Islet Amyloid Polypeptide Fibrils Research Articles

Islet amyloid polypeptide fibril catalyzes amyloid-β aggregation by promoting fibril nucleation rather than direct axial growth

Aberrant aggregation of amyloid-β (Aβ) and islet amyloid polypeptide (IAPP) into amyloid fibrils underlies the pathogenesis of Alzheimer's disease (AD) and type 2 diabetes (T2D), respectively. T2D significantly increases AD risk, with evidence suggesting that IAPP and Aβ co-aggregation and cross-seeding might contribute to the cross-talk between two diseases. Experimentally, preformed IAPP fibril seeds can accelerate Aβ aggregation, though the cross-seeding mechanism remains elusive. Here, we computationally demonstrated that Aβ monomer preferred to bind to the elongation ends of preformed IAPP fibrils. However, due to sequence mismatch, the Aβ monomer could not directly grow onto IAPP fibrils by forming multiple stable β-sheets with the exposed IAPP peptides. Conversely, in our control simulations of self-seeding, the Aβ monomer could axially grow on the Aβ fibril, forming parallel in-register β-sheets. Additionally, we showed that the IAPP fibril could catalyze Aβ fibril nucleation by promoting the formation of parallel in-register β-sheets in the C-terminus between bound Aβ peptides. This study enhances our understanding of the molecular interplay between Aβ and IAPP, shedding light on the cross-seeding mechanisms potentially linking T2D and AD. Our findings also underscore the importance of clearing IAPP deposits in T2D patients to mitigate AD risk.

IAPP - oligomerisation levels in plasma of people with type 2 diabetes

Islet amyloid polypeptide (IAPP) is co-secreted with insulin from pancreatic ß-cells. Its oligomerisation is regarded as disease driving force in type 2 diabetes (T2D) pathology. Up to now, IAPP oligomers have been detected in affected tissues. IAPP oligomer concentrations in blood have not been analysed so far. Using the IAPP single-oligomer-sensitive and monomer-insensitive surface-based fluorescence intensity distribution analysis (sFIDA) technology, levels of IAPP oligomers in blood plasma from healthy controls and people with T2D in different disease stages where determined. Subsequently, the level of IAPP oligomerisation was introduced as the ratio between the IAPP oligomers determined with sFIDA and the total IAPP concentration determined with ELISA. Highest oligomerisation levels were detected in plasma of people with T2D without late complication and without insulin therapy. Their levels stand out significantly from the control group. Healthy controls presented with the lowest oligomerisation levels in plasma. In people with T2D without complications, IAPP oligomerisation levels correlated with disease duration. The results clearly demonstrate that IAPP oligomerisation in insulin-naïve patients correlates with duration of T2D. Although a correlation per se does not identify, which is cause and what is consequence, this result supports the hypothesis that IAPP aggregation is the driving factor of T2D development and progression. The alternative and conventional hypothesis explains development of T2D with increasing insulin resistance causing exhaustion of pancreatic ß-cells due to over-secretion of insulin, and thus IAPP, too, resulting in subsequent IAPP aggregation and fibril deposition in the pancreas. Further experiments and comparative analyses with primary tissues are warranted.

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.

TPE conjugated islet amyloid polypeptide probe for detection of peptide oligomers

Islet amyloid polypeptide (IAPP), also known as amylin, is a polypeptide hormone co-secreted with insulin by pancreatic β-cells. In general, IAPP is soluble and lacks a defined structure. However, under certain conditions, these peptides tend to aggregate into soluble oligomers, eventually forming insoluble amyloid fibrils with typical cross-β-sheet structures. Amylin aggregates, therefore, have been regarded as one of the hallmarks of type II diabetes (T2D). Among these aggregated species, oligomers were shown to exhibit significant cytotoxicity, leading to impaired β-cell function and reduced β-cell mass. Monitoring of oligomer appearance during IAPP fibrillation is of particular interest. In this study, we successfully grafted an aggregation-induced emission molecule, tetraphenylethylene (TPE), at the N-terminus of IAPP. By mixing a small amount of TPE-labeled IAPP with unlabeled IAPP, we were able to detect an increase in TPE fluorescence during the nucleation phase of IAPP aggregation in vitro. It may enable real-time monitoring of IAPP oligomer formation and is further applied in the diagnosis of T2D.

A human antibody against pathologic IAPP aggregates protects beta cells in type 2 diabetes models

In patients with type 2 diabetes, pancreatic beta cells progressively degenerate and gradually lose their ability to produce insulin and regulate blood glucose. Beta cell dysfunction and loss is associated with an accumulation of aggregated forms of islet amyloid polypeptide (IAPP) consisting of soluble prefibrillar IAPP oligomers as well as insoluble IAPP fibrils in pancreatic islets. Here, we describe a human monoclonal antibody selectively targeting IAPP oligomers and neutralizing IAPP aggregate toxicity by preventing membrane disruption and apoptosis in vitro. Antibody treatment in male rats and mice transgenic for human IAPP, and human islet-engrafted mouse models of type 2 diabetes triggers clearance of IAPP oligomers resulting in beta cell protection and improved glucose control. These results provide new evidence for the pathological role of IAPP oligomers and suggest that antibody-mediated removal of IAPP oligomers could be a pharmaceutical strategy to support beta cell function in type 2 diabetes.

Diabetes mellitus drug discovery: insights into targeting feline and human amylin with small molecules

Background Type 2 diabetes (T2D) is a health concern for both humans and cats, with cases rising over the past decade. Around 70% of patients from either species exhibit pancreatic aggregates of islet amyloid polypeptide (IAPP), a protein that proves toxic upon misfolding. These misfolded protein aggregates congregate in the islets of Langerhans of the pancreas, diminishing the capability of β-cells to produce insulin and further perpetuating disease. Objective Our team’s drug discovery program is investigating newly synthesized compounds that could diminish aggregates of both human and feline IAPP, potentially disrupting the progression of T2D. Material and methods We prepared 24 compounds derived from diaryl urea, as ureas have previously demonstrated great potential at reducing accumulations of misfolded proteins. Biophysical methods were employed to analyze the anti-aggregation activity of these compounds at inhibiting and/or disrupting IAPP fibril formation in vitro. Results The results demonstrate that compounds 12 and 24 were most effective at reducing the fibrillization and aggregation of both human and feline IAPP. When compared with the control for each experiment, samples treated with either compound 12 or 24 exhibited fewer accumulations of amyloid-like fibrils. Conclusion Urea-based compounds, such as compounds 12 and 24, may prove crucial in future pre-clinical studies in the search for therapeutics for T2D.

Direct Observation of Seeded Conformational Conversion of hIAPP In Silico Reveals the Mechanisms for Morphological Dependence and Asymmetry of Fibril Growth.

Rapid growth of amyloid fibrils via a seeded conformational conversion of monomers is a critical step of fibrillization and important for disease transmission and progression. Amyloid fibrils often display diverse morphologies with distinct populations, and yet the molecular mechanisms of fibril elongation and their corresponding morphological dependence remain poorly understood. Here, we computationally investigated the single-molecular growth of two experimentally resolved human islet amyloid polypeptide fibrils of different morphologies. In both cases, the incorporation of monomers into preformed fibrils was observed. The conformational conversion dynamics was characterized by a small number of fibril growth intermediates. Fibril morphology affected monomer binding at fibril elongation and lateral surfaces as well as the seeded conformational conversion dynamics at the fibril ends, resulting in different fibril elongation rates and populations. We also observed an asymmetric fibril growth as in our prior experiments, attributing to differences of two fibril ends in terms of their local surface curvatures and exposed hydrogen-bond donors and acceptors. Together, our mechanistic findings afforded a theoretical basis for delineating different amyloid strains-entailed divergent disease progression.

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.

Destabilization of Human Islet Amyloid Polypeptide Fibrils by Charged Graphene Quantum Dots: A Molecular Dynamics Investigation with Implications for Nanomedicine

Destabilization of Human Islet Amyloid Polypeptide Fibrils by Charged Graphene Quantum Dots: A Molecular Dynamics Investigation with Implications for Nanomedicine

Studies on alpha-synuclein and islet amyloid polypeptide interaction.

Introduction: Parkinson's disease and type 2 diabetes have both elements of local amyloid depositions in their pathogenesis. In Parkinson's disease, alpha-synuclein (aSyn) forms insoluble Lewy bodies and Lewy neurites in brain neurons, and in type 2 diabetes, islet amyloid polypeptide (IAPP) comprises the amyloid in the islets of Langerhans. In this study, we assessed the interaction between aSyn and IAPP in human pancreatic tissues, both ex vivo and in vitro. Material and Methods: The antibody-based detection techniques, proximity ligation assay (PLA), and immuno-TEM were used for co-localization studies. Bifluorescence complementation (BiFC) was used for interaction studies between IAPP and aSyn in HEK 293 cells. The Thioflavin T assay was used for studies of cross-seeding between IAPP and aSyn. ASyn was downregulated with siRNA, and insulin secretion was monitored using TIRF microscopy. Results: We demonstrate intracellular co-localization of aSyn with IAPP, while aSyn is absent in the extracellular amyloid deposits. ASyn reactivity is present in the secretory granules of β-cells and some α-cells in human islets. The BiFC-expression of aSyn/aSyn and IAPP/IAPP in HEK293 cells resulted in 29.3% and 19.7% fluorescent cells, respectively, while aSyn/IAPP co-expression resulted in ∼10% fluorescent cells. Preformed aSyn fibrils seeded IAPP fibril formation in vitro, but adding preformed IAPP seeds to aSyn did not change aSyn fibrillation. In addition, mixing monomeric aSyn with monomeric IAPP did not affect IAPP fibril formation. Finally, the knockdown of endogenous aSyn did not affect β cell function or viability, nor did overexpression of aSyn affect β cell viability. Discussion: Despite the proximity of aSyn and IAPP in β-cells and the detected capacity of preformed aSyn fibrils to seed IAPP in vitro, it is still an open question if an interaction between the two molecules is of pathogenic significance for type 2 diabetes.

Piperic acid derivative as a molecular modulator to accelerate the IAPP aggregation process and alter its antimicrobial activity.

Piperic acid derivatives were found to affect the islet amyloid polypeptide (IAPP) aggregation process. Structure-activity relationship studies revealed that PAD-13 was an efficient molecular modulator to accelerate IAPP fibril formation by promoting primary and secondary nucleation and reducing its antimicrobial activity.

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.

Nanoparticles and Nanocolloidal Carbon: Will They Be the Next Antidiabetic Class That Targets Fibrillation and Aggregation of Human Islet Amyloid Polypeptide in Type 2 Diabetes?

Nanotechnology is revolutionizing human medicine. Nanoparticles (NPs) are currently used for treating various cancers, for developing vaccines, and for imaging, and other promises offered by NPs might come true soon. Due to the interplay between NPs and proteins, there is more and more evidence supporting the role of NPs for treating amyloid-based diseases. NPs can induce some conformational changes of the adsorbed protein molecules via various molecular interactions, leading to inhibition of aggregation and fibrillation of several and different amyloid proteins. Though an in depth understanding of such interactions between NPs and amyloid structures is still lacking, the inhibition of protein aggregation by NPs represents a new generation of innovative and effective medicines to combat metabolic diseases such as type 2 diabetes (T2D). Here, we lay out advances made in the field of T2D notably for optimizing protein aggregation inhibition strategies. This Account covers discussions about the current understanding of β-cells, the insulin producing cells within the pancreas, under diabetic conditions, notably increased glucose and fatty acid levels, and the implication of these conditions on the formation of human islet amyloid polypeptide (hIAPP) amylin oligomers and aggregates. Owing to the great potential of carbon nanostructures to interfere with protein aggregation, an important part of this Account will be devoted to the state of the art of therapeutic options in the form of emerging nanomaterials-based amyloidosis inhibitors. Our group has recently made some substantial progress in this regard by investigating the impact of glucose and fatty acid concentrations on hIAPP aggregation and β-cell toxicity. Furthermore, the great potential of carbon nanocolloids in reversing hIAPP aggregation under diabetic conditions will be highlighted as the approach has been validated on β-cell cultures from rats. We hope that this Account will evoke new ideas and concepts in this regard. We give some lead references below on pancreatic β-cell aspects and carbon quantum dots for managing diabetics and nanomedicine related aspects, a topic of interest in our laboratory.

Structural basis for the inhibition of IAPP fibril formation by the co-chaperonin prefoldin

Chaperones, as modulators of protein conformational states, are key cellular actors to prevent the accumulation of fibrillar aggregates. Here, we integrated kinetic investigations with structural studies to elucidate how the ubiquitous co-chaperonin prefoldin inhibits diabetes associated islet amyloid polypeptide (IAPP) fibril formation. We demonstrated that both human and archaeal prefoldin interfere similarly with the IAPP fibril elongation and secondary nucleation pathways. Using archaeal prefoldin model, we combined nuclear magnetic resonance spectroscopy with electron microscopy to establish that the inhibition of fibril formation is mediated by the binding of prefoldin’s coiled-coil helices to the flexible IAPP N-terminal segment accessible on the fibril surface and fibril ends. Atomic force microscopy demonstrates that binding of prefoldin to IAPP leads to the formation of lower amounts of aggregates, composed of shorter fibrils, clustered together. Linking structural models with observed fibrillation inhibition processes opens perspectives for understanding the interference between natural chaperones and formation of disease-associated amyloids.

Structural Dissection of the First Events Following Membrane Binding of the Islet Amyloid Polypeptide

The islet amyloid polypeptide (IAPP) is the main constituent of the amyloid fibrils found in the pancreas of type 2 diabetes patients. The aggregation of IAPP is known to cause cell death, where the cell membrane plays a dual role: being a catalyst of IAPP aggregation and being the target of IAPP toxicity. Using ATR-FTIR spectroscopy, transmission electron microscopy, and molecular dynamics simulations we investigate the very first molecular steps following IAPP binding to a lipid membrane. In particular, we assess the combined effects of the charge state of amino-acid residue 18 and the IAPP-membrane interactions on the structures of monomeric and aggregated IAPP. Distinct IAPP-membrane interaction modes for the various IAPP variants are revealed. Membrane binding causes IAPP to fold into an amphipathic α-helix, which in the case of H18K-, and H18R-IAPP readily moves beyond the headgroup region. For all IAPP variants but H18E-IAPP, the membrane-bound helix is an intermediate on the way to amyloid aggregation, while H18E-IAPP remains in a stable helical conformation. The fibrillar aggregates of wild-type IAPP and H18K-IAPP are dominated by an antiparallel β-sheet conformation, while H18R- and H18A-IAPP exhibit both antiparallel and parallel β-sheets as well as amorphous aggregates. Our results emphasize the decisive role of residue 18 for the structure and membrane interaction of IAPP. This residue is thus a good therapeutic target for destabilizing membrane-bound IAPP fibrils to inhibit their toxic actions.

Disaggregation of Islet Amyloid Polypeptide Fibrils as a Potential Anti-Fibrillation Mechanism of Tetrapeptide TNGQ.

Islet amyloid polypeptide (IAPP) fibrillation has been commonly associated with the exacerbation of type 2 diabetes prognosis. Consequently, inhibition of IAPP fibrillation to minimize β-cell cytotoxicity is an important approach towards β-cell preservation and type 2 diabetes management. In this study, we identified three tetrapeptides, TNGQ, MANT, and YMSV, that inhibited IAPP fibrillation. Using thioflavin T (ThT) fluorescence assay, circular dichroism (CD) spectroscopy, dynamic light scattering (DLS), and molecular docking, we evaluated the potential anti-fibrillation mechanism of the tetrapeptides. ThT fluorescence kinetics and microscopy as well as transmission electron microscopy showed that TNGQ was the most effective inhibitor based on the absence of normal IAPP fibrillar morphology. CD spectroscopy showed that TNGQ maintained the α-helical conformation of monomeric IAPP, while DLS confirmed the presence of varying fibrillation species. Molecular docking showed that TNGQ and MANT interact with monomeric IAPP mainly by hydrogen bonding and electrostatic interaction, with TNGQ binding at IAPP surface compared to YMSV, which had the highest docking score, but interact mainly through hydrophobic interaction in IAPP core. The highly polar TNGQ was the most active and appeared to inhibit IAPP fibrillation by disaggregation of preformed IAPP fibrils. These findings indicate the potential of TNGQ in the development of peptide-based anti-fibrillation and antidiabetic nutraceuticals.

Distinguishing islet amyloid polypeptide fibril structures with infrared isotope-label spectroscopy.

Here, we performed spectral simulations of the amide-I vibrational spectra for three proposed fibril structures of the human islet amyloid polypeptide, which is involved in type II diabetes. We modeled both the overall absorption and two-dimensional infrared spectra for these structures. We further analyzed the isotope-labeled spectra, including the variation between structures. The analysis suggests that the infrared spectra of the cryo-electron microscopy structure provide the best match with experimental data. We further simulated isotope-labeled dilution spectroscopy investigating the correlation between the predicted spectral peak shift and the coupling between the amide units. While this correlation works in most cases, failures were observed when the isotope-labeled spectra were broad compared to the coupling or exhibited structure. These findings will be useful in the quest for potential toxic fibril formation intermediates.

Single-molecule analysis of soluble IAPP oligomers at diverse membrane surfaces

Islet amyloid polypeptide (IAPP) is a 37 aa peptide that accumulates and fibrilizes in insulin-secreting β-cells in patients with type II diabetes. However, while pancreatic IAPP fibrils are a hallmark of the disease, their soluble oligomeric precursors are most potently correlated with their pathological function. IAPP oligomers (IAo) are thought to disrupt homeostasis through interactions with the proteasomal pathway and direct binding to physiological membranes, leading to membrane-poration and mitochondrial leakage.

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.

Biflavones inhibit the fibrillation and cytotoxicity of the human islet amyloid polypeptide.

Biflavones are a kind of natural compound with a variety of biological activities, which have the capability of reversing diabetes and neurodegenerative diseases. The human islet amyloid polypeptide (hIAPP) is closely related to the pathological process of type II diabetes mellitus (T2DM). The development of new inhibitors is crucial to prevent hIAPP aggregation against T2DM. However, the influences of biflavones on hIAPP aggregation are unknown. In this work, we utilized a series of biophysical and biochemical techniques to seek the inhibitory effects of two biflavones on hIAPP fibril formation and their interaction mechanism. The biflavones namely amentoflavone (1), and bilobetin (2), distinctly prevented the self-assembly behavior of hIAPP, and depolymerized the aged aggregates to small oligomers and monomers. In addition, the two compounds displayed strong binding affinity to hIAPP mainly through hydrophobic and hydrogen bonding interactions, and the hydroxyl substitution in 1 was superior to the methoxy substitution in 2 at the same C8 position in impeding hIAPP aggregation. 1 and 2 also decreased hIAPP-induced cytotoxicity by reducing peptide oligomerization. This work offers useful data for understanding the roles of biflavones in hIAPP fibrillation and for the treatment of T2DM and other amyloidosis related diseases.