The Role of Collagen α1(XI) in Mineralization

Collagen type XI is a quantitatively minor yet essential component of the collagen fibrils within cartilage. It functions in the assembly of embryonic cartilage collagen fibrils as the diameter of cartilage collagen fibrils is dependent on the relative ratioand microfibril structure of collagen types II and XI. However, very little is known about the role of collagen type XI in the formation of mineralized tissue. In this study, skeletal mineralization was evaluated in the absence and presence of collagen α1(XI) using the chondrodysplasia (cho) mouse. Skeletal deformities in the cho mouse indicate that collagen type XI acts in skeletal development distinct from its function in nucleating the formation and limiting the diameter of cartilage collagen fibrils. In this study, we quantified the differences in craniofacial bones between the cho and the wildtype mice to better understand the role of collagen type XI in mineralization. High-resolution three-dimensional models were created from x-ray microcomputed tomography images of the mandible, parietal, frontal, basioccipital, and exocciptal bones of cho and wildtype mice. Analysis revealed differences in bone density, size and microarchitecture. The differences in skeletal properties between these mice were quantified using geometric measurements and three-dimensional calculations of microarchitecture. Bone mineral density was increased in the absence of collagen α1(XI) in the parietal and frontal craniofacial bones, of the cho mouse. The increase in bone density correlated with observed differences in trabecular thickness, trabecular number, and trabecular separation. The craniofacial deformities observed include a shortened snout, abnormal frontal sinuses and decreased or absent mineralization in the mandible, parietal and frontal bones. These findings indicate a new function for collagen type XI in bone mineralization