Aberrant perichondrial BMP signaling mediates multiple osteochondromagenesis in mice
Toshihiro Inubushi, Satoshi Nozawa, Kazu Matsumoto, Fumitoshi Irie, Yu Yamaguchi
Toshihiro Inubushi, Satoshi Nozawa, Kazu Matsumoto, Fumitoshi Irie, Yu Yamaguchi
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Research Article Bone biology

Aberrant perichondrial BMP signaling mediates multiple osteochondromagenesis in mice

Abstract

Multiple hereditary exostoses (MHE) is characterized by the development of numerous benign bony tumors (osteochondromas). Although it has been well established that MHE is caused by mutations in EXT1 and EXT2, which encode glycosyltransferase essential for heparan sulfate (HS) biosynthesis, the cellular origin and molecular mechanisms of MHE remain elusive. Here, we show that in Ext1 mutant mice, osteochondromas develop from mesenchymal stem cell–like progenitor cells residing in the perichondrium, and we show that enhanced BMP signaling in these cells is the primary signaling defect that leads to osteochondromagenesis. We demonstrate that progenitor cells in the perichondrium, including those in the groove of Ranvier, highly express HS and that Ext1 ablation targeted to the perichondrium results in the development of osteochondromas. Ext1-deficient perichondrial progenitor cells show enhanced BMP signaling and increased chondrogenic differentiation both in vitro and in vivo. Consistent with the functional role for enhanced BMP signaling in osteochondromagenesis, administration of the small molecule BMP inhibitor LDN-193189 suppresses osteochondroma formation in two MHE mouse models. Together, our results demonstrate a role for enhanced perichondrial BMP signaling in osteochondromagenesis in mice, and they suggest the possibility of pharmacological treatment of MHE with BMP inhibitors.

Authors

Toshihiro Inubushi, Satoshi Nozawa, Kazu Matsumoto, Fumitoshi Irie, Yu Yamaguchi

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Figure 5

Pharmacological inhibition of BMP with LDN-193189 suppresses osteochondromagenesis in Col2a1-Ext1CKO mice.

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Pharmacological inhibition of BMP with LDN-193189 suppresses osteochondr...
Col2a1-Ext1CKO mice were treated with LDN-193189 as described in Methods. (A) Whole-mount skeletal preparations of the rib cage and the forelimb of LDN-193189- and vehicle-treated mice. LDN-193189 suppresses osteochondroma formation in rib bones (arrows) and cartilage overgrowth in the wrist joint area (white brackets). Swelling of the chondro-osseous junction are also mitigated. Data shown are representative images of 10 animals per genotype. Specimens of WT control (Ext1flox/flox; WT) mice are shown for comparison. (B) Quantitative assessment of the effect of LDN-193189. Treatment with LDN-193189 reduced the number of osteochondromas in rib bones and the length of cartilage overgrowth between the radius and ulna. Body weight and the longitudinal growth of the radius were not affected. Means ± SD (n = 10 for the number of osteochondroma and body weight; n = 6 for the size of cartilage overgrowth and the length of the radius) were shown as horizontal bars. **P < 0.01 by Student’s t test. (C) Safranin O–stained sections of the wrist joint area (top), the groove of Ranvier (middle), and the chondro-osseous junction of a rib bone (bottom). In LDN-193189–treated animals, the size of cartilage overgrowth between the radius and ulna is reduced (top panels) and the disorganization of perichondrium/cartilage boundaries in the groove of Ranvier and in the rib bone is reduced (middle and bottom panels). Representative images were obtained from at least 3 mice per genotype. (D) Effects of LDN-193189 on BMP signaling in situ. pSmad1/5/8 immunoreactivity in the overgrown cartilage (indicated by broken lines) is reduced in LDN-193189–treated animals compared with vehicle-treated animals. The bar graph shows the ratio of the number of pSmad1/5/8-immunoreactive cells relative to the total number of cells determined by TO-PRO-3 staining. Means ± SD (n = 8) are shown as horizontal bars. **P < 0.01 by Student’s t test. The representative images were shown. Scale bars: 1 mm (A); 0.1 mm (C, D).