A study of the proliferating activity in lens epithelium and the identification of tissue-type stem cells

Aquaporins contribute to vacuoles formation in Nile grass type II diabetic rats

Regulation of ion and water microcirculation within the lens is tightly controlled through aquaporin channels and connexin junctions. However, cataracts can occur when the lens becomes cloudy. Various factors can induce cataracts, including diabetes which is a well-known cause. The most common phenotype of diabetic cataracts is a cortical and/or posterior subcapsular opacity. In addition to the three main types and two subtypes of cataracts, a vacuole formation is frequently observed; however, their origin remains unclear. In this study, we focused on the aquaporins and connexins involved in diabetes-induced cataracts and vacuoles in Nile grass type II diabetes. The results showed that the expression of aquaporin 0 and aquaporin 5 increased, and that of connexin 43 decreased in diabetic rat lenses. Additionally, aquaporin 0 and 5 were strongly localized in peripheral of vacuoles, suggesting that aquaporins are involved in vacuoles formation. Transillumination photography revealed large vacuoles at the tip of the Y-suture in the anterior capsule of the diabetic lens, and several small vacuoles were observed in the posterior capsule. Within the vacuoles, cytoplasmic degradation and aggregation of fibrous material were observed. Our findings suggest that aquaporins are potential candidate proteins for preventing vacuole formation.

Towards the Identification and Characterization of Putative Adult Human Lens Epithelial Stem Cells

The anterior lens epithelium has the ability to differentiate into lens fibres throughout its life. The present study aims to identify and functionally characterize the adult stem cells in the human lens epithelium. Whole mounts of lens epithelium from donor eyes (normal/cataract) were immunostained for SOX2, gap junction protein alpha 1 (GJA1), PAX6, α, β and γ-crystallins, followed by a confocal analysis. The functional property of adult stem cells was analysed by their sphere forming ability using cultured lens epithelial cells from different zones. Based on marker expression, the lens epithelium was divided into four zones: the central zone, characterized by a small population of PAX6+, GJA1-, β-crystallin- and γ-crystallin- cells; the germinative zone, characterized by PAX6+, GJA1+, β-crystallin- and γ-crystallin-; the transitional zone, characterized by PAX6+, GJA1+, β-crystallin+ and γ-crystallin-; and the equatorial zone, characterized by PAX6+/-, GJA1+, β-crystallin+, and γ-crystallin+ cells. The putative lens epithelial stem cells identified as SOX2+ and GJA1 membrane expression negative cells were located only in the central zone (1.89 ± 0.84%). Compared to the other zones, a significant percentage of spheres were identified in the central zone (1.68 ± 1.04%), consistent with the location of the putative adult lens epithelial stem cells. In the cataractous lens, an absence of SOX2 expression and a significant reduction in sphere forming ability (0.33 ± 0.11%) were observed in the central zone. The above findings confirmed the presence of putative stem cells in the central zone of the adult human lens epithelium and indicated their probable association with cataract development.

Single-cell RNA sequencing reveals new subtypes of lens superficial tissue in humans

Although the cell atlas of the human ocular anterior segment of the human eye was revealed by single-nucleus RNA sequencing, whether subtypes of lens stem/progenitor cells exist among epithelial cells and the molecular characteristics of cell differentiation of the human lens remain unclear. Single-cell RNA sequencing is a powerful tool to analyse the heterogeneity of tissues at the single cell level, leading to a better understanding of the processes of cell differentiation. By profiling 18,596 cells in human lens superficial tissue through single-cell sequencing, we identified two subtypes of lens epithelial cells that specifically expressed C8orf4 and ADAMTSL4 with distinct spatial localization, a new type of fibre cells located directly adjacent to the epithelium, and a subpopulation of ADAMTSL4+ cells that might be lens epithelial stem/progenitor cells. We also found two trajectories of lens epithelial cell differentiation and changes of some important genes during differentiation.

The lens epithelium as a major determinant in the development, maintenance, and regeneration of the crystalline lens

The crystalline lens is a transparent and refractive biconvex structure formed by lens epithelial cells (LECs) and lens fibers. Lens opacity, also known as cataracts, is the leading cause of blindness in the world. LECs are the principal cells of lens throughout human life, exhibiting different physiological properties and functions. During the embryonic stage, LECs proliferate and differentiate into lens fibers, which form the crystalline lens. Genetics and environment are vital factors that influence normal lens development. During maturation, LECs help maintain lens homeostasis through material transport, synthesis and metabolism as well as mitosis and proliferation. If disturbed, this will result in loss of lens transparency. After cataract surgery, the repair potential of LECs is activated and the structure and transparency of the regenerative tissue depends on postoperative microenvironment. This review summarizes recent research advances on the role of LECs in lens development, homeostasis, and regeneration, with a particular focus on the role of cholesterol synthesis (eg., lanosterol synthase) in lens development and homeostasis maintenance, and how the regenerative potential of LECs can be harnessed to develop surgical strategies and improve the outcomes of cataract surgery (Fig. 1). These new insights suggest that LECs are a major determinant of the physiological and pathological state of the lens. Further studies on their molecular biology will offer possibility to explore new approaches for cataract prevention and treatment.

Methodologies to unlock the molecular expression and cellular structure of ocular lens epithelial cells

The transparent ocular lens in the anterior chamber of the eye is responsible for fine focusing of light onto the retina. The lens is entirely cellular with bulk of the tissue composed of fiber cells, and the anterior hemisphere of the lens is covered by a monolayer of epithelial cells. Lens epithelial cells are important for maintaining fiber cell homeostasis and for continual growth of the lens tissue throughout life. Cataracts, defined as any opacity in the lens, remain the leading cause of blindness in the world. Following cataract surgery, lens epithelial cells can undergo a process of epithelial-to-mesenchymal transition (EMT), leading to secondary cataracts due to posterior capsular opacification (PCO). Since the epithelial cells make up only a small fraction of the lens, specialized techniques are required to study lens epithelial cell biology and pathology. Studies using native lens epithelial cells often require pooling of samples to obtain enough cells to make sufficient samples for traditional molecular biology techniques. Here, we provide detailed protocols that enable the study of native mouse lens epithelial cells, including immunostaining of the native lens epithelium in flat mounts, extraction of RNA and proteins from pairs of lens epithelial monolayers, and isolation of lens epithelial cells for primary culture. These protocols will enable researchers to gain better insight on representative molecular expression and cellular structure of lens epithelial cells. We also provide comparative data between native, primary culture, and immortalized lens epithelial cells and discuss the advantages and disadvantages of each technique presented.

Iris-derived induced pluripotent stem cells that express GFP in all somatic cells of mice and differentiate into functional retinal neurons

When regenerated tissue is generated from induced pluripotent stem cells (iPSCs), it is necessary to track and identify the transplanted cells. Fluorescently-labeled iPSCs synthesize a fluorescent substance that is easily tracked. However, the expressed protein should not affect the original genome sequence or pluripotency. To solve this problem, we created a cell tool for basic research on iPSCs. Iris tissue-derived cells from GFP fluorescence-expressing mice (GFP-DBA/2 mice) were reprogrammed to generate GFP mouse iris-derived iPSCs (M-iris GFP iPSCs). M-iris GFP iPSCs expressed cell markers characteristic of iPSCs and showed pluripotency in differentiating into the three germ layers. In addition, when expressing GFP, the cells differentiated into functional recoverin- and calbindin-positive cells. Thus, this cell line will facilitate future studies on iPSCs.

Lens Epithelial Cell Removal in Routine Phacoemulsification: Is It Worth the Bother?

PURPOSE

To review the literature on crystalline lens epithelial cell (LEC) removal in routine phacoemulsification and determine whether it should be incorporated as part of a surgeon's standard technique.

DESIGN

Perspective.

METHODS

Expert commentary with video demonstrations on techniques of removal of LECs and associated potential complications. Discussion incorporates the importance of LEC removal, a review of techniques to prevent posterior capsular opacification (PCO), and the effects of intraocular lens design on LEC proliferation and PCO.

RESULTS

The evidence suggests that LEC removal should be routinely performed as it can be carried out safely and with considerable short- and long-term benefits for patients. With effective cleanup, there is reduced anterior capsule opacification, fibrosis, and decentration of the capsular bag as well as reduced rates of posterior capsular opacification. Techniques for removal are easy to learn, with very low complication rates, and can reduce the risk of the long-term need for technically complex procedures such as intraocular lens explantation.

CONCLUSIONS

LEC removal from both the anterior and posterior capsule is part of a continuous, incremental improvement of cataract surgery and should be introduced to ophthalmology trainees during their formative years as part of their regular cataract surgery armamentarium.

Formation of three‑dimensional cell aggregates expressing lens‑specific proteins in various cultures of human iris‑derived tissue cells and iPS cells

Induced pluripotent stem (iPS) cells are widely used as a research tool in regenerative medicine and embryology. In studies related to lens regeneration in the eye, iPS cells have been reported to differentiate into lens epithelial cells (LECs); however, to the best of our knowledge, no study to date has described their formation of three-dimensional cell aggregates. Notably, in vivo studies in newts have revealed that iris cells in the eye can dedifferentiate into LECs and regenerate a new lens. Thus, as basic research on lens regeneration, the present study investigated the differentiation of human iris tissue-derived cells and human iris tissue-derived iPS cells into LECs and their formation of three-dimensional cell aggregates using a combination of two-dimensional culture, static suspension culture and rotational suspension culture. The results revealed that three-dimensional cell aggregates were formed and differentiated into LECs expressing αA-crystallin, a specific marker protein for LECs, suggesting that the cell-cell interaction facilitated by cell aggregation may have a critical role in enabling highly efficient differentiation of LECs. However, the present study was unable to achieve transparency in the cell aggregates; therefore, we aim to continue to investigate the degradation of organelles and other materials necessary to make the interior of the formed cell aggregates transparent. Furthermore, we aim to expand on our current work to study the regeneration of the lens and ciliary body as a whole in vitro, with the aim of being able to restore focusing function after cataract surgery.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Lens regeneration: scientific discoveries and clinical possibilities

In the process of exploring new methods for cataract treatment, lens regeneration is an ideal strategy for effectively restoring accommodative vision and avoiding postoperative complications and has great clinical potential. Lens regeneration, which is not a simple repetition of lens development, depends on the complex regulatory network comprising the FGF, BMP/TGF-β, Notch, and Wnt signaling pathways. Current research mainly focuses on in situ and in vitro lens regeneration. On the one hand, the possibility of the autologous stem cell in situ regeneration of functional lenses has been confirmed; on the other hand, both embryonic stem cells and induced pluripotent stem cells have been induced into lentoid bodies in vitro which are similar to the natural lens to a certain extent. This article will briefly summarize the regulatory mechanisms of lens development, describe the recent progress of lens regeneration, explore the key molecular signaling pathways, and, more importantly, discuss the prospects and challenges of their clinical applications to provide reference for clinical transformations.

Effect of a Lens Protein in Low-Temperature Culture of Novel Immortalized Human Lens Epithelial Cells (iHLEC-NY2)

The prevalence of nuclear cataracts was observed to be significantly higher among residents of tropical and subtropical regions compared to those of temperate and subarctic regions. We hypothesized that elevated environmental temperatures may pose a risk of nuclear cataract development. The results of our in silico simulation revealed that in temperate and tropical regions, the human lens temperature ranges from 35.0 °C to 37.5 °C depending on the environmental temperature. The medium temperature changes during the replacement regularly in the cell culture experiment were carefully monitored using a sensor connected to a thermometer and showed a decrease of 1.9 °C, 3.0 °C, 1.7 °C, and 0.1 °C, after 5 min when setting the temperature of the heat plate device at 35.0 °C, 37.5 °C, 40.0 °C, and 42.5 °C, respectively. In the newly created immortalized human lens epithelial cell line clone NY2 (iHLEC-NY2), the amounts of RNA synthesis of αA crystallin, protein expression, and amyloid β (Aβ)1-40 secreted into the medium were increased at the culture temperature of 37.5 °C compared to 35.0 °C. In short-term culture experiments, the secretion of Aβ1-40 observed in cataracts was increased at 37.5 °C compared to 35.0 °C, suggesting that the long-term exposure to a high-temperature environment may increase the risk of cataracts.

Long-term myofibroblast persistence in the capsular bag contributes to the late spontaneous in-the-bag intraocular lens dislocation

Late spontaneous in-the-bag intraocular lens (IOL) dislocation is a complication presenting 6 months or later after cataract surgery. We aimed to characterize the cells in the lens capsules (LCs) of 18 patients with spontaneous late in-the-bag IOL dislocation. Patients' average age was 82.6 ± 1.5 years (range 72-98), and most of them had pseudoexfoliation syndrome (PEX). Cells from the LCs were positive for myofibroblast (αSMA), proliferation (Ki-67, PCNA), early lens development/lens progenitor (SOX2, PAX6), chemokine receptor (CXCR4), and transmembrane (N-cadherin) markers, while negative for epithelial (E-cadherin) marker. Moreover, the cells produced abundant fibronectin, type I and type V collagen in the nearby extracellular matrix (ECM). During ex vivo cultivation of dislocated IOL-LCs in toto, the cells proliferated and likely migrated onto the IOL's anterior side. EdU proliferation assay confirmed the proliferation potential of the myofibroblasts (MFBs) in dislocated IOL-LCs. Primary cultured lens epithelial cells/MFBs isolated from the LC of dislocated IOLs could induce collagen matrix contraction and continuously proliferated, migrated, and induced ECM remodeling. Taken together, this indicates that long-lived MFBs of dislocated IOLs might contribute to the pathogenic mechanisms in late in-the-bag IOL dislocation.

A Proteomic Approach for Understanding the Mechanisms of Delayed Corneal Wound Healing in Diabetic Keratopathy Using Diabetic Model Rat

Diabetes mellitus is a widespread metabolic disorder, and long-term hyperglycemia in diabetics leads to diabetic keratopathy. In the present study, we used a shotgun liquid chromatography/mass spectrometry-based global proteomic approach using the cornea of streptozotocin-induced diabetic (STZ) rats to examine the mechanisms of delayed corneal wound healing in diabetic keratopathy. Applying a label-free quantitation method based on spectral counting, we identified 188 proteins that showed expression changes of >2.0-fold in the cornea of STZ rats. In particular, the level of lumican expression in the cornea of STZ rats was higher than that of the normal rats. In the cornea of the normal rat, the expression level of lumican was elevated during the wound healing process, and it returned to the same expression level as before cornea injury after the wound was healed completely. On the other hand, a high expression level of lumican in the cornea of STZ rats was still maintained even after the wound was healed completely. In addition, adhesion deficiency in corneal basal cells and Bowman’s membrane was observed in the STZ rat. Thus, abnormally overexpressed lumican may lead to adhesion deficiency in the cornea of STZ rats.

Therapeutic Effect of Cilostazol Ophthalmic Nanodispersions on Retinal Dysfunction in Streptozotocin-Induced Diabetic Rats

We previously prepared ophthalmic formulations containing cilostazol (CLZ) nanoparticles by bead mill methods (CLZ_nano), and found that instillation of CLZ_nano into rat eyes supplies CLZ into the retina. In this study, we investigated changes in the electroretinograms (ERG) of streptozotocin-induced diabetic rats (STZ rats), a model of diabetes mellitus. In addition, we demonstrated that dispersions containing CLZ nanoparticles attenuate changes in the ERG of STZ rats. The instillation of CLZ_nano had no effect on body weight or plasma glucose and insulin levels. Furthermore, no corneal toxicity was observed in the in vivo study using STZ rats. The a-wave and b-wave levels in addition to oscillatory potentials (OP) amplitude decreased in STZ rats two weeks after the injection of streptozotocin, with the instillation of CLZ_nano attenuating these decreases. In addition, the level of vascular endothelial growth factor (VEGF) in the retinas of STZ rats was 9.26-fold higher than in in normal rats, with this increase also prevented by the instillation of CLZ_nano Thus, we have found that a-wave and b-wave levels in addition to OP amplitude are decreased in rats following the injection of excessive streptozotocin. Furthermore, the retinal disorders associated with diabetes mellitus are attenuated by the instillation of CLZ_nano. These findings provide significant information that can be used to design further studies aimed at developing anti-diabetic retinopathy drugs.

The lens growth process

The factors that regulate the size of organs to ensure that they fit within an organism are not well understood. A simple organ, the ocular lens serves as a useful model with which to tackle this problem. In many systems, considerable variance in the organ growth process is tolerable. This is almost certainly not the case in the lens, which in addition to fitting comfortably within the eyeball, must also be of the correct size and shape to focus light sharply onto the retina. Furthermore, the lens does not perform its optical function in isolation. Its growth, which continues throughout life, must therefore be coordinated with that of other tissues in the optical train. Here, we review the lens growth process in detail, from pioneering clinical investigations in the late nineteenth century to insights gleaned more recently in the course of cell and molecular studies. During embryonic development, the lens forms from an invagination of surface ectoderm. Consequently, the progenitor cell population is located at its surface and differentiated cells are confined to the interior. The interactions that regulate cell fate thus occur within the obligate ellipsoidal geometry of the lens. In this context, mathematical models are particularly appropriate tools with which to examine the growth process. In addition to identifying key growth determinants, such models constitute a framework for integrating cell biological and optical data, helping clarify the relationship between gene expression in the lens and image quality at the retinal plane.

Effect of methotrexate exposure at middle gestation on the inner plate of the ocular cup and lens in the rat fetus

Pregnant rats were treated intraperitoneally with a single dose of methotrexate (MTX) 90 mg/kg on gestation day (GD) 13, and fetal eyeballs were examined time-dependently from GD 13.5 to 15.5. Throughout the experimental period, the inner plate of the ocular cup in the MTX group was significantly thinner than that in the control group. In the inner plate of the ocular cup on GD 15 and 15.5, whereas a developed ganglion cell layer was observed in the control group, the ganglion cell layer in the MTX group was undeveloped and indistinguishable. Disturbance of the arrangement of lens fiber cells, narrowing of the hyaloid cavity of the optic cup, and hypoplasia of optic nerve fibers were observed in the MTX group on GD 15 and 15.5. Increase of pyknosis and decrease of mitosis were induced in the optic cup and the lens epithelium of the MTX group. In the inner plate of the optic cup and the lens epithelium of the MTX group, the cleaved caspase-3- and TUNEL-positive rates increased significantly throughout the experimental period. The phospho-histone H3-positive rate in the inner plate of the optic cup decreased significantly from GD 13.5 to 14.5, and it recovered on GD 15. On the other hand, the phospho-histone H3-positive rate in the lens epithelium decreased significantly throughout the experimental period. These results suggested that optic tissue on GD 13 in rats was sensitive to MTX.

Effects of senescent lens epithelial cells on the severity of age-related cortical cataract in humans: A case-control study

The aging of lens progenitor cell has been repeatedly proposed to play a key role in age-related cataracts (ARCs), but the mechanism is far from being understood. The present study aims to investigate the relationship between aging of lens progenitor/epithelial cells and the 4 subtypes of ARCs in humans.Lens capsules, which were collected from ARC patients during surgery, were divided into 3 groups according to the age of patients (50-60, 60-80, and >80 years). The expressions of lens progenitor cell-related markers Sox2, Abcg2, and Ki67 were first examined in human lens epithelial cells (HLECs) in situ. Then, the percentage of senescent and SA-β-gal HLECs isolated from lens capsules were quantified. Finally, the potential relationships between the percentage of senescent (and SA-β-gal) HLECs and the severity of ARCs were analyzed.Ki67, Sox2, and Abcg2 HLECs in lens capsules were clearly more abundant in young people than in patients older than 50 years, and they were almost absent in patients older than 60 years. The percentage of primary HLECs with aging morphology increased with age, consistent with the results of SA-β-gal primary HLECs. Only cortical cataract classification was found to be strongly related to the percentage of SA-β-gal and senescent HLECs.Our study gave the initial evidence on the dynamical change of lens stem/progenitor cells in human lens capsule with age and suggested that lens progenitor/epithelial cell aging is important in the severity of cortical cataracts.

Importance of the stem cell microenvironment for ophthalmological cell-based therapy

Cell therapy is a promising treatment for diseases that are caused by cell degeneration or death. The cells for clinical transplantation are usually obtained by culturing healthy allogeneic or exogenous tissue in vitro. However, for diseases of the eye, obtaining the adequate number of cells for clinical transplantation is difficult due to the small size of tissue donors and the frequent needs of long-term amplification of cells in vitro, which results in low cell viability after transplantation. In addition, the transplanted cells often develop fibrosis or degrade and have very low survival. Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPS) are also promising candidates for cell therapy. Unfortunately, the differentiation of ESCs can bring immune rejection, tumorigenicity and undesired differentiated cells, limiting its clinical application. Although iPS cells can avoid the risk of immune rejection caused by ES cell differentiation post-transplantation, the low conversion rate, the risk of tumor formation and the potentially unpredictable biological changes that could occur through genetic manipulation hinder its clinical application. Thus, the desired clinical effect of cell therapy is impaired by these factors. Recent research findings recognize that the reason for low survival of the implanted cells not only depends on the seeded cells, but also on the cell microenvironment, which determines the cell survival, proliferation and even reverse differentiation. When used for cell therapy, the transplanted cells need a specific three-dimensional structure to anchor and specific extra cellular matrix components in addition to relevant cytokine signaling to transfer the required information to support their growth. These structures present in the matrix in which the stem cells reside are known as the stem cell microenvironment. The microenvironment interaction with the stem cells provides the necessary homeostasis for cell maintenance and growth. A large number of studies suggest that to explore how to reconstruct the stem cell microenvironment and strengthen its combination with the transplanted cells are key steps to successful cell therapy. In this review, we will describe the interactions of the stem cell microenvironment with the stem cells, discuss the importance of the stem cell microenvironment for cell-based therapy in ocular diseases, and introduce the progress of stem cell-based therapy for ocular diseases.

Quantitative analysis of injury-induced anterior subcapsular cataract in the mouse: a model of lens epithelial cells proliferation and epithelial-mesenchymal transition

The mouse lens capsular injury model has been widely used in investigating the mechanisms of anterior subcapsular cataract (ASC) and posterior capsule opacification (PCO), and evaluating the efficacy of antifibrotic compounds. Nevertheless, there is no available protocol to quantitatively assess the treatment outcomes. Our aim is to describe a new method that can successfully quantify the wound and epithelial-mesenchymal transition (EMT) markers expression in vivo. In this model, lens anterior capsule was punctured with a hypodermic needle, which triggered lens epithelial cells (LECs) proliferation and EMT rapidly. Immunofluorescent staining of injured lens anterior capsule whole-mounts revealed the formation of ASC and high expression of EMT markers in the subcapsular plaques. A series of sectional images of lens capsule were acquired from laser scanning confocal microscopy (LSCM) three-dimensional (3D) scanning. Using LSCM Image Browser software, we can not only obtain high resolution stereo images to present the spatial structures of ASC, but also quantify the subcapsular plaques and EMT markers distribution sucessfully. Moreover, we also demonstrated that histone deacetylases (HDACs) inhibitor TSA significantly prevented injury-induced ASC using this method. Therefore, the present research provides a useful tool to study ASC and PCO biology as well as the efficacy of new therapies.

Ectopic activation of Wnt/β-catenin signaling in lens fiber cells results in cataract formation and aberrant fiber cell differentiation

The Wnt/β-catenin signaling pathway controls many processes during development, including cell proliferation, cell differentiation and tissue homeostasis, and its aberrant regulation has been linked to various pathologies. In this study we investigated the effect of ectopic activation of Wnt/β-catenin signaling during lens fiber cell differentiation. To activate Wnt/β-catenin signaling in lens fiber cells, the transgenic mouse referred to as αA-CLEF was generated, in which the transactivation domain of β-catenin was fused to the DNA-binding protein LEF1, and expression of the transgene was controlled by αA-crystallin promoter. Constitutive activation of Wnt/β-catenin signaling in lens fiber cells of αA-CLEF mice resulted in abnormal and delayed fiber cell differentiation. Moreover, adult αA-CLEF mice developed cataract, microphthalmia and manifested downregulated levels of γ-crystallins in lenses. We provide evidence of aberrant expression of cell cycle regulators in embryonic lenses of αA-CLEF transgenic mice resulting in the delay in cell cycle exit and in the shift of fiber cell differentiation to the central fiber cell compartment. Our results indicate that precise regulation of the Wnt/β-catenin signaling activity during later stages of lens development is essential for proper lens fiber cell differentiation and lens transparency.

Activation of the hedgehog signaling pathway in the developing lens stimulates ectopic FoxE3 expression and disruption in fiber cell differentiation

PURPOSE

The signaling pathways and transcriptional effectors responsible for directing mammalian lens development provide key regulatory molecules that can inform our understanding of human eye defects. The hedgehog genes encode extracellular signaling proteins responsible for patterning and tissue formation during embryogenesis. Signal transduction of this pathway is mediated through activation of the transmembrane proteins smoothened and patched, stimulating downstream signaling resulting in the activation or repression of hedgehog target genes. Hedgehog signaling is implicated in eye development, and defects in hedgehog signaling components have been shown to result in defects of the retina, iris, and lens.

METHODS

We assessed the consequences of constitutive hedgehog signaling in the developing mouse lens using Cre-LoxP technology to express the conditional M2 smoothened allele in the embryonic head and lens ectoderm.

RESULTS

Although initial lens development appeared normal, morphological defects were apparent by E12.5 and became more significant at later stages of embryogenesis. Altered lens morphology correlated with ectopic expression of FoxE3, which encodes a critical gene required for human and mouse lens development. Later, inappropriate expression of the epithelial marker Pax6, and as well as fiber cell markers c-maf and Prox1 also occurred, indicating a failure of appropriate lens fiber cell differentiation accompanied by altered lens cell proliferation and cell death.

CONCLUSIONS

Our findings demonstrate that the ectopic activation of downstream effectors of the hedgehog signaling pathway in the mouse lens disrupts normal fiber cell differentiation by a mechanism consistent with a sustained epithelial cellular developmental program driven by FoxE3.

Diverse roles of Eph/ephrin signaling in the mouse lens

Recent genetic studies show that the Eph/ephrin bidirectional signaling pathway is associated with both congenital and age-related cataracts in mice and humans. We have investigated the molecular mechanisms of cataractogenesis and the roles of ephrin-A5 and EphA2 in the lens. Ephrin-A5 knockout (-/-) mice often display anterior polar cataracts while EphA2(-/-) lenses show very mild cortical or nuclear cataracts at weaning age. The anterior polar cataract of ephrin-A5(-/-) lenses is correlated with multilayers of aberrant cells that express alpha smooth muscle actin, a marker for mesenchymal cells. Only select fiber cells are altered in ephrin-A5(-/-) lenses. Moreover, the disruption of membrane-associated β-catenin and E-cadherin junctions is observed in ephrin-A5(-/-) lens central epithelial cells. In contrast, EphA2(-/-) lenses display normal monolayer epithelium while disorganization is apparent in all lens fiber cells. Immunostaining of ephrin-A5 proteins, highly expressed in lens epithelial cells, were not colocalized with EphA2 proteins, mainly expressed in lens fiber cells. Besides the previously reported function of ephrin-A5 in lens fiber cells, this work suggests that ephrin-A5 regulates β-catenin signaling and E-cadherin to prevent lens anterior epithelial cells from undergoing the epithelial-to-mesenchymal transition while EphA2 is essential for controlling the organization of lens fiber cells through an unknown mechanism. Ephrin-A5 and EphA2 likely interacting with other members of Eph/ephrin family to play diverse functions in lens epithelial cells and/or fiber cells.

Aldose reductase-mediated induction of epithelium-to-mesenchymal transition (EMT) in lens

Cataract is a key factor in the morbidity associated with diabetes. While the pathogenesis of diabetic cataract formation is poorly understood, previous research has identified aldose reductase (ALR2) as a key player. To elucidate a potential role for this enzyme in diabetic cataract formation, we created a series of transgenic mice designed for expression of human ALR2 (AKR1B1) in epithelial and outer cortical fiber cells of the lens. One of the founder lines, designated PAR39, developed an early onset cataract that involved formation of a plaque of cells at the anterior aspect of the lens. These cells appear to separate from the anterior epithelium and undergo a dramatic change that is reminiscent of the epithelial to mesenchymal transition (EMT). We characterized this phenotype in the PAR39 strain by examining rates of cell proliferation and by immunostaining for markers of EMT. Incorporation of the thymidine analog bromodeoxyuridine (BrdU) was used to estimate cell proliferation in two functional areas of the lens epithelium: the mitotically active germinative zone (GZ) and the less proliferative center zone (CZ). Staining cell nuclei with diamido 4',6-diamidino-2-phenylindole (DAPI) was used to establish a total cell count in the demarcated areas. Lens epithelium in PAR39 transgenic mice demonstrated a decrease in the percentage of BrdU/DAPI staining within the GZ as compared to nontransgenic littermate controls (8.1% vs. 10.9%). A similar decrease in BrdU/DAPI was observed in the CZ (0.6% compared to 3.3%). However, cell density was greater within the GZ of PAR39 mice as compared with nontransgenic controls, while it was not significantly different in the CZ among the two groups. Furthermore, cells associated with the epithelial plaque did not stain positive for BrdU, but were strongly positive for alpha-smooth muscle actin, a classical marker for EMT. These findings suggest that ALR2 over-expression is associated with an alteration in the balance between proliferation and apoptosis of epithelial cells in the mouse lens, and that cells associated with epithelial plaques in the PAR39 lens have features in common with cells undergoing EMT.

Basic study of retinal stem/progenitor cell separation from mouse iris tissue

We described the possibility of retinal regeneration using a novel and efficient technique for culturing and separating retinal stem/progenitor cells from iris tissue. Immunohistochemical staining of adult agouti mouse iris tissue revealed the presence of nestin/low-affinity neurotrophin receptor p75 (p75(NTR))-positive cells on the endothelium camerae anterioris side. Cultured mouse iris-derived cells contained little or no melanin and were found to be positive for nestin. Most nestin-positive cells were analyzed for the coexpression of p75(NTR) as a cell membrane protein. When the p75(NTR) was used as a marker to sort the cells, we obtained a dense population of nestin-positive cells. Furthermore, the nestin/p75(NTR)-positive cells were able to differentiate into neural retina cells. Thus, this culture and separation technique is useful for obtaining retinal stem/progenitor cells from adult mouse iris tissue and for the efficient production of neural retina cells.

Differentiation of adipose-derived stromal vascular fraction culture cells into chondrocytes using the method of cell sorting with a mesenchymal stem cell marker

The incidence of arthritic diseases is rapidly increasing in most advanced countries. Articular cartilage, which is the most important tissue in the joint, consists of chondrocytes and abundant extracellular matrix, including aggrecan, and shows poor self-repair. We studied the potential of stem cells in mouse subcutaneous adipose tissue as a source of cells to regenerate cartilage tissue. Analysis of adipose-derived stromal vascular fraction culture cells (ADSVFs) using mesenchymal stem cell markers showed that CD90-positive cells accounted for 93.8%, CD105-positive cells for 68.5%, and p75 neurotrophin receptor (p75NTR, CD271)-positive cells for 36.1%. These results indicate that cells positive for mesenchymal stem cell markers are present in ADSVFs. The CD105-positive or -negative cells were isolated from ADSVFs by magnetic cell separation (MACS), and the efficiency of differentiation into chondrocytes was compared with using three methods of pellet method, gel-coating method, and gel-embedding sheet method. Using the CD105-positive cells and the gel-embedding sheet method, aggrecan mRNA was detected about three times higher than pellet and gel-coating methods. The above data suggest that ADSVFs could be differentiated into chondrocyte-like cells in the gel-embedding sheet method and could be useful in regenerative medicine to treat cartilage defects or cartilage degenerative disease. The use of cells sorted by mesenchymal stem cell markers from adipose tissue would gain position in the repair of cartilage tissue.