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Dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) adenosine 3',5'-cyclic adenosine monophosphate (cAMP) analogue increased surfactant protein-A (SP-A) gene expression levels in baboon lung aged 94 to 172 days. However, baboon fetal lung aged 140 days exhibited reduced sensitivity to cAMP and glucocorticoids. Furthermore, the dexamethasone decreased the levels of SP-A gene expression indicating the presence of two baboon SP-A genes that affect fetal lung development.

Baboon genomic clones of hSP-A1 and hSP-A2 surfactant protein-A genes were isolated and characterized by reverse transcriptase-polymerase chain reaction. The exon-intron organization of hSP-A2 messenger ribonucleotide (mRNA) is composed of sequences with six exons while the sequences of the hSP-A1 gene is contained in five exons. Furthermore, the exon II of VI of the hSP-A2 gene has a 30-bp sequence the encodes the 5'-untranslated region of the mRNA.

cAMP response element (CRE) like sequence plays an important role in catalyzing basal and cAMP-inducible expression of surfactant protein-A2 human gene in alveolar type II cells. Alterations in the nuclear protein complex bound to cAMP response element like sequence occur in association with surfactant protein-A gene expression. The element is capable of playing additional roles in tissue-specific and developmental regulation of surfactant protein-A2 gene expression.

Human surfactant protein (SP) encoding genes SP-A1 and SP-P2 in fetal lung tissues are differentially affected by glucocorticoids and 3',5'-cyclic monophosphate (cAMP). SP-P2 responds to a higher degree than SP-A1 to the inhibitory function of glucocorticoids and inducive effects of cAMP. SP-A2 mRNA transcripts occur more than the SP-A1 transcripts in the lung tissues that are tested with dibutyryl (DB) cAMP.

Sequence analysis of genes encoding human surfactant proteins (SP), SP-A1 and SP-A2, reveals the four mRNA transcripts in SP-A2 and five mRNA transcripts in SP-A1. The mRNA transcripts of SP-A2 gene contain six exons, unlike the SP-A1 mRNA sequence that contain only five exons. The exons in the mRNA sequences of SP-A1 and SP-A2 are alternately arranged. The regulation of the two genes in fetal lung culture by glucocorticoids and 3',5'-cyclic monophosphate is different.

The possibility that the differentiation of midtrimester human fetal lung in organ culture is partly due to increased oxygen availability was investigated. Alveolar lumenal volume density and epithelium volume density were evaluated by morphometric analysis. Changes in the biochemical marker of type II cell differentiation due to oxygen tension were analyzed by assays of surfactant protein A and its mRNA. The permissive function of oxygen in the differentiation of cultured human fetal lung was demonstrated.

The mechanisms for the transport and targetting of surfactant protein A (SP-A) to lamellar bodies was investigated. SP-A is a developmentally and hormonally regulated major protein component of lung surfactant. It is expressed in type II pneumonocytes and stored in lamellar bodies in preparation for secretion into the alveolar lumen. The study protocol involved pulse-chase analysis of methionine-labeled SP-A in rabbit lung tissue. The results showed that targetting to lamellar bodies is enhanced by N-linked oligosaccharide side chain, and that 60% to 80% of newly synthesized SP-A is stored in lamellar bodies.

Dysregulation of human trophoblast invasion and differentiation can result in preeclampsia (PE), a hypertensive disorder of pregnancy with significant morbidity and mortality for mother and offspring. miRNA microarray analysis of RNA from human cytotrophoblasts (CytT), before and after differentiation to syncytiotrophoblast (SynT) in primary culture, revealed that members of miR-515 family--including miR-515-5p, miR-519e-5p, miR-519c-3p, and miR-518f, belonging to the primate- and placenta-specific chromosome 19 miRNA cluster (C19MC)--were significantly down-regulated upon human SynT differentiation. The proto-oncogene, c-MYC, which declines during SynT differentiation, interacted with E-boxes upstream of pri-miR-515-1 and pri-miR-515-2, encoding these mRNAs, to enhance their expression. Predicted targets of miR-515-5p, known to be critical for human SynT differentiation, including hCYP19A1/aromatase P450, glial cells missing 1 (GCM1), frizzled 5 (FZD5), WNT2, Sp1, and estrogen receptor- α (ERα) mRNA, were markedly up-regulated during SynT differentiation. Notably, overexpression of miR-515-5p in cultured primary human trophoblasts impaired SynT differentiation and specifically decreased expression of hCYP19A1, GCM1, and Fzd5, which were validated as its direct targets. Interestingly, miR-515-5p levels were significantly increased in PE placentas, whereas mRNA and protein levels of targets, hCYP19A1, GCM1, and FZD5, were significantly decreased, compared with placentas of normotensive women. Thus, miR-515-5p may serve a key role in human trophoblast differentiation; its aberrant up-regulation may contribute to the pathogenesis of PE. [ABSTRACT FROM AUTHOR]

Lung alveolar type II cells uniquely synthesize surfactant, a developmentally regulated lipoprotein that is essential for breathing. Expression of the gene (SFTPA) encoding the major surfactant protein, SP-A, in midgestation human fetal lung (HFL) is dramatically induced by cyclic AMP (cAMP). cAMP induction of SP-A expression is repressed by transforming growth factor β (TGF-β) and by hypoxia. In this study, we found that expression of the microRNA 29 (miR-29) family was significantly upregulated in epithelial cells isolated from mouse fetal lung during late gestation and in epithelial cells isolated from HFL explants during type II cell differentiation in culture. miR-29 expression in cultured HFL epithelial cells was increased by cAMP and inhibited by hypoxia, whereas the miR-29 target, TGF-β2, was coordinately decreased. Knockdown of the miR-29 family in cultured HFL type II cells blocked cAMP-induced SP-A expression and accumulation of surfactant-containing lamellar bodies, suggesting their physiological relevance. This occurred through derepression of TGF-β signaling. Notably, cAMP increased binding of endogenous thyroid transcription factor 1 (TTF-1/Nkx2.1) to the miR-29ab1 promoter in HFL type II cells, and TTF-1 increased miR-29ab1 promoter-driven luciferase activity in cotransfection assays. Together, these findings identify miR-29 family members as TTF-1-driven mediators of SP-A expression and type II cell differentiation through repression of TGF-β signaling. [ABSTRACT FROM AUTHOR]