide synthase activity in uterine artery endothelial cells

During pregnancy, VEGF (vascular endothelial growth factor) regulates in part endothelial angiogenesis and vasodilation. In the present study we examine the relative roles of VEGFRs (VEGF receptors) and associated signalling pathways mediating the effects of VEGF(165) on eNOS (endothelial nitric oxide synthase) activation. Despite equal expression levels of VEGFR-1 and VEGFR-2 in UAECs (uterine artery endothelial cells) from NP (non-pregnant) and P (pregnant) sheep, VEGF(165) activates eNOS at a greater level in P- compared with NP-UAEC, independently of Akt activation. The selective VEGFR-1 agonist PlGF (placental growth factor)-1 elicits only a modest activation of eNOS in P-UAECs compared with VEGF(165), whereas the VEGFR-2 kinase inhibitor blocks VEGF(165)-stimulated eNOS activation, suggesting VEGF(165) predominantly activates eNOS via VEGFR-2. Although VEGF(165) also activates ERK (extracellular-signal-regulated kinase)-1/2, this is not necessary for eNOS activation since U0126 blocks ERK-1/2 phosphorylation, but not eNOS activation, and the VEGFR-2 kinase inhibitor inhibits eNOS activation, but not ERK-1/2 phosphorylation. Furthermore, the inability of PlGF to activate ERK-1/2 and the ability of the VEGFR-2 selective agonist VEGF-E to activate ERK-1/2 and eNOS suggests again that both eNOS and ERK-1/2 activation occur predominantly via VEGFR-2. The lack of VEGF(165)-stimulated Akt phosphorylation is consistent with a lack of robust phosphorylation of Ser(1179)-eNOS. Although VEGF(165)-stimulated eNOS phosphorylation is observed at Ser(617) and Ser(635), pregnancy does not significantly alter this response. Our finding that VEGF(165) activation of eNOS is completely inhibited by wortmannin but not LY294002 implies a downstream kinase, possibly a wortmannin-selective PI3K (phosphoinositide 3-kinase), is acting between the VEGFR-2 and eNOS independently of Akt.

Review article: steroid hormones and uterine vascular adaptation to pregnancy

Pregnancy is a physiological state that involves a significant decrease in uterine vascular tone and an increase in uterine blood flow, which is mediated in part by steroid hormones, including estrogen, progesterone, and cortisol. Previous studies have demonstrated the involvement of these hormones in the regulation of uterine artery contractility through signaling pathways specific to the endothelium and the vascular smooth muscle. Alterations in endothelial nitric oxide synthase expression and activity, nitric oxide production, and expression of enzymes involved in PGI(2) production contribute to the uterine artery endothelium-specific responses. Steroid hormones also have an effect on calcium-activated potassium channel activity, PKC signaling pathway and myogenic tone, and alterations in pharmacomechanical coupling in the uterine artery smooth muscle. This review addresses current understanding of the molecular mechanisms by which steroid hormones including estrogen, progesterone, and cortisol modulate uterine artery contractility to alter uterine blood flow during pregnancy with an emphasis on the pregnant ewe model.

Inhibition of MEK/ERK1/2 signalling alters endothelial nitric oxide synthase activity in an agonist-dependent manner

eNOS (endothelial nitric oxide synthase) activity is post-translationally regulated in a complex fashion by acylation, protein-protein interactions, intracellular trafficking and phosphorylation, among others. Signalling pathways that regulate eNOS activity include phosphoinositide 3-kinase/Akt, cyclic nucleotide-dependent kinases [PKA (protein kinase A) and PKG], PKC, as well as ERKs (extracellular-signal-regulated kinases). The role of ERKs in eNOS activation remains controversial. In the present study, we have examined the role of ERK1/2 in eNOS activation in HUVEC-CS [transformed HUVEC (human umbilical-vein endothelial cells)] as well as a widely used model for eNOS study, transiently transfected COS-7 cells. U0126 pretreatment of HUVEC-CS potentiated ATP-stimulated eNOS activity, independent of changes in intracellular Ca2+ concentration ([Ca2+]i). In COS-7 cells transiently expressing ovine eNOS, U0126 potentiated A23187-stimulated eNOS activity, but inhibited ATP-stimulated activity. Compensatory changes in phosphorylation of five key eNOS residues did not account for changes in A23187-stimulated activity. However, in the case of ATP, altered phosphorylation and changes in [Ca2+]i may partially contribute to U0126 inhibition of activity. Finally, seven eNOS alanine mutants of putative ERK1/2 targets were generated and the effects of U0126 pretreatment on eNOS activity were gauged with A23187 and ATP treatment. T97A-eNOS was the only construct significantly different from wild-type after U0126 pretreatment and ATP stimulation of eNOS activation. In the present study, eNOS activity was either potentiated or inhibited in COS-7 cells, suggesting agonist dependence for MEK/ERK1/2 signalling [where MEK is MAPK (mitogen-activated protein kinase)/ERK kinase] to eNOS and a complex mechanism including [Ca2+]i, phosphorylation and, possibly, intracellular trafficking.

Pregnancy attenuates uterine artery pressure-dependent vascular tone: role of PKC/ERK pathway

The mechanisms of adaptation of uterine artery vascular tone to pregnancy are not fully understood. The present study tested the hypothesis that pregnancy decreases the PKC-mediated Ca(2+) sensitivity of the contractile process and attenuates myogenic tone in resistance-sized uterine arteries. In pressurized uterine arteries from nonpregnant (NPUA) and near-term pregnant (PUA) sheep, we measured, simultaneously in the same tissue, vascular diameter and vessel wall intracellular Ca(2+) concentration ([Ca(2+)](i)) as a function of intraluminal pressure. In both NPUA and PUA, membrane depolarization with KCl caused a rapid increase in [Ca(2+)](i) and a decrease in diameter. A pressure increase from 20 to 100 mmHg resulted in a transient increase in diameter that was associated with an increase in [Ca(2+)](i), followed by myogenic contractions in the absence of further changes in [Ca(2+)](i). In addition, activation of PKC by phorbol 12,13-dibutyrate induced a decrease in diameter in the absence of changes in [Ca(2+)](i). Pressure-dependent myogenic responses were significantly decreased in PUA compared with NPUA. However, pressure-induced increases in [Ca(2+)](i) were not significantly different between PUA and NPUA. The ratio of changes in diameter to changes in [Ca(2+)](i) was significantly greater for pressure-induced contraction of NPUA than that of PUA. Inhibition of PKC by calphostin C significantly attenuated the pressure-induced vascular tone and eliminated the difference of myogenic responses between NPUA and PUA. In contrast, the MAPKK (MEK) inhibitor PD-098059 had no effect on NPUA but significantly enhanced myogenic responses of PUA. In the presence of PD-098059, there was no difference in pressure-induced myogenic responses between NPUA and PUA. The results suggest that pregnancy downregulates pressure-dependent myogenic tone of the uterine artery, which is partly due to increased MEK/ERK activity and decreased PKC signal pathway leading to a decrease in Ca(2+) sensitivity of myogenic mechanism in the uterine artery during pregnancy.

Upregulation of endothelial cell Ca2+ signaling contributes to pregnancy-enhanced vasodilation of rat uteroplacental arteries

Normal pregnancy is characterized by an increased uterine blood flow due to growth and remodeling of the maternal uterine vasculature and enhanced vasodilation of the uterine arteries. The objective of the present study was to examine the role of endothelial cell Ca2+ signaling in augmented endothelium-mediated vasodilation of uteroplacental arteries in late pregnancy. We performed fura-2-based measurements of the intracellular Ca2+ concentration ([Ca2+]i) in the cytoplasm of endothelial cells simultaneously with diameter in pressurized uterine arteries from nonpregnant (NP) and late-pregnant (LP) rats. Basal levels of endothelial cell [Ca2+]i were higher in arteries from LP rats compared with NP controls. Withdrawal of extracellular Ca2+ resulted in a decrease in the level of basal [Ca2+]i that was significantly larger in arteries of LP than NP rats. The rate of Mn2+ -induced quenching of fura-2 fluorescence was significantly elevated in late pregnancy, implicating augmented Ca2+ influx as a cause of increased basal levels of [Ca2+]i in endothelial cells. Elevation of intraluminal pressure resulted in a transient increase in endothelial [Ca2+]i that was markedly potentiated in late gestation. ACh-induced [Ca2+]i and vasodilator responses were significantly augmented in arteries of LP compared with NP rats and were abolished by BAPTA treatment, demonstrating a critical role of [Ca2+]i elevation in the production of endothelium-derived vasodilators. Together, these results indicate that late pregnancy is a state of enhanced basal and stimulated Ca2+ signaling in endothelial cells of uterine vessels, which may represent an important underlying mechanism for augmented vasodilation in the maternal uterine circulation.

Dissociation of endothelial nitric oxide synthase phosphorylation and activity in uterine artery endothelial cells

Pregnancy enhanced nitric oxide production by uterine artery endothelial cells (UAEC) is the result of reprogramming of both Ca(2+) and kinase signaling pathways. Using UAEC derived from pregnant ewes (P-UAEC), as well as COS-7 cells transiently expressing ovine endothelial nitric oxide synthase (eNOS), we investigated the role of phosphorylation of five known amino acids following treatment with physiological calcium-mobilizing agent ATP and compared with the effects of PMA (also known as TPA) alone or in combination with ATP. In P-UAEC, ATP stimulated eNOS activity and phosphorylation of eNOS S617, S635, and S1179. PMA promoted eNOS phosphorylation but without activation. PMA and ATP cotreatment attenuated ATP-stimulated activity despite no increase in phospho (p)-T497 and potentiation of p-S1179. In COS-7 cells, PMA inhibition of ATP-stimulated eNOS activity was associated with p-T497 phosphorylation. Although T497D eNOS activity was reduced to 19% of wild-type eNOS with ATP and 44% with A23187, we nonetheless observed more p-S1179 with ATP than with A23187 (3.4-fold and 1.8-fold of control, respectively). Furthermore, the S1179A eNOS mutation partly attenuated ATP- but not A23187-stimulated activity, but when combined with T497D, no further reduction of eNOS activity was observed. In conclusion, although phosphorylation of eNOS is associated with activation in P-UAEC, no single or combination of phosphorylation events predict activity changes. In COS-7 cells, phosphorylation of T497 can attenuate activity but also influences S1179 phosphorylation. We conclude that in both cell types, observed changes in phosphorylation of key residues may influence eNOS activation but are not sufficient alone to describe eNOS activation.

Pregnancy-specific modulatory role of mitochondria on adenosine 5'-triphosphate-induced cytosolic [Ca2+] signaling in uterine artery endothelial cells

Vascular endothelial cells respond to extracellular ATP by inositol 1,4,5-trisphosphate-mediated Ca2+ release from the endoplasmic reticulum followed by Ca2+ influx and subsequent synthesis of vasodilators. In this study, the contribution of mitochondria in shaping the ATP-induced Ca2+ increase was examined in ovine uterine artery endothelial cells from nonpregnant and pregnant (late gestation) ewes (NP- and P-UAEC, passage 4). The mitochondrial protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) induced a rapid mitochondrial depolarization. CCCP also slowly increased cytosolic [Ca2+] ([Ca2+]c), which then gradually declined to 10-20 nM above resting level. Pretreatment with CCCP for 30 min significantly inhibited both ATP and thapsigargin-induced [Ca2+]c, with inhibition in NP-UAEC more effective than in P-UAEC. Pretreatment of mitochondrial permeability transition pore inhibitor cyclosporine A did not affect CCCP-induced mitochondrial depolarization, but delayed CCCP-induced [Ca2+]c for about 12-15 min (we termed this the "window of time"). During the cyclosporine A-delayed window of time of CCCP-induced [Ca2+]c, ATP induced a normal Ca2+ response, but after this window of time, ATP-induced [Ca2+]c was significantly inhibited. Pretreatment of oligomycin B to prevent intracellular ATP depletion by F0F1-ATPase did not reduce the inhibition of ATP-induced [Ca2+]c by CCCP. Ruthenium red, a mitochondrial Ca2+ uptake blocker, did not mimic the inhibition of Ca2+ signaling by CCCP. In conclusion, our data show that mitochondrial Ca2+ depletion after dissipation of mitochondrial membrane potential with CCCP inhibits ATP-induced [Ca2+]c, mediated at the level of Ca2+ release from the endoplasmic reticulum. Moreover, our data revealed that P-UAEC is more resistant to the inhibitory effect of CCCP on [Ca2+]c than NP-UAEC.

Molecular cloning of ovine endothelial nitric oxide synthase and expression in COS-7 cells

While studies of human and bovine endothelial nitric oxide synthase (eNOS) demonstrate activation by Ca(2+)/calmodulin, recent progress demonstrates that eNOS phosphorylation can alter sensitivity to intracellular free calcium ([Ca(2+)](i)). The sheep, however, is widely used as a model for cardiovascular adaptation to pregnancy and ovine uterine artery endothelial cell (UAEC) eNOS undergoes pregnancy-specific (P) enhancement of activity associated with increased Ca(2+) and protein kinase signaling in response to a number of agonists, including adenosine triphosphate (ATP). The degree of homology between the ovine and human full-length cDNAs was not previously known and yet is necessary to determine the validity in using an ovine model to study human physiology. The objectives of this study were to isolate and validate the clone of ovine eNOS cDNA and investigate ovine eNOS activation when expressed in COS-7 cells. The ovine eNOS cDNA has high homology to published human and bovine sequences and shares identity with the bovine amino acid sequence. When ovine eNOS was transiently expressed in COS-7 cells (COS-7/oeNOS), A23187 increased specific catalytic activity in a dose- and time-dependent manner. A23187-stimulated activation of eNOS was, however, also accompanied by phosphorylation of eNOS S1179 and dephosphorylation of T497, demonstrating that an increase in [Ca(2+)](i) may not be the sole mechanism of activation. The physiologic relevance of this was further underscored by the finding that ATP dose-dependently increased peak [Ca(2+)](i) and eNOS activity in COS-7/oeNOS, but also increased eNOS p-S1179 and decreased p-T497. This finding was similar to those in ovine P-UAEC treated with the Ca(2+)-mobilizing agonist ATP, wherein activation of eNOS was again concomitant with a rise p-S1179 as well as a slight decrease in p-T497. In conclusion, we describe the full-length ovine eNOS cDNA sequence and show that both physiologic and nonphysiologic calcium-mobilizing agents, which activate ovine eNOS in COS-7 and P-UAEC, do so in association with changes in eNOS phosphorylation. Given this information we can now begin to dissect the relationship between Ca(2+) elevation and specific phosphorylation events in eNOS activation in the ovine model, and thereby gain insight into the possible basis for pregnancy-related dysfunction.

Adaptation of uterine artery thick- and thin-filament regulatory pathways to pregnancy

Little is known about the adaptation of uterine artery smooth muscle contractile mechanisms to pregnancy. The present study tested the hypothesis that pregnancy differentially regulates thick- and thin-filament regulatory pathways in uterine arteries. Isometric tension, intracellular free Ca(2+) concentration, and phosphorylation of 20-kDa myosin light chain (MLC(20)) were measured simultaneously in uterine arteries isolated from nonpregnant and near-term (140 days gestation) pregnant sheep. Phenylephrine-mediated intracellular free Ca(2+) concentration, MLC(20) phosphorylation, and contraction tension were significantly increased in uterine arteries of pregnant compared with nonpregnant animals. In contrast, phenylephrine-mediated Ca(2+) sensitivity of MLC(20) phosphorylation was decreased in the uterine arteries of pregnant sheep. Simultaneous measurement of phenylephrine-stimulated tension and MLC(20) phosphorylation in the same tissue indicated a decrease in MLC(20) phosphorylation-independent contractions in the uterine arteries of pregnant sheep. In addition, activation of PKC produced significantly lower sustained contractions in uterine arteries of pregnant compared with nonpregnant animals in the absence of changes in MLC(20) phosphorylation levels in either vessels. In uterine arteries of nonpregnant sheep, the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase inhibitor PD-098059 significantly increased phenylephrine-mediated, MLC(20) phosphorylation-independent contractions. The results suggest that in uterine arteries, pregnancy upregulates alpha(1)-adrenoceptor-mediated Ca(2+) mobilization and MLC(20) phosphorylation. In contrast, pregnancy downregulates the Ca(2+) sensitivity of myofilaments, which is mediated by both thick- and thin-filament pathways.

Simultaneous imaging of [Ca2+]i and intracellular NO production in freshly isolated uterine artery endothelial cells: effects of ovarian cycle and pregnancy

Pregnancy and the follicular phase of the ovarian cycle show elevation of uterine blood flow and associated increases in uterine artery endothelium (UAE) endothelial nitric oxide (NO) synthase (eNOS) expression. Nonetheless, a role for increased NO production during pregnancy and the follicular phase has only been inferred by indirect measures. The recent development of a uterine artery endothelial cell model further suggests that pregnancy is associated with reprogramming of cell signaling, such that eNOS may become more Ca(2+) sensitive and be subject to regulation by Ca(2+)-independent kinases. This study describes for the first time the direct and simultaneous monitoring of NO production and intracellular free Ca(2+) concentration ([Ca(2+)](i)) in freshly isolated UAE from pregnant, follicular, and luteal sheep. The pharmacological agonists ionomycin (calcium ionophore) and thapsigargin (TG; endoplasmic reticulum Ca(2+) pump inhibitor) were used to maximally elevate [Ca(2+)](i) and fully activate eNOS as a measure of eNOS expression. NO production stimulated by ionomycin (5 microM) and TG (10 microM) were 1.95- and 2.05-fold, respectively, in pregnant-UAE and 1.34- and 1.37-fold in follicular-UAE compared with luteal-UAE. In contrast, the physiological agonist ATP (100 microM) stimulated a 3.43-fold increase in NO in pregnant-UAE and a 1.90-fold increase in follicular-UAE compared with luteal-UAE, suggesting that pregnancy and follicular phase enhance eNOS activation beyond changes in expression in vivo. 2-aminoethoxydiphenyl borate (APB; an inositol 1,4,5-trisphosphate receptor blocker) totally prevented the ATP-induced [Ca(2+)](i) response but only partially inhibited NO production. Thus pregnancy-enhanced eNOS activation in UAE is mediated through [Ca(2+)](i)-insensitive pathways as well as through a greater eNOS sensitivity to [Ca(2+)](i).

Pregnancy-specific changes in uterine artery endothelial cell signaling in vivo are both programmed and retained in primary culture

Ovine uterine artery (UA) endothelial cells (UAEC) maintained in culture to passage 4 retain pregnancy-specific changes in vasodilator production, which in turn is associated with differences in Ca(2+) and ERK 1/2 signaling. The question remains whether this is an accurate portrayal of the situation in vivo, or more simply whether these same signaling responses seen at passage 4 accurately reflect those functioning in the cells in vivo. Small groups of endothelial nitric oxide synthase-positive cells from both pregnant and nonpregnant ewes were freshly isolated and used to image changes in the intracellular free calcium concentration ([Ca(2+)](i)) using fura 2 and to detect ERK 1/2 phosphorylation by immunocytochemistry. Furthermore, detailed comparisons of mRNA species were made between freshly isolated and cultured (passage 4) cells using cDNA microarray analysis and verified, where possible, using PowerBlot analysis. Freshly isolated cells showed no detectable [Ca(2+)](i) elevation in response to angiotensin II, epidermal growth factor, basic fibroblast growth factor, or vascular endothelial growth factor but did respond to ATP in a dose-dependent (1-300 microM) manner. At higher doses of ATP, [Ca(2+)](i) elevation was sustained longer and showed a high incidence of regular oscillations in cells from pregnant compared with nonpregnant ewes. Also, ATP and basic fibroblast growth factor treatment caused activation of ERK 1/2 in significantly greater numbers of freshly isolated cells from pregnant than from nonpregnant ewes. cDNA microarray analysis showed results consistent with endothelium but revealed few differences in mRNA species and levels between freshly isolated and passage 4 cells or between the pregnant and nonpregnant ewes. In conclusion, our data show for the first time that pregnancy-specific changes in Ca(2+) and ERK 1/2 signaling are indeed observed in freshly isolated UA endothelium. This suggests in turn that such pregnancy-specific changes in UA endothelial function in vivo in response to a variety of agonists during pregnancy are both programmed at the level of cell signaling and retained in culture.

P2Y6 nucleotide receptor activates PKC to protect 1321N1 astrocytoma cells against tumor necrosis factor-induced apoptosis

1. We recently reported that the activation by UDP of rat P2Y6 nucleotide receptors expressed in 1321N1 astrocytoma cells protected them from TNFalpha-induced apoptosis by suppressing activation of caspase 3 and 8. This study aims to characterize the involvement of intracellular signaling pathways, including kinases involved in the antiapoptotic effect of UDP. 2. Cell death was induced in 1321N1 astrocytoma cells permanently expressing the rat P2Y6 receptor by exposure to TNFalpha in the presence of cycloheximide. The apoptotic fraction was analyzed using flow cytometry. 3. The activation of P2Y6 receptors by UDP both protected the astrocytes from TNF-alpha induced apoptosis and activated protein kinase C (PKC) isotypes. The phorbol ester PMA also activated PKC and protected the cells from TNFalpha-induced cell death. The alpha- and epsilon-isotypes of PKC were both activated in a persistent fashion upon 5-min exposure to either UDP (10 microM) or the phorbol ester PMA (100 nM). The PKCzeta isotype was markedly activated upon UDP treatment. 4. The addition of PKC inhibitors, GF109203X or Gö6976, partially antagonized the protective effect of UDP and reduced the UDP-induced phosphorylation of extracellular signal-regulated protein kinases (Erk). The inhibitors of Erk, PD98,059 or U0126, antagonized UDP-induced protection. 5. The antiapoptotic protein, Akt, was not affected by P2Y6 receptor activation. Incubation of the astrocytes with calcium modifiers BAPTA-AM or dantrolene, did not affect the UDP-induced protection from apoptosis. 6. The addition of phospholipase C (PLC) inhibitors, D609 or U73122, partially antagonized both UDP-induced protection and PKC activation.

Possible mechanisms underlying pregnancy-induced changes in uterine artery endothelial function

The last 10 years has seen a dramatic increase in our understanding of the mechanisms underlying the pregnancy-specific adaptation in cardiovascular function in general and the dramatic changes that occur in uterine artery endothelium in particular to support the growing fetus. The importance of these changes is clear from a number of studies linking restriction of uterine blood flow (UBF) and/or endothelial dysfunction and clinical conditions such as intrauterine growth retardation (IUGR) and/or preeclampsia in both humans and animal models; these topics are covered only briefly here. The recent developments that prompts this review are twofold. The first is advances in an understanding of the cell signaling processes that regulate endothelial nitric oxide synthase (eNOS) in particular (Govers R and Rabelink TJ. Am J Physiol Renal Physiol 280: F193-F206, 2001). The second is the emerging picture that uterine artery (UA) endothelial cell production of nitric oxide (NO) as well as prostacyclin (PGI2) may be as much a consequence of cellular reprogramming at the level of cell signaling as due to tonic stimuli inducing changes in the level of expression of eNOS or the enzymes of the PGI2 biosynthetic pathway (cPLA2, COX-1, PGIS). In reviewing just how we came to this conclusion and outlining the implications of such a finding, we draw mostly on data from ovine or human studies, with reference to other species only where directly relevant.

Increased NO-mediated and reduced TxA2-dependent responses in skeletal muscle arterioles in pregnancy

The contribution of skeletal muscle microvessels to pregnancy-induced decrease in peripheral vascular resistance and its underlying mechanisms are not fully understood. We aimed to test the hypothesis that pregnancy enhances arteriolar dilation and reduces constriction by increasing NO-mediation and decreasing reactivity to TxA2. Thus, changes in diameter of isolated, pressurized gracilis muscle arterioles (d: approximately 180 microm) of non-pregnant (NP) and pregnant (P) rabbits to vasoactive agents were measured by videomicroscopy. Acetylcholine (ACh) elicited significantly greater dilations in P than in NP arterioles that could be inhibited by L-NAME, a NO synthase blocker. Dilations to the NO donor SNP did not differ between P and NP arterioles. Constrictions to norepinephrine and the TxA2 receptor agonist U46619 were significantly attenuated in P as compared to NP arterioles. L-NAME increased norepinephrine-induced arteriolar constrictions eliminating the difference between responses of NP and P arterioles. L-NAME enhanced constrictions to U46619 in P and NP arterioles, but the constrictions were still greater in NP vessels. The number of vascular TxA2 receptors-characterized by the TxA2 analog [125I]-BOP in aortic membrane preparations-was significantly less in P as compared to NP rabbits (NP: 284 +/- 83, P: 62 +/- 14 fmol/mg protein, p<0.01). Thus, pregnancy up-regulates endothelial NO- and down regulates TxA2-mediation of responses of skeletal muscle arterioles. These changes in the local regulation of microvascular tone are likely to favor a dilated state of skeletal muscle arterioles, which may contribute to the decreased peripheral vascular resistance during normal pregnancy.

ERK MAP kinases regulate smooth muscle contraction in ovine uterine artery: effect of pregnancy

The present study investigated the potential role of extracellular signal-regulated kinase (ERK) in uterine artery contraction and tested the hypothesis that pregnancy upregulated ERK-mediated function in the uterine artery. Isometric tension in response to phenylephrine (PE), serotonin (5-HT), phorbol 12,13-dibutyrate (PDBu), and KCl was measured in the ring preparation of uterine arteries obtained from nonpregnant and near-term (140 days gestation) pregnant sheep. Inhibiting ERK activation with PD-98059 did not change the KCl-evoked contraction but significantly inhibited the contraction to 5-HT in both nonpregnant and pregnant uterine arteries. PD-98059 did not affect PE-induced contraction in the uterine arteries of nonpregnant sheep but significantly decreased it in the uterine arteries of pregnant sheep. In accordance, PE stimulated activation of ERK in uterine arteries of pregnant sheep, which was blocked by PD-98059. PD-98059-mediated inhibition of the PE-induced contraction was associated with a decrease in both intracellular Ca(2+) concentration and Ca(2+) sensitivity of contractile proteins in the uterine arteries of pregnant sheep. PDBu-mediated contraction was significantly less in pregnant than in nonpregnant uterine arteries. PD-98059 had no effect on PDBu-induced contraction in nonpregnant but significantly increased it in pregnant uterine arteries. In addition, PD-98059 significantly enhanced PDBu-stimulated protein kinase C activity. The results indicate that ERK plays an important role in the regulation of uterine artery contractility, and its effect is agonist dependent. More importantly, pregnancy selectively enhances the role of ERK in alpha(1)-adrenoceptor-mediated contractions and its effect in suppressing protein kinase C-mediated contraction in the uterine artery.

Endothelial vasodilator production by uterine and systemic arteries. IX. eNOS gradients in cycling and pregnant ewes

The follicular phase (FOL) and pregnancy exhibit increases in uterine blood flow (UBF), estrogen levels, and uterine artery (UA) endothelial nitric oxide synthase (eNOS) expression. UA branching within the mesometrium increases the total vascular cross-sectional area, which reduces the vascular perfusion pressure gradient, thus locally decreasing the blood flow velocity. Shear stress (SS) activates eNOS and may be associated with UBF elevations during FOL and pregnancy. We hypothesized that regional differences in eNOS responses are observed with both decreases in vessel diameter and during the ovarian cycle and pregnancy. Endothelial isolated proteins were collected from renal (RA) and internal iliac arteries (II) as well as from primary (UA 1 degrees ), secondary (UA 2 degrees), and tertiary (UA 3 degrees) UA branches of nonpregnant luteal phase (LUT; n = 6) and FOL (n = 6) as well as midpregnant (MP; 82 +/- 1 days gestation, n = 6) and late pregnant (LP; 127 +/- 3 days gestation, n = 6) ewes (term = 145 +/- 3 days gestation) for Western blot analysis. LUT RA, II, and UA 1 degrees eNOS levels were similar. There was a 60.7 +/- 9.8% reduction in eNOS expression in UA 2 degrees and UA 3 degrees. A similar decreasing eNOS regional expression gradient was observed in LP ewes. No eNOS regional expression gradient was observed in FOL or MP ewes because eNOS increased in UA 2 degrees and UA 3 degrees. In UA 2 degrees and UA 3 degrees, MP > LP = FOL > LUT. Thus, with increasing UBF, FOL and pregnancy rises in SS may regulate eNOS protein expression in smaller diameter UAs. A decrease in LUT and LP UA 2 degrees and UA 3 degrees endothelial eNOS suggest a possible negative feedback mechanism due to downregulation of eNOS if SS is normalized.