Structural and physical basis for the elasticity of elastin.

Elastin function is to endow vertebrate tissues with elasticity so that they can adapt to local mechanical constraints. The hydrophobicity and insolubility of the mature elastin polymer have hampered studies of its molecular organisation and structure-elasticity relationships. Nevertheless, a growing number of studies from a broad range of disciplines have provided invaluable insights, and several structural models of elastin have been proposed. However, many questions remain regarding how the primary sequence of elastin (and the soluble precursor tropoelastin) governs the molecular structure, its organisation into a polymeric network, and the mechanical properties of the resulting material. The elasticity of elastin is known to be largely entropic in origin, a property that is understood to arise from both its disordered molecular structure and its hydrophobic character. Despite a high degree of hydrophobicity, elastin does not form compact, water-excluding domains and remains highly disordered. However, elastin contains both stable and labile secondary structure elements. Current models of elastin structure and function are drawn from data collected on tropoelastin and on elastin-like peptides (ELPs) but at the tissue level, elasticity is only achieved after polymerisation of the mature elastin. In tissues, the reticulation of tropoelastin chains in water defines the polymer elastin that bears elasticity. Similarly, ELPs require polymerisation to become elastic. There is considerable interest in elastin especially in the biomaterials and cosmetic fields where ELPs are widely used. This review aims to provide an up-to-date survey of/perspective on current knowledge about the interplay between elastin structure, solvation, and entropic elasticity.

Handedness and its genetic influences are associated with structural asymmetries of the cerebral cortex in 31,864 individuals.

Roughly 10% of the human population is left-handed, and this rate is increased in some brain-related disorders. The neuroanatomical correlates of hand preference have remained equivocal. We resampled structural brain image data from 28,802 right-handers and 3,062 left-handers (UK Biobank population dataset) to a symmetrical surface template, and mapped asymmetries for each of 8,681 vertices across the cerebral cortex in each individual. Left-handers compared to right-handers showed average differences of surface area asymmetry within the fusiform cortex, the anterior insula, the anterior middle cingulate cortex, and the precentral cortex. Meta-analyzed functional imaging data implicated these regions in executive functions and language. Polygenic disposition to left-handedness was associated with two of these regional asymmetries, and 18 loci previously linked with left-handedness by genome-wide screening showed associations with one or more of these asymmetries. Implicated genes included six encoding microtubule-related proteins: TUBB, TUBA1B, TUBB3, TUBB4A, MAP2, and NME7-mutations in the latter can cause left to right reversal of the visceral organs. There were also two cortical regions where average thickness asymmetry was altered in left-handedness: on the postcentral gyrus and the inferior occipital cortex, functionally annotated with hand sensorimotor and visual roles. These cortical thickness asymmetries were not heritable. Heritable surface area asymmetries of language-related regions may link the etiologies of hand preference and language, whereas nonheritable asymmetries of sensorimotor cortex may manifest as consequences of hand preference.

Elastin-Hyaluronan Bioconjugate as Bioactive Component in Electrospun Scaffolds.

Hyaluronic acid or hyaluronan (HA) and elastin-inspired peptides (EL) have been widely recognized as bioinspired materials useful in biomedical applications. The aim of the present work is the production of electrospun scaffolds as wound dressing materials which would benefit from synergic action of the bioactivity of elastin peptides and the regenerative properties of hyaluronic acid. Taking advantage of thiol-ene chemistry, a bioactive elastin peptide was successfully conjugated to methacrylated hyaluronic acid (MAHA) and electrospun together with poly-D,L-lactide (PDLLA). To the best of our knowledge, limited reports on peptide-conjugated hyaluronic acid were described in literature, and none of these was employed for the production of electrospun scaffolds. The conformational studies carried out by Circular Dichroism (CD) on the bioconjugated compound confirmed the preservation of secondary structure of the peptide after conjugation while Scanning Electron Microscopy (SEM) revealed the supramolecular structure of the electrospun scaffolds. Overall, the study demonstrates that the bioconjugation of hyaluronic acid with the elastin peptide improved the electrospinning processability with improved characteristics in terms of morphology of the final scaffolds.

Large-Scale Phenomic and Genomic Analysis of Brain Asymmetrical Skew.

The human cerebral hemispheres show a left-right asymmetrical torque pattern, which has been claimed to be absent in chimpanzees. The functional significance and developmental mechanisms are unknown. Here, we carried out the largest-ever analysis of global brain shape asymmetry in magnetic resonance imaging data. Three population datasets were used, UK Biobank (N = 39 678), Human Connectome Project (N = 1113), and BIL&GIN (N = 453). At the population level, there was an anterior and dorsal skew of the right hemisphere, relative to the left. Both skews were associated independently with handedness, and various regional gray and white matter metrics oppositely in the two hemispheres, as well as other variables related to cognitive functions, sociodemographic factors, and physical and mental health. The two skews showed single nucleotide polymorphisms-based heritabilities of 4-13%, but also substantial polygenicity in causal mixture model analysis, and no individually significant loci were found in genome-wide association studies for either skew. There was evidence for a significant genetic correlation between horizontal brain skew and autism, which requires future replication. These results provide the first large-scale description of population-average brain skews and their inter-individual variations, their replicable associations with handedness, and insights into biological and other factors which associate with human brain asymmetry.

Structural properties and anticoagulant/cytotoxic activities of heterochiral enantiomeric thrombin binding aptamer (TBA) derivatives.

The thrombin binding aptamer (TBA) possesses promising antiproliferative properties. However, its development as an anticancer agent is drastically impaired by its concomitant anticoagulant activity. Therefore, suitable chemical modifications in the TBA sequence would be required in order to preserve its antiproliferative over anticoagulant activity. In this paper, we report structural investigations, based on circular dichroism (CD) and nuclear magnetic resonance spectroscopy (NMR), and biological evaluation of four pairs of enantiomeric heterochiral TBA analogues. The four TBA derivatives of the d-series are composed by d-residues except for one l-thymidine in the small TT loops, while their four enantiomers are composed by l-residues except for one d-thymidine in the same TT loop region. Apart from the left-handedness for the l-series TBA derivatives, CD and NMR measurements have shown that all TBA analogues are able to adopt the antiparallel, monomolecular, 'chair-like' G-quadruplex structure characteristic of the natural D-TBA. However, although all eight TBA derivatives are endowed with remarkable cytotoxic activities against colon and lung cancer cell lines, only TBA derivatives of the l-series show no anticoagulant activity and are considerably resistant in biological environments.

Hydrogels from the Assembly of SAA/Elastin-Inspired Peptides Reveal Non-Canonical Nanotopologies.

Peptide-based hydrogels are of great interest in the biomedical field according to their biocompatibility, simple structure and tunable properties via sequence modification. In recent years, multicomponent assembly of peptides have expanded the possibilities to produce more versatile hydrogels, by blending gelating peptides with different type of peptides to add new features. In the present study, the assembly of gelating P5 peptide SFFSF blended with P21 peptide, SFFSFGVPGVGVPGVGSFFSF, an elastin-inspired peptides or, alternatively, with FF dipeptide, was investigated by oscillatory rheology and different microscopy techniques in order to shed light on the nanotopologies formed by the self-assembled peptide mixtures. Our data show that, depending on the added peptides, cooperative or disruptive assembly can be observed giving rise to distinct nanotopologies to which correspond different mechanical properties that could be exploited to fabricate materials with desired properties.

Novel characterization of the relationship between verbal list-learning outcomes and hippocampal subfields in healthy adults.

The relationship between hippocampal subfield volumetry and verbal list-learning test outcomes have mostly been studied in clinical and elderly populations, and remain controversial. For the first time, we characterized a relationship between verbal list-learning test outcomes and hippocampal subfield volumetry on two large separate datasets of 447 and 1,442 healthy young and middle-aged adults, and explored the processes that could explain this relationship. We observed a replicable positive linear correlation between verbal list-learning test free recall scores and CA1 volume, specific to verbal list learning as demonstrated by the hippocampal subfield volumetry independence from verbal intelligence. Learning meaningless items was also positively correlated with CA1 volume, pointing to the role of the test design rather than word meaning. Accordingly, we found that association-based mnemonics mediated the relationship between verbal list-learning test outcomes and CA1 volume. This mediation suggests that integrating items into associative representations during verbal list-learning tests explains CA1 volume variations: this new explanation is consistent with the associative functions of the human CA1.

Probing the Importance of the G-Quadruplex Grooves for the Activity of the Anti-HIV-Integrase Aptamer T30923.

In this paper, we report studies concerning four variants of the G-quadruplex forming anti-HIV-integrase aptamer T30923, in which specific 2'-deoxyguanosines have been singly replaced by 8-methyl-2'-deoxyguanosine residues, with the aim to exploit the methyl group positioned in the G-quadruplex grooves as a steric probe to investigate the interaction aptamer/target. Although, the various modified aptamers differ in the localization of the methyl group, NMR, circular dichroism (CD), electrophoretic and molecular modeling data suggest that all of them preserve the ability to fold in a stable dimeric parallel G-quadruplex complex resembling that of their natural counterpart T30923. However, the biological data have shown that the T30923 variants are characterized by different efficiencies in inhibiting the HIV-integrase, thus suggesting the involvement of the G-quadruplex grooves in the aptamer/target interaction.

Interactions between elastin-like peptides and an insulating poly(ortho-aminophenol) membrane investigated by AFM and XPS.

This investigation was undertaken to explore the mutual recognition of the pentapeptide (ValGlyGlyValGly)n, a hydrophobic elastin-like peptide (ELP), suspended in deionized water in monomer (n = 1) and trimer (n = 3) forms and the outer surface of a very thin, insulating polymer, poly(ortho-aminophenol) (PoAP), electrochemically grown on a platinum foil by cyclic voltammetry in a neutral medium (phosphate-buffered saline, I = 0.1M) immersed in the suspension. As a prior task, the proved propensity of the ValGlyGlyValGly sequence, at the given minimal length (three or more repeats), to self-assemble into amyloid-like fibrils when solubilized in an aqueous environment was considered within the framework of testing PoAP surfaces for the specific detection of amyloid precursors. From our knowledge of the chemical structure and physical properties of both biomacromolecule families obtained in previous studies, we focused on the efficacy of the binding sites offered to ELP fibrils by PoAP in its as-prepared form or properly modified either by postsynthesis oxidation or by adsorption/entrapping of ELP monomer(s) with or without protecting terminal groups. Consistent with all methods of preparation, the best surfaces, recognizable by the trimer fibrils, are those modified to carry a larger number of carbonyls, particularly by entrapment of ELP monomer(s) during PoAP electrosynthesis using an imprinting-inspired method. The degree of attachment of fibrillar aggregates, detected by atomic force microscopy and X-ray photoelectron spectroscopy, provides unequivocal evidence of the cooperative forces involving PoAP-ELP interactions. The results obtained suggest the prospect of using the proposed Pt/PoAP/ELP systems as biodetectors in Alzheimer disease. Graphical abstract Synthesis steps of Pt/PoAP/ELP electrodes for amyloid detection. AFM = Atomic Force Microscopy, CV = Cyclic Voltammetry, ELPs = Elastin like Peptides, PoAP = Poly ortho-Aminophenol, Pt = Platinum, XPS = X-ray Photoelectron Spectroscopy.

Photoinduced Thiol-ene Chemistry Applied to the Synthesis of Self-Assembling Elastin-Inspired Glycopeptides.

Synthetic (glyco)peptides inspired by proteins able to self-assemble are appealing biomaterials in the field of tissue engineering and regenerative medicine. Herein, for the first time, taking advantage of thiol-ene chemistry coupled to solid-phase peptide synthesis, a self-assembling peptide inspired by elastin protein was bioconjugated to three carbohydrates in order to obtain the corresponding glycopeptides. They were studied at the molecular and supramolecular level. The results show that the carbohydrate influences the molecular conformation of the glycopeptide and its self-aggregation properties as well. As future perspective, the results could enable us to tune the final self-aggregation properties of the glycopeptide by changing the sugar moiety.

Site-specific replacement of the thymine methyl group by fluorine in thrombin binding aptamer significantly improves structural stability and anticoagulant activity.

Here we report investigations, based on circular dichroism, nuclear magnetic resonance spectroscopy, molecular modelling, differential scanning calorimetry and prothrombin time assay, on analogues of the thrombin binding aptamer (TBA) in which individual thymidines were replaced by 5-fluoro-2'-deoxyuridine residues. The whole of the data clearly indicate that all derivatives are able to fold in a G-quadruplex structure very similar to the 'chair-like' conformation typical of the TBA. However, only ODNs TBA-F4: and TBA-F13: have shown a remarkable improvement both in the melting temperature (ΔTm ≈ +10) and in the anticoagulant activity in comparison with the original TBA. These findings are unusual, particularly considering previously reported studies in which modifications of T4 and T13 residues in TBA sequence have clearly proven to be always detrimental for the structural stability and biological activity of the aptamer. Our results strongly suggest the possibility to enhance TBA properties through tiny straightforward modifications.

Characterization of a Crosslinked Elastomeric-Protein Inspired Polypeptide.

Materials inspired by natural proteins have a great appeal in tissue engineering for their biocompatibility and similarity to extracellular matrix (ECM). Chimeric polypeptides inspired by elastomeric proteins such as silk, elastin, and collagen are of outstanding interest in the field. A recombinant polypeptide constituted of three different blocks, each of them having sequences derived from elastin, resilin, and collagen proteins, was demonstrated to be a good candidate as biomaterial for its self-assembling characteristics and biocompatibility. Herein, taking advantage of the primary amine functionalities present in the linear polypeptide, we crosslinked it with 1,6-hexamethylene-diisocyanate (HMDI). The characterization of the obtained polypeptide was realized by CD spectroscopy, AFM, and SEM microscopies. The obtained results, although not conclusive, demonstrate that the crosslinked polypeptide gave rise to porous networks, thin nanowires, and films not observable for the linear polypeptide. Chirality 28:606-611, 2016. © 2016 Wiley Periodicals, Inc.

Machine learning framework for early MRI-based Alzheimer's conversion prediction in MCI subjects.

Mild cognitive impairment (MCI) is a transitional stage between age-related cognitive decline and Alzheimer's disease (AD). For the effective treatment of AD, it would be important to identify MCI patients at high risk for conversion to AD. In this study, we present a novel magnetic resonance imaging (MRI)-based method for predicting the MCI-to-AD conversion from one to three years before the clinical diagnosis. First, we developed a novel MRI biomarker of MCI-to-AD conversion using semi-supervised learning and then integrated it with age and cognitive measures about the subjects using a supervised learning algorithm resulting in what we call the aggregate biomarker. The novel characteristics of the methods for learning the biomarkers are as follows: 1) We used a semi-supervised learning method (low density separation) for the construction of MRI biomarker as opposed to more typical supervised methods; 2) We performed a feature selection on MRI data from AD subjects and normal controls without using data from MCI subjects via regularized logistic regression; 3) We removed the aging effects from the MRI data before the classifier training to prevent possible confounding between AD and age related atrophies; and 4) We constructed the aggregate biomarker by first learning a separate MRI biomarker and then combining it with age and cognitive measures about the MCI subjects at the baseline by applying a random forest classifier. We experimentally demonstrated the added value of these novel characteristics in predicting the MCI-to-AD conversion on data obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. With the ADNI data, the MRI biomarker achieved a 10-fold cross-validated area under the receiver operating characteristic curve (AUC) of 0.7661 in discriminating progressive MCI patients (pMCI) from stable MCI patients (sMCI). Our aggregate biomarker based on MRI data together with baseline cognitive measurements and age achieved a 10-fold cross-validated AUC score of 0.9020 in discriminating pMCI from sMCI. The results presented in this study demonstrate the potential of the suggested approach for early AD diagnosis and an important role of MRI in the MCI-to-AD conversion prediction. However, it is evident based on our results that combining MRI data with cognitive test results improved the accuracy of the MCI-to-AD conversion prediction.

Tuning self-assembly in elastin-derived peptides.

Elastin-derived peptides are gaining increasing interest as potential biomaterials. Previous studies have demonstrated that short elastin-derived peptides are able to self-assemble into fibrils as the entire elastin protein. The motif responsible for that is the XGGZG motif at least three-fold repeated. In this work we have synthesized and studied, at molecular and supramolecular levels, four pentadecapeptides obtained by switching the X and Z residue with leucine and/or valine. We found that the four peptides formed different supramolecular structures corresponding to specific molecular conformations. Our results show that not only the residue type but also the exact position occupied by the residue in the motif is crucial in driving the self-aggregation. The aim of this work is to provide the basis for designing elastin-derived peptides with tunable supramolecular architecture.

An automatic framework for quantitative validation of voxel based morphometry measures of anatomical brain asymmetry.

The study of anatomical brain asymmetries has been a topic of great interest in the neuroimaging community in the past decades. However, the accuracy of brain asymmetry measurements has been rarely investigated. In this study, we propose a fully automatic methodology for the quantitative validation of brain tissue asymmetries as measured by Voxel Based Morphometry (VBM) from structural magnetic resonance (MR) images. Starting from a real MR image, the methodology generates simulated 3D MR images with a known and realistic pattern of inter-hemispheric asymmetry that models the left-occipital right-frontal petalia of a normal brain and the related rightward bending of the inter-hemispheric fissure. As an example, we generated a dataset of 64 simulated MR images and applied this dataset for the quantitative validation of optimized VBM measures of asymmetries in brain tissue composition. Our results suggested that VBM analysis strongly depended on the spatial normalization of the individual brain images, the selected template space, and the amount of spatial smoothing applied. The most accurate asymmetry detections were achieved by 9-degrees of freedom registration to the symmetrical template space with 4 to 8mm spatial smoothing.

The insertion of two 8-methyl-2'-deoxyguanosine residues in tetramolecular quadruplex structures: trying to orientate the strands.

In this article, we report a structural study, based on NMR and CD spectroscopies, and molecular modelling of all possible d(TG(3)T) and d(TG(4)T) analogues containing two 8-methyl-2'-deoxyguanosine residues (M). Particularly, the potential ability of these modified residues to orientate the strands and then to affect the folding topology of tetramolecular quadruplex structures has been investigated. Oligodeoxynucleotides (ODNs) TMMGT (T12) and TMMGGT (F12) form parallel tetramolecular quadruplexes, characterized by an all-syn M-tetrad at the 5'-side stacked to all-anti M- and G-tetrads. ODNs TMGMT (T13) and TMGGMT (F14) form parallel tetramolecular quadruplexes, in which an all-anti G core is sandwiched between two all-syn M-tetrads at the 5'- and the 3'-side. Notably, the quadruplex formed by T13 corresponds to an unprecedented structure in which the syn residues exceed in number the anti ones. Conversely, ODN TGMGMT (F24) adopts a parallel arrangement in which all-anti G-tetrads alternate with all-syn M-tetrads. Most importantly, all data strongly suggest that ODN TMGMGT (F13) forms an unprecedented anti-parallel tetramolecular quadruplex in which G and M residues adopt anti and syn glycosidic conformations, respectively. This article opens up new understandings and perspectives about the intricate relationship between the quadruplex strands orientation and the glycosidic conformation of the residues.

Chemical Modifications in Hyaluronic Acid-Based Electrospun Scaffolds.

Hyaluronic acid (HA) is a natural, non-sulfated glycosaminoglycan (GAG) present in ECM. It is involved in different biological functions with appealing properties in cosmetics and pharmaceutical preparations as well as in tissue engineering. Generally, HA has been electrospun in blends with natural or synthetic polymers to produce fibers having diameters in the order of nano and micro-scale whose pores can host cells able to regenerate damaged tissues. In the last decade, a rich literature on electrospun HA-based materials arose. Chemical modifications were generally introduced in HA scaffolds to favour crosslinking or conjugation with bioactive molecules. Considering the high solubility of HA in water, HA-based electrospun scaffolds are cross-linked to increase the stability in biological fluids. Crosslinking is necessary also to avoid the release of HA from the hybrid scaffold when implanted in-vivo. Furthermore, to endow the HA based scaffolds with new chemical or biological properties, conjugation of bioactive molecules to HA was widely reported. Herein, we review the existing research classifying chemical modifications on HA and HA-based electrospun fibers into three categories: i) in-situ crosslinking of electrospun HA-based scaffolds ii) off-site crosslinking of electrospun HA-based scaffolds; iii) conjugation of biofunctional molecules to HA with focus on peptides.

A Study on Thiol-Michael Addition to Semi-Synthetic Elastin-Hyaluronan Material for Electrospun Scaffolds.

Thiol-Michael addition is a chemical reaction extensively used for conjugating peptides to polysaccharides with applications as biomaterials. In the present study, for designing a bioactive element in electrospun scaffolds as wound dressing material, a chemical strategy for the semi-synthesis of a hyaluronan-elastin conjugate containing an amide linker (ELAHA) was developed in the presence of tris(2-carboxyethyl)phosphine hydrochloride (TCEP ⋅ HCl). The bioconjugate was electrospun with poly-D,L-lactide (PDLLA), obtaining scaffolds with appealing characteristics in terms of morphology and cell viability of dermal fibroblast cells. For comprehending the factors influencing the efficiency of the bioconjugation reaction, thiolated amino acids were also investigated as nucleophiles toward hyaluronan decorated with Michael acceptors in the presence of TCEP ⋅ HCl through the evaluation of byproducts formation.

Highly Cytocompatible Polylactic Acid Based Electrospun Microfibers Loaded with Silver Nanoparticles Generated onto Chestnut Shell Lignin for Targeted Antibacterial Activity and Antioxidant Action.

Electrospun (e-spun) fibers are generally regarded as powerful tools for cell growth in tissue regeneration applications, and the possibility of imparting functional properties to these materials represents an increasingly pursued goal. We report herein the preparation of hybrid materials in which an e-spun d,l-polylactic acid matrix, to which chitosan or crystalline nanocellulose was added to improve hydrophilicity, was loaded with different amounts of silver(0) nanoparticles (AgNP) generated onto chestnut shell lignin (CSL) (AgNP@CSL). A solvent-free mechanochemical method was used for efficient (85% of the theoretical value by XRD analysis) Ag(0) production from the reduction of AgNO3 by lignin. For comparison, e-spun fibers containing CSL alone were also prepared. SEM and TEM analyses confirmed the presence of AgNP@CSL (average size 30 nm) on the fibers. Different chemical assays indicated that the AgNP@CSL containing fibers exhibited marked antioxidant properties (EC50 1.6 ± 0.1 mg/mL, DPPH assay), although they were halved with respect to those of the CSL containing fibers, as expected because of the efficient silver ion reduction. All the fibers showed high cytocompatibility toward human mesenchymal stem cells (hMSCs) representative of the self-healing process, and their antibacterial properties were tested against the pathogens Escherichia coli (E. coli), Staphylococcus epidermidis, and Pseudomonas aeruginosa. Finally, competitive surface colonization as simulated by cocultures of hMSC and E. coli showed that AgNP@CSL loaded fibers offered the cells a targeted protection from infection, thus well balancing cytocompatibility and antibacterial properties.

Investigating the role of (2S,4R)-4-hydroxyproline in elastin model peptides.

Post-translational modifications play a key role in defining the biological functions of proteins. Among them, the hydroxylation of proline producing the (2S,4R)-4-hydroxyproline (Hyp) is one of the most frequent modifications observed in vertebrates, being particularly abundant in the proteins of the extracellular matrix. In collagen, hydroxylation of proline plays a critical role, conferring the correct structure and mechanical strength to collagen fibers. In elastin, the exact role of this modification is not yet understood. Here we show that Hyp-containing elastin polypeptides have flexible molecular structures, analogously to proline-containing polypeptides. In turn, the self-assembly of the elastin peptides is significantly altered by the presence of Hyp, evidencing different supramolecular structures. Also the in vitro susceptibility to protease digestion is changed. These findings give a better insight into the elastic fiber formation and degradation processes in the extracellular matrix. Furthermore, our results could contribute in defining the subtle role of proline structural variants in the folding and self-assembly of elastin-inspired peptides, helping the rational design of elastin biomaterials.