Elastin-like recombinamers as substrates for retinal pigment epithelial cell growth

Elastin turnover in ocular diseases: A special focus on age-related macular degeneration

The extracellular matrix (ECM) and its turnover play a crucial role in the pathogenesis of several inflammatory diseases, including age-related macular degeneration (AMD). Elastin, a critical protein component of the ECM, not only provides structural and mechanical support to tissues, but also mediates several intracellular and extracellular molecular signaling pathways. Abnormal turnover of elastin has pathological implications. In the eye elastin is a major structural component of Bruch's membrane (BrM), a critical ECM structure separating the retinal pigment epithelium (RPE) from the choriocapillaris. Reduced integrity of macular BrM elastin, increased serum levels of elastin-derived peptides (EDPs), and elevated elastin antibodies have been reported in AMD. Existing reports suggest that elastases, the elastin-degrading enzymes secreted by RPE, infiltrating macrophages or neutrophils could be involved in BrM elastin degradation, thus contributing to AMD pathogenesis. EDPs derived from elastin degradation can increase inflammatory and angiogenic responses in tissues, and the elastin antibodies are shown to play roles in immune cell activity and complement activation. This review summarizes our current understanding on the elastases/elastin fragments-mediated mechanisms of AMD pathogenesis.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

Factors influencing mesenchymal stromal cells in in vitro cellular models to study retinal pigment epithelial cell rescue

Mesenchymal stromal cells (MSC) stop or slow retinal pigment epithelium (RPE) and neuroretina (NR) degeneration by paracrine activity in oxidative stress-induced retinal degenerative diseases. However, it is mandatory to develop adequate in vitro models that allow testing new treatment strategies against oxidative stress before performing in vivo studies. The viable double- and triple-layered setups are composed of separate layers of NR, MSC, and RPE (NR-MSC-RPE, NR-RPE, MSC-RPE) partially mimic in vivo retinal conditions. In this study, the paracrine neuroprotective effect of each setup's microenvironment on hydrogen peroxide (H₂O₂)-stressed was compared with unstressed RPE cells. RPE cell proliferation viability was assessed on day 1, 3, and 6 using Alamar Blue® (10%), MTT (10%) and a cell viability/cytotoxicity assay kit followed by data analysis. The results showed that RPE cells, highly viable (> 90%) in mixed medium of DMEM and neurobasal A (1:1), lost 50% viability on exposure to 400 µM of H₂O₂ (P < 0.05). The unexposed groups differed significantly from exposed groups for RPE cell growth (RPE and [Formula: see text]RPE (P < 0.0001), NR-MSC-RPE, and NR-MSC-[Formula: see text]RPE (P < 0.05), NR-RPE and NR-[Formula: see text]RPE (P < 0.01), and MSC-RPE and MSC-[Formula: see text]RPE (P < 0.01). NR-[Formula: see text]RPE and NR-RPE supported RPE cell proliferation viability better than other setups (P < 0.01) and RPE cells proliferated 0.49-fold more in NR-MSC-[Formula: see text]RPE than NR-MSC-RPE. Thus, NR and MSC presence improved significantly each setup's microenvironment for cell rescue, nevertheless, each setup also showed limitations for its use as an in vitro study tool. Health of microenvironment of such setups depends on many factors including cell-secreted trophic factors.

Towards an In Vitro Retinal Model to Study and Develop New Therapies for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of vision loss in the elderly worldwide. So far, the etiology and the progression of AMD are not well known. Animal models have been developed to study the mechanisms involved in AMD; however, according to the "Three Rs" principle, alternative methods have been investigated. Here we present a strategy to develop a "Three Rs" compliant retinal three-dimensional (3D) in vitro model, including a Bruch's membrane model and retina pigment epithelium (RPE) layer. First, tensile testing was performed on porcine retina to set a reference for the in vitro model. The results of tensile testing showed a short linear region followed by a plastic region with peaks. Then, Bruch's membrane (BrM) was fabricated via electrospinning by using Bombyx mori silk fibroin (BMSF) and polycaprolactone (PCL). The BrM properties and ARPE-19 cell responses to BrM substrates were investigated. The BrM model displayed a thickness of 44 µm, with a high porosity and an average fiber diameter of 1217 ± 101 nm. ARPE-19 cells adhered and spread on the BMSF/PCL electrospun membranes. In conclusion, we are developing a novel 3D in vitro retinal model towards the replacement of animal models in AMD studies.

Biotechnology and Biomaterial-Based Therapeutic Strategies for Age-Related Macular Degeneration. Part II: Cell and Tissue Engineering Therapies

Age-related Macular Degeneration (AMD) is an up-to-date untreatable chronic neurodegenerative eye disease of multifactorial origin, and the main causes of blindness in over 65 y.o. people. It is characterized by a slow progression and the presence of a multitude of factors, highlighting those related to diet, genetic heritage and environmental conditions, present throughout each of the stages of the illness. Current therapeutic approaches, mainly consisting on intraocular drug delivery, are only used for symptoms relief and/or to decelerate the progression of the disease. Furthermore, they are overly simplistic and ignore the complexity of the disease and the enormous differences in the symptomatology between patients. Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, different treatment options have to be considered. Cell therapy is a very promising alternative to drug-based approaches for AMD treatment. Cells delivered to the affected tissue as a suspension have shown poor retention and low survival rate. A solution to these inconveniences has been the encapsulation of these cells on biomaterials, which contrive to their protection, gives them support, and favor their retention of the desired area. We offer a two-papers critical review of the available and under development AMD therapeutic approaches, from a biomaterials and biotechnological point of view. We highlight benefits and limitations and we forecast forthcoming alternatives based on novel biomaterials and biotechnology methods. In this second part we review the preclinical and clinical cell-replacement approaches aiming at the development of efficient AMD-therapies, the employed cell types, as well as the cell-encapsulation and cell-implant systems. We discuss their advantages and disadvantages and how they could improve the survival and integration of the implanted cells.

Regenerative medicine as a novel strategy for AMD treatment: a review

Age-related macular degeneration (AMD) is known as a major cause of irreversible blindness in elderly adults. The segment of the retina responsible for central vision damages in the disease process. Degeneration of retinal pigmented epithelium (RPE) cells, photoreceptors, and choriocapillaris associated with aging participate for visual loss. In 2010, AMD involved 6.6% of all blindness cases around the world. Some of the researches have evaluated the replacing of damaged RPE in AMD patients by using the cells from various sources. Today, the advancement of RPE differentiation or generation from stem cells has been gained, and currently, clinical trials are testing the efficiency and safety of replacing degenerated RPE with healthy RPE. However, the therapeutic success of RPE transplantation may be restricted unless the transplanted cells can be adhered, distributed and survive for long-term in the transplanted site without any infections. In recent years a variety of scaffold types were used as a carrier for RPE transplantation and AMD treatment. In this review, we have discussed types of scaffolds; natural or synthetic, solid or hydrogel and their results in RPE replacement. Eventually, our aim is highlighting the novel and best scaffold carriers that may have potentially promoting the efficacy of RPE transplantation.

An elastin-like recombinamer-based bioactive hydrogel embedded with mesenchymal stromal cells as an injectable scaffold for osteochondral repair

The aim of this study was to evaluate injectable, in situ cross-linkable elastin-like recombinamers (ELRs) for osteochondral repair. Both the ELR-based hydrogel alone and the ELR-based hydrogel embedded with rabbit mesenchymal stromal cells (rMSCs) were tested for the regeneration of critical subchondral defects in 10 New Zealand rabbits. Thus, cylindrical osteochondral defects were filled with an aqueous solution of ELRs and the animals sacrificed at 4 months for histological and gross evaluation of features of biomaterial performance, including integration, cellular infiltration, surrounding matrix quality and the new matrix in the defects. Although both approaches helped cartilage regeneration, the results suggest that the specific composition of the rMSC-containing hydrogel permitted adequate bone regeneration, whereas the ELR-based hydrogel alone led to an excellent regeneration of hyaline cartilage. In conclusion, the ELR cross-linker solution can be easily delivered and forms a stable well-integrated hydrogel that supports infiltration and de novo matrix synthesis.

Bioactive scaffolds based on elastin-like materials for wound healing

Wound healing is a complex process that, in healthy tissues, starts immediately after the injury. Even though it is a natural well-orchestrated process, large trauma wounds, or injuries caused by acids or other chemicals, usually produce a non-elastic deformed tissue that not only have biological reduced properties but a clear aesthetic effect. One of the main drawbacks of the scaffolds used for wound dressing is the lack of elasticity, driving to non-elastic and contracted tissues. In the last decades, elastin based materials have gained in importance as biomaterials for tissue engineering applications due to their good cyto- and bio-compatibility, their ease handling and design, production and modification. Synthetic elastin or elastin like-peptides (ELPs) are the two main families of biomaterials that try to mimic the outstanding properties of natural elastin, elasticity amongst others; although there are no in vivo studies that clearly support that these two families of elastin based materials improve the elasticity of the artificial scaffolds and of the regenerated skin. Within the next pages a review of the different forms (coacervates, fibres, hydrogels and biofunctionalized surfaces) in which these two families of biomaterials can be processed to be applied in the wound healing field have been done. Here, we explore the mechanical and biological properties of these scaffolds as well as the different in vivo approaches in which these scaffolds have been used.

Honeycomb porous films as permeable scaffold materials for human embryonic stem cell-derived retinal pigment epithelium

Age-related macular degeneration (AMD) is a leading cause of blindness in developed countries, characterised by the degeneration of the retinal pigment epithelium (RPE), a pigmented cell monolayer that closely interacts with the photoreceptors. RPE transplantation is thus considered a very promising therapeutic option to treat this disease. In this work, porous honeycomb-like films are for the first time investigated as scaffold materials for human embryonic stem cell-derived retinal pigment epithelium (hESC-RPE). By changing the conditions during film preparation, it was possible to produce films with homogeneous pore distribution and adequate pore size (∼3-5 µm), that is large enough to ensure high permeability but small enough to enable cell adherence and spreading. A brief dip-coating procedure with collagen type IV enabled the homogeneous adsorption of the protein to the walls and bottom of pores, increasing the hydrophilicity of the surface. hESC-RPE adhered and proliferated on all the collagen-coated materials, regardless of small differences in pore size. The differentiation of hESC-RPE was confirmed by the detection of specific RPE protein markers. These results suggest that the porous honeycomb films can be promising candidates for hESC-RPE tissue engineering, importantly enabling the free flow of ions and molecules across the material. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1646-1656, 2016.

Recombinant Technology in the Development of Materials and Systems for Soft-Tissue Repair

The field of biomedicine is constantly investing significant research efforts in order to gain a more in-depth understanding of the mechanisms that govern the function of body compartments and to develop creative solutions for the repair and regeneration of damaged tissues. The main overall goal is to develop relatively simple systems that are able to mimic naturally occurring constructs and can therefore be used in regenerative medicine. Recombinant technology, which is widely used to obtain new tailored synthetic genes that express polymeric protein-based structures, now offers a broad range of advantages for that purpose by permitting the tuning of biological and mechanical properties depending on the intended application while simultaneously ensuring adequate biocompatibility and biodegradability of the scaffold formed by the polymers. This Progress Report is focused on recombinant protein-based materials that resemble naturally occurring proteins of interest for use in soft tissue repair. An overview of recombinant biomaterials derived from elastin, silk, collagen and resilin is given, along with a description of their characteristics and suggested applications. Current endeavors in this field are continuously providing more-improved materials in comparison with conventional ones. As such, a great effort is being made to put these materials through clinical trials in order to favor their future use.

The influences of purple sweet potato anthocyanin on the growth characteristics of human retinal pigment epithelial cells

Background

Anthocyanins have been proven to be beneficial to the eyes. However, information is scarce about the effects of purple sweet potato (Ipomoea batatas, L.) anthocyanin (PSPA), a class of anthocyanins derived from purple sweet potato roots, on visual health.

Objective

The aim of this study was to investigate whether PSPA could have influences on the growth characteristics (cellular morphology, survival, and proliferation) of human retinal pigment epithelial (RPE) cells, which perform essential functions for the visual process.

Methods

The RPE cell line D407 was used in the present study. The cytotoxicity of PSPA was assessed by MTT assay. Then, cellular morphology, viability, cell cycle, Ki67expression, and PI3K/MAPK activation of RPE cells treated with PSPA were determined.

Results

PSPA exhibited dose-dependent promotion of RPE cell proliferation at concentrations ranging from 10 to 1,000 µg/ml. RPE cells treated with PSPA demonstrated a predominantly polygonal morphology in a mosaic arrangement, and colony-like cells displayed numerous short apical microvilli and typical ultrastructure. PSPA treatment also resulted in a better platform growing status, statistically higher viability, an increase in the S-phase, and more Ki67+ cells. However, neither pAkt nor pERK were detected in either group.

Conclusions

We found that PSPA maintained high cell viability, boosted DNA synthesis, and preserved a high percentage of continuously cycling cells to promote cell survival and division without changing cell morphology. This paper lays the foundation for further research about the damage-protective activities of PSPA on RPE cells or human vision.

Regenerating Retinal Pigment Epithelial Cells to Cure Blindness: A Road Towards Personalized Artificial Tissue

Retinal pigment epithelium (RPE) is a polarized monolayer tissue that functions to support the health and integrity of retinal photoreceptors (PRs). RPE atrophy has been linked to pathogenesis of age-related macular degeneration (AMD), a leading cause of blindness in elderly in the USA. RPE atrophy in AMD leads to the PR cell death and vision loss. It is thought that replacing diseased RPE with healthy RPE tissue can prevent PR cell death. Retinal surgical innovations have provided proof-of-principle data that autologous RPE tissue can replace diseased macular RPE and provide visual rescue in AMD patients. Current efforts are focused on developing an in vitro tissue using natural and synthetic scaffolds to generate a polarized functional RPE monolayer. In the future, these tissue-engineering approaches combined with pluripotent stem cell technology will lead to the development of personalized and "off-the-shelf" cell therapies for AMD patients. This review summarizes the historical development and ongoing efforts in surgical and in vitro tissue engineering techniques to develop a three-dimensional therapeutic native RPE tissue substitute.

Chitosan feasibility to retain retinal stem cell phenotype and slow proliferation for retinal transplantation

Retinal stem cells (RSCs) are promising in cell replacement strategies for retinal diseases. RSCs can migrate, differentiate, and integrate into retina. However, RSCs transplantation needs an adequate support; chitosan membrane (ChM) could be one, which can carry RSCs with high feasibility to support their integration into retina. RSCs were isolated, evaluated for phenotype, and subsequently grown on sterilized ChM and polystyrene surface for 8 hours, 1, 4, and 11 days for analysing cell adhesion, proliferation, viability, and phenotype. Isolated RSCs expressed GFAP, PKC, isolectin, recoverin, RPE65, PAX-6, cytokeratin 8/18, and nestin proteins. They adhered (28 ± 16%, 8 hours) and proliferated (40 ± 20 cells/field, day 1 and 244 ± 100 cells/field, day 4) significantly low (P < 0.05) on ChM. However, they maintained similar viability (>95%) and phenotype (cytokeratin 8/18, PAX6, and nestin proteins expression, day 11) on both surfaces (ChM and polystyrene). RSCs did not express alpha-SMA protein on both surfaces. RSCs express proteins belonging to epithelial, glial, and neural cells, confirming that they need further stimulus to reach a final destination of differentiation that could be provided in in vivo condition. ChM does not alternate RSCs behaviour and therefore can be used as a cell carrier so that slow proliferating RSCs can migrate and integrate into retina.

Primordium of an artificial Bruch's membrane made of nanofibers for engineering of retinal pigment epithelium cell monolayers

Transplanted retinal pigment epithelium (RPE) cells hold promise for treatment of age-related macular degeneration (AMD) and Stargardt disease (SD), but it is conceivable that the degenerated host Bruch's membrane (BM) as a natural substrate for RPE might not optimally support transplanted cell survival with correct cellular organization. We fabricated novel ultrathin three-dimensional (3-D) nanofibrous membranes from collagen type I and poly(lactic-co-glycolic acid) (PLGA) by an advanced clinical-grade needle-free electrospinning process. The nanofibrillar 3-D networks closely mimicked the fibrillar architecture of the native inner collagenous layer of human BM. Human RPE cells grown on our nanofibrous membranes bore a striking resemblance to native human RPE. They exhibited a correctly orientated monolayer with a polygonal cell shape and abundant sheet-like microvilli on their apical surfaces. RPE cells built tight junctions and expressed RPE65 protein. Flat 2-D PLGA film and cover glass as controls delivered inferior RPE layers. Our nanofibrous membranes may imitate the natural BM to such extent that they allow for the engineering of an in vivo-like human RPE monolayer that maintains the natural biofunctional characteristics. Such ultrathin membranes may provide a promising vehicle for a functional RPE cell monolayer implantation in the subretinal space in patients with AMD or SD.

Montmorillonite clay based polyurethane nanocomposite as substrate for retinal pigment epithelial cell growth

The subretinal transplantation of retinal pigment epithelial cells (RPE cells) grown on polymeric supports may have interest in retinal diseases affecting RPE cells. In this study, montmorillonite based polyurethane nanocomposite (PU-NC) was investigated as substrate for human RPE cell growth (ARPE-19 cells). The ARPE-19 cells were seeded on the PU-NC, and cell viability, proliferation and differentiation were investigated. The results indicated that ARPE-19 cells attached, proliferated onto the PU-NC, and expressed occludin. The in vivo ocular biocompatibility of the PU-NC was assessed by using the HET-CAM; and through its implantation under the retina. The direct application of the nanocomposite onto the CAM did not compromise the vascular tissue in the CAM surface, suggesting no ocular irritancy of the PU-NC film. The nanocomposite did not elicit any inflammatory response when implanted into the eye of rats. The PU-NC may have potential application as a substrate for RPE cell transplantation.

Application of elastin-mimetic recombinant proteins in chemotherapeutics delivery, cellular engineering, and regenerative medicine

With the remarkable increase in the fields of biomedical engineering and regenerative medicine, biomaterial design has become an indispensable approach for developing the biocompatible carriers for drug or gene cargo and extracellular matrix (ECM) for cell survival, proliferation and differentiation. Native ECM materials derived from animal tissues were believed to be the best choices for tissue engineering. However, possible pathogen contamination by cellular remnants from foreign animal tissues is an unavoidable issue that has limited the use of native ECM for human benefit. Some synthetic polymers have been used as alternative materials for manufacturing native ECM because of the biodegradability and ease of large-scale production of the polymers. However, the inherent polydispersity of the polymers causes batch-to-batch variation in polymer composition and possible cytotoxic interactions between chemical matrices and neighboring cells or tissues have not yet been fully resolved. Elastin-like proteins (ELPs) are genetically engineered biopolymers modeled after the naturally occurring tropoelastin and have emerged as promising materials for biomedical applications because they are biocompatible, non-immunogenic and biodegradable, and their composition, mechanical stiffness and even fate within the cell can be controlled at the gene level. This commentary highlights the recent progresses in the development of the ELP-based recombinant proteins that are being increasingly used for the delivery of chemotherapeutics and to provide a cell-friendly ECM environment.

Materials characterization and mechanobiology of the eye

The eye responds to a great deal of internal and external stimuli throughout its normal function. Due to this, a mechanical or chemical analysis alone is insufficient. A systematic materials characterization is needed. A mechanobiological approach is required for a full understanding of the unique properties and function of the eye. This review compiles the mechanical properties of select eye components, summarizes mechanical and chemical testing platforms, and overviews modeling approaches. Analysis is done across studies, experimental methods, and between species in order to summarize what is known about the mechanobiology of the eye. Several opportunities for future research are identified.

Human recombinant elastin-like protein coatings for muscle cell proliferation and differentiation

Recombinant proteins represent a new and promising class of polymeric materials in the field of biomaterials research. An important model for biomaterial design is elastin, the protein accounting for the elasticity of several tissues. Human elastin-like polypeptides (HELPs) have been developed as recombinant versions of elastin with the purpose of enhancing some peculiar characteristics of the native protein, like self-assembling. In this paper, we report on a comparative study of rat myoblasts response to coatings based on two different HELP macromolecules, with respect to control cultures on bare cell culture polystyrene and on a standard collagen coating. Cell behavior was analyzed in terms of adhesion, proliferation and differentiation. The collected data strongly suggest the use of HELPs as excellent biomaterials for tissue engineering and regenerative medicine applications.

Engineering membrane scaffolds with both physical and biomolecular signaling

We report on the combination of a top-down and bottom-up approach to develop thin bioactive membrane scaffolds based on functional elastin-like polymers (ELPs). Our strategy combines ELP cross-linking and assembly, and a variety of standard and novel micro/nanofabrication techniques to create self-supporting membranes down to ∼500 nm thick that incorporate both physical and biomolecular signals, which can be easily tailored for a specific application. In this study we used an ELP that included the cell-binding motif arginine-glycine-aspartic acid-serine (RGDS). Furthermore, fabrication processes were developed to create membranes that exhibited topographical patterns with features down to 200 nm in lateral dimensions and up to 10 μm in height on either one or both sides, uniform and well-defined pores, or multiple ELP layers. A variety of processing parameters were tested in order to optimize membrane fabrication, including ELP and cross-linker concentration, temperature, reaction time and ambient humidity. Membrane micro/nanopatterning, swelling and stiffness were characterized by atomic force microscopy, nanoindentation tests and scanning electron microscopy. Upon immersion in phosphate-buffered saline and an increase in temperature from 25 to 40°C, membranes exhibited a significant increase in surface stiffness, with the reduced Young's modulus increasing with temperature. Finally, rat mesenchymal stem cells were cultured on thin RGDS-containing membranes, which allowed cell adhesion, qualitatively enhanced spreading compared to membranes without RGDS epitopes and permitted proliferation. Furthermore, cell morphology was drastically affected by topographical patterns on the surface of the membranes.