Hans Berger Clinic of Neurology, Jena University Hospital, Jena, Germany.
PLoS One. 2011;6(8):e22408. doi: 10.1371/journal.pone.0022408. Epub 2011 Aug 5.
Following injury, microglia become activated with subsets expressing nestin as well as other neural markers. Moreover, cerebral microglia can give rise to neurons in vitro. In a previous study, we analysed the proliferation potential and nestin re-expression of retinal macroglial cells such as astrocytes and Müller cells after optic nerve (ON) lesion. However, we were unable to identify the majority of proliferative nestin(+) cells. Thus, the present study evaluates expression of nestin and other neural markers in quiescent and proliferating microglia in naïve retina and following ON transection in adult rats in vivo.
METHODOLOGY/PRINCIPAL FINDINGS: For analysis of cell proliferation and cells fates, rats received BrdU injections. Microglia in retinal sections or isolated cells were characterized using immunofluorescence labeling with markers for microglia (e.g., Iba1, CD11b), cell proliferation, and neural cells (e.g., nestin, vimentin, NG2, GFAP, Doublecortin etc.). Cellular analyses were performed using confocal laser scanning microscopy. In the naïve adult rat retina, about 60% of resting ramified microglia expressed nestin. After ON transection, numbers of nestin(+) microglia peaked to a maximum at 7 days, primarily due to in situ cell proliferation of exclusively nestin(+) microglia. After 8 weeks, microglia numbers re-attained control levels, but 20% were still BrdU(+) and nestin(+), although no further local cell proliferation occurred. In addition, nestin(+) microglia co-expressed vimentin and NG2, but not GFAP or neuronal markers. Fourteen days after injury and following retrograde labeling of retinal ganglion cells (RGCs) with Fluorogold (FG), nestin(+)NG2(+) microglia were positive for the dye indicating an active involvement of a proliferating cell population in phagocytosing apoptotic retinal neurons.
CONCLUSIONS/SIGNIFICANCE: The current study provides evidence that in adult rat retina, a specific resident population of microglia expresses proteins of immature neural cells that are involved in injury-induced cell proliferation and phagocytosis while transdifferentiation was not observed.
在受伤后，小胶质细胞被激活，其中一些子集表达巢蛋白和其他神经标志物。此外，脑小胶质细胞在体外可以产生神经元。在之前的一项研究中，我们分析了视神经（ON）损伤后视网膜大胶质细胞（如星形胶质细胞和 Müller 细胞）的增殖潜力和巢蛋白再表达。然而，我们无法识别大多数增殖的巢蛋白（+）细胞。因此，本研究评估了在成年大鼠体内正常视网膜和视神经切断后，静息和增殖的小胶质细胞中巢蛋白和其他神经标志物的表达。
方法/主要发现：为了分析细胞增殖和细胞命运，大鼠接受 BrdU 注射。使用免疫荧光标记小胶质细胞标志物（如 Iba1、CD11b）、细胞增殖和神经细胞标志物（如巢蛋白、波形蛋白、NG2、GFAP、双皮质蛋白等）对视网膜切片或分离的细胞进行特征分析。使用共聚焦激光扫描显微镜进行细胞分析。在正常成年大鼠视网膜中，约 60%的静息有分枝的小胶质细胞表达巢蛋白。视神经切断后，巢蛋白（+）小胶质细胞的数量在第 7 天达到峰值，主要是由于仅巢蛋白（+）小胶质细胞的原位细胞增殖。8 周后，小胶质细胞数量恢复到对照水平，但仍有 20%为 BrdU（+）和巢蛋白（+），尽管没有进一步的局部细胞增殖。此外，巢蛋白（+）小胶质细胞共表达波形蛋白和 NG2，但不表达 GFAP 或神经元标志物。视神经损伤后 14 天，用荧光金（FG）逆行标记视网膜神经节细胞（RGC）后，巢蛋白（+）NG2（+）小胶质细胞对染料呈阳性，表明增殖细胞群积极参与吞噬凋亡的视网膜神经元。
结论/意义：本研究提供的证据表明，在成年大鼠视网膜中，一种特定的小胶质细胞固有群体表达未成熟神经细胞的蛋白质，这些蛋白质参与了损伤诱导的细胞增殖和吞噬作用，而未观察到转分化。
