螺旋神经元KCNQ4钾通道在老年性耳聋中作用及其机制研究

Spiral ganglion neurons (SGNs) are the first relay neurons bringing auditory signals from hair cells to the central nervous system. They are essential for our appreciation of sound in the form of electrical signals. Our previous work has identified that KCNQ4 potassium channel plays an important role in maintaining physiological function of SGNs. Recently, it has been reported that KCNQ4 gene is associated with age-related hearing loss (AHL), known as presbycusis. However, whether KCNQ4 contributes to AHL as well as its underling mechanism is still unclear. Our previously results showed that the expression of KCNQ4 potassium channel in SGNs from AHL mice was decreased, while the expression of T-type calcium channel were increased. Interesting, the expression of T-type calcium channel in the SGNs from KCNQ4 knockout mice was increased as well. Since T-type calcium channel play a critical role in apoptosis, we hypothesized that downregulation of KCNQ4 potassium channel function may caused SGNs apoptosis and contribute to AHL by upregulating T-type calcium channel function. To identify our hypothesis, we first explore the role of KCNQ4 potassium channel as well as T-type calcium channel in AHL. Second, we will examine the effect of KCNQ4 channel on T-type calcium channel function in KCNQ4 knockout mice. Last, we will treat specific KCNQ potassium channel openers in AHL mouse model, and then evaluate the effect of treatment on apoptosis of SGN, the function of KCNQ4 potassium channel as well as T-type calcium channel in SGN, as well as the alteration of hearing.. Our finding will provide valuable insights into the mechanism underlying AHL.

螺旋神经元（SGN）是传导听觉信号的一级神经元，我们已发表工作证明KCNQ4钾通道在维持SGN生理功能中起重要作用。最近研究报道KCNQ4基因突变和老年性耳聋的发生密切相关，但SGN上KCNQ4通道在老年性耳聋中的作用和机制还不清楚。我们预实验发现老年性耳聋小鼠SGN上KCNQ4表达降低，而介导凋亡的T型钙通道表达升高；KCNQ4基因敲除小鼠SGN上T通道功能上调。我们推测SGN上KCNQ4通道功能下降，可以上调T通道功能，导致SGN发生凋亡而致老年性耳聋发生。本课题拟首先在老年性耳聋小鼠模型上探讨SGN上KCNQ4和T通道的功能改变情况；其次利用基因敲除小鼠探讨KCNQ4通道对T通道的调控作用；最后探讨KCNQ4通道开放剂对老年性耳聋小鼠SGN上T通道功能以及听力的影响，进而明确SGN上KCNQ4通道功能下降介导老年性耳聋的作用机制。为进一步揭示老年性耳聋的发病机理提供理论依据。

老年性耳聋是临床最常见的听力损失类型。其发生机制至今尚未完全阐明。目前研究认为耳蜗螺旋神经元(SGN)的功能失调、退变是导致老年性耳聋的重要原因。. 我们前期实验发现老年耳聋小鼠SGN兴奋性改变，数量减少，提示调控神经元兴奋性的离子通道可能参与老年性耳聋的发生。目前，哪些离子通道可通过调控SGN功能而介导老年性听力损失还不清楚。因此，本研究主要探讨了SGN上离子通道如何调控听力信号的传导，以及与老年性耳聋发生的关系。本研究主要包括：研究SGN上KCNQ4钾通道和HCN通道在老年性耳聋发生中的作用，以及TRPV3通道对听力的影响。. 我们研究发现：老年耳聋小鼠SGN上KCNQ4通道明显下调，伴随T型钙通道功能增强， KCNQ4敲除小鼠的SGN上T通道高表达，提示：KCNQ4通道可能通过上调T通道而参与老年性耳聋发生。进一步实验发现：T通道的亚型Cav3.1，Cav3.2在老年耳聋小鼠SGN上高表达，在老年耳聋小鼠SGN凋亡过程中，H2AX以及AIF均上调，AIF的上游调控分子calpain2也表达明显升高。给予T通道阻断剂进一步证实T通道可通过calpain2/AIF通路介导SGN凋亡，从而介导老年性耳聋的发生。HCN通道是调控神经元兴奋性的重要通道。本研究还发现，HCN通道在老年耳聋小鼠SGN上高表达，其可通过调控SGN兴奋性，参与老年性耳聋的发生。此外，我们还研究了TRPV3通道对小鼠听力的影响。采用TRPV3基因敲除小鼠模型，我们发现TRPV3基因缺失小鼠听力下降，提示TRPV3通道在小鼠听力的产生中也发挥重要作用。. 本研究首次揭示了KCNQ4通道和HCN通道可通过调控SGN的兴奋性和凋亡介导老年性耳聋的发生机制，以及TRPV3通道在听力发生中的作用。相关实验结果已发表在Front Aging Neurosci.（2018）和Front Mol Neurosci.（2019）。