Participation of Bcl-2/Bax-alpha in glutamate-induced apoptosis of human glioblastoma cells

Glutamate has been shown to function as a toxic agent in neuronal and glial cells, as well as an excitatory neurotransmitter throughout the central ne rvous system. In the present study, we examined the effect of increasing gl utamate concentration on the induction of apoptosis in the two human gliobl astoma cell lines GB-4 and GB-12. Glutamate exposure caused cell death of G B-4 and GB-12 in a dose-dependent manner. The cells were found to die via a poptosis in response to glutamate based on the following criteria: propidiu m iodide (PI) staining, H-E staining, electron microscopic analysis, and th e TdT-mediated dUTP-biotin nick end labeling (TUNEL) method. The glutamate- induced apoptosis appears to involve the modulation of Bcl-2 family gene pr oducts such as Bcl-2, Bcl-xL, and Bax-alpha. Both Bcl-2 and Bcl-xL were dow n-regulated by glutamate at 24 h and further at 48 h. The apoptosis-promoti ng product p21 Bax-alpha was also down-regulated in GB-12 but slightly up-r egulated in GB-4, accompanied by generation of variant form of p18 Bax-alph a in both cell lines. These findings suggest that glutamate toxicity result s in cellular death via an apoptotic mechanism which appears to involve the Bcl-2/Bax-alpha molecular complex.