Ferrer I, Krupinski J, Goutan E, Martí E, Ambrosio S, Arenas E
Unitat de Neuropatologia, Servei d'Anatomía Patològica, Hospital Princeps d'Espanya, Campus de Bellvitge, 08907 Hospitalet de Llobregat, Spain.
Acta Neuropathol. 2001 Mar;101(3):229-38. doi: 10.1007/s004010000268.
Stroke is the major cause of adult brain dysfunction. In an experimental approach to evaluate the possible beneficial effects of administration of neurotrophic factors in stroke, we have used a model of distal middle cerebral artery (MCA) occlusion in adult rats. In this model, we found: (1) a permanent reduction of brain-derived neurotrophic factor (BDNF) and its full-length receptor, TrkB, in the infarcted core; (2) a transient increase in BDNF immunoreactivity in the internal region of the border of the infarct (penumbra area) at 12 h after MCA occlusion; (3) increased truncated TrkB immunoreactivity in astrocytes surrounding the area of the infarction; and (4) increased full-length TrkB immunoreactivity in scattered neurons, distant from the infarct, in ipsilateral and contralateral cortices at 24 and 48 h after MCA occlusion. We next studied the regulation of TrkB expression by BDNF, after ischemia, and its neuroprotective effects in vivo. In control non-ischemic rats, grafting of mock- or BDNF-transfected fibroblasts (F3A-MT or F3N-BDNF cell lines, respectively) in the medial part of the somatosensory cortex increased truncated TrkB immunoreactivity in neighboring astrocytes. Grafting alone also increased full-length TrkB in the vicinity of the mock graft (at 24 and 48 h) and the BDNF-grafted graft (at 4 days). Interestingly, ischemic animals grafted with the mock-transfected cell line did not show any further regulation of TrkB receptors. However, ischemic animals grafted with the BDNF cell line showed an up-regulation of full-length TrkB expression in neurons located in the internal border of the infarct. Analysis of nuclear DNA fragmentation in situ, combined with microtubule-associated protein 2 immunohistochemistry, revealed that most cells dying in the borders of the infarct (penumbra area) at 48 h following MCA occlusion were neurons. No differences in the infarct size were found between MCA occluded, mock-transfected MCA-occluded, and BDNF-transfected MCA-occluded rats. Moreover, cell death was similar in nongrafted and mock-grafted rats subjected to MCA occlusion. However, the number of cells with nuclear DNA breaks was significantly reduced in the penumbra area close to the BDNF graft in ischemic rats. Thus, our results show that BDNF specifically up-regulates its full-length TrkB receptor in cortical neurons of the penumbra area and prevents their death in an in vivo model of focal ischemia.
中风是成人大脑功能障碍的主要原因。在一项评估神经营养因子给药对中风可能产生的有益作用的实验中，我们使用了成年大鼠大脑中动脉（MCA）远端闭塞模型。在这个模型中，我们发现：（1）梗死核心区脑源性神经营养因子（BDNF）及其全长受体TrkB永久性减少；（2）MCA闭塞后12小时，梗死边缘内部区域（半暗带区）的BDNF免疫反应性短暂增加；（3）梗死区域周围星形胶质细胞中截短型TrkB免疫反应性增加；（4）MCA闭塞后24小时和48小时，同侧和对侧皮质中远离梗死灶的散在神经元中全长TrkB免疫反应性增加。接下来，我们研究了缺血后BDNF对TrkB表达的调节及其在体内的神经保护作用。在对照非缺血大鼠中，将空载体或BDNF转染的成纤维细胞（分别为F3A-MT或F3N-BDNF细胞系）移植到体感皮层内侧部分，可增加邻近星形胶质细胞中截短型TrkB免疫反应性。单独移植也会在空载体移植附近（24小时和48小时）和BDNF移植附近（4天时）增加全长TrkB。有趣的是，移植空载体转染细胞系的缺血动物未显示TrkB受体有任何进一步调节。然而，移植BDNF细胞系的缺血动物在梗死灶内边界的神经元中显示全长TrkB表达上调。结合微管相关蛋白2免疫组化的原位核DNA片段化分析显示，MCA闭塞后48小时，梗死灶边缘（半暗带区）死亡的大多数细胞是神经元。MCA闭塞大鼠、空载体转染的MCA闭塞大鼠和BDNF转染的MCA闭塞大鼠之间梗死灶大小无差异。此外，接受MCA闭塞的未移植和空载体移植大鼠的细胞死亡情况相似。然而，缺血大鼠中靠近BDNF移植的半暗带区有核DNA断裂的细胞数量显著减少。因此，我们的结果表明，在局灶性缺血的体内模型中，BDNF特异性上调半暗带区皮质神经元中其全长TrkB受体，并防止其死亡。
