title: Identification of Senescent Cells in the Bone Microenvironment.
abstract: Cellular senescence is a fundamental mechanism by which cells remain metabolically active yet cease dividing and undergo distinct phenotypic alterations, including upregulation of p16Ink4a, profound secretome changes, telomere shortening, and decondensation of pericentromeric satellite DNA. Because senescent cells accumulate in multiple tissues with aging, these cells and the dysfunctional factors they secrete, termed the senescence-associated secretory phenotype (SASP), are increasingly recognized as promising therapeutic targets to prevent age-related degenerative pathologies, including osteoporosis. However, the cell type(s) within the bone microenvironment that undergoes senescence with aging in vivo has remained poorly understood, largely because previous studies have focused on senescence in cultured cells. Thus in young (age 6 months) and old (age 24 months) mice, we measured senescence and SASP markers in vivo in highly enriched cell populations, all rapidly isolated from bone/marrow without in vitro culture. In both females and males, p16Ink4aexpression by real-time quantitative polymerase chain reaction (rt-qPCR) was significantly higher with aging in B cells, T cells, myeloid cells, osteoblast progenitors, osteoblasts, and osteocytes. Further, in vivo quantification of senescence-associated distension of satellites (SADS), ie, large-scale unraveling of pericentromeric satellite DNA, revealed significantly more senescent osteocytes in old compared with young bone cortices (11% versus 2%, p < 0.001). In addition, primary osteocytes from old mice had sixfold more (p < 0.001) telomere dysfunction-induced foci (TIFs) than osteocytes from young mice. Corresponding with the age-associated accumulation of senescent osteocytes was significantly higher expression of multiple SASP markers in osteocytes from old versus young mice, several of which also showed dramatic age-associated upregulation in myeloid cells. These data show that with aging, a subset of cells of various lineages within the bone microenvironment become senescent, although senescent myeloid cells and senescent osteocytes predominantly develop the SASP. Given the critical roles of osteocytes in orchestrating bone remodeling, our findings suggest that senescent osteocytes and their SASP may contribute to age-related bone loss. © 2016 American Society for Bone and Mineral Research.
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Joshua N
authors.initials: JN
authors.lastname: Farr
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Fraser
authors.affiliation: Departments of Orthopaedic Surgery and Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Haitao
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Oral Biology, University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, USA.
authors.forename: Katharina
authors.initials: K
authors.lastname: Jaehn
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Mikolaj B
authors.initials: MB
authors.lastname: Ogrodnik
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Megan M
authors.initials: MM
authors.lastname: Weivoda
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Drake
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Tamara
authors.initials: T
authors.lastname: Tchkonia
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Nathan K
authors.initials: NK
authors.lastname: LeBrasseur
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: James L
authors.initials: JL
authors.lastname: Kirkland
authors.affiliation: Department of Oral Biology, University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, USA.
authors.forename: Lynda F
authors.initials: LF
authors.lastname: Bonewald
authors.affiliation: Departments of Orthopaedic Surgery and Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Pignolo
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Monroe
authors.affiliation: Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA.
authors.forename: Sundeep
authors.initials: S
authors.lastname: Khosla
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001842:Bone and Bones / Q000166:cytology*; D019070:Cell Lineage; D002478:Cells, Cultured; D060833:Cellular Microenvironment; D016922:Cellular Senescence; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D004276:DNA, Satellite / Q000378:metabolism; D005260:Female; D008297:Male; D008810:Mice, Inbred C57BL; D022423:Myeloid Cells / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D010011:Osteocytes / Q000378:metabolism; D010641:Phenotype
chemical_list: D015415:Biomarkers; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004276:DNA, Satellite
keywords: AGING; ANIMAL MODELS; CELL/TISSUE SIGNALING; OSTEOCYTES