The role of 12/15-lipoxygenases in ROS-mediated neuronal cell death
Oxidative stress has been established as a key trigger of neuronal dysfunction and death in age-related neurodegenerative diseases and in delayed neuronal death after acute brain injury by ischemic stroke or brain trauma. Despite increasing knowledge on the toxicity of reactive oxygen species (ROS)...
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|Summary:||Oxidative stress has been established as a key trigger of neuronal dysfunction and death in age-related neurodegenerative diseases and in delayed neuronal death after acute brain injury by ischemic stroke or brain trauma. Despite increasing knowledge on the toxicity of reactive oxygen species (ROS) and oxidized reaction products that may further accelerate neuronal cell death, the major sources of ROS formation and the mechanisms involved in cell death signaling triggered by oxidative stress in neurons are poorly defined. Therefore, major aims of this study included the characterization of key enzymes that contribute to the formation of ROS and key factors of the downstream signaling pathways that may amplify the oxidative cellular stress thereby causing irreversible damage and death in neurons.
Major parts of the study were performed in a model of glutamate toxicity in immortalized hippocampal HT-22 neurons, since glutamate selectively induced oxidative stress through glutathione depletion in these cells. To verify the relevance of the findings in HT-22 cells for post-mitotic neurons, further experiments included models of glutamate-induced excitotoxicity and oxygen-glucose deprivation primary embryonic neurons in vitro and in a mouse model of cerebral ischemia in vivo.
The findings of these studies revealed that 12/15-lipoxygenases (LOX), but neither 5-LOX nor COX activation, mediated glutamate-induced lipid peroxidation and oxidative cellular death (oxytosis) in HT-22 cells. Pharmacological inhibition of 12/15-LOX protected HT-22 cells as well as primary neurons against glutamate toxicity. This protective effect included significantly reduced ROS formation and attenuated deregulation of the intracellular calcium homeostasis in the cultured neurons. Moreover, the 12/15 LOX inhibitor PD146176 reduced neuronal cell death after OGD in primary neurons in vitro, and significantly reduced the infarct volume after MCAO in vivo.
Further experiments addressing the involved signaling pathways linked, for the first time, 12/15-LOX activation and key mediators of mitochondrial death pathways. In particular, the selective 12/15-LOX inhibitor PD146176 reduced mitochondrial fragmentation and ATP depletion after exposure to glutamate in HT-22 cells. Most interestingly, this study identified the pro-apoptotic Bcl-2 protein Bid as a key link between 12/15-LOX activation, mitochondrial demise and the translocation of the mitochondrial protein AIF to the nucleus. In fact, mitochondrial transactivation of Bid downstream of 12/15-LOX activation was exposed as the key step for the mitochondrial damage that resulted in a second burst of lipid peroxidation and marked the ‘point of no return’ in the glutamate-induced death cascade.
In summary, the glutamate-induced cell death mechanisms in HT-22 cells are highly relevant for neurodegenerative diseases and acute neurological disorders.
Thus, 12/15-LOX is proposed as a potential therapeutic target for neuroprotective strategies in neurological disorders.|