title: Decreased TCF7L2 protein levels in type 2 diabetes mellitus correlate with downregulation of GIP- and GLP-1 receptors and impaired beta-cell function.
abstract: Recent human genetics studies have revealed that common variants of the TCF7L2 (T-cell factor 7-like 2, formerly known as TCF4) gene are strongly associated with type 2 diabetes mellitus (T2DM). We have shown that TCF7L2 expression in the beta-cells is correlated with function and survival of the insulin-producing pancreatic beta-cell. In order to understand how variations in TCF7L2 influence diabetes progression, we investigated its mechanism of action in the beta-cell. We show robust differences in TCF7L2 expression between healthy controls and models of T2DM. While mRNA levels were approximately 2-fold increased in isolated islets from the diabetic db/db mouse, the Vancouver Diabetic Fatty (VDF) Zucker rat and the high fat/high sucrose diet-treated mouse compared with the non-diabetic controls, protein levels were decreased. A similar decrease was observed in pancreatic sections from patients with T2DM. In parallel, expression of the receptors for glucagon-like peptide 1 (GLP-1R) and glucose-dependent insulinotropic polypeptide (GIP-R) was decreased in islets from humans with T2DM as well as in isolated human islets treated with siRNA to TCF7L2 (siTCF7L2). Also, insulin secretion stimulated by glucose, GLP-1 and GIP, but not KCl or cyclic adenosine monophosphate (cAMP) was impaired in siTCF7L2-treated isolated human islets. Loss of TCF7L2 resulted in decreased GLP-1 and GIP-stimulated AKT phosphorylation, and AKT-mediated Foxo-1 phosphorylation and nuclear exclusion. Our findings suggest that beta-cell function and survival are regulated through an interplay between TCF7L2 and GLP-1R/GIP-R expression and signaling in T2DM.
authors.affiliation: Islet Biology Laboratory, Centre for Biomolecular Interactions Bremen, University of Bremen, Bremen, Germany.
authors.forename: Luan
authors.initials: L
authors.lastname: Shu
authors.forename: Aleksey V
authors.initials: AV
authors.lastname: Matveyenko
authors.forename: Julie
authors.initials: J
authors.lastname: Kerr-Conte
authors.forename: Jae-Hyoung
authors.initials: JH
authors.lastname: Cho
authors.forename: Christopher H S
authors.initials: CH
authors.lastname: McIntosh
authors.forename: Kathrin
authors.initials: K
authors.lastname: Maedler
mesh_terms: D000368:Aged; D000818:Animals; D015536:Down-Regulation; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000378:metabolism; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism / Q000502:physiology*; D007515:Islets of Langerhans / Q000378:metabolism / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D051381:Rats; D011924:Rats, Zucker; D011964:Receptors, Gastrointestinal Hormone / Q000235:genetics* / Q000378:metabolism; D018027:Receptors, Glucagon / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D051820:TCF Transcription Factors / Q000235:genetics / Q000378:metabolism*; D058118:Transcription Factor 7-Like 2 Protein
chemical_list: C000593833:GLP1R protein, human; C000593834:Glp1r protein, mouse; C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D011964:Receptors, Gastrointestinal Hormone; D018027:Receptors, Glucagon; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; C544895:Tcf7l2 protein, mouse; C553059:Tcf7l2 protein, rat; D058118:Transcription Factor 7-Like 2 Protein; D005749:Gastric Inhibitory Polypeptide; D052216:Glucagon-Like Peptide 1; C041086:gastric inhibitory polypeptide receptor