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Early embryonic lung branching morphogenesis is regulated by many growth factor-mediated pathways. Bone morphogenetic protein 4 (BMP4) is one of the morphogens that stimulate epithelial branching in mouse embryonic lung explant culture. To further understand the molecular mechanisms of BMP4-regulated lung development, we studied the biological role of Smad-ubiquitin regulatory factor 1 (Smurf1), an ubiquitin ligase specific for BMP receptor-regulated Smads, during mouse lung development. The temporo-spatial expression pattern of Smurf1 in mouse embryonic lung was first determined by quantitative real-time PCR and immunohistochemistry. Overexpression of Smurf1 in airway epithelial cells by intratracheal introduction of recombinant adenoviral vector dramatically inhibited embryonic day (E) 11.5 lung explant growth in vitro. This inhibition of lung epithelial branching was restored by coexpression of Smad1 or by addition of soluble BMP4 ligand into the culture medium. Studies at the cellular level show that overexpression of Smurf1 reduced epithelial cell proliferation and differentiation, as documented by reduced PCNA-positive cell index and by reduced mRNA levels for surfactant protein C and Clara cell protein 10 expression. Further studies found that overexpression of Smurfl reduced BMP-specific Smad1 and Smad5, but not Smad8, protein levels. Thus overexpression of Smurf1 specifically promotes Smad1 and Smad5 ubiquitination and degradation in embryonic lung epithelium, thereby modulating the effects of BMP4 on embryonic lung growth. lung development; bone morphogenetic protein; Smad-ubiquitin regulatory factor 1

Transforming growth factor-[beta] (TGF-[beta]) signaling plays an important regulatory role during lung fibrogenesis. Smad3 was identified in the pathway for transducing TGF-[beta] signals from the cell membrane to the nucleus. Using mice without Smad3 gene expression, we investigated whether Smad3 could regulate bleomycin-induced pulmonary fibrosis in vivo. Mice deficient in Smad3 demonstrated suppressed type I procollagen mRNA expression and reduced hydroxyproline content in the lungs compared with wild-type mice treated with bleomycin. Furthermore, loss of Smad3 greatly attenuated morphological fibrotic responses to bleomycin in the mouse lungs, suggesting that Smad3 is implicated in the pathogenesis of pulmonary fibrosis. These results show that Smad3 contributes to bleomycin-induced lung injury and that Smad3 may serve as a novel target for potential therapeutic treatment of lung fibrosis. transforming growth factor-[beta]; hydroxyproline

Molecular embryology of the lung is a relatively young field. Since 1992, however, much progress has been made in establishing the molecular basis for cell lineage differentiation and embryonic lung morphogenesis. Advances in this area include insights into gain- versus loss-of-function phenotypes of specific genes and gene families and findings regarding the conservation of functions between genes that regulate morphogenesis. As a result of such advances, the development of new therapeutic methods for pulmonary problems such as dysplasia has been accelerated.

Research was conducted to examine the effects of nicotine on murine lung development utilizing a serumless mouse lung culture system. A total RNA isolation kit was utilized to determine total RNA from cultured lungs in guanidinium thiocyanate while quantification was carried out by densitometric band scanning. Results indicated that nicotine exposure influences branching morphogenesis and suggested a direct, local effect on the developing lungs of tobacco smoke-exposed fetuses.

Research shows that the genetic expression of matrix gla protein (MGP) in early embryonic mouse lung culture is more pronounced in the presence of exogenous transforming growth factor-beta1 (TGF-beta1). MGP messenger ribonucleic acid expression under the influence of TGF-beta1 changes over time and in varying concentrations of TGF-beta1. Experimental evidence suggests that MGP may play a crucial role in lung morphogenesis, possibly via endogenous TGF-beta signaling.

Gremlin negatively modulates BMP-4 induction of embryonic mouse lung branching morphogenesis. Am J Physiol Lung Cell Mol Physiol 280: L1030-L1039, 2001.--Bone morphogenetic protein-4 (BMP-4) is a key morphogen for embryonic lung development that is expressed at high levels in the peripheral epithelium, but the mechanisms that modulate BMP-4 function in early mouse lung branching morphogenesis are unclear. Here, we studied the BMP-4 antagonist Gremlin, which is a member of the DAN family of BMP antagonists that can bind and block BMP-2/4 activity. The expression level of gremlin in embryonic mouse lungs is highest in the early embryonic pseudoglandular stage [embryonic days (E) 11.5-14.5] and is reduced during fetal lung maturation (E18.5 to postnatal day 1). In situ hybridization indicates that gremlin is diffusely expressed in peripheral lung mesenchyme and epithelium, but relatively high epithelial expression occurs in branching buds at E11.5 and in large airways after E16.5. In E11.5 lung organ culture, we found that exogenous BMP-4 dramatically enhanced peripheral lung epithelial branching morphogenesis, whereas reduction of endogenous gremlin expression with antisense oligonucleotides achieved the same gain-of-function phenotype as exogenous BMP-4, including increased epithelial cell proliferation and surfactant protein C expression. On the other hand, adenoviral overexpression of gremlin blocked the stimulatory effects of exogenous BMP-4. Therefore, our data support the hypothesis that Gremlin is a physiologically negative regulator of BMP-4 in lung branching morphogenesis. bone morphogenetic protein; lung development; organogenesis

Shi, Wei, Nora Heisterkamp, John Groffen, Jingsong Zhao, David Warburton, and Vesa Kaartinen. TGF-[Beta]3-null mutation does not abrogate fetal lung maturation in vivo by glucocorticoids. Am. J. Physiol. 277 (Lung Cell. Mol. Physiol. 21): L1205-L1213, 1999.--Newborn transforming growth factor (TGF)-[Beta]3-null mutant mice exhibit defects of palatogenesis and pulmonary development. Glucocorticoids, which play a central role in fetal lung maturation, have been postulated to mediate their stimulatory effects on tropoelastin mRNA expression through TGF-[Beta]3 in cultured lung fibroblasts. In the present study, we analyzed the abnormally developed lungs in TGF-[Beta]3-null mutant mice and compared the effects of glucocorticoids on gene expression and lung morphology between TGF-[Beta]3 knockout and wild-type mice. Lungs of TGF-[Beta]3-null mutant mice on embryonic day 18.5 did not form normal saccular structures and had a thick mesenchyme between terminal air spaces. Moreover, the number of surfactant protein C-positive cells was decreased in TGF-[Beta]3-null mutant lungs. Interestingly, glucocorticoids were able to promote lung maturation and increased expression of both tropoelastin and fibronectin but decreased the relative number of surfactant protein C-positive cells in fetal lungs of both genotypes. This finding provides direct evidence that glucocorticoid signaling in the lung can use alternative pathways and can exert its effect without the presence of TGF-[Beta]3. transforming growth factor-[Beta]3; tropoelastin expression

Research was conducted to study the capability of a naturally occurring inhibitor of transforming growth factor (TGF)-beta activity, the proteoglycan decorin, to overcome the inhibitory effects of exogenous TGF-beta. Results indicated that decorin can antagonize bioactive TGF-beta during lung growth and differentiation, establishing the rationale for decorin as a possible therapeutic approach to remedy excessive levels of TGF-beta signaling in the developing lung.

Presents a study to investigate the possible regulation of matrix Gla protein (MGP) by a exogenous transforming growth factor during lung development. Details of study; Detection of MGP message increment; Findings of study.