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Fibrous dysplasia (FD) is a mosaic skeletal disorder caused by somatic activating variants of GNAS encoding for Gαs and leading to excessive cyclic adenosine monophosphate signaling in bone-marrow stromal cells (BMSCs). The effect of Gαs activation in the BMSC transcriptome and how it influences FD lesion microenvironment are unclear. We analyzed changes induced by Gαs activation in the BMSC transcriptome and secretome. RNAseq analysis of differential gene expression of cultured BMSCs from patients with FD and healthy volunteers, and from an inducible mouse model of FD, was performed, and the transcriptomic profiles of both models were combined to build a robust FD BMSC genetic signature. Pathways related to Gαs activation, cytokine signaling, and extracellular matrix deposition were identified. To assess the modulation of several key secreted factors in FD pathogenesis, cytokines and other factors were measured in culture media. Cytokines were also screened in a collection of plasma samples from patients with FD, and positive correlations of several cytokines to their disease burden score, as well as to one another and bone turnover markers, were found. These data support the pro-inflammatory, pro-osteoclastic behavior of FD BMSCs and point to several cytokines and other secreted factors as possible therapeutic targets and/or circulating biomarkers for FD. [ABSTRACT FROM AUTHOR]

Chondrogenic induction of bone-marrow-derived stromal cells (BMSCs) is typically accomplished with medium supplemented with growth factors (GF) from the transforming growth factor-beta (TGF-β)/bone morphogenetic factor (BMP) superfamily. In a previous study, we demonstrated that brief (1–3 days) stimulation with TGF-β1 was sufficient to drive chondrogenesis and hypertrophy using small-diameter microtissues generated from 5000 BMSC each. This biology is obfuscated in typical large-diameter pellet cultures, which suffer radial heterogeneity. Here, we investigated if brief stimulation (2 days) of BMSC microtissues with BMP-2 (100 ng/mL) or growth/differentiation factor (GDF-5, 100 ng/mL) was also sufficient to induce chondrogenic differentiation, in a manner comparable to TGF-β1 (10 ng/mL). Like TGF-β1, BMP-2 and GDF-5 are reported to stimulate chondrogenic differentiation of BMSCs, but the effects of transient or brief use in culture have not been explored. Hypertrophy is an unwanted outcome in BMSC chondrogenic differentiation that renders engineered tissues unsuitable for use in clinical cartilage repair. Using three BMSC donors, we observed that all GFs facilitated chondrogenesis, although the efficiency and the necessary duration of stimulation differed. Microtissues treated with 2 days or 14 days of TGF-β1 were both superior at producing extracellular matrix and expression of chondrogenic gene markers compared to BMP-2 and GDF-5 with the same exposure times. Hypertrophic markers increased proportionally with chondrogenic differentiation, suggesting that these processes are intertwined for all three GFs. The rapid action, or "temporal potency", of these GFs to induce BMSC chondrogenesis was found to be as follows: TGF-β1 > BMP-2 > GDF-5. Whether briefly or continuously supplied in culture, TGF-β1 was the most potent GF for inducing chondrogenesis in BMSCs. [ABSTRACT FROM AUTHOR]