Disease state, age, sex, and post-mortem time-dependent expression of proteins in AD vs. control frontal cortex brain samples.

Human post-mortem brain samples are excellent source material for the analysis of age-related disorders such as Alzheimer's disease (AD). Moreover, data obtained from cell culture- or mouse model-related experiments often need to be validated by using human tissue. In a variety of studies over the last few years, a huge list of genes or proteins with differential expression or abundance between AD-related and control tissue has been reported. However, highly important issues such as changes in post-mortem time, sex, age etc. of the patients have been rarely included in the analysis. In our study we examined human frontal brain samples of 10 AD patients vs. 10 unaffected controls using state-of-the-art two dimensional DIGE proteomics in order to analyze protein expression of up to 10,000 proteins in parallel. Data were analyzed using well established DIGE-software tool as well as an analysis of covariance model including the factor effects of group and sex and the covariable effects of age and post-mortem time. Within this study we report protein expression changes in AD vs. control human frontal brain samples without any influence of other parameters as well as expression changes depending on the parameters mentioned above. In fact, some proteins previously suggested a state of being dysregulated in AD vs. controls revealed age or sex-dependent regulation. Our analysis suggests the necessity of integrating additionally available covariables in comparative proteome studies of two different sets of human tissue.

The AICD interacting protein DAB1 is up-regulated in Alzheimer frontal cortex brain samples and causes deregulation of proteins involved in gene expression changes.

AICD is the intracellular subdomain of the amyloid precursor protein thought to play a pivotal role as a potential transcription factor that might be of relevance for the pathophysiology of Alzheimer's disease. For its signal transduction potential AICD requires interacting proteins like FE65 and TIP60. However, many other proteins were described being able to bind to AICD. Here, we studied mRNA levels of AICD interacting proteins and found one of them (DAB1) strongly up-regulated in human post-mortem frontal cortex brain samples of AD patients. Subsequent cell culture experiments revealed that elevated DAB1 level results in the deregulation of the cellular proteome. We found the proliferation associated protein 2G4 as well as the guanine monophosphate synthetase (GMPS) significantly up-regulated in DAB1 over-expressing cells. Both proteins can be involved in cellular transcription processes supporting the hypothesis that DAB1 acts via modification of the AICD-dependent transcriptionally active complex. Of note, expression of the three components of the putative transcription complex (AICD, FE65, and TIP60 (AFT)) also revealed deregulation of the GMPS protein in an opposite fashion. Our results point to a putative relevance of AICD-dependent mechanisms in AD, caused by protein abundance changes of AICD interacting proteins, as shown for DAB1 in this work.