Estrogen inhibits vascular calcification via vascular RANKL system: common mechanism of osteoporosis and vascular calcification

The role of osteoprotegerin (OPG) receptor activator for nuclear factor kappaB ligand (RANKL) in cardiovascular pathology - a review

Initially described as key regulators in metabolic bone disease osteoprotegerin (OPG), receptor activator of nuclear factor kappa B (RANK) and RANK ligand (RANKL) have also been discriminated as regulators in immunologic function. Cardiovascular diseases (CVD) develop over many years in life and are often triggered by inflammatory processes within the vessel wall that lead to vascular remodeling. Recently some study groups have described OPG as a prognostic parameter for mortality and morbidity in cardiovascular patients.

Calcific aortic valve stenosis: methods, models, and mechanisms

Calcific aortic valve stenosis (CAVS) is a major health problem facing aging societies. The identification of osteoblast-like and osteoclast-like cells in human tissue has led to a major paradigm shift in the field. CAVS was thought to be a passive, degenerative process, whereas now the progression of calcification in CAVS is considered to be actively regulated. Mechanistic studies examining the contributions of true ectopic osteogenesis, nonosseous calcification, and ectopic osteoblast-like cells (that appear to function differently from skeletal osteoblasts) to valvular dysfunction have been facilitated by the development of mouse models of CAVS. Recent studies also suggest that valvular fibrosis, as well as calcification, may play an important role in restricting cusp movement, and CAVS may be more appropriately viewed as a fibrocalcific disease. High-resolution echocardiography and magnetic resonance imaging have emerged as useful tools for testing the efficacy of pharmacological and genetic interventions in vivo. Key studies in humans and animals are reviewed that have shaped current paradigms in the field of CAVS, and suggest promising future areas for research.

The roles of lipid oxidation products and receptor activator of nuclear factor-κB signaling in atherosclerotic calcification

This review focuses on the roles of oxylipids and receptor activator of nuclear factor-κB ligand signaling in calcific cardiovascular disease. Both intimal and valvular calcifications are closely associated with atherosclerosis, leading investigators to study the role of atherogenic oxidatively modified lipids (oxylipids). Results have identified the molecular signaling through which oxylipids induce osteogenic differentiation and calcification in vascular cells. A surprising concomitant finding was that, in bona fide osteoblasts from skeletal bone, oxylipids have the opposite effect, ie, inhibiting osteoblastic maturation. This is the basis for the lipid hypothesis of osteoporosis. Oxylipids also induce resorptive osteoclastic cells within the bone environment, raising the question of whether resorptive osteoclasts can be harnessed in the vascular context for cell-based therapy to remove artery wall mineral deposits. The challenge is that vascular cells produce antiosteoclastogenic factors, including the soluble decoy receptor for receptor activator of nuclear factor-κB ligand, possibly accounting for the paucity of resorptive cells and the dominance of mineral in atherosclerotic plaque. These factors may have therapeutic use in osteoclastogenic removal of mineral deposits from arteries.

Crystallizing nanoparticles derived from vascular smooth muscle cells contain the calcification inhibitor osteoprotegerin

Osteoprotegerin (OPG), a member of the TNF receptor superfamily, was initially found to modulate bone mass by blocking osteoclast maturation and function. Rodent models have also revealed a role for OPG as an inhibitor of vascular calcification. However, the precise mode of how OPG blocks mineralization is unclear. In this study, OPG was found in an in vitro assay to significantly inhibit calcification of vascular smooth muscle cells (VSMC) induced by high calcium/phosphate (Ca/P) treatment (p=0.0063), although this effect was blunted at high OPG concentrations. By confocal microscopy, OPG was detected in VSMC in the Golgi, the same localization seen in osteoblasts, which express OPG in bone. Treatment of VSMC by minerals (Ca, P, or both) induced OPG mRNA expression as assessed by real-time quantitative PCR, and VSMC derived from atherosclerotic plaque material also exhibited higher OPG expression as compared to control cells (p<0.05). Furthermore, OPG was detected by Western blotting in matrix vesicles (MV), nanoparticles that are released by VSMC with the capacity to nucleate mineral. In atherosclerotic arteries, OPG colocalized immunohistochemically with annexin VI, a calcium-dependent membrane and phospholipid binding protein found in MV. Thus, the calcification inhibitor OPG is contained in crystallizing MV and has a biphasic effect on VSMC: physiologic concentrations inhibit calcification, whereas high concentrations commonly seen in patients with vascular disease have no effect. Like other calcification inhibitors, OPG may be specifically loaded into these nanoparticles to be deposited at remote sites, where it acts to inhibit calcification.