Transient Exposure to PTHrP (107-139) Exerts Anabolic Effects through Vascular Endothelial Growth Factor Receptor 2 in Human Osteoblastic Cells In Vitro

Abstract

Intermittent administration of the N-terminal fragment of parathyroid hormone (PTH) and PTH-related protein (PTHrP) induces bone anabolic effects. However, the effects of the C-terminal domain of PTHrP on bone turnover remain controversial. We examined the putative mechanisms whereby this PTHrP domain can affect osteoblastic differentiation, using human osteosarcoma MG-63 cells and osteoblastic cells from human trabecular bone. Intermittent exposure to PTHrP (107-139), within 10-100 nM, for only <or=24 hours during cell growth stimulated alkaline phosphatase (ALP) and Runt homology domain protein (Runx2) activities as well as osteocalcin (OC) and osteoprotegerin (OPG) expression but inhibited receptor activator of nuclear factor kappaB (NF-kappaB) ligand. Continuous exposure to this PTHrP peptide reversed these effects. The stimulatory effects of transient treatment with PTHrP (107-139) on OC mRNA and/or OPG protein expression were unaffected by a neutralizing anti-insulin-like growth factor I antibody or [Asn(10), Leu(11), d-Trp(12)]PTHrP (7-34) in these cells. On the other hand, the former antibody and the latter PTHrP antagonist abrogated the PTHrP (1-36)-induced increase in these osteoblastic products. Transient exposure to PTHrP (107-139), in contrast to PTHrP (1-36), stimulated vascular endothelial growth factor receptor 2 (VEGFR2) mRNA levels in these cells. Moreover, induction of ALP activity as well as OC and OPG expression by PTHrP (107-139) was blunted by SU5614, a permeable tyrosine kinase inhibitor of VEGFR2. Protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) inhibitors abolished the PTHrP (107-139)-stimulated VEGFR2 and OPG mRNA levels in these cells. These results indicate that intermittent exposure to PTHrP (107-139) exerts potential anabolic effects through the PKC/ERK pathway and, subsequently, VEGFR2 upregulation in vitro in human osteoblastic cells.

Parathyroid hormone-related protein (107-111) improves the bone regeneration potential of gelatin–glutaraldehyde biopolymer-coated hydroxyapatite

“…VEGF gene expression was also up-regulated in this scenario (Fig. 7B), which is consistent with the action of PTHrP (107-111) and the native PTHrP (107-139) fragment in various osteoblastic cell preparations [25,26,28,33,34]. The unloaded HA Glu scaffolds failed to affect either cell growth or matrix mineralization in MC3T3-E1 cells within the time of the study (4-12 days), emphasizing the notion that PTHrP (107-111) gives bioactivity to these scaffolds (Figs.…”

“…This was not surprising, considering the ability of this peptide to reduce the number of trabecular osteoclasts when administered subcutaneously, as recently reported [45], and the observed increase in OPG/RANKL mRNA ratio induced by PTHrP (107-111)-loaded HA Glu scaffolds in osteoblast cultures in this work. In fact, PTHrP (107-139) has consistently been shown to display anti-resorptive features in rodents [17,[20][21][22], apparently by interacting with osteoclasts directly or indirectly through targeting osteoblasts [19,23,26,28]. Also in this regard, the local presence of PTHrP (107-111) was shown to inhibit the transient inflammatory response as well as the appearance of osteoclasts in a cavitary bone defect in the rabbit femur [27].…”

“…In addition, the C-terminal 107-111 domain (also known as osteostatin) of PTHrP also exhibits osteogenic features in vitro, and stimulates bone accrual in vivo [17][18][19][20][21][22][23][24][25]. Of note, we recently showed that loading non-degradable Si-based ceramics with the latter pentapeptide gives them osteogenic and angiogenic features both in vitro and in vivo as implants in a cavitary defect in the rabbit femur [26][27][28][29]. These effects of osteostatin were thought to be due to its release into the local environment, because this type of ceramic elicits the formation of a fibrous capsule that hampers close contact between the implant and the surrounding tissue [27,29].…”

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

“…However, this effect was no longer present at the end of the study (day 24). This might be related to the current notion, based on studies in various osteoblastic cell preparations, that the anabolic effect of the N-terminal domain of PTH and PTHrP seems to depend on both exposure time and the cell differentiation stage (Schiller et al, 1999;Fujita et al, 2001;Krishnan et al, 2003;de Gortazar et al, 2006). On the other hand, this effect of PTHrP (1-36) was not found to be elicited by PTHrP (107-139) in human MSCs; in fact, the latter peptide transiently decreased RUNX2 gene expression at day 18 in these cells.…”

“…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.…”