Organ culture, but not hypothermic storage, facilitates the repair of the corneal endothelium following mechanical damage

Expression of Yes-associated protein in endothelial cells of human corneas before and after storage in organ culture

The cornea, the anterior meniscus-shaped transparent and refractive structure of the eyeball, is the first mechanical barrier of the eye. Its functionality heavily relies on the health of its endothelium, its most posterior layer. The treatment of corneal endothelial cells (CECs) deficiency is allogeneic corneal graft using stored donor corneas. One of the main goals of eye banks is to maintain endothelial cell density (ECD) and endothelial barrier function, critical parameters influencing transplantation outcomes. Unlike in vivo, the stored cornea is not subjected to physiological mechanical stimuli, such as the hydrokinetic pressure of the aqueous humor and intraocular pressure (IOP). YAP (Yes-Associated Protein), a pivotal transcriptional coactivator, is recognized for its ability to sense diverse biomechanical cues and transduce them into specific biological signals, varying for each cell type and mechanical forces. The biomechanical cues that might regulate YAP in human corneal endothelium remain unidentified. Therefore, we investigated the expression and subcellular localization of YAP in the endothelium of corneas stored in organ culture (OC). Our findings demonstrated that CEC morphology, ECD and cell-cell interactions are distinctly and differentially associated with modifications in the expression, subcellular localization and phosphorylation of YAP. Notably, this phosphorylation occurs in the basal region of the primary cilium, which may play central cellular roles in sensing mechanical stimuli. The sustained recruitment of YAP in cellular junctions, nucleus, and cilium under long-term OC conditions strongly indicates its specific role in maintaining CEC homeostasis. Understanding these biophysical influences could aid in identifying molecules that promote homeostasis and enhance the functionality of CECs.

Effect of Low-Temperature Preservation in Optisol-GS on Preloaded, Endothelium-Out DMEK Grafts

The aim of the study was to assess different temperature ranges for the preservation of pre-loaded Descemet Membrane Endothelial Keratoplasty (DMEK) grafts in the DMEK RAPID Mini device.

METHODS

Three groups of 15 DMEK grafts (five per group) were pre-loaded in the DMEK RAPID Mini and preserved in Optisol-GS for 72 h at different temperatures: group A at >8 °C, group B between 2-8 °C and group C at <2 °C. After stripping and preservation, the viability of the endothelium, cell loss and morphology were assessed through light microscopy following trypan blue and alizarin red staining.

RESULTS

Overall mortality was 4.07%, 3.97% and 7.66%, in groups A, B and C, respectively, with percentages of uncovered areas of 0.31%, 1.36% and 0.20% (all p > 0.05). Endothelial cell density variation was 5.51%, 3.06% and 2.82% in groups A, B and C, respectively (p = 0.19). Total Endothelial Cell Loss (ECL) was 4.37%, 5.32% and 7.84% in groups A, B and C, respectively (p = 0.39). Endothelial cell morphology was comparable in all three groups.

CONCLUSIONS

In the DMEK RAPID Mini, low temperatures (<2 °C) may affect the quality of pre-loaded grafts, inducing a higher ECL after 72 h of preservation, although no significant differences among groups could be proved. Our data would suggest maintaining grafts loaded in the DMEK RAPID Mini at temperatures between 2-8 °C for appropriate preservation.

Ex vivo expansion and characterization of human corneal endothelium for transplantation: a review

The corneal endothelium plays a key role in maintaining corneal transparency. Its dysfunction is currently treated with penetrating or lamellar keratoplasty. Advanced cell therapy methods seek to address the persistent global deficiency of donor corneas by enabling the renewal of the endothelial monolayer with tissue-engineered grafts. This review provides an overview of recently published literature on the preparation of endothelial grafts for transplantation derived from cadaveric corneas that have developed over the last decade (2010–2021). Factors such as the most suitable donor parameters, culture substrates and media, endothelial graft storage conditions, and transplantation methods are discussed. Despite efforts to utilize alternative cellular sources, such as induced pluripotent cells, cadaveric corneas appear to be the best source of cells for graft preparation to date. However, native endothelial cells have a limited natural proliferative capacity, and they often undergo rapid phenotype changes in ex vivo culture. This is the main reason why no culture protocol for a clinical-grade endothelial graft prepared from cadaveric corneas has been standardized so far. Currently, the most established ex vivo culture protocol involves the peel-and-digest method of cell isolation and cell culture by the dual media method, including the repeated alternation of high and low mitogenic conditions. Culture media are enriched by additional substances, such as signaling pathway (Rho-associated protein kinase, TGF-β, etc.) inhibitors, to stimulate proliferation and inhibit unwanted morphological changes, particularly the endothelial-to-mesenchymal transition. To date, this promising approach has led to the development of endothelial grafts for the first in-human clinical trial in Japan. In addition to the lack of a standard culture protocol, endothelial-specific markers are still missing to confirm the endothelial phenotype in a graft ready for clinical use. Because the corneal endothelium appears to comprise phenotypically heterogeneous populations of cells, the genomic and proteomic expression of recently proposed endothelial-specific markers, such as Cadherin-2, CD166, or SLC4A11, must be confirmed by additional studies. The preparation of endothelial grafts is still challenging today, but advances in tissue engineering and surgery over the past decade hold promise for the successful treatment of endothelial dysfunctions in more patients worldwide.

Endothelial Cell Viability after DMEK Graft Preparation

Aim: To evaluate the effect of graft preparation and organ-culture storage on endothelial cell density (ECD) and viability of Descemet membrane endothelial keratoplasty (DMEK) grafts.Materials and methods: DMEK grafts (n = 27) were prepared at Amnitrans EyeBank Rotterdam from 27 corneas (15 donors) that were eligible for transplantation but could not be allocated due to the Covid-19-related cancellation of elective surgeries. Cell viability (by Calcein-AM staining) and ECD of five grafts originally scheduled for transplantation were evaluated on the originally planned surgery day, whereas 22 grafts from paired donor corneas were evaluated either directly post-preparation or after 3-7 days of storage. ECD was analyzed by light microscopy (LM ECD) and Calcein-AM staining (Calcein-ECD).Results: Light microscopy (LM) evaluation of all grafts showed an unremarkable endothelial cell monolayer directly after preparation. However, median Calcein-ECD for the five grafts initially allocated for transplantation was 18% (range 92-73%) lower than median LM ECD. For the paired DMEK grafts, Calcein-ECD determined by Calcein-AM staining on the day of graft preparation and after 3-7 days of graft storage showed a median decrease of 1% and 2%, respectively. Median percentage of central graft area populated by viable cells after preparation and after 3-7 days of graft storage was 88% and 92%, respectively.Conclusion: Cell viability of most of the grafts will not be affected by preparation and storage. Endothelial cell damage may be observed for some grafts within hours after preparation, with insignificant additional ECD changes during 3-7 days of graft storage. Implementing an additional post-preparation step in the eye bank to evaluate cell density before graft release for transplantation may help to reduce postoperative DMEK complications.

Polysaccharide-Based Biomaterials in Tissue Engineering: A Review

In addition to proteins and nucleic acids, polysaccharides are an important type of biomacromolecule widely distributed in plants, animals, and microorganisms. Polysaccharides are considered as promising biomaterials due to their significant bioactivities, natural abundance, immunoactivity, and chemical modifiability for tissue engineering (TE) applications. Due to the similarities of the biochemical properties of polysaccharides and the extracellular matrix of human bodies, polysaccharides are increasingly recognized and accepted. Furthermore, the degradation behavior of these macromolecules is generally nontoxic. Certain delicate properties, such as remarkable mechanical properties and tunable tissue response, can be obtained by modifying the functional groups on the surface of polysaccharide molecules. The applications of polysaccharide-based biomaterials in the TE field have been growing intensively in recent decades, for example, bone/cartilage regeneration, cardiac regeneration, neural regeneration, and skin regeneration. This review summarizes the main essential properties of polysaccharides, including their chemical properties, crosslinking mechanisms, and biological properties, and focuses on the association between their structures and properties. The recent progress in polysaccharide-based biomaterials in various TE applications is reviewed, and the prospects for future studies are addressed as well. We intend this review to offer a comprehensive understanding of and inspiration for the research and development of polysaccharide-based materials in TE.

A new storage solution for the hypothermic preservation of corneal grafts: an experimental study

In this experimental study we used for the first time Tiprotec^® as a solution for corneal preservation and cold storage. We compared the resultant endothelial cell morphology and viability with this obtained after preservation of the ex-vivo corneas with both usual standard techniques: conventional cold storage (using Eusol-C) and organ culture. This prospective, in vitro, 3-armed parallel study was performed with the use of 90 porcine corneas (examined for their endothelial quality and transparency) randomly selected for preservation in three storage methods (each 30 corneas): organ culture, standard cold storage (Eusol-C) and experimental cold storage (Tiprotec^®) Endothelium cell quantity and quality as well as corneal opacification were assessed. The degree of endothelial transparency was significantly reduced over time with all preservation media, without any significant difference among the three groups at any point of time. A reduction in endothelial cell density was also observed with all three preservation media after 30 days of storage without statistically significant differences between groups. The number of hexagonal and pentagonal endothelium cells was significantly reduced overtime in all media with significantly more hexagonal and pentagonal in the organ culture group compared to the cold storage groups. We could show that the cryopreservation medium Tiprotec^®, used until now for the preservation of vascular grafts, was of similar quality compared to the medium Eusol-C for the hypothermic storage of corneal tissue for an extended period of time up to 30 days. In comparison to organic culture with culture medium KII, both Tiprotec^® and Eusol-C were found less effective in preserving endothelial cell quality, as assessed by the morphometric analysis, and viability, as assessed by the degree of vacuolization at least up to the 30th day of storage. However, both, Tiprotec^®- and Eusol-C-preserved corneas demonstrated a certain capacity to recover after their submission in organ culture.

Endothelial Wound Repair of the Organ-Cultured Porcine Corneas

PURPOSE

To assess whether injured porcine endothelium of small and large corneoscleral disc differ in its reparative/regenerative capacity under various conditions of organ culture storage.

MATERIAL AND METHODS

166 paired porcine corneas were trephined to obtain tissues with diameter 12.0 mm and 17.5 mm (with area neighboring endothelial periphery). In tested discs, central endothelium was mechanically wounded. Density of live endothelial cells (LECD), percentage of dead cells (%DC), coefficient of variation and cell hexagonality were assessed in central and paracentral endothelium following 5- or 9-day incubation in medium with 2% or 10% fetal bovine serum. The parameters were assessed also in fresh and intact cultured discs. Dead endothelial cells (EC) were visualized by trypan blue, cell borders by Alizarin Red S dye. Endothelial imprints were immunoassayed for the proliferation marker Ki-67 and the nucleolar marker fibrillarin.

RESULTS

In fresh corneas, the LECD/mm² (mean ± standard deviation) were 3998.0 ± 215.4 (central area) and 3888.2 ± 363.1 (paracentral area). Only the length of storage had significant effect on wound repair. Lesion was repaired partially after 5-day and fully after 9-day cultivation. After 9-day storage in medium with 10% serum, the mean LECD detected in small discs were 2409.4 ± 881.8 (central area) and 3949.5 ± 275.5 (paracentral area) and in large discs the mean LECD were 2555.0 ± 347.0 (central area) and 4007.5 ± 261.2 (paracentral area). Ki-67 showed cell proliferation associated with healing of EC of both large and small corneas.

CONCLUSIONS

The lesions were completely repaired within 9 days of storage. Presence of the area, where stem cells appear to be located, contributes to stimulation of endothelial reparation less than serum concentration and time of culture. Both cell migration and proliferation contribute to the wound repair.

Cryopreservation: Evolution of Molecular Based Strategies

Cryopreservation (CP) is an enabling process providing for on-demand access to biological material (cells and tissues) which serve as a starting, intermediate or even final product. While a critical tool, CP protocols, approaches and technologies have evolved little over the last several decades. A lack of conversion of discoveries from the CP sciences into mainstream utilization has resulted in a bottleneck in technological progression in areas such as stem cell research and cell therapy. While the adoption has been slow, discoveries including molecular control and buffering of cell stress response to CP as well as the development of new devices for improved sample freezing and thawing are providing for improved CP from both the processing and sample quality perspectives. Numerous studies have described the impact, mechanisms and points of control of cryopreservation-induced delayed-onset cell death (CIDOCD). In an effort to limit CIDOCD, efforts have focused on CP agent and freeze media formulation to provide a solution path and have yielded improvements in survival over traditional approaches. Importantly, each of these areas, new technologies and cell stress modulation, both individually and in combination, are now providing a new foundation to accelerate new research, technology and product development for which CP serves as an integral component. This chapter provides an overview of the molecular stress responses of cells to cryopreservation, the impact of the hypothermic and cell death continuums and the targeted modulation of common and/or cell specific responses to CP in providing a path to improving cell quality.

Considering 3D topography of endothelial folds to improve cell count of organ cultured corneas

The posterior side of the cornea is covered by the endothelial monolayer, which governs corneal transparency but cannot proliferate. Determination of endothelial cell density (ECD) is therefore the minimal and mandatory quality control in all eye banks. It avoids primary graft failures caused by endothelial insufficiency, and allows allocation of corneas to surgical techniques requiring different numbers of endothelial cells (ECs). Corneas stored in organ culture (17% of grafts worldwide), are characterized by heavy stromal swelling and numerous deep endothelial folds, up to 200 µm high. During microscopic en face observation, flat surfaces are thus exceptional and EC counting is biased by parallax errors, resulting in overestimated eye bank ECD (ebECD). We used a motorized transmitted light microscope to acquire Z-stacks of images every 10 µm, and processed them to reconstruct the 3D surface of the folded endothelium. This method (3D-ECD) takes into account the local point-by-point slope in order to correct ECD. On a set of 30 corneas, we compared 3D-ECD and ebECD determined on five identical zones at the center of the cornea. 3D reconstruction allowed us to visualize twice as many cells, and ebECD was 8.1 ± 4.5% (95%CI 6.4-9.7) higher than 3D-ECD, with 1744 ± 488 versus 1606 ± 473 cells/mm². 3D counting makes it possible to increase cell sampling and to correct overestimation by the conventional en face counting still routinely performed in eye banks.

Organ culture storage of pre-prepared corneal donor material for Descemet's membrane endothelial keratoplasty

PURPOSE

To evaluate the effect of media composition and storage method on pre-prepared Descemet's membrane endothelial keratoplasty (DMEK) grafts.

METHODS

50 corneas were used. Endothelial wound healing and proliferation in different media were assessed using a standard injury model. DMEK grafts were stored using three methods: peeling with free scroll storage; partial peeling with storage on the stroma and fluid bubble separation with storage on the stroma. Endothelial cell (EC) phenotype and the extent of endothelial overgrowth were examined. Global cell viability was assessed for storage methods that maintained a normal cell phenotype.

RESULTS

1 mm wounds healed within 4 days. Enhanced media did not increase EC proliferation but may have increased EC migration into the wounded area. Grafts that had been trephined showed evidence of EC overgrowth, whereas preservation of a physical barrier in the bubble group prevented this. In grafts stored in enhanced media or reapposed to the stroma after trephination, endothelial migration occurred sooner and cells underwent endothelial-mesenchymal transformation. Ongoing cell loss, with new patterns of cell death, was observed after returning grafts to storage. Grafts stored as free scrolls retained more viable ECs than grafts prepared with the fluid bubble method (74.2± 3% vs 60.3±6%, p=0.04 (n=8).

CONCLUSION

Free scroll storage is superior to liquid bubble and partial peeling techniques. Free scrolls only showed overgrowth of ECs after 4 days in organ culture, indicating a viable time window for the clinical use of pre-prepared DMEK donor material using this method. Methods for tissue preparation and storage media developed for whole corneas should not be used in pre-prepared DMEK grafts without prior evaluation.

Microarray analysis of cell cycle gene expression in adult human corneal endothelial cells

Corneal endothelial cells (ECs) form a monolayer that controls the hydration of the cornea and thus its transparency. Their almost nil proliferative status in humans is responsible, in several frequent diseases, for cell pool attrition that leads to irreversible corneal clouding. To screen for candidate genes involved in cell cycle arrest, we studied human ECs subjected to various environments thought to induce different proliferative profiles compared to ECs in vivo. Donor corneas (a few hours after death), organ-cultured (OC) corneas, in vitro confluent and non-confluent primary cultures, and an immortalized EC line were compared to healthy ECs retrieved in the first minutes of corneal grafts. Transcriptional profiles were compared using a cDNA array of 112 key genes of the cell cycle and analysed using Gene Ontology classification; cluster analysis and gene map presentation of the cell cycle regulation pathway were performed by GenMAPP. Results were validated using qRT-PCR on 11 selected genes. We found several transcripts of proteins implicated in cell cycle arrest and not previously reported in human ECs. Early G1-phase arrest effectors and multiple DNA damage-induced cell cycle arrest-associated transcripts were found in vivo and over-represented in OC and in vitro ECs. Though highly proliferative, immortalized ECs also exhibited overexpression of transcripts implicated in cell cycle arrest. These new effectors likely explain the stress-induced premature senescence that characterizes human adult ECs. They are potential targets for triggering and controlling EC proliferation with a view to increasing the cell pool of stored corneas or facilitating mass EC culture for bioengineered endothelial grafts.

Wounding the cornea to learn how it heals

Corneal wound healing studies have a long history and rich literature that describes the data obtained over the past 70 years using many different species of animals and methods of injury. These studies have lead to reduced suffering and provided clues to treatments that are now helping patients live more productive lives. In spite of the progress made, further research is required since blindness and reduced quality of life due to corneal scarring still happens. The purpose of this review is to summarize what is known about different types of wound and animal models used to study corneal wound healing. The subject of corneal wound healing is broad and includes chemical and mechanical wound models. This review focuses on mechanical injury models involving debridement and keratectomy wounds to reflect the authors' expertise.

Revisited microanatomy of the corneal endothelial periphery: new evidence for continuous centripetal migration of endothelial cells in humans

The control of corneal transparency depends on the integrity of its endothelial monolayer, which is considered nonregenerative in adult humans. In pathological situations, endothelial cell (EC) loss, not offset by mitosis, can lead to irreversible corneal edema and blindness. However, the hypothesis of a slow, clinically insufficient regeneration starting from the corneal periphery remains debatable. The authors have re-evaluated the microanatomy of the endothelium in order to identify structures likely to support this homeostasis model. Whole endothelia of 88 human corneas (not stored, and stored in organ culture) with mean donor age of 80 ± 12 years were analyzed using an original flat-mounting technique. In 61% of corneas, cells located at the extreme periphery (last 200 μm of the endothelium) were organized in small clusters with two to three cell layers around Hassall-Henle bodies. In 68% of corneas, peripheral ECs formed centripetal rows 830 ± 295 μm long, with Descemet membrane furrows visible by scanning electron microscopy. EC density was significantly higher in zones with cell rows. When immunostained, ECs in the extreme periphery exhibited lesser differentiation (ZO-1, Actin, Na/K ATPase, CoxIV) than ECs in the center of the cornea but preferentially expressed stem cell markers (Nestin, Telomerase, and occasionally breast cancer resistance protein) and, in rare cases, the proliferation marker Ki67. Stored corneas had fewer cell clusters but more Ki67-positive ECs. We identified a novel anatomic organization in the periphery of the human corneal endothelium, suggesting a continuous slow centripetal migration, throughout life, of ECs from specific niches.

Impact of organ culturing on metabolic profile of human corneas: preliminary results

PURPOSE

It is suggested that the quality of corneal graft may depend on modifications that appear in the tissue during culturing. The aim of this study was to investigate the differences in the metabolic profile between cultured and noncultured human corneas.

METHODS

Corneas from 12 donors were obtained post-mortem and cultured for 6-20 days. Control corneas were obtained from four patients with malignant melanoma of the chorioidea and were kept frozen at -80 °C until analysed. The metabolic profiles of the samples were investigated using high-resolution, magic angle spinning (1) H nuclear magnetic resonance spectroscopy and special software for: (i) analysis of complex mixtures, (ii) principal component analysis and (iii) specialized statistical analysis.

RESULTS

Twenty metabolites were detected and assigned in the corneas. Significant differences in metabolic profiles between cultured and noncultured corneas were revealed. It was also shown in samples kept in culture for 9-14 days that the levels of (i) alanine, formate, lactate and (ii) acetate, alanine, arginine, lactate were elevated in comparison with the samples kept for <9 and more than 14 days, respectively.

CONCLUSIONS

Corneal culturing affects the metabolic profile of the tissue. The increases in the levels of some metabolites within the second week of culturing likely result from variations in tissue metabolic or enzymatic activity caused by changed (organ culture) environment. As the mechanisms responsible for these changes are not clear, further research is indicated.

Endothelial quality of pre-cut posterior corneal lamellae for Descemet membrane endothelial keratoplasty with a stromal rim (DMEK-S): two-year outcome of manual preparation in an ocular tissue bank

To assess the quantitative and qualitative parameters of pre-cut posterior corneal lamellae for Descemet membrane endothelial keratoplasty with a stromal rim (DMEK-S) prepared manually in the Ocular Tissue Bank Prague. All 65 successfully prepared pre-cut posterior corneal lamellae provided for grafting during a 2-year period were analyzed retrospectively. The lamellae, consisting of a central zone of endothelium-Descemet membrane surrounded by a supporting peripheral stromal rim, were prepared manually from corneoscleral buttons having an endothelial cell density higher than 2,500 cells/mm(2). The live endothelial cell density, the percentage of dead cells, the hexagonality and the coefficient of variation were assessed before and immediately after preparation as well as after 2 days of organ culture storage at 31 °C. Altogether, the endothelium of 57 lamellae was assessed. Immediately after preparation, the mean live endothelial cell density was 2,835 cells/mm(2) and, on average, 1.8 % of dead cells were found. After 2 days of storage, the cell density decreased significantly to 2,757 cells/mm(2) and the percentage of dead cells to 1.0 %. There was a significant change in the mean hexagonality and the coefficient of variation after lamellar preparation and subsequent storage. The amount of tissue wasted during the preparation was 23 %. The endothelial cell density of posterior corneal lamellae sent for DMEK-S was higher than 2,700 cells/mm(2) in average with a low percentage of dead cells; 65 pre-cut tissues were used for grafting during a 2-year period.

Aspirin-triggered lipoxin A4 (15-epi-LXA4) increases the endothelial viability of human corneas storage in Optisol-GS

PURPOSE

The human corneal endothelium has a very low mitotic rate, and with aging there is a decrease in the number of cells. 15-epi-LXA4 is an anti-inflammatory, bioactive lipid formed when aspirin acetylates cyclooxygenease-2 and redirects cyclooxygenease-2 catalytic activity away from prostaglandins. The purpose of the current study was to evaluate the action of 15-epi-LXA4 in the endothelium viability of human corneas stored in Optisol-GS.

METHODS

Human corneal endothelial (HCE) cells along with the Descemet's membrane were isolated from fresh human eyes obtained from National Disease Research Interchange. Cell phenotype was identified by using the tight junctions cell marker ZO-1. LXA4 receptor (FPR2/ALX) was detected by immunostaining of HCE cells and human corneal tissue using a polyclonal antibody. Cell proliferation was evaluated with Ki-67 antibody. To measure cell migration, confluent HCE cells were wounded by a linear scraping with a sterile pipette tip in the center of the well and incubated for 24 h with or without 15-epi-LXA4. To evaluate the reparative capacity of 15-epi-LXA4, 7 pairs of human corneas were incubated in Dulbecco's modified Eagle's medium/F12 media at 37°C with or without 100 nM 15-epi-LXA4 for 24 h and then stored at 4°C in Optisol-GS for 12 days. Endothelial viability was assessed by 2 staining techniques: a viability/cytotoxicity kit and trypan blue combined with alizarin red S.

RESULTS

HCE cells and the endothelium of human corneal sections strongly expressed the LXA4 receptor. There was a 3-fold increase in cell proliferation when HCE cells were incubated with 100 nM 15-epi-LXA4 for 24 h. No significant migration was observed after 24 h incubation with 15-epi-LXA4. Corneas incubated for 24 h in Dulbecco's modified Eagle's medium/F12 media in the presence of 15-epi-LXA4 and then stored for 12 days in Optisol-GS had a 36% to 56% increase in viability compared with controls without 15-epi-LXA4.

CONCLUSIONS

15-epi-LXA4 is an important mediator that protects the integrity of the human endothelium during corneal preservation in Optisol-GS.

The unfolded protein response in human corneal endothelial cells following hypothermic storage: implications of a novel stress pathway

Human corneal endothelial cells (HCEC) have become increasingly important for a range of eye disease treatment therapies. Accordingly, a more detailed understanding of the processing and preservation associated stresses experienced by corneal cells might contribute to improved therapeutic outcomes. To this end, the unfolded protein response (UPR) pathway was investigated as a potential mediator of corneal cell death in response to hypothermic storage. Once preservation-induced failure had begun in HCECs stored at 4°C, it was noted that necrosis accounted for the majority of cell death but with significant apoptotic involvement, peaking at several hours post-storage (4-8h). Western blot analysis demonstrated changes associated with apoptotic activation (caspase 9, caspase 3, and PARP cleavage). Further, the activation of the UPR pathway was observed through increased and sustained levels of ER folding and chaperone proteins (Bip, PDI, and ERO1-Lα) in samples experiencing significant cell death. Modulation of the UPR pathway using the specific inhibitor, salubrinal, resulted in a 2-fold increase in cell survival in samples experiencing profound cold-induced failure. Furthermore, this increased cell survival was associated with increased membrane integrity, cell attachment, and decreased necrotic cell death populations. Conversely, addition of the UPR inducer, tunicamycin, during cold exposure resulted in a significant decrease in HCEC survival during the recovery period. These data implicate for the first time that this novel cell stress pathway may be activated in HCEC as a result of the complex stresses associated with hypothermic exposure. The data suggest that the targeted control of the UPR pathway during both processing and preservation protocols may improve cell survival and function of HCEC thus improving the clinical utility of these cells as well as whole human corneas.