The powerful functions of peptide-based bioactive matrices for regenerative medicine

Abstract

In an effort to develop bioactive matrices for regenerative medicine, peptides have been used widely to promote interactions with cells and elicit desired behaviors in vivo. This paper describes strategies that utilize peptide-based molecules as building blocks to create supramolecular nanostructures that emulate not only the architecture but also the chemistry of the extracellular matrix in mammalian biology. After initiating a desired regenerative response in vivo, the innate biodegradability of these systems allow for the natural biological processes to take over in order to promote formation of a new tissue without leaving a trace of the nonnatural components. These bioactive matrices can either bind or mimic growth factors or other protein ligands to elicit a cellular response, promote specific mechano-biological responses, and also guide the migration of cells with programmed directionality. In vivo applications discussed in this review using peptide-based matrices include the regeneration of axons after spinal cord injury, regeneration of bone, and the formation of blood vessels in ischemic muscle as a therapy in peripheral arterial disease and cardiovascular diseases.

FIGURE 1

(a) Diagram showing the formation of H-bonding between two interacting QQRFQWQFEQQ (P₁₁-II) peptide molecules that promote the formation of fibril and ribbon structures. (b) Proposed self-assembly and chemical structure of the amphiphilic β-hairpin MAX 1. Panel (a) reprinted with permission from Fishwick et al. Copyright 2003 American Chemical Society. Panel (b) reprinted with permission from Kretsinger et al. Copyright 2005 Elsevier Ltd.

FIGURE 2

(a) Two different coiled-coil designs by the Woolfson group where changing ionic interactions between residues b and c yielded thick fibers (left), while changing residues b, c and f for weaker interaction such as hydrophobic and H-bonding resulted in fibrous hydrogels (right). (b) The same group was able to functionalized their coiled-coil peptides with RGDS via click chemistry without interrupting the formation of fibrous hydrogels as determined by SEM. Panel (a) reprinted with permission from Banwell et al. Copyright 2009 Macmillan Publishers Ltd. Panels (b) reprinted with permission from Mehrban et al. Copyright 2014 Wiley–VCH Verlag GmbH & Co.

FIGURE 3

(a) Chemical structure of the metal ligand-containing collagen peptide designed by the Chmielewski group (left). In the presence a divalent metal (such as Ni(II)), the peptide is able to form a reversible (with the addition of the metal chelator EDTA) three-dimensional porous collagen scaffold for cell encapsulation. (b) The Hartgerink group was able to design an collagen peptide that self-assembles by electrostatic interaction initiated between Lys and Asp at the ‘sticky end’ of a collagen triple helix into fibrous hydrogels. Panel (a) reprinted with permission from Pires et al. Copyright 2009 Wiley–VCH Verlag GmbH & Co. Panel (b) reprinted with permission from Kumar et al. Copyright 2014 American Chemical Society and from O’Leary et al. Copyright 2011 Macmillan Publishers Ltd.

FIGURE 4

(a) Chemical structure of a canonical peptide amphiphile (PA) molecule and a pictorial representation of their assembly into nanofibers. The four regions depicted above represent the unbranched alkyl (usually palmitic acid) tail (region I), a β-sheet amino acid sequence to promote cohesion through H-bonding (region II), charged amino acids for solubility and fiber crosslinking (region III) and a peptide signaling epitope to induce a biological response (region IV). (b) TEM micrograph depicting the self-assembly of PAs in solution as high aspect ratio of nanofibers with micrometer length. (c) Formation of a PA, coloured with tryptan blue into a noodle-like string in a phosphate-buffered saline solution. (d) SEM micrograph of the PA gel strings showing highly aligned PA nanofibers bundles. (e) These PA gel strings can be used to efficiently encapsulate and align cells, such as hMSCs, along the axis of the gel. (f) Alignment of fluorescently stained SMCs along a PA tube gel after 7 days in culture for the potential application of artery reconstruction. Panel (a) and (b) reprinted with permission from Matson et al. Copyright 2011 Elsevier Ltd. Panel (c), (d) and (e) reprinted with permission from Zhang et al. Copyright 2010 Macmillan Publishers Ltd. Panel (f) reprinted with permission from McClendon and Stupp Copyright 2012 Elsevier Ltd.

FIGURE 5

(a) Proposed mechanism of the assembly of EAK16 via antiparallel H-bonding in addition to the hydrophobic interactions between the alanine side chains and the ionic interactions between the charged Lys and Glu residues. (b) Diagram of the RADA16 molecule composed of both the positive (Arg) and negative residues (Asp) to promote the assembly of the peptide by electrostatic interactions into fibers and macroscopic hydrogels in buffer. Panels (a) and (b) reprinted with permission from Zhang et al. and Yokoi et al., respectively Copyright 1993 and 2005 Proceedings of the National Academy of Science.

FIGURE 6

Self-assembled peptide materials for nervous tissue regeneration. (a) Neural stem cells (NSCs) differentiated when cultured with IKVAV epitope-presenting PA matrix (green, beta-tubulin III; red, GFAP). (b) Faster development of hippocampal neurons was observed on a softer PA substrate. (c) Aligned PA nanofibers guided the direction of neurite outgrowth. (d) Transmission electron micrographs of sections of cavernous nerve in adult rats after crush injury and treatment with BSA PA (left) or SHH PA (right) for 6 weeks. Myelinated and nonmyelinated fibers (indicated by arrows) show and an enhanced regeneration after SHH PA treatment. (e) Self-assembled peptide nanofiber scaffolds (SAPNS) were used to treat optic tract transection, where the lesion was made at superior colliculus (SC) in 2 days old hamster (left to right). Dark-field images of lesion in control and SAPNS injected animals after 1 day and after 30 days. Panel (a) reprinted with permission from Silva et al. Copyright 2004 American Association for the Advancement of Science. Panels (b), (c) and (d) reprinted with permission from Sur et al., Berns et al. and Angeloni et al. Copyright 2013 Elsevier B.V. Panel (e) reprinted with permission from Ellis-Behnke et al. Copyright 2006 Proceedings of the National Academy of Science.

FIGURE 7

(a) In the ECM, the heparan sulfate (yellow)-syndecan (blue) complexes bind BMP-2 (pink) and regulate its interaction with the cell-surface receptor (purple). Fibronectin fibers (orange) also shown. (b) HBPA, which contains a consensus heparin-binding domain, can utilize heparin or heparan sulfate to deliver BMP-2. HBPA nanofibers-heparan sulfate nanofibers promoted enhanced bone regeneration in a rat critical-size defect model, as shown by (c) microcomputed tomography (μCT) reconstruction and (d) the amount of new bone. (e) PA nanofibers designed with an affinity to BMP-2 (BMP2b-PA) can bind the growth factor directly. The BMP-2-binding PA promoted greater spinal fusion than PA nanofibers without BMP-2-binding epitopes (Diluent PA) and absorbable collagen scaffold, as shown by (f) fusion scores from blind manual palpation analysis at 8 weeks, (g) fusion rate, and (h) representative μCT reconstruction. Panels (a–d) reprinted with permission from Lee et al. Copyright 2014 Elsevier B.V. Panels (f–h) reprinted with permission from Lee et al. Copyright 2014 Wiley–VCH Verlag GmbH & Co.

FIG. 8

(a) VEGF-PA, which contains the VEGF-mimetic sequence (QK) located at the C-terminus of the PA, can self-assemble into fibers to form a three-dimension gel as determined by (b) scanning electron microscopy (SEM). (b) Motor function scores were significantly higher when the PA was used in comparison to (QK), the mutant VEGF-PA and the saline control. (c) Laser Doppler Perfusion Imaging confirms the positive effect of VEGF-PA by portraying higher perfusion ratios after 28 days post-injection. (d) After 14 days post-injection of NFs with 100 and 1000 ng/mL (NF/V100 and NF/V1000), the infarct size has significantly decreased in size and (e) the arteriole density has increased indicating improved cardiac performance on the MI rat models through arteriogenesis (f) Dil fluorescence (red) corresponding to significant recruitment of circulating bone marrow cells (BMCs) into the infarct area with NF/V100. Panels (a–c) reprinted with permission from Webber et al. Copyright 2012 Proceedings of the National Academy of Science. Panels (d–f) reprinted with permission from Lin et al. Copyright 2012 American Association for the Advancement of Science.