Moderate superoxide production is an early promoter of mitochondrial biogenesis in differentiating N2a neuroblastoma cells

Reactive oxygen species (ROS) have been widely considered as harmful for cell development and as promoters of cell aging by increasing oxidative stress. However, ROS have an important role in cell signaling and they have been demonstrated to be beneficial by triggering hormetic signals, which could protect the organism from later insults. In the present study, N2a murine neuroblastoma cells were used as a paradigm of cell-specific (neural) differentiation partly mediated by ROS. Differentiation was triggered by the established treatments of serum starvation, forskolin or dibutyryl cyclic AMP. A marked differentiation, expressed as the development of neurites, was detected by fixation and staining with coomassie brilliant blue after 48 h treatment. This was accompanied by an increase in mitochondrial mass detected by mitotracker green staining, an increased expression of the peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1-alpha (PGC-1α) and succinate dehydrogenase activity as detected by MTT. In line with these results, an increase in free radicals, specifically superoxide anion, was detected in differentiating cells by flow cytometry. Superoxide scavenging by MnTBAP and MAPK inhibition by PD98059 partially reversed differentiation and mitochondrial biogenesis. In this way, we demonstrated that mitochondrial biogenesis and differentiation are mediated by superoxide and MAPK cues. Our data suggest that differentiation and mitochondrial biogenesis in N2a cells are part of a hormetic response which is triggered by a modest increase of superoxide anion concentration within the mitochondria.