Molecular mechanisms of adaptation to intrauterine and perinatal changes of oxygen partial pressure: The liver-to-kidney switch of Erythropoietin production as model system

充足的氧稳态是正常的宫内发育所必需的。胎盘对氧合的适应是由复杂的分子机制精确调控的，这些分子机制控制着氧感知和氧依赖基因的表达。对宫内缺氧的反应改变了一个发育程序，从个体的角度来看，只有当身体准备好切换到呼吸空气的高氧分压（pO2）时，这个程序才会发生巨大的变化。在非常早产的婴儿中，氧依赖基因如血管内皮生长因子（VEGF）或促红细胞生成素（EPO）的正常表达立即停止会导致特征性疾病，这些疾病可能对神经发育结局和显著发病率产生终身影响。为了研究氧稳态紊乱的病理生理学，EPO的调控是一个有趣的模型系统。EPO基因的转录受氧感应系统的调控，该系统包括脯氨酸羟化酶（PHDs）和缺氧诱导因子（HIF）。hif依赖性EPO表达受氧可用性（肾脏更高的生产能力）和血液灌注（肝-肾转换）反应的显著变化影响。因此，EPO模型将用于阐明与极早产儿疾病高度相关的缺氧和高氧条件下胎儿和新生儿氧传感系统的适应性。方法和工作计划：在发育过程中，通过使用PHD抑制剂来稳定HIF（从而模拟缺氧）或高氧来破坏HIF稳定，在调节氧传感条件下研究来自定时怀孕小鼠的胚胎/胎儿。HIF稳定和高氧都模仿胎儿或早期新生儿的氧稳态紊乱。这种治疗的效果以前还没有被研究过。我们将详细研究宫内和围产期pO2的变化对HIF-PHD氧传感系统自适应反应的影响。我们将通过短期或长期暴露于HIF稳定或降解与正常条件下的怀孕小鼠，来对比发育过程中急性和慢性pO2变化的影响。将胎儿氧合紊乱与急性围产期缺氧或高氧结合起来也将是有意义的。在HIF-PHD系统的下游，我们将分析促生成素的产生和促生成素表达的两个发育开关的分子机制：1)在肝脏发育过程中，促生成素表达从高水平（主要是缺氧不依赖）到低水平（但缺氧依赖），以及2)从肝脏到肾脏。目的：通过这个研究项目，我们将在开发过程中获得关于氧传感和促红细胞生成素生产的复杂调控的知识。结果将高度相关的理解非常早产儿特征性疾病的一般病理生理学。这将最终激发新的治疗概念，以改善长期疗效。

INTRODUCTION: The adequate oxygen homeostasis is essential for proper intrauterine development. The adaptation to placental oxygenation is precisely regulated by complex molecular mechanisms that control oxygen sensing and expression of oxygen-dependent genes. The response to intrauterine hypoxia modifies a developmental program that should, ontogenetically, only dramatically change at term when the body is prepared to switch to high oxygen partial pressure (pO2) of air-breathing life. In very preterm infants, the immediate stop of proper expression of oxygen-dependent genes such as Vascular Endothelial Growth Factor (VEGF) or Erythropoietin (EPO) causes characteristic diseases that may have life-long consequences for neurodevelopmental outcome and significant morbidities. To study the pathophysiology of disorders of oxygen homeostasis, regulation of EPO is an intriguing model system. EPO gene transcription is modulated by the oxygen sensing system which includes the Prolyl Hydroxylases (PHDs) and Hypoxia Inducible Factor (HIF). The HIF-dependent EPO expression is subject to significant changes in the response to oxygen availability (higher production capacity in kidneys), but also to blood perfusion (liver-to-kidney switch). Thus, the EPO model will be utilized to elucidate the adaptation of the oxygen sensing system of the fetus and neonate under hypoxia and hyperoxia that are highly relevant for diseases of very preterm infants. METHODS and WORK PROGRAMME: Embryos/fetuses from timed-pregnant mice will be studied under conditions of modulated oxygen sensing during development by using a PHD inhibitor to stabilize HIF (and thereby mimic hypoxia) or hyperoxia to destabilize HIF. HIF stabilization and hyperoxia both imitate disturbed fetal or early neonatal oxygen homeostasis. The effects of such treatments have not been studied before. In detail, we will examine the impact of intrauterine and perinatal changes of the pO2 on the adaptive response of the HIF-PHD oxygen sensing system. We will contrast the influence of acute and chronic pO2 changes during development by short- or long-term exposure of pregnant mice to HIF stabilization or degradation vs. normal conditions. It will also be of interest to combine disturbed fetal oxygenation with acute perinatal hypoxia or hyperoxia. Downstream of the HIF-PHD system, we will dissect the Epo production and the molecular mechanisms of the two developmental switches of Epo expression: 1) from high, mostly hypoxia-independent to lower, but hypoxia-dependent expression during liver development, and 2) from the liver to the kidney. OBJECTIVES: With this research project, we will gain knowledge on the complex regulation of oxygen sensing and Epo production during development. The results will be highly relevant for the understanding of the general pathophysiology of characteristic diseases of very premature infants. This will ultimately inspirit novel treatment concepts for improved long-term outcomes.