Deposition Of Islet Amyloid Polypeptide Research Articles

Structural Insights into Seeding Mechanisms of hIAPP Fibril Formation.

The deposition of islet amyloid polypeptide (hIAPP) fibrils is a hallmark of β-cell death in type II diabetes. In this study, we employ state-of-the-art MAS solid-state spectroscopy to investigate the previously elusive N-terminal region of hIAPP fibrils, uncovering both rigidity and heterogeneity. Comparative analysis between wild-type hIAPP and a disulfide-deficient variant (hIAPPC2S,C7S) unveils shared fibril core structures yet strikingly distinct dynamics in the N-terminus. Specifically, the variant fibrils exhibit extended β-strand conformations, facilitating surface nucleation. Moreover, our findings illuminate the pivotal roles of specific residues in modulating secondary nucleation rates. These results deepen our understanding of hIAPP fibril assembly and provide critical insights into the molecular mechanisms underpinning type II diabetes, holding promise for future therapeutic strategies.

Islet amyloid polypeptide triggers α-synuclein pathology in Parkinson's disease.

Pathologic aggregation and prion-like propagation of α-synuclein (α-syn) are the hallmarks of Parkinson's disease (PD). Emerging evidence shows that type 2 diabetes mellitus (T2DM) is a risk factor for PD. Interestingly, T2DM is characterized by the amyloid deposition of islet amyloid polypeptide (IAPP) in the pancreas. Although T2DM and PD share pathological similarities, the underlying molecular mechanisms bridging these two diseases remain unknown. Here, we report that IAPP co-deposits with α-syn in the brains of PD patients. IAPP interacts with α-syn and accelerates its aggregation. In addition, the IAPP-seeded α-syn fibrils show enhanced seeding activity and neurotoxicity compared with pure α-syn fibrils in vitro and in vivo. Strikingly, intravenous injection of IAPP fibrils into α-syn A53T transgenic mice or human SNCA transgenic mice accelerated the aggregation of α-syn and PD-like motor deficits. Taken together, these findings support that IAPP acts as a trigger of α-syn pathology in PD, and provide a mechanistic explanation for the increased risk and faster progression of PD in patients with T2DM.

Plasma IAPP-Autoantibody Levels in Alzheimer's Disease Patients Are Affected by APOE4 Status.

Pancreas-derived islet amyloid polypeptide (IAPP) crosses the blood-brain barrier and co-deposits with amyloid beta (Aβ) in brains of type 2 diabetes (T2D) and Alzheimer's disease (AD) patients. Depositions might be related to the circulating IAPP levels, but it warrants further investigation. Autoantibodies recognizing toxic IAPP oligomers (IAPPO) but not monomers (IAPPM) or fibrils have been found in T2D, but studies on AD are lacking. In this study, we have analyzed plasma from two cohorts and found that levels of neither immunoglobulin (Ig) M, nor IgG or IgA against IAPPM or IAPPO were altered in AD patients compared with controls. However, our results show significantly lower IAPPO-IgA levels in apolipoprotein E (APOE) 4 carriers compared with non-carriers in an allele dose-dependent manner, and the decrease is linked to the AD pathology. Furthermore, plasma IAPP-Ig levels, especially IAPP-IgA, correlated with cognitive decline, C-reactive protein, cerebrospinal fluid Aβ and tau, neurofibrillary tangles, and brain IAPP exclusively in APOE4 non-carriers. We speculate that the reduction in IAPPO-IgA levels may be caused by increased plasma IAPPO levels or masked epitopes in APOE4 carriers and propose that IgA and APOE4 status play a specific role in clearance of circulatory IAPPO, which may influence the amount of IAPP deposition in the AD brain.

Urolithin B: Two-way attack on IAPP proteotoxicity with implications for diabetes.

Diabetes is one of the major metabolic diseases worldwide. Despite being a complex systemic pathology, the aggregation and deposition of Islet Amyloid Polypeptide (IAPP), or amylin, is a recognized histopathological marker of the disease. Although IAPP proteotoxicity represents an important trigger of β-cell dysfunction and ultimately death, its exploitation as a therapeutic tool remains underdeveloped. The bioactivity of (poly)phenols towards inhibition of pathological protein aggregation is well known, however, most of the identified molecules have limited bioavailability. Using a strategy combining in silico, cell-free and cell studies, we scrutinized a unique in-house collection of (poly)phenol metabolites predicted to appear in the human circulation after (poly)phenols ingestion. We identified urolithin B as a potent inhibitor of IAPP aggregation and a powerful modulator of cell homeostasis pathways. Urolithin B was shown to affect IAPP aggregation pattern, delaying the formation of amyloid fibrils and altering their size and morphology. The molecular mechanisms underlying urolithin B-mediated protection include protein clearance pathways, mitochondrial function, and cell cycle ultimately rescuing IAPP-mediated cell dysfunction and death. In brief, our study uncovered urolithin B as a novel small molecule targeting IAPP pathological aggregation with potential to be exploited as a therapeutic tool for mitigating cellular dysfunction in diabetes. Resulting from the colonic metabolism of dietary ellagic acid in the human body, urolithin B bioactivity has the potential to be explored in nutritional, nutraceutical, and pharmacological perspectives.

Type 2 Diabetes Mellitus, Platelet Activation and Alzheimer's Disease: A Possible Connection.

Type 2 diabetes mellitus DM (T2DM) is associated with a 70% increased risk for dementia, including Alzheimer's disease (AD). Insulin resistance has been proposed to play a pivotal role in both T2DM and AD and the concept of "brain insulin resistance" has been suggested as an interpretation to the growing literature regarding cognitive impairment and T2DM. Subjects with T2DM present an abnormal platelet reactivity that together with insulin resistance, hyperglycaemia and dyslipidaemia effect the vascular wall by a series of events including endothelial dysfunction, oxidative stress and low-grade inflammation. Activated platelets directly contribute to cerebral amyloid angiopathy (CAA) by promoting the formation of β-amyloid (Aβ) aggregates and that Aβ, in turn, activates platelets, creating a feed-forward loop suggesting the involvement of platelets in the AD pathogenesis. Moreover, islet amyloid polypeptide deposition, co-localized with Aβ deposits, is a common finding in the brain of patients with T2DM. These observations raise the intriguing prospect that traditional or novel antiplatelet therapeutic strategies may alleviate fibril formation and could be used in the prevention or treatment of AD subjects with diabetes.

An environmentally sensitive molecular rotor as a NIR fluorescent probe for the detection of islet amyloid polypeptide

The deposits of human islet amyloid polypeptide (IAPP), also called amylin, in the pancreas have been postulated to be a factor of pancreatic β-cell dysfunction and is one of the common pathological hallmarks of type II diabetes mellitus (T2DM). Therefore, it is imperative to gain an in-depth understanding of the formation of these aggregates. In this study, we demonstrate a rationally-designed strategy of an environmentally sensitive near-infrared (NIR) molecular rotor utilizing thioflavin T (ThT) as a scaffold for IAPP deposits. We extended the π delocalized system not only to improve the viscosity sensitivity but also to prolong the emission wavelength to the NIR region. A naphthalene moiety was also introduced to adjust the sensitivity of our designed probes to differentiate the binding microenvironment polarity of different targeted proteins. As a result, a novel NIR fluorogenic probe toward IAPP aggregates, namely AmySP-4-Nap-Ene, was first developed. When attached to different protein aggregates, this probe exhibited distinct fluorescence emission profiles. In a comparison with ThT, the fluorescence emission of non-ionic AmySP-4-Nap-Ene exhibits a significant difference between the presence of non-fibrillar and fibrillar IAPP and displays a higher binding affinity toward IAPP fibrils. Further, the AmySP-4-Nap-Ene can be utilized to monitor IAPP accumulating process and image fibrils both in vitro and in living cells.

Islet amyloid polypeptide cross-seeds tau and drives the neurofibrillary pathology in Alzheimer\u2019s disease

BackgroundThe pathologic accumulation and aggregation of tau is a hallmark of tauopathies including Alzheimer’s disease (AD). However, the molecular mechanisms mediating tau aggregation in AD remain elusive. The incidence of AD is increased in patients with type 2 diabetes (T2DM), which is characterized by the amyloid deposition of islet amyloid polypeptide (IAPP) in the pancreas. However, the molecular mechanisms bridging AD and T2DM remain unknown.MethodsWe first examined the presence of IAPP in the neurofibrillary tangles of AD patients. Then we tested the effect of IAPP on tau aggregation. The biochemical and biological characteristics of the IAPP-tau fibrils were tested in vitro. The seeding activity and neurotoxicity of the IAPP-tau fibrils were confirmed in cultured neurons. Lastly, the effect of IAPP on tau pathology and cognitive impairments was determined by injecting the IAPP-tau fibrils and IAPP fibrils into the hippocampus of tau P301S mice.ResultsWe found that IAPP interacts with tau and accelerates the formation of a more toxic strain, which shows distinct morphology with enhanced seeding activity and neurotoxicity in vitro. Intrahippocampal injection of the IAPP-tau strain into the tau P301S transgenic mice substantially promoted the spreading of tau pathology and induced more severe synapse loss and cognitive deficits, when compared with tau fibrils. Furthermore, intracerebral injection of synthetic IAPP fibrils initiated tauopathy in the brain of tau P301S transgenic mice.ConclusionsThese observations indicate that IAPP acts as a crucial mediator of tau pathology in AD, and provide a mechanistic explanation for the higher risk of AD in individuals with T2DM.

Ablation of Kex2 activity enhances proIAPP proteotoxicity in yeast

Pancreatic deposition of Islet Amyloid PolyPeptide (IAPP) is a histopathological hallmark of type 2 diabetes. Inadequate processing of immature IAPP by proprotein convertases (PCs) leads to the accumulation of unprocessed forms, which in turn favors increased aggregate formation in pancreatic β-cells. Kexin 2 (Kex2) of Saccharomyces cerevisiae is the prototype of eukaryotic PCs family, but to date no direct correlations between Kex2 activity and preproIAPP processing in yeast have been reported. In this study we aimed to address the possible role of Kex2 on IAPP maturation as a tool to investigate the contribution of impaired processing towards IAPP proteototoxicity. Genetically modified S. cerevisiae models lacking the KEX2 gene and carrying different chimeric fusions of human IAPP linked to GFP were used. The cytotoxic effects of Kex2 ablation were assessed by means of growth curve analysis and cell viability assays using flow cytometry. IAPP protein profile was evaluated by immunoblotting assays using an anti-IAPP antibody. Intracellular IAPP aggregates were monitored by confocal fluorescence microscopy. Data showed that kex2 mutants exhibit growth defects, potentiated by preproIAPP-GFP, proIAPP-GFP and mature IAPP-GFP expression with an increased cytotoxicity for proIAPP-GFP. Notwithstanding, Kex2 absence does not seem to affect IAPP protein pattern nor the frequency/distribution of intracellular IAPP aggregates in yeast. Our findings suggest that Kex2 is not essential for IAPP processing in yeast, at least under the conditions tested. Keywords: Amylin, Islet Amyloid Polypeptide (IAPP), Kexin 2, Prohormone processing, Saccharomyces cerevisiae

Small molecules breaking down islet amyloid polypeptide self‐assembly

Amyloid deposition is a recognised feature of the islets in the majority of type 2 diabetic patients. These deposits originate from islet amyloid polypeptide (IAPP). Normally, IAPP is secreted along with insulin from pancreatic β‐cells and has hormonal functions related to satiety. However, IAPP is one of the most potent amyloidogenic proteins. Deposition of IAPP is associated with β‐cell death and diabetes progression. Drugs to inhibit pancreatic amyloidosis are not available. We have prepared a small molecule screening library to inhibit pancreatic amyloidosis. Our central hypothesis is that IAPP fibril formation (fibrillization) and deposition can be modulated by IAPP‐interactive compounds. We aim to establish structure‐activity relationships by which our small molecules impede IAPP fibrillization. Our primary approach, thioflavin T (ThT) assay, represented a major tool for the determination of IAPP fibrillization and inhibition by small molecules. For the most potent molecules, the abrogation of cytotoxic intermediate species (i.e. oligomerization leading to fibril formation) was determined with photo‐induced cross‐linking of unmodified protein. To confirm the inhibitory effect morphologically, electron microscopy analysis was performed to detect IAPP fibrils directly. Disaggregation of preformed fibrils by different compounds was studied with ThT assays and electron microscopy. The 1st‐tier screening method (ThT assay) identified several lead compounds to target IAPP. The oligomerization of IAPP was abrogated by JF‐19‐029. JF‐19‐029 and NBMI‐19‐013 deteriorated preformed fibrils. Few molecules have been reported to break down mature fibrils. We hope to open a new therapeutic approach to reduce type 2 diabetes progression.

Vaccination Against Amyloidogenic Aggregates in Pancreatic Islets Prevents Development of Type 2 Diabetes Mellitus.

Type 2 diabetes mellitus (T2DM) is a chronic progressive disease characterized by insulin resistance and insufficient insulin secretion to maintain normoglycemia. The majority of T2DM patients bear amyloid deposits mainly composed of islet amyloid polypeptide (IAPP) in their pancreatic islets. These—originally β-cell secretory products—extracellular aggregates are cytotoxic for insulin-producing β-cells and are associated with β-cell loss and inflammation in T2DM advanced stages. Due to the absence of T2DM preventive medicaments and the presence of only symptomatic drugs acting towards increasing hormone secretion and action, we aimed at establishing a novel disease-modifying therapy targeting the cytotoxic IAPP deposits in order to prevent the development of T2DM. We generated a vaccine based on virus-like particles (VLPs), devoid of genomic material, coupled to IAPP peptides inducing specific antibodies against aggregated, but not monomeric IAPP. Using a mouse model of islet amyloidosis, we demonstrate in vivo that our vaccine induced a potent antibody response against aggregated, but not soluble IAPP, strikingly preventing IAPP depositions, delaying onset of hyperglycemia and the induction of the associated pro-inflammatory cytokine Interleukin 1β (IL-1β). We offer the first cost-effective and safe disease-modifying approach targeting islet dysfunction in T2DM, preventing pathogenic aggregates without disturbing physiological IAPP function.

Mechanism study on the abnormal accumulation and deposition of islet amyloid polypeptide by cold-spray ionization mass spectrometry.

The abnormal accumulation and deposition of islet amyloid polypeptide (IAPP) are important causes of type-2 diabetes mellitus (T2DM). The common anti-amyloid strategy employs inhibitors to prevent the formation of oligomers and the cytotoxicity caused by them, thus reducing the production of amyloid fibres. Therefore, the real characterization of the oligomers formed at the early stage of aggregation is crucial to understanding the structure of IAPP and the drug development of T2DM. For the first time, in this study, native cold-spray ionization mass spectrometry (CSI-MS) technology was employed to characterize the oligomers. It was found that CSI was more suitable for the determination of these unstable species compared to traditional ESI-MS. The ionic strengths, organic solvent and pH all had effects on the characterization of oligomers and the stability of protein conformation. The MS/MS experiments showed that odd-charge dimer ions were mainly composed of two monomer products. Moreover, a CSI-MS method for the rapid screening of IAPP-inhibitors was established and two of the most potential inhibitors (rutin and quercitrin) were screened from a series of flavonoids. Then, the structure-activity relationship and the mechanism between flavonoids and IAPP were studied. The results showed that 3-OH and sugar chains play a vital role and hydrogen bonds are the main binding force. We further confirmed that rutin and quercitrin could effectively inhibit the fibre formation of IAPP by fluorescence and TEM experiments. This study provides a new insight for analyzing the structure of IAPP and screening potential drugs for T2DM.

P724Antibody treatment against pathological pancreatic islet amyloid polypeptide (IAPP) aggregates restores endothelial dysfunction in human-IAPP transgenic rats

Abstract Background Islet amyloid polypeptide (IAPP; or amylin) is produced in pancreatic B-cells and co-secreted with insulin in response to nutrients. In insulin resistance and type 2 diabetes (T2D), higher secretion and impaired processing of IAPP results in its aggregation, contributing to amyloid-induced apoptosis of pancreatic B-cells. Insight into IAPP's role in diabetic endothelial dysfunction is scarce. Purpose Rats transgenic for human IAPP (hIAPP), which in contrast to rodent IAPP produces amyloid deposits and contributes to diabetes due to B-cell failure, were studied to understand the mechanisms of endothelial dysfunction in T2D and test the vasoprotective actions of an anti-hIAPP antibody. Methods Male hemizygous transgenic Sprague-Dawley rats with islet B-cell expression of hIAPP (TG) and wild-type (WT) controls were sacrificed at 2, 3, 6- and 9-months age to assess endothelial function. In a second experiment, TG rats received weekly injections of antibody against aggregated hIAPP (3 mg/kg; TG-Ab) from 3–12 months of age; TG and WT controls received PBS. Oral glucose tolerance was assessed before harvesting. At the respective time points (12 mts in exp. 2), thoracic aortic rings were isolated and subjected to ex vivo isometric tension recording. After contraction with norepinephrine (NE 1x10–7 mol/L), cumulative relaxation responses were performed to glucagon-like peptide-1 (GLP-1; 10–12 to 10–6 mol/L) and insulin (10–11 to 10–6 mol/L). Pancreas and aortic arch samples were used for immunostaining of hIAPP antibody engagement. Results GLP-1 and insulin-mediated vasodilation was impaired in 3 month-old TG rats compared to WT. Glucose intolerance appeared in TG rats at 6 months in comparison to WT (p<0.0001), indicating that endothelial dysfunction in TG rats precedes the onset of glucose intolerance. Anti-hIAPP antibody showed selectivity against aggregated IAPP in pancreatic islets, but there was no target engagement in the aortic arch, questioning a pathogenic role of IAPP deposition in the aortic wall. At 12 months, glucose control in TG-Ab rats was improved in comparison to TG control rats (p<0.013). Vasodilatation in TG-Ab rats was restored in response to GLP-1 (35.5% ± 4.6 vs. 16.0% ± 3.1 in TG controls), similar to that of WT rats (35.5% ± 6.5). Vasodilatation in response to insulin (48.9% ± 4.2) was improved in comparison to both TG (29.4% ± 3.0) and WT controls (32.5% ± 5.7) (p<0.0001; 2-way ANOVA, n=6–11 for all groups. Conclusion Early endothelial dysfunction develops in hIAPP rats compared to WT. Endothelial dysfunction is restored by the anti-hIAPP antibody treatment via improved oral glucose tolerance, but it remains unclear whether this effect is due to a local action in the aorta or a secondary effect, e.g. due to a reduction in pancreatic IAPP deposition.

Zinc Chelator Inhibits Zinc-Induced Islet Amyloid Polypeptide Deposition and Apoptosis in INS-1 Cells

Amyloid deposition and beta cell apoptosis are characteristic pathological features of type 2 diabetes mellitus (DM). Islet amyloid polypeptide (IAPP) is the most abundant component of amyloid deposition. Monomeric IAPP does not form amyloid deposition, but the fibrous IAPP may aggregate and form amyloid deposits. Previous studies have shown that zinc is closely related to IAPP deposition through crosslink with monomeric IAPP into fibrous aggregates. In this study, we aimed to investigate whether chelating zinc could inhibit zinc-induced amyloid deposits and apoptosis of islet beta cell. N, N, N', N'-Tetrakis (2-pyridylmethyl) ethylenediamine (TPEN) is a specific chelator of zinc, with membrane permeability. It could effectively reduce the concentration of intracellular zinc. So, we used TPEN to treat hIAPP-transfected INS-1 cells. By MTT assay, the concentration (1μM) and incubation time (12h) of TPEN without affecting cell viability were determined. The results showed that TPEN reduced zinc-induced IAPP deposition in the culture system. Furthermore, we analyzed the effect of zinc and TPEN on the apoptosis and insulin level. The results showed that TPEN could reverse zinc-induced INS-1 cell apoptosis and insulin secretion. And the anti-apoptosis effects of TPEN is related to extracellular regulated protein kinases (ERK)/c-jun N-terminal kinase (JNK) signaling pathway. The present data indicated that chelating zinc could inhibit zinc-induced amyloid deposition and beta cell apoptosis. Thus, maintaining zinc homeostasis in islet beta cell might become a useful strategy for DM therapy.

ALZHEIMER’S DISEASE THERAPEUTIC APPROACHES

A protein is a large biomolecule which consists of one or more chains of amino acid residues. Proteins exhibit a biological phenomenon in which, they are misfolded as aggregates (i.e., accumulate and clump together) either intra- or extracellularly. This process plays a central role in the pathogenesis of Alzheimer’s disease (AD) and diabetes mellitus (DM) - 2 and common for many degenerative diseases. In this case, the histopathological consequences of protein misfolding such as sensile plaques and neurofibrillary tangles in AD and lewy bodies in Parkinson’s disease occur. 8–10% of adult population shares risk factors with AD. Amyloid fibrils which build up in tissue as an abnormal protein form Amyloidosis. Conformational change in three-dimensional structure forms amyloid fibrils. Type 2 DM is characterized by the deposition of islet amyloid polypeptide within beta cells of the pancreas which leads to chronic cerebral hypoperfusion that result in degeneration of neuroglial cells.

Induction of IAPP amyloid deposition and associated diabetic abnormalities by a prion-like mechanism.

Although a large proportion of patients with type 2 diabetes (T2D) accumulate misfolded aggregates composed of the islet amyloid polypeptide (IAPP), its role in the disease is unknown. Here, we show that pancreatic IAPP aggregates can promote the misfolding and aggregation of endogenous IAPP in islet cultures obtained from transgenic mouse or healthy human pancreas. Islet homogenates immunodepleted with anti-IAPP-specific antibodies were not able to induce IAPP aggregation. Importantly, intraperitoneal inoculation of pancreatic homogenates containing IAPP aggregates into transgenic mice expressing human IAPP dramatically accelerates IAPP amyloid deposition, which was accompanied by clinical abnormalities typical of T2D, including hyperglycemia, impaired glucose tolerance, and a substantial reduction on β cell number and mass. Finally, induction of IAPP deposition and diabetic abnormalities were also induced in vivo by administration of IAPP aggregates prepared in vitro using pure, synthetic IAPP. Our findings suggest that some of the pathologic and clinical alterations of T2D might be transmissible through a similar mechanism by which prions propagate in prion diseases.

Sex and Immunogen-Specific Benefits of Immunotherapy Targeting Islet Amyloid Polypeptide in Transgenic and Wild-Type Mice.

Type 2 diabetes mellitus is characterized by the deposition of islet amyloid polypeptide (IAPP) as amyloid in islets, a process thought to be toxic to β-cells. To determine the feasibility of targeting these aggregates therapeutically, we vaccinated transgenic (Tg) mice that overexpress human IAPP and were fed a high-fat diet to promote their diabetic phenotype. Our findings indicate that prophylactic vaccination with IAPP and its derivative IAPP7-19-TT, protects wild-type female mice, but not males, from obesity-induced early mortality, and the derivative showed a strong trend for prolonging the lifespan of Tg females but not males. Furthermore, IAPP7-19-TT-immunized Tg females cleared a glucose bolus more efficiently than controls, while IAPP-immunized Tg females showed an impaired ability to clear a glucose bolus compared to their adjuvant injected Tg controls. Interestingly, IAPP or IAPP7-19-TT treatments had no effect on glucose clearance in Tg males. Overall, these beneficial effects of IAPP targeted immunization depend on Tg status, sex, and immunogen. Hence, future studies in this field should carefully consider these variables that clearly affect the therapeutic outcome. In conclusion, IAPP targeting immunotherapy may have benefits in patients with type 2 diabetes.

Influence of the Human and Rat Islet Amyloid Polypeptides on Structure of Phospholipid Bilayers: Neutron Reflectometry and Fluorescence Microscopy Studies.

Neutron reflectivity (NR) and fluorescent microscopy (FM) were used to study the interactions of human (hIAPP) and rat (rIAPP) islet amyloid polypeptides with several formulations of supported model lipid bilayers at the solid-liquid interface. Aggregation and deposition of islet amyloid polypeptide is correlated with the pathology of many diseases, including Alzheimer's, Parkinson, and type II diabetes (T2DM). A central component of T2DM pathology is the deposition of fibrils in the endocrine pancreas, which is toxic to the insulin secreting β-cells. The molecular mechanism by which the cell death occurs is not yet understood, but existing evidence points toward interactions of IAPP oligomers with cellular membranes in a manner leading to loss of their integrity. Our NR and FM results showed that the human sequence variant, hIAPP, had little or no effect on bilayers composed of saturated-acyl chains like zwitterionic DPPC, anionic DPPG, and mixed 80:20 mol % DPPC:DPPG bilayers. In marked contrast, the bilayer structure and stability of anionic unsaturated DOPG were sensitive to protein interaction, and the bilayer was partly solubilized by hIAPP under the conditions used here. The rIAPP, which is considered less toxic, had no perturbing effects on any of the above membrane formulations. Understanding the conditions that result in membrane disruption by hIAPP can be crucial in developing counter strategies to fight T2DM and also physicochemically similar neurodegenerative diseases such as Alzheimer's.

Protein misfolding and aggregation in Alzheimer's disease and type 2 diabetes mellitus.

In general, proteins can only execute their various biological functions when they are appropriately folded. Their amino acid sequence encodes the relevant information required for correct three-dimensional folding, with or without the assistance of chaperones. The challenge associated with understanding protein folding is currently one of the most important aspects of the biological sciences. Misfolded protein intermediates form large polymers of unwanted aggregates and are involved in the pathogenesis of many human diseases, including Alzheimer's disease (AD) and Type 2 diabetes mellitus (T2DM). AD is one of the most prevalent neurological disorders and has worldwide impact; whereas T2DM is considered a metabolic disease that detrementally influences numerous organs, afflicts some 8% of the adult population, and shares many risk factors with AD. Research data indicates that there is a widespread conformational change in the proteins involved in AD and T2DM that form β-sheet like motifs. Although conformation of these β-sheets is common to many functional proteins, the transition from α-helix to β-sheet is a typical characteristic of amyloid deposits. Any abnormality in this transition results in protein aggregation and generation of insoluble fibrils. The abnormal and toxic proteins can interact with other native proteins and consequently catalyze their transition into the toxic state. Both AD and T2DM are prevalent in the aged population. AD is characterized by the accumulation of amyloid-β (Aβ) in brain, while T2DM is characterized by the deposition of islet amyloid polypeptide (IAPP, also known as amylin) within beta-cells of the pancreas. T2DM increases pathological angiogenesis and immature vascularisation. This also leads to chronic cerebral hypoperfusion, which results in dysfunction and degeneration of neuroglial cells. With an abundance of common mechanisms underpinning both disorders, a significant question that can be posed is whether T2DM leads to AD in aged individuals and the associations between other protein misfolding diseases.

Matrix Metalloproteinase-9 Reduces Islet Amyloid Formation by Degrading Islet Amyloid Polypeptide

Deposition of islet amyloid polypeptide (IAPP) as amyloid is a pathological hallmark of the islet in type 2 diabetes, which is toxic to β-cells. We previously showed that the enzyme neprilysin reduces islet amyloid deposition and thereby reduces β-cell apoptosis, by inhibiting fibril formation. Two other enzymes, matrix metalloproteinase (MMP)-2 and MMP-9, are extracellular gelatinases capable of degrading another amyloidogenic peptide, Aβ, the constituent of amyloid deposits in Alzheimer disease. We therefore investigated whether MMP-2 and MMP-9 play a role in reducing islet amyloid deposition. MMP-2 and MMP-9 mRNA were present in mouse islets but only MMP-9 activity was detectable. In an islet culture model where human IAPP (hIAPP) transgenic mouse islets develop amyloid but nontransgenic islets do not, a broad spectrum MMP inhibitor (GM6001) and an MMP-2/9 inhibitor increased amyloid formation and the resultant β-cell apoptosis. In contrast, a specific MMP-2 inhibitor had no effect on either amyloid deposition or β-cell apoptosis. Mass spectrometry demonstrated that MMP-9 degraded amyloidogenic hIAPP but not nonamyloidogenic mouse IAPP. Thus, MMP-9 constitutes an endogenous islet protease that limits islet amyloid deposition and its toxic effects via degradation of hIAPP. Because islet MMP-9 mRNA levels are decreased in type 2 diabetic subjects, islet MMP-9 activity may also be decreased in human type 2 diabetes, thereby contributing to increased islet amyloid deposition and β-cell loss. Approaches to increase islet MMP-9 activity could reduce or prevent amyloid deposition and its toxic effects in type 2 diabetes.

Inhibition of Deoxyhypusine Synthase Enhances Islet β Cell Function and Survival in the Setting of Endoplasmic Reticulum Stress and Type 2 Diabetes

Islet β cell dysfunction resulting from inflammation, ER stress, and oxidative stress is a key determinant in the progression from insulin resistance to type 2 diabetes mellitus. It was recently shown that the enzyme deoxyhypusine synthase (DHS) promotes early cytokine-induced inflammation in the β cell. DHS catalyzes the conversion of lysine to hypusine, an amino acid that is unique to the translational elongation factor eIF5A. Here, we sought to determine whether DHS activity contributes to β cell dysfunction in models of type 2 diabetes in mice and β cell lines. A 2-week treatment of obese diabetic C57BLKS/J-db/db mice with the DHS inhibitor GC7 resulted in improved glucose tolerance, increased insulin release, and enhanced β cell mass. Thapsigargin treatment of β cells in vitro induces a picture of ER stress and apoptosis similar to that seen in db/db mice; in this setting, DHS inhibition led to a block in CHOP (CAAT/enhancer binding protein homologous protein) production despite >30-fold activation of Chop gene transcription. Blockage of CHOP translation resulted in reduction of downstream caspase-3 cleavage and near-complete protection of cells from apoptotic death. DHS inhibition appeared to prevent the cytoplasmic co-localization of eIF5A with the ER, possibly precluding the participation of eIF5A in translational elongation at ER-based ribosomes. We conclude that hypusination by DHS is required for the ongoing production of proteins, particularly CHOP, in response to ER stress in the β cell.