SIRT1/FOXO3a axis plays an important role in the prevention of mandibular bone loss induced by 1,25(OH)₂D deficiency

Abstract

It has been reported that 1,25 dihydroxyvitamin D [1,25(OH) 2 D] deficiency leads to the loss of mandibular bone, however the mechanism is unclear. We investigated whether the Sirt1/FOXO3a signaling pathway is involved in this process. Using a 1,25(OH) 2 D deficiency model induced by genetic deletion in mice of 25-hydroxyvitamin D-1α hydroxylase [1α(OH)ase -/- mice]. We first documented a sharp reduction of expression levels of Sirt1 in the 1α(OH)ase -/- mice in vivo . Next, we demonstrated dose-dependent upregulation of Sirt1 by treatment with exogenous 1,25(OH) 2 D 3 in vitro . We then identified a functional VDR binding site in the Sirt1 promoter. By crossing Prx1-Sirt1 transgenic mice with 1α(OH)ase -/- mice we demonstrated that the overexpression of Sirt1 in mesenchymal stem cells (MSCs) greatly improved the 1α(OH)ase -/- mandibular bone loss phenotype by increasing osteoblastic bone formation and reducing osteoclastic bone resorption. In mechanistic studies, we showed, in 1α(OH)ase -/- mice, decreases of Sirt1 and FoxO3a, an increase in oxidative stress as reflected by a reduction of the antioxidant enzymes peroxiredoxin1 (Prdx1), SOD1 and SOD2 expression, and an increase of markers for osteocyte senescence and senescence associated secretory phenotypes (SASP), including β-galactosidase (β-gal), p16, p53 and p21. The targeted overexpression of Sirt1 in the 1α(OH)ase -/- mice restored the expression levels of these molecules. Finally, we demonstrated that a Sirt1 agonist can upregulate FOXO3a activity by increasing deacetylation and nuclear translocation. Overall, results from this study support the concept that targeted increases in Sirt1/FOXO3a signaling levels can greatly improve the bone loss caused by 1,25(OH) 2 D deficiency.

Vitamin D3 Stimulates Proliferation Capacity, Expression of Pluripotency Markers, and Osteogenesis of Human Bone Marrow Mesenchymal Stromal/Stem Cells, Partly through SIRT1 Signaling

“…Moreover, our results also showed that SIRT1 inhibition stimulated BM-MSCs’ cellular senescence, in agreement with previous studies evidencing SIRT1′s contribution to the prevention of MSCs’ senescence [ 42 , 65 , 66 , 67 ]. However, our results did not confirm the findings showing that vitamin-D3-mediated inhibition of senescence involves SIRT1 activation as it does in endothelial cells [ 68 , 69 ] and human-mandible-derived BM-MSCs [ 43 ]. Specifically, even in the presence of EX-527, VD3 led to the significant inhibition of BM-MSC senescence, indicating that VD3 exerted its anti-senescence effects in BM-MSCs via activation of other signaling pathways, which should be clarified in future studies.…”

“…During the past decade, many studies have indicated an important role of SIRT1 signaling in MSC self-renewal, demonstrating its protective effects against DNA damage, reactive oxygen species, and various inflammatory and apoptotic stimuli [ 22 ]. Moreover, SIRT1 has been implicated in the promotion of murine and human BM-MSCs’ proliferation, and its role in bone homeostasis is generally well documented [ 37 , 42 , 43 , 44 ]. It has been also shown that vitamin D3 exerts its effects on MSCs by increasing SIRT1 expression via VDR-mediated transcription [ 43 , 45 ].…”

“…Moreover, SIRT1 has been implicated in the promotion of murine and human BM-MSCs’ proliferation, and its role in bone homeostasis is generally well documented [ 37 , 42 , 43 , 44 ]. It has been also shown that vitamin D3 exerts its effects on MSCs by increasing SIRT1 expression via VDR-mediated transcription [ 43 , 45 ]. Accordingly, our results confirmed the ability of VD3 to stimulate the expression of SIRT1, as well as its downstream target FoxO3, in BM-MSCs.…”

Probing the Scope and Mechanisms of Calcitriol Actions Using Genetically Modified Mouse Models

“…The dental volume, reparative dentin volume, and dentin sialoprotein immunopositive areas were also reduced in 1α(OH)ase −/− mice, ( 37 ) and in the mandibles of 1α(OH)ase −/− mice, the cortical thickness, dental alveolar bone volume, and osteoblast number were also all decreased significantly, with accelerated alveolar bone loss. ( 38 ) The SIRT1/FOXO3a signaling axis appears to play an important role in the prevention of mandibular bone loss by 1,25(OH) 2 D. ( 39 )…”

“…The dental volume, reparative dentin volume, and dentin sialoprotein immunopositive areas were also reduced in 1α(OH)ase −/− mice, (37) and in the mandibles of 1α(OH)ase −/− mice, the cortical thickness, dental alveolar bone volume, and osteoblast number were also all decreased significantly, with accelerated alveolar bone loss. (38) The SIRT1/FOXO3a signaling axis appears to play an important role in the prevention of mandibular bone loss by 1,25(OH) 2 D. (39) Effects on skeletal aging Bone mineral density, bone volume, Cyp27b1 renal protein expression, and circulating 1,25(OH) 2 D all decrease progressively with age in haploinsufficient 1α(OH)ase +/− mice, and Cyp27b1 gene haploinsufficiency accelerated age-related bone loss and an osteoporotic phenotype, accompanied by declining osteoblastic bone formation and increasing osteoclastic bone resorption. (40) The INK4a/ARF locus encodes the INK4 family of cyclindependent kinase inhibitors, including p16 INK4a , and a tumor suppressor p19/p14 ARF .…”