Lai Pei F, Tribe Rachel M, Johnson Mark R
Academic Department of Obstetrics & Gynaecology, Imperial College London, London, SW10 9NH, UK.
Division of Women's Health, Kings College London and Women's Health Academic Centre, Kings Health Partners, London, SE1 7EH, UK.
J Physiol. 2016 Nov 1;594(21):6369-6393. doi: 10.1113/JP272320. Epub 2016 Aug 8.
Over 15 million babies are born prematurely each year with approximately 1 million of these babies dying as a direct result of preterm delivery. β -Adrenoreceptor agonists that act via cAMP can reduce uterine contractions to delay preterm labour, but their ability to repress uterine contractions lasts ≤ 48 h and their use does not improve neonatal outcomes. Previous research has suggested that cAMP inhibits myometrial contractions via protein kinase A (PKA) activation, but this has yet to be demonstrated with PKA-specific agonists. We investigated the role of PKA in mediating cAMP-induced human myometrial relaxation, and the impact of prolonged cAMP elevation on myometrial contractility. Our findings suggest that PKA is not the sole mediator of cAMP-induced myometrial relaxation and that prolonged prophylactic elevation of cAMP alone is unlikely to prevent preterm labour (PTL).
Acute cAMP elevation inhibits myometrial contractility, but the mechanisms responsible are not fully elucidated and the long-term effects are uncertain. Both need to be defined in pregnant human myometrium before the therapeutic potential of cAMP-elevating agents in the prevention of preterm labour can be realised. In the present study, we tested the hypotheses that PKA activity is necessary for cAMP-induced myometrial relaxation, and that prolonged cAMP elevation can prevent myometrial contractions. Myometrial tissues obtained from term, pre-labour elective Caesarean sections were exposed to receptor-independent cAMP agonists to determine the relationship between myometrial contractility (spontaneous and oxytocin-induced), PKA activity, HSP20 phosphorylation and expression of contraction-associated and cAMP signalling proteins. Acute (1 h) application of cAMP agonists promoted myometrial relaxation, but this was weakly related to PKA activation. A PKA-specific activator, 6-Bnz-cAMP, increased PKA activity (6.8 ± 2.0 mean fold versus vehicle; P = 0.0313) without inducing myometrial relaxation. Spontaneous myometrial contractility declined after 24 h but was less marked when tissues were constantly exposed to cAMP agonists, especially for 8-bromo-cAMP (4.3 ± 1.2 mean fold versus vehicle; P = 0.0043); this was associated with changes to calponin, cofilin and HSP20 phosphorylated/total protein levels. Oxytocin-induced contractions were unaffected by pre-incubation with cAMP agonists despite treatments being able to enhance PKA activity and HSP20 phosphorylation. These data suggest that cAMP-induced myometrial relaxation is not solely dependent on PKA activity and the ability of cAMP agonists to repress myometrial contractility is lost with prolonged exposure. We conclude that cAMP agonist treatment alone may not prevent preterm labour.
每年有超过1500万婴儿早产，其中约100万婴儿直接死于早产。通过环磷酸腺苷（cAMP）起作用的β-肾上腺素能受体激动剂可减少子宫收缩以延迟早产，但它们抑制子宫收缩的能力持续时间≤48小时，且其使用并不能改善新生儿结局。先前的研究表明，cAMP通过激活蛋白激酶A（PKA）来抑制子宫肌层收缩，但这尚未用PKA特异性激动剂得到证实。我们研究了PKA在介导cAMP诱导的人子宫肌层舒张中的作用，以及cAMP长期升高对子宫肌层收缩性的影响。我们的研究结果表明，PKA不是cAMP诱导的子宫肌层舒张的唯一介质，仅cAMP的长期预防性升高不太可能预防早产（PTL）。
急性cAMP升高可抑制子宫肌层收缩，但相关机制尚未完全阐明，长期影响也不确定。在能够实现cAMP升高剂在预防早产方面的治疗潜力之前，这两者都需要在妊娠人类子宫肌层中得到明确。在本研究中，我们检验了以下假设：PKA活性是cAMP诱导的子宫肌层舒张所必需的，且cAMP的长期升高可预防子宫肌层收缩。从足月、临产前择期剖宫产获取的子宫肌层组织暴露于不依赖受体的cAMP激动剂，以确定子宫肌层收缩性（自发性和催产素诱导性）、PKA活性、热休克蛋白20（HSP20）磷酸化以及收缩相关蛋白和cAMP信号蛋白表达之间的关系。急性（1小时）应用cAMP激动剂可促进子宫肌层舒张，但这与PKA激活的相关性较弱。一种PKA特异性激活剂6-苄基-cAMP可增加PKA活性（与载体相比平均增加6.8±2.0倍；P=0.0313），但未诱导子宫肌层舒张。24小时后自发性子宫肌层收缩性下降，但当组织持续暴露于cAMP激动剂时下降不太明显，尤其是对于8-溴-cAMP（与载体相比平均增加4.3±1.2倍；P=0.0043）；这与钙调蛋白、丝切蛋白和HSP20磷酸化/总蛋白水平的变化有关。尽管处理能够增强PKA活性和HSP20磷酸化，但催产素诱导的收缩不受与cAMP激动剂预孵育的影响。这些数据表明，cAMP诱导的子宫肌层舒张并不完全依赖于PKA活性，且cAMP激动剂抑制子宫肌层收缩性的能力会随着长期暴露而丧失。我们得出结论，单独使用cAMP激动剂治疗可能无法预防早产。
