Oleskovicz Scheyla P B, Martins Wagner C, Leal Rodrigo B, Tasca Carla I
Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Trindade, 88040-900 Florianópolis, SC, Brazil.
Neurochem Int. 2008 Feb;52(3):411-8. doi: 10.1016/j.neuint.2007.07.017. Epub 2007 Aug 1.
Guanine derivates have been implicated in many relevant extracellular roles, such as modulation of glutamate transmission, protecting neurons against excitotoxic damage. Guanine derivatives are spontaneously released to the extracellular space from cultured astrocytes during oxygen-glucose deprivation (OGD) and may act as trophic factors, glutamate receptors blockers or glutamate transport modulators, thus promoting neuroprotection. The aim of this study was to evaluate the mechanisms involved in the neuroprotective role of the nucleoside guanosine in rat hippocampal slices submitted to OGD, identifying a putative extracellular binding site and the intracellular signaling pathways related to guanosine-induced neuroprotection. Cell damage to hippocampal slices submitted to 15 min of OGD followed by 2 h of reperfusion was decreased by the addition of guanosine (100 microM) or guanosine-5'-monophosphate (GMP, 100 microM). The neuroprotective effect of guanosine was not altered by the addition of adenosine receptor antagonists, nucleosides transport inhibitor, glutamate receptor antagonists, glutamate transport inhibitors, and a non-selective Na(+) and Ca(2+) channel blocker. However, in a Ca(2+)-free medium (by adding EGTA), guanosine was ineffective. Nifedipine (a Ca(2+) channel blocker) increased the neuroprotective effect of guanosine and 4-aminopyridine, a K(+) channel blocker, reversed the neuroprotective effect of guanosine. Evaluation of the intracellular signaling pathways associated with guanosine-induced neuroprotection showed the involvement of PKA, PKC, MEK and PI-3 K pathways, but not CaMKII. Therefore, this study shows guanosine is acting via K(+) channels activation, depending on extracellular Ca(2+) levels and via modulation of the PKA, PKC, MEK and/or PI-3 K pathways.
鸟嘌呤衍生物在许多相关的细胞外作用中发挥了作用，例如调节谷氨酸传递，保护神经元免受兴奋性毒性损伤。在氧糖剥夺（OGD）期间，鸟嘌呤衍生物会从培养的星形胶质细胞自发释放到细胞外空间，并可能作为营养因子、谷氨酸受体阻滞剂或谷氨酸转运调节剂，从而促进神经保护。本研究的目的是评估核苷鸟苷在遭受OGD的大鼠海马切片中的神经保护作用机制，确定一个假定的细胞外结合位点以及与鸟苷诱导的神经保护相关的细胞内信号通路。加入鸟苷（100微摩尔）或5'-磷酸鸟苷（GMP，100微摩尔）可减少遭受15分钟OGD后再灌注2小时的海马切片的细胞损伤。加入腺苷受体拮抗剂、核苷转运抑制剂、谷氨酸受体拮抗剂、谷氨酸转运抑制剂以及非选择性的钠（+）和钙（2+）通道阻滞剂并不会改变鸟苷的神经保护作用。然而，在无钙培养基（通过添加乙二醇双四乙酸）中，鸟苷无效。硝苯地平（一种钙（2+）通道阻滞剂）增强了鸟苷的神经保护作用，而4-氨基吡啶（一种钾（+）通道阻滞剂）则逆转了鸟苷的神经保护作用。对与鸟苷诱导的神经保护相关的细胞内信号通路的评估表明，蛋白激酶A（PKA）、蛋白激酶C（PKC）、丝裂原活化蛋白激酶/细胞外信号调节激酶（MEK）和磷脂酰肌醇-3激酶（PI-3 K）通路参与其中，但钙/钙调蛋白依赖性蛋白激酶II（CaMKII）不参与。因此，本研究表明鸟苷通过激活钾（+）通道发挥作用，这取决于细胞外钙（2+）水平，并通过调节PKA、PKC、MEK和/或PI-3 K通路来实现。
