Mitochondrial respiratory activity is altered in osteoarthritic human articular chondrocytes

OBJECTIVE: Osteoarthritis (OA) is a degenerative rheumatic disease that is associated with extracellular matrix degradation and chondrocyte apoptosis in the articular cartilage. The role of mitochondria in degenerative diseases is widely recognized. We undertook this study to evaluate mitochondrial function in normal and OA chondrocytes and to examine age-related changes in mitochondria. METHODS: Mitochondrial function was evaluated by analyzing respiratory chain enzyme complexes and citrate synthase (CS) activities as well as changes in mitochondrial membrane potential (Delta Psi m). The activities of mitochondrial respiratory chain complexes (complex I: rotenone-sensitive NADH-coenzyme Q(1) reductase; complex II: succinate dehydrogenase; complex III: antimycin-sensitive ubiquinol cytochrome c reductase; and complex IV: cytochrome c oxidase) and CS were measured in human articular chondrocytes isolated from OA and normal cartilage. Delta Psi m was measured by JC-1 using flow cytometry. Statistical analysis was performed using the Mann-Whitney U test and Student's t-test as well as several models of multiple linear regression. RESULTS: OA articular chondrocytes had reduced activities of complexes II and III compared with cells from normal cartilage. However, the mitochondrial mass was increased in OA. Cultures of OA chondrocytes contained a higher proportion of cells with de-energized mitochondria. We found no relationship between mitochondrial function and donor age either in normal or in OA chondrocytes. CONCLUSION: These findings suggest the involvement of mitochondrial function in the pathophysiology of OA. Cartilage degradation by OA and cartilage aging may be two different processes.     

The ratio of circulating osteoprotegerin to RANKL in early rheumatoid arthritis predicts later joint destruction

OBJECTIVE: Rheumatoid arthritis (RA) is a chronic inflammatory disease that may result in debilitating joint deformities with destruction of bone and cartilage. Inflammation is still considered the pivotal inducer of both components of joint damage. Results of recent animal studies suggested a prominent contribution of osteoclastic bone resorption that could be dissociated from inflammation. RANKL and its natural decoy receptor, osteoprotegerin (OPG), play key roles in osteoclast activation. In a group of patients with early RA not treated with disease-modifying drugs, we tested the hypothesis that osteoclast activation, reflected by the serum OPG:RANKL ratio at baseline, is negatively associated with progression of bone damage, independent of inflammation. METHODS: OPG and RANKL levels, together with a parameter of inflammation (first-year time-averaged erythrocyte sedimentation rate [tESR]), were measured in 92 patients with newly diagnosed early active RA who were participants in a randomized study. The tESR and the OPG:RANKL ratio were evaluated for the ability to predict 5-year radiographic progression of joint damage. RESULTS: The first-year tESR and the OPG:RANKL ratio, as measured at baseline, independently predicted 5-year radiographic progression of joint damage (both P < or = 0.001). Progression of radiographic damage was greatest in patients with a high tESR and a low OPG:RANKL ratio and was lowest in patients with a low tESR and a high OPG:RANKL ratio. CONCLUSION: This study in patients with early untreated RA is the first to confirm the findings in animal models of arthritis, that radiographic progression of the bone component of joint destruction is dependent on both inflammation (tESR) and osteoclast activation (the OPG:RANKL ratio).     

The platelet P2Y12 receptor contributes to granule secretion through Ephrin A4 receptor

The main responses of P2Y₁ ligation are platelet shape change and transient aggregation while P2Y₁₂ ligation amplifies P2Y₁-induced aggregation and accelerates aggregation, secretion and thromboxane A₂ production induced by other agonist-receptor complexes. We searched for new targets of P2Y signalling using micro-arrays with 144 peptides representing known phosphosites of protein tyrosine kinases. ADP induced phosphorylation of peptides representing surface receptors, second messenger enzymes and cytoskeletal proteins. Strong phosphorylation was found in peptides representing Ephrin-receptor family members. Blockade of P2Y_1/12 inhibited phosphorylation of EphA4- and EphB1-peptides on micro-arrays. The EphA2/4 inhibitor 2,5-dimethylpyrrolyl benzoic acid derivative interfered with P2Y_1/12-induced EphA4 phosphorylation, left P2Y₁-induced aggregation unchanged but inhibited with P2Y₁₂-induced secretion, second phase aggregation and thrombus formation on collagen at 1600?s^?1. These results show that platelet EphA4 is an important intermediate in P2Y₁₂-induced granule secretion.     

Alpha-lipoic acid suppresses osteoclastogenesis despite increasing the receptor activator of nuclear factor kappaB ligand/osteoprotegerin ratio in human bone marrow stromal cells

Growing evidence has shown a biochemical link between increased oxidative stress and reduced bone density. Although alpha-lipoic acid (alpha-LA) has been shown to act as a thiol antioxidant, its effect on bone cells has not been determined. Using proteomic analysis, we identified six differentially expressed proteins in the conditioned media of alpha-LA-treated human bone marrow stromal cell line (HS-5). One of these proteins, receptor activator of nuclear factor kappaB ligand (RANKL), was significantly up-regulated, as confirmed by immunoblotting with anti-RANKL antibody. ELISA showed that alpha-LA stimulated RANKL production in cellular extracts (membranous RANKL) about 5-fold and in conditioned medium (soluble RANKL) about 23-fold, but had no effect on osteoprotegerin (OPG) secretion. Despite increasing the RANKL/OPG ratio, alpha-LA showed a dose-dependent suppression of osteoclastogenesis, both in a coculture system of mouse bone marrow cells and osteoblasts and in a mouse bone marrow cell culture system, and reduced bone resorption in a dose-dependent manner. In addition, alpha-LA-induced soluble RANKL was not inhibited by matrix metalloprotease inhibitors, indicating that soluble RANKL is produced by alpha-LA without any posttranslational processing. In contrast, alpha-LA had no significant effect on the proliferation and differentiation of HS-5 cells. These results suggest that alpha-LA suppresses osteoclastogenesis by directly inhibiting RANKL-RANK mediated signals, not by mediating cellular RANKL production. In addition, our findings indicate that alpha-LA-induced soluble RANKL is not produced by shedding of membranous RANKL.     

Cardiorenal anemia syndrome in chronic heart failure contributes to increased sympathetic nerve activity

Background

We sought to assess whether cardiorenal anemia syndrome (CRAS) in chronic heart failure (CHF) patients contributes to sympathetic overactivity through modulation of sympathetic reflexes.

Methods and results

We prospectively studied 15 patients with CRAS and CHF and 15 control CHF patients, matched for age, gender distribution, type of cardiomyopathy, left ventricular ejection fraction (LVEF) and BMI. We compared muscle sympathetic nerve activity (MSNA) and the effect of peripheral chemoreflex deactivation on MSNA in both groups. We also compared sympathetic baroreflex function, assessed by the slope of the relationship between MSNA and diastolic blood pressure in both groups and while peripheral chemoreflexes were (by breathing 100% oxygen for 15 min) or not deactivated. Baseline MSNA was significantly elevated in CHF patients with CRAS compared with control CHF patients (83.1 ± 4.6 versus 64.9 ± 2.9 bursts/100 heart beats; P < 0.05) and sympathetic baroreflex impaired (2.69 ± 0.44 vs 5.25 ± 0.60% bursts/mm Hg; P < 0.01). Chemoreflex deactivation with administration of 100% oxygen led to a significant decrease in muscle sympathetic nerve activity (77.8 ± 4.7 versus 82.1 ± 4.9 bursts/100 heart beats; P < 0.01) and to an increase in sympathetic baroreflex function (2.77 ± 0.45 vs 5.63 ± 0.73% bursts/mm Hg; P < 0.01) in patients with CRAS and CHF. In contrast, neither room air nor 100% oxygen changed MSNA, hemodynamic or sympathetic baroreflex function in control CHF patients.

Conclusions

CRAS in CHF patients is associated with elevated sympathetic activity mediated by both tonic activation of peripheral chemoreflex and baroreflex impairment.     

Circulating preprandial ghrelin to obestatin ratio is increased in human obesity

CONTEXT: Obestatin, a sibling of ghrelin derived from preproghrelin, opposes ghrelin's effects on food intake. Plasma obestatin profiles in relation to ghrelin have not been fully investigated in human obesity. OBJECTIVE: We hypothesize that obesity might present with imbalance of circulating ghrelin and obestatin levels. PARTICIPANTS AND SETTING: Sixteen obese (eight men, aged 58.8 +/- 4.9 yr; eight women, aged 59.9 +/- 9.6 yr) and 14 normal-weight individuals (seven men, aged 52.7 +/- 5.9 yr; seven women, aged 56.1 +/- 4.9 yr) were evaluated at the in-patient department of Changhai Hospital, Shanghai, China. MAIN OUTCOME MEASURES: Total plasma ghrelin and obestatin levels, 1 h before and 2 h after breakfast, were measured by RIA. RESULTS: Both preprandial plasma ghrelin levels (P < 0.01) and obestatin levels (P < 0.01) were lower in the obese compared with normal-weight controls. However, unexpectedly, the ratio of preprandial ghrelin to obestatin was higher in obese compared with normal-weight controls (P < 0.01) even after adjustment for gender and age (P < 0.01). The ratio of postprandial ghrelin to obestatin was decreased both in obese (P < 0.05) and controls (P < 0.01) compared with their preprandial levels. There were no significant differences in the ratio of postprandial ghrelin to obestatin between obese and normal-weight controls. Body mass index was positively correlated with and was a significantly independent determinant of the preprandial ghrelin to obestatin ratio. CONCLUSION: Circulating preprandial ghrelin to obestatin ratio is elevated in human obesity. We suggest that high preprandial ghrelin to obestatin ratio may be involved in the etiology and pathophysiology of obesity.     

Serum osteoprotegerin and receptor activator of nuclear factors kB (RANKL) concentrations in normal children and in children with pubertal precocity, Turner's syndrome and rheumatoid arthritis

BACKGROUND: Osteoprotegerin (OPG) is a secreted member of the TNF receptor superfamily. OPG is made by osteoblastic cells and is expressed in a wide variety of cell and tissue types. It acts as a decoy receptor by binding the receptor activator of nuclear factors kB (RANKL) and preventing RANKL-induced osteoclast formation and differentiation. Numerous cytokines and hormones (TGF-beta, PTH, vitamin D, glucocorticoids and oestrogens) exert their effects on osteoclastogenesis by regulating the production of OPG. PATIENTS AND METHODS: In the present study we compared serum OPG and RANKL concentrations in a group of normal children (1-14 years old) with those of pair-aged children affected by different diseases [Turner's syndrome (TS), early/precocious puberty (PP) and rheumatoid arthritis (RA)]. OPG and RANKL concentrations were measured by an enzyme immunoassay method using a commercial kit. RESULTS: Mean (+/- SD) OPG level in normal children was 4.05 +/- 1.63 pmol/l with no difference between males and females. OPG values in children 1-4 years old (5.87 +/- 2.22 pmol/l) were significantly higher than in children 4-14 years old (3.55 +/- 0.97 pmol/l). OPG levels in children with RA were significantly higher than in controls (6.33 +/- 2.57 pmol/l vs. 4.05 +/- 1.63 pmol/l, P < 0.01); patients with TS or PP had OPG levels superimposable to those of controls (2.61 +/- 0.67 pmol/l and 3.99 +/- 0.85 pmol/l, respectively), but in TS OPG levels were significantly lower than in age-matched females. Mean RANKL concentration in normal subjects was 0.81 +/- 1.55 pmol/l; there was a slight decline in RANKL levels with age. RANKL concentrations in subjects with TS, PP, RA and controls did not differ significantly, and did not differ from those published in adult normal subjects. CONCLUSIONS: It appears from our data that OPG serum levels in healthy children aged > 4 years are similar to those present in young adult men, with higher levels in the first 4 years of life. Although the meaning of the alterations of OPG levels observed in pathological conditions is still obscure, they appear potentially interesting in view of a key role played by this protein in bone homeostasis.     

前列腺素E2调节大鼠成骨细胞RANKL/OPG mRNA表达的信号通路研究

目的 探讨前列腺素E2(PGE2)对大鼠成骨细胞RANKL和OPG mRNA表达的调节及其信号转导机制.方法 培养大鼠UMR106成骨细胞,采用不同浓度的PGE2、不同信号通路的激动剂和阻断剂干预细胞不同时间后收集细胞提取总RNA,实时荧光定量PCR检测RANKL和OPG mRNA的表达水平.结果PGE2、Forskolin和db-cAMP均可促进RANKL mRNA表达,抑制OPG mRNA的表达.PMA促进RANKL和OPG mRNA表达而A23187则下调RANKL和OPG表达.KT-5720下调PGE2诱导的RANKL mRNA表达约53%(P<0.001),而chelerythrine、维拉帕米、W7、KN-62和PD98059则对PGE2>诱导的RANKL mRNA表达无明显影响(P>0.05).KT-5720(P=0.01)、维拉帕米(P=0.029)和W7(P<0.001)均能部分阻断PGE2对OPG mRNA表达的下调作用,KN-62、PD98059和chelerythrine则不影响PGE2对OPG表达的调节(P>0.05).结论 PGE2诱导的RANKL表达是由PKA信号通路介导的,而PKA和钙/钙调蛋白信号通路则介导了PGE2对OPG表达的抑制作用.     

Tonic activity of carotid body chemoreceptors contributes to the increased sympathetic drive in essential hypertension

Carotid chemoreceptors provoke an increase in muscle sympathetic nerve activation (MSNA) in response to hypoxia; they are also tonically active during normoxic breathing. The contribution of peripheral chemoreceptors to sympathetic activation in hypertension is incompletely understood. The aim of our study was to investigate the effect of chemoreceptor deactivation on sympathetic activity in untreated patients with hypertension. A total of 12 untreated hypertensive males and 11 male controls participated in this randomized, crossover, placebo-controlled study. MSNA, systolic blood pressure(BP), diastolic BP, heart rate (HR), electrocardiogram, hemoglobin oxygen saturation (Sat%) and respiratory movements were measured during repeated 10-min periods of respiration with 100% oxygen or 21% oxygen in a blinded fashion. Compared with controls, hypertensives had higher resting MSNA (38 ± 10 vs. 29 ± 0.9 burst per min, P<0.05), systolic BP (150 ± 12 vs. 124 ± 10 mm Hg, P< 0.001) and diastolic BP (92 ± 10 vs. 77 ± 9 mm Hg, P<0.005). Breathing 100% oxygen caused significant decrease in MSNA in hypertensive patients (38 ± 10 vs. 26 ± 8 burst per min and 100 ± 0 vs. 90 ± 10 arbitrary units, P<0.05) and no change in controls (29 ± 9 vs. 27 ± 7 burst per min and 100 ± 0 vs. 96 ± 11 arbitrary units). BP, respiratory frequency and end tidal CO(2) did not change during chemoreceptor deactivation with hyperoxia. HR decreased and Sat% increased in both the study groups. These results confirm the role of tonic chemoreceptor drive in the development of sympathetic overactivity in hypertension.     

A loss-of-function polymorphism in the human P2X4 receptor is associated with increased pulse pressure

The P2X4 receptor is involved in endothelium-dependent changes in large arterial tone in response to shear stress and is, therefore, potentially relevant to arterial compliance and pulse pressure. Four identified nonsynonymous polymorphisms in P2RX4 were reproduced in recombinantly expressed human P2X4. Electrophysiological studies showed that one of these, the Tyr315>Cys mutation (rs28360472), significantly reduced the peak amplitude of the ATP-induced inward current to 10.9% of wild-type P2X4 receptors in transfected HEK-293 cells (10 μmol/L of ATP; n=4-8 cells; P<0.001). Concentration-response curves for ATP and the partial agonist BzATP demonstrate that the 315Cys-P2X4 mutant had an increased EC(50) value for both ligands. Mutation of Tyr315>Cys likely disrupts the agonist binding site of P2X4 receptors, a finding supported by molecular modeling based on the zebrafish P2X4 receptor crystal structure. We tested inheritance of rs28360472 encoding the Tyr315>Cys mutation in P2RX4 against pulse pressure in 2874 subjects from the Victorian Family Heart Study. The minor allele frequency was 0.014 (1.4%). In a variance components analysis we found significant association with pulse pressure (P=0.023 for total association) where 1 minor allele increased pulse pressure by 2.84 mm Hg (95% CI: 0.41-5.27). This increase in pulse pressure associated with inheritance of 315Cys-P2X4 receptors might reflect reduced large arterial compliance as a result of impaired endothelium-dependent vasodilation in large arteries.     

Circulating levels of receptor activator of nuclear factor-kappaB ligand/osteoprotegerin/macrophage-colony stimulating factor in a presumably healthy human population

OBJECTIVES: To determine the ranges of variation of circulating receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoprotegerin (OPG)/macrophage-colony stimulating factor(M-CSF) and to ascertain their potential relationships with age, sex and menopausal status in women, and with sex hormones in a population-based healthy cohort. SUBJECTS AND METHODS: Blood samples were collected with EDTA after an overnight fast. The plasma levels of each of the above biochemical indices were measured by ELISA in a total of 566 apparently healthy individuals aged 18-75 years. RESULTS: The plasma concentrations of cytokine molecules in the entire sample ranged from 674 to 4929 pg/ml for OPG, from 105 to 4468 pg/ml for soluble RANKL (sRANKL), and from 187 to 7604 pg/ml for M-CSF. The OPG levels demonstrated a clear positive correlation with age in both sexes (r=0.42 and 0.43, P<0.001, for men and women respectively). Application of the two-interval mathematical model revealed that in females OPG levels were age-independent until age 42, but then showed clear and significant correlation with age (r=0.48, P<0.001). As a result, young females (before 42 years) had a substantially lower average OPG level, 1377.8+/-327.68 pg/ml, in comparison with older women, 1666.02+/-397.14 pg/ml. The M-CSF correlation with age was significantly greater in women (r=0.29, P<0.001) compared with men (r=0.17, P<0.01). Significant negative correlations between plasma levels of both OPG and M-CSF with estradiol concentrations were observed in women (r=-0.39, P<0.01; r=-0.25, P<0.001 respectively). sRANKL did not correlate with either age or sex hormones in either women or men. CONCLUSION: Age and sex affect differently the interindividual variation of OPG, RANKL and M-CSF. Our observations could form the basis for further research to establish provisional reference limits for OPG and RANKL, which are potential markers for benign and malignant processes in bone.     

Estrogen receptor alpha, but not estrogen receptor beta, is involved in the regulation of the OPG/RANKL (osteoprotegerin/receptor activator of NF-kappa B ligand) ratio and serum interleukin-6 in male mice.

Estrogens are important for the male skeleton. Osteoprotegerin (OPG), receptor activator of NF-kappa B ligand (RANKL), interleukin-6 (IL-6), IL-1 and tumor necrosis factor alpha (TNFalpha) have been suggested to be involved in the skeletal effects of estrogen. We treated orchidectomized mice with estradiol for 2 weeks and observed a 143% increase in the trabecular bone mineral density of the distal metaphysis of femur that was associated with a decreased OPG/RANKL mRNA ratio in vertebral bone. A similar decreased OPG/RANKL ratio was also seen after estrogen treatment of ovariectomized female mice. The effect of estrogen receptor (ER) inactivation on the OPG/RANKL ratio was dissected by using intact male mice lacking ER alpha (ERKO), ER beta (BERKO) or both receptors (DERKO). The expression of OPG was increased in ERKO and DERKO but not in BERKO male mice, resulting in an increased OPG/RANKL ratio. Furthermore, serum levels of IL-6 and tartrate-resistant acid phosphatase 5b (TRAP 5b) were decreased in ERKO and DERKO, but not in BERKO male mice. These results demonstrate that ER alpha, but not ER beta, is involved in the regulation of the vertebral OPG/RANKL ratio, serum levels of IL-6 and TRAP 5b in male mice.     

The differential expression of osteoprotegerin (OPG) and receptor activator of nuclear factor kappaB ligand (RANKL) in human osteoarthritic subchondral bone osteoblasts is an indicator of the metabolic state of these disease cells

OBJECTIVE: We previously reported that human OA subchondral bone osteoblasts could be discriminated into two subpopulations identified by their levels of endogenous production (low [L] or high [H]) of PGE(2). Here, we investigated the OPG and RANKL expression levels, the histologic analysis of the subchondral bone as well as the osteoclast differentiation effect of osteoblasts on normal and both OA subpopulations (L and H), and further examined on the L OA osteoblasts the modulation of bone remodelling factors on the OPG and RANKL levels, as well as on the resorption activity. METHODS: Gene expression was determined using real-time PCR, PGE2 and OPG levels by specific ELISA, and membranous RANKL by flow cytometry. Histological observation of the subchondral bone was performed on human knee specimens. Osteoclast differentiation and formation was assayed by using the pre-osteoclastic cell line RAW 264.7. OPG and RANKL modulation on L OA osteoblasts was monitored following treatment with osteotropic factors, and the resorption activity was studied by the co-culture of differentiated PBMC/osteoblasts. RESULTS: Human OA subchondral bone osteoblasts expressed less OPG than normal. Compared to normal, RANKL gene expression levels were increased in L OA and decreased in H OA cells. The OPG/RANKL mRNA ratio was significantly diminished in L OA compared to normal or H OA (p<0.02, p<0.03), and markedly increased in H OA compared to normal. Inhibition of endogenous PGE(2) levels by indomethacin markedly decreased the ratio of OPG/RANKL on the H OA. In contrast to H OA osteoblasts, L OA cells induced a significantly higher level of osteoclast differentiation and formation (p<0.05).Histological analysis showed a reduced subchondral bone on the L OA and an increased bone mass on the H OA compared to normal. Treatment of L OA osteoblasts with osteotropic factors revealed that the OPG/RANKL mRNA expression ratio was significantly reduced by vitamin D(3) and significantly increased by TNF-alpha, PTH and PGE(2), while IL-1Beta demonstrated no effect. OPG protein levels showed similar profiles. No true effect was noted on membranous RANKL upon treatment with IL-1Beta, PGE(2) and PTH, but a significant increase was observed with vitamin D3 and TNF-alpha. The resorption activity of the L OA cells was significantly inhibited by all treatments except IL-1Beta, with maximum effect observed with vitamin D(3) and PGE(2). CONCLUSION: OPG and RANKL levels, and consequently the OPG/RANKL ratio, differed according to human OA subchondral bone osteoblast classification; it is decreased in L and increased in H OA. These findings, in addition to those showing that L OA osteoblasts have a reduced subchondral bone mass and induce a higher level of osteoclast differentiation, strongly suggest that the metabolic state of the L OA osteoblasts favours bone resorption.