Brain aging and testosterone-induced neuroprotection: studies on cultured sheep cortical neurons.

Objective: This research reports the expression of topoisomerase βII in fetal 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.

Methods: Cortical neurons from 60-day-old sheep embryos underwent two protocols: the former based on rising time of culture (10, 20 and 30 days); the latter based on the 72hrs exposure to 3-nitro-L-tyrosine (oxidative/nitrosative stressor) and/or testosterone.

Results: Our results showed an increase in β-galactosidase activity and, in contrast, a reduction in topoisomerase βII expression with time (first protocol). The exposure of sheep primary neurons to 3-nitro-L-tyrosine led to an upregulation of βII topoisomerase 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 marker of aging β-galactosidase were observed in the cells exposed to 3-nitro-L-tyrosine and testosterone.

Conclusion: The protocol based on time could be of some interest as a model of neuronal senescence in vitro. Topoisomerase βII decrease with aging likely indicates 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 IIβ expression.