The involvement of Rho-associated kinases in agonist-dependent contractions of human maternal and placental arteries at term gestation

Mechanotransduction and Uterine Blood Flow in Preeclampsia: The Role of Mechanosensing Piezo 1 Ion Channels

There is a large increase in uterine arterial blood flow during normal pregnancy. Structural and cellular adjustments occur in the uterine vasculature during pregnancy to accommodate this increased blood flow through a complex adaptive process that is dependent on multiple coordinated and interactive influences and this process is known as "vascular remodeling." The etiology of preeclampsia involves aberrant placentation and vascular remodeling leading to reduced uteroplacental perfusion. The placental ischemia leads to development of hypertension and proteinuria in the mother, intrauterine growth restriction, and perinatal death in the fetus. However, the underlying source of the deficient vascular remodeling and the subsequent development of preeclampsia remain to be fully understood. Mechanoreceptors in the vascular system convert mechanical force (shear stress) to biochemical signals and feedback mechanisms. This review focuses on the Piezo 1 channel, a mechanosensitive channel that is sensitive to shear stress in the endothelium; it induces Ca2+ entry which is linked to endothelial nitric oxide synthase (eNOS) activation as the mechanoreceptor responsible for uterine vascular dilatation during pregnancy. Here we describe the downstream signaling pathways involved in this process and the possibility of a deficiency in expression of Piezo 1 in preeclampsia leading to the abnormal vascular dysfunction responsible for the pathophysiology of the disease. The Piezo 1 ion channel is expressed in the endothelium and vascular smooth muscle cells (VSMCs) of small-diameter arteries. It plays a role in the structural remodeling of arteries and is involved in mechanotransduction of hemodynamic shear stress by endothelial cells (ECs).

Human uterine and placental arteries exhibit tissue-specific acute responses to 17β-estradiol and estrogen-receptor-specific agonists

The discrete regulation of vascular tone in the human uterine and placental circulations is a key determinant of appropriate uteroplacental blood perfusion and pregnancy success. Humoral factors such as estrogen, which increases in the placenta and maternal circulation throughout human pregnancy, may regulate these vascular beds as studies of animal arteries have shown that 17β-estradiol, or agonists of estrogen receptors (ER), can exert acute vasodilatory actions. The aim of this study was to compare how acute exposure to ER-specific agonists, and 17β-estradiol, altered human placental and uterine arterial tone in vitro. Uterine and placental arteries were isolated from biopsies obtained from women with uncomplicated pregnancy delivering a singleton infant at term. Vessels were mounted on a wire myograph, exposed to the thromboxane receptor agonist U46619 (10⁻⁶ M), and then incubated with incremental doses (5 min, 0.03–30 µM) of either 17β-estradiol or agonists specific for the ERs ERα (PPT), ERβ (DPN) or the G-protein-coupled estrogen receptor GPER-1 (G1). ERα and ERβ mRNA expression was assessed. 17β-estradiol, PPT and DPN each relaxed myometrial arteries (P < 0.05) in a manner that was partly endothelium-dependent. In contrast, 17β-estradiol or DPN relaxed placental arteries (maximum relaxation to 42 ± 1.1 or 47.6 ± 6.53% of preconstriction, respectively) to a lesser extent than myometrial arteries (to 0.03 ± 0.03 or 8.0 ± 1.0%) and in an endothelial-independent manner whereas PPT was without effect. G1 exposure did not inhibit the constriction of myometrial nor placenta arteries. mRNA expression of ERα and ERβ was greater in myometrial arteries than placental arteries. ER-specific agonists, and 17β-estradiol, differentially modulate the tone of uterine versus placental arteries highlighting that estrogen may regulate human uteroplacental blood flow in a tissue-specific manner.

Differential vasodilation of human placental and myometrial arteries related to myofilament Ca(2+)-desensitization and the expression of Hsp20 but not MYPT1

Endothelial-dependent regulation of vascular tone occurs in part via protein kinase G1α-mediated changes in smooth muscle myofilament sensitivity to Ca(2+). Tissue-specific differences in PKG-dependent relaxation have been attributed to altered expression of myofilament-associated proteins that are substrates for PKG binding. These include the alternative splicing of the myosin targeting subunit (MYPT1) of myosin light chain phosphatase to yield leucine zipper positive (LZ(+)) and negative (LZ(-)) isovariants, with the former being required for PKG-mediated relaxation, and/or altered expressions of telokin, vasodilator-stimulated phosphoprotein (VASP) or heat shock protein Hsp20. During human pregnancy the uterine and placental circulations remain distinct entities and, as such, their mechanisms of vascular tone regulation may differ. Indeed, the sensitivity of myometrial arteries to endothelial-dependent agonists has been suggested to be greater than that of placental arteries. We tested the hypothesis that this was related to tissue-specific changes in PKG-mediated myofilament Ca(2+)-desensitization and/or the expressions of PKG-interacting myofilament-associated proteins. Permeabilized human placental and myometrial arteries were constricted with maximal activating Ca(2+) (pCa 4.5), or sub-maximal Ca(2+) (pCa 6.7) and the thrombane mimetic U46619, and exposed to 8-Br-cGMP. In each case, relaxation was significantly greater in myometrial arteries (e.g. relaxation in pCa 4.5 to 8-Br-cGMP was 49 ± 9.7%, n = 7) than placental arteries (relaxation of 23 ± 6.6%, n = 6, P < 0.05). MYPT1 protein levels, or MYPT1 LZ(+)/LZ(-) mRNA ratios, were similar for both artery types. Of other proteins examined, only Hsp20 expression was significantly elevated in myometrial arteries than placental arteries. These results demonstrate that the reduced human placental artery relaxation to PKG stimulation lies partly at the level of myofilament (de)activation and may be related to a lower expression of Hsp20 than in myometrial arteries.

Pregnancy reduces RhoA/Rho kinase and protein kinase C signaling pathways downstream of thromboxane receptor activation in the rat uterine artery

During pregnancy, reduced vascular responses to constrictors contribute to decreased uterine and total vascular resistance. Thromboxane A(2) (TxA(2)) is a potent vasoconstrictor that exerts its actions via diverse signaling pathways, and its biosynthesis increases in preeclampsia. In this study, we hypothesized that maternal vascular responses to TxA(2) will be attenuated via Rho kinase, PKC, p38 MAPK, and ERK1/2 signaling pathways. Isolated ring segments of uterine and small mesenteric arteries from late pregnant (19-21 days) and virgin rats were suspended in a myograph, and isometric force was measured. Pregnancy did not affect uterine and mesenteric artery responses to the TxA(2) analog U-46619 (10(-9)-10(-5) M), but transduction signals associated with these contractions were different between pregnant and nonpregnant rats. Inhibition of Rho kinase (10(-6) M Y-27632) reduced sensitivity to U-46619 in virgin uterine vessels but did not inhibit these contractions in pregnant uterine arteries and had no effect on mesenteric vessels. Treatment of arterial segments with a PKC inhibitor (10(-6) M bisindolylmaleimide I) reduced U-46619-induced contractions in virgin uterine and mesenteric arteries and in pregnant mesenteric arteries. Pregnant uterine arteries, however, were unresponsive to PKC inhibition. Inhibition of ERK1/2 (10(-5) M PD-98059) and p38 MAPK (10(-5) M SB-203580) reduced U46619-induced contractions in nonpregnant vessels and in pregnant uterine and mesenteric vessels. These data suggest that normal pregnancy does not affect uterine and mesenteric contractile responses to TxA(2) but reduces the contribution of Rho kinase and PKC signaling pathways to these contractions in the uterine vasculature. In contrast, the role of ERK1/2 and p38 MAPK in U-46619-induced uterine contractions remains unchanged with pregnancy. TxA(2)-associated transduction signals and its regulators might present potential targets for the development of new treatments for preeclampsia and other pregnancy-associated vascular diseases.

RHO protein regulation of contraction in the human uterus

The state of contraction in smooth muscle cells of the human uterus is dependent on the interaction of activated forms of actin and myosin. Ras homology (RHO) proteins are small monomeric GTP-binding proteins that regulate actin polymerisation and myosin phosphorylation in smooth muscle cells. Their action is determined by their level of expression, GTP-bound state, intracellular localisation and phosphorylated status. Agonist activated RHO proteins bind to effector kinases such as RHO kinase (ROCK) and diaphanous proteins (DIAPH) to regulate smooth muscle contraction by two mechanisms: ROCK activates smooth muscle myosin either by direct phosphorylation at Ser19/Thr18 or through inhibition of myosin phosphatase which is a trimeric protein regulated by ROCK and by other protein kinases. Actin-polymerising proteins such as DIAPH homolog 1 increase filamentous actin assembly to enhance acto-myosin cross bridge formation and contraction. This review explores recent advances in RHO protein signalling in human myometrium and proposes areas of further research to investigate the involvement of these proteins in the regulation of uterine contractility in pregnancy and labour.

Modulation of human arterial tone during pregnancy: the effect of the bioactive metabolite sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a potent bioactive lipid that has been implicated in cardiovascular disease. The objective of the present study was to determine the vasoactive effects and underlying mechanisms of S1P on adult human maternal arteries. The isometric tensions of the omental and myometrial arteries isolated from normal pregnant women at term were assessed in response to incremental doses of S1P in the presence or absence of the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). The putative involvement of Rho-associated kinases (ROCKs) in intact arteries and in those permeabilized with alpha-toxin, to study agonist-dependent calcium-sensitization, was assessed with the inhibitor Y27632. Real-time RT-PCR established the presence of mRNA encoding the S1P receptors (S1P(1) to (3)), previously known as endothelial differentiation gene receptors (EDG1, 3 and 5), in both artery types. S1P induced a dose-dependent increase in the isometric tension of all the arteries. Y27632 reduced constriction due to S1P in intact arteries and reduced S1P-induced sensitization of contraction to submaximal activating Ca(2+) in permeabilized arteries. L-NAME also modulated S1P vasoactive responses in a tissue-specific manner. Two subgroups of omental arteries were identified, one of which utilizes the NO pathway. In myometrial arteries, S1P evoked oscillatory constrictions, whereas pretreatment with L-NAME resulted in only tonic constrictions of unaltered peak magnitude. The prominent vasoactive actions of S1P in the maternal arteries of pregnant women are modulated by inhibitors of ROCKs and NO bioavailability. The subtle tissue-specific functional differences in the modulation of S1P actions by NO have important implications for vascular tone regulation by this bioactive circulatory metabolite during pregnancy.

Bronchial muscle peristaltic activity in the fetal rat

Aside for the potential for tonic contraction, the airway smooth muscle exhibits intermittent phasic rhythmic activity that may contribute to lung growth during fetal life. Therefore, we examined 4th generation rat 18-22 d gestation fetal, 4-6 d of age newborn and adult bronchial ring from Sprague Dawley rats to compare differences in smooth muscle function. We hypothesized that phasic contractions were greatest before birth. Bronchial muscle spontaneous rhythmic contractions were greatest in the fetus and absent in the adult. In response to KCl stimulation, the fetal bronchial smooth muscle only developed tonic force that was 3.5 +/- 0.6 and lower than measured in the newborn 9.0 +/- 0.3 and adult 13.7 +/- 1.4 mN/mm2. The thromboxane A2 analogue U46619 induced tonic and phasic muscle contractions and the amplitude and frequency of the phasic contractions were greater in the fetus as compared with the adult and increased with gestational age. The U46619-induced rhythmic contractions were abrogated by ryanodine, thapsigargin and reduction of extracellular Na+, suggesting intracellular Ca2+ dependence and involvement of the Na+/Ca2+ exchanger. The inward rectifier K+ blocker BaCl2 induced phasic contractions in unstimulated fetal, but not adult bronchial muscle of the same amplitude and frequency as for the spontaneous and U46619-induced ones. We conclude that the airway smooth muscle phasic activity is greatest in the fetus and tends to disappear post-natally with age suggesting an in utero role during lung development.

Mechanisms underlying the vasorelaxing effects of butylidenephthalide, an active constituent of Ligusticum chuanxiong, in rat isolated aorta

Butylidenephthalide (BDPH) is one of the most potent vasorelaxants isolated from Ligusticum chuanxiong Hort. The objective of the current study is to investigate the underlying vasorelaxation mechanisms in rat aorta. In 9,11-dideoxy-9alpha,11alpha-methanoepoxyprostaglandin F(2alpha) (U46619) precontracted preparations, endothelium removal, the nitric oxide (NO) synthase inhibitor Nomega-nitro-l-arginine methyl ester (l-NAME) and the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) partially inhibited the BDPH relaxation response to a similar extent. The cyclooxygenase inhibitor indomethacin, beta-adrenoceptor antagonist propranolol, adenylate cyclase inhibitors 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22536) and 2',5'-dideoxyadenosine, and K(+) channel blocker tetraethylammonium had no effect. BDPH produced full relaxation against contractions induced by KCl and U46619 in the presence of the l-type voltage-operated Ca(2+) channel (Ca(v) 1.2) blocker nifedipine. In a receptor-operated Ca(2+) channel protocol where contraction was mediated by Ca(2+) re-addition in the presence of U46619 and nifedipine, BDPH produced relaxation. In the absence of extracellular Ca(2+), BDPH inhibited contractions induced by phorbol-12,13-dibutyrate and U46619. Our results suggest that BDPH-mediated vasorelaxation comprises both endothelium-dependent (NO) and independent components. It is suggested that BDPH acting through an inhibitory mechanism downstream to l-type voltage-operated and prostanoid TP receptor-operated Ca(2+) channels operating late in the contractile pathway.

Sphingosine-1-Phosphate Acts via Rho-Associated Kinase and Nitric Oxide to Regulate Human Placental Vascular Tone1

Sphingosine-1-phosphate (S1P), a bioactive lipid released from activated platelets, has been demonstrated in animal models to regulate vascular tone through receptor-mediated activation of Rho-associated kinase 1 and nitric oxide synthase 3. The role of S1P in regulation of human vascular tone (particularly during pregnancy, with its unique vascular adaptations and localized platelet activation) is unknown. We hypothesized that S1P would constrict small placental arteries through activation of Rho-associated kinases with modulation by nitric oxide. Reverse transcription-polymerase chain reaction of chorionic plate artery preparations detected mRNAs encoding all five receptors for S1P, and S1P induced dose-dependent vasoconstriction of both chorionic plate and stem villous isobarically mounted arteries, which at 10 micromol/L was 32.9% +/- 3.86% (mean +/- SEM) and 34.6% +/- 7.01%, respectively. In stem villous arteries, S1P-induced vasoconstriction was enhanced significantly following inhibition of nitric oxide synthases with N(G)-nitro-L-arginine methyl ester (100 micromol/L, 52.6% +/- 6.28%, P < 0.05). The S1P-induced vasoconstriction was reversed by Y27632, an inhibitor of Rho-associated kinases (10 micromol/L) in both chorionic plate (to 14.9% +/- 4.95%) and stem villous arteries (to 2.71% +/- 6.13%). The S1P added to alpha-toxin-permeabilized, isometrically mounted chorionic plate arteries bathed in submaximal Ca(2+)-activating solution induced Ca(2+)-sensitization of constriction, which was 47.7% +/- 10.0% of that occurring to maximal Ca(2+)-activating solution. This was reduced by Y27632 to 18.4% +/- 18.4%. Interestingly, S1P-induced vasoconstriction occurred in all isobarically mounted arteries but was inconsistent in isometrically mounted chorionic plate arteries. In summary, S1P-induced vasoconstriction in human placental arteries is mediated by increased Ca(2+)-sensitization through activation of Rho-associated kinases, and this vasoconstriction also is modulated by nitric oxide. Identification of these actions of S1P in the placental vasculature is important for understanding both normal and potentially abnormal vascular adaptations with pregnancy.