The Effects of PTH1-34 on PTHrP mRNA of the Human Osteoblast-Like MG63 Under Supra-Mechanical Loading in Vitro

It is commonly recognized that damage to bone tissue begins to occur in response to these supra-physiologic mechanical loading. Parathyroid hormone (PTH) plays a key role on the anabolic effects of osteoblast. However, the effects of N-terminal 1-34 fragment of human PTH (hPTHl-34) on osteoblast under supra-threshold mechanical loading are unknown. We recently used a stretch-induced from the hypotonic solution system in which cells were bathed for different times. We have measured the effects of 240 mOsm and 163 mOsm hypotonic solution for 2 h, 4 h and 6 h, respectively on osteoblast-like cell MG63. We selected a supra-threshold stimuli parameter according to change of the mitochondrial membrane potential (MMP), alkaline phosphatase (ALP) activity and intracellular calcium ([Ca24]i). Then, hPTHl- 34 (20ng/L) was used for lh, 3 h, 6 h and 24 h respectively after cells treated by supra-threshold stimuli parameter. Parathyroid hormone-related protein (PTHrP) mRNA was examined by realtime PCR. We found that 163mOsm hypotonic solution for 4 h and 6 h decreased mitochondrial membrane potential and [Ca²⁺]i, while increased ALP activity. Transient PTH treatment for 6 h enhanced PTHrP mRNA expression in cells. In contrast, hPTHl- 34 for 1 h and 3 h was not available for resuming function of osteoblast differentiation and mineralization, which was obvious by lower expression of PTHrP mRNA.