Rundong Hu

Tanshinones Inhibit Amyloid Aggregation by Amyloid-β Peptide, Disaggregate Amyloid Fibrils, and Protect Cultured Cells

The misfolding and aggregation of amyloid-β (Aβ) peptides into amyloid fibrils is regarded as one of the causative events in the pathogenesis of Alzheimers disease (AD). Tanshinones extracted from Chinese herb Danshen (Salvia Miltiorrhiza Bunge) were traditionally used as anti-inflammation and cerebrovascular drugs due to their antioxidation and antiacetylcholinesterase effects. A number of studies have suggested that tanshinones could protect neuronal cells. In this work, we examine the inhibitory activity of tanshinone I (TS1) and tanshinone IIA (TS2), the two major components in the Danshen herb, on the aggregation and toxicity of Aβ1-42 using atomic force microscopy (AFM), thioflavin-T (ThT) fluorescence assay, cell viability assay, and molecular dynamics (MD) simulations. AFM and ThT results show that both TS1 and TS2 exhibit different inhibitory abilities to prevent unseeded amyloid fibril formation and to disaggregate preformed amyloid fibrils, in which TS1 shows better inhibitory potency than TS2. Live/dead assay further confirms that introduction of a very small amount of tanshinones enables protection of cultured SH-SY5Y cells against Aβ-induced cell toxicity. Comparative MD simulation results reveal a general tanshinone binding mode to prevent Aβ peptide association, showing that both TS1 and TS2 preferentially bind to a hydrophobic β-sheet groove formed by the C-terminal residues of I31-M35 and M35-V39 and several aromatic residues. Meanwhile, the differences in binding distribution, residues, sites, population, and affinity between TS1-Aβ and TS2-Aβ systems also interpret different inhibitory effects on Aβ aggregation as observed by in vitro experiments. More importantly, due to nonspecific binding mode of tanshinones, it is expected that tanshinones would have a general inhibitory efficacy of a wide range of amyloid peptides. These findings suggest that tanshinones, particularly TS1 compound, offer promising lead compounds with dual protective role in anti-inflammation and antiaggregation for further development of Aβ inhibitors to prevent and disaggregate amyloid formation.

Probing the weak interaction of proteins with neutral and zwitterionic antifouling polymers

Protein-polymer interactions are of great interest in a wide range of scientific and technological applications. Neutral poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) (pSBMA) are two well-known nonfouling materials that exhibit strong surface resistance to proteins. However, it still remains unclear or unexplored how PEG and pSBMA interact with proteins in solution. In this work, we examine the interactions between two model proteins (bovine serum albumin and lysozyme) and two typical antifouling polymers of PEG and pSBMA in aqueous solution using fluorescence spectroscopy, atomic force microscopy and nuclear magnetic resonance. The effect of protein:polymer mass ratios on the interactions is also examined. Collective data clearly demonstrate the existence of weak hydrophobic interactions between PEG and proteins, while there are no detectable interactions between pSBMA and proteins. The elimination of protein interaction with pSBMA could be due to an enhanced surface hydration of zwitterionic groups in pSBMA. New evidence is given to demonstrate the interactions between PEG and proteins, which are often neglected in the literature because the PEG-protein interactions are weak and reversible, as well as the structural change caused by hydrophobic interaction. This work provides a better fundamental understanding of the intrinsic structure-activity relationship of polymers underlying polymer-protein interactions, which are important for designing new biomaterials for biosensor, medical diagnostics and drug delivery applications.

Binding characteristics between polyethylene glycol (PEG) and proteins in aqueous solution

Polymer-protein interactions are crucial for determining the activity of both polymer and protein for many bio-related applications. Poly(ethylene glycol) (PEG) as a well-known antifouling material is often coated on surfaces to form highly solvated brushes, which exhibit excellent protein-repellent properties. However, unlike surface-induced antifouling effects, little is known about the intrinsic PEG-protein interactions in aqueous solution, which is an important yet neglected problem. Here, we investigate the interactions between PEG and proteins in aqueous solution using fluorescence spectroscopy, atomic force microscopy (AFM), and nuclear magnetic resonance (NMR). Two important characteristics, molecular weight of PEG and mass ratio of PEG : protein, are examined to determine the effect of each on PEG-protein interactions as well as binding characteristics between PEG and proteins. In contrast to too long and too short PEG chains, collective results have shown that PEG with optimal molecular weight (MW) is more capable of interacting with proteins, which induces the conformational change of proteins through more stable binding sites and stronger interactions with long chain PEG. Enhanced PEG-protein interactions are likely due to the change of hydrophilicity to amphiphilicity of PEG with increasing MWPEG. In contrast to almost none or weak interactions of PEG surfaces with proteins, this work provides new evidence to demonstrate the existence of interactions between PEG and proteins in aqueous solution, which is important not only for better understanding of the structure-activity relationship of PEG both in solution and on surfaces, but also for the rational design of new PEG-based materials for specific applications.

Synthesis and Characterization of Antifouling Poly(N-acryloylaminoethoxyethanol) with Ultralow Protein Adsorption and Cell Attachment

Rational design of effective antifouling polymers is challenging but important for many fundamental and applied applications. Herein we synthesize and characterize an N-acryloylaminoethoxyethanol (AAEE) monomer, which integrates three hydrophilic groups of hydroxyl, amide, and ethylene glycol in the same material. AAEE monomers were further grafted and polymerized on gold substrates to form polyAAEE brushes with well-controlled thickness via surface-initiated atomic transfer radical polymerization (SI-ATRP), with particular attention to a better understanding of the molecular structure-antifouling property relationship of hydroxyl-acrylic-based polymers. The surface hydrophilicity and antifouling properties of polyAAEE brushes as a function of film thickness are studied by combined experimental and computational methods including surface plasmon resonance (SPR) sensors, atomic force microscopy (AFM), cell adhesion assay, and molecular dynamics (MD) simulations. With the optimal polymer film thicknesses (∼10-40 nm), polyAAEE-grafted surfaces can effectively resist protein adsorption from single-protein solutions and undiluted human blood plasma and serum to a nonfouling level (i.e., <0.3 ng/cm(2)). The polyAAEE brushes also highly resist mammalian cell attachment up to 3 days. MD simulations confirm that the integration of three hydrophilic groups induce a stronger and closer hydration layer around polyAAEE, revealing a positive relationship between surface hydration and antifouling properties. The molecular structure-antifouling properties relationship of a series of hydroxyl-acrylic-based polymers is also discussed. This work hopefully provides a promising structural motif for the design of new effective antifouling materials beyond traditional ethylene glycol-based antifouling materials.

Non-selective ion channel activity of polymorphic human islet amyloid polypeptide (amylin) double channels.

Fundamental understanding of ion channel formation by amyloid peptides, which is strongly linked to cell toxicity, is very critical for (pre)clinical treatment of neurodegenerative diseases. Here, we combine atomistic simulations and experiments to demonstrate a broad range of conformational states of hIAPP double channels in lipid membranes. All individual channels display high selectivity for Cl(-) ions over cations, but the co-existence of polymorphic double channels of different conformations and orientations with different populations determines the non-ionic selectivity nature of the channels, which is different from the typical amyloid-β channels that exhibit Ca(2+) selective ion-permeable characteristics. This work provides a more complete physicochemical mechanism of amyloid-channel-induced toxicity.

Cross-Seeding Interaction between β-Amyloid and Human Islet Amyloid Polypeptide.

Alzheimers disease (AD) and type 2 diabetes (T2D) are two common protein misfolding diseases. Increasing evidence suggests that these two diseases may be correlated with each other via cross-sequence interactions between β-amyloid peptide (Aβ) associated with AD and human islet amyloid polypeptide (hIAPP) associated with T2D. However, little is known about how these two peptides work and how they interact with each other to induce amyloidogenesis. In this work, we study the effect of cross-sequence interactions between Aβ and hIAPP peptides on hybrid amyloid structures, conformational changes, and aggregation kinetics using combined experimental and simulation approaches. Experimental results confirm that Aβ and hIAPP can interact with each other to aggregate into hybrid amyloid fibrils containing β-sheet-rich structures morphologically similar to pure Aβ and hIAPP. The cross-seeding of Aβ and hIAPP leads to the coexistence of both a retarded process at the initial nucleation stage and an accelerated process at the fibrillization stage, in conjunction with a conformational transition from random structures to α-helix to β-sheet. Further molecular dynamics simulations reveal that Aβ and hIAPP oligomers can efficiently cross-seed each other via the association of two highly similar U-shaped β-sheet structures; thus, conformational compatibility between Aβ and hIAPP aggregates appears to play a key role in determining barriers to cross-seeding. The cross-seeding effects in this work may provide new insights into the molecular mechanisms of interactions between AD and T2D.

Structural and Energetic Insight into the Cross-Seeding Amyloid Assemblies of Human IAPP and Rat IAPP

The misfolding and aggregation of human islet amyloid polypeptide (hIAPP or amylin) into small oligomers and large amyloid fibrils is believed to be responsible for the dysfunction and death of pancreatic β-cells in diabetes type II. However, rat IAPP (rIAPP), which differs from the hIAPP by only 6 of 37 residues, lacks the ability to form amyloid fibrils and to induce cell death. Little is known about the cross-sequence interactions and cross-seeding structures between hIAPP and rIAPP peptides. Herein using explicit-solvent molecular dynamics (MD) simulations, we modeled and simulated different heteroassemblies formed by the amyloidogenic hIAPP and the nonamyloidogenic rIAPP peptides. Simulations showed that the U-shaped hIAPP monomer and oligomers can interact with conformationally similar rIAPP to form stable complexes and to coassemble into heterogeneous structures. Stable heterointeractions between hIAPP and rIAPP were shown to arise from hydrophobic contacts and hydrogen bonds at the interface, particularly at N- and C-terminal β-sheet regions. Because of the enhanced interpeptide interactions at the interface, upon binding to hIAPP oligomers, the β-sheet population of rIAPP was greatly increased as compared to that of rIAPP alone. More importantly, the conformational energies of rIAPP monomers at the bound state were observed to be consistently higher than those of rIAPP monomers at the unbound state. However, rIAPP monomers enable one to adopt different conformations and follow different pathways for associating with hIAPP from the high energy of the bound state to the low energy of the unbound state, without encountering any large and abrupt energy barrier. In parallel, AFM study of cross-aggregation of hIAPP and rIAPP provided additional evidence that hIAPP can seed with rIAPP to form hybrid fibrils at all concentrations similar to pure hIAPP fibrils. This work demonstrates the existence of cross-interactions between the two different IAPP peptides, which provides an improved fundamental understanding of the cross-seeding of different amyloid sequences toward amyloid aggregation and toxicity mechanisms.

Enhanced Thermoelectric Properties of Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) by Binary Secondary Dopants.

UNLABELLED To simultaneously increase the electrical conductivity and Seebeck coefficient of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate ( PEDOT PSS) was a challenge for realizing efficient organic thermoelectrics. In this study, for the first time, we report both increased electrical conductivities and Seebeck coefficients, hence, enhanced thermoelectric properties of PEDOT PSS thin films by doped with binary secondary dopants, dimethyl sulfoxide (DMSO) and poly(ethylene oxide) (PEO). Without modifying film morphology, the molar ratios of PEDOT to PSS are tuned by PEO, resulting in increased proportions of PEDOT in the bipolaron states. Our study provides a facile route to optimizing thermoelectric properties of PEDOT PSS thin films.

Cross-Sequence Interactions between Human and Rat Islet Amyloid Polypeptides

Human islet amyloid polypeptide (hIAPP) can assemble into toxic oligomers and fibrils, which are associated with cell degeneration and the pathogenesis of type 2 diabetes. Cross-interaction of hIAPP with rat IAPP (rIAPP)--a non-amyloidogenic peptide with high sequence similarity to hIAPP--might influence the aggregation and toxicity of hIAPP. However, the exact role of rIAPP in hIAPP aggregation and toxicity still remains unclear. In this work, we investigated the effect of cross-sequence interactions between full-length hIAPP(1-37) and rIAPP(1-37) on hybrid amyloid structures, aggregation kinetics, and cell toxicity using combined computational and experimental approaches. Experimental results indicate a contrasting role of rIAPP in hIAPP aggregation, in which rIAPP initially inhibits the early aggregation and nuclei formation of hIAPP, but hIAPP seeds can also recruit both hIAPP and rIAPP to form more hybrid fibrils, thus promoting amyloid fibrillation ultimately. The coincubation of hIAPP and rIAPP also decreases cell viability, presumably due to the formation of more toxic hybrid oligomers at the prolonged lag phase. Comparative MD simulations confirm that the cross-sequence interactions between hIAPP and rIAPP stabilize β-sheet structure and thus likely promote their fibrillization. This work provides valuable insights into a critical role of cross-amyloid interactions in protein aggregation.

Polymorphic Associations and Structures of the Cross-Seeding of Aβ1–42 and hIAPP1–37 Polypeptides

Emerging evidence have shown that the patients with Alzheimers disease (AD) often have a higher risk of later developing type II diabetes (T2D), and vice versa, suggesting a potential pathological link between AD and T2D. Amyloid-β (Aβ) and human islet amyloid polypeptide (hIAPP) are the principle causative components responsible for the pathologies of AD and T2D, respectively. The cross-sequence interactions between Aβ and hIAPP may provide a molecular basis for better understanding the potential link between AD and T2D. Herein, we systematically modeled and simulated the cross-sequence aggregation process, molecular interactions, and polymorphic structures of full-length Aβ and hIAPP peptides using a combination of coarse-grained (CG) replica-exchange molecular dynamics (REMD) and all-atom molecular dynamics (MD) simulations, with particular focus on the effect of association models between Aβ and hIAPP on the structural stability and polymorphic populations of hybrid Aβ-hIAPP aggregates. Four distinct association models (double-layer, elongation, tail-tail, and block models) between Aβ and hIAPP oligomers were identified, and the associated polymorphic Aβ-hIAPP structures were determined as well. Among them, different association models led to different Aβ-hIAPP aggregates, with large differences in structural morphologies and populations, interacting interfaces, and underlying association forces. The computational models support the cross-sequence interactions between Aβ and hIAPP pentamers, which would lead to the complex hybrid Aβ-hIAPP assemblies. This computational work may also provide a different point of view to a better understanding of a potential link between AD and T2D.