gms | German Medical Science

Introduction: As all neurodegenerative diseases Alzheimer´s disease (AD) starts insidiously and ends in area- and layer-specific nerve cell loss. These phenomena are described in a staging system commonly accepted. Aside from changes in gene transcription there is growing evidence that mitochondrial dysfunction plays an important role in both age- and AD- related neuronal degeneration.

Methods: In order to unravel the differential vulnerability of neuronal types we analyzed 150 to 500 neurons respectively from the cerebellar granule layer, hippocampal pyramidal layer and the nucleus of the spinal trigeminal tract from control-, intermediate AD Stages (iAD) - and late AD-cases (lAD). Neurons were laser microdissected from 10 µm cresylviolet-stained slices for either direct lysis and cDNA-synthesis or isolation of DNA. DNA is used in a multiplex real-time PCR to reveal the level of mitochondrial DNA (mtDNA) deletions. For gene expression studies different regulated candidate genes were achieved by previous microarray analysis. The validation of target genes by means of quantitative PCR using a strategy of normalization with multiple reference genes is in progress.

Results and conclusions: Suprisingly, the analysis of the mtDNA reveals constant high deletion levels in cerebellar granule cells of all three groups. MtDNA deletion levels of CA 2 pyramidal cells slightly icreases from intermedidiate to late AD stages. Neurons of brainstem and CA1 region show higher deletion levels in group iAD compared to controls. However, the data show high inter-individual variations independent of AD stages and regions indicating a celltype specific vulnerability. Transcription profile analysis of neurons from the hippocampal CA1 region revealed downregulation of genes related to DNA repair (FANCM), MAPK-signaling (MAPK1,TAOK3), mitochondrial biogenesis (SSBP1) and Aß binding (TM2D1) in cases of AD compared to controls. SLC1A3, a gene coding for a glutamate carrier was upregulated in case of AD. We hypothesize that the dysregulation of genes directly or indirectly implicated in DNA damage repair contributes to the progression of AD in vulnerable neurons. Strengthen the analysis of gene expression to all brain regions included in the study our experimental design promises to unravel new insights into the pathogenesis of AD depending on selective vulnerability of individual cell types.