Glutamine Suppresses Airway Neutrophilia by Blocking Cytosolic Phospholipase A2 via an Induction of MAPK Phosphatase-1

Abstract

Neutrophils are inflammatory cells that may contribute in a crucial way to the pathophysiology of steroid-resistant severe asthma. We previously reported that the nonessential amino acid l-glutamine (Gln) suppressed the recruitment of neutrophils into the airway in a murine model of asthma. In this study, we investigated the mechanisms by which Gln exerts beneficial effects in airway neutrophilia. We used the model we previously developed, which is suitable for examining sequential early asthmatic events, including neutrophil infiltration. Gln suppressed airway neutrophilia in a CXC chemokine-independent way. Airway neutrophilia was associated with cytosolic phospholipase A2 (cPLA2) and 5-lipoxygenase (5-LO) activities. p38 MAPK, the upstream pathway of cPLA2 and 5-LO, played a key role in inducing airway neutrophilia. Gln inhibited not only the phosphorylation of cPLA2 and p38 MAPK but also leukotriene B4 levels in the airways. Gln induced the early induction of MAPK phosphatase-1 (MKP-1) protein, a negative regulator of p38. MKP-1 small interfering RNA abrogated all the effects of Gln. Our results suggest that pathways involving p38/cPLA2/5-LO have a major role in airway neutrophilia. Gln suppresses airway neutrophilia via inhibiting p38 MAPK and its downstream pathways in an MKP-1–dependent way, which may provide a novel therapeutic strategy for pulmonary neutrophilic inflammatory diseases.

Mechanism of glutamine inhibition of cytosolic phospholipase a2 (cPLA2): Evidence of physical interaction between glutamine-Induced mitogen-activated protein kinase phosphatase-1 and cPLA2

“…Both MKP-1 induction and MKP-1 mediated p38 dephosphorylation within 5 min following Gln administration, suggesting that Gln dephosphorylated cPLA 2 indirectly through MKP-1-mediated p38 dephosphorylation. However, Gln dephosphorylated p-cPLA 2 rapidly within 5 min, as in the case of p38 in LPS-injected mice [13,14,20], suggesting that phosphatase is involved. Gln injection resulted in a rapid induction of MKP-1 within 5 min, which coincided with Gln-induced dephosphorylation of cPLA 2 (Fig.…”

“…Importantly, LTs play a key role in dendritic cell influx into airways in asthma [37][38][39] which, in turn, results in inhibition of recruitment of T cells and eosinophils into asthmatic airways and late AHR. Regarding neutrophil infiltration, we reported previously that airway neutrophilia in the asthmatic lungs is mediated by LTB4 rather than CXC chemokines such as keratinocyte-derived chemokine and macrophage inflammatory protein (MIP)-2 [20], which are principally chemotactic for neutrophils. Taken together, cPLA 2 metabolites play an important role in induction of airway neutrophilia and Th2-dependent asthmatic phenotypes.…”

“…cPLA 2 phosphorylation is known to depend upon the kinase activity of p38. In fact, pretreatment of p38 inhibitor SB202190 inhibited cPLA 2 phosphorylation significantly [20]. Injection of Gln resulted in a rapid dephosphorylation of p38 through MKP-1 induction [15].…”

“…We have reported previously a beneficial effect of Gln on allergic asthma in mice [14,20]. In this study, we assessed whether cPLA 2 /MKP-1 linkage was involved in the beneficial effect of Gln.…”

Glutamine Prevents Late-Phase Anaphylaxis via MAPK Phosphatase 1-Dependent Cytosolic Phospholipase A₂ Deactivation

“…was injected twice 24 h and 30 min before challenge [17,22]. U0126 (12.5 mg/kg in 5% DMSO) [23] was dissolved in DMSO and injected intraperitoneally 24 h before challenge injection. LTB 4 was purchased from Cayman Chemical Company.…”