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Exploring bone formation mechanism and pattern during RANKL inhibition in a fibrous dysplasia mouse model
Giorgia Farinacci1, Ilenia Coletta2, Biagio Palmisano3
1Department of Experimental Medicine, Sapienza University of Rome, Rome, Italy.
Abstract:
Fibrous dysplasia (FD) of bone is a fibro-osseous disorder caused by GNAS mutations with defective osteogenic differentiation and increased bone remodeling activity. Inhibition of RANKL leads to the replacement of FD lesions with bone. However, the mechanism and pattern of deposition of the newly formed bone remain unclear. Here, we perform morphological and molecular analyses on EF1α-GsαR201C (FD) mice receiving an anti-mouse RANKL antibody. We show that, although the treatment reduces the expression of osteogenic genes, osteoblastic cells continue to produce bone matrix within FD lesions. However, bone formation does not occur in a diffuse or stochastic manner but follows an ordered spatial pattern that is restricted to the surfaces of the lesional bone. These results suggest that during RANKL inhibition the amount of intra-lesional bone trabecular surfaces is critical to the process of cell differentiation and to the skeletal improvement that FD patients may achieve during the treatment.
Insights
Fibrous dysplasia (FD) treatment with RANKL inhibition shows new bone formation is spatially organized on existing lesional surfaces, not random. This surface-dependent bone deposition is key for skeletal improvement in FD patients.
Area of Science:
- Skeletal biology
- Bone remodeling
- Genetic disorders
Background:
- Fibrous dysplasia (FD) is a rare bone disorder caused by GNAS mutations.
- FD is characterized by defective osteogenic differentiation and increased bone remodeling.
- RANKL inhibition has shown promise in replacing FD lesions with bone.
Purpose of the Study:
- To elucidate the mechanism and pattern of new bone formation during RANKL inhibition in FD.
- To investigate the spatial organization of bone deposition in FD lesions under anti-RANKL treatment.
Main Methods:
- Morphological and molecular analyses were performed.
- EF1α-GsαR201C (FD) mice treated with an anti-mouse RANKL antibody were studied.
Main Results:
- RANKL inhibition reduced osteogenic gene expression but did not halt matrix production by osteoblastic cells.
- New bone formation occurred in an ordered spatial pattern, restricted to the surfaces of lesional bone.
- Bone formation was not diffuse or stochastic.
Conclusions:
- The amount of intra-lesional bone trabecular surfaces is critical for cell differentiation during RANKL inhibition.
- Surface-dependent bone deposition is a key factor for skeletal improvement in FD patients undergoing RANKL inhibition.
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