[Expression of telomerase reverse transcriptase and its significance in human fetal lung development].

Objective: To investigate the expression and distribution of telomerase reverse transcriptase (hTERT) and its significance during the development of epithelial stem cells in human fatal lungs.
Methods: Human lung tissues were obtained at abortion from 37 fetuses 10-34 weeks of gestational age with parental consent, and the expression of hTERT in these tissues was examined by immunohistochemistry.
Results: In fetuses of 10 weeks old, hTERT was detected mainly in the epithelial cells of the proximal bronchi in the fetal lung, and migrated gradually to the distal bronchi as the lung developed. The hTERT expression level peaked at 17-20 weeks of gestation and then decreased over the period of alveolarization that occurred at about 25-26 weeks. In the later gestation period, strongly positive epithelial cells became concentrated in discrete patches near the basal membrane of the airway and scattered in only a few of the pulmonary alveoli. Morphologically, these cells resembled the basal cells and type II alveolar epithelial cells (AEC) or their progenitor cells.
Conclusions: Telomerase expression and activity are hallmarks of the pulmonary stem or progenitor cells that maintain undifferentiated state and self-renewal capacity, and it plays a crucial role in the normal differentiation and regeneration of the bronchial and alveolar epithelial cells to maintain the epithelial integrity.