Mancuso Cesare, Capone Caterina, Ranieri Sofia Chiatamone, Fusco Salvatore, Calabrese Vittorio, Eboli Maria Luisa, Preziosi Paolo, Galeotti Tommaso, Pani Giovambattista
Institute of Pharmacology, Catholic University School of Medicine, Roma, Italy.
J Neurosci Res. 2008 Aug 1;86(10):2235-49. doi: 10.1002/jnr.21665.
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.
胆红素在大脑中过量积累时具有神经毒性，但它也因其抗氧化特性发挥着重要的生理作用。在此我们报告，将PC12细胞和原代大鼠小脑颗粒神经元暴露于胆红素（0.5 - 10微摩尔）中，会显著降低神经生长因子（NGF）/脑源性神经营养因子向Akt和细胞外信号调节激酶（ERK）的信号传导，这表明该分子直接干扰了关键的促生存信号通路。这种效应可能涉及胆红素的清除能力，胆红素能够在PC12细胞中抑制细胞内活性氧的积累以及Akt和ERK对细胞外过氧化氢的磷酸化反应。有趣的是，在没有外源性生长因子的情况下，胆红素会引发ERK和环磷酸腺苷反应元件结合（CREB）转录因子的磷酸化，这是NGF依赖性生存信号的特征。这些生长因子样的信号效应与神经元型一氧化氮合酶（nNOS）的诱导和一氧化氮（NO）的产生同时出现。对胆红素触发的信号级联进行药理学剖析发现，ERK的磷酸化需要通过可溶性鸟苷酸环化酶的NO信号传导，并且在更上游，细胞外钙的内流对于nNOS的诱导和NO的释放是必需的，这可能是通过CREB的钙依赖性磷酸化实现的。重要的是，胆红素通过NO和ERK引发的信号级联具有细胞保护作用，这在使用NOS或MEK抑制剂处理的培养物中胆红素毒性加剧的情况下得到了证实。综上所述，这些观察结果表明胆红素对神经营养因子的氧化还原信号传导具有重要作用，根据生长因子的可用性具有抑制或激动作用。
