Secreted Wnt antagonists in scrub typhus

Abstract

The mechanisms that control local and systemic inflammation in scrub typhus have only been partially elucidated. The wingless (Wnt) signaling pathways are emerging as important regulators of inflammation and infection, but have not been investigated in scrub typhus. Plasma levels of secreted Wnt antagonists (i.e. DKK-1, sFRP-3, WIF-1 and SOST) were analyzed in patients with scrub typhus (n = 129), patients with similar febrile illness without O. tsutsugamushi infection (n = 31), febrile infectious disease controls, and in healthy controls (n = 31) from the same area of South India, and were correlated to markers of inflammation, immune and endothelial cell activation as well as for their association with organ specific dysfunction and mortality in these patients. We found i) Levels of SOST and in particular sFRP-3 and WIF-1 were markedly increased and DKK-1 decreased in scrub typhus patients at admission to the hospital compared to healthy controls. ii) In recovering scrub typhus patients, SOST, sFRP-3 and WIF-1 decreased and DKK-1 increased. iii) SOST was positively correlated with markers of monocyte/macrophage and endothelial/vascular activation as well as with renal dysfunction and poor outcome iv) Finally, regulation of Wnt pathways by O. tsutsugamushi in vitro in monocytes and ex vivo in mononuclear cells isolated from patients with scrub typhus, as evaluated by gene expression studies available in public repositories, revealed markedly attenuated canonical Wnt signaling. Our findings suggest that scrub typhus is characterized by attenuated Wnt signaling possibly involving dysregulated levels of several secreted pathway antagonists. The secreted Wnt antagonist SOST was strongly associated with renal dysfunction and poor prognosis in these patients. Scrub typhus, a systemic infection caused by Orientia tsutsugamushi is manifested by fever and multiple organ involvement with significant mortality if untreated. O. tsutsugamushi infects endothelial cells triggering inflammatory responses in endothelial and monocyte-derived macrophages. The wingless (Wnt) pathways are important regulators of the interaction between microbes and the immune system promoting inflammatory and anti-inflammatory responses. Wnt signaling is regulated by multiple extracellular secreted proteins that are readily measurable and may reflect activity in the Wnt pathways. We measured plasma levels of the secreted Wnt modulators in patients with scrub typhus and infectious controls and correlated them with markers of inflammation and immune activation. We also evaluated the regulation of Wnt pathways by O. tsutsugamushi in vitro in monocytes and ex vivo in mononuclear cells isolated from patients in microarray experiments available in public repositories. Our study suggests a pathogenic role for dysregulated Wnt signaling during acute O. tsutsugamushi infection.