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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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Ox-LDL induced a time-dependent decrease in Sirt1 expression during theosteogenic differentiation of BMSCs fromapoE−/− mice in vitro. BMSCsfrom 18-week-old apoE−/− mice were treatedwith ox-LDL (20 μg/mL). The relative mRNA expression of Sirt1, Runx2,ALP and OCN (A) and protein levels of Sirt1 and Runx2 (Western blotting, B)in BMSCs after exposure to ox-LDL for 0, 12, 24, 48, and 72 h.Mean±SD, n=4. bP<0.05,cP<0.01 vs 0 h.
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fig6: Ox-LDL induced a time-dependent decrease in Sirt1 expression during theosteogenic differentiation of BMSCs fromapoE−/− mice in vitro. BMSCsfrom 18-week-old apoE−/− mice were treatedwith ox-LDL (20 μg/mL). The relative mRNA expression of Sirt1, Runx2,ALP and OCN (A) and protein levels of Sirt1 and Runx2 (Western blotting, B)in BMSCs after exposure to ox-LDL for 0, 12, 24, 48, and 72 h.Mean±SD, n=4. bP<0.05,cP<0.01 vs 0 h.

Mentions: Ox-LDL was much higher in aged apoE−/− micethan in WT mice (Figure 3B); therefore, weexamined whether Sirt1 was involved in the osteogenic differentiation ofBMSCs during long-term exposure of apoE−/−mice to ox-LDL (Figure 6A and 6B). RT-PCR analysis showed that ox-LDL (20 μg/mL)enhanced the expression of Sirt1 mRNA in BMSCs in the first 12 h(3.3-fold; P<0.05). However, after prolonged treatment withox-LDL, the expression of Sirt1 mRNA decreased at 72 h comparedwith that at 0 h (−48%; P<0.05), which indicatedthat the long-term effects of ox-LDL accumulation downregulatedSirt1 expression in the BMSCs ofapoE−/− mice. Similar results wereobserved for Runx2 mRNA and protein levels.


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)

Ox-LDL induced a time-dependent decrease in Sirt1 expression during theosteogenic differentiation of BMSCs fromapoE−/− mice in vitro. BMSCsfrom 18-week-old apoE−/− mice were treatedwith ox-LDL (20 μg/mL). The relative mRNA expression of Sirt1, Runx2,ALP and OCN (A) and protein levels of Sirt1 and Runx2 (Western blotting, B)in BMSCs after exposure to ox-LDL for 0, 12, 24, 48, and 72 h.Mean±SD, n=4. bP<0.05,cP<0.01 vs 0 h.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4816239&req=5

fig6: Ox-LDL induced a time-dependent decrease in Sirt1 expression during theosteogenic differentiation of BMSCs fromapoE−/− mice in vitro. BMSCsfrom 18-week-old apoE−/− mice were treatedwith ox-LDL (20 μg/mL). The relative mRNA expression of Sirt1, Runx2,ALP and OCN (A) and protein levels of Sirt1 and Runx2 (Western blotting, B)in BMSCs after exposure to ox-LDL for 0, 12, 24, 48, and 72 h.Mean±SD, n=4. bP<0.05,cP<0.01 vs 0 h.
Mentions: Ox-LDL was much higher in aged apoE−/− micethan in WT mice (Figure 3B); therefore, weexamined whether Sirt1 was involved in the osteogenic differentiation ofBMSCs during long-term exposure of apoE−/−mice to ox-LDL (Figure 6A and 6B). RT-PCR analysis showed that ox-LDL (20 μg/mL)enhanced the expression of Sirt1 mRNA in BMSCs in the first 12 h(3.3-fold; P<0.05). However, after prolonged treatment withox-LDL, the expression of Sirt1 mRNA decreased at 72 h comparedwith that at 0 h (−48%; P<0.05), which indicatedthat the long-term effects of ox-LDL accumulation downregulatedSirt1 expression in the BMSCs ofapoE−/− mice. Similar results wereobserved for Runx2 mRNA and protein levels.

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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Related in: MedlinePlus