Age-Related Changes in Parathyroid Hormone-Related Protein and Vascular Endothelial Growth Factor in Human Osteoblastic Cells

Abstract

Osteogenesis and angiogenesis occur in a coordinated manner in skeletal tissue, so that impaired angiogenesis is associated with decreased bone formation in aged subjects. However, the interaction between bone endothelium and osteoblastic cells is poorly understood. Parathyroid hormone-related protein (PTHrP), a bone factor which modulates osteoblastic cell growth and/or differentiation, stimulates vascular endothelial growth factor (VEGF), a potent angiogenic factor, in primary cultures of human osteoblastic (hOB) cells. In the present study, we examined the age-related changes of both factors in these cells. Human OB cells were isolated from trabecular bone samples from knee or hip explants obtained from 45 osteoarthritic patients: 12 <60 years (21-59 years), 5 women and 7 men, and 33 >60 years (61-82 years), 20 women and 13 men. Cell total RNA was isolated, and mRNA analysis was performed by reverse transcription-polymerase chain reaction. Relative ratios of amplified products with respect to glyceraldehyde-3-phosphate dehydrogenase were then calculated. PTHrP and VEGF were measured in the cell-conditioned medium, after stimulation with (or without) 10 nM 1,25(OH)(2)D(3) for 72 h, using specific immunoradiometric assay and a competitive immunoassay, respectively. A positive correlation was found between PTHrP and VEGF (both mRNA and secreted protein), and also between PTHrP mRNA and the secreted protein levels, in these cells. PTHrP, both mRNA and protein secretion levels, and VEGF secreted values were higher in knee hOB cells than in hip hOB cells only in the younger group. In addition, a decrease in the secreted levels of these factors occurs with aging only in hOB cells from knee. Treatment with 10 nM 1,25(OH)(2)D(3) induced a lower inhibitory response of PTHrP secretion, and a higher stimulatory response of secreted VEGF, in hOB cells with age. These findings indicate that age-related bone loss in humans is associated with a decrease in the osteoblastic secretion of both PTHrP and VEGF in the knee, a predominantly trabecular bone. These data might provide a rationale to explain the impaired angiogenesis associated with trabecular bone loss in aging.

Characterization of skeletal alterations in a model of prematurely aging mice

“…Furthermore, the onset of these changes occurred earlier in PAM than in NPAM. An age-related decrease in PTHrP mRNA levels in the mouse long bones is consistent with previous findings in human osteoblastic cells derived from hip and knee of elderly donors (Martinez et al 2002). It has previously been reported that a decrease in Wnt pathway activation occurs with aging (Almeida et al 2007a).…”

“…Furthermore, this age-related diminution also occurred for the gene expression of OC, a late osteoblast differentiation marker (Pockwinse et al 1992;Zhang et al 2010). It has been demonstrated that PTHrP production-an important modulator of bone formation and remodeling in adult bone (Bisello (Martinez et al 2002). Here, we found that PTHrP gene expression was significantly downregulated in both NPAM and PAM with aging.…”

Differential Expression of Vascular Endothelial Growth Factor in Glucocorticoid-related Osteonecrosis of the Femoral Head

“…Other authors have reported an age-related decrease in the secreted levels of VEGF in osteoblasts [16] and an increase in VEGF and a decrease in parathyroid hormone-related protein after vitamin D incubation. Since VEGF is a key factor of angiogenesis, we hypothesized a decrease in VEGF in the early stage of ON and an increase in the late stage of ON.…”

Spatiotemporal control over growth factor signaling for therapeutic neovascularization☆

“…Moreover, aged or diseased patients may have distinct capabilities for neovascularization. For example, diabetic patients have reduced angiogenic responsiveness [77,78] as do aged subjects [79]. This could result from impaired growth factor/receptor signaling [80], a reduction in endothelial cell responsiveness, or a reduction of the number of circulating progenitor cells [81,82].…”