Phagocytic Function Of Olfactory Ensheathing Cells For Removal Of Apoptotic Olfactory Neurons

Olfactory receptor neurons (ORNs) , the first class neurons in olfactory system , arethe only neurons that locate at the olfactory epithelium. ORNs are the only part of thecentral nervous system (CNS) contacting with the external environment in the nasal cavity,so they are highly susceptible to airborne pathogens and easily apoptotic. Clearance ofdebris in the olfactory system is a critical step for turnover and restoration of ORNs.However, little is known about how ORNs corpses are removed. To clarify thephenomenon of olfactory nerve turnover throughout life will provide the basis for deeplyundestanding the function and regulation of olfactory system.Olfactory ensheathing cells (OECs) are a unique type of glia cells that exist inolfactory system. They share the phenotypes of both Schwann cells and astrocytes. OECswrap olfactory receptor neuron axon bundles in olfactory system. Recently, OECs havebeen suggested to function as immune cells. In the present study, we examined the effect ofOECs phagocytosis on clearance apoptotic ORNs. Our data demonstrated that OECs canrecognize??engulf and remove apoptotic ORNs, which are similar to the function ofmacrophages. The results are shown as follow:1. Confocal analysis revealed that apoptotic ORNs were engulfed by OECs in vitro.2. The phagocytosis of OECs is not specially for ORNs. OECs also can phagocytoseapoptotic cortical neurons induced by staurosporine .3. The corpses of apoptotic neurons were shown to co-localize with LAMP1 (lysosomeassociated membrane protein).4. OECs were found to express phosphatidylserine receptor (PSR) in vitro and in vivo.PSR was shown to mediate the effect of OECs to phagocytose apoptotic ORNs orcortical neurons.5. Importantly, engulfment of ORNs corpses by OECs was observed in olfactory mucosaby histological analysis.