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Gli1+ progenitors mediate bone anabolic function of teriparatide via Hh and Igf signaling

ABSTRACT: Teriparatide, a bioactive fragment of human parathyroid hormone (PTH), is the most widely prescribed bone anabolic drug in the world, but its cellular targets remain incompletely defined. The Gli1+ metaphyseal mesenchymal progenitors (MMPs) are a main source for osteoblasts in postnatal growing mice, but their potential response to teriparatide is unknown. Here, by lineage tracing we find that teriparatide stimulates both proliferation and osteoblast differentiation of MMPs. Single-cell RNA sequencing reveals heterogeneity among MMPs including a chondrocyte-like osteoprogenitor (herein COP) population that expands in response to teriparatide. COPs express the highest level of Hedgehog (Hh) target genes and the insulin-like growth factor receptor Igf1r. Inhibition of Hh signaling, or selective deletion of Igf1r in MMPs diminishes the proliferative and osteogenic effects of teriparatide. The study therefore identifies MMPs as teriparatide target cells wherein Hh and Igf signaling are critical for osteoblast production.

ORGANISM(S): Mus musculus

PROVIDER: GSE169560 | GEO | 2021/06/06

REPOSITORIES: GEO

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Project description:Osteoporosis affects over 200 million women worldwide, one third of whom are predicted to suffer from an osteoporotic fracture in their lifetime. The most promising anabolic drugs involve administration of expensive antibodies. Because mechanical loading stimulates bone formation, our current data, using a mouse model, replicates the anabolic effects of loading in humans and may identify novel pathways amenable to oral treatment. Murine tibial compression produces axially-varying deformations along the cortical bone, inducing highest strains at the mid-diaphysis and lowest at the metaphyseal shell. To test the hypothesis that load-induced transcriptomic responses at different axial locations of cortical bone would vary as a function of strain magnitude, we loaded the left tibiae of 10wk female C57Bl/6 mice in vivo in compression, with contralateral limbs as controls. Animals were euthanized at 1, 3 or 24 h post-loading or loaded for 1 wk (n=4-5/group). Bone marrow and cancellous bone were removed, cortical bone was segmented into the metaphyseal shell, proximal diaphysis and mid-diaphysis, and load-induced differential gene expression and enriched biological processes were examined for the three segments. At each time point, the mid-diaphysis (highest strain) had the greatest transcriptomic response. Similarly, biological processes regulating bone formation and turnover increased earlier and to the greatest extent at the mid-diaphysis. Higher strain induced greater levels of osteoblast and osteocyte genes, whereas expression was lower in osteoclasts. Among the top differentially-expressed genes at 24-hours post-loading, seventeen had known functions in bone biology, of which twelve were present only in osteoblasts, three exclusively in osteoclasts, and two were present in both cell types. Based on these results, we conclude that murine tibial loading induces spatially-unique transcriptomic responses correlating with strain magnitude in cortical bone.

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Gli1+ progenitors mediate bone anabolic function of teriparatide via Hh and Igf signaling

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