4PBA reduces growth deficiency in osteogenesis imperfecta by enhancing transition of hypertrophic chondrocytes to osteoblasts
Amanda L. Scheiber, Kevin J. Wilkinson, Akiko Suzuki, Motomi Enomoto-Iwamoto, Takashi Kaito, Kathryn S.E. Cheah, Masahiro Iwamoto, Sergey Leikin, Satoru Otsuru
Amanda L. Scheiber, Kevin J. Wilkinson, Akiko Suzuki, Motomi Enomoto-Iwamoto, Takashi Kaito, Kathryn S.E. Cheah, Masahiro Iwamoto, Sergey Leikin, Satoru Otsuru
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Research Article Bone biology Cell biology

4PBA reduces growth deficiency in osteogenesis imperfecta by enhancing transition of hypertrophic chondrocytes to osteoblasts

Abstract

Short stature is a major skeletal phenotype in osteogenesis imperfecta (OI), a genetic disorder mainly caused by mutations in genes encoding type I collagen. However, the underlying mechanism is poorly understood, and no effective treatment is available. In OI mice that carry a G610C mutation in COL1A2, we previously found that mature hypertrophic chondrocytes (HCs) are exposed to cell stress due to accumulation of misfolded mutant type I procollagen in the endoplasmic reticulum (ER). By fate mapping analysis of HCs in G610C OI mice, we found that HCs stagnate in the growth plate, inhibiting translocation of HC descendants to the trabecular area and their differentiation to osteoblasts. Treatment with 4-phenylbutyric acid (4PBA), a chemical chaperone, restored HC ER structure and rescued this inhibition, resulting in enhanced longitudinal bone growth in G610C OI mice. Interestingly, the effects of 4PBA on ER dilation were limited in osteoblasts, and the bone fragility was not ameliorated. These results highlight the importance of targeting HCs to treat growth deficiency in OI. Our findings demonstrate that HC dysfunction induced by ER disruption plays a critical role in the pathogenesis of OI growth deficiency, which lays the foundation for developing new therapies for OI.

Authors

Amanda L. Scheiber, Kevin J. Wilkinson, Akiko Suzuki, Motomi Enomoto-Iwamoto, Takashi Kaito, Kathryn S.E. Cheah, Masahiro Iwamoto, Sergey Leikin, Satoru Otsuru

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Figure 2

Hypertrophic chondrocytes stagnate in the growth plate in G610C mice.

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Hypertrophic chondrocytes stagnate in the growth plate in G610C mice. (A...
(A) μCT analysis of femora from female G610C OI mice and female WT littermates at 3 weeks of age (n = 4 mice per group, 2-tailed Student’s t test). (B) Representative images of femoral sections from Col10a1-Cre;Ai9;Col1a1 2.3-GFP and Col10a1-Cre;Ai9;Col1a1 2.3-GFP;G610C mice at 3 weeks of age. The white boxes are enlarged in the right panels. Green osteoblasts are indicated by white asterisks. Scale bars: 500 μm. (C) Percentage of HC-derived cells (red + yellow cells) in the trabecular area relative to those in Col10a1-Cre;Ai9;Col1a1 2.3-GFP mice in B (n = 5 mice per group, P = 0.001, 2-tailed Student’s t test). (D) Percentage of HC-derived osteoblasts (100% × [yellow cells]/[red + yellow cells]) in the trabecular area in B (n = 5 mice per group, P < 0.001, 2-tailed Student’s t test). (E) Percentage of TUNEL-positive apoptotic cells in HCs (WT, n = 3 mice; G610C, n = 4 mice; P = 0.014; 2-tailed Student’s t test). (F) Representative images of the tibial growth plate/primary spongiosa area labeled with calcein and alizarin red. Scale bar: 100 μm. (G) Quantification of mineralized area in the hypertrophic zone indicated by white brackets in F (WT, n = 5 mice; G610C, n = 6 mice; P = 0.014; 2-tailed Student’s t test). (H) Height of newly formed primary spongiosa during the interval between calcein and alizarin red injections (47 hours) indicated by double arrows in F (WT, n = 5 mice; G610C, n = 6 mice; P = 0.002; 2-tailed Student’s t test). Data are shown as mean ± SEM.