title: Bilirubin as an endogenous modulator of neurotrophin redox signaling.
abstract: Bilirubin is neurotoxic upon excess accumulation in the brain, but it also plays important physiological roles related to its antioxidant properties. Here we report that exposure of PC12 and primary rat cerebellar granule neurons to bilirubin (0.5-10 microM) drastically decreases nerve growth factor (NGF)/brain-derived neurotrophic factor signaling to Akt and extracellular signal-regulated kinases (ERKs), indicating a direct interference of the molecule with crucial prosurvival signaling pathways. This effect likely involves the scavenging capacity of bilirubin, the latter being able to inhibit, in PC12 cells, accumulation of intracellular reactive oxygen species and phosphorylation of Akt and ERKs in response to extracellular hydrogen peroxide. Interestingly, in the absence of exogenous growth factor, bilirubin elicited the phosphorylation of ERKs and of the cAMP responsive element binding (CREB) transcription factor, a signature of NGF-dependent survival signaling. These growth factor-like signaling effects were paralleled by the induction of the neuronal nitric oxide synthase (nNOS) and generation of nitric oxide (NO). Pharmacological dissection of the signaling cascade triggered by bilirubin revealed that phosphorylation of ERKs requires NO signaling through soluble guanylyl cyclase, and, further upstream, influx of extracellular calcium is necessary for nNOS induction and NO release, likely through calcium-dependent phosphorylation of CREB. Importantly, the cascade elicited by bilirubin through NO and ERK is cytoprotective, as revealed by exacerbated bilirubin toxicity in cultures treated by either NOS or MEK inhibitors. Taken together, these observations indicate an important action of bilirubin on redox signaling by neurotrophins, with either inhibitory or agonistic effects based on growth factor availability.
authors.affiliation: Institute of Pharmacology, Catholic University School of Medicine, Roma, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Mancuso
authors.forename: Caterina
authors.initials: C
authors.lastname: Capone
authors.forename: Sofia Chiatamone
authors.initials: SC
authors.lastname: Ranieri
authors.forename: Salvatore
authors.initials: S
authors.lastname: Fusco
authors.forename: Vittorio
authors.initials: V
authors.lastname: Calabrese
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Eboli
authors.forename: Paolo
authors.initials: P
authors.lastname: Preziosi
authors.forename: Tommaso
authors.initials: T
authors.lastname: Galeotti
authors.forename: Giovambattista
authors.initials: G
authors.lastname: Pani
mesh_terms: D000818:Animals; D001663:Bilirubin / Q000378:metabolism*; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism*; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D020932:Nerve Growth Factor / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D010084:Oxidation-Reduction; D016716:PC12 Cells; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D017382:Reactive Oxygen Species; D009569:Nitric Oxide; D020932:Nerve Growth Factor; D052248:Nitric Oxide Synthase Type I; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D001663:Bilirubin