Abstract
Fibrous Dysplasia/McCune-Albright Syndrome (FD/MAS) is a rare skeletal disorder caused by somatic activating mutations in the GNAS gene, encoding the Gsα subunit of G-protein-coupled receptors. These mutations lead to constitutive activation of adenylyl cyclases, resulting in persistently elevated cyclic adenosine monophosphate (cAMP) levels and dysregulated intracellular signaling. Consequently, osteogenic differentiation is impaired, leading to structurally weak, fibrotic bone lesions. Current treatments, including bisphosphonates and surgical interventions, primarily address symptoms rather than the underlying molecular pathology, highlighting the need for targeted therapeutic strategies.This study aimed to establish a reproducible in vitro model of FD/MAS by overexpressing GNAS mutant variants (R201C and R201H) in human bone marrow-derived mesenchymal stromal cells (MSCs) and investigate the role of autocrine and paracrine signaling in FD/MAS pathophysiology. We found that mutant MSCs exhibit impaired mineralization, suggesting intrinsic defects in osteogenic differentiation. However, paracrine signaling from mutant MSCs to unmodified MSCs enhanced mineralization of normal MSCs, indicating that secreted factors influence the osteogenic microenvironment. Co-culture experiments further demonstrated a dominant-negative effect of mutant MSCs on normal osteoblast progenitors in a dose-dependent manner, reinforcing the concept that mutational load dictates FD/MAS lesion severity.
To explore potential therapeutic interventions, we screened compounds identified through high-throughput screening and artificial intelligence-driven computational modeling that selectively target cAMP signaling. Our screening revealed variability in efficacy, with limited specificity for mutant GNAS variants, emphasizing the complexity of modulating cAMP levels in FD/MAS. This study provides novel insights into FD/MAS pathology by elucidating the interplay between mutant and normal MSCs and their role in bone remodeling. These findings establish a crucial framework for developing targeted therapies aimed at restoring normal osteogenic function and improving skeletal integrity in FD/MAS patients.