Association of the proliferation of lung fibroblasts with the ERK1/2 signaling pathway in neonatal rats with hyperoxia-induced lung fibrosis

CXCL10 deficiency limits macrophage infiltration, preserves lung matrix, and enables lung growth in bronchopulmonary dysplasia

Preterm infants with oxygen supplementation are at high risk for bronchopulmonary dysplasia (BPD), a neonatal chronic lung disease. Inflammation with macrophage activation is central to the pathogenesis of BPD. CXCL10, a chemotactic and pro-inflammatory chemokine, is elevated in the lungs of infants evolving BPD and in hyperoxia-based BPD in mice. Here, we tested if CXCL10 deficiency preserves lung growth after neonatal hyperoxia by preventing macrophage activation. To this end, we exposed Cxcl10 knockout (Cxcl10-/-) and wild-type mice to an experimental model of hyperoxia (85% O2)-induced neonatal lung injury and subsequent regeneration. In addition, cultured primary human macrophages and murine macrophages (J744A.1) were treated with CXCL10 and/or CXCR3 antagonist. Our transcriptomic analysis identified CXCL10 as a central hub in the inflammatory network of neonatal mouse lungs after hyperoxia. Quantitative histomorphometric analysis revealed that Cxcl10-/- mice are in part protected from reduced alveolar. These findings were related to the preserved spatial distribution of elastic fibers, reduced collagen deposition, and protection from macrophage recruitment/infiltration to the lungs in Cxcl10-/- mice during acute injury and regeneration. Complimentary, studies with cultured human and murine macrophages showed that hyperoxia induces Cxcl10 expression that in turn triggers M1-like activation and migration of macrophages through CXCR3. Finally, we demonstrated a temporal increase of macrophage-related CXCL10 in the lungs of infants with BPD. In conclusion, our data demonstrate macrophage-derived CXCL10 in experimental and clinical BPD that drives macrophage chemotaxis through CXCR3, causing pro-fibrotic lung remodeling and arrest of alveolarization. Thus, targeting the CXCL10-CXCR3 axis could offer a new therapeutic avenue for BPD.

Development of a novel humanized mouse model to study bronchopulmonary dysplasia

Rationale

The role of circulating fetal monocytes in bronchopulmonary dysplasia is not known. We utilized a humanized mouse model that supports human progenitor cell engraftment (MISTRG) to test the hypothesis that prenatal monocyte programming alters early lung development and response to hyperoxia.

Methods

Cord blood-derived monocytes from 10 human infants were adoptively transferred into newborn MISTRG mice at p0 (1 × 106 cells/mouse, intrahepatic injection) followed by normoxia versus hyperoxia (85% oxygen × 14 days). Lungs were harvested at p14 for alveolar histology (alveolar count, perimeter and area) and vascular parameters (vWF staining for microvessel density, Fulton's index). Human CD45 staining was conducted to compare presence of hematopoietic cells. Murine lung parameters were compared among placebo and monocyte-injected groups. The individual profiles of the 10 patients were further considered, including gestational age (GA; n = 2 term, n = 3 moderate/late preterm, and n = 5 very preterm infants) and preeclampsia (n = 4 patients). To explore the monocyte microenvironment of these patients, 30 cytokines/chemokines were measured in corresponding human plasma by multiplex immunoassay.

Results

Across the majority of patients and corresponding mice, MISTRG alveolarization was simplified and microvessel density was decreased following hyperoxia. Hyperoxia-induced changes were seen in both placebo (PBS) and monocyte-injected mice. Under normoxic conditions, alveolar development was altered modestly by monocytes as compared with placebo (P < 0.05). Monocyte injection was associated with increased microvessel density at P14 as compared with placebo (26.7 ± 0.73 vs. 18.8 ± 1.7 vessels per lung field; P < 0.001). Pooled analysis of patients revealed that injection of monocytes from births complicated by lower GA and preeclampsia was associated with changes in alveolarization and vascularization under normoxic conditions. These differences were modified by hyperoxia. CD45+ cell count was positively correlated with plasma monocyte chemoattractant protein-1 (P < 0.001) and macrophage inflammatory protein-1β (P < 0.01). Immunohistochemical staining for human CD206 and mouse F4/80 confirmed absence of macrophages in MISTRG lungs at P14.

Conclusions

Despite the inherent absence of macrophages in early stages of lung development, immunodeficient MISTRG mice revealed changes in alveolar and microvascular development induced by human monocytes. MISTRG mice exposed to neonatal hyperoxia may serve as a novel model to study isolated effects of human monocytes on alveolar and pulmonary vascular development.

Efficacy and safety of ultra-short wave diathermy on COVID-19 pneumonia: a pioneering study

Background

The ultra-short wave diathermy (USWD) is widely used to ameliorate inflammation of bacterial pneumonia, however, for COVID-19 pneumonia, USWD still needs to be verified. This study aimed to investigate the efficacy and safety of USWD in COVID-19 pneumonia patients.

Methods

This was a single-center, evaluator-blinded, randomized controlled trial. Moderate and severe COVID-19 patients were recruited between 18 February and 20 April 2020. Participants were randomly allocated to receive USWD + standard medical treatment (USWD group) or standard medical treatment alone (control group). The negative conversion rate of SARS-CoV-2 and Systemic Inflammatory Response Scale (SIRS) on days 7, 14, 21, and 28 were assessed as primary outcomes. Secondary outcomes included time to clinical recovery, the 7-point ordinal scale, and adverse events.

Results

Fifty patients were randomized (USWD, 25; control, 25), which included 22 males (44.0%) and 28 females (56.0%) with a mean (SD) age of 53 ± 10.69. The rates of SARS-CoV-2 negative conversion on day 7 (p = 0.066), day 14 (p = 0.239), day 21 (p = 0.269), and day 28 (p = 0.490) were insignificant. However, systemic inflammation by SIRS was ameliorated with significance on day 7 (p = 0.030), day 14 (p = 0.002), day 21 (p = 0.003), and day 28 (p = 0.011). Time to clinical recovery (USWD 36.84 ± 9.93 vs. control 43.56 ± 12.15, p = 0.037) was significantly shortened with a between-group difference of 6.72 ± 3.14 days. 7-point ordinal scale on days 21 and 28 showed significance (p = 0.002, 0.003), whereas the difference on days 7 and 14 was insignificant (p = 0.524, 0.108). In addition, artificial intelligence-assisted CT analysis showed a greater decrease in the infection volume in the USWD group, without significant between-group differences. No treatment-associated adverse events or worsening of pulmonary fibrosis were observed in either group.

Conclusion

Among patients with moderate and severe COVID-19 pneumonia, USWD added to standard medical treatment could ameliorate systemic inflammation and shorten the duration of hospitalization without causing any adverse effects.Clinical Trial Registration: chictr.org.cn, identifier ChiCTR2000029972.

Extracellular Signal-Regulated Kinase 1 Alone Is Dispensable for Hyperoxia-Mediated Alveolar and Pulmonary Vascular Simplification in Neonatal Mice

Bronchopulmonary dysplasia (BPD) is a morbid lung disease distinguished by lung alveolar and vascular simplification. Hyperoxia, an important BPD causative factor, increases extracellular signal-regulated kinases (ERK)-1/2 expression, whereas decreased lung endothelial cell ERK2 expression reduces angiogenesis and potentiates hyperoxia-mediated BPD in mice. However, ERK1′s role in experimental BPD is unclear. Thus, we hypothesized that hyperoxia-induced experimental BPD would be more severe in global ERK1-knockout (ERK1^-/-) mice than their wild-type (ERK1^+/+ mice) littermates. We determined the extent of lung development, ERK1/2 expression, inflammation, and oxidative stress in ERK1^-/- and ERK1^+/+ mice exposed to normoxia (FiO₂ 21%) or hyperoxia (FiO₂ 70%). We also quantified the extent of angiogenesis and hydrogen peroxide (H₂O₂) production in hyperoxia-exposed neonatal human pulmonary microvascular endothelial cells (HPMECs) with normal and decreased ERK1 signaling. Compared with ERK1^+/+ mice, ERK1^-/- mice displayed increased pulmonary ERK2 activation upon hyperoxia exposure. However, the extent of hyperoxia-induced inflammation, oxidative stress, and interrupted lung development was similar in ERK1^-/- and ERK1^+/+ mice. ERK1 knockdown in HPMECs increased ERK2 activation at baseline, but did not affect in vitro angiogenesis and hyperoxia-induced H₂O₂ production. Thus, we conclude ERK1 is dispensable for hyperoxia-induced experimental BPD due to compensatory ERK2 activation.

Effects of the p16/cyclin D1/CDK4/Rb/E2F1 pathway on aberrant lung fibroblast proliferation in neonatal rats exposed to hyperoxia

p16^INK4a (p16) inhibits the vital G₁ to S phase transition during cell cycle progression through the p16/cyclin D1/CDK4/retinoblastoma(Rb)/E2F1 pathway. Hyperoxia can suppress the G₁/S checkpoint and induce more lung fibroblasts (LFs) to transition from the G₁ phase to the S phase and undergo cell proliferation. The present study investigated the rate of p16 gene promoter methylation and the protein expression levels of p16, cyclin D1, CDK4, Rb and E2F1 in LFs from the lungs of rats exposed to hyperoxia and normoxia on postnatal days 3, 7 and 14. In the hyperoxia-exposed group, the methylation rate was 50 and 80% on days 7 and 14, respectively. Cyclin D1 and CDK4 overexpression was associated with p16 loss and Rb inactivation by phosphorylation. Rb phosphorylation induced E2F1 release in the G₁ phase, which promoted cell proliferation. No methylation was observed in the normoxia-exposed group. These observations suggested that p16 loss may stimulate aberrant LF proliferation via the p16/cyclin D1/CDK4/Rb/E2F1 pathway.

ERK1/2 Signaling Pathway Activated by EGF Promotes Proliferation, Transdifferentiation, and Migration of Cultured Primary Newborn Rat Lung Fibroblasts

Background

Bronchopulmonary dysplasia (BPD) is a common and serious complication in premature infants. Lung fibroblasts (LFs) are present in the extracellular matrix and participate in pulmonary development in response to BPD. The aim of this study was to investigate the effect of extracellular signal-regulated kinase (ERK) on LFs cultured from newborn rats. Material and Methods. Primary LFs were isolated and treated with epidermal growth factor (EGF, 20 ng/mL) in the presence or absence of an ERK inhibitor, PD98059 (10 μmol/L). Phosphorylated ERK1/2 (p-ERK1/2) protein levels were determined using immunocytochemistry, western blotting, and real-time reverse transcription quantitative (RT–q)PCR. LF proliferation was examined by flow cytometry and a cell counting kit-8 assay. LF transdifferentiation was examined by protein and mRNA expression of α-smooth muscle actin (α-SMA) by immunocytochemistry, western blotting, and RT–qPCR. LF migration was examined by the transwell method.

Results

Phosphorylated ERK1/2, which was activated by EGF, promoted LF proliferation by accelerating cell-cycle progression from the G1 to S phase. After treatment with PD98059, the expression of p-ERK1/2 in LFs, cellular proliferation, and the percentage of cells in S phase were significantly decreased. Phosphorylated ERK1/2 also promoted the differentiation of LFs into myofibroblasts through increased α-SMA synthesis and migration.

Conclusion

The activation of ERK promotes proliferation, transdifferentiation, and migration of lung fibroblasts from newborn rats.

Tie-2 Cre-Mediated Deficiency of Extracellular Signal-Regulated Kinase 2 Potentiates Experimental Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension in Neonatal Mice

Bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) is a significant lung morbidity of infants, and disrupted lung angiogenesis is a hallmark of this disease. We observed that extracellular signal-regulated kinases (ERK) 1/2 support angiogenesis in vitro, and hyperoxia activates ERK1/2 in fetal human pulmonary microvascular endothelial cells (HPMECs) and in neonatal murine lungs; however, their role in experimental BPD and PH is unknown. Therefore, we hypothesized that Tie2 Cre-mediated deficiency of ERK2 in the endothelial cells of neonatal murine lungs would potentiate hyperoxia-induced BPD and PH. We initially determined the role of ERK2 in in vitro angiogenesis using fetal HPMECs. To disrupt endothelial ERK2 signaling in the lungs, we decreased ERK2 expression by breeding ERK2^flox/flox mice with Tie-Cre mice. One-day-old endothelial ERK2-sufficient (eERK2^+/+) or –deficient (eERK2^+/−) mice were exposed to normoxia or hyperoxia (FiO₂ 70%) for 14 d. We then performed lung morphometry, gene and protein expression studies, and echocardiography to determine the extent of inflammation, oxidative stress, and development of lungs and PH. The knockdown of ERK2 in HPMECs decreased in vitro angiogenesis. Hyperoxia increased lung inflammation and oxidative stress, decreased lung angiogenesis and alveolarization, and induced PH in neonatal mice; however, these effects were augmented in the presence of Tie2-Cre mediated endothelial ERK2 deficiency. Therefore, we conclude that endothelial ERK2 signaling is necessary to mitigate hyperoxia-induced experimental BPD and PH in neonatal mice. Our results indicate that endothelial ERK2 is a potential therapeutic target for the management of BPD and PH in infants.