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Old age causes de novo intracortical bone remodeling and porosity in mice
Marilina Piemontese, … , Charles A. O’Brien, Robert L. Jilka
Marilina Piemontese, … , Charles A. O’Brien, Robert L. Jilka
Published September 7, 2017
Citation Information: JCI Insight. 2017;2(17):e93771. https://doi.org/10.1172/jci.insight.93771.
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Research Article Aging Bone biology

Old age causes de novo intracortical bone remodeling and porosity in mice

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Abstract

Decreased cortical thickness and increased cortical porosity are the key anatomic changes responsible for osteoporotic fractures in elderly women and men. The cellular basis of these changes is unbalanced endosteal and intracortical osteonal remodeling by the osteoclasts and osteoblasts that comprise the basic multicellular units (BMUs). Like humans, mice lose cortical bone with age, but unlike humans, this loss occurs in the face of sex steroid sufficiency. Mice are therefore an ideal model to dissect age-specific osteoporotic mechanisms. Nevertheless, lack of evidence for endosteal or intracortical remodeling in mice has raised questions about their translational relevance. We show herein that administration of the antiosteoclastogenic cytokine osteoprotegerin to Swiss Webster mice ablated not only osteoclasts, but also endosteal bone formation, demonstrating the occurrence of BMU-based endosteal remodeling. Femoral cortical thickness decreased in aged male and female C57BL/6J mice, as well as F1 hybrids of C57BL/6J and BALB/cBy mice. This decrease was greater in C57BL/6J mice, indicating a genetic influence. Moreover, endosteal remodeling became unbalanced because of increased osteoclast and decreased osteoblast numbers. The porosity of the femoral cortex increased with age but was much higher in females of both strains. Notably, the increased cortical porosity resulted from de novo intracortical remodeling by osteon-like structures. Age-dependent cortical bone loss was associated with increased osteocyte DNA damage, cellular senescence, the senescence-associated secretory phenotype, and increased levels of RANKL. The demonstration of unbalanced endosteal and intracortical remodeling in old mice validates the relevance of this animal model to involutional osteoporosis in humans.

Authors

Marilina Piemontese, Maria Almeida, Alexander G. Robling, Ha-Neui Kim, Jinhu Xiong, Jeff D. Thostenson, Robert S. Weinstein, Stavros C. Manolagas, Charles A. O’Brien, Robert L. Jilka

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Figure 1

Age-related bone loss is greater in B6 than in CB6F1 mice.

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Age-related bone loss is greater in B6 than in CB6F1 mice.
Bone mineral ...
Bone mineral density was determined in the (A) femur, (B) lumbar vertebrae, and (C) total body excluding the head. Number of mice analyzed, ordered by increasing age: female B6 (20, 20, 19), male B6 (10, 10), female CB6F1 (10, 10, 10), male CB6F1 (9, 9, 8). *P < 0.05 vs. 6- to 7-month-old sex-matched animals of the same strain, **P < 0.05 vs. 6- to 7-month and 18- to 19-month sex-matched animals of the same strain, as determined by two-tailed t test (B6 males) or one-way ANOVA (B6 females and CB6F1 females and males).

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ISSN 2379-3708

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