No bacterial proteins were Galeterone detected inside the tissues in present study, but the presence of bacteria has previously been detected in other cholesteatoma studies. As bacteria are ubiquitous on epidermis surfaces, their role in cholesteatoma is not clear. A constant presence of bacteria may chronically attract and activate immune cells, which have been found in high numbers in cholesteatoma. This possible chronic bacteriainduced inflammatory activation of proteases may explain the low abundance of extracellular matrix proteins in cholesteatoma. Among the up-regulated proteases in cholesteatoma tissues, HTRA1 is a novel finding which has interesting characteristics. This protease has been found in high levels in rheumatoid arthritis, osteoarthritis, and Alzheimer��s disease. It has a variety of targets, degrades extracellular matrix proteins, and inhibits matrix mineralization and mineral deposition by osteoblasts. HTRA1 may therefore also have a role in the erosion of the ossicles that that is associated with cholesteatoma disease. A down-regulation of this pathway, which is a known reaction to cellular stress, reduces the global protein synthesis to limit the detrimental effects of toxins and ROS. All 11 associated proteins from this pathway were down-regulated in the large-scale analysis. However, the down-regulation of two representative proteins, NRAS and EIF3K did not reach significance in the validation analyses, Chlorzoxazone indicating that parts of this stress pathway have high biological variation. The proteins associated with other high scoring stress-related canonical pathways were down-regulated as well. Chronic inflammatory cellular stress, as seen in cholesteatoma, is associated with a down-regulation of the Nrf2 pathway, which in turn leads to reduced transcription of glutathione metabolism related proteins ; the result is increased sensitivity to stress followed by increased cell death. Two recent studies measured a significantly higher total oxidant and significantly lower total antioxidant status in serum of patients with cholesteatoma.