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Epithelial-mesenchymal interactions in postnatal rat lung growth
Insights
Intercellular communication between lung epithelial and interstitial cells influences postnatal lung growth. Reduced cell contacts correlate with decreased cell division and altered cell function during lung development.
Area of Science:
- Pulmonary Biology
- Cell Biology
- Developmental Biology
Background:
- Epithelial-mesenchymal interactions are crucial for fetal lung development.
- The role of intercellular communication in postnatal lung growth requires further investigation.
Purpose of the Study:
- To evaluate intercellular communication's role in postnatal lung growth.
- To correlate cell contacts with cell division and biochemical function.
Main Methods:
- Utilized newborn rats, administered 3H-thymidine for cell proliferation analysis.
- Quantified cell division, hydroxyproline levels, and phosphatidylcholine.
- Examined basement membrane (BM) and foot processes (FP) using electron microscopy.
Main Results:
- Rapid cell proliferation observed between 3-10 days, with increased labeling index in interstitial and type 2 cells.
- Hydroxyproline levels rose as interstitial cell division slowed; epithelial growth linked to phosphatidylcholine.
- Decreased type 2-interstitial cell contacts during proliferation, followed by an increase possibly indicating differentiation.
Conclusions:
- Mesenchymal factor transfer may regulate pulmonary epithelial growth and differentiation.
- Postnatal lung development involves dynamic changes in cell-cell communication.
- Minimal cell-cell contacts in mature lungs may maintain type 2 cell function.
Abstract:
Epithelial-mesenchymal interactions have been implicated in epithelial cell differentiation in fetal lung. The role of such intercellular communication during postnatal lung growth is now evaluated to correlate intercellular contacts with cell division and with biochemical function of epithelial and interstitial cells. Sexed newborn rats, killed at frequent intervals to 8 weeks, received 3H-thymidine 1 h before death. A period of rapid cell proliferation between 3 and 10 days involved a five-fold increase in labeling index of both interstitial and type 2 epithelial cells. Hydroxyproline levels increased rapidly as interstitial cell division slowed, and epithelial growth was associated with elevated levels of disaturated phosphatidylcholine. Compared to the time of birth when epithelial cell division was slow, continuous basement membrane (BM) was more frequently found beneath type 2 cells during the postnatal proliferative phase, and fewer foot processes (FP) penetrated the BM; type 1 cells had few FP and uninterrupted BM. The number of intercellular contacts between type 2 cells and interstitial cells, one per two epithelial cell profiles at birth, decreased rapidly during the postnatal proliferative phase. There was a subsequent increase between 2 and 4 weeks that may reflect postmitotic epithelial differentiation. These observations support the hypothesis that transfer of mesenchymal factors may be important in the control of pulmonary epithelial growth and differentiation. The low incidence of cell-cell contacts seen after 4 weeks, one per five epithelial cell profiles, may reflect base levels of communication necessary to retain type 2 cell function in a resting cell population.