Neurogenesis takes place in the adult mammalian brain in three areas: Subgranular zone of the dentate gyrus (DG); subventricular zone of the lateral ventricle; olfactory bulb. Different molecular markers can be used to characterize the cells involved in adult neurogenesis. It has been recently suggested that a population of bone marrow (BM) progenitor cells may migrate to the brain and differentiate into neuronal lineage. To explore this hypothesis, we injected recombinant SV40-derived vectors into the BM and followed the potential migration of the transduced cells. Long-term BM-directed gene transfer using recombinant SV40-derived vectors leads to expression of the genes delivered to the BM firstly in circulating cells, then after several months in mature neurons and microglial cells, and thus without central nervous system (CNS) lesion. Most of transgene-expressing cells expressed NeuN, a marker of mature neurons. Thus, BM-derived cells may function as progenitors of CNS cells in adult animals. The mechanism by which the cells from the BM come to be neurons remains to be determined. Although the observed gradual increase in transgene-expressing neurons over 16 mo suggests that the pathway involved differentiation of BM-resident cells into neurons, cell fusion as the principal route cannot be totally ruled out. Additional studies using similar viral vectors showed that BM-derived progenitor cells migrating in the CNS express markers of neuronal precursors or immature neurons. Transgene-positive cells were found in the subgranular zone of the DG of the hippocampus 16 mo after intramarrow injection of the vector. In addition to cells expressing markers of mature neurons, transgene-positive cells were also positive for nestin and doublecortin, molecules expressed by developing neuronal cells. These cells were actively proliferating, as shown by short term BrdU incorporation studies. Inducing seizures by using kainic acid increased the number of BM progenitor cells transduced by SV40 vectors migrating to the hippocampus, and these cells were seen at earlier time points in the DG. We show that the cell membrane chemokine receptor, CCR5, and its ligands, enhance CNS inflammation and seizure activity in a model of neuronal excitotoxicity. SV40-based gene delivery of RNAi targeting CCR5 to the BM results in downregulating CCR5 in circulating cells, suggesting that CCR5 plays an important role in regulating traffic of BM-derived cells into the CNS, both in the basal state and in response to injury. Furthermore, reduction in CCR5 expression in circulating cells provides profound neuroprotection from excitotoxic neuronal injury, reduces neuroinflammation, and increases neuronal regeneration following this type of insult. These results suggest that BM-derived, transgene-expressing, cells can migrate to the brain and that they become neurons, at least in part, by differentiating into neuron precursors and subsequently developing into mature neurons.

中文翻译：

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骨髓祖细胞在大鼠和兔子的成年大脑中的迁移。

神经发生发生在成年哺乳动物的大脑中的三个区域：齿状回的齿下亚区（DG）；和 侧脑室的脑室下区；嗅球。可以使用不同的分子标记物来表征参与成年神经发生的细胞。最近已经提出，骨髓（BM）祖细胞群可能迁移到大脑并分化为神经元谱系。为了探索这一假设，我们将重组SV40衍生的载体注射到BM中，然后追踪转导细胞的潜在迁移。使用重组SV40衍生的载体进行的BM定向基因的长期转移会导致传递至BM的基因首先在循环细胞中表达，然后在成熟的神经元和小神经胶质细胞中存活数月，因此不会出现中枢神经系统（CNS）病变。大多数表达转基因的细胞表达NeuN，这是成熟神经元的标志物。因此，BM来源的细胞可以在成年动物中充当CNS细胞的祖细胞。来自BM的细胞成为神经元的机制尚待确定。尽管观察到的超过16 mo的表达转基因神经元的逐渐增加表明该途径涉及BM驻留细胞向神经元的分化，但不能完全排除细胞融合作为主要途径的情况。使用类似病毒载体的其他研究表明，在CNS中迁移的BM来源的祖细胞表达神经元前体或未成熟神经元的标记。骨髓内注射载体后16 mo，在海马DG的亚颗粒区发现了转基因阳性细胞。除了表达成熟神经元标记的细胞外，转基因阳性细胞的巢蛋白和双皮质素也呈阳性，这是发育中的神经元细胞表达的分子。如短期BrdU掺入研究所示，这些细胞正在积极增殖。通过使用海藻酸诱导癫痫发作，增加了由SV40载体迁移到海马中转导的BM祖细胞的数量，这些细胞在DG的早期出现。我们显示，细胞膜趋化因子受体，CCR5及其配体在神经元兴奋性毒性模型中增强CNS炎症和癫痫发作活性。基于SV40的RNAi靶向CCR5传递至BM导致循环细胞中CCR5的下调，这表明CCR5在调节BM来源的细胞进入CNS的基础状态和对损伤的反应中均起着重要作用。此外，循环细胞中CCR5表达的减少可提供对兴奋性毒性神经元损伤的深层神经保护，减少神经发炎，并增加这种类型的伤害后的神经元再生。这些结果表明，源自BM，表达转基因的细胞可以迁移到大脑，并且至少部分地通过分化为神经元前体并随后发育为成熟的神经元而成为神经元。