title: Bone Marrow Stress Decreases Osteogenic Progenitors.
abstract: 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.
authors.affiliation: Department of Laboratory Medicine & Pathobiology, University of Toronto, Toronto, ON, Canada.|Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 25 Orde Street, Suite 417, Toronto, ON, M5T 3H7, Canada.
authors.forename: Adeline H
authors.initials: AH
authors.lastname: Ng
authors.affiliation: Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, ON, Canada.
authors.forename: Gurpreet S
authors.initials: GS
authors.lastname: Baht
authors.affiliation: Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, ON, Canada.|Department of Orthopaedic Surgery, Duke University, Durham, NC, USA.
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Alman
authors.affiliation: Department of Laboratory Medicine & Pathobiology, University of Toronto, Toronto, ON, Canada. grynpas@mshri.on.ca.|Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 25 Orde Street, Suite 417, Toronto, ON, M5T 3H7, Canada. grynpas@mshri.on.ca.|, 60 Murray Street, Box 42, Toronto, ON, M5T 3L9, Canada. grynpas@mshri.on.ca.
authors.forename: Marc D
authors.initials: MD
authors.lastname: Grynpas
mesh_terms: D000375:Aging; D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001842:Bone and Bones / Q000000981:diagnostic imaging; D004195:Disease Models, Animal; D059630:Mesenchymal Stem Cells / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology; D010012:Osteogenesis / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D013234:Stem Cells / Q000378:metabolism* / Q000473:pathology; D013312:Stress, Physiological; D055114:X-Ray Microtomography
keywords: Aging; Bone quality; Mouse model; Osteoblast; Osteogenic progenitors