Synergistic effects of high dietary calcium and exogenous parathyroid hormone in promoting osteoblastic bone formation in mice.

Yuxu Feng,Min Zhou,Yong Xu,Lei Shu,Jue Zhang,Huan Liu,Dengshun Miao,Qunhu Zhang,Yongxin Ren

doi:10.1017/s0007114514004309

Abstract

In the present study, we investigated whether high dietary Ca and exogenous parathyroid hormone 1-34 fragments (PTH 1-34) have synergistic effects on bone formation in adult mice, and explored the related mechanisms. Adult male mice were fed a normal diet, a high-Ca diet, a PTH-treated diet, or a high-Ca diet combined with subcutaneously injected PTH 1-34 (80 μg/kg per d) for 4 weeks. Bone mineral density, trabecular bone volume, osteoblast number, alkaline phosphatase (ALP)- and type I collagen-positive areas, and the expression levels of osteoblastic bone formation-related genes and proteins were increased significantly in mice fed the high-Ca diet, the PTH-treated diet, and, even more dramatically, the high-Ca diet combined with PTH. Osteoclast number and surface and the ratio of receptor activator for nuclear factor-κB ligand (RANKL):osteoprotegerin (OPG) were decreased in the high-Ca diet treatment group, increased in the PTH treatment group, but not in the combined treatment group. Furthermore, third-passage osteoblasts were treated with high Ca (5 mM), PTH 1-34 (10⁻⁸ M) or high Ca combined with PTH 1-34. Osteoblast viability and ALP activity were increased in either the high Ca-treated or PTH-treated cultures and, even more dramatically, in the cultures treated with high Ca plus PTH, with consistent up-regulation of the expression levels of osteoblast proliferation and differentiation-related genes and proteins. These results indicate that dietary Ca and PTH play synergistic roles in promoting osteoblastic bone formation by stimulating osteoblast proliferation and differentiation.

Highlights

In the present study, we investigated whether high dietary Ca and exogenous parathyroid hormone 1– 34 fragments (PTH 1 – 34) have synergistic effects on bone formation in adult mice, and explored the related mechanisms
The results showed that bone mineral density (BMD) and trabecular bone volume were increased significantly in either the high-Ca diet group or the Parathyroid hormone (PTH) treatment group compared with the vehicle-treated group, and were significantly higher in the combined treatment group than in the high-Ca diet or PTH treatment group (Fig. 1(a)– (e))
To determine whether alterations of trabecular bone volume in adult mice are associated with changes in osteoblast function, bone formation parameters were assessed by haematoxylin and eosin staining (Fig. 2(a)), histochemical staining for alkaline phosphatase (ALP) (Fig. 2(b)), immunostaining for Col-I (Fig. 2(c)), and histomorphometric analyses for osteoblast number (Fig. 2(d)), ALP-positive area (Fig. 2(e)) and Col-I-positive area (Fig. 2(f))

Summary

Introduction

We investigated whether high dietary Ca and exogenous parathyroid hormone 1– 34 fragments (PTH 1 – 34) have synergistic effects on bone formation in adult mice, and explored the related mechanisms. Osteoblast viability and ALP activity were increased in either the high Ca-treated or PTH-treated cultures and, even more dramatically, in the cultures treated with high Ca plus PTH, with consistent up-regulation of the expression levels of osteoblast proliferation and differentiation-related genes and proteins These results indicate that dietary Ca and PTH play synergistic roles in promoting osteoblastic bone formation by stimulating osteoblast proliferation and differentiation. Studies have found that high concentrations of Ca ions can cause osteoclast apoptosis[7] as well as function as a chemical chemokine to promote osteoblast precursors to move to bone absorption sites, and stimulate osteoblast proliferation and differentiation to produce new bone[8,9]. Recent research has shown that PTH and Ca can each exert cooperative effects on osteoblastic bone formation in the neonate[15]

Methods

Results

Conclusion