Activation of peroxisome proliferator-activated receptor gamma inhibits osteoprotegerin gene expression in human aortic smooth muscle cells

Osteoprotegerin mediates adipogenesis in obesity

INTRODUCTION

Adipogenesis, the process of white adipose tissue expansion, plays a critical role in the development of obesity. Osteoprotegerin (OPG), known for its role in bone metabolism regulation, emerges as a potential regulator in mediating adipogenesis during obesity onset.

OBJECTIVES

This study aims to elucidate the involvement of OPG in adipogenesis during the early phases of diet-induced obesity and explore its therapeutic potential in obesity management.

METHODS

Using a diet-induced obesity model, we investigated OPG expression patterns in adipocytes and explored the mechanisms underlying its involvement in adipogenesis. We also assessed the effects of targeted silencing of OPG and recombinant OPG administration on obesity progression and insulin resistance. Additionally, the impact of electroacupuncture treatment on OPG levels and obesity management was evaluated in both animal models and human participants.

RESULTS

OPG expression was prominently activated in adipocytes of white adipose tissues during the early phase of diet-induced obesity. Hyperlipidemia induced Cbfa1-dependent OPG transcription, initiating and promoting adipogenesis, leading to cell-size expansion and lipid storage. Intracellular OPG physically bound to RAR and released the PPARɤ/RXR complex, activating adipogenesis-associated gene expression. Targeted silencing of OPG suppressed obesity development, while recombinant OPG administration promoted disease progression and insulin resistance in obese mice. Electroacupuncture treatment suppressed obesity development in an OPG-dependent manner and improved obesity parameters in obese human participants.

CONCLUSION

OPG emerges as a key regulator in mediating adipogenesis during obesity development. Targeting OPG holds promise for the prevention and treatment of obesity, as evidenced by the efficacy of electroacupuncture treatment in modulating OPG levels and managing obesity-related outcomes.

Genetic and Epigenetic Mechanisms Underlying Vascular Smooth Muscle Cell Phenotypic Modulation in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) refers to the localized dilatation of the infra-renal aorta, in which the diameter exceeds 3.0 cm. Loss of vascular smooth muscle cells, degradation of the extracellular matrix (ECM), vascular inflammation, and oxidative stress are hallmarks of AAA pathogenesis and contribute to the progressive thinning of the media and adventitia of the aortic wall. With increasing AAA diameter, and left untreated, aortic rupture ensues with high mortality. Collective evidence of recent genetic and epigenetic studies has shown that phenotypic modulation of smooth muscle cells (SMCs) towards dedifferentiation and proliferative state, which associate with the ECM remodeling of the vascular wall and accompanied with increased cell senescence and inflammation, is seen in in vitro and in vivo models of the disease. This review critically analyses existing publications on the genetic and epigenetic mechanisms implicated in the complex role of SMCs within the aortic wall in AAA formation and reflects the importance of SMCs plasticity in AAA formation. Although evidence from the wide variety of mouse models is convincing, how this knowledge is applied to human biology needs to be addressed urgently leveraging modern in vitro and in vivo experimental technology.

The Role of Osteoprotegerin as a Cardioprotective Versus Reactive Inflammatory Marker: the Chicken or the Egg Paradox

Cardiovascular disease is one of the most frequent causes of mortality and morbidity worldwide. Several variables have been identified as risk factors for cardiovascular disease. Recently, the role of receptor activator of nuclear factor kappa B, receptor activator of nuclear factor kappa B ligand, and the osteoprotegerin system has been recognized as more important in the pathogenesis of cardiovascular disease. Besides their roles in the regulation of bone resorption, these molecules have been reported to be associated with the pathophysiology of cardiovascular disease. There are conflicting data regarding the impact of osteoprotegerin, a glycoprotein with a regulatory role in the cardiovascular system. The aim of this review is to discuss the current knowledge and the role of osteoprotegerin in cardiovascular disease.

Roles and Clinical Applications of OPG and TRAIL as Biomarkers in Cardiovascular Disease

Cardiovascular diseases (CVD) remain the major cause of death and premature disability in Western societies. Assessing the risk of CVD is an important aspect in clinical decision-making. Among the growing number of molecules that are studied for their potential utility as CVD biomarkers, a lot of attention has been focused on osteoprotegerin (OPG) and its ligands, which are receptor activator of nuclear factor κB ligand (RANKL) and TNF-related apoptosis-inducing ligand. Based on the existing literature and on our experience in this field, here we review what the possible roles of OPG and TRAIL in CVD are and their potential utility as CVD biomarkers.

Comparative effects of metformin and pioglitazone on fetuin-A and osteoprotegerin concentrations in patients with newly diagnosed diabetes: A randomized clinical trial

AIMS

Fetuin-A is a circulating glycoprotein capable of inhibiting insulin signaling both in vivo and in vitro and is positively associated with insulin resistance. Osteoprotegerin (OPG) acts as a regulatory molecule with increased levels in the early stages of diabetes and atherosclerosis, and is also associated with insulin resistance. We investigated the effects of pioglitazone and metformin as representative insulin-sensitizing therapies on fetuin-A and OPG levels.

MATERIALS AND METHODS

In a randomized clinical trial setting (NCT02027103), 88 patients with newly diagnosed type 2 diabetes were randomly assigned to pioglitazone (30 mg/day, n=46) or metformin (1000 mg/day, n=42) for 12 weeks. Various anthropometric and metabolic parameters, fetuin-A, OPG, highly sensitive C-reactive protein (hsCRP), and homeostasis model assessment of insulin resistance (HOMA-IR) were measured at baseline and after three months.

RESULTS

The reduction in fasting plasma glucose and haemoglobin A1c levels was comparable in the two arms. Pioglitazone resulted in a significant reduction in both fetuin-A and OPG in men, but only fetuin-A in women. Metformin was only effective in lowering OPG levels in women. When compared, both medications were equally effective with regard to fetuin-A and OPG reduction in women (p=0.413 and 0.359, respectively). In men, pioglitazone more effectively decreased fetuin-A levels in both uni- (p=0.011) and multivariate models (p=0.015) and OPG levels in only uni- (p=0.023) but not the multivariate model (p=0.547).

CONCLUSIONS

Metformin and pioglitazone differentially affect fetuin-A and osteoprotegrin levels in diabetic women and men. The level of change may not necessarily be associated with the amelioration of insulin resistance.

Osteoprotegerin deficiency limits angiotensin II-induced aortic dilatation and rupture in the apolipoprotein E-knockout mouse

OBJECTIVE

Mounting evidence links osteoprotegerin with cardiovascular disease. Elevated serum and aortic tissue osteoprotegerin are associated with the presence and growth of abdominal aortic aneurysm in humans; however, a role for osteoprotegerin in abdominal aortic aneurysm pathogenesis remains to be shown. We examined the functional significance of osteoprotegerin in aortic aneurysm using an Opg-deficient mouse model and in vitro investigations.

APPROACH AND RESULTS

Homozygous deletion of Opg in apolipoprotein E-deficient mice (ApoE(-/-)Opg(-/-)) inhibited angiotensin II-induced aortic dilatation. Survival free from aortic rupture was increased from 67% in ApoE(-/-)Opg(+/+) controls to 94% in ApoE(-/-)Opg(-/-) mice (P=0.040). Serum concentrations of proinflammatory cytokines/chemokines, and aortic expression for cathepsin S (CTSS), matrix metalloproteinase 2, and matrix metalloproteinase 9 after 7 days (early-phase) of angiotensin II infusion were significantly reduced in ApoE(-/-)Opg(-/-) mice compared with ApoE(-/-)Opg(+/+) controls. In addition, aortic expression of markers for an inflammatory phenotype in aortic vascular smooth muscle cells in response to early-phase of angiotensin II infusion was significantly lower in Opg-deficient mice. In vitro, human abdominal aortic aneurysm vascular smooth muscle cells produced more CTSS and exhibited increased CTSS-derived elastolytic activity than healthy aortic vascular smooth muscle cells, whereas recombinant human osteoprotegerin stimulated CTSS-dependent elastase activity in aortic vascular smooth muscle cells.

CONCLUSIONS

These findings support a role for osteoprotegerin in aortic aneurysm through upregulation of CTSS, matrix metalloproteinase 2, and matrix metalloproteinase 9 within the aorta, promoting an inflammatory phenotype in aortic vascular smooth muscle cells in response to angiotensin II.

Peroxisome proliferator-activated receptor γ ligands retard cultured vascular smooth muscle cells calcification induced by high glucose

Peroxisome proliferator-activated receptor γ (PPARγ) and its ligands have profound effects on glucose homeostasis, cardiovascular diseases, and bone metabolism. To explore the pathophysiological roles of PPARγ in diabetes with concomitant vascular calcification, we investigated changes in PPARγ expression and the effect of the PPARγ ligands troglitazone and rosiglitazone on vascular smooth muscle cell (VSMC) calcification induced by high glucose (HG, 25 mmol/L). Compared with low glucose, HG-induced VSMC calcification, and PPARγ mRNA, protein level was decreased. Troglitazone and rosiglitazone treatment markedly attenuated the VSMC calcification, whereas PPARγ antagonist GW9662 abolished the effect of rosiglitazone on calcification. Pretreatment of VSMCs with rosiglitazone, but not troglitazone, restored the loss of lineage marker expression: the protein levels of α-actin and SM-22α were increased 52 % (P < 0.05) and 53.1% (P < 0.01), respectively, as compared with HG alone. Troglitazone and rosiglitazone reversed the change in bone-related protein expression induced by HG: decreased the mRNA levels of osteocalcin, bone morphogenetic protein 2 (BMP2), and core binding factor α 1 (Cbfα-1) by 26.9% (P > 0.05), 50.0 % (P < 0.01), and 24.4% (P < 0.05), and 48.4% (P < 0.05), 41.4% (P < 0.01) and 56.2% (P < 0.05), respectively, and increased that of matrix Gla protein (MGP) 84.2% (P < 0.01) and 70.0%, respectively (P < 0.05), as compared with HG alone. GW9662 abolished the effect of rosiglitazone on Cbfα-1 and MGP expression. PPARγ ligands can inhibit VSMCs calcification induced by high glucose.

TRAIL-deficiency accelerates vascular calcification in atherosclerosis via modulation of RANKL

The osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) cytokine system, not only controls bone homeostasis, but has been implicated in regulating vascular calcification. TNF–related apoptosis-inducing ligand (TRAIL) is a second ligand for OPG, and although its effect in vascular calcification in vitro is controversial, its role in vivo is not yet established. This study aimed to investigate the role of TRAIL in vascular calcification in vitro using vascular smooth muscle cells (VSMCs) isolated from TRAIL^−/− and wild-type mice, as well as in vivo, in advanced atherosclerotic lesions of TRAIL^−/−ApoE^−/− mice. The involvement of OPG and RANKL in this process was also examined. TRAIL dose-dependently inhibited calcium-induced calcification of human VSMCs, while TRAIL^−/− VSMCs demonstrated accelerated calcification induced by multiple concentrations of calcium compared to wild-type cells. Consistent with this, RANKL mRNA was significantly elevated with 24 h calcium treatment, while OPG and TRAIL expression in human VSMCs was inhibited. Brachiocephalic arteries from TRAIL^−/−ApoE^−/− and ApoE^−/− mice fed a high fat diet for 12 w demonstrated increased chondrocyte-like cells in atherosclerotic plaque, as well as increased aortic collagen II mRNA expression in TRAIL^−/−ApoE^−/− mice, with significant increases in calcification observed at 20 w. TRAIL^−/−ApoE^−/− aortas also had significantly elevated RANKL, BMP-2, IL-1β, and PPAR-γ expression at 12 w. Our data provides the first evidence that TRAIL deficiency results in accelerated cartilaginous metaplasia and calcification in atherosclerosis, and that TRAIL plays an important role in the regulation of RANKL and inflammatory markers mediating bone turn over in the vasculature.

Osteoprotegerin inhibits calcification of vascular smooth muscle cell via down regulation of the Notch1-RBP-Jκ/Msx2 signaling pathway

Objective

Vascular calcification is a common pathobiological process which occurs among the elder population and in patients with diabetes and chronic kidney disease. Osteoprotegerin, a secreted glycoprotein that regulates bone mass, has recently emerged as an important regulator of the development of vascular calcification. However, the mechanism is not fully understood. The purpose of this study is to explore novel signaling mechanisms of osteoprotegerin in the osteoblastic differentiation in rat aortic vascular smooth muscle cells (VSMCs).

Methods and Results

VSMCs were isolated from thoracic aorta of Sprague Dawley rats. Osteoblastic differentiation of VSMCs was induced by an osteogenic medium. We confirmed by Von Kossa staining and direct cellular calcium measurement that mineralization was significantly increased in VSMCs cultured in osteogenic medium; consistent with an enhanced alkaline phosphatase activity. This osteoblastic differentiation in VSMCs was significantly reduced by the addition of osteoprotegerin in a dose responsive manner. Moreover, we identified, by real-time qPCR and western blotting, that expression of Notch1 and RBP-Jκ were significantly up-regulated in VSMCs cultured in osteogenic medium at both the mRNA and protein levels, these effects were dose-dependently abolished by the treatment of osteoprotegerin. Furthermore, we identified that Msx2, a downstream target of the Notch1/RBP-Jκ signaling, was markedly down-regulated by the treatment of osteoprotegerin.

Conclusion

Osteoprotegerin inhibits vascular calcification through the down regulation of the Notch1-RBP-Jκ signaling pathway.

trans-10,cis-12 conjugated linoleic acid promotes bone formation by inhibiting adipogenesis by peroxisome proliferator activated receptor-γ-dependent mechanisms and by directly enhancing osteoblastogenesis from bone marrow mesenchymal stem cells

The bone undergoes continuous remodeling of osteoblastic bone formation and osteoclastic bone resorption to maintain proper bone mass. It is also reported that bone marrow adiposity has a reciprocal role in osteoblasts due to their same origin from mesenchymal stem cells. In addition, one of the key mediators of adipogenesis, peroxisome-proliferator activated receptor-γ (PPARγ), plays a significant role in osteoblastogenesis in bone marrow mesenchymal stem cells. One dietary component that is known to have significant impact on adiposity and bone mass is conjugated linoleic acid (CLA). However, the link between controlling adiposity to improving bone mass by CLA has not been studied intensively. Thus, the purpose of this study is to determine the role of CLA on bone marrow adiposity and bone formation using murine mesenchymal stem cells. The results confirmed that the trans-10,cis-12 CLA, but not the cis-9,trans-11 CLA isomer, significantly inhibited adipogenesis and promoted osteoblastogenesis from mesenchymal stem cells. The inhibition of adipogenesis by the trans-10,cis-12 CLA was mediated by PPARγ; however, the trans-10,cis-12 CLA had a direct effect on osteoblastogenesis which was independent to PPARγ in this model. The trans-10,cis-12 CLA also had significant effects on osteoclastogenesis inhibitory factor, which suggests potential influence of CLA on osteoclastogenesis. Overall, the results suggest that the trans-10,cis-12, but not the cis-9,trans-11 CLA isomer, has a positive impact on bone health by both PPARγ mediated and independent mechanisms in mesenchymal stem cells.

Osteoprotegerin as a marker of atherosclerosis in diabetic patients

Atherosclerosis is the principal cause of cardiovascular disease (CVD) and has many risk factors, among which is diabetes. Osteoprotegerin (OPG) is a soluble glycoprotein, involved in bone metabolism. OPG is also found in other tissues, and studies have shown that it is expressed in vascular smooth muscle cells. OPG has been implicated in various inflammations and also has been linked to diabetes mellitus. Increased serum OPG levels were found in patients with diabetes and poor glycemic control. Furthermore, prepubertal children with type 1 diabetes have significantly increased OPG levels. Receptor activator of nuclear factor kappa-B ligand (RANKL) is not found in the vasculature in normal conditions, but may appear in calcifying areas. OPG and RANKL are important regulators of mineral metabolism in both bone and vascular tissues. Few data are available on the relationship between plasma OPG/RANKL levels and endothelial dysfunction as assessed using noninvasive methods like ultrasound indexes, neither in the general population nor, more specifically, in diabetic patients. The aim of our review study was to investigate, based on the existing data, these interrelationships in order to identify a means of predicting, via noninvasive methods, later development of endothelial dysfunction and vascular complications in diabetic patients.

4-O-carboxymethyl ascochlorin causes ER stress and induced autophagy in human hepatocellular carcinoma cells

The synthetic derivative of ascochlorin, 4-O-carboxymethyl ascochlorin (AS-6) is an agonist of the nuclear hormone receptor PPARγ and has been shown to induce differentiation in mouse pre-adipocytes and to ameliorate type II diabetes in a murine model. AS-6 was cytotoxic when added at micromolar concentrations to cultures of three different human cancer cell lines. We used gel electrophoresis and mass spectrometry to identify proteins with altered expression in human hepatocarcinoma cells (HepG2) cells after 12 h in the presence of AS-6 and found 58 proteins that were differentially expressed. Many of the proteins showing increased expression in cells treated with AS-6 are involved in protein quality control, including glucose-regulated protein 78 (GRP78/BiP), a regulator of ER stress responses, and the transcriptional regulator CHOP, which mediates ER stress-induced apoptosis. Cells treated with AS-6 undergo an autophagic response accompanied by increased expression of beclin1, ATG5, and LC3-II and autophagosome formation marked by the appearance of large vesicles containing LC3-II. Grp78 induction was inhibited when the PPARγ antagonist, GW9662, was added together with AS-6, and autophagy and cell death were partially blocked. 3-methyl-adenine (3-MA), an inhibitor of phosphatidyl inositol 3-kinase (PI3-kinase) prevented induction of ATG5 and activation of LC3-II and blocked autophagosome formation. 3-MA also blocked induction of GRP78 and CHOP, suggesting that PI3-kinase, which is known to mediate ER stress-induced autophagy, also plays a role in initiating apoptosis in response to ER stress. Together these data establish that the cytotoxicity of AS-6 operates by a mechanism dependent on ER stress-induced autophagy and apoptosis.

Paigen diet-fed apolipoprotein E knockout mice develop severe pulmonary hypertension in an interleukin-1-dependent manner

Inflammatory mechanisms are proposed to play a significant role in the pathogenesis of pulmonary arterial hypertension (PAH). Previous studies have described PAH in fat-fed apolipoprotein E knockout (ApoE(-/-)) mice. We have reported that signaling in interleukin-1-receptor-knockout (IL-1R1(-/-)) mice leads to a reduction in diet-induced systemic atherosclerosis. We subsequently hypothesized that double-null (ApoE(-/-)/IL-1R1(-/-)) mice would show a reduced PAH phenotype compared with that of ApoE(-/-) mice. Male IL-1R1(-/-), ApoE(-/-), and ApoE(-/-)/IL-1R1(-/-) mice were fed regular chow or a high-fat diet (Paigen diet) for 8 weeks before phenotyping for PAH. No abnormal phenotype was observed in the IL-1R1(-/-) mice. Fat-fed ApoE(-/-) mice developed significantly increased right ventricular systolic pressure and substantial pulmonary vascular remodeling. Surprisingly, ApoE(-/-)/IL-1R1(-/-) mice showed an even more severe PAH phenotype. Further molecular investigation revealed the expression of a putative, alternatively primed IL-1R1 transcript expressed within the lungs but not aorta of ApoE(-/-)/IL-1R1(-/-) mice. Treatment of ApoE(-/-) and ApoE(-/-)/IL-1R1(-/-) mice with IL-1-receptor antagonist prevented progression of the PAH phenotype in both strains. Blocking IL-1 signaling may have beneficial effects in treating PAH, and alternative IL-1-receptor signaling in the lung may be important in driving PAH pathogenesis.

Effect of pioglitazone on serum concentrations of osteoprotegerin in patients with type 2 diabetes mellitus

OBJECTIVE

Osteoprotegerin (OPG) acts as an important regulatory molecule in atherosclerosis. Recent studies report that thiazolidinediones could affect OPG expression. We investigated the relationship between OPG and inflammatory cytokines and the effects of pioglitazone (a PPARγ (PPARG) agonist) versus metformin on serum OPG levels in type 2 diabetic patients.

DESIGN AND METHODS

Sixty-seven type 2 diabetic patients were included in this study. They were assigned to pioglitazone (15 mg/day, n=34) or metformin (1000 mg/day, n=33) during 24 weeks. Various anthropometric and metabolic parameters, OPG, interleukin 6 (IL6), C-reactive protein (CRP), adiponectin, and homeostasis model assessment of insulin resistance (HOMA-IR), were measured at baseline and at 6 months of treatment.

RESULTS

Serum OPG levels correlated significantly with fasting plasma glucose (FPG), HbAlc, HOMA-IR, IL6, and CRP, and inversely correlated with adiponectin after adjusting for age (P<0.05). Multiple regression analysis showed that FPG, HbAlc, and adioponectin were independently correlated with OPG level. After 6 months of treatment, the reduction in FPG and HbAlc levels was similar between the two groups. Pioglitazone treatment significantly increased body mass index (P<0.05) and waist circumference (P<0.05) and decreased triglycerides (P<0.05) and HOMA-IR (P<0.01). The adiponectin concentration was increased (P<0.05), and OPG and CRP levels were decreased in the pioglitazone group (P<0.05), but were unchanged in the metformin group. The changes in serum OPG in the pioglitazone group showed significant correlation with changes in FPG, HbAlc, and adiponectin.

CONCLUSIONS

In type 2 diabetic patients, pioglitazone decreases OPG levels, and this decrease in OPG levels might be associated with the increase in adiponectin.

Thiazolidinediones up-regulate insulin-like growth factor-1 receptor via a peroxisome proliferator-activated receptor gamma-independent pathway

There is increasing evidence that thiazolidinediones (TZDs), antidiabetic compounds that are synthetic ligands for the peroxisome proliferator-activated receptor γ (PPARγ), have cardiovascular effects through as yet poorly defined mechanisms. We tested the effect of two TZD class drugs, rosiglitazone and pioglitazone, on human aortic smooth muscle cell (SMC) expression of insulin-like growth factor-1 receptor (IGF-1R). Both TZDs dose dependently up-regulated IGF-1R protein levels (rosiglitazone, 10 μmol/liter, 67% increase, n = 4, p < 0.01; pioglitazone, 10 μmol/liter, 41% increase, n = 4, p < 0.01) and increased IGF-1R signaling activity (36% increase in Akt phosphorylation). However, the endogenous PPARγ ligand, 15-deoxy-Δ(12,14)-prostaglandin J(2), dose dependently reduced IGF-1R (10 μmol/liter, 80% decrease, n = 4, p < 0.01), and overexpression of PPARγ using an adenovirus likewise reduced IGF-1R (50% decrease versus SMC infected with control adenovirus), suggesting a PPARγ-independent action of TZDs. All three PPARγ ligands (rosiglitazone, pioglitazone, and 15-deoxy-Δ(12,14)-prostaglandin J(2)), however, did not change IGF-1R mRNA levels, indicating that their effects were posttranscriptional. Use of bicistronic constructs revealed that TZD induction of IGF-1R translation occurred via internal ribosomal entry. To examine the potential physiological relevance of TZD up-regulation of IGF-1R, we determined the effect of rosiglitazone on oxidized LDL (oxLDL)-induced apoptosis. 20 μmol/liter of rosiglitazone reduced oxidized LDL-induced apoptosis by 40% and neutralizing antibody to IGF-1R (αIR3) counteracted this rescue, suggesting the rosiglitazone survival effect was, at least in part, mediated by IGF-1R. In conclusion, TZDs markedly up-regulate SMC IGF-1R expression and signaling, likely via a PPARγ-independent mechanism. This novel action of TZDs may play an important role in their cardiovascular effects.

Peroxisome proliferator-activated receptor gamma (PPAR) agonism reduces the insulin-stimulated increase in circulating interleukin-6 in GH replaced GH-deficient adults

CONTEXT

Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists modify cardiovascular risk factors and inflammatory markers in patients with type 2 diabetes. GH treatment in GH-deficient (GHD) patients may cause insulin resistance and exerts ambiguous effects on inflammatory markers.

OBJECTIVE

To investigate circulating markers of inflammation and endothelial function in GH replaced GHD patients before and after 12 weeks administration of either pioglitazone 30 mg/day (N = 10) or placebo (N = 10) in a randomized double-blind parallel design.

METHODS

Circulating levels of interleukins (ILs)-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, tumour necrosis factor (TNF)-alpha, high sensitivity C-reactive protein, vascular cell adhesion molecule-I, and osteoprotegerin (OPG) were measured in the basal state and after a 2.5 h hyperinsulinaemic euglycaemic clamp.

RESULTS

Insulin sensitivity improved in the group receiving PPARgamma agonist (P = 0.03). Serum IL-6 levels increased by 114 +/- 31% (mean +/- SE) in the entire group (N = 20) following the hyperinsulinaemic euglycaemic clamp (P = 0.01) performed at study start. Twelve weeks of PPARgamma agonist treatment significantly abrogated this insulin-stimulated increment in IL-6 levels compared to placebo (P = 0.01). Furthermore PPARgamma agonist treatment significantly lowered basal IL-4 levels (P < 0.05).

CONCLUSIONS

(i) IL-6 levels increase during a hyperinsulinaemic clamp in GH replaced patients (ii) This increase in IL-6 is abrogated by PPARgamma agonist treatment (iii) we hypothesize that PPARgamma agonist-induced improvement of insulin sensitivity may obviate a compensatory rise in IL-6.

Ghrelin inhibits early osteogenic differentiation of C3H10T1/2 cells by suppressing Runx2 expression and enhancing PPARgamma and C/EBPalpha expression

Ghrelin is a 28-residue peptide identified in the stomach as an endogenous ligand of the growth hormone secretagogue receptor that is expressed in a variety of peripheral tissues, as well as in the brain. In previous studies, ghrelin has been shown to stimulate both adipogenic differentiation from preadipocytes and osteogenic differentiation from preosteoblasts or primary osteoblasts. This study was undertaken to investigate the direct effect of ghrelin on the lineage allocation of mesenchymal stem cells (MSCs). We identified ghrelin receptor mRNA in C3H10T1/2 cells, and we found the levels of this mRNA to be attenuated during osteogenic differentiation. Treatment of cells with ghrelin resulted in both proliferation and inhibition of caspase-3 activity. In addition, ghrelin decreased serum deprivation-induced bax protein expression and release of cytochrome c from the mitochondria, whereas it increased bcl-2 protein expression. Moreover, ghrelin inhibited early osteogenic differentiation, as shown by alkaline phosphatase activity and staining, and inhibited osteoblast-specific genes expression by altering Runx2, PPARgamma, and C/EBPalpha protein expression.

PPARs and the cardiovascular system

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone-receptor superfamily. Originally cloned in 1990, PPARs were found to be mediators of pharmacologic agents that induce hepatocyte peroxisome proliferation. PPARs also are expressed in cells of the cardiovascular system. PPAR gamma appears to be highly expressed during atherosclerotic lesion formation, suggesting that increased PPAR gamma expression may be a vascular compensatory response. Also, ligand-activated PPAR gamma decreases the inflammatory response in cardiovascular cells, particularly in endothelial cells. PPAR alpha, similar to PPAR gamma, also has pleiotropic effects in the cardiovascular system, including antiinflammatory and antiatherosclerotic properties. PPAR alpha activation inhibits vascular smooth muscle proinflammatory responses, attenuating the development of atherosclerosis. However, PPAR delta overexpression may lead to elevated macrophage inflammation and atherosclerosis. Conversely, PPAR delta ligands are shown to attenuate the pathogenesis of atherosclerosis by improving endothelial cell proliferation and survival while decreasing endothelial cell inflammation and vascular smooth muscle cell proliferation. Furthermore, the administration of PPAR ligands in the form of TZDs and fibrates has been disappointing in terms of markedly reducing cardiovascular events in the clinical setting. Therefore, a better understanding of PPAR-dependent and -independent signaling will provide the foundation for future research on the role of PPARs in human cardiovascular biology.

Mesenchymal stem cells-derived vascular smooth muscle cells release abundant levels of osteoprotegerin

Although several studies have shown that the serum levels of osteoprotegerin (OPG) are significantly elevated in patients affected with atherosclerotic lesions in coronary and peripheral arteries, the cellular source and the role of OPG in the physiopathology of atherosclerosis are not completely defined. Therefore, we aimed to investigate the potential contribution of mesenchymal stem cells in the production/release of OPG. OPG was detectable by immunohistochemistry in aortic and coronary atherosclerotic plaques, within or in proximity of intimal vascular smooth muscle cells (SMC). In addition, bone marrow mesenchymal stem cell (MSC)-derived vascular SMC as well as primary aortic SMC released in the culture supernatant significantly higher levels of OPG with respect to MSC-derived endothelial cells (EC) or primary aortic EC. On the other hand, in vitro exposure to full-length human recombinant OPG significantly increased the proliferation rate of aortic SMC cultures, as monitored by bromodeoxyuridine incorporation. Taken together, these data suggest that OPG acts as an autocrine/paracrine growth factor for vascular SMC, which might contribute to the progression of atherosclerotic lesions.

Osteoprotegerin, vascular calcification and atherosclerosis

The association of bone pathologies with atherosclerosis has stimulated the search for common mediators linking the skeletal and the vascular system. Since its initial discovery as a key regulator in bone metabolism, osteoprotegerin (OPG) has become the subject of intense interest for its role in vascular disease and calcification. Studies in vitro and in animal models suggest that OPG inhibits vascular calcification. Paradoxically however, clinical studies suggest that serum OPG levels increase in association with vascular calcification, coronary artery disease, stroke and future cardiovascular events. This has led to an extensive debate on the potential of OPG as a biomarker of vascular disease. However the exact significance and mechanisms by which this bone-regulatory protein influences cardiovascular pathophysiology is still unclear. The need for a more complete picture is being addressed in increasing valuable research indicating OPG as not only a marker but also a mediator of vascular pathology modulating osteogenic, inflammatory and apoptotic responses. By integrating the results of recent experimental research, animal models and clinical studies, this review summarises the present understanding of the role of OPG in vascular disease and calcification.

Thiazolidinediones inhibit the growth of PC12 cells both in vitro and in vivo

Thiazolidinediones (TZDs) have recently been proposed as a therapy for PPARgamma-expressing tumors. Pheochromocytoma (PHEO) is associated with high morbidity and mortality due to excess catecholamine production, and few effective drug therapies currently exist. We investigated the effects of TZDs on PHEO both in vitro and in vivo. PPARgamma protein was expressed in human adrenal PHEO tissues as well as in rat PHEO cells, PC12. TZDs, including rosiglitazone (RGZ) and pioglitazone (PGZ), inhibited proliferation of PC12 cells in a dose-dependent manner and increased casapse-3 expression of PC12 cells. TZDs also reduced expression of cyclin E and cyclin-dependent kinase2. RGZ inhibited nerve growth factor-induced neurite outgrowth and reduced expression of catecholamine-synthesizing enzymes. Finally, rat PHEO growth generated by subcutaneous injection of PC12 cells was slowed in an RGZ-treated mouse. These data suggest that TZDs may be a promising therapeutic approach for medical treatment for PHEO.

Evidence of a role for osteoprotegerin in the pathogenesis of pulmonary arterial hypertension

Pulmonary artery smooth muscle cell (PA-SMC) migration and proliferation are key processes in the pathogenesis of pulmonary arterial hypertension (PAH). Recent information suggests that abnormalities in the bone morphogenetic protein (BMP) receptor 2 (BMP-R2) signaling pathway are important in PAH pathogenesis. It remains unclear whether and how this pathway interacts with, for example, serotonin (5-HT) and inflammation to trigger and/or sustain the development of PAH. The secreted glycoprotein osteoprotegerin (OPG) is emerging as an important regulatory molecule in vascular biology and is modulated by BMPs, 5-HT, and interleukin-1 in other cell types. However, whether OPG is expressed by PA-SMCs within PAH lesions and plays a role in PAH is unknown. Immunohistochemistry of human PAH lesions demonstrated increased OPG expression, and OPG was significantly increased in idiopathic PAH patient serum. Recombinant OPG stimulated proliferation and migration of PA-SMCs in vitro, and BMP-R2 RNA interference increased OPG secretion. Additionally, both 5-HT and interleukin-1 also increased OPG secretion. These data are the first to demonstrate that OPG is increased in PAH and that it can regulate PA-SMC proliferation and migration. OPG may provide a common link between the different pathways associated with the disease, potentially playing an important role in the pathogenesis of PAH.

Osteoprotegerin increases leukocyte adhesion to endothelial cells both in vitro and in vivo

Recombinant osteoprotegerin (OPG) promoted the adhesion of both primary polymorphonuclear neutrophils (PMNs) and leukemic HL60 cells to endothelial cells. Leukocyte/endothelial cell adhesion was promoted by short (peak at 1 hour) preincubation of either endothelial cells or PMNs with OPG, and the peak of proadhesive activity was observed in the same range of OPG concentrations detected in the sera of patients affected by cardiovascular diseases. Although the cognate high-affinity ligands for OPG, membrane receptor activator of nuclear factor-kappaB ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), were detected at significant levels on both PMNs and HL60 cells, they were not expressed on the surface of endothelial cells. However, preincubation of OPG with heparin abrogated its proadhesive activity, whereas pretreatment of endothelial cells with chondroitinase plus heparinases significantly decreased the proadhesive activity of OPG. Taken together, these findings suggest the involvement of both the ligand binding and the N-terminal heparin-binding domains of OPG in mediating its pro-adhesive activity. The relevance of these in vitro findings was underscored by in vivo experiments, in which the topical administration of recombinant OPG increased leukocyte rolling and adhesion to rat mesenteric postcapillary venules. Our data suggest that a pathological increase of OPG serum levels might play an important role in promoting leukocyte/endothelial cell adhesion.

The osteoprotegerin/RANK/RANKL system: a bone key to vascular disease

Owing to the common coincidence of osteoporosis and vascular disease, pathophysiological links between both disorders have long been sought. The osteoprotegerin (OPG)/receptor activator of NF-kappaB (RANK)/receptor activator of NF-kappaB ligand (RANKL) cytokine network, a key regulatory system in bone homeostasis, has been implicated recently in vascular calcification, changes in matrix composition and diabetic macroangiopathy, aortic aneurysm development, heart failure and, most importantly, advanced atherosclerosis, plaque destabilization and manifestation of cardiovascular diseases. The concept of an active role of RANKL and OPG in vascular pathophysiology is intriguing and is gaining increasing support from both epidemiological and basic research. OPG serum level is considered to be a stable and reliable indicator of the overall activity of the OPG/RANK/RANKL axis and may find application as a biomarker of vascular risk and prognosis. RANKL in turn may be a suitable target for novel therapies. Pharmacological strategies for specific interference with the OPG/RANK/RANKL axis are currently being developed and evaluated in osteoporosis therapy.

An increased osteoprotegerin serum release characterizes the early onset of diabetes mellitus and may contribute to endothelial cell dysfunction

Serum osteoprotegerin (OPG) is significantly increased in diabetic patients, prompting expanded investigation of the correlation between OPG production/release and glycemic levels. Serum levels of OPG, but not of its cognate ligand receptor activator of nuclear factor-kappaB ligand (RANKL), were significantly increased in type 2 diabetes mellitus patients compared with healthy blood donors. Serum OPG was also significantly elevated in a subgroup of recently diagnosed diabetic patients (within 2 years). The relationship between serum OPG and diabetes mellitus onset was next investigated in apoE-null and littermate mice. Serum OPG increased early after diabetes induction in both mouse strains and showed a positive correlation with blood glucose levels and an inverse correlation with the levels of free (OPG-unbound) RANKL. The in vitro addition of tumor necrosis factor-alpha to human vascular endothelial cells, but not human peripheral blood mononuclear cells, markedly enhanced OPG release in culture. In contrast, high glucose concentrations did not modulate OPG release when used alone or in association with tumor necrosis factor-alpha. Moreover, the ability of soluble RANKL to activate the extracellular signal-regulated kinase/mitogen-activated protein kinase and endothelial nitric-oxide synthase pathways in endothelial cells was neutralized by preincubation with recombinant OPG. Altogether, these findings suggest that increased OPG production represents an early event in the natural history of diabetes mellitus, possibly contributing to disease-associated endothelial cell dysfunction.

Endothelial function and biochemical vascular markers in first-degree relatives of type 2 diabetic patients: the effect of exercise training

Endothelial dysfunction (ED) is associated with the presence of atherosclerosis. However, ED is also considered a sign of the early vascular changes preceding atherosclerosis. By measuring flow-mediated vasodilation (FMD) and circulating markers of endothelial function we sought to explore whether impaired endothelial function is already present in healthy subjects at increased risk of developing type 2 diabetes mellitus. Furthermore, we aimed to assess the impact of short-term lifestyle intervention (10 weeks endurance exercise) on the potentially primary defects of endothelial function. Twenty-nine healthy but insulin-resistant first-degree relatives of patients diagnosed with type 2 diabetes mellitus (33 +/- 5 years; body mass index, 26.3 +/- 1.6 kg/m2) were compared with 19 control subjects without a family history of diabetes mellitus (31 +/- 5 years; body mass index, 25.8 +/- 3.0 kg/m2). At baseline the von Willebrand factor was significantly increased in the relatives (P < .05). Furthermore, mannose-binding lectin (P = .06), soluble intercellular adhesion molecule 1 (P = .08), and osteoprotegerin (P = .08) tended to be increased in relatives. The following markers of endothelial function were comparable at baseline: FMD, C-reactive protein, plasminogen activator inhibitor 1, and soluble vascular cell adhesion molecule 1. Exercise training resulted in a decrease in mannose-binding lectin (P = .02) and osteoprotegerin (P < .01) in relatives only, whereas other biochemical markers were unaffected in both groups. Moreover, the relatively high-intensity exercise training tended weakly to reduce FMD in the relatives (P = .15). In conclusion, healthy subjects predisposed for type 2 diabetes mellitus show only minor signs of endothelial dysfunction. Under these almost normal vascular conditions, exercise training has little effect on endothelial function.

Plasma osteoprotegerin levels are associated with glycaemic status, systolic blood pressure, kidney function and cardiovascular morbidity in type 1 diabetic patients

OBJECTIVE

The bone-related peptide osteoprotegerin (OPG) has recently been found in increased amounts in the vasculature in diabetes. It is produced by vascular smooth muscle and endothelial cells, and may be implicated in the development of vascular calcifications. OPG is present in the circulation, where increased amounts have been observed in patients with diabetes. In this study, we examined whether plasma OPG is associated with the glycaemic and vascular status of patients with type 1 diabetes.

METHODS

Two gender-, age- and duration-comparable groups of type 1 diabetic patients either with (n = 199) or without (n = 192) signs of diabetic nephropathy were studied. Plasma OPG was determined by an ELISA.

RESULTS

The plasma OPG concentration was significantly higher in patients with nephropathy than those without (3.11 (2.49-3.99) vs 2.57 (2.19-3.21) (median (interquartiles), ng/ml), P < 0.001). Plasma OPG correlated with haemoglobin A1c (HbA1c), systolic blood pressure and age in both groups and, in addition, with kidney function in the nephropathic group. These correlations remained significant in multivariate models. In addition, we found that plasma OPG concentrations were increased among patients with cardiovascular diseases (CVD), both in the normoalbuminuric and the nephropathic groups. The differences between nephropathic and normoalbuminuric, as well as subgroups with and without CVD, could largely be ascribed to changes in HbA1c, age, systolic blood pressure and creatinine.

CONCLUSION

OPG is associated with glycaemic control and CVD in patients with type 1 diabetes, compatible with the hypothesis that OPG is associated with the development of diabetic vascular complications.

Osteoprotegerin and bone mineral density in hemodialysis patients

INTRODUCTION

Osteoprotegerin is a soluble glycoprotein that belongs to the tumor-necrosis-factor receptor superfamily. In vitro, osteoprotegerin blocks osteoclastogenesis in a dose-dependent manner. The serum osteoprotegerin level shows a positive correlation with bone metabolism markers and a negative correlation with bone mineral density in healthy persons, but these relationships are unclear in hemodialysis patients. We investigated the role of osteoprotegerin in bone loss in hemodialysis patients.

METHODS

We measured baseline serum osteoprotegerin, bone metabolism markers, and bone mineral density in hemodialysis patients. A total of 201 patients (114 men and 87 women) were followed for 12 months, and bone mineral density was measured again to calculate the annual percent change in bone mineral density. Serum osteoprotegerin was also measured in 20 healthy persons.

RESULTS

The osteoprotegerin levels of the hemodialysis patients were about three times higher than those of the healthy controls. The osteoprotegerin level showed a negative correlation with various bone metabolism markers. In multiple regression analysis, the annual percent change in bone mineral density showed a positive correlation with osteoprotegerin level, while there was a negative correlation with duration of hemodialysis and intact parathyroid hormone level. The osteoprotegerin levels of the hemodialysis patients were about three times higher than those of the healthy controls. The osteoprotegerin level showed a negative correlation with various bone metabolism markers. In multiple regression analysis, the annual percent change in bone mineral density showed a positive correlation with osteoprotegerin level, while there was a negative correlation with duration of hemodialysis and intact parathyroid hormone level.

CONCLUSIONS

These correlations of osteoprotegerin are opposite to those found in healthy persons. However, osteoprotegerin might act to prevent bone loss even in hemodialysis patients.

Osteoporosis and atherosclerosis: biological linkages and the emergence of dual-purpose therapies

Osteoporosis and atherosclerosis are both widely prevalent in an ageing population, and induce serious morbidities and death. There is growing evidence that in addition to their relationship to ageing, osteoporosis and atherosclerosis are also linked by biological associations. This article reviews their clinical interrelations, discusses the basic biology of bone and the arterial wall, and presents five examples that illustrate their biological linkages. Current therapeutic approaches emerging from these linkages, including statins, bisphosphonates, and the thiazolidinediones, have dual effects on bone and the vasculature. Additional therapies derived from experimental studies that enhance bone density and reduce atherogenesis hold further promise to diminish the morbidity and mortality of osteoporosis and atherosclerosis, with attendant benefits to society.

Regulation of vascular calcification by osteoclast regulatory factors RANKL and osteoprotegerin

Vascular calcification often occurs with advancing age, atherosclerosis, various metabolic disorders such as diabetes mellitus and end-stage renal disease, or in rare genetic diseases, leading to serious clinical consequences. Such mineralization can occur at various sites (cardiac valves, arterial intima or media, capillaries), involve localized or diffuse widespread calcification, and result from numerous causes that provoke active inflammatory and osteogenic processes or disordered mineral homeostasis. Although valuable research has defined many key factors and cell types involved, surprising new insights continue to arise that deepen our understanding and suggest novel research directions or strategies for clinical intervention in calcific vasculopathies. One emerging area in vascular biology involves the RANKL/RANK/OPG system, molecules of the tumor necrosis factor-related family recently discovered to be critical regulators of immune and skeletal biology. Evidence is accumulating that such signals may be expressed, regulated, and function in vascular physiology and pathology in unique ways to promote endothelial cell survival, angiogenesis, monocyte or endothelial cell recruitment, and smooth muscle cell osteogenesis and calcification. Concerted research efforts are greatly needed to understand these potential roles, clarify whether RANKL (receptor activator of nuclear factor kappaB ligand) promotes and osteoprotegerin (OPG) protects against vascular calcification, define how OPG genetic polymorphisms relate to cardiovascular disease, and learn whether elevated serum OPG levels reflect endothelial dysfunction in patients. Overall, the RANKL/RANK/OPG system may mediate important and complex links between the vascular, skeletal, and immune systems. Thus, these molecules may play a central role in regulating the development of vascular calcification coincident with declines in skeletal mineralization with age, osteoporosis, or disease.

The peroxisome proliferator-activated receptor-gamma ligand 15-deoxyDelta12,14 prostaglandin J2 reduces the organ injury in hemorrhagic shock

The cyclopentenone prostaglandin 15-deoxyDelta12,14PGJ2 (15d-PGJ2) exerts potent anti-inflammatory effects in vivo, which are in part caused by the activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Here we investigate the effects of 15d-PGJ2 on the multiple organ injury/dysfunction associated with severe hemorrhage and resuscitation. Male Wistar rats were subjected to hemorrhage (to lower mean arterial blood pressure to 45 mmHg) for 90 min and subsequently resuscitated with shed blood for 4 h. Rats were treated with either 15d-PGJ2 (0.3 mg/kg i.v.) or its vehicle (10% dimethyl sulfoxide) at 30 min before the hemorrhage. In some experiments, the selective PPAR-gamma antagonist GW9662 (1 mg/kg i.v.) or its vehicle (10% dimethyl sulfoxide) was given 45 min before the hemorrhage. Hemorrhage and resuscitation resulted in an increase in serum levels of (a) urea and creatinine and, hence renal dysfunction; alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and, hence, hepatic injury. The potent PPAR-gamma agonist 15d-PGJ2 abolished the renal dysfunction and largely reduced the liver injury caused by hemorrhagic shock. In addition, 15d-PGJ2 also attenuated the lung and intestinal injury (determined by histology) caused by hemorrhage and resuscitation. The specific PPAR-gamma antagonist GW9662 reduced the protective effects afforded by 15d-PGJ2. 15d-PGJ2 did not affect the delayed fall in blood pressure caused by hemorrhage and resuscitation. The mechanisms of the protective effect of this cyclopentenone prostaglandin are, at least in part, PPAR-gamma dependent, as the protection afforded by 15d-PGJ2 was reduced by the PPAR-gamma antagonist GW9662. We propose that 15d-PGJ2 or other ligands for PPAR-gamma may be useful in the therapy of the organ injury associated with hemorrhagic shock.

Arterial osteoprotegerin: increased amounts in diabetes and modifiable synthesis from vascular smooth muscle cells by insulin and TNF-alpha

AIMS/HYPOTHESIS

Extracellular matrix modifications and linear medial calcifications are elements of diabetic macroangiopathy. We hypothesised that the bone-related protein osteoprotegerin (OPG) may occur in altered amounts in the arterial wall in diabetes, putatively associated with altered synthesis from vascular cells.

METHODS

The amount of OPG in the thoracic aorta, obtained at autopsy from 21 diabetic and 42 sex- and age-matched controls, was measured in tissue extracts by an ELISA. The production of OPG was estimated in conditioned media by an ELISA, and OPG mRNA was estimated by RT-PCR in vascular cells grown in vitro.

RESULTS

The content of OPG was increased in tunica media samples from diabetic individuals. No differences between diabetic and non-diabetic subjects were observed in tunica intima. Human vascular smooth muscle cells (HVSMCs) produced approximately 30 times more OPG than human umbilical vein endothelial cells. The OPG production into the medium decreased dose- and time-dependently after insulin treatment (maximal effect approximately 60% of control) in HVSMCs, whereas TNF-alpha supplement gave rise to increased OPG synthesis in a time- and dose-dependent manner (maximal effect approximately 200% of control). Similar effects on OPG mRNA expression were observed. Addition of growth hormone (10 ng/ml) or extra glucose (25 mmol/l) to the growth medium had no effect.

CONCLUSIONS/INTERPRETATION

Increased OPG concentrations in the arterial wall in diabetes may be part of generalised matrix alterations, putatively related to the development of vascular calcifications. Altered arterial OPG content may be a consequence of the effects of hormones and cytokines, like insulin and TNF-alpha.

15d-prostaglandin J2 reduces multiple organ failure caused by wall-fragment of Gram-positive and Gram-negative bacteria

Septic shock is still the major cause of death in surgical intensive care units. Both gram-positive (G+) and gram-negative (G-) bacteria have been isolated in the blood of a large portion of septic patients, and these polymicrobial infections often have a higher mortality than infections due to a single organism. Cell wall fragments from G+ and G- bacteria synergise to cause shock and multiple organ dysfunction in vivo (G+/G- shock). Male Wistar rats were anaesthetised and received a coadministration of wall fragments from G+ and G- bacteria, Staphilococcus aureus (S. aureus) peptidoglycan [0.3 mg/kg, intravenously (i.v.)] and Escherichia coli (E. coli) lipopolysaccharide (1 mg/kg, i.v.) or vehicle (saline, 1 ml/kg, i.v.). G+/G- shock for 6 h resulted in an increase in serum levels of creatinine (indicator of renal dysfunction), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (gamma-GT), bilirubin (markers for hepatic injury and dysfunction) and creatine kinase (CK, an indicator of neuromuscular, skeletal muscle or cardiac injury). Pretreatment of rats with the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist 15d-prostaglandin J2 (0.3 mg/kg, i.v., 30 min prior to G+/G-) reduced the multiple organ injury/dysfunction caused by coadministration of peptidoglycan+lipopolysaccharide. The selective PPAR-gamma antagonist GW9662 (2-Chloro-5-nitrobenzanilide) (1 mg/kg, i.v., given 45 min prior to G+/G-) abolished the protective effects of 15d-prostaglandin J2. 15d- prostaglandin J2 did not affect the biphasic fall in blood pressure or the increase in heart rate caused by administration of peptidoglycan+lipopolysaccharide. The mechanism(s) of the protective effect of this cyclopentenone prostaglandin are-at least in part-PPAR-gamma dependent, as the protection afforded by 15d-prostaglandin J2 was reduced by the PPAR-gamma antagonist GW9662. We propose that 15d-prostaglandin J2 or other ligands for PPAR-gamma may be useful in the therapy of the organ injury associated with septic shock.

The Cardioprotective Effects of Preconditioning with Endotoxin, but Not Ischemia, Are Abolished by a Peroxisome Proliferator-Activated Receptor-γ Antagonist

We investigated whether endogenous ligands of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) protect the heart against ischemia-reperfusion (I/R) injury. The selective PPAR-gamma antagonist GW9662 (2-chloro-5-nitrobenzanilide) was used in rat models of 1) regional myocardial I/R, 2) ischemic preconditioning, and 3) delayed cardioprotection by endotoxin. We also investigated the effects of the selective cyclooxygenase-2 inhibitor, parecoxib, on ischemic preconditioning and delayed cardioprotective effects of endotoxin. Male Wistar rats were anesthetized with sodium thiopentone. Animals were subjected to either 15 or 25 min of regional myocardial I/R and pretreated with the PPAR-gamma agonist ciglitazone (0.3 mg/kg), the PPAR-gamma antagonist GW9662 (1 mg/kg), or GW9662 and ciglitazone. Animals were also subjected to either 1) ischemic preconditioning alone, ischemic preconditioning, and pretreated with either GW9662 or parecoxib (20 mg/kg) or 2) lipopolysaccharide (LPS) (1 mg/kg) alone, LPS, and pretreated with ciglitazone, GW9662, or parecoxib (20 mg/kg). Myocardial infarct size was determined by p-nitroblue tetrazolium staining. The PPAR-gamma antagonist GW9662 (1 mg/kg) abolished the cardioprotection afforded by the potent PPAR-gamma agonist ciglitazone (0.3 mg/kg). Neither GW9662 nor parecoxib affected the cardioprotective effects of ischemic preconditioning. Pretreatment with ciglitazone did not provide additional cardioprotection to LPS-treated animals. Both GW9662 and parecoxib abolished the delayed cardioprotective effects of endotoxin. Thus, we propose that 1) endogenous ligands of PPAR-gamma are being generated by myocardial ischemia in sufficient amounts to attenuate myocardial I/R injury, and 2) that cyclooxygenase-2 metabolites contribute to (or even account for) the cardioprotective effects of endotoxin (second window of protection) by acting as endogenous PPAR-gamma ligands.

Circulating osteoprotegerin levels are associated with age, waist-to-hip ratio, serum total cholesterol, and low-density lipoprotein cholesterol levels in healthy Korean women

Osteoprotegerin (OPG) is a recently identified cytokine that acts as a decoy receptor for the receptor activator of nuclear factor I masculine B ligand. Osteoprotegerin has been shown to be an important inhibitor of osteoclastogenesis and arterial calcification in animal models. Recently, OPG has been proposed as a link molecule between osteoporosis and arterial calcification, but the relationship between circulating OPG levels and cardiovascular disease in human populations is unclear. Thus, the aim of this study was to investigate the relationship between circulating OPG levels and cardiovascular risk factors in healthy Korean women. The subjects were 286 women aged 37 to 73 (mean +/- SD, 51.5 +/- 6.9 years). We examined blood pressure, body mass index, and waist-to-hip ratio. Serum concentrations of OPG were determined by enzyme-linked immunosorbent assay. Fasting plasma glucose levels, serum lipid profiles, insulin levels, and serum follicle-stimulating hormone (FSH) levels were determined by standard methods and homeostasis model assessment of insulin resistance was calculated. We observed a significant association between serum OPG levels and age, waist-to-hip ratio, total cholesterol, low-density lipoprotein cholesterol, and FSH levels (P < .05). Among the metabolic components, the older, obese, and hypercholsterolemic subjects had higher serum OPG levels (P < .05). However, no significant relationship was found between serum OPG levels and blood pressure and fasting plasma glucose levels. We found that mean serum OPG levels were about 11% greater in postmenopausal women (mean +/- SD, 1358.5 +/- 380.0 pg/mL) than in premenopausal women (mean +/- SD, 1228.8 +/- 407.7 pg/mL, P < .001). In multiple regression analysis with OPG as the dependent variable, serum FSH and low-density lipoprotein cholesterol levels were the significant predictor for serum OPG level (R(2) = 0.051, P < .05). In conclusion, our results show that circulating OPG levels are partly associated with cardiovascular risk factors and menopausal status in healthy Korean women. Out findings suggest that OPG may be an important paracrine factor of cardiovascular disease in the female population.

The molecular triad OPG/RANK/RANKL: involvement in the orchestration of pathophysiological bone remodeling

The past decade has seen an explosion in the field of bone biology. The area of bone biology over this period of time has been marked by a number of key discoveries that have opened up entirely new areas for investigation. The recent identification of the receptor activator of nuclear factor kappaB ligand (RANKL), its cognate receptor RANK, and its decoy receptor osteoprotegerin (OPG) has led to a new molecular perspective on osteoclast biology and bone homeostasis. Specifically, the interaction between RANKL and RANK has been shown to be required for osteoclast differentiation. The third protagonist, OPG, acts as a soluble receptor antagonist for RANKL that prevents it from binding to and activating RANK. Any dysregulation of their respective expression leads to pathological conditions such as bone tumor-associated osteolysis, immune disease, or cardiovascular pathology. In this context, the OPG/RANK/RANKL triad opens novel therapeutic areas in diseases characterized by excessive bone resorption. The present article is an update and extension of an earlier review published by Kwan Tat et al. [Kwan Tat S, Padrines M, Theoleyre S, Heymann D, Fortun Y. IL-6, RANKL, TNF-alpha/IL-1: interrelations in bone resorption pathophysiology. Cytokine Growth Factor Rev 2004;15:49-60].

Kidney-bone, bone-kidney, and cell-cell communications in renal osteodystrophy

The relationship between bone and the kidney in renal osteodystrophy is a complex interplay of kidney to bone connections, bone to kidney connections, and cell to cell connections. In addition, such interactions have a profound effect on the vasculature. In this review, we discuss the role of the bone morphogenetic proteins (BMPs) in the skeleton, kidney, and vasculature. In addition, we propose that deficiencies of these BMPs seen in chronic kidney disease (CKD) result in decreased bone remodeling and a compensatory secondary hyperparathyroidism (high turnover state). Treatment of the hyperparathyroidism blocks this compensatory arm and thus decreased bone remodeling occurs (low turnover). We review animal models of CKD in which treatment with BMP-7 resulted in normalization of both high and low turnover states. Finally, we discuss vascular calcification as it relates to bone metabolism. We discuss the roles of BMP-7 and 2 other bone regulatory proteins, osteoprotegerin (OPG) and alpha2-HS glycoprotein (AHSG, human fetuin), in the human vasculature and their implications for vascular calcification.

Osteoprotegerin is a risk factor for progressive atherosclerosis and cardiovascular disease

BACKGROUND

Osteoprotegerin is a novel member of the tumor necrosis factor receptor superfamily and a soluble decoy receptor of the receptor activator of nuclear factor-kappaB ligand. Recent experimental research has implicated osteoprotegerin in atherogenesis, but epidemiological confirmation of this concept is sparse.

METHODS AND RESULTS

As part of the prospective, population-based Bruneck Study, severity, initiation, and progression of atherosclerosis were assessed in carotid arteries. Cases of incident cardiovascular disease and vascular mortality were carefully recorded over a 10-year period (1990 to 2000). Osteoprotegerin levels were measured in samples obtained at baseline and during follow-up. Serum osteoprotegerin showed a strong association with numerous vascular risk factors, including age, diabetes, markers of systemic inflammation, chronic infection, and smoking. In multivariate analyses, osteoprotegerin was significantly related to severity and 10-year progression of carotid atherosclerosis. Furthermore, a high level of osteoprotegerin was an independent risk factor for incident cardiovascular disease (adjusted relative risk for the top versus bottom tertile group for osteoprotegerin 2.2 [1.3 to 3.8]; P=0.001) and vascular mortality (adjusted relative risk for the top versus bottom tertile group for osteoprotegerin 3.1 [1.2 to 8.2]; P=0.010) but not for mortality due to nonvascular causes.

CONCLUSIONS

Osteoprotegerin is an independent risk factor for the progression of atherosclerosis and onset of cardiovascular disease.

Interferon regulatory factor-1 mediates PPARgamma-induced apoptosis in vascular smooth muscle cells

OBJECTIVE

Peroxisome proliferator-activated receptor gamma (PPARgamma) possesses general beneficial effects on the cardiovascular system, such as inhibition of vascular lesion formation and atherosclerosis. However, molecular mechanisms for these effects are yet to be fully defined. The aim of this study is to elucidate whether interferon regulatory factor-1 (IRF-1), a transcriptional factor with anti-proliferative and pro-apoptotic properties, mediates PPARgamma-induced apoptosis in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Using Northern and Western blot analyses, we documented that PPARgamma ligands, including ciglitazone, troglitazone, and GW7845, significantly increased IRF-1 expression in VSMCs; however, the PPARalpha ligand (Wy14643) and PPARdelta ligand (GW0742) did not affect its expression. PPARgamma-induced IRF-1 expression was abrogated by pretreatment with the PPARgamma antagonist GW9662. In contrast, adenoviral expression of PPARgamma in VSMCs dramatically increased IRF-1 level. Furthermore, PPARgamma activation increased IRF-1 promoter activity but did not affect IRF-1 mRNA stability. Finally, reducing IRF-1 expression by antisense technology attenuated PPARgamma-induced VSMC apoptosis through decreasing cyclin-dependent kinase inhibitor p21(cip1) and caspase-3 activity.

CONCLUSIONS

Our data demonstrate that IRF-1 is a novel PPARgamma target gene and mediates PPARgamma-induced VSMC apoptosis.

Peroxisome proliferator-activated receptors and the cardiovascular system

Insulin resistance syndrome (also called syndrome X) includes obesity, diabetes, hypertension, and dyslipidemia and is a complex phenotype of metabolic abnormalities. The disorder poses a major public health problem by predisposing individuals to coronary heart disease and stroke, the leading causes of mortality in Western countries. Given that hypertension, diabetes, dyslipidemia, and obesity exhibit a substantial heritable component, it is postulated that certain genes may predispose some individuals to this cluster of cardiovascular risk factors. Emerging data suggest that peroxisome proliferator-activated receptors (PPARs), including alpha, gamma, and delta, are important determinants that may provide a functional link between obesity, hypertension, and diabetes. It has been well documented that hypolipidemic fibrates and antidiabetic thiazolidinediones are synthetic ligands for PPAR alpha and PPAR gamma, respectively. In addition, PPAR natural ligands, such as leukotriene B4 for PPAR alpha, 15-deoxy-delta 12,14-prostaglandin J2 for PPAR gamma, and prostacyclin for PPAR delta, are known to be eicosanoids and fatty acids. Studies have documented that PPARs are present in all critical vascular cells: endothelial cells, vascular smooth muscle cells, and monocyte-macrophages. These observations suggest that PPARs not only control lipid metabolism but also regulate vascular diseases such as atherosclerosis and hypertension. In this review, we present structure and tissue distribution of PPAR nuclear receptors, discuss the mechanisms of action and regulation, and summarize the rapid progress made in this area of study and its impact on the cardiovascular system.

Activation of PPARgamma increases PTEN expression in pancreatic cancer cells

The PI3K pathway contributes to the invasive properties and apoptosis resistance that epitomize pancreatic cancers. PPARgamma is a ligand-activated transcription factor with anti-inflammatory and anti-tumor effects; the mechanisms of tumor suppression are unknown. The purpose of this study was to examine whether activation of PPARgamma can increase the expression of the tumor suppressor PTEN and inhibit PI3K activity. AsPC-1 human pancreatic cancer cells, transfected with a PPRE-luciferase construct, demonstrated increased luminescence following treatment with PPARgamma ligands, indicating the presence of functional PPARgamma protein. The selective PPARgamma ligand rosiglitazone increased PTEN expression in AsPC-1 cells; concurrent treatment with GW9662, which inhibits PPARgamma activation, prevented the increase in PTEN protein levels. Levels of phosphorylated Akt decreased as PTEN levels increased, indicating inhibition of PI3K activity. Taken together, our results suggest that activation of PPARgamma may represent a novel approach for the treatment of pancreatic cancer by increasing PTEN levels and inhibiting PI3K activity.