GENETICS OF MURINE AIRWAY SODIUM ABSORPTION: ROLE IN CF

上皮离子运输被认为是囊性纤维化（CF）等疾病的重要因素，但体内离子运动的调控尚不清楚。在CF中，氯离子通道（CFTR）的突变导致呼吸粘膜钠吸收增加，这一过程被认为有助于CF气道的病理生理。如果增加的吸收确实导致了疾病，尚不清楚它是否影响了允许细菌感染开始的过程，或者它是否有助于允许感染持续存在，或者两者兼而有之。盐转运改变的机制存在争议，但包括1)电解质水平降低导致粘膜干燥和清除率差，2)以降低抗菌肽杀菌活性的方式改变气道衬里液的组成，或3)一些其他机制。也有证据表明，钠吸收增加可能与病理生理无关，而是CF上皮中响应CFTR缺陷而改变的信号通路的结果。为了更好地了解钠转运的体内调控以及CFTR在这一调控中的作用，本申请拟利用小鼠自交系C57 3L/6J和A/J及其杂交后代、重组自交系和经济系，定位和鉴定导致鼻上皮钠转运自然变异的基因。我们发现，品系间变异具有很强的遗传性，很可能是由少数基因引起的。为了解决钠转运在CF中的作用，小鼠CF等位基因将在与不同钠吸收水平相关的近交系背景下进行同源。在这些小鼠中，钠吸收对细菌介导的肺部疾病的影响将被评估，方法是将携带细菌的琼脂珠注入气道，诱导小鼠慢性感染。将监测动物清除感染的能力以及它们的炎症反应。

Epithelial ion transport is thought to be an important factor in disorders such as cystic fibrosis (CF), but the regulation of ion movement in vivo is not well understood. In CF, mutations in the chloride channel, CFTR, lead to increased sodium absorption across the respiratory mucosa, a process thought to contribute to the pathophysiology of the CF airway. If the increased absorption does contribute to the disease, it is not clear if it impacts on processes that allow bacterial infection to initiate, or if it aids in allowing the infection to persist, or both. Mechanisms implicating altered salt transport are controversial, but include l) reduced electrolyte levels leading to desiccated mucosa and poor clearance, 2) altering composition of the airway lining fluid in a way that lessens bactericidal activity of antimicrobial peptides, or 3) some other mechanism. Evidence also exists suggesting that the increased sodium absorption may not contribute to the pathophysiology, but is instead a consequence of signaling pathways altered in CF epithelia in response to the CFTR defect. To better understand the in vivo regulation of sodium transport and the role of CFTR in that regulation, this application proposes to map and identify genes contributing to natural variation in nasal transepithelial sodium transport by using inbred mouse lines C57)3L/6J and A/J and their hybrid progeny, recombinant inbred lines, and consomic lines. We have found that the inter-strain variation is quite heritable and is likely due to a small number of genes. To address the role of sodium transport m CF, murine CF alleles will be made congenic on inbred backgrounds associated with different levels of sodium absorption. The influence of sodium absorption on bacterially-mediated lung disease in these mice will be assessed using mice are induced to have a chronic infection by instilling bacteria-laden agar beads into the airway. The ability of the animals to clear the infection, as well as their inflammatory responses, will be monitored.