Metabolic Regulation of Stem Cell Fate and Function

Abstract

The overarching goal of this project is to understand how diet‐derived nutrients regulate stem cell metabolism and downstream fate decisions in the setting of normal development and disease. Quiescent adult stem cells typically favor glycolytic metabolism over the oxidative metabolism utilized by differentiating cells. Importantly, manipulating stem cell metabolism is sufficient to alter cell fate decisions. While the serum concentrations of endogenous metabolites such as glucose and lactate are under homeostatic constraints, diet can cause vast fluctuations in circulating levels of certain metabolites that serve as co‐factors for chromatin and DNA modifying enzymes. As such, exogenous nutrients can control the epigenome and gene expression programs, thus altering differentiation and cell fate. However, little is known about how changing nutrient levels will affect the metabolism and chromatin status in the adult stem cell populations. To address this question, we have adapted a recently described mouse liver organoid system. The liver coordinates whole‐body metabolism and detoxification, and therefore is acutely tuned to respond to dietary changes. Liver organoids generate 3D assemblies that mirror the native physiology of the tissue and self‐renew in vitro due to the activity of Wnt‐responsive stem cells that reside in the hepatic ductal compartment. We have found that treatment with physiologically attainable concentrations of ascorbic acid inhibits hepatic organoid expansion in a dose‐dependent manner. Ascorbic acid, commonly known as Vitamin C, is a water‐soluble antioxidant that is obtained exclusively through the diet in humans. Ascorbic acid is an essential co‐factor for the Fe‐ and α‐ketoglutarate dependent dioxygenase (α‐KGDDs) class of enzymes, which includes collagen hydroxylases, prolyl hydroxylases, and epigenetic erasers such as DNA and histone demethylases. To determine if activation of α‐KGDDs enzymes suppresses organoid expansion, we treated hepatic organoids with a cell permeable form of α‐KG and observed growth inhibition identical to that observed with ascorbic acid treatment. α‐KG/succinate ratios and expression of the ascorbate transporters increases in differentiated hepatic organoids compared to cultures maintained in expansion media, suggesting that ascorbic acid may preferentially accumulate and function during terminal differentiation. Taken together, we propose that ascorbic acid acts as a cofactor for α‐KGDD enzymes in order to restrain stem cell activity and may play a role in promoting differentiation to the hepatic lineage.Support or Funding InformationS.N.S is supported by a postdoctoral grant from the Eli and Edythe Broad Stem Cell Research Center at UCLA. H.R.C is supported by a CTSI seed grant from the David Geffen School of Medicine at UCLA.