The Effect of Long-Term Ovarian Hormone Deficiency on Transforming Growth Factor β and Bone Matrix Protein mRNA Expression in Rat Femora

Abstract

Estrogen deficiency results in increased bone turnover and osteopenia. Decreased transforming growth factor beta (TGF-β) has been implicated as having a role in ovariectomy (OVX)-induced bone loss; however the decrease in TGF-β mRNA may simply be due to the reduction in cancellous bone volume that occurs following OVX. This investigation characterized the effect of long-term OVX (11.5 months) on mRNA levels for TGF-β, osteocalcin (OC), and type I collagen (TYPE I) and expressed these data relative to the amount of cancellous bone surface. Additionally, the short-term effect of estrogen administration on TGF-β, OC, and TYPE I mRNA was evaluated. OVX resulted in a 56% loss of bone surface. At the tissue level, TGF-β was reduced, OC was increased, and TYPE I was unchanged. Expressed relative to bone surface, TGF-β was unchanged and OC and TYPE I were significantly elevated. Four hours after estrogen administration, TGF-β mRNA was unchanged compared to vehicle-treated controls. The data suggest that bone turnover is elevated after long-term OVX, but do not suggest a direct role of TGF-β in OVX-induced bone loss.