Purpose: Mucopolysaccharidosis (MPS) VII is a genetic, lysosomal storage disease characterized by abnormal accumulation of glycosaminoglycans in cells and tissues. MPS VII patients exhibit multiple failures of endochondral ossification during postnatal growth, including markedly delayed cartilage-to-bone conversion in the vertebrae and long bones. Cartilage canals provide the template for vascularization at the onset of secondary ossification. The objective of this study was to investigate whether abnormal cartilage canal architecture and enzyme-mediated extracellular matrix (ECM) remodeling contribute to delayed cartilage-to-bone conversion in MPS VII. Materials and Methods: The epiphyseal cartilage canal networks of 9-day-old healthy control and MPS VII-affected dog vertebrae were characterized using high-resolution, contrast-free quantitative susceptibility mapping magnetic resonance imaging. Relative expression levels of matrix metalloproteinases (MMPs) 9, 13 and 14 were examined using immunohistochemistry, while tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP) were examined using in situ enzyme staining. Results: Interestingly, the density, number, connectivity and thickness of cartilage canals was not significantly different between MPS VII and control vertebrae. Immunohistochemistry revealed diminished MMP-9, but normal MMP-13 and 14 expression by epiphyseal cartilage chondrocytes, while ALP and TRAP enzyme expression by chondrocytes and chondroclasts, respectively, were both diminished in MPS VII. Conclusions: Our findings suggest that while the epiphyseal cartilage canal network in MPS VII is normal at the onset of secondary ossification, expression of enzymes required for cartilage resorption and replacement with mineralized ECM, and initiation of angiogenesis, is impaired.
Bibliographical noteFunding Information:
Funding for this work was received from the National Institutes of Health (R01AR071975 and K01AR070894), the National MPS Society, and the WM Keck Foundation. Additional support was received from the Penn Center for Musculoskeletal Disorders Histology and MicroCT Cores (NIH P30AR069619). Animal care provided by staff at the Penn Referral Center for Animal Models (NIH P40OD010939) is gratefully acknowledged. Special thanks to Dr Kai D. Ludwig for providing the Frangi filtering code.
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- cartilage canals
- endochondral ossification
- lysosomal storage disorder
- magnetic resonance imaging
- quantitative susceptibility mapping
PubMed: MeSH publication types
- Journal Article