ABSTRACT
Brown adipocytes (BA) are a specialized fat cell which possesses a high capacity for fuel oxidation combined with heat production. The maintenance of high metabolic activity in BA requires elevated oxidation of fuel through the tricarboxylic acid cycle. Pyruvate carboxylase (PC) was previously proposed to be essential for coordination between fuel oxidation and thermogenesis. By differentiating human pluripotent stem cells to mature BA in vitro, we showed that ablation of PC gene by CRISPR Cas9 genome engineering did not impair the ability of stem cells to generate mature BA. However, brown adipocytes deficient for PC expression displayed a 35% reduction in ATP-linked respiration, but not thermogenesis under both basal and isoproterenol-stimulated conditions. This relatively mild impairment of ATP-link respiration in PC knockout BA was protected by increased spare mitochondrial respiratory capacity. Taken together, this study highlights the role of PC in supporting fuel oxidation rather than thermogenesis in human BA.
Subject(s)
Adenosine Triphosphate/metabolism , Adipocytes, Brown/metabolism , Cell Differentiation/physiology , Oxygen Consumption/physiology , Pluripotent Stem Cells/metabolism , Pyruvate Carboxylase/metabolism , Adipocytes, Brown/cytology , Adipocytes, Brown/drug effects , Blotting, Western , Bronchodilator Agents/pharmacology , Cell Differentiation/genetics , Cells, Cultured , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Gene Expression , Gene Knockout Techniques , Humans , Isoproterenol/pharmacology , Oxidation-Reduction/drug effects , Oxygen Consumption/genetics , Pluripotent Stem Cells/cytology , Pyruvate Carboxylase/genetics , Reverse Transcriptase Polymerase Chain Reaction , Thermogenesis/drug effects , Thermogenesis/genetics , Transcription Factors/genetics , Transcription Factors/metabolism , Uncoupling Protein 1/genetics , Uncoupling Protein 1/metabolismABSTRACT
Brown adipocytes (BAs) are a potential cell source for the treatment of metabolic disease, including type 2 diabetes. In this report, human pluripotent stem cells (hPSCs) are subject to directed differentiation through a paraxial mesoderm progenitor state that generates BAs at high efficiency. Molecular analysis identifies potential regulatory networks for BA development, giving insight into development along this lineage. hPSC-derived BAs undergo elevated rates of glycolysis, uncoupled respiration, and lipolysis that are responsive to changes in cyclic AMP (cAMP)-dependent signaling, consistent with metabolic activity in BA tissue depots. Transplanted human BAs engraft into the inter-scapular region of recipient mice and exhibit thermogenic activity. Recipient animals have elevated metabolic activity, respiratory exchange ratios, and whole-body energy expenditure. Finally, transplanted BAs reduce circulating glucose levels in hyperglycemic animals. These data provide a roadmap for brown adipocyte development and indicate that BAs generated from hPSCs have potential as a tool for therapeutic development.
Subject(s)
Diabetes Mellitus, Type 2 , Pluripotent Stem Cells , Adipocytes, Brown , Animals , Cell Differentiation , Humans , Mesoderm , Mice , ThermogenesisABSTRACT
Metabolism has been shown to alter cell fate in human pluripotent stem cells (hPSC). However, current understanding is almost exclusively based on work performed at 20% oxygen (air), with very few studies reporting on hPSC at physiological oxygen (5%). In this study, we integrated metabolic, transcriptomic, and epigenetic data to elucidate the impact of oxygen on hPSC. Using 13C-glucose labeling, we show that 5% oxygen increased the intracellular levels of glycolytic intermediates, glycogen, and the antioxidant response in hPSC. In contrast, 20% oxygen increased metabolite flux through the TCA cycle, activity of mitochondria, and ATP production. Acetylation of H3K9 and H3K27 was elevated at 5% oxygen while H3K27 trimethylation was decreased, conforming to a more open chromatin structure. RNA-seq analysis of 5% oxygen hPSC also indicated increases in glycolysis, lysine demethylases, and glucose-derived carbon metabolism, while increased methyltransferase and cell cycle activity was indicated at 20% oxygen. Our findings show that oxygen drives metabolite flux and specifies carbon fate in hPSC and, although the mechanism remains to be elucidated, oxygen was shown to alter methyltransferase and demethylase activity and the global epigenetic landscape.
ABSTRACT
As human pluripotent stem cells (hPSCs) exit pluripotency, they are thought to switch from a glycolytic mode of energy generation to one more dependent on oxidative phosphorylation. Here we show that, although metabolic switching occurs during early mesoderm and endoderm differentiation, high glycolytic flux is maintained and, in fact, essential during early ectoderm specification. The elevated glycolysis observed in hPSCs requires elevated MYC/MYCN activity. Metabolic switching during endodermal and mesodermal differentiation coincides with a reduction in MYC/MYCN and can be reversed by ectopically restoring MYC activity. During early ectodermal differentiation, sustained MYCN activity maintains the transcription of "switch" genes that are rate-limiting for metabolic activity and lineage commitment. Our work, therefore, shows that metabolic switching is lineage-specific and not a required step for exit of pluripotency in hPSCs and identifies MYC and MYCN as developmental regulators that couple metabolism to pluripotency and cell fate determination.
