Follicle-Stimulating Hormone Increases the Risk of Postmenopausal Osteoporosis by Stimulating Osteoclast Differentiation

Abstract

Objective: The objectives of this study were to observe the changes in follicle-stimulating hormone (FSH) and bone mineral density (BMD) in postmenopausal women, to research the relationship between FSH and postmenopausal osteoporosis, and to observe the effects of FSH on osteoclast differentiation in RAW264.7 cells.

Methods: We analyzed 248 postmenopausal women with normal bone metabolism. A radioimmunoassay (RIA) was used to detect serum FSH, luteinizing hormone (LH), and estradiol (E2). Dual-energy X-ray absorptiometry was used to measure forearm BMD. Then, we analyzed the age-related changes in serum FSH, LH and E2. Additionally, FSH serum concentrations were compared between a group of postmenopausal women with osteoporosis and a control group. Osteoclasts were induced from RAW264.7 cells in vitro by receptor activator of nuclear factor kappa B ligand (RANKL), and these cells were treated with 0, 5, 10, and 20 ng/ml FSH. After the osteoclasts matured, tartrate-resistant acid phosphatase (TRAP) staining was used to identify osteoclasts, and the mRNA expression levels of genes involved in osteoclastic phenotypes and function, such as receptor activator of NF-κB (Rank), Trap, matrix metalloproteinase-9 (Mmp-9) and Cathepsin K, were detected in different groups using real-time PCR (polymerase chain reaction).

Results: 1. FSH serum concentrations in postmenopausal women with osteoporosis increased notably compared with the control group. 2. RANKL induced RAW264.7 cell differentiation into mature osteoclasts in vitro. 3. FSH increased mRNA expression of genes involved in osteoclastic phenotypes and function, such as Rank, Trap, Mmp-9 and Cathepsin K, in a dose-dependent manner.

Conclusions: The circulating concentration of FSH may play an important role in the acceleration of bone loss in postmenopausal women. FSH increases osteoclastogenesis in vitro.

Fig 1. Osteoclast differentiation of RAW264.7 cells induced by RANKL.

RAW264.7 cells were induced to differentiate into osteoclasts as described in the Materials and Methods section, for 1, 4 and 7 days. (A, B, and C) Morphological changes in the cells were observed under a light microscope (original magnification 100x). (D) Representative images of TRAP staining (original magnification 100x). Bars: 50 μm.

Fig 2. mRNA expression of genes involved in osteoclast phenotypes and function.

The mRNA expression levels of Rank, Trap, Mmp-9 and Cathepsin K were significantly upregulated when the RAW264.7 cells were induced to osteoclasts (*P < 0.05 compared with control).

Fig 3. FSH increased Rank, Trap, Mmp-9 and Cathepsin K mRNA expression in osteoclasts.

(*P < 0.05 compared with the control group).