Inflammatory signalling pathways involved in astroglial activation by unconjugated bilirubin.
During neonatal hyperbilirubinaemia, astrocytes activated by unconjugated bilirubin (UCB) may contribute to brain toxicity through the production of cytokines. As a first step in addressing the signal transduction cascades involved in the UCB-induced astroglial immunological response, we tested whether tumour necrosis factor (TNF)-alpha receptor 1 (TNFR1), mitogen-activated protein kinase (MAPK) and nuclear factor kappaB (NF-kappaB) would be activated in astrocytes exposed to UCB, and examined the profile of cytokine production. Astrocyte cultures stimulated with UCB showed a rapid rise in TNFR1 protein levels, followed by activation of the MAPKs p38, Jun N-terminal kinase1/2 and extracellular signal-regulated kinase1/2, and NF-kappaB. Interestingly, the induction of these signal effectors preceded the early up-regulation of TNF-alpha and interleukin (IL)-1beta mRNAs, and later secretion of TNF-alpha, IL-1beta and IL-6. Treatment of astrocytes with UCB also induced cell death, with levels comparable to those obtained after exposure of astrocytes to recombinant TNF-alpha and IL-1beta. Moreover, loss of cell viability and cytokine secretion were reduced when the NF-kappaB signal transduction pathway was inhibited, suggesting a key role for NF-kappaB in the astroglial response to UCB. These results demonstrate the complexity of the molecular mechanisms involved in cell injury by UCB during hyperbilirubinaemia and provide a basis for the development of novel therapeutic strategies.
Centro de Patogénese Molecular, UBMBE, Faculdade de Farmácia, University of Lisbon, Lisbon, Portugal.
Adelaide
A
Fernandes
Ana S
AS
Falcão
Rui F M
RF
Silva
Ana C
AC
Gordo
Maria J
MJ
Gama
Maria A
MA
Brito
Dora
D
Brites
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001663:Bilirubin / Q000378:metabolism* / Q000633:toxicity; D001921:Brain / Q000276:immunology / Q000378:metabolism* / Q000503:physiopathology; D016923:Cell Death / Q000187:drug effects / Q000276:immunology; D002478:Cells, Cultured; D016207:Cytokines / Q000276:immunology / Q000378:metabolism / Q000633:toxicity; D004660:Encephalitis / Q000209:etiology / Q000276:immunology / Q000378:metabolism*; D005911:Gliosis / Q000209:etiology / Q000276:immunology / Q000378:metabolism*; D051556:Hyperbilirubinemia, Neonatal / Q000276:immunology / Q000378:metabolism / Q000503:physiopathology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism; D009410:Nerve Degeneration / Q000139:chemically induced / Q000276:immunology / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018124:Receptors, Tumor Necrosis Factor / Q000187:drug effects / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I; D015398:Signal Transduction / Q000276:immunology; D053319:Tumor Necrosis Factor Decoy Receptors; D015854:Up-Regulation / Q000187:drug effects / Q000276:immunology
D016207:Cytokines; D016328:NF-kappa B; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D053319:Tumor Necrosis Factor Decoy Receptors; C069521:recombinant human tumor necrosis factor-binding protein-1; D001663:Bilirubin