Increased levels of osteoprotegerin (OPG), an antiosteogenic factor, is used as a biomarker of vascular dysfunction and cardiovascular risk in metabolic diseases, suggesting pleiotropic effects independent of regulation of vascular calcification. Syndecan-1 (SDC1) may be involved in OPG-induced vascular responses, as it is involved in OPG-induced inflammation. We assessed whether OPG, through SDC1 and redox sensitive processes, regulates vascular function and injury.Design and Method:
Vascular reactivity of resistance vessels from WKY rats was studied by wire myography in the presence or absence of OPG (50 ng/mL) and/or synstatin (SSNT - 10–6 M - syndecan-1 inhibitor). Rat endothelial cells (EC) and vascular smooth muscle cells (VSMC) were used. Reactive oxygen species (ROS) were measured by chemiluminescence and Amplex Red.Results:
Exposure of resistance arteries to OPG induced endothelial (decreased relaxation to acetylcholine) and VSMC (decreased relaxation to sodium nitroprusside - SNP) dysfunction, as well as, increased contraction to phenylephrine. All responses were blocked by SSNT. OPG-induced ROS production in VSMCs (1.5 fold increase, p < 0.05) was blocked by SDC1 signalling inhibitors such as SSNT, chondroitinase/heparinase (removal of SDC1 sulfate chains), γ-secretase inhibitor (SDC1 intracellular domain) and MMP2/MMP9 inhibitor (SDC1 extracellular domain). In ECs, OPG decreased H2O2 (0.5 fold) and NO (0.5 fold) production/release. In VSMCs, OPG increased ONOO- (0.5 fold) levels, protein oxidation (0.5 fold), Rho kinase (1.5 fold) and myosin light chain activation (1 fold) (p < 0.05) through SDC1. OPG increased mRNA levels of IL6 (2 fold), IL-1β (2 fold), MMP2 (1 fold) and MMP9 (2 fold) in vascular cells; all inhibited by SSNT.Conclusions:
In conclusion, vascular dysfunction/damage elicited by OPG is mediated by syndecan-1 and ROS. Identification of syndecan-1 as the upstream effector of OPG-induced vascular injury suggests that membrane proteoglycans may be potential targets for the treatment of vascular diseases, where the protective role of OPG is preserved.