Collins, M. T. | bioRxiv Science

bioRxiv2024

Transcriptomic signature and pro-osteoclastic secreted factors of abnormal bone marrow stromal cells in fibrous dysplasia

Fibrous dysplasia (FD) is a mosaic skeletal disorder caused by somatic activating variants in GNAS, encoding for Gs, which leads to excessive cAMP signaling in bone marrow stromal cells (BMSCs). Despite advancements in our understanding of FD pathophysiology, the effect of Gs activation in the BMSC transcriptome remains unclear, as well as how this translates into their local influence in the lesional microenvironment. In this study, we analyzed changes induced by Gs activation in BMSC transcriptome and performed a comprehensive analysis of their production of cytokines and other secreted factors. We performed RNAseq of cultured BMSCs from patients with FD and healthy volunteers, and from an inducible mouse model of FD, and combined their transcriptomic profiles to build a robust FD BMSC genetic signature. Pathways related to Gs activation, cytokine signaling, and extracellular matrix deposition were identified. In addition, a comprehensive profile of their secreted cytokines and other factors was performed to identify modulation of several key factors we hypothesized to be involved in FD pathogenesis. We also screened circulating cytokines in a collection of plasma samples from patients with FD, finding positive correlations of several cytokines to their disease burden score, as well as to one another and bone turnover markers. Overall, these data support a pro-inflammatory, pro-osteoclastic behavior of BMSCs bearing hyperactive Gs variants, and point to several cytokines and other secreted factors as possible therapeutic targets and/or circulating biomarkers for FD.

pathology↗

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↗