Mechanisms of Ventilatory Adaptations to Chronic Hypercapnia

慢性肺部或神经肌肉疾病损害气体交换，导致慢性高碳酸血症(CH)。中国是 不幸的是，退伍军人事务部患者中很常见，并与长期贫困有关 预后、更高的死亡率和认知功能下降。而系统的生理适应可能 限制先天性心脏病的负面后果，先天性心脏病患者可能容易发生病理性适应不良 对慢性急性加重的反应，特别是在控制呼吸的中枢神经系统网络内。 然而，人们对这些由不同程度引起的适应和/或适应不良机制知之甚少 中的一种。我们建议的研究集中于检验CH诱导补偿的总体假设 控制呼吸和/或认知功能的关键细胞群体内基因表达的变化，其中进一步 高碳酸血症的加重会导致基因表达和生理功能的不适应变化。 我们最近建立了对慢性慢性肝炎30天以上轻度CH的时间依赖的生理适应。 在我们的行为自由的成年山羊模型中，暴露于6%的激励二氧化碳(InCO2；PaCO2~55 mm Hg)。其中， 轻度CH可引起稳态通气量、呼吸机CO2/H+敏感性、 心率、血压、肾小苏打和钾回收及代谢率，但受损 认知功能。通气量在1-3小时内显著增加，但在24小时后降至稳定状态 高于正常水平。相反，呼吸性CO2/H+化学反射在1-2d内下降，7d后恢复正常。 在整个30d的CH中，稳态通气量大于预期，这表明尚未确定的 呼吸的“缺失刺激”，我们假设这代表了CH诱导的呼吸神经可塑性。 为了深入了解轻微的CH诱导的神经可塑性，我们确定了选定的标记物随时间的变化 脑干和皮质部位的神经可塑性对呼吸控制和认知很重要。我们发现 白介素1、谷氨酸受体亚单位表达/磷酸化的一过性变化 5-羟色胺能系统标志物。然而，这些神经可塑性标记物的相关变化未能 充分解释了脑出血时神经适应的机制。因此，我们建议将散装组织 (BT)和/或单核(SN)RNA测序技术，以查询 CH对山羊的生理性呼吸适应和认知功能减退我们的团队之前已经和 成功地在大鼠身上应用这些尖端方法来识别差异表达基因(Deg) 脑干区(btRNA-seq)或特定细胞类型(snRNA-seq)，并因此准备应用这些 技术应用到我们的山羊模型中。模拟急慢性高碳酸血症的初步生理学研究 (通过进一步将吸入二氧化碳从6%增加到8%以诱导中度高碳酸血症)显示出 急性和严重高碳酸血症期间心肺变量的病理性抑制。因此，我们的 已公布的和初步的数据支持我们的总体假设，这一假设将通过应用切割- 边缘，已建立的方法学，以填补有关基础神经生物学知识的现有空白 CH.的影响我们将通过四个具体目标来实现我们的目标：目标1.1测试3到24小时的假设 轻度脑出血导致中枢神经系统区域内基因表达/细胞信号通路的动态适应性变化 控制心肺功能和认知功能。Aim 1.2测试7d轻度CH诱导的假说 适应性CH诱导呼吸的基因表达/信号通路的细胞类型特异性变化 神经可塑性。目的2验证中度CH使山羊易患病理生理学的假说 由于基因表达的不适应转变而导致的严重高碳酸血症(急性-慢性加重)的反应 中枢神经系统区域内控制心肺和认知功能的轮廓/细胞信号通路。

Chronic lung or neuromuscular diseases impair gas exchange leading to chronic hypercapnia (CH). CH is unfortunately common in the Veteran’s Affairs patient population, and is associated with poor long-term prognoses, higher mortality rates and reduced cognitive function. While systemic physiologic adaptations may limit the negative consequences of CH, patients with CH may be predisposed to pathological maladaptive responses to acute-on-chronic exacerbations thereof, especially within CNS networks that control breathing. However, very little is known about these adaptive and/or maladaptive mechanisms elicited by varying degrees of CH. Our proposed studies are focused on testing the overall hypothesis that CH induces compensatory shifts in gene expression within key cell populations controlling breathing and/or cognitive function, where further exacerbation of hypercapnia cause maladaptive changes in gene expression and physiologic function. We recently established the time-dependent physiologic adaptions to mild CH over 30 days (d) of chronic exposure to 6% inspired CO2 (InCO2; PaCO2 ~55 mmHg) in our freely behaving adult goat model. Among others, mild CH induced time-dependent adaptive changes in steady state ventilation, ventilatory CO2/H+ sensitivity, heart rate, blood pressure, renal bicarbonate and potassium reclamation and metabolic rate, but impaired cognitive function. Ventilation dramatically increased within 1-3 hours (h) but by 24h decreased to a steady-state above normal. In contrast, the ventilatory CO2/H+ chemoreflex decreased within 1-2d but normalized by 7d. Steady-state ventilation was greater than predicted throughout the 30d CH, indicative of a yet-to-be-identified “missing stimulus” to breathe which we hypothesize represents a CH-induced respiratory neuroplasticity. To gain insight into mild CH-induced neuroplasticity, we identified time-dependent shifts in select markers of neuroplasticity within brainstem and cortical sites important in respiratory control and cognition. We found transient changes in interleukin 1-ß (IL-1ß), glutamate receptor subunit expression/phosphorylation, and serotonergic system markers. However, these correlative changes in markers of neuroplasticity failed to adequately explain the mechanisms of neuroadaption during CH. Accordingly, we propose to apply bulk tissue (bt) and/or single nuclear (sn)RNA sequencing technologies to query the molecular underpinnings of the physiologic respiratory adaptations and cognitive decline induced by CH in goats. Our team has previously and successfully applied these cutting-edge approaches in rats to identify differentially-expressed genes (DEGs) in brainstem regions (btRNA-Seq) or within specific cell types (snRNA-seq), and are thus poised to apply these technologies to our goat model of CH. Preliminary physiologic studies simulating acute-on-chronic hypercapnia (by further chronically increasing inspired CO2 from 6% to 8% to induce moderate hypercapnia) showed a pathological depression of cardiorespiratory variables during acute and severe hypercapnia. Thus, our published and preliminary data support our overall hypothesis, which will be further tested by applying cutting- edge, established methodologies to fill existing gaps in knowledge regarding the fundamental neurobiological effects of CH. We will achieve our goal through four Specific Aims: Aim 1.1 tests the hypothesis that 3 to 24h of mild CH induces dynamic, adaptive shifts in gene expression/cellular signaling pathways within CNS regions controlling cardiorespiratory and cognitive functions. Aim 1.2 tests the hypothesis that 7d of mild CH induces cell type-specific changes in gene expression/signaling pathways that underlie adaptive CH-induced respiratory neuroplasticity. Aim 2 tests the hypothesis that moderate CH predisposes goats to pathophysiological responses to severe hypercapnia (acute-on-chronic exacerbation) due to maladaptive shifts in gene expression profiles/cellular signaling pathways within CNS regions controlling cardiorespiratory and cognitive functions.