Early events of target deprivation/axotomy‐induced neuronal apoptosis in vivo: oxidative stress, DNA damage, p53 phosphorylation and subcellular redistribution of death proteins

Abstract

The mechanisms of injury-and disease-associated apoptosis of neurons within the CNS are not understood. We used a model of cortical injury in rat and mouse to induce retrograde neuronal apoptosis in thalamus. In this animal model, unilateral ablation of the occipital cortex induces apoptosis of corticopetal projection neurons in the dorsal lateral geniculate nucleus (LGN), by 7 days post-lesion, that is p53 modulated and Bax dependent. We tested the hypothesis that this degenerative process is initiated by oxidative stress and early formation of DNA damage and is accompanied by changes in the levels of pro-apoptotic mediators of cell death. Immunoblotting revealed that the protein profiles of Bax, Bak and Bad were different during the progression of neuronal apoptosis in the LGN. Bax underwent a subcellular redistribution by 1 day post-lesion, while Bak increased later. Bad showed an early sustained increase. Cleaved caspase-3 was elevated maximally at 5 and 6 days. Active caspase-3 underwent a subcellular translocation to the nucleus. A dramatic phosphorylation of p53 was detected at 4 days post-lesion. DNA damage was assessed immunocytochemically as hydroxyl radical adducts (8-hydroxy-2-deoxyguanosine) and singlestranded DNA. Both forms of DNA damage accumulated early in target-deprived LGN neurons. Transgenic overexpression of superoxide dismutase-1 provided significant protection against the apoptosis but antioxidant pharmacotreatments with trolox and ascorbate were ineffective. We conclude that overlapping and sequential signaling pathways are involved in the apoptosis of adult brain neurons and that DNA damage generated by superoxide derivatives is an upstream mechanism for p53-regulated, Bax-dependent apoptosis of targetdeprived neurons.

Arginase 1 Regulation of Nitric Oxide Production Is Key to Survival of Trophic Factor-Deprived Motor Neurons

“…When deprived of trophic support or after stimulation of death receptors, motor neurons die by apoptosis, which is dependent on de novo synthesis of neuronal NOS, nitric oxide production, and peroxynitrite formation (Estévez et al, 1998a(Estévez et al, , 2000Martin et al, 1999Martin et al, , 2003Martin et al, , 2005. Herein we propose a model to explain the differential vulnerability of motor neurons after trophic factor deprivation.…”

Stimulation of autophagy by rapamycin protects neurons from remote degeneration after acute focal brain damage

“…29 A large percentage of CNS pathologies present acute focal brain lesions and their consequences have been studied in various animal models. 21,40,41 The HCb model is well established, in which neuronal degeneration can be analyzed remotely from the primary site of damage, where effects of the primary lesion can confound the study of degeneration. These remote phenomena can be used to exploit therapeutic approaches, because they are active long after the primary damage has subsided and influence postlesion impairments.…”

Oxidative stress and modification of synaptic proteins in hippocampus after traumatic brain injury

“…The pathophysiological mechanisms of secondary injury are complex and include inflammation, production of ROS/ RNS, increased intracellular calcium and lipid peroxidation [41,42]. The breakdown of the blood-brain-barrier and a neuroinflammatory response after brain injury also contribute to neuronal death [43,44]. Oxidative stress and peroxidation of PUFA damage neuronal membranes, leading to the generation of 4-HNE and acrolein, which in turn can damage proteins.…”