Recombinant adiponectin protects the newborn rat lung from lipopolysaccharide-induced inflammatory injury

Unleashing AdipoRon's Potential: A Fresh Approach to Tackle Pseudomonas aeruginosa Infections in Bronchiectasis via Sphingosine Metabolism Modulation

Purpose

Bronchiectasis patients are prone to Pseudomonas aeruginosa infection due to decreased level of sphingosine in airway. Adiponectin receptor agonist AdipoRon activates the intrinsic ceramidase activity of adiponectin receptor 1 (AdipoR1) and positively regulates sphingosine metabolism. This study aimed to investigate the potential therapeutic benefit of AdipoRon against Pseudomonas aeruginosa infection.

Methods

A mouse model of Pseudomonas aeruginosa lung infection and a co-culture model of human bronchial epithelial cells with Pseudomonas aeruginosa were established to explore the protective effect of AdipoRon. Liquid chromatography-mass spectrometry was used to detect the effect of AdipoRon on sphingosine level in lung of Pseudomonas aeruginosa-infected mouse models.

Results

The down-regulation of adiponectin and AdipoR1 in airway of bronchiectasis patients was linked to Pseudomonas aeruginosa infection. By activating AdipoR1, AdipoRon reduced Pseudomonas aeruginosa adherence on bronchial epithelial cells and protected cilia from damage in vitro. With the treatment of AdipoRon, the load of Pseudomonas aeruginosa in lung significantly decreased, and peribronchial inflammatory cell infiltration was lessened in vivo. The reduced level of sphingosine in the airway of Pseudomonas aeruginosa infected mice was replenished by AdipoRon, thus playing a protective role in the airway. Moreover, AdipoRon activated P-AMPKα/PGC1α, inhibited TLR4/P-NF-κB p65, and reduced expression of pro-apoptotic bax. However, the protective effect of AdipoRon on resisting Pseudomonas aeruginosa infection was weakened when AdipoR1 was knocked down.

Conclusion

AdipoRon protects bronchial epithelial cells and lung by enhancing their resistance to Pseudomonas aeruginosa infection. The mechanism might be modulating sphingosine metabolism and activating P-AMPKα/PGC1α while inhibiting TLR4/P-NF-κB p65.

Maturational effect of leptin on CO2 chemosensitivity in newborn rats

BACKGROUND

Leptin augments central CO2 chemosensitivity and stabilizes breathing in adults. Premature infants have unstable breathing and low leptin levels. Leptin receptors are on CO2 sensitive neurons in the Nucleus Tractus Solitarius (NTS) and locus coeruleus (LC). We hypothesized that exogenous leptin improves hypercapnic respiratory response in newborn rats by improving central CO2 chemosensitivity.

METHODS

In rats at postnatal day (p)4 and p21, hyperoxic and hypercapnic ventilatory responses, and pSTAT and SOCS3 protein expression in the hypothalamus, NTS and LC were measured before and after treatment with exogenous leptin (6 µg/g).

RESULTS

Exogenous leptin increased the hypercapnic response in p21 but not in p4 rats (P ≤ 0.001). At p4, leptin increased pSTAT expression only in the LC, and SOCS3 expression in the NTS and LC; while at p21 pSTAT and SOCS3 levels were higher in the hypothalamus, NTS, and LC (P ≤ 0.05).

CONCLUSIONS

We describe the developmental profile of the effect of exogenous leptin on CO2 chemosensitivity. Exogenous leptin does not augment central CO2 sensitivity during the first week of life in newborn rats. The translational implication of these findings is that low plasma leptin levels in premature infants may not be contributing to respiratory instability.

IMPACT

Exogenous leptin does not augment CO2 sensitivity during the first week of life in newborn rats, similar to the developmental period when feeding behavior is resistant to leptin. Exogenous leptin increases CO2 chemosensitivity in newborn rats after the 3rd week of life and upregulates the expression of pSTAT and SOC3 in the hypothalamus, NTS and LC. Low plasma leptin levels in premature infants are unlikely contributors to respiratory instability via decreased CO2 sensitivity in premature infants. Thus, it is highly unlikely that exogenous leptin would alter this response.

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.

Recombinant adiponectin protects the newborn rat lung from lipopolysaccharide-induced inflammatory injury

Preterm infants are at high risk for developing bronchopulmonary dysplasia and pulmonary hypertension from inflammatory lung injury. In adult models, adiponectin (APN)—an adipocyte‐derived hormone—protects the lung from inflammatory injury and pulmonary vascular remodeling. Cord blood APN levels in premature infants born < 26 weeks gestation are 5% of the level in infants born at term. We previously reported the expression profile of APN and its receptors in neonatal rat lung homogenates during the first 3 weeks of postnatal development. Here, we characterize the expression profile of APN and its receptors in specific lung cells and the effects of exogenous recombinant APN (rAPN) on lipopolysaccharide‐(LPS)‐induced cytokine and chemokine production in total lung homogenates and specific lung cells. In vitro, rAPN added to primary cultures of pulmonary artery smooth muscle cells attenuated the expression of LPS‐induced pro‐inflammatory cytokines while increasing the expression of anti‐inflammatory cytokines. In vivo, intraperitoneal rAPN (2 mg/kg), given 4 hr prior to intrapharyngeal administration of LPS (5 mg/kg) to newborn rats at postnatal day 4, significantly reduced gene and protein expression of the pro‐inflammatory cytokine IL‐1ß and reduced protein expression of the chemokines monocyte chemoattractant protein (MCP‐1) and macrophage inflammatory protein‐1 alpha (MIP‐1α) in the lung. LPS‐induced histopathological changes in the lung were also decreased. Moreover, rAPN given 20 hr after intrapharyngeal LPS had a similar effect on lung inflammation. These findings suggest a role for APN in protecting the lung from inflammation during early stages of lung development.