Transforming Growth Factor-α Attenuates N-Methyl-D-aspartic Acid Toxicity in Cortical Cultures by Preventing Protein Synthesis Inhibition through an Erk1/2-dependent Mechanism

Abstract

Transforming growth factor-␣ (TGF-␣), a ligand of the epidermal growth factor receptor, reduces the infarct size after focal cerebral ischemia in rat, but the molecular basis underlying the protection is unknown. Excitotoxicity and global inhibition of translation are acknowledged to contribute significantly to the ischemic damage. Here we studied whether TGF-␣ can rescue neurons from excitotoxicity in vitro and how it affects calcium homeostasis, protein synthesis, and the associated Akt and extracellular signal-regulated kinase 1/2 (Erk1/2) intracellular signaling pathways in mixed neuron-glia cortical cultures. We found that 100 ng/ml TGF-␣ attenuated neuronal cell death induced by a 30-min exposure to 35 M N-methyl-D-aspartic acid (NMDA) (as it reduced lactate dehydrogenase release, propidium iodide staining, and caspase-3 activation) and decreased the elevation of intracellular Ca 2؉ elicited by NMDA. TGF-␣ induced a prompt and sustained phosphorylation of Erk1/2 and prevented the loss of Akt-P induced by NMDA 3 h after exposure. The protective effect of TGF-␣ was completely prevented by PD 98059, an inhibitor of the Erk1/2 pathway. Studies of incorporation of [ 3 H]leucine into proteins showed that NMDA decreased the rate of protein synthesis, and TGF-␣ attenuated this effect. TGF-␣ stimulated the phosphorylation of the eukaryotic initiation factor 4E (eIF4E) but did not affect eIF2␣, two proteins involved in translation regulation. PD 98059 abrogated the TGF-␣ effect on eIF4E. Our data demonstrate that TGF-␣ exerts a neuroprotective action against NMDA toxicity, in which Erk1/2 activation plays a key role, and suggest that the underlying mechanisms involve recovery of translation inhibition, mediated at least in part by eIF4E phosphorylation.TGF-␣ 1 is protective in models of permanent and transient focal ischemia induced by occlusion of the middle cerebral artery in the rat (1, 2). Although TGF-␣ is known to promote neuronal survival (3) and to induce proliferation and differentiation of astrocytes in vitro (4), little is known about its effects on neural cells. TGF-␣ binds to the epidermal growth factor receptor (EGFR), which stimulation induces its dimerization, autophosphorylation on tyrosine residues, and triggers a cascade of reactions that requires the contribution of adapter proteins and kinases. EGFR activates several signal transduction pathways, among others are phosphatidylinositol 3-kinase/protein kinase B (PI 3-kinase/Akt) and the p44/p42 mitogen-activated protein kinase, also referred to as extracellular signal-regulated kinases 1/2 (Erk1/2) (5).Among the very early consequences of energy depletion after an ischemic insult to the brain are membrane depolarization that induces excitatory amino acid release and inhibition of global protein synthesis, and both significantly contribute to the development of brain infarct (6 -8). Indeed, glutamate receptor overactivation results in an increase in intracellular calcium and extensive neuronal death by excitotoxicity (9). Likewise, persistent block...

Transforming growth factor alpha attenuates the functional expression of AMPA receptors in cortical GABAergic neurons

“…At the adult stage, TGFα and HB-EGF are induced by seizures and suggested to protect neurons from glutamate-induced excitotoxic damage (Petegnief et al, 2003;Opanashuk et al, 1999). These previous results are consistent with the present finding.…”

“…In the adult brain, brain injury, ischemic stress or seizure activity markedly induces TGFα and HB-EGF expression (Kawahara et al, 1999;Kornblum et al, 1994;Opanashuk et al, 1999). Accordingly, the neuroprotective activity of these factors is implicated in post-ischemic neurodegeneration as well as in counteracting glutamatergic neurotoxicity (Peng et al, 1998;Opanashuk et al, 1999;Petegnief et al, 2003).…”

Anthocyanins in aged blueberry-fed rats are found centrally and may enhance memory

“…If this is the case, then it could be surmised that the multiple downstream effects that could take place include those involving enhancements in neuronal survival and proliferation (e.g. Petegnief et al 2003) via activation of mitogen and stress activated kinases, e.g. MSK1 (Deak et al 1998, Hughes et al 2003) and bcl2 (Deak et al 1998), and those which might directly affect cognition through activation of such factors as cyclic AMP response element binding protein (CREB) (Scott et al 2002).…”

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