Parathyroid hormone regulates fates of murine osteoblast precursors in vivo
Deepak H. Balani, … , Noriaki Ono, Henry M. Kronenberg
Deepak H. Balani, … , Noriaki Ono, Henry M. Kronenberg
Published July 31, 2017
Citation Information: J Clin Invest. 2017;127(9):3327-3338. https://doi.org/10.1172/JCI91699.
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Research Article Bone biology

Parathyroid hormone regulates fates of murine osteoblast precursors in vivo

Abstract

Teriparatide, a recombinant form of parathyroid hormone (PTH), is the only approved treatment for osteoporosis that increases the rate of bone formation. Teriparatide increases osteoblast numbers by suppressing osteoblast apoptosis and activating bone-lining cells. No direct evidence for teriparatide’s actions on early cells of the osteoblast lineage has been demonstrated. Here, we have employed a lineage-tracing strategy that uses a tamoxifen-dependent, promoter-driven cre to mark early cells of the osteoblast lineage in adult mice. We show that teriparatide increases the numbers of osteoblast precursors and drives their differentiation into mature osteoblasts. Unexpectedly, following withdrawal of teriparatide therapy, bone marrow adipocytes increased dramatically in number. Some of these adipocytes derived from cells marked by Sox9-cre expression weeks earlier. Continued therapy with teriparatide prevented the appearance of adipocytes. Selective, inducible deletion of the PTH receptor in Sox9-cre cells demonstrated that PTH receptor expression is required for teriparatide-mediated increases in early osteoblast precursors. The increase in early precursors after teriparatide administration was associated with robust suppression of precursor apoptosis without affecting their rate of proliferation. Thus, teriparatide increases the numbers of early cells of the osteoblast lineage, hastens their differentiation into osteoblasts, and suppresses their differentiation into adipocytes in vivo.

Authors

Deepak H. Balani, Noriaki Ono, Henry M. Kronenberg

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Figure 2

Sox9-creERT2+ cells are undifferentiated mesenchymal precursors in adult mice in vivo.

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Sox9-creERT2+ cells are undifferentiated mesenchymal precursors in adul...
(A) Lineage tracing of adult Sox9-creERT2; R26RTomato mice was performed by injecting 2 mg tamoxifen (red arrow) into Sox9-creERT2; R26RTomato mice at P42. Each panel reflects data from 3 mice/genotype from 3 independent experiments. (B) Representative tibia from Sox9-creERT2; R26RTomato mice 2 days after tamoxifen administration. Sox9-creERT2; R26RTomato cells at P44 were seen as (no. 1) articular chondrocytes, (no. 2) growth plate chondrocytes, (no. 3) metaphysis, (no. 4) endocortical, and (no. 5) on periosteal surfaces. (C) Staining with anti-Sox9 Ab overlapped with tomato expression in the growth plate and, occasionally, in the metaphysis (arrows) of Sox9-creERT2; R26RTomato mice. Right, magnified image showing overlapping of TdTomato+ and anti-Sox9 Ab staining (arrows). (D) Quantitative RT-PCR of Sox9 transcript levels (normalized to Gapdh). Data represent mean ± SD from 3 independent experiments. Data were subjected to Bonferroni’s correction for multiple testing. ***P < 0.0001. (E) Representative section of tibia from Sox9-creERT2; R26RZsgreen1; Osx-mCherry mice. Note that most of the Osx-mCherry expression did not overlap with Zsgreen1 protein. (F and G) Representative sections of higher magnification confocal images of (G) metaphysis and (H) endocortical surface of tibia of Sox9-creERT2; R26RZsgreen1; Osx-mCherry mice, pointing to Sox9-creERT2; Zsgreen1+ cells in the metaphysis and endocortical surface that do not express osterix 2 days after tamoxifen (arrows). Sox9-creERT2; Zsgreen1+ cells ultimately gave rise to Osx-mCherry+ cells when followed for 3 weeks after tamoxifen-induced labeling (Supplemental Figure 1). (H–K) Representative flow cytometry dot plot analysis showing, on day 2, lack of overlap of Osx-mCherry+ cells with Sox9-creERT2; R26RTomato+ cells (H). Note that a fraction of nestin+ cells overlapped with Sox9-creERT2; Zsgreen1+ cells (I). A small fraction of CXCL12–GFP+ cells also overlapped with Sox9-creERT2; R26RTomato+ cells (J). No overlap was seen between Sox9-creERT2+ cells and Ocn-GFP+ cells (K). The data represent mean ± SD from 3 mice from 3 independent experiments. Scale bars: 500 μm (B); 100 μm (C (insert magnified 2×), E); 20 μm (F, G).