Surfactant Protein B in Human Fetal Lung: Developmental and Glucocorticoid Regulation

Abstract

ABSTRAGT Vol. 38, No.5, 1995 Printed ill U.S.A.Pulm onary surfac tant protein B (SP-B) enhances phospholip id film formation in vitro and is essential for normal surfactant functio n in vivo. We examined hum an fetal lung before and during explant culture for content and cellular localization of SP-B mRNA and prote in. SP-B mRNA was low in preculture specime ns (18 -20 wk) but hybridization signal increased ove r epithelial cells dur ing culture and was enha nced by dexa methasone treatment (10 nM). SP-B immunofluorescence was very low in preculture specimens, increased duri ng culture, and was uniformly intense in epithelial cells of dexam ethasone-treated tissue. With a newly developed immunoassay, SP-B protein was undetectable in preculture lung «2% of adult), appeared during culture (26 % of adul t), and was furth er increased~3-fo ld by dexamethasone treatment (86 % of adult); lung tissu e of two newborn infants contained 7-9-fold more SP-B than is found in the adult. Using Western blot with enhanced chemiluminescence, mature SP-B was undetectable in 16-wk specimens but was Pulmonary surfactant isolated from bronchoalveolar lavage fluid contains a variety of lipids and proteins. Three SP have been identified that influence surfactant structure, function, or metabolism. SP-A is a hydrophili c protein of 28 -36-kD monomer size that has a numb er of demonstrated effects on surfactant in vitro both alone and interacting with other surfactant proteins. SP-B and SP-C are lipophilic proteins of approx imately 8 and 4 kD, respectively, that co-isolate with surfactant lipids. Both of these proteins enhance the rate of phospholipid film formation and improve the surface activity of lipid mixtures in vivo (rev iewed in Ref. 1).SP-B appears to be critically important for surfactant function in vivo. Antib odies to SP-B inactivate a replacement surfactant prepared from pig lungs and cause severe respiratory Received November 17, 1994; accepted May 9, 1995 present in 19-24-wk preculture tissue at 0.2-2.9% of the adult level. By comparison, SP-B mRNA content is 14 and 50 % of adult leve l in 19-and 24-wk lung tissue, respec tively; levels increase 3-fold during culture and a further 3-fold with dexamethason e. Based on these observed differences between mRNA and protein content, we conclude that basal SP-B gene exp ression in epithe lial ce lls of hum an fetal lung is regulated primarily at the level of translatio n or prote in stabil ity, where as glucocorticoids act transc riptionally. We specu late that SP-B protein acc umulates only as type II cells differentiate and acquire lamellar bodies for processing and storage of SP-B. (Pediatr R es 38: 668-675, 1995) Abbreviations SP , surfactant protein TBS, Tris-buffered salin e distress when instilled into the trachea of newborn animals or inoculated intraperitoneally into adult mice (2-4). In pulmonary function studies with preterm rabbits, Rider et al. (5) found that the activity of lipid-SP-B preparations was equivalent to that of natural surfactan t. Recently, Nog...

Mechanical Ventilation Down-Regulates Surfactant Protein A and Keratinocyte Growth Factor Expression in Premature Rabbits

“…The expression of pro-SP-B protein increased from birth in all groups but was not inhibited by MV nor increased with dex. These differential responses between SP-B mRNA and pro-SP-B protein expression are consistent with literature using human fetal lung explants (32). These experiments suggest that SP-B gene expression is regulated primarily at the level of translation or protein stability, whereas glucocorticoids appear to act transcriptionally.…”

“…A number of both cell and animal studies have demonstrated increased SP-B expression after corticosteroid treatment (23,32). In our experiments, SP-B mRNA levels were increased with the addition of postnatal dex in both SB and MV rabbits.…”

Maintenance of surfactant protein A and D secretion by rat alveolar type II cells in vitro

“…Dexamethasone also stimulates some but not all markers of type II cell differentiation (46). For example, dexamethasone increases expression of SP-B and fatty acid synthase (2,38,46). In our studies, there was increased expression of SP-B when dexamethasone was added from day 1 through day 7 in culture, whereas there was little effect on the other surfactant protein mRNA levels.…”

“…Both SP-A and SP-D are increased in lavage fluid of rats instilled with KGF (54). Corticosteroids are especially stimulatory for the expression of SP-B but may be inhibitory for SP-A and SP-C (2,46). The type of serum in which the cells are maintained also alters type II cell phenotype.…”

ABCA3 Is Critical for Lamellar Body Biogenesis in Vivo

“…The surfactant proteins SP-B and SP-C and lipids are transported to and stored in lamellar bodies, the intracellular secretory organelles of the alveolar epithelial type 2 (AT2) cell through which pulmonary surfactant homeostasis is regulated (4 -6). The final steps in post-translational modification of both SP-B and SP-C occur in lamellar bodies (7)(8)(9)(10)(11). One of the striking abnormalities observed in hereditary SP-B deficiency, which is characterized by deficiencies of surfactant quantity and function, is derangement of lamellar body morphology (12), abnormalities that are replicated in the SP-B knock-out mouse (13,14).…”