ATF6 enables pathogen infection in ticks by inducingstomatinand altering cholesterol dynamics
Authors: Vosbigian Kaylee A. , Wright Sarah J. , Rosche Kristin L. , Fisk Elis A. , Ramirez-Zepp Elisabeth , Shelden Eric A. , Shaw Dana K. 
Published: January 2025

How tick-borne pathogens interact with their hosts has been primarily studied in vertebrates where disease is observed. Comparatively less is known about pathogen interactions within the tick. Here, we report thatIxodes scapularisticks infected with eitherAnaplasma phagocytophilum(causative agent of anaplasmosis) orBorrelia burgdorferi(causative agent of Lyme disease) show activation of the ATF6 branch of the unfolded protein response (UPR). Disabling ATF6 functionally restricts pathogen survival in ticks. When stimulated, ATF6 functions as a transcription factor, but is the least understood out of the three UPR pathways. To interrogate theIxodesATF6 transcriptional network, we developed a custom R script to query tick promoter sequences. This revealedstomatinas a potential gene target, which has roles in lipid homeostasis and vesical transport.Ixodes stomatinwas experimentally validated as a bona fide ATF6-regulated gene through luciferase reporter assays, pharmacological activators, and RNAi transcriptional repression. SilencingstomatindecreasedA. phagocytophilumcolonization inIxodesand disrupted cholesterol dynamics in tick cells. Furthermore, blockingstomatinrestricted cholesterol availability to the bacterium, thereby inhibiting growth and survival. Taken together, we have identified theIxodesATF6 pathway as a novel contributor to vector competence through Stomatin-regulated cholesterol homeostasis. Moreover, our custom, web-based transcription factor binding site search tool “ArthroQuest” revealed that the ATF6-regulated nature ofstomatinis unique to blood-feeding arthropods. Collectively, these findings highlight the importance of studying fundamental processes in non-model organisms.

IMPORTANCE

Host-pathogen interactions for tick-borne pathogens likeAnaplasma phagocytophilum(causative agent of Anaplasmosis) have been primarily studied in mammalian hosts. Comparatively less is known about interactions within the tick. Herein, we find that tick-borne pathogens activate the cellular stress response receptor, ATF6, inIxodesticks. Upon activation, ATF6 is cleaved and the cytosolic portion translocates to the nucleus to function as a transcription factor that coordinates gene expression networks. Using a custom script in R to query theIxodesATF6 regulome,stomatinwas identified as an ATF6-regulated target that supportsAnaplasmacolonization by facilitating cholesterol availability to the bacterium. Moreover, our custom, web-based tool “ArthroQuest” found that the ATF6-regulated nature ofstomatinis unique to arthropods. Given that lipid hijacking is common among arthropod-borne microbes, ATF6-mediated induction ofstomatinmay be a mechanism that is exploited in many vector-pathogen relationships for the survival and persistence of transmissible microbes. Collectively, this study identified a novel contributor to vector competence and highlights the importance of studying molecular networks in non-model organisms.