Alveolar type II cell-fibroblast interactions, synthesis and secretion of surfactant and type I collagen.
During alveolar development and alveolar repair close contacts are established between fibroblasts and lung epithelial cells through gaps in the basement membrane. Using co-culture systems we have investigated whether these close contacts influence synthesis and secretion of the principal surfactant apoprotein (SP-A) by cultured rat lung alveolar type II cells and the synthesis and secretion of type I collagen by fibroblasts. The alveolar type II cells remained cuboidal and grew in colonies on fibroblast feeder layers and on Matrigel-coated cell culture inserts but were progressively more flattened on fixed fibroblast monolayers and plastic. Alveolar type II cells cultured on plastic released almost all their SP-A into the medium by 4 days. Alveolar type II cells cultured on viable fibroblasts or Matrigel-coated inserts above fibroblasts accumulated SP-A in the medium at a constant rate for the first 4 days, and probably recycle SP-A by endocytosis. The amount of mRNA for SP-A was very low after 4 days of culture of alveolar type II cells on plastic, Matrigel-coated inserts or fixed fibroblast monolayers: relatively, the amount of mRNA for SP-A was increased 4-fold after culture of alveolar type II cells on viable fibroblasts. Co-culture of alveolar type II cells with confluent human dermal fibroblasts stimulated by 2- to 3-fold the secretion of collagen type I into the culture medium, even after the fibroblasts' growth had been arrested with mitomycin C. Collagen secretion, by fibroblasts, also was stimulated 2-fold by conditioned medium from alveolar type II cells cultured on Matrigel. The amount of mRNA for type I collagen increased only modestly when fibroblasts were cultured in this conditioned medium. This stimulation of type I collagen secretion diminished as the conditioned medium was diluted out, but at high dilutions further stimulation occurred, indicating that a factor that inhibited collagen secretion also was being diluted out. The conditioned medium contained low levels of IGF-1 and the stimulation of type I collagen secretion was abolished when the conditioned medium was pre-incubated with antibodies to insulin-like growth factor 1 (IGF-1). There are important reciprocal interactions between alveolar type II cells and fibroblasts in co-culture. Direct contacts between alveolar type II cells and fibroblasts appear to have a trophic effect on cultured alveolar type II cells, increasing the levels of mRNA for SP-A. Rat lung alveolar type II cells appear to release a factor (possibly IGF-1) that stimulates type I collagen secretion by fibroblasts.
Griffin
M
M
Department of Biochemistry, Charing Cross and Westminister Medical School, London, UK.
Bhandari
R
R
Hamilton
G
G
Chan
Y C
YC
Powell
J T
JT
D000818:Animals; D001059:Apoproteins / Q000096:biosynthesis* / Q000378:metabolism; D001485:Basement Membrane; D002450:Cell Communication; D002478:Cells, Cultured; D003094:Collagen / Q000096:biosynthesis* / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007365:Intercellular Junctions / Q000502:physiology*; D016685:Mitomycin / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000096:biosynthesis* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats
D001059:Apoproteins; D017077:Culture Media, Conditioned; D016895:Culture Media, Serum-Free; D007328:Insulin; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; C046616:pulmonary surfactant apoprotein; D016685:Mitomycin; D007334:Insulin-Like Growth Factor I; D003094:Collagen