Abstract
Introduction
Parathyroid hormone-related peptide (PTHrP) has been shown to be an important regulator of bone remodelling1. The aim of this study was to investigate the effect of the N-terminal domain of PTHrP (1–36) on osteogenic and angiogenic gene expression in human osteoblasts (HOB) and human bone marrow stromal cells (hBMSCs).
Materials and Methods
Primary hBMSC's and HOBs were cultured in standard or osteogenic media with different concentrations of PTHrP, either continuously for 8, 24, 48 h and 9 days, or with 3 cycles of intermittent exposure (24 h with PTHrP, 24 h without) over 6 days. Cell lysates were then processed for analysis of gene expression. Expression of the osteogenic markers runt-related transcription factor 2 (RUNX-2), alkaline phosphatase (ALP) and Collagen 1, and the angiogenic marker; vascular endothelial growth factor (VEGF), were measured.
Results
Exposure to PTHrP for ≤ 48 hours resulted in an upregulation of the angiogenic marker VEGF and the osteogenic markers RUNX-2, ALP and Collagen 1 in both cell types, peaking at a 1 nM PTHrP. Conversely, continuous exposure for 9 days, resulted in a downregulation of all osteogenic and angiogenic gene expression. HOB cells exposed intermittently to PTHrP showed an upregulation in VEGF and ALP, peaking at 10nM PTHrP.
Discussion and Conclusion
Continuous exposure for short durations (<48 hours) and intermittent exposures of both HOB cells and BMSC's to PTHrP upregulated both osteogenic and angiogenic gene expression. Continuous exposure to 9 days however had the opposite effect, with a downregulation in gene transcription.
