The Role of GLUT1 and Glucose in Intestinal Stem Cell Homeostasis and Regeneration

ABSTRACT. In eukaryotic cells, the facilitative glucose transporters (GLUTs) provide critical metabolic control by regulating glucose uptake rate. In the intestinal epithelial cells (IECs), comprising intestinal stem cells (ISCs), the GLUT2- SGLT1 (sodium/glucose cotransporter 1) axis, which facilitates post-prandial luminal dietary glucose absorption,

has been conventionally assumed to be also responsible for their basal glucose uptake. Yet, transgenic mice with Sglt1 or Glut2 ablation have not been reported to exhibit any perturbation on epithelial cell composition. Moreover, the basolaterally localized GLUT2 has a very low affinity for glucose (Km=20 mM), which is

significantly higher than that of the basal blood glucose concentration (~7 mM). Thus, GLUT2 can only take up glucose during high glycemic states (e.g., after feeding). These observations suggest that other glucose transporters may be involved in ISC glucose uptake. Identifying such transporter would be significant as it would

also enable mechanistic investigations into the role of glucose in ISC homeostasis. Specifically, ISCs are known to be susceptible to their metabolic milieu, rapidly adapting their proliferation and differentiation to various types of metabolites, including ketone bodies, bile acids, and fatty acids. Surprisingly, despite constituting one of the

most prevalent metabolic substrates, the role of glucose and its derivatives in ISC homeostasis and regeneration is poorly understood. Our recent findings indicate that contrary to the established paradigm, both small intestinal and colonic ISCs express GLUT1. Importantly, GLUT1 is vital to ISC homeostasis, wherein its genetic ablation

specifically in Lgr5+ ISCs or across IECs profoundly compromises ISC glucose metabolism, proliferation, and differentiation. Notably, we observed that ISC function is crucially dependent on a GLUT1-fueled generation of nucleosides through the pentose phosphate pathway (PPP). As such, PPP inhibition also hampers organoid

growth, whereas supplementation with nucleosides, the key byproducts of PPP, recovers both Glut1-ablated mice and PPP-inhibited organoids. Notably, nucleosides administration stimulates ISC and epithelial regeneration following irradiation and DSS-induced injuries. Based on these observations, we hypothesize that

ISCs vitally rely on the GLUT1-mediated glucose uptake, which they primarily use in the PPP. We will test our hypothesis in three Specific Aims: In Aim 1, we will determine the in vivo role of GLUT1 in intestinal epithelial homeostasis. In Aim 2, we will elucidate the metabolic dependency of ISCs on glucose in homeostasis. In Aim

3, we will identify the role of the GLUT1-PPP axis in intestinal epithelium regeneration. Successful achievement of our objectives will reveal that GLUT1 plays a pivotal role in ISC function. We will also determine the functional role and metabolic fate of glucose in ISC homeostasis and during regeneration. This information will set the

stage for follow-up mechanistic studies into the potential role of GLUT1-glucose-PPP in pathological conditions such as diabetes and inflammatory bowel disease.