RESUMEN

Islet transplantation for treatment of diabetes is limited by availability of donor islets and requirements for immunosuppression. Stem cell-derived islets might circumvent these issues. SC-islets effectively control glucose metabolism post transplantation, but do not yet achieve full function in vitro with current published differentiation protocols. We aimed to identify markers of mature subpopulations of SC-ß cells by studying transcriptional changes associated with in vivo maturation of SC-ß cells using RNA-seq and co-expression network analysis. The ß cell-specific hormone islet amyloid polypeptide (IAPP) emerged as the top candidate to be such a marker. IAPP+ cells had more mature ß cell gene expression and higher cellular insulin content than IAPP- cells in vitro. IAPP+ INS+ cells were more stable in long-term culture than IAPP- INS+ cells and retained insulin expression after transplantation into mice. Finally, we conducted a small molecule screen to identify compounds that enhance IAPP expression. Aconitine up-regulated IAPP and could help to optimize differentiation protocols.

RESUMEN

Insulin resistance is the major risk factor for Type 2 diabetes (T2D). In vulnerable individuals, insulin resistance induces a progressive loss of insulin secretion with islet pathology revealing a partial deficit of beta cells and islet amyloid derived from islet amyloid polypeptide (IAPP). IAPP is co-expressed and secreted with insulin by beta cells, expression of both proteins being upregulated in response to insulin resistance. If IAPP expression exceeds the threshold for clearance of misfolded proteins, beta cell failure occurs exacerbated by the action of IAPP toxicity to compromise the autophagy lysosomal pathway. We postulated that suppression of IAPP expression by an IAPP antisense oligonucleotide delivered to beta cells by the GLP-1 agonist exenatide (eGLP1-IAPP-ASO) is a potential disease modifying therapy for T2D. While eGLP1-IAPP-ASO suppressed mouse IAPP and transgenic human IAPP expression in mouse islets, it had no discernable effects on IAPP expression in human islets under the conditions studied. Suppression of transgenic human IAPP expression in mouse islets attenuated disruption of the autophagy lysosomal pathway in beta cells, supporting the potential of this strategy.

RESUMEN

Polyphenols are natural compounds abundantly found in plants. They are known for their numerous benefits to human health, including antioxidant properties and anti-inflammatory activities. Interestingly, many studies have revealed that polyphenols can also modulate the formation of amyloid fibrils associated with disease states and can prevent the formation of cytotoxic oligomer species. In this review, we underline the numerous effects of four hydrolysable gallotannins (HGTs) with high conformational flexibility, low toxicity, and multi-targeticity, e.g., tannic acid, pentagalloyl glucose, corilagin, and 1,3,6-tri-O-galloyl-ß-D-glucose, on the aggregation of amyloidogenic proteins associated with the Alzheimer's Disease (AD). These HGTs have demonstrated interesting abilities to reduce, at different levels, the formation of amyloid fibrils involved in AD, including those assembled from the amyloid ß-peptide, the tubulin-associated unit, and the islet amyloid polypeptide. HGTs were also shown to disassemble pre-formed fibrils and to diminish cognitive decline in mice. Finally, this manuscript highlights the importance of further investigating these naturally occurring HGTs as promising scaffolds to design molecules that can interfere with the formation of proteotoxic oligomers and aggregates associated with AD pathogenesis.

Asunto(s)

Enfermedad de Alzheimer , Glucosa , Polifenoles , Humanos , Animales , Ratones , Enfermedad de Alzheimer/tratamiento farmacológico , Péptidos beta-Amiloides , Taninos Hidrolizables/farmacología

RESUMEN

Amyloids are a subset of intrinsically disordered proteins (IDPs) that self-assemble into cross-ß oligomers and fibrils. The structural plasticity of amyloids leads to sampling of metastable, low-molecular-weight oligomers that contribute to cytotoxicity. Of interest are amyloid-ß (Aß) and islet amyloid polypeptide (IAPP), which are involved in the pathology of Alzheimer's disease and Type 2 Diabetes Mellitus, respectively. In addition to forming homogenous oligomers and fibrils, these species have been found to cross-aggregate in heterogeneous structures. Biophysical properties, including electronic effects, that are unique or conserved between homogenous and heterogenous amyloids oligomers are thus far unexplored. Here, we simulated homogenous and heterogenous amyloid oligomers of Aß16-22 and IAPP20-29 fragments using the Drude oscillator model to investigate the impact of electronic polarization on the structural morphology and stability of preformed hexamers. Upon simulation of preformed, ß-strand rich oligomers with Drude, structural rearrangement occurred causing some loss of ß-strand structure in favor of random coil content for all oligomers. Homogenous Aß16-22 was the most stable system, deriving stability from low polarization in hydrophobic residues and through salt bridge formation. Changes in polarization were observed primarily for Aß16-22 residues in heterogenous cross-amyloid systems, displaying a decrease in charged residue dipole moments and an increase in hydrophobic sidechain dipole moments. This work is the first study utilizing the Drude-2019 force field with amyloid oligomers, providing insight into the impact of electronic effects on oligomer structure and highlighting the importance of different microenvironments on amyloid oligomer stability.

RESUMEN

Islet amyloid polypeptide (IAPP) is a 37-residue amyloidogenic hormone implicated in the progression of Type II Diabetes (T2D). T2D affects an estimated 422 million people yearly and is a comorbidity with numerous diseases. IAPP forms toxic oligomers and amyloid fibrils that reduce pancreatic ß-cell mass and exacerbate the T2D disease state. Toxic oligomer formation is attributed, in part, to the formation of interpeptide ß-strands comprised of residues 20-29 (IAPP(20-29)). Flavonoids, a class of polyphenolic natural products, have been found experimentally to inhibit IAPP aggregate formation. Many of these small flavonoids differ structurally only slightly; the influence of functional group placement on inhibiting the aggregation of the IAPP(20-29) has yet to be explored. To probe the role of small-molecule structural features that impede IAPP aggregation, molecular dynamics simulations were performed to observe trimer formation on a model fragment of IAPP(20-29) in the presence of morin, quercetin, dihydroquercetin, epicatechin, and myricetin. Contacts between Phe23 residues were critical to oligomer formation, and small-molecule contacts with Phe23 were a key predictor of ß-strand reduction. Structural properties influencing the ability of compounds to disrupt Phe23-Phe23 contacts included aromaticity and carbonyl and hydroxyl group placement. This work provides key information on design considerations for T2D therapeutics that target IAPP aggregation.

Asunto(s)

Polipéptido Amiloide de los Islotes Pancreáticos , Fragmentos de Péptidos , Amiloide/química , Flavonoides/química , Humanos , Polipéptido Amiloide de los Islotes Pancreáticos/química , Simulación de Dinámica Molecular , Fragmentos de Péptidos/química , Agregado de Proteínas

RESUMEN

This paper is based on a presentation given at the Annual Meeting of the Society for the Study of Ingestive Behavior in July 2021 and provides a personal view on some of the milestones in the discovery of amylin as a constituent of pancreatic islet amyloid deposits, as a pancreatic beta-cell hormone, and on its role in physiology and pathophysiology. Only selected effects of amylin are discussed here because we recently published extensive reviews on the physiology and pathophysiology of amylin. Amylin was discovered as the main constituent of islet amyloid that is predominantly found in pancreatic islets in type 2 diabetics. These deposits, and in particular small oligomer aggregates of amylin seem to contribute to the progressive beta-cell damage seen in type 2 diabetics. Amylin is also a physiologically relevant circulating hormone with diverse metabolic functions, e.g. inhibition of eating, of pancreatic glucagon secretion and of gastric emptying. Knowledge of these types of functions and amylin's mechanisms of action lead to the development of amylin analogues that are now among the most promising anti-obesity targets in clinical testing. With this review, I want to give a short overview of 35 exciting years of amylin research.

Asunto(s)

Amiloide , Polipéptido Amiloide de los Islotes Pancreáticos , Amiloide/metabolismo , Conducta Alimentaria , Vaciamiento Gástrico/fisiología , Humanos , Polipéptido Amiloide de los Islotes Pancreáticos/metabolismo , Polipéptido Amiloide de los Islotes Pancreáticos/farmacología , Obesidad

RESUMEN

Type 2 Diabetes Mellitus (T2DM) is a chronic progressive disease, defined by insulin resistance and insufficient insulin secretion to maintain normoglycemia. Amyloidogenic aggregates are a hallmark of T2DM patients; they are cytotoxic for the insulin producing ß-cells, and cause inflammasome-dependent secretion of IL-1ß. To avoid the associated ß-cell loss and inflammation in advanced stage T2DM, we developed a novel monoclonal therapy targeting the major component of aggregates, islet amyloid polypeptide (IAPP). The here described monoclonal antibody (mAb) m81, specific for oligomeric and fibrils, but not for soluble free IAPP, is able to prevent oligomer growth and aggregate formation in vitro, and blocks islet inflammation and disease progression in vivo. Collectively, our data show that blocking fibril formation and prevention of new amyloidogenic aggregates by monoclonal antibody therapy may be a potential therapy for T2DM.

RESUMEN

The pancreatic ß-cell is purpose-built for the production and secretion of insulin, the only hormone that can remove glucose from the bloodstream. Insulin is kept inside miniature membrane-bound storage compartments known as secretory granules (SGs), and these specialized organelles can readily fuse with the plasma membrane upon cellular stimulation to release insulin. Insulin is synthesized in the endoplasmic reticulum (ER) as a biologically inactive precursor, proinsulin, along with several other proteins that will also become members of the insulin SG. Their coordinated synthesis enables synchronized transit through the ER and Golgi apparatus for congregation at the trans-Golgi network, the initiating site of SG biogenesis. Here, proinsulin and its constituents enter the SG where conditions are optimized for proinsulin processing into insulin and subsequent insulin storage. A healthy ß-cell is continually generating SGs to supply insulin in vast excess to what is secreted. Conversely, in type 2 diabetes (T2D), the inability of failing ß-cells to secrete may be due to the limited biosynthesis of new insulin. Factors that drive the formation and maturation of SGs and thus the production of insulin are therefore critical for systemic glucose control. Here, we detail the formative hours of the insulin SG from the luminal perspective. We do this by mapping the journey of individual members of the SG as they contribute to its genesis.

RESUMEN

Amyloidosis is a concept that implicates disorders and complications that are due to abnormal protein accumulation in different cells and tissues. Protein aggregation-associated diseases are classified according to the type of aggregates and deposition sites, such as neurodegenerative disorders and type 2 diabetes mellitus. Polyphenolic phytochemicals such as curcumin and its derivatives have anti-amyloid effects both in vitro and in animal models; however, the underlying mechanisms are not understood. In this review, we summarized possible mechanisms by which curcumin could interfere with self-assembly processes and reduce amyloid aggregation in amyloidosis. Furthermore, we discuss clinical trials in which curcumin is used as a therapeutic agent for the treatment of diseases linking to protein aggregates.

Asunto(s)

Enfermedad de Alzheimer/tratamiento farmacológico , Amiloidosis/prevención & control , Síndrome de Creutzfeldt-Jakob/tratamiento farmacológico , Curcumina/uso terapéutico , Diabetes Mellitus Tipo 2/tratamiento farmacológico , Enfermedad de Huntington/tratamiento farmacológico , Fármacos Neuroprotectores/uso terapéutico , Enfermedad de Parkinson/tratamiento farmacológico , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/patología , Péptidos beta-Amiloides/antagonistas & inhibidores , Péptidos beta-Amiloides/genética , Péptidos beta-Amiloides/metabolismo , Amiloidosis/genética , Amiloidosis/metabolismo , Amiloidosis/patología , Ensayos Clínicos como Asunto , Síndrome de Creutzfeldt-Jakob/genética , Síndrome de Creutzfeldt-Jakob/metabolismo , Síndrome de Creutzfeldt-Jakob/patología , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/metabolismo , Diabetes Mellitus Tipo 2/patología , Humanos , Enfermedad de Huntington/genética , Enfermedad de Huntington/metabolismo , Enfermedad de Huntington/patología , Hipoglucemiantes/uso terapéutico , Mitocondrias/efectos de los fármacos , Mitocondrias/metabolismo , Mitocondrias/patología , Estrés Oxidativo , Enfermedad de Parkinson/genética , Enfermedad de Parkinson/metabolismo , Enfermedad de Parkinson/patología , Agregado de Proteínas/efectos de los fármacos , alfa-Sinucleína/antagonistas & inhibidores , alfa-Sinucleína/genética , alfa-Sinucleína/metabolismo , Proteínas tau/antagonistas & inhibidores , Proteínas tau/genética , Proteínas tau/metabolismo

RESUMEN

Human islet amyloid polypeptide (hIAPP), otherwise known as amylin, is a 37-residue peptide hormone which is reported to be a common factor in protein misfolding disorders such as type-2 diabetes mellitus, Alzheimer's disease and Parkinson's disease, due to deposition of insoluble hIAPP amyloid in the pancreas and brain. Multiple studies point to the importance of the peptide's interaction with biological membranes and the cytotoxicity of hIAPP species. Here, we discuss the aggregation pathways of hIAPP amyloid fibril formation and focus on the complex interplay between membrane-mediated assembly of hIAPP and the associated mechanisms of membrane damage caused by the peptide species. Mitochondrial membranes, which are unique in their lipid composition, are proposed as prime targets for the early intracellular formation of hIAPP toxic entities. We suggest that future studies should include more physiologically-relevant and in-cell studies to allow a more accurate model of in vivo interactions. Finally, we underscore an urgent need for developing effective therapeutic strategies aimed at hindering hIAPP-phospholipid interactions.

Asunto(s)

Polipéptido Amiloide de los Islotes Pancreáticos/metabolismo , Lípidos/química , Deficiencias en la Proteostasis/metabolismo , Humanos , Polipéptido Amiloide de los Islotes Pancreáticos/química , Agregado de Proteínas , Conformación Proteica

RESUMEN

The islet amyloid polypeptide (IAPP) is a 37-residue peptide hormone whose deposition as amyloid fibrils in the pancreatic islets is associated with type 2 diabetes. Previous studies have suggested that residue Asn-21 plays a critical role in the in vitro self-assembly of IAPP. Herein, we studied structure-self-assembly relationships focusing on position 21 to gain detailed insights into the molecular mechanisms of IAPP self-assembly and to probe the conformational nature of the toxic assemblies associated with ß-cell death. Thioflavin T (ThT) fluorescence, CD spectroscopy, and transmission EM analysis revealed that the Asn-21 amide side chain is not required for IAPP nucleation and amyloid elongation, as N21A and N21G variants assembled into prototypical fibrils. In contrast, Asn-21 substitution with the conformationally constrained and turn-inducing residue Pro accelerated IAPP self-assembly. Successive substitutions with hydrophobic residues led to the formation of ThT-negative ß-sheet-rich aggregates having high surface hydrophobicity. Cell-based assays revealed no direct correlation between the in vitro amyloidogenicity of these variants and their toxicity. In contrast, leakage of anionic lipid vesicles disclosed that membrane disruption is closely associated with cytotoxicity. We observed that the N21F variant self-assembles into worm-like aggregates, causing loss of lipid membrane structural integrity and inducing ß-cell apoptosis. These results indicate that specific intra- and intermolecular interactions involving Asn-21 promote IAPP primary nucleation events by modulating the conformational conversion of the oligomeric intermediates into amyloid fibrils. Our study identifies position 21 as a hinge residue that modulates IAPP amyloidogenicity and cytotoxicity.

Asunto(s)

Apoptosis/efectos de los fármacos , Membrana Celular/metabolismo , Células Secretoras de Insulina/metabolismo , Polipéptido Amiloide de los Islotes Pancreáticos , Péptidos , Animales , Línea Celular Tumoral , Membrana Celular/patología , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Células Secretoras de Insulina/patología , Polipéptido Amiloide de los Islotes Pancreáticos/química , Polipéptido Amiloide de los Islotes Pancreáticos/metabolismo , Polipéptido Amiloide de los Islotes Pancreáticos/farmacología , Péptidos/química , Péptidos/metabolismo , Péptidos/farmacología , Estructura Secundaria de Proteína , Ratas

RESUMEN

BACKGROUND: Amylin and oligomers formed from amylin are implicated in demise of beta cells in type 2 diabetes. However, whether putative toxicity is exerted intra or extracellularly is unclear. Use of photochemical internalization (PCI) technique may give clues for impact of intracellular toxicity. AIM: (a) To optimize the concentration and exposure set up of the photosensitizing compound meso-disulfonated tetraphenyl chlorin TPCS2a (Amphinex®) for use in insulin producing beta cells and (b) to utilize the photosensitizing technique to probe for intracellular effects in beta cells by amylin. MATERIALS AND METHODS: The titration of TPCS2a and blue light exposure was evaluated by MTT assay. The insulin producing INS-1 832/13 beta cells were incubated with the photosensitizing agent TPCS2a prior to exposure of amylin. Viability and function were further evaluated by standard biochemical techniques. RESULTS: A protocol was developed for use in INS-1 832/13 cells in which the optimal concentration of TPCS2a was found to be 4ng/ml. Using this protocol human amylin (10 µM, 8 h) in combination with TPCS2a (4 ng/ml, 18 h) and blue light exposure (60 s) exerted toxic effects above those by TPCS2a and illumination alone as measured by MTT (15 ±â€¯3.6%, n = 6, p < 0.007) for effect of amylin exposure. On the other hand, rat amylin (which does not form oligomers) had no effect. Insulin secretion was non-significantly reduced by the combination of human amylin with TPCS2a and illumination compared to TPCS2a and illumination alone. Cellular insulin content was not affected, nor were measured parameters of apoptosis and necrosis. CONCLUSION: PCI technology could be a useful tool to induce endosomal rupture in clonal beta cells. The present results using PCI are compatible with intracellular negative effects following exposure to amylin.

Asunto(s)

Células Secretoras de Insulina/efectos de los fármacos , Polipéptido Amiloide de los Islotes Pancreáticos/farmacología , Fotoquimioterapia/métodos , Fármacos Fotosensibilizantes/farmacología , Porfirinas/farmacología , Animales , Supervivencia Celular , Diabetes Mellitus Tipo 2 , Relación Dosis-Respuesta a Droga , Insulina/biosíntesis , Ratas

RESUMEN

Alzheimer's disease (AD) is the most common type of dementia. Recent studies suggest that metabolic disturbances, particularly type 2 diabetes (T2D) increase the risk of cognitive decline and AD. AD is also a risk factor for T2D, and a growing body of evidence indicates that these diseases are connected both at clinical and molecular levels. In T2D, peripheral insulin resistance, hyperglycemia and eventually insulin deficiency develops, leading to an overall decline in tissue health. More recently, brain insulin resistance has been shown to be a key feature of AD that is linked to neuronal dysfunction and cognitive impairment. Furthermore, both AD and T2D are amyloidogenic diseases, with abnormal aggregation of amyloid-ß peptide (Aß) and islet amyloid polypeptide (IAPP) respectively contributing to cellular death and disease pathogenesis. Emerging data suggests that Aß may have peripheral effects including its co-deposition in the pancreas. In this review, we discuss how peripheral effects of Aß and metabolic disturbances may impact AD pathogenesis. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Asunto(s)

Enfermedad de Alzheimer/metabolismo , Glucosa/metabolismo , Homeostasis/fisiología , Animales , Humanos

RESUMEN

BACKGROUND: Enhanced IAPP production may contribute to islet amyloid formation in type 2 diabetes. The objective of this study was to determine the effects of the saturated fatty acid palmitate on IAPP levels in human ß-cells. METHODS: EndoC-ßH1 cells and human islets were cultured in the presence of sodium palmitate. Effects on IAPP/insulin mRNA expression and secretion were determined using real-time qPCR/ELISA. Pharmacological activators and/or inhibitors and RNAi were used to determine the underlying mechanisms. RESULTS: We observed that EndoC-ßH1 cells exposed to palmitate for 72 h displayed decreased expression of Pdx-1 and MafA and increased expression of thioredoxin-interacting protein (TXNIP), reduced insulin mRNA expression and glucose-induced insulin secretion, as well as increased IAPP mRNA expression and secretion. Further, these effects were independent of fatty acid oxidation, but abolished in response to GPR40 inhibition/downregulation. In human islets both a high glucose concentration and palmitate promoted increased IAPP mRNA levels, resulting in an augmented IAPP/insulin mRNA ratio. This was paralleled by elevated IAPP/insulin protein secretion and content ratios. CONCLUSIONS: Addition of exogenous palmitate to human ß-cells increased the IAPP/insulin expression ratio, an effect contributed to by activation of GPR40. These findings may be pertinent to our understanding of the islet amyloid formation process.

Asunto(s)

Insulina/metabolismo , Polipéptido Amiloide de los Islotes Pancreáticos/metabolismo , Ácido Palmítico/farmacología , ARN Mensajero/genética , Receptores Acoplados a Proteínas G/metabolismo , Animales , Línea Celular , Ácidos Grasos/metabolismo , Glucosa/metabolismo , Humanos , Insulina/genética , Polipéptido Amiloide de los Islotes Pancreáticos/genética , Islotes Pancreáticos/efectos de los fármacos , Islotes Pancreáticos/metabolismo , Ratones , Oxidación-Reducción , Proteína Quinasa C/metabolismo , Transducción de Señal , Factores de Transcripción/metabolismo

RESUMEN

Type 2 diabetes (T2D) is characterised by hyperglycaemia resulting from defective insulin secretion, insulin resistance, or both. The impact of over-nutrition and reduced physical activity, evidenced by the exponential rise in obesity and the prevalence of T2D, strongly supports the implementation of lifestyle modification programs. Accordingly, an increased consumption of fruits and plant-derived foods has been advocated, as their intake is inversely correlated with T2D prevalence; this has been attributed, in part, to their contained polyphenolic compounds. Over the last decade, a body of work has focussed on establishing the mechanisms by which polyphenolic compounds exert beneficial effects to limit carbohydrate digestion, enhance insulin-mediated glucose uptake, down-regulate hepatic gluconeogenesis and decrease oxidative stress; the latter anti-oxidative property being the most documented. Novel effects on the inhibition of glucocorticoid action and the suppression of amylin misfolding and aggregation have been identified more recently. Amyloid fibrils form from spontaneously misfolded amylin, depositing in islet cells to elicit apoptosis, beta cell degeneration and decrease insulin secretion, with amyloidosis affecting up to 80% of pancreatic islet cells in T2D. Therefore, intervening with polyphenolic compounds offers a novel approach to suppressing risk or progression to T2D. This review gives an update on the emerging mechanisms related to dietary polyphenol intake for the maintenance of glycaemic control and the prevention of T2D.

Asunto(s)

Glucemia/metabolismo , Polipéptido Amiloide de los Islotes Pancreáticos/metabolismo , Polifenoles/farmacología , Amiloide/sangre , Amiloidosis/tratamiento farmacológico , Animales , Diabetes Mellitus Tipo 2/tratamiento farmacológico , Humanos , Hiperglucemia/tratamiento farmacológico , Insulina/metabolismo , Secreción de Insulina , Células Secretoras de Insulina/efectos de los fármacos , Células Secretoras de Insulina/metabolismo , Islotes Pancreáticos/efectos de los fármacos , Islotes Pancreáticos/metabolismo , Modelos Animales , Ensayos Clínicos Controlados Aleatorios como Asunto

RESUMEN

Increasing evidence points to the cytotoxicity of islet amyloid polypeptide (IAPP) aggregates as a major contributor to the loss of ß-cell mass in type 2 diabetes. Prevention of IAPP formation represents a potential treatment to increase ß-cell survival and function. The IAPP inhibitory peptide, D-ANFLVH, has been previously shown to prevent islet amyloid accumulation in cultured human islets. To assess its activity in vivo, D-ANFLVH was administered by intraperitoneal injection into a human IAPP transgenic mouse model, which replicates type 2 diabetes islet amyloid pathology. The peptide was a potent inhibitor of islet amyloid deposition, resulting in reduced islet cell apoptosis and preservation of ß-cell area leading to improved glucose tolerance. These findings provide support for a key role of islet amyloid in ß-cell survival and validate the application of anti-amyloid compounds as therapeutic strategies to maintain normal insulin secretion in patients with type 2 diabetes.

Asunto(s)

Glucemia/efectos de los fármacos , Diabetes Mellitus Experimental/tratamiento farmacológico , Diabetes Mellitus Tipo 2/tratamiento farmacológico , Homeostasis/efectos de los fármacos , Polipéptido Amiloide de los Islotes Pancreáticos/antagonistas & inhibidores , Animales , Apoptosis/efectos de los fármacos , Diabetes Mellitus Experimental/sangre , Diabetes Mellitus Tipo 2/sangre , Modelos Animales de Enfermedad , Células Secretoras de Insulina/efectos de los fármacos , Polipéptido Amiloide de los Islotes Pancreáticos/uso terapéutico , Islotes Pancreáticos/efectos de los fármacos , Ratones , Ratones Transgénicos

RESUMEN

Amyloid deposits to the islets of Langerhans are responsible for the gradual loss of pancreatic ß-cells leading to type II diabetes mellitus. Human mature islet amyloid polypeptide (hIAPP), a 37-residue pancreatic hormone, has been identified as the primary component of amyloid fibrils forming these deposits. Several individual segments along the entire sequence length of hIAPP have been nominated as regions with increased amyloidogenic potential, such as regions 8-20, 20-29, and 30-37. A smaller fragment of the 8-20 region, spanning residues 8-16 of hIAPP has been associated with the formation of early transient α-helical dimers that promote fibrillogenesis and also as a core part of hIAPP amyloid fibrils. Utilizing our aggregation propensity prediction tools AmylPred and AmylPred2, we have identified the high aggregation propensity of the 8-16 segment of hIAPP. A peptide analog corresponding to this segment was chemically synthesized and its amyloidogenic properties were validated using electron microscopy, X-ray fiber diffraction, ATR FT-IR spectroscopy, and polarized microscopy. Additionally, two peptides introducing point mutations L12R and L12P, respectively, to the 8-16 segment, were chemically synthesized. Both mutations disrupt the α-helical properties of the 8-16 region and lower its amyloidogenic potential, which was confirmed experimentally. Finally, cytotoxicity assays indicate that the 8-16 segment of hIAPP shows enhanced cytotoxicity, which is relieved by the L12R mutation but not by the L12P mutation. Our results indicate that the chameleon properties and the high aggregation propensity of the 8-16 region may significantly contribute to the formation of amyloid fibrils and the overall cytotoxic effect of hIAPP.

Asunto(s)

Citotoxinas , Polipéptido Amiloide de los Islotes Pancreáticos , Péptidos , Agregado de Proteínas , Línea Celular , Citotoxinas/síntesis química , Citotoxinas/química , Citotoxinas/farmacología , Humanos , Polipéptido Amiloide de los Islotes Pancreáticos/química , Polipéptido Amiloide de los Islotes Pancreáticos/farmacología , Péptidos/síntesis química , Péptidos/química , Péptidos/farmacología

RESUMEN

BACKGROUND: The biologic attributes of the endocrine pancreas and the comparative endocrinology of islet amyloid polypeptide (IAPP) of fish are not well described in the literature. This study describes the endocrine pancreasof one teleostean fish. Ten captive Atlantic wolffish (Anarhichas lupus)from the Montreal Biodome were submitted for necropsy and their pancreata were collected. RESULTS: Grossly, all the fish pancreata examined contained 1-3 nodules of variable diameter (1-8 mm). Microscopically, the nodules were uniform, highly cellular, and composed of polygonal to elongated cells. Immunofluorescence for pancreatic hormones was performed. The nodules were immunoreactive for insulin most prominent centrally, but with IAPP and glucagon only in the periphery of the nodules. Exocrine pancreas was positive for chromogranin A. Not previously recognized in fish, IAPP immunoreactivity occurred in α, glucagon-containing, cells and did not co-localize with insulin in ß cells. The islet tissues were devoid of amyloid deposits. IAPP DNA sequencing was performed to compare the sequence among teleost fish and the potency to form amyloid fibrils. In silico analysis of the amino acid sequences 19-34 revealed that it was not amyloidogenic. CONCLUSIONS: Amyloidosis of pancreatic islets would not be expected as a spontaneous disease in the Atlantic wolffish. Our study underlines that this teleost fish is a potential candidate for pancreatic xenograft research.

RESUMEN

Herein, we report a 25-year-old male polar bear suffering from a pancreatic islet cell tumor. The aim of this report is to present a case of this rare tumor in a captive polar bear. The implication of potential risk factors such as high carbohydrate diet or the presence of amyloid fibril deposits was assessed. Necropsy examination revealed several other changes, including nodules observed in the liver, spleen, pancreas, intestine, and thyroid glands that were submitted for histopathologic analysis. Interestingly, the multiple neoplastic nodules were unrelated and included a pancreatic islet cell tumor. Immunohistochemistry of the pancreas confirmed the presence of insulin and islet amyloid polypeptide (IAPP) within the pancreatic islet cells. The IAPP gene was extracted from the paraffin-embedded liver tissue and sequenced. IAPP cDNA from the polar bear exhibits some differences as compared to the sequence published for several other species. Different factors responsible for neoplasms in bears such as diet, infectious agents, and industrial chemical exposure are reviewed. This case report raised several issues that further studies may address by evaluating the prevalence of cancers in captive or wild animals.

Asunto(s)

Animales de Zoológico , Tumores Neuroendocrinos/patología , Tumores Neuroendocrinos/veterinaria , Ursidae , Adenoma de Células de los Islotes Pancreáticos , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Resultado Fatal , Técnicas Histológicas/veterinaria , Inmunohistoquímica/veterinaria , Insulina/sangre , Polipéptido Amiloide de los Islotes Pancreáticos/genética , Polipéptido Amiloide de los Islotes Pancreáticos/metabolismo , Masculino , Datos de Secuencia Molecular , Factores de Riesgo , Análisis de Secuencia de ADN/veterinaria , Especificidad de la Especie

RESUMEN

Objective To investigate the ontogeny of the islet amyloid polypeptide(IAPP)and explore the relationship IAPP and other classical hormones in human fetal colon and rectum. Methods The localization of IAPP immunoreactive(IR) cells and 5 hydroxytryptamine(5 HT) IR cells in 31 human fetal colon and rectum from 9\|27 weeks of gestation was investigated with immunohistochemical SABC method. Results At 9 weeks of fetal age,a lot of 5 HT IR cells were found in the colon,but IAPP IR cells appeared at 18 weeks.In the rectum,both 5 HT and IAPP IR cells were present at 11 weeks,the number of 5 HT IR cells ascended gradually with fetus aged,reached a peak at 20 weeks and dropped gradually after 21 weeks,while in the whole fetus period,IAPP IR cells appeared fewer and scattered.The co localization of IAPP and 5 HT in some cells of colon and rectum was proved as compared with adjacent sections.Immunohistochemical double staining procedures on the same tissue section also showed that IAPP co existed with 5 HT in some cells.Conclusion\ During the human fetus,IAPP were synthesized and co existed with 5 HT in endocrine cells of the colon and rectum.The possible function on the co existence of IAPP and 5 HT in the colon and rectum of fetal was discussed. [