Reconstruction of auto-tissue-engineered lamellar cornea by dynamic culture for transplantation: a rabbit model. PLoS One. 2014;9:e93012. [PMID: 24705327 PMCID: PMC3976280 DOI: 10.1371/journal.pone.0093012]

Bio-fabrication of stem-cell-incorporated corneal epithelial and stromal equivalents from silk fibroin and gelatin-based biomaterial for canine corneal regeneration

Corneal grafts are the imperative clinical treatment for canine corneal blindness. To serve the growing demand, this study aimed to generate tissue-engineered canine cornea in part of the corneal epithelium and underlying stroma based on canine limbal epithelial stem cells (cLESCs) seeded silk fibroin/gelatin (SF/G) film and canine corneal stromal stem cells (cCSSCs) seeded SF/G scaffold, respectively. Both cell types were successfully isolated by collagenase I. SF/G corneal films and stromal scaffolds served as the prospective substrates for cLESCs and cCSSCs by promoting cell adhesion, cell viability, and cell proliferation. The results revealed the upregulation of tumor protein P63 (P63) and ATP-binding cassette super-family G member 2 (Abcg2) of cLESCs as well as Keratocan (Kera), Lumican (Lum), aldehyde dehydrogenase 3 family member A1 (Aldh3a1) and Aquaporin 1 (Aqp1) of differentiated keratocytes. Moreover, immunohistochemistry illustrated the positive staining of tumor protein P63 (P63), aldehyde dehydrogenase 3 family member A1 (Aldh3a1), lumican (Lum) and collagen I (Col-I), which are considerable for native cornea. This study manifested a feasible platform to construct tissue-engineered canine cornea for functional grafts and positively contributed to the body of knowledge related to canine corneal stem cells.

Hydrogels derived from acellular porcine corneal stroma enhance corneal wound healing

Acellular cornea derived hydrogels provide significant advantages in preserving native corneal stromal keratocyte cells and endothelial cells. However, for clinical application, hydrogel physical properties need to be improved, and their role in corneal epithelial wound healing requires further investigation. In this study, an acellular porcine corneal stroma (APCS) hydrogel (APCS-gel) was successfully prepared from 20 mg/ml APCS, demonstrated optimal light transmittance and gelation kinetic properties and retained critical corneal ECM of collagens and growth factors. Compared with fibrin gel, the APCS-gel had a higher porosity ratio and faster nutrition diffusion with an accompanying improvement in the proliferation of primary rabbit corneal epithelial cells (RCECs) and stromal cells (RCSCs). These corneal cell types also displayed improved viability and cellular infiltration. Furthermore, the APCS-gel provides significant advantages in the preservation of RCECs stemness and enhancement of corneal wound healing in vitro and in vivo. After 7 days of culture, 3-4 layers of RCECs were formed on the APCS-gel in vitro, while only 1-2 layers were found on the fibrin gel. More corneal stem/progenitor cell phenotypes (K12-, p63+, ABCG2+) and proliferation phenotypes (Ki67+) were detected on the APCS-gel than fibrin gel. Using a corneal epithelial wound healing model, we also found faster reepithelization in corneas that received APCS-gel compared to fibrin gel. Additionally, our APCS-gel demonstrated better physical and biological properties when compared to Tisseel, a clinically used type of fibrin gel. In conclusion, our APCS-gel provided better corneal epithelial and stromal cell biocompatibility to fibrin gels and due to its transparency and faster gelation time could potentially be superior for clinical purposes. STATEMENT OF SIGNIFICANCE: Extracellular matrix (ECM) can be used to provide tissue specific physical microstructure and biochemical cues for tissue regeneration. Here, we produced an ECM hydrogel derived from acellular porcine cornea stroma (APCS-gel) that retained critical biological characteristics of the native tissue and provided significant transparency and fast gelation time. Our data demonstrated that the APCS-gel was superior to clinically used fibrin gel, as the APCS-gel showed high porosity and permeability, better corneal stromal keratocytes infiltration, increased cellular proliferation and retention of corneal epithelial cells stemness. The APCS-gel improved corneal wound healing in vitro and in vivo. This APCS-gel may have clinical utility for corneal diseases, and the more general approach used to make this hydrogel might be used in other tissues.

Paracrine activity of adipose derived stem cells on limbal epithelial stem cells

Limbal stem cells deficiency (LSCD) is an eye disease caused by the loss of stem cells in the corneal limbus as a succession of an injury due physical, biological, or chemical agents. Current therapies of LSCD are focused on the transplantation of donor corneas or tissue equivalents produced from autologous limbal stem cells. Every year there are waiting millions of patients for the cornea transplantation all over the world and the list is growing due to the relatively low number of cornea donors. On the other hand, the transplantation of tissue or cells into the recipient’s body is associated with the higher risk of possible side effects. The possibility of the application of an indirect treatment using the properties of the paracrine activity of stem cells, would be beneficial for the patients with transplant failures. This study was to evaluate the paracrine effect of mesenchymal stem cells derived from adipose tissue (ADSC) on the viability of limbal epithelial stem cells (LESC). The paracrine effect was assessed by treating LESC with conditioned medium collected from ADSC culture. Cell viability, cytotoxicity, apoptosis and proliferation were evaluated using in vitro assays in standard conditions and induced inflammation. After the exposure to the examined conditions, the expression of genes related to pro- and anti- inflammatory factors was evaluated and compared to the secretion of selected cytokines by ELISA test. Moreover, the changes in LESC phenotype were assessed using of phenotype microarrays. Our findings suggest that paracrine activity of ADSC on LESC promotes its proliferation and has a potential role in mitigation of the adverse impact of inflammation induced by lipopolysaccharide.

The progress in corneal translational medicine

Cornea tissue is in high demand by tissue donation centres globally, and thus tissue engineering cornea, which is the main topic of corneal translational medicine, can serve as a limitless alternative to a donated human cornea tissue. Tissue engineering aims to produce solutions to the challenges associated with conventional cornea tissue, including transplantation and use of human amniotic membrane (HAM), which have issues with storage and immune rejection in patients. Accordingly, by carefully selecting biomaterials and fabrication methods to produce these therapeutic tissues, the demand for cornea tissue can be met, with an improved healing outcome for recipients with less associated harmful risks. In this review paper, we aim to present the recent advancements in the research and clinical applications of cornea tissue, applications including biomaterial selection, fabrication methods, scaffold structure, cellular response to these scaffolds, and future advancements of these techniques.

Corneal pain and experimental model development

The cornea is a valuable tissue for studying peripheral sensory nerve structure and regeneration due to its avascularity, transparency, and dense innervation. Somatosensory innervation of the cornea serves to identify changes in environmental stimuli at the ocular surface, thereby promoting barrier function to protect the eye against injury or infection. Due to regulatory demands to screen ocular safety of potential chemical exposure, a need remains to develop functional human tissue models to predict ocular damage and pain using in vitro-based systems to increase throughput and minimize animal use. In this review, we summarize the anatomical and functional roles of corneal innervation in propagation of sensory input, corneal neuropathies associated with pain, and the status of current in vivo and in vitro models. Emphasis is placed on tissue engineering approaches to study the human corneal pain response in vitro with integration of proper cell types, controlled microenvironment, and high-throughput readouts to predict pain induction. Further developments in this field will aid in defining molecular signatures to distinguish acute and chronic pain triggers based on the immune response and epithelial, stromal, and neuronal interactions that occur at the ocular surface that lead to functional outcomes in the brain depending on severity and persistence of the stimulus.

Hyaluronic Acid Combined with Serum Rich in Growth Factors in Corneal Epithelial Defects

The aim of this study is to assess if an adhesive biopolymer, sodium hyaluronate (NaHA), has synergistic effects with s-PRGF (a serum derived from plasma rich in growth factors and a blood derivative that has already shown efficacy in corneal epithelial wound healing), to reduce time of healing or posology. In vitro proliferation and migration studies, both in human corneal epithelial (HCE) cells and in rabbit primary corneal epithelial (RPCE) cultures, were carried out. In addition, we performed studies of corneal wound healing in vivo in rabbits treated with s-PRGF, NaHA, or the combination of both. We performed immunohistochemistry techniques (CK3, CK15, Ki67, ß4 integrin, ZO-1, α-SMA) in rabbit corneas 7 and 30 days after a surgically induced epithelial defect. In vitro results show that the combination of NaHA and s-PRGF offers the worst proliferation rates in both HCE and RPCE cells. Addition of NaHA to s-PRGF diminishes the re-epithelializing capability of s-PRGF. In vivo, all treatments, given twice a day, showed equivalent efficacy in corneal epithelial healing. We conclude that the combined use of s-PRGF and HaNA as an adhesive biopolymer does not improve the efficacy of s-PRGF alone in the wound healing of corneal epithelial defects.

Preparation of high bioactivity multilayered bone-marrow mesenchymal stem cell sheets for myocardial infarction using a 3D-dynamic system

Cell sheet techniques offer a promising future for myocardial infarction (MI) therapy; however, insufficient nutrition supply remains the major limitation in maintaining stem cell bioactivity in vitro. In order to enhance cell sheet mechanical strength and bioactivity, a decellularized porcine pericardium (DPP) scaffold was prepared by the phospholipase A2 method, and aspartic acid was used as a spacer arm to improve the vascular endothelial growth factor crosslink efficiency on the DPP scaffold. Based on this scaffold, multilayered bone marrow mesenchymal stem cell sheets were rapidly constructed, using RAD16-I peptide hydrogel as a temporary 3D scaffold, and cell sheets were cultured in either the 3D-dynamic system (DCcs) or the traditional static condition (SCcs). The multilayered structure, stem cell bioactivity, and ultrastructure of DCcs and SCcs were assessed. The DCcs exhibited lower apoptosis, lower differentiation, and an improved paracrine effect after a 48 h culture in vitro compared to the SCcs. Four groups were set to evaluate the cell sheet effect in rat MI model: sham group, MI control group, DCcs group, and SCcs group. The DCcs group improved cardiac function and decreased the infarcted area compared to the MI control group, while no significant improvements were observed in the SCcs group. Improved cell survival, angiogenesis, and Sca-1⁺ cell and c-kit⁺ cell amounts were observed in the DCcs group. In conclusion, the DCcs maintained higher stem cell bioactivity by using the 3D-dynamic system to provide sufficient nutrition, and transplanting DCcs significantly improved the cardiac function and angiogenesis.

STATEMENT OF SIGNIFICANCE

This study provides an efficient method to prepare vascular endothelial growth factor covalent decellularized pericardium scaffold with aspartic acid, and a multilayered bone marrow mesenchymal stem cell (BMSC) sheet is constructed on it using a 3D-dynamic system. The dynamic nutrition supply showed a significant benefit on BMSC bioactivity in vitro, including decreasing cell apoptosis, reducing stem cell differentiation, and improving growth factor secretion. These favorable bioactivity improved BMSC survival, angiogenesis, and cardiac function of the infarcted myocardium. The study highlights the importance of dynamic nutrition supply on maintaining stem cell bioactivity within cell sheet, and it stresses the necessity and significance of setting a standard for assessing cell sheet products before transplantation in the future application.

Serum from plasma rich in growth factors regenerates rabbit corneas by promoting cell proliferation, migration, differentiation, adhesion and limbal stemness

PURPOSE

To evaluate the regenerating potential and the mechanisms through which the autologous serum derived from plasma rich in growth factors (s-PRGF) favours corneal wound healing in vitro and in vivo.

METHODS

We compared the effect of various concentrations of s-PRGF versus fetal bovine serum (FBS) and control treatment in rabbit primary corneal epithelial and stromal cells and wounded rabbit corneas. Cell proliferation was measured using an enzymatic colorimetric assay. In vitro and in vivo wound-healing progression was assessed by image-analysis software. Migration and invasion were evaluated using transfilter assays. Histological structure was analysed in stained sections. Protein expression was evaluated by immunohistochemistry.

RESULTS

s-PRGF promoted the robust proliferation of epithelial cultures at any concentration, similar to FBS. Likewise, s-PRGF and FBS produced similar re-epithelialization rates in in vitro wound-healing assays. In vivo, s-PRGF treatment accelerated corneal wound healing in comparison with control treatment. This difference was significant only for 100% s-PRGF treatment in our healthy rabbit model. Histological analysis confirmed normal epithelialization in all cases. Immunohistochemistry showed a higher expression of cytokeratins 3/76 and 15, zonula occludens-1 and alpha-smooth muscle actin proteins as a function of s-PRGF concentration. Notably, keratocyte density in the anterior third of the stroma increased with increase in s-PRGF concentration, suggesting an in vivo chemotactic effect of s-PRGF on keratocytes that was further confirmed in vitro.

CONCLUSION

s-PRGF promotes proliferation and migration and influences limbal stemness, adhesion and fibrosis during corneal healing.

Construction of Anterior Hemi-Corneal Equivalents Using Nontransfected Human Corneal Cells and Transplantation in Dog Models

Tissue-engineered human anterior hemi-cornea (TE-aHC) is a promising equivalent for treating anterior lamellar keratopathy to surmount the severe shortage of donated corneas. This study was intended to construct a functional TE-aHC with nontransfected human corneal stromal (ntHCS) and epithelial (ntHCEP) cells using acellular porcine corneal stromata (aPCS) as a carrier scaffold, and evaluate its biological functions in a dog model. To construct a TE-aHC, ntHCS cells were injected into an aPCS scaffold and cultured for 3 days; then, ntHCEP cells were inoculated onto the Bowman's membrane of the scaffold and cultured for 5 days under air-liquid interface condition. After its morphology and histological structure were characterized, the constructed TE-aHC was transplanted into dog eyes via lamellar keratoplasty. The corneal transparency, thickness, intraocular pressure, epithelial integrity, and corneal regeneration were monitored in vivo, and the histological structure and histochemical property were examined ex vivo 360 days after surgery, respectively. The results showed that the constructed TE-aHC was highly transparent and composed of a corneal epithelium of 7-8 layer ntHCEP cells and a corneal stroma of regularly aligned collagen fibers and well-preserved glycosaminoglycans with sparsely distributed ntHCS cells, mimicking a normal anterior hemi-cornea (aHC). Moreover, both ntHCEP and ntHCS cells maintained positive expression of their marker and functional proteins. After transplantation into dog eyes, the constructed TE-aHC acted naturally in terms of morphology, structure and inherent property, and functioned well in maintaining corneal clarity, thickness, normal histological structure, and composition in dog models by reconstructing a normal aHC, which could be used as a promising aHC equivalent in corneal regenerative medicine and aHC disorder therapy.

In vitro biomimetic platforms featuring a perfusion system and 3D spheroid culture promote the construction of tissue-engineered corneal endothelial layers

Corneal endothelial cells (CECs) are very important for the maintenance of corneal transparency. However, in vitro, CECs display limited proliferation and loss of phenotype via endothelial to mesenchymal transformation (EMT) and cellular senescence. In this study, we demonstrate that continuous supplementary nutrition using a perfusion culture bioreactor and three-dimensional (3D) spheroid culture can be used to improve CEC expansion in culture and to construct a tissue-engineered CEC layer. Compared with static culture, perfusion-derived CECs exhibited an increased proliferative ability as well as formed close cell-cell contact junctions and numerous surface microvilli. We also demonstrated that the CEC spheroid culture significantly down-regulated gene expression of the proliferation marker Ki67 and EMT-related markers Vimentin and α-SMA, whereas the gene expression level of the CEC marker ATP1A1 was significantly up-regulated. Furthermore, use of the perfusion system in conjunction with a spheroid culture on decellularized corneal scaffolds and collagen sheets promoted the generation of CEC monolayers as well as neo-synthesized ECM formation. This study also confirmed that a CEC spheroid culture on a curved collagen sheet with controlled physiological intraocular pressure could generate a CEC monolayer. Thus, our results show that the use of a perfusion system and 3D spheroid culture can promote CEC expansion and the construction of tissue-engineered corneal endothelial layers in vitro.

Bridging the gap between traditional cell cultures and bioreactors applied in regenerative medicine: practical experiences with the MINUSHEET perfusion culture system

To meet specific requirements of developing tissues urgently needed in tissue engineering, biomaterial research and drug toxicity testing, a versatile perfusion culture system was developed. First an individual biomaterial is selected and then mounted in a MINUSHEET(®) tissue carrier. After sterilization the assembly is transferred by fine forceps to a 24 well culture plate for seeding cells or mounting tissue on it. To support spatial (3D) development a carrier can be placed in various types of perfusion culture containers. In the basic version a constant flow of culture medium provides contained tissue with always fresh nutrition and respiratory gas. For example, epithelia can be transferred to a gradient container, where they are exposed to different fluids at the luminal and basal side. To observe development of tissue under the microscope, in a different type of container a transparent lid and base are integrated. Finally, stem/progenitor cells are incubated in a container filled by an artificial interstitium to support spatial development. In the past years the described system was applied in numerous own and external investigations. To present an actual overview of resulting experimental data, the present paper was written.

Limbal Stem Cell Deficiency: Current Treatment Options and Emerging Therapies

Severe ocular surface disease can result in limbal stem cell deficiency (LSCD), a condition leading to decreased visual acuity, photophobia, and ocular pain. To restore the ocular surface in advanced stem cell deficient corneas, an autologous or allogenic limbal stem cell transplantation is performed. In recent years, the risk of secondary LSCD due to removal of large limbal grafts has been significantly reduced by the optimization of cultivated limbal epithelial transplantation (CLET). Despite the great successes of CLET, there still is room for improvement as overall success rate is 70% and visual acuity often remains suboptimal after successful transplantation. Simple limbal epithelial transplantation reports higher success rates but has not been performed in as many patients yet. This review focuses on limbal epithelial stem cells and the pathophysiology of LSCD. State-of-the-art therapeutic management of LSCD is described, and new and evolving techniques in ocular surface regeneration are being discussed, in particular, advantages and disadvantages of alternative cell scaffolds and cell sources for cell based ocular surface reconstruction.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Corneal stem cells and tissue engineering: Current advances and future perspectives

Major advances are currently being made in regenerative medicine for cornea. Stem cell-based therapies represent a novel strategy that may substitute conventional corneal transplantation, albeit there are many challenges ahead given the singularities of each cellular layer of the cornea. This review recapitulates the current data on corneal epithelial stem cells, corneal stromal stem cells and corneal endothelial cell progenitors. Corneal limbal autografts containing epithelial stem cells have been transplanted in humans for more than 20 years with great successful rates, and researchers now focus on ex vivo cultures and other cell lineages to transplant to the ocular surface. A small population of cells in the corneal endothelium was recently reported to have self-renewal capacity, although they do not proliferate in vivo. Two main obstacles have hindered endothelial cell transplantation to date: culture protocols and cell delivery methods to the posterior cornea in vivo. Human corneal stromal stem cells have been identified shortly after the recognition of precursors of endothelial cells. Stromal stem cells may have the potential to provide a direct cell-based therapeutic approach when injected to corneal scars. Furthermore, they exhibit the ability to deposit organized connective tissue in vitro and may be useful in corneal stroma engineering in the future. Recent advances and future perspectives in the field are discussed.

Importance of the stem cell microenvironment for ophthalmological cell-based therapy

Cell therapy is a promising treatment for diseases that are caused by cell degeneration or death. The cells for clinical transplantation are usually obtained by culturing healthy allogeneic or exogenous tissue in vitro. However, for diseases of the eye, obtaining the adequate number of cells for clinical transplantation is difficult due to the small size of tissue donors and the frequent needs of long-term amplification of cells in vitro, which results in low cell viability after transplantation. In addition, the transplanted cells often develop fibrosis or degrade and have very low survival. Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPS) are also promising candidates for cell therapy. Unfortunately, the differentiation of ESCs can bring immune rejection, tumorigenicity and undesired differentiated cells, limiting its clinical application. Although iPS cells can avoid the risk of immune rejection caused by ES cell differentiation post-transplantation, the low conversion rate, the risk of tumor formation and the potentially unpredictable biological changes that could occur through genetic manipulation hinder its clinical application. Thus, the desired clinical effect of cell therapy is impaired by these factors. Recent research findings recognize that the reason for low survival of the implanted cells not only depends on the seeded cells, but also on the cell microenvironment, which determines the cell survival, proliferation and even reverse differentiation. When used for cell therapy, the transplanted cells need a specific three-dimensional structure to anchor and specific extra cellular matrix components in addition to relevant cytokine signaling to transfer the required information to support their growth. These structures present in the matrix in which the stem cells reside are known as the stem cell microenvironment. The microenvironment interaction with the stem cells provides the necessary homeostasis for cell maintenance and growth. A large number of studies suggest that to explore how to reconstruct the stem cell microenvironment and strengthen its combination with the transplanted cells are key steps to successful cell therapy. In this review, we will describe the interactions of the stem cell microenvironment with the stem cells, discuss the importance of the stem cell microenvironment for cell-based therapy in ocular diseases, and introduce the progress of stem cell-based therapy for ocular diseases.