Discordant tissue-specific expression of SAPK/MAPK(JNK)-related cofactors in hypoxia and hypoxia/reoxygenation in a model of anoxia-tolerance.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Haddad
John J
JJ
Molecular Signaling Research Group, Division of Biological Sciences, Department of Biology, Faculty of Arts and Sciences, Lebanese International University, Beirut, Lebanon. john.haddad@yahoo.co.uk
D000818:Animals; D001921:Brain / Q000201:enzymology; D002540:Cerebral Cortex / Q000201:enzymology; D000860:Hypoxia / Q000503:physiopathology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000096:biosynthesis*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology; D048055:Mitogen-Activated Protein Kinase 8 / Q000096:biosynthesis*; D009928:Organ Specificity; D015427:Reperfusion Injury / Q000503:physiopathology*; D014426:Turtles
D048031:JNK Mitogen-Activated Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D048670:MAP Kinase Kinase 4