Novel LRP5 Missense Mutation in a Patient With a High Bone Mass Phenotype Results in Decreased DKK1-Mediated Inhibition of Wnt Signaling*

Increasing peak bone mass is a promising strategy to prevent osteoporosis. A mouse model of global progesterone receptor (PR) ablation showed increased bone mass through a sex-dependent mechanism. Cre-Lox recombination was used to generate a mouse model of osteoprogenitor-specific PR inactivation, which recapitulated the high bone mass phenotype seen in the PR global knockout mouse mode. In this work, we employed RNA sequencing analysis to evaluate sex-independent and sex-dependent differences in gene transcription of osteoprogenitors of wild-type and PR conditional knockout mice. PR deletion caused marked sex hormone-dependent changes in gene transcription in male mice as compared to wild-type controls. These transcriptional differences revealed dysregulation in pathways involving immunomodulation, osteoclasts, bone anabolism, extracellular matrix interaction and matrix interaction. These results identified many potential mechanisms that may explain our observed high bone mass phenotype with sex differences when PR was selectively deleted in the MSCs.

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Interrelationship between Metabolic and High Bone Mass Phenotype in a Mouse Model of Adult-Onset, Isolated, GH-Deficiency (AOiGHD).

10.1210/endo-meetings.2010.part1.p5.p1-219 ◽

2010 ◽

pp. P1-219-P1-219

Author(s):

JW Bracey ◽

RA Skinner ◽

NS Akel ◽

AB Reddy ◽

J Cordoba-Chacon ◽

...

Keyword(s):

Mouse Model ◽

Bone Mass ◽

Gh Deficiency ◽

Adult Onset ◽

High Bone Mass ◽

High Bone ◽

High Bone Mass Phenotype

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NFATC2-knock-out mice reveal a high bone mass phenotype

Bone ◽

10.1016/j.bone.2010.04.069 ◽

2010 ◽

Vol 47 ◽

pp. S40

Author(s):

M. Rauner⁎ ◽

W. Bauer ◽

I. Habermann ◽

M. Haase ◽

C. Goettsch ◽

...

Keyword(s):

Bone Mass ◽

High Bone Mass ◽

Knock Out ◽

High Bone ◽

High Bone Mass Phenotype ◽

Knock Out Mice

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Reduced Affinity to and Inhibition by DKK1 Form a Common Mechanism by Which High Bone Mass-Associated Missense Mutations in LRP5 Affect Canonical Wnt Signaling

Molecular and Cellular Biology ◽

10.1128/mcb.25.12.4946-4955.2005 ◽

2005 ◽

Vol 25 (12) ◽

pp. 4946-4955 ◽

Cited By ~ 188

Author(s):

Minrong Ai ◽

Sheri L. Holmen ◽

Wim Van Hul ◽

Bart O. Williams ◽

Matthew L. Warman

Keyword(s):

Cell Surface ◽

Bone Mass ◽

Wnt Signaling ◽

Common Mechanism ◽

Missense Mutations ◽

Canonical Wnt Signaling ◽

High Bone Mass ◽

Mutant Proteins ◽

High Bone ◽

Canonical Wnt

ABSTRACT The low-density-lipoprotein receptor-related protein 5 (LRP5), a coreceptor in the canonical Wnt signaling pathway, has been implicated in human disorders of low and high bone mass. Loss-of-function mutations cause the autosomal recessive osteoporosis-pseudoglioma syndrome, and heterozygous missense mutations in families segregating autosomal dominant high bone mass (HBM) phenotypes have been identified. We expressed seven different HBM-LRP5 missense mutations to delineate the mechanism by which they alter Wnt signaling. None of the mutations caused activation of the receptor in the absence of ligand. Each mutant receptor was able to reach the cell surface, albeit at differing amounts, and transduce exogenously supplied Wnt1 and Wnt3a signal. All HBM mutant proteins had reduced physical interaction with and reduced inhibition by DKK1. These data suggest that HBM mutant proteins can transit to the cell surface in sufficient quantity to transduce Wnt signal and that the likely mechanism for the HBM mutations' physiologic effects is via reduced affinity to and inhibition by DKK1.

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F-Spondin Deficient Mice Have a High Bone Mass Phenotype

PLoS ONE ◽

10.1371/journal.pone.0098388 ◽

2014 ◽

Vol 9 (5) ◽

pp. e98388 ◽

Cited By ~ 14

Author(s):

Glyn D. Palmer ◽

Mukundan G. Attur ◽

Qing Yang ◽

James Liu ◽

Paxton Moon ◽

...

Keyword(s):

Bone Mass ◽

High Bone Mass ◽

High Bone ◽

High Bone Mass Phenotype ◽

Deficient Mice

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The LRP5 High-Bone-Mass G171V Mutation Disrupts LRP5 Interaction with Mesd

Molecular and Cellular Biology ◽

10.1128/mcb.24.11.4677-4684.2004 ◽

2004 ◽

Vol 24 (11) ◽

pp. 4677-4684 ◽

Cited By ~ 122

Author(s):

Yazhou Zhang ◽

Yang Wang ◽

Xiaofeng Li ◽

Jianhong Zhang ◽

Junhao Mao ◽

...

Keyword(s):

Cell Surface ◽

Bone Mass ◽

Wnt Signaling ◽

Cell Surfaces ◽

Osteoblast Cells ◽

High Bone Mass ◽

Chaperone Protein ◽

Repeat Domain ◽

High Bone ◽

Canonical Wnt

ABSTRACT The mechanism by which the high-bone-mass (HBM) mutation (G171V) of the Wnt coreceptor LRP5 regulates canonical Wnt signaling was investigated. The mutation was previously shown to reduce DKK1-mediated antagonism, suggesting that the first YWTD repeat domain where G171 is located may be responsible for DKK-mediated antagonism. However, we found that the third YWTD repeat, but not the first repeat domain, is required for DKK1-mediated antagonism. Instead, we found that the G171V mutation disrupted the interaction of LRP5 with Mesd, a chaperone protein for LRP5/6 that is required for transport of the coreceptors to cell surfaces, resulting in fewer LRP5 molecules on the cell surface. Although the reduction in the number of cell surface LRP5 molecules led to a reduction in Wnt signaling in a paracrine paradigm, the mutation did not appear to affect the activity of coexpressed Wnt in an autocrine paradigm. Together with the observation that osteoblast cells produce autocrine canonical Wnt, Wnt7b, and that osteocytes produce paracrine DKK1, we think that the G171V mutation may cause an increase in Wnt activity in osteoblasts by reducing the number of targets for paracrine DKK1 to antagonize without affecting the activity of autocrine Wnt.

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Role of CaMKK2 in Osteocytes within the Bone Microenvironment

Proceedings of IMPRS ◽

10.18060/22676 ◽

2018 ◽

Vol 1 (1) ◽

Author(s):

Nick Clough ◽

Justin Williams ◽

Uma Sankar

Keyword(s):

Bone Mass ◽

Bone Cell ◽

T Antigen ◽

Dendritic Morphology ◽

Bone Biology ◽

High Bone Mass ◽

High Bone ◽

High Bone Mass Phenotype ◽

Outstanding Question

Background and Hypothesis: The Ca+2/calmodulin (CaM)-mediated protein kinase kinase 2 (CaMKK2) is a multi-functional kinase with effects on cell proliferation, differentiation and metabolism. The role of CaMKK2 in bone has been explored with its ablation favoring osteoblasts to osteoclasts and bone mass accrual as observed in Camkk2-/- mice, or following its inhibition by STO-609. One outstanding question is whether the anabolic effects of CaMKK2 are bone-cell intrinsic. While analyzing mice harboring bone-cell specific deletion of CaMKK2, we observed a high bone mass phenotype when the kinase is deleted from osteocytes, the most abundant cells within the bone. We therefore hypothesized that the loss of CaMKK2 enhances osteocyte differentiation. Experimental Design or Project Methods: We used two osteocyte cell lines MLO-Y4 and MLO-A5, both generated from mice expressing the immortalizing T-antigen, to test our hypothesis. The MLO-A5 line has post-osteoblast/pre-osteocyte characteristics while the MLO-Y4 line has mature osteocyte characteristics. CaMKK2 expression was silenced in MLO-A5 cells using Lentiviruses encoding CaMKK2 short hairpin (sh) RNA constructs. STO-609 was employed to inhibit CaMKK2 in the MLO-Y4 line as it proved resistant to transfection. Immunoblotting was used to verify CaMKK2 silencing/inhibition. Comparisons on cell morphologies were observed using immunofluorescence. As osteocytes are defined by dendritic morphology, the number of dendritic processes were analyzed. Additionally, the differences in the expression of the osteocyte markers SOST, E11 and DMP1 were examined by qRT-PCR. Results: To be finalized. Conclusion and Potential Impact: Overall, our studies will provide more information towards understanding the role of CaMKK2 in bone biology and aid its development as a therapeutic target in the treatment of osteoporosis.

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