上皮钠通道在被动吸烟气道黏液高分泌状态中的作用及相关的蛋白酶调控机制

气道黏液分泌增多是由吸烟引起的支气管炎和慢性阻塞性肺疾病的主要表现，也是导致细菌定植、气道炎症反复发作并不断进展的关键。来源于气道上皮细胞的上皮钠通道（Epithelial Na+ channels，ENaC）所介导的离子和液体吸收脱偶联能导致黏液纤毛清除功能受损以及气管阻塞，ENaC活性的增强似乎是慢性阻塞性肺疾病患者气道黏液高分泌现象的病理生理学基础。既往研究发现胰蛋白酶能够通过剪切ENaC亚单位而提高ENaC活性，我们前期工作结果发现α1抗胰蛋白酶能够下调ENaC的活性，据此推测被动吸烟可能通过破坏蛋白酶-抗蛋白酶之间的平衡而上调气道上皮细胞的ENaC。应用剪切和定点突变的方法我们将获取胰蛋白酶、基质金属蛋白酶-9和弹性蛋白酶对ENaC亚单位进行裂解的关键位点，这将为临床采用新的治疗策略（给予ENaC和蛋白酶的抑制剂）治疗被动吸烟引发的肺脏疾病中致命的气道黏液阻塞提供分子学基础。

Mucus hypersecretion in airway is a major manifestation in both bronchitis and chronic obstructive pulmonary disease (COPD) caused by cigarette smoking, also a key point leading to bacterial colonization and recurrent episodes of airway inflammation. Epithelial Na+ channels (ENaC) govern the volume of the watery sol layer by generating an osmotic gradient across lining epithelial cells, but little is known about the expression and regulation of ENaC in the hypersecretive airway. Uncoupling of ion and fluid absorption via ENaC from airway epithelial cells leads to an impaired mucociliary clearance and airway obstruction. Hyperactive ENaC activity appears to be the fundamental alteration that underlies mucus hypersecretion in the airways in COPD. Previous studies showed that trypsin can stimulate ENaC activity by cleaving ENaC subunits, whereas α1-antitrypsin down-regulates ENaC activity as shown in our preliminary data. We hypothesize that passive smoke exposure (PSE) up-regulates ENaC in tracheal epithelial cells by interrupting the protease-antiprotease balance. We will systematically mutate putative proteolytic substrates and key amino acid residues in ENaC subunits for trypsin, matrix metal protease-9, and elastases. Results of these studies may provide novel information that will provide the molecular basis for developing novel therapeutic strategies (ENaC and protease inhibitors) to combat life-threatening mucus occlusion in chronic PSE-challenged lungs.