Matrix metalloproteinase expression in the olfactory epithelium

The olfactory epithelium contains neuronal progenitor cells capable of continuous neurogenesis and is a unique model for studying neural degeneration, regeneration, axon outgrowth and recovery from injury. Matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs), have been implicated in cell turnover, development, migration, and metastatic processes. We used Western blot and immunohistochemistry to determine whether MMP-2 and associated proteins TIMP-2 and membrane type I matrix metalloproteinase (MTI-MMP) are present in the olfactory epithelium of mice. We found MMP-2 expression localized to the olfactory basal cells and immature neurons. After injury-induced neural degeneration, MMP-2 and MTI-MMP levels decreased while TIMP-2 levels increased. However, following 35 days of neurogenesis and cell replacement TIMP-2 and MTI-MMP returned to control levels. The results show a correlation between MMP and TIMP levels and the stages of neural degeneration, regeneration and recovery of the olfactory epithelium following injury.