Abstract
TGF beta has opposing effects on osteoblasts which are thought to be differentiation stage dependent; however, little is known concerning the effects of TGF beta on osteoblastic characteristics at different stages of maturation. The purpose of this study was to characterize the pattern of mRNA expression for the PTH/PTHrP receptor during normal osteoblastic differentiation in vitro, and evaluate the effects of TGF beta 1 on PTH/PTHrP receptor and osteocalcin (OCN) steady-state mRNA at different stages of osteoblastic differentiation. MC3T3-E1 preosteoblasts were plated at low density and induced to differentiate with ascorbic acid and beta-glycerophosphate. The first group served as a vehicle control and the remaining five groups received a single 48 h TGF beta 1 (3.0 ng/ml)-pulse staggered on a weekly basis for 30 days. Cell cultures were harvested weekly and evaluated for: steady-state PTH/PTHrP receptor and OCN mRNA levels via northern analysis, calcium and phosphorous levels, bone nodules via Von Kossa staining, alkaline phosphatase enzyme levels, and hydroxyproline levels. Group 1 (control) samples followed a normal pattern of proliferation, extracellular matrix deposition, and mineralization. PTH/PTHrP receptor and OCN mRNA expression increased 8-fold and 10-fold respectively, over the collection periods. When TGF beta 1 was administered during the first 48 h period (group 2) while cells were rapidly proliferating, there was a persistent inhibition of PTH/PTHrP receptor expression and a striking reduction in OCN mRNA expression at all time points. There was also a down-regulation of PTH/PTHrP receptor and OCN expression when TGF beta 1 was administered later during osteoblast differentiation (groups 3-6); however, these effects were not persistent. In addition there was a total lack of bone nodule formation in group two cultures, whereas groups 3-6 had increasing bone nodule formation because the TGF beta 1 was administered later in the culture period. These studies indicate that expression of the PTH/PTHrP receptor increases with osteoblastic differentiation and suggest that TGF beta 1 inhibits osteoblastic maturation with more persistent effects found in less differentiated osteoblastic cells.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
More From: Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.