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Temporal-spatial distribution of SP-B and SP-C proteins and mRNAs in developing respiratory epithelium of human lung
A Khoor1, M T Stahlman, M E Gray
1Department of Pediatrics, Vanderbilt University, Nashville, Tennessee 37232-2370.
Insights
Surfactant proteins B and C (SP-B and SP-C) are expressed early in human fetal lung development, appearing in airway epithelium before birth. This distribution suggests their crucial role in lung function prior to the infant
Area of Science:
- Pulmonary Biology
- Cell Biology
- Developmental Biology
Background:
- Surfactant proteins B (SP-B) and C (SP-C) are essential components of pulmonary surfactant.
- Their expression patterns during human lung development are not fully elucidated.
Purpose of the Study:
- To determine the temporal and spatial distribution of SP-B and SP-C mRNAs and proteins in the developing human lung.
- To investigate the cellular localization and expression patterns of SP-B and SP-C throughout fetal, neonatal, and adult lung development.
Main Methods:
- Immunohistochemistry and in situ hybridization were employed to detect SP-B and SP-C at both mRNA and protein levels.
- Analysis was performed on human lung tissue samples from fetal, neonatal, and adult stages.
Main Results:
- SP-B and SP-C mRNAs and proteins were detected in airway epithelial cells as early as 15 weeks' gestation.
- Post-25 weeks gestation, co-localization of SP-B and SP-C with Type II epithelial cells and bronchiolo-alveolar portal cells was observed.
- Distinct cellular localization patterns for SP-B precursor and active peptide suggest cell-specific processing or routing.
Conclusions:
- SP-B and SP-C are expressed in the distal conducting and terminal airway epithelium of the human fetal lung significantly before surfactant lipid synthesis.
- These findings highlight the early developmental importance of SP-B and SP-C, preceding their immediate physiological requirement at birth.
Abstract:
We determined the temporal and spatial distribution of surfactant protein B (pro-SP-B) and C (pro-SP-C) mRNAs and proteins by immunohistochemistry and in situ hybridization in fetal, neonatal, and adult human lung. Pro-SP-B and SP-B mRNA were detected in bronchi and bronchioles by 15 weeks' gestation. After 25 weeks, pro-SP-B, active SP-B peptide, and SP-B mRNA were co-localized in bronchiolo-alveolar portal cells and in Type II epithelial cells. In adult lung, pro-SP-B and SP-B mRNA were detected primarily in non-ciliated bronchiolar epithelial cells and in Type II cells in the alveolus. Pro-SP-C and SP-C mRNA were detected in cells lining terminal airways from 15 weeks' gestation and thereafter. After 25 weeks, SP-C mRNA and precursor protein were detected in epithelial cells of the bronchiolo-alveolar portals and in Type II cells, where expression increased with advancing gestational age. Distinct cellular patterns of staining for pro-SP-B compared with SP-B active peptide support the concept that its proteolytic processing or cellular routing may be influenced by cell type and/or cell differentiation. SP-B and SP-C are expressed primarily in distal conducting and terminal airway epithelium of human fetal lung well in advance of surfactant lipid synthesis or physiologic requirements to produce pulmonary surfactant at the time of birth.