Aim: To
investigate the mechanism of the bone-forming effects of intermittent
parathyroid hormone (PTH) administration and to search for novel molecules of
bone anabolism via the PTH signaling pathway.
Methods: Primary cultures of rat osteoblasts (ROBs) were divided into an intermittent PTH-treated group (Itm) and a control group (Ctr). Imitating the pharmacokinetics of
intermittent PTH administration in vivo, the ROBs in the Itm group were exposed to PTH for 6 h in a
24-h incubation cycle, and the ROBs in the Ctr group were exposed to vehicle for the entire incubation
cycle. The cells were collected at
6 h and 24 h of the final cycle, and the proteins in the Itm and Ctr groups were analyzed by two-dimensional
electrophoresis (2-DE) coupled with peptide mass fingerprinting and matrix
assisted laser desorption/ionization time-of-flight mass spectrometry
(MALDI-TOF-MS) to detect proteins that were differentially expressed. The proteins with the most significant
changes in vitro were validated by immunohistochemistry (IHC) in a rat model.
Results: The proteomics analysis indicated that a total of 26 proteins were
up- or down-regulated in the Itm group compared with
the Ctr group at 6 h and 24 h; among these, 15
proteins were successfully identified. These proteins mainly belong to the cytoskeleton and molecular chaperone
protein families, and most of these have anti-apoptotic effects in various
cells.
Rho
GDP-dissociation inhibitor α (RhoGDIα) and vimentin were the
most significantly changed proteins. Further studies by IHC showed that the expression of RhoGDIα in ROBs was significantly higher in PTH-treated
sham-operated rats than in vehicle-treated sham-operated rats, but the
difference was not significant between PTH-treated and vehicle-treated OVX
rats. Vimentin expression was not changed in either PTH-treated sham-operated rats or
PTH-treated OVX rats.
Conclusion: Our research suggests that intermittent PTH treatment induces
changes in expression of many proteins in ROBs in
vitro, and it results in RhoGDIα up-regulation in ROBs both in vitro and in vivo when
estrogen is present. This
up-regulation of RhoGDIα may be one of the mechanisms
underlying the synergistic bone-forming effect of PTH and estrogen.
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