ABSTRACT
Receptors to glucose-dependent insulinotropic polypeptide (GIP), have been identified on bone and GIP receptor (GIPr) knockout mice exhibit reduced bone strength and quality. Despite this, little is known on the potential beneficial bone effects of exogenous GIP on bone physiology. The aim of the present study was to assess whether stable GIP analogues were capable of ameliorating bone strength in mice with diet-induced obesity. The stable GIP analogue (D-Ala²)-GIP, and (D-Ala²)-GIP-Tag, a specific GIP analogue homing exclusively to bone, were employed. In vitro studies were used to assess effects of (D-Ala²)-GIP and (D-Ala²)-GIP-Tag on bone mineralization, lysyl oxidase activity, collagen maturity as well as osteoclast formation and activity. Subsequent in vivo studies employed obese-prediabetic Swiss NIH mice subjected to a 42-day period of daily administration of saline, (D-Ala²)-GIP or (D-Ala²)-GIP-Tag. In vitro studies confirmed that (D-Ala²)-GIP and (D-Ala²)-GIP-Tag had similar beneficial biological effects on bone cells. Administration of (D-Ala²)-GIP and (D-Ala²)-GIP-Tag resulted in lower blood glucose levels without any effects on body weight. Both GIP analogues augmented bone strength to a similar extent. Trabecular or cortical bone microarchitecture were not changed over the time course of the study. However, (D-Ala²)-GIP and (D-Ala²)-GIP-Tag augmented enzymatic collagen crosslinking as well as the heterogeneity of enzymatic collagen crosslinking, mineral-to-matrix ratio and significantly reduced the heterogeneity in mineral bone crystallite size. This study demonstrates that activation of skeletal GIPr by stable GIP analogues enhance bone strength in prediabetes and suggest that these analogues may be beneficial in the treatment of bone disease.
Subject(s)
Bone and Bones/drug effects , Diet/adverse effects , Gastric Inhibitory Polypeptide/pharmacology , Gastrointestinal Agents/pharmacology , Insulin/metabolism , Obesity/physiopathology , Receptors, Gastrointestinal Hormone/metabolism , Animals , Blood Glucose/metabolism , Body Weight , Bone and Bones/metabolism , Bone and Bones/pathology , Cells, Cultured , Disease Models, Animal , Humans , Male , Mice , Mice, Obese , Obesity/etiologyABSTRACT
Myostatin (MSTN), a member of transforming growth factor-ß (TGF-ß) superfamily, is a negative regulator of the skeletal muscle growth, and suppresses the proliferation and differentiation of myoblast cells. Dysfunction of MSTN gene either by natural mutation or genetic manipulation (knockout or knockdown) has been reported to interrupt its proper function and to increase the muscle mass in many mammalian species. RNA interference (RNAi) mediated by small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs) has become a powerful tool for gene knockdown studies. In the present study transient silencing of MSTN gene in chicken embryo fibroblast cells was evaluated using five different shRNA expression constructs. We report here up to 68% silencing of myostatin mRNA using these shRNA constructs in transiently transfected fibroblasts (p<0.05). This was, however, associated with induction of interferon responsive genes (OAS1, IFN-ß) (3.7-64 folds; p<0.05). Further work on stable expression of antimyostatin shRNA with minimum interferon induction will be of immense value to increase the muscle mass in the transgenic animals.
