title: Expression and regulation of nampt in human islets.
abstract: Nicotinamide phosphoribosyltransferase (Nampt) is a rate-limiting enzyme in the mammalian NAD+ biosynthesis of a salvage pathway and exists in 2 known forms, intracellular Nampt (iNampt) and a secreted form, extracellular Nampt (eNampt). eNampt can generate an intermediate product, nicotinamide mononucleotide (NMN), which has been reported to support insulin secretion in pancreatic islets. Nampt has been reported to be expressed in the pancreas but islet specific expression has not been adequately defined. The aim of this study was to characterize Nampt expression, secretion and regulation by glucose in human islets. Gene and protein expression of Nampt was assessed in human pancreatic tissue and isolated islets by qRT-PCR and immunofluorescence/confocal imaging respectively. Variable amounts of Nampt mRNA were detected in pancreatic tissue and isolated islets. Immunofluorescence staining for Nampt was found in the exocrine and endocrine tissue of fetal pancreas. However, in adulthood, Nampt expression was localized predominantly in beta cells. Isolated human islets secreted increasing amounts of eNampt in response to high glucose (20 mM) in a static glucose-stimulated insulin secretion assay (GSIS). In addition to an increase in eNampt secretion, exposure to 20 mM glucose also increased Nampt mRNA levels but not protein content. The secretion of eNampt was attenuated by the addition of membrane depolarization inhibitors, diazoxide and nifedipine. Islet-secreted eNampt showed enzymatic activity in a reaction with increasing production of NAD+/NADH over time. In summary, we show that Nampt is expressed in both exocrine and endocrine tissue early in life but in adulthood expression is localized to endocrine tissue. Enzymatically active eNampt is secreted by human islets, is regulated by glucose and requires membrane depolarization.
authors.affiliation: Section of Endocrine/Diabetes, Children's Mercy Hospital and University of Missouri-Kansas City School of Medicine, Kansas City, Missouri, United States of America. kkover@cmh.edu
authors.forename: Karen
authors.initials: K
authors.lastname: Kover
authors.forename: Pei Ying
authors.initials: PY
authors.lastname: Tong
authors.forename: Dara
authors.initials: D
authors.lastname: Watkins
authors.forename: Mark
authors.initials: M
authors.lastname: Clements
authors.forename: Lisa
authors.initials: L
authors.lastname: Stehno-Bittel
authors.forename: Lesya
authors.initials: L
authors.lastname: Novikova
authors.forename: Doug
authors.initials: D
authors.lastname: Bittel
authors.forename: Nataliya
authors.initials: N
authors.lastname: Kibiryeva
authors.forename: Jacob
authors.initials: J
authors.lastname: Stuhlsatz
authors.forename: Yun
authors.initials: Y
authors.lastname: Yan
authors.forename: Shui Qing
authors.initials: SQ
authors.lastname: Ye
authors.forename: Wayne V
authors.initials: WV
authors.lastname: Moore
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D004789:Enzyme Activation; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D005934:Glucagon / Q000378:metabolism; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007328:Insulin / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D054409:Nicotinamide Phosphoribosyltransferase / Q000235:genetics* / Q000378:metabolism; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding; D040901:Proteomics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D055815:Young Adult
chemical_list: D007328:Insulin; D012333:RNA, Messenger; D005934:Glucagon; D054409:Nicotinamide Phosphoribosyltransferase; D005947:Glucose
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