Biology subjects

Ramirez-Zepp, E.

Publications and source records attributed to Ramirez-Zepp, E..

3 recordsLinked to original sources

bioRxiv2025

Acquired tick resistance in Peromyscus leucopus alters Ixodes scapularis infection

Ticks are obligate hematophagous parasites and pathogen vectors responsible for morbidity and mortality worldwide. Ixodes scapularis is a vector for at least seven pathogens relevant to human and animal health including the Lyme disease microbe, Borrelia burgdorferi, and the causative agent of anaplasmosis, Anaplasma phagocytophilum. Tick-host interactions are a driving influence on the maintenance of tick-borne pathogens in a population. Here, we report that repeated I. scapularis larval infestations on the wild host species Peromyscus leucopus leads to immune-mediated rejection of the tick, a phenomenon termed acquired tick resistance (ATR). We found that over 50% fewer larvae reached repletion and had decreased blood meal weights compared to larvae fed on naive hosts. Additionally, mice exhibited increasingly severe inflammation at tick bite sites characterized by an influx of basophils, eosinophils, neutrophils, and T lymphocytes. Larvae fed on sensitized mice ingested higher quantities of host leukocytes when compared to ticks fed on naive hosts, which rarely ingested nucleated cells. When challenged with B. burgdorferi or A. phagocytophilum, larvae fed on sensitized mice ingested more bacteria. Altogether, we demonstrate that reservoir host species develop ATR against larval I. scapularis, which reduces tick feeding success and affects pathogen ingestion by larvae. These results indicate that ATR could impact Ixodes population dynamics, prevalence of infected ticks, and pathogen circulation in the wild.

immunology↗

bioRxiv2025

ATF6 enables pathogen infection in ticks by inducing stomatin and altering cholesterol dynamics

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 that Ixodes scapularis ticks infected with either Anaplasma phagocytophilum (causative agent of anaplasmosis) or Borrelia 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 the Ixodes ATF6 transcriptional network, we developed a custom R script to query tick promoter sequences. This revealed stomatin as a potential gene target, which has roles in lipid homeostasis and vesical transport. Ixodes stomatin was experimentally validated as a bona fide ATF6-regulated gene through luciferase reporter assays, pharmacological activators, and RNAi transcriptional repression. Silencing stomatin decreased A. phagocytophilum colonization in Ixodes and disrupted cholesterol dynamics in tick cells. Furthermore, blocking stomatin restricted cholesterol availability to the bacterium, thereby inhibiting growth and survival. Taken together, we have identified the Ixodes ATF6 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 of stomatin is unique to blood-feeding arthropods. Collectively, these findings highlight the importance of studying fundamental processes in non-model organisms. IMPORTANCEHost-pathogen interactions for tick-borne pathogens like Anaplasma 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, in Ixodes ticks. 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 the Ixodes ATF6 regulome, stomatin was identified as an ATF6-regulated target that supports Anaplasma colonization by facilitating cholesterol availability to the bacterium. Moreover, our custom, web-based tool "ArthroQuest" found that the ATF6-regulated nature of stomatin is unique to arthropods. Given that lipid hijacking is common among arthropod-borne microbes, ATF6-mediated induction of stomatin may 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.

microbiology↗

bioRxiv2023

PERK-mediated antioxidant response is key for pathogen persistence in ticks

A crucial phase in the lifecycle of tick-borne pathogens is the time spent colonizing and persisting within the arthropod. Tick immunity is emerging as a key force shaping how transmissible pathogens interact with the vector. How pathogens remain in the tick despite immunological pressure remains unknown. In persistently infected Ixodes scapularis, we found that Borrelia burgdorferi (Lyme disease) and Anaplasma phagocytophilum (granulocytic anaplasmosis) activate a cellular stress pathway mediated by the endoplasmic reticulum receptor PERK and the central regulatory molecule, eIF2. Disabling the PERK pathway through pharmacological inhibition and RNAi significantly decreased microbial numbers. In vivo RNA interference of the PERK pathway not only reduced the number of A. phagocytophilum and B. burgdorferi colonizing larvae after a bloodmeal, but also significantly reduced the number of bacteria that survive the molt. An investigation into PERK pathway-regulated targets revealed that A. phagocytophilum and B. burgdorferi induce activity of the antioxidant response regulator, Nrf2. Tick cells deficient for nrf2 expression or PERK signaling showed accumulation of reactive oxygen and nitrogen species in addition to reduced microbial survival. Supplementation with antioxidants rescued the microbicidal phenotype caused by blocking the PERK pathway. Altogether, our study demonstrates that the Ixodes PERK pathway is activated by transmissible microbes and facilitates persistence in the arthropod by potentiating an Nrf2-regulated antioxidant environment.

microbiology↗