title: Altered Toll-like receptor 9 signaling in Mycobacterium avium subsp. paratuberculosis-infected bovine monocytes reveals potential therapeutic targets.
abstract: Mycobacterium avium subsp. paratuberculosis is the causative agent of Johne's disease in cattle. The complex, multifaceted interaction of M. avium subsp. paratuberculosis with its host includes dampening the ability of infected cells to respond to stimuli that promote M. avium subsp. paratuberculosis clearance. By disrupting host defenses, M. avium subsp. paratuberculosis creates an intracellular environment that favors the establishment and maintenance of infection. Toll-like receptors (TLRs) are important sensors that initiate innate immune responses to microbial challenge and are also immunotherapeutic targets. For example, TLR9 contributes to host defense against M. avium subsp. paratuberculosis, and its agonists (CpG oligodeoxynucleotides [ODNs]) are under investigation for treatment of Johne's disease and other infections. Here we demonstrate that M. avium subsp. paratuberculosis infection changes the responsiveness of bovine monocytes to TLR9 stimulation. M. avium subsp. paratuberculosis inhibits classical TLR9-mediated responses despite a 10-fold increase in TLR9 expression and maintained uptake of CpG ODNs. Other TLR9-mediated responses, such as oxidative burst, which occur through noncanonical signaling, remain functional. Kinome analysis verifies that classic TLR9 signaling is blocked by M. avium subsp. paratuberculosis infection and that signaling instead proceeds through a Pyk2-mediated mechanism. Pyk2-mediated signaling does not hinder infection, as CpG ODNs fail to promote M. avium subsp. paratuberculosis clearance. Indeed, Pyk2 signaling appears to be an important aspect of M. avium subsp. paratuberculosis infection, as Pyk2 inhibitors significantly reduce the number of intracellular M. avium subsp. paratuberculosis bacteria. The actions of M. avium subsp. paratuberculosis on TLR9 signaling may represent a strategy to generate a host environment which is better suited for infection, revealing potential new targets for therapeutic intervention.
authors.affiliation: Vaccine and Infectious Disease Organization, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Arsenault
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.forename: Pekka
authors.initials: P
authors.lastname: Maattanen
authors.forename: Erin
authors.initials: E
authors.lastname: Scruten
authors.forename: Kimberley
authors.initials: K
authors.lastname: Doig
authors.forename: Andrew
authors.initials: A
authors.lastname: Potter
authors.forename: Philip
authors.initials: P
authors.lastname: Griebel
authors.forename: Anthony
authors.initials: A
authors.lastname: Kusalik
authors.forename: Scott
authors.initials: S
authors.lastname: Napper
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D051418:Focal Adhesion Kinase 2 / Q000276:immunology / Q000378:metabolism; D016753:Interleukin-10 / Q000276:immunology / Q000378:metabolism; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D016927:Mycobacterium avium subsp. paratuberculosis / Q000276:immunology / Q000378:metabolism*; D010283:Paratuberculosis / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology; D016897:Respiratory Burst / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology; D051217:Toll-Like Receptor 9 / Q000378:metabolism*
chemical_list: D051217:Toll-Like Receptor 9; D016753:Interleukin-10; D051418:Focal Adhesion Kinase 2