Regulation of ?V?3 and ?V?5 integrins by dexamethasone in normal human osteoblastic cells

Abstract

Long-term administration of pharmacological doses of glucocorticoids inhibits bone formation and results in osteoporosis. Since integrin-mediated cell-matrix interactions are essential for osteoblast function, we hypothesized that the detrimental effect of glucocorticoids on bone derived, at least in part, from decreased integrin-matrix interactions. Because alphavbeta3 and alphavbeta5 integrins can interact with several bone matrix proteins, we analyzed the effects of dexamethasone (Dex) on the expression of these integrins in normal human osteoblastic cells. We found adhesion of these cells to osteopontin and vitronectin to be dependent on alphavbeta3 and alphavbeta5, respectively; this ligand specificity was not altered by Dex. The effects of Dex on the adhesion of human osteoblastic cells to osteopontin and vitronectin were biphasic with an increase after 2 days, followed by a decrease after 8 days of treatment. Consistently, surface alphavbeta3 and alphavbeta5 integrins, which were increased after 2 days of Dex treatment, were decreased after 8 days. Similarly, total cellular alphav, beta3, and beta5 proteins, which were increased by Dex early in the culture, were diminished after 8 days. Metabolic labeling studies indicated that Dex exhibited biphasic regulation on the biosynthesis of alphavbeta5, with stimulation observed during the second day of treatment, followed by inhibition during the 8th day of exposure. By contrast, the biosynthesis of alphavbeta3 was inhibited by Dex on day 1 and remained inhibited on day 8. Analysis of the mRNA indicated that alphav and beta5 levels were increased by Dex during early exposure (1-3 days), followed by inhibition after prolonged exposure (>/=7 days). By contrast, Dex decreased beta3 mRNA level at all the time points analyzed. Consistently, Dex decreased beta3 promoter activity after 1 day and persisted over 8-day period. By contrast, Dex stimulated beta5 promoter activity after 1 or 2 days but had no effect after 8 days. To further evaluate mechanism(s) leading to the decreased integrin expression after prolonged Dex treatment, mRNA stability was analyzed. Dex was found to accelerate the degradation of alphav, beta3 and beta5 mRNA after an 8-day treatment. Thus, the regulation of alphavbeta3 was dependent on transcription and posttranscriptional events whereas the expression of alphavbeta5 was dependent mainly on posttranscriptional events after prolonged Dex treatment. In conclusion, Dex exhibited time-dependent regulation on the expression of alphavbeta3 and alphavbeta5 integrins in normal human osteoblastic cells. Short-term exposure to Dex increased the levels of alphavbeta3 and alphavbeta5 on the surface and cell adhesion to osteopontin and vitronectin whereas long-term exposure to Dex decreased the expression of both integrins and inhibited the cell adhesion to matrix proteins.

Hypoxia Stimulates Osteopontin Expression and Proliferation of Cultured Vascular Smooth Muscle Cells

“…To examine a role for OPN in hypoxiainduced proliferation, quiescent VSM cells were exposed to hypoxia and normoxia for 24 h in the absence or presence of neutralizing antibodies to OPN, ␤3 integrin receptor, ␤5 integrin receptor, or control IgG, and then [ 3 H]thymidine incorporation was assessed. OPN binds specifically to the ␤3 integrin receptor in VSM cells (38), whereas the ␤5 integrin is a preferential binding receptor for another arginine-glycine-aspartic acid-containing adhesion molecule called vitronectin (39,40). Similar to our observations in Fig.…”

The effect of integrin-specific bioactive coatings on tissue healing and implant osseointegration

“…Nonetheless, these biomimetic approaches have elicited marginal improvements in in vivo functional performance [12][13][14]. We hypothesized that these marginal healing responses result from uncontrolled signaling responses at the tissue-implant interface arising from unregulated or sub-optimal integrin binding.…”

“…For example, α vcontaining integrins are essential for steroid hormone and growth factor induction of osteoblast differentiation. [11,12] Because of the central roles of integrin-mediated adhesion in tissue formation, maintenance, and repair, recent bio-inspired biomaterial strategies have focused on presenting integrin ligands such as extracellular matrix proteins and short bioadhesive motifs derived from these components on implant surfaces [13]. The most common approach relies on the presentation of the arginine-glycine-aspartic acid (RGD) adhesive sequence derived from FN.…”

Optimal Intensity Shock Wave Promotes the Adhesion and Migration of Rat Osteoblasts via Integrin β1-mediated Expression of Phosphorylated Focal Adhesion Kinase

“…Cell Cultures-Primary rat osteoblasts were isolated from calvaria of 3-day-old Sprague-Dawley rats and cultured using methods described previously (25,26). Briefly, the newborn rats were sacrificed by decapitation and immersed in 75% alcohol for 5 min.…”