We investigated the role of insufficiency of the active form of
vitamin D,
1,25-dihydroxyvitamin D [1,25(
OH)2D] in
age-related bone loss. We employed mice with heterozygous deletion of
Cyp27b1, the gene encoding the
enzyme that synthesizes 1,25(
OH)2D, as a model for 1,25(
OH)2D insufficiency and compared the phenotype of lumber vertebrae from 3-, 9- and 18-month-old
Cyp27b1+/- mice and their wild-type littermates. We found that in wild-type mice, bone mineral density, bone volume, and
Cyp27b1 protein expression levels decreased progressively with age, accompanied by declining osteoblastic bone formation and increasing osteoclastic
bone resorption, however these age-related skeletal alterations were more severe in
Cyp27b1+/- mice which had significantly lower serum 1,25(
OH)2D levels. We then assessed the effect of 1,25(
OH)2D haploinsufficiency on oxidative stress and DNA damage, cell senescence and senescence-associated secretory phenotype (SASP) in 9-month-old wild-type and
Cyp27b1+/- mice. Our results demonstrated that, in
Cyp27b1+/- mice compared with their wild-type littermates, the parameters of oxidative stress and DNA damage were significantly increased, whereas the expression levels of
antioxidant enzymes were significantly down-regulated; the percentage of senescent osteocytes and bone marrow mesenchymal stem cells, and the expression levels of SASP molecules and p16, p19 and p53
proteins were all significantly increased in bone tissues. Taken together, the results of this study indicate that 1,25(
OH)2D insufficiency accelerates
age-related bone loss by increasing oxidative stress and DNA damage, inducing bone cell senescence and SASP, and subsequently inhibiting osteoblastic bone formation while stimulating osteoclastic
bone resorption.