2 DIFFERENT PATTERNS OF AIRWAY BRANCHING REGULATED BY DIFFERENT COMPONENTS OF THE EXTRACELLULAR-MATRIX IN-VITRO

This study examined the effects of beta-D-xyloside (an inhibitor of pr oteoglycan synthesis) and cis-4-hydroxyl-L-proline (an inhibitor of co llagen synthesis) on branching morphogenesis in cultures of fetal rat lung. Lungs from day 15 gestation were incubated for 4 days in (1) the control medium (Dulbecco's Modified Eagle Medium + 10% Fetal Bovine S erum) alone (control), (2) control medium plus 2 mM beta-D-xyloside (b eta-XYL), (3) control medium plus 2 mM alpha-D-xyloside (alpha-XYL), ( 4) control medium plus 50 mu g/mL cis-4-hydroxy-L-proline (cis-HYP). T he number of peripheral buds of left lungs was counted daily. Histolog ical examination was performed on lungs on days 2 and 4. beta-XYL inhi bited proximal monopodial branching on day 2 without affecting lung si ze, but produced numerous peripheral buds on day 4 which were of abnor mal appearance, suggesting that lung airway branching and growth may b e regulated by different mechanisms. Histology and morphometry showed significantly enlarged airspaces and diminished mesenchyme. cis-HYP di d not affect proximal branching on 2 days in culture, but inhibited fu rther dichotomous branching and lung growth after 2 days. On day 4, di minished branching and lung growth was accompanied by a proportional d ecrease in mesenchyme. The difference between effects of beta-XYL and cis-HYP on the branching pattern suggests that proteoglycans and colla gen are involved in different patterns of branching morphogenesis.