ROS-Responsive Methionine-Containing Amphiphilic Peptides Impart Enzyme-Triggered Phase Transition and Antioxidant Cell Protection.

Reactive oxygen species (ROS) are produced by cellular activities, such as metabolism and immune response, and play important roles in cell signaling and homeostasis. However, overproduced ROS causes irreversible damage to nucleic acids and membrane lipids, supporting genetic mutations and enhancing the effects of aging. Cells defend themselves against ROS using antioxidant systems based on redox-active sulfur and transition metals. Inspired by such biological redox-responsive systems, we developed methionine-containing self-assembling peptides. The Met-containing peptides formed hydrogels that underwent a gel-to-sol phase transition upon oxidation by H2O2, and the sensitivity of the peptides to the oxidant increased as the number of Met residues increased. The peptide containing three Met residues, the largest number of Met residues in our series of designed peptides, showed the highest sensitivity to oxidation and detoxification to protect cells from ROS damage. In addition, this peptide underwent a phase transition in response to H2O2 produced by an oxidizing enzyme. This study demonstrates the design of a supramolecular biomaterial that is responsive to enzymatically generated ROS and can protect cells against oxidative stress.

ROS-Triggered Gel-Sol Transition and Kinetics-Controlled Cargo Release by Methionine-Containing Peptides.

The gel-sol transition of self-assembling peptides is a useful switch for environment-dependent drug release. For their applications, kinetics control of the responses is important for matching the velocity of release to the target biological events. Here we demonstrate the chemical control of redox-triggered gel-sol transition kinetics of self-assembling peptides by altering the amino acid sequence. Amphiphilic peptides were developed in which a methionine residue was located in the middle (JigSAP-IMI) or near the N terminus (JigSAP-MII). Both peptides formed hydrogels under physiological conditions-forming ß-sheet-based supramolecular nanofibers. In contrast, the oxidized forms remained in the solution state under identical conditions-adopting α-helix-rich secondary structures. Upon oxidation with H2 O2 , a reactive oxygen species, JigSAP-MII showed a faster gel-to-sol transition and cargo-releasing than JigSAP-IMI, thus indicating that the phase-transition and releasing kinetics of self-assembling peptides can be rationally controlled by the position of the reactive amino acid residue.

Amphiphilic peptide-tagged N-cadherin forms radial glial-like fibers that enhance neuronal migration in injured brain and promote sensorimotor recovery.

The mammalian brain has very limited ability to regenerate lost neurons and recover function after injury. Promoting the migration of young neurons (neuroblasts) derived from endogenous neural stem cells using biomaterials is a new and promising approach to aid recovery of the brain after injury. However, the delivery of sufficient neuroblasts to distant injured sites is a major challenge because of the limited number of scaffold cells that are available to guide neuroblast migration. To address this issue, we have developed an amphiphilic peptide [(RADA)3-(RADG)] (mRADA)-tagged N-cadherin extracellular domain (Ncad-mRADA), which can remain in mRADA hydrogels and be injected into deep brain tissue to facilitate neuroblast migration. Migrating neuroblasts directly contacted the fiber-like Ncad-mRADA hydrogel and efficiently migrated toward an injured site in the striatum, a deep brain area. Furthermore, application of Ncad-mRADA to neonatal cortical brain injury efficiently promoted neuronal regeneration and functional recovery. These results demonstrate that self-assembling Ncad-mRADA peptides mimic both the function and structure of endogenous scaffold cells and provide a novel strategy for regenerative therapy.

Efficient protein incorporation and release by a jigsaw-shaped self-assembling peptide hydrogel for injured brain regeneration.

During injured tissue regeneration, the extracellular matrix plays a key role in controlling and coordinating various cellular events by binding and releasing secreted proteins in addition to promoting cell adhesion. Herein, we develop a cell-adhesive fiber-forming peptide that mimics the jigsaw-shaped hydrophobic surface in the dovetail-packing motif of glycophorin A as an artificial extracellular matrix for regenerative therapy. We show that the jigsaw-shaped self-assembling peptide forms several-micrometer-long supramolecular nanofibers through a helix-to-strand transition to afford a hydrogel under physiological conditions and disperses homogeneously in the hydrogel. The molecular- and macro-scale supramolecular properties of the jigsaw-shaped self-assembling peptide hydrogel allow efficient incorporation and sustained release of vascular endothelial growth factor, and demonstrate cell transplantation-free regenerative therapeutic effects in a subacute-chronic phase mouse stroke model. This research highlights a therapeutic strategy for injured tissue regeneration using the jigsaw-shaped self-assembling peptide supramolecular hydrogel.

Hydrogel-Stiffening and Non-Cell Adhesive Properties of Amphiphilic Peptides with Central Alkylene Chains.

Invited for the cover of this issue is the group of Takahiro Muraoka at Tokyo University of Agriculture and Technology and collaborators. The image depicts nanofiber formation of an amphiphilic peptide with a central alkylene chain that shows non-cell adhesive properties. Read the full text of the article at 10.1002/chem.202100739.

Hydrogel-Stiffening and Non-Cell Adhesive Properties of Amphiphilic Peptides with Central Alkylene Chains.

Amphiphilic peptides bearing terminal alkyl tails form supramolecular nanofibers that are increasingly used as biomaterials with multiple functionalities. Insertion of alkylene chains in peptides can be designed as another type of amphiphilic peptide, yet the influence of the internal alkylene chains on self-assembly and biological properties remains poorly defined. Unlike the terminal alkyl tails, the internal alkylene chains can affect not only the hydrophobicity but also the flexibility and packing of the peptides. Herein, we demonstrate the supramolecular and biological effects of the central alkylene chain length inserted in a peptide. Insertion of the alkylene chain at the center of the peptide allowed for strengthened ß-sheet hydrogen bonds and modulation of the packing order, and consequently the amphiphilic peptide bearing C2 alkylene chain formed a hydrogel with the highest stiffness. Interestingly, the amphiphilic peptides bearing internal alkylene chains longer than C2 showed a diminished cell-adhesive property. This study offers a novel molecular design to tune mechanical and biological properties of peptide materials.