Anaplasma phagocytophilumincreases the levels of histone modifying enzymes to inhibit cell apoptosis and facilitate pathogen infection in the tick vectorIxodes scapularis

Abstract

Epigenetic mechanisms have not been characterized in ticks despite their importance as vectors of human and animal diseases worldwide. The objective of this study was to characterize the histones and histone modifying enzymes (HMEs) of the tick vector Ixodes scapularis and their role during Anaplasma phagocytophilum infection. We first identified 5 histones and 34 HMEs in I. scapularis in comparison with similar proteins in model organisms. Then, we used transcriptomic and proteomic data to analyze the mRNA and protein levels of I. scapularis histones and HMEs in response to A. phagocytophilum infection of tick tissues and cultured cells. Finally, selected HMEs were functionally characterized by pharmacological studies in cultured tick cells. The results suggest that A. phagocytophilum manipulates tick cell epigenetics to increase I. scapularis p300/CBP, histone deacetylase, and Sirtuin levels, resulting in an inhibition of cell apoptosis that in turn facilitates pathogen infection and multiplication. These results also suggest that a compensatory mechanism might exist by which A. phagocytophilum manipulates tick HMEs to regulate transcription and apoptosis in a tissue-specific manner to facilitate infection, but preserving tick fitness to guarantee survival of both pathogens and ticks. Our study also indicates that the pathogen manipulates arthropod and vertebrate cell epigenetics in similar ways to inhibit the host response to infection. Epigenetic regulation of tick biological processes is an essential element of the infection by A. phagocytophilum and the study of the mechanisms and principal actors involved is likely to provide clues for the development of anti-tick drugs and vaccines.

The intracellular bacterium Anaplasma phagocytophilum selectively manipulates the levels of vertebrate host proteins in the tick vector Ixodes scapularis

“…The transcriptomics and proteomics data used in this study was previously validated by real-time RT-PCR and Western blot or immunofluorescence for selected genes and proteins, respectively [12, 43]. Nevertheless, 5 selected genes coding for hemoglobin digesting enzymes differentially regulated in response to A. phagocytophilum infection were used for analysis by real-time RT-PCR in individual tick midguts and salivary glands (see Additional file 2: Figure S1).…”

“…How A. phagocytophilum modify tick proteolytic pathways is not known, but may include the regulation of gene expression through epigenetic mechanisms recently shown to be affected by pathogen infection in I. scapularis [43]. These epigenetic mechanisms are probably controlled by secreted bacterial effectors [55–58].…”

Tick-Pathogen Interactions and Vector Competence: Identification of Molecular Drivers for Tick-Borne Diseases

“…The results of this study suggested that a compensatory mechanism might exist by which A. phagocytophilum differentially manipulates tick HMEs to regulate transcription and apoptosis in a tissue-specific manner to facilitate infection but preserving tick fitness to guarantee survival of both pathogens and ticks (Cabezas-Cruz et al, 2016). As previously discussed (Cabezas-Cruz et al, 2016), the mechanisms by which A. phagocytophilum affects tick cell epigenetics is unknown but effector proteins such as AnkA, secreted through T4SS or other secretion mechanisms probably control it (Garcia-Garcia et al, 2009a,b; Rennoll-Bankert et al, 2015). It has been previously demonstrated that A. phagocytophilum AnkA recruits host histone deacetylase 1 (HDAC1) and modifies neutrophils gene expression (Garcia-Garcia et al, 2009a,b; Rennoll-Bankert et al, 2015).…”

“…Recently, A. phagocytophilum was shown to manipulate tick cell epigenetics to increase the levels of the histone modifying enzymes (HMEs), histone acetyltransferases (HATs; 300/CBP), and histone deacetylases (HDACs and Sirtuins) resulting in the inhibition of cell apoptosis to facilitate pathogen infection and multiplication (Cabezas-Cruz et al, 2016). The results of this study suggested that a compensatory mechanism might exist by which A. phagocytophilum differentially manipulates tick HMEs to regulate transcription and apoptosis in a tissue-specific manner to facilitate infection but preserving tick fitness to guarantee survival of both pathogens and ticks (Cabezas-Cruz et al, 2016). As previously discussed (Cabezas-Cruz et al, 2016), the mechanisms by which A. phagocytophilum affects tick cell epigenetics is unknown but effector proteins such as AnkA, secreted through T4SS or other secretion mechanisms probably control it (Garcia-Garcia et al, 2009a,b; Rennoll-Bankert et al, 2015).…”

“…It has been previously demonstrated that A. phagocytophilum AnkA recruits host histone deacetylase 1 (HDAC1) and modifies neutrophils gene expression (Garcia-Garcia et al, 2009a,b; Rennoll-Bankert et al, 2015). Interestingly, the homolog of HDAC1 in I. scapularis was overrepresented upon A. phagocytophilum infection in tick salivary glands (Cabezas-Cruz et al, 2016). It remains to be tested whether A. phagocytophilum AnkA plays the same role in ticks as in vertebrate neutrophils.…”