Pax-6 expression and activity are induced in the reepithelializing cornea and control activity of the transcriptional promoter for matrix metalloproteinase gelatinase B

Knockout of signal peptide peptidase in the eye reduces HSV-1 replication and eye disease in ocularly infected mice

We previously reported that knocking out signal peptide peptidase (SPP), a glycoprotein K (gK) binding partner, in mouse peripheral sensory neurons reduced latency-reactivation in infected mice without affecting primary virus replication or eye disease. Since virus replication in the eye plays an essential role in eye disease, we generated a conditional knockout mouse lacking SPP expression in the eye by crossing Pax6 (paired box 6)-Cre mice that have intact Pax6 expression with SPPflox/flox mice. Significantly less SPP protein expression was detected in the eyes of Pax6-SPP-/- mice than in WT control mice. HSV-1 replication in the eyes of Pax6-SPP-/- mice was significantly lower than in WT control mice. Levels of gB, gK, and ICP0 transcripts in corneas, but not trigeminal ganglia (TG), of Pax6-SPP-/- infected mice were also significantly lower than in WT mice. Corneal scarring and angiogenesis were significantly lower in Pax6-SPP-/- mice than in WT control mice, while corneal sensitivity was significantly higher in Pax6-SPP-/- mice compared with WT control mice. During acute viral infection, absence of SPP in the eye did not affect CD4 expression but did affect CD8α and IFNγ expression in the eye. However, in the absence of SPP, latency-reactivation was similar in Pax6-SPP-/- and WT control groups. Overall, our results showed that deleting SPP expression in the eyes reduced primary virus replication in the eyes, reduced CD8α and IFNγ mRNA expression, reduced eye disease and reduced angiogenesis but did not alter corneal sensitivity or latency reactivation to HSV-1 infection. Thus, blocking gK binding to SPP in the eye may have therapeutic potential by reducing both virus replication in the eye and eye disease associated with virus replication.

Thirty Years' History since the Discovery of Pax6: From Central Nervous System Development to Neurodevelopmental Disorders

Pax6 is a sequence-specific DNA binding transcription factor that positively and negatively regulates transcription and is expressed in multiple cell types in the developing and adult central nervous system (CNS). As indicated by the morphological and functional abnormalities in spontaneous Pax6 mutant rodents, Pax6 plays pivotal roles in various biological processes in the CNS. At the initial stage of CNS development, Pax6 is responsible for brain patterning along the anteroposterior and dorsoventral axes of the telencephalon. Regarding the anteroposterior axis, Pax6 is expressed inversely to Emx2 and Coup-TF1, and Pax6 mutant mice exhibit a rostral shift, resulting in an alteration of the size of certain cortical areas. Pax6 and its downstream genes play important roles in balancing the proliferation and differentiation of neural stem cells. The Pax6 gene was originally identified in mice and humans 30 years ago via genetic analyses of the eye phenotypes. The human PAX6 gene was discovered in patients who suffer from WAGR syndrome (i.e., Wilms tumor, aniridia, genital ridge defects, mental retardation). Mutations of the human PAX6 gene have also been reported to be associated with autism spectrum disorder (ASD) and intellectual disability. Rodents that lack the Pax6 gene exhibit diverse neural phenotypes, which might lead to a better understanding of human pathology and neurodevelopmental disorders. This review describes the expression and function of Pax6 during brain development, and their implications for neuropathology.

PAX2 induces vascular‑like structures in normal ovarian cells and ovarian cancer

In adult tissue, the paired box 2 (PAX2) protein is expressed in healthy oviductal, but not normal ovarian surface epithelial cells. PAX2 is expressed in a subset of cases of serous ovarian carcinoma; however, the role of PAX2 in the initiation and progression of ovarian cancer remains unknown. The aim of the present study was to determine the biological effects of PAX2 expression in normal and cancerous epithelial cells. By culturing the normal and cancerous ovarian cells that express PAX2 in 3D culture and staining the cells with vasculogenic mimicry markers such as CD31 and PAS, it was shown that PAX2 overexpression in both normal and cancerous ovarian epithelial cells induced formation of vascular-like structures both in vitro and in vivo. These results indicated a potential role of PAX2 in ovarian cancer progression by increasing the presence of vascular-like structures to promote the supply of nutrients to tumor cells and facilitate cancer cell proliferation and invasion.

Unilateral zebrafish corneal injury induces bilateral cell plasticity supporting wound closure

The cornea, transparent and outermost structure of camera-type eyes, is prone to environmental challenges, but has remarkable wound healing capabilities which enables to preserve vision. The manner in which cell plasticity impacts wound healing remains to be determined. In this study, we report rapid wound closure after zebrafish corneal epithelium abrasion. Furthermore, by investigating the cellular and molecular events taking place during corneal epithelial closure, we show the induction of a bilateral response to a unilateral wound. Our transcriptomic results, together with our TGF-beta receptor inhibition experiments, demonstrate conclusively the crucial role of TGF-beta signaling in corneal wound healing. Finally, our results on Pax6 expression and bilateral wound healing, demonstrate the decisive impact of epithelial cell plasticity on the pace of healing. Altogether, our study describes terminally differentiated cell competencies in the healing of an injured cornea. These findings will enhance the translation of research on cell plasticity to organ regeneration.

Decreased FABP5 and DSG1 protein expression following PAX6 knockdown of differentiated human limbal epithelial cells

PAX6 haploinsufficiency related aniridia is characterized by disorder of limbal epithelial cells (LECs) and aniridia related keratopathy. In the limbal epithelial cells of aniridia patients, deregulated retinoic acid (RA) signaling components were identified. We aimed to visualize differentiation marker and RA signaling component expression in LECs, combining a differentiation triggering growth condition with a small interfering RNA (siRNA) based aniridia cell model (PAX6 knock down). Primary LECs were isolated from corneoscleral rims of healthy donors and cultured in serum free low Ca²⁺ medium (KSFM) and in KSFM supplemented with 0.9 mmol/L Ca²⁺. In addition, LECs were treated with siRNA against PAX6. DSG1, PAX6, KRT12, KRT 3, ADH7, RDH10, ALDH1A1, ALDH3A1, STRA6, CYP1B1, RBP1, CRABP2, FABP5, PPARG, VEGFA and ELOVL7 expression was determined using qPCR and western blot. DSG1, FABP5, ADH7, ALDH1A1, RBP1, CRABP2 and PAX6 mRNA and FABP5 protein expression increased (p ≤ 0.03), PPARG, CYP1B1 mRNA expression decreased (p ≤ 0.0003) and DSG1 protein expression was only visible after Ca²⁺ supplementation. After PAX6 knock down and Ca²⁺ supplementation, ADH7 and ALDH1A1 mRNA and DSG1 and FABP5 protein expression decreased (p ≤ 0.04), compared to Ca²⁺ supplementation alone. Using our cell model, with Ca²⁺ supplementation and PAX6 knockdown with siRNA treatment against PAX6, we provide evidence that haploinsufficiency of the master regulatory gene PAX6 contributes to differentiation defect in the corneal epithelium through alterations of RA signalling. Upon PAX6 knockdown, DSG1 differentiation marker and FABP5 RA signaling component mRNA expression decreases. A similar effect becomes apparent at protein level though differentiation triggering Ca²⁺ supplementation in the siRNA-based aniridia cell model. Expression data from this cell model and from our siRNA aniridia cell model strongly indicate that FABP5 expression is PAX6 dependent. These new findings may lead to a better understanding of differentiation processes in LECs and are able to explain the insufficient cell function in AAK.

Aniridia and the ocular surface: Medical and surgical problems and solutions

Congenital aniridia is a multisystemic genetic disease due to a mutation in PAX6 gene which severely affects the development and functionality of the human eyes. In patients affected by the mutation, aside from the absence or defects of iris tissue formation, abnormalities in position or opacities of the crystalline lens, macular hypoplasia, ocular surface disease is the main cause of visual loss and the deterioration of the quality of life of most patients. Limbal stem cell deficiency combined with tear film instability and secondary dry eye cause aniridic keratopathy which, in advanced stages, ends up in corneal opacification. In this paper, the actual knowledge about congenital aniridia keratopathy physiopathology and medical and surgical treatment options and their efficacy are discussed. Indications and results of topical treatments with artificial tears and blood-derivatives in its initial stages, and different surgical techniques as limbal stem cell transplantation, keratoplasty and keratoprostheses are reviewed. Finally, recent advances and results in regenerative medicine techniques with ex vivo stem cell cultivation or other types of cultivated cells are presented.

Pathophysiology of aniridia-associated keratopathy: Developmental aspects and unanswered questions

Aniridia, a rare congenital disease, is often characterized by a progressive, pronounced limbal insufficiency and ocular surface pathology termed aniridia-associated keratopathy (AAK). Due to the characteristics of AAK and its bilateral nature, clinical management is challenging and complicated by the multiple coexisting ocular and systemic morbidities in aniridia. Although it is primarily assumed that AAK originates from a congenital limbal stem cell deficiency, in recent years AAK and its pathogenesis has been questioned in the light of new evidence and a refined understanding of ocular development and the biology of limbal stem cells (LSCs) and their niche. Here, by consolidating and comparing the latest clinical and preclinical evidence, we discuss key unanswered questions regarding ocular developmental aspects crucial to AAK. We also highlight hypotheses on the potential role of LSCs and the ocular surface microenvironment in AAK. The insights thus gained lead to a greater appreciation for the role of developmental and cellular processes in the emergence of AAK. They also highlight areas for future research to enable a deeper understanding of aniridia, and thereby the potential to develop new treatments for this rare but blinding ocular surface disease.

Limbal Stem Cell Dysfunction in Ichthyosis Follicularis, Alopecia, and Photophobia Syndrome

PURPOSE

To describe the presentation and management of limbal stem cell dysfunction in ichthyosis follicularis, alopecia, and photophobia (IFAP) syndrome.

METHODS

A retrospective case report.

RESULTS

A 6-day-old male infant was diagnosed with IFAP syndrome based on family history and a mutation detected in the MBTPS2 gene. Initial examination showed hyperkeratotic eyelids, madarosis, and lagophthalmos, but otherwise clear corneas. He developed bilateral central corneal epithelial defects spontaneously 6 months later, which were managed with aggressive lubrication, prophylactic antibiotics, and bilateral permanent lateral tarsorrhaphies at 7 months of age. During the procedure, the patient was noted to have bilateral limbal thickening, peripheral corneal pannus with underlying stromal scarring, and late fluorescein staining of the corneal surface. Anterior segment optical coherence tomography demonstrated a significantly abnormal and hyperreflective epithelial surface overlying a thinned corneal stroma, suggestive of limbal stem cell dysfunction. The corneal surface was maintained with lubrication and tarsorrhaphy and has remained stable since.

CONCLUSIONS

The progressive conjunctivalization, spontaneous epithelial defects, and anterior segment optical coherence tomography features are highly suggestive of limbal stem cell dysfunction in IFAP syndrome. Optimizing the ocular surface is of importance in the management of children with this rare disease.

Usefulness of PAX8 Immunohistochemistry in Adult Intraocular Tumor Diagnosis

PURPOSE

To evaluate the distribution of the PAX8 transcription factor protein in ocular tissues and to investigate if immunohistochemical stains for this biomarker are useful in the diagnosis of intraocular tumors.

DESIGN

Observational case series.

PARTICIPANTS

Excision and cytologic analysis specimens of 6 ciliary body epithelial neoplasms, 2 iris epithelial neoplasms, 3 retinal pigment epithelial neoplasms, 3 intraocular medulloepitheliomas, 15 uveal melanomas, and 5 uveal melanocytomas.

METHODS

Hematoxylin-eosin and PAX8 immunohistochemical stains were performed on all specimens. In appropriate cases, bleached preparations and other immunohistochemical stains, including AE1/AE3 cytokeratin, Lin28A, and CD45, were performed.

MAIN OUTCOME MEASURES

Distribution of PAX8 expression in normal and neoplastic tissue.

RESULTS

Strong nuclear PAX8 expression was observed in the normal corneal epithelium, iris sphincter pupillae muscle, iris pigment epithelium and dilator muscle complex, nonpigmented and pigmented epithelia of the ciliary body, lens epithelium, and a subset of retinal neurons. The normal retinal pigment epithelium and uveal melanocytes did not stain for PAX8. The ciliary body epithelial and neuroepithelial tumors (adenoma, adenocarcinoma, and medulloepithelioma) showed uniform strong nuclear PAX8 immunoreactivity. All melanocytic tumors (iris melanoma, ciliary-choroidal melanoma, and melanocytoma) and retinal pigment epithelial neoplasms showed negative results for PAX8. A subset of tumor-associated lymphocytes, most prominent in uveal melanoma, showed positive results for PAX8. The uniformity of the PAX8 staining was superior to the variable cytokeratin staining in the ciliary epithelial neoplasms and the variable Lin28A staining in malignant medulloepithelioma. The veracity of PAX8 staining was equally as robust on cytologic analysis and open-flap biopsy specimens of ciliary epithelial and iris epithelial neoplasms, melanocytoma, and melanoma.

CONCLUSIONS

PAX8 has proven to be a very useful diagnostic marker in a select group of adult intraocular tumors, and we highly recommend its inclusion in diagnostic antibody panels of morphologically challenging intraocular neoplasms.

Evaluation of Cryopreservation Media for the Preservation of Human Corneal Stromal Stem Cells

Introduction: Human corneal stromal stem cells (CSSCs) have gained increasing attention in the treatment of corneal stromal scars. In view of this, the preparation and storage of CSSCs are critical to maintaining the regenerative potential of CSSCs. The goal of the study was to investigate the human serum (HS) concentration in the cryomedia that could best preserve CSSCs. Materials and Methods: Three different cryopreservation media, varying in HS concentration were evaluated in their ability to preserve the viability and phenotype of CSSCs: 2% HS (FS1), 4% HS (FS2), and 90% HS (FS3). After thawing, CSSCs morphology, recovery rate, cell proliferation, relative gene expression of CSSC markers (ABCG2, SOX2, NANOG, PAX6, and SIX3), and their anti-inflammatory response (level of TNFAIP6) were compared with those of unfrozen CSSCs (control). Results: Cryopreserved CSSCs had similar cell morphology as the control. Cell viability was significantly higher using FS2 (92.7 ± 1.3%) compared with FS1 (88 ± 0.8%, p = 0.018). Doubling times of CSSCs were maintained in all cryopreserved conditions, as in the control (p > 0.05), which were 0.9 ± 0.1 days and 1.8 ± 0.0 days at passages 3 and 4, then increased to 18.2 ± 1.9 days at passage 6 (p > 0.05). The expression level of stem cell/progenitor cell markers investigated was not affected by the cryopreservation with any of the three media. In addition, cryopreserved CSSCs have a similar expression level of TNFAIP6 after stimulation with proinflammatory cytokines as the control (p > 0.05). Conclusion: Our results indicated that all three cryopreservation media maintained CSSCs phenotype after undergoing one freezing/thawing cycle. Impact Statement Corneal stromal stem cells (CSSCs) offer an alternative for the treatment of corneal stromal scars. Cryopreservation of CSSCs is necessary as it enables feasibility of using CSSCs as a cell therapy candidate. The current study shows that media used to cryopreserve CSSCs could be optimized to maintain cell viability, phenotype, and potency of CSSCs after thawing.

Transcription Factors That Govern Development and Disease: An Achilles Heel in Cancer

Development requires the careful orchestration of several biological events in order to create any structure and, eventually, to build an entire organism. On the other hand, the fate transformation of terminally differentiated cells is a consequence of erroneous development, and ultimately leads to cancer. In this review, we elaborate how development and cancer share several biological processes, including molecular controls. Transcription factors (TF) are at the helm of both these processes, among many others, and are evolutionarily conserved, ranging from yeast to humans. Here, we discuss four families of TFs that play a pivotal role and have been studied extensively in both embryonic development and cancer-high mobility group box (HMG), GATA, paired box (PAX) and basic helix-loop-helix (bHLH) in the context of their role in development, cancer, and their conservation across several species. Finally, we review TFs as possible therapeutic targets for cancer and reflect on the importance of natural resistance against cancer in certain organisms, yielding knowledge regarding TF function and cancer biology.

Conserved characteristics of ocular refractive development - Did the eye evolve once?

It has been speculated that the unitary eyes of vertebrates and molluscs, and the compound eyes of insects and crustaceans, evolved separately. On the other hand, the common use of rhodopsin as a photoreceptor molecule, and the conservation of Pax6 as a master control gene for eye development, suggest instead that the eye evolved once. Yet, recently the molecular genetics that had seemed to suggest a definitive answer to this evolutionary point has once again become cloudy. Here we propose an alternative approach to addressing the question of eye evolution through comparative analyses of physiological optics. Serendipitous discoveries involving form deprivation and defocusing with young monkeys and chicks demonstrated the conserved importance of visual experience on eye development. Similar results have been demonstrated in teleosts, although differences exist in eye anatomy, physiology and optics. In particular, since fish grow throughout life, these effects can also be demonstrated in adults. In comparison, the cephalopod eye is an often-cited example of convergent evolution with the vertebrate eye, although considerable developmental differences exist. Nevertheless, squid eyes from animals raised under alternative lighting exhibit anatomical and refractive changes that agree with those found in vertebrates. Together, these observations provide functional and structural support for the view that the eye evolved once. Because of their very compressed lifespans (only one to two years) cephalopods may be ideal animal models for the study of ocular refractive development.

Glucocorticoid Effects on Cerebellar Development in a Chicken Embryo Model: Exploring Changes in PAX6 and Metalloproteinase-9 After Exposure to Dexamethasone

The developing cerebellum is vulnerable to effects of glucocorticoids and cerebellar dysfunction is associated with neurodevelopmental disorders (e.g. autism). Transcription factor PAX6 and matrix metalloproteinase-9 (MMP-9) are critical for normal cerebellar development and are highly expressed in migrating neurones. Alterations in MMP-9 and PAX6 are associated with altered cerebellar development. In the present study, we characterised the growth rate and development of the cortical layers, and further investigated how the levels of PAX6 and MMP-9, as well as glucocorticoid receptor (GR) and proliferating cell nuclear antigen (PCNA), change in the cerebellum during the foetal period [embryonic day (E)12-21] in chicken, which corresponds to the human perinatal period. Dexamethasone (DEX) was administered in ovo at E13 and E16, aiming to investigate how prenatal exposure to glucocorticoids interferes with normal development. DEX reduced foetal and cerebellar weight at E17 in a dose-dependent manner linked to a reduced level of PCNA and, over time, down-regulation of GR. We report that promoter activity of PAX6 and MMP-9 increased as a result of GR-stimulation in vitro. Prenatal DEX increased the protein level of PAX6 in a transient manner. PAX6 is reduced in mature granule neurones, and this occurred earlier in embryos exposed to DEX than in non-exposed controls. DEX exposure also led to a slow-onset down-regulation of MMP-9. Taken together, these findings indicate that excess prenatal glucocorticoid stimulation disturbs normal development of the cerebellum through mechanisms associated with reduced proliferation and accelerated maturation where PAX6 and MMP-9 play important roles.

Type I collagen accelerates the spreading of lens epithelial cells through the expression and activation of matrix metalloproteinases

PURPOSE

Matrix metalloproteinases (MMPs) are involved in posterior capsule opacification (PCO), but the mechanisms that promote MMP expression are yet to be determined. In this study, we investigated whether type I collagen, which is only detected in aged or cataractous lens capsules, affects the expression and activation of MMPs in primary-cultured chicken lens epithelial cells (LECs).

MATERIALS AND METHODS

Chicken LECs were isolated from chicken embryos and cultured in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum (FBS) on type I collagen-coated dishes. The activity of secreted MMPs was examined using gelatin zymography, and cell spreading was determined as the average area of randomly distributed cells. For some experiments, LECs were cultured in the presence of the broad-spectrum MMP inhibitor, GM6001. LECs cultured on uncoated dishes were used as controls. To examine the involvement of MMP in cell migration, a wound-healing assay was performed in the presence of the MMP inhibitor.

RESULTS

Chicken LECs constitutively express the pro-form of MMP-2. When LECs were cultured on type I collagen-coated dishes, they expressed the active form of MMP-2 and the pro-form of MMP-9. This expression and activation by type I collagen was also observed in the human LEC line SRA-01/04, but not the human Müller glial cell line, MIO-M1. Type I collagen enhanced cell spreading, which was suppressed by the MMP inhibitor. Type I collagen also accelerated α-smooth muscle actin expression. In addition, LEC migration was inhibited by the MMP inhibitor in a dose-dependent manner in the wound-healing assay.

CONCLUSION

Type I collagen promotes the expression and activation of MMPs in a LEC-specific manner. These results suggest that type I collagen may play a role in PCO development.

Ocular surface development and gene expression

The ocular surface-a continuous epithelial surface with regional specializations including the surface and glandular epithelia of the cornea, conjunctiva, and lacrimal and meibomian glands connected by the overlying tear film-plays a central role in vision. Molecular and cellular events involved in embryonic development, postnatal maturation, and maintenance of the ocular surface are precisely regulated at the level of gene expression by a well-coordinated network of transcription factors. A thorough appreciation of the biological characteristics of the ocular surface in terms of its gene expression profiles and their regulation provides us with a valuable insight into the pathophysiology of various blinding disorders that disrupt the normal development, maturation, and/or maintenance of the ocular surface. This paper summarizes the current status of our knowledge related to the ocular surface development and gene expression and the contribution of different transcription factors to this process.

Critical role of Klf5 in regulating gene expression during post-eyelid opening maturation of mouse corneas

BACKGROUND

Klf5 plays an important role in maturation and maintenance of the mouse ocular surface. Here, we quantify WT and Klf5-conditional null (Klf5CN) corneal gene expression, identify Klf5-target genes and compare them with the previously identified Klf4-target genes to understand the molecular basis for non-redundant functions of Klf4 and Klf5 in the cornea.

METHODOLOGY/PRINCIPAL FINDINGS

Postnatal day-11 (PN11) and PN56 WT and Klf5CN corneal transcriptomes were quantified by microarrays to compare gene expression in maturing WT corneas, identify Klf5-target genes, and compare corneal Klf4- and Klf5-target genes. Whole-mount corneal immunofluorescent staining was employed to examine CD45+ cell influx and neovascularization. Effect of Klf5 on expression of desmosomal components was studied by immunofluorescent staining and transient co-transfection assays. Expression of 714 and 753 genes was increased, and 299 and 210 genes decreased in PN11 and PN56 Klf5CN corneas, respectively, with 366 concordant increases and 72 concordant decreases. PN56 Klf5CN corneas shared 241 increases and 98 decreases with those previously described in Klf4CN corneas. Xenobiotic metabolism related pathways were enriched among genes decreased in Klf5CN corneas. Expression of angiogenesis and immune response-related genes was elevated, consistent with neovascularization and CD45+ cell influx in Klf5CN corneas. Expression of 1574 genes was increased and 1915 genes decreased in WT PN56 compared with PN11 corneas. Expression of ECM-associated genes decreased, while that of solute carrier family members increased in WT PN56 compared with PN11 corneas. Dsg1a, Dsg1b and Dsp were down-regulated in Klf5CN corneas and their corresponding promoter activities were stimulated by Klf5 in transient co-transfection assays.

CONCLUSIONS/SIGNIFICANCE

Differences between PN11 and PN56 corneal Klf5-target genes reveal dynamic changes in functions of Klf5 during corneal maturation. Klf5 contributes to corneal epithelial homeostasis by regulating the expression of desmosomal components. Klf4- and Klf5-target genes are largely distinct, consistent with their non-redundant roles in the mouse cornea.

3T3 cell lines stably expressing Pax6 or Pax6(5a)--a new tool used for identification of common and isoform specific target genes

Pax6 and Pax6(5a) are two isoforms of the evolutionary conserved Pax6 gene often co-expressed in specific stochiometric relationship in the brain and the eye during development. The Pax6(5a) protein differs from Pax6 by having a 14 amino acid insert in the paired domain, causing the two proteins to have different DNA binding specificities. Difference in functions during development is proven by the fact that mutations in the 14 amino acid insertion for Pax6(5a) give a slightly different eye phenotype than the one described for Pax6. Whereas quite many Pax6 target genes have been published during the last years, few Pax6(5a) specific target genes have been reported on. However, target genes identified by Pax6 knockout studies can probably be Pax6(5a) targets as well, since this isoform also will be affected by the knockout. In order to identify new Pax6 target genes, and to try to distinguish between genes regulated by Pax6 and Pax6(5a), we generated FlpIn-3T3 cell lines stably expressing Pax6 or Pax6(5a). RNA was harvested from these cell lines and used in gene expression microarrays where we identified a number of genes differentially regulated by Pax6 and Pax6(5a). A majority of these were associated with the extracellular region. By qPCR we verified that Ncam1, Ngef, Sphk1, Dkk3 and Crtap are Pax6(5a) specific target genes, while Tgfbi, Vegfa, EphB2, Klk8 and Edn1 were confirmed as Pax6 specific target genes. Nbl1, Ngfb and seven genes encoding different glycosyl transferases appeared to be regulated by both. Direct binding to the promoters of Crtap, Ctgf, Edn1, Dkk3, Pdgfb and Ngef was verified by ChIP. Furthermore, a change in morphology of the stably transfected Pax6 and Pax6(5a) cells was observed, and the Pax6 expressing cells were shown to have increased proliferation and migration capacities.

PAX Genes in Cancer; Friends or Foes?

PAX genes have been shown to be critically required for the development of specific tissues and organs during embryogenesis. In addition, PAX genes are expressed in a handful of adult tissues where they are thought to play important roles, usually different from those in embryogenesis. A common theme in adult tissues is a requirement for PAX gene expression in adult stem cell maintenance or tissue regeneration. The connections between adult stem cell PAX gene expression and cancer are intriguing, and the literature is replete with examples of PAX gene expression in either situation. Here we systematically review the literature and present an overview of postnatal PAX gene expression in normal and cancerous tissue. We discuss the potential link between PAX gene expression in adult tissue and cancer. In addition, we discuss whether persistent PAX gene expression in cancer is favorable or unfavorable.

Overexpression of Pax6 in mouse cornea directly alters corneal epithelial cells: changes in immune function, vascularization, and differentiation

PURPOSE

To assess whether Pax6 functions directly in the cornea, a corneal-preferred promoter was used to overexpress Pax6 specifically in the cornea.

METHODS

Transgenic mice harboring a construct containing mouse Pax6 coding sequences fused downstream of the aldehyde dehydrogenase 3a1 (Aldh3a1) promoter were generated (Pax6 Tg). Pax6 expression was analyzed by Western blot and immunohistochemistry. Eye sections were stained with hematoxylin and eosin, Schiff reagent, and fluorescein, to assess morphologic changes, the presence of goblet cells, and barrier integrity, respectively. Gene expression changes in mildly affected Pax6 Tg corneas were compared to age-matched, wild-type (WT) corneas by microarray analysis and quantitative PCR. Promoter regulation of several differentially expressed genes was examined by monitoring luciferase activity of reporter constructs after cotransfection with Pax6 in COS7 cells.

RESULTS

Corneal overexpression of Pax6 produces an abnormal cornea with altered epithelial cell morphology, neovascularization, immune cell invasion, and a compromised barrier; the lens appeared normal. Major changes in expression of genes involved in immune function, vascularization, and epithelial differentiation occurred in corneas from Pax6 Tg versus WT mice. The keratin (K) profile was dramatically altered in the Pax6 Tg corneas, as were several components of the Wnt signaling pathway. In severely affected Pax6 Tg corneas, K12 was reduced, and Pax6 was redistributed into the cytoplasm. Promoters from the chitinase 3-like 3, Wnt inhibitory factor 1, and fms-related tyrosine kinase 1/soluble VEGF receptor genes were upregulated five-, seven-, and threefold, respectively, by Pax6 in transfected COS7 cells.

CONCLUSIONS

Pax6 functions directly to maintain normal, corneal epithelial cells.

3-D spheroid culture of bone marrow mesenchymal stem cell of rhesus monkey with improved multi-differentiation potential to epithelial progenitors and neuron in vitro

BACKGROUND

Bone mesenchymal stem cells are an attractive source of cells with potential applications in ocular regenerative medicine. However, the low differentiation efficiency in the traditional two-dimensional (2-D) culture system limits their application for clinical therapy. Here, we describe a simple and innovative 3-D culture environment and assess the potential for bone mesenchymal stem cells to differentiate into a variety of cell types in the 3-D system.

METHODS

Bone mesenchymal stem cells of rhesus monkey were isolated and cultured using a density gradient centrifugation and adherence screening method. Cells at passage three were cultured by hanging drop and formed spheres. After 3 days, the spheres were collected and plated onto culture plates and maintained in a floating state by a rotary method for 10 days. Under appropriate induction conditions, the sphere cells were induced into adipocytes, osteoblasts, epithelial progenitors and neuronal cells. Differentiated cells were identified by histochemical staining, immunofluorescence and reverse transcription-polymerase chain reaction.

RESULTS

Bone mesenchymal stem cells of rhesus monkey in the 3-D spheroid culture system acquired improved efficient multipotency for not only adipogenic and osteogeneic differentiation, but ectodermal epithelial progenitor-like cells and neuron-like cells compared with the 2-D culture system.

CONCLUSION

Our 3-D spheroid culture system provides a useful technique to gain insight into the mechanisms of bone mesenchymal stem cells differentiation, and may have potential applications for the treatment of ocular surface and optic nerve disease.

Conditional disruption of mouse Klf5 results in defective eyelids with malformed meibomian glands, abnormal cornea and loss of conjunctival goblet cells

Members of the Krüppel-like family of transcription factors regulate diverse developmental processes in various organs. Previously, we have demonstrated the role of Klf4 in the mouse ocular surface. Herein, we determined the role of the structurally related Klf5, using Klf5-conditional null (Klf5CN) mice derived by mating Klf5-LoxP and Le-Cre mice. Klf5 mRNA was detected as early as embryonic day 12 (E12) in the cornea, conjunctiva and eyelids, wherein its expression increased during development. Though the embryonic eye morphogenesis was unaltered in the Klf5CN mice, postnatal maturation was defective, resulting in smaller eyes with swollen eyelids that failed to separate properly. Klf5CN palpebral epidermis was hyperplastic with 7-9 layers of keratinocytes, compared with 2-3 in the wild type (WT). Klf5CN eyelid hair follicles and sebaceous glands were significantly enlarged, and the meibomian glands malformed. Klf5CN lacrimal glands displayed increased vasculature and large number of infiltrating cells. Klf5CN corneas were translucent, thicker with defective epithelial basement membrane and hypercellular stroma. Klf5CN conjunctiva lacked goblet cells, demonstrating that Klf5 is required for conjunctival goblet cell development. The number of Ki67-positive mitotic cells was more than doubled, consistent with the increased number of Klf5CN ocular surface epithelial cells. Co-ablation of Klf4 and Klf5 resulted in a more severe ocular surface phenotype compared with Klf4CN or Klf5CN, demonstrating that Klf4 and Klf5 share few if any, redundant functions. Thus, Klf5CN mice provide a useful model for investigating ocular surface pathologies involving meibomian gland dysfunction, blepharitis, corneal or conjunctival defects.

Cytokines and signaling pathways regulating matrix metalloproteinase-9 (MMP-9) expression in corneal epithelial cells

Matrix metalloproteinase-9 (MMP-9) is a well-known regulator and effecter of many cellular processes including wound healing. In the cornea, either too much or too little MMP-9 can be detrimental to overall wound repair. We investigated the secreted factors as well as the intracellular signaling pathways and the promoter sequences that mediate this regulation. Primary culture rabbit corneal epithelial cells were treated with various cytokines alone or in different combinations and MMP-9 induction was assessed by gel zymography. Pharmacological inhibitors were used to determine the intracellular signaling pathways induced by the cytokines tested and deletion promoter constructs were created to determine the regions of the MMP-9 promoter involved in the cytokine regulation, thereby assessing the exact transcription factors binding the MMP-9 promoter. We found that two cytokine families, transforming growth factor beta (TGF-beta) and interleukin 1 (IL-1), act additively in an isoform non-specific manner to induce MMP-9 in this cell type. Our data suggest TGF-beta mediated MMP-9 induction may be regulated by the NF-kappaB, Smad3, and JNK pathways, whereas the IL-1beta mediated induction may be regulated by the NF-kappaB and p38 pathways. Inhibition of the p38, NF-kappaB, or JNK pathways significantly reduced, but did not abrogate, basal MMP-9 levels. Inhibition of the ERK pathway did not have an effect on MMP-9 mediated expression in either the treated or untreated co-transfected cells.

Conditional deletion of Cited2 results in defective corneal epithelial morphogenesis and maintenance

Cited2 is an important transcriptional cofactor involved in multiple organ development. Gene profile analysis has identified Cited2 as one of the transcription factors expressed at high levels in adult mouse cornea. To address the function of Cited2 in corneal morphogenesis, we deleted Cited2 in surface ectoderm derived ocular structures including cornea by crossing Cited2-floxed mice with Le-Cre transgenic mice. Cited2(flox/flox);Le-Cre(+) eyes invariably displayed corneal opacity and developed spontaneous corneal neovascularization at older age. Fewer layers of corneal epithelial cells and the absence of cytokeratin 12 (K12) expression featured Cited2 deficient postnatal and adult eyes. Cited2 deficient cornea exhibited impaired healing in response to corneal epithelial debridement by manifesting abnormal histology, lack of K12 expression and corneal neovascularization. Moreover, mechanistic studies suggest that Cited2 may play a role in corneal morphogenesis in part through modulating the expression of Pax6 and Klf4. Collectively, these findings demonstrate a novel function of Cited2 in postnatal corneal morphogenesis and maintenance. Our study will help better understand the molecular mechanisms involved in corneal biology, and more importantly, it may provide a valuable animal model for testing therapeutics in the treatment of corneal disorders, especially blindness as a result of corneal epithelial cell deficiency.

Essential role for Pbx1 in corneal morphogenesis

PURPOSE

The Pbx TALE (three-amino-acid loop extension) homeodomain proteins interact with class 1 Hox proteins, which are master regulators of cell fate decisions. This study was performed to elucidate the role of the Pbx1 TALE protein in the corneal epithelium of mice.

METHODS

Pbx1(f/f) mice were crossed with mice containing Cre recombinase under the control of the K14 promoter. Subsequently, the eyes of these mice were dissected and prepared for histologic or molecular analysis.

RESULTS

Tissue-specific deletion of Pbx1 in the corneal epithelium of mice resulted in corneal dystrophy and clouding that was apparent in newborns and progressively worsened with age. Thickening of the cornea epithelium was accompanied by stromal infiltration with atypical basal cells, severe disorganization of stromal collagen matrix, and loss of corneal barrier function. High epithelial cell turnover was associated with perturbed expression of developmental regulators and aberrant differentiation, suggesting an important function for Pbx1 in determining corneal identity.

CONCLUSIONS

These studies establish an essential role of the Pbx1 proto-oncogene in corneal morphogenesis.

Chronic wound state exacerbated by oxidative stress in Pax6+/- aniridia-related keratopathy

Heterozygosity for the transcription factor PAX6 causes eye disease in humans, characterized by corneal opacity. The molecular aetiology of such disease was investigated using a Pax6+/- mouse model. We found that the barrier function of uninjured Pax6+/- corneas was compromised and that Ca2+-PKC/PLC-ERK/p38 signalling pathways were abnormally activated, mimicking a 'wounded' epithelial state. Using proteomic analysis and direct assay for oxidized proteins, Pax6+/- corneas were found to be susceptible to oxidative stress and they exhibited a wound-healing delay which could be rescued by providing reducing agents such as glutathione. Pax6 protein was oxidized and excluded from the nucleus of stressed corneal epithelial cells, with concomitant loss of corneal epithelial markers and expression of fibroblast/myofibroblast markers. We suggest a chronic wound model for Pax6-related corneal diseases, in which oxidative stress underlies a positive feedback mechanism by depleting nuclear Pax6, delaying wound healing, and activating cell signalling pathways that lead to metaplasia of the corneal epithelium. The study mechanistically links a relatively minor dosage deficiency of a transcription factor with potentially catastrophic degenerative corneal disease.

Identification of candidate Klf4 target genes reveals the molecular basis of the diverse regulatory roles of Klf4 in the mouse cornea

PURPOSE

Krüppel-like factor 4 (Klf4) plays a crucial role in the development and maintenance of the mouse cornea. In the current study, wild-type (WT) and Klf4-conditional null (Klf4CN) corneal gene expression patterns were examined, to gain understanding of the molecular basis of the Klf4CN corneal phenotype.

METHODS

Expression of more than 22,000 genes in 10 WT and Klf4CN corneas was compared by microarrays, analyzed using BRB ArrayTools (National Cancer Institute, Bethesda, MD) and validated by Q-RT-PCR. Transient cotransfections were used to test whether Klf4 activates the aquaporin-3, Aldh3a1, and TKT promoters.

RESULTS

Scatterplot analysis identified 740 and 529 genes up- and downregulated by more than twofold, respectively, in the Klf4CN corneas. Cell cycle activators were upregulated, whereas the inhibitors were downregulated, consistent with the increased Klf4CN corneal epithelial cell proliferation. Desmosomal components were downregulated, consistent with the Klf4CN corneal epithelial fragility. Downregulation of aquaporin-3, detected by microarray, was confirmed by immunoblot and immunohistochemistry. Aquaporin-3 promoter activity was stimulated 7- to 10-fold by cotransfection with pCI-Klf4. The corneal crystallins Aldh3A1 and TKT were downregulated in the Klf4CN cornea, and their respective promoter activities were upregulated 16- and 9-fold by pCI-Klf4 in cotransfections. The expression of epidermal keratinocyte differentiation markers was affected in the Klf4CN cornea. Although the cornea-specific keratin-12 was downregulated, most other keratins were upregulated, suggesting hyperkeratosis.

CONCLUSIONS

Functionally diverse candidate Klf4 target genes were identified, revealing the molecular basis of the diverse aspects of the Klf4CN corneal phenotype. These results establish Klf4 as an important node in the genetic network of transcription factors regulating the corneal homeostasis.

Corneal epithelial stem cells: deficiency and regulation

The corneal epithelium is continuously renewed by a population of stem cells that reside in the corneoscleral junction, otherwise known as the limbus. These limbal epithelial stem cells (LESC) are imperative for corneal maintenance with deficiencies leading to in-growth of conjunctival cells, neovascularisation of the corneal stroma and eventual corneal opacity and visual loss. One such disease that has traditionally been thought to be due to LESC deficiency is aniridia, a pan-ocular congenital eye disease due to mutations in the PAX6 gene. Corneal changes or aniridia related keratopathy (ARK) seen in aniridia are typical of LESC deficiency. However, the pathophysiology behind ARK is still ill defined, with current theories suggesting it may be caused by a deficiency in the stem cell niche and adjacent corneal stroma, with altered wound healing responses also playing a role (Ramaesh et al, International Journal of Biochemistry & Cell Biology 37:547-557, 2005) or abnormal epidermal differentiation of LESC (Li et al., The Journal of Pathology 214:9, 2008). PAX6 is considered the master control gene for the eye and is required for normal eye development with expression continuing in the adult cornea, thus inferring a role for corneal repair and regeneration (Sivak et al., Developments in Biologicals 222:41-54, 2000). Studies of models of Pax6 deficiency, such as the small eyed (sey) mouse, should help to reveal the intrinsic and extrinsic mechanisms involved in normal LESC function.

PAX6 dosage effects on corneal development, growth, and wound healing

The requirement for correct dosage of the transcription factor Pax6 during corneal growth and development was investigated using the Pax6-overexpressing (PAX77) transgenic mouse. Transgenics had a microcornea phenotype due to failure of postnatal growth, associated with reduction in the number of cells layers in the corneal epithelium. Cell cycle progression was monitored using bromodeoxyuridine, p63, cyclin E, and phosphohistone-3 labeling: proliferation rates were higher in PAX77+ than wild-type, without a concomitant increase in apoptosis. Hence, failure of proliferation did not underlie microcornea. PAX77+ corneal epithelia had reduced levels of cytokeratin-12, and exhibited severe wound healing delay that, in contrast to Pax6+/- mice, could not be modulated by exogenous growth factors. PAX77+ lenses showed partial failure of lens fiber differentiation. The data demonstrate that anterior eye development is very sensitive to Pax6 dosage. Although there are similarities between the eye phenotype of Pax6 heterozygotes and overexpressing mice, there are also striking differences. Developmental

Autologous Serum Eyedrops in the Treatment of Aniridic Keratopathy

OBJECTIVE

To study the effect of autologous serum eyedrop application in aniridic keratopathy.

DESIGN

Prospective, consecutive, comparative, interventional case series.

PARTICIPANTS

Twenty-six eyes from 13 patients (7 males and 6 females) with aniridic keratopathy treated with autologous serum eyedrops.

METHODS

All patients underwent a complete ophthalmic examination. The ocular surface examinations included corneal impression cytologic analysis and tear film evaluation. The eyes were divided into 4 groups according to the Mackman classification. Ocular surface photography was used to evaluate the corneal surface and tear film before treatment and every 2 or 3 days until serum drops were stopped. Tear films were evaluated by tear film break-up time (BUT) (normal, 10 seconds or more), Schirmer's test with anesthesia (normal, 10 mm/5 minutes or more), tear meniscus level (normal, 0.5 mm or more), and rose bengal and fluorescein staining pattern of the cornea. Impression cytologic analysis was carried out both before starting the serum eyedrops treatment and a few days after its finalization.

MAIN OUTCOMES MEASURES

Tear film production and stability, corneal epithelialization, and corneal epithelium squamous metaplasia.

RESULTS

There were no local side effects from autologous serum treatment. Clinical manifestations and slit-lamp findings were in relation to the severity of keratopathy. All patients showed a subjective improvement of keratopathy symptoms after the autologous serum applications. The corneal epithelialization, corneal epithelial cell squamous metaplasia, and tear stability improved significantly with the treatment, but visual acuity, regression of vascular pannus, and subepithelial scarring showed only slight improvement with treatment.

CONCLUSIONS

Autologous serum eyedrops improved the aniridic keratopathy in all patients, particularly in patients with light or moderate severity. In these patients, use of autologous serum eyedrops was superior to conventional therapy with substitute tears for improving the ocular surface and subjective comfort.

Down-regulation of Pax6 is associated with abnormal differentiation of corneal epithelial cells in severe ocular surface diseases

Pax6 is the universal master control gene for eye morphogenesis. Other than retina and lens, Pax6 also expressed in the ocular surface epithelium from early gestation until the postnatal stage, in which little is known about the function of Pax6. In this study, corneal pannus tissues from patients with ocular surface diseases such as Stevens-Johnson syndrome (SJS), chemical burn, aniridia and recurrent pterygium were investigated. Our results showed that normal ocular surface epithelial cells expressed Pax6. However, corneal pannus epithelial cells from the above patients showed a decline or absence of Pax6 expression, accompanied by a decline or absence of K12 keratin but an increase of K10 keratin and filaggrin expression. Pannus basal epithelial cells maintained nuclear p63 expression and showed activated proliferation, evidenced by positive Ki67 and K16 keratin staining. On 3T3 fibroblast feeder layers, Pax6 immunostaining was negative in clones generated from epithelial cells harvested from corneal pannus from SJS or aniridia, but positive in those from the normal limbal epithelium; whereas western blots showed that some epithelial clones expanded from pannus retained Pax6 expression. Transient transfection of an adenoviral vector carrying EGFP-Pax6 transgenes into these Pax6(-) clones increased both Pax6 and K12 keratin expression. These results indicate that Pax6 helps to maintain the normal corneal epithelial phenotype postnatally, and that down-regulation of Pax6 is associated with abnormal epidermal differentiation in severe ocular surface diseases. Reintroduction of activation of the Pax6 gene might be useful in treating squamous metaplasia of the ocular surface epithelium.

Coordinating cell proliferation and migration in the lens and cornea

Migration is a complex process for epithelial tissues, because the epithelium must move as an intact sheet to preserve its barrier function. The requirement for structural integrity is met by coupling cell-to-matrix and cell-to-cell adhesion at the cellular level, and by coordinating cell proliferation and cell migration in the tissue as a whole. Proliferation is suppressed at the migrating cell front, allowing cells in this region to remain tightly packed while advancing rapidly. At the same time, proliferation is enhanced in a region behind the advancing cell front to expand the epithelial cell sheet. This review considers the extracellular signals and intracellular signaling pathways that regulate these processes in the lens and corneal epithelium, with emphasis on the commonalities that link these tissues.

PAX6 suppresses the invasiveness of glioblastoma cells and the expression of the matrix metalloproteinase-2 gene

Glioblastoma multiforme (GBM) is the most invasive brain tumor. We have previously reported that the transcription factor PAX6 suppresses the tumorigenecity of GBM cells. By an in vitro Matrigel invasion assay on two GBM cell lines stably transfected with wild-type and/or two mutant forms of PAX6, this study displays the first evidence that PAX6 inhibits the invasiveness of GBM cells and that the DNA-binding domain of PAX6 is required for this function. Using real-time quantitative reverse transcription-PCR (RT-PCR), gelatin zymography, and immunohistochemistry assays, the expression of the gene encoding matrix metalloproteinase-2 (MMP2) in GBM cell lines grown in vitro or in intracranial xenografts in nude mice was shown to be repressed by either stable or adenoviral-mediated overexpression of PAX6. Luciferase promoter assays revealed PAX6-mediated suppression of MMP2 promoter activity. Electrophoretic mobility shift assays showed direct binding of PAX6 to the MMP2 promoter. A significant reverse correlation (P < 0.05) occurred between PAX6 and MMP2 expression quantified by real-time quantitative RT-PCR in 41 GBMs, 43 anaplastic astrocytomas, and 7 adjacent normal tissues. Interestingly, the degree and significance of the reverse correlation increased after excluding astrocytomas, whereas it became insignificant after excluding GBMs. In GBM cells stably transfected with a dominant negative mutant PAX6 showing increased MMP2 expression and invasiveness, knock-down of MMP2 revealed that MMP2 is one of the PAX6 target genes mediating its suppression of invasion. Overall data delineated a mechanism for the suppressive function of PAX6 in GBM: suppression of cell invasion by repressing the expression of proinvasive genes such as MMP2.

Cell surface glycoconjugate abnormalities and corneal epithelial wound healing in the pax6+/- mouse model of aniridia-related keratopathy

PURPOSE

Congenital aniridia due to heterozygosity for Pax6 is associated with ocular surface disease, including keratopathy. This study investigated how defects in glycoconjugate component of the cell surface of Pax6+/- could cause the abnormal cellular migration phenotypes associated with the disease.

METHODS

Immunohistochemistry, lectin-based histochemistry, conventional staining techniques, and proteomic assays were performed on eyes and cultured corneal epithelial cells from wild-type and Pax6+/- littermates. Wild-type cells were manipulated in culture to replicate the glycoconjugate abnormalities found in Pax6 heterozygotes and determine the consequences for wound healing.

RESULTS

Multiple glycoconjugate defects were found in Pax6-mutant cells. Lectin cytochemistry of corneal epithelial cells suggested a partial failure of glycoprotein trafficking. Blocking cell surface carbohydrate moieties in wild-type corneal cells caused wound-healing delays similar to those seen in untreated Pax6+/- cells.

CONCLUSIONS

Alterations to the cell surface glycoconjugate signature of Pax6+/- corneal epithelia restrict the ability of cells to initiate migration in response to wounding. This underlies the observed wound-healing delay in cultured Pax6+/- epithelia.

Conditional deletion of the mouse Klf4 gene results in corneal epithelial fragility, stromal edema, and loss of conjunctival goblet cells

The Krüppel-like transcription factor KLF4 is among the most highly expressed transcription factors in the mouse cornea (B. Norman, J. Davis, and J. Piatigorsky, Investig. Ophthalmol. Vis. Sci. 45:429-440, 2004). Here, we deleted the Klf4 gene selectively in the surface ectoderm-derived structures of the eye (cornea, conjunctiva, eyelids, and lens) by mating Klf4-LoxP mice (J. P. Katz, N. Perreault, B. G. Goldstein, C. S. Lee, P. A. Labosky, V. W. Yang, and K. H. Kaestner, Development 129:2619-2628, 2002) with Le-Cre mice (R. Ashery-Padan, T. Marquardt, X. Zhou, and P. Gruss, Genes Dev. 14:2701-2711, 2000). Klf4 conditional null (Klf4CN) embryos developed normally, and the adult mice were viable and fertile. Unlike the wild type, the Klf4CN cornea consisted of three to four epithelial cell layers; swollen, vacuolated basal epithelial and endothelial cells; and edematous stroma. The conjunctiva lacked goblet cells, and the anterior cortical lens was vacuolated in Klf4CN mice. Excessive cell sloughing resulted in fewer epithelial cell layers in spite of increased cell proliferation at the Klf4CN ocular surface. Expression of the keratin-12 and aquaporin-5 genes was downregulated, consistent with the Klf4CN corneal epithelial fragility and stromal edema, respectively. These observations provide new insights into the role of KLF4 in postnatal maturation and maintenance of the ocular surface and suggest that the Klf4CN mouse is a useful model for investigating ocular surface pathologies such as dry eye, Meesmann's dystrophy, and Steven's-Johnson syndrome.

The roles of calcium signaling and ERK1/2 phosphorylation in a Pax6+/- mouse model of epithelial wound-healing delay

Background

Congenital aniridia caused by heterozygousity at the PAX6 locus is associated with ocular surface disease including keratopathy. It is not clear whether the keratopathy is a direct result of reduced PAX6 gene dosage in the cornea itself, or due to recurrent corneal trauma secondary to defects such as dry eye caused by loss of PAX6 in other tissues. We investigated the hypothesis that reducing Pax6 gene dosage leads to corneal wound-healing defects. and assayed the immediate molecular responses to wounding in wild-type and mutant corneal epithelial cells.

Results

Pax6^+/- mouse corneal epithelia exhibited a 2-hour delay in their response to wounding, but subsequently the cells migrated normally to repair the wound. Both Pax6^+/+ and Pax6^+/- epithelia activated immediate wound-induced waves of intracellular calcium signaling. However, the intensity and speed of propagation of the calcium wave, mediated by release from intracellular stores, was reduced in Pax6^+/- cells. Initiation and propagation of the calcium wave could be largely decoupled, and both phases of the calcium wave responses were required for wound healing. Wounded cells phosphorylated the extracellular signal-related kinases 1/2 (phospho-ERK1/2). ERK1/2 activation was shown to be required for rapid initiation of wound healing, but had only a minor effect on the rate of cell migration in a healing epithelial sheet. Addition of exogenous epidermal growth factor (EGF) to wounded Pax6^+/- cells restored the calcium wave, increased ERK1/2 activation and restored the immediate healing response to wild-type levels.

Conclusion

The study links Pax6 deficiency to a previously overlooked wound-healing delay. It demonstrates that defective calcium signaling in Pax6^+/- cells underlies this delay, and shows that it can be pharmacologically corrected. ERK1/2 phosphorylation is required for the rapid initiation of wound healing. A model is presented whereby minor abrasions, which are quickly healed in normal corneas, transiently persist in aniridic patients, compromising the corneal stroma.

Regulation of the poly(ADP-ribose) polymerase-1 gene expression by the transcription factors Sp1 and Sp3 is under the influence of cell density in primary cultured cells

PARP-1 [poly(ADP-ribose) polymerase-1) is a nuclear enzyme that is involved in several cellular functions, including DNA repair, DNA transcription, carcinogenesis and apoptosis. The activity directed by the PARP-1 gene promoter is mainly dictated through its recognition by the transcription factors Sp1 and Sp3 (where Sp is specificity protein). In the present study, we investigated whether (i) both PARP-1 expression and PARP-1 enzymatic activity are under the influence of cell density in primary cultured cells, and (ii) whether its pattern of expression is co-ordinated with that of Sp1/Sp3 at varying cell densities and upon cell passages. All types of cultured cells expressed PARP-1 in Western blot when grown to sub-confluence. However, a dramatic reduction was observed at post-confluence. Similarly, high levels of Sp1/Sp3 were observed by both Western blot and EMSAs (electrophoretic mobility-shift assays) in sub-confluent,but not post-confluent, cells. Consistent with these results, the promoter of the rPARP-1 (rat PARP-1) gene directed high levels of activity in sub-confluent, but not confluent, cells upon transfection of various CAT (chloramphenicol acetyltransferase)-rPARP-1 promoter constructs into cultured cells. The positive regulatory influence of Sp1 was not solely exerted on the rPARP-1 promoter constructs, as inhibition of endogenous Sp1 expression in HDKs(human dermal keratinocytes) through the transfection of Sp1 RNAi (RNA interference) considerably reduced endogenous hPARP-1 (human PARP-1) expression as well. The reduction in PARP-1 protein expression as cells reached confluence also translated into a corresponding reduction in PARP-1 activity. In addition, expression of both Sp1/Sp3, as well as that of PARP-1,was dramatically reduced as cells were passaged in culture and progressed towards irreversible terminal differentiation. PARP-1 gene expression therefore appears to be co-ordinated with that of Sp1 and Sp3 in primary cultured cells, suggesting that PARP-1 may play some important functions during the proliferative burst that characterizes wound healing.

Targeted deletion of AP-2alpha leads to disruption in corneal epithelial cell integrity and defects in the corneal stroma

PURPOSE

The present study was undertaken to create a conditional knockout of AP-2alpha in the corneal epithelium.

METHODS

A line of mice expressing Cre-recombinase specifically in the early lens placode was crossed with mice in which the AP-2alpha allele is flanked by two loxP sites. The resultant Le-AP-2alpha mutants exhibited a targeted deletion of AP-2alpha in lens placode derivatives, including the differentiating corneal epithelium.

RESULTS

The Le-AP-2alpha mutant mice were viable and had a normal lifespan. The adult corneal epithelium exhibited a variation in the number of stratified epithelial layers, ranging from 2 to 10 cell layers. A substantial decrease in expression of the cell-cell adhesion molecule, E-cadherin, was observed in all layers of the Le-AP-2alpha mutant corneal epithelium. The basement membrane, or Bowman's layer, was thinner in the mutant cornea and in many regions was discontinuous. These defects corresponded with altered distribution of laminin and entactin, and to a lesser degree, type IV collagen. The Le-AP-2alpha mutant cornea also exhibited stromal defects, including disrupted organization of the collagen lamellae and accumulation of fibroblasts beneath the epithelium that showed increased immunoreactivity for proliferating cell nuclear antigen (PCNA), alpha-smooth muscle actin (alpha-SMA), p-Smad2, and TGF-beta2.

CONCLUSIONS

In the absence of AP-2alpha, the corneal epithelium exhibits altered cell adhesion and integrity and defects in its underlying basement membrane. These defects likely caused the alterations in the corneal stroma.

Developmental and cellular factors underlying corneal epithelial dysgenesis in the Pax6+/- mouse model of aniridia

Heterozygosity for a PAX6 deficiency (PAX6+/-) results in low levels of the PAX6 transcription factor and causes aniridia. Corneal changes in aniridia-related keratopathy (ARK) include peripheral pannus and epithelial abnormalities, which eventually result in corneal opacity and contribute to visual loss. The corneal abnormalities of Pax6+/- mice provide an excellent model for the corneal changes seen in PAX6+/- humans. The aim of the present study was to investigate the contributions of different factors (including altered cell proliferation, abnormal epithelial differentiation and incursion of the conjunctival epithelium) that may underlie the pathogenesis of the corneal changes caused by low levels of Pax6 in heterozygous Pax6+/Sey-Neu (Pax6+/-) mice. BrdU incorporation showed enhanced proliferation of Pax6+/- corneal epithelium compared to wild-type controls and analysis of p63 (a marker of high proliferative potential) revealed a slight increase in frequency of p63-positive basal corneal epithelial cells in Pax6+/- mice. Immunohistochemical investigation of K12 (a Pax6-regulated marker of corneal epithelial differentiation) in 2-52-week-old mice showed that K12 expression was delayed and down-regulated in the Pax6+/- corneal epithelium, implying that differentiation of the Pax6+/- corneal epithelium was delayed and abnormal. Goblet cells were identified within the peripheral corneal epithelium of the Pax6+/- eyes, but some were surrounded by cells expressing K12, suggesting they may have arisen in situ in the corneal epithelium. These findings suggest that low levels of Pax6 may be directly responsible for failure or delay of proper differentiation of the corneal epithelial cells, but the proliferative component of the mutant epithelium is probably not impaired. This abnormal differentiation suggests that ARK is not entirely attributable to a limbal stem cell deficiency.

Multipotent stem cells in human corneal stroma

Keratocytes of the corneal stroma secrete a specialized extracellular matrix essential for vision. These quiescent cells exhibit limited capacity for self-renewal and after cell division become fibroblastic, secreting nontransparent tissue. This study sought to identify progenitor cells for human keratocytes. Near the corneal limbus, stromal cells expressed ABCG2, a protein present in many adult stem cells. The ABCG2-expressing cell population was isolated as a side population (SP) by cell sorting after exposure to Hoechst 33342 dye. The SP cells exhibited clonal growth and continued to express ABCG2 and also PAX6, product of a homeobox gene not expressed in adult keratocytes. Cloned SP cells cultured in medium with fibroblast growth factor-2 lost ABCG2 and PAX6 expression and upregulated several molecular markers of keratocytes, including keratocan, aldehyde dehydrogenase 3A1, and keratan sulfate. Cloned corneal SP cells under chondrogenic conditions produced matrix staining with toluidine blue and expressed cartilage-specific markers: collagen II, cartilage oligomatrix protein, and aggrecan. Exposure of cloned SP cells to neurogenic culture medium upregulated mRNA and protein for glial fibrillary acidic protein, neurofilament protein, and beta-tubulin II. These results demonstrate the presence of a population of cells in the human corneal stroma expressing stem cell markers and exhibiting multipotent differentiation potential. These appear to be the first human cells identified with keratocyte progenitor potential. Further analysis of these cells will aid elucidation of molecular mechanisms of corneal development, differentiation, and wound healing. These cells may be a resource for bioengineering of corneal stroma and for cell-based therapeutics.

Evolving concepts on the pathogenic mechanisms of aniridia related keratopathy

Heterozygosity for PAX6 deficiency (PAX6+/-) results in aniridia. Corneal changes in aniridia-related keratopathy (ARK) include corneal vascular pannus formation, conjunctival invasion of the corneal surface, corneal epithelial erosions and epithelial abnormalities, which eventually result in corneal opacity and contribute to visual loss. Corneal changes in aniridia have been attributed to congenital deficiency of corneal limbal stem cells. The aim of this paper is to review the potential mechanisms that may underlie the pathogenesis of aniridia related keratopathy. Current evidence, based on clinical observations and an animal model of aniridia suggest that the proliferative potential of the corneal limbal stem cells may not primarily be impaired. The corneal changes in aniridia may be related to an abnormality within the limbal stem cell niche. The mechanisms underlying progressive corneal pathology in aniridia appear multi-factorial and include: (1) abnormal corneal healing responses secondary to anomalous extracellular matrix metabolism; (2) abnormal corneal epithelial differentiation leading to fragility of epithelial cells; (3) reduction in cell adhesion molecules in the PAX6 heterozygous state, rendering the cells susceptible to natural shearing forces; and (4) conjunctival and corneal changes leading to the presence of cells derived from conjunctiva on the corneal surface.

Inherited eye disease: cause and late effect

Molecular genetics has provided relatively few insights into late-onset eye disorders, but epidemiological data indicate that genetic factors are important in some late-onset eye disorders that cause major health burdens. Much clinical genetic research is based on the belief that developmental and late-onset disorders are not necessarily the result of defects in different genes, but are often caused by different mutations in the same collection of genes. Thus, mutations that either abolish or radically change gene function might cause early-onset disorders, whereas more-subtle changes in gene expression might underlie late-onset diseases. We present arguments and examples that indicate that this principle might be a fruitful guide to investigating the causes of late-onset eye disorders.

Transcription Factors Pax6 and AP-2alpha Interact To Coordinate Corneal Epithelial Repair by Controlling Expression of Matrix Metalloproteinase Gelatinase B

Pax6 is a paired box containing transcription factor that resides at the top of a genetic hierarchy controlling eye development. It continues to be expressed in tissues of the adult eye, but its role in this capacity is unclear. Pax6 is present in the adult corneal epithelium, and we showed that the amount of Pax6 is increased at the migrating front as the epithelium resurfaces the cornea after injury. We also showed that Pax6 controls activity of the transcriptional promoter for the matrix metalloproteinase, gelatinase B (gelB; MMP-9) in cell culture transfection studies. gelB expression is turned on at the migrating epithelial front in the cornea, and it coordinates and effects aspects of epithelial regeneration. We define here two positively acting Pax6 response elements in the gelB promoter. Pax6 binds directly to one of these sites through the paired DNA-binding domain. It binds the second site indirectly by interaction with AP-2alpha, a transcription factor that also exerts control over eye development. Pax6 control of gelB expression was examined in vivo by using a corneal reepithelialization model in mice heterozygous for a Pax6 paired-domain mutation (Sey(+/-)). A reduced Pax6 dosage in these mice resulted in a loss of gelB expression at the migrating epithelial front. This effect was correlated with an increase in inflammation and the rate of reepithelialization, a finding consistent with the phenotype of gelB knockout mice. Together, these data indicate that Pax6 controls activity of the gelB promoter through cooperative interactions with AP-2alpha and support an active role for Pax6 in maintenance and repair of the adult corneal epithelium.

Requirement for Pax6 in corneal morphogenesis: a role in adhesion

The Pax6 transcription factor functions early during embryogenesis to control key steps in brain, pancreas, olfactory and ocular system development. A requirement for Pax6 in proper formation of lens, iris and retina is well documented. By examining the corneas of heterozygous Small eye (SEY) mice, this report shows that Pax6 is also necessary for normal corneal morphogenesis. In particular, the epithelial component of the postnatal and adult SEY (+/-) cornea is thinner owing to a reduction in the number of cell layers, despite a tenfold increase in the proliferative index and no change in TUNEL labeling. Ultrastructural views revealed large gaps between corneal epithelial cells and a change in the appearance of desmosomes, suggesting that adhesion abnormalities contribute to the corneal phenotype of SEY (+/-) mice. Western blot analysis and immunofluorescence showed equivalent amounts and normal localization of E-cadherin in SEY (+/-) corneas, and the actin cytoskeleton appeared normal as judged by phalloidin staining. By contrast, the levels of desmoglein, beta-catenin and gamma-catenin were reduced in the SEY (+/-) cornea. In addition, the amount of keratin-12 mRNA and protein, the major intermediate filament, was reduced in SEY (+/-) corneal epithelium as shown by in situ hybridization and immunohistochemistry. Finally, the SEY (+/-) corneal epithelium adheres less well than wild-type when challenged with gentle rubbing using a microsponge. In conclusion, our results indicate that cellular adhesion is compromised in the SEY (+/-) corneal epithelium and suggests a role for Pax6 in the proper generation and maintenance of the adult cornea.

Positive influence of AP-2alpha transcription factor on cadherin gene expression and differentiation of the ocular surface

The family of transcription factors Activating protein-2 (AP-2) are known to play important roles in numerous developmental events, including those associated with differentiation of stratified epithelia. However, to date, the influence of the AP-2 genes on endogenous gene expression in the stratified epithelia and how this affects differentiation has not been well defined. The following study examines the detailed expression of the AP-2alpha and AP-2beta proteins in the stratified epithelia of the ocular surface, including that in the cornea and developing eyelids. The effect of altered levels of the AP-2alpha gene on ocular surface differentiation was also examined using a corneal epithelial cell line and AP-2alpha chimeric mice. Immunolocalization studies revealed that, while AP-2beta was broadly expressed throughout all cell layers of the stratified corneal epithelium, AP-2alpha expression was confined to cell compartments more basally located. AP-2alpha was also highly expressed in the less differentiated cell layers of the eyelid epidermis. Overexpression of the AP-2alpha gene in the corneal cell line, SIRC, resulted in a dramatic change in cell phenotype including a clumping growth behavior that was distinct from the smooth monolayer of the parent cell line. Accompanying this change was an up-regulation in levels of the cell adhesion molecule, N-cadherin. Examination of the ocular surface of AP-2alpha chimeric mice, derived from a mixed population of AP-2alpha-/- and AP-2alpha+/+, revealed that a down-regulation in E-cadherin expression is correlated with location of the AP-2alpha-/- null cells. Together, these findings demonstrate that AP-2alpha participates in regulating differentiation of the ocular surface through induction in cadherin expression.