Changes in vascular contractility are among the most important physiological effects of acute and chronic fetal hypoxia. Given the essential role of Myosin Light Chain Kinase (MLCK) in smooth muscle contractility, and its heterogeneous distribution, this study explores the hypothesis that subcellular changes in MLCK distribution contribute to hypoxic modulation of fetal carotid artery contractility. Relative to common carotid arteries from normoxic term fetal lambs (FN), carotids from fetal lambs gestated at high altitude (3802m) (FH) exhibited depressed contractility without changes in MLCK mRNA or protein abundance. Patterns of confocal colocalization of MLCK with aActin and MLC₂₀ enabled calculation of subcellular MLCK fractions: 1) colocalized with the contractile apparatus; 2) colocalized with aActin distant from the contractile apparatus; 3) not colocalized with aActin. Chronic hypoxia did not affect MLCK abundance in the contractile fraction, despite a concurrent decrease in contractility. Organ culture for 72h under 1% O₂ decreased total MLCK abundance in FN and FH carotid arteries, but decreased the contractile MLCK abundance only in FH carotid arteries. Correspondingly, culture under 1% O₂ depressed contractility more in FH than FN carotid arteries. In addition, hypoxia appeared to attenuate ubiquitin-independent proteasomal degradation of MLCK, as reported for other proteins. In aggregate, these results demonstrate that the combination of chronic hypoxia followed by hypoxic culture can induce MLCK translocation among at least three subcellular fractions with possible influences on contractility, indicating that changes in MLCK distribution are a significant component of fetal vascular responses to hypoxia.

中文翻译：

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胎儿血管 MLCK 丰度、定位和功能的缺氧调节

血管收缩力的变化是急性和慢性胎儿缺氧最重要的生理效应之一。鉴于肌球蛋白轻链激酶 (MLCK) 在平滑肌收缩力及其异质分布中的重要作用，本研究探讨了 MLCK 分布的亚细胞变化有助于胎儿颈动脉收缩力的缺氧调节的假设。相对于含氧量正常的足月羔羊 (FN) 的颈总动脉，在高海拔 (3802m) (FH) 孕育的羔羊颈动脉表现出收缩力下降，而 MLCK mRNA 或蛋白质丰度没有变化。_{MLCK 与 aActin 和 MLC 20}的共聚焦共定位模式启用亚细胞 MLCK 分数的计算：1）与收缩装置共定位；2) 与远离收缩装置的肌动蛋白共定位；3) 不与 aActin 共定位。慢性缺氧不影响收缩部分中的 MLCK 丰度，尽管收缩力同时下降。_{在 1% O 2}下 72 小时的器官培养降低了 FN 和 FH 颈动脉中的总 MLCK 丰度，但仅降低了 FH 颈动脉中的收缩性 MLCK 丰度。相应地，在 1% O _2下培养FH 比 FN 颈动脉更能抑制收缩力。此外，缺氧似乎减弱了 MLCK 的泛素依赖性蛋白酶体降解，正如其他蛋白质所报道的那样。总的来说，这些结果表明，慢性缺氧和缺氧培养相结合可以诱导 MLCK 在至少三个亚细胞部分之间易位，并可能影响收缩力，表明 MLCK 分布的变化是胎儿血管对缺氧反应的重要组成部分。