Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
J Neurosci. 2012 Sep 5;32(36):12421-30. doi: 10.1523/JNEUROSCI.6381-11.2012.
Small GTPases mediate transmembrane signaling and regulate the actin cytoskeleton in eukaryotic cells. Here, we characterize the auditory pathology of adult male CBA/J mice exposed to traumatic noise (2-20 kHz; 106 dB; 2 h). Loss of outer hair cells was evident 1 h after noise exposure in the basal region of the cochlea and spread apically with time, leading to permanent threshold shifts of 35, 60, and 65 dB at 8, 16, and 32 kHz. Several biochemical and molecular changes correlated temporally with the loss of cells. Immediately after exposure, the concentration of ATP decreased in cochlear tissue and reached a minimum after 1 h while the immunofluorescent signal for p-AMPKα significantly increased in sensory hair cells at that time. Levels of active Rac1 increased, whereas those of active RhoA decreased significantly 1 h after noise attaining a plateau at 1-3 h; the formation of a RhoA-p140mDia complex was consistent with an activation of Rho GTPase pathways. Also at 1-3 h after exposure, the caspase-independent cell death marker, Endo G, translocated to the nuclei of outer hair cells. Finally, experiments with the inner ear HEI-OC1 cell line demonstrated that the energy-depleting agent oligomycin enhanced both Rac1 activity and cell death. The sum of the results suggests that traumatic noise induces transient cellular ATP depletion and activates Rho GTPase pathways, leading to death of outer hair cells in the cochlea.
小分子 GTP 酶介导跨膜信号转导，并调节真核细胞中的肌动蛋白细胞骨架。在这里，我们描述了暴露于创伤性噪声（2-20 kHz；106 dB；2 h）的成年雄性 CBA/J 小鼠的听觉病理学。噪声暴露后 1 小时，耳蜗底部的外毛细胞明显丢失，并随时间向顶部扩散，导致 8、16 和 32 kHz 处的永久性阈值移位分别为 35、60 和 65 dB。一些生化和分子变化与细胞丢失时间相关。暴露后立即，耳蜗组织中的 ATP 浓度降低，1 小时后达到最低值，而此时感觉毛细胞中 p-AMPKα 的免疫荧光信号显著增加。活性 Rac1 的水平在噪声暴露 1 小时后显著增加，而活性 RhoA 的水平显著降低，达到 1-3 小时的平台期；Rho GTPase 途径的激活与 RhoA-p140mDia 复合物的形成一致。同样在暴露后 1-3 小时，无细胞凋亡标记物 Endo G 转移到外毛细胞核中。最后，用内耳 HEI-OC1 细胞系进行的实验表明，能量耗竭剂寡霉素增强了 Rac1 活性和细胞死亡。结果表明，创伤性噪声诱导细胞内 ATP 短暂耗竭，并激活 Rho GTP 酶途径，导致耳蜗中外毛细胞死亡。
