Objective: Spondyloepiphyseal dysplasia tarda with progressive arthropathy (SEDT-PA) is an autosomal-recessive hereditary disorder of cartilage homeostasis. The pathogenesis of SEDT-PA is unknown though it has been demonstrated that CCN6 is the SEDT-PA causing gene. The present study characterized the biologic behaviors and cDNA differential expression profile of articular chondrocytes in SEDT-PA.
Methods: The morphologic and functional features of growth, proliferation, differentiation and DNA synthesis of SEDT-PA chondrocytes were determined with cell growth curve, (3)H-TDR incorporation, MTT and flow cytometry. cDNA differential expression profile was carried out with gene microarray containing 8000 genes. Differentially expressed genes were verified by RT-PCR, Western blot and immunohistochemistry.
Results: As compared with normal control, the variant chondrocytes were much larger in size with an enhanced ability of proliferation and DNA synthesis and increased ratio of G(2)-M (10.72% vs 0.11%) to S phases (37.0% vs 15.8%). Matrix metalloproteinases (MMPs), which decompose the extra-cellular matrix of the cartilage, accumulated at the endochylema and failed in exocytosis, which lead to the negative feedback of the mRNA transcriptions. The mRNA expression of MMPs was down-regulated. At the same time, the mRNA expression of genes related to cell growth, proliferation and progression of cell cycles were up-regulated, while most of those associated with extracellular matrix, non-collagen proteins and poly-proteoglycans were down-regulated.
Conclusions: The accumulation and failure in exocytosis of the MMPs decompose the extra-cellular matrix of the cartilage. The decreased expression of matrix proteins and polyproteoglycans is involved in the pathogenesis of arthropathy resulted from CCN6 mutation.