Gsα Controls Cortical Bone Quality by Regulating Osteoclast Differentiation via cAMP/PKA and β-Catenin Pathways

Abstract

Skeletal bone formation and maintenance requires coordinate functions of several cell types, including bone forming osteoblasts and bone resorbing osteoclasts. Gsα, the stimulatory subunit of heterotrimeric G proteins, activates downstream signaling through cAMP and plays important roles in skeletal development by regulating osteoblast differentiation. Here, we demonstrate that Gsα signaling also regulates osteoclast differentiation during bone modeling and remodeling. Gnas, the gene encoding Gsα, is imprinted. Mice with paternal allele deletion of Gnas (Gnas+/p−) have defects in cortical bone quality and strength during early development (bone modeling) that persist during adult bone remodeling. Reduced bone quality in Gnas+/p− mice was associated with increased endosteal osteoclast numbers, with no significant effects on osteoblast number and function. Osteoclast differentiation and resorption activity was enhanced in Gnas+/p− cells. During differentiation, Gnas+/p− cells showed diminished pCREB, β-catenin and cyclin D1, and enhanced Nfatc1 levels, conditions favoring osteoclastogenesis. Forskolin treatment increased pCREB and rescued osteoclast differentiation in Gnas+/p− by reducing Nfatc1 levels. Cortical bone of Gnas+/p− mice showed elevated expression of Wnt inhibitors sclerostin and Sfrp4 consistent with reduced Wnt/β-catenin signaling. Our data identify a new role for Gsα signaling in maintaining bone quality by regulating osteoclast differentiation and function through cAMP/PKA and Wnt/β-catenin pathways.

Multi-omics Data Integration for Identifying Osteoporosis Biomarkers and Their Biological Interaction and Causal Mechanisms

“…The GNAS gene is a complex imprinted locus that produces multiple transcripts (such as Gsa, XLAS, NESP55) through the use of alternative promoters and alternative splicing. A recent study by Ramaswamy et al (Ramaswamy et al, 2017) demonstrated that Gnas inactivation in mice negatively affects cortical bone quality and strength, with mutation of the paternal allele causing more severe effects than maternal mutations. These effects of Gsa deletion on bone maintenance were exerted through enhanced osteoclast differentiation and increased bone resorption, mediated by Gsa signaling via cAMP/PKA and WNT/b-catenin pathways (Ramaswamy et al, 2017).…”

“…A recent study by Ramaswamy et al (Ramaswamy et al, 2017) demonstrated that Gnas inactivation in mice negatively affects cortical bone quality and strength, with mutation of the paternal allele causing more severe effects than maternal mutations. These effects of Gsa deletion on bone maintenance were exerted through enhanced osteoclast differentiation and increased bone resorption, mediated by Gsa signaling via cAMP/PKA and WNT/b-catenin pathways (Ramaswamy et al, 2017). SMYD3 encodes a histone methyltransferase that functions in RNA polymerase II complexes by an interaction with a specific RNA helicase (Hamamoto et al, 2004) and controls a WNT-responsive epigenetic switch (Wang et al, 2018).…”

HDAC8, A Potential Therapeutic Target, Regulates Proliferation and Differentiation of Bone Marrow Stromal Cells in Fibrous Dysplasia

“…cAMP activation and phosphorylation of CREB in osteoblasts play important roles in skeletal development by regulating osteoblast differentiation . Additionally, CREB, acting as a potent trans‐activating factor, promotes gene transcription although p‐CREB binding to the promoter regions of target genes.…”

Ablation of Gsα signaling in osteoclast progenitor cells adversely affects skeletal bone maintenance

“…In additional to osteoblasts and osteogenesis, cAMP/PKA signaling has also been shown to regulate osteoclastogenesis, and other pathways such as Wnt/β-catenin and calmodulin-dependent kinase have been shown to act as upstream regulators of this process[9,10]. Using a mouse model with heterozygous germline inactivation of Gsα, we demonstrated that Gsα maintains bone quality by regulating osteoclast differentiation and bone resorption activity [11]. However, given that the mouse model used globally reduced Gsα expression, we could not distinguish the contributions of a cell-autonomous role of Gsα in osteoclasts versus additional cell types.…”