Phenotypic change and induction of cytokeratin expression during in vitro culture of corneal stromal cells

Purpose: Cells of the corneal epithelium and stroma can be distinguished in vivo by different intermediate filaments, cytokeratins for corneal epithelial cells (CEC) and vimentin for keratocytes. Isolated and cultured keratocytes change phenotype, losing expression of keratocyte markers and gaining markers associated with mesenchymal stromal cells (MSC). This study investigates this change in phenotype in relation to intermediate filament expression in cultured corneal stromal cells (CSC) compared to CEC. Methods: Expression of epithelial markers (CK3, CK12, CK19, pan cytokeratin, E-cadherin), keratocyte markers (CD34, vimentin) and MSC markers (CD73, CD90 and CD105) were compared in CEC and CSC by immunocytochemistry and RT-qPCR. Expression was evaluated at different stages of CSC culture and compared to another stromal cell type, extracted from Wharton’s jelly (WJ-MSC). Results: In vivo keratocytes did not express cytokeratins. However, cultured CSC expressed epithelial-associated CK3, CK12 and CK19 but other cytokeratins. Expression of cytokeratins increased as CSC were passaged and decreased as CSC were induced to become quiescent. Comparatively, WJ-MSC, expressed lower levels of CK3, CK12 and CK19, but also stained for pan cytokeratin and expressed KRT5. Conclusions: Cultured CSC undergo phenotypic change during culture, expressing specific cytokeratin filaments normally associated with CEC. Cytokeratin expression begins as cells are cultured on plastic and increases with passage. This discovery may influence the way that differences are discerned between cultured CEC and CSC. Investigators need to be aware that the expression of cytokeratins does not necessarily represent epithelial contamination, and that CEC and CSC may be more related than previously recognised

Tissue engineering in hostile environments: the effects and control of inflammation in bone tissue engineering

The potential effects of introducing bone regeneration strategies into environments of disease and damage are often overlooked, despite the fact that many of the signalling pathways in inflammation have effects on bone development and healing. Embryonic stem cells (ESCs) are increasingly being used to develop models of disease and have potential in osteogenic-cell based therapies. Osteogenic differentiation strategies for ESCs are well established, but the response of these cells to tissue damage and inflammation has not yet been investigated, particularly in comparison to primary osteoblasts. Here, proinflammatory cytokines were used as part of an in vitro model to mimic elements of skeletal disease, such as rheumatoid arthritis and non-union fractures. The response of osteogenically differentiated mouse embryonic stem cells (osteo-mESCs) to the proinflammatory cytokines interleukin 1-β (IL-1β), tumour necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), was compared to that of primary mouse calvarial osteoblasts, already well-described in literature and used as a “benchmark” in this study. Although histology, immunocytochemistry and PCR showed similarities in osteogenic differentiation of the osteo-mESCs and the primary calvarial cells, over 21 days in culture, there were marked differences in the response to the proinflammatory cytokines. Viability of the osteo-mESCs was maintained in response to cytokines, whereas viability of primary cells was significantly reduced. There were marked increases in nitric oxide (NO) and prostaglandin E2 (PGE2) production in primary calvarial cells over the entire 21-day culture period, but this was not seen with osteo-mESCs until day 21. The study then went on to look at the effects of proinflammatory signalling on the in vitro bone formation of the two cell types. Significant differences in the effects of proinflammatory cytokines on bone nodule formation and matrix production were seen when comparing the osteo-mESCs and the calvarial cells. This study demonstrates that while osteo-mESCs share phenotypic characteristics with primary osteoblasts, there are some distinct differences in their biochemistry and response to cytokines. This is relevant to understanding differentiation of stem cells, developing in vitro models of disease, testing new drugs and developing cell therapies. An additional objective in this investigation was to look at tissue engineering strategies as a means of controlling inflammation in bone disease. The primary calvarial osteoblasts were utilised as an in vitro inflammation model, and used to study the effects of anti-inflammatory mediators. Anti-inflammatory-releasing porous scaffolds were manufactured from poly(lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG). The calvarial osteoblast inflammation model was used successfully to show successful release of diclofenac sodium from the PLGA/PEG scaffolds. This study demonstrates that there is much to consider in the development of regenerative strategies for bone disease, particularly the role that the effect and control of inflammation will play in bone healing

Tissue engineering in hostile environments: the effects and control of inflammation in bone tissue engineering

The potential effects of introducing bone regeneration strategies into environments of disease and damage are often overlooked, despite the fact that many of the signalling pathways in inflammation have effects on bone development and healing. Embryonic stem cells (ESCs) are increasingly being used to develop models of disease and have potential in osteogenic-cell based therapies. Osteogenic differentiation strategies for ESCs are well established, but the response of these cells to tissue damage and inflammation has not yet been investigated, particularly in comparison to primary osteoblasts. Here, proinflammatory cytokines were used as part of an in vitro model to mimic elements of skeletal disease, such as rheumatoid arthritis and non-union fractures. The response of osteogenically differentiated mouse embryonic stem cells (osteo-mESCs) to the proinflammatory cytokines interleukin 1-β (IL-1β), tumour necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), was compared to that of primary mouse calvarial osteoblasts, already well-described in literature and used as a “benchmark” in this study. Although histology, immunocytochemistry and PCR showed similarities in osteogenic differentiation of the osteo-mESCs and the primary calvarial cells, over 21 days in culture, there were marked differences in the response to the proinflammatory cytokines. Viability of the osteo-mESCs was maintained in response to cytokines, whereas viability of primary cells was significantly reduced. There were marked increases in nitric oxide (NO) and prostaglandin E2 (PGE2) production in primary calvarial cells over the entire 21-day culture period, but this was not seen with osteo-mESCs until day 21. The study then went on to look at the effects of proinflammatory signalling on the in vitro bone formation of the two cell types. Significant differences in the effects of proinflammatory cytokines on bone nodule formation and matrix production were seen when comparing the osteo-mESCs and the calvarial cells. This study demonstrates that while osteo-mESCs share phenotypic characteristics with primary osteoblasts, there are some distinct differences in their biochemistry and response to cytokines. This is relevant to understanding differentiation of stem cells, developing in vitro models of disease, testing new drugs and developing cell therapies. An additional objective in this investigation was to look at tissue engineering strategies as a means of controlling inflammation in bone disease. The primary calvarial osteoblasts were utilised as an in vitro inflammation model, and used to study the effects of anti-inflammatory mediators. Anti-inflammatory-releasing porous scaffolds were manufactured from poly(lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG). The calvarial osteoblast inflammation model was used successfully to show successful release of diclofenac sodium from the PLGA/PEG scaffolds. This study demonstrates that there is much to consider in the development of regenerative strategies for bone disease, particularly the role that the effect and control of inflammation will play in bone healing

Potential of mesenchymal stem cells as topical immunomodulatory cell therapies for ocular surface inflammatory disorders

Ocular surface inflammatory disorders (OSIDs) are a group of highly prevalent, heterogeneous diseases which display a variety of aetiologies and symptoms and are risk factors for serious complications including ocular and cornea impairment. Corneal inflammation is a common factor of all OSIDs, regardless of their cause or symptoms. Current medications include over‐the‐counter lubricating eye drops, corticosteroids, and ciclosporin, which either do not treat the corneal inflammation or have been associated with multiple side effects leading to alternative treatments being sought. Regenerative medicine cell therapies, particularly mesenchymal stem cells (MSCs), have shown great promise for immunosuppression and disease amelioration across multiple tissues, including the cornea. However, for successful development and clinical translation of MSC therapy for OSIDs, significant problems must be addressed. This review aims to highlight considerations, including whether the source of MSC isolation impacts the efficacy and safety of the therapy, in addition to assessing the feasibility of MSC topical application to the cornea and ocular surface through analysis of potential scaffolds and cell carriers for application to the eye. The literature contains limited data assessing MSCs incorporated into scaffolds for corneal administration, thus here we highlight the necessity of further investigations to truly exploit the potential of an MSC‐based cell therapy for the treatment of OSIDs

Corneal decellularization: a method of recycling unsuitable donor tissue for clinical translation?

Background: There is a clinical need for biomimetic corneas that are as effective, preferably superior, to cadaveric donor tissue. Decellularized tissues are advantageous compared to synthetic or semi-synthetic engineered tissues in that the native matrix ultrastructure and intrinsic biological cues including growth factors, cytokines and glycosaminoglycans may be retained. However, there is currently no reliable, standardized human corneal decellularization protocol. Methods: Corneal eye-bank tissue unsuitable for transplantation was utilized to systematically compare commonly used decellularization protocols. Hypertonic sodium chloride; an ionic reagent, sodium dodecyl sulphate; a non-ionic detergent, tert-octylphenol polyoxyethylene (Triton-X); enzymatic disaggregation using Dispase; mechanical agitation; and the use of nucleases were investigated. Decellularization efficacy, specifically for human corneal tissue, was extensively evaluated. Removal of detectable cellular material was evidenced by histological, immunofluorescence and biochemical assays. Preservation of macroscopic tissue transparency and light transmittance was evaluated. Retention of corneal architecture, collagen and glycosaminoglycans was assessed via histological, immunofluorescence and quantitative analysis. Biocompatibility of the resulting scaffolds was assessed using cell proliferation assays. Results: None of the decellularization protocols investigated successfully removed 100% of cellular components. The techniques with the least residual cellular material were most structurally compromised. Biochemical analysis of glycosaminoglycans demonstrated the stripping effects of the decellularization procedures. Conclusion: The ability to utilize, reprocess and regenerate tissues deemed “unsuitable” for transplantation allows us to salvage valuable tissue. Reprocessing the tissue has the potential to have a considerable impact on addressing the problems associated with cadaveric donor shortage. Patients would directly benefit by accessing greater numbers of corneal grafts and health authorities would fulfill their responsibility for the delivery of effective corneal reconstruction to alleviate corneal blindness. However, in order to progress, we may need to take a step back to establish a “decellularization” criterion; which should balance effective removal of immune reactive material with maintenance of tissue functionality

Keeping an eye on decellularized corneas: a review of methods, characterization and applications

The worldwide limited availability of suitable corneal donor tissue has led to the development of alternatives, including keratoprostheses (Kpros) and tissue engineered (TE) constructs. Despite advances in bioscaffold design, there is yet to be a corneal equivalent that effectively mimics both the native tissue ultrastructure and biomechanical properties. Human decellularized corneas (DCs) could offer a safe, sustainable source of corneal tissue, increasing the donor pool and potentially reducing the risk of immune rejection after corneal graft surgery. Appropriate, human-specific, decellularization techniques and high-resolution, non-destructive analysis systems are required to ensure reproducible outputs can be achieved. If robust treatment and characterization processes can be developed, DCs could offer a supplement to the donor corneal pool, alongside superior cell culture systems for pharmacology, toxicology and drug discovery studies

Increased Anti-Inflammatory Therapeutic Potential and Progenitor Marker Expression of Corneal Mesenchymal Stem Cells Cultured in an Optimized Propagation Medium

There is a huge unmet need for new treatment modalities for ocular surface inflammatory disorders (OSIDs) such as dry eye disease and meibomian gland dysfunction. Mesenchymal stem cell therapies may hold the answer due to their potent immunomodulatory properties, low immunogenicity, and ability to modulate both the innate and adaptive immune response. MSC-like cells that can be isolated from the corneal stroma (C-MSCs) offer a potential new treatment strategy; however, an optimized culture medium needs to be developed to produce the ideal phenotype for use in a cell therapy to treat OSIDs. The effects of in vitro expansion of human C-MSC in a medium of M199 containing fetal bovine serum (FBS) was compared to a stem cell medium (SCM) containing knockout serum replacement (KSR) with basic fibroblast growth factor (bFGF) and human leukemia inhibitory factor (LIF), investigating viability, protein, and gene expression. Isolating populations expressing CD34 or using siRNA knockdown of CD34 were investigated. Finally, the potential of C-MSC as a cell therapy was assessed using co-culture with an in vitro corneal epithelial cell injury model and the angiogenic effects of C-MSC conditioned medium were evaluated with blood and lymph endothelial cells. Both media supported proliferation of C-MSC, with SCM increasing expression of CD34, ABCG2, PAX6, NANOG, REX1, SOX2, and THY1, supported by increased associated protein expression. Isolating cell populations expressing CD34 protein made little difference to gene expression, however, knockdown of the CD34 gene led to decreased expression of progenitor genes. C-MSC increased viability of injured corneal epithelial cells whilst decreasing levels of cytotoxicity and interleukins-6 and -8. No pro-angiogenic effect of C-MSC was seen. Culture medium can significantly influence C-MSC phenotype and culture in SCM produced a cell phenotype more suitable for further consideration as an anti-inflammatory cell therapy. C-MSC show considerable potential for development as therapies for OSIDs, acting through anti-inflammatory action

Corneal Decellularization: A Method of Recycling Unsuitable Donor Tissue for Clinical Translation?

Background: There is a clinical need for biomimetic corneas that are as effective, preferably superior, to cadaveric donor tissue. Decellularized tissues are advantageous compared to synthetic or semi-synthetic engineered tissues in that the native matrix ultrastructure and intrinsic biological cues including growth factors, cytokines and glycosaminoglycans may be retained. However, there is currently no reliable, standardized human corneal decellularization protocol.Methods: Corneal eye-bank tissue unsuitable for transplantation was utilized to systematically compare commonly used decellularization protocols. Hypertonic sodium chloride; an ionic reagent, sodium dodecyl sulphate; a non-ionic detergent, tert-octylphenol polyoxyethylene (Triton-X); enzymatic disaggregation using Dispase; mechanical agitation; and the use of nucleases were investigated. Decellularization efficacy, specifically for human corneal tissue, was extensively evaluated. Removal of detectable cellular material was evidenced by histological, immunofluorescence and biochemical assays. Preservation of macroscopic tissue transparency and light transmittance was evaluated. Retention of corneal architecture, collagen and glycosaminoglycans was assessed via histological, immunofluorescence and quantitative analysis. Biocompatibility of the resulting scaffolds was assessed using cell proliferation assays.Results: None of the decellularization protocols investigated successfully removed 100% of cellular components. The techniques with the least residual cellular material were most structurally compromised. Biochemical analysis of glycosaminoglycans demonstrated the stripping effects of the decellularization procedures.Conclusion: The ability to utilize, reprocess and regenerate tissues deemed “unsuitable” for transplantation allows us to salvage valuable tissue. Reprocessing the tissue has the potential to have a considerable impact on addressing the problems associated with cadaveric donor shortage. Patients would directly benefit by accessing greater numbers of corneal grafts and health authorities would fulfill their responsibility for the delivery of effective corneal reconstruction to alleviate corneal blindness. However, in order to progress, we may need to take a step back to establish a “decellularization” criterion; which should balance effective removal of immune reactive material with maintenance of tissue functionality

The use of innovative scaffolds in the development of corneal stroma-derived stem cell therapies for future corneal regeneration strategies [Abstract]

The use of innovative scaffolds in the development of corneal stroma-derived stem cell therapies for future corneal regeneration strategies [Abstract

Terminal sterilization: conventional methods versus emerging cold atmospheric pressure plasma technology for non-viable biological tissues

Tissue products are susceptible to microbial contamination from different sources, which may cause disease transmission upon transplantation. Terminal sterilization using gamma radiation, electron-beam, and ethylene oxide protocols are well-established and accepted, however, such methods have known disadvantages associated with compromised tissue integrity, functionality, safety, complex logistics, availability, and cost. Non-thermal (cold) atmospheric pressure plasma (CAP) is an emerging technology that has several biomedical applications including sterilization of tissues, and the potential to surpass current terminal sterilization techniques. This review discusses the limitations of conventional terminal sterilization technologies for biological materials, and highlights the benefits of utilizing CAP