Faculty Bibliography

Types 1 and 2 diabetes are on the rise worldwide. Although the treatment of hyperglycemia has benefitted from recent advances, aggressive efforts to maintain euglycemia may be fraught with risk, especially in older subjects or in subjects vulnerable to hypoglycemic unawareness. Hence, strategies to prevent and treat the complications of hyperglycemia are essential. In this review, we summarize recent updates on the biology of the receptor for advanced glycation endproducts (RAGE) in the pathogenesis of both micro- and macrovascular complications of diabetes, insights from the study of mouse models of obesity and diabetic complications, and from associative studies in human subjects. The study of the mechanisms and consequences of the interaction of the RAGE cytoplasmic domain with the formin, mDia1, in RAGE signal transduction, will be discussed. Lastly, we review the 'state-of-the-art' on RAGE-directed therapeutics. Tackling RAGE/mDia1 may identify a novel class of therapeutics preventing diabetes and its complications

Dietary n-3 fatty acids (FAs) may reduce cardiovascular disease risk. We questioned whether acute administration of n-3 rich triglyceride (TG) emulsions could preserve cardiac function and decrease injury after ischemia/reperfusion (I/R) insult. We used two different experimental models: in vivo, C57BL/6 mice were exposed to acute occlusion of the left anterior descending coronary artery (LAD), and ex-vivo, C57BL/6 murine hearts were perfused using Langendorff technique (LT). In the LAD model, mice treated with n-3 TG emulsion (1.5g/kg body weight), immediately after ischemia and 1h later during reperfusion, significantly reduced infarct size and maintained cardiac function (p<0.05). In the LT model, administration of n-3 TG emulsion (300mgTG/100ml) during reperfusion significantly improved functional recovery (p<0.05). In both models, lactate dehydrogenase (LDH) levels, as a marker of injury, were significantly reduced by n-3 TG emulsion. To investigate the mechanisms by which n-3 FAs protects hearts from I/R injury, we investigated changes in key pathways linked to cardioprotection. In the ex-vivo model, we showed that n-3 FAs increased phosphorylation of AKT and GSK3beta proteins (p<0.05). Acute n-3 TG emulsion treatment also increased Bcl-2 protein level and reduced an autophagy marker, Beclin-1 (p<0.05). Additionally, cardioprotection by n-3 TG emulsion was linked to changes in PPARgamma protein expression (p<0.05). Rosiglitazone and p-AKT inhibitor counteracted the positive effect of n-3 TG; GSK3beta inhibitor plus n-3 TG significantly inhibited LDH release. We conclude that acute n-3 TG injection during reperfusion provides cardioprotection. This may prove to be a novel acute adjunctive reperfusion therapy after treating patients with myocardial infarction.

In mammals, changes in the metabolic state, including obesity, fasting, cold challenge and high fat diets activate complex immune responses. In many strains of rodents, high fat diets induce a rapid systemic inflammatory response and lead to obesity. Little is known about the molecular signals required for high fat diet (HFD)-induced phenotypes. Here we studied the function of the receptor for advanced glycation products (RAGE) in the development of phenotypes associated with high fat feeding in mice. RAGE is highly expressed on immune cells, including macrophages. High fat feeding induced expression of RAGE ligand HMGB1 and carboxy methyl lysine (CML)-advanced glycation endproducts (AGE) epitopes in liver and adipose tissue. Genetic deficiency of RAGE prevented the effects of HFD on energy expenditure, weight gain, adipose tissue inflammation, and insulin resistance. RAGE deficiency had no effect on genetic forms of obesity caused by impaired melanocortin signaling. Hematopoietic deficiency of RAGE or treatment with soluble RAGE partially protected against peripheral HFD-induced inflammation and weight gain. These data argue that high fat feeding induces peripheral inflammation and weight gain in a RAGE-dependent manner, providing a foothold in the pathways that regulate diet-induced obesity and offering the potential for therapeutic intervention.

Sustained increases in glucose flux via the aldose reductase (AR) pathway have been linked to diabetic vascular complications. Previous studies revealed that glucose flux via AR mediates endothelial dysfunction and leads to lesional hemorrhage in diabetic human AR (hAR) expressing mice in an apoE(-/-) background. Our studies revealed sustained activation of Egr-1 with subsequent induction of its downstream target genes tissue factor (TF) and vascular cell adhesion molecule-1 (VCAM-1) in diabetic apoE(-/-)hAR mice aortas and in high glucose-treated primary murine aortic endothelial cells expressing hAR. Furthermore, we observed that flux via AR impaired NAD(+) homeostasis and reduced activity of NAD(+)-dependent deacetylase Sirt-1 leading to acetylation and prolonged expression of Egr-1 in hyperglycemic conditions. In conclusion, our data demonstrate a novel mechanism by which glucose flux via AR triggers activation, acetylation, and prolonged expression of Egr-1 leading to proinflammatory and prothrombotic responses in diabetic atherosclerosis.

The discovery of the receptor for advanced glycation end-products (RAGE) set the stage for the elucidation of important mechanisms underpinning diabetic complications. RAGE transduces the signals of advanced glycation end-products (AGEs), proinflammatory S100/calgranulins, and high mobility group box 1 (HMGB1), and is a one of a family of receptors for lysophosphatidic acid (LPA). These ligand tales weave a theme of vascular perturbation and inflammation linked to the pathogenesis of the chronic complications of diabetes. Once deemed implausible, this concept of inflammatory cues participating in diabetic complications is now supported by a plethora of experimental evidence in the macro- and microvasculature. We review the biology of ligand-RAGE signal transduction and its roles in diabetic microvascular complications, from animal models to human subjects.

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.

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.

n-3 fatty acids may decrease cardiovascular disease risk. We questioned if acute intervention of n-3 triglyceride (TG) emulsion (48% of fatty acids = EPA+DHA) is protective and improves cardiac function after ischemia/reperfusion (I/R). n-3 TG were administered after I/R in two models: a) hearts (C57BL/6 mice) were perfused ex-vivo using the Langendorff technique (LT); b) hearts with acute occlusion of the left anterior descending coronary artery (LAD) in vivo. After LAD occlusion n-3 TG emulsion (1.5g/kg body weight) was injected intraperitoneally at the end of ischemia and 1h later. In the LT model of I/R, perfusion with KREBS-Hensleit buffer (KH) led to markedly decreased left ventricular developed pressure (LVDP) (by 60%) and arrhythmias, but reperfusion with KH+ n-3 TG (300mg/100ml) improved LVDP recovery. In the LAD model, near normal echo-and electrocardiograms were maintained 48hrs after I/R and left ventricular infarct size was reduced by 80% in TG treated animals vs control. For both I/R models, markers of injury, lactate dehydrogenase and creatine kinase, were significantly reduced in n-3 TG treated mice. After I/R, in LT model, n-3 TG increased a marker of apoptosis Bcl-2 (by 50%), reduced markers of autophagy beclin 1 (by 60%) and HIF1 (by 80%). We conclude that an acute n-3 TG injection after ischemia provides cardioprotection. This may provide a novel therapy after acute myocardial infarction in humans