Fig. 8. BM stromal cells from WS patients displayed in vitro impaired osteogenic capacities.

A Relative expression levels of osteogenic genes were determined by quantitative PCR at day 14 in osteogenic-induced cultures of two WS patients-derived BMSCs and 7 healthy donors-derived BMSCs. Each individual sample was run in triplicate and was standardized for 36B4 expression levels. Results (means ± SEM) are expressed as relative expression compared to healthy samples (set at 1 and representing the mean of the 7 healthy donors) and are from 2 independent experiments. Statistics were calculated using the nonparametric Mann–Whitney test, two-sided, **p = 0.0079 for OSX, RUNX2, and OCN; *p = 0.0179 for OPN. B Alizarin Red staining was performed 21 days after initiation of the culture of 1.5 × 10³ healthy or WS BMSCs in pro-osteogenic medium (left panel). Representative images for healthy (H) and WS donors #1 and #2 are shown. Quantitative analyses of staining (means ± SEM) were performed using the osteogenesis assay kit in 3 independent cultures with 2 WS and 6 healthy donors (right panel). Statistics were calculated using the nonparametric Mann–Whitney test, two-sided, **p = 0.0022 for healthy. C Oil Red O staining was performed 21 days after initiation of cultures of healthy or WS BMSCs in pro-adipogenic differentiation medium. Bars: 200 μm. D Proposed model: Proper Cxcr4 signaling termination is essential for bone tissue homeostasis. Absence of Cxcr4 desensitization leads to imbalance in bone remodeling with decreased OBL-mediated bone formation and increased OCL-mediated bone resorption, leading to severe trabecular and cortical alterations and a subsequent osteoporotic-like phenotype. Mechanistically, impaired Cxcr4 desensitization disrupts the osteogenic commitment of SSCs, while strikingly increasing their pro-osteoclastogenic capacities. Graphical abstract was created using the Biorender software (Biorender.com, agreement number: EL255UV5RI). Source data are provided as a Source data file.