Journal Article

PKR deficiency alters E. coli-induced sickness behaviors but does not exacerbate neuroimmune responses or bacterial load

Ho, Yuen-Shan, You, Ran, Poon, David Chun-Hei, Chang, Raymond Chuen-Chung, Tse, Hei-Long, Chiu, Kin

2015

Overview

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.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V
• Subject: Animals / Anorexia nervosa / Bacterial Load / Behavior, Animal / Biomedical and Life Sciences / Biomedicine / Brain Chemistry - genetics / Care and treatment / Corticosterone / Corticosterone - blood / Cytokines - blood / eIF-2 Kinase - genetics / Escherichia coli / Escherichia coli Infections - immunology / Escherichia coli Infections - psychology / Genetic aspects / Immunology / Liver - metabolism / Male / Mice / Mice, Inbred C57BL / Mice, Knockout / Neurobiology / Neurology / Neurosciences / Neutrophils / Physiological aspects / Receptors, Corticotropin-Releasing Hormone - biosynthesis / Receptors, Corticotropin-Releasing Hormone - genetics / RNA, Ribosomal, 16S - genetics / Tumor Necrosis Factor-alpha - blood