Cultured sheep cortical neurons as model to study brain aging and testosterone-induced neuroprotection

This work describes the expression of topoisomerase βII in foetal sheep neuronal cells. The β isoform of DNA topoisomerase II plays a role in DNA repair process in non proliferating cells as neurons and its expression tends to be downregulated with senescence. Cortical neurons from 60-day-old sheep embryos underwent two protocols: the former based on increasing culture time (10, 20 and 30 days); the latter based on the 72hrs exposure to 3-nitro-L-tyrosine (oxidative/nitrosative stressor) and/or testosterone, a hormone that can be also considered as neuroprotective. Our findings revealed that β-galactosidase activity increased throughout time, while topoisomerase βII expression decreased (first protocol). The exposure of sheep primary neurons to 3-nitro-L-tyrosine led to an upregulation of topoisomerase βII expression to be likely seen as a reaction to nitrosative stress. Testosterone addition to 3-nitro-L-tyrosine-exposed cells results in topoisomerase βII decrease possibly due to the neuroprotective properties of testosterone (second protocol). No significant variations in the amount of the marker of aging β-galactosidase were observed in the cells exposed to 3-nitro-L-tyrosine and testosterone. The protocol based on time could be of some interest as a model of neuronal senescence in vitro. Topoisomerase βII decreases with aging likely indicating a reduced ability to repair DNA during neuronal senescence. In contrast, the second protocol may not be seen as a reliable model of aging since 3-nitro-L-tyrosine does not lead to a topoisomerase βII decrease. Testosterone was able to cope with oxidative/nitrosative damage, allowing cells to reduce their needs in DNA repair which in turn leads to a downregulation of topoisomerase βII expression.