Follicle-stimulating hormone promotes RANK expression on human monocytes

Abstract

Elevated serum concentrations of follicle-stimulating hormone (FSH) are associated with diminished bone density in women, beginning years before menopause and the decline in estradiol. We hypothesized that FSH promotes development of myeloid cells toward the bone-resorbing osteoclast phenotype. This was tested by isolating peripheral blood mononuclear cells from nine healthy adults, incubating them in the presence of FSH at three different concentrations spanning the physiological range, and then measuring the expression of receptor activator for NF-κB (RANK, a surface marker for osteoclasts) on CD14(+) cells by flow cytometry. In the absence of FSH, 3.3±0.5% of the cells expressed high levels of the receptor (RANK(high)). Increasing concentrations of FSH caused a biphasic dose-response, with a maximal (1.5-fold) increase in RANK(high) cells achieved with 50 mIU/ml FSH (P=0.02). Cytokines that influence development of osteoclasts were also measured in culture supernatants: macrophage colony stimulating factor (M-CSF), osteoprotegerin (OPG) and tumor necrosis factor-α (TNFα) concentrations were not significantly influenced by FSH, whereas RANK-ligand was undetectable. This study supports the concept that the elevated circulating concentrations of FSH during perimenopause may contribute to the increased rate of bone loss by promoting the development of osteoclast precursor cells.

Figure 1

Flow cytometry results from a single subject. A: Scatter plot for CD14⁺ gated cells (vertical axis) versus PE- conjugated isotype control (horizontal axis); B: Histogram of the PE fluorescence data of panel A; C: Scatter plot for CD14⁺ gated cells versus PE-conjugated anti-RANK under control conditions without FSH; D: Histogram of the PE fluorescence data of panel C; E and F: same as panels C and D, except cells were cultured with 50 mIU/ml FSH. The vertical line indicates the demarcation between nonspecific and specific staining (at an RFI of 300 for this subject).

Figure 2

Mean RANK expression on CD14⁺ mononuclear cells (panel A) and CD14-negative cells (panel B). The top of the white bars indicates the total percentage of RANK positive cells, the black bars indicate the percentage of RANK^high cells (RFI > 3000, extremely low in panel B). *P = 0.02, compared to control condition (0 FSH). N=9.

Figure 3

Concentrations of M-CSF (black bars, scale on left), OPG (dark gray bars, scale on right), and TNFα (light gray bars, scale on left) in the supernatants of mononuclear cells cultured with FSH.