Plasmodium berghei NK65 in Combination with IFN-γ Induces Endothelial Glucocorticoid Resistance via Sustained Activation of p38 and JNK

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is an often lethal complication of malaria. Currently, no adequate therapy for this syndrome exists. Although glucocorticoids (GCs) have been used to improve clinical outcome of ARDS, their therapeutic benefits remain unclear. We previously developed a mouse model of MA-ARDS, in which dexamethasone treatment revealed glucocorticoid resistance. In the present study, we investigated glucocorticoid sensitivity of mouse microvascular lung endothelial cells stimulated with interferon-g (IFN-g) and Plasmodium berghei NK65 (PbNK65). Upon challenge with IFN-g alone, dexamethasone inhibited the expression of CCL5 (RANTES) by 90% and both CCL2 (MCP-1) and CXCL10 (IP-10) by 50%. Accordingly, whole transcriptome analysis revealed that dexamethasone differentially affected several gene clusters and in particular inhibited a large cluster of IFN-g-induced genes, including chemokines. In contrast, combined stimulation with IFN-g and PbNK65 extract impaired inhibitory actions of glucocorticoids on chemokine release, without affecting the capacity of the glucocorticoid receptor to accumulate in the nucleus. Subsequently, we investigated the effects of glucocorticoids on two signaling pathways activated by IFN-g. Dexamethasone left phosphorylation and protein levels of signal transducer and activator of transcription 1 (STAT1) unhampered. In contrast, dexamethasone inhibited the IFN-g-induced activation of two mitogen-activated protein kinases (MAPK), JNK and p38. However, PbNK65 extract abolished the inhibitory effects of glucocorticoids on MAPK signaling, inducing glucocorticoid resistance. These data provide novel insights into the mechanisms of glucocorticoid actions in endothelial cells and show how malaria may impair the beneficial effects of glucocorticoids.