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Chondrocytes-Specific Expression of Osteoprotegerin Modulates Osteoclast Formation in Metaphyseal Bone.

Wang B, Jin H, Shu B, Mira RR, Chen D - Sci Rep (2015)

Bottom Line: TRAP staining showed that osteoclast numbers were reduced in both secondary ossification center and proximal metaphysis.In contrast, the mineral apposition rates were not changed in Col2-Opg transgenic mice.Our results demonstrated that OPG expression in chondrocyte increases bone mass in the proximal metaphysis of tibiae through negative regulation of osteoclast formation.

View Article: PubMed Central - PubMed

Affiliation: Key Lab of Hormone and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin 300070, China.

ABSTRACT
Bone marrow stromal cells/osteoblasts were originally thought to be the major player in regulating osteoclast differentiation through expressing RANKL/OPG cytokines. Recent studies have established that chondrocytes also express RANKL/OPG and support osteoclast formation. Till now, the in vivo function of chondrocyte-produced OPG in osteoclast formation and postnatal bone growth has not been directly investigated. In this study, chondrocyte-specific Opg transgenic mice were generated by using type II collagen promoter. The Col2-Opg transgenic mice showed delayed formation of secondary ossification center and localized increase of bone mass in proximal metaphysis of tibiae. TRAP staining showed that osteoclast numbers were reduced in both secondary ossification center and proximal metaphysis. This finding was further confirmed by in vitro chondrocyte/spleen cell co-culture assay. In contrast, the mineral apposition rates were not changed in Col2-Opg transgenic mice. TUNEL staining revealed more apoptotic hypertrophic chondrocytes in the growth plate of Col2-Opg mice. Flow cytometry analysis showed fewer RANK-expressing cells in the marrow of Col2a1-Opg mice, suggesting the role of OPG in blocking the differentiation of early mesenchymal progenitors into RANK-expressing pre-osteoclasts. Our results demonstrated that OPG expression in chondrocyte increases bone mass in the proximal metaphysis of tibiae through negative regulation of osteoclast formation.

No MeSH data available.


Related in: MedlinePlus

Osteoblast and adipocyte differentiation was slightly altered in Col2-Opg mice.(A,B) ALP and Alizarin red O staining was performed using BMSCs from WT and Col2-Opg mice. (C) Real-time PCR was performed to examine expression of osteoblast marker genes. (D) Oil red O staining was performed to determine adipocyte differentiation from BMSCs derived from WT and Col2-Opg mice (green arrows: Oil red O staining-positive cells). (E) Real-time PCR was performed to examine expression of adipocyte marker genes. Data are presented as means ± SD (n = 4 per group).
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f7: Osteoblast and adipocyte differentiation was slightly altered in Col2-Opg mice.(A,B) ALP and Alizarin red O staining was performed using BMSCs from WT and Col2-Opg mice. (C) Real-time PCR was performed to examine expression of osteoblast marker genes. (D) Oil red O staining was performed to determine adipocyte differentiation from BMSCs derived from WT and Col2-Opg mice (green arrows: Oil red O staining-positive cells). (E) Real-time PCR was performed to examine expression of adipocyte marker genes. Data are presented as means ± SD (n = 4 per group).

Mentions: We then examined osteoblast differentiation in BMSCs of Col2-Opg mice. ALP and Alizarin red staining showed similar osteoblast differentiation tendency in Col2-Opg mice compared to WT controls (Fig. 7A,B). Interestingly, results of real-time PCR assay revealed that the mRNA expression of Runx2 was not changed, while expression levels of Col1a1, Alp, OC and Bsp were slightly reduced (p < 0.05) when BMSCs of Col2-Opg mice were cultured with osteoblast differentiation medium (Fig. 7C). These results likely reflect the coupling between osteoclast-mediated resorption and osteoblast-mediated bone formation.


Chondrocytes-Specific Expression of Osteoprotegerin Modulates Osteoclast Formation in Metaphyseal Bone.

Wang B, Jin H, Shu B, Mira RR, Chen D - Sci Rep (2015)

Osteoblast and adipocyte differentiation was slightly altered in Col2-Opg mice.(A,B) ALP and Alizarin red O staining was performed using BMSCs from WT and Col2-Opg mice. (C) Real-time PCR was performed to examine expression of osteoblast marker genes. (D) Oil red O staining was performed to determine adipocyte differentiation from BMSCs derived from WT and Col2-Opg mice (green arrows: Oil red O staining-positive cells). (E) Real-time PCR was performed to examine expression of adipocyte marker genes. Data are presented as means ± SD (n = 4 per group).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4556963&req=5

f7: Osteoblast and adipocyte differentiation was slightly altered in Col2-Opg mice.(A,B) ALP and Alizarin red O staining was performed using BMSCs from WT and Col2-Opg mice. (C) Real-time PCR was performed to examine expression of osteoblast marker genes. (D) Oil red O staining was performed to determine adipocyte differentiation from BMSCs derived from WT and Col2-Opg mice (green arrows: Oil red O staining-positive cells). (E) Real-time PCR was performed to examine expression of adipocyte marker genes. Data are presented as means ± SD (n = 4 per group).
Mentions: We then examined osteoblast differentiation in BMSCs of Col2-Opg mice. ALP and Alizarin red staining showed similar osteoblast differentiation tendency in Col2-Opg mice compared to WT controls (Fig. 7A,B). Interestingly, results of real-time PCR assay revealed that the mRNA expression of Runx2 was not changed, while expression levels of Col1a1, Alp, OC and Bsp were slightly reduced (p < 0.05) when BMSCs of Col2-Opg mice were cultured with osteoblast differentiation medium (Fig. 7C). These results likely reflect the coupling between osteoclast-mediated resorption and osteoblast-mediated bone formation.

Bottom Line: TRAP staining showed that osteoclast numbers were reduced in both secondary ossification center and proximal metaphysis.In contrast, the mineral apposition rates were not changed in Col2-Opg transgenic mice.Our results demonstrated that OPG expression in chondrocyte increases bone mass in the proximal metaphysis of tibiae through negative regulation of osteoclast formation.

View Article: PubMed Central - PubMed

Affiliation: Key Lab of Hormone and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin 300070, China.

ABSTRACT
Bone marrow stromal cells/osteoblasts were originally thought to be the major player in regulating osteoclast differentiation through expressing RANKL/OPG cytokines. Recent studies have established that chondrocytes also express RANKL/OPG and support osteoclast formation. Till now, the in vivo function of chondrocyte-produced OPG in osteoclast formation and postnatal bone growth has not been directly investigated. In this study, chondrocyte-specific Opg transgenic mice were generated by using type II collagen promoter. The Col2-Opg transgenic mice showed delayed formation of secondary ossification center and localized increase of bone mass in proximal metaphysis of tibiae. TRAP staining showed that osteoclast numbers were reduced in both secondary ossification center and proximal metaphysis. This finding was further confirmed by in vitro chondrocyte/spleen cell co-culture assay. In contrast, the mineral apposition rates were not changed in Col2-Opg transgenic mice. TUNEL staining revealed more apoptotic hypertrophic chondrocytes in the growth plate of Col2-Opg mice. Flow cytometry analysis showed fewer RANK-expressing cells in the marrow of Col2a1-Opg mice, suggesting the role of OPG in blocking the differentiation of early mesenchymal progenitors into RANK-expressing pre-osteoclasts. Our results demonstrated that OPG expression in chondrocyte increases bone mass in the proximal metaphysis of tibiae through negative regulation of osteoclast formation.

No MeSH data available.


Related in: MedlinePlus