Structural and functional characterization of siadenovirus core protein VII nuclear localization demonstrates the existence of multiple nuclear transport pathways.

Adenovirus protein VII (pVII) plays a crucial role in the nuclear localization of genomic DNA following viral infection and contains nuclear localization signal (NLS) sequences for the importin (IMP)-mediated nuclear import pathway. However, functional analysis of pVII in adenoviruses to date has failed to fully determine the underlying mechanisms responsible for nuclear import of pVII. Therefore, in the present study, we extended our analysis by examining the nuclear trafficking of adenovirus pVII from a non-human species, psittacine siadenovirus F (PsSiAdV). We identified a putative classical (c)NLS at pVII residues 120-128 (120PGGFKRRRL128). Fluorescence polarization and electrophoretic mobility shift assays demonstrated direct, high-affinity interaction with both IMPα2 and IMPα3 but not IMPß. Structural analysis of the pVII-NLS/IMPα2 complex confirmed a classical interaction, with the major binding site of IMPα occupied by K124 of pVII-NLS. Quantitative confocal laser scanning microscopy showed that PsSiAdV pVII-NLS can confer IMPα/ß-dependent nuclear localization to GFP. PsSiAdV pVII also localized in the nucleus when expressed in the absence of other viral proteins. Importantly, in contrast to what has been reported for HAdV pVII, PsSiAdV pVII does not localize to the nucleolus. In addition, our study demonstrated that inhibition of the IMPα/ß nuclear import pathway did not prevent PsSiAdV pVII nuclear targeting, indicating the existence of alternative pathways for nuclear localization, similar to what has been previously shown for human adenovirus pVII. Further examination of other potential NLS signals, characterization of alternative nuclear import pathways, and investigation of pVII nuclear targeting across different adenovirus species is recommended to fully elucidate the role of varying nuclear import pathways in the nuclear localization of pVII.

Analysis and pharmacological modulation of senescence in human epithelial stem cells.

Human epithelial stem cells (ESCs) are characterized by long-term regenerative properties, much dependent on the tissue of origin and varying during their lifespan. We analysed such variables in cultures of ESCs isolated from the skin, conjunctiva, limbus and oral mucosa of healthy donors and patients affected by ectrodactyly-ectodermal dysplasia-clefting syndrome, a rare genetic disorder caused by mutations in the p63 gene. We cultured cells until exhaustion in the presence or in the absence of DAPT (γ-secretase inhibitor; N-[N-(3, 5-difluorophenacetyl)-L-alanyl]-S-phenylglycine T-butyl ester). All cells were able to differentiate in vitro but exhibited variable self-renewal potential. In particular, cells carrying p63 mutations stopped prematurely, compared with controls. Importantly, administration of DAPT significantly extended the replicative properties of all stem cells under examination. RNA sequencing analysis revealed that distinct sets of genes were up- or down-regulated during their lifetime, thus allowing to identify druggable gene networks and off-the-shelf compounds potentially dealing with epithelial stem cell senescence. These data will expand our knowledge on the genetic bases of senescence and potentially pave the way to the pharmacological modulation of ageing in epithelial stem cells.

On the mechanism of tumor cell entry of aloe-emodin, a natural compound endowed with anticancer activity.

Aloe-emodin (1,8-dihydroxy-3-[hydroxymethyl]-anthraquinone), AE, is one of the active constituents of a number of plant species used in traditional medicine. We have previously identified, for the first time, AE as a new antitumor agent and shown that its selective in vitro and in vivo killing of neuroblastoma cells was promoted by a cell-specific drug uptake process. However, the molecular mechanism underlying the cell entry of AE has remained elusive as yet. In this report, we show that AE enters tumor cells via two of the five somatostatin receptors: SSTR2 and SSTR5. This observation was suggested by gene silencing, receptor competition, imaging and molecular modeling experiments. Furthermore, SSTR2 was expressed in all surgical neuroblastoma specimens we analyzed by immunohistochemistry. The above findings have strong implications for the clinical adoption of this natural anthraquinone molecule as an antitumor agent.

Visualization of DNA G-quadruplexes in herpes simplex virus 1-infected cells.

We have previously shown that clusters of guanine quadruplex (G4) structures can form in the human herpes simplex-1 (HSV-1) genome. Here we used immunofluorescence and immune-electron microscopy with a G4-specific monoclonal antibody to visualize G4 structures in HSV-1 infected cells. We found that G4 formation and localization within the cells was virus cycle dependent: viral G4s peaked at the time of viral DNA replication in the cell nucleus, moved to the nuclear membrane at the time of virus nuclear egress and were later found in HSV-1 immature virions released from the cell nucleus. Colocalization of G4s with ICP8, a viral DNA processing protein, was observed in viral replication compartments. G4s were lost upon treatment with DNAse and inhibitors of HSV-1 DNA replication. The notable increase in G4s upon HSV-1 infection suggests a key role of these structures in the HSV-1 biology and indicates new targets to control both the lytic and latent infection.

Correction of Mutant p63 in EEC Syndrome Using siRNA Mediated Allele-Specific Silencing Restores Defective Stem Cell Function.

Ectrodactyly-Ectodermal dysplasia-Clefting (EEC) syndrome is a rare autosomal dominant disease caused by heterozygous mutations in the p63 gene and characterized by limb defects, orofacial clefting, ectodermal dysplasia, and ocular defects. Patients develop progressive total bilateral limbal stem cell deficiency, which eventually results in corneal blindness. Medical and surgical treatments are ineffective and of limited benefit. Oral mucosa epithelial stem cells (OMESCs) represent an alternative source of stem cells capable of regenerating the corneal epithelium and, combined with gene therapy, could provide an attractive therapeutic avenue. OMESCs from EEC patients carrying the most severe p63 mutations (p.R279H and p.R304Q) were characterized and the genetic defect of p.R279H silenced using allele-specific (AS) small interfering RNAs (siRNAs). Systematic screening of locked nucleic acid (LNA)-siRNAs against R279H-p63 allele in (i) stable WT-ΔNp63α-RFP and R279H-ΔNp63α-EGFP cell lines, (ii) transient doubly transfected cell lines, and (iii) p.R279H OMESCs, identified a number of potent siRNA inhibitors for the mutant allele, which had no effect on wild-type p63. In addition, siRNA treatment led to longer acquired life span of mutated stem cells compared to controls, less accelerated stem cell differentiation in vitro, reduced proliferation properties, and effective ability in correcting the epithelial hypoplasia, thus giving rise to full thickness stratified and differentiated epithelia. This study demonstrates the phenotypic correction of mutant stem cells (OMESCs) in EEC syndrome by means of siRNA mediated AS silencing with restoration of function. The application of siRNA, alone or in combination with cell-based therapies, offers a therapeutic strategy for corneal blindness in EEC syndrome. Stem Cells 2016;34:1588-1600.

Towards xeno-free cultures of human limbal stem cells for ocular surface reconstruction.

Isolated limbal epithelial stem cells (LESCs) were cultured with or without a 3T3 murine fibroblast feeder-layer (FL) in 4 different culture media on culture plates or on denuded human amniotic membrane (AM) support and fibrin gel support: (1) control medium supplemented with fetal bovine serum; (2) control medium supplemented with the synthetic serum "XerumFree™ XF205" (XF); (3) CnT-20 medium supplemented with "XerumFree™ XF205" (CnT-XF) and (4) CnT-20 medium supplemented with human AB serum (CnT-AB). The three xenogeneic media were compared to standard condition (control + FL) and parameters assessed included cell morphology, proliferative potential, number of passages, assessment of clonogenic and abortive colonies, life span, ∆Np63α expression and epithelial morphology on AM. During serial cultivation of LESCs, most of the tested xeno-free media supported similar numbers of cell passages, total colony number, cumulative cell doublings (CCD) rates and expression of ∆Np63α compared to control. The conditions cultivated with a FL showed a non-statistically significant higher number of cell passages and CCD rates before senescence when compared to the same conditions cultured without FL. Except for the control medium, only XF medium enabled the growth of cells on AM. The expression of ∆Np63α was comparable in all the cultures grown onto AM, when compared to the controls on fibrin gel. In conclusion, the xeno-free media enabled LESC culture both on plastic and on denuded human AM. Despite the analyses were carried out in a statistically low number of samples and need re-assessment in a larger cohort, our results suggest that the production of a completely xeno-free LESC graft could be beneficial for future clinical applications.

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.

In Vivo Confocal Microscopy 1 Year after Autologous Cultured Limbal Stem Cell Grafts.

PURPOSE: To correlate clinical, impression cytologic, and in vivo confocal microscopy findings on the corneal surface after cultured limbal stem cell transplantation. DESIGN: Prospective, interventional, noncomparative, masked case series. PARTICIPANTS: Thirteen patients with limbal stem cell deficiency after unilateral (9 eyes) or bilateral (2 eyes) chemical burn, liquid nitrogen injury (1 eye), or herpes simplex virus infection (1 eye). METHODS: Limbal cells were harvested from healthy or less affected eyes, cultured on 3T3 cells and fibrin glue, and transplanted to the patient's injured eye. Patients underwent clinical examination and impression cytologic examination of the central cornea before and 1 year after intervention. In vivo confocal microscopy scans were obtained in all corneal quadrants after 1 year. The interexamination agreement was established by calculation of the Cohen's κ coefficient. MAIN OUTCOME MEASURES: Results of surgery were assessed considering clinical signs (successful: restoration of transparent, avascular, and stable corneal epithelium without neovascularization in central corneal surface; partially successful: recurrence of superficial neovascularization; failed: recurrent epithelial defects, pannus, and inflammation), phenotype of cells covering the corneal surface (conjunctivalized corneal surface: cytokeratin 12 [cK12]-negative and mucin 1 [MUC1]-positive cells; mixed epithelium: cK12-positive and MUC1-positive cells; corneal epithelium: cK12-positive and MUC1-negative cells), and cell morphologic features (corneal epithelium: multilayered polygonal and flat cells with hyperreflective nuclei; conjunctival epithelium: stratified cuboidal or polygonal cells, hyperreflective cytoplasm, and barely defined borders; epithelial transition: transition of epithelial cells from the cornea to the conjunctiva over the corneal surface). RESULTS: We found a moderate to substantial degree of concordance between confocal microscopy and clinical evaluation (κ = 0.768) and between confocal microscopy and impression cytologic analysis (κ = 0.629). Confocal microscopy showed that 46.2% of patients exhibited corneal epithelium in the central and peripheral cornea, 30.8% showed an irregular mixed corneal and conjunctival epithelium, and 23.0% showed conjunctival epithelium. Palisades of Vogt were absent in all (100.0%) patients, and the cornea-conjunctiva epithelial transition localized approximately 1 mm internally on the cornea. CONCLUSIONS: Confocal microscopy provides objective measures of the corneal epithelium and may significantly improve the evaluation of outcomes after cultured limbal stem cell graft.

Nuclear Akt2 opposes limbal keratinocyte stem cell self-renewal by repressing a FOXO-mTORC1 signaling pathway.

Signals downstream of Akt can either favor or oppose stem cell (SC) maintenance, but how this dual role can be achieved is still undefined. Using human limbal keratinocyte stem cells (LKSCs), a SC type used in transplantation therapies for corneal regeneration, we show that Akt signaling is prominent in SC populations both in vivo and in vitro, and that Akt1 promotes while Akt2 opposes SC self-renewal. Noteworthy, loss of Akt2 signaling enhances LKSC maintenance ex vivo, whereas Akt1 depletion anticipates SC exhaustion. Mechanistically, the antagonistic functions of Akt1 and Akt2 in SC control are mainly dictated by their differential subcellular distribution, being nuclear Akt2 selectively implicated in FOXO inhibition. Akt2 downregulation favors LKSC maintenance as a result of a gain of FOXO functions, which attenuates the mechanistic target of rapamycin complex one signaling via tuberous sclerosis one gene induction, and promotes growth factor signaling through Akt1. Consistently, Akt2 deficiency also enhances limbal SCs in vivo. Thus, our findings reveal distinct roles for nuclear versus cytosolic Akt signaling in normal epithelial SC control and suggest that the selective Akt2 inhibition may provide novel pharmacological strategies for human LKSC expansion in therapeutic settings and mechanistic research.

Structural determinants of phosphorylation-dependent nuclear transport of HCMV DNA polymerase processivity factor UL44.

Human cytomegalovirus DNA polymerase processivity factor UL44 is transported into the nucleus by importin (IMP) α/ß through a classical nuclear localization signal (NLS), and this region is susceptible to cdc2-mediated phosphorylation at position T427. Whilst phosphorylation within and close to the UL44 NLS regulates nuclear transport, the details remain elusive, due to the paucity of structural information regarding the role of negatively charged cargo phosphate groups. We addressed this issue by studying the effect of UL44 T427 phosphorylation on interaction with several IMPα isoforms by biochemical and structural approaches. Phosphorylation decreased UL44/IMPα affinity 10-fold, and a comparative structural analysis of UL44 NLS phosphorylated and non-phosphorylated peptides complexed with mouse IMPα2 revealed the structural rearrangements responsible for phosphorylation-dependent inhibition of UL44 nuclear import.

Correction of junctional epidermolysis bullosa by transplantation of genetically modified epidermal stem cells.

The continuous renewal of human epidermis is sustained by stem cells contained in the epidermal basal layer and in hair follicles. Cultured keratinocyte stem cells, known as holoclones, generate sheets of epithelium used to restore severe skin, mucosal and corneal defects. Mutations in genes encoding the basement membrane component laminin 5 (LAM5) cause junctional epidermolysis bullosa (JEB), a devastating and often fatal skin adhesion disorder. Epidermal stem cells from an adult patient affected by LAM5-beta3-deficient JEB were transduced with a retroviral vector expressing LAMB3 cDNA (encoding LAM5-beta3), and used to prepare genetically corrected cultured epidermal grafts. Nine grafts were transplanted onto surgically prepared regions of the patient's legs. Engraftment was complete after 8 d. Synthesis and proper assembly of normal levels of functional LAM5 were observed, together with the development of a firmly adherent epidermis that remained stable for the duration of the follow-up (1 year) in the absence of blisters, infections, inflammation or immune response. Retroviral integration site analysis indicated that the regenerated epidermis is maintained by a defined repertoire of transduced stem cells. These data show that ex vivo gene therapy of JEB is feasible and leads to full functional correction of the disease.

Innovative Therapeutic Approaches for the Treatment of the Ocular Morbidities in Patients with EEC Syndrome.

Ectrodactyly-Ectodermal dysplasia-Clefting (EEC) syndrome is caused by heterozygous missense point mutations in the p63 gene, an important transcription factor during embryogenesis and for stem cell differentiation in stratified epithelia. Most of the cases are sporadic, related to de novo mutations arising during early-stage development. Familial cases show an autosomic dominant inheritance. The major cause of visual morbidity is limbal stem cell failure, which develops in the second to third decade of life. Patients often show ocular surface alterations, such as recurrent blepharitis and conjunctivitis, superficial microlesions of the cornea, and spontaneous corneal perforation and ulceration, leading to progressive corneal clouding and eventually visual loss. No definitive cures are currently available, and treatments to alleviate symptoms are only palliative. In this review, we will discuss the proposed therapeutic strategies that have been tested or are under development for the management of the ocular defects in patients affected by EEC syndrome: (i) gene therapy-based approaches by means of Allele-Specific (AS) siRNAs to correct the p63 mutations; (ii) cell therapy-based approaches to replenish the pool of limbal stem cells; and (iii) drug therapy to correct/bypass the genetic defect. However, as the number of patients with EEC syndrome is too limited, further studies are still necessary to prove the effectiveness (and safety) of these innovative therapeutic approaches to counteract the premature differentiation of limbal stem cells.

Ocular Manifestations in Patients Affected by p63-Associated Disorders: Ectrodactyly-Ectodermal Dysplasia-Clefting (EEC) and Ankyloblepharon-Ectodermal Defects-Cleft Lip Palate (AEC) Syndromes.

BACKGROUND/AIMS: The Ectrodactyly-Ectodermal dysplasia-Clefting (EEC) and Ankyloblepharon-ectodermal defect-cleft lip/palate (AEC) syndromes are rare autosomal dominant diseases caused by heterozygous mutations in the p63 gene. Patients are characterized by abnormalities of the skin, teeth, and hair and have limb defects, orofacial clefting and ectodermal dysplasia. In addition, they often show ocular surface alterations, leading to progressive corneal clouding and eventually blindness. Here, we present 8 cases describing patients affected by EEC (n = 6, with 5 sporadic and 1 familial cases) and AEC (n = 2, both sporadic cases) syndromes. We attempt to provide a description of the ocular disease progression over the years. METHODS: Clinical examinations and monitoring of ocular parameters for the assessment of limbal stem cell deficiency were constantly performed on patients between 2009 and 2023. Quantitative data and comparison with existing cases described in the literature are reported. RESULTS: The therapies supplied to patients were essential for the management of the symptoms, but unfortunately did not halt the progression of the pathology. CONCLUSIONS: A constant monitoring of the patients would help avoid the sudden worsening of symptoms. If the progression of the disease slows down, it would allow for the development of newer therapeutic strategies aimed at correcting the genetic defect.

Limbal stem cell deficiency and ocular phenotype in ectrodactyly-ectodermal dysplasia-clefting syndrome caused by p63 mutations.

OBJECTIVE: To describe the ocular phenotype in patients with ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome (MIM#604292) and to determine the pathogenic basis of visual morbidity. DESIGN: Retrospective case series. PARTICIPANTS: Nineteen families (23 patients) affected by EEC syndrome from the United Kingdom, Ireland, and Italy. METHODS: General medical examination to fulfill the diagnostic criteria for EEC syndrome and determine the phenotypic severity. Mutational analysis of p63 was performed by polymerase chain reaction-based bidirectional Sanger sequencing. All patients with EEC syndrome underwent a complete ophthalmic examination and ocular surface assessment. Limbal stem cell deficiency (LSCD) was diagnosed clinically on the basis of corneal conjunctivalization and anatomy of the limbal palisades of Vogt. Impression cytology using immunofluorescent antibodies was performed in 1 individual. Histologic and immunohistochemical analyses were performed on a corneal button and corneal pannus from 2 EEC patients. MAIN OUTCOME MEASURES: The EEC syndrome phenotypic severity (EEC score), best-corrected Snellen visual acuity (decimal fraction), slit-lamp biomicroscopy, tear function index, tear breakup time, LSCD, p63 DNA sequence variants, impression cytology, and corneal histopathology. RESULTS: Eleven heterozygous missense mutations in the DNA binding domain of p63 were identified in all patients with EEC syndrome. All patients had ocular involvement and the commonest was an anomaly of the meibomian glands and lacrimal drainage system defects. The major cause of visual morbidity was progressive LSCD, which was detected in 61% (14/23). Limbal stem cell deficiency was related to advancing age and caused a progressive keratopathy, resulting in a dense vascularized corneal pannus, and eventually leading to visual impairment. Histologic analysis and impression cytology confirmed LSCD. CONCLUSIONS: Heterozygous p63 mutations cause the EEC syndrome and result in visual impairment owing to progressive LSCD. There was no relationship of limbal stem cell failure with the severity of EEC syndrome, as classified by the EEC score, or the underlying molecular defect in p63. FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any of the materials discussed in this article.

C/EBPdelta 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 delta (C/EBPdelta), Bmi1, and DeltaNp63alpha identifies mitotically quiescent limbal stem cells, which generate holoclones in culture. Upon corneal injury, a fraction of these cells switches off C/EBPdelta and Bmi1, proliferates, and differentiates into mature corneal cells. Forced expression of C/EBPdelta inhibits the growth of limbal colonies and increases the cell cycle length of primary limbal cells through the activity of p27(Kip1) and p57(Kip2). These effects are reversible; do not alter the limbal cell proliferative capacity; and are not due to apoptosis, senescence, or differentiation. C/EBPdelta, but not DeltaNp63alpha, 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/EBPdelta is recruited to the chromatin of positively (p27(Kip1) and p57(Kip2)) and negatively (p16(INK4A) and involucrin) regulated gene loci, suggesting a direct role of this transcription factor in determining limbal stem cell identity.

A novel de novo missense mutation in TP63 underlying germline mosaicism in AEC syndrome: implications for recurrence risk and prenatal diagnosis.

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare autosomal dominant ectodermal dysplasia syndrome. It is caused by heterozygous mutations in TP63, encoding a transcriptional factor of the p53 family. Mutations in TP63, mainly missense in exons 13 and 14 encoding the sterile alpha motif (SAM) and the transactivation inhibitory (TI) domains, account for 99% of mutations in individuals with AEC syndrome. Of these, ≥70% are de novo mutations, present in the affected patient, but not in parents nor in healthy siblings. However, when a mutation appears de novo, it is not possible to differentiate between a sporadic mutation, or germline mosaicism in the parents. In this latter case, there is a risk of having additional affected offspring. We describe two sisters with AEC syndrome, whose parents were unaffected. Both patients carried the heterozygous c.1568T>C substitution in exon 13 of TP63, resulting in a p.L523P change in the SAM domain of the protein. Analyses of DNA from parental blood cells, seminal fluid (from the father) and maternal cells (buccal, vaginal, and cervical) did not reveal the mutation, suggesting that the mosaicism may involve a very low percentage of cells (very low grade somatic mosaicism) or, more likely, maternal gonadal mosaicism. Mosaicism must be considered for the assessment of recurrence risk during genetic counseling in AEC syndrome, and pre-implantation/prenatal genetic diagnosis should be offered to all couples, even when the mutation is apparently de novo.

Long-term effectiveness of autologous cultured limbal stem cell grafts in patients with limbal stem cell deficiency due to chemical burns.

BACKGROUND: Chemical burns cause depletion of limbal stem cells and eventually lead to corneal opacity and visual loss. We investigated the long-term effectiveness of autologous cultured limbal stem cell grafts in patients with limbal stem cell deficiency. DESIGN: Prospective, non-comparative interventional case series. PARTICIPANTS: Sixteen eyes from 16 patients with severe, unilateral limbal stem cell deficiency caused by chemical burns. METHODS: Autologous ex vivo cultured limbal stem cells were grafted onto the recipient eye after superficial keratectomy. MAIN OUTCOME MEASURES: Clinical parameters of limbal stem cell deficiency (stability/transparency of the corneal epithelium, superficial corneal vascularization and pain/photophobia), visual acuity, cytokeratin expression on impression cytology specimens and histology on excised corneal buttons. RESULTS: At 12 months post-surgery, evaluation of the 16 patients showed that 10 (62.6%) experienced complete restoration of a stable and clear epithelium and 3 (18.7%) had partially successful outcomes (re-appearance of conjunctiva in some sectors of the cornea and instable corneal surface). Graft failure (no change in corneal surface conditions) was seen in three (18.7%) patients. Penetrating keratoplasty was performed in seven patients, with visual acuity improving up to 0.8 (best result). For two patients, regeneration of the corneal epithelium was confirmed by molecular marker (p63, cytokeratin 3, 12 and 19, mucin 1) analysis. Follow-up times ranged from 12 to 50 months. CONCLUSIONS: Grafts of autologous limbal stem cells cultured onto fibrin glue discs can successfully regenerate the corneal epithelium in patients with limbal stem cell deficiency, allowing to perform successful cornea transplantation and restore vision.

Localization and expression of CHST6 and keratan sulfate proteoglycans in the human cornea.

Macular corneal dystrophy (MCD; OMIM 217800) is a rare autosomal recessive inherited disorder caused by mutations in the carbohydrate sulfotransferase 6 (CHST6) and characterised by the presence of unsulfated keratan sulfate proteoglycans (KSPGs) forming abnormal deposits that eventually lead to visual impairment. The aim of this study is to understand in which corneal cells CHST6 and KSPGs are expressed and exert their activity. Expression and localization of CHST6, keratan sulfate (KS) and proteins of the KSPGs, such as mimecan and lumican, were assessed both in human cornea sections and in cultured primary keratinocytes (n = 3) and keratocytes (n = 4). Immunohistochemistry, semiquantitative RT-PCR, in situ RNA hybridization and HPLC analysis of glycosaminoglycans were used as read-outs. In human corneas KS was predominantly found in the stroma, but absent, or barely detectable, in the corneal epithelium. A similar pattern of distribution was found in the epidermis, with KS mainly localised in the derma. As expected, in the cornea CHST6 (the gene encoding the enzyme which transfers sulfate residues onto KSPGs) was found expressed in the suprabasal, but not basal, layers of the epithelium, in the stroma and in the endothelium. Analyses of KS by means of HPLC showed that in vitro cultured stromal keratocytes express and secrete more KS than keratinocytes, thus mirroring results observed in vivo. Similarly expression of the CHST6 gene and of KS proteoglycans such as mimecan, lumican is limited to stromal keratocytes. Unlike keratocytes, corneal keratinocytes do not synthesize mimecan or lumican, and express very little, if none, CHST6. Any drug/gene therapy or surgical intervention aimed at curing this rare genetic disorder must therefore involve and target stromal keratocytes. If coupled to the accuracy of HPLC-based assay that we developed to determine the amount of KS in serum, our findings could lead to more targeted therapeutic treatments of the ocular features in MCD patients.

Techniques for culture and assessment of limbal stem cell grafts.

The therapeutic use of limbal cultures for the permanent regeneration of corneal epithelium in patients with limbal stem cell deficiency (LSCD) has been reported in many studies. According to the guidelines for good manufacturing practice (GMP), strictly regulated procedures and stringent quality control tests are now required to manipulate stem cells as "medicinal products" and make engraftment safer and eventually more successful. This paper describes techniques for optimal preparation of limbal stem cell grafts, including 1) a reliable impression cytology assay for the grading of LSCD, 2) culture methods that maintain high percentages of limbal stem cells, 3) the use of specific markers for the detection of corneal, conjunctival, and limbal stem cells, namely keratin 12, mucin 1, and DeltaNp63alpha, and 4) assays to assess the presence of contaminants, such as murine fibroblasts, endotoxins, mycoplasmae, and viral particles, in the cultured graft. The use of some of these assays allowed us to obtain a regenerated normal corneal epithelium in approximately 80% of 166 LSCD patients who received transplants from 2004 to 2008.

Reconstruction of a human hemicornea through natural scaffolds compatible with the growth of corneal epithelial stem cells and stromal keratocytes.

PURPOSE: To reconstruct a human hemicornea in vitro by means of limbal stem cells cultured onto human keratoplasty lenticules (HKLs) and to obtain a natural corneal graft for clinical applications. METHODS: Limbal stem cells were seeded onto HKLs with or without the presence of feeder layers of lethally irradiated 3T3-J2 cells and compared with the current "gold standard" scaffold, i.e., the fibrin glue. The effects of the scaffold on the preservation of stemness and/or induction of differentiation pathways were investigated through analysis of a variety of markers, including p63 and DeltaNp63alpha for stemness, 14-3-3sigma for early differentiation, keratins 3, 14, 12, and 19 to determine cell phenotype, and alpha6, beta1, and beta4 integrins to evaluate interactions with the stroma. Integrity of the stroma was assessed through analysis of keratan sulfate, CD-34 and aldehyde dehydrogenase 3A1 (ALDH3A1) (for keratocytes), visual system homeobox 1 (VSX1), and alpha-smooth muscle actin (alpha-SMA) (for fibroblasts and myofibroblasts). The structural properties of the reconstructed "hemicornea" were investigated through scanning electron microscopy. To evaluate the preservation of the stemness potential, cells were trypsinized from each scaffold and clonogenic/proliferative characteristics analyzed. RESULTS: Limbal stem cells expanded onto HKLs gave rise to a stratified squamous keratinized epithelium morphologically similar to that of normal corneas. The resulting corneal epithelium was characterized by basal expression of p63 and DeltaNp63alpha, while expression of 14-3-3sigma, keratin 3, and keratin 12 was found in the upper cell layers. The basal cuboidal epithelial cells were anchored to the basement membrane and expressed keratin 14 and alpha6, beta1, and beta4 integrins. In the stroma of HKLs, keratocytes maintained the biosynthetic and phenotypic appearances typical of resting/quiescent cells and expressed keratan sulfate, CD-34, and ALDH3A1. Fibroblastic transformation was observed with the appearance of VSX1 and alpha-SMA. Scanning electron microscopy analysis showed that HKLs maintained their native conformation with collagen fibrils interconnected to the network and parallel to the corneal surface. HKLs did not alter the clonogenic/proliferative capacity of limbal stem cells. No differences were seen when HKL was compared to fibrin glue, one of the scaffolds currently used for limbal stem cell transplantation. CONCLUSIONS: Our findings demonstrate that HKL could be a suitable scaffold for corneal epithelial stem cells as they were shown to proliferate, express differentiation markers, and bind to the underlying stroma with no alterations in clonogenic potential. HKLs have some advantages over currently used scaffolds, such as the possibility to allow cell growth with no feeder layers, to be freeze dried, and to preserve the integrity and viability of stromal keratocytes. The development of a tissue-engineered "hemicornea" might offer new therapeutic perspectives to patients affected by total limbal stem cell deficiency with stromal scarring.