Mitochondrial Dysfunction in Bronchopulmonary Dysplasia

Mitochondrial dynamics in pulmonary disease: Implications for the potential therapeutics

Mitochondria are dynamic organelles that continuously undergo fusion/fission to maintain normal cell physiological activities and energy metabolism. When mitochondrial dynamics is unbalanced, mitochondrial homeostasis is broken, thus damaging mitochondrial function. Accumulating evidence demonstrates that impairment in mitochondrial dynamics leads to lung tissue injury and pulmonary disease progression in a variety of disease models, including inflammatory responses, apoptosis, and barrier breakdown, and that the role of mitochondrial dynamics varies among pulmonary diseases. These findings suggest that modulation of mitochondrial dynamics may be considered as a valid therapeutic strategy in pulmonary diseases. In this review, we discuss the current evidence on the role of mitochondrial dynamics in pulmonary diseases, with a particular focus on its underlying mechanisms in the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis (PF), pulmonary arterial hypertension (PAH), lung cancer and bronchopulmonary dysplasia (BPD), and outline effective drugs targeting mitochondrial dynamics-related proteins, highlighting the great potential of targeting mitochondrial dynamics in the treatment of pulmonary disease.

Predictive value of serum MED1 and PGC-1α for bronchopulmonary dysplasia in preterm infants

OBJECTIVE

This study aimed to predict the bronchopulmonary dysplasia (BPD) in preterm infants with a gestational age(GA) < 32 weeks utilizing clinical data, serum mediator complex subunit 1 (MED1), and serum peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α).

METHODS

This prospective observational study enrolled 70 preterm infants with GA < 32 weeks. The infants were categorized into two groups: non-BPD group(N = 35) and BPD group(N = 35), including 25 cases with mild BPD and 10 patients with moderate/severe subgroups. We performed multifactorial regression analysis to investigate the postnatal risk factors for BPD. Furthermore, we compared serum levels of biomarkers, including MED1 and PGC-1α, among infants with and without BPD at postnatal days 1, 7, 14, 28, and PMA 36 weeks. A logistic regression model was constructed to predict BPD's likelihood using clinical risk factors and serum biomarkers.

RESULTS

Serum levels of MED1 on the first postnatal day, PGC-1α on the 1st, 7th, and 28th days, and PMA at 36 weeks were significantly lower in the BPD group than in the non-BPD group (P < 0.05). Furthermore, the predictive model for BPD was created by combing serum levels of MED1 and PGC-1α on postnatal day 1 along with clinical risk factors such as frequent apnea, mechanical ventilation time > 7 d, and time to reach total enteral nutrition. Our predictive model had a high predictive accuracy(C statistics of 0.989) .

CONCLUSION

MED1and PGC-1α could potentially serve as valuable biomarkers, combined with clinical factors, to aid clinicians in the early diagnosis of BPD.

PGC-1α activity and mitochondrial dysfunction in preterm infants

Extremely low gestational age neonates (ELGANs) are born in a relatively hyperoxic environment with weak antioxidant defenses, placing them at high risk for mitochondrial dysfunction affecting multiple organ systems including the nervous, respiratory, ocular, and gastrointestinal systems. The brain and lungs are highly affected by mitochondrial dysfunction and dysregulation in the neonate, causing white matter injury (WMI) and bronchopulmonary dysplasia (BPD), respectively. Adequate mitochondrial function is important in providing sufficient energy for organ development as it relates to alveolarization and axonal myelination and decreasing oxidative stress via reactive oxygen species (ROS) and reactive nitrogen species (RNS) detoxification. Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a master regulator of mitochondrial biogenesis and function. Since mitochondrial dysfunction is at the root of WMI and BPD pathobiology, exploring therapies that can regulate PGC-1α activity may be beneficial. This review article describes several promising therapeutic agents that can mitigate mitochondrial dysfunction through direct and indirect activation and upregulation of the PGC-1α pathway. Metformin, resveratrol, omega 3 fatty acids, montelukast, L-citrulline, and adiponectin are promising candidates that require further pre-clinical and clinical studies to understand their efficacy in decreasing the burden of disease from WMI and BPD in preterm infants.

Metabolic dysregulation in bronchopulmonary dysplasia: Implications for identification of biomarkers and therapeutic approaches

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease in premature infants. Accumulating evidence shows that dysregulated metabolism of glucose, lipids and amino acids are observed in premature infants. Animal and cell studies demonstrate that abnormal metabolism of these substrates results in apoptosis, inflammation, reduced migration, abnormal proliferation or senescence in response to hyperoxic exposure, and that rectifying metabolic dysfunction attenuates neonatal hyperoxia-induced alveolar simplification and vascular dysgenesis in the lung. BPD is often associated with several comorbidities, including pulmonary hypertension and neurodevelopmental abnormalities, which significantly increase the morbidity and mortality of this disease. Here, we discuss recent progress on dysregulated metabolism of glucose, lipids and amino acids in premature infants with BPD and in related in vivo and in vitro models. These findings suggest that metabolic dysregulation may serve as a biomarker of BPD and plays important roles in the pathogenesis of this disease. We also highlight that targeting metabolic pathways could be employed in the prevention and treatment of BPD.

Mitochondrial Fission-Mediated Lung Development in Newborn Rats With Hyperoxia-Induced Bronchopulmonary Dysplasia With Pulmonary Hypertension

Background: Bronchopulmonary dysplasia (BPD) is the most common chronic respiratory disease in premature infants. Oxygen inhalation and mechanical ventilation are common treatments, which can cause hyperoxia-induced lung injury, but the underlying mechanism is not yet understood. Mitochondrial fission is essential for mitochondrial homeostasis. The objective of this study was to determine whether mitochondrial fission (dynamin-related protein 1, Drp1) is an important mediator of hyperoxia lung injury in rats. Methods: The animal model of BPD was induced with high oxygen (80-85% O₂). Pulmonary histological changes were observed by hematoxylin-eosin (HE) staining. Pulmonary microvessels were observed by immunofluorescence staining of von Willebrand Factor (vWF). Protein expression levels of Drp1 and p-Drp1 (Ser616) were observed using Western Blot. We used echocardiography to measure pulmonary artery acceleration time (PAT), pulmonary vascular resistance index (PVRi), peak flow velocity of the pulmonary artery (PFVP), pulmonary arteriovenous diameter, and pulmonary vein peak velocity. Mitochondrial division inhibitor-1 (Mdivi-1) was used as an inhibitor of Drp1, and administered through intraperitoneal injection (25 mg/kg). Results: Pulmonary artery resistance of the hyperoxide-induced neonatal rat model of BPD increased after it entered normoxic convalescence. During the critical stage of alveolar development in neonatal rats exposed to high oxygen levels for an extended period, the expression and phosphorylation of Drp1 increased in lung tissues. When Drp1 expression was inhibited, small pulmonary vessel development improved and PH was relieved. Conclusion: Our study shows that excessive mitochondrial fission is an important mediator of hyperoxia-induced pulmonary vascular injury, and inhibition of mitochondrial fission may be a useful treatment for hyperoxia-induced related pulmonary diseases.

Recent advances in our understanding of the mechanisms of lung alveolarization and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.