Genetic disruption of both the CB1 and the CB2 receptor in mice enhances trabecular bone mass but reduces cortical bone mass

Wingless-type MMTV integration site family (WNT)16 is a key regulator of bone mass with high expression in cortical bone, and Wnt16−/− mice have reduced cortical bone mass. As Wnt16 expression is enhanced by estradiol treatment, we hypothesized that the bone-sparing effect of estrogen in females is WNT16-dependent. This hypothesis was tested in mechanistic studies using two genetically modified mouse models with either constantly high osteoblastic Wnt16 expression or no Wnt16 expression. We developed a mouse model with osteoblast-specific Wnt16 overexpression (Obl-Wnt16). These mice had several-fold elevated Wnt16 expression in both trabecular and cortical bone compared with wild type (WT) mice. Obl-Wnt16 mice displayed increased total body bone mineral density (BMD), surprisingly caused mainly by a substantial increase in trabecular bone mass, resulting in improved bone strength of vertebrae L3. Ovariectomy (ovx) reduced the total body BMD and the trabecular bone mass to the same degree in Obl-Wnt16 mice and WT mice, suggesting that the bone-sparing effect of estrogen is WNT16-independent. However, these bone parameters were similar in ovx Obl-Wnt16 mice and sham operated WT mice. The role of WNT16 for the bone-sparing effect of estrogen was also evaluated in Wnt16−/− mice. Treatment with estradiol increased the trabecular and cortical bone mass to a similar extent in both Wnt16−/− and WT mice. In conclusion, the bone-sparing effects of estrogen and WNT16 are independent of each other. Furthermore, loss of endogenous WNT16 results specifically in cortical bone loss, whereas overexpression of WNT16 surprisingly increases mainly trabecular bone mass. WNT16-targeted therapies might be useful for treatment of postmenopausal trabecular bone loss.

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Mutation of the Galectin-3 Glycan Binding Domain (Lgals3-R200S) Enhances Cortical Bone Expansion in Male and Trabecular Bone Mass in Female Mice

10.1101/2020.01.09.900787 ◽

2020 ◽

Author(s):

Kevin A. Maupin ◽

Daniel Dick ◽

VARI Vivarium ◽

Transgenics Core ◽

Bart O. Williams

Keyword(s):

Bone Mass ◽

Trabecular Bone ◽

Cortical Bone ◽

Mutant Mice ◽

Slight Variation ◽

Female Mice ◽

Bone Phenotype ◽

Bone Expansion ◽

Galectin 3 ◽

Trabecular Bone Mass

AbstractThe study of galectin-3 is complicated by its ability to function both intracellularly and extracellularly. While the mechanism of galectin-3 secretion is unclear, studies have shown that the mutation of a highly conserved arginine to a serine in human galectin-3 (LGALS3-R186S) blocks glycan binding and secretion. To gain insight into the roles of extracellular and intracellular functions of galectin-3, we generated mice with the equivalent mutation (Lgals3-R200S) using CRISPR/Cas9-directed homologous recombination. Consistent with a reduction in galectin-3 secretion, we observed significantly reduced galectin-3 protein levels in the plasma of heterozygous and homozygous mutant mice. We observed a similar increased bone mass phenotype in Lgals3-R200S mutant mice at 36 weeks as we previously observed in Lgals3-KO mice with slight variation. Like Lgals3-KO mice, Lgals3-R200S females, but not males, had significantly increased trabecular bone mass. However, only male Lgals3-R200S mice showed increased cortical bone expansion, which we had previously observed in both male and female Lgals3-KO mice and only in female mice using a separate Lgals3 null allele (Lgals3). These results suggest that the trabecular bone phenotype of Lgals3-KO mice was driven primarily by loss of extracellular galectin-3. However, the cortical bone phenotype of Lgals3-KO mice may have also been influenced by loss of intracellular galectin-3. Future analyses of these mice will aid in identifying the cellular and molecular mechanisms that contribute to the Lgals3-deficient bone phenotype as well as aid in distinguishing the extracellular vs. intracellular roles of galectin-3 in various signaling pathways.

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Caloric Restriction Decreases Cortical Bone Mass but Spares Trabecular Bone in the Mouse Skeleton: Implications for the Regulation of Bone Mass by Body Weight

Journal of Bone and Mineral Research ◽

10.1359/jbmr.080213 ◽

2008 ◽

Vol 23 (6) ◽

pp. 870-878 ◽

Cited By ~ 89

Author(s):

Mark W Hamrick ◽

Ke-Hong Ding ◽

Sumant Ponnala ◽

Serge L Ferrari ◽

Carlos M Isales

Keyword(s):

Body Weight ◽

Bone Mass ◽

Trabecular Bone ◽

Cortical Bone ◽

Caloric Restriction ◽

Cortical Bone Mass

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Vertebral cortical bone mass measurement by a new quantitative computer tomography method: Correlations with vertebral trabecular bone measurements

Calcified Tissue International ◽

10.1007/bf02555922 ◽

1990 ◽

Vol 47 (4) ◽

pp. 215-220 ◽

Cited By ~ 27

Author(s):

Roberto Pacifici ◽

Reta C. Rupich ◽

Louis V. Avioli

Keyword(s):

Bone Mass ◽

Trabecular Bone ◽

Cortical Bone ◽

Computer Tomography ◽

Mass Measurement ◽

Bone Mass Measurement ◽

Vertebral Trabecular Bone ◽

Quantitative Computer Tomography ◽

Cortical Bone Mass ◽

Tomography Method

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Osteocyte- and late Osteoblast-derived NOTUM Reduces Cortical Bone Mass in Mice

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00565.2020 ◽

2021 ◽

Author(s):

Karin H. Nilsson ◽

Petra Henning ◽

Maha El Shahawy ◽

Jianyao Wu ◽

Antti Koskela ◽

...

Keyword(s):

Bone Mass ◽

Trabecular Bone ◽

Cortical Bone ◽

Vertebral Fractures ◽

Volume Fraction ◽

Substantial Reduction ◽

Lumbar Vertebrae ◽

Bone Homeostasis ◽

Increased Risk ◽

Cortical Bone Mass

Osteoporosis is a common skeletal disease, with increased risk of fractures. Currently available osteoporosis treatments reduce the risk of vertebral fractures, mainly dependent on trabecular bone, whereas the effect on non-vertebral fractures, mainly dependent on cortical bone, is less pronounced. WNT signaling is a crucial regulator of bone homeostasis, and the activity of WNTs is inhibited by NOTUM, a secreted WNT lipase. We previously demonstrated that conditional inactivation of NOTUM in all osteoblast lineage cells increases the cortical but not the trabecular bone mass. The aim of the present study was to determine if NOTUM increasing cortical bone is derived from osteoblast precursors/early osteoblasts or from osteocytes/late osteoblasts. First, we demonstrated Notum mRNA expression in Dmp1-expressing osteocytes and late osteoblasts in cortical bone using in situ hybridization. We then developed a mouse model with inactivation of NOTUM in Dmp1 expressing osteocytes and late osteoblasts (Dmp1-creNotumflox/flox mice). We observed that the Dmp1-creNotumflox/flox mice displayed a substantial reduction of Notum mRNA in cortical bone, resulting in increased cortical bone mass and decreased cortical porosity in femur, but no change in trabecular bone volume fraction (BV/TV) in femur or in the lumbar vertebrae L5 in Dmp1-creNotumflox/flox mice as compared to control mice. In conclusion, osteocytes and late osteoblasts are the principal source of NOTUM in cortical bone, and NOTUM derived from osteocytes/late osteoblasts reduces cortical bone mass. These findings demonstrate that inhibition of osteocyte/late osteoblast-derived NOTUM might be an interesting pharmacological target to increase cortical bone mass and reduce non-vertebral fracture risk.

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