Global Transcription Profiles of Anaplasma phagocytophilum at Key Stages of Infection in Tick and Human Cell Lines and Granulocytes

Abstract

The incidence of human diseases caused by tick-borne pathogens is increasing but little is known about the molecular interactions between the agents and their vectors and hosts. Anaplasma phagocytophilum (Ap) is an obligate intracellular, tick-borne bacterium that causes granulocytic anaplasmosis in humans, dogs, sheep, and horses. In mammals, neutrophil granulocytes are a primary target of infection, and in ticks, Ap has been found in gut and salivary gland cells. To identify bacterial genes that enable Ap to invade and proliferate in human and tick cells, labeled mRNA from Ap bound to or replicating within human and tick cells (lines HL-60 and ISE6), and replicating in primary human granulocytes ex vivo, was hybridized to a custom tiling microarray containing probes representing the entire Ap genome. Probe signal values plotted over a map of the Ap genome revealed antisense transcripts and unannotated genes. Comparisons of transcript levels from each annotated gene between test conditions (e.g., Ap replicating in HL-60 vs. ISE6) identified those that were differentially transcribed, thereby highlighting genes associated with each condition. Bacteria replicating in HL-60 cells upregulated 122 genes compared to those in ISE6, including numerous p44 paralogs, five HGE-14 paralogs, and 32 hypothetical protein genes, of which 47% were predicted to be secreted or localized to the membrane. By comparison, 60% of genes upregulated in ISE6 encoded hypothetical proteins, 60% of which were predicted to be secreted or membrane associated. In granulocytes, Ap upregulated 120 genes compared to HL-60, 33% of them hypothetical and 43% of those predicted to encode secreted or membrane associated proteins. HL-60-grown bacteria binding to HL-60 cells barely responded transcriptionally, while ISE6-grown bacteria binding to ISE6 cells upregulated 48 genes. HL-60-grown bacteria, when incubated with ISE6 cells, upregulated the same genes that were upregulated by ISE6-grown bacteria exposed to uninfected ISE6. Hypothetical genes (constituting about 29% of Ap genes) played a disproportionate role in most infection scenarios, and particular sets of them were consistently upregulated in bacteria binding/entering both ISE6 and HL-60 cells. This suggested that the encoded proteins played central roles in establishing infection in ticks and humans.

Comparative transcriptomic analysis of Rickettsia conorii during in vitro infection of human and tick host cells

“…The effect of host environment (human vis-à-vis arthropod) on bacterial transcriptional landscape has been documented for several other vector-borne pathogens, including Borrelia , Anaplasma , and Ehrlichia [ 9 – 11 ]. Comparative transcriptomic analysis of A. phagocytophilum grown in human (HL-60) and tick (ISE6) cells results in differential expression of 41.5% of the genes, of which 117 exhibit greater than two-fold change [ 12 ].…”

Low NETosis Induced in Anaplasma phagocytophilum-Infected Cells

“…In conclusion, the results of the study support that A. phagocytophilum can manipulate host cells for its own benefit [ 15 , 25 , 26 ] through molecular mechanisms, including manipulation of the immune response and apoptosis in both tick vectors and vertebrate hosts [ 4 , 11 , 24 , 36 , 37 ]. In this process, the induction of NETosis by A. phagocytophilum constitutes a new mechanism triggered by pathogen infection to facilitate infection of human cells.…”

Interspecies bacterial communication produces a delicate balance between Vibrio cholerae and the chironomid egg mass microbiome

“…Studying alternative signalling pathways in a naturally occurring environmental system may provide differing perspectives and results from artificial mouse‐based experimental systems. The physiologic and microbiotic environment of a chironomid egg mass is also very different from that of a mammalian gut, raising the likelihood of protein synthesis pathways unique to that system as is often the case with bacteria that inhabit multiple divergent environments, such as vector‐borne pathogens that circulate between arthropod and vertebrate host species (Nelson et al, 2020).…”