Changes in gene expression in human skeletal stem cells transduced with constitutively active Gsα correlates with hallmark histopathological changes seen in fibrous dysplastic bone

Abstract

Fibrous dysplasia (FD) of bone is a complex disease of the skeleton caused by dominant activating mutations of the GNAS locus encoding for the α subunit of the G protein-coupled receptor complex (Gsα). The mutation involves a substitution of arginine at position 201 by histidine or cysteine (Gsα R201H or R201C), which leads to overproduction of cAMP. Several signaling pathways are implicated downstream of excess cAMP in the manifestation of disease. However, the pathogenesis of FD remains largely unknown. The overall FD phenotype can be attributed to alterations of skeletal stem/progenitor cells which normally develop into osteogenic or adipogenic cells (in cis), and are also known to provide support to angiogenesis, hematopoiesis, and osteoclastogenesis (in trans). In order to dissect the molecular pathways rooted in skeletal stem/progenitor cells by FD mutations, we engineered human skeletal stem/progenitor cells with the Gsα R201C mutation and performed transcriptomic analysis. Our data suggest that this FD mutation profoundly alters the properties of skeletal stem/progenitor cells by pushing them towards formation of disorganized bone with a concomitant alteration of adipogenic differentiation. In addition, the mutation creates an altered in trans environment that induces neovascularization, cytokine/chemokine changes and osteoclastogenesis. In silico comparison of our data with the signature of FD craniofacial samples highlighted common traits, such as the upregulation of ADAM (A Disintegrin and Metalloprotease) proteins and other matrix-related factors, and of PDE7B (Phosphodiesterase 7B), which can be considered as a buffering process, activated to compensate for

Nanostring technology on Fibrous Dysplasia bone biopsies. A pilot study suggesting different histology-related molecular profiles

“…S3), the most significant biological processes and pathways were associated with immunity and inflammatory responses, including cytokine-mediated signaling pathways, cytokine-cytokine receptor interaction, as well as JAK-STAT signaling pathway. This agrees with what reported in ( Raimondo et al, 2020 ) regarding the upregulation of cytokines and chemokines in FD, suggesting an activation of immune cell trafficking and inflammatory phenomena in FD patients.…”

“…PPI network for the 189 genes of FD cluster 1 was constructed and used to identify clusters of highly interconnected nodes. In this way we were able to underline pathways dysregulated in FD pathogenesis, confirming what we deduced from single genes overexpression data and comparing our results with two microarray-based analyses that were previously performed on Fibrous Dysplasia using tissue and cell samples ( Raimondo et al, 2020 ; Zhou et al, 2014 ). Fig.…”

“…The first, performed on a pool of fresh pathological samples ( Zhou et al, 2014 ), did not provide any correlation between the molecular data and the actual histological features of the lesions. The second did not use pathological tissue and was conducted on normal osteoprogenitor cells transduced with the Gsα R201C mutation ( Raimondo et al, 2020 ).…”

Quantitative proteomic study reveals differential expression of matricellular proteins between fibrous dysplasia and cemento‐ossifying fibroma pathogenesis

“…Further supporting this hypothesis, the levels of alpha‐2‐macroglobulin (α 2 m), which influences the availability of osteogenic growth peptide (OGP) and modulates TGF‐β1 and TGF‐β2 activities, 16,17 were decreased in COF. Recently, it has been proposed that activating GNAS1 mutations may influence the expression of ECM‐related genes 18 . Therefore, the differential regulation of ECM proteins levels between these diseases may arise from the differences in their genetic background.…”

“…Recently, it has been proposed that activating GNAS1 mutations may influence the expression of ECM-related genes. 18 Therefore, the differential regulation of ECM proteins levels between these diseases may arise from the differences in their genetic background. Notably, alterations of ECM components in FD have been previously shown in studies evaluating the gene expression of affected subjects compared to unaffected controls.…”