Faculty Bibliography

Human islet amyloid polypeptide (hIAPP) is a hormone secreted from β-cells in the Islets of Langerhans in response to the same stimuli that lead to insulin secretion. hIAPP plays an adaptive role in glucose homeostasis, but misfolds to form insoluble, fibrillar aggregates in type-II diabetes that are associated with the disease. Along the misfolding pathway, hIAPP forms species that are toxic to β-cells, resulting in reduced β-cell mass. hIAPP contains a strictly conserved disulfide bond between residues 2-7, which forms a small loop at the N-terminus of the molecule. The loop is located outside of the cross β-core in all models of the hIAPP amyloid fibrils. Mutations in this region are rare, and the disulfide loop plays a role in receptor binding, but the contribution of this region to the aggregation of hIAPP is not well understood. We define the role of the disulfide by analyzing a collection of analogues that remove the disulfide, by mutation of Cys to Ser, by reduction and modification of the Cys residues, or by deletion of the first seven residues. The cytotoxic properties of hIAPP are retained in the Cys to Ser disulfide free mutant. Removal of the disulfide bond accelerates amyloid formation in all constructs, both in solution and in the presence of model membranes. Removal of the disulfide reduces the ability of hIAPP to induce leakage of vesicles made up of POPS and POPC. Smaller effects are observed with vesicle that contain 40 mole percent cholesterol, although N-terminal truncation still reduces leakage.

PURPOSE/OBJECTIVE:integrins in a mouse hindlimb ischemia model of peripheral artery disease. PROCEDURES/METHODS:, VEGFR-1, VEGFR-2, as well as certain cell lineage markers. RESULTS:with endothelial cell marker FVIII, but not with CD31. Immunostaining for VEGFR-1 and VEGFR-2 additionally co-localized with lineage markers for endothelial progenitor cell and monocytes/macrophages, with a more diverse pattern of co-localization for VEGFR-2. CONCLUSION/CONCLUSIONS:Tc]scV may be due to the presence of VEGF receptors on additional cell types.

Proteotoxicity plays a key role in many devastating human disorders, including Alzheimer's, Huntington's and Parkinson's diseases; type 2 diabetes; systemic amyloidosis; and cardiac dysfunction, to name a few. The cellular mechanisms of proteotoxicity in these disorders have been the focus of considerable research, but their role in prevalent and morbid disorders, such as diabetes, is less appreciated. There is a large body of literature on the impact of glucotoxicity and lipotoxicity on insulin-producing pancreatic β-cells, and there is increasing recognition that proteotoxicty plays a key role. Pancreatic islet amyloidosis by the hormone IAPP, the production of advanced glycation endproducts, and insulin misprocessing into cytotoxic aggregates are all sources of β-cell proteotoxicity in diabetes. Advanced glycation endproducts, produced by the reaction of reducing sugars with proteins and lipids are ligands for the receptor for advanced glycation endproducts (RAGE), as are the toxic pre-fibrillar aggregates of IAPP produced during amyloid formation. The mechanisms of amyloid formation by IAPP in vivo or in vitro are not well understood, and the cellular mechanisms of IAPP-induced β-cell death are not fully defined. Here, we review recent findings that illuminate the factors and mechanisms involved in β-cell proteotoxicity in diabetes. Together, these new insights have far-reaching implications for the establishment of unifying mechanisms by which pathological amyloidoses imbue their injurious effects in vivo.

Islet amyloidosis is characterized by the aberrant accumulation of islet amyloid polypeptide (IAPP) in pancreatic islets, resulting in β cell toxicity, which exacerbates type 2 diabetes and islet transplant failure. It is not fully clear how IAPP induces cellular stress or how IAPP-induced toxicity can be prevented or treated. We recently defined the properties of toxic IAPP species. Here, we have identified a receptor-mediated mechanism of islet amyloidosis-induced proteotoxicity. In human diabetic pancreas and in cellular and mouse models of islet amyloidosis, increased expression of the receptor for advanced glycation endproducts (RAGE) correlated with human IAPP-induced (h-IAPP-induced) β cell and islet inflammation, toxicity, and apoptosis. RAGE selectively bound toxic intermediates, but not nontoxic forms of h-IAPP, including amyloid fibrils. The isolated extracellular ligand-binding domains of soluble RAGE (sRAGE) blocked both h-IAPP toxicity and amyloid formation. Inhibition of the interaction between h-IAPP and RAGE by sRAGE, RAGE-blocking antibodies, or genetic RAGE deletion protected pancreatic islets, β cells, and smooth muscle cells from h-IAPP-induced inflammation and metabolic dysfunction. sRAGE-treated h-IAPP Tg mice were protected from amyloid deposition, loss of β cell area, β cell inflammation, stress, apoptosis, and glucose intolerance. These findings establish RAGE as a mediator of IAPP-induced toxicity and suggest that targeting the IAPP/RAGE axis is a potential strategy to mitigate this source of β cell dysfunction in metabolic disease.

BACKGROUND:An influx of lipid-loaded macrophages characterizes visceral adipose tissue (VAT) inflammation, which is an important factor in the development of insulin resistance (IR) in obesity. Depletion of macrophage lipids accompanies increased whole body insulin sensitivity, but the underlying mechanism is unknown. Deficiency of autophagy protein ATG16L1 is associated with increases in inflammatory diseases and lipid metabolism, but the connection between ATG16L1, IR, and obesity remains elusive. We hypothesize that myeloid ATG16L1 contributes to lipid loading in macrophages and to IR. METHODS:Wild-type (WT) bone marrow derived macrophages (BMDMs) were treated with fatty acids and assessed for markers of autophagy. Myeloid-deficient Atg16l1 and littermate control male mice were fed high fat diet (HFD) or low fat diet (LFD) for 3 months starting at 8 weeks of age. Mice were assessed for body mass, fat and lean mass, glucose and insulin sensitivity, food consumption and adipose inflammation. Fluorescence-activated cell sorted VAT macrophages were assessed for lipid content and expression of autophagy related genes. RESULTS:VAT and VAT macrophages from HFD-fed WT mice did not show differences in autophagy protein and gene expression compared to tissue from LFD-fed mice. Fatty acid-treated BMDMs increased neutral lipid content but did not change autophagy protein expression. HFD-fed Atg16l1 myeloid-deficient and littermate mice demonstrated no differences in body mass, glucose or insulin sensitivity, food consumption, fat or lean mass, macrophage lipid content, or adipose tissue inflammation. CONCLUSION/CONCLUSIONS:ATG16L1 does not contribute to obesity, IR, adipose tissue inflammation or lipid loading in macrophages in mice fed HFD.

BACKGROUND:The United Arab Emirates (UAE) is faced with a rapidly increasing burden of non-communicable diseases including obesity, diabetes, and cardiovascular disease. The UAE Healthy Future study is a prospective cohort designed to identify associations between risk factors and these diseases amongst Emiratis. The study will enroll 20,000 UAE nationals aged ≥18 years. Environmental and genetic risk factors will be characterized and participants will be followed for future disease events. As this was the first time a prospective cohort study was being planned in the UAE, a pilot study was conducted in 2015 with the primary aim of establishing the feasibility of conducting the study. Other objectives were to evaluate the implementation of the main study protocols, and to build adequate capacity to conduct advanced clinical laboratory analyses. METHODS:Seven hundred sixty nine UAE nationals aged ≥18 years were invited to participate voluntarily in the pilot study. Participants signed an informed consent, completed a detailed questionnaire, provided random blood, urine, and mouthwash samples and were assessed for a series of clinical measures. All specimens were transported to the New York University Abu Dhabi laboratories where samples were processed and analyzed for routine chemistry and hematology. Plasma, serum, and a small whole blood sample for DNA extraction were aliquoted and stored at -80 °C for future analyses. RESULTS:Overall, 517 Emirati men and women agreed to participate (68% response rate). Of the total participants, 495 (95.0%), 430 (82.2%), and 492 (94.4%), completed the questionnaire, physical measurements, and provided biological samples, respectively. CONCLUSIONS:The pilot study demonstrated the feasibility of recruitment and completion of the study protocols for the first large-scale cohort study designed to identify emerging risk factors for the major non-communicable diseases in the region.

Background: Chronic kidney disease (CKD) is associated with extensive vascular wall remodelling and vasculopathy as well as accumulation of uremic toxins. Among these toxins, advanced glycation end-products (AGEs) interact with the receptor for advanced glycation end-products (RAGE). In this study, we aimed to analyze the impact of CKD on arterial thrombosis and the potential role of RAGE in this process.
Method(s): We used a mouse model of uremic vasculopathy consisting in a 2-step 5/6 nephrectomy. Four groups of animals were studied: Apoe^-/- mice sham operated (n=12) or uremic (n=10) and Apoe^-/-/Ager^-/- (= Apoe^-/-RAGE -/-) mice sham operated (n=11) or uremic (n=15). Twelve weeks after surgery: 1) arterial thrombosis was induced by ferric chloride application on the carotid artery and complete carotid occlusion time was measured, 2) platelet function was analysed in whole blood and in platelet rich plasma (PRP).
Result(s): In-vivo, uremia significantly accelerates the occlusion time in Apoe^-/- mice (9.2 +/-1,1min vs 11.1 +/-0,6 min, p<0.01) compared to sham animals. IIn contrast, uremia had no effect on Apoe^-/-/Ager^-/- mice carotid occlusion time (14,5 +/-2,3 min, vs 13 +/-1,5 min in sham, NS). Moreover occlusion time of the uremic Apoe^-/- mice was significantly accelerated compared to uremic Apoe^-/- /Ager^-/- mice (p<0,0001). Ex-vivo, agonistinduced platelet aggregation in whole blood was significantly increased in uremic condition in both Apoe-/-and Apoe^-/- /Ager^-/- mice. In PRP, aggregation of uremic Apoe^-/- mice platelets was significantly increased compared to that of uremic Apoe^-/-/Ager^-/- mice. In agreement, agonist induced expression of activated integrin alphaIIbbeta3 and P-selectin were both significantly increased at the surface of Apoe-/-uremic platelets compared to 1) Apoe^-/- sham platelets and to 2) Apoe^-/-/Ager^-/- platelets (uremic & sham).
Conclusion(s): In this murine model of thrombosis we report that uremia accelerates arterial thrombus formation and induces platelets hyperreactivity. We found that Ager deletion had a protective role on uremia-induced arterial thrombosis, and in uremiainduced platelet hyperreactivity. We suggest that RAGE signaling may be involved in CKD-induced atherothrombosis

Much of our knowledge of diabetes is derived from studies of rodent models. An alternative approach explores evolutionary solutions to physiological stress by studying organisms that face challenging metabolic environments. Polar bears eat an enormously lipid-rich diet without deleterious metabolic consequences. In contrast, transgenic rodents expressing the human neuropancreatic polypeptide hormone amylin develop hyperglycemia and extensive pancreatic islet amyloid when fed a high fat diet. The process of islet amyloid formation by human amylin contributes to β-cell dysfunction and loss of β-cell mass in type-2 diabetes. We show that ursine amylin is considerably less amyloidogenic and less toxic to β-cells than human amylin, consistent with the hypothesis that part of the adaptation of bears to metabolic challenges might include protection from islet amyloidosis-induced β-cell toxicity. Ursine and human amylin differ at four locations: H18R, S20G, F23L, and S29P. These are interesting from a biophysical perspective since the S20G mutation accelerates amyloid formation but the H18R slows it. An H18RS20G double mutant of human amylin behaves similarly to the H18R mutant, indicating that the substitution at position 18 dominates the S20G replacement. These data suggest one possible mechanism underpinning the protection of bears against metabolic challenges and provide insight into the design of soluble analogs of human amylin.

Aims/UNASSIGNED:The transformation of the United Arab Emirates (UAE) from a semi-nomadic to a high income society has been accompanied by increasing rates of obesity and Type 2 diabetes mellitus. We examined if the AGE-RAGE (receptor for advanced glycation endproducts) axis is associated with obesity and diabetes mellitus in the pilot phase of the UAE Healthy Futures Study (UAEHFS). Methods/UNASSIGNED:517 Emirati subjects were enrolled and plasma/serum levels of AGE, carboxy methyl lysine (CML)-AGE, soluble (s)RAGE and endogenous secretory (es)RAGE were measured along with weight, height, waist and hip circumference (WC/HC), blood pressure, HbA1c, Vitamin D levels and routine chemistries. The relationship between the AGE-RAGE axis and obesity and diabetes mellitus was tested using proportional odds models and linear regression. Results/UNASSIGNED:After covariate adjustment, AGE levels were significantly associated with diabetes status. Levels of sRAGE and esRAGE were associated with BMI and levels of sRAGE were associated with WC/HC. Conclusions/UNASSIGNED:The AGE-RAGE axis is associated with diabetes status and obesity in this Arab population. Prospective serial analysis of this axis may identify predictive biomarkers of obesity and cardiometabolic dysfunction in the UAEHFS.