Detection of type I collagen fibrils formation and dissociation by a fluorescence method based on thioflavin T

Collagen Mimicry with a Short Collagen Model Peptide

Mimicking triple helix and fibrillar network of collagen through collagen model peptide(CMP) with short GPO tripeptide repeats is a great challenge. Herein, a minimalistic CMP comprising only five GPO repeats [(GPO)5 ] is presented. This novel approach involves the fusion of ultrashort peptide with the synergetic power of π-system and β-sheet formation to short CMP (GPO)5 . Accordingly, a hydrogel-forming, fluorenylmethoxycarbonyl (Fmoc)-functionalized ultrashort peptide (NFGAIL) is fused at the N-terminus and phenylalanine at the C-terminus of (GPO)5 (Fmoc-NFGAIL-(GPO)5 -F-COOH, FmP-5GPO). At room temperature, it forms a robust triple helix in aqueous buffer solution and has a relatively high melting point of 35 °C. The fluorenyl motif stabilizes the triple helix by aromatic π-π interactions as in its absence, triple helix is not formed. NFGAIL, which forms a β-sheet, also aids in triple helix stabilization via intermolecular hydrogen bonding and hydrophobic interactions. FmP-5GPO forms highly entangled nanofibrils with a micrometer length, which have excellent cell viability. The achievement of stable triple helix and fibrils in such a short CMP(FmP-5GPO) sequence is a challenging feat, and its significance in CMP-based biomaterials is undeniable. The present strategy highlights the potential for developing new CMP sequences through intelligent tuning of fusion peptides and GPO repeats.

Development of biomimetic co-culture and tri-culture models to mimic the complex structure of the alveolar-capillary barrier

Alveoli are the functional area of respiratory system where the gaseous exchanges take place at level of the alveolar-capillary barrier. The development of safe and effective therapeutic approaches for treating lung disease is currently limited due to the lack of realistic preclinical models for their testing and validation. In this work, tissue engineering approaches were exploited to develop a biomimetic platform that provide an appropriate mimicking of the extracellular environment and the multicellular architecture of human alveoli. Here, we propose the implementation of two biomimetic in vitro models to reproduce the features of the main anatomic portions of the physiological alveolar-capillary barrier. First, a co-culture barrier model was obtained by integrating an electrospun polycaprolactone-gelatin (PCL-Gel) membrane in a modified transwell insert (PCL-Gel TW) to mimic the alveolar basement membrane (coded as thin model). Alveolar epithelial (A549) and lung microvascular endothelial (HULEC-5a) cells were cultured on the apical and basolateral side of the PCL-Gel membrane, respectively, under physiologic air-liquid interface (ALI) conditions for 7 days. The ALI condition promoted the expression of type I and type II alveolar epithelial cell markers and the secretion of mucus in A549 cells. Increased cell viability and barrier properties in co-cultures of A549 and HULEC-5a compared to mono-cultures revealed the effectiveness of the model to reproduce in vitro physiological-relevant features of the alveolar-capillary barrier. The second portion of the alveolar-capillary barrier was developed implementing a tri-culture model (coded as thick model) including a type I collagen (COLL) hydrogel formulated to host lung fibroblasts (MRC-5). The thick barrier model was implemented by seeding HULEC-5a on the basolateral side of PCL-Gel TW and then pouring sequentially MRC-5-laden COLL hydrogel and A549 cells on the apical side of the electrospun membrane. The thick model was maintained up to 7 days at ALI and immunofluorescence staining of tight and adherent junctions demonstrated the formation of a tight barrier. Lastly, the ability of models to emulate pathological inflammatory conditions was validated by exposing the apical compartment of the PCL-Gel TW to lipopolysaccharide (LPS). The damage of A549 tight junctions, the increase of barrier permeability and IL-6 pro-inflammatory cytokine release was observed after 48 h exposure to LPS.

Thioflavin-T: A Quantum Yield-Based Molecular Viscometer for Glycerol-Monohydroxy Alcohol Mixtures

Molecular rotor dye thioflavin T (ThT) is almost nonfluorescent in low-viscosity solvents but highly fluorescent when bound to amyloid fibrils. This unique property arises from the rotation of the dimethylaniline moiety relative to the benzothiazole moiety in the excited state, which drives the dye from an emissive locally excited state to a twisted intramolecular charge-transfer state. This process is viscosity-controlled, and therefore, we can use the quantum yield of ThT to assess the viscosity of the environment. In this study, we have investigated the quantum yield of ThT (φThT) in various compositions of six alcoholic solvent mixtures of glycerol with methanol, ethanol, n-propanol, iso-propanol, n-butanol, and tert-butanol. We have proposed an empirical model using φThT as a function of the mole fraction of glycerol to estimate the interaction parameters between the components of the solvent mixtures. This analysis allowed us to predict the extent of nonideality of the solvent mixtures. The Förster-Hoffmann- and Loutfy-Arnold-type power law relationship was established between the quantum yield of ThT and bulk viscosity for solvent mixtures of methanol, ethanol, n-butanol, and tert-butanol with glycerol, and it was found to be similar in nature in all the four mixtures. Applying this knowledge, we proposed a methodology to quantify and predict the bulk viscosity coefficient values of several compositions of n-propanol-glycerol and iso-propanol-glycerol mixtures which have not been previously documented.

Extracellular Targets to Reduce Excessive Scarring in Response to Tissue Injury

Excessive scar formation is a hallmark of localized and systemic fibrotic disorders. Despite extensive studies to define valid anti-fibrotic targets and develop effective therapeutics, progressive fibrosis remains a significant medical problem. Regardless of the injury type or location of wounded tissue, excessive production and accumulation of collagen-rich extracellular matrix is the common denominator of all fibrotic disorders. A long-standing dogma was that anti-fibrotic approaches should focus on overall intracellular processes that drive fibrotic scarring. Because of the poor outcomes of these approaches, scientific efforts now focus on regulating the extracellular components of fibrotic tissues. Crucial extracellular players include cellular receptors of matrix components, macromolecules that form the matrix architecture, auxiliary proteins that facilitate the formation of stiff scar tissue, matricellular proteins, and extracellular vesicles that modulate matrix homeostasis. This review summarizes studies targeting the extracellular aspects of fibrotic tissue synthesis, presents the rationale for these studies, and discusses the progress and limitations of current extracellular approaches to limit fibrotic healing.

Hierarchical approach for the rational construction of helix-containing nanofibrils using α,β-peptides

The rational design of novel self-assembled nanomaterials based on peptides remains a great challenge in modern chemistry. A hierarchical approach for the construction of nanofibrils based on α,β-peptide foldamers is proposed. The incorporation of a helix-promoting trans-(1S,2S)-2-aminocyclopentanecarboxylic acid residue in the outer positions of the model coiled-coil peptide led to its increased conformational stability, which was established consistently by the results of CD, NMR and FT-IR spectroscopy. The designed oligomerization state in the solution of the studied peptides was confirmed using analytical ultracentrifugation. Moreover, the cyclopentane side chain allowed additional interactions between coiled-coil-like structures to direct the self-assembly process towards the formation of well-defined nanofibrils, as observed using AFM and TEM techniques.

Fibrillogenesis of acrylic acid-grafted-collagen without self-assembly property inspired by the hybrid fibrils of xenogeneic collagen

Along with advancements in both protein and chemistry science, the chemical modification of proteins is attracting more and more attention. More specifically, the attachment of polymers or reactive moieties into collagen offers a method to add novel functions to this protein. However, the fibrillogenesis of the modified collagen with high grafting density cannot always be achieved. Here, inspired by the hybrid fibrils of xenogeneic collagen, fibrillogenesis of acrylic acid-grafted-collagen (AAc-g-Col) without self-assembly property was achieved by the induction of natural collagen (Col). The step-by-step co-assembly process of AAc-g-Col and Col was confirmed by turbidity assay. The formation of Col/AAc-g-Col hybrid fibrils was verified by TEM since the acryloyl groups of the hybrid fibrils were labelled using HS-AuNPs based on the Michael addition. Moreover, rheology, SEM, and MTT assays revealed that the fibrillary structures and biocompatibility of the Col/AAc-g-Col hydrogel were comparable to that of the Col hydrogel, although they presented a lower viscoelasticity.

Characterization of biocompatible pig skin collagen and application of collagen-based films for enzyme immobilization

Based on the excellent biocompatibility of collagen, collagen was extracted from pig skin by acid-enzymatic method. The films were prepared by the self-aggregation behavior of collagen, and the catalase was immobilized by adsorption, cross-linking and embedding. The experiment investigated the effects of glutaraldehyde on the mechanical properties, external sensory properties, and denaturation temperature of the films. The results showed that self-aggregating material could maintain the triple helix structure of pig skin collagen. The self-aggregation treatment and cross-linking treatment can improve the mechanical properties to 53 MPa, while the glutaraldehyde cross-linking agent can increase the denaturation temperature of the pig skin collagen self-aggregating membrane by 20.35% to 84.48 °C. This means that its application to immobilized catalase has better stability. The comparison shows that the catalase immobilized by the adsorption method has strong activity and high operational stability, and the cross-linking agent glutaraldehyde and the initial enzyme concentration have a significant effect on the immobilization, and the activity can reach 175 U g-1. After 16 uses of the film, the catalase was completely inactivated. This study provides a reference for the preparation of a catalase sensor that can be used to detect hydrogen peroxide in food by a catalase sensor.

Temperature-responsive collagen–PNIPAAm conjugate: preparation and fibrillogenesis

A collagen–PNIPAAm conjugate is prepared using the “grafting from” method under mild conditions, and fibrillogenesis was realized by the induction of natural collagen.

The effect of alkaline pretreatment on the biochemical characteristics and fibril-forming abilities of types I and II collagen extracted from bester sturgeon by-products

Non-mammalian collagens have attracted increasing attention for industrial and biomedical use. We have therefore evaluated extraction conditions and the biochemical properties of collagens from aquacultured sturgeon. Pepsin-soluble type I and type II collagen were respectively extracted from the skin and notochord of bester sturgeon by-products, with yields of 63.9 ± 0.19% and 35.5 ± 0.68%. Collagen extraction efficiency was improved by an alkaline pretreatment of the skin and notochord (fewer extraction cycles were required), but the final yields decreased to 56.2 ± 0.84% for type I and 31.8 ± 1.13% for type II. Alkaline pretreatment did not affect the thermal stability or triple-helical structure of both types of collagen. Types I and II collagen formed re-assembled fibril structures in vitro, under different conditions. Alkaline pretreatment slowed down the formation of type I collagen fibrils and specifically inhibited the formation of thick fibril-bundle structures. In contrast, alkaline pretreatment did not change type II collagen fibril formation. In conclusion, alkaline pretreatment of sturgeon skin and notochord is an effective method to accelerate collagen extraction process of types I and II collagen without changing their biochemical properties. However, it decreases the yield of both collagens and specifically changes the fibril-forming ability of type I collagen.

Insight into the role of grafting density in the self-assembly of acrylic acid-grafted-collagen

Side chain modification of collagen provides an attractive way to enhance their structure and functions, which is highly desirable for the development of promising biomaterials. However, the impact of structural change of side chains on the intrinsic self-assembly property of collagen was always ignored. Here, a series of acrylic acid-grafted-collagen (AA-g-Col) with different grafting density were prepared to explore the impact of side chain structural variation on the self-assembly of collagen. The results showed that excessive grafting density would weaken or even disappear the self-assembly property of AA-g-Col, but only affects the triple helix to a minor extent. Compared to pristine collagen, the mechanical property and cytocompatibility of AA-g-Col based matrices also deteriorated, along with the increase of grafting density. Therefore, this work contributed a new insight into the importance of grafting density for the study of modified collagen, which would be helpful for the design of optimized formulate collagen-based hybrid materials with both additional novel functions and tissue-mimicking fibrillary structures.

Study on the kinetic self-assembly of type I collagen from tilapia (Oreochromis niloticus) skin using the fluorescence probe thioflavin T

The kinetic self-assembly of type I collagen from tilapia (Oreochromis niloticus) skin was characterized by the fluorescence method based on thioflavin T (ThT). The fluorescence probe could bind to the active monomeric collagen with a higher ordered degree of molecule, which displayed the pH and ionic strength dependence, the binding constant higher at neutral pH and proportional to the NaCl concentration. Compared to the turbidity method, ThT was more suitable to characterize the nucleation phase of collagen self-assembly. The nucleus size was determined through the ThT fluorescence and linear-polymerization model. At various pH and ionic strength, the nucleus size was nearly identical, either one or two monomers, demonstrating that one or two active monomeric collagen formed into the nucleus and different pH and ionic strength didn't alter the self-assembly mechanism of collagen. This approach was beneficial to advance the understanding of the kinetic self-assembly of the fish-sourced collagen in vitro.