Protracted downregulation of CX3CR1 on microglia of aged mice after lipopolysaccharide challenge.
Fractalkine (CX(3)CL1) to fractalkine receptor (CX(3)CR1) interactions in the brain are involved in the modulation of microglial activation. Our recent findings indicate that there is microglial hyperactivity in the aged brain during an inflammatory challenge. The underlying cause of this amplified microglial response in the aged brain is unknown. Therefore, the purpose of this study was to determine the degree to which age-associated impairments of CX(3)CL1 and CX(3)CR1 in the brain contribute to exaggerated microglial activation after intraperitoneal (i.p.) injection of lipopolysaccharide (LPS). Here we show that CX(3)CL1 protein was reduced in the brain of aged (18-22 mo) BALB/c mice compared to adult (3-6 mo) controls. CX(3)CL1 protein, however, was unaltered by LPS injection. Next, CX(3)CR1 levels were determined in microglia (CD11b(+)/CD45(low)) isolated by Percoll density gradient separation at 4 and 24h after LPS injection. Flow cytometric and mRNA analyses of these microglia showed that LPS injection caused a marked decrease of CX(3)CR1 and a simultaneous increase of IL-1β at 4h after LPS injection. While surface expression of CX(3)CR1 was enhanced on microglia of adult mice by 24h, it was still significantly downregulated on a subset of microglia from aged mice. This protracted reduction of CX(3)CR1 corresponded with a delayed recovery from sickness behavior, prolonged IL-1β induction, and decreased TGFß expression in the aged brain. In the last set of studies BV2 microglia were used to determine effect of TGFß on CX(3)CR1. These results showed that TGFβ enhanced CX(3)CR1 expression and attenuated the LPS-induced increase in IL-1β expression.
Wynne
Angela M
AM
Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University, 333 W. 10th Avenue, Columbus, OH 43210, USA.
Henry
Christopher J
CJ
Huang
Yan
Y
Cleland
Anthony
A
Godbout
Jonathan P
JP
D000375:Aging / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000166:cytology* / Q000187:drug effects; D039481:CD11b Antigen / Q000378:metabolism; D000073883:CX3C Chemokine Receptor 1; D002452:Cell Count; D002478:Cells, Cultured; D054428:Chemokine CX3CL1 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D007274:Injections, Intraperitoneal; D053583:Interleukin-1beta / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D017493:Leukocyte Common Antigens / Q000378:metabolism; D008070:Lipopolysaccharides; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D017628:Microglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000187:drug effects; D019707:Receptors, Chemokine / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects
D039481:CD11b Antigen; D000073883:CX3C Chemokine Receptor 1; D054428:Chemokine CX3CL1; C515539:Cx3cl1 protein, mouse; C471885:Cx3cr1 protein, mouse; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D019707:Receptors, Chemokine; D016212:Transforming Growth Factor beta; D017493:Leukocyte Common Antigens