Neural stem cells (NSCs) in the brain must find a balance between maintaining their multipotency by self renewing and proliferating as opposed to differentiating and becoming quiescent. The PI3K/AKT pathway is crucial in this decision making process. NSCs are able to sense and respond to changes in the brain or throughout the organism. When blood glucose levels are elevated acutely, insulin is released from the pancreas. Activation of insulin receptors activates the PI3K/AKT pathway, which promotes proliferation. In this way, when there is high glucose and abundant energy in the organism, the PI3K/AKT pathway is activated and NSCs tend to proliferate. When there are low amounts of available energy, the PI3K/AKT pathway is less active and cells adopt a quiescent state.
This occurs, in part, when AKT phosphorylates FOXO, keeping FOXO in the cytoplasm. FOXO, when dephosphorylated, can enter the nucleus and work as a transcription factor to promote the expression of various tumor suppressors such as p27 and p21. These tumor suppressors push the NSC to enter quiescence. FOXO knockouts lose the ability for cells to enter a quiescent state as well as cells losing their neural stem cell character, possibly entering a cancer like state.