Regulation of cell proliferation by insulin-like growth factor 1 in hyperoxia-exposed neonatal rat lung

The Role of Insulin Receptor Substrate Proteins in Bronchopulmonary Dysplasia and Asthma: New Potential Perspectives

Insulin receptor substrates (IRSs) are proteins that are involved in signaling through the insulin receptor (IR) and insulin-like growth factor (IGFR). They can also interact with other receptors including growth factor receptors. Thus, they represent a critical node for the transduction and regulation of multiple signaling pathways in response to extracellular stimuli. In addition, IRSs play a central role in processes such as inflammation, growth, metabolism, and proliferation. Previous studies have highlighted the role of IRS proteins in lung diseases, in particular asthma. Further, the members of the IRS family are the common proteins of the insulin growth factor signaling cascade involved in lung development and disrupted in bronchopulmonary dysplasia (BPD). However, there is no study focusing on the relationship between IRS proteins and BPD yet. Unfortunately, there is still a significant gap in knowledge in this field. Thus, in this review, we aimed to summarize the current knowledge with the major goal of exploring the possible roles of IRS in BPD and asthma to foster new perspectives for further investigations.

Alveolar Epithelial Cells Promote IGF-1 Production by Alveolar Macrophages Through TGF-β to Suppress Endogenous Inflammatory Signals

To maintain alveolar gas exchange, the alveolar surface has to limit unnecessary inflammatory responses. This involves crosstalk between alveolar epithelial cells (AECs) and alveolar macrophages (AMs) in response to damaging factors. We recently showed that insulin-like growth factor (IGF)-1 regulates the phagocytosis of AECs. AMs secrete IGF-1 into the bronchoalveolar lavage fluid (BALF) in response to inflammatory stimuli. However, whether AECs regulate the production of IGF-1 by AMs in response to inflammatory signals remains unclear, as well as the role of IGF-1 in controlling the alveolar balance in the crosstalk between AMs and AECs under inflammatory conditions. In this study, we demonstrated that IGF-1 was upregulated in BALF and lung tissues of acute lung injury (ALI) mice, and that the increased IGF-1 was mainly derived from AMs. In vitro experiments showed that the production and secretion of IGF-1 by AMs as well as the expression of TGF-β were increased in LPS-stimulated AEC-conditioned medium (AEC-CM). Pharmacological blocking of TGF-β in AECs and addition of TGF-β neutralizing antibody to AEC-CM suggested that this AEC-derived cytokine mediates the increased production and secretion of IGF-1 from AMs. Blocking TGF-β synthesis or treatment with TGF-β neutralizing antibody attenuated the increase of IGF-1 in BALF in ALI mice. TGF-β induced the production of IGF-1 by AMs through the PI3K/Akt signaling pathway. IGF-1 prevented LPS-induced p38 MAPK activation and the expression of the inflammatory factors MCP-1, TNF-α, and IL-1β in AECs. However, IGF-1 upregulated PPARγ to increase the phagocytosis of apoptotic cells by AECs. Intratracheal instillation of IGF-1 decreased the number of polymorphonuclear neutrophils in BALF of ALI model mice, reduced alveolar congestion and edema, and suppressed inflammatory cell infiltration in lung tissues. These results elucidated a mechanism by which AECs used TGF-β to regulate IGF-1 production from AMs to attenuate endogenous inflammatory signals during alveolar inflammation.

Upregulated IGF‑1 in the lungs of asthmatic mice originates from alveolar macrophages

Asthma is characterized by inflammation and remodeling of the airways. Insulin‑like growth factor-1 (IGF‑1) serves an important role in the repair of lung tissue injury and airway remodeling by elevating collagen and elastin content, increasing the thickness of smooth muscle and promoting the proliferation of lung epithelial and interstitial cells, as well as fibroblasts; however, the content of IGF‑1 and its cellular origin in the lungs of patients with asthma remain unknown. In the present study, a mouse model of asthma was constructed. Following isolation of alveolar macrophages (AMs), the content of IGF‑1 in lung tissue and bronchoalveolar lavage fluid (BALF) was detected by ELISA. The proliferation and phagocytosis of alveolar epithelial cells (AECs) stimulated by IGF‑1 were detected by Cell Counting Kit‑8 method and flow cytometry, respectively. In the present study, IGF‑1 was upregulated in the lung tissues of asthmatic mice, and the content of IGF‑1 in BALF was also elevated. Depletion of AMs by treating mice with 2‑chloroadenosine via nose dripping reversed the increase of IGF‑1 by 80% in lung tissues and by ~100% in BALF of asthmatic mice, suggesting that elevated IGF‑1 in asthmatic mice predominantly originated from AMs. As IGF‑1 promotes the proliferation and phagocytosis of AECs, AM‑derived IGF‑1 may serve an important role in the regulation of airway inflammation and remodeling in asthmatic mice.

Novel functional role of GH/IGF-I in neonatal lung myofibroblasts and in rat lung growth after intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a risk factor for neonatal chronic lung disease (CLD) characterized by reduced alveoli and perturbed matrix remodeling. Previously, our group showed an activation of myofibroblasts and matrix remodeling in rat lungs after IUGR. Because growth hormone (GH) and insulin-like growth factor I (IGF-I) regulate development and growth, we queried 1) whether GH/IGF-I signaling is dysregulated in lungs after IUGR and 2) whether GH/IGF-I signaling is linked to neonatal lung myofibroblast function. IUGR was induced in Wistar rats by isocaloric low-protein diet during gestation. Lungs were obtained at embryonic day (E) 21, postnatal day (P) 3, P12, and P23. Murine embryonic fibroblasts (MEF) or primary neonatal myofibroblasts from rat lungs of control (pnF^Co) and IUGR (pnF^IUGR) were used for cell culture studies. In the intrauterine phase (E21), we found a reduction in GH receptor (GH-R), Stat5 signaling and IGF-I expression in lungs after IUGR. In the postnatal phase (P3-P23), catchup growth after IUGR was linked to increased GH mRNA, GH-R protein, activation of proliferative Stat5/Akt signaling, cyclin D1 and PCNA in rat lungs. On P23, a thickening of the alveolar septae was related to increased vimentin and matrix deposition, indicating fibrosis. In cell culture studies, nutrient deprivation blocked GH-R/IGF-IR signaling and proliferation in MEFs; this was reversed by IGF-I. Proliferation and Stat5 activation were increased in pnF^IUGR. IGF-I and GH induced proliferation and migration of pnF^Co; only IGF-I had these effects on pnF^IUGR. Thus, we show a novel mechanism by which the GH/IGF-I axis in lung myofibroblasts could account for structural lung changes after IUGR.

Insulin-Like Growth Factor-1 Signaling in Lung Development and Inflammatory Lung Diseases

Insulin-like growth factor-1 (IGF-1) was firstly identified as a hormone that mediates the biological effects of growth hormone. Accumulating data have indicated the role of IGF-1 signaling pathway in lung development and diseases such as congenital disorders, cancers, inflammation, and fibrosis. IGF-1 signaling modulates the development and differentiation of many types of lung cells, including airway basal cells, club cells, alveolar epithelial cells, and fibroblasts. IGF-1 signaling deficiency results in alveolar hyperplasia in humans and disrupted lung architecture in animal models. The components of IGF-1 signaling pathways are potentiated as biomarkers as they are dysregulated locally or systemically in lung diseases, whereas data may be inconsistent or even paradoxical among different studies. The usage of IGF-1-based therapeutic agents urges for more researches in developmental disorders and inflammatory lung diseases, as the majority of current data are collected from limited number of animal experiments and are generally less exuberant than those in lung cancer. Elucidation of these questions by further bench-to-bedside researches may provide us with rational clinical diagnostic approaches and agents concerning IGF-1 signaling in lung diseases.

Loss of CD73-mediated extracellular adenosine production exacerbates inflammation and abnormal alveolar development in newborn mice exposed to prolonged hyperoxia

BackgroundHyperoxic lung injury is characterized by cellular damage from high oxygen concentrations that lead to an inflammatory response and it disrupts normal alveolarization in the developing newborn lung. Adenosine is a signaling molecule that is generated extracellularly by ecto-5'-nucleotidase (CD73) in response to injury. Extracellular adenosine signals through cell surface receptors and has been found to have a protective role in acute injury situations; however, chronic elevations have been associated with detrimental changes in chronic lung diseases. We hypothesized that hyperoxia-induced lung injury leads to CD73-mediated increases in extracellular adenosine, which are detrimental to the newborn lung.MethodsC57Bl/6 and CD73-/- mice were exposed to 95% oxygen, 70% oxygen, or room air. Adenosine concentration and markers of pulmonary inflammation and lung development were measured.ResultsExposure to hyperoxia caused pulmonary inflammation and disrupted normal alveolar development in association with increased pulmonary adenosine levels. Loss of CD73-mediated extracellular adenosine production led to decreased survival with exposure to 95% oxygen, and exacerbated pulmonary inflammation and worsened lung development with 70% oxygen exposure.ConclusionExposure to hyperoxia causes lung injury associated with an increase in adenosine concentration, and loss of CD73-mediated adenosine production leads to worsening of hyperoxic lung injury.Pediatric Research advance online publication, 23 August 2017; doi:10.1038/pr.2017.176.

Non-linear actions of physiological agents: Finite disarrangements elicit fitness benefits

Finite disarrangements of important (vital) physiological agents and nutrients can induce plethora of beneficial effects, exceeding mere attenuation of the specific stress. Such response to disrupted homeostasis appears to be universally conserved among species. The underlying mechanism of improved fitness and longevity, when physiological agents act outside their normal range is similar to hormesis, a phenomenon whereby toxins elicit beneficial effects at low doses. Due to similarity with such non-linear response to toxins described with J-shaped curve, we have coined a new term “mirror J-shaped curves” for non-linear response to finite disarrangement of physiological agents. Examples from the clinical trials and basic research are provided, along with the unifying mechanisms that tie classical non-linear response to toxins with the non-linear response to physiological agents (glucose, oxygen, osmolarity, thermal energy, calcium, body mass, calorie intake and exercise). Reactive oxygen species and cytosolic calcium seem to be common triggers of signaling pathways that result in these beneficial effects. Awareness of such phenomena and exploring underlying mechanisms can help physicians in their everyday practice. It can also benefit researchers when designing studies and interpreting growing number of scientific data showing non-linear responses to physiological agents.

Postnatal growth restriction augments oxygen-induced pulmonary hypertension in a neonatal rat model of bronchopulmonary dysplasia

BACKGROUND

Prematurity and fetal growth restriction are risk factors for pulmonary hypertension (PH) in infants with bronchopulmonary dysplasia (BPD). Neonatal rats develop PH and vascular remodeling when exposed to hyperoxia. We hypothesize that postnatal growth restriction (PNGR) due to under-nutrition increases the severity of PH induced by hyperoxia in neonatal rats.

METHODS

Pups were randomized at birth to litters maintained in room air or 75% oxygen (hyperoxia), together with litters of normal milk intake (10 pups) or PNGR (17 pups). After 14 d, right ventricular hypertrophy (RVH) was assessed by Fulton's index (right ventricular weight/left ventricular plus septal weight) and PH by echocardiography. Lungs were analyzed by immunohistochemistry, morphometrics, western blotting, and metabolomics.

RESULTS

Hyperoxia and PNGR each significantly increased pulmonary arterial pressure, RVH and pulmonary arterial medial wall thickness, and significantly decreased pulmonary vessel number. These changes were significantly augmented in pups exposed to both insults. Hyperoxia and PNGR both significantly decreased expression of proteins involved in lung development and vasodilation.

CONCLUSION

PNGR induces right ventricular and pulmonary vascular remodeling and augments the effects of oxygen in neonatal rats. This may be a powerful tool to investigate the mechanisms that induce PH in low-birth-weight preterm infants with BPD.

Role of IGF-1 pathway in lung fibroblast activation

Background

IGF-1 is elevated in pulmonary fibrosis and acute lung injury, where fibroblast activation is a prominent feature. We previously demonstrated that blockade of IGF pathway in murine model of lung fibrosis improved outcome and decreased fibrosis. We now expand that study to examine effects of IGF pathway on lung fibroblast behaviors that could contribute to fibrosis.

Methods

We first examined mice that express αSMA promoter upstream of GFP reporter treated with A12, a blocking antibody to IGF-1 receptor, after bleomycin induced lung injury. We then examined the effect of IGF-1 alone, or in combination with the pro-fibrotic cytokine TGFβ on expression of markers of myofibroblast activation in vitro, including αSMA, collagen α1, type 1, collagen α1, type III, and TGFβ expression.

Results

After bleomycin injury, we found decreased number of αSMA-GFP + cells in A12 treated mice, validated by αSMA immunofluorescent staining. We found that IGF-1, alone or in combination with TGF-β, did not affect αSMA RNA expression, promoter activity, or protein levels when fibroblasts were cultured on stiff substrate. IGF-1 stimulated Col1a1 and Col3a1 expression on stiff substrate. In contrast, IGF-1 treatment on soft substrate resulted in upregulation of αSMA gene and protein expression, as well as Col1a1 and Col3a1 transcripts. In conclusion, IGF-1 stimulates differentiation of fibroblasts into a myofibroblast phenotype in a soft matrix environment and has a modest effect on αSMA stress fiber organization in mouse lung fibroblasts.

The IGF-I/IGF-R1 pathway regulates postnatal lung growth and is a nonspecific regulator of alveologenesis in the neonatal rat

IGF-I, IGF-II, and the IGF-I receptor are widely distributed throughout the neonatal rat lung on days 4, 7, 10, and 14 of life, with a similar abundance at each of these time points. Injection of 20 μg/g of a truncated soluble IGF-I receptor on days 2 and 5 of life, to decoy ligand away from the endogenous IGF-I receptor, reduced lung weight and lung-to-body weight ratio, reduced lung tissue fraction, and impaired alveolar formation, as assessed by secondary crest formation and mean linear intercepts on day 7 of life. Lung procollagen I content and elastin fiber density were also reduced. Injection of 100 μg/day of neutralizing anti-IGF-I, to prevent IGF-I from binding to the IGF-I receptor, on days 3, 4, and 5 of life reduced tissue fraction and elastin fiber density and impaired alveolar formation on day 6 of life. Both interventions reduced total lung cell and secondary crest cell DNA synthesis and small vessel counts per unit area, but these effects were lost after normalization to the reduced tissue fraction. These findings are consistent with a role for IGF-I binding to the IGF-I receptor in postnatal lung growth and on alveologenesis through a nonspecific positive effect on DNA synthesis. Injection of 100 μg/day of neutralizing anti-IGF-II, to prevent IGF-II from binding to the IGF-I receptor, on days 3, 4, and 5 of life had no effect on total lung cell DNA synthesis per unit area on day 6 of life, and a role for IGF-II in postnatal alveologenesis was not further pursued.

Effect of insulin-like growth factor blockade on hyperoxia-induced lung injury

Insulin-like growth factor (IGF)-1 is increased in different models of acute lung injury, and is an important determinant of survival and proliferation in many cells. We previously demonstrated that treatment of mice with IGF-1 receptor-blocking antibody (A12) improved early survival in bleomycin-induced lung injury. We have now examined whether administration of A12 improved markers of lung injury in hyperoxia model of lung injury. C57BL/6 mice underwent intraperitoneal administration of A12 or control antibody (keyhole limpet hemocyanin [KLH]), then were exposed to 95% hyperoxia for 88-90 hours. Mice were killed and bronchoalveolar lavage (BAL) and lung tissue were obtained for analysis. Hyperoxia caused a significant increase in IGF levels in BAL and lung lysates. Peripheral blood neutrophils expressed IGF-1R at baseline and after hyperoxia. BAL neutrophils from hyperoxia-treated mice and patients with acute lung injury also expressed cell surface IGF-1R. A12-treated mice had significantly decreased polymorphonuclear cell (PMN) count in BAL compared with KLH control mice (P = 0.02). BAL from A12-treated mice demonstrated decreased PMN chemotactic activity compared with BAL from KLH-treated mice. Pretreatment of PMNs with A12 decreased their chemotactic response to BAL from hyperoxia-exposed mice. Furthermore, IGF-1 induced a dose-dependent chemotaxis of PMNs. There were no differences in other chemotactic cytokines in BAL, including CXCL1 and CXCL2. In summary, IGF blockade decreased PMN recruitment to the alveolar space in a mouse model of hyperoxia. Furthermore, the decrease in BAL PMNs was at least partially due to a direct effect of A12 on PMN chemotaxis.

Vitamin A and retinoic acid act synergistically to increase lung retinyl esters during normoxia and reduce hyperoxic lung injury in newborn mice

We have shown that vitamin A (VA) and retinoic acid (RA) synergistically increase lung retinyl ester content in neonatal rats. To confirm whether this biochemical synergism attenuates early neonatal hyperoxic lung injury in mice, we exposed newborn C57BL/6 mice to 95% O2 or air from birth to 4 d. The agent [vehicle, VA, RA, or the combination vitamin A+retinoic acid (VARA)] was given orally daily. Lung and liver retinyl ester content was measured, and lung injury and development were evaluated. We observed that lung, but not liver, retinyl ester levels were increased more by VARA than by VA or RA alone. Hyperoxic lung injury was reduced by VA and RA, and more so by VARA. VARA attenuated the hyperoxia-induced increases in macrophage inflammatory protein (MIP)-2 mRNA and protein expression, but did not alter hyperoxia-induced effects on peptide growth factors (PDGF, VEGF, and TGF-beta1). The 4-d exposure to hyperoxia or retinoids did not lead to observable differences in lung development. We conclude that the VARA combination has synergistic effects on lung retinyl ester concentrations and on the attenuation of hyperoxia-induced lung injury in newborn mice, possibly by modulation of inflammatory mediators.

Diabetes, insulin, and development of acute lung injury

OBJECTIVES

Recently, many studies have investigated the immunomodulatory effects of insulin and glucose control in critical illness. This review examines evidence regarding the relationship between diabetes and the development of acute lung injury/acute respiratory distress syndrome (ALI/ARDS), reviews studies of lung injury related to glycemic and nonglycemic metabolic features of diabetes, and examines the effect of diabetic therapies.

DATA SOURCES AND STUDY SELECTION

A MEDLINE/PubMed search from inception to August 1, 2008, was conducted using the search terms acute lung injury, acute respiratory distress syndrome, hyperglycemia, diabetes mellitus, insulin, hydroxymethylglutaryl-CoA reductase inhibitors (statins), angiotensin-converting enzyme inhibitor, and peroxisome proliferator-activated receptors, including combinations of these terms. Bibliographies of retrieved articles were manually reviewed.

DATA EXTRACTION AND SYNTHESIS

Available studies were critically reviewed, and data were extracted with special attention to the human and animal studies that explored a) diabetes and ALI; b) hyperglycemia and ALI; c) metabolic nonhyperglycemic features of diabetes and ALI; and d) diabetic therapies and ALI.

CONCLUSIONS

Clinical and experimental data indicate that diabetes is protective against the development of ALI/ARDS. The pathways involved are complex and likely include effects of hyperglycemia on the inflammatory response, metabolic abnormalities in diabetes, and the interactions of therapeutic agents given to diabetic patients. Multidisciplinary, multifaceted studies, involving both animal models and clinical and molecular epidemiology techniques, are essential.

ErbB4 regulates fetal surfactant phospholipid synthesis in primary fetal rat type II cells

Insufficient fetal surfactant production leads to respiratory distress syndrome among preterm infants. Neuregulin signals the onset of fetal surfactant phospholipid synthesis through formation of erbB receptor dimers. We hypothesized that erbB4 downregulation in fetal type II epithelial cells will downregulate not only fetal surfactant phospholipid synthesis, but also affect proliferation and erbB receptor localization. We tested these hypotheses using small interfering RNA (siRNA) directed against the erbB4 gene to silence erbB4 receptor function in cultures of primary day 19 fetal rat lung type II cells. ErbB4 siRNA treatment inhibited erbB4 receptor protein expression, fibroblast-conditioned medium induced erbB4 phosphorylation, and fetal surfactant phospholipid synthesis. Cell proliferation, measured as thymidine incorporation, was also inhibited by erbB4 siRNA treatment. Downregulation of erbB4 receptor protein changed erbB1 localization at baseline and after stimulation, as determined by confocal microscopy and subcellular fractionation. We conclude that erbB4 is an important receptor in the control of fetal lung type II cell maturation.

Insulin-like Growth Factor-I signaling mechanisms, type I collagen and alpha smooth muscle actin in human fetal lung fibroblasts

Bronchial wall remodeling is a major morbidity component in oxidant injury in bronchopulmonary dysplasia (BPD) and asthma.

HYPOTHESIS

IGF-1 enhances alpha smooth muscle expression and collagen synthesis in developing lung fibroblasts leading to fibrosis through nuclear NF-(k)B -dependent transcription. We studied NF-(k)B dependent transcription by transfecting HFLF with a NF-(k)B responsive promoter driving the luciferase gene and treating with IGF-1 (100 ng/mL) and measuring luciferase activity. We exposed cells to the PI-3 kinase inhibitor or the Erk1/2 inhibitor one hr before stimulating with IGF-1. We also used IGF-1 receptor antibody to inhibit the action of IGF-1 and studied its effect on alpha-sma and type I collagen. IGF-1 treatment significantly increased luciferase activity. This was attenuated by PI-3 kinase and MAP-Kinase inhibitors. Western blot analysis showed PI-3 kinase mediates IGF-1 activation of NF-(k)B independent of I(K)B phosphorylation. We found an up-regulation of phospho NF-kB in the nuclear extract compared with total NFKB showing that IGF-1 regulates NF-(k)B transcriptional activity downstream of NF-(k)B nuclear translocation. IGF-1-induced increase in alpha-sma expression and type-I collagen was significantly inhibited by pretreatment with LY294002 and IGF-1 receptor antibody. IGF-1 cell signaling leading to collagen synthesis in fetal lung fibroblasts is mediated by PI3 Kinase acting through NF-(k)B in HFLF.

Expression profile of IGF system during lung injury and recovery in rats exposed to hyperoxia: a possible role of IGF-1 in alveolar epithelial cell proliferation and differentiation

Although several studies have shown that an induction of insulin-like growth factor (IGF) components occurs during hyperoxia-mediated lung injury, the role of these components in tissue repair is not well known. The present study aimed to elucidate the role of IGF system components in normal tissue remodeling. We used a rat model of lung injury and remodeling by exposing rats to > 95% oxygen for 48 h and allowing them to recover in room air for up to 7 days. The mRNA expression of IGF-I, IGF-II, and IGF-1 receptor (IGF-1R) increased during injury. However, the protein levels of these components remained elevated until day 3 of the recovery and were highly abundant in alveolar type II cells. Among IGF binding proteins (IGFBPs), IGFBP-5 mRNA expression increased during injury and at all the recovery time points. IGFBP-2 and -3 mRNA were also elevated during injury phase. In an in vitro model of cell differentiation, the expression of IGF-I and IGF-II increased during trans-differentiation of alveolar epithelial type II cells into type-I like cells. The addition of anti-IGF-1R and anti-IGF-I antibodies inhibited the cell proliferation and trans-differentiation to some extent, as evident by cell morphology and the expression of type I and type II cell markers. These findings demonstrate that the IGF signaling pathway plays a critical role in proliferation and differentiation of alveolar epithelium during tissue remodeling.

Differential response of the epithelium and interstitium in developing human fetal lung explants to hyperoxia

Hyperoxia is closely linked with the development of chronic lung disease of prematurity (CLD), but the exact mechanisms whereby hyperoxia alters the lung architecture in the developing lung remain largely unknown. We developed a fetal human lung organ culture model to investigate (a) the morphologic changes induced by hyperoxia and (b) whether hyperoxia resulted in differential cellular responses in the epithelium and interstitium. The effects of hyperoxia on lung morphometry were analyzed using computer-assisted image analysis. The lung architecture remained largely unchanged in normoxia lasting as long as 4 d. In contrast, hyperoxic culture of pseudoglandular fetal lungs resulted in significant dilatation of airways, thinning of the epithelium, and regression of the interstitium including the pulmonary vasculature. Although there were no significant differences in Ki67 between normoxic and hyperoxic lungs, activated caspase-3 was significantly increased in interstitial cells, but not epithelial cells, under hyperoxic conditions. These changes show that exposure of pseudoglandular lungs to hyperoxia modulates the lung architecture to resemble saccular lungs.

Modulation of IGF-binding protein-2 and -3 in hyperoxic injury in developing rat lung

Retinoids play an important role in lung development and repair. We showed that retinoic acid (RA) inhibits O(2)-induced fibroblast proliferation in rat lung explants. IGF-1, which enhances the proliferation of human fetal lung fibroblasts and stimulates collagen production during lung injury, has an important role in the lung injury/repair process. Interactions of IGF-1 with its receptor are modulated by IGF-binding proteins IGFBPs. We hypothesized that RA alters IGFBP-2 and -3 in hyperoxia-exposed neonatal lung and alters collagen production. Neonatal rat lungs were cultured in room air or 95% O(2) and 5% CO(2) for 3 d with or without RA. IGFBP-2 and -3 were measured both in culture medium and in lung tissue. Type I collagen and procollagen propeptide were analyzed in the lung tissue. Hyperoxia induced an increase in type I collagen that was significantly inhibited in the presence of RA. IGFBP-2 and IGFBP-3 in the lungs were decreased in hyperoxia but significantly increased in hyperoxia plus RA. In the culture medium, IGFBP-2 and -3 were not increased with hyperoxia but significantly increased in the presence of RA plus hyperoxia. There was no increase in IGFBP-3 RNA transcript after RA treatment in either room air or O(2) exposure. In conclusion, RA modulates the secreted IGFBP-2 and -3 during O(2) exposure and inhibits the increase in collagen that occurs during lung injury. We speculate that RA protects against O(2)-induced neonatal lung injury through modulation of the IGFBPs.

Deranged Kv channel regulation in fibroblasts from mice lacking the serum and glucocorticoid inducible kinase SGK1

Coexpression of the serum and glucocorticoid inducible kinase 1 (SGK1) up-regulates Kv channel activity in Xenopus oocytes and human embryonic kidney cells. To investigate the physiological impact of SGK1 dependent Kv channel regulation, we recorded whole-cell currents in lung fibroblasts from SGK1 knockout mice (sgk1-/-) and wild-type littermates (sgk1+/+). Serum-grown mouse lung fibroblasts (MLF) from both genotypes exhibited voltage-gated outwardly rectifying K(+)-currents with time-dependent activation (tau(act) approximately 3 msec), slow inactivation (tau(inact) approximately 700 msec), use-dependent inactivation, and (partial) inhibition by K(+) channel blockers TEA, 4-AP, and margatoxin. In serum grown MLF peak Kv current density at +100 mV was significantly lower in sgk1-/- (14 +/- 2 pA/pF, n = 13) than in sgk1+/+ (31 +/- 4 pA/pF, n = 16). PCR amplification of different Kv1 and Kv3 subunits from mouse fibroblasts demonstrated the expression of Kv1.1-1.7, Kv3.1, and Kv3.3 mRNA in both sgk1+/+ and sgk1-/- cells. Upon serum deprivation Kv currents almost disappeared in sgk1+/+ (4 +/- 1 pA/pF, n = 11) but not in sgk1-/- (10 +/- 1 pA/pF, n = 6) MLF. Accordingly, following serum deprivation Kv current density was significantly lower in sgk1+/+ than in sgk1-/-. Stimulation of serum-depleted cells with dexamethasone (dex) (1 microM, 1 day), IGF-1 (6.7 microM, 4-6 h) or both, significantly activated Kv currents in sgk1+/+ but not in sgk1-/- MLF. In the presence of both, dex and IGF-1, the Kv current density was significantly larger in sgk1+/+ (27 +/- 3 pA/pF, n = 12) than in sgk1-/- (13 +/- 3 pA/pF, n = 10) cells. Similar to MLF, Kv currents were significantly higher in sgk1+/+ mouse tail fibroblasts (MTF). In sgk1+/+ but not sgk1-/- MTF the Kv currents were inhibited upon serum deprivation and reincreased after stimulation of serum deprived MTF with dex (1 microM, 1 day) and afterwards with IGF-1 (6.7 microM, 4-6 h). According to Fura-2-fluorescence capacitative Ca(2+) entry was lower in sgk1-/- MTF compared to sgk1+/+ MTF. Upon serum deprivation capacitative Ca(2+) entry decreased significantly in sgk1+/+ but not in sgk1-/- MTF. Stimulation of depleted cells with dex (1 microM, 1 day) and afterwards with IGF-1 (6.7 microM, 4-6 h) reincreased capacitative Ca(2+) entry in sgk1+/+ MTF, whereas in sgk1-/- cells it remained unchanged. In conclusion, lack of SGK1 does not abrogate Kv channel activity but abolishes regulation of those channels by serum, glucocorticoids and IGF-1, an effect influencing capacitative Ca(2+) entry.

Control mechanisms of lung alveolar development and their disorders in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that occurs in very premature infants and is characterized by impaired alveologenesis. This ultimate phase of lung development is mostly postnatal and allows growth of gas-exchange surface area to meet the needs of the organism. Alveologenesis is a highly integrated process that implies cooperative interactions between interstitial, epithelial, and vascular compartments of the lung. Understanding of its underlying mechanisms has considerably progressed recently with identification of structural, signaling, or remodeling molecules that are crucial in the process. Thus, the pivotal role of elastin deposition in lung walls has been demonstrated, and many key control-molecules have been identified, including various transcription factors, growth factors such as platelet-derived growth factor, fibroblast growth factors, and vascular endothelial growth factor, matrix-remodeling enzymes, and retinoids. BPD-associated changes in lung expression/content have been evidenced for most of these molecules, especially for signaling pathways, through both clinical investigations in premature infants and the use of animal models, including the premature baboon or lamb, neonatal exposure to hyperoxia in rodents, and maternal-fetal infection. These findings open therapeutic perspectives to correct imbalanced signaling. Unraveling the intimate molecular mechanisms of alveolar building appears as a prerequisite to define new strategies for the prevention and care of BPD.

Deficiency in type 1 insulin-like growth factor receptor in mice protects against oxygen-induced lung injury

Background

Cellular responses to aging and oxidative stress are regulated by type 1 insulin-like growth factor receptor (IGF-1R). Oxidant injury, which is implicated in the pathophysiology of a number of respiratory diseases, acutely upregulates IGF-1R expression in the lung. This led us to suspect that reduction of IGF-1R levels in lung tissue could prevent deleterious effects of oxygen exposure.

Methods

Since IGF-1R null mutant mice die at birth from respiratory failure, we generated compound heterozygous mice harboring a hypomorphic (Igf-1r^neo) and a knockout (Igf-1r^-) receptor allele. These IGF-1R^neo/- mice, strongly deficient in IGF-1R, were subjected to hyperoxia and analyzed for survival time, ventilatory control, pulmonary histopathology, morphometry, lung edema and vascular permeability.

Results

Strikingly, after 72 h of exposure to 90% O₂, IGF-1R^neo/- mice had a significantly better survival rate during recovery than IGF-1R^+/+ mice (77% versus 53%, P < 0.05). The pulmonary injury was consistently, and significantly, milder in IGF-1R^neo/- mice which developed conspicuously less edema and vascular extravasation than controls. Also, hyperoxia-induced abnormal pattern of breathing which precipitated respiratory failure was elicited less frequently in the IGF-1R^neo/- mice.

Conclusion

Together, these data demonstrate that a decrease in IGF-1R signaling in mice protects against oxidant-induced lung injury.

Gene silencing in alveolar type II cells using cell-specific promoter in vitro and in vivo

RNA interference (RNAi) is a sequence-specific post-transcriptional gene silencing process. Although it is widely used in the loss-of-function studies, none of the current RNAi technologies can achieve cell-specific gene silencing. The lack of cell specificity limits its usage in vivo. Here, we report a cell-specific RNAi system using an alveolar epithelial type II cell-specific promoter--the surfactant protein C (SP-C) promoter. We show that the SP-C-driven small hairpin RNAs specifically depress the expression of the exogenous reporter (enhanced green fluorescent protein) and endogenous genes (lamin A/C and annexin A2) in alveolar type II cells, but not other lung cells, using cell and organ culture in vitro as well as in vivo. The present study provides an efficient strategy in silencing a gene in one type of cell without interfering with other cell systems, and may have a significant impact on RNAi therapy.

Regulation of the voltage gated K+ channel Kv1.3 by the ubiquitin ligase Nedd4-2 and the serum and glucocorticoid inducible kinase SGK1

The stimulation of cell proliferation by insulin like growth factor IGF-1 has previously been shown to depend on activation of voltage gated K(+) channels. The signaling involved in activation of voltage gated K(+) channel Kv1.3 includes the phosphatidylinositol-3 (PI3) protein kinase, 3-phosphoinositide dependent protein kinase PDK1 and the serum and glucocorticoid inducible kinase SGK1. However, nothing is known about mechanisms mediating the stimulation of Kv1.3 by SGK1. Most recently, SGK1 has been shown to phosphorylate and thus inactivate the ubiquitin ligase Nedd4-2. The present study has been performed to explore whether the regulation of Kv1.3 involves Nedd4-2. To this end Kv1.3 has been expressed in Xenopus oocytes with or without coexpression of Nedd4-2 and/or constitutively active (S422D)SGK1. In oocytes expressing Kv1.3 but not in water injected oocytes, depolarization from a holding potential of -80 mV to +20 mV triggers rapidly inactivating currents typical for Kv1.3. Coexpression of Nedd4-2 decreases, coexpression of (S422D)SGK1 enhances the currents significantly. The effects of either Nedd4-2 or of SGK1 are abrogated by destruction of the respective catalytic subunits ((C938S)Nedd4-2 or (K127N)SGK1). Further experiments revealed that wild type SGK1 and SGK3 and to a lesser extent SGK2 are similarly effective in stimulating Kv1.3 in both, presence and absence of Nedd4-2. It is concluded that Kv1.3 is downregulated by Nedd4-2 and stimulates by SGK1, SGK2, and SGK3. The data thus disclose a novel mechanism of Kv1.3 channel regulation.