糖皮质激素调节内耳内淋巴液平衡的分子机制及其在抗运动病中的作用

Previous studies have suggested that endolymph disequilibrium of the inner ears will trigger vestibulo-autonomous reflex, and induce the symptoms such as vertigo, nausea and vomit. glucocorticoid is an important hormone in transporting of ion and water through its effects on the kidney. Glucocorticoid receptors (GR) are also distributed in the inner ears, and similar to its effects in the kidney, glucocorticoid may regulate the expression of its target proteins such as aquaporins (AQPs) and epithelial natrium channels (ENaC), and is supposed to influence the endolymph and ion balances. Our preliminary results revealed that motion sickness-evoking rotatory stimulus in rat elevated the blood level of glucocorticoid. And dexamethasone, a GR agonist, increased the tolerance to motion sickness in rats and beagles. These results suggested that glucocorticoid might be involved in the development of motion sickness. Based on these information, the current study will explore the mechanism of glucocorticoid on endolymph and motion sickness: 1) The relationship between the sensitivity of motion sickness and the level of endolymph and glucocorticoids, the expression of glucocorticoid receptor and downstream target proteins (AQPs, ENaC and Na+-K+-ATPase); 2) The effect of glucocorticoid on endolymph and motion sickness and the expression of glucocorticoid receptor and downstream target proteins (AQPs, ENaC and Na+-K+-ATPase); 3) The effect of glucocorticoid receptor agonists and antagonists on endolymph and motion sickness and the expression of glucocorticoid receptor and downstream target proteins (AQPs, ENaC and Na+-K+-ATPase).

现有研究表明内耳内淋巴失衡会诱导前庭-植物神经反射的活动，出现眩晕，恶心，呕吐等症状。糖皮质激素在肾脏中不仅影响离子的转运，同样影响水的跨膜运输。内耳同样存在大量糖皮质激素受体，可能与肾脏中作用类似，糖皮质激素通过影响水通道蛋白、上皮钠通道等蛋白，调节内淋巴液的平衡。我们初步实验发现，旋转刺激后糖皮质激素水平升高，以及糖皮质激素受体激动剂地塞米松可以提高大鼠和比格犬对运动病的耐受，提示糖皮质激素参与运动病的过程。在此基础上，本项目主要研究:（1）运动病不同个体敏感性与内淋巴液、糖皮质激素水平、内耳糖皮质激素受体及下游靶蛋白表达的基础水平和反应性改变的关系；（2）糖皮质激素对内淋巴液和运动病的作用及其对糖皮质激素受体及下游靶蛋白表达的影响；（3）糖皮质激素受体激动剂和拮抗剂对内淋巴液和运动病的作用及其对糖皮质激素受体及下游靶蛋白表达的影响。

运动病详细的发病机制迄今未明，亦缺乏理想的防治药物。现有研究表明内耳内淋巴失衡会诱导前庭-植物神经反射的活动，出现眩晕，恶心，呕吐等症状。糖皮质激素在肾脏中不仅影响离子的转运，同样影响水的跨膜运输。内耳同样存在大量糖皮质激素受体，可能与肾脏中作用类似，糖皮质激素通过影响水通道蛋白、上皮钠通道等蛋白，调节内淋巴液的平衡。本项目主要研究：(1)运动病不同个体敏感性与内淋巴液、糖皮质激素水平、内耳糖皮质激素受体及下游靶蛋白表达的基础水平和反应性改变的关系；(2)糖皮质激素对内淋巴液和运动病的作用及其对糖皮质激素受体及下游靶蛋白表达的影响；(3)糖皮质激素受体激动剂和拮抗剂对内淋巴液和运动病的作用及其对糖皮质激素受体及下游靶蛋白表达的影响。结果表明：(1)提前肌注地塞米松有效缓解比格犬对旋转刺激的反应；(2)腹腔及鼓室注射地塞米松（0.5 mg/kg）能有效改善旋转刺激或腹腔注射AVP引起的大鼠条件性味觉厌恶行为，糖皮质激素受体拮抗剂米非司酮减弱了地塞米松对大鼠条件性味觉厌恶行为的改善；(3)鼓室注射地塞米松后，大鼠内耳组织V2R、Na+-K+-ATPase、ENaC蛋白表达无明显改变，而GR蛋白表达升高，AQP2、p-AQP2蛋白表达降低，以上变化被糖皮质激素受体拮抗剂米非司酮抑制；(4)对原代培养的内耳内淋巴囊上皮细胞给予AVP刺激，AQP2、p-AQP2蛋白表达升高，荧光强度增强；(5)地塞米松处理使内淋巴囊上皮细胞AQP2、p-AQP2蛋白表达降低，GR蛋白表达升高，并抑制AVP引起的荧光强度改变；(6)米非司酮拮抗地塞米松对内淋巴囊上皮细胞AQP2、p-AQP2、GR蛋白表达和荧光强度的影响。糖皮质激素可能通过其受体 GR调控内耳AQP2、p-AQP2的表达，以拮抗由旋转或AVP刺激导致的运动病。