Human Cochlear Stem Cells and the Aging Inner Ear

成体干细胞存在于包括耳蜗在内的多种组织和器官中，它们通过替换或修复一生中受损的细胞来维持组织的稳态和可塑性。耳蜗侧壁的非感觉细胞如纤维细胞和中间细胞在耳蜗电位的产生中起重要作用。这些细胞在幼龄动物的耳蜗中不断得到补充，但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）产生多种间充质细胞类型，包括耳蜗侧壁的非感觉细胞，其活性的变化可能导致非感觉细胞随着年龄的增长而减少，这是代谢性耳聋的一个主要病理特征。NCSCs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，与年轻的对照组相比，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显示，成年小鼠耳蜗组织中versican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，并且versican的消耗会导致年轻成年小鼠的听觉阈值升高。CBA/CaJ小鼠的microRNA （miRNA）水平分析显示，在第一次出现外侧壁变性和EP下降的年龄，几种ECM调节miRNA水平上调。基于这些发现，我们假设ECM成分及其调控分子的年龄依赖性变化导致NCSCs数量减少和功能下降，导致耳蜗外侧壁非感觉细胞的消耗和随后的听力损失。提出了三个具体目标。目的4.1确定NCSCs在老年小鼠和人耳耳蜗外侧壁病理改变和听力功能丧失中的作用。Aim 4.2验证了年龄相关的ECM变化是耳蜗外侧壁NCSCs数量减少和功能下降的原因。Aim 4.3通过小鼠模型和从颞骨供体获得的人耳蜗组织鉴定代谢性耳聋中调节ECM成分年龄相关变化的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和代谢性耳聋的基本细胞和分子机制的理解。

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.