Faculty Bibliography

BACKGROUND: Receptor for advanced glycated end product (RAGE) expression is a prominent feature of atherosclerosis. We have previously shown in apoE null mice uptake of a radiolabeled anti-RAGE antibody in atherosclerotic plaque and now evaluate RAGE-directed imaging to identify advanced plaques in a large animal model. METHODS: Nine hyperlipidemic (HL) pigs were injected with 603.1 +/- 129.5 MBq of (99m)Tc-anti-RAGE F(ab')2, and after 6 h (blood pool clearance), they underwent single-photon emission computed tomography/computed tomography (SPECT/CT) imaging of the neck, thorax, and hind limbs. Two HL pigs received (99m)Tc non-immune IgG F(ab')2, and three farm pigs were injected with (99m)Tc-anti-RAGE F(ab')2. After imaging, the pigs were euthanized. The aorta from the root to bifurcation was dissected, and the innominates, proximal carotids, and coronaries were dissected and counted, stained for H&E and RAGE, and AHA-classified. RESULTS: On pathology, 24% of the arterial segments showed AHA class III or IV lesions, and these lesions were confined almost exclusively to coronaries and carotids with % stenosis from 15% to 65%. Scatter plots of %ID/g for class III/IV vs. I/II lesions showed almost complete separation. Focal vascular uptake of tracer visualized on SPECT scans corresponded to class III/IV lesions in the coronary and carotid vessels. In addition, uptake in the hind limbs was noted in the HL pigs and corresponded to RAGE staining of small arteries in the muscle sections. Correlations for the vascular lesions were r = 0.747, P = 0.001 for %ID vs. %ID/g and r = 0.83, P = 0.002 for %ID/g vs. % RAGE staining. CONCLUSIONS: Uptake of radiolabeled anti-RAGE antibody in coronary and carotid fibroatheroma and in the small arteries of the hind limbs in a relevant large animal model of atherosclerosis supports the important role of RAGE in atherosclerosis and peripheral artery disease as a target for imaging and treatment.

Objective. Receptor for advanced glycated endproducts (RAGE) plays an important role in atherogenesis in diabetes. We imaged RAGE to investigate the effect of glucose control to suppress RAGE and reduce atherosclerosis in apolipoprotein E null (apoE(-/-)) diabetic mice. Methods and Results. Thirty-three apoE(-/-) mice received streptozotocin and 6 weeks later 15 began treatment with insulin implants. Blood glucose measurements during study averaged: 140 +/- 23 mg/dL (treated) and 354 +/- 14 mg/dL (untreated). After 15 wk 30 mice were injected with (99m)Tc-anti-RAGE F(ab')2, 3 with (99m)Tc-nonimmune IgG F(ab')2, and all with CT contrast agent and underwent SPECT/CT imaging. At necropsy, the proximal aorta was weighed, counted, and sectioned and the % injected dose per gram (%ID/g) was calculated. From the merged SPECT/CT scans, tracer uptake localized to arteries was lower in the treated mice: 3.15 +/- 1.82 x 10(-3) versus 8.69 +/- 4.58 x 10(-3)%ID (P = 0.001). Percent cross-sectional lesion area was smaller in the treated (14.3 +/- 7.8% versus 29.5 +/- 10.9%) (P = 0.03). RAGE uptake on scans (%ID) correlated with quantitative RAGE staining in the atheroma and with %ID/g (R = 0.6887; P = 0.01). Lesion size as percent cross-sectional area was smaller in the treated (14.3 +/- 7.8% versus 29.5 +/- 10.9%) (P = 0.03). RAGE uptake on scans (%ID) correlated with quantitative RAGE staining in the atheroma and with %ID/g (R = 0.6887; P = 0.01). Conclusions. These results support the importance of suppressing RAGE to reduce atherosclerotic complications of diabetes and value of molecular imaging to assess treatment effect.

The receptor for glycation end products (RAGE) has been previously implicated in shaping the adaptive immune response. RAGE is expressed in T cells after activation and constitutively in T cells from patients with diabetes. The effects of RAGE on adaptive immune responses are not clear: Previous reports show that RAGE blockade affects Th1 responses. To clarify the role of RAGE in adaptive immune responses and the mechanisms of its effects, we examined whether RAGE plays a role in T cell activation in a Th2 response involving ovalbumin (OVA)-induced asthma in mice. WT and RAGE deficient wild-type and OT-II mice, expressing a T cell receptor specific for OVA, were immunized intranasally with OVA. Lung cellular infiltration and T cell responses were analyzed by immunostaining, FACS, and multiplex bead analyses for cytokines. RAGE deficient mice showed reduced cellular infiltration in the bronchial alveolar lavage fluid and impaired T cell activation in the mediastinal lymph nodes when compared with WT mice. In addition, RAGE deficiency resulted in reduced OT-II T cell infiltration of the lung and impaired IFNgamma and IL-5 production when compared with WT mice and reduced infiltration when transferred into WT hosts. When cultured under conditions favoring the differentiation of T cells subsets, RAGE deficient T cells showed reduced production of IFNgamma but increased production of IL-17. Our data show a stimulatory role for RAGE in T activation in OVA-induced asthma. This role is largely mediated by the effects of RAGE on T cell proliferation and differentiation. These findings suggest that RAGE may play a regulatory role in T cell responses following immune activation.

RATIONALE: A major conceptual challenge in sarcoidosis is to understand how fibrosis occurs in an environment dominated by the expression of Th1 cytokines such as interferon-gamma, which is known to inhibit collagen synthesis. RAGE and its ligands are histologically co-localized to areas of sarcoidosis granulomatous, and a RAGE polymorphism is associated with increased risk of developing sarcoidosis. We recently identified that histological expression of the RAGE ligand serum amyloid A (SAA) was correlated with collagen deposition around sarcoidosis granulomas (AJRCCM 2010, 181:360). We explored the effects of RAGE stimulation by SAA on lung inflammation and fibrosis using a model of mKatG-induced granulomatous inflammation. METHODS: Wild-type (C57wt) RAGE-deficient (RAGEko) C57BL/6 mice were sensitized to recombinant mKatG, then re-exposed to mKatG-coated sepharose beads via orotracheal instillation, with or without SAA administration on days 0 and 7, and evaluated at 2wks. Inflammation and collagen deposition were quantified by digital microscopy and reported as group median values. Steady state whole-lung mRNA expression of cytokine and fibrosis-related genes was assessed by real-time PCR and reported as fold-change in SAA-treated vs untreated mice. RESULTS: In C57wt, granuloma area around mKatG-coated beads was 48% greater in SAA-treated animals vs. mKatG-beads alone (76907 vs 51582, p<0.0004), and this was associated with higher whole-lung mRNA expression of IFNg (1.27-fold), TNF (3.00-fold), and IL10 (3.25-fold) in SAA treated vs untreated C57wt (p<0.05, all comparisons). In RAGEko, the effect of SAA on granuloma area was attenuated (12% increase; 52576 vs 46710, p=ns) and failed to up-regulate IFNg (0.85-fold, p=ns), TNF (0.95-fold, p=ns), or IL10 (0.71-fold, p<0.05) expression. SAA administration resulted in 36% greater collagen deposition around mKatG granulomas identified by Sirius Red staining in C57wt (48 vs 35.5, p<0.03) and higher mRNA expression of type-1 collagen (2.32-fold), type-3 collagen (1.33-fold), and the collagen molecular chaperone Hsp47 (1.68-fold) (p<0.05, all comparisons). Consistent with the known effects of other RAGE ligands, SAA also up-regulated the expression of RAGE (1.59-fold, p<0.05). In contrast to C57wt, SAA administration did not significantly alter granuloma collagen content (16.5 vs 31) nor up-regulate mRNA expression of type-1 collagen (1.12-fold) or Hsp47 (1.14-fold) in RAGEko (p=ns, all comparisons). SAA administration was associated with reduced type-3 collagen expression (0.62-fold, p<0.05) in RAGEko. CONCLUSION: These results suggest that local inflammatory and fibrotic responses in experimental granulomatous lung inflammation are mediated, in part, through RAGE stimulation and support the therapeutic use of strategies that block this pathway in the management of sarcoidosis

Abstract We investigated the pre-clinical utility of carbon monoxide form of PEGylated hemoglobin (PEG-Hb also named SANGUINATE()) in myocardial infarction (MI) and in particular the response of diabetic tissues to superimposed ischemia/reperfusion injury. SANGUINATE() was evaluated in diabetic and normal mice subjected to 30 min of coronary artery ligation followed by either 48 h or 28 days of reperfusion. Our results demonstrate that SANGUINATE() was effective in reducing infarct size when administered either prior to left anterior descending coronary artery (LAD) occlusion or during reperfusion. This finding is an important step in exploring the efficacy of a pharmacoinvasive strategy using SANGUINATE() in patients with acute coronary syndromes.

Islet amyloid polypeptide (IAPP) is responsible for amyloid formation in type 2 diabetes and contributes to the failure of islet cell transplants, however the mechanisms of IAPP-induced cytotoxicity are not known. Interactions with model anionic membranes are known to catalyze IAPP amyloid formation in vitro. Human IAPP damages anionic membranes, promoting vesicle leakage, but the features that control IAPP-membrane interactions and the connection with cellular toxicity are not clear. Kinetic studies with wild-type IAPP and IAPP mutants demonstrate that membrane leakage is induced by prefibrillar IAPP species and continues over the course of amyloid formation, correlating additional membrane disruption with fibril growth. Analyses of a set of designed mutants reveal that membrane leakage does not require the formation of beta-sheet or alpha-helical structures. A His-18 to Arg substitution enhances leakage, whereas replacement of all of the aromatic residues via a triple leucine mutant has no effect. Biophysical measurements in conjunction with cytotoxicity studies show that nonamyloidogenic rat IAPP is as effective as human IAPP at disrupting standard anionic model membranes under conditions where rat IAPP does not induce cellular toxicity. Similar results are obtained with more complex model membranes, including ternary systems that contain cholesterol and are capable of forming lipid rafts. A designed point mutant, I26P-IAPP; a designed double mutant, G24P, I26P-IAPP; a double N-methylated variant; and pramlintide, a US Food and Drug Administration-approved IAPP variant all induce membrane leakage, but are not cytotoxic, showing that there is no one-to-one relationship between disruption of model membranes and induction of cellular toxicity.

BACKGROUND: Diabetic neuropathy and idiopathic neuropathy are among the most prevalent neuropathies in human patients. The molecular mechanism underlying pathological changes observed in the affected nerve remains unclear but one candidate molecule, the receptor for advanced glycation end-products (RAGE), has recently gained attention as a potential contributor to neuropathy. Our previous studies revealed that RAGE expression is higher in porcine and murine diabetic nerve, contributing to the inflammatory mechanisms leading to diabetic neuropathy. Here, for the first time, we focused on the expression of RAGE in human peripheral nerve. METHODS: Our study utilized de-identified human sural nerve surplus obtained from 5 non-neuropathic patients (control group), 6 patients with long-term mild-to-moderate diabetic neuropathy (diabetic group) and 5 patients with mild-to-moderate peripheral neuropathy of unknown etiology (idiopathic group). By using immunofluorescent staining and protein immunoblotting we studied the expression and colocalization patterns of RAGE and its ligands: carboxymethyllysine (CML), high mobility group box 1 (HMBG1) and mammalian Diaphanous 1 (mDia1) in control and neuropathic nerves. RESULTS: We found that in a normal, healthy human nerve, RAGE is expressed in almost 30% of all nerve fibers and that number is higher in pathological states such as peripheral neuropathy. We established that the levels of RAGE and its pro-inflammatory ligands, CML and HMBG1, are higher in both idiopathic and diabetic nerve, while the expression of the RAGE cytoplasmic domain-binding partner, mDia1 is similar among control, diabetic, and idiopathic nerve. The highest number of double stained nerve fibers was noted for RAGE and CML: approximately 76% (control), approximately 91% (idiopathic) and approximately 82% (diabetic) respectively. CONCLUSIONS: Our data suggest roles for RAGE and its inflammatory ligands in human peripheral neuropathies and lay the foundation for further, more detailed and clinically oriented investigation involving these proteins and their roles in disorders of the human peripheral nerve.

Oxidative stress is a central mechanism by which the receptor for advanced glycation endproducts (RAGE) mediates its pathological effects. Multiple experimental inquiries in RAGE-expressing cultured cells have demonstrated that ligand-RAGE interaction mediates generation of reactive oxygen species (ROS) and consequent downstream signal transduction and regulation of gene expression. The primary mechanism by which RAGE generates oxidative stress is via activation of NADPH oxidase; amplification mechanisms in the mitochondria may further drive ROS production. Recent studies indicating that the cytoplasmic domain of RAGE binds to the formin mDia1 provide further support for the critical roles of this pathway in oxidative stress; mDia1 was required for activation of rac1 and NADPH oxidase in primary murine aortic smooth muscle cells treated with RAGE ligand S100B. In vivo, in multiple distinct disease models in animals, RAGE action generates oxidative stress and modulates cellular/tissue fate in range of disorders, such as in myocardial ischemia, atherosclerosis, and aneurysm formation. Blockade or genetic deletion of RAGE was shown to be protective in these settings. Indeed, beyond cardiovascular disease, evidence is accruing in human subjects linking levels of RAGE ligands and soluble RAGE to oxidative stress in disorders such as doxorubicin toxicity, acetaminophen toxicity, neurodegeneration, hyperlipidemia, diabetes, preeclampsia, rheumatoid arthritis and pulmonary fibrosis. Blockade of RAGE signal transduction may be a key strategy for the prevention of the deleterious consequences of oxidative stress, particularly in chronic disease.