Recombinant spider silk as matrices for cell culture

Functional analysis of the engineered cardiac tissue grown on recombinant spidroin fiber meshes

In the present study, we examined the ability of the recombinant spidroin to serve as a substrate for the cardiac tissue engineering. For this purpose, isolated neonatal rat cardiomyocytes were seeded on the electrospun spidroin fiber matrices and cultured to form the confluent cardiac monolayers. Besides the adhesion assay and immunostaining analysis, we tested the ability of the cultured cardiomyocytes to form a functional cardiac syncytium by studying excitation propagation in the cultured tissue with the aid of optical mapping. It was demonstrated that recombinant spidroin fiber meshes are directly suitable for the adherence and growth of the cardiomyocytes without additional coating with the attachment factors, such as fibronectin.

Silk fibroin scaffolds promote formation of the ex vivo niche for salivary gland epithelial cell growth, matrix formation, and retention of differentiated function

Salivary gland hypofunction often results from a number of causes, including the use of various medications, radiation for head and neck tumors, autoimmune diseases, diabetes, and aging. Since treatments for this condition are lacking and adult salivary glands have little regenerative capacity, there is a need for cell-based therapies to restore salivary gland function. Development of these treatment strategies requires the establishment of a system that is capable of replicating the salivary gland cell "niche" to support the proliferation and differentiation of salivary gland progenitor cells. In this study, a culture system using three-dimensional silk fibroin scaffolds (SFS) and primary salivary gland epithelial cells (pSGECs) from rat submandibular (SM) gland and parotid gland (PG) was established and characterized. pSGECs grown on SFS, but not tissue culture plastic (TCP), formed aggregates of cells with morphological features resembling secretory acini. High levels of amylase were released into the media by both cell types after extended periods in culture on SFS. Remarkably, cultures of PG-derived cells on SFS, but not SM cells, responded to isoproterenol, a β-adrenergic receptor agonist, with increased enzyme release. This behavior mimics that of the salivary glands in vivo. Decellularized extracellular matrix (ECM) formed by pSGECs in culture on SFS contained type IV collagen, a major component of the basement membrane. These results demonstrate that pSGECs grown on SFS, but not TCP, retain important functional and structural features of differentiated salivary glands and produce an ECM that mimics the native salivary gland cell niche. These results demonstrate that SFS has potential as a scaffold for creating the salivary gland cell niche in vitro and may provide an approach for inducing multipotent stem cells to provide therapeutically meaningful numbers of salivary gland progenitor cells for regenerating these tissues in patients.

In planta production of ELPylated spidroin-based proteins results in non-cytotoxic biopolymers

BACKGROUND

Spider silk is a tear-resistant and elastic biopolymer that has outstanding mechanical properties. Additionally, exiguous immunogenicity is anticipated for spider silks. Therefore, spider silk represents a potential ideal biomaterial for medical applications. All known spider silk proteins, so-called spidroins, reveal a composite nature of silk-specific units, allowing the recombinant production of individual and combined segments.

RESULTS

In this report, a miniaturized spidroin gene, named VSO1 that contains repetitive motifs of MaSp1 has been synthesized and combined to form multimers of distinct lengths, which were heterologously expressed as elastin-like peptide (ELP) fusion proteins in tobacco. The elastic penetration moduli of layered proteins were analyzed for different spidroin-based biopolymers. Moreover, we present the first immunological analysis of synthetic spidroin-based biopolymers. Characterization of the binding behavior of the sera after immunization by competitive ELISA suggested that the humoral immune response is mainly directed against the fusion partner ELP. In addition, cytocompatibility studies with murine embryonic fibroblasts indicated that recombinant spidroin-based biopolymers, in solution or as coated proteins, are well tolerated.

CONCLUSION

The results show that spidroin-based biopolymers can induce humoral immune responses that are dependent on the fusion partner and the overall protein structure. Furthermore, cytocompatibility assays gave no indication of spidroin-derived cytotoxicity, suggesting that recombinant produced biopolymers composed of spider silk-like repetitive elements are suitable for biomedical applications.

Physical and biological regulation of neuron regenerative growth and network formation on recombinant dragline silks

Recombinant spider silks produced in transgenic goat milk were studied as cell culture matrices for neuronal growth. Major ampullate spidroin 1 (MaSp1) supported neuronal growth, axon extension and network connectivity, with cell morphology comparable to the gold standard poly-lysine. In addition, neurons growing on MaSp1 films had increased neural cell adhesion molecule (NCAM) expression at both mRNA and protein levels. The results indicate that MaSp1 films present useful surface charge and substrate stiffness to support the growth of primary rat cortical neurons. Moreover, a putative neuron-specific surface binding sequence GRGGL within MaSp1 may contribute to the biological regulation of neuron growth. These findings indicate that MaSp1 could regulate neuron growth through its physical and biological features. This dual regulation mode of MaSp1 could provide an alternative strategy for generating functional silk materials for neural tissue engineering.

Analysis of transcriptomes of three orb-web spider species reveals gene profiles involved in silk and toxin

As an ancient arthropod with a history of 390 million years, spiders evolved numerous morphological forms resulting from adaptation to different environments. The venom and silk of spiders, which have promising commercial applications in agriculture, medicine and engineering fields, are of special interests to researchers. However, little is known about their genomic components, which hinders not only understanding spider biology but also utilizing their valuable genes. Here we report on deep sequenced and de novo assembled transcriptomes of three orb-web spider species, Gasteracantha arcuata, Nasoonaria sinensis and Gasteracantha hasselti which are distributed in tropical forests of south China. With Illumina paired-end RNA-seq technology, 54 871, 101 855 and 75 455 unigenes for the three spider species were obtained, respectively, among which 9 300, 10 001 and 10 494 unique genes are annotated, respectively. From these annotated unigenes, we comprehensively analyzed silk and toxin gene components and structures for the three spider species. Our study provides valuable transcriptome data for three spider species which previously lacked any genetic/genomic data. The results have laid the first fundamental genomic basis for exploiting gene resources from these spiders.

Coatings and films made of silk proteins

Silks are a class of proteinaceous materials produced by arthropods for various purposes. Spider dragline silk is known for its outstanding mechanical properties, and it shows high biocompatibility, good biodegradability, and a lack of immunogenicity and allergenicity. The silk produced by the mulberry silkworm B. mori has been used as a textile fiber and in medical devices for a long time. Here, recent progress in the processing of different silk materials into highly tailored isotropic and anisotropic coatings for biomedical applications such as tissue engineering, cell adhesion, and implant coatings as well as for optics and biosensors is reviewed.

Spider silk for xeno-free long-term self-renewal and differentiation of human pluripotent stem cells

Human pluripotent stem cells (hPSCs) can undergo unlimited self-renewal and have the capacity to differentiate into all somatic cell types, and are therefore an ideal source for the generation of cells and tissues for research and therapy. To realize this potential, defined cell culture systems that allow expansion of hPSCs and subsequent controlled differentiation, ideally in an implantable three-dimensional (3D) matrix, are required. Here we mimic spider silk - Nature's high performance material - for the design of chemically defined 2D and 3D matrices for cell culture. The silk matrices do not only allow xeno-free long-term expansion of hPSCs but also differentiation in both 2D and 3D. These results show that biomimetic spider silk matrices enable hPSC culture in a manner that can be applied for experimental and clinical purposes.

Spider silk as guiding biomaterial for human model neurons

Over the last years, a number of therapeutic strategies have emerged to promote axonal regeneration. An attractive strategy is the implantation of biodegradable and nonimmunogenic artificial scaffolds into injured peripheral nerves. In previous studies, transplantation of decellularized veins filled with spider silk for bridging critical size nerve defects resulted in axonal regeneration and remyelination by invading endogenous Schwann cells. Detailed interaction of elongating neurons and the spider silk as guidance material is unknown. To visualize direct cellular interactions between spider silk and neurons in vitro, we developed an in vitro crossed silk fiber array. Here, we describe in detail for the first time that human (NT2) model neurons attach to silk scaffolds. Extending neurites can bridge gaps between single silk fibers and elongate afterwards on the neighboring fiber. Culturing human neurons on the silk arrays led to an increasing migration and adhesion of neuronal cell bodies to the spider silk fibers. Within three to four weeks, clustered somata and extending neurites formed ganglion-like cell structures. Microscopic imaging of human neurons on the crossed fiber arrays in vitro will allow for a more efficient development of methods to maximize cell adhesion and neurite growth on spider silk prior to transplantation studies.

Controlled assembly: a prerequisite for the use of recombinant spider silk in regenerative medicine?

Recent biotechnological progress has enabled the production of spider silk proteins, spidroins, in heterologous hosts. Matrices based on recombinant spidroins support stem cell growth and are well tolerated when implanted in living tissue, thus the material is highly attractive for use in regenerative medicine. However, the matrices made are far from natural silk in terms of mechanical properties and are either spontaneously assembled, which results in heterogeneous products, or spun from harsh solvents with the concomitant risk of harmful remnants in the final products. If we could mimic the spider's aqueous silk spinning process we would likely obtain a material that had reproducible and better characteristics and that more easily could be transferred to clinical practice. Herein, the knowledge of the spiders' silk production system and the prerequisites for artificial spinning and assembly of recombinant proteins are reviewed and discussed in a biomedical context.

Recombinant spider silk with cell binding motifs for specific adherence of cells

Silk matrices have previously been shown to possess general properties governing cell viability. However, many cell types also require specific adhesion sites for successful in vitro culture. Herein, we have shown that cell binding motifs can be genetically fused to a partial spider silk protein, 4RepCT, without affecting its ability to self-assemble into stable matrices directly in a physiological-like buffer. The incorporated motifs were exposed in the formed matrices, and available for binding of integrins. Four different human primary cell types; fibroblasts, keratinocytes, endothelial cells and Schwann cells, were applied to the matrices and investigated under serum-free culture conditions. Silk matrices with cell binding motifs, especially RGD, were shown to promote early adherence of cells, which formed stress fibers and distinct focal adhesion points. Schwann cells acquired most spread-out morphology on silk matrices with IKVAV, where significantly more viable cells were found, also when compared to wells coated with laminin. This strategy is thus suitable for development of matrices that allow screening of various cell binding motifs and their effect on different cell types.

Natural and Genetically Engineered Proteins for Tissue Engineering

To overcome the limitations of traditionally used autografts, allografts and, to a lesser extent, synthetic materials, there is the need to develop a new generation of scaffolds with adequate mechanical and structural support, control of cell attachment, migration, proliferation and differentiation and with bio-resorbable features. This suite of properties would allow the body to heal itself at the same rate as implant degradation. Genetic engineering offers a route to this level of control of biomaterial systems. The possibility of expressing biological components in nature and to modify or bioengineer them further, offers a path towards multifunctional biomaterial systems. This includes opportunities to generate new protein sequences, new self-assembling peptides or fusions of different bioactive domains or protein motifs. New protein sequences with tunable properties can be generated that can be used as new biomaterials. In this review we address some of the most frequently used proteins for tissue engineering and biomedical applications and describe the techniques most commonly used to functionalize protein-based biomaterials by combining them with bioactive molecules to enhance biological performance. We also highlight the use of genetic engineering, for protein heterologous expression and the synthesis of new protein-based biopolymers, focusing the advantages of these functionalized biopolymers when compared with their counterparts extracted directly from nature and modified by techniques such as physical adsorption or chemical modification.

Biological responses to spider silk-antibiotic fusion protein

The development of a new generation of multifunctional biomaterials is a continual goal for the field of materials science. The in vivo functional behaviour of a new fusion protein that combines the mechanical properties of spider silk with the antimicrobial properties of hepcidin was addressed in this study. This new chimeric protein, termed 6mer + hepcidin, fuses spider dragline consensus sequences (6mer) and the antimicrobial peptide hepcidin, as we have recently described, with retention of bactericidal activity and low cytotoxicity. In the present study, mouse subcutaneous implants were studied to access the in vivo biological response to 6mer + hepcidin, which were compared with controls of silk alone (6mer), polylactic-glycolic acid (PLGA) films and empty defects. Along with visual observations, flow cytometry and histology analyses were used to determine the number and type of inflammatory cells at the implantation site. The results show a mild to low inflammatory reaction to the implanted materials and no apparent differences between the 6mer + hepcidin films and the other experimental controls, demonstrating that the new fusion protein has good in vivo biocompatibility, while maintaining antibiotic function.

Multizone paper platform for 3D cell cultures

In vitro 3D culture is an important model for tissues in vivo. Cells in different locations of 3D tissues are physiologically different, because they are exposed to different concentrations of oxygen, nutrients, and signaling molecules, and to other environmental factors (temperature, mechanical stress, etc). The majority of high-throughput assays based on 3D cultures, however, can only detect the average behavior of cells in the whole 3D construct. Isolation of cells from specific regions of 3D cultures is possible, but relies on low-throughput techniques such as tissue sectioning and micromanipulation. Based on a procedure reported previously (“cells-in-gels-in-paper” or CiGiP), this paper describes a simple method for culture of arrays of thin planar sections of tissues, either alone or stacked to create more complex 3D tissue structures. This procedure starts with sheets of paper patterned with hydrophobic regions that form 96 hydrophilic zones. Serial spotting of cells suspended in extracellular matrix (ECM) gel onto the patterned paper creates an array of 200 micron-thick slabs of ECM gel (supported mechanically by cellulose fibers) containing cells. Stacking the sheets with zones aligned on top of one another assembles 96 3D multilayer constructs. De-stacking the layers of the 3D culture, by peeling apart the sheets of paper, “sections” all 96 cultures at once. It is, thus, simple to isolate 200-micron-thick cell-containing slabs from each 3D culture in the 96-zone array. Because the 3D cultures are assembled from multiple layers, the number of cells plated initially in each layer determines the spatial distribution of cells in the stacked 3D cultures. This capability made it possible to compare the growth of 3D tumor models of different spatial composition, and to examine the migration of cells in these structures.