Research ArticleCELL BIOLOGY

Cyclooxygenase 2 augments osteoblastic but suppresses chondrocytic differentiation of CD90+ skeletal stem cells in fracture sites

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Science Advances  31 Jul 2019:
Vol. 5, no. 7, eaaw2108
DOI: 10.1126/sciadv.aaw2108
  • Fig. 1 Local COX-2 overexpression selectively increased the abundance and prolonged the presence of CD90+ mSSCs in the fractured bones.

    (A) B6 mice were subjected to femur fracture surgery (Fx). On the following day, animals received in fracture sites one of the following treatments (Tx): no treatment (No), a control AAV vector (Ctr), or the AAV.COX-2 vector (COX-2). On days 3, 4, 7 and 10 following the treatments, the fractured bones and contralateral intact bones were harvested and the MNCs were isolated as described in Materials and Methods. The isolated MNCs were analyzed by FACS. (B) Gating strategy. SSC, side scatter; FSC, forward scatter. (C) Representative FACS plots show the expressions of AlphaV (top), AlphaV and CD90 (middle), and AlphaV and 6C3 (bottom) among CD45Tie2 cells. (D) Cumulative data show the frequencies of CD90+ mSSCs on day 7 following the treatments. (E) Representative FACS plots show the expressions of CD90 and 6C3 among mSSCs. (F) Representative FACS plots show the expressions of AlphaV and CD90 among CD45Tie2 cells on days 3, 4, and 10 following the treatments. Where applicable, data are means ± SEM. **P < 0.01, ***P < 0.001, ****P < 0.0001, #not significant; n = 3 to 5.

  • Fig. 2 The increase in CD90+ mSSC abundance in fractured bones following local COX-2 overexpression depended on MCP-1.

    (A) B6 mice received femur fracture surgery and treatments as described in Fig. 1. On day 4 following the treatments, the fractured bones and contralateral intact bones were harvested and analyzed by RT-qPCR. Data are shown in (B). (B) Data show the expression of MCP-1 mRNA. GAPDH, glyceraldehyde-3-phosphate dehydrogenase. (C) B6 mice received femur fracture surgery. Beginning on the day of fracture surgery, the mice subcutaneously received a daily dose of either PBS or the neutralizing anti–MCP-1 mAb (anti–MCP-1, clone 2H5) near the fracture sites for three consecutive days (±mAb). In addition, on the day following the fracture surgery, half of the animals from each group received a treatment of a control AAV vector and the other half the AAV.COX-2 vector in fracture sites. On day 4 following the treatments, the fractured bones and contralateral intact bones were harvested and the MNCs were isolated for analyses by FACS. Data are shown in (D) and (E). (D) Representative FACS plots show the expression of CD90 among mSSCs. (E) Cumulative data show the frequencies of CD90+ mSSCs in the fractured bones. Where applicable, data are means ± SEM. **P < 0.01, ***P < 0.001, ****P < 0.0001; n = 3 to 5.

  • Fig. 3 CD90+ mSSCs isolated from COX-2–overexpressed fractured bones, when compared to controls, displayed significantly augmented and accelerated osteoblast differentiation in vitro.

    (A) B6 mice received femur fracture surgery and treatments as described in Fig. 1. On day 4 following the treatments, the fractured bones were harvested and the CD90+ mSSCs were purified as described in Materials and Methods. The purified CD90+ mSSCs were analyzed by RT-qPCR. Data are shown in (B). (B) Data show the mRNA expressions of the following genes: Runx2, OCN, OSX, BMP2, and ALP. (C) The purified CD90+ mSSCs in (A) were analyzed by FACS. Data show the frequencies of OSX+ and Runx2+ cells among the CD90+ mSSCs (left), as well as the MFIs of the expressions of OSX and Runx2 (right). (D) The purified CD90+ mSSCs in (A) were directly cultured in an osteoblast differentiation medium for 21 days. Data are representative images of the cultured cells stained with Alizarin Red. (E) The purified CD90+ mSSCs in (A) were first expanded in an MSC medium for 1 week and then cultured in the osteoblast differentiation medium for 21 days. Data are representative images of the cultured cells stained with Alizarin Red. (F) The purified CD90+ mSSCs in (A) were cultured in the osteoblast differentiation medium. On weeks 1, 2, and 3, the cultured cells were stained with Alizarin Red. Data show representative images of the cultured cells stained with Alizarin Red. (G) Data show the absorbance at 405 nm of solubilized Alizarin Red–stained cells in (F). Where applicable, data are means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; n = 3 to 5. Photo credit: Samiksha Wasnik, Loma Linda University.

  • Fig. 4 CD90+ mSSCs isolated from COX-2–overexpressed fractured bones, when compared to control-treated fractured bones, displayed significantly reduced chondrogenic differentiation in vitro.

    (A) B6 mice were subjected to femur fracture surgery and, on the following day, received one of the following treatments in the fracture sites: a control vector and the AAV.COX-2 vector. Four days later, the fractured bones were harvested and CD90+ mSSCs and CD90 mesenchymal cells were purified for analyses by RT-qPCR and an in vitro chondrogenesis assay. Data are shown in (B) and (C). (B) The mRNA expressions of Sox9, Nkx3.2, and Col2a1 in the cells purified in (A) are shown. (C) A total of 5.0 × 104 CD90+ mSSCs purified in (A) were seeded in 24-well tissue culture plates for a chondrogenic micromass culture for 21 days as described in Materials and Methods. Representative images of Alcian blue staining are shown. (D) B6 mice were subjected to femur fracture surgery and received vector treatments as described in (A). Four days later, the fractured bones were harvested and the MNCs were purified for analyses by FACS. Data are shown in (E) and (F). (E) Representative FACS histograms show CD200+ cells among CD90+ mSSCs. (F) Cumulative data of (E) show the percentage of CD200+ cells among CD90+ mSSCs (left) and the percentage of CD200 cells among CD90+ mSSCs (right). Where applicable, data are means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001; n = 3 to 5.

  • Fig. 5 Blocking of WNT/β-catenin signaling pathway completely abolished COX-2 overexpression–mediated augmentation of CD90+ mSSC osteoblast differentiation potential in fractured bones.

    (A) B6 mice were subjected to femur fracture surgery and, on the second day, received one of the following treatments in the fracture sites: a control AAV vector and the AAV.COX-2 vector. Four days after the fracture surgery, the fractured bones were collected and the CD90+ mSSCs were purified as described in Materials and Methods. The purified CD90+ mSSCs were analyzed by RT-qPCR. Data are shown in (B). (B) mRNA expressions of WNT ligands (WNT3a and WNT7a; top), WNT signaling molecules (β-catenin, TCF-1, and TCF-3; middle), and negative regulators of WNT signaling (Axin-2 and SOST; bottom). (C) B6 mice were subjected to femur fracture surgery and, beginning on the same day, subcutaneously received a daily dose of either vehicle (VC) or ICG001 (an inhibitor for WNT/β-catenin/TCF-mediated transcription) near fracture sites until bones were harvested. On the second day following the fracture surgery, half of the animals in each group received a control AAV vector and the other half received the AAV.COX-2 vector in the fracture sites. Four days after the fracture surgery, the fractured bones were harvested and the CD90+ mSSCs were purified. The purified CD90+ mSSCs were analyzed by RT-qPCR and an in vitro nodule assay. Data are shown in (D) to (F). (D) Data show the mRNA expression of β-catenin. (E) Data show mRNA expressions of the genes necessary for bone formation, i.e., Runx2, OSX, and OCN. (F) Data show representative images of CD90+ mSSCs that were cultured in the osteoblast differentiation medium for 14 and 21 days and stained with Alizarin Red. Where applicable, data are means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; n = 3 to 5. Photo credit: Samiksha Wasnik, Loma Linda University.

  • Fig. 6 Local COX-2 overexpression targeted CD90+ mSSCs to accelerate bone repair.

    (A) B6 mice were subjected to tibial fracture surgery. Immediately after the fracture surgery and on the following two consecutive days, the animals subcutaneously received a daily dose of either PBS or the depleting anti-CD90 mAb (clone 30H12) near fracture sites (±mAb). The Ab doses were 200, 100, and 100 μg on days 0, 1, and 2, respectively. Ten days after the fracture surgery, the fractured bones were harvested and the MNCs were isolated for analysis of the expressions of CD90 and CD11b by FACS. Data are shown in (B). (B) Representative FACS plots show the frequencies of CD90+ and CD11b+ cells. (C) B6 mice were subjected to tibial fracture surgery and received either PBS or the clone 30H12 (mAb) as described in (A). In addition, on the second day following the fracture surgery, half of the animals that were administered with PBS or the clone 30H12 received no treatment and the other half received the AAV.COX-2 vector in the fracture sites. In addition, a group of animals that received only a control AAV vector in fracture sites was also included as a control. On days 4, 10, and 21, the fractured bones were examined by x-ray. On day 21, the fractured bones were harvested and analyzed by micro-computed tomography (μCT). Data are shown in (D) to (G). (D) Representative x-ray images on day 21 are shown (the contours indicate callus sizes). (E) The callus sizes were quantified by an imaging software. Data show the cumulative callus areas of five mice in each group. (F) The following parameters of new bone formation from the μCT analysis are shown: connectivity density (Conn. density), bone volume/volume of interest (BV/TV), bone mineral density (BMD), trabecular number (DT-Tb.N), trabecular thickness (DT-Tb.Th), and trabecular space (DT-Tb.sp). (G) Representative reconstructed three-dimensional images are shown. Where applicable, data are means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001; n = 3 to 5.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/7/eaaw2108/DC1

    Table S1. Primers used in this study.

    Fig. S1. CD90+ MSCs were preferentially recruited into fractured bones from progenitor niches near fracture sites.

    Fig. S2. Soluble factors, secreted by COX-2–transduced cells, augmented the proliferation and CD90+ conversion of CD90 MSCs.

    Fig. S3. CD90+ mSSCs purified from fractured bones were stable for at least 3 weeks in culture, expressed common MSC markers, and differentiated into osteoblasts in fracture sites.

    Fig. S4. Effects of COX-2 signaling blockade on the osteogenic potential of CD90+ mSSCs.

    Fig. S5. COX-2 overexpression in fracture sites augmented local expression of WNT ligands.

    Fig. S6. Local COX-2 overexpression reduced callus sizes, and this effect was abolished by the administration of the anti-CD90 mAb 30H12 (see Fig. 6 for details of experimental designs).

    Fig. S7. A model for COX-2 overexpression–mediated acceleration of bone repair.

    Fig. S8. Delivery of vectors into fracture sites.

  • Supplementary Materials

    This PDF file includes:

    • Table S1. Primers used in this study.
    • Fig. S1. CD90+ MSCs were preferentially recruited into fractured bones from progenitor niches near fracture sites.
    • Fig. S2. Soluble factors, secreted by COX-2–transduced cells, augmented the proliferation and CD90+ conversion of CD90 MSCs.
    • Fig. S3. CD90+ mSSCs purified from fractured bones were stable for at least 3 weeks in culture, expressed common MSC markers, and differentiated into osteoblasts in fracture sites.
    • Fig. S4. Effects of COX-2 signaling blockade on the osteogenic potential of CD90+ mSSCs.
    • Fig. S5. COX-2 overexpression in fracture sites augmented local expression of WNT ligands.
    • Fig. S6. Local COX-2 overexpression reduced callus sizes, and this effect was abolished by the administration of the anti-CD90 mAb 30H12 (see Fig. 6 for details of experimental designs).
    • Fig. S7. A model for COX-2 overexpression–mediated acceleration of bone repair.
    • Fig. S8. Delivery of vectors into fracture sites.

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