α‐Tocotrienol protects primary hippocampal neurons against oxidative stress‐mediated ΔN‐Bcl‐xL formation in the mitochondria

The mitochondrial pro‐survival protein, B‐cell lymphoma‐extra large(Bcl‐xL) enhances energy metabolism and mitochondrial/neuronal function, but it is also capable of forming an N‐terminus cleaved‐, pro‐death fragment, ΔN‐Bcl‐xL, under excitotoxic stimulation. Neuroprotective properties of α‐tocotrienol (TCT) have been previously reported in both in vivo and in vitro systems. However, the mechanism of neuroprotection, particularly in mitochondrial targets, is not fully understood. In this study, we tested whether excitotoxic (glutamate)‐induced ΔN‐Bcl‐xL formation is mediated by redox homeostasis in neurons, and whether the neuroprotective properties of α‐TCT occur via regulation of ΔN‐Bcl‐xL formation in the mitochondria. Primary hippocampal neurons were treated with α‐TCT, glutamate, or a combination of both, and then assayed for caspase 3 and ΔN‐Bcl‐xL formation, mitochondrial function, redox status, and neuronal viability. Glutamate caused abnormalities in mitochondrial function leading to neuronal death. The antioxidant α‐TCT protected neurons from glutamate‐induced mitochondrial dysfunction and cytotoxicity. α‐TCT treatment protected against cleavage of full length anti‐apoptotic Bcl‐xL to form pro‐death ΔN‐Bcl‐xL. α‐TCT significantly attenuated glutamate‐induced reactive oxygen species (ROS) formation in primary hippocampal neurons, reduced caspase 3 activation at the mitochondria and reduced‐ΔN‐Bcl‐xL formation at the mitochondria. Our data suggest that mitochondrial ROS production is responsible for glutamate‐induced ΔN‐Bcl‐xL expression. We find that ΔN‐Bcl‐xL is formed at mitochondria, suggesting that caspase 3 is activated there to cleave a specific mitochondrial protein, full length Bcl‐xL. Clearance of mitochondrial ROS may be an important protective mechanism against ΔN‐Bcl‐xL‐mediated mitochondrial dysfunction and neuronal death. Support or Funding Information NIH NS045876