Amyloids Are Novel Cell-Adhesive Matrices

Phenylalanine-based fibrillar systems

Phenylketonuria (PKU) is an inborn metabolic disorder characterized by excess accumulation of phenylalanine (Phe) and its fibril formation, resulting in progressive intellectual disability. Several research groups have approached from various directions to understand the formation of toxic amyloid fibrils from the essential amino acid Phe. Different parameters like the nature of the solvent, pH, Phe concentration, temperature, etc. influence the fibril formation kinetics. In this article, we have summarized all major findings regarding the formation of Phe-based fibrils in aqueous and organic media and discussed how non-covalent interactions are involved in the self-assembly process using spectroscopic and microscopic techniques. The toxicity of Phe-based fibrils is compared with other neurodegenerative peptides. It is noted that the Phe-based fibrils can also induce various globular proteins into toxic fibrils. Later, we discuss the different approaches to inhibit fibril formation and reduce its toxicity. The presence of polyphenolic compounds, drugs, amino acids, nanoparticles, metal ions, crown ethers, and others showed a remarkable inhibitory effect on fibril formation. To the best of our knowledge, this is the first-ever etymological analysis of the Phe-fibrillar system and its inhibition to create a strong database against PKU.

Amyloid fibril-based thixotropic hydrogels for modeling of tumor spheroids in vitro

Biomaterials mimicking extracellular matrices (ECM) for three-dimensional (3D) cultures have gained immense interest in tumor modeling and in vitro organ development. Here, we introduce a new class of amyloid fibril-based peptide hydrogels as a versatile biomimetic ECM scaffold for 3D cell culture and homogenous tumor spheroid modeling. We show that these amyloid fibril-based hydrogels are thixotropic and allow cancer cell adhesion, proliferation, and migration. All seven designed hydrogels support 3D cell culture with five different cancer cell lines forming spheroid with necrotic core and upregulation of the cancer biomarkers. We further developed the homogenous, single spheroid using the drop cast method and the data suggest that all hydrogels support the tumor spheroid formation but with different necrotic core diameters. The detailed gene expression analysis of MCF7 spheroid by microarray suggested the involvement of pro-oncogenes and significant regulatory pathways responsible for tumor spheroid formation. Further, using breast tumor tissue from a mouse xenograft model, we show that selected amyloid hydrogels support the formation of tumor spheroids with a well-defined necrotic core, cancer-associated gene expression, higher drug resistance, and tumor heterogeneity reminiscent of the original tumor. Altogether, we have developed an easy-to-use, rapid, cost-effective, and scalable platform for generating in vitro cancer models for the screening of anti-cancer therapeutics and developing personalized medicine.

Effects of phase-transited lysozyme on adhesion, migration and odontogenic differentiation of human dental pulp cells: An in vitro study

AIM

To explore the effects of phase-transited lysozyme (PTL) coated dentine slices on cell adhesion, migration and odontogenic differentiation of human dental pulp cells (HDPCs).

METHODOLOGY

Cell growth and cell cycle analysis were conducted to verify the biocompatibility of PTL for HDPCs. Cell adhesion, cell morphology and proliferation were explored by DiI staining, Scanning electron microscopy and MTT assay. Cell migration was investigated by Transwell assay. The effects of PTL on odontogenesis and mineralization of HDPCs were assessed by real-time quantitative polymerase chain reaction and Western blot. The mineralization of HDPCs was evaluated by Alizarin red staining. HDPCs were isolated from extracted third molars. The level of statistically significant difference was accepted at p < .05.

RESULTS

PTL showed no negative effect on cell cycle of HDPCs and compared with the blank group, HDPCs labelled with DiI staining showed significantly more adhered cells at 48 h (p < .05), extending cell processes and more finger-like or reticular pseudopodia on PTL-coated dentine slices. The results of MTT and Transwell assay showed that PTL promoted the proliferation (p < .05) and migration (p < .01) of HDPCs, respectively. Compared with the blank group, the gene expression of dentine sialophosphoprotein (DSPP), osteopontin and bone sialoprotein in HDPCs cultured on PTL was significantly upregulated on day 3 and 7 (p < .05), while the protein expression of DSPP showed no significant change on both day 7 and day 14. Alizarin red staining showed that PTL promoted more mineralization nodules formation of HDPCs (p < .05).

CONCLUSIONS

PTL promoted the adhesion, proliferation and migration of HDPCs on dentine slices, and positively affected odontogenic differentiation and mineralization of HDPCs.

Phase Behavior, Self-Assembly, and Adhesive Potential of Cellulose Nanocrystal-Bovine Serum Albumin Amyloid Composites

Structural organization is ubiquitous throughout nature and contributes to the outstanding mechanical/adhesive performance of organisms including geckoes, barnacles, and crustaceans. Typically, these types of structures are composed of polysaccharide and protein-based building blocks, and therefore, there is significant research interest in using similar building blocks in the fabrication of high-performance synthetic materials. Via evaporation-induced self-assembly, the organization of cellulose nanocrystals (CNCs) into a chiral nematic regime results in the formation of structured CNC films with prominent mechanical, optical, and photonic properties. However, there remains an important knowledge gap in relating equilibrium suspension behavior to dry film structuring and other functional properties of CNC-based composite materials. Herein, we systematically investigate the phase behavior of composite suspensions of rigid CNCs and flexible bovine serum albumin (BSA) amyloids in relation to their self-assembly into ordered films and structural adhesives. Increasing the concentration of BSA amyloids in the CNC suspensions results in a clear decrease in the anisotropic fraction volume percent via the preferential accumulation of BSA amyloids in the isotropic regime (as a result of depletion interactions). This translates to a blue shift or compression of the chiral nematic pitch in dried films. Finally, we also demonstrate the synergistic adhesive potential of CNC-BSA amyloid composites, with ultimate lap shear strengths in excess of 500 N/mg. We anticipate that understanding the systematic relationships between material interactions and self-assembly in suspension such as those investigated here will pave the way for a new generation of structured composite materials with a variety of enhanced functionalities.

Highly Adhesive Amyloid-Polyphenol Hydrogels for Cell Scaffolding

Rationally designing microstructures of soft hydrogels for specific biological functionalization is a challenge in tissue engineering applications. A novel and affordable soft hydrogel scaffold is constructed here by incorporating polyphenol modules with lysozyme amyloid fibrils (Lys AFs) via non-covalent self-assembly. Embedded polyphenols not only trigger hydrogel formation but also determine gel behavior by regulating the polyphenol gallol density and complex ratio. The feasibility of using a polyphenol-Lys AF hydrogel as a biocompatible cell scaffold, which is conducive to cell proliferation and spreading, is also shown. Notably, introducing polyphenols imparts the corresponding hydrogels a superior cell bioadhesive efficiency without further biofunctional decoration and thus may be successfully employed in both healthy and cancer cell lines. Confocal laser scanning microscopy also reveals that the highly expressed integrin-mediated focal adhesions form due to stimulation of the polyphenol-AF composite hydrogel, direct cell adhesion, proliferation, and spreading. Overall, this work constitutes a significant step forward in creating highly adhesive tissue culture platforms for in vitro culture of different cell types and may greatly expand prospects for future biomaterial design and development.