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，在那里它们通过在整个生命过程中替换或修复受损细胞来促进组织稳态和可塑性。耳蜗外侧壁的纤维细胞和中间细胞等非感觉细胞在耳蜗内电位的产生中起重要作用。这些细胞已经被证明在年轻动物的耳蜗中经历持续的补充，但是这种细胞更新随着年龄的增长而减少。神经嵴源性干细胞（Neural crest-derived stem cells，NCSCs）在耳蜗外侧壁产生包括非感觉细胞在内的多种间充质细胞类型，其活性变化可能导致非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。NCSC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样细胞的数量显著下降。平行基因和蛋白质分析表明，多功能蛋白聚糖和其他几种ECM蛋白在耳蜗组织中的基因表达随着成年小鼠年龄的增长而下调。我们还发现多能蛋白聚糖及其相关的ECM蛋白存在于耳蜗球龛内，并且多能蛋白聚糖的耗尽导致年轻成年小鼠的听觉阈值升高。CBA/CaJ小鼠中microRNA（miRNA）水平的分析揭示了在外侧壁变性和EP下降首次出现的年龄时几种ECM调节miRNA的上调。基于这些发现，我们假设ECM成分及其调节分子的年龄依赖性变化导致NCSC数量减少和功能下降，导致耳蜗外侧壁非感觉细胞的耗竭和随后的听力损失。提出了三个具体目标。目的4.1确定NCSC在老年小鼠和人耳耳蜗外侧壁病理改变和听觉功能丧失中的作用。目的4.2检验年龄相关的ECM变化是耳蜗外侧壁NCSC数量减少和功能下降的原因的假设。目的4.3使用小鼠模型和从颞骨供体获得的人耳蜗组织鉴定调节代谢性老年性聋中ECM组分的年龄相关变化的miRNA。这些实验将增强我们对耳蜗外侧壁随年龄增长功能障碍的基本细胞和分子机制的理解，并由此产生代谢性老年性聋。

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.