The human adult hippocampus retains the capacity to produce new neurons throughout our lifetime, in a process known as adult neurogenesis. It is now well documented that external factors making up our macro-environment regulate both positively and negatively adult hippocampal neurogenesis: contextual and spatial stimulation, along with exercise, increase adult neurogenesis (1). Age, alcohol abuse, inflammation, and nutritional factors, on the other hand, decrease adult neurogenesis (2–5). They do so through the neurovascular niche, composed of the close physical apposition of stem cells to the dense blood vasculature found in the hippocampus(6–9). Indeed, blood-circulating factors – such as CCL11 in ageing rodents and humans and irisin, an exercise- induced myokine – have been identified as one of the vessels for the effects of external regulating factors on the internal process of adult neurogenesis (9)(10).
Exploiting this link between blood-circulating factors and stem cell proliferation is the ToniLab Blood-Brain-Axis (BBA) assay, consisting in exposing rat hippocampal dentate gyrus adult neural progenitor stem cells (aNPSCs) – representing the brain-axis – to serum taken from mice exposed to different conditions – representing the blood-axis. The proliferation rate of the cells following serum exposure was then evaluated using immunocytochemistry (ICC). Larrieu and colleagues found a decrease in stem cell proliferation following exposure to high-anxious rodent sera in relation to sera from low-anxious rodents. Concomitantly, sera from chronic restraint stressed rodents correlated with a decrease in stem cell proliferation in relation to sera from non-stressed rodents. Finally, sera from human patients diagnosed with MDD corresponded to a decrease in neural stem cell proliferation relative to the serum from healthy individuals. These findings confirm the sensitivity of the BBA assay model to both human and mouse sera.
The aim of the Masters project was to test the viability and the specificity of the BBA assay. By comparing apoptosis rates in state-anxiety and trait-anxiety assays following sera exposure to a positive control staurosporine assay, we were able to conclude on the lack of cytotoxicity in the state-anxiety and trait-anxiety assays and the consequent viability of the assays. By exposing DG mouse stem cells to four sera samples having demonstrated the greatest decrease in stem cell proliferation in previous trait-anxiety and state-anxiety BBA assays, we were able to observe a trend towards a decrease in mouse stem cell proliferation in both the trait-anxiety and state-anxiety assays. These results led to the conclusion that the BBA assay is not species-specific, producing similar results when using mouse stem cells and rat stem cells. By exposing rat stem cells to sera taken from mice before and after a period of chronic voluntary wheel running, we were able to observe an increase in stem cell proliferation after exposure to post-exercise period sera and therefore conclude on the sensitivity of the BBA assay to both negative and positive regulating factors.
In conclusion, the BBA assay is a viable cell culture approach applicable to rodents and humans that might provide an in vitro correlate of neurogenesis. The BBA assay paves the way for the development of a potential future clinical tool to probe brain health. In the long term, the BBA assay could contribute to a better understanding, as well as better prevention, detection, and treatment options for neurogenesis-mediated disorders.