By active ion transport mechanisms, which balance the swelling pressure of

By active ion transport mechanisms, which balance the swelling pressure of the cornea. HCEn is arrested in the post-mitotic state and does not proliferate in vivo [1]. Age- and disease-related loss of human corneal endothelial cells (HCEnCs) is a major cause of corneal blindness and the most common cause for corneal transplantation in the US. HCEn is derived from cranial neural crest cells (subsequently mesenchymal cells) whose order 69-25-0 migration from the margins of the optic cup is triggered by the separation of lens vesicle from surface ectoderm [2]. Although initially a double layer, HCEn becomes a single layer of flattened hexagonal cells that rests on its basal lamina, Descemets membrane, and starts forming apical-basal polarization and apical tight junctions, which characteristically persist throughout adult life. Several reports on the existence of endothelial progenitor cells situated in the peripheral cornea have not been confirmed. Refutability of the existence of corneal endothelial progenitor cells in the adult population is supported bythe very low proliferative potential and limited passaging ability of HCEn in vitro, rapid cellular senescence, and eventual endothelial-to-mesenchymal transition (EMT) [3,4,5]. EMT is a pathophysiologic mechanism resulting in fibroblast-like transformation and loss of the endothelial-specific cell phenotype that is frequently observed in pathologic conditions and in primary HCEn cell PD 168393 cost cultures [6]. To date, we do not know how to generate uniform and functional corneal endothelial monolayers from stem cells or other cell types and corneal tissue remains the only predictable source of HCEnCs. However, use of this tissue has significant drawbacks due to limited mitotic capacity and loss of characteristic morphology in vitro, which, in turn, hamper development of disease models and regenerative cell therapies. Previous investigations aiming 1531364 at establishing long-term cultures of HCEnCs relied solely on oncogenic manipulation of HCEnCs, for example, transformation using the viral oncogenes SV40 large T antigen and HPV E6/E7 or overexpression of mutant CDK4 [7,8,9,10]. Viral oncogenes are well known to abrogate the p53 pathway, which strongly interferes with studies on stress-related mechanisms and apoptosis, both of which have been of special interest to endothelial cell biologists studying common corneal endothelial disorders such as Fuchs dystrophy [11]. In addition, mutant CDK4-expressing HCEnCs lost the crucial corneal endothelial cell morphology and tight junction formation, thus bringing into question their usefulness as a model system to study HCEnCs. In contrast, human telomerase reverse transcriptase (hTERT) expression has been shown to be effective in extendingTelomerase-Immortalized Human Corneal Endotheliumthe life span of various cell types, with minimal impact on cell physiology and differentiation state; however, the role of hTERT in immortalization of HCEnCs has not been explored in the past [12,13]. The hTERT catalytic subunit has been employed extensively to extend the life span of a variety of human cell types, because its expression is not accompanied by cancer-associated changes or chromosomal abnormalities [14]. However, whether or not hTERT alone would be sufficient to immortalize a certain cell will depend on tissue-specific characteristics and mitotic competence. Bodnar et al. were the first to describe immortalization of foreskin fibroblasts and retinal pigment epithelial cells by.By active ion transport mechanisms, which balance the swelling pressure of the cornea. HCEn is arrested in the post-mitotic state and does not proliferate in vivo [1]. Age- and disease-related loss of human corneal endothelial cells (HCEnCs) is a major cause of corneal blindness and the most common cause for corneal transplantation in the US. HCEn is derived from cranial neural crest cells (subsequently mesenchymal cells) whose migration from the margins of the optic cup is triggered by the separation of lens vesicle from surface ectoderm [2]. Although initially a double layer, HCEn becomes a single layer of flattened hexagonal cells that rests on its basal lamina, Descemets membrane, and starts forming apical-basal polarization and apical tight junctions, which characteristically persist throughout adult life. Several reports on the existence of endothelial progenitor cells situated in the peripheral cornea have not been confirmed. Refutability of the existence of corneal endothelial progenitor cells in the adult population is supported bythe very low proliferative potential and limited passaging ability of HCEn in vitro, rapid cellular senescence, and eventual endothelial-to-mesenchymal transition (EMT) [3,4,5]. EMT is a pathophysiologic mechanism resulting in fibroblast-like transformation and loss of the endothelial-specific cell phenotype that is frequently observed in pathologic conditions and in primary HCEn cell cultures [6]. To date, we do not know how to generate uniform and functional corneal endothelial monolayers from stem cells or other cell types and corneal tissue remains the only predictable source of HCEnCs. However, use of this tissue has significant drawbacks due to limited mitotic capacity and loss of characteristic morphology in vitro, which, in turn, hamper development of disease models and regenerative cell therapies. Previous investigations aiming 1531364 at establishing long-term cultures of HCEnCs relied solely on oncogenic manipulation of HCEnCs, for example, transformation using the viral oncogenes SV40 large T antigen and HPV E6/E7 or overexpression of mutant CDK4 [7,8,9,10]. Viral oncogenes are well known to abrogate the p53 pathway, which strongly interferes with studies on stress-related mechanisms and apoptosis, both of which have been of special interest to endothelial cell biologists studying common corneal endothelial disorders such as Fuchs dystrophy [11]. In addition, mutant CDK4-expressing HCEnCs lost the crucial corneal endothelial cell morphology and tight junction formation, thus bringing into question their usefulness as a model system to study HCEnCs. In contrast, human telomerase reverse transcriptase (hTERT) expression has been shown to be effective in extendingTelomerase-Immortalized Human Corneal Endotheliumthe life span of various cell types, with minimal impact on cell physiology and differentiation state; however, the role of hTERT in immortalization of HCEnCs has not been explored in the past [12,13]. The hTERT catalytic subunit has been employed extensively to extend the life span of a variety of human cell types, because its expression is not accompanied by cancer-associated changes or chromosomal abnormalities [14]. However, whether or not hTERT alone would be sufficient to immortalize a certain cell will depend on tissue-specific characteristics and mitotic competence. Bodnar et al. were the first to describe immortalization of foreskin fibroblasts and retinal pigment epithelial cells by.