Increased ROS generation in subsets of OGG1 knockout fibroblast cells

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 (^HROS cells), while ∼85% of Ogg1^-/- cells exhibit physiological levels of ROS (^LROS cells). Ogg1^-/- cells were sorted based on their DCF fluorescence intensity to obtain ^LROS and ^HROS cell cultures. ^LROS cultures proliferated at a rate comparable to Ogg1^+/+ and gradually accumulated cells exhibiting increased ROS and 8-oxoG levels. ^LROS cells show a 2.8-fold increase in 8-oxoG level vs. ^HROS cells (7-27-fold). Mitochondria of ^HROS cells released more H₂O₂ than ^LROS 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 mechanisms exists in tissues of Ogg1^-/- mice is the focus of future investigations.