A dual-specific macrophage colony-stimulating factor antagonist of c-FMS and αvβ3 integrin for osteoporosis therapy.

Yuval Zur,Niv Papo,Ayelet Orenbuch,Chen Anna Keshelman,Yulia Einav,Lior Rosenfeld,Nofar Dalal,Noam Levaot,Gali Guterman-Ram,Imelda Mcgonnell

doi:10.1371/journal.pbio.2002979

Yuval Zur, Niv Papo + Show 8 more

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https://doi.org/10.1371/journal.pbio.2002979

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Abstract

There is currently a demand for new highly efficient and specific drugs to treat osteoporosis, a chronic bone disease affecting millions of people worldwide. We have developed a combinatorial strategy for engineering bispecific inhibitors that simultaneously target the unique combination of c-FMS and αvβ3 integrin, which act in concert to facilitate bone resorption by osteoclasts. Using functional fluorescence-activated cell sorting (FACS)-based screening assays of random mutagenesis macrophage colony-stimulating factor (M-CSF) libraries against c-FMS and αvβ3 integrin, we engineered dual-specific M-CSF mutants with high affinity to both receptors. These bispecific mutants act as functional antagonists of c-FMS and αvβ3 integrin activation and hence of osteoclast differentiation in vitro and osteoclast activity in vivo. This study thus introduces a versatile platform for the creation of new-generation therapeutics with high efficacy and specificity for osteoporosis and other bone diseases. It also provides new tools for studying molecular mechanisms and the cell signaling pathways that mediate osteoclast differentiation and function.

Highlights

Osteoporosis, a chronic skeletal disorder common in both women and men beyond the age of 50 [1], is the underlying cause of more than 8.9 million fractures annually worldwide, with the consequent high burden of social and economic costs [2]
Osteoclast differentiation and function are coordinated by cell surface receptors, including c-FMS and αvβ3 integrin, which cooperate with one another to drive signals that are essential for osteoclast functions
The macrophage colony-stimulating factor (M-CSF) glycoprotein is secreted as a homodimer that, upon binding to two c-FMS receptors, induces c-FMS autophosphorylation followed by activation of downstream signaling pathways [23]

Summary

Introduction

Osteoporosis, a chronic skeletal disorder common in both women and men beyond the age of 50 [1], is the underlying cause of more than 8.9 million fractures annually worldwide, with the consequent high burden of social and economic costs [2]. Central to the pathogenesis of osteoporosis is excessive bone resorption by osteoclasts [9] These cells differentiate from cells of the monocyte/macrophage lineage upon stimulation of two essential factors, monocyte/macrophage colony-stimulating factor (M-CSF) and RANKL [10]. The importance of M-CSF and its receptor c-FMS in osteoclast function has been clearly illustrated in a study showing that both M-CSF–deficient and c-FMS–deficient mice suffer from retarded skeletal growth and osteopetrosis [11] Another factor that is essential for osteoclast functioning is αvβ integrin, as indicated, for example, in studies showing increased bone mass in integrin β3 knockout mice due to a functional defect in their osteoclasts [12,13,14,15]. The interaction of αvβ integrin with the bone matrix induces a cytoskeleton organization that polarizes the osteoclast’s resorptive machinery to the bone/cell interface, where it creates an isolated compartment consisting of an actin ring surrounding a ruffled border essential for resorption by the matured osteoclasts

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