Emerging data indicate that tumor necrosis factor (TNF) exerts a neuroprotective effect in response to brain injury. Here we examined the mechanism of TNF in preventing neuronal death in primary hippocampal neurons. TNF protected neurons against hypoxia-or nitric oxide-induced injury, with an increase in the antiapoptotic proteins Bcl-2 and Bcl-x as determined by Western blot and reverse transcriptase-polymerase chain reaction analysis. Treatment of neurons with an antisense oligonucleotide to bcl-2 mRNA or that to bcl-x mRNA blocked the up-regulation of Bcl-2 or Bcl-x expression, respectively, and partially inhibited the neuroprotective effect induced by TNF. Moreover, adenovirus-mediated overexpression of Bcl-2 significantly inhibited hypoxia-or nitric oxide-induced neuronal death. To examine the possible involvement of a transcription factor, NFB, in the regulation of Bcl-2 and Bcl-x expression in TNF-treated neurons, an adenoviral vector capable of expressing a mutated form of IB was used to infect neurons prior to TNF treatment. Expression of the mutant NFB completely inhibited NFB DNA binding activity and inhibited both TNF-induced up-regulation of Bcl-2 and Bcl-x expression and neuroprotective effect. These findings indicate that induction of Bcl-2 and Bcl-x expression through NFB activation is involved in the neuroprotective action of TNF against hypoxia-or nitric oxide-induced injury.

Oxygen-regulated protein 150 kD (ORP150) is a novel endoplasmic-reticulum-associated chaperone induced by hypoxia/ischemia. Although ORP150 was sparingly upregulated in neurons from human brain undergoing ischemic stress, there was robust induction in astrocytes. Cultured neurons overexpressing ORP150 were resistant to hypoxemic stress, whereas astrocytes with inhibited ORP150 expression were more vulnerable. Mice with targeted neuronal overexpression of ORP150 had smaller strokes compared with controls. Neurons with increased ORP150 demonstrated suppressed caspase-3-like activity and enhanced brain-derived neurotrophic factor (BDNF) under hypoxia signaling. These data indicate that ORP150 is an integral participant in ischemic cytoprotective pathways.

We have made a rat cDNA library using nerve-transected hypoglossal nuclei. Using this library, we performed expressed-sequence tag analysis coupled with in situ hybridization to identify genes whose expression is altered in response to nerve injury. In this gene screening, a member of Rho family GTPases, TC10, which had not yet been characterized in neuronal cells, was identified. TC10 mRNA expression was very low in normal motor neurons; however, axotomy induced its expression dramatically. Other family members such as RhoA, Rac1, and Cdc42 were moderately expressed in normal motor neurons and showed slight upregulation after axotomy. The expression level of TC10 mRNA was low in the embryonic brain and gradually increased with development. However, the expression of TC10 mRNA in the adult brain was lower and more restricted than that of RhoA, Rac1, and Cdc42. Cultured dorsal root ganglia exhibited dramatic neurite extension secondary to adenovirus-mediated expression of TC10. It can be concluded that although TC10 expression is lower in developing and mature motor neurons compared with other Rho family members, TC10 expression is induced by nerve injury to play a crucial role in nerve regeneration, particularly neurite elongation, in cooperation with other family members.