Cartilage collagen fibril network in newborn transgenic mice analyzed by electron microscopic stereology

The objective was to investigate by electron microscopic stereology the properties of the cartilage collagen fibril network in newborn transgenic mice. The mice harbored transgenes targeted to affect the structure or assembly of the collagen fibrils. The mouse lines investigated here harbored either (i) one or (ii) two human COL2A1 genes with Arg519Cys mutation in addition to one or (iii) no active allele(s) of the murine COL2A1 gene, (iv) two inactive alleles of the procollagen N-proteinase genes, or (v) a human COL2A1 gene with deleted exons 16-27. In all newborn mice carrying the COL2A1 transgene with Arg519Cys mutation, the growth plate collagen fibrils were thinner than in the wild-type (wt) mice and showed clearly reduced volume fraction of the fibril network. In mice with the inactive procollagen N-proteinase genes, the fibril thickness and the volume fraction of collagen did not differ from the wt mice. In mice harboring the transgene of human COL2A1 gene with internally deleted exons 16-27, the collagen fibril diameter remained the same, but the volume density of collagen network was reduced. Using the indirect stereology, the differences in the collagen fibril stereological estimates could be reliably detected in newborn mice harboring mutations that affect the structure and assembly of collagen fibrils. The EM stereology permitted early detection of altered phenotype of the collagen fibril network in newborn transgenic mice. It is recommended that the indirect model-based stereological technique is utilized instead of the direct design-based technique for the estimation of collagen volume, surface, and length densities.