Mechanism Study Of Gna13Negatively Regulating Osteoclast Formation And Activation And Cbfβ Positively Regulating Skeletal Formation To Maintain Bone Density

Bone modeling by osteoblast and bone resorption by osteoclast regulates bone homeostasis. Osteoclast aberration results in diseases like osteoporosis. Positive regulation of osteoclast has been extensively studied while negative regulation remains unclear. Using microarray assay, RNAi knockdown and in vitro function analysis approaches, Gna13and TANK were identified as the candidate negative regulators. Then mice specifically lacking Gna13in the monocyte and osteoclast (CKO) were constructed by crossing Gna13f/f mice with LysM-cre mice and Cathepsin K-Cre mice. X-ray, u-CT, and histology showed that CKO mice demonstrated severe osteoporosis phenotype with two-fold increased osteoclast number. CKO cells displayed increased osteoclastogenesis, larger cell size, larger actin ring on bone slides, increased Cathepsin K secretion,2-fold increased bone resorption. Furhtermore, AKT and GSK3β phosphorylation in CKO cells were shown largely increased, and much more NFATcl was observed in the nuclei of CKO osteoclasts. Meanwhile, c-Src and Racl activity were increased in mature CKO osteoclasts. Gna13was interacting with p110a, a catalytic subunit of Class IA PI3K confirmed by co-immunoprecipitation. Over-expression of constitutive active form of Gna13(Gnal3CA) in monocyte/macrophage blocked pre-osteoclast fusion, spoiled actin ring formation, reduced bone resoprtion, inhibited Ctsk secretion, decreased Osteoclast-specific genes expression and promoted AKT phosphorylation. In conclusion, our study demonstrates Gna13as a novel negative regulator of bone resorption and osteoclastogenesis, by antagonizing AKT/GSK3β/NFATc1signaling and c-Src/rac1activity.Then we constructed mesenchymal stem cell specific Cbfβ knockout mice (Prxl Cbfβf/f) and chondrocyte specific Cbfβ knockout mice (Col2α1Cbfβf/f to study the role of Cbfβ in skeletal homeostasis. On one hand, Cbfβ promotes osteoblastogenesis and bone formation. On the other hand, Cbfβ regulates growth plate development through Runx2and Ihh-PTHrP signalin, which further regulates endochondral bone formation.Our results indicate that Gnal3and Cbfβ may serve as a novel therapeutic target for osteoporosis.