Short-term administration of glucocorticoids (GCs) impairs muscle insulin sensitivity at least in part via the reduction of undercarboxylated osteocalcin (ucOC). However, whether ucOC treatment reverses the GC-induced muscle insulin resistance remains unclear. To test the hypothesis that ucOC directly ameliorates impaired insulin-stimulated glucose uptake (ISGU) induced by short-term GC administration in mice muscle and to identify the molecular mechanisms, mice were implanted with placebo or corticosterone (CS) slow-release pellets. Two days post-surgery, insulin-tolerance tests (ITTs) were performed. On day 3, serum was collected and extensor digitorum longus (EDL) and soleus muscles were isolated and treated ex vivo with vehicle, ucOC (30 ng/mL), insulin (60 µU/mL), or both. Circulating hormone levels, muscle glucose uptake, and muscle signaling proteins were assessed. CS administration reduced both serum osteocalcin and ucOC levels, whole-body insulin sensitivity, and muscle ISGU in EDL. Ex vivo ucOC treatment restored ISGU in CS-affected muscle, without increasing non-insulin-stimulated glucose uptake. In CS-affected EDL muscle, ucOC enhanced insulin action on phosphorylated (p-)protein kinase B (Akt)
Ser473and the p-extracellular signal-regulated kinase isoform 2 (ERK2)
Thr202/Tyr204/total (t)ERK2 ratio, which correlated with ISGU. In CS-affected soleus muscle, ucOC enhanced insulin action on p-mammalian target of rapamycin (mTOR)
Ser2481, the p-mTOR
Ser2481/tmTOR ratio, p-Akt substrate of 160kD (AS160)
Thr642, and p-protein kinase C (PKC) (pan)
Thr410, which correlated with ISGU. Furthermore, p-PKC (pan)
Thr410 correlated with p-Akt
Ser473 and p-AS160
Thr642. ucOC exerts direct insulin-sensitizing effects on CS-affected mouse muscle, likely through an enhancement in activity of key proteins involved in both insulin and ucOC signaling pathways. Furthermore, these effects are muscle type-dependent. © 2019 The Authors.
Journal of Bone and Mineral Research published by Wiley Periodicals, Inc.
相似文献