beta(2)-Microglobulin modified with advanced glycation end products delays monocyte apoptosis

Role of moesin and its phosphorylation in VE-cadherin expression and distribution in endothelial adherens junctions

BACKGROUND AND AIM

Vascular endothelial cadherin (VE-cadherin) is an important element of adherens junctions (AJs) between endothelial cells. Its expression and proper distribution are critical for AJ formation and vascular integrity. Our previous studies have demonstrated that moesin phosphorylation mediated the hyper-permeability in endothelial monolayer and microvessels. However, the role of moesin and its phosphorylation in VE-cadherin expression and distribution is not clear.

METHODS AND RESULTS

In vivo, expression of VE-cadherin was significantly reduced in retina and other various tissues in moesin knock out mice (Msn-/Y). In vitro, by regulating moesin expression with siRNA and adenovirus transfection, we verified that moesin has an effect on VE-cadherin expression in HUVECs, while transcription factor KLF4 may participate in this process. In addition, treatment of advanced glycation end products (AGEs) induced abnormal distribution of VE-cadherin in retinal microvessels from C57BL/6 wild type mice, and in vitro studies indicated that moesin Thr558 phosphorylation had a critical role in AGE-induced VE-cadherin internalization from cytomembrane to cytoplasm. Further investigation demonstrated that the inhibition of F-actin polymerization with cytochalasin D could abolish AGE- and Thr558 phosphor-moesin-mediated VE-cadherin internalization.

CONCLUSION

This study suggests that moesin regulates VE-cadherin expression through KLF4 and the state of moesin phosphorylation at Thr558 affects the integrity of VE-cadherin-based AJs. Thr558 phosphor-moesin mediates AGE-induced VE-cadherin internalization through cytoskeleton reassembling.

Advanced glycation end products induce immature angiogenesis in in vivo and ex vivo mouse models

Proliferative diabetic retinopathy (PDR) is a progressive disease predominantly involving pathological angiogenesis and is characterized by the development of immature, fragile, and easily hemorrhagic new vessels. Advanced glycation end products (AGEs) and the receptor for AGEs (RAGE) play important roles in the progression of diabetic retinopathy. Our previous studies demonstrated that AGEs promoted HUVEC angiogenesis by inducing moesin phosphorylation via RhoA/Rho-associated protein kinase (ROCK) pathway. The aim of this study was to further confirm AGE-induced angiogenesis in vivo and the involvement of RAGE, ROCK, and moesin phosphorylation in this process. We performed the study in an AGE-treated mouse model with various angiogenesis assays in multiple in vivo and ex vivo models. The results demonstrated that AGEs promoted significant neovascularization in whole mount retina and mouse aortic ring of adult and postnatal mice and in Matrigel plug as well, which were consistently accompanied by increased moesin phosphorylation. The increase of AGE-evoked neovascularization and moesin phosphorylation were both attenuated by RAGE knockout or ROCK inhibitor Y27632 administration in mice. We also revealed the pathological characteristics of AGE-promoted angiogenesis by demonstrating the decrease of pericyte coverage and the disarranged endothelial alignment in microvessels. In conclusion, this study provides in vivo evidences that AGEs induce immature angiogenesis by binding to RAGE, activating the RhoA/ROCK signal pathway and inducing moesin phosphorylation.NEW & NOTEWORTHY Advanced glycation end product (AGE)-induced formation of neovessels and phosphorylation of moesin in retina and aortic ring required AGE receptors. AGEs increased neovessels and the phosphorylation of moesin in retina and aortic ring via RhoA/ROCK pathway. AGE-induced immature angiogenesis in AGE-treated mouse retina and aortic ring. The AGE-RAGE axis and moesin could be candidate targets for overcoming relative diseases.

Role of Moesin Phosphorylation in Retinal Pericyte Migration and Detachment Induced by Advanced Glycation Endproducts

Proliferative diabetic retinopathy (PDR) involves persistent, uncontrolled formation of premature blood vessels with reduced number of pericytes. Our previous work showed that advanced glycation endproducts (AGEs) induced angiogenesis in human umbilical vein endothelial cells, mouse retina, and aortic ring, which was associated with moesin phosphorylation. Here we investigated whether moesin phosphorylation may contribute to pericyte detachment and the development of PDR. Primary retinal microvascular pericytes (RMPs) were isolated, purified from weanling rats, and identified by cellular markers α-SMA, PDGFR-β, NG2, and desmin using immunofluorescence microscopy. Effects of AGE-BSA on proliferation and migration of RMPs were examined using CCK-8, wound healing, and transwell assays. Effects on moesin phosphorylation were examined using western blotting. The RMP response to AGE-BSA was also examined when cells expressed the non-phosphorylatable Thr558Ala mutant or phospho-mimicking Thr558Asp mutant of moesin or were treated with ROCK inhibitor Y27632. Colocalization and interaction between CD44, phospho-moesin, and F-actin were observed. Experiments with cultured primary RMPs showed that AGE-BSA inhibited the proliferation, enhanced the migration, and increased moesin phosphorylation in a dose- and time-dependent manner. AGE-BSA also triggered the rearrangement of F-actin and promoted the interaction of CD44 with phospho-moesin in RMPs. These effects were abrogated in cells expressing the non-phosphorylatable moesin mutant and the application of ROCK inhibitor Y27632 attenuated AGE-induced alteration in cultured RMPs by abolishing the phosphorylation of moesin. However, those AGE-induced pathological process occurred in RMPs expressed the phospho-mimicking moesin without AGE-BSA treatment. It is concluded that AGEs could activate ROCK to mediate moesin phosphorylation at Thr558, and resulting phospho-moesin interacts with CD44 to form CD44 cluster, which might stimulate the migration of RMPs and subsequent RMP detachment in microvessel. This pathway may provide new drug targets against immature neovessel formation in PDR.

Wnt/β-catenin links oxidative stress to podocyte injury and proteinuria

Podocyte injury is the major cause of proteinuria in primary glomerular diseases. Oxidative stress has long been thought to play a role in triggering podocyte damage; however, the underlying mechanism remains poorly understood. Here we show that the Wnt/β-catenin pathway is involved in mediating oxidative stress-induced podocyte dysfunction. Advanced oxidation protein products, a marker and trigger of oxidative stress, were increased in the serum of patients with chronic kidney disease and correlated with impaired glomerular filtration, proteinuria, and circulating level of Wnt1. Both serum from patients with chronic kidney disease and exogenous advanced oxidation protein products induced Wnt1 and Wnt7a expression, activated β-catenin, and reduced expression of podocyte-specific markers in vitro and in vivo. Blockade of Wnt signaling by Klotho or knockdown of β-catenin by shRNA in podocytes abolished β-catenin activation and the upregulation of fibronectin, desmin, matrix metalloproteinase-9, and Snail1 triggered by advanced oxidation protein products. Furthermore, conditional knockout mice with podocyte-specific ablation of β-catenin were protected against podocyte injury and albuminuria after treatment with advanced oxidation protein products. The action of Wnt/β-catenin was dependent on the receptor of advanced glycation end products (RAGE)-mediated NADPH oxidase induction, reactive oxygen species generation, and nuclear factor-κB activation. These studies uncover a novel mechanistic linkage of oxidative stress, Wnt/β-catenin activation, and podocyte dysfunction.

Glycated collagen – a 3D matrix system to study pathological cell behavior

Anin vitro3D glycated matrix system to study the interplay of diabetes and cancer.

Src Plays an Important Role in AGE-Induced Endothelial Cell Proliferation, Migration, and Tubulogenesis

Advanced glycation end products (AGEs), produced by the non-enzymatic glycation of proteins and lipids under hyperglycemia or oxidative stress conditions, has been implicated to be pivotal in the development of diabetic vascular complications, including diabetic retinopathy. We previously demonstrated that Src kinase played a causative role in AGE-induced hyper-permeability and barrier dysfunction in human umbilical vein endothelial cells (HUVECs). While the increase of vascular permeability is the early event of angiogenesis, the effect of Src in AGE-induced angiogenesis and the mechanism has not been completely revealed. Here, we investigated the impact of Src on AGE-induced HUVECs proliferation, migration, and tubulogenesis. Inhibition of Src with inhibitor PP2 or siRNA decreased AGE-induced migration and tubulogenesis of HUVECs. The inactivation of Src with pcDNA3/flag-Src^K298M also restrained AGE-induced HUVECs proliferation, migration, and tube formation, while the activation of Src with pcDNA3/flag-Src^Y530F enhanced HUVECs angiogenesis alone and exacerbated AGE-induced angiogenesis. AGE-enhanced HUVECs angiogenesis in vitro was accompanied with the phosphorylation of ERK in HUVECs. The inhibition of ERK with its inhibitor PD98059 decreased AGE-induced HUVECs angiogenesis. Furthermore, the inhibition and silencing of Src suppressed the AGE-induced ERK activation. And the silencing of AGEs receptor (RAGE) inhibited the AGE-induced ERK activation and angiogenesis as well. In conclusions, this study demonstrated that Src plays a pivotal role in AGE-promoted HUVECs angiogenesis by phosphorylating ERK, and very likely through RAGE-Src-ERK pathway.

Spontaneous PMN apoptosis in type 2 diabetes and the impact of periodontitis

The purpose of this study was to test the hypothesis that peripheral blood neutrophils (PMN) exhibit delayed spontaneous apoptosis in individuals with diabetes mellitus type 2 (T2DM) and that the delay is exacerbated further among people who coexpress chronic periodontitis (CP). Seventy-three individuals were enrolled, including those with T2DM (n = 16), CP (n = 15), T2DM + CP (n = 21), and healthy volunteers (n = 21). PMN apoptosis was determined by flow cytometry using TUNEL and Annexin V assays. The activity of caspase-3, -8, and -9 was measured by colorimetric assay. PMN surface death receptor quantification was performed by flow cytometry staining with fluorescence-conjugated anti-CD120a (TNFR1) and anti-CD95 [Fas receptor (FasR)] antibody. Analysis of inflammatory markers in serum samples was performed using multiplexed sandwich immunoassays. In healthy volunteers and individuals with T2DM, CP, and T2DM + CP, spontaneous PMN apoptosis observed at 12 h reached 85.3 ± 3.1, 67.3 ± 3.9, 62.9 ± 3.5 and 62.5 ± 5.4%, respectively (P < 0.05). Caspase-3 activity was significantly reduced in individuals with T2DM and T2DM + CP (P < 0.05) when compared with healthy volunteers. Caspase-8 activity was also significantly decreased in CP and T2DM + CP (P < 0.05), associated with reduced cell-surface FasR, TNFRs, and Fas ligand (FasL) serum levels. Glucose alone was not observed to impact PMN apoptosis; simultaneous incubation with the receptor for advanced glycation endproducts (RAGE) agonist S100B induced significant PMN apoptosis (P < 0.05). These data support the premise that the inhibition of PMN apoptosis in individuals with T2DM occurs through an advanced glycation endproducts/RAGE ligand/receptor-mediated interaction.

Glycation stimulates cutaneous monocyte differentiation in reconstructed skin in vitro

Glycation reaction is a recognized mechanism related to chronological aging. Previous investigations in cutaneous biology have considered the effect of glycation on the dermal matrix molecules, involved in tissue stiffening during skin aging. However, little is known about a possible direct effect of glycation upon cell differentiation. To address such issue, the effect of glycation has been re-investigated in a reconstructed skin model integrating monocytes that are cells capable of differentiating according to different pathways. The results showed that, in the absence of glycation, a small number of these CD45⁺ cells could differentiate either into dendritic-like cells (DC-SIGN⁺, BDC1a⁺, DC-LAMP⁺) or macrophage- like cells (CD14⁺, CD68⁺, CD163⁺) whereas, with glycation, the number of monocytes, dendritic cells, macrophage-like cells were found surprisingly increased. In-vivo our results showed also that dendritic and macrophage-like cells were increased and suggest a possible link with the age-dependent glycation level in the skin. In addition, we found that, unlike fibroblasts incorporated in the reconstructed skin, these cells expressed specific receptors for AGEs (RAGE and SRA). Taken altogether, our data show that cells of the monocyte lineage, in the presence of AGEs, can differentiate into dendritic or macrophage-like cells and could lead to a micro inflammatory environment.

Glucagon-like peptide-1 inhibits the receptor for advanced glycation endproducts to prevent podocyte apoptosis induced by advanced oxidative protein products

OBJECTIVE

To investigate whether and how glucagon-like peptide-1 (GLP-1) can protect podocytes from apoptosis induced by advanced oxidative protein products (AOPPs).

METHODS

Murine podocytes were stimulated with 200 μg/ml AOPP for 48 h in the presence or absence of GLP-1. Cell viability was assessed using the cell counting kit-8 assay. Podocyte apoptosis was detected by flow cytometry and Hoechst 33258 staining. Superoxide radical production was assayed using lucigenin-enhanced chemiluminescence, and Western blotting was used to measure expression of RAGE, NADPH oxidase subunits p47^phox and gp91^phox, as well as apoptosis-associated proteins p53, Bax, Bcl-2 and caspase-3.

RESULTS

Incubating podocytes with AOPPs reduced cell viability, triggered changes in cell morphology and promoted apoptosis. GLP-1 partially inhibited AOPP-induced apoptosis, O₂^- overproduction, and AOPP-induced expression of RAGE. GLP-1 inhibited expression of p47^phox and gp91^phox in AOPP-treated podocytes, and it attenuated AOPP-induced expression of p53, Bax and cleaved caspase-3, whereas it restored expression of Bcl-2.

CONCLUSION

GLP-1 partially inhibits AOPP-induced apoptosis in podocytes, perhaps by interfering with the AOPP-RAGE axis, decreasing oxidative stress and inhibiting the downstream p53/Bax/caspase-3 apoptotic pathway. GLP-1 may be a useful anti-apoptotic agent for early intervention in diabetic nephropathy.

Role of Moesin in Advanced Glycation End Products-Induced Angiogenesis of Human Umbilical Vein Endothelial Cells

Disorders of angiogenesis are related to microangiopathies during the development of diabetic vascular complications, but the effect of advanced glycation end products (AGEs) on angiogenesis and the mechanism has not been completely unveiled. We previous demonstrated that moesin belonging to the ezrin-radixin-moesin (ERM) protein family protein played a critical role in AGE-induced hyper-permeability in human umbilical vein endothelial cells (HUVECs). Here, we investigated the impact of moesin on AGE-induced HUVEC proliferation, migration, and tubulogenesis. Silencing of moesin decreased cell motility and tube formation but not cell proliferation. It also attenuated cellular F-actin reassembly. Further, phosphorylation of threonine at the 558 amino acid residue (Thr 558) in moesin suppressed AGE-induced HUVEC proliferation, migration, and tube formation, while the activating mutation of moesin at Thr 558 enhanced HUVEC angiogenesis. Further, the inhibition of either RhoA activity by adenovirus or ROCK activation with inhibitor Y27632 decreased AGE-induced moesin phosphorylation and subsequently suppressed HUVEC angiogenesis. These results indicate that the Thr 558 phosphorylation in moesin mediates endothelial angiogenesis. AGEs promoted HUVEC angiogenesis by inducing moesin phosphorylation via RhoA/ROCK pathway.

Role of Src in Vascular Hyperpermeability Induced by Advanced Glycation End Products

The disruption of microvascular barrier in response to advanced glycation end products (AGEs) stimulation contributes to vasculopathy associated with diabetes mellitus. Here, to study the role of Src and its association with moesin, VE-cadherin and focal adhesion kinase (FAK) in AGE-induced vascular hyperpermeability, we verified that AGE induced phosphorylation of Src, causing increased permeability in HUVECs. Cells over-expressed Src displayed a higher permeability after AGE treatment, accompanied with more obvious F-actin rearrangement. Activation of Src with pcDNA3/flag-Src^Y530F alone duplicated these effects. Inhibition of Src with siRNA, PP2 or pcDNA3/flag-Src^K298M abolished these effects. The pulmonary microvascular endothelial cells (PMVECs) isolated from receptor for AGEs (RAGE)-knockout mice decreased the phosphorylation of Src and attenuated the barrier dysfunction after AGE-treatment. In vivo study showed that the exudation of dextran from mesenteric venules was increased in AGE-treated mouse. This was attenuated in RAGE knockout or PP2-pretreated mice. Up-regulation of Src activity induced the phosphorylation of moesin, as well as activation and dissociation of VE-cadherin, while down-regulation of Src abolished these effects. FAK was also proved to interact with Src in HUVECs stimulated with AGEs. Our studies demonstrated that Src plays a critical role in AGE-induced microvascular hyperpermeability by phosphorylating moesin, VE-cadherin, and FAK respectively.

Advanced oxidation protein products induce apoptosis in podocytes through induction of endoplasmic reticulum stress

Although podocyte apoptosis has been shown to be induced by the accumulation of advanced oxidation protein products (AOPPs), the mechanisms through which AOPPs trigger apoptosis in these cells remain unclear. In this study, we investigated the role of endoplasmic reticulum (ER) stress in AOPP-induced podocyte apoptosis. AOPP treatment induced overexpression of glucose-regulated protein 78 and CCAAT/enhancer-binding protein-homologous protein (CHOP) in podocytes, indicating that AOPPs induced ER stress. Notably, AOPP-induced increase in the rate of podocyte apoptosis was partly reversed by salubrinal, an ER stress inhibitor, whereas the AOPP effect was reproduced by an inducer of ER stress, thapsigargin, suggesting that AOPPs triggered podocyte apoptosis by inducing ER stress. Furthermore, AOPP-induced reactive oxygen species (ROS) generation, ER stress, and podocyte apoptosis were significantly inhibited by an nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, a ROS scavenger, or receptor of advanced glycation end products (RAGE) small interfering RNA (siRNA). Moreover, silencing of the three ER stress sensors, protein kinase-like ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol requiring 1 (IRE1), respectively, significantly lowered the apoptotic rate of the cells compared with that of the scramble siRNA-transfected cells. Lastly, our data suggested that CHOP- and caspase-12-dependent pathways were involved in ER stress-mediated podocyte apoptosis and that Bcl-2 suppression was involved in CHOP-mediated apoptosis. Collectively, our results indicate for the first time that AOPPs trigger podocyte apoptosis through induction of ER stress, which might be regulated by NADPH oxidase-dependent ROS through RAGE, and that this apoptosis is mediated by three unfolded protein response pathways, the PERK, ATF6, and IRE1 pathways, and the mediators, CHOP and caspase-12.

Effects of advanced glycation end products on calcium handling in cardiomyocytes

BACKGROUND AND AIMS

Advanced glycation end products (AGEs) accumulate in diabetes and the engagement of receptor for AGE (RAGE) by AGEs contributes to the pathogenesis of diabetic cardiomyopathy. This study aims to investigate the effects of AGE/RAGE on ryanodine receptor (RyR) activity and Ca(2+) handling in cardiomyocytes to elucidate the possible mechanism underlying cardiac dysfunction in diabetic cardiomypathy.

METHODS AND RESULTS

Confocal imaging Ca(2+) spark, the elementary Ca(2+) release event reflecting RyR activity in intact cell, as well as SR Ca(2+) content and systolic Ca(2+) transient were performed in cultured neonatal rat ventricular myocytes. The results show that 50 mg/ml AGE increased the frequency of Ca(2+) sparks by 160%, while 150 mg/ml AGE increased it by 53%. AGE decreased the amplitude, width and duration of Ca(2+) sparks. Blocking RAGE with anti-RAGE IgG completely abolished the alteration of Ca(2+) sparks. The SR Ca(2+) content indicated by the amplitude (ΔF/F0) of 20 mM caffeine-elicited Ca(2+) transient was significantly decreased by 150 mg/ml AGE. In parallel, the amplitude of systolic Ca(2+) transient evoked by 1 Hz-field stimulation was remarkably decreased by 150 mg/ml AGE. The anti-RAGE antibody completely restored the impaired SR load and systolic Ca(2+) transient.

CONCLUSION

AGE/RAGE signal enhanced Ca(2+) spark-mediated SR Ca(2+) leak, causing partial depletion of SR Ca(2+) content and consequently decreasing systolic Ca(2+) transient, which may contribute to contractile dysfunction in diabetic cardiomyopathy.

Controlling the receptor for advanced glycation end-products to conquer diabetic vascular complications

Diabetic vascular complications, such as cardiovascular disease, stroke and microangiopathy, lead to high rates of morbidity and mortality in patients with long‐term diabetes. Extensive intracellular and extracellular formation of advanced glycation end‐products (AGE) is considered a causative factor in vascular injuries in diabetes. Receptor‐dependent mechanisms are involved in AGE‐induced cellular dysfunction and tissue damage. The receptor for AGE (RAGE), originally an AGE‐binding receptor, is now recognized as a member of pattern‐recognition receptors and a pro‐inflammatory molecular device that mediates danger signals to the body. Previous animal studies have shown RAGE dependent of diabetic vascular injuries. Prophylactic and therapeutic strategies focusing on RAGE and its ligand axis will be of great importance in conquering diabetic vascular complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00191.x, 2012)

Advanced glycation end products of beta2-microglobulin in uremic patients as determined by high resolution mass spectrometry

By using a high resolution top-down and bottom-up approach we identified and characterized the AGEs of beta2-microglobulin (β2-m) formed by incubating the protein in the presence of glucose and of the main reactive carbonyl species. Glucose induced glycation on the N-terminal residue, while glyoxal (GO) and methylglyoxal (MGO) covalently reacted with Arg3. Carboxymethyl (CM-R) and imidazolinone (R-GO) derivatives were identified in the case of GO and carboxyethyl arginine (CE-R) and methyl-imidazolinone (R-MGO) for MGO. Interestingly, α,β-unsaturated aldehydes [4-hydroxy-2-nonenal (HNE); 4-oxo-2-nonenal (ONE); acrolein (ACR)] did not induce any covalent modifications up to 100μM. The different reactivity of β2-m towards the different RCS was then rationalized by molecular modeling studies. The MS method was then applied to fully characterize the AGEs of β2-m isolated from the urine of uremic subjects. CM-R, CE-R and R-MGO were easily identified on Arg3 and their relative abundance in respect to the native protein determined by a semi-quantitative approach. Overall, the AGEs content of urinary β2-m ranged from 0.2 to 1% in uremic subjects. The results here reported offer novel insights and technical achievements for a potential biological role of AGEs-β2-m in pathological conditions.

Uremia-related oxidative stress in leukocytes is not triggered by β2-microglobulin

BACKGROUND

Chronic kidney disease (CKD) is characterized by low-grade inflammation and increased risk for cardiovascular disease. The interest in β2-microglobulin (B2M) as a marker for cardiovascular outcome with and without CKD has grown. Clinical studies suggested that B2M could be involved in the pathogenesis of vascular disease, for which chronic leukocyte activation is a pathogenic factor. We investigated whether B2M is proinflammatory by inducing oxidative burst in leukocytes.

METHODS

Oxidative burst was measured at baseline and after stimulation with N-formyl-methionine-leucine-phenylalanine (fMLP), Escherichia coli, or phorbol-12-myristate-acetate (PMA) in the whole blood of healthy volunteers in the absence (saline) and presence of human B2M (hB2M; 10 and 50 mg/L) versus uremic whole blood. Because of suspicion of contamination, hB2M was dialyzed for purification and purified B2M (dB2M) and dialysates were tested in the burst test. As a comparator, reactive oxygen species (ROS) in response to lipopolysaccharide (LPS) was measured.

RESULTS

Unpurified hB2M strongly enhanced ROS in monocytes and granulocytes after E. coli and PMA and moderately after fMLP stimulation compared with control (P < .01) and uremia (P < .01) whereas at baseline hB2M only induced ROS in granulocytes (P < .05). After purification, dB2M no longer increased burst activity, suggesting that contamination was responsible for the initial effect. An endotoxin concentration of less than 1.5 EU/mL, as observed in hB2M, could not induce oxidative stress.

CONCLUSION

This study suggests that B2M, a traditional marker for middle molecule retention and a novel marker for cardiovascular outcome, may not by itself cause vascular damage by influencing inflammatory response due to induction of leukocyte free radical production. However, an effect on other cell types involved cannot be excluded. Our data further reveal that this type of research might be skewed by non-LPS contaminants, and that care should be taken to exclude this bias.

HLA-B27 misfolding and ankylosing spondylitis

Understanding how HLA-B27 contributes to the pathogenesis of spondyloarthritis continues to be an important goal. Current efforts are aimed largely on three areas of investigation; peptide presentation to CD8T cells, abnormal forms of the HLA-B27 heavy chain and their recognition by leukocyte immunoglobulin-like receptors on immune effector cells, and HLA-B27 heavy chain misfolding and intrinsic biological effects on affected cells. In this chapter we review our current understanding of the causes and consequences of HLA-B27 misfolding, which can be defined biochemically as a propensity to oligomerize and form complexes in the endoplasmic reticulum (ER) with the chaperone BiP (HSPA5/GRP78). HLA-B27 misfolding is linked to an unusual combination of polymorphisms that identify this allele, and cause the heavy chain to fold and load peptides inefficiently. Misfolding can result in ER-associated degradation (ERAD) of heavy chains, which is mediated in part by the E3 ubiquitin ligase HRD1 (SYVN1), and the ubiquitin conjugating enzyme UBE2JL. Upregulation of HLA-B27 and accumulation of misfolded heavy chains can activate ER stress signaling pathways that orchestrate the unfolded protein response. In transgenic rats where HLA-B27 is overexpressed, UPR activation is prominent. However, it is specific for heavy chain misfolding, since overexpression of HLA-B7, an allele that does not misfold, fails to generate ER stress. UPR activation has been linked to cytokine dysregulation, promoting lL-23, IFNβ, and lL-1α production, and may activate the IL-23/IL-17 axis in these rats. IL-1α and IFNβ are pro- and anti-osteoclastogenic cytokines, respectively, that modulate osteoclast development in HLA-B27-expressing transgenic rat monocytes. Translational studies of patient derived cells expressing HLA-B27 at physiologic levels have provided evidence that ER stress and UPR activation can occur in peripheral blood, but this has not been reported to date in isolated macrophages. Inflamed gastrointestinal tissue reveals evidence for HLA-B27 misfolding, ERAD, and autophagy, without acute UPR activation. A more complete picture of conditions that impact HLA-B27 folding and misfolding, the full spectrum and time course of consequences of ER stress, and critical cell types involved is needed to understand the role of HLA-B27 misfolding in spondyloarthritis pathogenesis.

AGE-LDL activates Toll like receptor 4 pathway and promotes inflammatory cytokines production in renal tubular epithelial cells

Background/Aims:Accumulation of advanced glycation end-products, the well-recognized pro-inflammatory molecules, has been detected in renal tissues including tubules. The aim of the present study was to investigate the role of advanced glycation end-products modified low density lipoprotein (AGE-LDL) in inflammatory cytokines production in human proximal tubular epithelial cells and the underlying mechanism. Methods: The Interleukin-6 (IL-6) and Interleukin-8 (IL-8) production was examined by real-time PCR and ELISA. The expression of Toll-like receptor 2 and 4 (TLR2/4) was detected by flow cytometry and western blot. The interaction of TLR2/4 with AGE-LDL was examined by co-immunoprecipitation assay. The involvement of MyD88 and the downstream molecules in inflammatory cytokines production was examined by siRNA and pharmacologic inhibitors, respectively. Results: AGE-LDL interacted with TLR2 and TLR4. TLR4 siRNA showed stronger inhibition on AGE-LDL-induced IL-6 and IL-8 production than that of TLR2 siRNA. Silencing MyD88, but not TRIF, inhibited AGE-LDL-induced IL-6 and IL-8 production. AGE-LDL stimulation led to phosphorylation of JNK, p38, Akt and the p65 subunit of nuclear factor-κB (NF-κB). Pharmacologic inhibitor of Akt suppressed AGE-LDL-induced activation of NF-κB, but the inhibitor of JNK, p38 or ERK1/2 had no effect. Blocking MyD88, p38, JNK, Akt or NF-κB attenuated AGE-LDL-triggered IL-6 production. Conclusion: AGE-LDL induced IL-6 and IL-8 production via TLR2/4-MyD88-dependent pathway in tubular epithelial cells. These data suggest that activation of TLRs signaling in tubular epithelial cells by AGE-LDL might be a novel mechanism for the tubulointerstitial inflammation.

Fever associated with severe dialysis-related amyloidosis

Dialysis-related amyloidosis (DRA) is one of the most important complications in patients on long-term hemodialysis (HD). DRA often affects the osteoarticular system; however, little is known about the role of β₂-microglobulin in the induction of fever in HD patients. We report a 64-year-old woman on long-term (24 years) HD who developed polyarthralgia and intermittent fever. Infectious diseases, connective tissue diseases, and malignant neoplasm were ruled out. Computed tomography and magnetic resonance imaging showed swelling of the soft tissues around bilateral shoulder and hip joints, suggestive of amyloid deposits. Gallium scintigraphy showed abnormal uptake in the vicinity of several large joints. It was presumed that the fever was related to the amyloid joint deposits, and the patient was treated with prednisolone and β₂-microglobulin adsorption therapy. The treatment resulted in the resolution of fever, relief of arthralgia, and normalization of several inflammatory cytokines and C-reactive protein. The findings suggest that massive DRA could cause systemic inflammatory response in patients on long-term HD.

An update on advanced glycation endproducts and atherosclerosis

Advanced glycation endproducts (AGEs) are a group of modified molecular species formed by nonenzymatic reactions between the aldehydic group of reducing sugars with proteins, lipids, or nucleic acids. Formation and accumulation of AGEs are related to the aging process and are accelerated in diabetes. AGEs are generated in hyperglycemia, but their production also occurs in settings characterized by oxidative stress and inflammation. These species promote vascular damage and acceleration of atherosclerotic plaque progression mainly through two mechanisms: directly, altering the functional properties of vessel wall extracellular matrix molecules, or indirectly, through activation of cell receptor-dependent signaling. Interaction between AGEs and the key receptor for AGEs (RAGE), a transmembrane signaling receptor which is present in all cells relevant to atherosclerosis, alters cellular function, promotes gene expression, and enhances the release of proinflammatory molecules. The importance of the AGE-RAGE interaction and downstream pathways, leading to vessel wall injury and plaque development, has been amply established in animal studies. Moreover, the deleterious link of AGEs with diabetic vascular complications has been suggested in many human studies. Blocking the vicious cycle of AGE-RAGE axis signaling may be essential in controlling and preventing cardiovascular complications. In this article, we review the pathogenetic role of AGEs in the development, progression and instability of atherosclerosis, and the potential targets of this biological system for the prevention and treatment of cardiovascular disease.

The receptor of advanced glycation end products plays a central role in advanced oxidation protein products-induced podocyte apoptosis

The accumulation of plasma advanced oxidation protein products (AOPPs) is prevalent in chronic kidney disease. We previously showed that accumulation of AOPPs resulted in podocyte apoptosis and their deletion by a cascade of signaling events coupled with intracellular oxidative stress. The transmembrane receptor that specifically transmits the AOPPs' signals to elicit cellular activity, however, remains unknown. Using co-immunoprecipitation and immunofluorescence, we found that AOPPs colocalized and interacted with the receptor of advanced glycation end products (RAGE) on podocytes. Blocking RAGE by anti-RAGE immunoglobulin G or its silencing by siRNA significantly protected podocytes from AOPPs-induced apoptosis both in vitro and in vivo and ameliorated albuminuria in AOPPs-challenged mice. AOPPs-induced activation of nicotinamide adenine dinucleotide phosphate oxidase and the excessive generation of intracellular superoxide were largely inhibited by anti-RAGE immunoglobulin G or RAGE siRNA. Moreover, blockade of RAGE decreased the activation of the p53/Bax/caspase-dependent proapoptotic pathway induced by AOPPs. Thus, AOPPs interact with RAGE to induce podocyte apoptosis and this, in part, may contribute to the progression of chronic kidney disease.

Advanced glycation end products induce moesin phosphorylation in murine retinal endothelium

Increase in vascular permeability is the most important pathological event during the development of diabetic retinopathy. Deposition of advanced glycation end products (AGEs) plays a crucial role in the process of diabetes. This study was to investigate the role of moesin and its underlying signal transduction in retinal vascular hyper-permeability induced by AGE-modified mouse serum albumin (AGE-MSA). Female C57BL/6 mice were used to produce an AGE-treated model by intraperitoneal administration of AGE-MSA for seven consecutive days. The inner blood-retinal barrier was quantified by Evans blue leakage assay. Endothelial F-actin cytoskeleton in retinal vasculature was visualized by fluorescence probe staining. The expression and phosphorylation of moesin in retinal vessels were detected by RT-PCR and western blotting. Further studies were performed to explore the effects of Rho kinase (ROCK) and p38 MAPK pathway on the involvement of moesin in AGE-induced retinal vascular hyper-permeability response. Treatment with AGE-MSA significantly increased the permeability of the retinal microvessels and induced the disorganization of F-actin in retinal vascular endothelial cells. The threonine (T558) phosphorylation of moesin in retinal vessels was enhanced remarkably after AGE administration. The phosphorylation of moesin was attenuated by inhibitions of ROCK and p38 MAPK, while this treatment also prevented the dysfunction of inner blood-retinal barrier and the reorganization of F-actin in retinal vascular endothelial cells. These results demonstrate that moesin is involved in AGE-induced retinal vascular endothelial dysfunction and the phosphorylation of moesin is triggered via ROCK and p38 MAPK activation.

RhoA/ROCK-dependent moesin phosphorylation regulates AGE-induced endothelial cellular response

BACKGROUND

The role of advanced glycation end products (AGEs) in the development of diabetes, especially diabetic complications, has been emphasized in many reports. Accumulation of AGEs in the vasculature triggers a series of morphological and functional changes in endothelial cells (ECs) and induces an increase of endothelial permeability. This study was to investigate the involvement of RhoA/ROCK-dependent moesin phosphorylation in endothelial abnormalities induced by AGEs.

METHODS

Using human dermal microvascular endothelial cells (HMVECs), the effects of human serum albumin modified-AGEs (AGE-HSA) on the endothelium were assessed by measuring monolayer permeability and staining of F-actin in HMVECs. Activations of RhoA and ROCK were determined by a luminescence-based assay and immunoblotting. Transfection of recombinant adenovirus that was dominant negative for RhoA (RhoA N19) was done to down-regulate RhoA expression, while adenovirus with constitutively activated RhoA (RhoA L63) was transfected to cause overexpression of RhoA in HMVECs. H-1152 was employed to specifically block activation of ROCK. Co-immunoprecipitation was used to further confirm the interaction of ROCK and its downstream target moesin. To identify AGE/ROCK-induced phosphorylation site in moesin, two mutants pcDNA3/HA-moesinT(558A) and pcDNA3/HA-moesinT(558D) were applied in endothelial cells.

RESULTS

The results showed that AGE-HSA increased the permeability of HMVEC monolayer and triggered the formation of F-actin-positive stress fibers. AGE-HSA enhanced RhoA activity as well as phosphorylation of ROCK in a time- and dose-dependent manner. Down-regulation of RhoA expression with RhoA N19 transfection abolished these AGE-induced changes, while transfection of RhoA L63 reproduced the AGE-evoked changes. H-1152 attenuated the AGE-induced alteration in monolayer permeability and cytoskeleton. The results also confirmed the AGE-induced direct interaction of ROCK and moesin. Thr558 was further identified as the phosphorylating site of moesin in AGE-evoked endothelial responses.

CONCLUSION

These results confirm the involvement of RhoA/ROCK pathway and subsequent moesin Thr558 phosphorylation in AGE-mediated endothelial dysfunction.

Role of miR-150-targeting c-Myb in colonic epithelial disruption during dextran sulphate sodium-induced murine experimental colitis and human ulcerative colitis

Chronic inflammatory bowel diseases (IBDs) are associated with differential expression of genes involved in inflammation and tissue remodelling. We surveyed the expression profile of apoptosis-related microRNAs by real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) in a dextran sulphate sodium (DSS) murine model of colitis. We found that miR-150 was strongly elevated, whereas c-Myb, a transcription factor and a target gene of miR-150, was significantly reduced in colon tissue after DSS treatment. Interestingly, elevation of miR-150 and down-regulation of c-Myb were also observed in human colon with active ulcerative colitis compared to the normal colon. Supporting the observation of DSS treatment inducing colonic cell apoptosis, Bcl-2, an anti-apoptotic protein known to be regulated by c-Myb, was reduced in colon tissue of DSS-treated mice. Furthermore, forced expression of pre-miR-150 in colonic epithelial HT29 cells strongly elevated miR-150 levels and decreased c-Myb and Bcl-2 levels, thus enhancing cell apoptosis induced by serum deprivation. Together, the present study presents the first evidence that miR-150 and its targeting of c-Myb may serve as a new mechanism underlying the colonic epithelial disruption in DSS-induced murine experimental colitis and in active human IBD.

Role of microRNA-214-targeting phosphatase and tensin homolog in advanced glycation end product-induced apoptosis delay in monocytes

Advanced glycation end products (AGEs) delay spontaneous apoptosis of monocytes and contribute to the development of inflammatory responses. However, the mechanism by which AGEs affect monocyte apoptosis is unclear. We studied the role of microRNA-214 (miR-214) and its target gene in AGE-induced monocytic apoptosis delay. Using microRNA (miRNA) microarray and stem-loop, quantitative RT-PCR assay, we studied genome-wide miRNA expression in THP-1 cells treated with or without AGEs. Significant upregulation of miR-214 was consistently observed in THP-1 and human monocytes treated with various AGEs, and AGE-induced monocytic miR-214 upregulation was likely through activation of receptor for AGEs. A striking increase in miR-214 was also detected in monocytes from patients with chronic renal failure. Luciferase reporter assay showed that miR-214 specifically binds to the phosphatase and tensin homolog (PTEN) mRNA 3'-untranslated region, implicating PTEN as a target gene of miR-214. PTEN expression is inversely correlated with miR-214 level in monocytes. Compared with normal monocytes, AGE-treated monocytes and monocytes from chronic renal failure patients exhibited lower PTEN levels and delayed apoptosis. Overexpression of pre-miR-214 led to impaired PTEN expression and delayed apoptosis of THP-1 cells, whereas knockdown of miR-214 level largely abolished AGE-induced cell survival. Our findings define a new role for miR-214-targeting PTEN in AGE-induced monocyte survival.

The RAGE axis: a fundamental mechanism signaling danger to the vulnerable vasculature

The immunoglobulin superfamily molecule RAGE (receptor for advanced glycation end product) transduces the effects of multiple ligands, including AGEs (advanced glycation end products), advanced oxidation protein products, S100/calgranulins, high-mobility group box-1, amyloid-beta peptide, and beta-sheet fibrils. In diabetes, hyperglycemia likely stimulates the initial burst of production of ligands that interact with RAGE and activate signaling mechanisms. Consequently, increased generation of proinflammatory and prothrombotic molecules and reactive oxygen species trigger further cycles of oxidative stress via RAGE, thus setting the stage for augmented damage to diabetic tissues in the face of further insults. Many of the ligand families of RAGE have been identified in atherosclerotic plaques and in the infarcted heart. Together with increased expression of RAGE in diabetic settings, we propose that release and accumulation of RAGE ligands contribute to exaggerated cellular damage. Stopping the vicious cycle of AGE-RAGE and RAGE axis signaling in the vulnerable heart and great vessels may be essential in controlling and preventing the consequences of diabetes.

RAGE, glomerulosclerosis and proteinuria: roles in podocytes and endothelial cells

The multi-ligand Receptor for Advanced Glycation Endproducts (RAGE) is expressed in podocytes and endothelial cells in the human and murine glomerulus. Although present at low levels in homeostasis, RAGE expression is increased during disease. Pharmacological antagonism of RAGE or its genetic deletion imparts marked protection from podocyte effacement, albuminuria and glomerular sclerosis in disease models. In human subjects, associations between specific genetic polymorphisms of RAGE and levels of soluble forms of RAGE are linked to disease states in the kidney. In this review, we summarize the evidence from mouse to man, linking RAGE to the pathogenesis of nephropathy.

From HLA-B27 to spondyloarthritis: a journey through the ER

Almost four decades of research into the role of human leukocyte antigen-B27 (HLA-B27) in susceptibility to spondyloarthritis has yet to yield a convincing answer. New results from an HLA-B27 transgenic rat model now demonstrate quite convincingly that CD8(+) T cells are not required for the inflammatory phenotype. Discoveries that the HLA-B27 heavy chain has a tendency to misfold during the assembly of class I complexes in the endoplasmic reticulum (ER) and to form aberrant disulfide-linked dimers after transport to the cell surface have forced the generation of new ideas about its role in disease pathogenesis. In transgenic rats, HLA-B27 misfolding generates ER stress and leads to activation of the unfolded protein response, which dramatically enhances the production of interleukin-23 (IL-23) in response to pattern recognition receptor agonists. These findings have led to the discovery of striking T-helper 17 cell activation and expansion in this animal model, consistent with results emerging from humans with spondyloarthritis and the discovery of IL23R as an additional susceptibility gene for ankylosing spondylitis. Together, these results suggest a novel link between HLA-B27 and the T-helper 17 axis through the consequences of protein misfolding and open new avenues of investigation as well as identifying new targets for therapeutic intervention in this group of diseases.

Accumulation of advanced oxidation protein products induces podocyte apoptosis and deletion through NADPH-dependent mechanisms

The accumulation of plasma advanced oxidation protein products (AOPPs) is prevalent in diverse disorders such as diabetes, metabolic syndromes, and chronic kidney disease. To study whether accumulated AOPPs have an important role in the progression of proteinuria and glomerulosclerosis, we chronically treated normal Sprague-Dawley rats with AOPP-modified rat serum albumin. Podocyte apoptosis was significantly increased coincident with the onset of albuminuria and preceded significant losses of glomerular podocytes. Increasing the amount of AOPPs in the media of conditionally immortalized podocytes rapidly triggered the production of intracellular superoxide by activation of NADPH oxidase and this, in turn, led to an upregulation of p53, Bax, caspase 3 activity, and apoptosis. Chronic inhibition of NADPH oxidase by apocynin prevented podocyte apoptosis, ameliorated podocyte depletion, and decreased albuminuria in AOPP-challenged rats. Our study demonstrates that accumulation of AOPPs promotes NADPH oxidase-dependent podocyte depletion by a p53-Bax apoptotic pathway both in vivo and in vitro.

ERM protein moesin is phosphorylated by advanced glycation end products and modulates endothelial permeability

Advanced glycation end products (AGEs) accumulated in different pathological conditions have the potent capacity to alter cellular properties that include endothelial structural and functional regulations. The disruption of endothelial barrier integrity may contribute to AGE-induced microangiopathy and macrovasculopathy. Previous studies have shown that AGEs induced the rearrangement of actin and subsequent hyperpermeability in endothelial cells (ECs). However, the mechanisms involved in this AGE-evoked EC malfunction are not well understood. This study directly evaluated the involvement of moesin phosphorylation in AGE-induced alterations and the effects of the RhoA and p38 MAPK pathways on this process. Using immortalized human dermal microvascular ECs (HMVECs), we first confirmed that the ezrin/radixin/moesin (ERM) protein moesin is required in AGE-induced F-actin rearrangement and hyperpermeability responses in ECs by knockdown of moesin protein expression with small interfering RNA. We then detected AGE-induced moesin phosphorylation by Western blot analysis. The mechanisms involved in moesin phosphorylation were analyzed by blocking AGE receptor binding and inhibiting Rho and MAPK pathways. AGE-treated HMVECs exhibited time- and dose-dependent increases in the Thr(558) phosphorylation of moesin. The increased moesin phosphorylation was attenuated by preadministrations of AGE receptor antibody, Rho kinase (ROCK), or p38 inhibitor. Suppression of p38 activation via the expression of dominant negative mutants with Ad.MKK6b or Ad.p38alpha also decreased moesin phosphorylation. The activation of the p38 pathway by transfection of HMVECs with an adenoviral construct of dominant active MKK6b resulted in moesin phosphorylation. These results suggest a critical role of moesin phosphorylation in AGE-induced EC functional and morphological regulations. Activation of the ROCK and p38 pathways is required in moesin phosphorylation.

Tempering the wrath of RAGE: an emerging therapeutic strategy against diabetic complications, neurodegeneration, and inflammation

The multiligand receptor RAGE (receptor for advanced glycation end-products) is emerging as a central mediator in the immune/inflammatory response. Epidemiological evidence accruing in the human suggests upregulation of RAGE's ligands (AGEs, S100/calgranulins, high mobility group box-1 (HMGB1), and amyloid beta-peptide and beta-sheet fibrils) and the receptor itself at sites of inflammation and in chronic diseases such as diabetes and neurodegeneration. The consequences of ligand-RAGE interaction include upregulation of molecules implicated in inflammatory responses and tissue damage, such as cytokines, adhesion molecules, and matrix metalloproteinases. In this review, we discuss the localization of RAGE and its ligand families and the biological impact of this axis in multiple cell types implicated in chronic diseases. Lastly, we consider findings from animal model studies suggesting that although tissue-damaging effects ensue from recruitment of the ligand-RAGE interaction, in distinct settings, adaptive and repair/regeneration outcomes appear to override detrimental effects of RAGE. As RAGE blockade moves further into clinical development, clarifying the biology of RAGE garners ever-increasing importance.

Advanced oxidation protein products activate vascular endothelial cells via a RAGE-mediated signaling pathway

The accumulation of advanced oxidation protein products (AOPPs) has been linked to vascular lesions in diabetes, chronic renal insufficiency, and atherosclerosis. However, the signaling pathway involved in AOPPs-induced endothelial cells (ECs) perturbation is unknown and was investigated. AOPPs modified human serum albumin (AOPPs-HSA) bound to the receptor for advanced glycation end products (RAGE) in a dose-dependent and saturable manner. AOPPs-HSA competitively inhibited the binding of soluble RAGE (sRAGE) with its preferential ligands advanced glycation end products (AGEs). Incubation of AOPPs, either prepared in vitro or isolated from uremic serum, with human umbilical vein ECs induced superoxide generation, activation of NAD(P)H oxidase, ERK 1/2 and p38, and nuclear translocation of NF-kappaB. Activation of signaling pathway by AOPPs-ECs interaction resulted in overexpression of VCAM-1 and ICAM-1 at both gene and protein levels. This AOPPs-triggered biochemical cascade in ECs was prevented by blocking RAGE with either anti-RAGE IgG or excess sRAGE, but was not affected by the neutralizing anti-AGEs IgG. These data suggested that AOPPs might be new ligands of endothelial RAGE. AOPPs-HSA activates vascular ECs via RAGE-mediated signals.

Advanced oxidation protein products promote inflammation in diabetic kidney through activation of renal nicotinamide adenine dinucleotide phosphate oxidase

The involvement of inflammatory processes has been recognized in development and/or progression of diabetic nephropathy. However, the mechanisms involved in the pathogenesis of renal inflammation have not been completely understood. In this study, we tested the hypothesis that accumulation of advanced oxidation protein products (AOPPs), which occurs in diabetes, may promote inflammatory responses in diabetic kidney. Streptozotocin-induced diabetic rats were randomized to iv injection of vehicle, native rat serum albumin (RSA), and AOPPs-modified RSA (AOPPs-RSA) in the presence or absence of oral administration of apocynin. A control group was followed concurrently. Compared with RSA- or vehicle-treated diabetic rats, AOPPs-RSA-treated animals displayed significant increase in renal macrophage infiltration and overexpression of monocyte chemoattractant protein-1 and TGF-beta1. This was associated with deteriorated structural and functional abnormalities of diabetic kidney, such as glomerular hypertrophy, fibronectin accumulation, and albuminuria. AOPP challenge significantly increased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent superoxide generation in renal homogenates and up-regulated membrane expression of renal NADPH oxidase subunits p47(phox) and gp91(phox). All these AOPPs-induced perturbations in diabetic kidney could be prevented by the NADPH oxidase inhibitor apocynin. These data suggest that chronic accumulation of AOPPs may promote renal inflammation in diabetes probably through activation of renal NADPH oxidase.

CB2 cannabinoid receptor agonist JWH-015 modulates human monocyte migration through defined intracellular signaling pathways

Recruitment of leukocytes to inflammatory sites is crucial in the pathogenesis of chronic inflammatory diseases. The aim of this study was to investigate if activation of CB2 cannabinoid receptors would modulate the chemotactic response of human monocytes. Human monocytes treated with the CB2 agonist JWH-015 for 12-18 h showed significantly reduced migration to chemokines CCL2 and CCL3, associated with reduced mRNA and surface expression of their receptors CCR2 and CCR1. The induction of ICAM-1 in response to IFN-gamma was inhibited by JWH-015. Moreover, JWH-015 cross-desensitized human monocytes for migration in response to CCL2 and CCL3 by its own chemoattractant properties. The CB2-selective antagonist SR-144528, but not the CB1 antagonist SR-147778, reversed JWH-015-induced actions, whereas the CB2 agonist JWH-133 mimicked the effects of JWH-015. The investigation of underlying pathways revealed the involvement of phosphatidylinositol 3-kinase/Akt and ERK1/2 but not p38 MAPK. In conclusion, selective activation of CB2 receptors modulates chemotaxis of human monocytes, which might have crucial effects in chronic inflammatory disorders such as atherosclerosis or rheumatoid arthritis.

Measurement of advanced glycation endproducts in skin of patients with rheumatoid arthritis, osteoarthritis, and dialysis-related spondyloarthropathy using non-invasive methods

Advanced glycation endproducts (AGEs) are the products of non-enzymatic glycation and oxidation of proteins and lipids. Low-turnover tissues such as articular cartilage seem to be susceptible to the accumulation of AGEs, which might lead to cartilage degradation. Recently, a non-invasive method for measuring skin AGE accumulation was developed by using the Autofluorescence Reader (AFR). To examine the usefulness of measuring skin AGE in patients with bone and joint diseases, we examined autofluorescence (AF) levels in skin of patients with osteoarthritis (OA), rheumatoid arthritis (RA), and dialysis-related spondyloarthropathy (DRSA). Ninety-three patients with RA, 24 patients with OA, and 29 patients with DRSA were examined, and 43 healthy volunteers were used as controls. Skin AF was assessed on the lower arm with the AGE-Reader. Mean AF was significantly higher in the patients with RA (median 2.13 and range 1.25-2.94) or with DRSA (median 2.21 and range 1.29-3.88) than in the patients with OA (median 1.63 and range 1.07-2.31) or in the controls (median 1.74 and range 1.10-2.46). There was no significant difference between OA and the controls, or between RA and DRSA. These findings suggest that differences of AGE accumulation in the skin might reflect the different pathologies of these diseases.

Restricted intake of dietary advanced glycation end products retards renal progression in the remnant kidney model

Diet-derived advanced glycation end products (AGEs) contribute significantly to accumulation of AGEs in renal insufficiency. To test whether modulation of dietary AGEs would impact on progression of chronic renal disease, 5/6 nephrectomy rats were randomly placed on three diets that differed only in AGEs content (low AGEs diet (LAD), high AGEs diet (HAD), and standard rodent diet (SRD)) for 5-13 weeks. Compared with SRD- or HAD-fed rats, LAD-treated animals showed decreased proteinuria and retarded decline of creatinine clearance without alteration of blood pressure. Glomerular volume was reduced by 23% compared with HAD-fed rats at week 13 (P<0.001). Renal fibrosis progressed with time in the remnant kidneys from HAD-fed rats. However, LAD-fed animals presented a better-preserved structure of the kidneys. LAD-fed rats demonstrated significantly decreased serum and renal AGEs concentration (P<0.01 and P<0.01). This was associated with marked decrease of intrarenal advanced oxidation protein products and thiobarbituric acid reactive substances, as well as increase of glutathione peroxidase activity. LAD treatment also downregulated expression of monocyte chemoattractant protein-1 and transforming growth factor-1 and ameliorated macrophage infiltration in the remnant kidney. These results demonstrated that restriction of dietary AGEs intake retards progression of renal fibrosis and dysfunction in the remnant kidney model.

The ligand/RAGE axis: lighting the fuse and igniting vascular stress

Vascular inflammation contributes critically to the initiation and progression of atherosclerosis. These processes are accelerated in hyperglycemia and play key roles in the increased incidence and severity of myocardial infarction and stroke observed in diabetes. Evidence suggests that the ligands of the receptor for advanced glycation endproducts (RAGE), a multiligand member of the immunoglobulin superfamily, interact with this receptor to play important roles in both early development and progression of atherosclerosis and vascular inflammation. Studies in animal models of vascular injury underscored the potent impact of RAGE blockade; administration of ligand-binding decoys of RAGE or antibodies to the receptor reduced the consequences of diabetes, hyperlipidemia, and physical injury to the vessel wall. This review focuses on the ligand repertoire of RAGE, the impact of ligand-RAGE interaction, and the potent effect of RAGE blockade in rodent models of vascular injury.

Advanced glycation end products induce actin rearrangement and subsequent hyperpermeability of endothelial cells�THIS ARTICLE HAS BEEN RETRACTED

This study aimed to determine the effects of advanced glycation end products (AGEs) on endothelial cytoskeleton morphology and permeability, and to detect the underlying signaling mechanisms involved in these responses. Cultured endothelial cells (ECs) were exposed to AGE-modified human serum albumin (AGE-HSA), and EC cytoskeletal changes were evaluated by observing fluorescence of F-actin following ligation with labeled antibodies. Endothelial permeability was detected by measuring the flux of TRITC-albumin across the EC monolayers. To explore the signaling pathways behind AGE-induced EC alteration, ECs were treated with either soluble anti-AGE receptor (RAGE) IgG, or the MAPK inhibitors PD98059 and SB203580 before AGE-HSA administration. To further elucidate possible involvement of the ERK and p38 pathways in AGE-induced EC changes, adenovirus-carried recombinant constitutive dominant-negative forms of upstream ERK and p38 kinases, namely MEK1(A) and MKK6b(A), were pre-infected into ECs 24 h prior to AGE-HSA exposure. AGE-HSA induced actin cytoskeleton rearrangement, as well as EC hyperpermeability, in a dose and time-dependent manner. The effects were attenuated in cells pretreated with anti-RAGE IgG, PD98059 or SB203580, respectively. EC pre-infection with MEK1(A) and MKK6b(A) also alleviated the effect of AGEs. Furthermore, adenovirus-mediated administration of activated forms of either MEK1 or MKK6b alone induced rearrangement of F-actin and hyperpermeability. The results indicate that ERK and p38 MAPK play important roles in the mediation of AGE-induced EC barrier dysfunction associated with morphological changes of the F-actin.

HLA–B27 up-regulation causes accumulation of misfolded heavy chains and correlates with the magnitude of the unfolded protein response in transgenic rats: Implications for the pathogenesis of spondylarthritis-like disease

OBJECTIVE

HLA-B27 is implicated in the pathogenesis of spondylarthritis (SpA), yet the molecular mechanisms are incompletely defined. HLA-B27 misfolding has been associated with endoplasmic reticulum stress and activation of the unfolded protein response (UPR) in macrophages from HLA-B27/human beta(2)-microglobulin-transgenic (B27-transgenic) rats. This study was performed to assess the mechanisms that drive activation of the HLA-B27-induced UPR and to determine whether splenocytes respond in a similar manner.

METHODS

Splenocytes were isolated and bone marrow macrophages were derived from B27-transgenic and wild-type rats. Cells were treated for up to 24 hours with cytokines that induce class I major histocompatibility complex expression. HLA-B27 expression and misfolding were assessed by real-time reverse transcription-polymerase chain reaction, flow cytometry, and immunoblotting. Activation of the UPR was measured by quantifying UPR target gene expression and X-box binding protein 1 messenger RNA (mRNA) splicing.

RESULTS

HLA-B27 mRNA up-regulation was accompanied by a dramatic increase in the accumulation of misfolded heavy chains and preceded robust activation of the UPR in macrophages. When macrophages were treated with various cytokines, the magnitude of the UPR correlated strongly with the degree of HLA-B27 up-regulation. In contrast, B27-transgenic splenocytes exhibited only low-level differences in the expression of UPR target genes after exposure to interferon-gamma or concanavalin A, which resulted in minimal HLA-B27 up-regulation.

CONCLUSION

These results suggest that HLA-B27-associated activation of the UPR in macrophages is attributable to the accumulation of misfolded heavy chains, and that certain cell types may be more susceptible to the effects of HLA-B27 misfolding. Strategies that eliminate HLA-B27 up-regulation and/or the accumulation of misfolded heavy chains may be useful in evaluating the role of these events in the pathogenesis of SpA.

Monocytes promote natural killer cell interferon gamma production in response to the endogenous danger signal HMGB1

Substantial attention has been paid to the role of the toll-like receptor (TLR) ligands of late and their role in regulating the innate immune response. They serve as exogenous danger signals important in informing and driving the distal adaptive immune response to pathogens. Less clear has been the role of the nominal endogenous danger signals released and recognized in stressed cells following genotoxic or metabolic stress as occurs in progressively growing tumors. HMGB1 (high-mobility group B1) is a nuclear protein well characterized for its ability to modify DNA access to transcriptional proteins that is released from necrotic cells as well as secreted through the endosomal route from hematopoietic cells, serving as a late mediator of sepsis. It interacts with high-affinity RAGE (receptor for advanced glycation end products) and TLR2 receptors. Here we show that HMGB1 enhances interferon gamma release from macrophage (but not dendritic cell)-stimulated NK cells. This is effective only when coupled with other pro-inflammatory cytokines particularly with IL-2 in combination with IL-1 or IL-12. We have used this information to suggest that HMGB1, which also promotes epithelial migration and proliferation, drives repair in the absence or inhibition of other factors but enhances inflammation in their presence. The implications for tumorigenesis and tumor progression are quite important as they may be for other states of chronic inflammation.

In vitro study of the potential role of guanidines in leukocyte functions related to atherogenesis and infection

BACKGROUND

The blunted immune response upon stimulation in chronic renal failure (CRF) is often coupled to a baseline inflammatory status which has been related to atherogenesis. Uremic biologic fluids and several specific uremic retention solutes alter cell-mediated immune responses, as well as the interaction of calcitriol with the immune system.

METHODS

The present study evaluated the influence of different guanidino compounds on DNA synthesis, chemiluminescence production, and CD14 expression of undifferentiated and calcitriol-differentiated HL-60 cells. In a second setup, these guanidino compounds were evaluated for their specific effect on normal human leukocyte oxidative burst activity and tumor necrosis factor-alpha (TNF-alpha) expression.

RESULTS

First, several guanidino compounds elicited proinflammatory effects on leukocytes. Methylguanidine and guanidine stimulated the proliferation of undifferentiated HL-60 cells and the antiproliferative effect of calcitriol (P < 0.05) was neutralized in the presence of methylguanidine (P < 0.05) and guanidinosuccinic acid (P < 0.05). The phorbol-myristate-acetate (PMA)-stimulated chemiluminescence production of the calcitriol differentiated HL-60 cells was enhanced in the presence of guanidine (P < 0.05). Methylguanidine and guanidinoacetic acid enhanced the lipopolysaccharide (LPS)-stimulated intracellular production of TNF-alpha by normal human monocytes (P < 0.05). Second, several guanidino compounds inhibited the function of leukocytes if they were activated. The PMA-stimulated chemiluminescence production of the calcitriol differentiated HL-60 cells was inhibited by the presence of methylguanidine (P < 0.05), guanidinoacetic acid (P < 0.05) and guanidinosuccinic acid (P < 0.05). After incubation of whole blood in the presence of methylguanidine, the Escherichia coli stimulated oxidative burst activity of the granulocyte population was significantly inhibited (P < 0.05). In addition, guanidinosuccinic acid had an inhibitory effect on the LPS-stimulated intracellular production of TNF-alpha by human monocytes (P < 0.01).

CONCLUSION

Guanidino compounds exert proinflammatory as well as anti-inflammatory effects on monocyte/macrophage function. This could contribute to the altered prevalence of cardiovascular disease and propensity to infection in patients with CRF.

Advanced glycation end products in uremia

The term "advanced glycation end products" (AGEs) stands for a heterogeneous group of amino acid derivatives that are formed via glycation processes between peptide-bound lysine or arginine derivatives and carbonyl compounds, processes originally known from food systems as "Maillard reactions." AGEs accumulate in plasma and tissues with advancing age, diabetes, and particular renal failure. In vivo and in vitro studies indicate that AGEs represent an important class of uremic toxins. This review focuses on the chemistry behind the formation of AGEs, possible mechanisms underlying the accumulation of AGEs in uremia, clinical and therapeutic implications, and possible nutritional consequences.

Effect of a novel adsorbent on cytokine responsiveness to uremic plasma

BACKGROUND

Middle molecules such as beta2-microglobulin (beta2M) and advanced glycation end products (AGE)-modified proteins contribute to inflammation in uremia. The BetaSorb column is a new adsorptive device, which contains copolymeric beads, suitable for removal of beta2M and other middle molecules. We assessed the effect of this column on the bioreactivity of uremic plasma, as measured by cytokine responsiveness.

METHODS

Uremic plasma was perfused in vitro through the column (10 mL/min) and samples were collected after 10 to 30 passes. Endotoxin-stimulated tumor necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10) production by THP-1-derived monocytes was measured following brief exposure to uremic plasma. beta2M levels were measured. The contribution of AGE-modified proteins to the bioreactivity of uremic plasma was explored.

RESULTS

TNF-alpha and IL-10 production markedly decreased after 30 passes (629 +/- 78 vs. 144 +/- 62 pg/mL; 207 +/- 25 vs. 117 +/- 23 pg/mL; P=0.04). The column removed beta2M efficiently with a marked decline in plasma levels by 99% after 30 passes. Neutralization of AGE receptor (RAGE) resulted in a further reduction in the bioreactivity of uremic plasma. This was observed with nonperfused, as well as perfused, uremic plasma, suggesting that AGE-modified proteins were biologically active and still present after perfusion.

CONCLUSION

The sorbent beads removed uremic solute(s) that prime monocytes to enhanced cytokine production. Removal of beta2M was efficient, and of native and AGE-modified middle molecules likely.