Michael Schoppet

Human Decidua Contains Potent Immunostimulatory CD83+ Dendritic Cells

Dendritic cells (DCs) are sentinel cells of the immune system important in initiating antigen-specific T-cell responses to microbial and transplantation antigens. DCs are particularly found in surface tissues such as skin and mucosa, where the organism is threatened by infectious agents. The human decidua, despite its proposed immunosuppressive function, hosts a variety of immunocompetent CD45 cells such as natural killer cells, macrophages, and T cells. Here we describe the detection, isolation, and characterization of CD45(+), CD40(+), HLA-DR(++), and CD83(+) cells from human early pregnancy decidua with typical DC morphology. CD83(+) as well as CD1a(+) cells were found in close vicinity to endometrial glands, with preference to the basal layer of the decidua. In vitro, decidual CD83(+) cells could be enriched to approximately 30%, with the remainder of cells encompassing DC-bound CD3(+) T cells. Stimulation of allogeneic T cells in a mixed leukocyte reaction by the decidual cell fraction enriched for CD83(+) cells, was similar to that obtained with blood monocyte-derived DCs, demonstrating the potent immunostimulatory capacity of these cells. Decidual DCs with morphological, phenotypic, and functional characteristics of immunostimulatory DCs might be important mediators in the regulation of immunological balance between maternal and fetal tissue, leading to successful pregnancy.

The circulating calcification inhibitors, fetuin-A and osteoprotegerin, but not Matrix Gla protein, are associated with vascular stiffness and calcification in children on dialysis

BACKGROUND Vascular calcification occurs in the majority of patients with chronic kidney disease, but a subset of patients does not develop calcification despite exposure to a similar uraemic environment. Physiological inhibitors of calcification, fetuin-A, osteoprotegerin (OPG) and undercarboxylated-matrix Gla protein (uc-MGP) may play a role in preventing the development and progression of ectopic calcification, but there are scarce and conflicting data from clinical studies. METHODS We measured fetuin-A, OPG and uc-MGP in 61 children on dialysis and studied their associations with clinical, biochemical and vascular measures. RESULTS Fetuin-A and OPG were higher and uc-MGP lower in dialysis patients than controls. In controls, fetuin-A and OPG increased with age. Fetuin-A showed an inverse correlation with dialysis vintage (P = 0.0013), time-averaged serum phosphate (P = 0.03) and hs-CRP (P = 0.001). Aortic pulse wave velocity (PWV) and augmentation index showed a negative correlation with fetuin-A while a positive correlation was seen with PWV and OPG. Patients with calcification had lower fetuin-A and higher OPG than those without calcification. On multiple linear regression analysis Fetuin-A independently predicted aortic PWV (P = 0.004, beta = -0.45, model R(2) = 48%) and fetuin-A and OPG predicted cardiac calcification (P = 0.02, beta = -0.29 and P = 0.014, ss = 0.33, respectively, model R(2) = 32%). CONCLUSIONS This is the first study to define normal levels of the calcification inhibitors in children and show that fetuin-A and OPG are associated with increased vascular stiffness and calcification in children on dialysis. Higher levels of fetuin-A in children suggest a possible protective upregulation of fetuin-A in the early stages of exposure to the pro-calcific and pro-inflammatory uraemic environment.

Inhibition of Receptor Activator of NF-κB Ligand by Denosumab Attenuates Vascular Calcium Deposition in Mice

Osteoporosis and vascular calcification frequently coincide. A potential mediator of bone metabolism and vascular homeostasis is the triad cytokine system, which consists of receptor activator of nuclear factor-kappaB (RANK) ligand (RANKL), its receptor RANK, and the decoy receptor osteoprotegerin. Unopposed RANKL activity in osteoprotegerin-deficient mice resulted in osteoporosis and vascular calcification. We therefore analyzed the effects of RANKL inhibition by denosumab, a human monoclonal antibody against RANKL, on vascular calcium deposition following glucocorticoid exposure. Prednisolone pellets were implanted into human RANKL knock-in (huRANKL-KI) mice, which unlike wild-type mice are responsive to denosumab. No histomorphological abnormalities or differences in aortic wall thickness were detected between wild-type and huRANKL-KI mice, regardless of treatment with prednisolone, denosumab, or both. However, concurrent treatment with denosumab reduced aortic calcium deposition of prednisolone-treated huRANKL-KI mice by up to 50%, based on calcium measurement. Of note, aortic calcium deposition in huRANKL-KI mice was correlated negatively with bone mineral density at the lumbar spine (P = 0.04) and positively with urinary excretion of deoxypyridinoline, a marker of bone resorption (P = 0.01). In summary, RANKL inhibition by denosumab reduced vascular calcium deposition in glucocorticoid-induced osteoporosis in mice, which is further evidence for the link between the bone and vascular systems. Therefore, the prevention of bone loss by denosumab might also be associated with reduced vascular calcification in certain conditions.

Prevention of glucocorticoid‐induced bone loss in mice by inhibition of RANKL

OBJECTIVE RANKL has been implicated in the pathogenesis of glucocorticoid-induced osteoporosis. This study was undertaken to evaluate the efficacy of denosumab, a neutralizing monoclonal antibody against human RANKL (hRANKL), in a murine model of glucocorticoid-induced osteoporosis. METHODS Eight-month-old male homozygous hRANKL-knockin mice expressing a chimeric RANKL protein with a humanized exon 5 received 2.1 mg/kg of prednisolone or placebo daily over 4 weeks via subcutaneous slow-release pellets and were additionally treated with phosphate buffered saline or denosumab (10 mg/kg subcutaneously twice weekly). Two groups of wild-type mice were also treated with either prednisolone or vehicle. RESULTS The 4-week prednisolone treatment induced loss of vertebral and femoral volumetric bone mineral density in the hRANKL-knockin mice. Glucocorticoid-induced bone loss was associated with suppressed vertebral bone formation and increased bone resorption, as evidenced by increases in the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, TRAP-5b protein in bone extracts, serum levels of TRAP-5b, and urinary excretion of deoxypyridinoline. Denosumab prevented prednisolone-induced bone loss by a pronounced antiresorptive effect. Biomechanical compression tests of lumbar vertebrae revealed a detrimental effect of prednisolone on bone strength that was prevented by denosumab. CONCLUSION Our findings indicate that RANKL inhibition by denosumab prevents glucocorticoid-induced loss of bone mass and strength in hRANKL-knockin mice.

Mineral Surface in Calcified Plaque Is Like That of Bone: Further Evidence for Regulated Mineralization

Objectives—Cell biological studies demonstrate remarkable similarities between mineralization processes in bone and vasculature, but knowledge of the components acting to initiate mineralization in atherosclerosis is limited. The molecular level microenvironment at the organic–inorganic interface holds a record of the mechanisms controlling mineral nucleation. This study was undertaken to compare the poorly understood interface in mineralized plaque with that of bone, which is considerably better characterized. Methods and Results—Solid state nuclear magnetic resonance (SSNMR) spectroscopy provides powerful tools for studying the organic–inorganic interface in calcium phosphate biominerals. The rotational echo double resonance (REDOR) technique, applied to calcified human plaque, shows that this interface predominantly comprises sugars, most likely glycosaminoglycans (GAGs). In this respect, and in the pattern of secondary effects seen to protein (mainly collagen), calcified plaque strongly resembles bone. Conclusion—The similarity between biomineral formed under highly controlled (bone) and pathological (plaque) conditions suggests that the control mechanisms are more similar than previously thought, and may be adaptive. It is strong further evidence for regulation of plaque mineralization by osteo/chondrocytic vascular smooth muscle cells.

Atorvastatin stimulates the production of osteoprotegerin by human osteoblasts

Recently, HMG‐CoA reductase inhibitors (statins), potent inhibitors of cholesterol biosynthesis, have been linked to protective effects on bone metabolism. Because of their widespread use, prevention of bone loss and fractures would be a desirable side effect. However, the mechanisms how statins may affect bone metabolism are poorly defined. Here, we evaluated the effect of atorvastatin on osteoblastic production of receptor activator of nuclear factor‐κB ligand (RANKL) and osteoprotegerin (OPG), cytokines that are essential for osteoclast cell biology. While RANKL enhances osteoclast formation and activation, thereby, promoting bone loss, OPG acts as a soluble decoy receptor and antagonizes the effects of RANKL. In primary human osteoblasts (hOB), atorvastatin increased OPG mRNA levels and protein secretion by hOB by up to three fold in a dose‐dependent manner with a maximum effect at 10−6 M (P < 0.001). Time course experiments indicated a time‐dependent stimulatory effect of atorvastatin on OPG mRNA levels after 24 h and on OPG protein secretion after 48–72 h (P < 0.001). Treatment of hOB with substrates of cholesterol biosynthesis that are downstream of the HMG‐CoA reductase reaction (mevalonate, geranylgeranyl pyrophosphate) reversed atorvastatin‐induced enhancement of OPG production. Of note, atorvastatin abrogated the inhibitory effect of glucocorticoids on OPG production. Treatment of hOB with atorvastatin enhanced the expression of osteoblastic differentiation markers, alkaline phosphatase and osteocalcin. In summary, our data suggest that atorvastatin enhances osteoblastic differentiation and production of OPG. This may contribute to the bone‐sparing effects of statins.

Serum level of the phosphaturic factor FGF23 is associated with abdominal aortic calcification in men: the STRAMBO study.

CONTEXT Calcification inhibitor deficiencies, mineral imbalance, and phenotypic transformation of vascular cells to osteogenic cells initiate and sustain vascular calcification. Fibroblast growth factor-23 (FGF23) is a key molecule regulating mineral homeostasis. OBJECTIVE Our objective was to assess the association of serum FGF23 levels with mineral metabolism parameters and abdominal aortic calcification (AAC) in men. DESIGN This was a cross-sectional analysis in the STRAMBO cohort. SETTING Men holding a private health insurance cover with Mutuelle de Travailleurs de la Région Lyonnaise were included in the study. PARTICIPANTS Participants included male volunteers aged 20-87 (n = 1130). INTERVENTIONS Nonfasting blood collection was done. AAC was semiquantitatively assessed from vertebral fracture assessment scans obtained using dual-energy x-ray absorptiometry. MAIN OUTCOME MEASURES We evaluated the association between FGF23 concentration and AAC severity in men. RESULTS In 350 men aged 60 yr or younger, FGF23 levels decreased with age (r = -0.21; P < 0.001) but were not associated with any other parameter. In 780 men aged over 60 yr, serum FGF23 correlated with age (r = 0.37; P < 0.001) and, after adjustment for confounders, with glomerular filtration rate (r = -0.31; P < 0.001) and PTH levels (r = 0.25; P < 0.001). After adjustment for confounders, self-reported ischemic heart disease, diabetes mellitus as well as higher concentrations of C-reactive protein and osteoprotegerin were all associated with higher FGF23 levels. After adjustment for confounders, subjects in the highest FGF23 quartile had higher prevalence of severe AAC compared with the three lower quartiles combined (odds ratio = 1.88; 95% confidence interval = 1.22-2.85; P < 0.005). CONCLUSIONS In healthy older men, circulating FGF23 is associated with parameters of mineral metabolism, including bone metabolism-regulating cytokines, and with severe AAC independent of traditional risk factors.

Low Serum Levels of Soluble RANK Ligand Are Associated With the Presence of Coronary Artery Disease in Men

To the Editor: Receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) represent the ligand and decoy receptor, respectively, of a pleiotropic cytokine system that regulates bone metabolism and vascular biology.1 Elevated OPG serum levels have recently been shown to be associated with increased cardiovascular mortality in postmenopausal women.2 In the September 3, 2002 issue of Circulation , Jono et al3 reported increased OPG serum levels in 201 Japanese patients with coronary artery disease (CAD) and a positive correlation of OPG serum levels with the severity of CAD. In a cohort of 522 white men who underwent coronary angiography, we have confirmed that OPG serum levels are highest in those with advanced CAD, …

Effects of oral contraceptives on circulating osteoprotegerin and soluble RANK ligand serum levels in healthy young women

objective  Osteoprotegerin (OPG) represents a secreted cytokine which regulates bone mass by blocking receptor activator of nuclear factor‐κB ligand (RANKL), the principal regulator of osteoclast function. In vitro, OPG production is upregulated by oestrogens in osteoblastic lineage cells, a mechanism that has been discussed as a protective paracrine mechanism of oestrogens on the skeleton. To define the effects of oestrogens on the RANKL/OPG system in vivo, we evaluated OPG and both free and total soluble RANKL (sRANKL) serum levels in healthy young women with or without oral contraceptives.

Interleukin-4 and interleukin-13 stimulate the osteoclast inhibitor osteoprotegerin by human endothelial cells through the STAT6 pathway.

Introduction: Endothelial cells of the bone vasculature modulate development, remodeling, and repair of bone by secreting osteotropic cytokines and hormones, which can act on osteoblastic and osteoclastic lineage cells. RANKL is the essential factor for differentiation, activation, and survival of osteoclasts, whereas osteoprotegerin (OPG) is a soluble decoy receptor and inhibitor for RANKL.