Post-Transcriptional Regulation of Osteoblastic Platelet-Derived Growth Factor Receptor-Alpha Expression by Co-Cultured Primary Endothelial Cells

Abstract

Platelet-derived growth factor receptor (PDGFR) signaling plays an important role in osteoblast function. Inhibition of PDGFR activity leads to a suppression of osteoblast proliferation, whereas mineralized matrix production is enhanced. In previous experiments, we showed that co-cultivation of human primary endothelial cells and human primary osteoblasts (hOBs) leads to a cell contact-dependent downregulation of PDGFR-α expression in the osteoblasts. In this study, we investigated this effect in more detail, revealing that human umbilical vein endothelial cell (HUVEC)-mediated PDGFR-α downregulation is dependent on time and cell number. This effect was specific to endothelial cells and was not observed when hOBs were co-cultured with human primary chondrocytes or fibroblasts. Likewise, HUVEC-mediated suppression of PDGFR-α expression was only seen in hOBs and mesenchymal stem cells but not in immortalized osteoblastic cell lines. Functional inhibition of gap junctional communication between HUVECs and hOBs by 18α-glycyrrhetinic acid had no effect on HUVEC-mediated PDGFR-α downregulation, whereas inhibition of p38 mitogen-activated protein kinase (MAPK) prevented the HUVEC-mediated reduction in osteoblastic PDGFR-α expression. To delineate the molecular mechanism underlying the PDGFR-α downregulation, we examined the effect of HUVEC co-cultivation on osteoblastic PDGFR-α promoter activity as well as mRNA stability. Co-cultivation of HUVECs with hOBs significantly shortened the half-life of osteoblastic PDGFR-α mRNA, but did not decrease its promoter activity. In summary, our data show that PDGFR-α is downregulated in hOBs by co-cultivation with human primary endothelial cells through a p38 MAPK-dependent post-transcriptional mechanism.

The proliferation and differentiation of osteoblasts in co-culture with human umbilical vein endothelial cells: An improved analysis using fluorescence-activated cell sorting

“…A previous study suggested that osteoblasts may stimulate the proliferation of ECs by producing VEGF, and that the stimulated ECs may reciprocally enhance the proliferation of osteoblasts in direct co-culture [5]. The inhibition of MG-63 cell proliferation by HUVECs after 120 h of culture could be due to the mechanisms recently described by Finkenzeller et al [29]. According to this direct co-culture study, HUVECs inhibited proliferation of primary OBs due to down-regulation of platelet-derived growth factor receptor expression on the OB surface.…”

Cancer treatment adherence among low‐income women with breast or gynecologic cancer

“…It is known that osteogenesis, as well as angiogenesis, rely on complex cell‐to‐cell interactions [Nguyen and D'Amore, 2001]. Over the recent years we [Stahl et al, 2004; Finkenzeller et al, 2006; Hager et al, 2009; Finkenzeller et al, 2010], and others [Guenther et al, 1986; Wang et al, 1997; Villars et al, 2002; Sun et al, 2007; Guillotin et al, 2008; Grellier et al, 2009a], have shown that the interaction between hOBs and ECs is likely to be crucial for proper development of vascularized bone. For example, our group demonstrated that direct cell‐to‐cell contact causes an increase in transcript stability of the early osteoblastic marker alkaline phosphatase in osteoblasts [Hager et al, 2009] and others have confirmed this observation [Villars et al, 2002; Sun et al, 2007].…”

“…There is ample scientific literature dealing with the interaction between endothelial cells and cocultivated osteoblasts [reviews in Grellier et al, 2009a; Das and Botchwey, 2011]. The osteoinductive and proliferative effect on osteoblasts, as well as importance of different communication modalities in this interaction such as paracrine signaling or direct cell contacts has been extensively studied by us and others [Guenther et al, 1986; Decker et al, 1995; Stevens and Williams, 1999; Street et al, 2002; Villars et al, 2002; Carano and Filvaroff, 2003; Stahl et al, 2004; Finkenzeller et al, 2006, 2010; Guillotin et al, 2008; Hager et al, 2009].…”

Induction of Osteogenic Differentiation in Human Mesenchymal Stem Cells by Crosstalk with Osteoblasts

“…Human primary osteoblasts were isolated from cancellous bone of the femoral heads by cell outgrowth from small pieces. 10 MSCs were extracted from the bone marrow of cancellous bone of the same femoral heads. 5 Briefly, for MSC isolation small pieces of cancellous bone were transferred in a conical tube with medium and vortexed.…”