Mechanisms of Ventilatory Adaptations to Chronic Hypercapnia

慢性肺或神经肌肉疾病损害气体交换，导致慢性高碳酸血症（CH）。CH是 不幸的是，在退伍军人事务部的患者人群中很常见，并且与不良的长期 更高的死亡率和认知功能下降。虽然全身生理适应可能 限制CH的负面后果，CH患者可能倾向于病理适应不良 对慢性急性加重的反应，特别是在控制呼吸的CNS网络内。 然而，很少有人知道这些适应性和/或适应不良的机制引起的不同程度的， 我们提出的研究集中在测试的总体假设，CH诱导代偿性 控制呼吸和/或认知功能的关键细胞群内基因表达的变化，其中进一步 高碳酸血症的加重导致基因表达和生理功能的不适应性变化。 我们最近建立了对轻度CH超过30天（d）的时间依赖性生理适应， 暴露于6%吸入CO2（InCO 2; PaCO 2 ~55 mmHg）。其中， 轻度CH诱导稳态通气、呼吸CO2/H+敏感性的时间依赖性适应性变化， 心率、血压、肾碳酸氢盐和钾回收率以及代谢率，但受损 认知功能通气量在1-3小时（h）内显著增加，但到24小时降至稳定状态 高于正常水平相反，诱导性CO2/H+化学反射在1-2d内下降，但在7 d时恢复正常。 在整个30天CH中，稳态通气量大于预测值，表明存在尚未确定的 我们假设这代表CH诱导的呼吸神经可塑性。 为了深入了解轻度CH诱导的神经可塑性，我们确定了选择的标记物的时间依赖性变化， 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 白细胞介素1-β（IL-1 β）、谷氨酸受体亚单位表达/磷酸化的瞬时变化，以及 肾上腺素能系统标志物。然而，这些神经可塑性标志物的相关变化未能 充分解释CH期间的神经适应机制。因此，我们建议应用大块组织 (bt)和/或单核（sn）RNA测序技术，以查询细胞的分子基础。 生理呼吸适应和认知能力下降。我们的团队以前和 成功地将这些尖端方法应用于大鼠中，以识别大鼠中的差异表达基因（DEG）。 脑干区域（btRNA-Seq）或特定细胞类型内（snRNA-seq），并因此准备应用这些 技术，我们的山羊CH模型。模拟急性慢性高碳酸血症的初步生理学研究 (by进一步将吸入的CO2从6%慢性增加到8%以诱导中度高碳酸血症）显示， 急性和严重高碳酸血症期间心肺变量的病理性抑制。所以我们 已发表的和初步的数据支持我们的整体假设，这将进一步测试，通过应用切割- 边缘，建立的方法，以填补现有的知识差距，有关的基本神经生物学 我们将通过四个具体目标实现我们的目标：目标1.1测试假设，3至24小时 轻度CH诱导CNS区域内基因表达/细胞信号传导途径的动态适应性变化 控制心肺和认知功能。目的1.2检验7天轻度CH诱导的假设 适应性CH诱导的呼吸道疾病的基因表达/信号通路的细胞类型特异性变化 神经可塑性目的2检验中度CH使山羊易于发生病理生理学改变的假设。 由于基因表达的不适应性变化而对重度高碳酸血症（慢性加急性加重）的反应 控制心肺和认知功能的CNS区域内的细胞信号传导通路。

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.