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Pelvic Girdle Pain during or after Pregnancy: a review of recent evidence and a clinical care path proposal. PDF

2013·0.78 MB·English
by  MitchellB.F.
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mitchell-_Opmaak 1 26/03/13 09:55 Pagina 72 FVV inObGyn, 2013, 5 (1): 72-81 Review The uterine myocyte as a target for prevention of preterm birth b.F. Mitchell1,2, h.n. AGuilAR2, A. MOsheR3, s. WOOd4, d.M. slAteR3 University of Alberta Departments of Obstetrics and Gynecology1and of Physiology2, Edmonton AB and University of Calgary Department of Physiology and Pharmacology3and of Obstetrics and Gynecology4, Calgary AB Canada. correspondence at: b.F. Mitchell, 220 hMRc, university of Alberta, edmonton Ab canada t6R 1J1. tel.: 780-492-8561; Fax: 780-492-1308; e-mail: [email protected] Abstract Preterm birth (PTB) remains the most common cause of neonatal morbidity and mortality as well as long-term dis- ability. Current strategies to prevent or arrest spontaneous preterm labor (SPTL) have limited success. For almost three decades, there have been no novel pharmacological agents used clinically to address this important obstetrical complication. In this review, we focus on the uterine myocyte as a target for prevention of spontaneous PTB. After presenting an overview of intracellular signaling pathways that are important in regulation of smooth muscle contractility, we discuss previous and current pharmacological approaches to manage SPTL. We also present recent evidence from our own laboratories suggesting a potentially novel and uterine-specific approach to maintain or impose uterine relaxation. Finally, we briefly discuss extrinsic systems that might affect uterine activity and reinforce the concept that SPTL represents a syndrome that is the end result of a variety of pathophysiologic etiologies leading to PTB. We conclude by emphasizing the need for much more research to provide sufficient understanding of the mechanisms of SPTL and to make inroads towards reducing the incidence and adverse consequences of this com- mon and serious syndrome. Key words:Prematurity, preterm labour, myosin regulatory light chain, rhoA-associated kinase, tocolysis, uterine contractility. Introduction premature contractions (tocolysis) could logically diminish the occurrence of complications due to Preterm birth (Ptb) is widely recognized as the Ptb and generally enhance neonatal outcomes. this major cause of neonatal mortality and long-term group is the focus of this paper. disability. there are three broad categories of Ptb. despite increasing awareness within the scientific Approximately one-third of cases are associated with community of the importance of sPtl (behrman et and result from intrauterine infection. current ob- al., 2007; howson et al., 2012), there has been little stetrical practice is to terminate these pregnancies advancement towards understanding the mecha- immediately, regardless of gestational age, because nisms that determine the timing of birth. the result of potential serious complication to either the baby of this relative lack of progress is a dearth of novel or the mother. the second and increasingly large strategies to prevent Ptb. indeed, over the past three category is the iatrogenic group where concerns decades, there have been no new, clinically proven about maternal or fetal health dictate that the out- pharmacological approaches to prevent Ptb arising come of the fetus would be better with immediate from sPtl. delivery, again regardless of gestational age. the the objective of this paper is to discuss potential third category, and the one most relevant to this new strategies for the prevention of Ptb. We will discussion is the group that enters spontaneous begin by describing the general mechanisms that preterm labor (sPtl) without evidence of maternal regulate smooth muscle contractility. We have or fetal factors that would preclude attempts to recently reviewed this topic in more detail than will prolong gestation. these are the pregnancies where be presented here (Aguilar and Mitchell, 2010). the prevention of sPtl or treatment to arrest the then we will consider potential mechanisms that are 72 mitchell-_Opmaak 1 26/03/13 09:55 Pagina 73 intrinsic to the smooth muscle myocyte and could this is known as the ‘ca2+- dependent’ pathway of act either by inhibition of pro-contractile mecha- smooth muscle contraction. nisms or stimulation of pro-relaxant pathways. We More recently, there has been growing awareness will then discuss the concept of specific regulatory of a ‘ca2+-independent’ pathway. in the classical mechanisms intrinsic to uterine myocytes that might description of this pathway (Kozasa et al., 1998), the support development of targets specifically to affect Gα subunit family initiates the signaling by 12-14 the uterus but without risk of adverse effects on other activation, through a yet unknown mechanism, of a smooth muscle beds, particularly the cardiovascular guanidine nucleotide exchange factor (GeF). this system. Finally, we will discuss the potential of tar- results in activation of the small monomeric G- geting pathways extrinsic to the uterine myocyte that protein rhoA-GdP by exchanging GtP for GdP. the could affect uterine contractility. major target of activated rhoA-GtP is rhoA- associated kinase (ROK), which is the principal Regulation of smooth muscle contractility effector of this pathway. A major target of ROK is the substrate binding subunit of MlcP. Phosphory- the pivotal event for triggering the contractile lation of the targeting subunit prevents targeting to machinery in smooth muscle is the phosphorylation and dephosphorylation of pRlc by MlcP, thus of myosin regulatory light chains (Rlc). As promoting muscle contraction. this mechanism has illustrated in Figure 1, this reaction is catalyzed by been recognized as the explanation of the phenome- myosin regulatory light chain kinase (MlcK). the non of ‘ca2+-sensitization,’ which describes a situa- reverse reaction, leading to muscle relaxation, is me- tion where the rise in intracellular ca2+concentration diated by myosin regulatory light chain phosphatase produces a larger-than-expected contraction. this ef- (MlcP). Oxytocin (Ot) is the best-characterized fect is thought to be the result of simultaneous and most potent uterine agonist. this hormone is MlcP inhibition alongside MlcK activation produced in the hypothalamus and stored in the (somlyo and somlyo, 2003). As we will discuss neurohypophysis of both mother and fetus. Perhaps later, we believe this pathway may represent an more relevant to parturition, Ot also is produced in important target for future tocolytics. the maternal decidua immediately adjacent to the A third potential pathway for uterine myocyte uterine smooth muscle (myometrium) (chibbar et stimulation is mediated by Gα. this pathway does i al., 1993). Other potent agonists include endothelin- not appear to be a major regulator of uterine contrac- 1 and prostaglandin (PG) F , which also are tility but may be involved in transduction of signals 2α produced by maternal decidua (Arthuret al., 2008). arising from the PGe receptor isoform eP (Kotani 2 3 each of these agonists interact with specific mem- et al., 2000) and Ot (Phaneufet al., 1996). brane receptors linked to signaling pathways through heterotrimeric G-proteins also mediate a major small heterotrimeric GtPase proteins (G-proteins). mechanism for uterine relaxation. in this instance, the Gαsubunits are key to determining which path- the predominant isoform is Gα. Activation of this s way will be activated. the Gα subunit mediates subunit causes increased activity of membrane q/11 activation of adjacent phospholipase c , which adenylyl cyclase (Ac), which converts adenosine β hydrolyses membrane phosphatidylinositol bispho- trisphosphate (AtP) to cyclic-5’-adenosine sphate into two small ‘second messengers,’ inositol monophosphate (cAMP) and this in turn activates trisphosphate (iP) and diacyl glycerol (dAG) protein kinase A (PKA). this pathway is stimulated 3 (berridge, 1993). iP stimulates the release of ca2+ by endogenous and exogenous β-adrenergic agonists 3 from the intracellular sarcoplasmic reticulum stores to cause uterine relaxation. similarly, nitric oxide resulting in increased free intracellular ca2+. the re- (nO) can directly activate cytosolic guanylyl cyclase sultant depolarization activates and opens the volt- (Gc) in uterine myocytes to stimulate production of age-dependent l-type ca2+ channels on the myocyte cyclic-5’-guanosine monophosphate (cGMP) with membrane. since the extracellular concentration of subsequent activation of PKG. PKA and PKG ca2+is approximately 5 orders of magnitude greater exhibit their relaxant effects on smooth muscle by than the intracellular ca2+concentration, this results acting on at least three targets. PKA mediates phos- in rapid and massive influx of ca2+ from the extra- phorylation of the ca2+-caM binding site on MlcK, cellular space to the intracellular space. the free in- thereby hindering enzyme activation. PKA and PKG tracellular ca2+ binds to calmodulin (caM) and the also increase the activity of the ca2+-AtPases in the ca2+-caM complex subsequently binds to the acti- plasma membrane (PMcA) and sarcoplasmic and vation site on MlcK, resulting in phosphorylation endoplasmic reticulum (seRcA) resulting in active of Rlc (here referred to as ‘pRlc’) and activation extrusion of ca2+ from the intracellular compartment of the contractile apparatus. because of this central and repolarization of the plasma membrane. lastly, role for ca2+in the initiation of myocyte shortening, PKA and PKG can phosphorylate the MlcP PhARMAcOlOGicAl tARGetinG OF uteRine MyOcytes – MitchelletAl. 73 mitchell-_Opmaak 1 26/03/13 09:55 Pagina 74 targeting subunit at a site adjacent to the ROK target monly the non-steroidal anti-inflammatory drug site, thus rendering MlcP insensitive to the (nsAid) indomethacin. Although the original stud- inhibitory effects of ROK. ies showed dramatic beneficial effects (Zuckerman et al., 1974; Zuckerman et al., 1984), more recent Non-specific mechanisms of tocolysis studies have not demonstrated such strong effects. Other studies pointed to major fetal-neonatal side essentially all the above pathways regulating uterine effects including oligohydramnios, patent ductus contractility have been exploited in attempts to arteriosus, cerebral hemorrhage and necrotizing develop a useful tocolytic drug to arrest sPtl. here, enterocolitis (norton et al., 1993). Again, there has we will provide only a brief overview of these trials. been no evidence suggesting improved outcome for More authoritative and in-depth reviews are avail- the infant. Other nsAids, including cOX-2-specific able in the cochrane collaboration databases. un- inhibitors have been used but have not been shown fortunately, most of these pathways are active in all to be safer or more effective (Groom et al., 2005). types of smooth muscle. therefore, use of doses that the cOX inhibitors block production of all will arrest uterine activity is often associated with prostanoids, including PGe and PGi. the physio- 2 2 serious off-target side effects, most notably hypoten- logical roles of these hormones on human uterine sion and related cardiovascular complications. function are extremely complex and may differ in the β-adrenergic agonists are the best-studied to- the upper and lower segments of the uterus. it is colytic class of drugs. Multiple good-quality ran- likely that they affect uterine myocytes as well as domized control trials (Rcts) demonstrated efficacy connective tissue cells. When the roles of the various to delay delivery for at least 48-72 hours (King et PGs are more clearly understood, it is possible that al., 1988) but there is no compelling evidence of im- development of more selective drugs targeting proved infant outcome. the maternal cardiovascular enzymes or receptors in the PG pathway will be use- complications, such as hypotension and others noted ful for clinical control of uterine contractility. At above, were common and often led to serious ad- present, the nsAids appear not to have fulfilled verse outcomes, including mortality. use of lower their initial promise (Mitchell and Olson, 2004). doses to avoid these complications has not been Another approach to tocolysis involves the use of shown to produce effective tocolysis. in addition, nO donors to induce activation of PKG, as described these drugs mimic the metabolic effects of β-adren- above (smith et al., 2007). Once again, due to the ergic agents that can lead to hyperinsulinemia and lack of uterine specificity of this approach, it is likely hypokalemia, further potentiating the cardiovascular that significant uterine relaxation will be accompa- complications. these drugs are uncommonly used in nied by vascular relaxation and increased maternal current practice, though they have been introduced side effects, including the potential for decreased and are being promoted in developing countries. uterine blood flow. drugs that block ca2+ channels, for example nifedipine, are among the most commonly used Potential uterine-specific mechanisms of tocolysis tocolytic agents today (King et al., 2003). unfortu- nately, their use is not supported by clinical trial Oxytocin antagonists comparison to a placebo. this is an important consideration since, depending on the criteria for the most potent contractile agonist for uterine diagnosing sPtl and the rigor of the diagnosis, the m yocytes appears to be Ot. Relative to other tissues, success rate of placebo treatment might be well over Ot receptor (OtR) is most highly expressed in the 50%. since there is no evidence that uterine myoctes myometrium, decidua and myoepithelial cells of the in sPtl have any greater sensitivity to ca2+channel breast. therefore, regarding smooth muscle targets, blockers than do vascular myocytes, it seems likely OtR is relatively tissue specific for the uterus. the that concentrations required to provide effective to- development of OtR antagonists began approxi- colysis would be associated with similar cardiovas- mately 25 years ago and clinical trials demonstrated cular complications as the β-adrenergic drugs. their efficacy just over a decade ago. in general, indeed, safety concerns regarding the use of these these drugs are short polypeptides that mimic the drugs in pregnancy is the focus of a recent system- native molecule and interfere with Ot binding to atic review (Khan et al., 2010). OtR. not surprisingly, there is overlap with the Another pharmacological approach has targeted receptor for vasopressin, which is a hormone with the synthesis of PGF , which may activate the similar structure to Ot. these drugs are expensive 2α uterus, ripen the cervix or directly stimulate contrac- to produce and, as peptides, need to be administered tions. Most studies have used non-specific inhibitors parenterally. though there is strong evidence of of cyclooxygenase (cOX-1 and cOX-2), most com- beneficial effects and few side effects in comparison 74 FVV inObGyn mitchell-_Opmaak 1 26/03/13 09:55 Pagina 75 to other tocolytic drugs, atosiban never received approval for use in the united states, perhaps be- cause of a flaw in the placebo-controlled Rct to demonstrate the efficacy of the drug. in this trial (Romero et al., 2000), there was a very significant imbalance in the number of extremely preterm preg- nancies (22-26 weeks) randomized to receive atosi- ban. the death rate in these babies at the brink of viability was very high. because of this, when all ba- bies were considered, there was an overall increase in the perinatal mortality rate of the babies receiving the drug compared to the placebo. the drug has been approved and is in common use in europe. there are non-peptide OtR agonists that can be administered orally but trials of these in humans have not yet been published (Pettibone et al., 1995). More recently, a different approach has been taken in the development of receptor antagonists. Rather than interfering with ligand binding, these ‘al- losteric’ inhibitors interfere with other extracellular components of the seven transmembrane receptors Fig. 1.— Regulation of smooth muscle contractility. uterine stimulants generally stimulate specific G-protein coupled recep- and interfere with the signal transduction mecha- tors (GPcR) on the myocyte membrane. this triggers two stim- nisms. indeed, such an inhibitor has been developed ulatory pathways. the Gα subunit activates phospholipase c q for the PGFαreceptor. interestingly, this experimen- (Plc) in the adjacent membrane and this results in hydrolysis 2 tal drug (thG113.31) had little effect on PGFα- of membrane phosphoinositides to from inositol trisphosphate 2 (iP) and diacyl glycerol, which can activate protein kinase c induced contractions in human uterine strips ex vivo 3 (PKc; see text). iP stimulates release of ca2+from the sarco - 3 but was a good inhibitor of Ot-induced contractions plasmic reticulum and the resulting decrease in cell membrane (Friel et al., 2005). Further studies demonstrated that resting potential leads to massive influx of ca2+from the extra- cellular space through voltage–gated l-type ca2+-channels. ca2+ this inhibitor has an inhibitory effect on the Gα 12-14 binds to calmodulin (caM). the ca2+-caM complex interacts signaling cascade but appears to enhance the Gαq/11 with and activates myosin regulatory light chain kinase pathway (Goupil et al., 2010). this emphasizes that (MlcK). MlcK mediates the phosphorylation of myosin regulatory lights chains (Rlc) and initiates the contractile uterine contractility is regulated by two distinct and apparatus. the second stimulatory pathway is mediated through counterbalanced systems – the ca2+-dependent, Gα . this causes activation of a guanidine nucleotide 12-14 MlcK-mediated phosphorylation of Rlc and the exchange factor (GeF), which activates membrane rhoA-GdP ca2+-independent, MlcP-mediated dephosphoryla- by substituting GtP for the GdP. the rhoA-GtP activates rhoA- associated kinase (ROK). ROK phosphorylates myosin regula- tion of pRlc. development of effective tocolytic tory light chain phosphatase (MlcP), which inhibits its activity. drugs requires consideration of both pathways. to since MlcP is normally responsible for removing the phosphate date, most drug development has focused on the for- from pRlc to cause uterine relaxation, enhanced ROK activity prolongs the effectiveness of pRlc and promotes enhanced con- mer. Our recent research has examined regulation of tractile activity. the major inhibitory pathways might also be MlcP and, we believe, has uncovered a potentially mediated by GPcR, linked through Gα resulting in activation s important and unique feature of uterine myocytes of adenylate cyclase (Ac) or direct activation of guanylate cy- clase (Gc), which in turn activates protein kinase A (PKA) or that could provide an effective and specific pharma- PKG. these kinases inhibit contractility through a variety of cological target for tocolysis. mechanisms described in the text. the green lines indicate stim- ulatory activity and the red lines inhibitory. the broken line in- Inhibition of the MLCP pathway dicates an indirect effect. As would be expected from the schematic in Figure1, inhibitors of ROK reduce the inhibitory re- of the ROK pathway also affects vascular smooth straints on MlcP, promote dephosphorylation of muscle so this may represent a non-specific pathway pRlc, and thereby lead to diminished contractility and the potential use of ROK inhibitors for preven- of smooth muscle. several studies have shown inhi- tion or treatment of sPtl would be complicated by bition of basal and Ot-stimulated uterine contrac- intolerable off-target effects in vascular or other tions both in vivo and ex vivo in human and rat smooth muscle. myometrium (niiro et al., 1997; Kupittayanant et al., We considered that the logical focus of our ap- 2001; Moran et al., 2002; Woodcock et al., 2004; proach to modification of uterine myocyte activity Woodcock et al., 2006). unfortunately, interruption would be the reversible phosphorylation of Rlc. We PhARMAcOlOGicAl tARGetinG OF uteRine MyOcytes – MitchelletAl. 75 mitchell-_Opmaak 1 26/03/13 09:55 Pagina 76 Fig. 2. — expression of mRnA for oxytocin receptor in myocytes derived from upper and lower uterine segments. PcR of extracts from primary cultures of uterine myocytes derived from paired samples of uterine muscle (n = 2 patients) obtained from the upper fundal portion of the uterus (u) or the lower uterine segment (l) along with molecular weight markers (M), blanks (bl) and extracts from myometrial tissues (My). the cells were used at passage 3, 4 and 5 (P3-P5). the upper panels demonstrate expression of OtR (476 bp) and the bottom panels show expression of GAPdh (598 bp) as a control. OtR is expressed in upper and lower segment myocytes and does not change with passage number. developed relatively high throughput assays to assess this reaction using human uterine myocytes (Aguilar et al., 2010; Aguilar., 2011). since we were primarily interested in uterine contractility during late preg- Fig. 3.— intracellular concentrations of ca2+following stimu- lation of uterine myocytes with oxytocin. Primary cultures of nancy, we obtained uterine biopsies from the upper fundal (upper panel) and lower (lower panel) segment uterine flap of the lower segment transverse uterine incision myocytes were plated in Greiner bio-One black plates (5.0 × at the time of elective cesarean section at term but 104cells/ml) and grown for 48 hours. cells were then loaded with Fluo-4 dye and incubated at 37°c for 30 minutes. Ot prior to clinical labor onset. since it has been sug- (0.1µM, 1 µM, 10 µM) was added to the cells and fluorescence gested that there might be regional differences in was measured. data are presented as peak fluorescence over physiological function for myocytes located in the baseline fluorescence (F/F; mean ± seM; n = 4 patients). 0 upper more contractile part of the uterus compared myocytes located in the lower segment, we isolated myocytes from both uterine regions to validate that the cells from the lower segment were representative We then demonstrated (Fig. 4) concentration-de- of those in the fundus. For these experiments, we pendent, and statistically significant increases in obtained paired (upper and lower) uterine biopsies. concentrations of pRlc following stimulation with the lower segment biopsies were taken as described Ot. these responses were similar in cells from fun- above. the fundal biopsy was obtained by first dal and lower segment biopsies. the peak responses excising the overlying decidua, then excising a small in phosphorylation of Rlc occurred within the first myometrial biopsy using iris scissors. 20s, in accord with the ca2+ data in Figure 3. We For the first step in validation, we used Rt-PcR noted that the potent and specific ROK inhibitor to examine expression of mRnA for OtR in primary glycyl-h1152 (g-h) caused a 40-50% reduction of cultures of uterine myocytes from the upper (fundal) resting pRlc concentrations but the response to Ot and lower parts of the uterus at several passages. in was maintained. A similar response profile was Figure 2 it is seen that OtR expression is similar in demonstrated using the MlcK inhibitor Ml7. both regions and is maintained through several Again, these responses were similar in cells from the passages of cells. A ca2+ assay was then used to fundal and lower uterine segments. We also meas- investigate the response of these cells to Ot (Fig. 3). ured responses for diphosphorylated Rlc (ppRlc; treatment of fundal and lower segment myocytes Fig. 5) and again noted significant responses to Ot, with Ot resulted in a concentration-dependent which were similar in the cells from fundal and increase in intracellular ca2+. there was no lower segments. treatment with the inhibitors of difference in the responses between the fundal and ROK or MlcK again caused suppression of basal lower segment cells. ppRlc concentrations. however, unlike pRlc, the 76 FVV inObGyn mitchell-_Opmaak 1 26/03/13 09:55 Pagina 77 Fig. 4.— concentrations of pRlc in uterine myocytes from Fig. 5.— concentrations of ppRlc in uterine myocytes from upper and lower uterine segments following stimulation by upper and lower uterine segments following stimulation by oxytocin. Primary cultures of myocytes from the uterine fundus oxytocin. Primary cultures of myocytes from the uterine fundus and lower uterine segments (n = 5 patients) were treated with and lower uterine segments (n = 5 patients) were treated with increasing concentrations of Ot for 20 s and the response increasing concentrations of Ot for 20 s and the response measured using a specific antibody for pRlc phosphorylated at measured using a specific antibody for ppRlc phosphorylated s19 in an in-cell westernassay. there were significant, concen- at t18 and s19 in an in-cell western assay. there were signifi- tration-dependent increases that were similar in cells from upper cant, concentration-dependent increases in ppRlc in cells from and lower segments. 15-minute pretreatment with the rho-kinase upper and lower segments. As for pRlc, 15-mimute pretreat- inhibitor (g-h; 1 µM) or the myosin regulatory light chain kinase ment with the rho-kinase inhibitor (g-h; 1 µM) or the myosin inhibitor (Ml7; 25 µM) caused approximately 20-30% suppres- regulatory light chain kinase inhibitor (Ml7; 25 µM) caused sion of basal pRlc but the response to Ot was maintained. approximately 20-30% suppression of basal ppRlc. however, in contrast to the results for pRlc, the ppRlc responses to Ot were completely abolished in the presence of the kinase inhibitors. responses of ppRlc to Ot were blocked by either increased ppRlc was produced by ROK-mediated of the inhibitors, again similarly in cells from the phosphorylation of pRlc to ppRlc. since this bio- fundal and lower segments. chemical conversion of pRlc to ppRlc was not We have reported previously on the results of a noted in the vascular myocytes, we speculated that series of experiments specifically exploring the role it might be a unique feature of smooth muscle with of ROK and MlcK in mono- and diphosphorylation a phasic contractile pattern, such as the uterus. since of Rlc in uterine myocytes following stimulation ppRlc causes 3-fold greater activation of myosin with physiological uterine agonists (Aguilar et al., AtPase, which provides the energy for the contrac- 2010; 2011; 2012). We made specific comparisons tile apparatus (ikebe et al., 1986; 1988), we reasoned to the responses of vascular myocytes to physiolog- that diphosphorylation of Rlc may represent an ical agonists. there were two major conclusions evolutionary adaptation of phasic smooth muscle from these experiments. the first conclusion was driven by the need to produce periodic but powerful that uterine myocytes respond to stimulation with contractions, in contrast to tonic smooth muscle such significant increases in both pRlc and ppRlc as vascular, which requires long-term stable tension whereas the vascular myocytes respond only with with relatively little change in amplitude. impor- pRlc. the responses in pRlc are due to the well- tantly, the ROK inhibitor prevented the ppRlc described effects of physiological agonists: increased response to Ot in uterine myocytes in vitro at ca2+- dependent MlcK-mediated phosphorylation of concentrations that were 100-fold lower that those Rlc and increased ROK-mediated inhibition of required to decrease the concentration of pRlc in MlcP. vascular myocytes. thus, inhibition of ROK has the second major conclusion of these studies was potential to be a clinically useful and utero-specific a novel and potentially important finding. the target to mediate uterine relaxation while avoiding PhARMAcOlOGicAl tARGetinG OF uteRine MyOcytes – MitchelletAl. 77 mitchell-_Opmaak 1 26/03/13 09:55 Pagina 78 relatively quiet. next was the period of uterine activation, which occurred over a few days prior to clinical labor onset. during this time, the density of ‘contraction associated proteins’ (cAPs) increased to transform the uterus into a sensitive contractile organ capable of responding to agonists with powerful, coordinated contractions. included among the cAPs are the receptors for uterine agonists (Ot, PGFα, etc.), a variety of ion channels, and the major 2 gap junction protein connexin 43. uterine stimula- tionoccurs due to the actions of endogenous agonists such as Ot, PGFα, etc. there remains only poor 2 understanding of the identity of the key endogenous agonist(s). Regulation of these processes can be considered ‘upstream’ of the uterine myocyte, though the mechanisms are similarly unclear. these mechanisms might represent earlier targets for inter- ruption of the cascade of events leading to parturi- tion. the following sections deal with two examples Fig. 6.— schematic diagram illustrating the unique pattern of phosphorylation of Rlc in uterine myocytes.As in all smooth of such potential extrinsic regulatory systems. muscle, myosin regulatory light chain (Rlc) is phosphorylated by myosin regulatory light chain kinase (MlcK) at s19. how- Estrogen/progesterone ratio ever, in uterine myocytes, pRlc is additionally phosphorylated at t18 to form ppRlc, a more potent activator of the myosin AtPase that supplies energy for the contraction. this diphos- Over the past half century, it has been demonstrated phorylation pathway might be a unique adaptive pathway for that, in most mammalian species, withdrawal of smooth muscle that contract in a phasic pattern. the green lines indicate stimulatory activity and the red lines inhibitory. progesterone from the maternal circulation is neces- sary and sufficient to cause parturition. however, in higher order primates, including humans, there is no vascular compromise. Our current concept of the such decline in maternal serum progesterone at the mechanisms regulating phosphorylation of Rlc time of parturition. it has been proposed that, in these specifically in uterine myocytes is presented in the species, progesterone still may be an essential prog- schematic in Figure 6. estational hormone but its withdrawal at the time of parturition occurs on a more local, intrauterine basis Extrinsic influences on uterine myocytes that is not reflected in maternal serum. Various mechanisms have been suggested for a ‘functional the previous discussions have considered mecha- progesterone withdrawal.’ these include decreased nisms that are intrinsic to the uterine myocyte. synthesis or increased metabolism within the clearly, there are mechanisms extrinsic to the amnion, chorion and decidua (Mitchell and Powell, myocyte that will influence myocyte responses to 1984). these tissues lay immediately adjacent to the agonists or antagonists. indeed, sPtl is likely the myometrium and thus might have significant influ- end result of many differing pathophysiologic path- ence over progesterone effects on uterine myocytes. ways that involve intrinsic and/or extrinsic path- similarly, changes in expression and activity of prog- ways. As such, sPtl represents a syndrome rather esterone receptors within the uterine myocyte could than a specific disease entity. here, we discuss some regulate progesterone-dependent transcriptional of the mechanisms extrinsic to the uterine myocyte activity (Mesiano et al., 2002; condon et al., 2003). that could provide pharmacological targets to influ- Over the past decade, there has been renewed ence uterine contractility. interest in the use of supplemental progesterone to prevent Ptb in women at high-risk. based on the Concept of uterine activation and stimulation results of a 30-year old trial (Johnson et al., 1975), an Rct demonstrated some efficacy in preventing several years ago, a useful concept was proposed Ptb using prophylactic progestin supplementation suggesting that the status of uterine contractility over the last half of gestation (Meis et al., 2003). the during pregnancy could be considered in three drug used was 17-hydroxyprogesterone caproate, categories (challis et al., 2000). uterine quiescence which clearly is not progesterone and its mechanism was the period that began at implantation and lasted of action is not fully understood. however, the most of pregnancy, during which the uterus remained results were supported by an additional Rct using 78 FVV inObGyn mitchell-_Opmaak 1 26/03/13 09:55 Pagina 79 natural progesterone administered by vaginal sup- beneficial. linking the two processes such that they pository, which also showed a statistically significant are interdependent would ensure the two distinct and improvement on the rates of Ptb (da Fonseca et al., vital activities act together. this might be analogous 2003). though there is increasing use of this prophy- to the situation in sheep where increased activity of lactic regimen for woman at high risk of Ptb, it the uterus is linked to the same mechanisms that remains unclear what the outcomes will be regarding mature the fetal lungs in preparation for extrauterine the health of the newborn. Prophylactic use of prog- existence. estin also has been shown to be efficacious in to date, the role of the immune system in the women with a short cervix demonstrated on routine initiation of parturition, though extensively studied, mid-pregnancy ultrasound (Romero et al., 2012). remains unresolved. it is clear that, in the presence the cost-effectiveness of this strategy of ultrasound of intrauterine infection, this inflammatory reaction screening and progestin administration and the is markedly enhanced. there is convincing evidence potential longer-term effects of this approach remain that a severe intrauterine inflammatory event, such to be determined. as infection or chemical irritation can provoke par- Research from several animal species has also turition at any stage of gestation. however, the role suggested that estrogen plays an important role in of the pro-inflammatory reactions in regulation of the timing of parturition. in general, its effects tend term labor and sPtl require further clarification. to oppose those of progesterone. this has given rise similarly, there has been elegant demonstration of to the concept of the ratio of estrogen/progesterone the effects of uterine stretch on pathways thought to as a key factor. in particular, estrogen has been be important in regulating parturition, such as the demonstrated to enhance transcription of many of up-regulation of cAPs (Ou et al., 1997; terzidou et the genes that code for cAP proteins while al., 2005). however, again, the role of such mecha- progesterone can block the increase in cAP mRnA nisms in determining the occurrence of labor at term expression (Ou et al., 1997; 1998; 2000). As with or preterm is not well understood. progesterone, local estrogen synthesis and metabo- At present, the research has yet to produce clini- lism might be of primary importance (Mitchell & cally effective therapeutic tools for tocolysis. his- Wong, 1993; Romero et al., 1988). estrogen torically, the extensive Rcts using large doses of antagonists will cause delay in rat parturition but this glucocorticoids administered to women with sPtl is complicated by decreased growth rate of the pups to accelerate fetal lung maturation have demon- (Fang et al., 1996). in theory, the potentially impor- strated clearly that these potent anti-inflammatory tant negative effects of administration of estrogen agents had no clinically significant effect on the tim- antagonists outweigh their potential to delay birth. ing of birth. in the cases of infection-associated Ptl, in addition, there is no evidence that they are where the inflammatory response may be the driving effective in sPtl. force to Ptb, current practice is to hasten delivery and avoid the use of tocolytics. in summary, despite Immune system massive research activity, the role of immuno - modulators in the management of sPtl has yet to it has been known for decades that parturition, be defined. whether at term or preterm, is accompanied by an inflammatory response resulting in an invasion of Conclusions leukocytes into intrauterine tissues (liggins, 1981). Abundant recent research has extensively character- it is clear that Ptb can arise from many distinct ized the pro-inflammatory responses that accompany etiologic pathways involving a myriad of physiolog- parturition, either with or without infection at term ical and pathophysiological mechanisms. some of or preterm. however, the purpose of this inflamma- these arise from within the target cells – the uterine tory response remains unclear. some have reasoned myocytes – and some involve systemic extrinsic that this enhanced activity of the immune system is systems that modulate uterine myocyte activity. the focused on healing the placental site following mechanistic pathways concern many membrane parturition and mediating the process of uterine proteins of the uterine myocyte including GPcR and involution (Mitchell and taggart, 2009). Others have ion channels, among many others. Many intracellu- suggested that the inflammatory response initiates lar signal transduction pathways, including the ca2+- the process of parturition. it is possible that both caM-MlcK and the rhoA-ROK-MlcP pathways, lines of thought could be correct. From the evolu- are likely to be important. extrinsic influences such tionary perspective, activation of the healing re- as the estrogen/progesterone ratio, uterine stretch sponse concurrently with the process that leads to and the immune system are likely to play important increased uterine contractility would be logical and modulatory or even causative roles. We have PhARMAcOlOGicAl tARGetinG OF uteRine MyOcytes – MitchelletAl. 79 mitchell-_Opmaak 1 26/03/13 09:55 Pagina 80 considered each of these pathways, and undoubtedly condon Jc, Jeyasuria P, Faust JMet al. A decline in the levels of Progesterone Receptor coactivators in the Pregnant uterus many more, to be modules that affect uterine con- at term May Antagonize Progesterone Receptor Function tractions. though not included in this discussion, and contribute to the initiation of Parturition. Proc natl Acad there are many more modules that potentially sci usA. 2003;100:9518-9523. regulate the process of cervical ripening. When a da Fonseca eb, bittar Re, carvalho Mh et al. Prophylactic Administration of Progesterone by Vaginal suppository to critical number of modules are activated, labor will Reduce the incidence of spontaneous Preterm birth in occur: this is the concept of modular accumulation Women at increased Risk: A Randomized Placebo- of physiological systems (MAPs) that we have controlled double-blind study. Am J Obstet Gynecol. 2003; 188:419-424. proposed earlier (Mitchell and taggart, 2009). Fang X, Wong s, Mitchell bF. Relationships among sex in view of this probable heterogeneity of path- steroids, Oxytocin, and their Receptors in the Rat uterus ways contributing to the occurrence of sPtl, future during late Gestation and at Parturition. endocrinology. 1996;137:3213-3219. attempts at tocolytic therapy might need to be broad- Friel AM, O'Reilly MW, sexton dJet al.specific Pgf(2alpha) based and include combinations of targets. Future Receptor (Fp) Antagonism and human uterine contractility research using genomic, proteomic and metabolomic in Vitro. bJOG 2005;112:1034-1042. technologies holds the promise of predicting women Goupil e, tassy d, bourguet cet al. A novel biased Allosteric compound inhibitor of Parturition selectively impedes the at risk of sPtl and hopefully indicate the modules Prostaglandin F2alpha-Mediated Rho/Rock signaling that are prematurely activated. this will facilitate a Pathway. J biol chem. 2010;285:25624-25636. preventative rather than a therapeutic (tocolytic) Groom KM, shennan Ah, Jones bA et al. tocox – a Randomised, double-blind, Placebo-controlled trial of approach, which is likely to have many advantages. Rofecoxib (a cox-2-specific Prostaglandin inhibitor) for the combination pharmacological regimens will neces- Prevention of Preterm delivery in Women at high Risk. sitate even more attention to uterine-specific thera- bJOG. 2005;112:725-730. howson cP, Kinney MV, lawn Je. Born Too Soon: The Global pies to avoid off-target effects that will preclude the Action Report on Preterm Birth.March of dimes, PMnch, ability to use effective doses. drug interactions will save the children, Geneva. 2012. then become even more important considerations ikebe M, hartshorne dJ, elzinga M. identification, Phosphory- and pharmacogenomic approaches may help resolve lation, and dephosphorylation of a second site for Myosin light chain Kinase on the 20,000-dalton light chain of these issues. Whereas the past has been disappoint- smooth Muscle Myosin. J biol chem. 1986;261:36-39. ing with respect to prevention of Ptb, the future ikebe M, Koretz J, hartshorne dJ. effects of Phosphorylation hold new promise that every baby can be born at its of light chain Residues threonine 18 and serine 19 on the Properties and conformation of smooth Muscle Myosin. optimal time. Jbiol chem 1988;263:6432-6437. Johnson JW, Austin Kl, Jones Gset al. efficacy of 17alpha- hydroxyprogesterone caproate in the Prevention of Prema- References ture labor. n engl J Med. 1975;293:675-680. Khan K, Zamora J, lamont RF et al. safety concernsfor the use Aguilar hn, Mitchell bF. Physiological Pathways and of calcium channel blockersin pregnancy for the treatment Molecular Mechanisms Regulating uterine contractility. of spontaneous preterm labour and hyprtension: a systematic hum Reprod update. 2010;16:725-744. review and regression analysis. J Mat-Fetal neonatal Med. Aguilar hn, tracey cn, tsang sc et al. Phos-tag-based 2010;23(9);1030-1038. Analysis of Myosin Regulatory light chain Phosphorylation King JF, Flenady VJ, Papatsonis dn et al. calcium channel in human uterine Myocytes. Plos One. 2011;6:e20903. blockers for inhibiting Preterm labour. cochrane database Aguilar hn, tracey cn, Zielnik b, Mitchell bF. Quantification syst Rev. 2003:cd002255. of Rapid Myosin Regulatory light chain Phosphorylation King JF, Grant A, Keirse MJ et al. beta-Mimetics in Preterm using high-throughput in-cell Western Assays: compari- labour: An Overview of the Randomized controlled trials. son to Western immunoblots. Plos One. 2010;5:e9965. br J Obstet Gynaecol. 1988;95:211-222. Aguilar hn, tracey cn, Zielnik b, Mitchell bF. Rho-kinase Kotani M, tanaka i, Ogawa yet al.Multiple signal transduc- mediates diphosphorylation of myosin regulatory light chain tion Pathways through two Prostaglandin e Receptor ep3 in cultured uterine but not vascular smooth muscle cells. subtype isoforms expressed in human uterus. J clin en- J cell Mol Med. 2012;http://onlinelibrary.wiley.com/doi/ docrinol Metab. 2000;85:4315-4322. 10.1111/j.1582-4934.2012.01625.x/abstract. Kozasa t, Jiang X, hart MJ et al. P115 Rhogef, a Gtpase Arthur P, taggart MJ, Zielnik b, Mitchell bF. Relationship Activating Protein for Galpha12 and Galpha13. science. between Gene expression and Function of uterotonic sys- 1998;280:2109-2111. tems in the Rat during Gestation, uterine Activation and both Kupittayanant s, burdyga t, Wray s the effects of inhibiting term and Preterm labour. J Physiol. 2008;586:6063-6076. Rho-Associated Kinase with y-27632 on Force and intra - behrman Re, butler As. Preterm birth: causes, consequences, cellular calcium in human Myometrium. Pflugers Arch. and Prevention. Preterm Birth: Causes, Consequences, and 2001;443:112-114. Prevention, 2007, national Academies Press, Washington. liggins Gc. cervical Ripening as an inflammatory Reaction. in berridge M J. inositol trisphosphate and calcium signalling. elwood dA, Anderson AbM (ed), The Cervix in Pregnancy nature. 1993;361:315-325. and Labour, Clinical and Biochemical Investigations. challis JRG, Matthews sG, Gibb W et al. endocrine and churchill livigstone, edinburgh. 1981. Paracrine Regulation of birth at term and Preterm. endocr Meis PJ, Klebanoff M, thom eet al.Prevention of Recurrent Rev. 2000;21:514-550. Preterm delivery by 17 Alpha-hydroxyprogesterone chibbar R, Miller Fd, Mitchell bF. synthesis of Oxytocin in caproate. n engl J Med. 2003;348:2379-2385. Amnion, chorion, and decidua May influence the timing of Mesiano s, chan ec, Fitter Jtet al.Progesterone Withdrawal human Parturition. J clin invest 1993;91:185-192. and estrogen Activation in human Parturition Are coordi- 80 FVV inObGyn mitchell-_Opmaak 1 26/03/13 09:55 Pagina 81 nated by Progesterone Receptor a expression in the metrial cells: implication for Oxytocin Action. J clin Myometrium. J clin endocrinol Metab. 2002;87:2924-2930. endocrinol Metab. 1996;81:2098-2103. Mitchell bF, Olson dM. Prostaglandin endoperoxide h Romero R, nicolaides K, conde-Agudelo A et al. Vaginal synthase inhibitors and Other tocolytics in Preterm labour. Progesterone in Women with an Asymptomatic sonographic Prostaglandins leukot essent Fatty Acids. 2004;70:167-187. short cervix in the Midtrimester decreases Preterm delivery Mitchell bF, Powell WA. Progesterone Production by human and neonatal Morbidity: A systematic Review and Meta- Fetal Membranes: An in Vitro incubation system for analysis of individual Patient data. Am J Obstet Gynecol. studying hormone Production and Metabolism. Am J Obstet 2012;206:124. e1-19. Gynecol. 1984;148:303-309. Romero R, sibai bM, sanchez-Ramos l et al. An oxytocin Mitchell bF, taggart MJ. Are Animal Models Relevant to Key receptor antagonist (atosiban) in the treatment of preterm Aspects of human Parturition? Am J Physiol Regul integr labor: a randomized, double-blind, placebo-controlled trial comp Physiol. 2009;297:R525-545. with tocolytic rescue. Am J Obstet Gynecol. 2000;182:1173- Mitchell bF, Wong s. changes in 17 beta,20 Alpha-hydro - 1183. xysteroid dehydrogenase Activity supporting an increase in Romero R, scoccia b, Mazor M et al. evidence for a local the estrogen/Progesterone Ratio of human Fetal Membranes change in the Progesterone/estrogen Ratio in human at Parturition. Am J Obstet Gynecol.1993;168:1377-1385. Parturition at term. Am J Obstet Gynecol. 1988;159:657- Moran cJ, Friel AM, smith,tJ et al. expression and Modulation 660. of Rho Kinase in human Pregnant Myometrium. Mol hum smith Gn, Walker, Mc, Ohlsson Aet al.Randomized double- Reprod. 2002;8:196-200. blind Placebo-controlled trial of transdermal nitroglycerin niiro n, nishimura J, sakihara cet al.up-Regulation of Rho a for Preterm labor. Am J Obstet Gynecol 2007;196:37 e31- and Rho-Kinase mRnas in the Rat Myometrium during 38. Pregnancy. biochem biophys Res commun. 1997;230:356- somlyo AP, somlyo AV. ca2+ sensitivity of smooth Muscle 359. and nonmuscle Myosin ii: Modulated by G Proteins, Ki- norton Me, Merrill J, cooper bA et al.neonatal complications nases, and Myosin Phosphatase. Physiol Rev. 2003;83:1325- after the Administration of indomethacin for Preterm labor. 1358. n engl J Med. 1993;329:1602-1607. terzidou V, sooranna sR, Kim luet al.Mechanical stretch up- Ou cW, chen ZQ, Qi s et al. expression and Regulation of Regulates the human Oxytocin Receptor in Primary human theMessenger Ribonucleic Acid encoding the Prostaglandin uterine Myocytes. J clin endocrinol Metab. 2005;90:237- F(2alpha) Receptor in the Rat Myometrium during 246. Pregnancy and labor. Am J Obstet Gynecol. 2000;182: Woodcock nA, taylor W, thornton s. effect of an Oxytocin 919-925. Receptor Antagonist and Rho Kinase inhibitor on the Ou cW, chen ZQ, Qi s et al.increased expression of the Rat [ca++]i sensitivity of human Myometrium. Am J Obstet Myometrial Oxytocin Receptor Messenger Ribonucleic Acid Gynecol. 2004;190:222-228. during labor Requires both Mechanical and hormonal Woodcock nA, taylor cW, thornton s. Prostaglandin F2alpha signals. biol Reprod. 1998;59:1055-1061. increases the sensitivity of the contractile Proteins to ca2+ Ou cW, Orsino A, lye sJ. expression of connexin-43 and in human Myometrium. Am J Obstet Gynecol. 2006;195: connexin-26 in the Rat Myometrium during Pregnancy and 1404-1406. labor is differentially Regulated by Mechanical and Zuckerman h, Reiss u, Rubinstein i. inhibition of human hormonal signals. endocrinology. 1997;138:5398-5407. Premature labor by indomethacin. Obstet Gynecol. 1974; Pettibone dJ, Guidotti M, harrell cM et al. Progress in the 44:787-792. development of Oxytocin Antagonists for use in Preterm Zuckerman h, shalev e, Gilad G et al. Further study of the labor. Adv exp Med biol. 1995;395:601-612. inhibition of Premature labor by indomethacin. Part i. Phaneuf s, carrasco MP, europe-Finner Gnet al. Multiple G JPerinat Med. 1984;12:19-23. Proteins and Phospholipase c isoforms in human Myo - PhARMAcOlOGicAl tARGetinG OF uteRine MyOcytes – MitchelletAl. 81

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