title: Immune-induced expression of lipocalin-2 in brain endothelial cells: relationship with interleukin-6, cyclooxygenase-2 and the febrile response.
abstract: Interleukin (IL)-6 is critical for the febrile response to peripheral immune challenge. However, the mechanism by which IL-6 enables fever is still unknown. To characterise the IL-6-dependent fever generating pathway, we used microarray analysis to identify differentially expressed genes in the brain of lipopolysaccharide (LPS)-treated IL-6 wild-type and knockout mice. Mice lacking IL-6 displayed a two-fold lower expression of the lipocalin-2 gene (lcn2), and this difference was confirmed by real-time reverse transcriptase-polymerase chain reaction. Conversely, the induction of lipocalin-2 protein was observed in brain vascular cells following i.p. administration of recombinant IL-6, suggesting a direct relationship between IL-6 and lipocalin-2. Immunohistochemical analysis also revealed that LPS-induced lipocalin-2 is expressed by brain endothelial cells and is partly co-localised with cyclooxygenase-2 (Cox-2), the rate-limiting enzyme for the production of inflammatory induced prostaglandin E(2)  (PGE(2) ), which is the key mediator of fever. The direct role of lipocalin-2 in fever was examined in LPS-challenged lipocalin-2 knockout mice. In both male and female mice, normal fever responses were observed at near-thermoneutral conditions (29-30 °C) but when recorded at normal room temperature (19-20 °C), the body temperature of lipocalin-2 knockout female mice displayed an attenuated fever response compared to their wild-type littermates. This difference was reflected in significantly attenuated mRNA expression of Cox-2 in the brain of lipocalin-2 knockout female mice, but not of male mice, following challenge with peripheral LPS. Our findings suggest that IL-6 influences the expression of lipocalin-2, which in turn may be involved in the control of the formation of Cox-2, and hence central PGE(2) -production. We have thus identified lipocalin-2 as a new factor in the pathway of inflammatory IL-6 signalling. However, the effect of lipocalin-2 on fever is small, being sex-dependent and ambient temperature-specific, and thus lipocalin-2 cannot be considered as a major mediator of the IL-6-dependent fever generating pathway.
authors.affiliation: Division of Cell Biology, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: N
authors.initials: N
authors.lastname: Hamzic
authors.forename: A
authors.initials: A
authors.lastname: Blomqvist
authors.forename: C
authors.initials: C
authors.lastname: Nilsberth
mesh_terms: D000209:Acute-Phase Proteins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D004727:Endothelium / Q000166:cytology / Q000378:metabolism; D005260:Female; D005334:Fever / Q000378:metabolism*; D007150:Immunohistochemistry; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D000071068:Lipocalin-2; D054834:Lipocalins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D000209:Acute-Phase Proteins; D015850:Interleukin-6; D000071068:Lipocalin-2; D054834:Lipocalins; D015513:Oncogene Proteins; C071332:Lcn2 protein, mouse; D051546:Cyclooxygenase 2