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

CD73: Friend or Foe in Lung Injury

Ecto-5′-nucleotidase (CD73) plays a strategic role in calibrating the magnitude and chemical nature of purinergic signals that are delivered to immune cells. Its primary function is to convert extracellular ATP to adenosine in concert with ectonucleoside triphosphate diphosphohydrolase-1 (CD39) in normal tissues to limit an excessive immune response in many pathophysiological events, such as lung injury induced by a variety of contributing factors. Multiple lines of evidence suggest that the location of CD73, in proximity to adenosine receptor subtypes, indirectly determines its positive or negative effect in a variety of organs and tissues and that its action is affected by the transfer of nucleoside to subtype-specific adenosine receptors. Nonetheless, the bidirectional nature of CD73 as an emerging immune checkpoint in the pathogenesis of lung injury is still unknown. In this review, we explore the relationship between CD73 and the onset and progression of lung injury, highlighting the potential value of this molecule as a drug target for the treatment of pulmonary disease.

Neonatal Hyperoxia Activates Activating Transcription Factor 4 to Stimulate Folate Metabolism and Alveolar Epithelial Type 2 Cell Proliferation

Oxygen supplementation in preterm infants disrupts alveolar epithelial type 2 (AT2) cell proliferation through poorly understood mechanisms. Here, newborn mice are used to understand how hyperoxia stimulates an early aberrant wave of AT2 cell proliferation that occurs between Postnatal Days (PNDs) 0 and 4. RNA-sequencing analysis of AT2 cells isolated from PND4 mice revealed hyperoxia stimulates expression of mitochondrial-specific methylenetetrahydrofolate dehydrogenase 2 and other genes involved in mitochondrial one-carbon coupled folate metabolism and serine synthesis. The same genes are induced when AT2 cells normally proliferate on PND7 and when they proliferate in response to the mitogen fibroblast growth factor 7. However, hyperoxia selectively stimulated their expression via the stress-responsive activating transcription factor 4 (ATF4). Administration of the mitochondrial superoxide scavenger mitoTEMPO during hyperoxia suppressed ATF4 and thus early AT2 cell proliferation, but it had no effect on normative AT2 cell proliferation seen on PND7. Because ATF4 and methylenetetrahydrofolate dehydrogenase are detected in hyperplastic AT2 cells of preterm infant humans and baboons with bronchopulmonary dysplasia, dampening mitochondrial oxidative stress and ATF4 activation may provide new opportunities for controlling excess AT2 cell proliferation in neonatal lung disease.

CD73 Attenuates Alcohol-Induced Liver Injury and Inflammation via Blocking TLR4/MyD88/NF-κB Signaling Pathway

Background

Alcoholic liver disease (ALD) is liver damage caused by long-term drinking. Inflammation plays a central role in the progression of ALD. CD73 is a ubiquitously expressed glycosylphosphatidylinositol-anchored glycoprotein that is a key enzyme that converts ATP into adenosine. Evidence has shown that CD73 plays an important role in many diseases, but the role and mechanism of CD73 in alcohol-induced liver injury and inflammation is still unclear.

Methods

The alcohol-induced liver injury and inflammation mouse model was established. The rAAV9-CD73 was used to overexpress CD73. Isolation of primary macrophages (MΦ) from the liver was conducted. The effects of CD73 on alcohol-induced liver injury and inflammation were evaluated by quantitative real‑time PCR, Western blotting, ELISA, and immunohistochemical assay. Flow cytometry was used to detect the cell cycle and apoptosis.

Results

Our results showed that overexpression of CD73 can reduce alcohol-induced liver damage, lipid accumulation, and the secretion of inflammatory cytokines. pEX3-CD73 can promote RAW264.7 cells proliferation and inhibit apoptosis via suppressing the activation of TLR4/MyD88/NF-κB signaling pathway. Inhibition of TLR4 further enhanced the anti-inflammatory effect of overexpression of CD73.

Conclusion

Overexpression of CD73 can reduce alcohol-induced liver injury and inflammation. CD73 may serve as a potential therapeutic target for ALD.

Expression and Regulation of CD73 during the Estrous Cycle in Mouse Uterus

Cluster of differentiation 73 (CD73, also known as ecto-5′-nucleotidase) is an enzyme that converts AMP into adenosine. CD73 is a surface enzyme bound to the outside of the plasma membrane expressed in several cells and regulates immunity and inflammation. In particular, it is known to inhibit T cell-mediated immune responses. However, the regulation of CD73 expression by hormones in the uterus is not yet clearly known. In this study, we investigated the expression of CD73 in ovariectomized mice treated with estrogen or progesterone and its regulation in the mouse uterus during the estrous cycle. The level of CD73 expression was dynamically regulated in the uterus during the estrous cycle. CD73 protein expression was high in proestrus, estrus, and diestrus, whereas it was relatively low in the metestrus stage. Immunofluorescence revealed that CD73 was predominantly expressed in the cytoplasm of the luminal and glandular epithelium and the stroma of the endometrium. The expression of CD73 in ovariectomized mice was gradually increased by progesterone treatment. However, estrogen injection did not affect its expression. Moreover, CD73 expression was increased when estrogen and progesterone were co-administered and was inhibited by the pretreatment of the progesterone receptor antagonist RU486. These findings suggest that the expression of CD73 is dynamically regulated by estrogen and progesterone in the uterine environment, and that there may be a synergistic effect of estrogen and progesterone.

Possible Beneficial Actions of Caffeine in SARS-CoV-2

The COVID-19 pandemic has established an unparalleled necessity to rapidly find effective treatments for the illness; unfortunately, no specific treatment has been found yet. As this is a new emerging chaotic situation, already existing drugs have been suggested to ameliorate the infection of SARS-CoV-2. The consumption of caffeine has been suggested primarily because it improves exercise performance, reduces fatigue, and increases wakefulness and awareness. Caffeine has been proven to be an effective anti-inflammatory and immunomodulator. In airway smooth muscle, it has bronchodilator effects mainly due to its activity as a phosphodiesterase inhibitor and adenosine receptor antagonist. In addition, a recent published document has suggested the potential antiviral activity of this drug using in silico molecular dynamics and molecular docking; in this regard, caffeine might block the viral entrance into host cells by inhibiting the formation of a receptor-binding domain and the angiotensin-converting enzyme complex and, additionally, might reduce viral replication by the inhibition of the activity of 3-chymotrypsin-like proteases. Here, we discuss how caffeine through certain mechanisms of action could be beneficial in SARS-CoV-2. Nevertheless, further studies are required for validation through in vitro and in vivo models.

Exacerbation of Allergic Airway Inflammation in Mice Lacking ECTO-5'-Nucleotidase (CD73)

The airways are a target tissue of type I allergies and atopy is the main etiological factor of bronchial asthma. A predisposition to allergy and individual response to allergens are dependent upon environmental and host factors. Early studies performed to clarify the role of extracellular adenosine in the airways highlighted the importance of adenosine-generating enzymes CD73, together with CD39, as an innate protection system against lung injury. In experimental animals, deletion of CD73 has been associated with immune and autoimmune diseases. Our experiments have been performed to investigate the role of CD73 in the assessment of allergic airway inflammation following sensitization. We found that in CD73^−/− mice sensitization, induced by subcutaneous ovalbumin (OVA) administration, increased signs of airway inflammation and atopy developed, characterized by high IgE plasma levels and increased pulmonary cytokines, reduced frequency of lung CD4⁺CD25+Foxp3+ T cells, but without bronchial hyperreactivity, compared to sensitized wild type mice. Our results provide evidence that the lack of CD73 causes an uncontrolled allergic sensitization, suggesting that CD73 is a key molecule at the interface between innate and adaptive immune response. The knowledge of host immune factors controlling allergic sensitization is of crucial importance and might help to find preventive interventions that could act before an allergy develops.

Prevention of Oxygen-Induced Inflammatory Lung Injury by Caffeine in Neonatal Rats

Background

Preterm birth implies an array of respiratory diseases including apnea of prematurity and bronchopulmonary dysplasia (BPD). Caffeine has been introduced to treat apneas but also appears to reduce rates of BPD. Oxygen is essential when treating preterm infants with respiratory problems but high oxygen exposure aggravates BPD. This experimental study is aimed at investigating the action of caffeine on inflammatory response and cell death in pulmonary tissue in a hyperoxia-based model of BPD in the newborn rat. Material/Methods. Lung injury was induced by hyperoxic exposure with 80% oxygen for three (P3) or five (P5) postnatal days with or without recovery in ambient air until postnatal day 15 (P15). Newborn Wistar rats were treated with PBS or caffeine (10 mg/kg) every two days beginning at the day of birth. The effects of caffeine on hyperoxic-induced pulmonary inflammatory response were examined at P3 and P5 immediately after oxygen exposure or after recovery in ambient air (P15) by immunohistological staining and analysis of lung homogenates by ELISA and qPCR.

Results

Treatment with caffeine significantly attenuated changes in hyperoxia-induced cell death and apoptosis-associated factors. There was a significant decrease in proinflammatory mediators and redox-sensitive transcription factor NFκB in the hyperoxia-exposed lung tissue of the caffeine-treated group compared to the nontreated group. Moreover, treatment with caffeine under hyperoxia modulated the transcription of the adenosine receptor (Adora)1. Caffeine induced pulmonary chemokine and cytokine transcription followed by immune cell infiltration of alveolar macrophages as well as increased adenosine receptor (Adora1, 2a, and 2b) expression.

Conclusions

The present study investigating the impact of caffeine on the inflammatory response, pulmonary cell degeneration and modulation of adenosine receptor expression, provides further evidence that caffeine acts as an antioxidative and anti-inflammatory drug for experimental oxygen-mediated lung injury. Experimental studies may broaden the understanding of therapeutic use of caffeine in modulating detrimental mechanisms involved in BPD development.

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.

Cell type- and tissue-specific functions of ecto-5'-nucleotidase (CD73)

Ecto-5'-nucleotidase [cluster of differentiation 73 (CD73)] is a ubiquitously expressed glycosylphosphatidylinositol-anchored glycoprotein that converts extracellular adenosine 5'-monophosphate to adenosine. Anti-CD73 inhibitory antibodies are currently undergoing clinical testing for cancer immunotherapy. However, many protective physiological functions of CD73 need to be taken into account for new targeted therapies. This review examines CD73 functions in multiple organ systems and cell types, with a particular focus on novel findings from the last 5 years. Missense loss-of-function mutations in the CD73-encoding gene NT5E cause the rare disease "arterial calcifications due to deficiency of CD73." Aside from direct human disease involvement, cellular and animal model studies have revealed key functions of CD73 in tissue homeostasis and pathology across multiple organ systems. In the context of the central nervous system, CD73 is antinociceptive and protects against inflammatory damage, while also contributing to age-dependent decline in cortical plasticity. CD73 preserves barrier function in multiple tissues, a role that is most evident in the respiratory system, where it inhibits endothelial permeability in an adenosine-dependent manner. CD73 has important cardioprotective functions during myocardial infarction and heart failure. Under ischemia-reperfusion injury conditions, rapid and sustained induction of CD73 confers protection in the liver and kidney. In some cases, the mechanism by which CD73 mediates tissue injury is less clear. For example, CD73 has a promoting role in liver fibrosis but is protective in lung fibrosis. Future studies that integrate CD73 regulation and function at the cellular level with physiological responses will improve its utility as a disease target.