Telomerase in alveolar epithelial development and repair

Telomerase expression and activity were examined in the developing lung and in the adult lung during repair after injury. Both whole lung tissue and p rimary cultures of type 2 alveolar epithelial cells (AEC2) isolated from fe tal and adult rodents were analyzed for 1) telomerase expression by immunoh istochemistry and 2) telomerase activity with a telomerase repeat amplifica tion protocol. We found that telomerase was expressed in a temporally regul ated manner in fetal lung through the late stages of gestation, with peak e xpression just before birth. Expression persisted for a brief period in neo nates, then decreased to nearly undetectable levels by postnatal day 9. Tel omerase expression and activity were reinduced in normally quiescent adult lung by in vivo treatment with hyperoxia. In populations of AEC2 isolated f rom both developing and repairing lungs, telomerase expression and activity showed a strong correlation with the proliferation marker proliferating ce ll nuclear antigen. It has been suggested that telomerase expression and ac tivity are hallmarks of stem or progenitor cells. Our observations suggest that a telomerase-positive subpopulation is present within the general AEC2 population. Telomerase may act as a marker for the proliferative status of this subpopulation.