Highlights
- •Sirt1 overexpression in MSCs promotes osteoblastic bone formation.
- •Sirt1 overexpression in MSCs reduces the acetylation level of FOXO3a.
- •Sirt1 overexpression in MSCs prevents bone loss in Bmi-1 deficient mice.
- •Sirt1 overexpression in MSCs restores the redox balance in Bmi-1 deficient mice.
- •NAM blocks the effect of overexpression of Sirt1 on osteogenesis and cell senescence.
Abstract
Objective
B cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1) deficiency
(Bmi-1−/−) leads to an osteoporotic phenotype with a significant downregulation of Sirt1 protein
expression. Sirtuin 1 (Sirt1) haploinsufficiency results in a bone loss by decreased
bone formation; however, it is unclear whether Sirt1 overexpression in mesenchymal
stem cells (MSCs) plays an anti-osteoporotic role. The aim of the study is to identify
whether the overexpression of Sirt1 in MSCs could restore skeletal growth retardation
and osteoporosis in Bmi-1 deficient mice.
Methods
We used our new generated transgenic mouse model that overexpresses Sirt1 in its MSCs
(Sirt1TG) to cross with Bmi-1−/− mice to generate Bmi-1−/− mice with Sirt1 overexpression in MSCs, and compared their skeletal metabolism with
those of their Bmi-1−/− and wild-type (WT) littermates (6 mice for each genotype) at 4 weeks of age using
imaging, histopathological, immunohistochemical, histomorphometric, cellular, and
molecular methods.
Results
The levels of expression for Sirt1 were noticeably higher in the skeletal tissue of
Sirt1TG mice than in those of WT mice. In Comparison to WT mice, the body weight and size,
skeletal size, bone volume, osteoblast number, alkaline phosphatase and type I collagen
positive areas, osteogenic related gene expression levels were all significantly increased
in the Sirt1TG mice. Overexpression of Sirt1 in Bmi-1−/− mouse MSCs resulted in a longer lifespan, improved skeletal growth and significantly
increased bone mass by stimulating osteoblastic bone formation and inhibiting osteoclastic
bone resorption in the Bmi-1−/− mice, although the defects were not completely restored. Furthermore, Sirt1 overexpression
in MSCs reduced the acetylation level of FOXO3a (Forkhead box O3a), increasing levels
of expression for FOXO3a and SOD2 (Superoxide dismutase 2) in bony tissue, enhanced
osteogenesis and reduced osteogenic cell senescence. We also demonstrated that nicotinamide,
a Sirt1 inhibitor, blocks the effect of overexpression of Sirt1 in MSCs on osteogenesis
and osteogenic cell senescence.
Conclusions
Taken together, these results demonstrate that Sirt1 overexpression in MSCs increased
the osteoblastic bone formation and partially restores the defects in skeletal growth
and osteogenesis in Bmi-1−/− mice by FOXO3a deacetylation and oxidative stress inhibition. Our data support the
proposal that Sirt1 is a target for promoting bone formation as an anabolic approach
for the treatment of osteoporosis.
Abbreviations:
ALP (alkaline phosphatase), Bmi-1 (B cell-specific Moloney murine leukemia virus integration site 1), Bmi-1−/− (Bmi1 deficiency), Bmi-1+/− (Bmi-1 heterozygous), Col-I (type I collagen), Col-II (type II collagen), FOXO (Forkhead box O), GPX1 (Glutathione peroxidase 1), GSR (Glutathione reductase), H&E (hematoxylin and eosin), IP (immunoprecipitation), LPR (Low-density lipoprotein receptor-related protein), Micro-CT (micro-computed tomography), MSC (mesenchymal stem cell), NAM (nicotinamide), OCN (Osteocalcin), OPG (Osteoprotegerin), Prx1 (Paired Related Homeobox 1), RANKL (Receptor Activator for Nuclear Factor-κ B Ligand), ROS (Reactive Oxygen Species), Runx2 (Runt-related transcription factor 2), SA-β-Gal (Senescence associated β-Galactosidase), Sirt1 (Sirtuin 1), Sirt1TG (a transgenic mouse model overexpressing Sirt1 in MSCs driven by the Prx1 promoter), SOD1 (Superoxide dismutase 1), SOD2 (Superoxide dismutase 2), TRAP (tartrate-resistant acid phosphatase), TXN (Thioredoxin), WT (wild-type)Keywords
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Article info
Publication history
Published online: July 03, 2018
Accepted:
June 17,
2018
Received:
February 9,
2018
Footnotes
☆Disclosure: The authors have declared that no conflict of interest exists.
Identification
Copyright
© 2018 Published by Elsevier Inc.
