Parathyroid hormone‐related protein (107–139) increases human osteoblastic cell survival by activation of vascular endothelial growth factor receptor‐2

Abstract

Parathyroid hormone-related protein (PTHrP) (107-139), in contrast to the N-terminal fragment PTHrP (1-36), has been shown to interact with the vascular endothelial growth factor (VEGF) system to modulate human osteoblast differentiation. In this study, we evaluated whether this interaction might affect human osteoblastic cell survival. Pre-incubation with PTHrP (107-139) for 1-24 h dose-dependently (0.1-100 nM) inhibited dexamethasone- or etoposide-induced cell death in human osteoblastic MG-63 cells and human osteoblast-like cells from trabecular bone. This effect, but not that elicited by PTHrP (1-36), was abolished by the VEGF receptor (VEGFR)-2 inhibitors SU5614 and SU1498 or VEGFR-2 siRNA transfection in these cells. PTHrP (107-139), but not PTHrP (1-36), at 100 nM, rapidly (within 2 min) increased VEGFR-2 tyrosine-phosphorylation in MG-63 cells; an effect unaffected by several inhibitors of metalloproteinases, neutralizing VEGF(165) or VEGFR-2 antibodies, or the VEGF binding inhibitor CBO-PP1. The latter two antagonists also failed to affect (125)I-[Tyr(116)] PTHrP (107-115) binding to these cells. Consistent with its effect on VEGFR-2 activation, PTHrP (107-139) rapidly induced extracellular signal-regulated kinase (ERK) 1/2 and Akt activaton, and both ERK and phosphatidylinsositol-3 kinase (PI3K) inhibitors abolished its pro-survival effect in human osteoblastic cells. In addition, SU5614 and the latter two types of inhibitors abrogated Runx2 activation by this peptide in MG-63 cells. Transfection with a dominant-negative Runx2 construct abolished the pro-survival effect of PTHrP (107-139), associated with a decrease in Bcl-2/Bax protein ratio. Our findings demonstrate that PTHrP (107-139) interacts with VEGFR-2 to promote human osteoblastic cell survival by a mechanism involving Runx2 activation.

Parathyroid Hormone-Related Protein Analogs as Osteoporosis Therapies

“…In these cells, cyclic AMP-dependent signaling cascades, involving PKA and cAMP-guanine nucleotide exchange factor/Epac, are considered to play a prominent role in several osteogenic actions resulting from PTH1R activation [5]. Indeed, native PTH or PTHrP ligands of the PTH1R activate cAMP/PKA-and phosphoinositide 3-kinase (PI-3K)/Akt-dependent pathways to induce, with the concourse of transcription factor Runx2, pro-survival actions in various osteoblastic cell preparations [21][22][23]. Moreover, recent data indicate the relevant role of intracellular calcium as well as PKA and ERK pathways related to PTHrP/PTH1R system activation in the pro-survival effects triggered by mechanical stimulus in osteocytes [24].…”

The N- and C-terminal domains of parathyroid hormone-related protein affect differently the osteogenic and adipogenic potential of human mesenchymal stem cells

“…This PTHrP domain is known to interact with an uncharacterized receptor, but different from the PTH1R in osteoblasts (Valin et al, 1997(Valin et al, , 2001Alonso et al, 2008). It has been previously demonstrated that PTHrP (107-139) can rapidly increase VEGF expression in human osteoblastic cells (Esbrit et al, 2000).…”

“…It has been previously demonstrated that PTHrP (107-139) can rapidly increase VEGF expression in human osteoblastic cells (Esbrit et al, 2000). In addition, recent studies have shown that its intermittent administration induces various osteogenic effects through interaction with VEGF receptor 2 in these cells (de Gortazar et al, 2006;Alonso et al, 2008). However, the putative effects of this Cterminal PTHrP fragment on human osteoprogenitors are currently unknown.…”

El receptor 2 de VEGF (VEGFR2) y el receptor 1 de la PTH (PTH1R) actúan como mediadores de la respuesta anti-apoptótica al estímulo mecánico en las células osteocíticas MLO-Y4

“…The system of VEGF is involved in the mechanisms of survival in various cell types including osteoblasts 29,30,40 . This growth factor promotes survival of endothelial cells by stimulating the formation of a multi-transmembrane protein complex that includes VEGFR2, VE-cadherin and β-catenina 40 .…”

“…VEGF / VEGFR2 system is an important mediator of proliferation, survival and differentiation of osteoblasts and osteoclasts 28,29 . The VEGFR2 mediates the actions of PTHrP on the differentiation and apoptosis in osteoblasts [29][30][31] . In endothelial cells, this receptor is activated by mechanical stimuli in a manner independent of ligand VEGF 32 .…”