Possible effects of EXT2 on mesenchymal differentiation - lessons from the zebrafish

Orphanet Journal of Rare Diseases

Pancras C W Hogendoorn⁴  Zhe Zhao²  Karel W F Scheepstra⁴  Carlos E de Andrea¹  Malgorzata I Wiweger³ 

[1] Department of Histology and Pathology, University of Navarra, Pamplona, Spain;Nuffield Department of Medicine, Ludwig Institute for Cancer Research, University of Oxford, Oxford, UK;Current address: Zebrafish Core Facility, International Institute of Molecular and Cell Biology, Warsaw, Poland;Department of Pathology, Leiden University Medical Center, Leiden, The Netherlands

关键词: Bone tumour;    Differentiation;    Osteoblasts;    MHE/HME;    Exostosis;    Osteochondroma;    Fat;    Bone;    Heparan sulphate;    Zebrafish;   

Others  :  863234
DOI  :  10.1186/1750-1172-9-35

 received in 2013-10-18, accepted in 2014-02-10,  发布年份 2014

【 摘 要 】

Background

Mutations in the EXT genes disrupt polymerisation of heparan sulphates (HS) and lead to the development of osteochondroma, an isolated/sporadic- or a multifocal/hereditary cartilaginous bone tumour. Zebrafish (Danio rerio) is a very powerful animal model which has shown to present the same cartilage phenotype that is commonly seen in mice model and patients with the rare hereditary syndrome, Multiple Osteochondroma (MO).

Methods

Zebrafish dackel (dak) mutant that carries a nonsense mutation in the ext2 gene was used in this study. A panel of molecular, morphological and biochemical analyses was used to assess at what step bone formation is affected and what mechanisms underlie changes in the bone formation in the ext2 mutant.

Results

During bone development in the ext2^-/- zebrafish, chondrocytes fail to undergo terminal differentiation; and pre-osteoblasts do not differentiate toward osteoblasts. This inadequate osteogenesis coincides with increased deposition of lipids/fats along/in the vessels and premature adipocyte differentiation as shown by biochemical and molecular markers. Also, the ext2-null fish have a muscle phenotype, i.e. muscles are shorter and thicker. These changes coexist with misshapen bones. Normal expression of runx2 together with impaired expression of osterix and its master regulator - xbp1 suggest that unfolded protein responses might play a role in MO pathogenesis.

Conclusions

Heparan sulphates are required for terminal differentiation of the cartilaginous template and consecutive formation of a scaffold that is needed for further bone development. HS are also needed for mesenchymal cell differentiation. At least one copy of ext2 is needed to maintain the balance between bone and fat lineages, but homozygous loss of the ext2 function leads to an imbalance between cartilage, bone and fat lineages. Normal expression of runx2 and impaired expression of osterix in the ext2^-/- fish indicate that HS are required by osteoblast precursors for their further differentiation towards osteoblastic lineage. Lower expression of xbp1, a master regulator of osterix, suggests that HS affect the ‘unfolded protein response’, a pathway that is known to control bone formation and lipid metabolism. Our observations in the ext2-null fish might explain the musculoskeletal defects that are often observed in MO patients.

【 授权许可】

   
2014 Wiweger et al.; licensee BioMed Central Ltd.

【 图 表 】

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