The search for molecular targets/pathways that can be manipulated to improve bone properties is a highly active area of investigation. Recently, particular interest has been expressed in targeting biomolecules that can augment mechanical signaling in bone; the next generation of osteoporosis drugs is likely to work in conjunction with physical activity/loading in order to disproportionately direct new bone formation to skeletal areas that need it most (i.e., those regions that endure the greatest strains and are at the greatest risk of failure). The WNT signaling pathway has emerged as a key regulator of bone mass and strength, but also of bone cell mechanotransduction. Recent work by Professor Wim van Hul in Antwerp and by Novartis Pharma in Basel identified an accessory protein?LRP4?that regulates the activity of SOST, which is a secreted inhibitor of the WNT co-receptors LRP5/LRP6. Specific missense mutations in LRP4 cause high bone mass (HBM) phenotypes by eliminating SOST-mediated inhibition of LRP5/LRP6. The goal of the present application is to understand precisely how LRP4, LRP5, and LRP6 function to regulate bone metabolism and mechanotransduction, which ultimately will reveal new approaches for preventing or treating bone disorders?a primary mission of NIAMS/NIH. Among the key questions we addressed are: (1) Is the principal role of LRP4 in bone to bind SOST? (2) Does LRP4 directly present SOST to LRP5/LRP6 or simply increase local concentration of this inhibitor? (3) Does LRP4 function throughout osteoprogenitor differentiation, or does it have stage-specific roles? (4) Does LRP4 regulate LRP5 and LRP6 equally, or is LRP4 more important for one of these two WNT co-receptors? (5) Will bone-specific deletion/inhibition of LRP4 prevent the bone-wasting effects of mechanical disuse? (6) Does LRP4 coordinate the deposition of new bone to high-strain surfaces during mechanical loading? (7) Do LRP5 and LRP6 differ in terms of when (early vs. late in differentiation) and where (cortical vs. trabecular envelopes) they are active? (8) Which upstream and downstream mechanical signaling pathways will be identified in specific bone cell subtypes using single-cell transcriptomics of loaded and unloaded bone? We will use cutting-edge, novel, mouse models (CRISPR-based Lrp4 and Lrp6 knockins), single-cell transcriptomic approaches (Drop-seq and 10XGenomics), live cell microscopic techniques (FRET/FLIM), mechanotransduction models (strain mapping in ulnar loading and tail suspension), and radiographic/histologic/biochemical approaches to reveal the underlying biology and therapeutic potential of LRP4, LRP5, and LRP6 manipulation in bone tissue. The project is a continuation of the close collaboration between the Robling (Indiana Univ.) and Warman (Harvard Univ.) labs, an extremely fruitful partnership for more than 12 yrs. We have assembled a unique combination of expertise, resources, biological models/tools, and technical innovation to elucidate the role of LRP4 in bone biology.

Public Health Relevance

The research program described in this application seeks to elucidate the molecular biology of a cell surface receptor known as LRP4. Human patients with mutations in the gene for LRP4 exhibit skeletal phenotypes (very dense bone) that attest to the therapeutic potential of harnessing this receptor?s activity to improve skeletal health in patients with low bone mass disease. We will study mice that express different forms of LRP4, to determine the mechanism of action of this receptor, and whether it works as a function of exercise to improve bone properties.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR053237-13
Application #
9761831
Study Section
Skeletal Biology Structure and Regeneration Study Section (SBSR)
Program Officer
Nicks, Kristy
Project Start
2005-09-30
Project End
2022-07-31
Budget Start
2019-08-01
Budget End
2020-07-31
Support Year
13
Fiscal Year
2019
Total Cost
Indirect Cost
Name
Indiana University-Purdue University at Indianapolis
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
603007902
City
Indianapolis
State
IN
Country
United States
Zip Code
46202
Bird, Ian M; Kim, Susie H; Schweppe, Devin K et al. (2018) The skeletal phenotype of achondrogenesis type 1A is caused exclusively by cartilage defects. Development 145:
Kang, Kyung Shin; Hong, Jung Min; Horan, Daniel J et al. (2018) Induction of Lrp5 HBM-causing mutations in Cathepsin-K expressing cells alters bone metabolism. Bone 120:166-175
Williams, Justin N; Kambrath, Anuradha Valiya; Patel, Roshni B et al. (2018) Inhibition of CaMKK2 Enhances Fracture Healing by Stimulating Indian Hedgehog Signaling and Accelerating Endochondral Ossification. J Bone Miner Res 33:930-944
Caetano-Lopes, J; Lessard, S G; Hann, S et al. (2017) Clcn7F318L/+ as a new mouse model of Albers-Schönberg disease. Bone 105:253-261
Shao, Yu; Hernandez-Buquer, Selene; Childress, Paul et al. (2017) Improving Combination Osteoporosis Therapy in a Preclinical Model of Heightened Osteoanabolism. Endocrinology 158:2722-2740
Alam, Imranul; Reilly, Austin M; Alkhouli, Mohammed et al. (2017) Bone Mass and Strength are Significantly Improved in Mice Overexpressing Human WNT16 in Osteocytes. Calcif Tissue Int 100:361-373
Piemontese, Marilina; Almeida, Maria; Robling, Alexander G et al. (2017) Old age causes de novo intracortical bone remodeling and porosity in mice. JCI Insight 2:
Williams, Bart O; Warman, Matthew L (2017) CRISPR/CAS9 Technologies. J Bone Miner Res 32:883-888
Bullock, Whitney A; Robling, Alexander G (2017) WNT-mediated Modulation of Bone Metabolism: Implications for WNT Targeting to Treat Extraskeletal Disorders. Toxicol Pathol 45:864-868
Alam, Imranul; Alkhouli, Mohammed; Gerard-O'Riley, Rita L et al. (2016) Osteoblast-Specific Overexpression of Human WNT16 Increases Both Cortical and Trabecular Bone Mass and Structure in Mice. Endocrinology 157:722-36

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