Abstract
The process of heterotopic bone formation by bone morphogenetic protein (BMP) implanted in mouse muscle tissue was immunohistochemically studied in terms of the detection of glycosaminoglycans (GAGs) (chondroitin 4 sulfate, C4S; chondroitin 6 sulfate, C6S; keratan sulfate, KS; dermatan sulfate, DS; chondroitin sulfate, CS). Following BMP implantation into mouse muscle tissues, undifferentiated mesenchymal cells were found to infiltrate in situ, and C4S and KS were highly expressed at the initial phase. On day 5, undifferentiated cells expressed positive immunoreactivity for C4S, C6S, KS, CS, and DS, and chondroid matrices stained positively for C4S, C6S, KS, and DS, but weakly for CS. On day 7, they resemble hyalin cartilage tissues with positive reaction for all GAGs. In the cartilage cells, the expression of KS was particularly prominent. On day 14 to 21, chondro-osseous transformation was progressed with gradual calcification and with reduced stainings for all GAGs in their matrices. The calcified bone tissue indicated negative or trace positive reaction for GAGs. During BMP induced chondro-osteogenesis, the expression and accumulation of GAGs in the intercellular matrix play significant roles in chondrogenesis preceding endochondral ossification.
