Popa-Wagner Aurel, Dinca Ivona, Yalikun Suofu, Walker Lary, Kroemer Heyo, Kessler Christof
Department of Neurology, University of Greifswald, Greifswald, Germany.
Curr Neurovasc Res. 2006 Feb;3(1):3-13. doi: 10.2174/156720206775541732.
An important cellular event associated with reduced structural and functional recovery after stroke in aged animals is the early formation of a scar in the infarcted region that impairs neural recovery and repair. Despite the detrimental impact of infarct scar formation, the brain regions and cell types that supply the components of the scar are not well characterized. We hypothesized that premature cerebral scar formation in aged animals is associated with an altered cellular response to cerebral ischemia. Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3 month- and 20 month-old male Sprague Dawley rats. After 3, 7, 14, and 28 days, brain tissue was subjected to real-time reverse-transcriptase-PCR (RT-PCR) and immunostaining for 1) a cellular proliferation marker (BrdU); 2) a neuroepithelial marker (nestin); 3) an astrocytic marker (glial fibrillary acidic protein [GFAP]); 4) a neuronal marker, doublecortin; and 5) a basal lamina marker (laminin), and analyzed using 3D-reconstruction of confocal images. In this model the infarct was localized primarily in the parietal cortex. By RT-PCR there was a robust increase in nestin mRNA transcripts shortly after stroke, and this increase was particularly intense in aged rats. Accordantly, we found in aged rats a rapid delimitation of the infarct area by nestin-positive cells and an early incorporation of these cells into the glial scar. The capillaries of the corpus callosum were the major source of proliferating, nestin-positive cells, many of which were also immunoreactive for doublecortin, although a smaller population of nestin cells were associated with the ventricular walls. Despite the proliferation of nestin cells, they did not make a significant contribution to neurogenesis in the infarcted cortex, possibly because the corpus callosum impedes the migration of subventricular zone-derived nestin-positive cells into the lesioned area. We conclude that: (i) the aged brain has the capability to mount a cytoproliferative response to injury, but the timing of the cellular and genetic reaction to cerebral insult is accelerated in aged animals; (ii) the proliferating cells contribute to the formation of the glial scar, but few of the cells appear to become neurons; and (iii) the vasculature plays a hitherto unrecognized role as a source of proliferating cells after stroke. Because capillary-derived cells help to form the glial scar, elucidating the molecular basis of this phenomenon and its acceleration in the aging brain could yield novel approaches to enhancing neurorestoration in the elderly.
在老年动物中，与中风后结构和功能恢复降低相关的一个重要细胞事件是梗死区域早期形成瘢痕，这会损害神经恢复和修复。尽管梗死瘢痕形成有不利影响，但提供瘢痕成分的脑区和细胞类型尚未得到很好的表征。我们假设老年动物中过早的脑瘢痕形成与对脑缺血的细胞反应改变有关。通过可逆性闭塞3月龄和20月龄雄性Sprague Dawley大鼠的右侧大脑中动脉来产生局灶性脑缺血。在3、7、14和28天后，对脑组织进行实时逆转录聚合酶链反应（RT-PCR）和免疫染色，检测：1）细胞增殖标志物（BrdU）；2）神经上皮标志物（巢蛋白）；3）星形胶质细胞标志物（胶质纤维酸性蛋白[GFAP]）；4）神经元标志物双皮质素；5）基膜标志物（层粘连蛋白），并使用共聚焦图像的三维重建进行分析。在这个模型中，梗死主要位于顶叶皮质。通过RT-PCR检测发现，中风后不久巢蛋白mRNA转录本有强劲增加，且这种增加在老年大鼠中尤为强烈。相应地，我们发现在老年大鼠中，梗死区域迅速被巢蛋白阳性细胞界定，并且这些细胞早期就融入了胶质瘢痕。胼胝体的毛细血管是增殖的巢蛋白阳性细胞的主要来源，其中许多细胞对双皮质素也有免疫反应，尽管一小部分巢蛋白细胞与脑室壁有关。尽管巢蛋白细胞增殖，但它们对梗死皮质中的神经发生没有显著贡献，可能是因为胼胝体阻碍了室下区来源的巢蛋白阳性细胞迁移到损伤区域。我们得出以下结论：（i）老年脑有能力对损伤产生细胞增殖反应，但老年动物对脑损伤的细胞和基因反应时间加快；（ii）增殖细胞有助于胶质瘢痕的形成，但很少有细胞似乎能变成神经元；（iii）脉管系统在中风后作为增殖细胞的来源发挥了迄今未被认识的作用。由于毛细血管来源的细胞有助于形成胶质瘢痕，阐明这一现象及其在衰老大脑中加速的分子基础可能会产生增强老年人神经恢复的新方法。
