Bmi1 Overexpression in Mesenchymal Stem Cells Exerts Antiaging and Antiosteoporosis Effects by Inactivating p16/p19 Signaling and Inhibiting Oxidative Stress

Abstract

We previously demonstrated that Bmi1 deficiency leads to osteoporosis phenotype by inhibiting the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs), but it is unclear whether overexpression of Bmi1 in MSCs stimulates skeletal development and rescues Bmi1 deficiency‐induced osteoporosis. To answer this question, we constructed transgenic mice (Bmi1Tg) that overexpressed Bmi1 driven by the Prx1 gene and analyzed their skeletal phenotype differences with that of wild‐type littermates. We then hybridized Bmi1Tg to Bmi1−/− mice to generate Bmi1−/− mice overexpressing Bmi1 in MSCs and compared their skeletal phenotypes with those of Bmi1−/− and wild‐type mice using imaging, histopathological, immunohistochemical, histomorphometric, cellular, and molecular methods. Bmi1Tg mice exhibited enhanced bone growth and osteoblast formation, including the augmentation of bone size, cortical and trabecular volume, number of osteoblasts, alkaline phosphatase (ALP)‐positive and type I collagen‐positive areas, number of total colony forming unit fibroblasts (CFU‐f) and ALP+ CFU‐f, and osteogenic gene expression levels. Consistently, MSC overexpressing Bmi1 in the Bmi1−/− background not only largely reversed Bmi1 systemic deficiency‐induced skeletal growth retardation and osteoporosis, but also partially reversed Bmi1 deficiency‐induced systemic growth retardation and premature aging. To further explore the mechanism of action of MSCs overexpressing Bmi1 in antiosteoporosis and antiaging, we examined changes in oxidative stress and expression levels of p16 and p19. Our results showed that overexpression of Bmi1 in MSCs inhibited oxidative stress and downregulated p16 and p19. Taken together, the results of this study indicate that overexpression of Bmi1 in MSCs exerts antiaging and antiosteoporosis effects by inactivating p16/p19 signaling and inhibiting oxidative stress. stem cells 2019;37:1200–1211

The Polycomb Protein Bmi1 Plays a Crucial Role in the Prevention of 1,25(OH)2D Deficiency-Induced Bone Loss

“…We have previously reported that Bmi1 deficiency‐induced osteoporosis was caused by the impaired proliferation of BM‐MSCs and activation of the p16 Ink4a /p19 Arf signaling pathway . Recently we generated transgenic mice overexpressing Bmi1 in MSCs (driven by the Prx1 gene) and showed that overexpression of Bmi1 in MSCs stimulated osteogenesis of BM‐MSCs, accelerated skeletal growth and increased bone mass . In the current study, we generated Cyp27b1 +/− mice with Bmi1 overexpression in MSCs.…”

“…The Cyp27b1 +/− mice, originally on a BALB/c background, were repeatedly backcrossed with WT mice on a C57BL/6J background for over 12 generations to obtain Cyp27b1 +/− mice on a C57BL/6J background. Bmi1 Tg mice that highly express Bmi1 under the control of a 2.4‐kilobase (kb) Prx1 promoter were generated in Nanjing Medical University (Nanjing, China), and genotyped by PCR as described . Bmi1 Tg mice were maintained on a C57BL/6J genetic background.…”

“…Mouse BM‐MSCs were isolated and cultured as described . Bmi1 −/− mice survive up to 12 weeks; we previously showed that bone mass was significantly decreased in Bmi1 −/− mice compared to WT mice at the age of 6 to 8 weeks . Therefore, we used the 8‐week‐old mice to test the impact of Bmi1 deficiency.…”

“…Bmi1 Tg mice that highly express Bmi1 under the control of a 2.4-kilobase (kb) Prx1 promoter were generated in Nanjing Medical University (Nanjing, China), and genotyped by PCR as described. (24) Bmi1 Tg mice were maintained on a C57BL/6J genetic background. Adult Bmi1 +/− female mice were crossed with Bmi1 +/− male mice (both also maintained on a C57BL/6J genetic background) to obtain Bmi1 −/− male mice.…”

“…(25) Bmi1 −/− mice survive up to 12 weeks (26) ; we previously showed that bone mass was significantly decreased in Bmi1 −/− mice compared to WT mice at the age of 6 to 8 weeks. (24) Therefore, we used the 8-week-old mice to test the impact of Bmi1 deficiency. Primary BM-MSCs from 8-week-old WT and Bmi1 −/− mice were seeded in six-well plates in vitro, treated with 1,25(OH) 2 D 3 at a concentration of 1 × 10 −8 M for 24 hours (27) to induce osteogenic differentiation, and stained for clonal formation and alkaline phosphatase (ALP) at 8 days as described.…”