The repair function of the multifunctional DNA repair/redox protein APE1 is neuroprotective after ionizing radiation

Abstract

Although exposure to ionizing radiation (IR) can produce significant neurotoxicity, the mechanisms mediating this toxicity remain to be determined. Previous studies using neurons isolated from the central nervous system show that IR produces reactive oxygen species and oxidative DNA damage in those cells. Because the base excision DNA repair pathway repairs single-base modifications caused by ROS, we asked whether manipulating this pathway by altering APE1 expression would affect radiation-induced neurotoxicity. In cultures of adult hippocampal and sensory neurons, IR produces DNA damage as measured by phosphorylation of histone H2A.X and results in dose-dependent cell death. In isolated sensory neurons, we demonstrate for the first time that radiation decreases the capsaicin-evoked release of the neuropeptide CGRP. Reducing APE1 expression in cultured cells augments IR-induced neurotoxicity, whereas overexpressing APE1 is neuroprotective. Using lentiviral constructs with a neuronal specific promoter that selectively expresses APE1’s different functions in neurons, we show that selective expression of the DNA repair competent (redox inactive) APE1 constructs in sensory neurons resurrects cell survival and neuronal function, whereas use of DNA-repair deficient (redox active) constructs is not protective. Use of an APE1 redox-specific inhibitor, APX3330, also facilitates neuronal protection against IR-induced toxicity. These results demonstrate for the first time that the repair function of APE1 is required to protect both hippocampal and DRG neuronal cultures—specifically neuronal cells—from IR-induced damage, while the redox activity of APE1 does not appear to be involved.

Identification and Characterization of New Chemical Entities Targeting Apurinic/Apyrimidinic Endonuclease 1 for the Prevention of Chemotherapy-Induced Peripheral Neuropathy

“…2A), confirming our previous work (Vasko et al, 2005(Vasko et al, , 2011Jiang et al, 2008;Kelley et al, 2014). In a similar manner, exposing cultures to various concentrations of APX2009 did not result in a significant reduction in cell viability ( Fig.…”

“…Sensory neuronal culture trypan blue exclusion analysis was performed as previously described (Vasko et al, 2011). Cells were detached by adding a 0.05% trypsin-EDTA solution and media to each well.…”

“…Reducing the expression of a critical enzyme in the BER pathway, apurinic/apyrimidinic endonuclease (APE)-1 (also called , in sensory neurons amplifies the toxicity to sensory neurons exposed to anticancer therapies; by contrast, overexpressing APE1 and an APE1 DNA repair-proficient, redox-deficient mutant protein attenuates the neurotoxicity (Vasko et al, 2005(Vasko et al, , 2011Jiang et al, 2008;Kelley et al, 2014). The neuronal protection afforded by overexpressing APE1 is mimicked by a first-generation APE1 redox signaling small molecule inhibitor, E3330 [(2E)-2-[(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cyclohexadien-1-yl)-methylene]-undecanoic acid; also called APX3330] (Vasko et al, 2011;Kelley et al, 2014). This compound is well tolerated in mice and displays suitable pharmacokinetic characteristics (half-life, area under the curve, bioavailability) with no evidence of acute drug-related severe toxicity or lethality observed in our in vivo studies (Fishel et al, 2011).…”

“…Therapies including platinum agents and ionizing radiation cause DNA damage in sensory neurons, and augmenting the base excision repair (BER) pathway reverses the toxic effects of these chemotherapies (Vasko et al, 2005(Vasko et al, , 2011Jiang et al, 2008;Kelley et al, 2014;Kim et al, 2015). Reducing the expression of a critical enzyme in the BER pathway, apurinic/apyrimidinic endonuclease (APE)-1 (also called , in sensory neurons amplifies the toxicity to sensory neurons exposed to anticancer therapies; by contrast, overexpressing APE1 and an APE1 DNA repair-proficient, redox-deficient mutant protein attenuates the neurotoxicity (Vasko et al, 2005(Vasko et al, , 2011Jiang et al, 2008;Kelley et al, 2014). The neuronal protection afforded by overexpressing APE1 is mimicked by a first-generation APE1 redox signaling small molecule inhibitor, E3330 [(2E)-2-[(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cyclohexadien-1-yl)-methylene]-undecanoic acid; also called APX3330] (Vasko et al, 2011;Kelley et al, 2014).…”

Apurinic/Apyrimidinic Endonuclease 1 Upregulation Reduces Oxidative DNA Damage and Protects Hippocampal Neurons from Ischemic Injury

“…APE1 has been shown to be neuroprotective in vitro after ionizing radiation (62) and oxidative stress (61). Thus, APE1 deficiency exacerbates the negative impact of both oxidative injury and DNA damaging agents (48,52,61).…”