Generation of lyso-phospholipids from surfactant in acute lung injury is mediated by type-II phospholipase A2 and inhibited by a direct surfactant protein A-phospholipase A2 protein interaction.

Abstract

Lyso-phospholipids exert a major injurious effect on lung cell membranes during Acute Respiratory Distress Syndrome (ARDS), but the mechanisms leading to their in vivo generation are still unknown. Intratracheal administration of LPS to guinea pigs induced the secretion of type II secretory phospholipase A2 (sPLA2-II) accompanied by a marked increase in fatty acid and lyso-phosphatidylcholine (lyso-PC) levels in the bronchoalveolar lavage fluid (BALF). Administration of LY311727, a specific sPLA2-II inhibitor, reduced by 60% the mass of free fatty acid and lyso-PC content in BALF. Gas chromatography/mass spectrometry analysis revealed that palmitic acid and palmitoyl-2-lyso-PC were the predominant lipid derivatives released in BALF. A similar pattern was observed after the intratracheal administration of recombinant guinea pig (r-GP) sPLA2-II and was accompanied by a 50-60% loss of surfactant phospholipid content, suggesting that surfactant is a major lung target of sPLA2-II. In confirmation, r-GP sPLA2-II was able to hydrolyze surfactant phospholipids in vitro. This hydrolysis was inhibited by surfactant protein A (SP-A) through a direct and selective protein-protein interaction between SP-A and sPLA2-II. Hence, our study reports an in vivo direct causal relationship between sPLA2-II and early surfactant degradation and a new process of regulation for sPLA2-II activity. Anti-sPLA2-II strategy may represent a novel therapeutic approach in lung injury, such as ARDS. (

Inhibitory Effects of Surfactant Protein A on Surfactant Phospholipid Hydrolysis by Secreted Phospholipases A2

“…3). As previously found (14), sPLA 2 -IIA hydrolyzed surfactant phospholipids, and PG was the most preferred substrate for this enzyme. By contrast, the other type II sPLA 2 s, including IIC, IID, IIE, and IIF enzymes, were ineffective in hydrolysis.…”

“…We first checked whether mouse sPLA 2 -IIA was able to hydrolyze surfactant phospholipids under in vivo conditions in mice. Several studies have shown that intratracheal administration of sPLA 2 s can induce lung injury with interstitial and alveolar edema, accumulation of inflammatory cells, and free fatty acid release (14,39,40), which are pathological features typical of those seen in the lungs of ARDS patients. However, these studies have often used heterologous sPLA 2 s from snake venoms, which have much higher ability than mammalian sPLA 2 s to hydrolyze phospholipids on packed monolayer structures.…”

“…However, the type of sPLA 2 involved in this disorder remains unclear. While sPLA 2 -IIA is able to efficiently hydrolyze surfactant phospholipids, thereby contributing to surfactant alteration as observed in ARDS (14), the involvement of the other cloned sPLA 2 s in this process is not yet defined, and their roles in ARDS lung disease remain uncertain. In this study we investigated the potential pathological contribution of the newly cloned sPLA 2 s in ARDS by analyzing their ability to hydrolyze surfactant phospholipids in vitro.…”

“…Indeed, despite recent advances in intensive care, the ARDS mortality rate still exceeds 40%, and there is no effective therapy apart from mechanical ventilation and other supportive measures (15). Interestingly, we previously showed that surfactant protein A (SP-A), which is the major surfactant-associated protein, inhibits the in vitro sPLA 2 -IIA activity through a direct protein-protein interaction (14). SP-A, which is a member of the C-type lectin superfamily and contains a COOH-terminal carbohydrate recognition domain (CRD) (16), plays an important role in pulmonary host defense and seems to inhibit inflammation following lung infection.…”

“…We previously demonstrated the inhibitory effect of SP-A on sPLA 2 -IIA activity on synthetic PG substrates in vitro (14). To assess the relationship between SP-A and surfactant phospholipid hydrolysis by sPLA 2 -IIA, surfactants purified from wild-type mice, mice deficient in SP-A (SP-A Ϫ/Ϫ mice), or mice with increased alveolar SP-A (GM-CSF Ϫ/Ϫ mice) were used as substrates.…”