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保护，使其终生不受细胞凋亡的影响，从而维持正常的耳蜗神经功能。耳蜗细胞的不同特化决定了它们对细胞特定应激做出反应的抗凋亡途径也相应地不同。在过去的资助期间，我们积累了证据表明，螺旋韧带细胞对耳蜗应激的反应在保护整个器官中发挥着关键作用。NFkappaB(NFkappaB)转录因子家族是抗细胞凋亡途径中的主要参与者。我们使用了一只转基因报告鼠来证明，是螺旋韧带纤维细胞，而不是Corti器官内的细胞，对噪音暴露表现出强大的NFkappaB活性。同样，我们发现生长因子受体(GDNF)，已知可以保护感觉细胞免受噪音和耳毒性药物的影响，不存在于毛细胞上，而存在于螺旋韧带纤维细胞中，在非创伤性噪音暴露后，它的表达强烈上调，已知可以保护耳朵免受随后的声音损伤。我们假设，噪声诱导的这种受体的上调是NFkappaB激活的下游，并且螺旋韧带中的这种上调是通过预先暴露于噪声应激源而诱导耳蜗保护的关键，也是听力正常的CBA/CalphaJ小鼠中发现的与年龄相关的噪声易感性差异的关键。在这一建议中，我们检验了以下假设：(1)通过使用已建立的噪声诱导的对噪声创伤的保护的小鼠模型来比较保护的诱导和减少的时间过程与噪声诱导的NFkappaB、GDNF受体和其他相关应激基因的表达和翻译的时间过程；(2)通过使用已经消除了NFkappaB的关键上游激活物的转基因小鼠来测试选择性地阻断噪声诱导的NFkappaB在螺旋韧带纤维细胞中的激活的效果；以及(3)通过比较噪声诱导的NFkappaB、GDNF受体NFkappaB的表达和翻译的变化以及其他相关的压力基因，在脆弱的幼鼠和耐药的中年鼠之间进行比较。这些研究的结果将阐明NFkappaB--抗凋亡应激诱导基因表达通路的复杂级联中的重要臂--在诱导耳蜗保护状态中的作用，并将有助于我们理解螺旋韧带纤维细胞的功能作用(S)，目前已知螺旋韧带纤维细胞是各种遗传性和获得性耳聋的主要组织病理学位点。

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.