Lkb1 deletion in periosteal mesenchymal progenitors induces osteogenic tumors through mTORC1 activation
Yujiao Han, … , Tiebang Kang, Weiguo Zou
Yujiao Han, … , Tiebang Kang, Weiguo Zou
Published February 26, 2019
Citation Information: J Clin Invest. 2019;129(5):1895-1909. https://doi.org/10.1172/JCI124590.
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Research Article Bone biology Oncology

Lkb1 deletion in periosteal mesenchymal progenitors induces osteogenic tumors through mTORC1 activation

Abstract

Bone osteogenic sarcoma has a poor prognosis, as the exact cell of origin and the signaling pathways underlying tumor formation remain undefined. Here, we report an osteogenic tumor mouse model based on the conditional knockout of liver kinase b1 (Lkb1, also known as Stk11) in Cathepsin K–Cre–expressing (Ctsk-Cre–expressing) cells. Lineage-tracing studies demonstrated that Ctsk-Cre could label a population of periosteal cells. The cells functioned as mesenchymal progenitors with regard to markers and functional properties. LKB1 deficiency increased proliferation and osteoblast differentiation of Ctsk+ periosteal cells, while downregulation of mTORC1 activity, using a Raptor genetic mouse model or mTORC1 inhibitor treatment, ameliorated tumor progression of Ctsk-Cre Lkb1fllfl mice. Xenograft mouse models using human osteosarcoma cell lines also demonstrated that LKB1 deficiency promoted tumor formation, while mTOR inhibition suppressed xenograft tumor growth. In summary, we identified periosteum-derived Ctsk-Cre–expressing cells as a cell of origin for osteogenic tumor and suggested the LKB1/mTORC1 pathway as a promising target for treatment of osteogenic tumor.

Authors

Yujiao Han, Heng Feng, Jun Sun, Xiaoting Liang, Zhuo Wang, Wenhui Xing, Qinggang Dai, Yang Yang, Anjia Han, Zhanying Wei, Qing Bi, Hongbin Ji, Tiebang Kang, Weiguo Zou

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Figure 4

Ctsk-Cre–expressing periosteal mesenchymal stem cells are potential sources for osteogenic tumor.

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Ctsk-Cre–expressing periosteal mesenchymal stem cells are potential sou...
(A) Schematic of experiments on Rosa26-loxp-mTomato-stop-loxp-GFP (Rosa26-mT/mG) Cre reporter mice. (B) Confocal images of the tibiae of 4-week-old male LysM-Cre; Rosa26-mT/mG and Ctsk-Cre; Rosa26-m/TmG reporter mice showing that Ctsk-Cre; GFP (green), but not LysM-Cre; GFP (green) was expressed in the periosteum of cortical bone (indicated with the white arrow). Right panel: in Ctsk-CKO mice, Ctsk-positive cells at the periosteum expanded within the cortical bone. Scale bar: 50 μm. (C) Confocal images showing that the majority of the cells in the tumor region of 20-week-old male Ctsk-CKO; Rosa26-mT/mG mice are Ctsk-Cre; GFP–expressing cells (green). Scale bars: 300 μm (left); 50 μm (right). (D) Schematic of experiments on Rosa26-loxp-stop-loxp-tdTomato (Rosa26-Ai9) Cre reporter mice. (E) Images of 4-week-old male Ctsk-Ctrl; Rosa26-Ai9 and Ctsk-CKO; Rosa26-Ai9 tibiae showing expansion of Ctsk-Cre–expressing cells (red) in Ctsk-CKO mice. Scale bars: 300 μm (left): 20 μm (right). (F) Flow cytometry of cells from periosteum of 4-week-old male Ctsk-Ctrl; Rosa-Ai9 mice to identify expression of SSC markers CD105 and CD200 in Lin–CD90.2–6C3–Ctsk-Ai9+ cells. (G and H) Immunostaining of LKB1 showing that LKB1 (green) was conditionally deleted in Ctsk+ periosteal cells (red) from Ctsk-CKO; Rosa-Ai9 mice, but not in Ctsk-Ai9 cells of Ctsk-Ctrl; Rosa-Ai9 mice. Scale bar: 20 μm. (I and J) Immunostaining showing Ctsk-Cre–positive cells (red) in the cortical bone display osteoblast markers OSX (green), COL1A1 (green), and OPN (green) in the tibiae of 4-week-old male Ctsk-Ctrl; Rosa26-Ai9 and Ctsk-CKO; Rosa26-Ai9 mice (white arrow). Scale bar: 20 μm. (K) Ctsk-Ai9 cells isolated from the cortical bone of tibiae from Ctsk-Cre; Rosa26-Ai9 mice showed expression of osteoblastic markers OSX (green), COL1A1 (green), and OPN (green). Scale bar: 10 μm. Data are represented as mean ± SEM. *P < 0.05; **P < 0.01; ***P < 0.001, unpaired Student’s t test.