醛固酮降低钠通道ENaC表达参与心衰引起减压反射功能降低的分子机制

Blunted baroreflex sensitivity is observed in heart failure (HF) patients and animals, which is thought to increase the morbidity and mortality in HF state. However, the mechanisms responsible for the impairment of the baroreflex are still poorly understood. Our previous studies have shown that decreased baroreflex afferent nerve excitability is involved in blunted baroreflex sensitivity in HF. However, until now it is not clear why the sensitivity of the afferent nerve to blood pressure is decreased in HF. Epithelial sodium channel (ENaC) was found in aortic baroreceptor neurons and aortic depressor nerve terminal, and this ion channel could contribute to the aortic baroreceptor sensitivity.Our preliminary data show that the expression and function of ENaC are decreased. Aldosterone is significantly elevated in HF. In addition, elevated plasma aldosterone reduces arterial baroreflex sensitivity. These data lead to hypothesis that the elevated aldosterone decreases aortic baroreceptor sensitivity via down regulation of the ENaC expression and function in the aortic baroreceptor terminals, and then blunts the arterial baroreflex in HF state. The hypothesis of this proposal will be tested in the following specific aims. (1) Determine whether the activation and expression of ENaC are reduced in baroreceptor in HF rats; (2) Determine whether the over expression of ENaC restores the attenuated aortic baroreceptor sensitivity and arterial baroreflex function in HF rats; (3) Determine whether aldosterone modulates the activation and expression of ENaC in baroreceptor in HF rats; (4) Determine whether ErK1/2 pathway is involved in ENaC modulation by aldosterone in HF rats; （5） Detrmine whether Erk1/2 activation ehances ubiqutination and degradation of ENaC.Results of this study may provide an important and new pharmacological target for the baroreflex dysfunction in HF and the mortality rate of HF.

减压反射(baroreflex)敏感性降低增加心力衰竭(Heart failure, HF)引起的猝死。研究发现HF降低减压神经兴奋性，进而减弱减压反射的敏感性。HF引起减压神经兴奋性降低的机制尚不清楚。钠通道ENaC (Epithelial sodium channel, ENaC)影响减压神经兴奋性。预实验发现HF大鼠减压神经ENaC表达降低。因此设想，HF引起醛固酮升高，降低减压神经末梢ENaC的表达及压力感受器的敏感性，降低减压反射。为验证该设想，采用结扎大鼠冠状动脉诱导HF,通过在体和离体实验方法研究：①HF是否降低减压神经ENaC表达；②升高ENaC表达是否恢复HF大鼠减压反射；③醛固酮是否降低减压神经ENaC表达；④ErK1/2是否参与醛固酮对ENaC的调节；⑤Erk1/2激活是否参与ENaC泛素化降解，阐明HF降低减压反射的分子机制，为临床防治HF引起猝死提供新的策略。

研究背景：减压反射(baroreflex)对心血管活动起重要调节作用，心力衰竭（Heart failure, HF）引起反射功能降低增加死亡率。我们以往实验和文献报道HF降低了减压神经的兴奋性，使减压反射的敏感性降低，其机制尚不清楚。上皮细胞钠通道(Epithelial sodium channel, ENaC)在减压神经胞体和末梢都有分布，抑制ENaC的功能降低神经对血压变化的敏感性，抑制减压神经兴奋性，但HF是否影响减压神经中ENaC的表达和功能及其可能的分子机制迄今未有报道。心衰患者和动物模型体内醛固酮水平都有升高，升高正常动物体内醛固酮可以降低减压反射的敏感性，而醛固酮又影响ENaC的功能。目前尚不清楚心衰升高醛固酮是否影响减压神经ENaC的表达进而影响减压反射。课题目标：①制备HF大鼠模型，观察HF是否影响减压神经中ENaC的表达和功能；②确定醛固酮是否影响减压神经中ENaC的表达及功能：③确定HF是否促进减压神经中ENaC分子泛素化；④确定HF促进ENaC分子泛素化的细胞内分子途径。研究结果：①心衰(HF)大鼠减压神经ENaC表达和功能降低；②升高正常大鼠体内醛固酮，降低结状神经节ENaC的表达，减弱减压反射；③醛固酮受体阻断剂螺旋内酯（spironolactone）可阻断心衰引起的大鼠结状神经节ENaC表达降低，部分恢复减压反射；④心衰大鼠升高醛固酮，促进泛素连接酶(ubiquitin ligase) Nedd4-2与ENaC结合，泛素化降解ENaC。结论：以上研究结果表明心衰大鼠醛固酮升高，通过促进ENaC泛素化降解，降低减压反射。科学意义：这一研究结果提示醛固酮受体阻断可部分恢复心衰引起的减压反射功能降低，为临床预防HF引起自主神经紊乱及猝死提供治疗依据。