Searching for Regulatory Genes that Improve Aged Neural Stem Cell Performance
Stem cell populations provide a supply of daughter cells needed for tissue function, but their activity - and this supply of new cells - declines with age. Stem cell populations can shrink in size, but aged stem cells also spend more time in quiescence rather than the production of daughter cells. This happens due to some combination of (a) age-related damage to stem cells and (b) age-related damage to the stem cell niche, the supporting cells that provide an environment in which the stem cells reside. For many stem cell types, researchers have demonstrated that old stem cells become more active when placed in a young environment, which suggests that there will be ways to improve stem cell function in older individuals.
The traditional approach to finding approaches to stem cell functional restoration, or indeed any other goal in medicine, is to (a) identify regulatory genes controlling the process of interest, here the maladaptive reduction in stem cell activity in response to an aged tissue environment, then (b) find small molecules that alter expression or protein interactions to either upregulate or downregulate the activity of a target regulatory gene. Today's open access paper is an example of the first step, in which researchers search for genes regulating the activity of neural stem cells. The generation of new neurons by neural stem cell populations and their subsequent integration into neural circuits is vital to memory and learning, but also critical to what little capacity the brain has to maintain itself and recover from injury. As for all stem cell populations, the activity of neural stem cells is reduced in older people. Forcing these cells back into action may produce a beneficial improvement in cognitive function.
CRISPR-Cas9 screens reveal regulators of ageing in neural stem cells
Ageing impairs the ability of neural stem cells (NSCs) to transition from quiescence to proliferation in the adult mammalian brain. Functional decline of NSCs results in the decreased production of new neurons and defective regeneration following injury during ageing. Several genetic interventions have been found to ameliorate old brain function, but systematic functional testing of genes in old NSCs - and more generally in old cells - has not been conducted. Here we develop in vitro and in vivo high-throughput CRISPR-Cas9 screening platforms to systematically uncover gene knockouts that boost NSC activation in old mice.
Our genome-wide screens in primary cultures of young and old NSCs uncovered more than 300 gene knockouts that specifically restore the activation of old NSCs. The top gene knockouts are involved in cilium organization and glucose import. We also establish a scalable CRISPR-Cas9 screening platform in vivo, which identified 24 gene knockouts that boost NSC activation and the production of new neurons in old brains. Notably, the knockout of Slc2a4, which encodes the GLUT4 glucose transporter, is a top intervention that improves the function of old NSCs. Glucose uptake increases in NSCs during ageing, and transient glucose starvation restores the ability of old NSCs to activate. Thus, an increase in glucose uptake may contribute to the decline in NSC activation with age.
Our work provides scalable platforms to systematically identify genetic interventions that boost the function of old NSCs, including in vivo, with important implications for countering regenerative decline during ageing.