Analysis of the microRNA signature driving adaptive right ventricular hypertrophy in an ovine model of congenital heart disease.

The right ventricular (RV) response to pulmonary arterial hypertension (PAH) is heterogeneous. Most patients have maladaptive changes with RV dilation and RV failure, whereas some, especially patients with PAH secondary to congenital heart disease, have an adaptive response with hypertrophy and preserved systolic function. Mechanisms for RV adaptation to PAH are unknown, despite RV function being a primary determinant of mortality. In our congenital heart disease ovine model with fetally implanted aortopulmonary shunt (shunt lambs), we previously demonstrated an adaptive physiological RV response to increased afterload with hypertrophy. In the present study, we examined small noncoding microRNA (miRNA) expression in shunt RV and characterized downstream effects of a key miRNA. RV tissue was harvested from 4-wk-old shunt and control lambs ( n = 5), and miRNA, mRNA, and protein were quantitated. We found differential expression of 40 cardiovascular-specific miRNAs in shunt RV. Interestingly, this miRNA signature is distinct from models of RV failure, suggesting that miRNAs might contribute to adaptive RV hypertrophy. Among RV miRNAs, miR-199b was decreased in the RV with eventual downregulation of nuclear factor of activated T cells/calcineurin signaling. Furthermore, antifibrotic miR-29a was increased in the shunt RV with a reduction of the miR-29 targets collagen type A1 and type 3A1 and decreased fibrosis. Thus, we conclude that the miRNA signature specific to shunt lambs is distinct from RV failure and drives gene expression required for adaptive RV hypertrophy. We propose that the adaptive RV miRNA signature may serve as a prognostic and therapeutic tool in patients with PAH to attenuate or prevent progression of RV failure and premature death. NEW & NOTEWORTHY This study describes a novel microRNA signature of adaptive right ventricular hypertrophy, with particular attention to miR-199b and miR-29a.

Claudin-18 deficiency results in alveolar barrier dysfunction and impaired alveologenesis in mice.

Claudins are a family of transmembrane proteins that are required for tight junction formation. Claudin (CLDN)-18.1, the only known lung-specific tight junction protein, is the most abundant claudin in alveolar epithelial type (AT) 1 cells, and is regulated by lung maturational agonists and inflammatory mediators. To determine the function of CLDN18 in the alveolar epithelium, CLDN18 knockout (KO) mice were generated and studied by histological, biochemical, and physiological approaches, in addition to whole-genome microarray. Alveolar epithelial barrier function was assessed after knockdown of CLDN18 in isolated lung cells. CLDN18 levels were measured by quantitative PCR in lung samples from fetal and postnatal human infants. We found that CLDN18 deficiency impaired alveolar epithelial barrier function in vivo and in vitro, with evidence of increased paracellular permeability and architectural distortion at AT1-AT1 cell junctions. Although CLDN18 KO mice were born without evidence of a lung abnormality, histological and gene expression analysis at Postnatal Day 3 and Week 4 identified impaired alveolarization. CLDN18 KO mice also had evidence of postnatal lung injury, including acquired AT1 cell damage. Human fetal lungs at 23-24 weeks gestational age, the highest-risk period for developing bronchopulmonary dysplasia, a disease of impaired alveolarization, had significantly lower CLDN18 expression relative to postnatal lungs. Thus, CLDN18 deficiency results in epithelial barrier dysfunction, injury, and impaired alveolarization in mice. Low expression of CLDN18 in human fetal lungs supports further investigation into a role for this tight junction protein in bronchopulmonary dysplasia.

Vascular endothelial growth factor isoform and receptor expression during compensatory lung growth.

BACKGROUND: Vascular endothelial growth factor (VEGF) is required for blood vessel formation during lung growth and repair. Alteration of VEGF isoform expression has been demonstrated in response to fetal tracheal occlusion and in models of lung injury. The purpose of this study was to investigate VEGF expression during compensatory lung growth in the mouse. METHODS: Under general anesthesia, adult mice underwent left thoracotomy with (n = 5) or without (sham, n = 5) pneumonectomy. The right lungs were harvested at 1, 3, and 7 d after the operation. Lung-to-body weight ratio as well as total DNA and protein content were measured. VEGF protein expression was analyzed by Western blot and ELISA. VEGF isoform expression was evaluated using semi-quantitative PCR followed by Imagequant optical densitometry. Values were compared by Student's t-test and ANOVA using Fisher's protected least significant difference post-hoc test where appropriate. RESULTS: Compensatory lung growth was observed as measured by increases in right lung-to-body weight ratio and in DNA and protein content. Total VEGF RNA and protein expression did not change after pneumonectomy. However, on post-operative day 1, there was a decrease in the relative percentage of VEGF188 mRNA (P < 0.01), and an increase in the relative percentage of VEGF164 mRNA (P = 0.05). At 3 d postpneumonectomy, low relative VEGF188 expression persisted (P < 0.05), VEGF164 expression normalized, and relative VEGF120 expression increased (P < 0.01). Isoform expression in the pneumonectomy animals was identical to sham animals by the seventh d. There were no differences observed in VEGF receptor expression. CONCLUSION: During compensatory lung growth, we have observed an early postoperative reversion of VEGF isoform expression to the pattern seen during fetal lung development and in lung injury models.

Congenital diaphragmatic hernia prevents absorption of distal air space fluid in late-gestation rat fetuses.

We hypothesized that congenital diaphragmatic hernia (CDH) may decrease distal air space fluid absorption due to immaturity of alveolar epithelial cells from a loss of the normal epithelial Na+ transport, as assessed by amiloride and epithelial Na+ channel (ENaC) and Na-K-ATPase expression, as well as failure to respond to endogenous epinephrine as assessed by propranolol. Timed-pregnant dams were gavage fed 100 mg of nitrofen at 9.5-day gestation to induce CDH in the fetuses, and distal air space fluid absorption experiments were carried out on 22-day gestation (term) fetuses. Controls were nitrofen-exposed fetuses without CDH. Absorption of distal air space fluid was measured from the increase in 131I-albumin concentration in an isosmolar, physiological solution instilled into the developing lungs. In controls, distal air space fluid absorption was rapid and mediated by beta-adrenoceptors as demonstrated by reversal to fluid secretion after propranolol. Normal lung fluid absorption was also partially inhibited by amiloride. In contrast, CDH fetuses continued to show lung fluid secretion, and this secretion was not affected by either propranolol or amiloride. CDH lungs showed a 67% reduction in alpha-ENaC and beta-ENaC expression, but no change in alpha1-Na-K-ATPase expression. These studies demonstrate: 1) CDH delays lung maturation with impaired distal air space fluid absorption secondary to inadequate Na+ uptake by the distal lung epithelium that results in fluid-filled lungs at birth with reduced capacity to establish postnatal breathing, and 2) the main stimulus to lung fluid absorption in near-term control fetuses, elevated endogenous epinephrine levels, is not functional in CDH fetuses.

Changes in fetal lung distension alter expression of vascular endothelial growth factor and its isoforms in developing rat lung.

Vascular endothelial growth factor A (VEGF-A) is essential for normal pulmonary vascular and parenchymal development. Changes in fetal lung distension profoundly affect lung growth and maturation, including vascular development. To define developmental lung expression of VEGF-A and its receptors and investigate effects of changes in fetal lung distension, we studied fetal rats at embryonic day (ED) 16, 19, and 22, postnatal rats at postnatal day (PD) 5, 10, and 21, and adult rats. We used reverse transcriptase PCR to measure mRNA expression for VEGF-A isoforms (VEGF-A(120), (-144), (-164), and (-188)) and VEGF-A receptors, Flt-1 and Flk-1. With advancing development, mRNA content increased only for VEGF-A(188) (p < 0.05) and for Flt-1 (p < 0.02) and Flk-1 (p < 0.005). As a percentage of total VEGF-A mRNA, VEGF-A(188) (15% at ED 16) increased to become the dominant isoform at PD 21 (40%, p < 0.005) and adulthood; in contrast, there were decreases in both VEGF-A(144) (p < 0.05) and (-120) (p < 0.005). VEGF-A protein was expressed in alveolar epithelium (type I and II cells) and interstitium. Increasing fetal lung distension by tracheal occlusion (TO) accelerated the normal maturational pattern of VEGF-A isoforms and increased VEGF-A protein; decreasing fetal lung distension by congenital diaphragmatic hernia (CDH) retarded the normal developmental pattern and decreased VEGF-A protein. Neither TO nor CDH consistently affected Flt-1 or Flk-1 mRNA content. These results show that mechanical factors significantly affect lung VEGF-A expression and suggest that VEGF-A mediates previously described changes in lung vascular and parenchymal development caused by CDH and by TO.

Congenital diaphragmatic hernia, tracheal occlusion, thyroid transcription factor-1, and fetal pulmonary epithelial maturation.

Congenital diaphragmatic hernia (CDH) occurs in approximately 1:2,500 human births and has high morbidity and mortality rates, primarily due to pulmonary hypoplasia and pulmonary hypertension. Tracheal occlusion (TO), in experimental animals, distends lungs and increases lung growth and alveolar type I cell maturation but decreases surfactant components and reduces alveolar type II cell density. We examined effects of CDH and CDH+TO on lung growth and maturation in fetal rats. To induce CDH, we administered nitrofen (100 mg) to dams at 9.5 days of gestation. We compared lungs from fetuses with CDH, CDH+TO, and those exposed to nitrofen without CDH. CDH decreased lung wet weight bilaterally (P < 0.0001) and DNA content in lung ipsilateral to CDH (P < 0.05). CDH+TO significantly increased lung wet weights bilaterally; DNA content was intermediate between CDH and NC. To evaluate effects on the distal pulmonary epithelium, we examined surfactant mRNA and protein levels, type I and II cell-specific markers (RTI(40) and RTII(70), respectively), and transcriptional regulator thyroid transcription factor-1 (TTF-1). Decreased lung distension (due to CDH) increased SP-C mRNA and TTF-1 protein expression and reduced RTI(40) (P < 0.05 for all). Increased lung distension (due to CDH+TO) reduced expression of SP mRNAs and pro-SP-C and TTF-1 proteins and enhanced expression of RTI(40) (mRNA and protein; P < 0.05 for all). We conclude that CDH+TO partially reverses effects of CDH; it corrects the pulmonary hypoplasia and restores type I cell differentiation but adversely affects SP expression in type II cells. These effects may be mediated through changes in TTF-1 expression.

Nitric oxide decreases surfactant protein gene expression in primary cultures of type II pneumocytes.

Inhaled nitric oxide (NO) is a selective pulmonary vasodilator effective in treating persistent pulmonary hypertension in newborns and in infants following congenital heart disease surgery. Recently, multiple in vivo and in vitro studies have shown a negative effect of NO on surfactant activity as well as surfactant protein gene expression. Although the relationship between NO and surfactant has been studied previously, the data has been hard to interpret due to the model systems used. The objective of the current study was to characterize the effect of NO on surfactant protein gene expression in primary rat type II pneumocytes cultured on a substratum that promoted the maintenance of type II cell phenotype. Exposure to a NO donor, S-nitroso-N-acetylpenicillamine (SNAP), decreased surfactant protein (SP)-A, (SP)-B, and (SP)-C mRNA levels in type II pneumocytes in a time- and dose-dependent manner. The effect was mediated in part by an increase in endothelin-1 secretion and a decrease in the intracellular messenger, phosphorylated ERK1/2 mitogen-activated protein kinases (MAPK). Exposing type II pneumocytes to endothelin-1 receptor antagonists PD-156707 or bosentan before exposure to SNAP partially prevented the decrease in surfactant protein gene expression. The results showed that NO mediated the decrease in surfactant protein gene expression at least in part through an increase in endothelin-1 secretion and a decrease in phosphorylated ERK1/2 MAPKs.

Ontogeny of poly(ADP-ribose) polymerase-1 in lung and developmental implications.

Poly(ADP-ribose) polymerase 1 (PARP-1) is the predominant NAD-dependent modifying enzyme in DNA repair, transcription, and apoptosis; its involvement in development has not been defined. Here, we report expression and cellular localization of PARP-1 in developing rat and human fetal lung, in vivo and in explant culture, and effects of inhibiting PARP-1 activity on lung surfactant protein (SP) expression. PARP-1 was expressed as 113-kD (p113) and 85-kD (p85) fragment in both rat and human lung. In rat lung, p113 content by Western was maximal at Embryonic Days 16-18, decreased sharply by Embryonic Day 20, and continued to decrease postnatally. p85 level was constant in the fetus and decreased postnatally. In human fetal lung, both PARP-1 mRNA expression and protein content changed little between 15 and 24 wk. Immunohistochemistry for PARP-1 in Embryonic Day 18 rat lung showed predominantly nuclear staining in most cells. In later gestation and postnatally, PARP-1 staining was primarily cytoplasmic and progressively restricted to a subset of cells, mainly bronchial epithelial and smooth muscle cells. Cell subfractionation showed that p113 localized to nucleus and p85 to cytoplasm. Inhibition of PARP-1 activity by 5-iodo-6-amino-1,2-benzopyrone in fetal rat lung explant culture did not affect SP-A and -B mRNA, but significantly increased SP-C mRNA. These findings indicate that in lung (i) PARP-1 is abundantly expressed during fetal development; (ii) p113 and p85 levels are differentially regulated; (iii) PARP-1 undergoes complex developmental changes in cellular and subcellular expression, including extensive cytoplasmic localization; and (iv) inhibition of PARP-1 activity differentially affects expression of SPs.

Maternally administered dexamethasone transiently increases apoptosis in lungs of fetal rats.

In late gestation, morphological maturation of fetal lung includes septal thinning of potential airspaces, a process accelerated by exogenous glucocorticoids. Apoptosis occurs in normal fetal lung. Glucocorticoids increase apoptosis in several tissues. The authors hypothesized that exogenous glucocorticoids would increase apoptosis in fetal lung, primarily in the interstitium. They administered dexamethasone (DEX), 1 mg/kg, or vehicle (Control) to pregnant rats at 19 days of gestation. Fetuses were delivered at 3, 7, 12, or 24 hours post injection. DEX decreased fetal body weight and lung weight, DNA, and protein 12 hours post injection. Using the terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) reaction to label apoptotic cells in lung, they calculated an apoptotic index (AI, apoptotic cells/1000 total cells) for each fetus. Average DEX AI (3.6+/-2.6, mean+/-SD) was greater than Control (1.7+/-0.5) (P<.02). All DEX AIs were greater than Control AIs at 3, 7, and 12 hours, but were similar to Controls at 24 hours post injection. Apoptotic cells appeared to be interstitial, based on colocalization with vimentin staining. Presence of apoptotic cells was confirmed by electron microscopy and detection of the nucleosomal ladder pattern on DNA electrophoresis. The authors conclude that maternal administration of dexamethasone increases apoptosis in fetal lung, primarily in the interstitium. They speculate that apoptosis may contribute to morphological fetal lung maturation induced by endogenous glucocorticoids.

Tracheal occlusion stimulates cell cycle progression and type I cell differentiation in lungs of fetal rats.

Fetal tracheal occlusion (TO) has been reported to stimulate lung growth but decreases number and maturation of type II cells, effects that vary with gestational age and duration of TO. We examined effects of a novel method of TO (unipolar microcautery to seal the trachea) produced at 19.5-20 days (d) of gestation in fetal rats; fetuses were delivered at term, 22 d. Controls were sham operated and unoperated littermates. TO increased wet lung weight but not dry lung weight or lung DNA and protein. To evaluate further the effects of TO, we examined the cell cycle regulators, cyclins D1 and A, in fetal lungs. Cyclin D1 increased with TO (P < 0.005). TO also increased expression of the type I epithelial cell marker RTI40 (mRNA and protein). TO decreased mRNA for surfactant proteins (SP)-A and -C but did not affect protein levels of SP-A and -B and of RTII70, a type II epithelial cell marker. We conclude that TO by microcautery, even of short duration, has diverse pulmonary effects including stimulating increased levels of cyclin D1 with probable cell cycle progression, type I cell differentiation, and possibly inhibiting type II cell function.

Effects of oligohydramnios on lung growth and maturation in the fetal rat.

Oligohydramnios (OH) retards fetal lung growth by producing less lung distension than normal. To examine effects of decreased distension on fetal lung development, we produced OH in rats by puncture of uterus and fetal membranes at 16 days of gestation; fetuses were delivered at 21 or 22 days of gestation. Controls were position-matched littermates in the opposite uterine horn. OH lungs had lower weights and less DNA, protein, and water, but no differences in saturated phosphatidylcholine, surfactant proteins (SP)-A and -B, and mRNA for SP-A, -B, -C, and -D. To evaluate effects on epithelial differentiation, we used RTI(40) and RTII(70), proteins specific in lung to luminal surfaces of alveolar type I and II cells, respectively. At 22 days of gestation, OH lungs had less RTI(40) mRNA (P < 0.05) and protein (P < 0.001), but RTII(70) did not differ from controls. With OH, type I cells (in proportion to type II cells) covered less distal air space perimeter (P < 0.01). We conclude that OH, which retards lung growth, has little effect on surfactant and impedes formation of type I cells relative to type II cells.

Distal air space epithelial fluid clearance in near-term rat fetuses is fast and requires endogenous catecholamines.

Knowledge about the conversion of the epithelium in the distal air spaces of the lung from secretion to absorption is imperative to the understanding of postnatal lung development; little such information is available in rats. Distal air space fluid clearance was therefore measured in 21- to 22-day gestation rat fetuses and newborn (40 h) rats. Distal air space fluid clearance was measured from the increase in (131)I-albumin concentration in an isosmolar, physiological solution instilled into the developing lungs. There was no net fluid movement across the distal air space epithelium in the lungs of 21-day gestation fetuses. Twenty-four hours later, distal air space fluid was cleared at a rapid rate in the 22-day gestation fetuses. Within the first 40 h after birth, the rate rapidly declined to adult levels. The high distal air space fluid clearance at 22 days gestation and at 40 h after birth was mediated by beta-adrenergic receptors as demonstrated by elevated plasma epinephrine levels and inhibition by propranolol. Interestingly, the elevated distal air space fluid clearance in the 22-day gestation fetuses was only minimally amiloride sensitive; however, amiloride sensitivity increased over the first 40 h after birth. In conclusion, these studies demonstrate that 1) rapid rates of net alveolar fluid clearance occur late in gestation in the rat and 2) this clearance is driven by elevations of endogenous epinephrine.