title: Loss of neuronatin promotes "browning" of primary mouse adipocytes while reducing Glut1-mediated glucose disposal.
abstract: Failure of white adipose tissue to appropriately store excess metabolic substrate seems to underpin obesity-associated type 2 diabetes. Encouraging "browning" of white adipose has been suggested as a therapeutic strategy to help dispose of excess stored lipid and ameliorate the resulting insulin resistance. Genetic variation at the DNA locus encoding the novel proteolipid neuronatin has been associated with obesity, and we recently observed that neuronatin expression is reduced in subcutaneous adipose tissue from obese humans. Thus, to explore the function of neuronatin further, we used RNAi to silence its expression in murine primary adipocyte cultures and examined the effects on adipocyte phenotype. We found that primary adipocytes express only the longer isoform of neuronatin. Loss of neuronatin led to increased mitochondrial biogenesis, indicated by greater intensity of MitoTracker Green staining. This was accompanied by increased expression of UCP1 and the key genes in mitochondrial oxidative phosphorylation, PGC-1α, Cox8b, and Cox4 in primary subcutaneous white adipocytes, indicative of a "browning" effect. In addition, phosphorylation of AMPK and ACC was increased, suggestive of increased fatty acid utilization. Similar, but less pronounced, effects of neuronatin silencing were also noted in primary brown adipocytes. In contrast, loss of neuronatin caused a reduction in both basal and insulin-stimulated glucose uptake and glycogen synthesis, likely mediated by a reduction in Glut1 protein upon silencing of neuronatin. In contrast, loss of neuronatin had no effect on insulin signaling. In conclusion, neuronatin appears to be a novel regulator of browning and metabolic substrate disposal in white adipocytes.
authors.affiliation: Department of Comparative Biomedical Sciences, Royal Veterinary College, University of London, London, UK.
authors.forename: Valentina
authors.initials: V
authors.lastname: Gburcik
authors.forename: Mark E
authors.initials: ME
authors.lastname: Cleasby
authors.forename: James A
authors.initials: JA
authors.lastname: Timmons
mesh_terms: D052438:Adipocytes, White / Q000166:cytology / Q000502:physiology*; D050156:Adipogenesis / Q000502:physiology; D002001:Adipose Tissue, Brown / Q000166:cytology / Q000502:physiology*; D000328:Adult; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D051272:Glucose Transporter Type 1 / Q000378:metabolism*; D006003:Glycogen / Q000096:biosynthesis; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D008875:Middle Aged; D008928:Mitochondria / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009765:Obesity / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D010641:Phenotype; D061251:Primary Cell Culture
chemical_list: D001786:Blood Glucose; D051272:Glucose Transporter Type 1; D008565:Membrane Proteins; C490237:NNAT protein, human; D009419:Nerve Tissue Proteins; C490239:Nnat protein, mouse; C495677:SLC2A1 protein, human; C495678:Slc2a1 protein, mouse; D006003:Glycogen