Evidence that Brain‐Derived Neurotrophic Factor Neuroprotection Is Linked to Its Ability to Reverse the NMDA‐Induced Inactivation of Protein Kinase C in Cortical Neurons

Abstract

Several lines of evidence indicate that a rapid loss of neuronal protein kinase C (PKC) activity is a characteristic feature of cerebral ischemia and is a necessary step in the NMDA-induced death of cultured neurons. Exposing embryonic day 18 primary rat cortical neurons to 50 M NMDA or 50 M glutamate for 10 min caused ϳ80% cell death over the next 24 h, but excitotoxic death was largely averted, i.e., by 70 -80%, in cells pretreated with brain-derived neurotrophic factor (BDNF). An 8-h preexposure to BDNF (50 -100 ng/ml) maximally protected cortical cells from the effects of NMDA and glutamate, although the transient application of BDNF between 8 and 4 h before NMDA was equally protective. These effects of BDNF were abolished at supralethal, i.e., Ͼ100 M, NMDA concentrations. It is significant that BDNF pretreatment prevented the inactivation of PKC in cortical cells normally seen 30 min to 2 h following lethal NMDA or glutamate exposure. This BDNF effect did not arise from changes in NMDA channel activity because neither whole-cell NMDA current amplitudes nor increases in intracellular free Ca 2ϩ concentration were altered by the 8-h BDNF pretreatment. Furthermore, BDNF offered no neuroprotection to cells treated with the PKC inhibitors staurosporine (10 -20 nM), calphostin C (1-2.5 M), or GF-109203X (100 nM) at the time of NMDA addition. These results underscore the importance of PKC inactivation in glutamate-induced neuronal death. They also suggest that BDNF neuroprotection arises, at least in part, via its ability to block the mechanism by which pathophysiological Ca 2ϩ influx through the NMDA receptor causes membrane PKC inactivation. Key Words: Glutamate toxicity-Protein kinase C-Brain-derived neurotrophic factor-Cortical cultures.

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“…It is consistent with the report that TrkB receptor directly activates this protein kinase (51). In particular, the activation of PKC is noteworthy because Matveeva et al (52) demonstrated that PKC, which is activated by a calcium influx, phosphorylates NSF.…”

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“…¶ To whom correspondence should be addressed: mary rat cortical neurons (28). Consistent with that, activation of PKC by phorbol 12-myristate 13-acetate (PMA) protected the hippocampal cell line from glutamate toxicity, and this effect was mediated through activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and c-Jun N-terminal kinase (JNK) (26).…”

Transient NMDA Receptor Inactivation Provides Long-Term Protection to Cultured Cortical Neurons from a Variety of Death Signals

“…1 B). In contrast, the addition of BDNF, under conditions that strongly protect cortical cultures from excitotoxicity (Tremblay et al, 1999), had no ability to protect cells from hypoxia-induced damage (Fig. 1 B).…”