Axin2 controls bone remodeling through the β-catenin–BMP signaling pathway in adult mice

Abstract

To investigate the role of Wnt–β-catenin signaling in bone remodeling, we analyzed the bone phenotype of female Axin2-lacZ knockout (KO) mice. We found that trabecular bone mass was significantly increased in 6- and 12-month-old Axin2 KO mice and that bone formation rates were also significantly increased in 6-month-old Axin2 KO mice compared with wild-type (WT) littermates. In vitro studies were performed using bone marrow stromal (BMS) cells isolated from 6-month-old WT and Axin2 KO mice. Osteoblast proliferation and differentiation were significantly increased and osteoclast formation was significantly reduced in Axin2 KO mice. Nuclear β-catenin protein levels were significantly increased in BMS cells derived from Axin2 KO mice. In vitro deletion of the β-catenin gene under Axin2 KO background significantly reversed the increased alkaline phosphatase activity and the expression of osteoblast marker genes observed in Axin2 KO BMS cells. We also found that mRNA expression of Bmp2 and Bmp4 and phosphorylated Smad1/5 protein levels were significantly increased in BMS cells derived from Axin2 KO mice. The chemical compound BIO, an inhibitor of glycogen synthase kinase 3β, was utilized for in vitro signaling studies in which upregulated Bmp2 and Bmp4 expression was measured in primary calvarial osteoblasts. Primary calvarial osteoblasts were isolated from Bmp2fx/fx;Bmp4fx/fx mice and infected with adenovirus-expressing Cre recombinase. BIO induced Osx, Col1, Alp and Oc mRNA expression in WT cells and these effects were significantly inhibited in Bmp2/4-deleted osteoblasts, suggesting that BIO-induced Osx and marker gene expression were Bmp2/4-dependent. We further demonstrated that BIO-induced osteoblast marker gene expression was significantly inhibited by Osx siRNA. Taken together, our findings demonstrate that Axin2 is a key negative regulator in bone remodeling in adult mice and regulates osteoblast differentiation through the β-catenin–BMP2/4–Osx signaling pathway in osteoblasts.

Osteocyte Wnt/β-Catenin Signaling Is Required for Normal Bone Homeostasis

“…7A and B). However, consistent with OPG being a Wnt/␤-catenin target gene (19,26,69), OPG expression was significantly decreased by about 50% in femoral diaphyseal bone (Fig. 7C).…”

“…Wnt/␤-catenin signaling has been implicated in the regulation of apoptotic cell death of cells of the osteoblast lineage in some instances (4,7,39), but not others (5,31,69). Moreover, osteocyte apoptosis correlates with increased osteoclast recruitment and bone resorption (1,16,20,22,34,49,61).…”

A Comprehensive Overview of Skeletal Phenotypes Associated with Alterations in Wnt/β-catenin Signaling in Humans and Mice

“…The mice show evidence of aberrant activation of Wnt signaling, which likely accounts for the increased osteoblast proliferation and differentiation seen ex vivo, and ultimately for the enhanced bone mineralization and ossification in vivo (130). Further assessment of these mice revealed an important role of axin-2 in mature bone: significant differences in bone volume and BMD are seen at 6 and 12 months when compared with wild-type mice, but no differences in bone volume or BMD are observed at 2 months of age (129). These mice also show an abnormal chondrocyte phenotype due to expedited maturation, resulting in a shorter hypertrophic zone in the growth plate of long bones (128).…”

Effect of micro-nano-hybrid structured hydroxyapatite bioceramics on osteogenic and cementogenic differentiation of human periodontal ligament stem cell via Wnt signaling pathway

“…β-Catenin is the key factor of the canonical Wnt signaling pathway and plays an important role in cell proliferation and differentiation processes. 54 The LRP5 gene is known as a coreceptor of Wnt and plays an important role in the development and maintenance of several tissues. LRP5 could help regulate bone mineral density, and loss of this gene results in reduced skeletal strength, while gain of function results in higher bone mass.…”