Incorporation of cortical bone allografts and autografts in rats: expression patterns of mRNAs for the TGF-betas.

Healing of bone grafts is dependent on the rate of new bone formation. To understand better the regulation of new bone formation in the graft we have studied local production of TGF-beta1, 2 and 3, and of the small proteoglycans by determining their mRNA levels in a rat bone graft model. These mRNA levels were compared to the healing rates of autografts and allografts, as determined by histology, UV-microscopic evaluation of tetracycline-labeled new bone formation, microradiography and mechanical testing at 1, 2, 4 and 8 weeks of healing. Analyses showed that, analogous to slower bone formation in allografts, the induction of TGF-beta1 gene expression was slower than in allografts, when compared with autografts. A similar delay was seen in decorin gene expression. The results agree with the suggested role of TGF-beta1 in induction of type I collagen and osteonectin production. Our findings thus support the view that locally produced TGF-beta1 plays a role in normal graft incorporation, while local production of TGF-beta3, and particularly TGF-beta2, may be less important in this respect.