Transthyretin Is Commonly Upregulated in the Hippocampus of Two Stress-Induced Depression Mouse Models.

Chronic stress can affect gene expression in the hippocampus, which alters neural and cerebrovascular functions, thereby contributing to the development of mental disorders such as depression. Although several differentially expressed genes in the depressed brain have been reported, gene expression changes in the stressed brain remain underexplored. Therefore, this study examines hippocampal gene expression in two mouse models of depression induced by forced swim stress (FSS) and repeated social defeat stress (R-SDS). Transthyretin (Ttr) was commonly upregulated in the hippocampus of both mouse models, as determined by microarray, RT-qPCR, and Western blot analyses. Evaluation of the effects of overexpressed Ttr in the hippocampus using adeno-associated virus-mediated gene transfer revealed that TTR overexpression induced depression-like behavior and upregulation of Lcn2 and several proinflammatory genes (Icam1 and Vcam1) in the hippocampus. Upregulation of these inflammation-related genes was confirmed in the hippocampus obtained from mice vulnerable to R-SDS. These results suggest that chronic stress upregulates Ttr expression in the hippocampus and that Ttr upregulation may be involved in the induction of depression-like behavior.

Emerging Role of AP-1 Transcription Factor JunB in Angiogenesis and Vascular Development.

Blood vessels are essential for the formation and maintenance of almost all functional tissues. They play fundamental roles in the supply of oxygen and nutrition, as well as development and morphogenesis. Vascular endothelial cells are the main factor in blood vessel formation. Recently, research findings showed heterogeneity in vascular endothelial cells in different tissue/organs. Endothelial cells alter their gene expressions depending on their cell fate or angiogenic states of vascular development in normal and pathological processes. Studies on gene regulation in endothelial cells demonstrated that the activator protein 1 (AP-1) transcription factors are implicated in angiogenesis and vascular development. In particular, it has been revealed that JunB (a member of the AP-1 transcription factor family) is transiently induced in endothelial cells at the angiogenic frontier and controls them on tip cells specification during vascular development. Moreover, JunB plays a role in tissue-specific vascular maturation processes during neurovascular interaction in mouse embryonic skin and retina vasculatures. Thus, JunB appears to be a new angiogenic factor that induces endothelial cell migration and sprouting particularly in neurovascular interaction during vascular development. In this review, we discuss the recently identified role of JunB in endothelial cells and blood vessel formation.

Role of Arginine Methylation in Alternative Polyadenylation of VEGFR-1 (Flt-1) pre-mRNA.

Mature mRNA is generated by the 3' end cleavage and polyadenylation of its precursor pre-mRNA. Eukaryotic genes frequently have multiple polyadenylation sites, resulting in mRNA isoforms with different 3'-UTR lengths that often encode different C-terminal amino acid sequences. It is well-known that this form of post-transcriptional modification, termed alternative polyadenylation, can affect mRNA stability, localization, translation, and nuclear export. We focus on the alternative polyadenylation of pre-mRNA for vascular endothelial growth factor receptor-1 (VEGFR-1), the receptor for VEGF. VEGFR-1 is a transmembrane protein with a tyrosine kinase in the intracellular region. Secreted forms of VEGFR-1 (sVEGFR-1) are also produced from the same gene by alternative polyadenylation, and sVEGFR-1 has a function opposite to that of VEGFR-1 because it acts as a decoy receptor for VEGF. However, the mechanism that regulates the production of sVEGFR-1 by alternative polyadenylation remains poorly understood. In this review, we introduce and discuss the mechanism of alternative polyadenylation of VEGFR-1 mediated by protein arginine methylation.

JunB regulates angiogenesis and neurovascular parallel alignment in mouse embryonic skin.

Blood vessels and nerve fibers are often closely arranged in parallel throughout the body. Therefore, neurovascular interactions have been suggested to be important for the development of vascular networks. However, the molecular mechanisms and genes regulating this process remain unclear. In the present study, we investigated the genes that are activated in endothelial cells (ECs) following interactions with neurons during vascular development. Microarray analyses of human primary microvascular ECs co-cultured with mouse primary dorsal root ganglion cells showed that JunB is strongly upregulated in ECs by neurovascular interactions. Furthermore, the forced expression of JunB in ECs stimulated a tip-like cell formation and angiogenesis in vitro and induced vascular endothelial growth factor A (VEGFA) and the pro-angiogenic integrin subunit ITGB3 expression. Moreover, in vivo knockdown of JunB in ECs from developing mouse limb skin considerably decreased the parallel alignments of blood vessels and nerve fibers. Taken together, the present data demonstrates for the first time that JunB plays an important role in the formation of embryonic vascular networks. These results contribute to the molecular understanding of neurovascular interactions during embryonic vascular development.

Regulation of soluble Flt-1 (VEGFR-1) production by hnRNP D and protein arginine methylation.

Soluble fms-like tyrosine kinase-1 (sFlt-1) functions as a potent inhibitor of angiogenesis by trapping vascular endothelial growth factor (VEGF). However, the precise regulatory mechanism of sFlt-1 production is unknown. Here, we report that vascular sFlt-1 production is regulated by heterogeneous nuclear ribonucleoprotein D (hnRNP D) and arginine methylation. We showed that hnRNP D bound to Flt-1 pre-mRNA and that hnRNP D overexpression decreased sFlt-1 mRNA in human microvascular endothelial cells (HMVECs). In contrast, the reduction of hnRNP D levels induced an increase in sFlt-1 production. Overexpression of an hnRNP D mutant in which the arginine residue of the known arginine methylation motif (arginine-glycine-glycine; RGG) was replaced with alanine did not reduce the level of soluble-form RNA produced from the Flt-1 minigene. Moreover, we demonstrated that overexpression of arginine methyltransferase decreased the soluble-form RNA level, whereas overexpression of arginine demethylase and addition of methyltransferase inhibitors increased sFlt-1 mRNA levels. These findings indicate that hnRNP D and arginine methylation play important roles in the regulation of Flt-1 mRNA alternative polyadenylation.

Osteocytic cell necrosis is caused by a combination of glucocorticoid-induced Dickkopf-1 and hypoxia.

Osteonecrosis is a major glucocorticoid-induced complication in the orthopedics field. Despite the extensive researches, mechanisms underlining the glucocorticoid-induced osteonecrosis are largely unknown. Here, we first provide the evidence that a combined treatment of cultured osteocytic cells with glucocorticoid and hypoxia caused necrotic cell death, which is assumed to occur in the acute bone injuries induced by glucocorticoids. We cultured MLO-Y4 murine osteocytic cells under hypoxia in the presence or absence of Dexamethasone (Dex) and examined the rates of apoptotic and necrotic cell death. Dex or hypoxia alone increased apoptotic cells, but not necrotic cells. The combination of Dex and hypoxia dramatically increased osteocytic cell death, notably necrotic cell death. The expression of Dickkopf-1 (Dkk-1), an inhibitor of Wnt/ß-catenin signal, was scarcely expressed in the control and hypoxic cells, but a dramatic increase of the Dkk-1 expression was detected in Dex-treated cells. siRNA-mediated knockdown of Dkk-1 in Dex and hypoxia-treated osteocytic cells showed the significant decreases in both apoptotic and necrotic cells. The results indicated that the combination of Dkk-1 overexpression by Dex and hypoxia causes the necrotic osteocytic cell death. The results also indicated that blocking of Dkk-1 can protect bone cells from glucocorticoid and hypoxia-induced cell injury.

Low molecular weight heparin suppresses receptor for advanced glycation end products-mediated expression of malignant phenotype in human fibrosarcoma cells.

The receptor for advanced glycation end products (RAGE) is a pattern-recognition receptor and its engagement by ligands such as high mobility group box 1 (HMGB1) is implicated in tumor growth and metastasis. Low molecular weight heparin (LMWH) has an antagonistic effect on the RAGE axis and is also reported to exert an antitumor effect beyond the known activity of anticoagulation. However, the link between the anti-RAGE and antitumor activities of LMWH has not yet to be fully elucidated. In this study, we investigated whether LMWH could inhibit tumor cell proliferation, invasion, and metastasis by blocking the RAGE axis using in vitro and in vivo assay systems. Stably transformed HT1080 human fibrosarcoma cell lines were obtained, including human full-length RAGE-overexpressing (HT1080(RAGE)), RAGE dominant-negative, intracellular tail-deleted RAGE-overexpressing (HT1080(dnRAGE)), and mock-transfected control (HT1080(mock)) cells. Confocal microscopy showed the expression of HMGB1 and RAGE in HT1080 cells. The LMWH significantly inhibited HMGB1-induced NFκB activation through RAGE using an NFκB-dependent luciferase reporter assay and the HT1080 cell lines. Overexpression of RAGE significantly accelerated, but dnRAGE expression attenuated HT1080 cell proliferation and invasion in vitro, along with similar effects on local tumor mass growth and lung metastasis in vivo. Treatment with LMWH significantly inhibited the migration, invasion, tumor formation, and lung metastasis of HT1080(RAGE) cells, but not of HT1080(mock) or HT1080(dnRAGE) cells. In conclusion, this study revealed that RAGE exacerbated the malignant phenotype of human fibrosarcoma cells, and that this exacerbation could be ameliorated by LMWH. It is suggested that LMWH has therapeutic potential in patients with certain types of malignant tumors.

Septic shock is associated with receptor for advanced glycation end products ligation of LPS.

Septic shock is a severe systemic response to bacterial infection. Receptor for advanced glycation end products (RAGE) plays a role in immune reactions to recognize specific molecular patterns as pathogen recognition receptors. However, the interaction between LPS, the bioactive component of bacterial cell walls, and RAGE is unclear. In this study, we found direct LPS binding to RAGE by a surface plasmon resonance assay, a plate competition assay, and flow cytometry. LPS increased TNF-α secretion from peritoneal macrophages and an NF-κB promoter-driven luciferase activity through RAGE. Blood neutrophils and monocytes expressed RAGE, and TLR2 was counterregulated in RAGE(-/-) mice. After LPS injection, RAGE(+/+) mice showed a higher mortality, higher serum levels of IL-6, TNF-α, high mobility group box 1, and endothelin-1, and severe lung and liver pathologies compared with RAGE(-/-) mice without significant differences in plasma LPS level. Administration of soluble RAGE significantly reduced the LPS-induced cytokine release and tissue damage and improved the LPS-induced lethality even in RAGE(-/-) as well as RAGE(+/+) mice. The results thus suggest that RAGE can associate with LPS and that RAGE system can regulate inflammatory responses. Soluble RAGE would be a therapeutic tool for LPS-induced septic shock.

Biosynthesis and Function of VIP and Oxytocin: Mechanisms of C-terminal Amidation, Oxytocin Secretion and Transport.

In this review, we provide the status of research on vasoactive intestinal peptide (VIP) and oxytocin, typical C-terminal α-amidated peptide hormones, including their precursor protein structures, processing and C-terminal α-amidation, and the recently identified mechanisms of regulation of oxytocin secretion and its transportation through the blood brain barrier. More than half of neural and endocrine peptides, such as VIP and oxytocin, have the α-amide structure at their C-terminus, which is essential for biological activities. We have studied the synthesis and function of C-terminal α-amidated peptides, including VIP and oxytocin, since the 1980s. Human VIP mRNA encoded not only VIP but also another related C-terminal α-amidated peptide, PHM-27 (peptide having amino-terminal histidine, carboxy-terminal methionine amide, and 27 amino acid residues). The human VIP/PHM-27 gene is composed of 7 exons and regulated synergistically by cyclic AMP and protein kinase C pathways. VIP has an essential role in glycemic control using transgenic mouse technology. The peptide C-terminal α-amidation proceeded through a 2-step mechanism catalyzed by 2 different enzymes encoded in a single mRNA. In the oxytocin secretion from the hypothalamus/the posterior pituitary, the CD38-cyclic ADP-ribose signal system, which was first established in the insulin secretion from pancreatic ß cells of the islets of Langerhans, was found to be essential. A possible mechanism involving RAGE (receptor for advanced glycation end-products) of the oxytocin transportation from the blood stream into the brain through the blood-brain barrier has also been suggested.

Suppression of a neocortical potassium channel activity by intracellular amyloid-ß and its rescue with Homer1a.

It is proposed that intracellular amyloid-ß (Aß), before extracellular plaque formation, triggers cognitive deficits in Alzheimer disease (AD). Here we report how intracellular Aß affects neuronal properties. This was done by injecting Aß protein into rat and mouse neocortical pyramidal cells through whole-cell patch pipettes and by using 3xTg AD model mice, in which intracellular Aß is accumulated innately. In rats, intracellular application of a mixed Aß(1-42) preparation containing both oligomers and monomers, but not a monomeric preparation of Aß(1-40), broadened spike width and augmented Ca(2+) influx via voltage-dependent Ca(2+) channels in neocortical neurons. Both effects were mimicked and occluded by charybdotoxin, a blocker of large-conductance Ca(2+)-activated K(+) (BK) channels, and blocked by isopimaric acid, a BK channel opener. Surprisingly, augmented Ca(2+) influx was caused by elongated spike duration, but not attributable to direct Ca(2+) channel modulation by Aß(1-42). The Aß(1-42)-induced spike broadening was blocked by electroconvulsive shock (ECS), which we previously showed to facilitate BK channel opening via expression of the scaffold protein Homer1a. In young 3xTg and wild mice, we confirmed spike broadening by Aß(1-42), which was again mimicked and occluded by charybdotoxin and blocked by ECS. In Homer1a knock-out mice, ECS failed to block the Aß(1-42) effect. Single-channel recording on BK channels supported these results. These findings suggest that the suppression of BK channels by intracellular Aß(1-42) is a possible key mechanism for early dysfunction in the AD brain, which may be counteracted by activity-dependent expression of Homer1a.

Identification of a major enzyme for the synthesis and hydrolysis of cyclic ADP-ribose in amphibian cells and evolutional conservation of the enzyme from human to invertebrate.

Cyclic ADP-ribose (cADPR), a metabolite of NAD(+), is known to function as a second messenger for intracellular Ca(2+) mobilization in various vertebrate and invertebrate tissues. In this study, we isolated two Xenopus laevis cDNAs (frog cd38 and cd157 cDNAs) homologous to the one encoding the human cADPR-metabolizing enzyme CD38. Frog CD38 and CD157 are 298-amino acid proteins with 35.9 and 27.2 % identity to human CD38 and CD157, respectively. Transfection of expression vectors for frog CD38 and CD157 into COS-7 cells revealed that frog CD38 had NAD(+) glycohydrolase, ADP-ribosyl cyclase (ARC), and cADPR hydrolase activities, and that frog CD157 had no enzymatic activity under physiological conditions. In addition, when recombinant CD38 and frog brain homogenate were electrophoresed on an SDS-polyacrylamide gel, ARC of the brain homogenate migrated to the same position in the gel as that of frog CD38, suggesting that frog CD38 is the major enzyme responsible for cADPR metabolism in amphibian cells. The frog cd38 gene consists of eight exons and is ubiquitously expressed in various tissues. These findings provide evidence for the existence of the CD38-cADPR signaling system in frog cells and suggest that the CD38-cADPR signaling system is conserved during vertebrate evolution.

Hypoxia down-regulates sFlt-1 (sVEGFR-1) expression in human microvascular endothelial cells by a mechanism involving mRNA alternative processing.

sFlt-1 (soluble Flt-1) potently inhibits angiogenesis by binding extracellularly to VEGF (vascular endothelial growth factor). In the present paper, we report that hypoxia down-regulates sFlt-1 expression in HMVECs (human microvascular endothelial cells), a constituent of microvessels where angiogenesis occurs. Hypoxia (5-1% O2) increased VEGF expression in HMVECs. In contrast, the levels of sFlt-1 mRNA and protein in HMVECs decreased significantly as the O2 concentration fell, whereas mFlt-1 (membrane-bound Flt-1) mRNA and protein remained unchanged. This suggested that hypoxia selectively regulates alternative 3'-end processing of sFlt-1 pre-mRNA. We have also demonstrated that sFlt-1 overexpression in lentiviral-construct-infected HMVECs counteracted VEGF-induced endothelial cell growth. We next identified cis-elements involved in sFlt-1 mRNA processing in HMVECs using a human Flt-1 minigene and found that two non-contiguous AUUAAA sequences function as the poly(A) signal. Furthermore, we identified a cis-element in intron 13 that regulates sFlt-1 mRNA processing. Mutagenesis of the U-rich region in intron 13 caused a significant decrease in the soluble-form/membrane-form RNA ratio in the minigene-transfected HMVECs. These results suggest that decreased sFlt-1 expression due to hypoxia contributes to hypoxia-induced angiogenesis and reveals a novel mechanism regulating angiogenesis by alternative mRNA 3'-end processing.

Ultraviolet B-induced expression of amphiregulin and growth differentiation factor 15 in human lens epithelial cells.

PURPOSE: Epidemiological and experimental studies have revealed that exposure to ultraviolet B (UVB) light can induce cataractogenesis. The objective of this study was to determine gene expression changes in human lens epithelial cells in response to UVB exposure and identify factors that can be involved in UVB-induced cataractogenesis. METHODS: SV40 T-antigen-transformed human lens epithelial cells (SRA01/04) were irradiated at various UVB-energy levels (10-80 mJ/cm²) and checked for viability. An irradiation condition of 30 mJ/cm² was adopted for transcriptome analysis. Total RNAs isolated from UVB-exposed and unexposed cells at 12 h and 24 h after UVB exposure were examined for global gene expression changes using Affymetrix Human Gene 1.0 ST array. mRNA levels of specific genes were examined by RT-PCR and real-time PCR, and protein levels in the conditioned media were assayed by ELISA. To examine mRNA expression in human lens, primary cultured human lens epithelial (HLE) cells were prepared from surgically removed lens epithelium, and used for UVB-irradiation and expression analysis. Effects of certain gene products on SRA01/04 cell metabolism were examined using commercially available recombinant proteins. RESULTS: Expression of most the genes analyzed was essentially unchanged (between 0.5 and 2.0 fold) in UVB-irradiated cells compared to non-irradiated cells at both 12 and 24 h after UVB exposure. Sixty one and 44 genes were upregulated more than twofold by UVB exposure at 12 h and 24 h, respectively. Emphasis was placed on genes encoding extracellular proteins, especially growth factors and cytokines. A total of 18 secreted protein genes were upregulated more than twofold at either or both time points. Amphiregulin (AREG) and growth differentiation factor 15 (GDF15) were chosen because of their higher upregulation and novelty, and their upregulation was confirmed in SRA01/04 cells using RT-PCR and real-time PCR analysis. AREG and GDF15 protein levels in conditioned media significantly increased at all UVB-energy points at 24 h, while they were scarcely detectable at 12 h. AREG and GDF15 mRNA levels were also significantly upregulated in UVB-irradiated primary cultured HLE cells compared with the corresponding control culture. AREG significantly stimulated ³H-thymidine and ³H-leucine uptake in SRA01/04 cells as did a positive control epidermal growth factor (EGF). Recombinant GDF15 did not stimulate ³H-thymidine incorporation at any concentration tested, but significantly stimulated ³H-leucine uptake. RT-PCR analysis demonstrated that primary cultured HLE and SRA01/04 cells expressed not only epidermal growth factor receptor (EGFR) mRNA but also transforming growth factor ß receptors (TGFBR1 and TGFBR2) mRNAs. CONCLUSIONS: These results indicate that AREG and GDF15 produced in response to UVB exposure can affect the growth and protein synthesis of lens epithelial cells, suggesting that they have autocrine and paracrine roles related to pathological changes of lens tissue during long-term UVB exposure.

EPAC2 acts as a negative regulator in Matrigel-driven tubulogenesis of human microvascular endothelial cells.

Angiogenesis is physiologically essential for embryogenesis and development and reinitiated in adult animals during tissue growth and repair. Forming new vessels from the walls of existing vessels occurs as a multistep process coordinated by sprouting, branching, and a new lumenized network formation. However, little is known regarding the molecular mechanisms that form new tubular structures, especially molecules regulating the proper network density of newly formed capillaries. This study conducted microarray analyses in human primary microvascular endothelial cells (HMVECs) plated on Matrigel. The RAPGEF4 gene that encodes exchange proteins directly activated by cAMP 2 (EPAC2) proteins was increased in Matrigel-driven tubulogenesis. Tube formation was suppressed by the overexpression of EPAC2 and enhanced by EPAC2 knockdown in endothelial cells. Endothelial cell morphology was changed to round cell morphology by EPAC2 overexpression, while EPAC2 knockdown showed an elongated cell shape with filopodia-like protrusions. Furthermore, increased EPAC2 inhibited endothelial cell migration, and ablation of EPAC2 inversely enhanced cell mobility. These results suggest that EPAC2 affects the morphology and migration of microvascular endothelial cells and is involved in the termination and proper network formation of vascular tubes.

Role of Decorin in Posterior Capsule Opacification and Eye Lens Development.

Decorin (DCN) is involved in a variety of physiological and pathological processes. Epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) has been proposed as a major cause for the development of posterior capsule opacification (PCO) after cataract surgery. We investigated the plausible target gene(s) that suppress PCO. The expression of Dcn was significantly upregulated in rat PCO tissues compared to that observed in the control using a microarray-based approach. LECs treated with fibroblast growth factor (FGF) 2 displayed an enhanced level of DCN expression, while LECs treated with transforming growth factor (TGF)ß-2 showed a decrease in DCN expression. The expression of tropomyosin 1 (Tpm1), a marker of lens EMT increased after the addition of TGFß-2 in human LEC; however, upregulation of Tpm1 mRNA or protein expression was reduced in human LECs overexpressing human DCN (hDCN). No phenotypic changes were observed in the lenses of 8- and 48-week-old transgenic mice for lens-specific hDCN (hDCN-Tg). Injury-induced EMT of the mouse lens, and the expression patterns of α smooth muscle actin, were attenuated in hDCN-Tg mice lenses. Overexpression of DCN inhibited the TGFß-2-induced upregulation of Tpm1 and EMT observed during wound healing of the lens, but it did not affect mouse lens morphology until 48 weeks of age. Our findings demonstrate that DCN plays a significant role in regulating EMT formation of LECs and PCO, and suggest that for therapeutic intervention, maintenance of physiological expression of DCN is essential to attenuate EMT progression and PCO formation.

Protective Effects of Collagen Tripeptides in Human Aortic Endothelial Cells by Restoring ROS-Induced Transcriptional Repression.

Collagen tripeptide (CTP) is defined as a functional food material derived from collagenase digests of type I collagen and contains a high concentration of tripeptides with a Gly-X-Y sequence. CTP has several biological effects, including the acceleration of fracture healing, ameliorating osteoarthritis, and improving dryness and photoaging of the skin. Recently, an antiatherosclerotic effect of CTP has been reported, although its molecular mechanism is yet to be determined. In this study, we examined the effects of CTP on primary cultured human aortic endothelial cells (HAECs) under oxidative stress, because oxidative endothelial dysfunction is a trigger of atherosclerosis. DNA microarray and RT-qPCR analyses showed that CTP treatment recovered the downregulated expression of several genes, including the interleukin-3 receptor subunit alpha (IL3RA), which were suppressed by reactive oxygen species (ROS) treatment in HAECs. Furthermore, IL3RA knockdown significantly decreased the viability of HAECs compared with control cells. RT-qPCR analysis also showed that solute carrier 15 family peptide transporters, which are involved in CTP absorption into cells, were expressed in HAECs at levels more than comparable to those of a CTP-responsive human osteoblastic cell line. These results indicated that CTP exerts a protective effect for HAECs, at least in part, by regulating the recovery of ROS-induced transcriptional repression.

Ultraviolet B-induced Otx2 expression in lens epithelial cells promotes epithelial-mesenchymal transition.

Ultraviolet (UV) radiation of eyes is a major risk factor for cataractogenesis, although the molecular mechanisms underlying this process remain poorly understood and genes that are affected by UV radiation have not been fully identified. In this study, we examined the UV-related gene regulation in lens epithelial cells (LECs) of mouse eyes and investigated the molecular mechanisms of UV-triggered cataractogenesis. Forty-one genes were significantly upregulated in LECs following UVB exposure in vivo in two independent experiments. Among these, Otx2 was strongly upregulated in LECs, suggesting that it may act as an upstream regulator of UVB-induced changes in gene expression. Accordingly, Otx2 overexpression in LECs in vitro induced morphological changes in cell shapes. Epithelial-mesenchymal transition (EMT)-related molecules, such as TGFß2, αSMA and fibronectin were upregulated in Otx2-overexpressing LECs, concomitant with suppression of lens fiber cell marker genes, such as CRYAA and DNASEIIB. In vitro experiments suggested that UVB upregulated Otx2 through hydrogen peroxide generation. Aberrant upregulation of Otx2 in LECs following UV irradiation induces the EMT and alteration of the lens cell characteristics, likely contributing to cataractogenesis.

Solution structure of the variable-type domain of the receptor for advanced glycation end products: new insight into AGE-RAGE interaction.

Diabetes is defined by chronic hyperglycemia due to deficiency in insulin action. It has been found that the amount of advanced glycation end products (AGE) from the Maillard reaction between proteins and sugar molecules increases in blood of diabetic patients and furthermore that AGE binding to their cell surface receptor (RAGE) triggers both macrovascular and microvascular impairments to cause diabetic complications. Due to the clinical significance of the vascular complications, RAGE is currently a focus as an attractive target for drug discovery of candidates which interfere with AGE-RAGE binding to prevent the subsequent intracellular signaling related to pathogenical effects. Here, we determined the three-dimensional structure of the recombinant AGE-binding domain by using multidimensional heteronuclear NMR spectroscopy and showed that the domain assumes a structure similar to those of other immunoglobulin V-type domains. The site-directed mutagenesis studies identified the basic amino acids which play a key role in the AGE binding activities. Our results obtained from this study provide new insight into AGE-RAGE interaction.

De-N-glycosylation or G82S mutation of RAGE sensitizes its interaction with advanced glycation endproducts.

Interactions between advanced glycation endproducts (AGE) and the receptor for AGE (RAGE) have been implicated in the development of diabetic vascular complications. RAGE has two N-glycosylation sites in and near the AGE-binding domain, and G82S mutation in the second N-glycosylation motif was recently reported in human. In this study, we examined whether de-N-glycosylation or G82S of RAGE affect its ability to bind AGE and cellular response to AGE. Recombinant wild-type, de-N-glycosylation and G82S RAGE proteins were produced in COS-7 cells, purified and assayed for ligand-binding abilities. De-N-glycosylation at N81 and G82S mutation decreased Kd for glycolaldehyde-derived AGE to three orders of magnitude lower levels compared with wild-type. AGE-induced upregulation of VEGF mRNA was significantly augmented in endothelial cell-derived ECV304 cells expressing de-N-glycosylated and G82S RAGE when compared with wild-type expressor. Exposure to low glucose resulted in the appearance of RAGE proteins of deglycosylated size in wild-type RAGE-expressing cells and significantly enhanced glycolaldehyde-derived AGE-induced VEGF mRNA expression. De-N-glycosylation or G82S mutation of RAGE increases affinity for AGE ligands, and may sensitize cells or conditions with it to AGE.

RAGE in diabetic nephropathy.

As is diabetes itself, diabetic angiopathy is a multi-factorial disease. Advanced glycation endproducts (AGE) cause vascular cell derangement characteristic of diabetes, and this is mainly mediated by their interaction with receptor for AGE (RAGE). When made diabetic, RAGE-overexpressing transgenic mice exhibited exacerbation of the indices of nephropathy, and this was prevented by the inhibition of AGE formation. On the other hand, RAGE-deficient animals showed amelioration of diabetic nephropathy. Accordingly, AGE and RAGE should be regarded as environmental and cellular accounts and as a potential therapeutic target for diabetic nephropathy. In effect, substances that inhibit the formation of AGE, break preformed AGE, change metabolic flows away from glycation, antagonize RAGE, and capture RAGE ligands have been proven as effective remedies against this life-threatening disease.