Surfactant protein A binds TGF-ß1 with high affinity and stimulates the TGF-ß pathway.

We were able to demonstrate reversible, specific and high-affinity binding of radioactively-labelled TGF-ß1 ((125)I-TGF-ß1) to immobilized surfactant protein A (SP-A), with an apparent dissociation constant of 53 picomolar at ∼21. Addition of a 200-fold molar excess of the latency associated peptide (LAP) prevented and dissociated the binding of (125)I-TGF-ß1 to SP-A, whereas latent TGF-ß1 had no effect. Using a bioassay for TGF-ß1 activity--a luciferase reporter assay--we were able to show that SP-A in the presence of TGF-ß1 stimulated the TGF-ß1 pathway, whereas SP-A alone had no effect. Studies with structural analogues of the distinct SP-A tail domain and head domain indicated that stimulatory activity of SP-A resided in the head domain. No activation of latent TGF-ß1 by SP-A was observed. In addition, we observed that SP-A inhibited TGF-ß1 inactivation by LAP. These results indicate that SP-A may have a regulatory role in the TGF-ß1-mediated processes in the lung.

Comparison of recruitment manoeuvres in ventilated sheep with acute respiratory distress syndrome.

BACKGROUND: Recruitment manoeuvres are widely used in clinical practice to open the lung and prevent lung injury by derecruitment, although the evidence is still discussed. In this study two different recruitment manoeuvres were compared to no recruitment manoeuvres (control) in ventilated sheep with acute respiratory distress syndrome (ARDS), induced by lung lavage. METHODS: We performed a prospective, randomised study in 26 ventilated sheep with ARDS, to evaluate the effect of two different recruitment manoeuvres on gas exchange, blood pressure and lung injury. The two different recruitment manoeuvres, the high pressure recruitment manoeuvre (HPRM), with high peak pressure, and the smooth and moderate recruitment manoeuvre (SMRM), with lower peak pressure, were compared to controls (no recruitment) after disconnection. Oxygenation index and ventilation efficacy index were calculated to evaluate gas exchange. Lung injury was assessed by inflammatory response in broncho-alveolar lavage fluid (BALF) and blood and histology of the lung. RESULTS: Oxygenation index improved significantly after both recruitment manoeuvres compared with controls, but no significant difference was found between the recruitment manoeuvres. Blood pressure decreased after HPRM but not after SMRM. HPRM induced a higher number of total cells and more neutrophils in the BALF. In the histology of the lung, mean alveolar size was increased in the dorsocranial region of the lung of SMRM compared to controls. CONCLUSION: Recruitment manoeuvres improved oxygenation, but SMRM was superior, with respect to hemodynamics and pulmonary inflammation, in ventilated sheep suffering from ARDS induced by lung lavage.

Alveolocapillary model system to study alveolar re-epithelialization.

In the present study an in vitro bilayer model system of the pulmonary alveolocapillary barrier was established to investigate the role of the microvascular endothelium on re-epithelialization. The model system, confluent monolayer cultures on opposing sides of a porous membrane, consisted of a human microvascular endothelial cell line (HPMEC-ST1.6R) and an alveolar type II like cell line (A549), stably expressing EGFP and mCherry, respectively. These fluorescent proteins allowed the real time assessment of the integrity of the monolayers and the automated analysis of the wound healing process after a scratch injury. The HPMECs significantly attenuated the speed of re-epithelialization, which was associated with the proximity to the A549 layer. Examination of cross-sectional transmission electron micrographs of the model system revealed protrusions through the membrane pores and close contact between the A549 cells and the HPMECs. Immunohistochemical analysis showed that these close contacts consisted of heterocellular gap-, tight- and adherens-junctions. Additional analysis, using a fluorescent probe to assess gap-junctional communication, revealed that the HPMECs and A549 cells were able to exchange the fluorophore, which could be abrogated by disrupting the gap junctions using connexin mimetic peptides. These data suggest that the pulmonary microvascular endothelium may impact the re-epithelialization process.

Surfactant protein A influences reepithelialization in an alveolocapillary model system.

PURPOSE: Restoring the barrier integrity of the alveolar epithelium after injury is pivotal. In the current study, we evaluated the effects of surfactant, surfactant protein A (SP-A), transforming growth factor ß (TGF-ß), and analogues of SP-A on alveolar epithelial repair. Additionally, we assessed the influence of microvascular endothelial cells on reepithelialization. METHODS: Repair was studied in an in vitro model system consisting of a bilayer coculture of A549 and human pulmonary microvascular endothelial cells (HPMECs), which stably expressing fluorescent proteins. The epithelial repair was assessed in a scratch assay using vital fluorescence microscopy and compared with a monolayer of A549 cells. RESULTS: HMPEC cells differentially modulated the response of the A549 cells. Surfactant and SP-A augmented the reepithelialization in the presence of HPMECs, whereas in the absence of HPMECs, surfactant inhibited wound healing and SP-A failed to alter the response. Like SP-A, a structural analogue of its collagenous tail domain augmented the reepithelialization in the model system, whereas an analogue of its head domain did not alter the response. Additionally, we demonstrated that TGF-ß associated with SP-A was able to initiate the Smad-dependent TGF-ß pathway and that both TGF-ß and TGF-ß free SP-A were able to stimulate wound healing in the bilayer model. CONCLUSIONS: These data show that surfactant, SP-A and TGF-ß, influence epithelial repair in vitro and that the microvascular endothelial cells can modulate the response. This indicates that surfactant and SP-A could play a role in alveolar epithelial repair and that the microvascular endothelium may be involved in these processes.

Dissociation of transforming growth factors ß1 and ß2 from surfactant protein A (SP-A) by deglycosylation or deoxycholate treatment.

We were able to demonstrate the presence of transforming growth factor ß1 and transforming growth factor ß2 (TGF-ß1,2) in human as well as porcine pulmonary surfactants and SP-A purified from these surfactants. Human SP-A contained 480±74 pg TGF-ß1 and 61±16 pg TGF-ß2 per mg SP-A and human pulmonary surfactant contained 140±28 pg TGF-ß1 and 67±13 TGF-ß2 per mg protein. Porcine SP-A contained 306±46 pg TGF-ß1 and 43±12 pg TGF-ß2 per mg SP-A and porcine pulmonary surfactant contained 75±18 pg TGF-ß1 and 22±13 TGF-ß2 per mg protein. Size-exclusion chromatography indicated binding of TGF-ß1,2 to SP-A. Deglycosylation of SP-A released TGF-ß1,2 from SP-A indicating a role for the carbohydrate moieties of SP-A in binding of TGF-ß1,2. TGF-ß-free SP-A was obtained by incubating SP-A with 5 mM deoxycholate at pH 9.2 followed by size-exclusion chromatography, a protocol which can be used to study the biological activities of SP-A and TGF-ß1,2 separately. In addition, we demonstrated that after incubation of SP-A with TGF-ß1,2, only a part of the added TGF-ß1,2 can be measured, whereas after acid treatment almost all added TGF-ß1,2 was determined, suggesting that complex formation between SP-A and TGF-ß1,2 influences the measurements of TGF-ß1,2 in biological samples.