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Abstract
The Wnt/β-catenin signaling pathway plays an essential role in osteoblast biology. Sclerostin is a soluble antagonist of Wnt/β-catenin signaling secreted primarily by osteocytes. Current evidence indicates that sclerostin likely functions as a local/paracrine regulator of bone metabolism rather than as an endocrine hormone. Nonetheless, circulating sclerostin levels in humans often reflect changes in the bone microenvironment, although there may be exceptions to this observation. Using existing assays, circulating sclerostin levels have been shown to be altered in response to both hormonal stimuli and across a variety of normal physiological and pathophysiological conditions. In both rodents and humans, parathyroid hormone provided either intermittently or continuously suppresses sclerostin levels. Likewise, most evidence from both human and animal studies supports a suppressive effect of estrogen on sclerostin levels. Efforts to examine non-hormonal/systemic regulation of sclerostin have in general shown less consistent findings or have provided associations rather than direct interventional information, with the exception of mechanosensory studies which have consistently demonstrated increased sclerostin levels with skeletal unloading, and conversely decreases in sclerostin with enhanced skeletal loading. Herein, we will review the existent literature on both hormonal and non-hormonal/systemic factors which have been studied for their impact on sclerostin regulation.
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Affiliation(s)
- Matthew T Drake
- Department of Endocrinology, Kogod Center on Aging, Mayo Clinic College of Medicine, Rochester, MN, USA.
| | - Sundeep Khosla
- Department of Endocrinology, Kogod Center on Aging, Mayo Clinic College of Medicine, Rochester, MN, USA
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Farr JN, Fraser DG, Wang H, Jaehn K, Ogrodnik MB, Weivoda MM, Drake MT, Tchkonia T, LeBrasseur NK, Kirkland JL, Bonewald LF, Pignolo RJ, Monroe DG, Khosla S. Identification of Senescent Cells in the Bone Microenvironment. J Bone Miner Res 2016; 31:1920-1929. [PMID: 27341653 PMCID: PMC5289710 DOI: 10.1002/jbmr.2892] [Citation(s) in RCA: 316] [Impact Index Per Article: 39.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2016] [Revised: 06/04/2016] [Accepted: 06/20/2016] [Indexed: 12/27/2022]
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, p16Ink4a expression 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.
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Affiliation(s)
- Joshua N Farr
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Daniel G Fraser
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Haitao Wang
- Departments of Orthopaedic Surgery and Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Katharina Jaehn
- Department of Oral Biology, University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, USA
| | - Mikolaj B Ogrodnik
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Megan M Weivoda
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Matthew T Drake
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Tamara Tchkonia
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Nathan K LeBrasseur
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - James L Kirkland
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Lynda F Bonewald
- Department of Oral Biology, University of Missouri-Kansas City, School of Dentistry, Kansas City, MO, USA
| | - Robert J Pignolo
- Departments of Orthopaedic Surgery and Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - David G Monroe
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Sundeep Khosla
- Robert and Arlene Kogod Center on Aging and Endocrine Research Unit, Mayo Clinic College of Medicine, Rochester, MN, USA
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Kim MH, Lee HJ. Osteoporosis, vitamin C intake, and physical activity in Korean adults aged 50 years and over. J Phys Ther Sci 2016; 28:725-30. [PMID: 27134348 PMCID: PMC4842429 DOI: 10.1589/jpts.28.725] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 11/19/2015] [Indexed: 01/26/2023] Open
Abstract
[Purpose] To investigate associations between vitamin C intake, physical activity, and osteoporosis among Korean adults aged 50 and over. [Subjects and Methods] This study was based on bone mineral density measurement data from the 2008 to 2011 Korean National Health and Nutritional Examination Survey. The study sample comprised 3,047 subjects. The normal group was defined as T-score ≥ -1.0, and the osteoporosis group as T-score ≤ -2.5. The odds ratios for osteoporosis were assessed by logistic regression of each vitamin C intake quartile. [Results] Compared to the lowest quartile of vitamin C intake, the other quartiles showed a lower likelihood of osteoporosis after adjusting for age and gender. In the multi-variate model, the odds ratio for the likelihood of developing osteoporosis in the non-physical activity group significantly decreased to 0.66, 0.57, and 0.46 (p for trend = 0.0046). However, there was no significant decrease (0.98, 1.00, and 0.97) in the physical activity group. [Conclusion] Higher vitamin C intake levels were associated with a lower risk of osteoporosis in Korean adults aged over 50 with low levels of physical activity. However, no association was seen between vitamin C intake and osteoporosis risk in those with high physical activity levels.
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Affiliation(s)
- Min Hee Kim
- Department of Physical Therapy, College of Health Science, Eulji University, Republic of Korea
| | - Hae-Jeung Lee
- Department of Food and Nutrition, College of Bionano Technology, Gachon University: 1342 Seongnam-daero, Sujeong-gu, Seongnam-si, Gyeonggi-do 461-701, Republic of Korea
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