The role of Alpha1-Adrenergic Receptors Promoter Methylation in Cerebral Autoregulation in Fetus

概述：生物体对全身血压突然升高作出反应，减少脑血流量的能力 (BP)称为大脑自动调节（CAR）。与足月新生儿相比，早产儿不能减少 脑血流量（CBF）对全身血压升高的反应。在早产儿中，这暴露了脆弱的脑血管 在高压下血液流量显著增加，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，近足月胎儿可以收缩颈动脉并减少CBF;然而， 早产儿的能力没有发展。我们还观察到，颈动脉收缩减少CBF， 受肾上腺素能神经系统调节，特别是受α-1肾上腺素能受体（α1-AR）的活性调节。这些 受体在早产儿颈动脉中以显著较低的数量表达。此外，我们观察到， 通过切断上级颈神经节（SCG）来消除近足月胎儿的肾上腺素能控制， 随着全身血压的升高，减少颈动脉血流量（CaBF）的能力。因此，在去除SCG之后， 早产和近足月胎儿不能在全身血压升高后降低CBF。在体外实验期间， 在颈动脉段，我们观察到对α1-ARs激动剂反应的早产动脉收缩显著低于 那些来自于近期的羊羔。因此，我们得出结论，α1-AR活性降低在调节 CaBF随全身血压升高而升高。我们还观察到早产儿α1-AR激动剂活性的降低， 与近足月胎羊相比，α1-AR的表达减少。此外，我们提出证据， 通过荧光素酶报告基因分析，DNA超甲基化降低了α1-AR启动子活性， 修改.因此，我们将检验启动子DNA超甲基化和组蛋白修饰减少了细胞凋亡的假设。 α1-AR亚型（α1A-、α1B-、α1D）在颈动脉中的表达和功能，并在颈动脉的成熟中起重要作用。 从早产儿到足月胎儿的大脑自动调节。我们还将收集两性（男性与女性）的数据， 识别与性别有关的变化。这些研究将在离体颈动脉上进行，并在体内长期进行。 插入导管的胎羊。将以两个具体目标来检验这一假设。目的1：从早产到足月胎儿的性别- 具体的方式，我们将进行深入的机制分析启动子DNA甲基化和组蛋白修饰 α1-AR亚型在颈动脉的差异表达。目的2：从早产到足月胎儿，以性别特异性的方式， 我们将确定不同α1-AR亚型启动子甲基化，组蛋白修饰， 以及基因表达对颈动脉收缩性和脑血流调节的影响， 系统压力。测量将在实时体内进行，每周进行一次宫内胎儿成熟 从105天到137天。这将提供有关α1-AR亚型和表观遗传学作用的有价值的信息。 参与CAR成熟的机制。

Summary: The ability of an organism to reduce the brain blood flow in response to sudden surges in systemic blood pressure (BP) is known as cerebral autoregulation (CAR). In contrast to term neonates, preterm neonates are not able to reduce cerebral blood flow (CBF) in response to increased systemic BP. In preterm neonates, this exposes fragile cerebral vessels to a significantly increased blood flow at high pressure, leading to their rupture and brain damage. Our preliminary studies demonstrate that near-term fetuses can constrict carotid arteries and reduce CBF when systemic BP rises; however, this capability is not developed in the preterm fetus. We also observed that the constriction of carotid arteries to reduce CBF is regulated by the adrenergic nervous system, specifically by the activities of alpha-1 adrenergic receptors (α1-ARs). These receptors are expressed at a significantly lower number in preterm carotid arteries. Also, we observed that following the removal of adrenergic control in the near-term fetus by severing the superior cervical ganglion (SCG) made them lose their ability to reduce carotid blood flow (CaBF) to the brain with the rise in systemic BP. Thus, after the removal of SCG, both preterm and near-term fetuses cannot reduce CBF following an increase in systemic BP. During ex-vivo experiments on carotid segments, we observed that preterm arterial constriction in response to α1-ARs agonist was significantly lower than those from near-term lambs. Thus, we concluded that reduced activities of α1-ARs play a fundamental role in regulating CaBF with the rise in systemic BP. We also observed that the reduction in the activities of α1-ARs agonists in preterm resulted from reduced expression of α1-ARs compared to those in near-term fetal lambs. Furthermore, we present evidence that DNA hypermethylation reduces α1-ARs promoter activities by luciferase reporter assays and the involvement of histone modifications. Thus, we will test the hypothesis that promoter DNA hypermethylation and histone modifications reduce the expression and function of α1-AR subtypes (α1A-, α1B-, α1D) in the carotid arteries and play an essential role in the maturation of cerebral autoregulation from preterm to term fetus. We will also collect data from both sexes (male versus female) to identify sex-related changes. The studies will be conducted ex-vivo on isolated carotid arteries and in vivo in chronically catheterized fetal sheep. 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 and histone modifications on differential expression of α1-AR subtypes in carotid arteries. Aim 2: From preterm to term fetus, in a sex-specific manner, we will determine the functional significance of differential α1-AR subtypes promoter methylation, histone modifications, and gene expression on carotid artery contractility and blood flow regulation to the brain in response to an increase in systemic pressure. The measurements will be conducted in real-time, in-vivo, with in-utero fetal maturation every week from 105 to 137 days. This will provide valuable information regarding the role of α1-AR subtypes and the epigenetic mechanisms involved in the maturation of CAR.