Silencing SFRP1 in bone mesenchymal stem cells alleviates pediatric B-ALL-driven bone loss by activating Wnt/β-catenin signaling.

BACKGROUND: Bone loss is the most common skeletal complication of childhood acute lymphoblastic leukemia (ALL) and seriously affects the long-term survival quality of children. However, the mechanisms behind bone loss are complicated and need to be elucidated. This study seeks to examine the principal parameters influencing the osteogenic development of bone marrow mesenchymal stem cells (BMSCs) in pediatric patients with B-cell acute lymphoblastic leukemia (B-ALL) experiencing bone loss, and to identify viable ways for alleviating bone loss. METHODS: Firstly, bone mass of adolescent B-ALL patients and mice were evaluated with aged-matched cohorts. Then, human BMSCs (hBMSCs) were isolated from pediatric B-ALL patients and characterized by Flow Cytometry Assay (FCA). ALP, ARS, Oil Red O and toluidine blue staining were used to evaluate the trilineage differentiation of hBMSCs. Integrated RNA-seq and proteomic analyses were employed to identify differentially target osteogenic regulators in B-ALL-derived hBMSCs. On the based that secreted frizzled-related protein 1 (SFRP1) was demonstrated to be a regulator on B-ALL BMSC osteogenesis, BMSC-targeted liposomal nanocarriers were engineered to encapsulate lentiviral particles carrying therapeutic shSFRP1 RNA and grafted with E7 peptide (shSFRP1@Lipo-E7), enabling cell-specific gene silencing in BMSCs. Subsequently, shSFRP1@Lipo-E7 was delivered into B-ALL mice by tail vein injection and bone quality were evaluated by mico-CT and histomorphometric analysis. RESULTS: Adolescent B-ALL patients exhibited significant vertebral bone loss, with 33.8% of patients affected. In B-ALL mice, BMD and newbone formation were markedly reduced, while osteoclast activity increased. An increased expression of SFRP1 was identified to impair osteogenesis of BMSCs from B-ALL patients. Consequently, a BMSC-targeted nanoplatform, E7 peptide-modified liposomes containing lentiviral shSFRP1 (shSFRP1@Lipo-E7) was constructed successfully. As anticipated, shSFRP1@Lipo-E7 effectively suppressed SFRP1 expression in trabecular osteoblasts and rescued B-ALL mice from bone loss, supported by significantly increasing BMD and improved trabecular structure. Both in vitro and vivo studies evidenced that silencing of SFRP1 activated Wnt/β-catenin signaling to promote BMSC osteogenesis and bone formation in B-ALL mice. CONCLUSION: High SFRP1 expression in B-ALL BMSCs suppresses osteogenesis and contributes to bone loss in B-ALL cohorts by inhibiting Wnt/β-catenin signaling, which afford a potential translatable target to reprogram bone homeostasis and prevent bone fragility in ALL patients. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: Given the negative correlation between SFRP1 overexpression in BMSCs of pediatric B-ALL related bone mass loss, precisely targeting SFRP1 in MSCs for intervention holds promise as a therapeutic strategy to rescue bone loss in this disease category.