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Sirt1 is involved in decreased bone formation in aged apolipoprotein E-deficient mice.

Hong W, Xu XY, Qiu ZH, Gao JJ, Wei ZY, Zhen L, Zhang XL, Ye ZB - Acta Pharmacol. Sin. (2015)

Bottom Line: In contrast, aged apoE(-/-) mice showed reduced bone formation and lower bone mass relative to age-matched WT mice, accompanied by lower serum OCN levels, and markedly reduced expression levels of Sirt1, Runx2, ALP and OCN in bone tissue.After BMSCs were exposed to ox-LDL (20 μg/mL), the expression of Sirt1 and Runx2 proteins was significantly increased at 12 h, and then decreased at 72 h.Treatment with the Sirt1 inhibitor EX527 (10 μmol/L) suppressed the expression of Runx2, ALP and OCN in BMSCs.

View Article: PubMed Central - PubMed

Affiliation: Department of Geriatrics, Huadong Hospital, Research Center on Aging and Medicine, Fudan University, Shanghai 200040, China.

ABSTRACT

Aim: Apolipoprotein E (ApoE) plays an important role in the transport and metabolism of lipids. Recent studies show that bone mass is increased in young apoE(-/-) mice. In this study we investigated the bone phenotype and metabolism in aged apoE(-/-) mice.

Methods: Femurs and tibias were collected from 18- and 72-week-old apoE(-/-) mice and their age-matched wild-type (WT) littermates, and examined using micro-CT and histological analysis. Serum levels of total cholesterol, oxidized low-density lipoprotein (ox-LDL) and bone turnover markers were measured. Cultured bone mesenchymal stem cells (BMSCs) from tibias and femurs of 18-week-old apoE(-/-) mice were used in experiments in vitro. The expression levels of Sirt1 and Runx2 in bone tissue and BMSCs were measured using RT-PCR and Western blot analysis.

Results: Compared with age-matched WT littermates, young apoE(-/-) mice exhibited high bone mass with increased bone formation, accompanied by higher serum levels of bone turnover markers OCN and TRAP5b, and higher expression levels of Sirt1, Runx2, ALP and OCN in bone tissue. In contrast, aged apoE(-/-) mice showed reduced bone formation and lower bone mass relative to age-matched WT mice, accompanied by lower serum OCN levels, and markedly reduced expression levels of Sirt1, Runx2, ALP and OCN in bone tissue. After BMSCs were exposed to ox-LDL (20 μg/mL), the expression of Sirt1 and Runx2 proteins was significantly increased at 12 h, and then decreased at 72 h. Treatment with the Sirt1 inhibitor EX527 (10 μmol/L) suppressed the expression of Runx2, ALP and OCN in BMSCs.

Conclusion: In contrast to young apoE(-/-) mice, aged apoE(-/-) mice showe lower bone mass than age-matched WT mice. Long-lasting exposure to ox-LDL decreases the expression of Sirt1 and Runx2 in BMSCs, which may explain the decreased bone formation in aged apoE(-/-) mice.

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Changes of histochemistry in tibias of 18- and 72-week-oldapoE−/− mice and their age-matched WTmice. (A and B) The H&E stained sections of trabecular bone intibias. The trabecular bone volumes (BV/TV) were determined byhistomorphometric analysis. Alkaline phosphatase (ALP) staining to quantifythe osteoblast surface/bone surface (OB.S/BS) from 18-week-old (C) and72-week-old (D) mice. The tartrate-resistant acid phosphatase (TRAP)staining of sections of trabecular bone in tibias from 18-week-old (E) and72-week-old (F) mice to quantify the osteoclast surface/bone surface(OC.S/BS). Statistical analysis was performed using a two-way ANOVA followedby a Dunnett's test. Mean±SD, n=5.bP<0.05 vs WT.
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fig2: Changes of histochemistry in tibias of 18- and 72-week-oldapoE−/− mice and their age-matched WTmice. (A and B) The H&E stained sections of trabecular bone intibias. The trabecular bone volumes (BV/TV) were determined byhistomorphometric analysis. Alkaline phosphatase (ALP) staining to quantifythe osteoblast surface/bone surface (OB.S/BS) from 18-week-old (C) and72-week-old (D) mice. The tartrate-resistant acid phosphatase (TRAP)staining of sections of trabecular bone in tibias from 18-week-old (E) and72-week-old (F) mice to quantify the osteoclast surface/bone surface(OC.S/BS). Statistical analysis was performed using a two-way ANOVA followedby a Dunnett's test. Mean±SD, n=5.bP<0.05 vs WT.

Mentions: To determine whether the differences in bone architecture were accompanied bycorresponding changes in markers of bone formation and resorption, weperformed histomorphometric analysis of tibias from 18- and 72-week-old WTand apoE−/− mice for markers associated withbone turnover (Figure 2). In 18-week-old mice,the results showed that the ratio of the ALP-positive osteoblast surfacerelative to the total bone surface (OB.S/BS) was increased (+28.70%,P<0.05) in apoE−/− micecompared with that in WT mice (Figure 2C).Somewhat contradictory to the results in the youngapoE−/− mice, the ALP-positive area(OB.S/BS) decreased significantly in 72-week-oldapoE−/− mice compared with that in WTmice (−40.7%, P<0.05; Figure2D). No changes were observed in the osteoclast surface/bonesurface (OC.S/BS) between the aged apoE−/−mice and WT mice at both young and old ages (Figure2E and 2F). Consistently withresults from previous studies, serum levels of OCN, a marker of boneformation, increased 1.22-fold in apoE−/−mice compared with that in WT mice at 18 weeks of age(P<0.05, Figure 3C). Serumlevels of Trap5b also increased significantly (P<0.05,Figure 3D), whereas in 72-week-old animals,the serum levels of OCN were decreased relative to those of WT mice(−31.57%, P<0.05; Figure3C). However, the serum levels of Trap5b did not changesignificantly in aged apoE−/− mice relativeto that in WT mice (Figure 3D). The serum levelsof TC and ox-LDL were significantly higher in both 18-week- and 72-week-oldapoE−/− mice compared with those inage-matched WT mice (P<0.01, Figure3A and 3B).


Sirt1 is involved in decreased bone formation in aged apolipoprotein E-deficient mice.

Hong W, Xu XY, Qiu ZH, Gao JJ, Wei ZY, Zhen L, Zhang XL, Ye ZB - Acta Pharmacol. Sin. (2015)

Changes of histochemistry in tibias of 18- and 72-week-oldapoE−/− mice and their age-matched WTmice. (A and B) The H&E stained sections of trabecular bone intibias. The trabecular bone volumes (BV/TV) were determined byhistomorphometric analysis. Alkaline phosphatase (ALP) staining to quantifythe osteoblast surface/bone surface (OB.S/BS) from 18-week-old (C) and72-week-old (D) mice. The tartrate-resistant acid phosphatase (TRAP)staining of sections of trabecular bone in tibias from 18-week-old (E) and72-week-old (F) mice to quantify the osteoclast surface/bone surface(OC.S/BS). Statistical analysis was performed using a two-way ANOVA followedby a Dunnett's test. Mean±SD, n=5.bP<0.05 vs WT.
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Related In: Results  -  Collection

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fig2: Changes of histochemistry in tibias of 18- and 72-week-oldapoE−/− mice and their age-matched WTmice. (A and B) The H&E stained sections of trabecular bone intibias. The trabecular bone volumes (BV/TV) were determined byhistomorphometric analysis. Alkaline phosphatase (ALP) staining to quantifythe osteoblast surface/bone surface (OB.S/BS) from 18-week-old (C) and72-week-old (D) mice. The tartrate-resistant acid phosphatase (TRAP)staining of sections of trabecular bone in tibias from 18-week-old (E) and72-week-old (F) mice to quantify the osteoclast surface/bone surface(OC.S/BS). Statistical analysis was performed using a two-way ANOVA followedby a Dunnett's test. Mean±SD, n=5.bP<0.05 vs WT.
Mentions: To determine whether the differences in bone architecture were accompanied bycorresponding changes in markers of bone formation and resorption, weperformed histomorphometric analysis of tibias from 18- and 72-week-old WTand apoE−/− mice for markers associated withbone turnover (Figure 2). In 18-week-old mice,the results showed that the ratio of the ALP-positive osteoblast surfacerelative to the total bone surface (OB.S/BS) was increased (+28.70%,P<0.05) in apoE−/− micecompared with that in WT mice (Figure 2C).Somewhat contradictory to the results in the youngapoE−/− mice, the ALP-positive area(OB.S/BS) decreased significantly in 72-week-oldapoE−/− mice compared with that in WTmice (−40.7%, P<0.05; Figure2D). No changes were observed in the osteoclast surface/bonesurface (OC.S/BS) between the aged apoE−/−mice and WT mice at both young and old ages (Figure2E and 2F). Consistently withresults from previous studies, serum levels of OCN, a marker of boneformation, increased 1.22-fold in apoE−/−mice compared with that in WT mice at 18 weeks of age(P<0.05, Figure 3C). Serumlevels of Trap5b also increased significantly (P<0.05,Figure 3D), whereas in 72-week-old animals,the serum levels of OCN were decreased relative to those of WT mice(−31.57%, P<0.05; Figure3C). However, the serum levels of Trap5b did not changesignificantly in aged apoE−/− mice relativeto that in WT mice (Figure 3D). The serum levelsof TC and ox-LDL were significantly higher in both 18-week- and 72-week-oldapoE−/− mice compared with those inage-matched WT mice (P<0.01, Figure3A and 3B).

Bottom Line: In contrast, aged apoE(-/-) mice showed reduced bone formation and lower bone mass relative to age-matched WT mice, accompanied by lower serum OCN levels, and markedly reduced expression levels of Sirt1, Runx2, ALP and OCN in bone tissue.After BMSCs were exposed to ox-LDL (20 μg/mL), the expression of Sirt1 and Runx2 proteins was significantly increased at 12 h, and then decreased at 72 h.Treatment with the Sirt1 inhibitor EX527 (10 μmol/L) suppressed the expression of Runx2, ALP and OCN in BMSCs.

View Article: PubMed Central - PubMed

Affiliation: Department of Geriatrics, Huadong Hospital, Research Center on Aging and Medicine, Fudan University, Shanghai 200040, China.

ABSTRACT

Aim: Apolipoprotein E (ApoE) plays an important role in the transport and metabolism of lipids. Recent studies show that bone mass is increased in young apoE(-/-) mice. In this study we investigated the bone phenotype and metabolism in aged apoE(-/-) mice.

Methods: Femurs and tibias were collected from 18- and 72-week-old apoE(-/-) mice and their age-matched wild-type (WT) littermates, and examined using micro-CT and histological analysis. Serum levels of total cholesterol, oxidized low-density lipoprotein (ox-LDL) and bone turnover markers were measured. Cultured bone mesenchymal stem cells (BMSCs) from tibias and femurs of 18-week-old apoE(-/-) mice were used in experiments in vitro. The expression levels of Sirt1 and Runx2 in bone tissue and BMSCs were measured using RT-PCR and Western blot analysis.

Results: Compared with age-matched WT littermates, young apoE(-/-) mice exhibited high bone mass with increased bone formation, accompanied by higher serum levels of bone turnover markers OCN and TRAP5b, and higher expression levels of Sirt1, Runx2, ALP and OCN in bone tissue. In contrast, aged apoE(-/-) mice showed reduced bone formation and lower bone mass relative to age-matched WT mice, accompanied by lower serum OCN levels, and markedly reduced expression levels of Sirt1, Runx2, ALP and OCN in bone tissue. After BMSCs were exposed to ox-LDL (20 μg/mL), the expression of Sirt1 and Runx2 proteins was significantly increased at 12 h, and then decreased at 72 h. Treatment with the Sirt1 inhibitor EX527 (10 μmol/L) suppressed the expression of Runx2, ALP and OCN in BMSCs.

Conclusion: In contrast to young apoE(-/-) mice, aged apoE(-/-) mice showe lower bone mass than age-matched WT mice. Long-lasting exposure to ox-LDL decreases the expression of Sirt1 and Runx2 in BMSCs, which may explain the decreased bone formation in aged apoE(-/-) mice.

Show MeSH
Related in: MedlinePlus