The Mitochondrial Peptide Humanin Targets but Does Not Denature Amyloid Oligomers in Type II Diabetes

Neuroprotective Action of Humanin and Humanin Analogues: Research Findings and Perspectives

Humanin is a 24-mer peptide first reported in the early 2000s as a new neuroprotective/cytoprotective factor rescuing neuronal cells from death induced by various Alzheimer's disease-associated insults. Nowadays it is known that humanin belongs to the novel class of the so-called mitochondrial-derived peptides (which are encoded by mitochondrial DNA) and has been shown to exert beneficial cytoprotective effects in a series of in vitro and/or in vivo experimental models of human diseases, including not only neurodegenerative disorders but other human diseases as well (e.g., age-related macular degeneration, cardiovascular diseases, or diabetes mellitus). This review article is focused on the presentation of recent in vitro and in vivo research results associated with the neuroprotective action of humanin as well as of various, mainly synthetic, analogues of the peptide; moreover, the main mode(s)/mechanism(s) through which humanin and humanin analogues may exert in vitro and in vivo regarding neuroprotection have been reported. The prospects of humanin and humanin analogues to be further investigated in the frame of future research endeavors against neurodegenerative/neural diseases have also been briefly discussed.

Exploring the Curvature-Dependence of Boron Nitride Nanoparticles on the Inhibition of hIAPP Aggregation

Nanoparticles, particularly carbon nanoparticles, have gathered significant interest in the field of anti-aggregation research. However, due to their cytotoxicity, the exploration of biocompatible nanoparticles has become a new frontier in the quest for drugs against human amyloid diseases. The application of non-cytotoxic and biocompatible boron nitride (BN) nanoparticles against amyloid aggregation has been probed to tackle this issue. BN nanoparticles displayed inhibitory activity against the aggregation of Aβ and α-syn peptides. In this work, the effect of BN nanoparticles on the dimerization of hIAPP, which is associated with the pathogenesis of type 2 diabetes, is studied. BN nanoparticles prevent the misfolding of hIAPP into β-sheet-rich aggregates. On varying the curvature, the nanoparticles display variation in the interaction preference with hIAPP. Interestingly, as the hydrophobicity of the nanoparticles increases from (5,5) BN nanotube to BN nanosheet, the interaction propensity shifts from N-terminal to the amyloid prone C-terminal of hIAPP. The hydrophobic and aromatic stacking interactions are a contributing factor toward the binding between hIAPP and BN. Due to this, the flat surface of the nanosheet shows better interaction potential toward hIAPP, compared to the nanotubes. Further, the nanoparticles can also disassemble preformed hIAPP fibrils, and the effect is more pronounced for (5,5) nanotube and the nanosheet. This study provides insight into the inhibitory mechanism of hIAPP aggregation by boron nitride nanoparticles and also an understanding of the significance of the curvature of nanoparticles in their interaction with amyloid peptides, which is valuable for the design of antiamyloid drugs.

Disparate Effect of Hybrid Peptidomimetics Containing Isomers of Aminobenzoic Acid on hIAPP Aggregation

The abnormal misfolding of human islet amyloid polypeptide (hIAPP) in pancreatic β-cells is implicated in the progression of type II diabetes (T2D). With the prevalence of T2D increasing worldwide, preventing the aggregation of hIAPP has been recognized as a promising therapeutic strategy to control this disease. Recently, a class of novel conformationally restricted β-sheet breaker hybrid peptidomimetics (BSBHps) was found to demonstrate efficient inhibitory ability toward amyloid formation of hIAPP. One (Ile26) or more (Gly24 and Ile26) residues in these six-membered peptide sequences, which have been extracted from the amyloidogenic core of hIAPP, N₂₂FGAIL₂₇, are substituted by three different isomers of the conformationally restricted aromatic amino acid, i.e., aminobenzoic acid (β, γ, and δ), to generate these BSBHps. The presence of the nonproteinogenic aminobenzoic acid moiety renders the BSBHps to be more stable toward proteolytic degradation. The different isomeric BSBHps exhibit contrasting influence on the self-assembly of hIAPP. The BSBHps containing β- and γ-aminobenzoic acid can sufficiently prevent hIAPP aggregation, but those with the δ-aminobenzoic group stabilize the β-sheet-rich aggregate of hIAPP. The difference in the angle between the amino and carboxyl groups in the isomers of the aminobenzoic moiety causes the BSBHps to attain discrete conformation and hence leads to variation in their binding preference with hIAPP and ultimately their inhibitory potency. This guides the pathway for the dissimilar effect of BSBHps on peptide aggregation and, therefore, provides insights into the design considerations for novel drugs against T2D.

In silico studies of the human IAPP in the presence of osmolytes

The human islet amyloid polypeptide or amylin is secreted along with insulin by pancreatic islets. Under the drastic environmental conditions, amylin can aggregate to form amyloid fibrils. This amyloid plaque of hIAPP in the pancreatic cells is the cause of type II diabetes. Early stages of amylin aggregates are more cytotoxic than the matured fibrils. Here, we have used the all-atom molecular dynamic simulation to see the effect of water, TMAO, urea and urea/TMAO having ratio 2:1 of different concentrations on the amylin protein. Our study suggest that the amylin protein forms β-sheets in its monomeric form and may cause the aggregation of protein through the residue 13-17 and the C-terminal region. α-Helical content of protein increases with an increase in TMAO concentration by decreasing the SASA value of protein, increase in intramolecular hydrogen bonds and on making the short-range hydrophobic interactions. Electrostatic potential surfaces show that hydrophobic groups are buried and normalised configurational entropy of backbone, and side-chain atoms is lesser in the presence of TMAO, whereas opposite behaviour is obtained in the case of urea. Counteraction effect of TMAO using Kast model towards urea is also observed in ternary solution of urea/TMAO.

Underlying Mechanisms of Allopurinol in Eliminating Renal Toxicity Induced by Melamine-Uric Acid Complex Formation: A Computational Study

Using molecular dynamics, we address uric acid (UA) replacement by a model small-molecule inhibitor, allopurinol (AP), from its aggregated cluster in a columnar fashion. Experimentally it has been affirmed that AP is efficient in preventing UA-mediated renal stone formation. However, no study has presented the underlying mechanisms yet. Hence, a theoretical approach is presented for mapping the AP, which binds to melamine (MM) and UA clusters. In AP's presence, the higher-order cluster of UA molecules turns into a lower-order cluster, which "drags" fewer MM to them. Consequently, the MM-UA composite structure gets reduced. It is worth noting that UA-AP and AP-MM hydrogen-bonding interactions often play an essential role in reducing the UA-MM cluster size. Interestingly, an AP around UA makes a pillar-like structure, confirmed by defining the point-plane distribution function. The decomposition of the preferential interaction by Kirkwood-Buff integral into different angles like 0°-30°, 30°-60°, and 60°-90° firmly establishes the phenomenon mentioned above. However, the structural order for such π-stacking interactions between AP and UA molecules is not hierarchical but rather more spontaneous. The driving force behind UA-AP-MM composite formation is the favorable complexation energy that can be inferred by computing pairwise binding free energies for all possible combinations. Performing enhanced sampling and quantum calculations further confirms the evidence for UA degradation.

Peptide Derived from AHNAK Inhibits Cell Migration and Proliferation in Hirschsprung's Disease by Targeting the ERK1/2 Pathway

Hirschsprung's disease (HSCR) is characterized by the lack of ganglion cells in the distal part of the digestive tract. It occurs due to migration disorders of enteric neural crest cells (ENCCs) from 5 to 12 weeks of embryonic development. More and more studies show that HSCR is a result of the interaction of multiple genes and the microenvironments, but its specific pathogenesis has not been fully elucidated. Studies have confirmed that many substances in the intestinal microenvironment, such as laminin and β1-integrin, play a vital regulatory role in cell growth and disease progression. In addition to these high-molecular-weight proteins, research on endogenous polypeptides derived from these proteins has been increasing in recent years. However, it is unclear whether these endogenous peptides have effects on the migration of ENCCs and thus participate in the occurrence of HSCR. Previously, our research group found that compared with the normal intestinal tissue, the expression of AHNAK protein in the stenosed intestinal tissue of HSCR patients was significantly upregulated, and overexpression of AHNAK could inhibit cell migration and proliferation. In this study, endogenous peptides were extracted from the normal control intestinal tissue and the stenosed HSCR intestinal tissue. The endogenous polypeptide expression profile was analyzed by liquid chromatography-mass spectrometry, and multiple peptides derived from AHNAK protein were found. We selected one of them, "EGPEVDVNLPK", for research. Because there is no uniform naming system, this peptide is temporarily named PDAHNAK (peptide derived from AHNAK). This project aims to clarify the potential role of PDAHNAK in the development of HSCR and to further understand its relationship with its precursor protein AHNAK and how they contribute to the development of HSCR.

Potential of ATP toward Prevention of hIAPP Oligomerization and Destabilization of hIAPP Protofibrils: An In Silico Perspective

The aggregation of an intrinsically disordered protein, human islet amyloid polypeptide (hIAPP), leads to one of the most prevalent endocrine disorders, type II diabetes mellitus (T2DM). Hence inhibition of hIAPP aggregation provides a possible therapeutic approach for the treatment of T2DM. In this regard, a new aspect of adenosine triphosphate (ATP), which is widely known as the energy source for biological reactions, has recently been discovered, where it can inhibit the formation of protein aggregates and simultaneously dissolve preformed aggregates at a millimolar concentration scale. In this work, we investigate the effect of ATP on the aggregation of an amyloidogenic segment of hIAPP, hIAPP_22-28, and also of the full length sequence. Using all-atom classical molecular dynamics simulations, we observe that the tendency of hIAPP to oligomerize into β-sheet conformers is inhibited by ATP, due to which the peptides remain distant, loosely packed random monomers. Moreover, it can also disassemble preformed hIAPP protofibrils. ATP preferentially interacts with the hydrophobic residues of hIAPP_22-28 fragment and the terminal and turn residues of the full length peptide. The hydrogen bonding, hydrophobic, π-π, and N-H-π stacking interactions are the driving forces for the ATP induced inhibition of hIAPP aggregation. Interestingly, the hydrophobic adenosine of ATP is found to be more in contact with the peptide residues than the hydrophilic triphosphate moiety. The insight into the inhibitory mechanism of ATP on hIAPP aggregation can prove to be beneficial for the design of novel amyloid inhibitors in the future.

α-CGRP disrupts amylin fibrillization and regulates insulin secretion: implications on diabetes and migraine

Despite being relatively benign and not an indicative signature of toxicity, fibril formation and fibrillar structures continue to be key factors in assessing the structure-function relationship in protein aggregation diseases. The inability to capture molecular cross-talk among key players at the tissue level before fibril formation greatly accounts for the missing link toward the development of an efficacious therapeutic intervention for Type II diabetes mellitus (T2DM). We show that human α-calcitonin gene-related peptide (α-CGRP) remodeled amylin fibrillization. Furthermore, while CGRP and/or amylin monomers reduce the secretion of both mouse Ins1 and Ins2 proteins, CGRP oligomers have a reverse effect on Ins1. Genetically reduced Ins2, the orthologous version of human insulin, has been shown to enhance insulin sensitivity and extend the life-span in old female mice. Beyond the mechanistic insights, our data suggest that CGRP regulates insulin secretion and lowers the risk of T2DM. Our result rationalizes how migraine might be protective against T2DM. We envision the new paradigm of CGRP : amylin interactions as a pivotal aspect for T2DM diagnostics and therapeutics. Maintaining a low level of amylin while increasing the level of CGRP could become a viable approach toward T2DM prevention and treatment.

Mechanistic Insights into the Co-Aggregation of Aβ and hIAPP: An All-Atom Molecular Dynamic Study

Patients with Alzheimer's disease (AD) have a high risk of developing Type II diabetes (T2D). The co-aggregation of the two disease-related proteins, Aβ and hIAPP, has been proposed as a potential molecular mechanism. However, the detailed Aβ-hIAPP interactions and structural characteristics of co-aggregates are mostly unknown at atomic level. Here, we explore the conformational ensembles of the Aβ-hIAPP heterodimer and Aβ or hIAPP homodimer by performing all-atom explicit-solvent replica exchange molecular dynamic simulations. Our simulations show that the interaction propensity of Aβ-hIAPP in the heterodimer is comparable with that of Aβ-Aβ/hIAPP-hIAPP in the homodimer. Similar hot spot residues of Aβ/hIAPP in the homodimer and heterodimer are identified, indicating that both Aβ and hIAPP have similar molecular recognition sites for self-aggregation and co-aggregation. Aβ in the heterodimer possesses three high β-sheet probability regions: the N-terminal region E3-H6, the central hydrophobic core region K16-E22, and the C-terminal hydrophobic region I31-A41, which is highly similar to Aβ in the homodimer. More importantly, in the heterodimer, the regions E3-H6, F19-E22, and I31-M35 of Aβ and the amyloid core region N20-T30 of hIAPP display higher β-sheet probability than they do in homodimer, implying their crucial roles in the formation of β-sheet-rich co-aggregates. Our study sheds light on the co-aggregation of Aβ and hIAPP at an atomic level, which will be helpful for an in-depth understanding of the molecular mechanism for epidemiological correlation of AD and T2D.

Defining the Neuropathological Aggresome across in Silico, in Vitro, and ex Vivo Experiments

The loss of proteostasis over the life course is associated with a wide range of debilitating degenerative diseases and is a central hallmark of human aging. When left unchecked, proteins that are intrinsically disordered can pathologically aggregate into highly ordered fibrils, plaques, and tangles (termed amyloids), which are associated with countless disorders such as Alzheimer's disease, Parkinson's disease, type II diabetes, cancer, and even certain viral infections. However, despite significant advances in protein folding and solution biophysics techniques, determining the molecular cause of these conditions in humans has remained elusive. This has been due, in part, to recent discoveries showing that soluble protein oligomers, not insoluble fibrils or plaques, drive the majority of pathological processes. This has subsequently led researchers to focus instead on heterogeneous and often promiscuous protein oligomers. Unfortunately, significant gaps remain in how to prepare, model, experimentally corroborate, and extract amyloid oligomers relevant to human disease in a systematic manner. This Review will report on each of these techniques and their successes and shortcomings in an attempt to standardize comparisons between protein oligomers across disciplines, especially in the context of neurodegeneration. By standardizing multiple techniques and identifying their common overlap, a clearer picture of the soluble neuropathological aggresome can be constructed and used as a baseline for studying human disease and aging.

Proteostasis of Islet Amyloid Polypeptide: A Molecular Perspective of Risk Factors and Protective Strategies for Type II Diabetes

The possible link between hIAPP accumulation and β-cell death in diabetic patients has inspired numerous studies focusing on amyloid structures and aggregation pathways of this hormone. Recent studies have reported on the importance of early oligomeric intermediates, the many roles of their interactions with lipid membrane, pH, insulin, and zinc on the mechanism of aggregation of hIAPP. The challenges posed by the transient nature of amyloid oligomers, their structural heterogeneity, and the complex nature of their interaction with lipid membranes have resulted in the development of a wide range of biophysical and chemical approaches to characterize the aggregation process. While the cellular processes and factors activating hIAPP-mediated cytotoxicity are still not clear, it has recently been suggested that its impaired turnover and cellular processing by proteasome and autophagy may contribute significantly toward toxic hIAPP accumulation and, eventually, β-cell death. Therefore, studies focusing on the restoration of hIAPP proteostasis may represent a promising arena for the design of effective therapies. In this review we discuss the current knowledge of the structures and pathology associated with hIAPP self-assembly and point out the opportunities for therapy that a detailed biochemical, biophysical, and cellular understanding of its aggregation may unveil.

[Gly14]-Humanin Ameliorates High Glucose-Induced Apoptosis by Inhibiting the Expression of MicroRNA-155 in Endothelial Microparticles

BACKGROUND

Humanin, a newly emerging endogenously expressed cytoprotective peptide, has been shown to have anti-apoptotic properties effects by protecting neuronal cells injury. Endothelial microparticles (EMPs) are considered as vital mediators in intercellular communication. EMPs may regulate various physiological and pathological processes by transferring mRNAs and microRNAs (miRNAs) to recipient cells.

METHODS

EMPs were isolated from human umbilical vein endothelial cells (HUVECs) by ultracentrifugation. EMPs were characterized by transmission electron microscopy and nanoparticle tracking analyses. Observation of EMPs uptake into HUVECs and the number of EMPs were realized by confocal microscopy. The expression of miR-155 was examined using real-time PCR. Cell apoptosis was examined by flow cytometry assay.

RESULTS

We found that high glucose (HG) increased the number of EMPs and upregulated the expression of miR-155 contained within EMPs, which was mitigated by HNG pretreatment. miR-155 overexpression in EMPs reversed the effects of HNG pretreatment and increased apoptosis of target cells. Effects of HNG pretreatment on HG-treated endothelial cells (ECs) were mitigated after miR-155 mimic transfection into HUVECs while were augmented after miR-155 inhibitor transfection into HUVECs.

CONCLUSION

HNG inhibited HG-induced apoptosis of ECs and the effect of HNG may be mediated by inhibiting the transfer of EMPs miR-155 from HG-induced HUVECs to normal cells. This study provides a new direction for biological products related to humanin to treat vascular complications associated with all forms of diabetes mellitus.

Oligomeric procyanidins inhibit insulin fibrillation by forming unstructured and off-pathway aggregates

Effects of natural polyphenols on insulin fibrillation were compared. OPCs show potent inhibitory effects at all stages of insulin fibrillation and redirect the insulin aggregation pathway via the formation of unstructured, off-pathway aggregates.

Investigation on the Mechanisms of Synchronous Interaction of K3Cit with Melamine and Uric Acid That Avoids the Formation of Large Clusters

Uric acid (UA) has an enormous competence to aggregate over melamine (Mel), producing large UA clusters that "drag" Mel toward them. Such a combination of donor-acceptor pairs provides a robust Mel-UA composite, thereby denoting a high complexity. Thus, a straightforward but pragmatic methodology might indeed require either destruction of the aggregation of UA or impediment of the hydrogen-bonded cluster of Mel and UA. Here, potassium citrate (K₃Cit) is used as a potent inhibitor for a significant decrease of large UA-Mel clusters. The underlying mechanisms of synchronous interactions between K₃Cit and the Mel-UA pair are examined by the classical molecular dynamics simulation coupled with the enhanced sampling method. K₃Cit binds to the Mel-UA pair profoundly to produce a Mel-UA-K₃Cit complex with favorable complexation energy (as indicated by the reckoning of pairwise ΔG_bind° employing the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method). The strength of interaction follows the order UA-K₃Cit > Mel-K₃Cit > Mel-UA, thus clearly demonstrating the instability caused by upsetting the π-stacking of UA and hydrogen bonding of Mel-UA simultaneously. The comprehensive, strategically designed "direct approach" and "indirect approach" cluster structure analysis shows that K₃Cit reduces the direct approach Mel-UA cluster size significantly irrespective of ensemble variation. Furthermore, the estimation of potentials of mean force (PMFs) reveals that the (UA)_decamer-Mel interaction prevails over (UA)_tetramer-Mel. The dynamic property (dimer existence autocorrelation functions) proves the essence of dimerization between Mel and UA in the absence and presence of K₃Cit. Moreover, the calculation of the preferential interaction parameter provides the concentration at which Mel-K₃Cit and UA-K₃Cit interactions are predominant over the interaction of Mel and UA.

Mechanisms of protection of retinal pigment epithelial cells from oxidant injury by humanin and other mitochondrial-derived peptides: Implications for age-related macular degeneration

The mitochondrial-derived peptides (MDPs) are a new class of small open reading frame encoded polypeptides with pleiotropic properties. The prominent members are Humanin (HN) and small HN-like peptide (SHLP) 2, which encode 16S rRNA, while mitochondrial open reading frame of the twelve S c (MOTS-c) encodes 12S rRNA of the mitochondrial genome. While the multifunctional properties of HN and its analog 14-HNG have been well documented, their protective role in the retinal pigment epithelium (RPE)/retina has been investigated only recently. In this review, we have summarized the multiple effects of HN and its analogs, SHLP2 and MOTS-c in oxidatively stressed human RPE and the regulatory pathways of signaling, mitochondrial function, senescence, and inter-organelle crosstalk. Emphasis is given to the mitochondrial functions such as biogenesis, bioenergetics, and autophagy in RPE undergoing oxidative stress. Further, the potential use of HN and its analogs in the prevention of age-related macular degeneration (AMD) are also presented. In addition, the role of novel, long-acting HN elastin-like polypeptides in nanotherapy of AMD and other ocular diseases stemming from oxidative damage is discussed. It is expected MDPs will become a promising group of mitochondrial peptides with valuable therapeutic applications in the treatment of retinal diseases.

The Effect of (-)-Epigallocatechin-3-Gallate on the Amyloid-β Secondary Structure

Amyloid-β (Aβ) is a macromolecular structure of great interest because its misfolding and aggregation, along with changes in the secondary structure, have been correlated with its toxicity in various neurodegenerative diseases. Small drug-like molecules can modulate the amyloid secondary structure and therefore have raised significant interest in applications to active and passive therapies targeting amyloids. In this study, we investigate the interactions of epigallocatechin-3-gallate (EGCG), found in green tea, with Aβ polypeptides, using a combination of in vitro immuno-infrared sensor measurements, docking, molecular dynamics simulations, and ab initio calculations. We find that the interactions of EGCG are dominated by only a few residues in the fibrils, including hydrophobic π-π interactions with aromatic rings of side chains and hydrophilic interactions with the backbone of Aβ, as confirmed by extended (1-μs-long) molecular dynamics simulations. Immuno-infrared sensor data are consistent with degradation of Aβ fibril induced by EGCG and inhibition of Aβ fibril and oligomer formation, as manifested by the recovery of the amide-I band of monomeric Aβ, which is red-shifted by 26 cm^-1 when compared to the amide-I band of the fibrillar form. The shift is rationalized by computations of the infrared spectra of Aβ42 model structures, suggesting that the conformational change involves interchain hydrogen bonds in the amyloid fibrils that are broken upon binding of EGCG.