Haddad John J
Molecular Signaling Research Group, Division of Biological Sciences, Department of Biology, Faculty of Arts and Sciences, Lebanese International University, Beirut, Lebanon.
Protein Pept Lett. 2007;14(4):373-80. doi: 10.2174/092986607780363952.
Pursuant to establishing the proteomic distribution of MAPK(ERK)/MAPK(p38) in the brain in a model of hypoxia-tolerance [Haddad, Protein Pept Lett, In press, 2007], I therein exclusively report the differential expression of MAPK(JNK) and related upstream and downstream kinases in various organs of the anoxia-tolerant turtle. Despite the fact that the aforementioned mechanisms involved dual expression of MAPK(ERK), the mechanistic distribution of MAPK(JNK) has not been previously unraveled. Changes in the phosphorylation state of MAPKs may occur during anoxia, thereby reversible protein phosphorylation could be a critical factor and major mechanism of metabolic reorganization for enduring anaerobiosis.
If a turtle were to undergo hypoxia akin to that experienced in its native habitat, it was placed in a glass aquarium filled with water to within a half inch of the top. After the turtle was anesthetized, through extended hypoxia or anesthesia, the animal was sacrificed by decapitation. The brain and other organs were then excised and placed in anoxic artificial cerebrospinal fluid. Total protein extraction was performed by homogenizing various organs in a suitable buffer, followed by determination of the phosphorylation states of SEK-1/MKK-4, SAPK/MAPK(JNK) and c-Jun activating protein (AP)-1.
SEK-1/MKK-4 expression was mild in the cortex as compared with the manifold hypoxic (2h) induction in the liver. Continuous imposition of hypoxia (1 day - 1 week) increased the expression of SEK-1/MKK-4, thereafter declined at 3 weeks hypoxia. Hypoxia/reoxygenation weakly induced SEK-1/MKK-4 expression in cortex, in contrast with a strong induction in the liver, but not in other organs. Hypoxia (2h - 3 weeks) did not induce SAPK/MAPK(JNK) expression in cortex, despite prominent increase in liver, with mild reoxygenation effect. The normoxic induction of c-Jun AP-1 in cortex and rest of brain (ROB) was reduced with imposition of hypoxia (2h - 1 week). Furthermore, hypoxia (2h - 3 weeks) upregulated expression of c-Jun AP-1 in liver, heart and spleen, an effect abrogated with hypoxia/reoxygenation.
These results indicate that hypoxia differentially up-regulates the expression of MAPK(JNK)-related cofactors with organ-specific distribution. Since these modules are involved with neuroprotection in Chrysemys picta bellii, the expression of MAPKs bears relative mechanisms of specific responses to hypoxia tolerance.
为了确定耐缺氧模型中大脑中丝裂原活化蛋白激酶（ERK）/丝裂原活化蛋白激酶（p38）的蛋白质组分布[哈达德，《蛋白质与肽快报》，即将发表，2007年]，我在其中专门报道了耐缺氧海龟各器官中丝裂原活化蛋白激酶（JNK）及其相关上下游激酶的差异表达。尽管上述机制涉及丝裂原活化蛋白激酶（ERK）的双重表达，但丝裂原活化蛋白激酶（JNK）的机制分布此前尚未阐明。丝裂原活化蛋白激酶磷酸化状态的变化可能在缺氧期间发生，因此可逆性蛋白质磷酸化可能是持久无氧代谢重组的关键因素和主要机制。
如果将一只海龟置于类似于其原生栖息地所经历的缺氧环境中，将其放入一个装满水、水面距顶部半英寸的玻璃水族箱中。海龟麻醉后，通过长时间缺氧或麻醉，将其断头处死。然后切除大脑和其他器官，并置于缺氧人工脑脊液中。通过在合适的缓冲液中匀浆各种器官进行总蛋白提取，随后测定SEK-1/MKK-4、SAPK/MAPK（JNK）和c-Jun激活蛋白（AP）-1的磷酸化状态。
与肝脏中多种缺氧（2小时）诱导相比，SEK-1/MKK-4在皮质中的表达较轻。持续缺氧（1天至1周）会增加SEK-1/MKK-4的表达，此后在缺氧3周时下降。缺氧/复氧在皮质中弱诱导SEK-1/MKK-4表达，而在肝脏中诱导强烈，但在其他器官中则不然。缺氧（2小时至3周）在皮质中未诱导SAPK/MAPK（JNK）表达，尽管在肝脏中显著增加，且有轻度复氧效应。随着缺氧（2小时至1周）的施加，皮质和大脑其余部分（ROB）中c-Jun AP-1的常氧诱导降低。此外，缺氧（2小时至3周）上调了肝脏、心脏和脾脏中c-Jun AP-1的表达，缺氧/复氧可消除这种效应。
这些结果表明，缺氧以器官特异性分布差异上调丝裂原活化蛋白激酶（JNK）相关辅因子的表达。由于这些模块参与了彩龟的神经保护，丝裂原活化蛋白激酶的表达具有对耐缺氧的特定反应的相关机制。
