Alpha Adrenergic Methylation and Developmental Maturation of Cerebral Autoregulation in Ovine Preterm Fetus

总结：早产儿由于大脑发育不成熟， 血流量（CBF）自动调节。与足月新生儿相反，早产儿不能减少CBF， 全身血压升高。在早产儿中，脆弱的脑血管暴露于增加的血流量， 升高的全身压力导致它们破裂和脑损伤。我们的初步研究表明， 当全身血压升高时，胎儿和足月新生羔羊可以收缩颈动脉并降低CBF;然而， 早产儿的能力没有发展。此外，我们观察到，在去除交感神经控制后， 通过切断上级颈神经节使他们失去了限制颈动脉血流到 随着全身血压的升高而升高我们还观察到，颈动脉收缩减少CBF是由 交感神经系统，特别是通过α-1肾上腺素能受体（α1-AR）的活性。这些受体是 在早产儿颈动脉中以显著较低的数量表达。因此，我们得出结论，α1-AR活性降低 在调节颈动脉血流量和全身血压升高方面起着重要作用。此外，我们提出证据， 差异DNA甲基化调节α1-ARs启动子活性和表达。因此，我们将测试假设， DNA甲基化和去甲基化对颈动脉α1-AR亚型（α1A-，α1B-，α1D）表达和功能的调节 在CAR从早产到足月胎儿的成熟过程中起着至关重要的作用。我们将从两性中收集数据 来识别任何与性别有关的变化这些研究将在长期插管的胎羊体内进行， 在离体颈动脉上将以两个具体目标来检验这一假设。目的1：从早产到足月胎儿， 性别特异性的方式，我们将进行深入的机制分析启动子DNA甲基化的差异 α1-AR亚型在颈动脉中的表达。目的2：以性别特异性的方式，我们将确定功能性 不同α1-AR亚型基因启动子甲基化及表达对颈动脉收缩力和血液流变学的影响 流测量将在实时、体内和子宫内胎儿成熟的情况下进行。这将提供宝贵的 关于α1-AR亚型的作用和CAR成熟中涉及的表观遗传机制的信息。

Summary: Preterm infants have a significantly higher incidence of brain damage as a consequence of immature cerebral blood flow (CBF) autoregulation. In contrast to term neonates, preterm neonates are not able to reduce CBF in response to increased systemic BP. In preterm neonates, exposure of fragile cerebral vessels to an increased amount of blood flow at elevated systemic pressure leads to their rupture and brain damage. Our preliminary studies demonstrate that near-term fetuses and term-newborn lambs can constrict carotid arteries and reduce CBF when systemic BP rises; however, this capability is not developed in the preterm fetus. Also, we observed that following the removal of sympathetic control in the near-term fetus by severing the superior cervical ganglion made them lose their ability to restrict carotid blood flow to the brain with the rise in systemic BP. We also observed that the constriction of carotid arteries to reduce CBF is regulated by the sympathetic nervous system, specifically by the activity of alpha-1 adrenergic receptors (α1-ARs). These receptors are expressed at a significantly lower number in preterm carotid arteries. Thus, we concluded that reduced activity of α1-ARs plays a fundamental role in regulating carotid blood flow with the rise in systemic BP. Furthermore, we present evidence that differential DNA methylation regulates α1-ARs promoter activity and expression. Thus, we will test the hypothesis that DNA methylation and demethylation regulate the expression and function of α1-AR subtypes (α1A-, α1B-, α1D) in the carotid arteries and play a crucial role in the maturation of CAR from preterm to term fetus. We will collect data from both sexes to identify any sex-related changes. The studies will be conducted in-vivo in chronically catheterized fetal sheep and ex-vivo on isolated carotid arteries. The hypothesis will be tested with two specific aims. Aim 1: From preterm to term fetus in a sex-specific manner, we will conduct an in-depth mechanistic analysis of promoter DNA methylation on differential expression of α1-AR subtypes in carotid arteries. Aim 2: In a sex-specific manner, we will determine the functional significance of differential α1-AR subtypes promoter methylation and expression on carotid artery contractility and blood flow. The measurements will be conducted in real-time, in-vivo, with in-utero fetal maturation. This will provide valuable information regarding the role of α1-AR subtypes and the epigenetic mechanisms involved in the maturation of CAR.