Upregulation of Cathepsins in Olfactory Bulbs Is Associated with Transient Olfactory Dysfunction in Mice with Experimental Autoimmune Encephalomyelitis.

Cathepsins are a family of lysosomal/endosomal proteolytic enzymes that include serine, aspartate, and cysteine proteases. The role of cathepsin in neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, remains elusive. We evaluated the expression level and localization of different cathepsins in the olfactory bulbs of mice with experimental autoimmune encephalomyelitis (EAE), a model of human multiple sclerosis. Quantitative real-time PCR results and Western blotting analyses revealed that serine, aspartate, and cysteine cathepsins are expressed at significantly higher levels in the olfactory bulbs of mice with EAE in the paralytic stage compared with those of control mice. Immunohistochemical analyses indicated that cathepsin A, D, and S were expressed in the glomerulus layer, external plexiform layer, and mitral cell layer. Furthermore, cathepsins were detected in astrocytes, microglia, inflammatory cells, and vascular cells in the olfactory bulb of EAE mice at the paralytic stage. Collectively, these results suggest that the upregulation of cathepsins in the olfactory bulb of mice with EAE is associated with transient olfactory dysfunction in autoimmune encephalomyelitis.