Systems Biology of Tissue-Specific Response to Anaplasma phagocytophilum Reveals Differentiated Apoptosis in the Tick Vector Ixodes scapularis

Abstract

Anaplasma phagocytophilum is an emerging pathogen that causes human granulocytic anaplasmosis. Infection with this zoonotic pathogen affects cell function in both vertebrate host and the tick vector, Ixodes scapularis. Global tissue-specific response and apoptosis signaling pathways were characterized in I. scapularis nymphs and adult female midguts and salivary glands infected with A. phagocytophilum using a systems biology approach combining transcriptomics and proteomics. Apoptosis was selected for pathway-focused analysis due to its role in bacterial infection of tick cells. The results showed tissue-specific differences in tick response to infection and revealed differentiated regulation of apoptosis pathways. The impact of bacterial infection was more pronounced in tick nymphs and midguts than in salivary glands, probably reflecting bacterial developmental cycle. All apoptosis pathways described in other organisms were identified in I. scapularis, except for the absence of the Perforin ortholog. Functional characterization using RNA interference showed that Porin knockdown significantly increases tick colonization by A. phagocytophilum. Infection with A. phagocytophilum produced complex tissue-specific alterations in transcript and protein levels. In tick nymphs, the results suggested a possible effect of bacterial infection on the inhibition of tick immune response. In tick midguts, the results suggested that A. phagocytophilum infection inhibited cell apoptosis to facilitate and establish infection through up-regulation of the JAK/STAT pathway. Bacterial infection inhibited the intrinsic apoptosis pathway in tick salivary glands by down-regulating Porin expression that resulted in the inhibition of Cytochrome c release as the anti-apoptotic mechanism to facilitate bacterial infection. However, tick salivary glands may promote apoptosis to limit bacterial infection through induction of the extrinsic apoptosis pathway. These dynamic changes in response to A. phagocytophilum in I. scapularis tissue-specific transcriptome and proteome demonstrated the complexity of the tick response to infection and will contribute to characterize gene regulation in ticks.

Integrated Metabolomics, Transcriptomics and Proteomics Identifies Metabolic Pathways Affected by Anaplasma phagocytophilum Infection in Tick Cells*

“…However, it has been demonstrated that the tick response to infection is a complex and dynamic process with tissuespecific differences (8). In an attempt to address this issue, a preliminary and complementary analysis of tissue-specific differences in response to infection of I. scapularis nymphs and adult female guts and salivary glands was included in the study.…”

“…Other hemolymph effector proteins associated with tick hemocytes such as defensins, Complement-like molecules and antimicrobial peptides were also identified and, although not differentially represented between infected and uninfected cells (Supplemental Table V), could serve as biomarkers for hemocyte-like function of ISE6 tick cells (51). Recent results showed how the I. scapularis nymphs and adult female guts and salivary glands respond to A. phagocytophilum infection at both RNA and protein levels (8). Using those results and the results reported in the present study, the expression/representation of selected genes/proteins involved in the protein processing in ER and glucose metabolic pathways were compared between in vitro and in vivo studies (Fig.…”

“…Postgenomic experimental approaches such as transcriptomics and proteomics have increased our understanding of tickpathogen interactions. Recent research by our group has focused on the characterization of the vector competency of ticks for A. phagocytophilum (8). Previous results demonstrated that tick vector competency involves molecular interactions that ensure that A. phagocytophilum bacteria infect, develop, and are transmitted by ticks (1, 8 -14).…”

“…Previous results demonstrated that tick vector competency involves molecular interactions that ensure that A. phagocytophilum bacteria infect, develop, and are transmitted by ticks (1, 8 -14). Two studies have characterized the tick transcriptome and proteome in response to A. phagocytophilum infection (8,10) and tick proteins have been identified that mediate A. phagocytophilum infection, multiplication, and transmission (1,8,9,(11)(12)(13)(14). Metabolomics is a postgenomic research field concerned with developing methods for analysis of low molecular weight compounds in biological systems such as cells, organs, and organisms.…”

Infection of Ixodes spp. tick cells with different Anaplasma phagocytophilum isolates induces the inhibition of apoptotic cell death

“…Recently, Ayllón et al (2015) showed that A. phagocytophilum (NY18) inhibits the intrinsic apoptosis pathway through porin downregulation to prevent Cytochrome c release in I. scapularis salivary glands. To characterize this mechanism in vitro, gene knockdown by RNAi was used for functional characterization of the porin gene during…”