Intratracheal Keratinocyte Growth Factor Enhances Surfactant Protein B Expression in Mechanically Ventilated Preterm Pigs

Bronchopulmonary dysplasia (BPD) is a devastating disease of prematurity that is associated with mechanical ventilation and hyperoxia. We used preterm pigs delivered at gestational day 102 as a translational model for 26–28-week infants to test the hypothesis administering recombinant human keratinocyte growth factor (rhKGF) at initiation of mechanical ventilation will stimulate type II cell proliferation and surfactant production, mitigate ventilator induced lung injury, and reduce epithelial to mesenchymal transition considered as a precursor to BPD. Newborn preterm pigs were intubated and randomized to receive intratracheal rhKGF (20 μg/kg; n = 6) or saline (0.5 ml 0.9% saline; control; n = 6) before initiating 24 h of ventilation followed by extubation to nasal oxygen for 12 h before euthanasia and collection of lungs for histopathology and immunohistochemistry to assess expression of surfactant protein B and markers of epithelial to mesenchymal transition. rhKGF pigs required less oxygen during mechanical ventilation, had higher tidal volumes at similar peak pressures indicative of improved lung compliance, and survival was higher after extubation (83% vs. 16%). rhKGF increased surfactant protein B expression (p < 0.05) and reduced TGF-1β (p < 0.05), that inhibits surfactant production and is a prominent marker for epithelial to mesenchymal transition. Our findings suggest intratracheal administration of rhKGF at initiation of mechanical ventilation enhances surfactant production, reduces ventilator induced lung injury, and attenuates epithelial-mesenchymal transition while improving pulmonary functions. rhKGF is a potential therapeutic strategy to mitigate pulmonary responses of preterm infants that require mechanical ventilation and thereby reduce the incidence and severity of bronchopulmonary dysplasia.

Immature Circulating SP-B, Bound to HDL, Represents an Early Sign of Smoke-Induced Pathophysiological Alterations

Cigarette smoking is a major independent risk factor for cardiovascular diseases (CVD). The underlying mechanisms, however, are not clearly understood. Lungs are the primary route of exposure to smoke, with pulmonary cells and surfactant being the first structures directly exposed, resulting in the leakage of the immature proteoform of surfactant protein B (proSP-B). Herein, we evaluated whether proSP-B joined the cargo of high-density lipoprotein (HDL) proteins in healthy young subjects (n = 106) without any CVD risk factor other than smoking, and if HDL-associated proSP-B (HDL-SPB) correlated with pulmonary function parameters, systemic inflammation, and oxidative stress. At univariable analysis, HDL-SPB resulted significantly higher in smokers (2.2-fold, p < 0.001) than in non-smokers. No significant differences have been detected between smokers and non-smokers for inflammation, oxidation variables, and alveolar-capillary diffusion markers. In a multivariable model, HDL-SPB was independently associated with smoking. In conclusion, HDL-SPB is not only a precocious and sensitive index of the acute effects of smoke, but it might be also a potential causal factor in the onset of the vascular damage induced by modified HDL. These findings contribute to the emerging concept that the quality of the HDL proteome, rather than the quantity of particles, plays a central role in CVD risk protection.

A Primate-Specific RNA-Binding Protein (RBMXL3) Is Involved in Glucocorticoid Regulation of Human Pulmonary Surfactant Protein B (SP-B) mRNA Stability

The ability of pulmonary surfactant to reduce alveolar surface tension requires adequate levels of surfactant protein B (SP-B). Dexamethasone (DEX) increases human SP-B expression, in part, through increased SP-B mRNA stability. A 30 nt-long hairpin element (RBE) in the 3'-untranslated region of human SP-B mRNA mediates both DEX-induced and intrinsic mRNA stability, but the mechanism is unknown. Proteomic analysis of RBE-interacting proteins identified a primate-specific protein; RNA binding motif X-linked-like-3 (RBMXL3). siRNA directed against RBMXL3 reduces DEX-induced SP-B mRNA expression in human bronchoalveolar cells. Human SP-B mRNA stability, measured by our dual cistronic plasmid assay, is unaffected by DEX in mouse lung epithelial cells lacking RBMXL3, but DEX increases human SP-B mRNA stability when RBMXL3 is expressed and requires the RBE. In the absence of DEX, RBE interacts with cellular proteins, reducing intrinsic SP-B mRNA stability in human and mouse lung epithelial cells. RBMXL3 specifically binds the RBE in vitro while RNA immunoprecipitation and affinity chromatography analyses indicate that binding is enhanced in the presence of DEX. These results describe a model where intrinsic stability of human SP-B mRNA is reduced through binding of cellular mRNA decay factors to RBE, which is then relieved through DEX-enhanced binding of primate-specific RBMXL3.

Intratracheal Keratinocyte Growth Factor Enhances Surfactant Protein B Expression in Mechanically Ventilated Preterm Pigs

Background: Bronchopulmonary dysplasia is a devastating disease of the premature newborn with high morbidity and mortality. Surfactant deficient preterm lungs are susceptible to ventilator induced lung injury, thereby developing bronchopulmonary dysplasia. Despite surfactant therapy and newer ventilation strategies, associated morbidity and mortality remains unchanged. Enhancing surfactant production and reducing ventilator induced lung injury in premature infants are critical. Recombinant keratinocyte growth factor previously been studied to treat adult respiratory distress syndrome. We hypothesized that administering recombinant human keratinocyte growth factor when initiating mechanical ventilation would help stimulate type II cell proliferation and surfactant production. Recombinant human keratinocyte growth factor may also help mitigate ventilator induced lung injury hereby reducing epithelial to mesenchymal transition, a possible precursor to later development of bronchopulmonary dysplasia. Methods: To test our hypothesis, we delivered preterm pigs via cesarean section on day 102. We performed intubation and ventilation for 24 hr. using intermittent positive pressure ventilation. After ventilation began, pigs randomly received intratracheal recombinant human keratinocyte growth factor (20 µg/kg; n=6) or sham treatment (0.5 ml 0.9% saline; n= 6). We recorded physiology data and arterial blood gases during ventilation. After 24 hr. pigs were extubated and received oxygen via nasal cannulation 12 hr. before euthanasia to collect lungs for histopathology and immunohistochemistry. Immunohistochemistry staining was graded and analyzed for surfactant protein B and epithelial to mesenchymal transition markers. Data were analyzed using t-test and Fisher’s exact test. Continuous variables analyzed using ANOVA.Results: Compared with control pigs, recombinant human keratinocyte growth factor pretreated pigs had improved ventilation with higher tidal volumes and required less oxygen (FiO2) during mechanical ventilation for similar peak pressures demonstrating improved lung compliance. Recombinant human keratinocyte growth factor pretreated pig lungs showed increased surfactant protein B expression (p< 0.05) and significantly reduced TGF-β (p< 0.05), a prominent marker for epithelial to mesenchymal transition.Conclusions: Intratracheal recombinant human keratinocyte growth factor administered at initiation of mechanical ventilation enhances surfactant production, reduce lung injury by mitigation of the changes by epithelial mesenchymal transition, thereby improving outcomes. Thus, recombinant human keratinocyte growth factor may represent a potential therapeutic strategy to prevent bronchopulmonary dysplasia.