Resolving the mechanism of osteoclast multinucleation and signaling in bone remodeling

PROJECT SUMMARY: Essential, life-long bone remodeling is coordinated by osteoclasts (OCs) that resorb old bone and osteoblasts that deposit new bone. Elevated OC formation/function erodes excess bone, weakens the skeleton, and underpins bone disease in >200 million individuals world-wide. Mononucleated preOCs fuse and form

multinucleated OCs through a formative process – multinucleation. OC multinucleation regulates how much bone OCs resorb and is often elevated in OC-based bone disease. Despite its role in skeletal health and disease, how OC multinucleation is regulated remains poorly understood. We discovered that lupus la protein’s

(La) expression, cleavage, and trafficking to the plasma membrane (PM) regulate OC fusion, multinucleation, and bone resorption. Moreover, our preliminary findings demonstrate that inhibiting PM La during OC multinucleation suppresses the progression of OC-based bone disease. Resolving the mechanism of OC

multinucleation will fill fundamental gaps in our understanding of skeletal health, identify pathways perturbed in disease, and establish novel therapeutic targets for preventing bone loss. In this study, we will resolve the mechanism by which La regulates OC multinucleation (Aims 1 & 3) and employ a novel, ex vivo model to characterize the contribution of perturbed OC-to-osteoblast signaling in the progression

of OC-based bone disease. First, we will use a semi-automated peptide screening assay to identify the La domain that facilitates its regulatory function in OC multinucleation (Aim 1). Second, we will resolve how La traffics to the OC PM to promote multinucleation, is removed and degraded to stop multinucleation, and how

perturbed La membrane trafficking contributes to the uncontrolled multinucleation observed in SNX10-linked infantile osteopetrosis (Aim 3). Finally, we find that ectopic OC multinucleation in fibrous dysplasia, an OC-based bone disease, leads to excessive OC signaling and disease related changes in preosteoblasts. In Aim 2, we will

characterize perturbed OC signaling in a novel ex vivo model of fibrous dysplasia, assess its impact on preosteoblast function, and test whether perturbed OC-to-osteoblast signaling contributes to disease progression in vivo. This research firmly aligns with NICHD’s mission to resolve fundamental gaps in our

understanding of life-long human development and will identify novel targets and test treatment strategies for addressing the childhood bone diseases fibrous dysplasia and infantile osteopetrosis. In addition to completing the proposed aims, I will gain critical experience in the implementation of in vivo models to study the development

of bone diseases, machine learning approaches for studying osteoclast multinucleation, and effective mentorship and management strategies for leading my independent laboratory. My proposed aims will generate new research directions, and my career development, networking, and training goals will prepare me to become a

leading independent investigator that expands our understanding of skeletal health and disease.