title: ENPP1 affects insulin action and secretion: evidences from in vitro studies.
abstract: The aim of this study was to deeper investigate the mechanisms through which ENPP1, a negative modulator of insulin receptor (IR) activation, plays a role on insulin signaling, insulin secretion and eventually glucose metabolism. ENPP1 cDNA (carrying either K121 or Q121 variant) was transfected in HepG2 liver-, L6 skeletal muscle- and INS1E beta-cells. Insulin-induced IR-autophosphorylation (HepG2, L6, INS1E), Akt-Ser(473), ERK1/2-Thr(202)/Tyr(204) and GSK3-beta Ser(9) phosphorylation (HepG2, L6), PEPCK mRNA levels (HepG2) and 2-deoxy-D-glucose uptake (L6) was studied. GLUT 4 mRNA (L6), insulin secretion and caspase-3 activation (INS1E) were also investigated. Insulin-induced IR-autophosphorylation was decreased in HepG2-K, L6-K, INS1E-K (20%, 52% and 11% reduction vs. untransfected cells) and twice as much in HepG2-Q, L6-Q, INS1E-Q (44%, 92% and 30%). Similar data were obtained with Akt-Ser(473), ERK1/2-Thr(202)/Tyr(204) and GSK3-beta Ser(9) in HepG2 and L6. Insulin-induced reduction of PEPCK mRNA was progressively lower in untransfected, HepG2-K and HepG2-Q cells (65%, 54%, 23%). Insulin-induced glucose uptake in untransfected L6 (60% increase over basal), was totally abolished in L6-K and L6-Q cells. GLUT 4 mRNA was slightly reduced in L6-K and twice as much in L6-Q (13% and 25% reduction vs. untransfected cells). Glucose-induced insulin secretion was 60% reduced in INS1E-K and almost abolished in INS1E-Q. Serum deficiency activated caspase-3 by two, three and four folds in untransfected INS1E, INS1E-K and INS1E-Q. Glyburide-induced insulin secretion was reduced by 50% in isolated human islets from homozygous QQ donors as compared to those from KK and KQ individuals. Our data clearly indicate that ENPP1, especially when the Q121 variant is operating, affects insulin signaling and glucose metabolism in skeletal muscle- and liver-cells and both function and survival of insulin secreting beta-cells, thus representing a strong pathogenic factor predisposing to insulin resistance, defective insulin secretion and glucose metabolism abnormalities.
authors.affiliation: Research Unit of Diabetes and Endocrine Diseases, IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy.
authors.forename: Rosa
authors.initials: R
authors.lastname: Di Paola
authors.forename: Nunzia
authors.initials: N
authors.lastname: Caporarello
authors.forename: Antonella
authors.initials: A
authors.lastname: Marucci
authors.forename: Claudia
authors.initials: C
authors.lastname: Dimatteo
authors.forename: Claudia
authors.initials: C
authors.lastname: Iadicicco
authors.forename: Silvia
authors.initials: S
authors.lastname: Del Guerra
authors.forename: Sabrina
authors.initials: S
authors.lastname: Prudente
authors.forename: Dora
authors.initials: D
authors.lastname: Sudano
authors.forename: Claudia
authors.initials: C
authors.lastname: Miele
authors.forename: Cristina
authors.initials: C
authors.lastname: Parrino
authors.forename: Salvatore
authors.initials: S
authors.lastname: Piro
authors.forename: Francesco
authors.initials: F
authors.lastname: Beguinot
authors.forename: Piero
authors.initials: P
authors.lastname: Marchetti
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Trischitta
authors.forename: Lucia
authors.initials: L
authors.lastname: Frittitta
mesh_terms: D002460:Cell Line; D005838:Genotype; D005947:Glucose / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D056945:Hep G2 Cells; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011110:Polymorphism, Genetic / Q000235:genetics; D011755:Pyrophosphatases / Q000235:genetics / Q000378:metabolism*
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases; D005947:Glucose; D005905:Glyburide