Abstract
Estrogen depletion causes postmenopausal osteoporosis. Here we report that steady state mRNA levels of transforming growth factor-β 1 (TGF-β 1) and osteocalcin in bone persistently decreased and increased, respectively, in vivo in estrogen-depleted rats after ovariectomy (OVX). 21 female Wistar rats (7-month-old) were randomized and underwent OVX or sham-operation, total RNA was extracted from tibiae and assessed by Northern blot analysis. OVX induced 70-80 % decrease in TGF-β 1 mRNA levels and 2- to 3-fold increase in mRNA levels of osteocalcin compared with controls three weeks after surgery. These changes persisted up to twelve weeks post-operation. OVX caused 15 % reduction in femoral bone mineral density and 2-fold elevation in serum osteocalcin levels as early as two weeks post-operation. Moreover, estrogen depletion resulted in marked decrease and increase, respectively, in steady state mRNA levels of TGF-β 1 and osteocalcin in vitro in osteoblastic rat osteosarcoma cells, ROS 17/2.8. Our results provide the first in vivo evidence that expression of TGF-β and osteocalcin in bone is reciprocally regulated at the transcriptional level in estrogen deficient OVX rats and suggests that TGF-β 1 may play a role in estrogen-dependent maintenance of normal bone density.
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