Quantitative analysis and localization of mRNA transcripts of type I collagen, osteocalcin, MMP 2, MMP 8, and MMP 13 during bone healing in a rat calvarial experimental defect model

The study examined the expression of matrix metalloproteinases (MMPs), type I collagen and osteocalcin during bone healing in a rat calvarial experimental defect model. Twelve-week-old male Wistar rats were used. A full-thickness standardized trephine defect was made in the parietal bone, with the rat under anesthesia. RNA was extracted from tissue that filled the original bone defect on days 1 and 3 and in weeks 1, 2, 3, 5, 8, 10, 12, 18, and 24 and processed for quantitative analysis of expression of type I collagen, osteocalcin and matrix metalloproteinases (MMPs) 2, 8, and 13 by using real-time polymerase chain reaction. Alternatively, the rats were fixed by perfusion through the aorta and resected calvaria were processed for in situ hybridization for these molecules. The expression of type I collagen, osteocalcin and MMPs 2 and 13 increased toward week 2 and decreased thereafter, whereas the expression of MMP 8 was the highest on day 1. The mRNA transcripts of type I collagen and osteocalcin were localized in osteoblasts and osteocytes, some of which expressed MMPs 2, 8, and 13. Osteoblasts and osteocytes may play a role in the remodeling of extracellular matrices with MMPs during healing of a defect in bone.