Influence of Estradiol on Vascular Endothelial Growth Factor Expression in Bone: A Study in Göttingen Miniature Pigs and Human Osteoblasts

Abstract

Ovariectomy (OVX) in animal models is an accepted method to simulate postmenopausal osteoprosis. Vascular endothelial growth factor (VEGF) has been recently shown to play an important role during endochondral bone formation, hypertrophic cartilage remodeling, ossification, and angiogenesis. We hypothesized that reduced VEGF expression in bone contributes to OVX-induced bone loss and tested it in a miniature pig model and in vitro using human osteoblasts. Seventeen primiparous sows (Göttingen miniature pigs) were allocated to two experimental groups when they were 30 months old: a control group (n = 9) and an OVX group (n = 8). After 15 months, VEGF levels in lumbar vertebrae were measured by enzyme-linked immunosorbent assay and verified by Western blot analysis. VEGF and its receptor (VEGFR) were localized by immunohistochemistry. Expression of VEGF mRNA was analyzed by real-time reverse-transcription polymerase chain reaction. Differently sulfated glycosaminoglycans were localized in subchondral bone histochemically. Osteoblasts were immunopositive for VEGF. VEGF concentration in the vertebra was 27% lower in OVX miniature pigs. VEGFR-2 could be immunostained on osteoblasts. VEGF mRNA and protein were detectable in the lumbar vertebrae of all animals. In subchondral trabecular bone of OVX animals, significantly more islands of mineralized cartilage containing chondroitin 4- and 6-sulfate or keratan sulfate occurred compared to the control group. The occurrence of remnants of mineralized cartilage in subchondral bone of the OVX group may be caused by a delayed bone turnover due to low VEGF levels. In vitro experiments revealed an increase of VEGF in the supernatant of osteoblasts after incubation with estradiol. In conclusion, estrogen seems to be a key factor for regulation of VEGF expression in bone. Loss of VEGF due to menopause may be a reason for reduction of bone density.

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

“…This is the same pattern of splice variants observed in fracture healing [21]. These small splice variants have the potency to react over long distances.…”

“…Migita et al [17] examined the downregulation of COX-2 in response to glucocorticoids in human rheumatoid synovial fibroblasts and concluded glucocorticoids could reduce VEGF levels by downregulating COX-2 with subsequent reduction of PGE2. Under pathologic conditions, VEGF is strongly expressed during the time course of fracture healing [21]. During the remodeling of the osseous fracture callus, VEGF is expressed by osteocytes while the receptor of VEGF, VEGFR-2, is expressed by osteoblasts, osteoclasts, and endothelial cells [21].…”

“…Under pathologic conditions, VEGF is strongly expressed during the time course of fracture healing [21]. During the remodeling of the osseous fracture callus, VEGF is expressed by osteocytes while the receptor of VEGF, VEGFR-2, is expressed by osteoblasts, osteoclasts, and endothelial cells [21]. Thus, it appeared promising to us to investigate the role of angiogenic factors, specifically VEGF, in femoral head ON.…”

The phytoestrogens daidzein and genistein enhance the insulin-stimulated sulfate uptake in articular chondrocytes

“…There is increasing evidence that phytoestrogens may offer protection against a wide range of human conditions, including breast cancer, cardiovascular disease, brain dysfunction, and especially menopausal symptoms (Ewies 2002). Daidzein and genistein have protective effects on osteoporosis (Beck et al 2005) and might prevent postmenopausal bone loss (Ullmann et al 2005), as was shown for 17β-estradiol in ovariectomized Göttingen miniature pigs (Pufe et al 2007). Whereas some reports stress that phytoestrogens have neuroprotective effects (Zhao et al 2002;Lephart et al 2005;Azcoitia et al 2006), little information exists concerning the influence of these sex-hormone-like substances on articular cartilage.…”

Immunohistochemical and CBCT-based examination of differences between deformed and normal human condylar processes

“…These findings have been corrabrated by the detection of proteins associated with revascularization and osteogenesis (e.g., VEGF and ALP) at resorption sites in bone 10) . Recently, VEGF was detected at the site of bone growth 14) and was demonstrated to be an important marker of bone density maintenance 26) . VEGF was detected in chondrocytes, and its receptor, VEGF-R, has been shown to be expressed in osteoclasts at the head of the mandible in rats 1) .…”