Culture of adult mouse olfactory epithelial cells and modulation of their differentiation in vitro

Olfactory epithelium (OE) is unique, because it contains neuronal progenitor cells that provide the continuous turnover of olfactory receptor neurons (ORNs) in vertebrates throughout life. This unique feature enables the OE to be used as a source tissue for autologous transplantation to treat neurological diseases. For years, part of our lab's interests was to grow the ORNs from the adult OE tissue and use them for transplantation studies. A previous study in our lab has demonstrated that a ZnSO₄ injury produced by nasal irrigation of adult mouse OE stimulates mitotic activity of the stem cell population in situ which facilitates the survival and growth of OE cells in vitro. The OE cultures established following the chemical injury contain a heterogeneous cell population (Sosnowski et al., 1995). The purposes of the present study were (1) to improve the culture system to obtain more ORNs or glial cells in vitro, (2) to further characterize the heterogeneous cell population, (3) to find growth factors that can be used to manipulate the development of the OE cells in culture, and (4) to test if the OE cells would survive when implanted into the central nervous system. We also improved the chemical injury delivery by using the mist inhalation treatment, which provided more productive and consistent OE cultures than nasal irrigation treatment. The characterization studies demonstrated that the OE cultures contained the major cell types found in intact OE, including the progenitor cells and olfactory receptor neurons. Each major cell type retained characteristics found in situ. Olfactory ensheathment cells (OECs), a special glial cell population, were also identified in the OE cultures. Two growth factors BDNF and bFGF were found to promote the differentiation of the ORNs and OECs. The distribution of the bFGF receptors in OE cells was examined both in vitro and in vivo. Furthermore, our study also revealed that K252a, a protein kinase inhibitor, exhibited a unique neurotrophic effect on the OE cultures. The possible mechanism underlying the K252a action has been examined. Finally, the OE cells, when implanted into the rat spinal cord grey matter, survived for at least 6 weeks. Our study demonstrates that the chemical injury/culture paradigm provides dependable adult-derived neurons and glial cells for in vitro studies as well as in vivo transplantation.