17 beta-estradiol versus progesterone in the expression of osteoprotegerin gene in human osteoblast-like cells

Jun OUYANG; Eryuan LIAO; Xianghang LUO; Huige SHAO; Houde ZHOU

ABSTRACT

BACKGROUND:

Estrogen/progestins replacement therapy prevents excess bone loss in postmenopausal women.Recently osteoprotegerin (OPG) has been identified in osteoblast and displayed to inhibit bone resorption.

OBJECTIVE:

To compare the action between 17β-estradiol (E2) and progesterone on OPG expression in cultured normal human osteoblast-like cells (hOB).

DESIGN:

A comparative investigation.

SETTING:

Institute of Metabolic Endocrinology, the Second Xiangya Hospital of Central South University.MATERIALS α-MEM (Sigma Chemical Corp., St. Louis, MO, USA); Type Ⅳ collagenase (Sigma); Fetal bovine serum (Gibco-BRL Corp., Grand Island, NY, USA); Osteocalcin radioimmunoassay kit (DiaSorin Corp., Stillwater, MN, USA).

METHODS:

The experiments were carried out in the Institute of Metabolic Endocrinology, Second Xiangya Hospital of Central South University from January 2003 to March 2006. The osteoblasts were extracted from the cancelous bone of anterior superior iliac spine of normal people, then cultured. The hOB were treated with E2 and progesterone, and the expressions of OPG mRNA and OPG protein were determined by Northern blot analysis and enzyme-linked immunoabsorbent assay (ELISA) respectively.MAIN OUTCOME

MEASURES:

①Characterization of human osteoblast-like cells; ②Effect of E2 and progesterone on OPG mRNA levels by Northern blot analysis; ③ Effect of E2 and progesterone on OPG protein levels in the conditioned medium by ELISA.

RESULTS:

① Characterization of hOB in vitro The ALP levels in normal human osteoblasts were (74.3±4.7) U/g protein,and the detectable osteocalcin levels was (3.84±0.39) μg/L protein], which suggested that osteoblasts were the primary cell type found in our bone-derived cell cultures from donors. ② Effects of E2 and progesterone on the levels of OPG mRNA by Northern blot

analysis:

The OPG mRNA band was week in the control group [(12.3±3.5)%], treatment with 1 × 10-10, 1 ×10-9 1 ×10-8 mol/L E2 caused an increase in the levels of OPG mRNA. The expression of OPG mRNA in the 1×10-8 mol/L E2 group was gradually increased at 12, 24 and 48 hours. Progesterone had no influence on OPG mRNA expression. ③ Effects of E2 and progesterone on OPG protein production in conditioned medium determined with ELISA ELISA revealed that treatment with 1 ×10-10, 1 ×10-9, 1 ×10-8 mol/L E2 induced obvious increase in the levels of OPG protein in cells media as compared with that in the control group [(1.27±0.26), (2.34±0.35), (3.62±0.23), (0.64±0.14)μg/L, P ＜ 0.01]. In the presence of 1×10-8 mol/L E2, OPG protein production in cells media at 12, 24 and 48 hours were significantly higher than that in the control group [(1.30±0.30), (3.07±0.14), (3.50±0.33), (0.62±0.12) μg/L, P ＜ 0.01]. 1 × 10-10, 1 ×10-9 1 × 10-8 mol/L progesterone had no influence on the OPG protein production after 12-24 hours (P ＞ 0.05).

CONCLUSION:

The different regulation of OPG production in osteoblasts by E2 and progesterone may contribute to the mechanisms by which estrogen or progestins exerts its different action on bone resorption.