Bone Marrow Stress Decreases Osteogenic Progenitors
- 326 Downloads
Age-related bone loss may be a result of declining levels of stem cells in the bone marrow. Using the Col2.3Δtk (DTK) transgenic mouse, osteoblast depletion was used as a source of marrow stress in order to investigate the effects of aging on osteogenic progenitors which reside in the marrow space. Five-month-old DTK mice were treated with one or two cycles of ganciclovir to conditionally ablate differentiated osteoblasts, whereas controls were saline-treated. Treatment cycles were two weeks in length followed by four weeks of recovery. All animals were sacrificed at 8 months of age; bone marrow stromal cells (BMSCs) were harvested for cell culture and whole bones were excised for bone quality assessment. Colony-forming unit (CFU) assays were conducted to investigate the osteogenic potential of BMSC in vitro, and RNA was extracted to assess the expression of osteoblastic genes. Bone quality assessments included bone histomorphometry, TRAP staining, microcomputed tomography, and biomechanical testing. Osteoblast depletion decreased CFU-F (fibroblast), CFU-ALP (alkaline phosphatase), and CFU-VK (von Kossa) counts and BMSC osteogenic capacity in cell culture. Ex vivo, there were no differences in bone mineral density of vertebrae or femurs between treatment groups. Histology showed a decrease in bone volume and bone connectivity with repeated osteoblast depletion; however, this was accompanied by an increase in bone formation rate. There were no notable differences in osteoclast parameters or observed bone marrow adiposity. We have developed a model that uses bone marrow stress to mimic age-related decrease in osteogenic progenitors. Our data suggest that the number of healthy BMSCs and their osteogenic potential decline with repeated osteoblast depletion. However, activity of the remaining osteoblasts increases to compensate for this loss in progenitor osteogenic potential.
KeywordsAging Osteogenic progenitors Mouse model Bone quality Osteoblast
This work was supported by a Grant from the Canadian Institutes for Health Research to Marc Grynpas and Benjamin Alman. Adeline Ng was supported by scholarships from the University of Toronto, Lunenfeld-Tanenbaum Research Institute, Ontario Graduate Scholarship fund, and Canadian Institutes for Health Research. The authors wish to thank PuviindranNadesan for his technical assistance.
Compliance with Ethical Standards
Conflict of Interest
Adeline H. Ng, Gurpreet S. Baht, Benjamin A. Alman, and Marc D. Grynpas state that they have no conflicts of interest.
Human and Animal Rights and Informed Consent
All animal work was approved by the Animal Care Committee at the Toronto Center for Phenogenomics.
- 4.Shamsul BS, Aminuddin BS, Ng MH, Ruszymah BH (2004) Age and gender effect on the growth of bone marrow stromal cells in vitro. Med J Malays 59(Suppl B):196–197Google Scholar
- 14.Dempster DW, Compston JE, Drezner MK, Glorieux FH, Kanis JA, Malluche H, Meunier PJ, Ott SM, Recker RR, Parfitt AM (2013) Standardized nomenclature, symbols, and units for bone histomorphometry: a 2012 update of the report of the ASBMR Histomorphometry Nomenclature Committee. J Bone Miner Res 28:2–17PubMedCentralCrossRefPubMedGoogle Scholar
- 36.Almeida M, Han L, Martin-Millan M, Plotkin LI, Stewart SA, Roberson PK, Kousteni S, O’Brien CA, Bellido T, Parfitt AM, Weinstein RS, Jilka RL, Manolagas SC (2007) Skeletal involution by age-associated oxidative stress and its acceleration by loss of sex steroids. J Biol Chem 282:27285–27297PubMedCentralCrossRefPubMedGoogle Scholar
- 37.Almeida M, Ambrogini E, Han L, Manolagas SC, Jilka RL (2009) Increased lipid oxidation causes oxidative stress, increased peroxisome proliferator-activated receptor-gamma expression, and diminished pro-osteogenic Wnt signaling in the skeleton. J Biol Chem 284:27438–27448PubMedCentralCrossRefPubMedGoogle Scholar
- 39.Akune T, Ohba S, Kamekura S, Yamaguchi M, Chung UI, Kubota N, Terauchi Y, Harada Y, Azuma Y, Nakamura K, Kadowaki T, Kawaguchi H (2004) PPARgamma insufficiency enhances osteogenesis through osteoblast formation from bone marrow progenitors. J Clin Investig 113:846–855PubMedCentralCrossRefPubMedGoogle Scholar
- 42.Kajkenova O, Lecka-Czernik B, Gubrij I, Hauser SP, Takahashi K, Parfitt AM, Jilka RL, Manolagas SC, Lipschitz DA (1997) Increased adipogenesis and myelopoiesis in the bone marrow of SAMP6, a murine model of defective osteoblastogenesis and low turnover osteopenia. J Bone Miner Res 12:1772–1779CrossRefPubMedGoogle Scholar
- 43.Kang S, Bennett CN, Gerin I, Rapp LA, Hankenson KD, Macdougald OA (2007) Wnt signaling stimulates osteoblastogenesis of mesenchymal precursors by suppressing CCAAT/enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma. J Biol Chem 282:14515–14524CrossRefPubMedGoogle Scholar
- 44.Okamura M, Kudo H, Wakabayashi K, Tanaka T, Nonaka A, Uchida A, Tsutsumi S, Sakakibara I, Naito M, Osborne TF, Hamakubo T, Ito S, Aburatani H, Yanagisawa M, Kodama T, Sakai J (2009) COUP-TFII acts downstream of Wnt/beta-catenin signal to silence PPARgamma gene expression and repress adipogenesis. Proc Natl Acad Sci USA 106:5819–5824PubMedCentralCrossRefPubMedGoogle Scholar