Limits...
Mediator MED23 cooperates with RUNX2 to drive osteoblast differentiation and bone development.

Liu Z, Yao X, Yan G, Xu Y, Yan J, Zou W, Wang G - Nat Commun (2016)

Bottom Line: In vitro, Med23-deficient progenitor cells are refractory to osteoblast differentiation, and Med23 deficiency reduces Runx2-target gene activity without changing Runx2 expression.Mechanistically, MED23 binds to RUNX2 and modulates its transcriptional activity.Collectively, our results establish a genetic and physical interaction between RUNX2 and MED23, suggesting that MED23 constitutes a molecular node in the regulatory network of anabolic bone formation and related diseases.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China.

ABSTRACT
How lineage specifiers are regulated during development is an outstanding question, and the molecular regulation of osteogenic factor RUNX2 remains to be fully understood. Here we report that the Mediator subunit MED23 cooperates with RUNX2 to regulate osteoblast differentiation and bone development. Med23 deletion in mesenchymal stem cells or osteoblast precursors results in multiple bone defects similar to those observed in Runx2(+/-) mice. In vitro, Med23-deficient progenitor cells are refractory to osteoblast differentiation, and Med23 deficiency reduces Runx2-target gene activity without changing Runx2 expression. Mechanistically, MED23 binds to RUNX2 and modulates its transcriptional activity. Moreover, Med23 deficiency in osteoprogenitor cells exacerbates the skeletal abnormalities observed in Runx2(+/-) mice. Collectively, our results establish a genetic and physical interaction between RUNX2 and MED23, suggesting that MED23 constitutes a molecular node in the regulatory network of anabolic bone formation and related diseases.

Show MeSH

Related in: MedlinePlus

Inactivation of Med23 in osteoblast progenitors results in defects in bone formation.(a) Illustration of Med23 deletion in Osx-expressing osteoblast progenitors. (b) Representative view of 1-month-old control (Med23ob+/−) and Med23ob−/− mice. (c) Body weight of male control mice and Med23ob−/− littermates measured at different age points (n=3). Data represent means±s.d. t-test, *P<0.05, **P<0.01, ***P<0.001. (d) Skeletal preparations from control and Med23ob−/− newborns were double stained with Alizarin red and Alcian blue. (e) μCT image of skulls from control and Med23ob−/− mice at postnatal day 6 (P6). (f) μCT images of distal femurs from 1-month-old control and Med23ob−/− mice. Scale bar, 1 mm. (g) Quantitative μCT analysis of trabecular bone in the distal femurs from 1-month-old control and Med23ob−/− mice (n=3). Data represent means±s.e.m. t-test, *P<0.05. (h) ELISA analysis of serum PINP (ng ml−1) from 1-month-old control and Med23ob−/− mice (n=4). Data represent means±s.d. t-test, *P<0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4821994&req=5

f2: Inactivation of Med23 in osteoblast progenitors results in defects in bone formation.(a) Illustration of Med23 deletion in Osx-expressing osteoblast progenitors. (b) Representative view of 1-month-old control (Med23ob+/−) and Med23ob−/− mice. (c) Body weight of male control mice and Med23ob−/− littermates measured at different age points (n=3). Data represent means±s.d. t-test, *P<0.05, **P<0.01, ***P<0.001. (d) Skeletal preparations from control and Med23ob−/− newborns were double stained with Alizarin red and Alcian blue. (e) μCT image of skulls from control and Med23ob−/− mice at postnatal day 6 (P6). (f) μCT images of distal femurs from 1-month-old control and Med23ob−/− mice. Scale bar, 1 mm. (g) Quantitative μCT analysis of trabecular bone in the distal femurs from 1-month-old control and Med23ob−/− mice (n=3). Data represent means±s.e.m. t-test, *P<0.05. (h) ELISA analysis of serum PINP (ng ml−1) from 1-month-old control and Med23ob−/− mice (n=4). Data represent means±s.d. t-test, *P<0.05.

Mentions: To further determine whether the abnormal osteogenesis in Med23MSC−/− mice results from a primary defect in osteoblast development, we generated an osteoblast-specific Med23-deleted mouse model (Med23ob−/− mice) by crossing Med23fl/fl mice with osterix (Osx)-Cre mice, a line in which Cre expression is primarily restricted to osteoblast precursors21 (Fig. 2a). Western blot assays showed that MED23 decreased in the bone of both Med23ob+/− and Med23ob−/− mice (Supplementary Fig. 3b). Consistent with decline in protein of MED23, histological analysis by alcian blue and alizarin red (ARS) staining showed defects in the skeleton occurring in both Med23ob+/− and Med23ob−/− newborns, and more severe in the latter, including abnormality in calvarial and clavicle ossification (Supplementary Fig. 3a). However, Osx-Cre transgenic mice have been found to manifest defects in bone phenotype, such as to delay bone mineralization and develop scapula calluses2223. To exclude such effect of Osx-Cre, we made a comparison between Med23ob−/− mice and Med23ob+/− control littermates that were both in the context of Osx-Cre. Again, Med23ob−/−mice developed runty and underweight compared with age-matched control littermates (Fig. 2b,c). Mice with Med23 deficiency in osteoblast reproduced the phenotype of Med23MSC−/− mice, including impaired membranous ossification of calvarial bones and dysplasia of the clavicles, although the sternum appeared normal. In the Med23ob−/− mice, the bone was obviously porous; this feature was more evident in the bones of the skull (Fig. 2d,e). μCT analysis further confirmed the osteopenic phenotype of Med23ob−/− mice (Fig. 2f,g). Likewise, relatively lower levels of serum PINP indicated a decreased bone formation rate in Med23ob−/− mice (Fig. 2h). Again, in vivo and in vitro osteoclastogenesis showed comparable levels of osteoclasts between Med23ob−/− mice and control littermates (Supplementary Fig. 4a–c). Hence, the Med23ob−/− mice recapitulate the defects observed in Med23MSC−/− mice with striking fidelity, supporting the conclusion that Med23 is necessary to the differentiation and function of committed osteoblast precursors.


Mediator MED23 cooperates with RUNX2 to drive osteoblast differentiation and bone development.

Liu Z, Yao X, Yan G, Xu Y, Yan J, Zou W, Wang G - Nat Commun (2016)

Inactivation of Med23 in osteoblast progenitors results in defects in bone formation.(a) Illustration of Med23 deletion in Osx-expressing osteoblast progenitors. (b) Representative view of 1-month-old control (Med23ob+/−) and Med23ob−/− mice. (c) Body weight of male control mice and Med23ob−/− littermates measured at different age points (n=3). Data represent means±s.d. t-test, *P<0.05, **P<0.01, ***P<0.001. (d) Skeletal preparations from control and Med23ob−/− newborns were double stained with Alizarin red and Alcian blue. (e) μCT image of skulls from control and Med23ob−/− mice at postnatal day 6 (P6). (f) μCT images of distal femurs from 1-month-old control and Med23ob−/− mice. Scale bar, 1 mm. (g) Quantitative μCT analysis of trabecular bone in the distal femurs from 1-month-old control and Med23ob−/− mice (n=3). Data represent means±s.e.m. t-test, *P<0.05. (h) ELISA analysis of serum PINP (ng ml−1) from 1-month-old control and Med23ob−/− mice (n=4). Data represent means±s.d. t-test, *P<0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4821994&req=5

f2: Inactivation of Med23 in osteoblast progenitors results in defects in bone formation.(a) Illustration of Med23 deletion in Osx-expressing osteoblast progenitors. (b) Representative view of 1-month-old control (Med23ob+/−) and Med23ob−/− mice. (c) Body weight of male control mice and Med23ob−/− littermates measured at different age points (n=3). Data represent means±s.d. t-test, *P<0.05, **P<0.01, ***P<0.001. (d) Skeletal preparations from control and Med23ob−/− newborns were double stained with Alizarin red and Alcian blue. (e) μCT image of skulls from control and Med23ob−/− mice at postnatal day 6 (P6). (f) μCT images of distal femurs from 1-month-old control and Med23ob−/− mice. Scale bar, 1 mm. (g) Quantitative μCT analysis of trabecular bone in the distal femurs from 1-month-old control and Med23ob−/− mice (n=3). Data represent means±s.e.m. t-test, *P<0.05. (h) ELISA analysis of serum PINP (ng ml−1) from 1-month-old control and Med23ob−/− mice (n=4). Data represent means±s.d. t-test, *P<0.05.
Mentions: To further determine whether the abnormal osteogenesis in Med23MSC−/− mice results from a primary defect in osteoblast development, we generated an osteoblast-specific Med23-deleted mouse model (Med23ob−/− mice) by crossing Med23fl/fl mice with osterix (Osx)-Cre mice, a line in which Cre expression is primarily restricted to osteoblast precursors21 (Fig. 2a). Western blot assays showed that MED23 decreased in the bone of both Med23ob+/− and Med23ob−/− mice (Supplementary Fig. 3b). Consistent with decline in protein of MED23, histological analysis by alcian blue and alizarin red (ARS) staining showed defects in the skeleton occurring in both Med23ob+/− and Med23ob−/− newborns, and more severe in the latter, including abnormality in calvarial and clavicle ossification (Supplementary Fig. 3a). However, Osx-Cre transgenic mice have been found to manifest defects in bone phenotype, such as to delay bone mineralization and develop scapula calluses2223. To exclude such effect of Osx-Cre, we made a comparison between Med23ob−/− mice and Med23ob+/− control littermates that were both in the context of Osx-Cre. Again, Med23ob−/−mice developed runty and underweight compared with age-matched control littermates (Fig. 2b,c). Mice with Med23 deficiency in osteoblast reproduced the phenotype of Med23MSC−/− mice, including impaired membranous ossification of calvarial bones and dysplasia of the clavicles, although the sternum appeared normal. In the Med23ob−/− mice, the bone was obviously porous; this feature was more evident in the bones of the skull (Fig. 2d,e). μCT analysis further confirmed the osteopenic phenotype of Med23ob−/− mice (Fig. 2f,g). Likewise, relatively lower levels of serum PINP indicated a decreased bone formation rate in Med23ob−/− mice (Fig. 2h). Again, in vivo and in vitro osteoclastogenesis showed comparable levels of osteoclasts between Med23ob−/− mice and control littermates (Supplementary Fig. 4a–c). Hence, the Med23ob−/− mice recapitulate the defects observed in Med23MSC−/− mice with striking fidelity, supporting the conclusion that Med23 is necessary to the differentiation and function of committed osteoblast precursors.

Bottom Line: In vitro, Med23-deficient progenitor cells are refractory to osteoblast differentiation, and Med23 deficiency reduces Runx2-target gene activity without changing Runx2 expression.Mechanistically, MED23 binds to RUNX2 and modulates its transcriptional activity.Collectively, our results establish a genetic and physical interaction between RUNX2 and MED23, suggesting that MED23 constitutes a molecular node in the regulatory network of anabolic bone formation and related diseases.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China.

ABSTRACT
How lineage specifiers are regulated during development is an outstanding question, and the molecular regulation of osteogenic factor RUNX2 remains to be fully understood. Here we report that the Mediator subunit MED23 cooperates with RUNX2 to regulate osteoblast differentiation and bone development. Med23 deletion in mesenchymal stem cells or osteoblast precursors results in multiple bone defects similar to those observed in Runx2(+/-) mice. In vitro, Med23-deficient progenitor cells are refractory to osteoblast differentiation, and Med23 deficiency reduces Runx2-target gene activity without changing Runx2 expression. Mechanistically, MED23 binds to RUNX2 and modulates its transcriptional activity. Moreover, Med23 deficiency in osteoprogenitor cells exacerbates the skeletal abnormalities observed in Runx2(+/-) mice. Collectively, our results establish a genetic and physical interaction between RUNX2 and MED23, suggesting that MED23 constitutes a molecular node in the regulatory network of anabolic bone formation and related diseases.

Show MeSH
Related in: MedlinePlus