Hypoxia-induced inhibition of lung development is attenuated by the peroxisome proliferator-activated receptor-γ agonist rosiglitazone

Hypoxia enhances transforming growth factor-β (TGF-β) signaling, inhibiting alveolar development and causing abnormal pulmonary arterial remodeling in the newborn lung. We hypothesized that, during chronic hypoxia, reduced peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling may contribute to, or be caused by, excessive TGF-β signaling. To determine whether PPAR-γ was reduced during hypoxia, C57BL/6 mice were exposed to hypoxia from birth to 2 wk and evaluated for PPAR-γ mRNA and protein. To determine whether rosiglitazone (RGZ, a PPAR-γ agonist) supplementation attenuated the effects of hypoxia, mice were exposed to air or hypoxia from birth to 2 wk in combination with either RGZ or vehicle, and measurements of lung histology, function, parameters related to TGF-β signaling, and collagen content were made. To determine whether excessive TGF-β signaling reduced PPAR-γ, mice were exposed to air or hypoxia from birth to 2 wk in combination with either TGF-β-neutralizing antibody or vehicle, and PPAR-γ signaling was evaluated. We observed that hypoxia reduced PPAR-γ mRNA and protein, in association with impaired alveolarization, increased TGF-β signaling, reduced lung compliance, and increased collagen. RGZ increased PPAR-γ signaling, with improved lung development and compliance in association with reduced collagen and TGF-β signaling. However, no reduction was noted in hypoxia-induced pulmonary vascular remodeling. Inhibition of hypoxia-enhanced TGF-β signaling increased PPAR-γ signaling. These results suggest that hypoxia-induced inhibition of lung development is associated with a mutually antagonistic relationship between reduced PPAR-γ and increased TGF-β signaling. PPAR-γ agonists may be of potential therapeutic significance in attenuating TGF-β signaling and improving alveolar development.     

Transforming growth factor-β regulates endothelin-1 signaling in the newborn mouse lung during hypoxia exposure

We have previously shown that inhibition of transforming growth factor-β (TGF-β) signaling attenuates hypoxia-induced inhibition of alveolar development and abnormal pulmonary vascular remodeling in the newborn mice and that endothelin-A receptor (ETAR) antagonists prevent and reverse the vascular remodeling. The current study tested the hypothesis that inhibition of TGF-β signaling attenuates endothelin-1 (ET-1) expression and thereby reduces effects of hypoxia on the newborn lung. C57BL/6 mice were exposed from birth to 2 wk of age to either air or hypoxia (12% O(2)) while being given either BQ610 (ETAR antagonist), BQ788 (ETBR antagonist), 1D11 (TGF-β neutralizing antibody), or vehicle. Lung function and development and TGF-β and ET-1 synthesis were assessed. Hypoxia inhibited alveolar development, decreased lung compliance, and increased lung resistance. These effects were associated with increased TGF-β synthesis and signaling and increased ET-1 synthesis. BQ610 (but not BQ788) improved lung function, without altering alveolar development or increased TGF-β signaling in hypoxia-exposed animals. Inhibition of TGF-β signaling reduced ET-1 in vivo, which was confirmed in vitro in mouse pulmonary endothelial, fibroblast, and epithelial cells. ETAR blockade improves function but not development of the hypoxic newborn lung. Reduction of ET-1 via inhibition of TGF-β signaling indicates that TGF-β is upstream of ET-1 during hypoxia-induced signaling in the newborn lung.     

Transforming growth factor-beta signaling mediates hypoxia-induced pulmonary arterial remodeling and inhibition of alveolar development in newborn mouse lung

Hypoxia causes abnormal neonatal pulmonary artery remodeling (PAR) and inhibition of alveolar development (IAD). Transforming growth factor (TGF)-beta is an important regulator of lung development and repair from injury. We tested the hypothesis that inhibition of TGF-beta signaling attenuates hypoxia-induced PAR and IAD. Mice with an inducible dominant-negative mutation of the TGF-beta type II receptor (DNTGFbetaRII) and nontransgenic wild-type (WT) mice were exposed to hypoxia (12% O(2)) or air from birth to 14 days of age. Expression of DNTGFbetaRII was induced by 20 microg/g ZnSO(4) given intraperitoneally daily from birth. PAR, IAD, cell proliferation, and expression of extracellular matrix (ECM) proteins were assessed. In WT mice, hypoxia led to thicker, more muscularized resistance pulmonary arteries and impaired alveolarization, accompanied by increases in active TGF-beta and phosphorylated Smad2. Hypoxia-induced PAR and IAD were greatly attenuated in DNTGFbetaRII mice given ZnSO(4) compared with WT control mice and DNTGFbetaRII mice not given ZnSO(4). The stimulatory effects of hypoxic exposure on pulmonary arterial cell proliferation and lung ECM proteins were abrogated in DNTGFbetaRII mice given ZnSO(4). These data support the conclusion that TGF-beta plays an important role in hypoxia-induced pulmonary vascular adaptation and IAD in the newborn animal model.     

A Sub-population of Group A Streptococcus Elicits a Population-wide Production of Bacteriocins to Establish Dominance in the Host

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Nitric Oxide Administration Using an Oxygen Hood: A Pilot Trial

Background

We have shown earlier that inhaled nitric oxide (iNO) administered by oxygen hood reduces pulmonary hypertension in an animal model (J Perinatol 2002; 22:50-6). Our objective in this study was to determine feasibility of iNO by oxygen hood in neonates with elevated alveolar-arterial oxygen gradients (A-aDO₂).

Methods/Principal Findings

Masked randomized controlled pilot trial. Inclusion criteria were: gestation≥34 weeks, age<7 days, with post-ductal arterial line, and A-aDO₂ 400–600. Infants were randomized to study gas (iNO 20 ppm or equivalent O₂ flow) for 1 hr which was then weaned over the next 4 hours. Primary outcome was PaO₂ one hour post-randomization. Four infants each were randomized to iNO or O₂ (controls). Two of the four infants given iNO had an increase in PaO₂ of >100 torr, while oxygenation was unchanged in the controls. Methemoglobinemia and other adverse effects were not noted in any infant. Environmental levels of NO and NO₂ were minimal (<1 ppm) at >0.3 m from the hood.

Conclusions

Administration of iNO by oxygen hood is feasible. Larger randomized controlled trials are required to measure the efficacy and determine an appropriate target population for this technique.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00041548","term_id":"NCT00041548"}}NCT00041548     

De Novo Mutations in Moderate or Severe Intellectual Disability

Genetics is believed to have an important role in intellectual disability (ID). Recent studies have emphasized the involvement of de novo mutations (DNMs) in ID but the extent to which they contribute to its pathogenesis and the identity of the corresponding genes remain largely unknown. Here, we report a screen for DNMs in subjects with moderate or severe ID. We sequenced the exomes of 41 probands and their parents, and confirmed 81 DNMs affecting the coding sequence or consensus splice sites (1.98 DNMs/proband). We observed a significant excess of de novo single nucleotide substitutions and loss-of-function mutations in these cases compared to control subjects, suggesting that at least a subset of these variations are pathogenic. A total of 12 likely pathogenic DNMs were identified in genes previously associated with ID (ARID1B, CHD2, FOXG1, GABRB3, GATAD2B, GRIN2B, MBD5, MED13L, SETBP1, TBR1, TCF4, WDR45), resulting in a diagnostic yield of ∼29%. We also identified 12 possibly pathogenic DNMs in genes (HNRNPU, WAC, RYR2, SET, EGR1, MYH10, EIF2C1, COL4A3BP, CHMP2A, PPP1CB, VPS4A, PPP2R2B) that have not previously been causally linked to ID. Interestingly, no case was explained by inherited mutations. Protein network analysis indicated that the products of many of these known and candidate genes interact with each other or with products of other ID-associated genes further supporting their involvement in ID. We conclude that DNMs represent a major cause of moderate or severe ID.     

ABO Blood Group Is Associated with Response to Inhaled Nitric Oxide in Neonates with Respiratory Failure

Background

Inhaled nitric oxide (iNO) reduces death or need for extracorporeal membrane oxygenation (ECMO) in infants with persistent pulmonary hypertension of the newborn (PPHN). However, the response to iNO is variable and only 50–60% of infants demonstrate a response to iNO. It is not known why only some infants respond to iNO. Adults and children with blood groups B or AB do not respond as well to iNO as those with blood groups O/A.

Methods/Principal Findings

To determine if blood group was associated with iNO response in newborn infants, a retrospective medical record review was done of infants admitted to a regional NICU from 2002-9 with a diagnosis of PPHN. Data were collected during the first twelve hours post-initiation of treatment. Of 86 infants diagnosed with PPHN, 23 infants had blood group A [18 received iNO], 21 had group B [18 with iNO], 40 had group O [36 with iNO], and 2 had group AB [both received iNO]. Change in PaO₂/FiO₂ was less in infants with blood group A, of whom less than half were responders (ΔPaO₂/FiO₂>20%) at 12 h versus 90% of infants with either O or B. Race, sex, birth weight, gestational age, Apgar scores at 1 and 5 minutes, and baseline PaO₂/FiO₂ were similar among groups. Outcomes including need for ECMO, death, length of ventilatory support, length of iNO use, and hospital stay were statistically not different by blood groups.

Conclusions/Significance

Our results indicate that blood group influences iNO response in neonates. We hypothesize that either there is genetic linkage of the ABO gene locus with vasoregulatory genes, or that blood group antigens directly affect vascular reactivity.     

Atrial natriuretic peptide-dependent modulation of hypoxia-induced pulmonary vascular remodeling

Hypoxic stress upsets the balance in the normal relationships between mitogenic and growth inhibiting pathways in lung, resulting in pulmonary vascular remodeling characterized by hyperplasia of pulmonary arterial smooth muscle cells (PASMCs) and fibroblasts and enhanced deposition of extracellular matrix. Atrial natriuretic peptide (ANP) reduces pulmonary vascular resistance and attenuates hypoxia-induced pulmonary hypertension in vivo and PASMC proliferation and collagen synthesis in vitro. The current study utilized an ANP null mouse model (Nppa-/-) to test the hypothesis that ANP modulates the pulmonary vascular and alveolar remodeling response to normobaric hypoxic stress. Nine-10 wk old male ANP null (Nppa-/-) and wild type nontransgenic (NTG) mice were exposed to chronic hypoxia (10% O(2), 1 atm) or air for 6 wks. Measurement: pulmonary hypertension, right ventricular hypertrophy, and pulmonary arterial and alveolar remodeling were assessed. Hypoxia-induced pulmonary arterial hypertrophy and muscularization were significantly increased in Nppa-/- mice compared to NTG controls. Furthermore, the stimulatory effects of hypoxia on alveolar myofibroblast transformation (8.2 and 5.4 fold increases in Nppa-/- and NTG mice, respectively) and expression of extracellular matrix molecule (including osteopontin [OPN] and periostin [PN]) mRNA in whole lung were exaggerated in Nppa-/- mice compared to NTG controls. Combined with our previous finding that ANP signaling attenuates transforming growth factor (TGF)-beta-induced expression of OPN and PN in isolated PASMCs, the current study supports the hypothesis that endogenous ANP plays an important anti-fibrogenic role in the pulmonary vascular adaptation to chronic hypoxia.     

SNO-hemoglobin is not essential for red blood cell-dependent hypoxic vasodilation

The coupling of hemoglobin sensing of physiological oxygen gradients to stimulation of nitric oxide (NO) bioactivity is an established principle of hypoxic blood flow. One mechanism proposed to explain this oxygen-sensing-NO bioactivity linkage postulates an essential role for the conserved Cys93 residue of the hemoglobin beta-chain (betaCys93) and, specifically, for S-nitrosation of betaCys93 to form S-nitrosohemoglobin (SNO-Hb). The SNO-Hb hypothesis, which conceptually links hemoglobin and NO biology, has been debated intensely in recent years. This debate has precluded a consensus on physiological mechanisms and on assessment of the potential role of SNO-Hb in pathology. Here we describe new mouse models that exclusively express either human wild-type hemoglobin or human hemoglobin in which the betaCys93 residue is replaced with alanine to assess the role of SNO-Hb in red blood cell-mediated hypoxic vasodilation. Substitution of this residue, precluding hemoglobin S-nitrosation, did not change total red blood cell S-nitrosothiol abundance but did shift S-nitrosothiol distribution to lower molecular weight species, consistent with the loss of SNO-Hb. Loss of betaCys93 resulted in no deficits in systemic or pulmonary hemodynamics under basal conditions and, notably, did not affect isolated red blood cell-dependent hypoxic vasodilation. These results demonstrate that SNO-Hb is not essential for the physiologic coupling of erythrocyte deoxygenation with increased NO bioactivity in vivo.