Mosch Birgit, Morawski Markus, Mittag Anja, Lenz Dominik, Tarnok Attila, Arendt Thomas
Paul Flechsig Institute of Brain Research, Department of Neuroanatomy, University of Leipzig, D-04109 Leipzig, Germany.
J Neurosci. 2007 Jun 27;27(26):6859-67. doi: 10.1523/JNEUROSCI.0379-07.2007.
Reactivation of the cell cycle, including DNA replication, might play a major role in Alzheimer's disease (AD). A more than diploid DNA content in differentiated neurons might alternatively result from chromosome mis-segregation during mitosis in neuronal progenitor cells. It was our objective to distinguish between these two mechanisms for aneuploidy and to provide evidence for a functional cell cycle in AD. Using slide-based cytometry, chromogenic in situ hybridization, and PCR amplification of alu-repeats, we quantified the DNA amount of identified cortical neurons in normal human brain and AD and analyzed the link between a tetraploid DNA content and expression of the early mitotic marker cyclin B1. In the normal brain, the number of neurons with a more than diploid content amounts to approximately 10%. Less than 1% of neurons contains a tetraploid DNA content. These neurons do not express cyclin B1, most likely representing constitutional tetraploidy. This population of cyclin B1-negative tetraploid neurons, at a reduced number, is also present in AD. In addition, a population of cyclin B1-positive tetraploid neurons of approximately 2% of all neurons was observed in AD. Our results indicate that at least two different mechanisms need to be distinguished giving rise to a tetraploid DNA content in the adult brain. Constitutional aneuploidy in differentiated neurons might be more frequent than previously thought. It is, however, not elevated in AD. In addition, in AD some neurons have re-entered the cell cycle and entirely passed through a functional interphase with a complete DNA replication.
细胞周期的重新激活，包括DNA复制，可能在阿尔茨海默病（AD）中起主要作用。分化神经元中超过二倍体的DNA含量可能是由于神经祖细胞有丝分裂期间染色体错分离所致。我们的目标是区分这两种非整倍体形成机制，并为AD中功能性细胞周期提供证据。我们使用基于玻片的细胞计数法、显色原位杂交和alu重复序列的PCR扩增，对正常人类大脑和AD中已识别的皮质神经元的DNA量进行了定量，并分析了四倍体DNA含量与早期有丝分裂标记物细胞周期蛋白B1表达之间的联系。在正常大脑中，DNA含量超过二倍体的神经元数量约为10%。不到1%的神经元含有四倍体DNA含量。这些神经元不表达细胞周期蛋白B1，很可能代表先天性四倍体。在AD中也存在数量减少的这一群细胞周期蛋白B1阴性四倍体神经元。此外，在AD中观察到约占所有神经元2%的一群细胞周期蛋白B1阳性四倍体神经元。我们的结果表明，在成人大脑中至少需要区分两种不同的机制来产生四倍体DNA含量。分化神经元中的先天性非整倍体可能比以前认为的更常见。然而，在AD中其并未增加。此外，在AD中一些神经元已重新进入细胞周期，并完全经历了一个具有完整DNA复制的功能性间期。
