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Biomedical subjects

Michael Schoppet

Publications and source records attributed to Michael Schoppet.

At least 19 recordsLinked to original sources
PubMed2007

Osteoprotegerin expression in dendritic cells increases with maturation and is NF-kappaB-dependent.

Dendritic cells (DC) comprise a unique leukocyte population which controls primary immune responses. Recent studies indicate that DC express osteoprotegerin (OPG), a secreted tumor necrosis factor receptor homolog, which regulates DC survival, monocyte chemotaxis, and B cell development and function by ligating TNF family member receptor activator of NF-kappaB ligand (RANKL). The precise regulators of OPG expression in DC have not been investigated. In this study, we assessed OPG mRNA steady state levels by Northern blot analysis and OPG protein secretion by an immunoassay in monocyte-derived DC of different maturation, and the effect of different cytokines and hormones on OPG expression. OPG was upregulated with maturation of DC, whereas pretreatment of DC with 1alpha,25(OH)(2) vitamin D(3), tamoxifen, or dexamethasone, agents that inhibit differentiation of DC, decreased OPG expression. In vivo, OPG was found to be colocalized with mature CD83(+) DC in human tonsils by immunofluorescence confocal microscopy analysis. Furthermore, OPG was upregulated by TNF superfamily members TNF-alpha, anti-CD40, and RANKL, and by ligands of the Toll-like/IL-1 receptor family including IL-1beta, double-stranded RNA (poly I:C), or lipopolysaccharide (LPS), all of which induce maturation of DC. Gene silencing by small interfering RNA (siRNA) directed against transcription factor NF-kappaB abrogated the expression of OPG as demonstrated by real-time PCR. In summary, we describe that the expression of OPG by DC increases with maturation and is NF-kappaB-dependent, possibly regulating immune responses in lymphoid tissues.

Blotting, Northern↗
PubMed2006

Interleukin-4 differentially regulates osteoprotegerin expression and induces calcification in vascular smooth muscle cells.

Vascular calcification is characterized by cellular transdifferentiation and expression of bone-related matrix proteins that result in the presence of bone-like structures in the vascular wall. Interleukin (IL)-4, a pleiotropic cytokine, and osteoprotegerin (OPG), an essential regulator of osteoclast biology, have both been linked to vascular disease. Here, we assessed the role of IL-4 and OPG in vascular calcification in vitro. IL-4 induced OPG mRNA levels and protein secretion by 5-fold in a dose- and time-dependent fashion in human coronary artery smooth muscle cells (CASMC). Activation of the transcription factor STAT6 preceded IL-4-induced OPG expression, and blockade of IL-4-induced STAT6 activation by the phospholipase C inhibitor D609 decreased OPG expression. Long-term exposure of IL-4 for 4 weeks resulted in transformation of CASMC towards an osteoblastic phenotype, based on the expression of the transcription factor Cbfa1 and increased mineral deposition. Notably, calcification of CASMC was inhibited by gene silencing of Cbfa1. During osteogenic transformation, IL-4 down-regulated OPG production in CASMC. IL-4 has differential effects in CASMC: While short-term exposure enhances OPG production through a STAT6-dependent mechanism, long-term exposure causes Cbfa1-dependent osteogenic transformation and a decreased production of OPG, an inhibitor of bone resorption.

Bone Resorption↗
PubMed2005

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-kappaB 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.

Adult↗
PubMed2005

TNF-related apoptosis-inducing ligand and its decoy receptor osteoprotegerin in nonischemic dilated cardiomyopathy.

Apoptosis has been attributed an essential role in dilated cardiomyopathy (DCM) recently. We assessed expression of TNF-related apoptosis-inducing ligand (TRAIL) and its decoy receptor osteoprotegerin (OPG) in men with nonischemic DCM, who underwent coronary angiography and endomyocardial biopsy (EMB) after exclusion of coronary artery disease compared to control patients. TRAIL plasma concentrations were elevated in DCM (p=0.02 vs. controls), and were positively correlated with left ventricular enddiastolic diameter (r=0.15, p=0.04), whereas OPG plasma levels did not differ between both groups (p=0.96). In EMB of DCM patients, TRAIL and OPG protein were detected by immunohistochemistry but not in controls. Furthermore, gene expression in EMB or peripheral blood leukocytes (PBL) of DCM patients assessed by real-time PCR showed an increase of TRAIL mRNA in PBL (p=0.01 vs. controls), whereas OPG mRNA was upregulated in endomyocardial specimens (p<0.001 vs. controls). In conclusion, myocardial overexpression of antiapoptotic OPG in DCM patients may represent a compensatory mechanism to limit systemic activation of TRAIL in patients with congestive heart disease.

Adult↗
PubMed2005

Isopropanolic extract of black cohosh stimulates osteoprotegerin production by human osteoblasts.

UNLABELLED: An isopropanolic extract (iCR) from the rhizomes of Cimicifuga racemosa (black cohosh) is used an alternative in the treatment of menopausal symptoms, and animal studies suggest positive skeletal effects. iCR stimulated osteoblastic OPG protein secretion by 3- to 5-fold as early as 12 h without affecting RANKL expression. The iCR effect, abrogated by the pure estrogen receptor antagonist ICI 182,780, also enhanced ALP activity (4-fold) and osteocalcin expression (3-fold), possibly contributing to the skeletal effects of black cohosh. INTRODUCTION: Despite its positive effects on the skeleton, estrogen replacement therapy is no longer recommended as first-line therapy for the prevention and treatment of postmenopausal osteoporosis because it increases cardiovascular, thromboembolic, and breast cancer risk. Recently, herbal therapeutics such as an isopropanolic extract (iCR) from the rhizomes of Cimicifuga (=Actaea) racemosa (black cohosh) are gaining interest as an alternative in the treatment of menopausal symptoms. Whereas animal studies in rats suggest positive skeletal effects, the mechanism of its actions on bone cells remain unclear. RANKL is essential for osteoclast formation and activation, while osteoprotegerin (OPG) neutralizes RANKL. MATERIALS AND METHODS: In this study, we assessed the effects of iCR on OPG and RANKL mRNA steady-state levels by semiquantitative RT-PCR and on protein production by an ELISA system in human osteoblasts (hOBs). RESULTS: Under serum-free conditions, treatment with iCR increased OPG mRNA levels and protein secretion of hOBs by 2- to 3-fold in a dose-dependent manner, with a maximum effect at a 10(6)-fold dilution of iCR (p < 0.001) after 24-48 h. Time-course experiments indicated a stimulatory effect of iCR on osteoblastic OPG protein secretion by 3- to 5-fold (p < 0.001) as early as 12 h, whereas RANKL expression was very low and was not found to be modulated by iCR. Of note, the stimulatory effect of iCR on OPG production was abrogated by the pure estrogen receptor antagonist ICI 182,780. Moreover, iCR enhanced two osteoblastic differentiation markers, bone-specific alkaline phosphatase activity and osteocalcin expression, by up to 4- and 3-fold, respectively (p < 0.001). CONCLUSIONS: Our data suggest that iCR enhances differentiation and increases the OPG-to-RANKL ratio of normal human osteoblasts. These effects may contribute to the positive skeletal effects of black cohosh.

2-Propanol↗
PubMed2005

Matrix metalloproteinases and their inhibitors in malignant and autoreactive pericardial effusion.

Matrix metalloproteinases (MMPs) are proteolytic enzymes essentially involved in tissue remodeling and tumor invasion, and their activity is counterbalanced by endogenous antagonists, the tissue inhibitors of matrix proteinases (TIMPs). Recent reports have suggested a potential role of MMPs in the evolution of pericardial effusion (PE). In this study, we determined the levels of MMP-2 and MMP-9 and their inhibitors TIMP-1 and TIMP-2 in 19 patients who had malignant PE that was confirmed by histology or cytology and 30 patients who had nonmalignant, autoreactive PE compared with pericardial fluid of 19 patients who had preserved left ventricular function and who underwent aortocoronary bypass surgery for control. Samples were assayed by zymography, immunoblotting, and quantitative enzyme-linked immunosorbent assay. We found significantly higher MMP-2 levels in malignant PE than in pericardial fluid (2,906 +/- 348 vs 1,493 +/- 114 ng/ml, p = 0.0005) or autoreactive PE (2,079 +/- 269 ng/ml, p = 0.01). No significant differences in MMP-9 levels were found between malignant PE and autoreactive PE (83 +/- 28.6 vs 106 +/- 30.4 ng/ml, p = 0.22), whereas MMP-9 was below the detection limit in pericardial fluid. No differences in TIMP-1 levels were found across the different study groups, whereas compared with pericardial fluid, TIMP-2 levels were significantly lower in autoreactive PE (113 +/- 18.9 vs 187 +/- 12.2 ng/ml, p = 0.002). In addition, there was a trend to lower TIMP-2 levels in malignant PE (137 +/- 27.1 ng/ml, p = 0.07). The present findings indicate that proteolytic enzymes and their inhibitors are involved in the pathogenesis of PE, with an expression pattern that depends on etiology. The involvement of MMP-2 in the pathogenesis of malignant PE may indicate a potential role of MMP inhibitors in the control of malignant PE.

Biopsy↗
PubMed2004

Clinical implications of the osteoprotegerin/RANKL/RANK system for bone and vascular diseases.

Bone resorption by osteoclasts is coupled with bone formation by osteoblasts, and this balanced process continuously remodels and adapts the skeleton. The receptor activator of nuclear factor kappaB ligand (RANKL) has been identified as an essential cytokine for the formation and activation of osteoclasts. The effects of RANKL are physiologically counterbalanced by the decoy receptor osteoprotegerin (OPG). Estrogen deficiency, glucocorticoid exposure, T-cell activation (eg, rheumatoid arthritis), and skeletal malignancies (eg, myeloma, metastases) enhance the ratio of RANKL to OPG and, thus, promote osteoclastogenesis, accelerate bone resorption, and induce bone loss. Moreover, alterations of the OPG/RANKL/RANK system have been implicated in vascular diseases. RANKL blockade (using OPG or RANK fusion proteins or RANKL antibodies) has prevented bone loss caused by osteoporosis, chronic inflammatory disorders, and malignant tumors in animal models and may emerge as a therapy in humans based on studies in postmenopausal osteoporosis, myeloma bone disease, and osteolytic metastases. This review summarizes the clinical implications of the OPG/RANKL/RANK system for bone and vascular diseases.

Animals↗
PubMed2004

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-kappaB 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. DESIGN AND PATIENTS: Serum levels of OPG and sRANKL were prospectively assessed in a cohort of healthy young women with (n = 30) or without (n = 25) combined oestrogen-progestin-based oral contraceptives. MEASUREMENTS: OPG, total and free sRANKL serum levels were determined by enzyme-linked immunosorbent assays (ELISA). RESULTS: In women using oral contraceptives, OPG serum levels were significantly higher (2.71 +/- 1.42 pmol/l) compared to nonusers (1.35 +/- 1.02 pmol/l; P = 0.0003), whereas free (P = 0.55) and total (P = 0.24) sRANKL serum levels did not differ between both groups. This resulted in an increased OPG/free sRANKL ratio (P = 0.02) in women on oral contraceptives. During the ovarian cycle, OPG (P = 0.22) and free sRANKL (P = 0.99) serum levels remained unchanged in women without oral contraceptives (n = 19), while total sRANKL levels were higher in the follicular than in the luteal phase (P = 0.02). CONCLUSIONS: Intake of oral contraceptives is associated with increased OPG serum levels, but not sRANKL levels, resulting in a higher OPG/sRANKL ratio. This may contribute to the positive effects of oral contraceptives on the skeleton.

Adult↗
PubMed2004

Localization of osteoprotegerin, tumor necrosis factor-related apoptosis-inducing ligand, and receptor activator of nuclear factor-kappaB ligand in Mönckeberg's sclerosis and atherosclerosis.

Vascular calcification may occur at different areas of the vessel wall, including the intima in atherosclerosis and the media in Mönckeberg's sclerosis. Medial calcification of arteries is common in patients with diabetes mellitus or chronic renal failure. Osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand are essential modulators of bone homeostasis and may be involved in the process of vascular calcification. In this study we investigated arteries from patients with Mönckeberg's sclerosis and atherosclerosis. Apoptosis, which precedes vascular calcification in vitro, was assessed by an in situ ligation assay and was localized to the medial layer of arteries (Mönckeberg's sclerosis) and the neointima (atherosclerosis). Immunohistochemistry and in situ hybridization revealed OPG immunoreactivity and mRNA expression surrounding calcified areas in the medial layer (Mönckeberg's sclerosis), whereas OPG was mainly expressed adjacent to calcified neointimal lesions (atherosclerosis). Receptor activator of nuclear factor-kappaB ligand protein and mRNA were barely or not detectable. Of note, TNF-related apoptosis-inducing ligand, an inducer of apoptosis that is also blocked by OPG, displayed a similar spatial distribution as OPG. In summary, we demonstrate enhanced apoptosis adjacent to vascular calcification, and the concurrent expression of regulators of apoptosis and osteoclastic differentiation, TNF-related apoptosis-inducing ligand and OPG, suggesting their involvement in the pathogenesis of vascular calcification.

Aged↗
PubMed2004

Osteoprotegerin gene polymorphisms in men with coronary artery disease.

Osteoprotegerin (OPG) antagonizes receptor activator of nuclear factor-kappaB ligand (RANKL), the principal regulator of osteoclasts. Of note, OPG-deficient mice display osteoporosis and arterial calcification. Recently, OPG gene polymorphisms have been associated with osteoporosis and early predictors of cardiovascular disease. In this study, we examined OPG gene polymorphisms in 468 men who had absence of coronary artery disease (CAD) or single-, double-, or triple-vessel disease on coronary angiography. Denaturing gradient gel electrophoresis followed by DNA sequencing revealed nucleotide substitutions 149 T-->C, 163 A-->G, 209 G-->A, 245 T-->G, 950 T-->C (all promoter), 1181 G-->C (exon 1), and 6890 A-->C (intron 4), respectively. Although single polymorphisms were not associated with CAD, linkage of polymorphisms 950 and 1181 revealed that haplotypes were overrepresented in men with CAD (chi(2) = 17.05; P = 0.03) with an increased risk of CAD in carriers of genotypes 950 TC/1181 GC and 950 CC/1181 CC (odds ratio, 1.67; 95% confidence interval, 1.02-2.72; P = 0.04). Furthermore, serum OPG levels were correlated with the presence of a C allele at position 950 (P = 0.02). In summary, linkage of genetic variations of the OPG gene at positions 950 and 1181 may confer an increased risk of CAD in Caucasian men.

Alleles↗
PubMed2003

Acute parvovirus B19 infection associated with myocarditis in an immunocompetent adult.

Inflammatory heart disease is causally linked with progressive left ventricular dysfunction and congestive heart failure. In childhood, infection with parvovirus B19 (PVB19) is usually benign, causing erythema infectiosum. However, severe fetal PVB19 infection may be associated with hydrops fetalis and fetal death caused by myocarditis. Here we report a PVB19-induced myocarditis in a previously healthy 37-year-old patient admitted to the hospital because of chest pain and dyspnea due to left ventricular dysfunction. Four weeks after the onset of symptoms, we found lymphocytic infiltrates and PVB19 genome in left ventricular endomyocardial biopsy specimens. Consistently, acute PVB19 infection was indicated serologically by elevated IgM titers and the presence of PVB19 genome in peripheral blood lymphocytes. In conclusion, PVB19 infection may be complicated by acute myocarditis in immunocompetent adults. Because PVB19 myocarditis may progress to chronic dilated cardiomyopathy, early diagnosis by endomyocardial biopsy is important to initiate anti-inflammatory treatment.

Acute Disease↗
PubMed2003

Increased osteoprotegerin serum levels in men with coronary artery disease.

Osteoprotegerin (OPG) regulates osteoclast and immune functions and appears to represent a protective factor for the vascular system. However, the role of OPG in human atherosclerosis has not been evaluated. In this study, we assessed OPG serum levels in 522 age-matched men who, on the basis of coronary angiography, had either absence of coronary artery disease (CAD) or presence of single-vessel disease, double-vessel disease, or severe triple-vessel disease. OPG serum levels were positively correlated with age (r = 0.28; P < 0.001) and were higher in men with diabetes mellitus (P < 0.01). OPG serum levels in men without CAD were 5.4 +/- 2.0 pmol/liter, compared with 6.1 +/- 2.1 pmol/liter in single-vessel disease (P < 0.005), 5.9 +/- 2.4 in double-vessel disease (P < 0.05), and 6.3 +/- 2.3 pmol/liter in triple-vessel disease (P < 0.001). Moreover, OPG serum levels were positively correlated with the severity of CAD as determined by a CAD scoring system (r = 0.17; P < 0.01). In conclusion, our data underline that OPG serum levels are associated with the severity of CAD and are increased in elderly men and patients with diabetes mellitus. We conclude that increased OPG serum levels may reflect advanced cardiovascular disease in men.

Aged↗
PubMed2003

Cardiac sarcoidosis: cytokine patterns in the course of the disease.

Sarcoidosis is a chronic systemic disease of unknown etiology, which is characterized by noncaseating epitheloid granulomas usually in multiple organs. Here we describe changes in cytokine mRNA expression by peripheral blood mononuclear cells (PBMCs) and changes of cytokine protein levels in plasma over a time course of 12 months in a patient with sarcoidosis confined to the heart as diagnosed by endomyocardial biopsy. Mitogen-stimulated PBMCs exhibited a more T(H)1 cytokine profile at onset of symptoms before immunosuppressive therapy was initiated, with a change to a T(H)0 response in the course of the disease as evidenced by multiplex-polymerase chain reaction. In plasma, high levels of interleukin-6 could be detected by an enzyme-linked immunosorbent assay system, with rapid decline correlating with immunosuppression and improving clinical course. These changes may point to a role of T(H)1 and T(H)2 cytokines in the pathogenesis and the healing process of cardiac sarcoidosis.

Adult↗