Neurons Efficiently Repair Glutamate-induced Oxidative DNA Damage by a Process Involving CREB-mediated Up-regulation of Apurinic Endonuclease 1

Abstract

Glutamate, the major excitatory neurotransmitter in the brain, activates receptors coupled to membrane depolarization and Ca 2؉ influx that mediates functional responses of neurons including processes such as learning and memory. Here we show that reversible nuclear oxidative DNA damage occurs in cerebral cortical neurons in response to transient glutamate receptor activation using non-toxic physiological levels of glutamate. This DNA damage was prevented by intracellular Ca 2؉ chelation, the mitochondrial superoxide dismutase mimetic MnTMPyP (Mn-5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine chloride tetrakis(methochloride)), and blockade of the permeability transition pore. The repair of glutamate-induced DNA damage was associated with increased DNA repair activity and increased mRNA and protein levels of apurinic endonuclease 1 (APE1 which mediate long lasting changes in neuronal structure and function (2-5). Glutamate receptor activation also stimulates an increase in mitochondrial respiration (electron transport) to generate the ATP necessary to drive the activity of ion-motive ATPases that restore ion gradients across cellular membranes (6). Mitochondrial Ca 2ϩ uptake and increased mitochondrial respiration can result in production of the damaging free radical superoxide (7, 8), as well as mitochondrial membrane permeability changes that trigger cell death, a process called excitotoxicity (9, 10).Damage to DNA in neurons occurs early during excitotoxicity (11, 12) and may be a pivotal event in cell death because selective inhibition or knockdown of the DNA damage response proteins p53 (13, 14) and PARP-1 (15, 16) can prevent glutamate-induced neuronal death. Ca 2ϩ and mitochondriaderived superoxide are believed to play key roles in glutamateinduced DNA damage and cell death because PARP-1 activation is mediated by Ca 2ϩ and mitochondrial reactive oxygen species (17), and because mitochondrial Mn-SOD and exogenous antioxidants protect neurons against excitotoxicity (18 -20). However, it is not known if oxidative lesions to nuclear DNA occur in response to non-pathological subtoxic levels of glutamate receptor activation, nor is it known if and how neurons might respond to such glutamate-induced DNA damage.Base excision repair (BER) is the primary DNA repair pathway for removal of small base modifications such as alkylation, deamination, and oxidation (21,22). This process occurs both in the nucleus and in mitochondria. By far most information on the molecular mechanisms of DNA damage and repair comes from studies of non-neuronal cells, and the extent of DNA damage and repair in neurons under physiological and pathological conditions is largely unknown (23

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“…[1][2][3][4] It is well documented that the interaction of ROS with lipids and proteins has a significant impact on cellular function in the brain. [5][6][7][8] However, recent investigations have revealed that DNA damage/repair can contribute to the age-associated neurodegeneration.…”

“…[5][6][7][8] However, recent investigations have revealed that DNA damage/repair can contribute to the age-associated neurodegeneration. [2][3][4] Indeed, significant damage to DNA causes activation of pro-apoptotic and DNA repair proteins. Depending on the size of DNA damage and the success of repair, cells either die or survive.…”

“…Depending on the size of DNA damage and the success of repair, cells either die or survive. 4,9,10 8-Oxo-7,8-dihydroguanine (8-oxoG) is the most abundant ROS-related product of DNA oxidation and has been implicated in mutagenesis. [11][12][13] The mammalian homolog 8-oxoguanine DNA glycosylase (OGG1) is enzyme specific for incising 8-oxoG to avoid the transversion of GC ?…”

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A reaction to mitochondria in action

“…On the other hand, activation of signaling cascades that modify activity of mitochondrial ETC activity is also a possibility for which there is precedence (Figure 1). For example, the activation of glutamate receptors in neurons has been reported to increase mitochondrial SO production by a mechanism involving Ca 2+ influx through ionotropic glutamate receptors in the plasma membrane [15].…”