Using high-throughput CRISPR-Cas9 screens, researchers have systematically uncovered gene knockouts that impact ageing in neural stem cells of the brain.
Neural stem cells
Neural stem cells (NSCs) are a group of self-renewing, multipotent, progenitor cells, which can differentiate into committed neural subtypes, such as neurons, astrocytes or oligodendrocytes. The adult mammalian brain contains several NSC regions. These regions give rise to newborn neurons and can also repair tissue damaged by stroke or brain injuries. The most active NSC niche is located in the subventricular zone (SVZ). This region comprises a pool of quiescent NSCs that can give rise to activated (proliferating) NSCs, which go on to differentiate into neurons. The ability of NSCs to activate is severely impaired in the ageing brain. This can contribute to deficits in cognition and regeneration.
Previous studies have identified several genetic interventions that improve old NSC activation, including signalling pathways and transcriptional regulators. However, these studies have been limited by throughput as they only focussed on a few genes at one time. A major challenge in identifying genetic interventions that improve old cells is establishing scalable genetic screens in mammals. As ageing occurs at both the cell and organismal levels, it is important to develop both in vitro and in vivo screens from old cells and tissues.
CRISPR screens in the brain
In a recent preprint article, published in biorxiv, researchers developed CRISPR-Cas9 screening platforms for old mammalian cells and organisms in the hope of identifying previously unknown manipulations that could restore tissue function. The team more specifically wanted to uncover gene knockouts that boosted NSC activation in old mice.
In total, their genome-wide screen in primary cultures identified over 300 gene knockouts that specifically restored old NSC activation. The top gene knockouts were involved in glucose import, cilium organisation and ribonucleoprotein structure.
They also aimed to determine which gene knockouts had a rejuvenating effect for the ageing brain. To do this, they established a scalable CRISPR-Cas9 screening platform in vivo in old mice. Of the 50 gene knockouts tested, 23 boosted old NSC activation and production of new neurons.
Most notably, the knockout Slc2a4 (encodes the GLUT4 glucose transporter) was a top rejuvenating intervention for old NSCs. The researchers found that old NSCs’ glucose uptake increased ~2-fold compared to their younger counterparts. Transient glucose starvation increased the ability of old NSCs to activate.
Overall, this study demonstrates the value of these scalable platforms to systematically identify genetic interventions that boost old NSC function. Most importantly, these results show that a shift in glucose uptake contributes to the decline in NSC activation with age, which can be reversed by genetic or external intervention. These findings have important implications for regenerative and cognitive decline during ageing.
Image credit: canva