Preactivation of -catenin in osteoblasts improves the osteoanabolic effect of PTH in type 1 diabetic mice

Type 1 diabetes (T1D) is correlated with osteopenia primarily due to low bone formation. Parathyroid hormone (PTH) is a known anabolic agent for bone, the anabolic effects of which are partially mediated through the Wnt/beta-catenin signaling pathway. In the present study, we first determined the utility of intermittent PTH treatment in a streptozotocin-induced T1D mouse model. It was shown that the PTH-induced anabolic effects on bone mass and bone formation were attenuated in T1D mice compared with nondiabetic mice. Further, PTH treatment failed to activate beta-catenin signaling in osteoblasts of T1D mice and was unable to improve osteoblast proliferation and differentiation. Next, the Col1-3.2 kb-CreERTM; beta-cateninfx(ex3) mice were used to conditionally activate beta-catenin in osteoblasts by injecting tamoxifen, and we addressed whether or not preactivation of beta-catenin boosted the anabolic action of PTH on T1D-related bone loss. The results demonstrated that pretreatment with activation of osteoblastic beta-catenin followed by PTH treatment outperformed PTH or beta-catenin activation monotherapy and led to greatly improved bone structure, bone mass, and bone strength in this preclinical model of T1DM. Further analysis demonstrated that osteoblast proliferation and differentiation, as well as osteoprogenitors in the marrow, were all improved in the combination treatment group. These findings indicated a clear advantage of developing beta-catenin as a target to improve the efficacy of PTH in the treatment of T1D-related osteopenia.