Department of Biomedical Engineering, Tufts University, Medford, Massachusetts, United States of America.
PLoS One. 2010 Feb 4;5(2):e9058. doi: 10.1371/journal.pone.0009058.
It has previously been shown that deletion of chrna9, the gene encoding the alpha9 nicotinic acetylcholine receptor (nAChR) subunit, results in abnormal synaptic terminal structure. Additionally, all nAChR-mediated cochlear activity is lost, as characterized by a failure of the descending efferent system to suppress cochlear responses to sound. In an effort to characterize the molecular mechanisms underlying the structural and functional consequences following loss of alpha9 subunit expression, we performed whole-transcriptome gene expression analyses on cochleae of wild type and alpha9 knockout (alpha9(-/-)) mice during postnatal days spanning critical periods of synapse formation and maturation.
Data revealed that loss of alpha9 receptor subunit expression leads to an up-regulation of genes involved in synaptic transmission and ion channel activity. Unexpectedly, loss of alpha9 receptor subunit expression also resulted in an increased expression of genes encoding GABA receptor subunits and the GABA synthetic enzyme, glutamic acid decarboxylase. These data suggest the existence of a previously unrecognized association between the nicotinic cholinergic and GABAergic systems in the cochlea. Computational analyses have highlighted differential expression of several gene sets upon loss of nicotinic cholinergic activity in the cochlea. Time-series analysis of whole transcriptome patterns, represented as self-organizing maps, revealed a disparate pattern of gene expression between alpha9(-/-) and wild type cochleae at the onset of hearing (P13), with knockout samples resembling immature postnatal ages.
We have taken a systems biology approach to provide insight into molecular programs influenced by the loss of nicotinic receptor-based cholinergic activity in the cochlea and to identify candidate genes that may be involved in nicotinic cholinergic synapse formation, stabilization or function within the inner ear. Additionally, our data indicate a change in the GABAergic system upon loss of alpha9 nicotinic receptor subunit within the cochlea.
先前的研究表明，编码α9 型烟碱型乙酰胆碱受体 (nAChR) 亚基的 chrna9 缺失会导致突触末梢结构异常。此外，所有 nAChR 介导的耳蜗活动都丧失了，这表现为下行传出系统无法抑制声音对耳蜗的反应。为了研究α9 亚基缺失表达后导致的结构和功能变化的分子机制，我们对出生后不同时期（突触形成和成熟的关键时期）野生型和α9 敲除（alpha9(-/-)）小鼠耳蜗进行了全转录组基因表达分析。
数据显示，α9 受体亚基缺失会导致参与突触传递和离子通道活性的基因上调。出乎意料的是，α9 受体亚基缺失还导致 GABA 受体亚基和 GABA 合成酶谷氨酸脱羧酶的基因表达增加。这些数据表明，在耳蜗中，尼古丁胆碱能和 GABA 能系统之间存在以前未被认识到的联系。计算分析突出了在耳蜗中尼古丁胆碱能活性丧失时几个基因集的差异表达。全转录组模式的时间序列分析，以自组织映射表示，揭示了在听力开始（P13）时 alpha9(-/-)和野生型耳蜗之间基因表达的明显差异模式，敲除样本类似于未成熟的出生后年龄。
我们采用系统生物学方法深入了解了耳蜗中尼古丁受体型胆碱能活性丧失所影响的分子程序，并确定了可能参与尼古丁胆碱能突触形成、稳定或功能的候选基因。此外，我们的数据表明，在耳蜗中α9 型烟碱型乙酰胆碱受体亚基缺失会导致 GABA 能系统发生变化。
