17β-estradiol attenuates ovariectomy‑induced bone deterioration through the suppression of the ephA2/ephrinA2 signaling pathway

Abstract

The present study aimed to investigate whether 17β‑estradiol (E2) exerts protective effects on bone deterioration induced by ovariectomy (OVX) through the ephA2/ephrinA2 signaling pathway in rats. Female rats were subjected to OVX, sham surgeryor OVX+E2 treatment. Levels of biomarkers were measured in serum and urine. Hematoxylin and eosin staining was performed on paraffin‑embedded bone sections. Expression of genes and proteins was analyzed by reverse transcription‑quantitative polymerase chain reaction and western blotting, respectively. Bone mineral density (BMD) was analyzed by dual‑energy X‑ray absorptiometry. Trabecular bone microarchitecture was also evaluated. Osteoclastogenesis was induced by in vitro culturing with mouse receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony‑stimulating factor 1. small interfering RNA was designed to knockdown ehpA2 receptor and its ligand ephrinA2. Results of the present study demonstrated that E2 had suppressive effects on OVX‑induced body weight gain and bone turnover factors in serum and urine. E2 inhibited the bone resorption function of osteoclasts by inhibiting the production of tartrate‑resistant acid phosphatase‑5b and RANKL, and induced bone formation function of osteoblasts by prompting runt‑related transcription factor 2, Sp7 transcription factor and collagen alpha‑1(I) chain expression in bone marrow cells. E2 treatment significantly increased the tibia BMD and prevented the deterioration of trabecular microarchitecture compared with the OVX group. Moreover, E2 significantly decreased the OVX‑stimulated expression of ephA2 and ephrinA2. EphA2 or ephrin A2 knockdown significantly suppressed osteoclastogenesis in vitro. In conclusion, E2 can attenuate OVX‑induced bone deterioration partially through the suppression of the ephA2/ephrinA2 signaling pathway. Therefore EphA2/ephrinA2 signaling pathway may be a potential target for osteoporosis treatment.

Figure 1.

Effect of E2 on the body weight of OVX rats. Data are presented as the mean ± standard deviation. *P<0.05, **P<0.01, ***P<0.001 vs. the SHAM group. ^#P<0.05, ^##P<0.01, ^###P<0.001 vs. the OVX group. Sham, placebo operated rats; OVX, ovariectomy; E2, 17β-estradiol.

Figure 2.

Effects of E2 on bone turnover markers. (A) Serum Ca at the end of the experiment. (B) Changes in urinary Ca/Cr levels. (C) b-ALP; and (D) TRAP-5b level sat the end of the experiment. *P<0.05, **P<0.01, ***P<0.001 vs. the SHAM group. ^#P<0.05, ^##P<0.01, ^###P<0.001 vs. the OVX group. Sham, placebo operated rats; OVX, ovariectomy; E2, 17β-estradiol; TRAP-5b, tartrate-resistant acid phosphatase-5b; b-ALP, bone specific alkaline phosphatase.

Figure 3.

Effects of E2 on expression levels of bone metabolism-associated genes. (A) Relative ALP; (B) TRAP; (C) Runx2, osterix and col1a1; (D) OPG and RANKL mRNA expression. Data are presented as the mean ± standard deviation. *P<0.05, ***P<0.001 vs. the SHAM group. ^#P<0.05, ^##P<0.01, ^###P<0.001 vs. the OVX group. Sham, placebo operated rats; OVX, ovariectomy; E2, 17β-estradiol; TRAP, tartrate-resistant acid phosphatase-5b; ALP, alkaline phosphatase; Runx2, runt-related transcription factor 2; osterix, Sp7 transcription factor; col1a1, collagen alpha-1(I) chain; OPG, osteoprotegerin; RANKL, receptor activator of nuclear factor κB ligand.

Figure 4.

Effects of E2 on bone morphology. (A) Effect of E2 on BMD in left tibiae of OVX rats evaluated by DXA (B) Effect of E2 on bone histomorphology analyzed by H&E staining (magnification, ×100). (C) Effects of E2 on the BV/TV; (D) Tb.N; (E) Tb.Sp; and (F) Tb.Th in the left tibiae of rats. Data are presented as the mean ± standard deviation. *P<0.05, **P<0.01, ***P<0.001 vs. the SHAM group. ^#P<0.05, ^###P<0.001 vs. the OVX group. DEXA, Dual-energy X-ray absorptiometry; Sham, placebo operated rats; OVX, ovariectomy; E2, 17β-estradiol; BV/TV, bone volume per tissue volume; Tb.Th, trabecular thickness; Tb.N, trabecular number; Tb.Sp, trabecular separation; BMD, bone mineral density; H&E, hematoxylin and eosin.

Figure 5.

Effect of E2 on OVX-induced bone deterioration through the suppression of the ephA2/ephrinA2 signaling pathway. (A) Reverse transcription-quantitative polymerase chain reaction; and (B) western blot analyses demonstrated that E2 significantly decreased the OVX-stimulated expression of ephA2 and ephrinA2. (C) EphA2; and (D) ephrinA2 knockdown significantly suppressed osteoclastogenesis, indicating their otherwise stimulating role on osteoclast differentiation. Data are presented as the mean ± standard deviation. *P<0.05 vs. the SHAM group. ^#P<0.05 vs. The OVX group. Sham, placebo operated rats; OVX, ovariectomy; E2, 17β-estradiol; siRNA, small interfering RNA; RANKL, receptor activator of nuclear factor κB ligand; M-CSF, macrophage colony-stimulating factor 1.