Intermittent Hypoxia-Induced Inflammation Modulates Respiratory Plasticity

描述（由申请人提供）：破坏控制呼吸的神经系统的因素降低了补偿病理的能力，威胁到生命本身。可塑性是神经系统的基本特征，包括控制呼吸的神经系统。指导这一建议的基本假设是，全身性炎症损害呼吸运动可塑性，破坏多种病理的补偿能力，包括慢性肺病、创伤性、缺血性和退行性神经疾病，以及阻塞性睡眠呼吸暂停。我们建议研究急性间歇缺氧后炎症损害呼吸运动可塑性，膈长期促进（pLTF）模型的机制。我们将脂多糖（LPS）诱导的炎症与1天严重间歇性缺氧（sIH）诱导的炎症进行对比；sIH模拟了阻塞性睡眠呼吸暂停的各个方面，这是一种广泛存在的临床疾病，对人类健康有重大影响。令人兴奋的初步数据表明，LPS和sIH均通过脊髓炎症阻断pLTF。由于LPS和sIH在不同的脊髓细胞类型中引起差异的基因表达，但对pLTF有相似的影响，我们提出了一个统一的假设，即多种炎症分子聚集在一个共同的“下游”信号级联上，限制呼吸运动的可塑性。一种创新的、多学科的方法将被用来检验我们的假设；实验方法包括：麻醉大鼠膈神经记录，未麻醉大鼠膈肌肌电图记录，标记膈运动神经元蛋白的免疫组织化学分析，新分离的脊髓星形胶质细胞和小胶质细胞中炎症基因表达分析，以及流式细胞术评估鉴定细胞类型中的蛋白。我们将测试五个特定的假设来推进我们的理解：1)系统性LPS和sIH引发脊髓炎症，从而损害膈肌和膈肌LTF；2) LPS和sIH对膈运动促进（pMF）通路的影响不同。我们将确定LPS和sIH对ERK依赖性（如pLTF）、akt依赖性和ERK/ akt依赖性pMF的影响；3) LPS和sIH引起不同的炎症。sIH仅影响脊髓小胶质细胞，而LPS也影响星形胶质细胞；4)尽管炎症特征不同，LPS和sIH通过共同的“下游”机制损害pLTF，该机制涉及膈运动神经元p38 MAP激酶的激活；5)脊髓p38活性增加膈运动神经元蛋白磷酸酶2A活性，从而抑制ERK，抑制pLTF。了解炎症破坏呼吸可塑性的机制是至关重要的，因为炎症可能会降低病理状态下自然代偿可塑性的能力。我们的长期目标是利用和促进呼吸可塑性作为一种治疗策略来治疗毁灭性的呼吸障碍，如颈椎损伤或运动神经元疾病。

DESCRIPTION (provided by applicant): Factors that undermine the neural system controlling breathing diminish the capacity to compensate for pathology, threatening life itself. Plasticity is an essential feature of neural systems, including the neural system controlling breathing. The fundamental hypothesis guiding this proposal is that systemic inflammation impairs respiratory motor plasticity, undermining the ability to compensate for multiple pathologies, including chronic lung disease, traumatic, ischemic and degenerative neural disorders, and obstructive sleep apnea. We propose to investigate mechanisms whereby inflammation impairs a well-studied model of respiratory motor plasticity, phrenic long-term facilitation (pLTF) following acute intermittent hypoxia. We will contrast inflammation induced by lipopolysaccharide (LPS) with that induced by one day of severe intermittent hypoxia (sIH); sIH simulates aspects of obstructive sleep apnea, a widespread clinical disorder with major implications for human health. Exciting preliminary data suggest that both LPS and sIH block pLTF via spinal inflammation. Since LPS and sIH elicit differential gene expression in different spinal cell types, yet have similar effects on pLTF, we propose a unifying hypothesis whereby multiple inflammatory molecules converge on a common "downstream" signaling cascade that constrains respiratory motor plasticity. An innovative, multidisciplinary approach will be used to test our hypotheses; experimental approaches include: phrenic nerve recordings in anesthetized rats, diaphragm EMG recordings in unanesthetized rats, immunohistochemical analysis of proteins in labeled phrenic motor neurons, analysis of inflammatory gene expression in freshly-isolated spinal astrocytes and microglia, and flow cytometry to assess proteins in identified cell types. Five specific hypotheses will be tested to advance our understanding: 1) Systemic LPS and sIH elicit spinal inflammation, thereby impairing phrenic and diaphragm LTF; 2) LPS and sIH differentially impair distinct pathways to phrenic motor facilitation (pMF). We will determine LPS and sIH effects on ERK- dependent (e.g., pLTF), Akt-dependent and ERK/Akt-dependent pMF; 3) LPS and sIH elicit distinct inflammatory profiles. sIH affects only spinal microglia, whereas LPS also affects astrocytes; 4) Despite different inflammatory profiles, LPS and sIH impair pLTF by a common "downstream" mechanism involving p38 MAP kinase activation in phrenic motor neurons; and 5) Spinal p38 activity increases protein phosphatase 2A activity in phrenic motor neurons, thereby inhibiting ERK and constraining pLTF. Understanding mechanisms whereby inflammation undermines respiratory plasticity is of fundamental importance since inflammation may diminish the capacity for natural, compensatory plasticity during pathological states. Our long-range goal is to harness and promote respiratory plasticity as a therapeutic strategy to treat devastating breathing disorders, such as during cervical spinal injury or motor neuron disease. PUBLIC HEALTH RELEVANCE: All lung and CNS disorders that challenge the ability to generate adequate breathing are associated with inflammation, including chronic lung diseases, traumatic, ischemic and degenerative neural disorders, and obstructive sleep apnea. Although these pathologies have profound consequences for public health, virtually nothing is known concerning the impact of inflammation on the neural system controlling breathing. Our goal is to investigate mechanisms whereby inflammation undermines a well-studied model of respiratory motor plasticity known as long-term facilitation since this knowledge may guide the development of novel therapeutic strategies to treat breathing disorders.