Hemin induces neuroglobin expression in neural cells

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Abstract
Neuroglobin is a newly identified vertebrate globin that binds O2 and is expressed in cerebral neurons. We found recently that neuronal expression of neuroglobin is stimulated by hypoxia and ischemia and protects neurons from hypoxic injury. Here we report that, like hemoglobin and myoglobin, neuroglobin expression can also be induced by hemin. Induction was concentration dependent and time dependent, with maximal (about 4-fold) increases in neuroglobin mRNA and protein levels occurring with 50 μM hemin and at 8 to 24 hours. The inductive effect of hemin was attenuated by the protein kinase G inhibitor KT5823 and the soluble guanylate cyclase inhibitor LY83583, was mimicked by treatment with 8-bromo–cyclic guanosine 3′,5′-monophosphate, and was accompanied by a greater than 10-fold increase in cGMP levels, suggesting that it is mediated through protein kinase G and soluble guanylate cyclase. In contrast, hypoxic induction of neuroglobin was blocked by the mitogen-activated protein kinase/extracellular signal–regulated kinase kinase inhibitor PD98059, indicating that hemin and hypoxia regulate neuroglobin expression by different mechanisms. These results provide evidence for regulation of neuroglobin expression by at least 2 signal transduction pathways.