Neuronal aneuploidy in health and disease: a cytomic approach to understand the molecular individuality of neurons

Abstract

Structural variation in the human genome is likely to be an important mechanism for neuronal diversity and brain disease. A combination of multiple different forms of aneuploid cells due to loss or gain of whole chromosomes giving rise to cellular diversity at the genomic level have been described in neurons of the normal and diseased adult human brain. Here, we describe recent advances in molecular neuropathology based on the combination of slide-based cytometry with molecular biological techniques that will contribute to the understanding of genetic neuronal heterogeneity in the CNS and its potential impact on Alzheimer's disease and age-related disorders.

Keywords: Alzheimer's disease; alu-repeats; cell cycle; cell death; chromosomal mosaicism; in situ hybridisation; laser capture microdissection; neurodegeneration; slide-based cytometry.

Figure 1.

Inter-method reliability of three independent methods for single cell DNA quantification. A set of 48 microscopically identified neurons of the entorhinal cortex in a patient with early AD was evaluated through subsequent application of SBC, CISH and PCR amplification of alu repeats. Tissue sections were first processed for SBC, followed by hybridization with a chromosome 17-specific probe. Subsequently, indentified neurons were captured through laser microdissection and subjected to PCR amplification of alu repeats. Regression analyses reveal correlation coefficients according to Bravais-Pearson of (A) r = 0.92 for the SBC data versus hybridization results (CISH), (B) of r = 0.80 for LSC versus PCR amplification and (C) r = 0.78 for PCR amplification versus hybridization. All correlation coefficients are significant at p < 0.001 (adapted from [5]).

Figure 2.

Quantification of single-neuron DNA content by SBC. Note the increase in aneuploid neurons in AD. (control: n=13; AD early stages, Braak stage I/II: n=6; AD late stages, Braak stage V/VI: n=7; * p<0.01; adapted from [5].

Figure 3.

Quantification of CISH signals (chromosome 17 probe) in neurons of the entorhinal cortex (For number of cases compare Figure 2; *p<0.01; adapted from [5]).

Figure 4.

Frequency distribution of single neuron DNA-content determined by PCR amplification of alu repeats. Note in AD the shift towards higher DNA content and the appearance of a second peak corresponding to a tetraploid DNA content (adapted from [5]).