Increased NF-κB Activity and Decreased Wnt/β-Catenin Signaling Mediate Reduced Osteoblast Differentiation and Function in ΔF508 Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Mice

Abstract The prevalent human ΔF508mutation in the cystic fibrosis transmembrane conductance regulator(CFTR) is associated with reduced bone formation and bone loss in mice. The molecular mechanisms by which the ΔF508-CFTR mutation causes alterations in bone formation are poorly known. In this study, we analyzed the osteoblastphenotype in ΔF508-CFTR mice and characterized the signaling mechanisms underlying this phenotype. Ex vivo studies showed that the ΔF508-CFTR mutation negatively impacted the differentiation of bone marrow stromal cells into osteoblastsand the activity of osteoblasts, demonstrating that the ΔF508-CFTR mutation alters both osteoblastdifferentiation and function. Treatment with a CFTR corrector rescued the abnormal collagen gene expression in ΔF508-CFTR osteoblasts. Mechanistic analysis revealed that NF-κB signaling and transcriptional activity were increased in mutant osteoblasts. Functional studies showed that the activation of NF-κB transcriptional activity in mutant osteoblastsresulted in increased β- cateninphosphorylation, reduced osteoblastβ- cateninexpression, and altered expression of Wnt/β- catenintarget genes. Pharmacological inhibition of NF-κB activity or activation of canonical Wnt signaling rescued Wnt target gene expression and corrected osteoblastdifferentiation and function in bone marrow stromal cells and osteoblastsfrom ΔF508-CFTR mice. Overall, the results show that the ΔF508-CFTR mutation impairs osteoblastdifferentiation and function as a result of overactive NF-κB and reduced Wnt/β- cateninsignaling. Moreover, the data indicate that pharmacological inhibition of NF-κB or activation of Wnt/β- cateninsignaling can rescue the abnormal osteoblastdifferentiation and function induced by the prevalent ΔF508-CFTR mutation, suggesting novel therapeutic strategies to correct the osteoblastdysfunctions in cystic fibrosis.