Groningen Institute for Evolutionary Life Sciences (GELIFES), Molecular Neurobiology, University of Groningen, Groningen, The Netherlands.
Division of Metabolic Diseases, Beatrix Children's Hospital, University Medical Center of Groningen, University of Groningen, Groningen, The Netherlands.
Neurobiol Learn Mem. 2019 Apr;160:139-143. doi: 10.1016/j.nlm.2018.05.002. Epub 2018 May 14.
Toxic levels of phenylalanine in blood and brain is a characteristic of (untreated) phenylketonuria (PKU), leading to cognitive deficits in PKU mice. In addition, our recent findings showed that PKU mice (as well as PKU patients) have a disturbed sleep/wake cycle. As a consequence, sleep loss may contribute to cognitive deficits in PKU. Sleep loss has been linked to increased activation of microglia in the hippocampus. In this study, we set out to examine morphological features of the microglia population in the hippocampus of the mouse PKU model, using both the C57Bl/6 and the BTBR strain and their wild-type controls (age 5.3 ± 0.5 months; n = 16 per group, both males and females; n = 8 each). Microglial activation is reflected by retraction and thickening of the dendritic branches and an increase in cell body size of a microglial cell. Such morphological changes of microglia were studied by way of immunohistochemical staining for Iba-1, a microglia-specific calcium binding protein. We measured the number of microglia in seven subregions of the dorsal hippocampus. The level of microglial activation was determined, based on the ratio between the soma size and total cell size (soma size plus the area covered by the dendritic branches). Results showed subtle but statistical significant activation of hippocampal microglia in the C57Bl6, but not in the BTBR, PKU mice when compared with their wild-type controls. Also the total number of microglia was higher in the C57Bl/6 PKU (compared to the wild-type) mouse, but not in the BTBR PKU mouse. It is concluded that the C57Bl/6 PKU mouse has mildly higher microglia activity, which may support rather than hamper hippocampal homeostasis. The results further indicate that high levels of phenylalanine or disturbed sleep patterns do not consequently cause hippocampal microglial activation in the PKU mouse. It is currently unknown why the two PKU mouse strains show these differences in number and activation level of their hippocampal microglia, and to what extent it influences hippocampal functioning. Further scrutinizing the role of microglia functioning in the context of PKU is therefore warranted.
血液和大脑中苯丙氨酸的毒性水平是未经治疗的苯丙酮尿症（PKU）的特征，导致 PKU 小鼠认知缺陷。此外，我们最近的研究结果表明，PKU 小鼠（以及 PKU 患者）的睡眠/觉醒周期紊乱。因此，睡眠不足可能导致 PKU 的认知缺陷。睡眠不足与海马体中小胶质细胞的过度激活有关。在这项研究中，我们使用 C57Bl/6 和 BTBR 品系及其野生型对照（年龄 5.3±0.5 个月；n=16 只/组，雄性和雌性各 8 只），研究了 PKU 小鼠模型中海马体中小胶质细胞群体的形态特征。小胶质细胞的激活反映为树突分支的回缩和增厚以及小胶质细胞细胞体大小的增加。通过免疫组织化学染色 Iba-1（一种小胶质细胞特异性钙结合蛋白）研究了小胶质细胞的这种形态变化。我们测量了背侧海马体七个亚区的小胶质细胞数量。基于体大小与总细胞大小（体大小加树突分支覆盖的区域）之间的比值，确定了小胶质细胞激活的水平。结果表明，与野生型对照相比，C57Bl6 中的 PKU 小鼠的海马体小胶质细胞有轻微但具有统计学意义的激活，但 BTBR 中的 PKU 小鼠则没有。此外，与野生型相比，C57Bl/6 PKU 小鼠中的小胶质细胞总数更高，但 BTBR PKU 小鼠则不然。结论是，C57Bl/6 PKU 小鼠具有轻度升高的小胶质细胞活性，这可能支持而不是干扰海马体的稳态。研究结果进一步表明，高水平的苯丙氨酸或睡眠模式紊乱不会导致 PKU 小鼠海马体中小胶质细胞的激活。目前尚不清楚为什么这两种 PKU 小鼠品系在其海马体中小胶质细胞的数量和激活水平上存在这些差异，以及它在多大程度上影响了海马体的功能。因此，有必要进一步研究 PKU 中小胶质细胞功能的作用。
