The aim of the current study was to investigate whether doublecortin (DCX), insulin-like growth factor receptor 1 (IGF-1R) and metabotropic glutamate receptor 5 (mGluR5) levels are indeed modified in the aging rat hippocampal individual subareas (rather than total hippocampal tissue as in previous reports) at the protein and mRNA level and whether the methylation status contributes to these changes. Since the aging population is not homogeneous in terms of spatial memory performance, we examined whether changes in DCX, IGF-1R and mGluR5 are linked to cognitive aging. Aged (22 months) male Sprague Dawley rats were trained in the hole-board, a spatial memory task, and were subdivided according to performance to aged impaired and aged unimpaired groups. Age- and memory performance-dependent changes in mRNA steady-state levels, protein levels and DNA methylation status of DCX, IGF-1R and mGluR5 were evaluated by RT-PCR, immunoblotting and bisulfite pyrosequencing. Extending previous findings, we detected decreased DCX protein and mRNA levels in dentate gyrus (DG) of aged animals. IGF-1 signaling is a key event and herein we show that mRNA levels for IGF-1R were unchanged although reduced at the protein level. This finding may simply reflect that these protein levels are regulated at the level of protein synthesis as well as protein degradation. We provide evidence that promoter methylation is not involved in regulation of mRNA and protein levels of DCX, IGF-1R and mGluR5 during aging. Moreover, there was no significant difference between aged rats with impaired and aged rats with unimpaired memory at the protein and mRNA level. Findings propose that changes in the abovementioned protein levels may not be relevant for performance in the spatial memory task used in aged rats.

中文翻译：

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尽管老年大鼠海马中的DNA甲基化未发生改变，但双皮质素和IGF-1R蛋白水平却降低了。

本研究的目的是研究在衰老的大鼠海马单个区域中是否确实改变了双皮质激素（DCX），胰岛素样生长因子受体1（IGF-1R）和代谢型谷氨酸受体5（mGluR5）的水平（而非总水平）。蛋白质和mRNA水平，以及甲基化状态是否有助于这些变化，如以前的报告所述。由于老龄化人口在空间记忆性能方面不均一，因此我们检查了DCX，IGF-1R和mGluR5的变化是否与认知老化有关。对成年（22个月）雄性Sprague Dawley大鼠进行了孔板训练，这是一项空间记忆任务，并根据其表现将其分为老年受损和老年无障碍组。与年龄和记忆力有关的mRNA稳态水平变化，通过RT-PCR，免疫印迹和亚硫酸氢盐焦磷酸测序评估DCX，IGF-1R和mGluR5的蛋白质​​水平和DNA甲基化状态。扩展以前的发现，我们检测到老年动物的齿状回（DG）中DCX蛋白和mRNA水平降低。IGF-1信号传导是关键事件，在这里我们表明IGF-1R虽然在蛋白质水平降低，但未发生变化。该发现可以简单地反映出这些蛋白质水平在蛋白质合成以及蛋白质降解的水平上受到调节。我们提供的证据表明，启动子甲基化在衰老过程中不参与DCX，IGF-1R和mGluR5的mRNA和蛋白质水平的调节。此外，在蛋白质和mRNA水平上，受损的老年大鼠和记忆力未受损的老年大鼠之间没有显着差异。研究结果表明，上述蛋白质水平的变化可能与老年大鼠在空间记忆任务中的表现无关。