Ciliary Neurotrophic Factor Induces Genes Associated with Inflammation and Gliosis in the Retina: A Gene Profiling Study of Flow-Sorted, Müller Cells

BackgroundCiliary neurotrophic factor (CNTF), a member of the interleukin-6 cytokine family, has been implicated in the development, differentiation and survival of retinal neurons. The mechanisms of CNTF action as well as its cellular targets in the retina are poorly understood. It has been postulated that some of the biological effects of CNTF are mediated through its action via retinal glial cells; however, molecular changes in retinal glia induced by CNTF have not been elucidated. We have, therefore, examined gene expression dynamics of purified Müller (glial) cells exposed to CNTF in vivo. Methodology/Principal FindingsMüller cells were flow-sorted from mgfap-egfp transgenic mice one or three days after intravitreal injection of CNTF. Microarray analysis using RNA from purified Müller cells showed differential expression of almost 1,000 transcripts with two- to seventeen-fold change in response to CNTF. A comparison of transcriptional profiles from Müller cells at one or three days after CNTF treatment showed an increase in the number of transcribed genes as well as a change in the expression pattern. Ingenuity Pathway Analysis showed that the differentially regulated genes belong to distinct functional types such as cytokines, growth factors, G-protein coupled receptors, transporters and ion channels. Interestingly, many genes induced by CNTF were also highly expressed in reactive Müller cells from mice with inherited or experimentally induced retinal degeneration. Further analysis of gene profiles revealed 20–30% overlap in the transcription pattern among Müller cells, astrocytes and the RPE. Conclusions/SignificanceOur studies provide novel molecular insights into biological functions of Müller glial cells in mediating cytokine response. We suggest that CNTF remodels the gene expression profile of Müller cells leading to induction of networks associated with transcription, cell cycle regulation and inflammatory response. CNTF also appears to function as an inducer of gliosis in the retina.

背景：睫状神经营养因子（Ciliary neurotrophic factor, CNTF）属于白细胞介素-6细胞因子家族，其参与视网膜神经元的发育、分化与存活过程已得到证实。目前关于CNTF的作用机制及其在视网膜内的细胞靶点仍不甚明确。已有研究推测CNTF的部分生物学效应通过视网膜胶质细胞介导，但CNTF诱导视网膜胶质细胞产生的分子变化尚未被阐明。因此，本研究对体内暴露于CNTF的纯化米勒（Müller）胶质细胞的基因表达动态展开了检测。
研究方法与主要结果：在向mgfap-egfp转基因小鼠玻璃体内注射CNTF后的1天或3天，通过流式分选技术分离纯化米勒细胞。利用纯化米勒细胞的总RNA进行微阵列分析，结果显示，响应CNTF刺激的转录本中有近1000个出现2至17倍的差异表达。对比CNTF处理后1天与3天的米勒细胞转录谱，发现转录基因的数量有所增加，且表达模式发生显著改变。Ingenuity通路分析（Ingenuity Pathway Analysis, IPA）显示，差异调控基因分属不同功能类别，包括细胞因子、生长因子、G蛋白偶联受体、转运蛋白及离子通道。值得注意的是，CNTF诱导的大量基因在遗传性或实验性视网膜退行性变小鼠的反应性米勒细胞中同样呈高表达。进一步的基因谱分析表明，米勒细胞、星形胶质细胞与视网膜色素上皮（retinal pigment epithelium, RPE）之间的转录模式存在20%至30%的重叠。
研究结论与意义：本研究为米勒胶质细胞介导细胞因子应答的生物学功能提供了全新的分子视角。我们提出，CNTF可重塑米勒细胞的基因表达谱，诱导与转录调控、细胞周期调节及炎症反应相关的信号网络。此外，CNTF似乎可作为视网膜胶质增生的诱导因子。