Protein expression overlap: more important than which proteins change in expression?

In recent years, a large number of proteomics studies for various diseases were conducted, such as for cancer, cardiovascular and neurodegenerative disorders (NDs). The availability of huge data sets with a large number of differentially expressed proteins showed for the first time that not all protein changes between a diseased and a control state were specific. This review focuses on this protein expression overlap, specifically between NDs, and tries to investigate the possible reasons for this overlap by investigating 14 ND proteomics studies of Alzheimer's (six studies), Parkinson's (four studies) and Huntington's disease (three studies), as well as amyotrophic lateral sclerosis (one study). Studies were selected according to the availability of quantitative changes, number of (biological) repeats and numbers of proteins changed. The studies include investigations of human tissue and mouse, as well as cell culture, models. A change in metabolism-related proteins was found to be common among all disorders. These changes can be explained by alterations in key regulatory proteins, such as those involved in transcription. Since most NDs affect, at least initially, very specific areas of the brain, the location of the changes may be more important than the kind of protein alterations that occur, since they are very similar among NDs.