Anxa2 attenuates osteoblast growth and is associated with hip BMD and osteoporotic fracture in Chinese elderly

Low bone mineral density (BMD) is a risk factor of osteoporotic fracture (OF). Peripheral blood monocytes (PBM) can differentiate into osteoclasts to resorb bone. It was known that PBM-expressed Anxa2 protein is associated with BMD, and extracellular Anxa2 protein promotes osteoclastogenesis. This study aimed to test 1) whether Anxa2 protein level in PBM differs significantly between subjects with OF and without fracture history (NF); 2) whether Anxa2 level in plasma is associated with BMD; 3) how Anxa2 protein at various concentrations would affect osteoblastic activity in vitro. All the study subjects were Chinese Han elderly. Firstly, Anxa2 protein in PBM was identified and quantitated by LC-MS/MS and compared between 45 OF cases and 42 healthy controls. Secondly, plasma Anxa2 protein level was quantitated by ELISA and compared between unrelated subjects with extremely low vs. high hip BMD (0.63±0.10 vs. 1.05±0.10 g/cm², n = 75). Furthermore, in vitro functional assay was utilized to test the effects of extracellular Anxa2 protein on osteoblastic growth. We found that Anxa2 protein expression in PBM was significantly up-regulated in OF vs. NF subjects (fold change [FC)] = 1.16, P<0.05). Plasma Anxa2 protein concentration (range: 31.69–227.35ng/ml) was significantly elevated in low vs. high BMD subjects (84.85 vs. 66.15ng/ml, FC = 1.28, P<0.05). Cellular dynamical monitoring demonstrated that the general shape of dose-response relationship is the inverse U-shaped curve. Specifically, lower dose of Anxa2 protein may promote osteoblast growth and the optimal concentration for osteoblastic growth was around 50ng/ml, but even higher concentration could attenuate hFOB1.19 osteoprogenitor cell growth. We concluded that Anxa2 protein could attenuate osteoblast growth and be associated with hip BMD and OF in Chinese elderly.