# Arthropod exosomal glycine-rich protein as a potential vaccine candidate effectively reduces tick blood-feeding and pathogen transmission

## TL;DR

A tick protein helps it feed and spread viruses, and targeting it could block disease transmission.

## Contribution

Identifies a tick exosomal glycine-rich protein as a novel vaccine target to block flavivirus transmission.

## Key findings

- Exosomal GRP promotes Langat virus transmission from ticks to hosts.
- RNAi silencing of GRP reduces tick feeding and viral transmission.
- Immunization with GRP disrupts tick feeding and pathogen spread.

## Abstract

During blood feeding, Ixodidae ticks secrete cement proteins, including glycine-rich proteins (GRPs), that facilitate attachment to the vertebrate host. However, the molecular mechanisms underlying exosomal GRP secretion at the feeding site and their roles in tick-pathogen interactions remain poorly understood. Here, we analyzed the Ixodes scapularis genome to identify salivary exosomal components involved in modulation of the tick-host skin interface. We identify an arthropod exosomal GRP (XM_002400035) that promotes transmission of Langat virus (LGTV), a tick-borne flavivirus, from ticks to vertebrate hosts. XM_002400035 was consistently upregulated in LGTV-infected I. scapularis ticks, tick-derived cells, and in tick exosomes. RNAi-mediated silencing of this exosomal GRP reduced viral loads, impaired tick blood-feeding efficiency, decreased tick body size and weights, and diminished LGTV acquisition and transmission. Similarly, active immunization of mice with recombinant GRP disrupted tick feeding, reduced tick fitness, and significantly impaired LGTV transmission from infected ticks to naive recipient hosts. Mechanistically, the exosomal GRP modulated host skin chemokine CXCL-12 levels at the feeding site. Together, these findings establish a dual role for a tick exosomal GRP in blood feeding and pathogen transmission and identify this tick exosomal GRP as a potential target for exosome-based transmission-blocking vaccines. More broadly, this work highlights arthropod exosomes as active mediators of flavivirus transmission and suggests new strategies for preventing and controlling tick-borne diseases.

Molecular mechanisms of arthropod-borne flavivirus transmission to vertebrate hosts are poorly understood. This study addresses how tick exosomal glycine-rich protein (GRP) secreted into the infectious saliva facilitates transmission of pathogens including Langat virus (LGTV, a tick-borne flavivirus) to the vertebrate host.

Arthropod exosomal GRP is upregulated upon tick feeding and LGTV infection to mediate pathogen transmission.RNAi-mediated silencing of this exosomal GRP molecule not only results in significant reduction in the tick blood feeding efficiency and tick body weight but also affects LGTV transmission from ticks to the vertebrate host.Treatment of primary cultures of human skin keratinocytes or HaCaT cells with recombinant GRP (rGRP) delayed wound closure and repair process.Treatment of primary cultures of human skin keratinocytes or HaCaT cells with antisera against rGRP blocked the effects of rGRP protein on wound closure and repair process.Immunization of mice with rGRP affects tick feeding and impaired transmission of LGTV to the vertebrate host.

Arthropod exosomal GRP is upregulated upon tick feeding and LGTV infection to mediate pathogen transmission.

RNAi-mediated silencing of this exosomal GRP molecule not only results in significant reduction in the tick blood feeding efficiency and tick body weight but also affects LGTV transmission from ticks to the vertebrate host.

Treatment of primary cultures of human skin keratinocytes or HaCaT cells with recombinant GRP (rGRP) delayed wound closure and repair process.

Treatment of primary cultures of human skin keratinocytes or HaCaT cells with antisera against rGRP blocked the effects of rGRP protein on wound closure and repair process.

Immunization of mice with rGRP affects tick feeding and impaired transmission of LGTV to the vertebrate host.

This study identifies a tick-derived exosomal glycine-rich protein that promotes blood feeding and facilitates transmission of a tick-borne flavivirus to vertebrate hosts.