Chronic Intermittent Hypoxia: Common PVN Adaptations Contribute to Neurogenic Hypertension and Ischemic Neuroprotection

项目摘要 睡眠呼吸暂停(SA)影响了大约15%的美国人口。大多数SA患者会患上神经源性高血压 (HTN)与交感神经活动(SNA)升高相关。在上一个资金周期中，我们 采用慢性间歇性低氧(CIH)致大鼠SAHTN模型。我们确定HTN是由 由夸大的NMDA驱动的交感前PVN神经元放电维持7天的脑出血 受体(NMDAR)音调。重要的是，我们发现CIH对PVN的激活涉及到局部适应性 反应(即可塑性)，其中神经元NMDAR亚单位(GluN1和GluN2B)的表达减少 胶质细胞L-谷氨酸转运体(L-谷氨酸)转运蛋白EEAT2表达增加。这些回应反映了 对夸大的谷氨酸能输入的动态平衡适应，我们假设这至少部分源于 后脑NTS(方案1)和前脑MnPO(方案2)。CIH还可降低大鼠脑室旁核的表达。 与NMDAR GluN2B亚基和神经元NO形成三元复合体的接头蛋白PSD95 一氧化氮合成酶(NNOS)。这种复合体将NMDAR钙离子内流与NO的产生结合在一起。我们 假设这些对CIH的适应有两个抵消作用。(1)NMDAR降低，NMDAR增加 EAAT2的表达抑制了谷氨酸能PVN的激活，从而抑制了HTN的发展。(2)减少 PSD95钝化NMDAR驱动的NO产生，减弱其对GABA释放的紧张性促进作用。这解除了对 并因此支持HTN的开发。这些相反的适应的最终结果是HTN 与他们不在时相比，CIH引起的影响不那么明显。除了HTN，SA还会增加风险 缺血性卒中的风险增加了~4倍。参与HTN开发的相同PVN适应SA/CIH 假设通过限制细胞外L-谷氨酸的升高和减少 产生神经毒性NO。这项修订提案中的研究将使大鼠暴露于CIH和CIH的7天和28天 高碳酸血症(CIHHC)，以更接近地模拟人类SA。我们的具体目标将：(1)决定 CIH和CIHHC对神经源性HTN、PVN突触/兴奋性毒性信号蛋白和PVN表达的影响 局部缺血后神经元/组织存活。(2)确定CIH/CIHHC适应对PVN控制的影响 SNA/MAP和神经元对局部缺血易感性的机制。(3)使用病毒介导的基因 转移/shRNA敲除以模拟和挽救特定的PVN适应并确定它们对 CIH和CIHHC的高血压及神经保护作用。

Project Summary Sleep apnea (SA) affects ~15% of the US population. Most people with SA develop neurogenic hypertension (HTN) associated with elevated sympathetic nerve activity (SNA). During the previous funding cycle, we modeled SA HTN by exposing rats to chronic intermittent hypoxia (CIH). We determined that HTN induced by 7 days of CIH is maintained by pre-sympathetic PVN neuronal discharge driven by exaggerated NMDA receptor (NMDAR) tone. Importantly, we discovered that PVN activation by CIH involves local adaptive responses (i.e., plasticity) wherein expression of neuronal NMDAR subunits (GluN1 & GluN2B) is reduced and expression of the glial L-glutamate (L-Glu) transporter EEAT2 is increased. These responses reflect homeostatic adaptations to exaggerated glutamatergic input, which we postulate arises, at least in part, from the hindbrain NTS (Project 1) and the forebrain MnPO (Project 2). CIH also decreased PVN expression of the adaptor protein PSD95 that forms a ternary complex with the NMDAR GluN2B subunit and neuronal nitric oxide (NO) synthase (nNOS). This complex couples NMDAR Ca2+ influx with production of NO. We hypothesize that these adaptations to CIH have two offsetting actions. (1) Reduced NMDAR and increased EAAT2 expression blunt glutamatergic PVN activation and thereby buffer development of HTN. (2) Reduced PSD95 blunts NMDAR-driven NO production and lessens its tonic facilitation of GABA release. This disinhibits the PVN and thereby supports development of HTN. The net effect of these opposing adaptations is that HTN induced by CIH is less pronounced than it would be in their absence. In addition to HTN, SA increases the risk of ischemic stroke by ~4 fold. The same PVN adaptations to SA/CIH that participate in development of HTN are hypothesized to reduce ischemic injury by limiting the rise of extracellular L-Glu and reducing the production of neurotoxic NO. Studies in this revised proposal will expose rats to 7 and 28 days of CIH and CIH with hypercapnia (CIHHC) to more closely model human SA. Our specific aims will: (1) Determine effects of CIH & CIHHC on neurogenic HTN, PVN expression of synaptic/excitotoxic signaling proteins and PVN neuronal/tissue survival after local ischemia. (2) Determine effects of CIH/CIHHC adaptations on PVN control of SNA/MAP and mechanisms of neuronal vulnerability to local ischemia. (3) Use viral-mediated gene transfer/shRNA knockdown to mimic and rescue specific PVN adaptations and determine their contributions to hypertensive and neuroprotective effects of CIH & CIHHC.