G protein inhibitory alpha subunits 1 and 3 regulate Wnt/beta-catenin signaling to promote osteogenesis and bone formation.

The Wnt/β-catenin signaling pathway is a classical pathway that regulates bone metabolism. The G protein inhibitory α subunits 1 and 3 (Gαi1/3) can couple with multiple growth factor/cytokine receptors and act as universal adaptor proteins to mediate the activation of key downstream signaling pathways. However, it remains unclear whether and how Gαi1/3 proteins mediate Wnt/β-catenin signal transduction. In this study, we utilized single-cell sequencing analysis and employed viral transfection and gene editing techniques to alter the expression of Gαi1/3 in mouse embryonic osteoblast precursor cells. We examined the relationship between Gαi1/3 expression and the Wnt/β-catenin signaling pathway. Immunoprecipitation and confocal experiments were conducted to further explore the mechanisms by which Gαi1/3 exerts its functions. Osteogenic-related protein levels were detected by Western blotting, and the effects of Gαi1/3 proteins on osteogenic function were examined through alkaline phosphatase and Alizarin red staining. Additionally, micro-CT was used to compare bone mass in mice with different levels of Gαi1/3 expression, showing the relationship between Gαi1/3 and bone formation. Our findings indicate that Gαi1/3 proteins are significantly inversely correlated with age. Gαi1/3, rather than Gαi2, mediates the Wnt/β-catenin signaling pathway and promotes osteogenesis. Mechanistically, Gαi1/3 interacts with Axin1 and recruits it to the cell membrane, leading to inactivation of the β-catenin degradation complex. This results in β-catenin accumulation and nuclear translocation, where it activates the transcription of osteogenic genes. In vivo experiments further confirm that knockdown of Gαi1/3 significantly inhibits bone formation in mice. Our study identified Gαi1/3 as key regulatory proteins in Wnt/β-catenin signaling-mediated osteogenesis, and further elucidated its molecular mechanism in bone formation, which may provide a new therapeutic target for osteoporosis.