GLUCOSE (SUGAR) AND AGING IMPAIR NEURAL STEM CELLS

CRISPR–CAS9 SCREENS REVEAL REGULATORS OF AGEING IN NEURAL STEM CELLS

Tyson J. Ruetz, Angela N. Pogson, Chloe M. Kashiwagi, Stephanie D. Gagnon, Bhek Morton, Eric D. Sun, Jeeyoon Na, Robin W. Yeo, Dena S. Leeman, David W. Morgens, C. Kimberly Tsui, Amy Li, Michael C. Bassik & Anne Brunet

Nature October 2, 2024

RONALD PETERS, MD – COMMENTS

Neural stem cells (NSCs) are specialized cells in the brain that can self-renew and differeniate into different types of cells in the nervous system. These powerful cells create the brain and nervous system for the developing child in the womb. In the adult brain they create plasticity and regeneration. The neural stem cels decline with aging and, accoding to this article, they decline with excess exposue to glucose. Blood sugar regulation is a key feature of health in body and mind and is key to longevity. Eating refined carbohydrates (simple sugar) creates a rapid rise in blood sugar (high glycemic index). Complex carbohdrates such as gluten free grains, beans and vegetables raise the blood sugar slowly (low glycemic index) and contribute to healthy glucose intake.

Abstract

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^1,2,3,4. Several genetic interventions have been found to ameliorate old brain function^5,6,7,8, but systematic functional testing of genes in old NSCs—and more generally in old cells—has not been done. 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.

Main

The adult mammalian brain contains several NSC regions that give rise to newborn neurons and can repair tissue damaged by stroke or brain injuries1,4,9,10,11,12,13,14. The most active NSC niche is located in the subventricular zone (SVZ) that lines the lateral ventricles of the brain1,2,4,10,13,14,15,16,17,18. NSCs from the SVZ region can generate thousands of newborn neurons each day in a young adult mouse10. The SVZ region comprises a pool of quiescent NSCs (qNSCs) that can give rise to activated (proliferating) NSCs (aNSCs), which in turn generate more committed progenitors that migrate out of the niche towards the olfactory bulb, where they differentiate into neurons. The ability of NSCs to activate and form newborn neurons is severely impaired in the ageing brain, and this can contribute to deficits in sensory and cognitive function1,2,3,15,19,20,21,22,23.

Identifying genes that affect NSC activation could lead to interventions that counter brain defects during ageing. Several genetic interventions, including signalling pathways and transcriptional regulators, have been shown to improve activation of old NSCs5,6,7,8,24,25,26,27. However, such studies have been limited in their throughput as they focus on one or a few genes at a time. Thus, we are still lacking a systematic understanding of the genes and pathways that functionally affect old NSCs.

More generally, a major challenge in identifying genetic interventions that improve the function of old cells is the establishment of scalable genetic screens in mammals. Ageing occurs at both the cell and organismal levels; therefore, it is important to develop screens in vitro in cells from old organisms and in vivo in old tissues. CRISPR–Cas9 genome-wide screens have been developed for several phenotypes in vitro28,29,30,31,32,33,34,35,36, including with stem cell models of Werner and Hutchinson–Gilford progeria syndrome37. However, genetic screens for regulators of ageing in normal old cells have not yet been performed. In addition, in vivo genetic screens are challenging in mammals and have currently been limited to development38,39,40, young tissues41,42,43 or cancer36,44,45,46,47. Thus, developing CRISPR–Cas9 screening platforms for old mammalian cells and organisms has the potential to identify previously unknown gene manipulations that could restore tissue function in older individuals. In the brain, such screens could help identify strategies to counter regenerative and cognitive decline with ageing.