Changes in the Expression of Insulin-like Growth Factor II/Mannose-6-phosphate Receptor during Endochondral Bone Development

Endochondral bone development can be induced by subcutaneous implantation of demineralized bone matrix (DBM) in rats. We used this in vivo model to study the relationship between endochondral bone formation and expression of IGF-II/M-6-P receptor, a multifunctional protein which binds not only IGF-II, but also lysosomal enzyme bearing mannose-6-phosphate motif. We found that IGF-II/M-6-P receptor was present in implants from day 1 to day 21; the highest levels were expressed on day 11 during bone differentiation. IGF-II/M-6-P receptor mRNA content was highest on day 9. We conclude from these data that IGF-II/M-6-P receptor expression is developmentally regulated during endochondral bone formation. This regulation occurs in part at the level of IGF-II/M-6-P receptor mRNA. The relatively high level of IGF-II/M-6-P receptor during ossification suggests that this receptor might play a role in bone formation and remodeling.