Yuichiro Higashimoto

Advanced glycation end products evoke endothelial cell damage by stimulating soluble dipeptidyl peptidase-4 production and its interaction with mannose 6-phosphate/insulin- like growth factor II receptor

BackgroundAdvanced glycation end products (AGEs) and receptor RAGE interaction play a role in diabetic vascular complications. Inhibition of dipeptidyl peptidase-4 (DPP-4) is a potential therapeutic target for type 2 diabetes. However, the role of DPP-4 in AGE-induced endothelial cell (EC) damage remains unclear.MethodsIn this study, we investigated the effects of DPP-4 on reactive oxygen species (ROS) generation and RAGE gene expression in ECs. We further examined whether an inhibitor of DPP-4, linagliptin inhibited AGE-induced soluble DPP-4 production, ROS generation, RAGE, intercellular adhesion molecule-1 (ICAM-1) and plasminogen activator inhibitor-1 (PAI-1) gene expression in ECs.ResultsDPP-4 dose-dependently increased ROS generation and RAGE gene expression in ECs, which were prevented by linagliptin. Mannose 6-phosphate (M6P) and antibodies (Ab) raised against M6P/insulin-like growth factor II receptor (M6P/IGF-IIR) completely blocked the ROS generation in DPP-4-exposed ECs, whereas surface plasmon resonance revealed that DPP-4 bound to M6P/IGF-IIR at the dissociation constant of 3.59 x 10-5 M. AGEs or hydrogen peroxide increased soluble DPP-4 production by ECs, which was prevented by N-acetylcysteine, RAGE-Ab or linagliptin. Linagliptin significantly inhibited the AGE-induced ROS generation, RAGE, ICAM-1 and PAI-1 gene expression in ECs.ConclusionsThe present study suggests that AGE-RAGE-induced ROS generation stimulates the release of DPP-4 from ECs, which could in turn act on ECs directly via the interaction with M6P/IGF-IIR, further potentiating the deleterious effects of AGEs. The blockade by linagliptin of positive feedback loop between AGE-RAGE axis and DPP-4 might be a novel therapeutic target for vascular injury in diabetes.

Glyceraldehyde-derived pyridinium (GLAP) evokes oxidative stress and inflammatory and thrombogenic reactions in endothelial cells via the interaction with RAGE

BackgroundWe have previously shown that serum levels of glyceraldehyde-derived advanced glycation end products (Gly-AGEs) are elevated under oxidative stress and/or diabetic conditions and associated with insulin resistance, endothelial dysfunction and vascular inflammation in humans. Further, Gly-AGEs not only evoke oxidative and inflammatory reactions in endothelial cells (ECs) through the interaction with a receptor for AGEs (RAGE), but also mimic vasopermeability effects of AGE-rich serum purified from diabetic patients on hemodialysis. These observations suggest that Gly-AGE-RAGE system might be a therapeutic target for vascular complications in diabetes. However, since incubation of glyceraldehyde with proteins will generate a large number of structurally distinct AGEs, it remains unclear what type of AGE structures could mediate the deleterious effects of Gly-AGEs on ECs.Aims and MethodsTherefore, in this study, we examined (1) whether glyceraldehyde-derived pyridinium (GLAP), one of the Gly-AGEs generated by the incubation of lysine with glyceraldehyde, elicited reactive oxygen species (ROS) generation and inflammatory and thrombogenic gene expression in human umbilical vein ECs (HUVECs) via the interaction with RAGE and (2) if DNA aptamers raised against Gly-AGEs or GLAP (AGE-aptamer or GLAP-aptamer) inhibited the binding of GLAP to RAGE and subsequently suppressed the harmful effects of GLAP on HUVECs.ResultsGLAP stimulated ROS generation in a bell-shaped manner; GLAP at 10xa0μg/ml increased ROS generation in HUVECs by 40%, which was blocked by the treatment with RAGE-antibody (RAGE-Ab). Ten μg/ml GLAP significantly up-regulated mRNA levels of RAGE, monocyte chemoattractant protein-1, intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and plasminogen activator inhibitor-1 in HUVECs, which were also suppressed by RAGE-Ab. AGE-aptamer or GLAP-aptamer significantly blocked these deleterious effects of GLAP on HUVECs. Moreover, quartz crystal microbalance analyses revealed that GLAP actually bound to RAGE and that AGE-aptamer or GLAP-aptamer inhibited the binding of GLAP to RAGE.ConclusionsThe present study suggests that GLAP might be a main glyceraldehyde-related AGE structure in Gly-AGEs that bound to RAGE and subsequently elicited ROS generation and inflammatory and thrombogenic reactions in HUVECs. Blockade of the GLAP-RAGE interaction by AGE-aptamer or GLAP-aptamer might be a novel therapeutic strategy for preventing vascular injury in diabetes.

DNA Aptamer Raised Against AGEs Blocks the Progression of Experimental Diabetic Nephropathy

Advanced glycation end products (AGEs) and their receptor (RAGE) play a role in diabetic nephropathy. We screened DNA aptamer directed against AGEs (AGEs-aptamer) in vitro and examined its effects on renal injury in KKAy/Ta mice, an animal model of type 2 diabetes. Eight-week-old male KKAy/Ta or C57BL/6J mice received continuous intraperitoneal infusion of AGEs- or control-aptamer for 8 weeks. AGEs-aptamer was detected and its level was increased in the kidney for at least 7 days. The elimination half-lives of AGEs-aptamer in the kidney were about 7 days. Compared with those in C57BL/6J mice, glomerular AGEs levels were significantly increased in KKAy/Ta mice, which were blocked by AGEs-aptamer. Urinary albumin and 8-hydroxy-2′-deoxy-guanosine levels were increased, and glomerular hypertrophy and enhanced extracellular matrix accumulation were observed in KKAy/Ta mice, all of which were prevented by AGEs-aptamer. Moreover, AGEs-aptamer significantly reduced gene expression of RAGE, monocyte chemoattractant protein-1, connective tissue growth factor, and type IV collagen both in the kidney of KKAy/Ta mice and in AGE-exposed human cultured mesangial cells. Our present data suggest that continuous administration of AGEs-aptamer could protect against experimental diabetic nephropathy by blocking the AGEs-RAGE axis and may be a feasible and promising therapeutic strategy for the treatment of diabetic nephropathy.

Structural basis for the electron transfer from an open form of NADPH-cytochrome P450 oxidoreductase to heme oxygenase

Significance Heme oxygenase (HO) is a key enzyme for heme degradation that is deeply involved in iron homeostasis, defensive reaction against oxidative stress, and signal transduction mediated by carbon monoxide. To complete a single HO reaction, seven electrons supplied from NADPH-cytochrome P450 reductase (CPR) are required. Based on crystallography, X-ray scattering, and NMR analyses of CPR, it has been proposed that CPR has a dynamic equilibrium of the “closed-open transition.” The crystal structure of the transient complex of CPR with heme-bound HO clearly demonstrated that it is the open form of CPR that can interact with and transfer electrons to heme-bound HO. Moreover, the complex structure provides a scaffold to research the protein–protein interactions between CPR and other redox partners. NADPH-cytochrome P450 oxidoreductase (CPR) supplies electrons to various heme proteins including heme oxygenase (HO), which is a key enzyme for heme degradation. Electrons from NADPH flow first to flavin adenine dinucleotide, then to flavin mononucleotide (FMN), and finally to heme in the redox partner. For electron transfer from CPR to its redox partner, the ‘‘closed-open transition’’ of CPR is indispensable. Here, we demonstrate that a hinge-shortened CPR variant, which favors an open conformation, makes a stable complex with heme–HO-1 and can support the HO reaction, although its efficiency is extremely limited. Furthermore, we determined the crystal structure of the CPR variant in complex with heme–HO-1 at 4.3-Å resolution. The crystal structure of a complex of CPR and its redox partner was previously unidentified. The distance between heme and FMN in this complex (6 Å) implies direct electron transfer from FMN to heme.

Blockade by phosphorothioate aptamers of advanced glycation end products-induced damage in cultured pericytes and endothelial cells.

Advanced glycation end products (AGEs) not only inhibit DNA synthesis of retinal pericytes, but also elicit vascular hyperpermeability, pathological angiogenesis, and thrombogenic reactions by inducing vascular endothelial growth factor (VEGF) and plasminogen activator inhibitor-1 (PAI-1) through the interaction with the receptor for AGEs (RAGE), thereby being involved in the pathogenesis of diabetic retinopathy. In this study, we screened novel phosphorothioate-modified aptamers directed against AGEs (AGEs-thioaptamers) using a combinatorial chemistry in vitro, and examined whether these aptamers could inhibit the AGE-induced damage in both retinal pericytes and human umbilical vein endothelial cells (HUVECs). We identified 11 AGEs-thioaptamers; among them, clones #4, #7s and #9s aptamers had higher binding affinity to AGEs-human serum albumin (HSA) than the others. Surface plasmon resonance analysis revealed that KD values of #4s, #7s and #9s were 0.63, 0.36, and 0.57nM, respectively. Furthermore, these 3 clones dose-dependently restored the decrease in DNA synthesis in AGE-exposed pericytes. AGEs significantly increased RAGE, VEGF and PAI-1 mRNA levels in HUVEC, all of which were completely blocked by the treatment with 20nM clone #4s aptamer. Quartz crystal microbalance analysis confirmed that #4s aptamer dose-dependently inhibited the binding of AGEs-HSA to RAGE. Our present study demonstrated that AGEs-thioaptamers could inhibit the harmful effects of AGEs in pericytes and HUVEC by suppressing the binding of AGEs to RAGE. Blockade by AGEs-thioaptamers of the AGEs-RAGE axis might be a novel therapeutic strategy for diabetic retinopathy.

Caveolin-1 is a competitive inhibitor of heme oxygenase-1 (HO-1) with heme: identification of a minimum sequence in caveolin-1 for binding to HO-1.

Heme oxygenase (HO) catalyzes the O(2)-dependent degradation of heme to biliverdin IXα, carbon monoxide (CO), and free ferrous iron through a multistep mechanism. Electrons required for HO catalysis in mammals are provided by NADPH-cytochrome P450 reductase. Recently, Kim et al. reported for the first time that HO, especially inducible HO-1, appears in caveolae and showed that caveolin-1, a principal isoform of the caveolin family, physically interacts with HO-1 [ Jung , N. H. et al. ( 2003 ) IUBMB Life 55 , 525 - 532 ; Kim , H. P. et al. ( 2004 ) FASEB J. 18 , 1080 - 1089 ]. In the present study, we confirmed by immunoprecipitation experiments that rat HO-1 and rat caveolin-1 (residues 1-101) directly interact with each other and that the HO-1 activity is inhibited by caveolin-1 (1-101). The 82-101 residues of caveolin-1 (CAV(82-101)), called the caveolin scaffolding domain, play essential roles in caveolin-related protein-protein interactions. The HO-1 activity is also inhibited by CAV(82-101) in a competitive manner with hemin, and a hemin titration experiment showed that CAV(82-101) interferes with hemin binding to HO-1. The enzyme kinetics and surface plasmon resonance experiments gave comparable K(i) and K(D) values of 5.2 and 1.0 μM for CAV(82-101), respectively, with respect to the interaction with HO-1. These observations indicated that CAV(82-101) and hemin share a common binding site within the HO-1 protein. The identified caveolin binding motif (FLLNIELF) of rat HO-1 is incomplete compared to the proposed consensus sequence. The affinity between HO-1 and CAV(82-101), however, was almost completely or remarkably eliminated by replacement of Phe(207) and/or Phe(214) with Ala, indicating that HO-1 binds to caveolin-1 via this motif. Among the peptide fragments derived from CAV(82-101), i.e., CAV(82-91), CAV(87-96), CAV(92-101), and CAV(97-101), CAV(92-101) and CAV(97-101) are able to inhibit the HO-1 activity to a similar extent; thus, the five-amino acid sequence (residues 97-101) is considered to be a minimum sequence for binding to HO-1.

DNA aptamer raised against advanced glycation end products inhibits melanoma growth in nude mice

Epidemiological studies have suggested that diabetes is associated with an increased risk of cancer. However, the underlying molecular mechanism remains unclear. We investigated here whether DNA aptamer directed against advanced glycation end products (AGE-aptamer) inhibited melanoma growth in nude mice. G361 melanoma cells were injected intradermally into the upper flank of athymic nude mice. Mice received continuous intraperitoneal infusion (0.136u2009μg/day) of either AGE-aptamer (n=9) or Control-aptamer (n=8) by an osmotic mini pump. Tumor volume was measured at 4-day interval, and G361 melanoma was excised at day 43 after the aptamer treatment. We further examined the effects of AGE-aptamer on proliferation of AGE-exposed endothelial cells and G361 cells. AGE-aptamer significantly inhibited the in vivo-tumor growth of G361 melanoma. Immunohistochemical and western blotting analyses of G361 melanoma revealed that AGE-aptamer decreased expression levels of proliferating nuclear antigen, CD31 and Mac-3, markers of endothelial cells and macrophages, respectively. AGE-aptamer significantly decreased the number of tumor-associated vessels. AGE, receptor for AGE (RAGE) and vascular endothelial growth factor levels were also reduced in AGE-aptamer-treated G361 melanoma. AGE-aptamer inhibited the AGE-induced proliferation and tube formation of endothelial cells as well as the growth of G361 cells in vitro. The present findings suggest that AGE-aptamer could inhibit the AGE–RAGE axis in G361 melanoma and resultantly suppress the tumor growth in nude mice by blocking the angiogenesis. AGE-aptamer might be a novel therapeutic strategy for preventing the progression of malignant melanoma in diabetes.

Protein phosphatase 2A dephosphorylates phosphoserines in nucleocytoplasmic shuttling and secretion of high mobility group box 1

High mobility group box 1 (HMGB1), a non-histone chromosomal protein, is a proinflammatory cytokine. There are two known pathways for the release of HMGB1 into the extracellular milieu-passive and active. The passive pathway is attributable to cell death from damage or necrosis, and the active pathway is secretion from immunocompetent cells activated by proinflammatory stimuli. Recent studies have shown that post-translational modifications of HMGB1, including phosphorylation, are involved in the relocation of HMGB1 to the cytoplasm and subsequent secretion. With regard to the HMGB1 phosphorylation, Youn and Shin [Nucleocytoplasmic shuttling of HMGB1 is regulated by phosphorylation that redirects it toward secretion. J Immunol 2006;177:7889-97] reported that treatment of the murine macrophage RAW264.7 with okadaic acid resulted in nucleocytoplasmic translocation and secretion of HMGB1. Herein, we demonstrate the physical interaction between HMGB1 and protein phosphatase 2A (PP2A) in the RAW264.7. The results of in vitro phosphatase assay further indicate that PP2A dephosphorylates specific phosphoserine residues within one of the two nuclear localization signals (NLSs) of HMGB1. The cytoplasmic relocation of HMGB1 through PP2A inhibition was markedly suppressed by replacement of the Ser residues within the NLS with Ala. These consequences imply that PP2A correlates in the nucleocytoplasmic shuttling of HMGB1.

EprS, an autotransporter protein of Pseudomonas aeruginosa, possessing serine protease activity induces inflammatory responses through protease-activated receptors

PA3535 (EprS), an autotransporter (AT) protein of Pseudomonas aeruginosa, is predicted to contain a serine protease motif. The eprS encodes a 104.5u2009kDa protein with a 30‐amino‐acid‐long signal peptide, a 51.2u2009kDa amino‐terminal secreted passenger domain and a 50.1u2009kDa carboxyl‐terminal outer membrane channel formed translocator. Although the majority of AT proteins have been reported to be virulence factors, little is known about the functions of EprS in the pathogenicity of P.u2009aeruginosa. In this study, we performed functional analyses of recombinant EprS secreted by Escherichia coli. The proteolytic activity of EprS was markedly decreased by changing Ser to Ala at position 308 or by serine protease inhibitors. EprS preferred to cleave substrates that terminated with arginine or lysine residues. Thus, these results indicate that EprS, a serine protease, displays the substrate specificity, cleaving after basic residues. We demonstrated that EprS activates NF‐κB‐driven promoters through protease‐activated receptor (PAR)‐1, ‐2 or ‐4 and induces IL‐8 production through PAR‐2 in a human bronchiole epithelial cell line. Moreover, EprS cleaved the peptides corresponding to the tethered ligand region of PAR‐1, ‐2 and ‐4 at a specific site with exposure oftheir tethered ligands. Collectively, these results suggest that EprS activates host inflammatory responses through PARs.

Mass spectrometric identification of lysine residues of heme oxygenase-1 that are involved in its interaction with NADPH-cytochrome P450 reductase.

The lysine residues of rat heme oxygenase-1 (HO-1) were acetylated by acetic anhydride in the absence and presence of NADPH-cytochrome P450 reductase (CPR) or biliverdin reductase (BVR). Nine acetylated peptides were identified by MALDI-TOF mass spectrometry in the tryptic fragments obtained from HO-1 acetylated without the reductases (referred to as the fully acetylated HO-1). The presence of CPR prevented HO-1 from acetylation of lysine residues, Lys-149 and Lys-153, located in the F-helix. The heme degradation activity of the fully acetylated HO-1 in the NADPH/CPR-supported system was significantly reduced, whereas almost no inactivation was detected in HO-1 in the presence of CPR, which prevented acetylation of Lys-149 and Lys-153. On the other hand, the presence of BVR showed no protective effect on the acetylation of HO-1. The interaction of HO-1 with CPR or BVR is discussed based on the acetylation pattern and on molecular modeling.