Increased ROS generation in subsets of OGG1 knockout fibroblast cells

Abstract

Oxoguanine DNA glycosylase (OGG1) is a major base excision repair protein responsible for excision of the mutagenic 8-oxoguanosine (8-oxoG) lesions from the genome. Despite OGG1's importance, the moderate phenotype of Ogg1-null (Ogg1 −/− ) mice is not well understood. This study addresses a mechanism by which Ogg1 −/− cells limit accumulation of 8-oxoG in their genome. Our data reveal that a subset of Ogg1 −/− cells shows higher ROS levels ( H ROS cells), while ~85% of Ogg1 −/− cells exhibit physiological levels of ROS ( L ROS cells). Ogg1 −/− cells were sorted based on their DCF fluorescence intensity to obtain L ROS and H ROS cell cultures. L ROS cultures proliferated at a rate comparable to Ogg1 +/+ and gradually accumulated cells exhibiting increased ROS and 8-oxoG levels. L ROS cells show a 2.8-fold increase in 8-oxoG level vs. H ROS cells (7-to 27-fold). Mitochondria of H ROS cells released more H 2 O 2 than L ROS and Ogg1 +/+ cells and were eliminated by apoptotic-like processes. These findings suggest that in the absence of OGG1, a surveillance system is activated that removes cells with extreme 8-oxoG levels from Ogg1 −/− cultures. Whether similar mechanism exists in tissues of Ogg1 −/− mice is the focus of future investigations.

Mitochondrial DNA Damage: Role of Ogg1 and Aconitase

“…Notably, overexpression of mitochondrial aconitase eliminated oxidant induced AEC apoptosis whereas Ogg1 underexpression using shRNA techniques reduced basal mitochondrial aconitase levels and augmented oxidant-induced AEC apoptosis (Panduri et al, 2009). These latter findings are in accord with several recent studies showing that Ogg1 deficiency increases oxidant-induced apoptosis (Youn et al, 2007;Bacsi et al, 2007;Xie et al, 2008). Collectively, these results suggest a novel interaction between an mtDNA repair enzyme (mt-Ogg1) and aconitase in preventing intrinsic AEC apoptosis following exposure to oxidative stress (e.g.…”

Neil2-null Mice Accumulate Oxidized DNA Bases in the Transcriptionally Active Sequences of the Genome and Are Susceptible to Innate Inflammation

“…Furthermore, we found a higher frequency (Fig. 6B, compare Increased Susceptibility of Neil2-null Mice to InflammationPrevious reports have indicated that Ogg1-null mice have decreased susceptibility to LPS-induced and oxidative stressinduced inflammation (44,45) and also to allergic immune responses (46,47). To address the susceptibility of Neil2-null mice to inflammation, animals were challenged intranasally with LPS (100 ng/per lung) or TNF-␣ (20 ng/lung) or GOx (1 milliunit/lung).…”

Cigarette Smoke Induces Nucleic-Acid Oxidation in Lung Fibroblasts

“…OGG1 is a DNA glycosylase with bifunctional activity that plays a critical role in both nuclear and mitochondrial oxidative DNA repair (34), and likely acts directly to control the accumulation of oxidized DNA. Although OGG1 null mice do not have a distinct phenotype and are only moderately more susceptible to cancer (35), OGG1-deficient fibroblasts exhibit an increased generation of ROS (36) and an enhanced sensitivity to DNA damage in response to oxidative stress (37). Our knockdown studies clearly show that nucleic-acid oxidation is increased at both the basal state and after exposure to CSE in human lung fibroblasts.…”