title: PKR deficiency alters E. coli-induced sickness behaviors but does not exacerbate neuroimmune responses or bacterial load.
abstract: BACKGROUND
  Systemic inflammation induces neuroimmune activation, ultimately leading to sickness (e.g., fever, anorexia, motor impairments, exploratory deficits, and social withdrawal). In this study, we evaluated the role of protein kinase R (PKR), a serine-threonine kinase that can control systemic inflammation, on neuroimmune responses and sickness.
  
  
  METHODS
  Wild-type (WT) PKR+/+ mice and PKR-/- mice were subcutaneously injected with live Escherichia coli (E. coli) or vehicle. Food consumption, rotarod test performance, burrowing, open field activity, object investigation, and social interaction were monitored. Plasma TNF-α and corticosterone were measured by ELISA. The percentage of neutrophils in blood was deduced from blood smears. Inflammatory gene expression (IL-1β, TNF-α, IL-6, cyclooxygenase (COX)-2, iNOS) in the liver and the brain (hypothalamus and hippocampus) were quantified by real-time PCR. Blood and lavage fluid (injection site) were collected for microbiological plate count and for real-time PCR of bacterial 16S ribosomal DNA (rDNA). Corticotrophin-releasing hormone (CRH) expression in the hypothalamus was also determined by real-time PCR.
  
  
  RESULTS
  Deficiency of PKR diminished peripheral inflammatory responses following E. coli challenge. However, while the core components of sickness (anorexia and motor impairments) were similar between both strains of mice, the behavioral components of sickness (reduced burrowing, exploratory activity deficits, and social withdrawal) were only observable in PKR-/- mice but not in WT mice. Such alteration of behavioral components was unlikely to be caused by exaggerated neuroimmune activation, by an impaired host defense to the infection, or due to a dysregulated corticosterone response, because both strains of mice displayed similar neuroimmune responses, bacterial titers, and plasma corticosterone profiles throughout the course of infection. Nevertheless, the induction of hypothalamic corticotrophin-releasing hormone (CRH) by E. coli was delayed in PKR-/- mice relative to WT mice, suggesting that PKR deficiency may postpone the CRH response during systemic inflammation.
  
  
  CONCLUSIONS
  Taken together, our findings show that (1) loss of PKR could alter E. coli-induced sickness behaviors and (2) this was unlikely to be due to exacerbated neuroimmune activation, (3) elevated bacterial load, or (4) dysregulation in the corticosterone response. Further studies can address the role of PKR in the CRH response together with its consequence on sickness.
authors.affiliation: Laboratory of Neurodegenerative Diseases, School of Biomedical Sciences, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. davidpoonhku@gmail.com.
authors.forename: David Chun-Hei
authors.initials: DC
authors.lastname: Poon
authors.affiliation: School of Nursing, Faculty of Health and Social Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China. Janice.ys.ho@polyu.edu.hk.
authors.forename: Yuen-Shan
authors.initials: YS
authors.lastname: Ho
authors.affiliation: Laboratory of Neurodegenerative Diseases, School of Biomedical Sciences, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. u3002472@connect.hku.hk.
authors.forename: Ran
authors.initials: R
authors.lastname: You
authors.affiliation: Laboratory of Neurodegenerative Diseases, School of Biomedical Sciences, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. heilong@connect.hku.hk.
authors.forename: Hei-Long
authors.initials: HL
authors.lastname: Tse
authors.affiliation: Department of Ophthalmology, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. ckirischiu@gmail.com.
authors.forename: Kin
authors.initials: K
authors.lastname: Chiu
authors.affiliation: Laboratory of Neurodegenerative Diseases, School of Biomedical Sciences, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. rccchang@hku.hk.|Research Centre of Heart, Brain, Hormone and Healthy Aging, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. rccchang@hku.hk.|State Key Laboratory of Brain and Cognitive Sciences, The University of Hong Kong, Hong Kong SAR, China. rccchang@hku.hk.|Rm. L1-49, Laboratory Block, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong SAR, China. rccchang@hku.hk.
authors.forename: Raymond Chuen-Chung
authors.initials: RC
authors.lastname: Chang
mesh_terms: D000818:Animals; D058491:Bacterial Load; D001522:Behavior, Animal; D001923:Brain Chemistry / Q000235:genetics; D003345:Corticosterone / Q000097:blood; D016207:Cytokines / Q000097:blood; D004927:Escherichia coli Infections / Q000276:immunology* / Q000523:psychology*; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009504:Neutrophils; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D018019:Receptors, Corticotropin-Releasing Hormone / Q000096:biosynthesis / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000097:blood; D019892:eIF-2 Kinase / Q000235:genetics*
chemical_list: D016207:Cytokines; D012336:RNA, Ribosomal, 16S; D018019:Receptors, Corticotropin-Releasing Hormone; D014409:Tumor Necrosis Factor-alpha; D019892:eIF-2 Kinase; C000605978:protein kinase R, mouse; D003345:Corticosterone