Human Cochlear Stem Cells and the Aging Inner Ear

成体干细胞存在于包括耳蜗在内的各种组织和器官中，它们通过在一生中替换或修复受损细胞来促进组织的动态平衡和可塑性。耳蜗侧壁非感觉细胞如纤维细胞和中间细胞在耳蜗内电位(EP)的产生中起着重要作用。这些细胞已经被证明在幼年动物的耳蜗中经历了持续的补充，但这种细胞周转率随着年龄的增长而下降。神经脊源性干细胞(NCSCs)可分化为多种类型的间充质细胞，包括耳蜗侧壁上的无感觉细胞，其活性的改变可导致无感觉细胞随年龄增长而减少，这是代谢性老年性聋的主要病理特征。神经干细胞的维持和自我更新依赖于细胞外基质(ECM)的完整性。我们最近的研究表明，与年轻对照组相比，老年小鼠耳蜗中NCSC样细胞的数量显著减少。平行的基因和蛋白质分析表明，在成年小鼠耳蜗组织中，Verscan和其他几种ECM蛋白的基因表达随着年龄的增长而下调。我们还发现VERSICAN及其相关的ECM蛋白存在于耳蜗球生态位中，VERSICAN的耗竭会导致年轻成年小鼠听力阈值的提高。对CBA/CAJ小鼠的microRNA(MiRNA)水平的分析表明，在侧壁退变和EP首次下降的年龄，几个ECM调节的miRNAs上调。基于这些发现，我们假设ECM成分及其调节分子的年龄相关性变化会导致NCSCs数量减少和功能下降，导致耳蜗侧壁非感觉细胞的枯竭和随后的听力损失。提出了三个具体目标。目的4.1研究神经干细胞在老年小鼠和人耳耳蜗侧壁病理改变及听觉功能丧失中的作用。目的4.2验证年龄相关的细胞外基质改变是耳蜗侧壁神经干细胞数量减少和功能下降的原因的假说。目的4.3利用小鼠模型和从颞骨捐赠者获得的人类耳蜗组织，确定调节代谢性老年性耳聋中ECM成分随年龄变化的miRNAs。这些实验将加深我们对耳蜗侧壁功能减退的基本细胞和分子机制的理解，以及由此导致的代谢性老聋。

Adult stem cells are present in a variety of tissues and organs including the cochlea, where they contribute to tissue homeostasis and plasticity by replacing or repairing injured cells throughout life. Nonsensory cells such as fibrocytes and intermediate cells in the lateral wall ofthe cochlea play an important role in the production of the endocochlear potential (EP). These cells have been shown to undergo continuous replenishment in the cochlea of young animals but this cell turnover decreases with age. Neural crest-derived stem cells (NCSCs), give rise to a wide variety of mesenchymal cell types including nonsensory cells in the cochlear lateral wall and changes in their activity may lead to the decrease in nonsensory cells with age which is a major pathological feature of metabolic presbyacusis. The maintenance and self-renewal of NCSCs is dependent on the integrity ofthe extracellular matrix (ECM). Our recent studies have shown a significant decline in the number of NCSC-like cells in the aged mouse cochlea as compared to younger controls. Parallel gene and protein analyses have revealed that the expression of genes for versican and several other ECM proteins in cochlear tissues is down-regulated with age in adult mice. We have also found that versican and its associated ECM proteins are present within the cochlear sphere niche and that depletion of versican results in elevated auditory thresholds in young adult mice. Analysis of microRNA (miRNA) levels in CBA/CaJ mice revealed an up-regulation of several ECM regulatory miRNAs at the age when lateral wall degeneration and EP declines first appear. Based on these findings, we hypothesize that age-dependent changes in ECM components and their regulatory molecules cause a reduction in the number and declines in the function of NCSCs, resulting in a depletion of non-sensory cells in the cochlear lateral wall and subsequent hearing loss. Three specific aims are proposed. Aim 4.1 determines the role of NCSCs in pathological alterations ofthe cochlear lateral wall and in the loss of auditory function in older mouse and human ears. Aim 4.2 tests the hypothesis that age-related ECM changes are responsible for the reduced number and functional declines of NCSCs in the cochlear lateral wall. Aim 4.3 identifies the miRNAs that regulate age-related changes in ECM components in metabolic presbyacusis using mouse models and human cochlear tissues obtained from temporal bone donors. These experiments will enhance our understanding ofthe fundamental cellular and molecular mechanisms responsible for cochlear lateral wall dysfunction with age and the resultant metabolic presbyacusis.