Hypoxia Upregulates MAPKp38/MAPKERK Phosphorylation In Vitro: Neuroimmunological Differential Time-Dependent Expression of MAPKs
John J. Haddad and Lama B. Hanbali
Affiliation: Department of Medical Laboratory Technology, Faculty of Health Sciences, Beirut Arab University, Beirut, Lebanon.
Keywords: Anaerobiosis, anoxia, cortical neurons, hippocampal slices, hypoxia, MAPKs, neuroprotection, phosphorylation.
In mammalian cells, responses to hypoxia at the molecular transduction level are hallmarks of adaptation and
survival under oxygen deprivation conditions. In this study, the protein expression patterns of mitogen-activated protein
kinases (MAPKs) are investigated under hypoxia in primary cortical neurons and in a model of organotypic hippocampal
slices in neonatal Sprague-Dawley rats. Abrupt fluctuations in MAPK expression can occur during anoxia, hypoxia, and
relative hyperoxic shifts (e.g., reoxygenation); therefore, phosphorylation and dephosphorylation states could be crucial
factors in metabolic reorganization for withstanding anaerobiosis. Whole cellular protein extracts were analyzed for the
phosphorylation of MAPKpp38 and MAPKERK-1/2 (p44/p42) at threonine and tyrosine residues (Thr180/Tyr182) at different time
periods of hypoxic exposure relative to a fixed normoxia control. The phospho-MAPKp38 (p-MAPKp38) to MAPKp38 relative
unit ratio revealed that MAPKp38 expression increased in cortical neurons after 5 and 10 min, but decreased abruptly
afterwards (20 – 120 min). The expression of phospho-MAPKERK-1 (p-MAPKERK-1/p44), however, decreased whereas that
of p-MAPKERK-2/p42 increased compared to normoxia. In rat hippocampal slices (RHS), the expression of p-MAPKp38 was
slightly but significantly higher in hypoxia, whereas the expression of p-MAPKERK-2/p42 increased and that of p-MAPKERK-1/p44 was intangible. This indicates that in cortical neurons hypoxia differentially upregulated the phosphorylation activation
states of MAPKp38 and MAPKERK-1/2 (p44/p42), whereas in the RHS model MAPKp38 and MAPKERK-2/p42, but not
MAPKERK-1/p44, phosphorylation states were upregulated in response to hypoxia. The neuroimmunological molecular patterns
of the differential MAPK phosphorylation in vitro and ex vivo in response to hypoxic shift indicated a significant
role for these kinases in cellular adaptation to oxygen deprivation, and thereby may identify physiologic and neuroprotective
responsive signaling cofactors and pathways in cortical and hippocampal neurons during hypoxia.
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