Laser Scanning Confocal Microscopy: Application in Manufacturing and Research of Corneal Stem Cells

Laser scanning confocal microscopes (LSCMs) are powerful devices used to acquire high definition optical images by choosing the required depth selectively. The presence of specific laser beams and features such as fluorescence recovery after photobleaching (FRAP), fluores\u2010 cence lifetime imaging microscopy (FLIM), and fluorescence resonance energy transfer (FRET) allow to: i. increase the quality of the image; ii. observe and analyze subcellular organelles; iii. track the localization of any given labeled molecule within the cell; iv. identify specific areas within a tissue/organ (Figure 1). In parallel, the development and manufacturing of fluorescent probes (=fluorophores) characterized by low toxicity profiles are allowing to perform the above mentioned studies using living cell cultures or tissues that are not fixed. Furthermore, fluorescent proteins such as the Green Fluorescent Protein (GFP) and its derivatives allow to detect how the biosynthetic machinery of the cell works or a transgene (driven by a plasmid or a genetically engineered virus) is expressed (Figure 2) or a chimeric protein interacts with other cellular components. The aim of this chapter is therefore to describe how LSCM functions and features have helped vision sciences and regenerative medicine applications in the field of ophthalmology. The next sections will analyze how LSCM-based analyses have helped to: 1. evaluate how the ocular surface is formed; 2. define the role of p63 as stem cell marker; 3. set up quality control assays required for clinical applications of limbal stem cells in patients with limbal stem cell deficiency (LSCD); 4. validate the use of impression citology as a diagnostic tool for LSCD; 5. study gene therapy-based potential ways to treat rare genetic disorders of the ocular surface

Retinitis Pigmentosa: Genes and Disease Mechanisms

Retinitis pigmentosa (RP) is a group of inherited disorders affecting 1 in 3000-7000 people and characterized by abnormalities of the photoreceptors (rods and cones) or the retinal pigment epithelium of the retina which lead to progressive visual loss. RP can be inherited in an autosomal dominant, autosomal recessive or X-linked manner. While usually limited to the eye, RP may also occur as part of a syndrome as in the Usher syndrome and Bardet-Biedl syndrome. Over 40 genes have been associated with RP so far, with the majority of them expressed in either the photoreceptors or the retinal pigment epithelium. The tremendous heterogeneity of the disease makes the genetics of RP complicated, thus rendering genotype-phenotype correlations not fully applicable yet. In addition to the multiplicity of mutations, in fact, different mutations in the same gene may cause different diseases. We will here review which genes are involved in the genesis of RP and how mutations can lead to retinal degeneration. In the future, a more thorough analysis of genetic and clinical data together with a better understanding of the genotype-phenotype correlation might allow to reveal important information with respect to the likelihood of disease development and choices of therapy

C/EBPδ regulates cell cycle and self-renewal of human limbal stem cells

Human limbal stem cells produce transit amplifying progenitors that migrate centripetally to regenerate the corneal epithelium. Coexpression of CCAAT enhancer binding protein δ (C/EBPδ), Bmi1, and ΔNp63α identifies mitotically quiescent limbal stem cells, which generate holoclones in culture. Upon corneal injury, a fraction of these cells switches off C/EBPδ and Bmi1, proliferates, and differentiates into mature corneal cells. Forced expression of C/EBPδ inhibits the growth of limbal colonies and increases the cell cycle length of primary limbal cells through the activity of p27Kip1 and p57Kip2. These effects are reversible; do not alter the limbal cell proliferative capacity; and are not due to apoptosis, senescence, or differentiation. C/EBPδ, but not ΔNp63α, indefinitely promotes holoclone self-renewal and prevents clonal evolution, suggesting that self-renewal and proliferation are distinct, albeit related, processes in limbal stem cells. C/EBPδ is recruited to the chromatin of positively (p27Kip1 and p57Kip2) and negatively (p16INK4A and involucrin) regulated gene loci, suggesting a direct role of this transcription factor in determining limbal stem cell identity

Generation of a transgene-free induced pluripotent stem cells line (UNIPDi002-A) from oral mucosa epithelial stem cells carrying the R304Q mutation in TP63 gene.

Abstract Transgene free UNIPDi002-A-human induced pluripotent stem cell (hiPSC) line was generated by Sendai Virus Vectors reprogramming from human oral mucosal epithelial stem cells (hOMESCs) of a patient affected by ectrodactyly-ectodermal dysplasia-clefting (EEC)-syndrome, carrying a mutation in exon 8 of the TP63 gene (R304Q). The UNIPDi002-A-hiPSC line retained the mutation of the parental R304Q-hOMESCs and displayed a normal karyotype. No residual expression of transgenes nor Sendai virus vector sequences were detected in the line at passage 8. UNIPDi002-A-hiPSC expressed a panel of pluripotency-associated markers and could form embryoid bodies expressing markers belonging to the three germ layers ectoderm, endoderm and mesoderm

Induced pluripotent stem cells line (UNIPDi003-A) from a patient affected by EEC syndrome carrying the R279H mutation in TP63 gene.

Abstract Oral mucosa epithelial stem cells from a patient affected by Ectrodactyly-Ectodermal dysplasia-Clefting (EEC) syndrome carrying the R279H mutation in the TP63 gene were reprogrammed into human induced pluripotent stem cells (hiPSCs) with episomal vectors. The generated UNIPDi003-A-hPSC line retained the mutation of the parental cells and showed a normal karyotype upon long term culture. Analysis of residual transgenes expression showed that the episomal vectors were eliminated from the cell line. UNIPDi003-A-hiPSCs expressed the undifferentiated state marker alkaline phosphatase along with a panel of pluripotency markers, and formed embryoid bodies capable of expressing markers belonging to all the three germ layers

Generation of a transgene-free human induced pluripotent stem cell line (UNIPDi001-A) from oral mucosa epithelial stem cells.

Abstract Human oral mucosa epithelial stem cells (hOMESCs) were obtained from a fresh oral biopsy collected from a healthy subject at the Fondazione Banca degli Occhi del Veneto (FBOV). An integration-free reprogramming protocol was applied exploiting episomal plasmids transfected into cells using a Nucleofector device. Around day 20 post transfection, several human induced pluripotent stem cell (hiPSC) colonies were manually picked and expanded. One of these (UNIPDi001-A-hiPSCs) expressed undifferentiated state marker alkaline phosphatase along with a panel of pluripotency state markers and was able to differentiate into the derivatives of all the three germ layers

A c.3037G > A mutation in FBN1 gene causing Marfan syndrome with an atypically severe phenotype.

Marfan syndrome is a pleiotropic connective tissue disease inherited as an autosomal dominant trait, mostly caused by mutations in the FBN1 gene, which is located on chromosome 15q21.1 and encoding fibrillin 1. We report a case of Marfan syndrome presenting with severe ocular and systemic manifestations, such as cardiac congenital anomalies. The patient underwent a multidisciplinary approach and his clinical diagnosis was associated with a c.3037G > A mutation in the FBN1 gene. Identification of this genetic alteration should instigate a prompt multidisciplinary assessment and monitoring, in order to prevent devastating consequences such as cardiac and ocular phenotype. Molecular modeling of the mutation highlighted the importance of the preservation of the calcium-dependent structure of an epidermal -growth-factor-like domain of fibrillin-1 and consequently the microfibrillar formation process. This report aims to highlight the importance of an early clinical and molecular diagnosis and once more, the importance of the multidisciplinary approach of this genetic entity

New Frontiers of Corneal Gene Therapy

Corneal diseases are among the most prevalent causes of blindness worldwide. The transparency and clarity of the cornea are guaranteed by a delicate physiological, anatomic, and functional balance. For this reason, all the disorders, including those of genetic origin, that compromise this state of harmony can lead to opacity and eventually vision loss. Many corneal disorders have a genetic etiology, and some are associated with rather rare and complex syndromes. Conventional treatments, such as corneal transplantation, are often ineffective, and to date, many of these disorders are still incurable. Gene therapy carries the promise of being a potential cure for many of these diseases, with solutions and strategies that did not seem possible until a few years ago. With its potential to treat genetic disease by means of deletion, replacement, or editing of a defective gene, the challenge can also be extended to corneal disorders in order to achieve long-term, if not definitive, relief. The aim of this paper is to review the state of the art of the different gene therapy approaches as potential treatments for corneal diseases and the future perspectives for the development of personalized gene-based medicine

Expression of VSX1 in human corneal keratocytes during differentiation into myofibroblasts in response to wound healing

PURPOSE. To characterize the expression of the visual system homeobox gene (VSX1) in human corneal keratocytes both in vitro and in vivo. METHODS. The expression of VSX1 was evaluated through semiquantitative RT-PCR, immunofluorescence and in situ hybridization both in corneas (either freshly obtained or wounded) and in collagenase/hyaluronidase-isolated keratocytes grown in the absence or presence of serum to promote keratocyteto-myofibroblast differentiation. RESULTS. Quiescent or resting keratocytes normally residing in the corneal stroma or cultured in vitro in the absence of serum did not express VSX1. In wounded corneas or when cultured in the presence of serum to mimic wound-healing responses, keratocytes underwent fibroblastic transformation (with appearance of ␣-SMA and disappearance of CD-34 and keratocan signals) and started expressing VSX1. CONCLUSIONS. The results show that VSX1 is expressed in vitro and in vivo during human corneal wound healing, a process in which differentiation of corneal keratocytes into myofibroblasts occurs. These data may help to elucidate the role of VSX1 in cornea physiology suggesting a potential involvement in cornea-related diseases such as keratoconus. (Invest Ophthalmol Vis Sci. 2006;47:5243-5250