Spatial-specific TGF-beta 1 adenoviral expression determines morphogeneticphenotypes in embryonic mouse lung

The precise spatial-temporal role that expression and activation of transfo rming growth factor (TGF)-beta plays in mammalian organ morphogenesis remai ns incompletely understood. Using replication deficient adenoviral vectors containing engineered TGF-beta 1 cDNAs, we studied the spatial effects of l ocally over-expressing either latent or mutated, constitutively active TGF- beta 1 protein during embryonic mouse lung branching morphogenesis in cultu re. Transfer of exogenous genes into lung epithelium was achieved by intra- tracheal microinjection of recombinant adenovirus, while submerging lungs i n virus resulted iii gene transfer into the pleura and subjacent mesenchyma l cells, as revealed by cytochemical staining for beta-galactosidase. Only lungs transfected with active, but not latent TGF-beta 1 gene, showed eleva ted levels of active TGF-beta. Epithelial over-expression of active, but no t latent TGF-beta 1, via intra-tracheal micro-injection inhibited lung bran ching morphogenesis by 36%. In contrast, lungs submerged with either active or latent TGF-beta 1 recombinant virus did not demonstrate an inhibitory e ffect upon branching. Pulmonary gene regulation was assayed by competitive polymerase chain reaction coupled with reverse transcription. Direct respir atory tract micro-injection of adenovirus over-expressing active TGF-beta 1 resulted in a dose-dependent inhibition of epithelial surfactant protein ( SP)-C and SP-B mRNA levels by up to 76 % and 70 %, respectively, while in c ontrast, fibronectin and matrix Gla protein (MGP) mRNA levels remained stab le. However, lungs that had been submerged in adenovirus expressing active TGF-beta 1 demonstrated a concentration-dependent induction of both fibrone ctin and MGP mRNA levels up to 4.3- and 4.7-fold respectively in the presen ce of 1x10(11) pfu/ml active TGF-beta 1 virus. On the other hand, lungs tre ated with adenovirus expressing latent TGF-beta 1 either by micro-injection or submerging failed to demonstrate any regulatory effect either upon epit helial or mesenchymal gene expression. We conclude that adenovector-mediate d overexpression of activated TGF-beta 1 in specific spatial compartments r esults respectively in either inhibition of branching morphogenesis and epi thelium-specific gene expression, or in induction of matrix gene expression without affecting morphogenesis or epithelium-specific gene expression, de pending on the route of administration. Also, the lack of effect of latent TGF-beta 1 over-expression strongly suggests that TGF-beta activation per s e provides an important locus of fine regulation of the spatial effects of TGF-beta signaling during embryonic lung branching morphogenesis.