Expression of SV40 virus large T antigen by recombinant adenoviruses activates proliferation of corneal endothelium in vitro

Magic Bullets: The Coming Age of Meaningful Pharmacological Control of the Corneal Responses to Injury and Disease

Corneal injuries from chemical burns, mechanical trauma, infections, immunological rejections, surgical complications, and some diseases are commonly associated with persistent epithelial defects (PED), neurotrophic epitheliopathy, scarring fibrosis, corneal neovascularization (CNV), and/or corneal endothelial damage that lead to vision loss. Several Food and Drug Administration (FDA) approved medications have recently become available, are currently in clinical trials, or are likely to enter clinical trials in the near future. For example, a 2-week course of topical human recombinant nerve growth factor is frequently an effective treatment for corneal neurotrophic epitheliopathy associated with PEDs. Topical losartan, an angiotensin converting enzyme II receptor antagonist that also inhibits TGF beta signaling, has been shown to effectively decrease myofibroblast generation and scarring fibrosis in alkali burn injury and Descemetorhexis rabbit models. Small molecule topical tyrosine kinase inhibitors, such as sunitinib and axitinib, FDA approved as chemotherapeutic agents to treat specific cancers, have also been found to be effective topical inhibitors of CNV in animal and human trials. Rho-kinase inhibitors, such as ripasudil and netarsudil, that are currently approved agents for the treatment of glaucoma in some countries, have been shown to stimulate corneal endothelial proliferation in animal studies and human trials, and may accelerate the regeneration of Descemet's membrane. These agents, as well as other drugs in development, will be used in targeted combinations to treat corneal pathophysiology associated with epithelial healing disorders, stromal scarring fibrosis, CNV, and corneal endothelial injury during the next decade.

Proliferation Increasing Genetic Engineering in Human Corneal Endothelial Cells: A Literature Review

The corneal endothelium is the inner layer of the cornea. Despite comprising only a monolayer of cells, dysfunction of this layer renders millions of people visually impaired worldwide. Currently, corneal endothelial transplantation is the only viable means of restoring vision for these patients. However, because the supply of corneal endothelial grafts does not meet the demand, many patients remain on waiting lists, or are not treated at all. Possible alternative treatment strategies include intracameral injection of human corneal endothelial cells (HCEnCs), biomedical engineering of endothelial grafts and increasing the HCEnC density on grafts that would otherwise have been unsuitable for transplantation. Unfortunately, the limited proliferative capacity of HCEnCs proves to be a major bottleneck to make these alternatives beneficial. To tackle this constraint, proliferation enhancing genetic engineering is being investigated. This review presents the diverse array of genes that have been targeted by different genetic engineering strategies to increase the proliferative capacity of HCEnCs and their relevance for clinical and research applications. Together these proliferation-related genes form the basis to obtain a stable and safe supply of HCEnCs that can tackle the corneal endothelial donor shortage.

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.

Long-term cultivation of human corneal endothelial cells by telomerase expression

The objective of this study was to explore the potential role of human telomerase reverse transcriptase (TERT) in extending the proliferative lifespan of human corneal endothelial cells (HCECs) under long-term cultivation. A primary culture was initiated with a pure population of HCECs in DMEM/F12 media containing 10% fetal bovine serum and other various supplements. TERT gene was successfully transfected into normal HCECs. A stable HCECs cell line (TERT-HCECs) that expressed TERT was established. The cells could be subcultured for 36 passages. Within this line of cells, TERT not only extended proliferative lifespan and inhibited apoptosis but also enhanced the cell line remaining the normal characteristics similar to HCECs. There were no significantly differences in the expression of the pump function related proteins voltage dependent anion channel 3 (VDAC3), sodium bicarbonate cotransporter member 4 (SLC4A4), chloride channel protein 3 (CLCN3), Na(+)/K(+)-ATPase α1, and ZO-1 in the cell line TERT-HCECs and primary HCECs. TERT-HCECs formed a monolayer cell sheet, maintained similar cell junction formation and pump function with primary HCECs. Karyotype analysis exhibited normal chromosomal numbers. The soft agar colony assay and tumor formation in nude mice assay showed no malignant alterations in TERT-HCECs. Our findings indicated that we had established a cell line with its similar phenotype and properties to primary HCECs. Further study of the TERT-HCECs may be valuable in studying the function of the cells in vivo.

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.

Enhanced survival in vitro of human corneal endothelial cells using mouse embryonic stem cell conditioned medium

Purpose

To determine whether mouse embryonic stem cell conditioned medium (ESC-CM) increases the proliferative capacity of human corneal endothelial cells (HCECs) in vitro.

Methods

Primary cultures of HCECs were established from explants of the endothelial cell layer, including the Descemet’s membrane. Cells were cultured in human corneal endothelium medium (CEM) containing 25% ESC-CM for the experimental group and CEM alone for the control group. Phase-contrast microscopy and reverse-transcription polymerase chain reaction (RT–PCR) were used to identify HCECs. The eruption time and HCEC morphology were observed under phase-contrast microscopy. We detected the protein expression of zona occludens protein-1 (ZO-1; a tight junction protein) and the Na⁺-K⁺-ATPase by western blot analysis and immunocytochemistry. The mRNA expression of the Na⁺-K⁺-ATPase, voltage-dependent anion channel 3 (VDAC3), solute carrier family 4, sodium bicarbonate cotransporter member 4 (SLC4A4), and chloride channel protein 3 (CLCN3) were detected by RT–PCR. To explore the proliferation capacity of HCECs, the colony forming efficiency (CFE) was determined by Giemsa staining and the cellular proliferation marker of Ki-67 protein (Ki-67) positive cells were detected by immunocytochemistry and flow cytometry. Progression of the cell cycle and apoptosis were analyzed by flow cytometry. Negative regulation of the cell cycle, as measured by cyclin-dependent kinase inhibitor p21 (p21) levels, was detected by western blot analysis and immunocytochemistry.

Results

In primary culture, HCECs in the 25%ESC-CM group erupted with polygonal appearance on day 2, while those in the CEM group erupted with slightly larger cells on day 3–4. HCECs in the 25%ESC-CM group could be subcultured until passage 6 without enlargement of cell volume, while those in the CEM group were enlarged and lost their polygonal appearance by passage 2. HCECs in both the 25%ESC-CM and CEM groups expressed ZO-1, Na⁺-K⁺-ATPase, VDAC3, SLC4A4, and CLCN3. The number of Ki67 positive cells, CFE, and percentage of cells entering the S and G₂ phases were higher in the 25%ESC-CM group than in the CEM group. The number of apoptotic cells and p21 protein expression both decreased in the 25%ESC-CM group.

Conclusions

Use of 25%ESC-CM significantly increased the number of proliferating cells. These effects may be achieved through inhibition of p21 expression and apoptosis. These results suggested that 25%ESC-CM may be a new tool for cultivating HCECs for transplantation.

[A comparative in vitro analysis of primary and immortalized keratocytes]

BACKGROUND

The cultivation of primary keratocytes (HCKp) is difficult and influenced by a multitude of factors. In this study it was examined if immortalized keratocytes (HCKi) can replace HCKp in experiments and be useful in the development of a cornea construct.

METHODS

HCKp and HCKi were cultivated and incubated for 72 h with benzalkonium chloride (BAC) or cetrimide at concentrations of 40-0.1 microg/ml or 100-0.01 microg/ml. The vitality and the doubling time (tv) were measured.

RESULTS

Treatment with 40 or 4 microg/ml BAC as well as 100 or 10 microg/ml cetrimide led to cell death. The tv was shortened in HCKi especially in cells that were treated with BAC, but only HCKp showed a significant loss of vitality. In cells treated with cetrimide the tv increased significantly in both cell lines and no loss of vitality was detected from 0.1 microg/ml onwards in both cell lines.

CONCLUSION

HCKi are more resistant and proliferative than HCKp but they can be used in preliminary experiments as an alternative to primary cells in for example toxicity studies if the detectable differences between the two cell lines, such as the capacity for proliferation and reaction to agents are taken into consideration.

Effects of SV40 T antigen transduction on human corneal endothelial cell wound healing in vitro

OBJECTIVE

The aim of this study was to investigate the endothelial wound healing effects of SV40 large T and small t antigen transduction on cultured human corneal endothelial cells (HCEC).

METHODS

Human corneal endothelial cells were infected with either mock solution, Ad green fluorescent protein (GFP), or Ad SV40 T/t antigen/GFP, then mechanically wounded 48 h later. The endothelial wound healing rate was quantified by an analysis of the photographs taken every 12 h after wounding. The characteristics of Ad SV40 T/t Ag/GFP-infected human corneal endothelial cells were evaluated with cell morphology, cell density, contact inhibition, and cytoskeletal features using rhodamine phalloidin to stain F-actin. DNA synthesis was assessed using 5-Bromo-2'-deoxy-uridine (BrdU) labeling.

RESULTS

Wound healing rates in the first 12 and 24 h after wounding were significantly faster in the Ad SV40 T/t antigen/GFP-infected group than the other two groups. In all three groups, the morphology, cell density, and cytoskeletal features of cells at confluency was similar and contact inhibition retained. There were no differences in the pattern of F-actin and endothelial cell density 4 d after wound closure. However, during the process of wound healing, prominent stress fibers in migrating cells near the wound edge were noted in normal cells at 36 h after wounding, whereas the Ad SV40 T/t Ag/GFP-infected cells showed similar changes as early as 12 h after wounding. BrdU staining results revealed that the Ad SV40 T/t antigen/GFP-infected group had labeled cells showing DNA synthesis in the wound area at 12 h after wounding, while no labeled cells were found in the other two groups.

CONCLUSIONS

In an in vitro model, transduction of human corneal endothelial cells using a recombinant adenoviral vector expressing SV40 T/t antigen enhanced both the wound healing rate and proliferative capacity, especially in the first 12 h after wounding, and the characteristic morphologic features of the infected cells were maintained.

Cell cycle status in human corneal endothelium

Corneal endothelium is the single-cell layer that forms a physical barrier between the corneal stroma and aqueous humour. The barrier and ionic 'pump' functions of corneal endothelium help regulate stromal hydration. Loss of endothelial cells due to increasing age, trauma, disease, dystrophy, or previous corneal transplants can reduce the density of endothelial cells to a critical point below which the stroma becomes edematous and visual acuity is lost. Throughout life, division of endothelial cells either does not occur or occurs at a rate too slow to adequately replace dead cells. Thus, the major means of repairing the monolayer is by cell migration and/or enlargement. The basis for the lack of endothelial cell proliferation is not yet fully understood, although it is clear that cells do retain proliferative capacity. Previous studies from this laboratory have identified certain environmental conditions that may be responsible for maintaining these cells in a non-replicative state in vivo. In addition, corneal endothelial cells exhibit intrinsic, age-related differences in relative proliferative capacity. The studies described below provide evidence to support the hypothesis that, with age, an increasing number of HCEC enter a replicative senescence-like state in which they become increasingly refractive to mitogenic stimulation. This decreasing sensitivity to mitogens appears to be mediated, at least in part, by age-dependent alterations in the relative expression and activity of the cyclin-dependent kinase inhibitors, p27KIP1, p16INK4A, and p21CIP1.

Human corneal endothelial cell proliferation: potential for use in regenerative medicine

PURPOSE

To review and update the experience of our laboratory in culturing human corneal endothelial cells (HCEC) from young and older donors.

METHODS

Corneas were obtained from National Disease Research Interchange, Philadelphia, PA. Data from the past 3 years were reviewed to develop criteria for selecting donor corneas to be used for endothelial cell culture. Immunocytochemical localization using mAb 9.3.E identified endothelial cells, and Ki67 staining demonstrated actively cycling cells. Cell counts demonstrated the effect of growth-promoting agents on proliferation of cells from young (<30 years old) and older (>50 years old) donors. Phase-contrast microscopy documented morphologic characteristics of cells in primary culture and the effect of growth factors on cell morphology.

RESULTS

Exclusion criteria were developed to increase the chance of successful culture of HCEC. Isolation methods to remove Descemet membrane with attached endothelial cells avoided contamination with other corneal cell types. EDTA treatment combined with mechanical disruption facilitated isolation of cells. Culture medium containing FBS, EGF, NGF, and bovine pituitary extract stimulated maximal growth and facilitated normal monolayer formation. Age-related differences were detected in the density of confluent cells in primary culture and in the proliferative response to growth-promoting agents.

CONCLUSIONS

Untransformed HCEC can be successfully cultured from the corneas of both young and older donors by using care in the selection of donor material. Care must also be taken in the early phases of endothelial cell isolation to obtain maximal numbers of healthy cells for culture. There appear to be true age-related differences in overall proliferative capacity; however, the relative response to specific growth factors was similar in cells from young and older donors. Results of these studies provide guidelines for successful growth of untransformed HCEC for use in regenerative medicine.

Mechanisms of staurosporine induced apoptosis in a human corneal endothelial cell line

BACKGROUND

Apoptosis very probably plays a key part in endothelial cell loss during corneal storage in organ culture as well as hypothermic storage. However, the mechanisms underlying endothelial apoptosis are poorly understood. The response of a human corneal endothelial cell (HCEC) line to staurosporine, a known inducer of apoptosis, was investigated to gain insights into the intracellular modulators that participate in endothelial cell death.

METHODS

Immortalised HCECs were studied after 3, 6, 12, and 24 hours of incubation with 0.2 micro M staurosporine. Cell shedding was monitored. Hoechst 33342 fluorescent DNA staining combined with propidium iodide was used for apoptosis/necrosis quantification and morphological examination. The caspase-3 active form was assessed using western blot, proteolytic activity detection, and immunocytochemistry. The cleaved form of poly(ADP-ribose) polymerase (PARP) was assessed using immunocytochemistry and western blot. The ultrastructural features of cells were screened after 12 hours with staurosporine or vehicle.

RESULTS

The specific apoptotic nature of staurosporine induced HCEC death was confirmed. The ultrastructural features of staurosporine treated cells were typical of apoptosis. HCEC shedding and DNA condensation increased with time. Caspase-3 activity was detected as early as 3 hours after exposure with staurosporine, peaking at 12 hours of incubation. The presence of cleaved PARP after 3 hours confirmed caspase-3 activation.

CONCLUSIONS

These data suggest strongly that HCEC cell death induced by staurosporine is apoptosis. The main consequence of HCEC apoptosis is shedding. Staurosporine induced apoptosis of endothelial cells involves activation of caspase-3, and could be a useful model to study strategies of cell death inhibition.

Infection of Endothelium With E1 − E4 + , but Not E1 − E4 − , Adenovirus Gene Transfer Vectors Enhances Leukocyte Adhesion and Migration by Modulation of ICAM-1, VCAM-1, CD34, and Chemokine Expression

Abstract —Intravascular introduction of replication-deficient adenoviral vectors (Advectors) provides an ideal model of delivery of transgenes for the treatment of various vascular abnormalities. On the basis of the knowledge that Advectors can induce inflammatory responses after intravascular administration, we speculated that cellular activation by Advector infection could directly modulate the endothelial cell (EC) adhesion molecule/chemokine expression repertoire. Infection of human umbilical vein ECs or bone marrow microvascular ECs with an E1 − E4 + Advector resulted in the upregulation of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and CD34, but not E-selectin, P-selectin, CD36, CD13, CD44, HLA-DR or PECAM. Upregulation of ICAM-1, VCAM-1, and CD34 was apparent 12 hours after infection and persisted for weeks after infection. Selective induction of adhesion molecules was mediated by the presence of the E4 gene in the Advector, because infection of ECs with an E1 − E4 − Advector had no effect on adhesion molecule expression. ECs infected with E1 − E4 + Advector, but not those infected with E1 − E4 − Advector, supported the adhesion of leukocytes. Monoclonal antibodies to ICAM-1 and VCAM-1 inhibited adhesion of leukocytes to E1 − E4 + -infected ECs. Infection of the ECs with E1 − E4 + Advector, but not E1 − E4 − Advector, resulted in downregulation of expression of chemocytokines, including interleukin-8, MCP-1, RANTES, and GM-CSF. Nonetheless, a large number of leukocytes migrated through ECs infected with E1 − E4 + , but not those infected with E1 − E4 l− , in response to exogenous chemokines. These results demonstrate that infection of ECs with E1 − E4 + Advectors, but not E1 − E4 − Advectors, may directly augment inflammatory responses by upregulating expression of adhesion molecules and enhancing migration through Advector-infected ECs and suggest that E1 − E4 − Advectors may be a better choice for gene-transfer strategies directed to the ECs.

Quantitative analysis of repeat adenovirus-mediated gene transfer into injured canine femoral arteries

We quantitatively evaluated the effectiveness of a repeat administration of a recombinant adenoviral vector expressing bacterial Escherichia coli lacZ into the same arterial site of a relatively large animal, the dog. The replication-defective adenoviral vector was introduced percutaneously into balloon-injured femoral arteries through a double-balloon catheter. After a single dose of adenoviral vector, up to 90% of surface (73 +/- 16%, n = 7) and smooth muscle cells in multiple layers of the media showed transgene expression as evaluated by 5-bromo-4-chloro-3-indoyl beta-D-galactopyranoside histostaining without extralocal expression, as assessed by polymerase chain reaction. High-level expression (measured as beta-galactosidase activity) peaked 7 days after transfer and was transient, although it was retained for a month. Second does of the same adenovirus to the same arterial site were given 1, 2, 5, or 8 weeks after the first administration. At 1 week the second dose significantly enhanced lacZ expression. At 2, 5, or 8 weeks the second dose reinduced lacZ expression at 25% to 30% of the full expression. lacZ expression was also detected in preimmuned dogs, although the expression levels correlated inversely to the titer of neutralizing antibodies in their serum. These results demonstrate that arterial gene expression can be enhanced by a second administration of the same adenovirus after a short interval and that a repeat dose after a long interval partially but significantly reinduces gene expression despite the presence of an immune response. These data may provide an additional scientific foundation for the use of adenovirus-mediated arterial gene transfer in future clinical practice.