Transcranial Temporal Interference Stimulation of the Right Globus Pallidus in Parkinson's Disease.

BACKGROUND: Invasive deep brain stimulation (DBS) has been shown to be effective in treating patients with Parkinson's disease (PD), yet its clinical use is limited to patients at the advanced stage of the disease. Transcranial temporal interference stimulation (tTIS) may be a novel nonneurosurgical and safer alternative, yet its therapeutic potential remains unexplored. OBJECTIVE: This pilot study aims to examine the feasibility and safety of tTIS targeting the right globus pallidus internus (GPi) for motor symptoms in patients with PD. METHODS: Twelve participants with mild PD completed this randomized, double-blind, and sham-controlled experiment. Each of them received either 20-minute or sham tTIS of the right GPi. Before and immediately after the stimulation, participants completed the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS-III) in the "medication-on" state to assess the motor symptoms. The blinding efficacy and side effects were also assessed. RESULTS: tTIS was well tolerated by participants, with only mild, transient adverse effects reported. tTIS significantly reduced MDS-UPDRS-III scores by 6.64 points (14.7%), particularly in bradykinesia (23.5%) and tremor (15.3%). The left side showed more significant alleviation in motor symptoms, particularly bradykinesia, compared to the right side. Participants with severer bradykinesia and tremor before stimulation experienced greater improvement after tTIS. CONCLUSION: This pilot study suggests that the tTIS, as a novel noninvasive DBS approach, is feasible and safe for alleviating motor symptoms in mild PD, especially bradykinesia and tremor. Future larger-scale and more definitive studies are needed to confirm the benefits. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Repetitive temporal interference stimulation improves jump performance but not the postural stability in young healthy males: a randomized controlled trial.

BACKGROUND: Temporal interference (TI) stimulation, an innovative non-invasive brain stimulation technique, has the potential to activate neurons in deep brain regions. The objective of this study was to evaluate the effects of repetitive TI stimulation targeting the lower limb motor control area (i.e., the M1 leg area) on lower limb motor function in healthy individuals, which could provide evidence for further translational application of non-invasive deep brain stimulation. METHODS: In this randomized, double-blinded, parallel-controlled trial, 46 healthy male adults were randomly divided into the TI or sham group. The TI group received 2 mA (peak-to-peak) TI stimulation targeting the M1 leg area with a 20 Hz frequency difference (2 kHz and 2.02 kHz). Stimulation parameters of the sham group were consistent with those of the TI group but the current input lasted only 1 min (30 s ramp-up and ramp-down). Both groups received stimulation twice daily for five consecutive days. The vertical jump test (countermovement jump [CMJ], squat jump [SJ], and continuous jump [CJ]) and Y-balance test were performed before and after the total intervention session. Two-way repeated measures ANOVA (group × time) was performed to evaluate the effects of TI stimulation on lower limb motor function. RESULTS: Forty participants completed all scheduled study visits. Two-way repeated measures ANOVA showed significant group × time interaction effects for CMJ height (F = 8.858, p = 0.005) and SJ height (F = 6.523, p = 0.015). The interaction effect of the average CJ height of the first 15 s was marginally significant (F = 3.550, p = 0.067). However, there was no significant interaction effect on the Y balance (p > 0.05). Further within-group comparisons showed a significant post-intervention increase in the height of the CMJ (p = 0.004), SJ (p = 0.010) and the average CJ height of the first 15 s (p = 0.004) in the TI group. CONCLUSION: Repetitive TI stimulation targeting the lower limb motor control area effectively increased vertical jump height in healthy adult males but had no significant effect on dynamic postural stability.

Dose-dependent binding behavior of anthraquinone derivative purpurin interacting with tau-derived peptide protofibril.

Alzheimer's disease is hallmarked by microtubule-associated protein tau tangles and amyloid-ß plaques. The ß-structure propensity of tau inclusions is closely related to the hexapeptide motif VQIVYK (termed PHF6), and disruption of this motif prevents tau aggregation. Small-molecule inhibitors are considered a promising therapeutic strategy, but the molecular mechanisms underlying the correlation between dose and inhibitory effects are still unclear. In this work, we investigated the dose-induced influence of purpurin, an anthraquinone derivative, on the structural stability of the PHF6 fibrillar nucleus by performing microsecond all-atom molecular dynamics simulations in explicit water. The stability of PHF6 protofibrils of different sizes was first examined, and it was found that the structural stability of fibrillar oligomers increases with oligomer size, and that the octamer is the minimal stable nucleus for fibril formation. When purpurin molecules were added to the protofibril octamer at a low purpurin/peptide ratio, they bound to the octamer with different coupling states, and the different states may transition to each of the other states through an uncoupling state or directly through a short-time transition. With increasing purpurin/peptide ratio, purpurins tend to self-aggregate rather than bind to the protein surface. Interestingly, the contacts between individual purpurins and the octamer as a function of the purpurin number show a power-law behavior, which may serve as a useful indicator to reflect the binding efficiency of ligands to proteins in drug screening. The interaction analysis reveals that purpurin prefers to bind to the hydrophilic and aromatic Tyr and has the lowest probability with the hydrophobic Val located in the middle of PHF6. Aromatic stacking plays a key role in the octamer-purpurin interaction, in which the three aromatic rings of purpurin have different contributions. In addition, purpurin shows a remarkable disruptive effect on the protofibril octamer when the molar ratio of purpurin to peptide is 1 : 2; above this ratio, the binding mode and disruption effect of purpurin do not change significantly. Our work provides a detailed picture of the dynamics and interactions of purpurin binding to the PHF6 protofibril and expands the understanding of the dose-induced inhibitory mechanism.

Temporal Interference (TI) Stimulation Boosts Functional Connectivity in Human Motor Cortex: A Comparison Study with Transcranial Direct Current Stimulation (tDCS).

Temporal interference (TI) could stimulate deep motor cortex and induce movement without affecting the overlying cortex in previous mouse studies. However, there is still lack of evidence on potential TI effects in human studies. To fill this gap, we collected resting-state functional magnetic resonance imaging data on 40 healthy young participants both before and during TI stimulation on the left primary motor cortex (M1). We also chose a widely used simulation approach (tDCS) as a baseline condition. In the stimulation session, participants were randomly allocated to 2 mA TI or tDCS for 20 minutes. We used a seed-based whole brain correlation analysis method to quantify the strength of functional connectivity among different brain regions. Our results showed that both TI and tDCS significantly boosted functional connection strength between M1 and secondary motor cortex (premotor cortex and supplementary motor cortex). This is the first time to demonstrate substantial stimulation effect of TI in the human brain.

Melatonin Inhibits hIAPP Oligomerization by Preventing ß-Sheet and Hydrogen Bond Formation of the Amyloidogenic Region Revealed by Replica-Exchange Molecular Dynamics Simulation.

The pathogenesis of type 2 diabetes (T2D) is highly related to the abnormal self-assembly of the human islet amyloid polypeptide (hIAPP) into amyloid aggregates. To inhibit hIAPP aggregation is considered a promising therapeutic strategy for T2D treatment. Melatonin (Mel) was reported to effectively impede the accumulation of hIAPP aggregates and dissolve preformed fibrils. However, the underlying mechanism at the atomic level remains elusive. Here, we performed replica-exchange molecular dynamics (REMD) simulations to investigate the inhibitory effect of Mel on hIAPP oligomerization by using hIAPP20-29 octamer as templates. The conformational ensemble shows that Mel molecules can significantly prevent the ß-sheet and backbone hydrogen bond formation of hIAPP20-29 octamer and remodel hIAPP oligomers and transform them into less compact conformations with more disordered contents. The interaction analysis shows that the binding behavior of Mel is dominated by hydrogen bonding with a peptide backbone and strengthened by aromatic stacking and CH-π interactions with peptide sidechains. The strong hIAPP-Mel interaction disrupts the hIAPP20-29 association, which is supposed to inhibit amyloid aggregation and cytotoxicity. We also performed conventional MD simulations to investigate the influence and binding affinity of Mel on the preformed hIAPP1-37 fibrillar octamer. Mel was found to preferentially bind to the amyloidogenic region hIAPP20-29, whereas it has a slight influence on the structural stability of the preformed fibrils. Our findings illustrate a possible pathway by which Mel alleviates diabetes symptoms from the perspective of Mel inhibiting amyloid deposits. This work reveals the inhibitory mechanism of Mel against hIAPP20-29 oligomerization, which provides useful clues for the development of efficient anti-amyloid agents.

Mechanisms of melatonin binding and destabilizing the protofilament and filament of tau R3-R4 domains revealed by molecular dynamics simulation.

The accumulation of ß-amyloid (Aß) and tau protein is considered to be an important pathological characteristic of Alzheimer's disease (AD). Failure of medicine targeting Aß has drawn more attention to the influence of tau protein and its fibrillization on neurodegeneration. Increasing evidence shows that melatonin (Mel) can effectively inhibit the formation of tau fibrils and disassemble preformed tau fibrils. However, the underlying mechanism is poorly understood. In this work, we investigated the kinetics of melatonin binding and destabilizing the tetrameric protofilament and octameric filament of tau R3-R4 domains by performing microsecond all-atom molecular dynamics simulations. Our results show that Mel is able to disrupt the C-shaped structure of the tau protofilament and filament, and destabilizes the association between N- and C-termini. Mel predominantly binds to ß1 and ß6-ß8 regions and favors contact with the elongation surface, which is dominantly driven by hydrogen bonding interactions and facilitated by other interactions. The strong π-π stacking interaction of Mel with Y310 impedes the intramolecular CH-π interaction between I308 and Y310, and the cation-π interaction of Mel with R379 interferes with the formation of the D348-R379 salt bridge. Moreover, Mel occupies the protofilament surface in the tetrameric protofilament and prevents the formation of intermolecular hydrogen bonds between residues K331 and Q336 in the octameric filament. Our work provides molecular insights into Mel hindering tau fibrillization or destabilizing the protofilament and filament, and the revealed inhibitory mechanisms provide useful clues for the design of efficient anti-amyloid agents.

Research and Development of a Wireless Self-Powered Sensing Device Based on Bridge Vibration Energy Collection.

Traditional bridge monitoring has found it difficult to meet the current diversified needs, and frequent replacement of sensor batteries is neither economical nor environmentally friendly. This paper presents a wireless acceleration sensor with low power consumption and high sensitivity through integrated circuit design, data acquisition and wireless communication design, package design, etc. The accuracy of the sensor in data collection was verified through calibration and performance comparison tests. The ability of triangular piezoelectric cantilever beam (PCB) was tested through design and physical manufacture. Finally, the self-powered performance of the sensor was tested by connecting the sensor and the triangular PCB through a circuit, which verifies the feasibility of using the PCB to collect bridge vibration energy and convert it into electrical energy to supply power for sensor, and also explore the green energy collection and application.

Critical nucleus of Greek-key-like core of α-synuclein protofibril and its disruption by dopamine and norepinephrine.

The formation of amyloid fibrils by α-synuclein (αS) protein inside the Lewy bodies and Lewy neurites is the prominent pathological hallmark of Parkinson's disease (PD). The fibrillation of αS in vitro is described by a nucleation-elongation process involving the formation of a critical nucleus. Finding the critical/smallest nuclei and effective inhibitors of αS aggregation is a crucial step for the development of drugs against PD. Recent experiments reported that dopamine (DA) and norepinephrine (NE), two prominent naturally occurring neurotransmitters, can effectively disrupt the preformed αS fibrils. The level of DA/NE in blood can be markedly increased by exercise. However, the size and structure of the critical nucleus and the disruptive mechanism by DA/NE are largely unknown. In this work, we performed multiple molecular dynamics (MD) simulations to find the critical nucleus size and examine the influences of DA/NE molecules on preformed αS44-96 (Greek-key-like core of full length αS) protofibrils. Our results show that the trimer is the critical nucleus for the αS44-96 fibril formation, and the tetramer is the minimal stable nucleus. When DA/NE molecules bind to the fibril-like trimer and tetramer, they strongly destabilize the αS protofibrils by disrupting the ß-sheet structure and inter-chain E46-K80 salt bridges. Two common binding sites are identified for both DA and NE molecules on αS oligomers: residues 57-70 and 81-83. A different binding site is also observed, which is located at the N-terminal region (residues 45-52). The binding of DA/NE molecules to αS oligomers is mostly driven by hydrophobic and electrostatic interactions. We found two disruptive modes, and binding to the turn region of αS oligomers but disrupting the adjacent ß-sheet structure is the dominant one. Our work identified the critical nucleus of Greek-key-like core of αS protofibrils and revealed the disruptive mechanism of αS protofibrils by DA/NE molecules, which may be helpful to the design of effective drugs against αS aggregation.

Distinct Binding Dynamics, Sites and Interactions of Fullerene and Fullerenols with Amyloid-ß Peptides Revealed by Molecular Dynamics Simulations.

The pathology Alzheimer's disease (AD) is associated with the self-assembly of amyloid-ß (Aß) peptides into ß-sheet enriched fibrillar aggregates. A promising treatment strategy is focused on the inhibition of amyloid fibrillization of Aß peptide. Fullerene C60 is proved to effectively inhibit Aß fibrillation while the poor water-solubility restricts its use as a biomedicine agent. In this work, we examined the interaction of fullerene C60 and water-soluble fullerenol C60(OH)6/C60(OH)12 (C60 carrying 6/12 hydroxyl groups) with preformed Aß40/42 protofibrils by multiple molecular dynamics simulations. We found that when binding to the Aß42 protofibril, C60, C60(OH)6 and C60(OH)12 exhibit distinct binding dynamics, binding sites and peptide interaction. The increased number of hydroxyl groups C60 carries leads to slower binding dynamics and weaker binding strength. Binding free energy analysis demonstrates that the C60/C60(OH)6 molecule primarily binds to the C-terminal residues 31-41, whereas C60(OH)12 favors to bind to N-terminal residues 4-14. The hydrophobic interaction plays a critical role in the interplay between Aß and all the three nanoparticles, and the π-stacking interaction gets weakened as C60 carries more hydroxyls. In addition, the C60(OH)6 molecule has high affinity to form hydrogen bonds with protein backbones. The binding behaviors of C60/C60(OH)6/C60(OH)12 to the Aß40 protofibril resemble with those to Aß42. Our work provides a detailed picture of fullerene/fullerenols binding to Aß protofibril, and is helpful to understand the underlying inhibitory mechanism.

Proline hydroxylation at different sites in hypoxia-inducible factor 1α modulates its interactions with the von Hippel-Lindau tumor suppressor protein.

Hypoxia-inducible factor 1 (HIF-1) plays an essential role in the regulation of hypoxia in humans. This regulation is mediated by the interaction of the von Hippel-Lindau tumor suppressor protein (pVHL) with the hydroxylated HIF-1α at proline564 (Pro564). Experimental studies reported that Pro567 could also be hydroxylated. However, the conformational dynamics of the complex of pVHL with hydroxylated HIF-1α at Pro564 is not well understood, and whether hydroxylated Pro567 plays the similar essential role as Pro564 in regulating HIF-1α-pVHL interaction remains elusive. Herein, we performed all-atom molecular dynamics (MD) simulations on the pVHL/HIF-1α complexes with single hydroxylation at Pro564 and Pro567, double hydroxylation at both Pro564 and Pro567, and without hydroxylation. Our multiple MD simulations and binding energy calculations show that hydroxylation at Pro567 is less favorable for the binding of HIF-1α to pVHL, whereas hydroxylation at Pro564 results in an increase of structural rigidity of the pVHL/HIF-1α complex and an enhancement of the interactions between HIF-1α and pVHL. The different roles revealed here for Pro564 and Pro567 in regulating HIF-1α-pVHL interactions, together with the previous finding that HIF-prolyl hydroxylase PHD-3 participates in a negative feedback loop controlling the HIF-1 level, suggest that hydroxylated HIF-1α at Pro567 may perturb or may not participate in this negative feedback loop. Intriguingly, our simulation data and community network analysis demonstrate that the binding of hydroxylated HIF-1α at Pro564 to the ß-domain of pVHL allosterically induces the conformational change of the α-domain via an optimal communication pathway from Pro564 of HIF-1α to S168 of the pVHL α-domain. This study reveals the different roles of Pro564 and Pro567 hydroxylation in HIF-1α in HIF-1α-pVHL interactions, which will be beneficial for developing effective strategies to treat hypoxia-related diseases and understanding the molecular basis of hypoxic training/exercise.

Iron overload in hereditary tyrosinemia type 1 induces liver injury through the Sp1/Tfr2/hepcidin axis.

BACKGROUND & AIMS: Iron is an essential metal for fundamental metabolic processes, but little is known regarding the involvement of iron in other nutritional disorders. In the present study, we investigated disordered iron metabolism in a murine model of hereditary tyrosinemia type I (HT1), a disease of the tyrosine degradation pathway. METHODS: We analysed the status of iron accumulation following NTBC withdrawal from Fah(-/-) mice, a murine model for HT1. Liver histology and serum parameters were used to assess the extent of liver injury and iron deposition. To determine the physiological significance of iron accumulation, mice were subjected to a low-iron food intake to reduce the iron accumulation. Mechanistic studies were performed on tissues and cells using immunoblotting, qRT-PCR, adenovirus transfection and other assays. RESULTS: Severe iron overload was observed in the murine model of HT1 with dramatically elevated hepatic and serum iron levels. Mechanistic studies revealed that downregulation and dysfunction of Tfr2 decreased hepcidin, leading to iron overload. The Fah(-/-) hepatocytes lost the ability of transferrin-sensitive induction of hepcidin. Forced expression of Tfr2 in the murine liver reduced the iron accumulation. Moreover, transcription factor Sp1 was downregulated and identified as a new regulator of Tfr2 here. Additionally, low-iron food intake effectively reduced the iron deposits, protected the liver and prolonged the survival in these mice. CONCLUSIONS: Iron was severely overloaded in the HT1 mice via the Sp1/Tfr2/Hepcidin axis. The iron overload induced liver injury in the HT1 mice, and reduction of the iron accumulation ameliorated liver injury. LAY SUMMARY: Primary and secondary iron overload is an abnormal status affecting millions of people worldwide. Here, we reported severe iron overload in a murine model of HT1, a disease of the tyrosine degradation pathway, and elucidated the mechanistic basis and the physiological significance of iron overload in HT1. These studies are of general interest not only with respect to secondary iron-induced liver injury in HT1 but also are important to elucidate the crosstalk between the two metabolic pathways.

The inhibitory mechanism of a fullerene derivative against amyloid-ß peptide aggregation: an atomistic simulation study.

Alzheimer's disease (AD) is associated with the pathological self-assembly of amyloid-ß (Aß) peptides into ß-sheet enriched fibrillar aggregates. Aß dimers formed in the initial step of Aß aggregation were reported to be the smallest toxic species. Inhibiting the formation of ß-sheet-rich oligomers and fibrils is considered as the primary therapeutic strategy for AD. Previous studies reported that fullerene derivatives strongly inhibit Aß fibrillation. However, the underlying inhibitory mechanism remains elusive. As a first step to understand fullerene-modulated full-length Aß aggregation, we investigated the conformational ensemble of the Aß1-42 dimer with and without 1,2-(dimethoxymethano)fullerene (DMF) - a more water-soluble fullerene derivative - by performing a 340 ns explicit-solvent replica exchange molecular dynamics simulation. Our simulations show that although disordered states are the most abundant conformations of the Aß1-42 dimer, conformations containing diverse extended ß-hairpins are also populated. The first most-populated ß-hairpins involving residues L17-D23 and A30-V36 strongly resemble the engineered ß-hairpin which is a building block of toxic Aß oligomers. We find that the interaction of DMFs with Aß peptides greatly impedes the formation of such ß-hairpins and inter-peptide ß-sheets. Binding energy analyses demonstrate that DMF preferentially binds not only to the central hydrophobic motif LVFFA of the Aß peptide as suggested experimentally, but also to the aromatic residues including F4 and Y10 and the C-terminal hydrophobic region I31-V40. This study reveals a complete picture of the inhibitory mechanism of full-length Aß1-42 aggregation by fullerenes, providing theoretical insights into the development of drug candidates against AD.

Amphiphilic Peptides A6K and V6K Display Distinct Oligomeric Structures and Self-Assembly Dynamics: A Combined All-Atom and Coarse-Grained Simulation Study.

Amphiphilic peptides can self-assemble into ordered nanostructures with different morphologies. However, the assembly mechanism and the structures of the early assemblies prior to nanostructure formation remain elusive. In this study, we investigated the oligomeric structures of two amphiphilic heptapeptides A6K and V6K by all-atom explicit-solvent replica-exchange molecular dynamics (REMD) simulations, and then examined the assembly dynamics of large aggregates by coarse-grained (CG) MD simulations. Our 200 ns REMD simulations show that A6K peptides predominantly adopt loosely packed disordered coil aggregates, whereas V6K peptides mostly assemble into compact ß-sheet-rich conformations, consistent with the signal measured experimentally in aqueous solution. Well-organized ß-sheet-rich conformations, albeit with low population, are also populated for V6K octamers, including bilayer ß-sheets and ß-barrels. These ordered ß-sheet-rich conformations are observed for the first time for amphiphilic peptides. Our 10-µs CG-MD simulations on 200 peptide chains demonstrate that A6K and V6K peptides follow two different self-assembly processes, and the former form monolayer lamellas while the latter assemble into plate-like assemblies. CG-MD simulations also show that V6K peptides display higher assembly capability than A6K, in support of our all-atom REMD simulation results. Interpeptide interaction analyses reveal that the marked differences in oligomeric structures and assembly dynamics between A6K and V6K result from the subtle interplay of competition among hydrophobic, hydrogen-bonding, and electrostatic interactions of the two peptides. Our study provides structural and mechanistic insights into the initial self-assembly process of A6K and V6K at the molecular level.

Electric-field-induced phase transition of confined water nanofilms between two graphene sheets.

A recent study reported that confined water nanofilms may freeze continuously or discontinuously depending on their densities. In this study, we report results from molecular dynamics simulations of the structures and the phase transition of water confined between two graphene sheets with a separation of 1.0 nm under the influence of an electric (E) field applied along the direction parallel to the sheets. We find that confined water can form three kinds of ice phases at atmospheric pressure: amorphous, hexagonal, or rhombic bilayer ice, depending on the E-field strength (0-1.5 V/nm). As the E-field strength changes, these ice configurations can transform into each other through a first-order phase transition. These E-field-induced water phases are different from those induced by high pressure (under high density). In addition, we find that all of the three ice nanofilms melt through a first-order transition. The heating and cooling processes are accompanied by a hysteresis loop between the solid and liquid phases. A phase diagram of confined water between two graphene sheets is given in the temperature-E-field plane.

In silico study on graphene quantum dots modified with various functional groups inhibiting α­synuclein dimerization.

HYPOTHESIS: Graphene quantum dots (GQDs) with various functional groups are hypothesized to inhibit the α-synuclein (αS) dimerization, a crucial step in Parkinson's disease pathogenesis. The potential of differently functionalized GQDs is systematically explored. EXPERIMENTS: All-atom replica-exchange molecular dynamics simulations (accumulating to 75.6 µs) in explicit water were performed to study the dimerization of the αS non-amyloid component region and the influence of GQDs modified with various functional groups. Conformation ensemble, binding behavior, and free energy analysis were conducted. FINDINGS: All studied GQDs inhibit ß-sheet and backbone hydrogen bond formation in αS dimers, leading to looser oligomeric conformations. Charged GQDs severely impede the growth of extended ß-sheets by providing extra contact surface. GQD binding primarily disrupts αS inter-peptide interactions through π-π stacking, CH-π interactions, and for charged GQDs, additionally through salt-bridge and hydrogen bonding interactions. GQD-COO- showed the most optimal inhibitory effect, binding mode, and intensity, which holds promise for the development of nanomedicines targeting amyloid aggregation in neurodegenerative diseases.

Understanding Pitfalls and Opportunities of Applying Heuristic Evaluation Methods to VR Training Systems: An Empirical Study.

The usability of virtual reality (VR) training applications is crucial for their success, but examining the usability in the early development stages remains challenging. A realistic and plausible solution would be revisiting and reconciling Heuristics Evaluation (HE) methods among the most widely used usability inspection methods in the human-computer interaction (HCI) domain. While research on studying and using HE methods is growing within the VR domain, few studies have considered the novel VR environment challenges new requirements for fitting HE methods to the context and applying them effectively. To this end, we conducted a user study with 14 evaluators using the standard HE methods to complete two HE sessions for a VR training application. We identified five critical challenges that evaluators encountered in the HE process by observing and interviewing them. Based on our findings, we discuss the importance of considering an easy-to-use heuristic set, how we can facilitate the HE procedures in the VR context, and the opportunities for developing HE-supporting tools.

Adsorption and Orientation of Human Islet Amyloid Polypeptide (hIAPP) Monomer at Anionic Lipid Bilayers: Implications for Membrane-Mediated Aggregation.

Protein misfolding and aggregation cause serious degenerative diseases, such as Alzheimer's and type II diabetes. Human islet amyloid polypeptide (hIAPP) is the major component of amyloid deposits found in the pancreas of type II diabetic patients. Increasing evidence suggests that ß-cell death is related to the interaction of hIAPP with the cellular membrane, which accelerates peptide aggregation. In this study, as a first step towards understanding the membrane-mediated hIAPP aggregation, we investigate the atomic details of the initial step of hIAPP-membrane interaction, including the adsorption orientation and conformation of hIAPP monomer at an anionic POPG lipid bilayer by performing all-atom molecular dynamics simulations. We found that hIAPP monomer is quickly adsorbed to bilayer surface, and the adsorption is initiated from the N-terminal residues driven by strong electrostatic interactions of the positively-charged residues K1 and R11 with negatively-charged lipid headgroups. hIAPP binds parallel to the lipid bilayer surface as a stable helix through residues 7-22, consistent with previous experimental study. Remarkably, different simulations lead to the same binding orientation stabilized by electrostatic and H-bonding interactions, with residues R11, F15 and S19 oriented towards membrane and hydrophobic residues L12, A13, L16 and V17 exposed to solvent. Implications for membrane-mediated hIAPP aggregation are discussed.

Membrane binding and insertion of a pHLIP peptide studied by all-atom molecular dynamics simulations.

Recent experiments in function mechanism study reported that a pH low-insertion peptide (pHLIP) can insert into a zwitterionic palmitoyloleoylphosphatidylcholine (POPC) lipid bilayer at acidic pH while binding to the bilayer surface at basic pH. However, the atomic details of the pH-dependent interaction of pHLIP with a POPC bilayer are not well understood. In this study, we investigate the detailed interactions of pHLIP with a POPC bilayer at acidic and basic pH conditions as those used in function mechanism study, using all-atom molecular dynamics (MD) simulations. Simulations have been performed by employing the initial configurations, where pHLIP is placed in aqueous solution, parallel to bilayer surface (system S), partially-inserted (system P), or fully-inserted (system F) in POPC bilayers. On the basis of multiple 200-ns MD simulations, we found (1) pHLIP in system S can spontaneously insert into a POPC bilayer at acidic pH, while binding to the membrane surface at basic pH; (2) pHLIP in system P can insert deep into a POPC bilayer at acidic pH, while it has a tendency to exit, and stays at bilayer surface at basic pH; (3) pHLIP in system F keeps in an α-helical structure at acidic pH while partially unfolding at basic pH. This study provides at atomic-level the pH-induced insertion of pHLIP into POPC bilayer.

Influence of Protonation on the Norepinephrine Inhibiting α-Synuclein 71-82 Oligomerization.

The pathogenesis of Parkinson's disease (PD) is closely linked to the massive presence of Lewy vesicles and Lewy axons in the cytoplasm of neurons, mainly consisting of α-synuclein (αS). Norepinephrine (NE), whose secretion can be increased by exercise, has been demonstrated to prevent the fibrillation of αS and to break down the mature αS fibrils. In this work, we focus on the influence of protonation on the inhibitory ability of NE by using amyloid core fragment αS71-82 as a template. All-atom replica-exchange molecular dynamics simulations (accumulating to 33.6 µs) in explicit water were performed to explore the inhibitory effect of protonated and nonprotonated NE on αS oligomerization. Our results show that NE/NE+ can lead to a significant decrease in ß-sheet content with increasing temperature, while isolated αS maintains relatively higher ß-sheet conformations until 363 K, implying that both NE and NE+ can lower the critical temperature required for αS fibril decomposition. NE and NE+ also lead to the formation of less compact αS oligomers by preventing the backbone hydrogen bonds and the side-chain packing. The protonation would affect the binding affinity, interaction modes, and binding intensity of NE with αS. Interesting, NE and NE+ have a distinct binding free energy in the electrostatic and solvation terms, which mostly counter each other and produce a weak binding intensity with αS. Our work contributes to a better understanding of the inhibitory mechanism of NE and NE+ on αS oligomerization relevant to PD pathogenesis, which may provide clues for the design of antiamyloid medicine.

Hydrogen Sulfide Prevents LPS-Induced Depression-like Behavior through the Suppression of NLRP3 Inflammasome and Pyroptosis and the Improvement of Mitochondrial Function in the Hippocampus of Mice.

Hydrogen sulfide (H2S) has been implicated to have antidepressive effects. We sought to investigate the prevention effects of H2S donor NaHS on depression-like behavior induced by lipopolysaccharide (LPS) in mice and its potential mechanisms. Sucrose preference, force swimming, open field, and elevate zero maze were used to evaluate depression-like behavior. NF-κB and NLRP3 inflammasome activation and mitochondrial function in the hippocampus were determined. It was found that depression-like behavior induced by LPS was prevented by NaHS pretreatment. LPS caused NF-κB and NLRP3 inflammasome activation in the hippocampus as evidenced by increased phosphorylated-p65 levels and increased NLRP3, ASC, caspase-1, and mature IL-1ß levels in the hippocampus, which were also blocked by NaHS. LPS increased GSDMD-N levels and TUNEL-positive cells in the hippocampus, which was prevented by NaHS. Abnormal mitochondrial morphology in the hippocampus was found in LPS-treated mice. Mitochondrial membrane potential and ATP production were reduced, and ROS production was increased in the hippocampus of LPS-treated mice. NaHS pretreatment improved impaired mitochondrial morphology and increased membrane potential and ATP production and reduced ROS production in the hippocampus of LPS-treated mice. Our data indicate that H2S prevents LPS-induced depression-like behaviors by inhibiting NLRP3 inflammasome activation and pyroptosis and improving mitochondrial function in the hippocampus.