Smooth muscle development during postnatal growth of distal bronchioles in infant rhesus monkeys.

Development of smooth muscle in conducting airways begins early in fetal life. Whereas the pattern and regulation of smooth muscle differentiation are well-defined, the impact of airway growth on the process is not. To evaluate the transformations in organization during postnatal growth, smooth muscle bundle organization (size, abundance, and orientation) was mapped in five generations of distal airways of infant rhesus monkeys (5 days and 1, 2, 3, and 6 mo old). On the basis of direct measurement of the bronchiole proximal to the terminal bronchiole, length increased by 2-fold, diameter by 1.35-fold, and surface area by 2.8-fold between 5 days and 6 mo of age. Smooth muscle bundle size was greater in proximal bronchioles than in respiratory bronchioles and did not change with age. However, relative bundle size decreased in proportion to airway size as the airways grew. Relative bundle abundance was constant regardless of airway generation or age. The distribution of smooth muscle bundle orientation changed with age in each airway generation, and there were significant changes in the terminal and respiratory bronchioles. We conclude that smooth muscle undergoes marked organizational changes as airways grow during postnatal development.

Fibroblast growth factor-2 in remodeling of the developing basement membrane zone in the trachea of infant rhesus monkeys sensitized and challenged with allergen.

SUMMARY: Remodeling of the epithelial basement membrane zone (BMZ) involves increased deposition of collagen, resulting in thickening of the BMZ. The current study focuses on fibroblast growth factor-2 (FGF-2) in the tracheal BMZ in house dust mite allergen (HDMA)-sensitized infant rhesus monkeys, challenged with HDMA at a time when the BMZ is undergoing active postnatal development. To detect structural changes in the BMZ, we measured collagens I, III, and V. To detect changes in the function of the BMZ, we measured immunoreactivity of the heparan sulfate proteoglycan, perlecan, and FGF-2. We found significant thickening of the tracheal BMZ (p < 0.05) with each of these parameters. We also found that all HDMA tracheal samples expressed thin focal areas of the BMZ associated with leukocyte trafficking. These areas were depleted of perlecan and FGF-2; however, increased FGF-2 immunoreactivity was present in the adjacent basal cells. We conclude that basal cells and FGF-2 are involved with significant remodeling of the BMZ in the developing trachea of infant rhesus monkeys exposed to HDMA.

Fibroblast growth factor-2 during postnatal development of the tracheal basement membrane zone.

Thickening of the basement membrane zone (BMZ) is a characteristic of several airway diseases; however, very little is known about how this process occurs. The purpose of this study was to define development of the BMZ in the trachea of growing rhesus monkeys at 1, 2, 3, and 6 mo of age. We measured immunoreactivity of collagen types I, III, and V to detect structural changes in the developing BMZ. To detect more dynamic, functional components of the epithelial-mesenchymal trophic unit, we evaluated the distribution of perlecan, fibroblast growth factor-2 (FGF-2), and fibroblast growth factor receptor-1 (FGFR-1). One-month-old monkeys had a mean collagen BMZ width of 1.5 +/- 0.7 microm that increased to 4.4 +/- 0.4 microm in 6-mo-old monkeys. Perlecan was localized in the BMZ of the epithelium at all ages. FGF-2 was strongly expressed in basal cells at 1-3 mo. At 6 mo, FGF-2 was expressed throughout the BMZ and weakly in basal cells. FGFR-1 immunoreactivity was expressed by basal cells and cilia and weakly in the nuclei of columnar cells at all time points. These data indicate that development of the BMZ is a postnatal event in the rhesus monkey that involves FGF-2.