The effects of dexamethasone and betamethasone on surfactant protein-B messenger RNA expression in human type II pneumocytes and human lung adenocarcinoma cells

Comparison of the effects of betamethasone and dexamethasone on surfactant protein A mRNA expression in human lung cells

OBJECTIVE

While prenatal administration of synthetic corticosteroids stimulates both fetal lung development and expression of pulmonary surfactant, the specific effects may depend on the corticosteroid formulation used. We compared the dose-dependent effects of various concentrations of two synthetic corticosteroids, betamethasone and dexamethasone, on steady state levels of surfactant protein A (SP-A) mRNA in human lung cells.

METHODS

Cultured human NCI-H441 bronchoalveolar epithelial cells were exposed to varying concentrations of betamethasone or dexamethasone (10^-7 to 10^-12 M) for 48 h alone or in combination with dibutyryl cAMP (1 mM), which augments surfactant protein gene expression. RNA was harvested and SP-A mRNA levels were quantified by real-time quantitative reverse transcriptase polymerase chain reaction analysis. Results were compared using the Kruskal-Wallis test.

RESULTS

A dose-dependent modification in SP-A mRNA levels was demonstrated with both dexamethasone and betamethasone. Cells treated with cAMP expressed higher levels of SP-A mRNA than untreated cells. A biphasic curve in the SP-A mRNA response to corticosteroids was elicited only in the presence of cAMP: at lower concentrations (10^-10 through 10^-12 M), SP-A mRNA levels were upregulated, whereas at higher concentrations (10^-7 and 10^-8 M), SP-A mRNA levels were reduced. Dexamethasone was more effective than betamethasone in inducing these changes.

CONCLUSIONS

Our results support a biphasic effect on SP-A mRNA levels after exposure to corticosteroids in combination with cAMP. At higher corticosteroid concentrations, betamethasone is less inhibitory than dexamethasone on SP-A mRNA.

Knockdown of Drosha in human alveolar type II cells alters expression of SP-A in culture: a pilot study

Human surfactant protein A (SP-A) plays an important role in surfactant metabolism and lung innate immunity. SP-A is synthesized and secreted by alveolar type II (ATII) cells, one of the two cell types of the distal lung epithelium (ATII and ATI). We have shown that miRNA interactions with sequence polymorphisms on the SP-A mRNA 3'UTRs mediate differential expression of SP-A1 and SP-A2 gene variants in vitro. In the present study, we describe a physiologically relevant model to study miRNA regulation of SP-A in human ATII. For these studies, we purified and cultured human ATII on an air-liquid interface matrix (A/L) or plastic wells without matrix (P). Gene expression analyses confirmed that cells cultured in A/L maintained the ATII phenotype for over 5 days, whereas P-cultured cells differentiated to ATI. When we transfected ATII with siRNAs to inhibit the expression of Drosha, a critical effector of miRNA maturation, the levels of SP-A mRNA and protein increased in a time dependent manner. We next characterized cultured ATII and ATI by studying expression of 1,066 human miRNAs using miRNA PCR arrays. We detected expression of >300 miRNAs with 24 miRNAs differentially expressed in ATII versus ATI, 12 of which predicted to bind SP-A 3'UTRs, indicating that these may be implicated in SP-A downregulation in ATI. Thus, miRNAs not only affect SP-A expression, but also may contribute to the maintenance of the ATII cell phenotype and/or the trans-differentiation of ATII to ATI cells, and may represent new molecular markers that distinguish ATII and ATI.

Corticosteroids effect on caspase 3 expression in an in-vitro model of hypoxic brain cells

OBJECTIVE

Effects of corticosteroids (CS) in the brain of growth-restricted fetus remain largely unstudied. We investigated if dexamethasone (DXM) exposure contributes to neuronal injury in an in-vitro model of neuronal cells under hypoxic conditions (surrogate for fetal growth restriction).

STUDY DESIGN

U87 glioblastoma cells exposed to hypoxic or normoxic conditions for 10 h were incubated in the absence or presence of DXM for 48 h. Apoptosis as possible indicator of neurotoxicity was determined using a caspase-3-specific activity assay and western blotting. Caspase-3 was calculated as percentage of mean caspase-3 cleavage. Each experiment was performed in triplicate (n = 48). Caspase 3 activity in cell culture media was also measured by ELISA.

RESULTS

Pro-caspase-3 (32 kDa) was expressed in culture, but activated 17 Kd caspase 3 was not expressed in cell lysate. There was no difference in ratio of caspase 3 activation when U87 cells were exposed to 10 v of hypoxia as compared to normoxia (0.46 ± 0.44 versus 0.37 ± 0.37). The pro-apoptotic effects of DXM were not increased by pre-exposure to hypoxia: (0.37 ± 0.37 versus 0.47 ± 0.40).

CONCLUSION

The addition of DXM to hypoxic U87 cells had no additive or synergistic effects on the activation of caspase 3. Therefore, we speculate that the administration of CS in the setting of fetal growth restriction would not lead to increased apoptosis with potential neuronal injury.

Glucocorticoids potentiate IL-6-induced SP-B expression in H441 cells by enhancing the JAK-STAT signaling pathway

The respiratory distress syndrome (RDS) contributes to perinatal morbidity and mortality associated with preterm birth. Surfactant protein B (SP-B) is decreased in RDS. Both maternal antenatal steroid administration and chorioamnionitis reduce the incidence and severity of RDS. An important mediator in chorioamnionitis is IL-6 using the JAK-STAT signaling pathway for signal transduction. We hypothesized that the steroids, betamethasone (BTM) and dexamethasone (DXM), and IL-6 had synergistic effects on SP-B gene expression and STAT3 phosphorylation in H441 cells. DXM and BTM increased SP-B mRNA levels by 16.5 (13.3)-fold and IL-6 alone by 2.3-fold. After 48-h exposure of cells to DXM or BTM, IL-6 caused a significantly greater increase in SP-B mRNA levels (28.1-fold) than IL-6 or glucocorticoids alone. Whereas IL-6 stimulated tyrosine phosphorylation of STAT3 in a time- and dose-dependent way, DXM and BTM had no effect on STAT3 phosphorylation. Both DXM and BTM could potentiate IL-6-induced phosphorylation of STAT3. The synergism of glucocorticoids and IL-6 on SP-B gene expression and the effect of glucocorticoids on IL-6-induced STAT3 phosphorylation could be blocked by a JAK inhibitor. Expression level analysis showed that glucocorticoids increased the expression of the IL-6-binding α-subunit receptor (IL-6R) on mRNA and protein level. Our findings could represent an example of a pulmonary regulation system in which one role of glucocorticoids is to increase the effect of a cytokine by upregulation of its receptor. The described in vitro interaction of IL-6 and glucocorticoids could help explain the clinical observation that prenatal inflammation in preterm babies with antenatal steroid administration can attenuate severity of RDS.

Prenatal glucocorticoids improve lung morphology and partially restores surfactant mRNA expression in lambs with diaphragmatic hernia undergoing fetal tracheal occlusion

In fetal sheep with surgically created diaphragmatic hernia (DH), tracheal occlusion (TO) can restore lung growth but does not ameliorate the increase in inter-alveolar wall thickness (T(W)). We determined whether prenatal exposure to glucocorticoids (GC) could reduce T(w) in fetuses with DH undergoing TO. At 65 days of gestation, DH was created in 12 fetal sheep, and TO subsequently performed at 110 days (DH/TO). Six of these fetuses were exposed to betamethasone (DH/TO + GC; 0.5 mg/kg; maternal, IM) 48 hr before delivery; Sham operated fetuses (n = 7) served as controls. At 139 days, we measured alveolar surface density (S(V)), parenchymal tissue fraction, T(W), alveolar type 2 (AE2) cell density and lung surfactant protein (SP) mRNA expression. Prenatal GC decreased T(W) and S(V) by 33% and 27% respectively, and increased fixed lung volume (by 55%), AE2 cell density and partially restored SPmRNA expression. Our data indicate that prenatal exposure to GC can reverse some of the negative effects of prolonged fetal TO. We hypothesize that a GC-induced reduction in lung liquid volume during TO contributes, in part, to the observed increase in AE2 cell density and SPmRNA expression.

Cell Type-specific Differential Induction of the Human γ-Fibrinogen Promoter by Interleukin-6

During an acute phase response, interleukin-6 (IL-6) and glucocorticoids up-regulate expression of the three fibrinogen (FBG) genes (fga, fgb, and fgg) in liver and lung epithelium; however, little constitutive lung expression occurs. Recently, we showed that the magnitude of Stat3 binding to three IL-6 motifs on the human gammaFBG promoter correlates negatively with their functional activity in hepatocytes, although these cis-elements are critical for promoter activity. We determined the role of IL-6-receptor-gp130-Stat3 signaling in IL-6 activation of the gammaFBG promoter in liver and lung epithelial cells. Although IL-6 induced gammaFBG promoter activity approximately 30-fold in HepG2 cells, it was increased only 2-fold in lung A549 cells. Equivalent production of gp130 was demonstrated in both cell types by Western blotting; however, lower production of both IL-6-receptor and Stat3 explains, in part, reduced activity of the gammaFBG promoter in lung cells. Dexamethasone potentiated IL-6 induction of the gammaFBG promoter 2.3-fold in both HepG2 and A549 cells for a combined increase in promoter activity of 70-fold or 4.5-fold, respectively. Dexamethasone potentiation is likely due to the induction of IL-6-receptor expression as well as prolonged intensity and duration of Stat3 activation. By circumventing IL-6-receptor-gp130-coupled signaling with ectopic expression of the granulocyte colony-stimulating factor receptor (GCSFR)-gp130(133) chimeric receptor, overexpression of Stat3 induced gammaFBG promoter activity 30-fold in A549 cells. Together, the data suggest tissue-specific differences in IL-6-receptor-gp130-coupled signaling, thereby limiting the extent of Stat3 activation and gammaFBG expression during lung inflammation.

11Beta-hydroxysteroid dehydrogenase type 2 and the regulation of surfactant protein A by dexamethasone metabolites

Glucocorticoid (GC) metabolism by the 11beta-hydroxysteroid dehydrogenase (HSD) system is an important prereceptor regulator of GC action. The HSD enzymes catalyze the interconversion of the endogenous, biologically active GC cortisol and its inactive 11-dehydro metabolite cortisone. The role of the HSD enzymes in the metabolism of synthetic GCs, such as dexamethasone (Dex), is more complex. The human lung is a classic GC-sensitive organ; however, the roles of the HSD enzymes (HSD1 and HSD2) in the human lung are poorly understood. In the present study, we examined the expression of the HSD enzymes in human adult and fetal lung tissues and the human lung epithelial cell line NCI-H441. We observed that human adult and fetal lung tissues, as well as H441 cells, express HSD2 protein and that it is upregulated by Dex (10(-7) M). By contrast, HSD1 protein was undetectable. We also show that the Dex-mediated regulation of surfactant protein A is attenuated by inhibition of HSD2 activity. Furthermore, we demonstrate that unlike the inactive, 11-dehydro metabolite of cortisol (i.e., cortisone), the 11-dehydro metabolite of Dex, 11-dehydro-Dex, competes for binding to the GC receptor (GR) in human lung epithelial cells and retains GR agonist activity. Together, these data suggest that differences exist in the biological activities of the metabolites of cortisol and Dex.

Characterization of corticosteroid redosing in an in vitro cell line model

OBJECTIVE

The purpose of this study was to investigate dexamethasone redosing as function of time and dose.

STUDY DESIGN

We studied the effect of 48 hours' exposure to various concentrations of dexamethasone in a human pulmonary adenocarcinoma cell line (H-441). We measured the level of surfactant protein B (SP-B) mRNA by quantitative reverse transcription-PCR after initial dexamethasone exposure, and after redosing, 1 or 2 weeks later. Values are mean +/- SE for 5 experiments. Comparisons were made by Mann-Whitney and Kruskal-Wallis test with significance set at P < .05.

RESULTS

Induction of SP-B mRNA was maximal within 48 hours of the initial dexamethasone exposure. Redosing with the same dexamethasone concentration resulted in levels more than double those initially observed. Redosing with dexamethasone concentration 10 times lower had an effect comparable to that of the initial, higher concentration.

CONCLUSION

Our results suggest a residual effect of the initial exposure that potentiates redosing, allowing significant dose reductions.