The Pathogenesis of Osteochondroma: Clues from Tracing Proteoglycans in Zebrafish Models and Human Cartilage.
Carlos E de Andrea, Malgorzata I Wiweger, Frans A Prins, Pancras CW Hogendoorn. Leiden University Medical Center, Netherlands
Background: Proteoglycans (PGs) are extracellular modulators of protein gradient formation. In cartilage, the gradient of heparan sulfate PGs can either regulate endochondral ossification in the growth plate or, when disrupted, originate osteochondroma, the most common bone tumor at adolescences. PGs may be traced electron microscopically by polyethyleneimine (PEI), which binds their negatively charged sites, providing insights into tumor formation.
Design: Pre-embedding PEI was studied by electron- and reflection contrast microscopy in human growth plate, osteochondroma and five different proteoglycan-deficient zebrafish. dackel (dak;ext2) mutant, a fish homologue of human multiple osteochondromas, has decreased levels of heparan sulfate; hi307 (β3gat3) has reduced heparan and chondroitin sulfates; hi954 (uxs1) has impaired PGs biosynthesis; pinscher (pic;papst1) lacks sulfate groups; and knypek (kny;gpc4) lacks Glypican-4. Gradient formation was analyzed using the plot profile tool of ImageJ software.
Results: Electron-dense deposits of PEI were observed within the extracellular matrix of the human growth plate and wild-type zebrafish cartilage. In both instances, the plot profile showed gradient formation, in which the size and number of PEI aggregates decreased with the distance from the cell surface. A similar pattern was found in the hi307 and kny mutants. In the pic and hi954 mutants, no PEI aggregates were identified. In dak, a prominent reduction of PEI and no gradient formation were observed. In osteochondroma the majority of the chondrocytes established a normal gradient. However, 10% of the osteochondroma cells resembled dak-chondrocytes. The matrix surrounding these cells were virtually free of PEI and gradient reflecting areas inside the tumor where cell-cell interactions might be impaired by the reduction of PGs especially heparan sulfate.
Conclusions: Pre-embedding PEI in cartilage provides a significant advance towards the regulation of growth plate and the pathogenesis of osteochondroma and leads to the hypotheses: 1. Osteochondroma is a mosaic of normal and PGs deficient cells. 2. Growth plate chondrocytes harboring homozygous mutation in EXT1/2 genes might disrupt the diffusion gradients and signal transduction initiating tumor formation.
Category: Bone & Soft Tissue
Monday, February 28, 2011 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 10, Monday Morning