Biofunctionalized self-assembly of peptide amphiphile induces the differentiation of bone marrow mesenchymal stem cells into neural cells

Elucidating the cell penetrating properties of self-assembling β-peptides

Self-assembling lipopeptide hydrogels have been widely developed for the delivery of therapeutics due to their rapid gelation, injectability, and highly controlled physicochemical properties. Lipopeptides are also known for their membrane-associating and cell penetrating properties, which may impact on their application in cell-encapsulation. Self-assembling lipidated-β3-peptide materials developed in our laboratory have previously been used in cell culture as 2D substrates, thus as a continuation of this work we aimed to encapsulate cells in 3D by forming a hydrogel. We therefore assessed the self-assembling lipidated-β3-peptides for cell-penetrating properties in mesenchymal stems cells (MSC) using fluorescence microscopy and membrane association with surface plasmon resonance spectroscopy (SPR). The results demonstrated that lipidated β3-peptides penetrate the MSC plasma membrane and localise to the mitochondrial network. While self-assembling lipopeptide hydrogels have shown tremendous potential for delivery of therapeutics, further optimisation may be required to minimise the membrane uptake of the lipidated-β3-peptides for cell encapsulation applications.

Designed peptide amphiphiles as scaffolds for tissue engineering

Peptide amphiphiles (PAs) are peptide-based molecules that contain a peptide sequence as a head group covalently conjugated to a hydrophobic segment, such as lipid tails. They can self-assemble into well-ordered supramolecular nanostructures such as micelles, vesicles, twisted ribbons and nanofibers. In addition, the diversity of natural amino acids gives the possibility to produce PAs with different sequences. These properties along with their biocompatibility, biodegradability and a high resemblance to native extracellular matrix (ECM) have resulted in PAs being considered as ideal scaffold materials for tissue engineering (TE) applications. This review introduces the 20 natural canonical amino acids as building blocks followed by highlighting the three categories of PAs: amphiphilic peptides, lipidated peptide amphiphiles and supramolecular peptide amphiphile conjugates, as well as their design rules that dictate the peptide self-assembly process. Furthermore, 3D bio-fabrication strategies of PAs hydrogels are discussed and the recent advances of PA-based scaffolds in TE with the emphasis on bone, cartilage and neural tissue regeneration both in vitro and in vivo are considered. Finally, future prospects and challenges are discussed.

Cell-binding peptides on the material surface guide stem cell fate of adhesion, proliferation and differentiation

Human cells, especially stem cells, need to communicate and interact with extracellular matrix (ECM) proteins, which not only serve as structural components but also guide and support cell fate and properties such as cell adhesion, proliferation, survival and differentiation. The binding of the cells with ECM proteins or ECM-derived peptides via cell adhesion receptors such as integrins activates several signaling pathways that determine the cell fate, morphological change, proliferation and differentiation. The development of synthetic ECM protein-derived peptides that mimic the biological and biochemical functions of natural ECM proteins will benefit academic and clinical application. Peptides derived from or inspired by specific ECM proteins can act as agonists of each ECM protein receptor. Given that most ECM proteins function in cell adhesion via integrin receptors, many peptides have been developed that bind to specific integrin receptors. In this review, we discuss the peptide sequence, immobilization design, reaction method, and functions of several ECM protein-derived peptides. Various peptide sequences derived from mainly ECM proteins, which are used for coating or grafting on dishes, scaffolds, hydrogels, implants or nanofibers, have been developed to improve the adhesion, proliferation or differentiation of stem cells and to culture differentiated cells. This review article will help to inform the optimal choice of ECM protein-derived peptides for the development of scaffolds, implants, hydrogels, nanofibers and 2D cell culture dishes to regulate the proliferation and direct the differentiation of stem cells into specific lineages.

Self-Assembled Peptide Nanostructures for ECM Biomimicry

Proteins are functional building blocks of living organisms that exert a wide variety of functions, but their synthesis and industrial production can be cumbersome and expensive. By contrast, short peptides are very convenient to prepare at a low cost on a large scale, and their self-assembly into nanostructures and gels is a popular avenue for protein biomimicry. In this Review, we will analyze the last 5-year progress on the incorporation of bioactive motifs into self-assembling peptides to mimic functional proteins of the extracellular matrix (ECM) and guide cell fate inside hydrogel scaffolds.

Spidroin Silk Fibers with Bioactive Motifs of Extracellular Proteins for Neural Tissue Engineering

The interaction of neural progenitor cells (NPCs) with the extracellular matrix (ECM) plays an important role in neural tissue regeneration. Understanding which motifs of the ECM proteins are crucial for normal NPC adhesion, proliferation, and differentiation is important in order to create more adequate tissue engineered models of neural tissue and to efficiently study the central nervous system regeneration mechanisms. We have shown earlier that anisotropic matrices prepared from a mixture of recombinant dragline silk proteins, such as spidroin 1 and spidroin 2, by electrospinning are biocompatible with NPCs and provide good proliferation and oriented growth of neurites. This study objective was to find the effects of spidroin-based electrospun materials, modified with peptide motifs of the extracellular matrix proteins (RGD, IKVAV, and VAEIDGIEL) on adhesion, proliferation, and differentiation of directly reprogrammed neural precursor cells (drNPCs). The structural and biomechanical studies have shown that spidroin-based electrospun mats (SBEM), modified with ECM peptides, are characterized by a uniaxial orientation and elastic moduli in the swollen state, comparable to those of the dura mater. It has been found for the first time that drNPCs on SBEM mostly preserve their stemness in the growth medium and even in the differentiation medium with brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor, while addition of the mentioned ECM-peptide motifs may shift the balance toward neuroglial differentiation. We have demonstrated that the RGD motif promotes formation of a lower number of neurons with longer neurites, while the IKVAV motif is characterized by formation of a greater number of NF200-positive neurons with shorter neurites. At the same time, all the studied matrices preserve up to 30% of neuroglial progenitor cells, phenotypically similar to radial glia derived from the subventricular zone. We believe that, by using this approach and modifying spidroin by various ECM-motifs or other substances, one may create an in vitro model for the neuroglial stem cell niche with the potential control of their differentiation.

An overview of latest advances in exploring bioactive peptide hydrogels for neural tissue engineering

Neural tissue engineering holds great potential in addressing current challenges faced by medical therapies employed for the functional recovery of the brain. In this context, self-assembling peptides have gained considerable interest owing to their diverse physicochemical properties, which enable them to closely mimic the biophysical characteristics of the native ECM. Additionally, in contrast to synthetic polymers, which lack inherent biological signaling, peptide-based nanomaterials could be easily designed to present essential biological cues to the cells to promote cellular adhesion. Moreover, injectability of these biomaterials further widens their scope in biomedicine. In this context, hydrogels obtained from short bioactive peptide sequences are of particular interest owing to their facile synthesis and highly tunable properties. In spite of their well-known advantages, the exploration of short peptides for neural tissue engineering is still in its infancy and thus detailed discussion is required to evoke interest in this direction. This review provides a general overview of various bioactive hydrogels derived from short peptide sequences explored for neural tissue engineering. The review also discusses the current challenges in translating the benefits of these hydrogels to clinical practices and presents future perspectives regarding the utilization of these hydrogels for advanced biomedical applications.

Pentapeptide IKVAV-engineered hydrogels for neural stem cell attachment

Spinal cord injury remains irreversible with current treatment paradigms, due to the inability to rebuild the regenerative environment for neurons after injury. Neural tissue engineering that encapsulates the neural stem/progenitor cells within an artificial scaffold provides a possibility to regenerate neurons for spinal cord injury repair. The attachment and survival of these neural cells usually require similar microenvironments to the extracellular matrix for support. Here, a three-dimensional pentapeptide IKVAV-functionalized poly(lactide ethylene oxide fumarate) (PLEOF) hydrogel is developed. In vitro tests demonstrate that the IKVAV-PLEOF hydrogels are biodegradable and hemo-biocompatible. This IKVAV-PLEOF hydrogel is shown to support neural stem cell attachment, growth, proliferation, and differentiation. Additionally, the neural stem cells could be readily formed as spheroids that subsequently encapsulated, attached, and proliferated within the three-dimensional hydrogel constructs. Additionally, an in vivo test confirms the biodegradability and biocompatibility of the IKVAV-PLEOF hydrogels revealing that the hydrogels biodegrade, new blood vessels form, and few inflammatory responses are observed after 4-week implantation. The neural stem cell spheroid-laden hydrogels may have further implications in spinal cord injury regenerative and brain repair in neural tissue engineering.

Peptide-Engineered Fluorescent Nanomaterials: Structure Design, Function Tailoring, and Biomedical Applications

Fluorescent nanomaterials have exhibited promising applications in biomedical and tissue engineering fields. To improve the properties and expand bioapplications of fluorescent nanomaterials, various functionalization and biomodification strategies have been utilized to engineer the structure and function of fluorescent nanomaterials. Due to their high biocompatibility, satisfied bioactivity, unique biomimetic function, easy structural tailoring, and controlled self-assembly ability, supramolecular peptides are widely used as versatile modification agents and nanoscale building blocks for engineering fluorescent nanomaterials. In this work, recent advance in the synthesis, structure, function, and biomedical applications of peptide-engineered fluorescent nanomaterials is presented. Firstly, the types of different fluorescent nanomaterials are introduced. Then, potential strategies for the preparation of peptide-engineered fluorescent nanomaterials via templated synthesis, bioinspired conjugation, and peptide assembly-assisted synthesis are discussed. After that, the unique structure and functions through the peptide conjugation with fluorescent nanomaterials are demonstrated. Finally, the biomedical applications of peptide-engineered fluorescent nanomaterials in bioimaging, disease diagnostics and therapy, drug delivery, tissue engineering, antimicrobial test, and biosensing are presented and discussed in detail. It is helpful for readers to understand the peptide-based conjugation and bioinspired synthesis of fluorescent nanomaterials, and to design and synthesize novel hybrid bionanomaterials with special structures and improved functions for advanced applications.

Cutting-edge progress and challenges in stimuli responsive hydrogel microenvironment for success in tissue engineering today

The field of tissue engineering has numerous potential for modified therapeutic results and has been inspired by enhancements in bioengineering at the recent decades. The techniques of regenerating tissues and assembling functional paradigms that are responsible for repairing, maintaining, and revitalizing lost organs and tissues have affected the entire spectrum of health care studies. Strategies to combine bioactive molecules, biocompatible materials and cells are important for progressing the renewal of damaged tissues. Hydrogels have been utilized as one of the most popular cell substrate/carrier in tissue engineering since previous decades, respect to their potential to retain a 3D structure, to protect the embedded cells, and to mimic the native ECM. The hydrophilic nature of hydrogels can provide an ideal milieu for cell viability and structure, which simulate the native tissues. Hydrogel systems have been applied as a favorable matrix for growth factor delivery and cell immobilization. This study reviews a brief explanation of the structure, characters, applications, fabrication methods, and future outlooks of stimuli responsive hydrogels in tissue engineering and, in particular, 3D bioprinting.

The lncRNA MCF2L-AS1 controls osteogenic differentiation by regulating miR-33a

Bone homeostasis is maintained by balanced osteoblast-mediated tissue production and osteoclast-mediated tissue destruction, and is disrupted in pathological conditions such as osteoporosis. The mechanisms underlying osteogenic differentiation of bone marrow mesenchymal stem cells, which is critical to bone homeostasis, are not completely clear, despite extensively studies. Long noncoding RNAs (lncRNAs) have recently emerged as novel therapeutic targets in various diseases. However, the expression pattern and biological function of lncRNAs in osteogenic differentiation remain unclear. In this study, we aimed to determine the role of lncRNAs in osteogenic differentiation of human bone marrow mesenchymal stem cells. We found high lncRNA MCF2L-AS1 expression in human bone marrow mesenchymal stem cells, and used bioinformatics analysis to analyze its function. MCF2L-AS1 knockdown induced inhibition of osteoblast differentiation. Silencing of MCF2L-AS1 increased the expression of miR-33a and subsequently inhibited Runx2 expression at the post-transcriptional level. Moreover, MCF2L-AS1 directly interacted with miR-33a, and downregulation of miR-33a efficiently reversed the suppression of Runx2 induced by MCF2L-AS1 short hairpin RNA (shRNA). Thus, MCF2L-AS1 positively regulated the expression of Runx2 by sponging miR-33a, and promoted osteogenic differentiation in BMSCs. Our results indicated that the lncRNA MCF2L-AS1 plays a critical role in the osteogenic differentiation of BMSCs, and targeting lncRNA MCF2L-AS1 could be a promising strategy to promote osteogenic differentiation.

Contribution of Bone Marrow-derived Cells to Reparative Dentinogenesis Using Bone Marrow Transplantation Model

INTRODUCTION

The aim of this study was to analyze the contribution of bone marrow-derived cells (BMDCs) to reparative dentinogenesis using bone marrow transplantation (BMT) and pulp capping as an in vivo model.

METHODS

A chimeric mouse model was created through the injection of BMDCs expressing green fluorescent protein (GFP+ BMDCs) from C57BL/6 GFP+ transgenic donor mice into irradiated C57BL/6 wild-type recipient mice (GFP- mice). These GFP- chimeric mice (containing transplanted GFP+ BMDCs) were subjected to microscopic pulp exposure and capping with white mineral trioxide aggregate (n = 18) or Biodentine (Septodont, St Maur-des-Fossés, France) (n = 18) in the maxillary first molar. Maxillary arches from GFP- chimeric mice (with the capped tooth) were isolated and histologically processed 5 (n = 9) and 7 (n = 9) weeks after BMT. Confocal laser microscopy and immunohistochemical analysis were performed to assess the presence of GFP+ BMDCs and the expression of dentin sialoprotein, an odontoblast marker, for those cells contributing to reparative dentinogenesis in the dental pulp.

RESULTS

Confocal laser microscopic analyses evidenced the presence of GFP+ BMDCs in close association with reparative dentin synthesized at the site of pulp exposure in GFP- mice 5 and 7 weeks after BMT. Immunohistochemical analysis revealed that GFP+ BMDCs in close association with reparative dentin expressed DSP, suggesting the contribution of nonresident GFP+ BMDCs to reparative dentinogenesis.

CONCLUSIONS

These data suggest the presence of nonresident BMDCs in reparative dentinogenesis and its contribution to dental pulp regeneration in the pulp healing process.

Isolation and Characterization of Neural Progenitor Cells From Bone Marrow in Cell Replacement Therapy of Brain Injury

Many studies supported that bone marrow mesenchymal stem cells (BM-MSCs) can differentiate into neural cells, but few researchers detected mature and function of nerve cells, especially in vivo study. Some researchers even suggested that BM-MSCs transplantation would not be able to differentiate into functional neural cells. To figure out the dispute, this study examined bone marrow-derived sphere-like cells, harvested via neural stem cell suspension culture, then identified as bone marrow-derived neural progenitor cells (BM-NPCs) by finding the expression of neural progenitor cells genes and proteins, neural progenitor cells characteristic and nerve cell differentiation induced through both methods. Moreover, BM-NPCs transplantation showed long-term survival and improved the ethological and histological indexes of brain injury rats, demonstrating functional nervous cells differentiated from BM-NPCs. These in vitro and in vivo results confirmed BM-NPCs differentiating into mature and functional nerve cells. This study provided valuable experimental data for BM-NPCs, suggesting a potential alternative treatment of central nervous injury disease.

H₂O₂ Damages the Stemness of Rat Bone Marrow-Derived Mesenchymal Stem Cells: Developing a "Stemness Loss" Model

Background

The number of patients with spinal cord injury caused by motor vehicle accidents, violent injuries, and other types of trauma increases year by year, and bone marrow mesenchymal stem cell (BMSC) transplants are being widely investigated to treat this condition. However, the success rate of BMSCs transplants is relatively low due to the presence of oxidative stress in the new microenvironment. Our main goals in the present study were to evaluate the damaging effects of H₂O₂ on BMSCs and to develop a model of “stemness loss” using rat BMSCs.

Material/Methods

Bone marrow-derived mesenchymal stem cells were obtained from the bone marrow of young rats reared under sterile conditions. The stem cells were used after 2 passages following phenotypic identification. BMSCs were divided into 4 groups to evaluate the damaging effects of H₂O₂: A. blank control; B. 100 uM H₂O₂; C. 200 uM H₂O₂ and D. 300 uM H₂O₂. The ability of the BMSCs to differentiate into 3 cell lineages and their colony formation and migration capacities were analyzed by gene expression, colony formation, and scratch assays.

Results

The cells we obtained complied with international stem cell standards demonstrated by their ability to differentiate into 3 cell lineages. We found that 200–300 uM H₂O₂ had a significant effect on the biological behavior of BMSCs, including their ability to differentiate into 3 cell lineages, the expression of stemness-related proteins, and their migration and colony formation capacities.

Conclusions

H₂O₂ can damage the stemness ability of BMSCs at a concentration of 200–300 uM.

Prion-based nanomaterials and their emerging applications

Protein misfolding and aggregation into highly ordered fibrillar structures have been traditionally associated with pathological processes. Nevertheless, nature has taken advantage of the particular properties of amyloids for functional purposes, like in the protection of organisms against environmental changing conditions. Over the last decades, these fibrillar structures have inspired the design of new nanomaterials with intriguing applications in biomedicine and nanotechnology such as tissue engineering, drug delivery, adhesive materials, biodegradable nanocomposites, nanowires or biosensors. Prion and prion-like proteins, which are considered a subclass of amyloids, are becoming ideal candidates for the design of new and tunable nanomaterials. In this review, we discuss the particular properties of this kind of proteins, and the current advances on the design of new materials based on prion sequences.