Supplemental Information for Intestinal epithelial NAD+ biosynthesis regulates GLP-1 production and postprandial glucose metabolism in mice

Obesity is associated with perturbations in incretin production and whole-body glucose metabolism, but the precise mechanism remains unclear. Here, we tested the hypothesis that nicotinamide phosphoribosyltransferase (NAMPT), which mediates the biosynthesis of nicotinamide adenine dinucleotide (NAD+), a key regulator of cellular energy metabolism, plays a critical role in obesity-associated intestinal pathophysiology and systemic metabolic complications. To this end, we generated a novel mouse model, namely intestinal epithelial cell-specific Nampt knockout (INKO) mice. INKO mice displayed diminished glucagon-like peptide-1 (GLP-1) production, at least partly contributing to reduced early-phase insulin secretion and postprandial hyperglycemia. Mechanistically, loss of NAMPT attenuated the Wnt signaling pathway, resulting in insufficient GLP-1 production. We also found that diet-induced obese mice had compromised intestinal NAMPT-mediated NAD+ biosynthesis and the Wnt signaling pathway, associated with impaired GLP-1 production and whole-body glucose metabolism, resembling the INKO mice. Finally, administration of a key NAD+ intermediate, nicotinamide mononucleotide (NMN), restored intestinal NAD+ levels and obesity-associated metabolic derangements, manifested by a decrease in ileal Proglucagon expression and GLP-1 production as well as postprandial hyperglycemia in INKO and diet-induced obese mice. Collectively, our study provides mechanistic and therapeutic insights into intestinal NAD+ biology related to obesity-associated dysregulation of GLP-1 production and postprandial hyperglycemia.This study was funded by the Scientific Research Fund of the Ministry of Education, Culture, Sports, Science, and Technology of Japan (grant no. 18K15399, 21K07377) and research grants from Keio University Medical Science Fund, Research Grants for Life Sciences and Medicine, Japan Diabetes Society Junior Scientist Development Grant supported by Novo Nordisk Pharma Ltd., Boehringer/Lilly Diabetes Research Grant in Japan Diabetes Foundation, MSD Life Science Foundation, Terumo Foundation for Life Sciences and Arts, Kowa Life Science Foundation, Mishima Kaiun Memorial Foundation, Japan Foundation for Applied Enzymology, YOKOYAMA Foundation for Clinical Pharmacology (YRY-2010), Takeda Science Foundation, The 2021 Inamori Research Grant Program, and the Japan Arteriosclerosis Prevention Fund