TYPE-X COLLAGEN IN FRACTURE CALLUS AND THE EFFECTS OF EXPERIMENTAL DIABETES

Studies of fracture repair in diabetes have shown decreased mechanical strength and total collagen in the callus. Type I and Type II collage n are synthesized by bone and cartilage cells, respectively, while Typ e X collagen is synthesized by hypertrophic chondrocytes in endochondr al ossification. A standardized fracture model was chosen to investiga te extracellular matrix changes during fracture healing of normal and diabetic rats. Histological examination of the fracture callus in both normal and diabetic animals showed progression from a fibrous tissue to cartilage to bone. An antiserum to Type X collagen was prepared, an d immunostaining was observed in the matrix surrounding the hypertroph ic chondrocytes. Fracture calluses from streptozotocin induced diabeti c rats had similar histology and immunostaining to controls. Radiolabe lled proteins were extracted from the calluses of normal and diabetic rats to measure Type X collagen. Type X collagen expression in the fra cture callus of normal rats reached a maximum at day fourteen and was decreased by between 54% and 70% in the fracture callus of diabetic ra ts. The decrease in Type X collagen synthesis may have a role in the d efect of fracture healing in diabetes.