Targeting phosphatidylinositol-3-kinase for inhibiting maxillary bone resorption

Previous studies have suggested a role of phosphatidylinositol-3-kinase gamma (PI3K gamma) in bone remodeling, but the mechanism remains undefined. Here, we explored the contribution of PI3K gamma in the resorption of maxillary bone and dental roots using models of orthodontic tooth movement (OTM), orthodontic-induced inflammatory root resorption, and rapid maxillary expansion (RME). PI3K gamma-deficient mice (PI3K gamma(-/-)), mice with loss of PI3K gamma kinase activity (PI3K gamma(KD/KD)) and C57BL/6 mice treated with a PI3K gamma inhibitor (AS605240) and respective controls were used. The maxillary bones of PI3K gamma(-/-), PI3K gamma(KD/KD), and C57BL/6 mice treated with AS605240 showed an improvement of bone quality compared to their controls, resulting in reduction of the OTM and RME in all experimental groups. PI3K gamma(-/-) mice exhibited increased root volume and decreased odontoclasts counts. Consistently, the pharmacological blockade or genetic deletion of PI3K resulted in increased numbers of osteoblasts and reduction in osteoclasts during OTM. There was an augmented expression of Runt-related transcription factor 2 (Runx2) and alkaline phosphatase (Alp), a reduction of interleukin-6 (Il-6), as well as a lack of responsiveness of receptor activator of nuclear factor kappa-Beta (Rank) in PI3K gamma(-/-) and PI3K gamma(KD/KD) mice compared to control mice. The maxillary bones of PI3K gamma(-/-) animals showed reduced p-Akt expression. In vitro, bone marrow cells treated with AS605240 and cells from PI3K gamma(-/-) mice exhibited significant augment of osteoblast mineralization and less osteoclast differentiation. The PI3K gamma/Akt axis is pivotal for bone remodeling by providing negative and positive signals for the differentiation of osteoclasts and osteoblasts, respectively.