Analysis of Cell Turnover in the Bronchiolar Epithelium Through the Normal Aging Process

Aging is associated with changes in the lung that leads to a decrease in its function. Alterations in structure and function in the small airways are well recognized in chronic lung diseases. The aim of this study was the assessment of cell turnover in the bronchiolar epithelium of mouse through the normal aging process.

Lungs from CD1 mice at the age of 2, 6, 12, 18, or 24 months were fixed in neutral-buffered formalin and paraffin-embedded. Proliferating cell nuclear antigen was examined by immunohistochemistry. Apoptosis was analyzed by in situ end-labeling of fragmented DNA. Epithelial dimensions were analyzed by morphometry.

The 2-month-old mice showed significantly higher number of proliferating cells when compared with mice at all other age groups. The number of apoptotic cells in mice at 24 months of age was significantly greater than in mice at all other age groups. Thus, the number of epithelial cells decreased as the age of the subject increased. We also found reductions in both area and height of the bronchiolar epithelium in mice at 18 and 24 months of age.

We found a decrease in the total number of epithelial cells in the aged mice, which was accompanied by a thinning of the epithelium. These changes reflect a dysregulated tissue regeneration process in the bronchiolar epithelium that might predispose to respiratory diseases in elderly subjects.