PTH regulates osteogenesis and suppresses adipogenesis through Zfp467 in a feed-forward, PTH1R-cyclic AMP-dependent manner.

Abstract

Conditional deletion of the PTH1R in mesenchymal progenitors reduces osteoblast differentiation, enhances marrow adipogenesis, and increases zinc finger protein 467 (<i>Zfp467</i>) expression. In contrast, genetic loss of <i>Zfp467</i> increased <i>Pth1r</i> expression and shifts mesenchymal progenitor cell fate toward osteogenesis and higher bone mass. PTH1R and ZFP467 could constitute a feedback loop that facilitates PTH-induced osteogenesis and that conditional deletion of <i>Zfp467</i> in osteogenic precursors would lead to high bone mass in mice. <i>Prrx1Cre; Zfp467^fl/fl</i> but not <i>AdipoqCre; Zfp467^fl/fl</i> mice exhibit high bone mass and greater osteogenic differentiation similar to the <i>Zfp467</i>^-/- mice. qPCR results revealed that PTH suppressed <i>Zfp467</i> expression primarily via the cyclic AMP/PKA pathway. Not surprisingly, PKA activation inhibited the expression of <i>Zfp467</i> and gene silencing of <i>Pth1r</i> caused an increase in <i>Zfp467</i> mRNA transcription. Dual fluorescence reporter assays and confocal immunofluorescence demonstrated that genetic deletion of <i>Zfp467</i> resulted in higher nuclear translocation of NFκB1 that binds to the P2 promoter of the <i>Pth1r</i> and increased its transcription. As expected, <i>Zfp467</i>^-/- cells had enhanced production of cyclic AMP and increased glycolysis in response to exogenous PTH. Additionally, the osteogenic response to PTH was also enhanced in <i>Zfp467</i>^-/- COBs, and the pro-osteogenic effect of <i>Zfp467</i> deletion was blocked by gene silencing of <i>Pth1r</i> or a PKA inhibitor. In conclusion, our findings suggest that loss or PTH1R-mediated repression of <i>Zfp467</i> results in a pathway that increases <i>Pth1r</i> transcription via NFκB1 and thus cellular responsiveness to PTH/PTHrP, ultimately leading to enhanced bone formation.