TNF-Α Protection of Hippocampal Neurons from Kainic Acid Induced Neurodegeneration is Associated with Up-Regulation of Nfκb and AKT as well as Down-Regulation of P38 MAPK Signaling Molecules

Abstract

Background: Previously, our study showed that TNF-α plays a protective role in kainic acid (KA) induced neurodegeneration in vivo in mice. Here, we further clarified the protective role of TNF-α in KA-induced hippocampal neuronal damage in vitro and elucidated the potential signaling pathways. Methods: Hippocampal neurons were isolated from embryonic 16 days (E16) TNF-α knockout (KO) and wild-type (WT) mice with C57BL/6 background, respectively, and exposed to KA with and without recombinant TNF-α, as well as anti-TNF-α antibody. After 24-hours exposure to KA, lactate dehydrogenase (LDH) production and neurotoxicity were detected for evaluating neuronal survival rates. The production of nitric oxide (NO) from supernatants and the expression of nuclear factor kappa B (NFкB), inhibitor of NFкB alpha (IκBα), p38 mitogen-activated protein kinase (MAPK) and AKT in hippocampal neurons were measured. Results: Comparing with WT mice, the neurons of TNF-α KO mice showed more susceptibility to KA-induced neurotoxicity, as demonstrated by higher production of LDH and lower neuronal survival rates, as well as elevated NO production. It is also evidenced that pre-blocked TNF-α molecule in the neuron cultures of WT mice with anti-TNF-α antibody significantly enhanced the production of LDH and NO, and decreased the neuronal survival rate. In contrast, the neurons from WT mice pre-exposed to recombinant TNF-α were more resistant to KA induced neurotoxicity. TNF-α deficiency down-regulated phospho-IκBα, NFкB, total AKT and phospho-AKT, as well as up-regulated phospho-p38 MAPK expressions after KA insult. The reverse results were achieved in WT hippocampal neurons with TNF-α pre-administration. Conclusion: Our findings demonstrated an association between the protective effect of TNF-α on neurons as assessed following KA insult, with the up-regulation of NFκB and AKT, as well as down-regulation of p38 MAPK signaling molecules..