Localization and potential role of matrix metalloproteinase-1 and tissue inhibitors of metalloproteinase-1 and -2 in different phases of bronchopulmonary dysplasia

Single-Cell RNA Sequencing-Based Characterization of Resident Lung Mesenchymal Stromal Cells in Bronchopulmonary Dysplasia

Late lung development is a period of alveolar and microvascular formation, which is pivotal in ensuring sufficient and effective gas exchange. Defects in late lung development manifest in premature infants as a chronic lung disease named bronchopulmonary dysplasia (BPD). Numerous studies demonstrated the therapeutic properties of exogenous bone marrow and umbilical cord-derived mesenchymal stromal cells (MSCs) in experimental BPD. However, very little is known regarding the regenerative capacity of resident lung MSCs (L-MSCs) during normal development and in BPD. In this study we aimed to characterize the L-MSC population in homeostasis and upon injury. We used single-cell RNA sequencing (scRNA-seq) to profile in situ Ly6a+ L-MSCs in the lungs of normal and O2-exposed neonatal mice (a well-established model to mimic BPD) at 3 developmental timepoints (postnatal days 3, 7, and 14). Hyperoxia exposure increased the number and altered the expression profile of L-MSCs, particularly by increasing the expression of multiple pro-inflammatory, pro-fibrotic, and anti-angiogenic genes. In order to identify potential changes induced in the L-MSCs transcriptome by storage and culture, we profiled 15 000 Ly6a+ L-MSCs after in vitro culture. We observed great differences in expression profiles of in situ and cultured L-MSCs, particularly those derived from healthy lungs. Additionally, we have identified the location of Ly6a+/Col14a1+ L-MSCs in the developing lung and propose Serpinf1 as a novel, culture-stable marker of L-MSCs. Finally, cell communication analysis suggests inflammatory signals from immune and endothelial cells as main drivers of hyperoxia-induced changes in L-MSCs transcriptome.

Expression of SP-C and Ki67 in lungs of preterm infants dying from respiratory distress syndrome

This study aimed at exploring the expression of Surfactant protein-C (SP-C) and Ki67 in autopsy lung tissues of premature infants dying from respiratory distress syndrome (RDS) who were exposed to mechanical ventilation and elevated oxygen concentrations. The possible influence of pulmonary surfactant (PS) on the expression of SP-C and Ki67 was also investigated. Thirty preterm infants were selected who were histologically and clinically diagnosed as RDS. Preterm infants with RDS were divided into 4 groups, according to the time of death: infants ventilated for 1–3 days, 4–8 days, 9–16 days and >6 days. Five premature infants died within 1 day after delivery for non- pulmonary reasons served as controls. The expression of SP-C and Ki67 in lungs was detected by immunohistochemistry. Compared with the control group, the expression of SP-C and Ki67 in RDS infants decreased significantly after 1–3 days of ventilation, but increased after 4 days and reached peak value after 9–16 days. No significant difference in the expression of SP-C and Ki67 was found between infants treated with PS and those without. Thus our results suggest SP-C and Ki67 may have participated in the pulmonary pathological process in ventilated/oxygen treated preterm infants with RDS, and exogenous surfactant had no effect on the expression of SP-C and Ki67 in the lungs of ventilated/oxygen treated preterm infants with RDS.

Inhibition of TGF-β signaling and decreased apoptosis in IUGR-associated lung disease in rats

Intrauterine growth restriction is associated with impaired lung function in adulthood. It is unknown whether such impairment of lung function is linked to the transforming growth factor (TGF)-β system in the lung. Therefore, we investigated the effects of IUGR on lung function, expression of extracellular matrix (ECM) components and TGF-β signaling in rats. IUGR was induced in rats by isocaloric protein restriction during gestation. Lung function was assessed with direct plethysmography at postnatal day (P) 70. Pulmonary activity of the TGF-β system was determined at P1 and P70. TGF-β signaling was blocked in vitro using adenovirus-delivered Smad7. At P70, respiratory airway compliance was significantly impaired after IUGR. These changes were accompanied by decreased expression of TGF-β1 at P1 and P70 and a consistently dampened phosphorylation of Smad2 and Smad3. Furthermore, the mRNA expression levels of inhibitors of TGF-β signaling (Smad7 and Smurf2) were reduced, and the expression of TGF-β-regulated ECM components (e.g. collagen I) was decreased in the lungs of IUGR animals at P1; whereas elastin and tenascin N expression was significantly upregulated. In vitro inhibition of TGF-β signaling in NIH/3T3, MLE 12 and endothelial cells by adenovirus-delivered Smad7 demonstrated a direct effect on the expression of ECM components. Taken together, these data demonstrate a significant impact of IUGR on lung development and function and suggest that attenuated TGF-β signaling may contribute to the pathological processes of IUGR-associated lung disease.

Conditional overexpression of connective tissue growth factor disrupts postnatal lung development

Connective tissue growth factor (CTGF) is a member of an emerging family of immediate-early gene products that coordinates complex biological processes during development, differentiation, and tissue repair. Overexpression of CTGF is associated with mechanical ventilation with high tidal volume and oxygen exposure in newborn lungs. However, the role of CTGF in postnatal lung development and remodeling is not well understood. In the present study, a double-transgenic mouse model was generated with doxycycline-inducible overexpression of CTGF in respiratory epithelial cells. Overexpression of CTGF from Postnatal Days 1-14 resulted in thicker alveolar septa and decreased secondary septal formation. This is correlated with increased myofibroblast differentiation and disorganized elastic fiber deposition in alveolar septa. Overexpression of CTGF also decreased alveolar capillary network formation. There were increased alpha-smooth muscle actin expression and collagen deposition, and dramatic thickening in the peribronchial/peribronchiolar and perivascular regions in the double-transgenic lungs. Furthermore, overexpression of CTGF increased integrin-linked kinase expression, activated its downstream signaling target, Akt, as well as increased mRNA expression of fibronectin. These data demonstrate that overexpression of CTGF disrupts alveologenesis and capillary formation, and induces fibrosis during the critical period of alveolar development. These histologic changes are similar to those observed in lungs of infants with bronchopulmonary dysplasia.

[Oxidative stress in the neonatal lung disease]

Oxidative stress is a risk factor for bronchopulmonary dysplasia in the preterm newborn. Antioxidant defense is impaired in the preterm newborn. Oxidative stress is also involved in cell growth and development. The relationship between oxidative stress and cell growth needs to be understood before antioxidant therapy can be routinely introduced. Several antioxidant therapies have been unsuccessfully tried until now. This review highlights the importance of oxygen free radicals in the pathogenesis of bronchopulmonary dysplasia.

Matrix metalloprotease-9 dysregulation in lower airway secretions of cystic fibrosis patients

Matrix metalloproteases (MMPs) are proteolytic enzymes that regulate extracellular matrix turnover and aid in restoring tissue architecture following injury. There is an emerging role for extracellular matrix destruction in the pathogenesis of chronic neutrophilic lung diseases. In this study, we examined the expression and activity profiles of MMPs in lower airway secretions from cystic fibrosis (CF) patients, patients with acute respiratory failure (ARF), and normal controls. A discrete repertoire of MMP isoforms was found in the CF samples, with robust MMP-9 expression compared with normal controls and ARF. CF samples possessed increased levels of active MMP-9, as well as decreased amounts of tissue inhibitor of metalloprotease-1 (TIMP-1), a natural inhibitor of MMP-9. The CF inpatient samples demonstrated fully active MMP-9 activity compared with CF outpatients, ARF, and normal controls. CF samples also demonstrated increased human neutrophil elastase (HNE) levels compared with ARF and normal controls. To examine potential mechanisms for the protease dysregulation seen in the CF clinical samples, in vitro studies demonstrated that HNE could activate pro-MMP-9 and also degrade TIMP-1; this HNE-based activation, however, was not seen with MMP-8. A strong correlation was seen between HNE and MMP-9 activity in CF inpatient samples. Finally, the dysregulated MMP-9 activity seen in CF inpatient sputum samples could be significantly reduced by the use of MMP-9 inhibitors. Collectively, these findings further emphasize the proposed protease/antiprotease imbalance in chronic neutrophilic lung disease, providing a potential mechanism contributing to this proteolytic dysregulation.

Bombesin-like peptides modulate alveolarization and angiogenesis in bronchopulmonary dysplasia

RATIONALE

The incidence of bronchopulmonary dysplasia (BPD), a chronic lung disease of newborns, is paradoxically rising despite medical advances. We demonstrated elevated bombesin-like peptide levels in infants that later developed BPD. In the 140-day hyperoxic baboon model of BPD, anti-bombesin antibody 2A11 abrogated lung injury.

OBJECTIVES

To test the hypothesis that bombesin-like peptides mediate BPD in extremely premature baboons (born at Gestational Day 125 and given oxygen pro re nata [PRN], called the 125-day PRN model), similar to "modern-day BPD."

METHODS

The 125-day animals were treated with 2A11 on Postnatal Day 1 (P1), P3, and P6. On P14 and P21, lungs were inflation-fixed for histopathologic analyses of alveolarization. Regulation of angiogenesis by bombesin was evaluated using cultured pulmonary microvascular endothelial cells.

MEASUREMENTS AND MAIN RESULTS

In 125-day PRN animals, urine bombesin-like peptide levels at P2-3 are directly correlated with impaired lung function at P14. Gastrin-releasing peptide (the major pulmonary bombesin-like peptide) mRNA was elevated eightfold at P1 and remained high thereafter. At P14, 2A11 reduced alveolar wall thickness and increased the percentage of secondary septa containing endothelial cells. At P21, 2A11-treated 125-day PRN animals had improved alveolarization according to mean linear intercepts and number of branch points per millimeter squared. Bombesin promoted tubulogenesis of cultured pulmonary microvascular endothelial cells, but cocultured fetal lung mesenchymal cells abrogated this effect.

CONCLUSIONS

Early bombesin-like peptide overproduction in 125-day PRN animals predicted alveolarization defects weeks later. Bombesin-like peptide blockade improved septation, with the greatest effects at P21. This could have implications for preventing BPD in premature infants.

Matrix metalloproteinase-9 and tissue inhibitor of matrix metalloproteinase-1 in the respiratory tracts of human infants following paramyxovirus infection

Respiratory syncytial (RSV) and parainfluenza (PIV) viruses are primary causes of acute bronchiolitis and wheezing illnesses in infants and young children. To further understand inflammation in the airways following infection, we tested for the presence of matrix metalloproteinases (MMP) and natural tissue inhibitors of MMP (TIMP) in primary and established human cell lines, and in the nasopharyngeal secretions (NPS) of human infants infected with RSV or PIV. Using ELISA and multiplex-based assays, MMP-9 and TIMP-1 proteins were, respectively, detected in 66/67 and 67/67 NPS. During PIV or RSV infection TIMP-1 concentrations were associated with hypoxic bronchiolitis. TIMP-1 amounts were also negatively correlated with O2 saturation, and positively correlated with IL-6, MIP-1alpha, and G-CSF amounts following RSV infection. IL-6, MIP-1alpha, and G-CSF were negatively correlated with O2 saturation during RSV infection. Acute respiratory tract disease was not associated with MMP-9 protein/protease activity. Additional studies using real-time quantitative PCR suggested that MMP-9 mRNA copy numbers were elevated in normal human bronchial epithelial (NHBE) cells infected with RSV, while TIMP-1 and TIMP-2 were not increased. However, ELISA did not reveal MMP-9 protein in the NHBE cell culture supernatants. Hence, the data implied that airway epithelial cells were not the primary source of MMP or TIMP following paramyxovirus infection. Taken together, the data suggested that paramyxovirus infection perturbs MMP-9/TIMP-1 homeostasis that in turn may contribute to the severity of respiratory tract disease.

Matrix metalloproteinases in lung: multiple, multifarious, and multifaceted

The matrix metalloproteinases (MMPs), a family of 25 secreted and cell surface-bound neutral proteinases, process a large array of extracellular and cell surface proteins under normal and pathological conditions. MMPs play critical roles in lung organogenesis, but their expression, for the most part, is downregulated after generation of the alveoli. Our knowledge about the resurgence of the MMPs that occurs in most inflammatory diseases of the lung is rapidly expanding. Although not all members of the MMP family are found within the lung tissue, many are upregulated during the acute and chronic phases of these diseases. Furthermore, potential MMP targets in the lung include all structural proteins in the extracellular matrix (ECM), cell adhesion molecules, growth factors, cytokines, and chemokines. However, what is less known is the role of MMP proteolysis in modulating the function of these substrates in vivo. Because of their multiplicity and substantial substrate overlap, MMPs are thought to have redundant functions. However, as we explore in this review, such redundancy most likely evolved as a necessary compensatory mechanism given the critical regulatory importance of MMPs. While inhibition of MMPs has been proposed as a therapeutic option in a variety of inflammatory lung conditions, a complete understanding of the biology of these complex enzymes is needed before we can reasonably consider them as therapeutic targets.

Effects of recombinant Clara cell secretory protein (rhCC10) on inflammatory-related matrix metalloproteinase activity in a preterm lamb model of neonatal respiratory distress

OBJECTIVE

To test the hypothesis that recombinant Clara cell secretory protein (rhCC10) instillation would foster improved lung function, acute structural preservation, and attenuation of matrix metalloproteinase (MMP) activity in a surfactant-deficient, mechanically ventilated lung.

DESIGN

Interventional laboratory study.

SETTING

An academic medical research facility in the northeastern United States.

SUBJECTS

Sedated, ventilated premature lambs.

INTERVENTIONS

Preterm lambs (n = 18; 126 +/- 3 days gestation) were instrumented, ventilated, and treated with 100 mg/kg exogenous surfactant. Lambs were randomized to receive 0, 0.5, or 5.0 mg/kg rhCC10 (n = 6 per group) and were ventilated for 4 hrs.

MEASUREMENTS AND MAIN RESULTS

Posttreatment, lung function and cardiopulmonary stability were monitored for the ventilation period and then animals were killed for in vitro surfactant function analysis, lung histomorphometry, and analysis of MMP-2, -7, and -9 as well as their tissue inhibitors (TIMP)-1 and -2. Ventilation efficiency and pulmonary compliance were improved in the 5.0-mg/kg rhCC10 group by 4 hrs. Lung expansion was variable in the apical regions only. MMP-2 quantity was greater in the apical than the base lung regions of rhCC10-treated groups, and rhCC10 decreased MMP-7 in the base of the lung.

CONCLUSIONS

These data suggest that improved lung function in the surfactant-treated preterm lamb following intratracheal rhCC10 may be related to the reduction of proteolytic activity of MMP-7.

Hyperoxia modulates TGF-beta/BMP signaling in a mouse model of bronchopulmonary dysplasia

Prematurely born infants who require oxygen therapy often develop bronchopulmonary dysplasia (BPD), a debilitating disorder characterized by pronounced alveolar hypoplasia. Hyperoxic injury is believed to disrupt critical signaling pathways that direct lung development, causing BPD. We investigated the effects of normobaric hyperoxia on transforming growth factor (TGF)-beta and bone morphogenetic protein (BMP) signaling in neonatal C57BL/6J mice exposed to 21% or 85% O(2) between postnatal days P1 and P28. Growth and respiratory compliance were significantly impaired in pups exposed to 85% O(2), and these pups also exhibited a pronounced arrest of alveolarization, accompanied by dysregulated expression and localization of both receptor (ALK-1, ALK-3, ALK-6, and the TGF-beta type II receptor) and Smad (Smads 1, 3, and 4) proteins. TGF-beta signaling was potentiated, whereas BMP signaling was impaired both in the lungs of pups exposed to 85% O(2) as well as in MLE-12 mouse lung epithelial cells and NIH/3T3 and primary lung fibroblasts cultured in 85% O(2). After exposure to 85% O(2), primary alveolar type II cells were more susceptible to TGF-beta-induced apoptosis, whereas primary pulmonary artery smooth muscle cells were unaffected. Exposure of primary lung fibroblasts to 85% O(2) significantly enhanced the TGF-beta-stimulated production of the alpha(1) subunit of type I collagen (Ialpha(1)), tissue inhibitor of metalloproteinase-1, tropoelastin, and tenascin-C. These data demonstrated that hyperoxia significantly affects TGF-beta/BMP signaling in the lung, including processes central to septation and, hence, alveolarization. The amenability of these pathways to genetic and pharmacological manipulation may provide alternative avenues for the management of BPD.

Pediatric lung disease: from proteinases to pulmonary fibrosis

One distinctive outcome of interstitial lung diseases in childhood is the abnormal accumulation of pulmonary extracellular matrix. The clinical consequence of such excessive connective tissue accumulation is known as pulmonary fibrosis. While numerous aspects of its pathogenesis have become familiar, many key events involved in its inception and progression still remain unclear. There is now compelling evidence that lung damage due to uncontrolled proteolysis may help drive critical processes that regulate fibrotic matrix remodeling. In this regard, a number of proteinases have been implicated in promoting both the initial lung injury and the fibroproliferative repair that follows. This review summarizes the knowledge of how different matrix-targeting enzymes may act to influence the development of pediatric pulmonary fibrosis. Understanding the scientific basis of this complex process may highlight opportunities to limit unwanted proteolysis and the intensity of its fibrotic sequelae.

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.

Increased lung matrix metalloproteinase-9 levels in extremely premature baboons with bronchopulmonary dysplasia

Matrix metalloproteinases (MMPs) regulate the formation of normal lung architecture. Extremely premature infants exposed to hyperoxia and mechanical ventilation often develop lung inflammation and injury. We hypothesized that an imbalance between MMPs and their tissue inhibitors plays a key role. Our hypothesis was tested to: 1) examine the ontogeny of lung MMPs and tissue inhibitors of metalloproteinases (TIMPs); and 2) determine the effects of hyperoxia and mechanical ventilation on lung MMPs and TIMPs in premature newborn baboons developing chronic lung disease/bronchopulmonary dysplasia (CLD/BPD). Lung specimens were obtained from five groups of gestational controls (GCs) sacrificed at 125, 140, 160, 175, and 185 (term) days of gestation, one fetal baboon model of CLD/BPD delivered at 125 days, and two at 140 days of gestation. Paraffin-embedded lung tissue sections were examined for pathological changes, and frozen lung specimens were analyzed for MMPs-1, -2, -8, and -9; TIMPs-1 and -2; and messenger RNA expression of type I collagen. In GCs, MMP-1 and -9 were elevated in the last trimester, whereas MMP-2 and -8 levels were decreased. Significant changes in lung architecture were noted in the BPD models. MMP-1 was increased in the 125-day model, but decreased in both 140-day models. MMP-8 and collagen mRNA levels were decreased, while MMP-9 and MMP-9 to TIMP-1 ratios were increased in all BPD models. We conclude that an imbalance between MMP-9 and TIMP-1 leading to excessive MMP-9 activity contributes to lung inflammation and edema in CLD/BPD.

Bronchopulmonary dysplasia: new insights

The pathology of BPD has changed over time, with the old BPD characterized by airway injury, inflammation, and parenchymal fibrosis giving way to the new BPD manifesting less fibrosis but with decreased alveolar and vascular development. The pathogenesis of BPD involves factors affecting the severity and management of RDS, alterations in lung development and maturation, alveolar-vascular interactions, and extracellular matrix remodeling. These factors in pathogenesis are mediated and modulated by hyperoxic lung injury, antioxidants, NO, the pulmonary neuroendocrine system and peptide growth factors, the immune system, and various genetic polymorphisms and predispositions. Future therapeutic interventions are likely to target one or more of these abnormalities in lung development, maturation, and response to injury.

Bronchopulmonary dysplasia-oxidative stress and antioxidants

There is increasing evidence that oxidative stress is implicated in the development of bronchopulmonary dysplasia. Several important factors contribute to augmented oxidative stress in the newborn and especially the preterm infant: first, because of its immaturity, the lung of preterm infants is frequently exposed to oxygen therapy and hyperoxia. Second, the antioxidant defense and its ability to be induced during an hyperoxic challenge are impaired. Third, the preterm infant has an increased susceptibility to infection and inflammation, which increases oxidative stress. Fourth, free iron, which catalyzes the production of toxic reactive oxygen species, can be detected in preterm infants. The molecular and cellular mechanisms for free radical-induced injury are now understood in more detail, and it is clear that oxidative stress plays an important role in triggering apoptosis, in serving as second messenger and in signal transduction. This new insight might lead to novel and efficient therapies. So far, there has been no significant breakthrough regarding antioxidant therapies. Care should, however, be exercised in supplementing the preterm infant with antioxidants since this may affect growth and development.

Metalloproteinase and growth factor interactions: do they play a role in pulmonary fibrosis?

Chronic lung disease due to interstitial fibrosis can be a consequence of acute lung injury and inflammation. The inflammatory response is mediated through the migration of inflammatory cells, actions of proinflammatory cytokines, and the secretion of matrix-degrading proteinases. After the initial inflammatory insult, successful healing of the lung may occur, or alternatively, dysregulated tissue repair can result in scarring and fibrosis. On the basis of recent insights into the mechanisms underlying acute lung injury and its long-term consequences, data suggest that proteinases, such as the matrix metalloproteinases (MMPs), may not only be involved in the breakdown and remodeling that occurs during the injury but may also cause the release of growth factors and cytokines known to influence growth and differentiation of target cells within the lung. Through the release of and activation of fibrosis-promoting cytokines and growth factors such as transforming growth factor-beta1, tumor necrosis factor-alpha, and insulin-like growth factors by MMPs, we propose that these metalloproteinases may be integral to the initiation and progression of pulmonary fibrosis.