Biology subjects

Whitlock, J. M.

Publications and source records attributed to Whitlock, J. M..

3 recordsLinked to original sources

bioRxiv2024

Formation of multinucleated osteoclasts depends on an oxidized species of cell surface associated La protein

The bone-resorbing activity of osteoclasts plays a critical role in the life-long remodeling of our bones that is perturbed in many bone loss diseases. Multinucleated osteoclasts are formed by the fusion of precursor cells, and larger cells - generated by an increased number of cell fusion events - have higher resorptive activity. We find that osteoclast fusion and bone-resorption are promoted by reactive oxygen species (ROS) signaling and by an unconventional low molecular weight species of La protein, located at the osteoclast surface. Here, we develop the hypothesis that Las unique regulatory role in osteoclast multinucleation and function is controlled by a ROS switch in La trafficking. Using antibodies that recognize reduced or oxidized species of La, we find that differentiating osteoclasts enrich an oxidized species of La at the cell surface, which is distinct from the reduced La species conventionally localized within cell nuclei. ROS signaling triggers the shift from reduced to oxidized La species, its dephosphorylation and delivery to the surface of osteoclasts, where La promotes multinucleation and resorptive activity. Moreover, intracellular ROS signaling in differentiating osteoclasts oxidizes critical cysteine residues in the C-terminal half of La, producing this unconventional La species that promotes osteoclast fusion. Our findings suggest that redox signaling induces changes in the location and function of La and may represent a promising target for novel skeletal therapies.

cell biology↗

bioRxiv2022

An inducible explant model for dissecting osteoclast-osteoblast coordination in health and disease.

Metabolic bone diseases are a collection of disorders resulting in diminished skeletal integrity and changes in bone mass due to perturbations in the life-long process of bone remodeling. Perturbations in the number, size and nuclear multiplicity of osteoclasts underpin the development of diverse metabolic bone diseases that impact >13% of adults over age 50 world-wide. Each metabolic bone disease (e.g., osteoporosis, Pagets disease, fibrous dysplasia (FD), osteopetrosis) presents with unique phenotypes, rises from distinct etiologies and progresses with disparate severities, but all are underpinned by a breakdown in osteoclast formation/function. These perturbations of osteoclast formation/function either stem from or cause dysfunctional osteoclast-osteoblast coordination. Unfortunately, a mechanistic understanding of osteoclast-osteoblast coordination and communication is lacking and represents a major barrier to understanding the biology underpinning bone remodeling and the development of effective treatments targeting this process. Here we have developed an inducible ex vivo culture model that models osteoclast-osteoblast coordination in the bone remodeling compartment. Doxycycline addition to cultures activates GsR201C expression and RANKL release from osteoprogenitors, which elicits the differentiation and fusion of neighboring preosteoclasts. In turn, multinucleated osteoclast formation promotes the proliferation of osteoprogenitors, accompanied by the robust release of RANK+ extracellular vesicles, all within [~]4 days. This system recapitulates many aspects of the complex osteoclast-osteoblast coordination required for the function of the bone remodeling compartment in both health and diseases underpinned by excessive osteoclast formation. Moreover, based on the ease of isolation, culture, reproducibility and the general adaptability of these cultures to a variety of assays, we expect that this new model will expedite the investigation of osteoclast-osteoblast coordination and osteoclast fusion in bone remodeling and offer a powerful tool for evaluating signaling cascades and novel therapeutic interventions in osteoclast-linked skeletal disease. One-Sentence SummaryConditional, inducible, ex vivo marrow explants offer a novel tool for studying osteoclast formation and osteoclast-osteoblast coordination in a rapid convenient culture model.

cell biology↗

bioRxiv2022

Cell Surface-Bound La Protein Regulates The Cell Fusion Stage Of Osteoclastogenesis

Multinucleated osteoclasts, essential for skeletal remodeling in health and diseases, are formed by fusion of osteoclast precursors with each fusion event raising their bone-resorbing activity. Here we report that nuclear RNA chaperone, La protein moonlights as an osteoclast fusion regulator. Monocyte-to-osteoclast differentiation starts with a drastic decrease in La levels. Then La reappears as a proteasecleaved species at the cell surface where it promotes fusion by mechanisms independent of La-RNA interactions. Appearance-and-disappearance of cell-surface La act as an on-and-off switch of the fusion activity with fusion slowing down when surface La is replaced in mature osteoclasts by full-length nuclear La. Inhibiting surface La in a novel explant model of fibrous dysplasia inhibits excessive osteoclast formation characteristic of this disease, highlighting Las potential as a therapeutic target. One-Sentence SummaryA nuclear RNA chaperon moves to the surface of osteoclasts to control their formation and function in bone metabolism.

cell biology↗