title: Inhibition of the canonical Wnt pathway by high glucose can be reversed by parathyroid hormone-related protein in osteoblastic cells.
abstract: Recent in vivo findings suggest that the bone sparing effect of parathyroid hormone-related protein (PTHrP) in diabetic mice might occur at least in part through targeting a suppressed Wnt/β-catenin pathway in osteoblasts. We here aimed to examine the inhibitory action of a high glucose environment on specific components of the canonical Wnt pathway, and the putative compensatory effects of PTHrP, in osteoblastic cell cultures. Mouse osteoblastic MC3T3-E1 cells and primary cultures of fetal mouse calvaria were exposed to normal (5.5 mM) or high (25 mM) D-glucose (HG), with or without PTHrP (1-36) or PTHrP (107-139) for different times. In some experiments, MC3T3-E1 cells were incubated with the Wnt pathway activators Wnt3a and LiCl, or were transfected with plasmids encoding either a mutated β-catenin that cannot be targeted for degradation or a human PTHrP (-36/+139) cDNA, or the corresponding empty plasmid, in the presence or absence of HG. The gene expression of Wnt3a and low density receptor-like proteins (LRP)-5 and 6, as well as β-catenin protein stabilization and β-catenin-dependent transcription activity were evaluated. Oxidative stress status under HG condition was also assessed. The present data demonstrate that HG can target different components of the canonical Wnt pathway, while β-catenin degradation appears to be a key event leading to inhibition of Wnt/β-catenin signaling in mouse osteoblastic cells. Both PTHrP peptides tested were able to counteract this deleterious action of HG. These in vitro findings also provide new clues to understand the underlying mechanisms whereby PTHrP can increase bone formation.
authors.affiliation: Laboratorio de Metabolismo Mineral y Óseo, Instituto de Investigación Sanitaria-Fundación Jiménez Díaz and Red Temática de Investigación Cooperativa en Envejecimiento y Fragilidad, Madrid, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: López-Herradón
authors.forename: Sergio
authors.initials: S
authors.lastname: Portal-Núñez
authors.forename: Adela
authors.initials: A
authors.lastname: García-Martín
authors.forename: Daniel
authors.initials: D
authors.lastname: Lozano
authors.forename: Francisco C
authors.initials: FC
authors.lastname: Pérez-Martínez
authors.forename: Valentín
authors.initials: V
authors.lastname: Ceña
authors.forename: Pedro
authors.initials: P
authors.lastname: Esbrit
mesh_terms: D000818:Animals; D018692:Antimanic Agents / Q000494:pharmacology; D002460:Cell Line; D005947:Glucose / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D018021:Lithium Chloride / Q000494:pharmacology; D060492:Low Density Lipoprotein Receptor-Related Protein-5 / Q000235:genetics / Q000378:metabolism; D060488:Low Density Lipoprotein Receptor-Related Protein-6 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009154:Mutation; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis / Q000187:drug effects / Q000235:genetics; D044162:Parathyroid Hormone-Related Protein / Q000378:metabolism / Q000494:pharmacology*; D055550:Protein Stability; D060449:Wnt Signaling Pathway / Q000187:drug effects* / Q000502:physiology; D060509:Wnt3A Protein / Q000378:metabolism / Q000494:pharmacology; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism
chemical_list: D018692:Antimanic Agents; C555482:LRP5 protein, human; C555475:LRP6 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C555483:Lrp5 protein, mouse; C555476:Lrp6 protein, mouse; D044162:Parathyroid Hormone-Related Protein; C555510:WNT3A protein, human; D060509:Wnt3A Protein; C555511:Wnt3a protein, mouse; D051176:beta Catenin; D018021:Lithium Chloride; D005947:Glucose