Ixodes scapularis salivary gland microRNAs are differentially expressed during Powassan virus transmission

Meghan E Hermance,Saravanan Thangamani,Thomas G Wood,Steven G Widen

doi:10.1038/s41598-019-49572-5

Abstract

Successful tick feeding is facilitated by an assortment of pharmacologically-active factors in tick saliva that create an immunologically privileged micro-environment in the host’s skin. Through a process known as saliva-assisted transmission, bioactive tick salivary factors modulate the host environment, promoting transmission and establishment of a tick-borne pathogen. This phenomenon was previously demonstrated for Powassan virus (POWV), a North American tick-borne flavivirus that is the causative agent of a severe neuroinvasive disease in humans. Here, we sought to characterize the Ixodes scapularis salivary gland microRNAs (miRNAs) expressed during the earliest period of POWV transmission to a mammalian host. POWV-infected and uninfected I. scapularis females were fed on naïve mice for 1, 3, and 6 hours, and Illumina next generation sequencing was used to characterize the salivary gland miRNA expression profiles of POWV-infected versus uninfected ticks. 379 salivary miRNAs were detected, of which 338 are reported here as putative novel I. scapularis miRNAs. 35 salivary gland miRNAs were significantly up-regulated and 17 miRNAs were significantly down-regulated in response to POWV infection. To investigate the potential role of salivary gland miRNAs in POWV replication in-vitro, we transfected miRNA inhibitors into VeroE6 cells to profile temporal POWV replication in mammalian cells. Together, the small RNA sequencing data and the in vitro miRNA inhibition assay suggest that the differentially expressed tick salivary miRNAs could act in regulating POWV replication in host tissues.

Highlights

Ixodes scapularis ticks, otherwise known as the Deer tick, are vectors for several bacterial, protozoal, and viral pathogens in North America
We previously showed that the presence of unfed I. scapularis salivary gland extract (SGE) enhances the transmission of Powassan virus (POWV) and accelerates the disease progression for naive BALB/c mice infected with a low dose of POWV17
POWV-infected and uninfected I. scapularis adult females were fed on naïve mice for 1, 3, and 6 hours (1 tick per mouse), and tick salivary glands were dissected at each time point

Summary

Introduction

Otherwise known as the Deer tick, are vectors for several bacterial, protozoal, and viral pathogens in North America One such pathogen is Powassan virus (POWV), an emerging tick-borne flavivirus (TBFV) that can result in severe neurological symptoms in humans with case fatality rates ranging from 10–15% in most reports[1,2,3,4,5]. I. scapularis ticks transmit POWV via saliva to the skin of a vertebrate host during blood meal acquisition. (Boophilus) microplus and H. longicornis[23,24], and one study has profiled the miRNAs expressed in uninfected I. ricinus saliva and salivary glands[27]. No study has examined tick saliva/salivary gland miRNAs in relation to virus infection

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