Post-translational modifications and protein-specific isoforms in endometriosis revealed by 2D DIGE

Endometriosis is a chronic disorder affecting approximately 10% of women in whom endometrial tissue forms painful lesions outside the uterus. It has a major impact on their physical, mental and social well-being but has no known cure, and there is no nonsurgical means of diagnosis. We have used a proteomic approach to identify proteins with altered abundance in the eutopic endometrium of endometriosis patients in the midsecretory phase of the menstrual cycle. 2D-differential in gel electrophoresis (DIGE) and mass spectrometry identified 20 proteins that were present at different levels in endometriosis patients (p < 0.05), many of which have not previously been associated with endometriosis. Protein abundance changes did not correlate well with published gene array data, emphasizing the extensive post-translational modification that occurs in this tissue. Abundance or localization changes in endometrial tissue were validated by immunohistochemistry and Western blotting for three proteins, vimentin (VIM), peroxiredoxin 6 (PRDX6), and ribonuclease/angiogenin inhibitor 1 (RNH1), while observed changes could not be confirmed for coronin 1A (CORO1A) or transgelin (TAGLN2). In addition, multiple charge and size isoforms were observed for PDRX6 and vimentin (VIM), and an additional PDRX6 isoform was observed in endometriosis patients that was below the level of detection in healthy women. Biological pathway analysis identified that cytoskeletal remodeling via keratin intermediate filaments, processing of the cystic fibrosis transmembrane receptor (CFTR), the glucocorticoid receptor subunit alpha (GCR), and heat shock factor 1 (HSF1) were all significantly over-represented features in endometriosis patients. This study highlights the highly dynamic nature of endometrial tissue and suggests that considerable post-translational modification of proteins is a key factor in the pathology of endometriosis.