Cochlear Homeostasis

耳蜗感觉细胞和非感觉细胞的有丝分裂后的性质需要对凋亡过程的保护，以维持正常的耳蜗功能。耳蜗细胞的多样化特化决定了它们对细胞特异性应激反应的抗凋亡途径也相应多样化。在过去的资助期内，我们积累的证据表明螺旋韧带细胞对耳蜗应激的反应在整个器官的保护中起着关键作用。抗凋亡途径的一个主要参与者是被称为NFkappaB （NFkappaB）的转录因子家族。我们使用转基因报告小鼠来证明是螺旋韧带纤维细胞，而不是Corti器官内的细胞，在对噪声暴露的反应中表现出强大的NFkappaB激活。同样，我们发现生长因子（GDNF）的受体，已知可以保护感觉细胞免受噪音和耳毒性药物的影响，并不存在于毛细胞中，而是存在于螺旋韧带纤维细胞中，在非创伤性噪音暴露后，其表达被强烈上调，已知可以保护耳朵免受随后的声损伤。我们假设噪声诱导的该受体的上调是NFkappaB激活的下游，螺旋韧带的这种上调是通过预暴露于噪声应激源诱导耳蜗保护的关键，也是正常听力的CBA/CalphaJ小鼠对噪声易感性的年龄相关差异的关键。在本文中，我们对这些假设进行了验证(1)，通过建立噪声诱导的噪声损伤保护小鼠模型，比较噪声诱导的保护作用的诱导和减少的时间过程与噪声诱导的耳蜗中NFkappaB、GDNF受体和其他相关应激基因表达和翻译变化的时间过程；(2)利用消除NFkappaB上游关键激活因子的转基因小鼠，测试选择性阻断噪声诱导的螺旋韧带纤维细胞中NFkappaB激活的效果；(3)比较噪声诱导的易感幼年小鼠与耐药中年小鼠耳蜗中NFkappaB、GDNF受体及其他相关应激基因表达和翻译的变化。这些研究的结果将阐明NFkappaB在诱导耳蜗保护状态中的作用，NFkappaB是抗凋亡应激诱导基因表达途径复杂级联中的一个重要分支，也将增加我们对螺旋韧带纤维细胞功能作用的理解，螺旋韧带纤维细胞现在已知是各种遗传性和获得性耳聋耳蜗组织病理学的主要位点。

The post mitotic nature of cochlear sensory and non-sensory cells requires protection against apoptotic processes for lifetime maintenance of normal cochlear function. The diverse specializations of cochlear cells dictates that their anti-apoptotic pathways, which respond to cell specific stresses are correspondingly diverse. In the past funding period, we accumulated evidence that spiral ligament cells' responses to cochlear stresses play a key role in protection of the entire organ. A major player in anti-apoptotic pathways is a family of transcription factors known as NFkappaB (NFkappaB). We used a transgenic reporter mouse to show that it is spiral ligament fibrocytes, not cells within the organ of Corti, that show robust NFkappaB activation in response to noise exposure. Similarly, we showed that the receptor for a growth factor (GDNF), known to protect sensory cells from noise and ototoxic drugs, is not present on hair cells, but in spiral ligament fibrocytes, where it's expression is robustly up-regulated following a non-traumatic noise exposure known to protect the ear from subsequent acoustic injury. We hypothesize that noise-induced up-regulation of this receptor is downstream of NFkappaB activation, and that this up-regulation in the spiral ligament is key to the induction of cochlear protection via pre-exposure to noise stressors, and to the age-related difference in vulnerability to noise seen in normal-hearing CBA/CalphaJ mice. In this proposal, we test these hypotheses (1) by using a well-established mouse model of noise-induced protection from noise trauma to compare the time course of induction and reduction of protection with the time course of noise-induced changes in cochlear expression and translation of NFkappaB, the GDNF receptor, and other related stress genes, (2) by testing the effects of selectively blocking noise-induced NFkappaB activation in spiral ligament fibrocytes using a transgenic mouse in which a key upstream activator of NFkappaB has been eliminated and (3) by comparing noise-induced changes in cochlear expression and translation of NFkappaB, the GDNF receptor, and other related stress genes in vulnerable young mice vs. resistant middle-aged mice. The results of these studies will clarify the role of NFkappaB, an important arm of the complex cascade of anti-apoptotic stress-induced gene expression pathways, in the induction of cochlear protected states and will also add to our understanding of the functional role(s) of the spiral ligament fibrocytes, which are now known to be a major locus of cochlear histopathology in a variety of inherited and acquired types of deafness.