Zeb1 represses Mitf and regulates pigment synthesis, cell proliferation, and epithelial morphology

Common lizard primary oviduct cell culture: A model system for the genetic and cellular basis of oviparity and viviparity

Reproduction by egg-laying (oviparity) or live-bearing (viviparity) is a genetically determined trait fundamental to the biology of amniotes. Squamates are an emerging model for the genetics of reproductive mode yet lack cell culture models valuable for exploring molecular mechanisms. Here, we report a novel primary culture model for reproductive biology: cell cultures derived from the oviduct tissues (infundibulum, uterus and vagina) of oviparous and viviparous common lizards (Lacertidae: Zootoca vivipara). We maintained and expanded these cultures for over 100 days, including repeated subculturing and successful revival of cryopreserved cells. Immunocytochemical investigation suggested expression of both epithelial and fibroblast-like proteins, and RNA sequencing of cultured cells as compared to in vivo oviduct tissue showed changes in gene expression in response to the cell culture environment. Despite this, we confirmed the maintenance of distinct gene expression patterns in viviparous and oviparous cells after 60+ days of cell culture, finding 354 differentially expressed genes between viviparous and oviparous cells. Furthermore, we confirmed the expression of 15 viviparity-associated candidate genes in cells maintained for 60+ days in culture. Our study demonstrates the feasibility and utility of oviduct cell culture for molecular analysis of reproductive mode and provides a tool for future genetic experiments.

Recent Achievements in the Heterogeneity of Mammalian and Human Retinal Pigment Epithelium: In Search of a Stem Cell

Retinal pigment epithelium (RPE) cells are important fundamentally for the development and function of the retina. In this regard, the study of the morphological and molecular properties of RPE cells, as well as their regenerative capabilities, is of particular importance for biomedicine. However, these studies are complicated by the fact that, despite the external morphological similarity of RPE cells, the RPE is a population of heterogeneous cells, the molecular genetic properties of which have begun to be revealed by sequencing methods only in recent years. This review carries out an analysis of the data from morphological and molecular genetic studies of the heterogeneity of RPE cells in mammals and humans, which reveals the individual differences in the subpopulations of RPE cells and the possible specificity of their functions. Particular attention is paid to discussing the properties of "stemness," proliferation, and plasticity in the RPE, which may be useful for uncovering the mechanisms of retinal diseases associated with pathologies of the RPE and finding new ways of treating them.

The First Homozygote Mutation c.499G>T (Asp167Tyr) in the RPE65 Gene Encoding Retinoid Isomerohydrolase Causing Retinal Dystrophy

RPE65, an abundant membrane-associated protein present in the retinal pigment epithelium (RPE), is a vital retinoid isomerase necessary for regenerating 11-cis-retinaldehyde from all-trans retinol in the visual cycle. In patients with inherited retinal dystrophy (IRD), precise genetic diagnosis is an indispensable approach as it is required to establish eligibility for the genetic treatment of RPE65-associated IRDs. This case report aims to report the specific phenotype−genotype correlation of the first patient with a homozygous missense variant RPE65 c.499G>T, p. (Asp167Tyr). We report a case of a 66-year-old male who demonstrated a unique phenotype manifesting less severe functional vision deterioration in childhood and adolescence, and extensive nummular pigment clusters. The underlying causes of the differences in the typical bone spicule and atypical nummular pigment clumping are unknown, but suggest that the variant itself influenced the rate of photoreceptor death. Functional studies are needed to define whether the substitution of aspartate impairs the folding of the tertiary RPE65 structure only and does not lead to the complete abolishment of chromophore production, thus explaining the less severe phenotype in adolescence.

Induced retinal pigment epithelial cells with anti-epithelial-to-mesenchymal transition ability delay retinal degeneration

The hostile microenvironment of the retina in patients with age-related macular degeneration (AMD) may trigger epithelial-to-mesenchymal transition (EMT) of grafted retinal pigment epithelial (RPE) cells, thus attenuating the therapeutic outcome. Here, we transformed human dedifferentiated induced pluripotent stem cell-derived RPE (iPSC-RPE) cells into induced RPE (iRPE) cells using a cocktail of four transcription factors (TFs)—CRX, MITF-A, NR2E1, and C-MYC. These critical TFs maintained the epithelial property of iRPE cells by regulating the expression of bmp7, forkhead box f2, lin7a, and pard6b, and conferred resistance to TGF-β-induced EMT in iRPE cells by targeting ppm1a. The iRPE cells with Tet-on system-regulated c-myc expression exhibited EMT resistance and better therapeutic function compared with iPSC-RPE cells in rat AMD model. Our study demonstrates that endowing RPE cells with anti-EMT property avoids the risk of EMT after cells are grafted into the subretinal space, and it may provide a suitable candidate for AMD treatment.

•

CRX, MITF-A, NR2E1, and C-MYC transform De-iPSC-RPE cells into iRPE cells

•

iRPE cells have resistance to TGF-β-induced EMT

•

BMP7, FOXF2, LIN7A, PARD6B, and PPM1A mediate the functions of TFs in iRPE cells

•

iRPE cells have better retinal protective function than iPSC-RPE cells

Zeb1 Regulation of Wound Healing-Induced Inflammation in Alkali-Damaged Corneas

The cornea is an avascular tissue for vision clarity. Alkali burn could cause severe traumatic damage on the cornea with inflammation and neovascularization (NV), leading to vision reduction and blindness. Mechanisms underlying corneal inflammation and NV are not as clear. We previously reported that Zeb1 is an important factor in corneal NV, and we sought to clarify whether it is also involved in regulation of corneal inflammation. We analyzed the alkali burn-induced corneal inflammation and wound healing in both Zeb1^+/+ and Zeb1^−/+ littermates through a multidisciplinary approach. We provide evidence that Zeb1 forms a positive regulatory loop with Tgfb to regulate early corneal inflammation by maintenance of immune cell viability and mobility and later wound healing by activation of both Nf-κb and Tgfb-related Stat3 signaling pathways. We believe that ZEB1 is a potential therapeutic target, and inactivation of ZEB1 could be a strategy to treat severe corneal inflammation condition.

•

Traumatic wound induces inflammation in the cornea, resulting in vision reduction

•

Zeb1 is a key factor to retain immune cell viability, mobility, and cytokine expression

•

Zeb1 regulates cytokine gene expression through both Nf-κb and Stat3 pathways

•

Inactivation of ZEB1 could be a strategy to treat severe corneal inflammation condition

Polarity and epithelial-mesenchymal transition of retinal pigment epithelial cells in proliferative vitreoretinopathy

Under physiological conditions, retinal pigment epithelium (RPE) is a cellular monolayer composed of mitotically quiescent cells. Tight junctions and adherens junctions maintain the polarity of RPE cells, and are required for cellular functions. In proliferative vitreoretinopathy (PVR), upon retinal tear, RPE cells lose cell-cell contact, undergo epithelial-mesenchymal transition (EMT), and ultimately transform into myofibroblasts, leading to the formation of fibrocellular membranes on both surfaces of the detached retina and on the posterior hyaloids, which causes tractional retinal detachment. In PVR, RPE cells are crucial contributors, and multiple signaling pathways, including the SMAD-dependent pathway, Rho pathway, MAPK pathways, Jagged/Notch pathway, and the Wnt/β-catenin pathway are activated. These pathways mediate the EMT of RPE cells, which play a key role in the pathogenesis of PVR. This review summarizes the current body of knowledge on the polarized phenotype of RPE, the role of cell-cell contact, and the molecular mechanisms underlying the RPE EMT in PVR, emphasizing key insights into potential approaches to prevent PVR.

Insights into Differentiation of Melanocytes from Human Stem Cells and Their Relevance for Melanoma Treatment

Simple Summary

The reactivation of embryonic developmental programs is crucial for melanoma cells to grow and to metastasize. In order to understand this process better, we first summarize the melanocytic differentiation process both in vivo and in vitro. Secondly, we compare and highlight important similarities between neural crest cell fate during differentiation and tumor cell characteristics during melanoma mestastasis. Finally, we suggest possible therapeutic targets, which could be used to inhibit phenotype switching by developmental cues and hence also suppress the metastatic melanoma spread.

Abstract

Malignant melanoma represents a highly aggressive form of skin cancer. The metastatic process itself is mostly governed by the so-called epithelial mesenchymal transition (EMT), which confers cancer cells migrative, invasive and resistance abilities. Since EMT represents a conserved developmental process, it is worthwhile further examining the nature of early developmental steps fundamental for melanocyte differentiation. This can be done either in vivo by analyzing the physiologic embryo development in different species or by in vitro studies of melanocytic differentiation originating from embryonic human stem cells. Most importantly, external cues drive progenitor cell differentiation, which can be divided in stages favoring neural crest specification or melanocytic differentiation and proliferation. In this review, we describe ectopic factors which drive human pluripotent stem cell differentiation to melanocytes in 2D, as well as in organoid models. Furthermore, we compare developmental mechanisms with processes described to occur during melanoma development. Finally, we suggest differentiation factors as potential co-treatment options for metastatic melanoma patients.

EMT-Inducing Transcription Factors, Drivers of Melanoma Phenotype Switching, and Resistance to Treatment

Transcription factors, extensively described for their role in epithelial-mesenchymal transition (EMT-TFs) in epithelial cells, also display essential functions in the melanocyte lineage. Recent evidence has shown specific expression patterns and functions of these EMT-TFs in neural crest-derived melanoma compared to carcinoma. Herein, we present an update of the specific roles of EMT-TFs in melanocyte differentiation and melanoma progression. As major regulators of phenotype switching between differentiated/proliferative and neural crest stem cell-like/invasive states, these factors appear as major drivers of intra-tumor heterogeneity and resistance to treatment in melanoma, which opens new avenues in terms of therapeutic targeting.

Zeb1 promotes corneal neovascularization by regulation of vascular endothelial cell proliferation

Angiogenesis is required for tissue repair; but abnormal angiogenesis or neovascularization (NV) causes diseases in the eye. The avascular status in the cornea is a prerequisite for corneal clarity and thought to be maintained by the equilibrium between proangiogenic and antiangiogenic factors that controls proliferation and migration of vascular endothelial cells (ECs) sprouting from the pericorneal plexus. VEGF is the most important intrinsic factor for angiogenesis; anti-VEGF therapies are available for treating ocular NV. However, the effectiveness of the therapies is limited because of VEGF-independent mechanism(s). We show that Zeb1 is an important factor promoting vascular EC proliferation and corneal NV; and a couple of small molecule inhibitors can evict Ctbp from the Zeb1-Ctbp complex, thereby reducing EC Zeb1 expression, proliferation, and corneal NV. We conclude that Zeb1-regulation of angiogenesis is independent of Vegf and that the ZEB1-CtBP inhibitors can be of potential therapeutic significance in treating corneal NV.

Yap1 is required for maintenance of adult RPE differentiation

Nuclear YAP1 plays a critical role in regulation of stem cell proliferation, tissue regeneration, and organ size in many types of epithelia. Due to rapid turnover of most epithelial cell types, the cytoplasmic function of YAP1 in epithelial cells has not been well studied. The retinal pigment epithelium (RPE) is a highly polarized epithelial cell type maintained at a senescence state, and offers an ideal cell model to study the active role of YAP1 in maintenance of the adult epithelial phenotype. Here, we show that the cytoplasmic function of YAP1 is essential to maintain adult RPE differentiation. Knockout of Yap1 in the adult mouse RPE caused cell depolarization and tight junction breakdown, and led to inhibition of RPE65 expression, diminishment of RPE pigments, and retraction of microvilli and basal infoldings. These changes in RPE further prompted the loss of adjacent photoreceptor outer segments and photoreceptor death, which eventually led to decline of visual function in older mice between 6 and 12 months of age. Furthermore, nuclear β-catenin and its activity were significantly increased in mutant RPE. These results suggest that YAP1 plays an important role in active inhibition of Wnt/β-catenin signaling, and is essential for downregulation of β-catenin nuclear activity and prevention of dedifferentiation of adult RPE.

Sphere-induced reprogramming of RPE cells into dual-potential RPE stem-like cells

Background

The retinal pigment epithelium (RPE) has the potential to regenerate the entire neuroretina upon retinal injury in amphibians. In contrast, this regenerative capacity has been lost in mammals. The reprogramming of differentiated somatic cells into induced pluripotent stem cells (iPSCs) by viral transduction of exogenous stem cell factors has triggered a revolution in regenerative medicine. However, the risks of potential mutation(s) caused by random viral vector insertion in host genomes and tumor formation in recipients hamper its clinical application. One alternative is to immortalize adult stem cells with limited potential or to partially reprogram differentiated somatic cells into progenitor-like cells through non-integration protocols.

Methods

Sphere-induced RPE stem cells (iRPESCs) were generated from adult mouse RPE cells. Their stem cell functionality was studied in a mouse model of retinal degeneration. The molecular mechanism underlying the sphere-induced reprogramming was investigated using microarray and loss-of-function approaches.

Findings

We provide evidence that our sphere-induced reprogramming protocol can immortalize and transform mouse RPE cells into iRPESCs with dual potential to differentiate into cells that express either RPE or photoreceptor markers both in vitro and in vivo. When subretinally transplanted into mice with retinal degeneration, iRPESCs can integrate to the RPE and neuroretina, thereby delaying retinal degeneration in the model animals. Our molecular analyses indicate that the Hippo signaling pathway is important in iRPESC reprogramming.

Interpretation

The Hippo factor Yap1 is activated in the nuclei of cells at the borders of spheres. The factors Zeb1 and P300 downstream of the Hippo pathway are shown to bind to the promoters of the stemness genes Oct4, Klf4 and Sox2, thereby likely transactivate them to reprogram RPE cells into iRPESCs.

Fund

National Natural Science Foundation of China and the National Institute of Health USA.

Self-Formation of RPE Spheroids Facilitates Enrichment and Expansion of hiPSC-Derived RPE Generated on Retinal Organoid Induction Platform

Purpose

Retinal pigment epithelium (RPE) and neural retina could be generated concurrently through retinal organoid induction approaches using human induced pluripotent stem cells (hiPSCs), providing valuable sources for cell therapy of retinal degenerations. This study aims to enrich and expand hiPSC-RPE acquired with this platform and explore characteristics of serially passaged RPE cells.

Methods

RPE has been differentiated from hiPSCs with a published retinal organoid induction method. After detachment of neural retina on the 4th week, the remaining mixture was scraped from the dish and subjected to suspension culture for the formation of RPE spheroids. RPE sheets were isolated and digested for expansion. The cellular, molecular, and functional features of expanded RPE cells were evaluated by different assays.

Results

Under suspension culture, hiPSC-RPE spheroids with pigmentation self-formed were readily enriched by removing the non-retinal tissues. RPE sheets were further dissected and purified from the spheroids. The individualized RPE cells could be passaged every week for at least 5 times in serum medium, yielding large numbers of cells with high quality in a short period. In addition, when switched to a serum-free medium, the passaged RPE cells could mature in cellular, molecular, and physiological levels, including repigmentation, markers expression, and phagocytosis.

Conclusions

We developed a simple and novel RPE spheroids formation approach to enrich and expand hiPSC-RPE cells generated along with retinal neurons on a universal retinal organoid induction platform. This achievement will reduce the cost and time in producing retinal cells for basic and translational researches, in particular for retinal cell therapy.

A cell culture condition that induces the mesenchymal-epithelial transition of dedifferentiated porcine retinal pigment epithelial cells

The pathological change of retinal pigment epithelial (RPE) cells is one of the main reasons for the development of age-related macular degeneration (AMD). Thus, cultured RPE cells are a proper cell model for studying the etiology of AMD in vitro. However, such cultured RPE cells easily undergo epithelial-mesenchymal transition (EMT) that results in changes of cellular morphology and functions of the cells. To restore and maintain the mesenchymal-epithelial transition (MET) of the cultured RPE cells, we cultivated dedifferentiated porcine RPE (pRPE) cells and compared their behaviors in four conditions: 1) in cell culture dishes with DMEM/F12 containing FBS (CC dish-FBS), 2) in petri dishes with DMEM/F12 containing FBS (Petri dish-FBS), 3) in cell culture dishes with DMEM/F12 containing N2 and B27 supplements (CC dish-N2B27), and 4) in petri dishes with DMEM/F12 containing N2 and B27 (Petri dish-N2B27). In addition to observing the cell morphology and behavior, RPE specific markers, as well as EMT-related genes and proteins, were examined by immunostaining, quantitative real-time PCR and Western blotting. The results showed that dedifferentiated pRPE cells maintained EMT in CC dish-FBS, Petri dish-FBS and CC dish-N2B27 groups, whereas MET was induced when the dedifferentiated pRPE cells were cultured in Petri dish-N2B27. Such induced pRPE cells showed polygonal morphology with increased expression of RPE-specific markers and decreased EMT-associated markers. Similar results were observed in induced pluripotent stem cell-derived RPE cells. Furthermore, during the re-differentiation of those dedifferentiated pRPE cells, Petri dish-N2B27 reduced the activity of RhoA and induced F-actin rearrangement, which promoted the nuclear exclusion of transcriptional co-activator with PDZ-binding motif (TAZ) and TAZ target molecule zinc finger E-box binding protein (ZEB1), both of which are EMT inducing factors. This study provides a simple and reliable method to reverse dedifferentiated phenotype of pRPE cells into epithelialized phenotype, which is more appropriate for studying AMD in vitro, and suggests that MET of other cell types might be induced by a similar approach.

Regulation of cell proliferation in the retinal pigment epithelium: Differential regulation of the death-associated protein like-1 DAPL1 by alternative MITF splice forms

Vertebrate eye development and homoeostasis critically depend on the regulation of proliferation of cells forming the retinal pigment epithelium (RPE). Previous results indicated that the death-associated protein like-1 DAPL1 cell autonomously suppresses RPE proliferation in vivo and in vitro. Here, we show in human RPE cell lines that the pigment cell transcription factor MITF regulates RPE cell proliferation by upregulating DAPL1 expression. DAPL1 regulation by MITF is, however, mediated predominantly by (-) MITF, one of two alternative splice isoforms of MITF that lacks six residues located upstream of the DNA-binding basic domain. Furthermore, we find that the regulation of DAPL1 by MITF is indirect in that (-) MITF stimulates the transcription of Musashi homolog-2 (MSI2), which negatively regulates the processing of the anti-DAPL1 microRNA miR-7. Our results provide molecular insights into the regulation of RPE cell proliferation and quiescence and may help us understand the mechanisms of normal RPE maintenance and of eye diseases associated with either RPE hyperproliferation or the lack of regenerative proliferation.

DAPL1, a susceptibility locus for age-related macular degeneration, acts as a novel suppressor of cell proliferation in the retinal pigment epithelium

The retinal pigment epithelium (RPE) forms a monolayer at the back of the vertebrate eye and is fundamental to retinal function and homoeostasis. During early development, RPE cells undergo rapid proliferation, but in the adult, they remain normally nonproliferative throughout life. Nevertheless, under pathological conditions such as in proliferative vitreoretinopathy or after retinal ablation, mature RPE cells can re-enter the cell cycle and form nodules or multiple cell layers. Here we show that Dapl1, whose human homolog represents a susceptibility locus for age-related macular degeneration (AMD), is highly up-regulated in quiescent but not proliferating RPE cells and that experimental overexpression of DAPL1 in proliferating RPE cells inhibits their proliferation. Consistent with this observation, the percent of Ki67-positive cells is significantly higher in E11.5 Dapl1 knockout mouse embryos compared to age-matched controls. In adult Dapl1-/- mice, which survive without showing any overt pathology, RPE overgrowth leads to multiple cell layers and/or cellular nodules. The antiproliferative effect of DAPL1 is associated with an increase in CDKN1A protein levels. Reduction of CDKN1A by siRNA in DAPL1-overexpressing RPE cells in vitro partially restores cell proliferation. Hence, we show that DAPL1 is a novel regulator of RPE cell proliferation that is important for the maintenance of the RPE as a monolayer. The findings suggest that DAPL1 dysregulation may be involved in abnormal RPE-related proliferative diseases and corresponding retinal dysfunctions in humans.

The T-Box Transcription Factor TBX2 Regulates Cell Proliferation in the Retinal Pigment Epithelium

PURPOSE

Vertebrate eye development and function critically depend on the regulation of proliferation of retinal pigment epithelium (RPE) cells. Hence, a thorough analysis of the molecular parameters controlling RPE cell proliferation is crucial for our understanding of the physiology of this cell type both in health and in disease. The T-box transcription factor TBX2 is an important cell cycle regulator in development and oncogenesis, but its specific role in RPE cell proliferation is far from clear. The purpose of the present study is to investigate whether TBX2 plays any role in regulating RPE cell proliferation.

MATERIALS AND METHODS

The expression of TBX2 in RPE cells was analyzed in wildtype mice and ARPE-19 cells by co-staining for RPE-specific markers and cell proliferation. In vitro, the role of TBX2 was studied by manipulating its levels using RNAi and analyzing the effects on DNA synthesis and cell growth and on gene expression at the RNA and protein levels.

RESULTS

Here, we find that TBX2 is expressed in RPE cells both in vivo and in vitro. Specific knockdown of TBX2 in the human RPE cell line ARPE-19 leads to an accumulation of cells at G1. This cell cycle arrest is accompanied by changes in the levels of known cell cycle regulators and, in particular, by an increase in the levels of the tumor-suppressor gene CCAAT/enhancer-binding protein delta (CEBPD). In fact, simultaneous knockdown of both TBX2 and CEBPD interferes with the reduction in cell proliferation brought about by TBX2 reduction alone.

CONCLUSIONS

Our results provide novel insights into the regulatory mechanisms of cell proliferation in the RPE and may contribute to our understanding of normal RPE maintenance and its pathology in degenerative and proliferative disorders of the eye.

ZEB1 Regulates Multiple Oncogenic Components Involved in Uveal Melanoma Progression

Human uveal melanoma (UM) is a major ocular malignant tumor with high risk of metastasis and requires multiple oncogenic factors for progression. ZEB1 is a zinc finger E-box binding transcription factor known for participating epithelial-mesenchymal transition (EMT), a critical cellular event for metastasis of malignant tumors of epithelium origin. ZEB1 is also expressed in UM and high expression of ZEB1 correlates with UM advancement, but has little effect on cell morphology. We show that spindle UM cells can become epithelioid but not vice versa; and ZEB1 exerts its tumorigenic effects by promoting cell dedifferentiation, proliferation, invasiveness, and dissemination. We provide evidence that ZEB1 binds not only to repress critical genes involving in pigment synthesis, mitosis, adherent junctions, but also to transactivate genes involving in matrix degradation and cellular locomotion to propel UM progression towards metastasis. We conclude that ZEB1 is a major oncogenic factor required for UM progression and could be a potential therapeutic target for treating UM in the clinic.

Proinflammatory cytokines decrease the expression of genes critical for RPE function

PURPOSE

Proinflammatory cytokines interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin-1 beta (IL-1β) secreted by infiltrating lymphocytes or macrophages may play a role in triggering RPE dysfunction associated with age-related macular degeneration (AMD). Binding of these proinflammatory cytokines to their specific receptors residing on the RPE cell surface can activate signaling pathways that, in turn, may dysregulate cellular gene expression. The purpose of the present study was to investigate whether IFN-γ, TNF-α, and IL-1β have an adverse effect on the expression of genes essential for RPE function, employing the RPE cell line ARPE-19 as a model system.

METHODS

ARPE-19 cells were cultured for 3-4 months until they exhibited epithelial morphology and expressed mRNAs for visual cycle genes. The differentiated cells were treated with IFN-γ, TNF-α, and/or IL-1β, and gene expression was analyzed with real-time PCR analysis. Western immunoblotting was employed for the detection of proteins.

RESULTS

Proinflammatory cytokines (IFN-γ + TNF-α + IL-1β) greatly increased the expression of chemokines and cytokines in cultured ARPE-19 cells that exhibited RPE characteristics. However, this response was accompanied by markedly decreased expression of genes important for RPE function, such as CDH1, RPE65, RDH5, RDH10, TYR, and MERTK. This was associated with decreased expression of the genes MITF, TRPM1, and TRPM3, as well as microRNAs miR-204 and miR-211, which are known to regulate RPE-specific gene expression. The decreased expression of the epithelial marker gene CDH1 was associated with increased expression of mesenchymal marker genes (CDH2, VIM, and CCND1) and epithelial-mesenchymal transition (EMT) promoting transcription factor genes (ZEB1 and SNAI1).

CONCLUSIONS

RPE cells exposed to proinflammatory cytokines IFN-γ, TNF-α, and IL-1β showed decreased expression of key genes involved in the visual cycle, epithelial morphology, and phagocytosis. This adverse effect of proinflammatory cytokines, which could be secreted by infiltrating lymphocytes or macrophages, on the expression of genes indispensable for RPE function may contribute to the RPE dysfunction implicated in AMD pathology.

Isolation, culture and characterization of primary mouse RPE cells

Mouse models are powerful tools for the study of ocular diseases. Alterations in the morphology and function of the retinal pigment epithelium (RPE) are common features shared by many ocular disorders. We report a detailed protocol to collect, seed, culture and characterize RPE cells from mice. We describe a reproducible method that we previously developed to collect and culture murine RPE cells on Transwells as functional polarized monolayers. The collection of RPE cells takes ∼3 h, and the cultures mimic in vivo RPE cell features within 1 week. This protocol also describes methods to characterize the cells on Transwells within 1-2 weeks by transmission and scanning electron microscopy (TEM and SEM, respectively), immunostaining of vibratome sections and flat mounts, and measurement of transepithelial electrical resistance. The RPE cell cultures are suitable to study the biology of the RPE from wild-type and genetically modified strains of mice between the ages of 10 d and 12 months. The RPE cells can also be manipulated to investigate molecular mechanisms underlying the RPE pathology in the numerous mouse models of ocular disorders. Furthermore, modeling the RPE pathology in vitro represents a new approach to testing drugs that will help accelerate the development of therapies for vision-threatening disorders such as macular degeneration (MD).

SOX5 is involved in balanced MITF regulation in human melanoma cells

Background

Melanoma is a cancer with rising incidence and new therapeutics are needed. For this, it is necessary to understand the molecular mechanisms of melanoma development and progression. Melanoma differs from other cancers by its ability to produce the pigment melanin via melanogenesis; this biosynthesis is essentially regulated by microphthalmia-associated transcription factor (MITF). MITF regulates various processes such as cell cycling and differentiation. MITF shows an ambivalent role, since high levels inhibit cell proliferation and low levels promote invasion. Hence, well-balanced MITF homeostasis is important for the progression and spread of melanoma. Therefore, it is difficult to use MITF itself for targeted therapy, but elucidating its complex regulation may lead to a promising melanoma-cell specific therapy.

Method

We systematically analyzed the regulation of MITF with a novel established transcription factor based gene regulatory network model. Starting from comparative transcriptomics analysis using data from cells originating from nine different tumors and a melanoma cell dataset, we predicted the transcriptional regulators of MITF employing ChIP binding information from a comprehensive set of databases. The most striking regulators were experimentally validated by functional assays and an MITF-promoter reporter assay. Finally, we analyzed the impact of the expression of the identified regulators on clinically relevant parameters of melanoma, i.e. the thickness of primary tumors and patient overall survival.

Results

Our model predictions identified SOX10 and SOX5 as regulators of MITF. We experimentally confirmed the role of the already well-known regulator SOX10. Additionally, we found that SOX5 knockdown led to MITF up-regulation in melanoma cells, while double knockdown with SOX10 showed a rescue effect; both effects were validated by reporter assays. Regarding clinical samples, SOX5 expression was distinctively up-regulated in metastatic compared to primary melanoma. In contrast, survival analysis of melanoma patients with predominantly metastatic disease revealed that low SOX5 levels were associated with a poor prognosis.

Conclusion

MITF regulation by SOX5 has been shown only in murine cells, but not yet in human melanoma cells. SOX5 has a strong inhibitory effect on MITF expression and seems to have a decisive clinical impact on melanoma during tumor progression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-016-0170-0) contains supplementary material, which is available to authorized users.

Neurotensin-induced miR-133α expression regulates neurotensin receptor 1 recycling through its downstream target aftiphilin

Neurotensin (NT) triggers signaling in human colonic epithelial cells by activating the G protein-coupled receptor, the neurotensin receptor 1 (NTR1). Activated NTR1 traffics from the plasma membrane to early endosomes, and then recycles. Although sustained NT/NTR1 signaling requires efficient NTR1 recycling, little is known about the regulation of NTR1 recycling. We recently showed that NT/NTR1 signaling increases expression of miR-133α. Herein, we studied the mechanism of NT-regulated miR-133α expression and examined the role of miR-133α in intracellular NTR1 trafficking in human NCM460 colonocytes. We found that NT-induced miR-133α upregulation involves the negative transcription regulator, zinc finger E-box binding homeobox 1. Silencing of miR-133α or overexpression of aftiphilin (AFTPH), a binding target of miR-133α, attenuated NTR1 trafficking to plasma membrane in human colonocytes, without affecting NTR1 internalization. We localized AFTPH to early endosomes and the trans-Golgi network (TGN) in unstimulated human colonic epithelial cells. AFTPH overexpression reduced NTR1 localization in early endosomes and increased expression of proteins related to endosomes and the TGN trafficking pathway. AFTPH overexpression and de-acidification of intracellular vesicles increased NTR1 expression. Our results suggest a novel mechanism of GPCR trafficking in human colonic epithelial cells by which a microRNA, miR-133α regulates NTR1 trafficking through its downstream target AFTPH.

A FOXM1 Dependent Mesenchymal-Epithelial Transition in Retinal Pigment Epithelium Cells

The integrity of the epithelium is maintained by a complex but regulated interplay of processes that allow conversion of a proliferative state into a stably differentiated state. In this study, using human embryonic stem cell (hESC) derived Retinal Pigment Epithelium (RPE) cells as a model; we have investigated the molecular mechanisms that affect attainment of the epithelial phenotype. We demonstrate that RPE undergo a Mesenchymal–Epithelial Transition in culture before acquiring an epithelial phenotype in a FOXM1 dependent manner. We show that FOXM1 directly regulates proliferation of RPE through transcriptional control of cell cycle associated genes. Additionally, FOXM1 modulates expression of the signaling ligands BMP7 and Wnt5B which act reciprocally to enable epithelialization. This data uncovers a novel effect of FOXM1 dependent activities in contributing towards epithelial fate acquisition and furthers our understanding of the molecular regulators of a cell type that is currently being evaluated as a cell therapy.

Decreased contact inhibition in mouse adipose mesenchymal stem cells

The proliferation of embryonic cells or adult stem cells in tissue is critically regulated during development and repair. How limited the proliferation of cells, so far, is not much explored. Cell-cell contact proliferation inhibition is known as a crucial mechanism regulating cell proliferation in vitro and in vivo. In this study we examined the characters of mouse subcutaneous adipose derived stem cells (msADSC) whether they lost or get contact inhibition during in vitro culture. The characters of msADSC growth after confluence were analyzed using confocal microscope and the expression profiles of contact inhibition related genes were analyzed according to the morphological changes using real-time PCR method. msADSC showed overlapping growth between them but not after passage 14. The cell shapes were also changed after passage 14. The expression profiles of genes which are involved in contact inhibition were modified in the msADSC after passage 14. The differentiation ability of msADSCs to adipocyte, chondrocyte and osteocyte was not changed by such changes of gene expression profiles. Based on these results, it is revealed that smADSC were characterized by getting of strong cell-cell contact inhibition after passage 14 but the proliferation and developmental ability were not blocked by the change of cell-cell contact proliferation inhibition. These finding will help to understand the growth of adipose tissue, although further studies are needed to evaluate the physiological meaning of the cell-cell contact proliferation inhibition during in vitro culture of msADSC.

An Rb1-dependent amplification loop between Ets1 and Zeb1 is evident in thymocyte differentiation and invasive lung adenocarcinoma

Background

Ras pathway mutation leads to induction and Erk phosphorylation and activation of the Ets1 transcription factor. Ets1 in turn induces cyclin E and cyclin dependent kinase (cdk) 2 to drive cell cycle progression. Ets1 also induces expression of the epithelial-mesenchymal transition (EMT) transcription factor Zeb1, and thereby links Ras mutation to EMT, which is thought to drive tumor invasion. Ras pathway mutations are detected by the Rb1 tumor suppression pathway, and mutation or inactivation of the Rb1 pathway is required for EMT.

Results

We examined linkage between Rb1, Ets1 and Zeb1. We found that an Rb1-E2F complex binds the Ets1 promoter and constitutively limits Ets1 expression. But, Rb1 repression of Zeb1 provides the major impact of Rb1 on Ets1 expression. We link Rb1 repression of Zeb1 to induction of miR-200 family members, which in turn target Ets1 mRNA. These findings suggest that Ets1 and Zeb1 comprise an amplification loop that is dependent upon miR-200 and regulated by Rb1. Thus, induction of Ets1 when the Rb1 pathway is lost may contribute to deregulated cell cycle progression through Ets1 induction of cyclin E and cdk2. Consistent with such an amplification loop, we correlate expression of Ets1 and Zeb1 in mouse and human lung adenocarcinoma. In addition we demonstrate that Ets1 expression in thymocytes is also dependent upon Zeb1.

Conclusions

Taken together, our results provide evidence of an Rb1-dependent Ets1-Zeb1 amplification loop in thymocyte differentiation and tumor invasion.

Electronic supplementary material

The online version of this article (doi:10.1186/s12867-015-0038-4) contains supplementary material, which is available to authorized users.

Efficient delivery and functional expression of transfected modified mRNA in human embryonic stem cell-derived retinal pigmented epithelial cells

Gene- and cell-based therapies are promising strategies for the treatment of degenerative retinal diseases such as age-related macular degeneration, Stargardt disease, and retinitis pigmentosa. Cellular engineering before transplantation may allow the delivery of cellular factors that can promote functional improvements, such as increased engraftment or survival of transplanted cells. A current challenge in traditional DNA-based vector transfection is to find a delivery system that is both safe and efficient, but using mRNA as an alternative to DNA can circumvent these major roadblocks. In this study, we show that both unmodified and modified mRNA can be delivered to retinal pigmented epithelial (RPE) cells with a high efficiency compared with conventional plasmid delivery systems. On the other hand, administration of unmodified mRNA induced a strong innate immune response that was almost absent when using modified mRNA. Importantly, transfection of mRNA encoding a key regulator of RPE gene expression, microphthalmia-associated transcription factor (MITF), confirmed the functionality of the delivered mRNA. Immunostaining showed that transfection with either type of mRNA led to the expression of roughly equal levels of MITF, primarily localized in the nucleus. Despite these findings, quantitative RT-PCR analyses showed that the activation of the expression of MITF target genes was higher following transfection with modified mRNA compared with unmodified mRNA. Our findings, therefore, show that modified mRNA transfection can be applied to human embryonic stem cell-derived RPE cells and that the method is safe, efficient, and functional.

MITF in melanoma: mechanisms behind its expression and activity

MITF (microphthalmia-associated transcription factor) represents a melanocytic lineage-specific transcription factor whose role is profoundly extended in malignant melanoma. Over the last few years, the function of MITF has been tightly connected to plasticity of melanoma cells. MITF participates in executing diverse melanoma phenotypes defined by distinct gene expression profiles. Mutation-dependent alterations in MITF expression and activity have been found in a relatively small subset of melanomas. MITF activity is rather modulated by its upstream activators and suppressors operating on transcriptional, post-transcriptional and post-translational levels. These regulatory mechanisms also include epigenetic and microenvironmental signals. Several transcription factors and signaling pathways involved in the regulation of MITF expression and/or activity such as the Wnt/β-catenin pathway are broadly utilized by various types of tumors, whereas others, e.g., BRAF^V600E/ERK1/2 are more specific for melanoma. Furthermore, the MITF activity can be affected by the availability of transcriptional co-partners that are often redirected by MITF from their own canonical signaling pathways. In this review, we discuss the complexity of a multilevel regulation of MITF expression and activity that underlies distinct context-related phenotypes of melanoma and might explain diverse responses of melanoma patients to currently used therapeutics.

Studying melanin and lipofuscin in RPE cell culture models

The retinal pigment epithelium contains three major types of pigment granules; melanosomes, lipofuscin and melanolipofuscin. Melanosomes in the retinal pigment epithelium (RPE) are formed during embryogenesis and mature during early postnatal life while lipofuscin and melanolipofuscin granules accumulate as a function of age. The difficulty in studying the formation and consequences of melanosomes and lipofuscin granules in RPE cell culture is compounded by the fact that these pigment granules do not normally occur in established RPE cell lines and pigment granules are rapidly lost in adult human primary culture. This review will consider options available for overcoming these limitations and permitting the study of melanosomes and lipofuscin in cell culture and will briefly evaluate the advantages and disadvantages of the different protocols.

Genetic basis of continuous variation in the levels and modular inheritance of pigmentation in cichlid fishes

Variation in pigmentation type and levels is a hallmark of myriad evolutionary radiations, and biologists have long been fascinated by the factors that promote and maintain variation in coloration across populations. Here, we provide insights into the genetic basis of complex and continuous patterns of colour variation in cichlid fishes, which offer a vast diversity of pigmentation patterns that have evolved in response to both natural and sexual selection. Specifically, we crossed two divergent cichlid species to generate an F2 mapping population that exhibited extensive variation in pigmentation levels and patterns. Our experimental design is robust in that it combines traditional quantitative trait locus (QTL) analysis with population genomics, which has allowed us to move efficiently from QTL interval to candidate gene. In total, we detected 41 QTL and 13 epistatic interactions that underlie melanocyte- and xanthophore-based coloration across the fins and flanks of these fishes. We also identified 2 QTL and 1 interaction for variation in the magnitude of integration among these colour traits. This finding in particular is notable as there are marked differences both within and between species with respect to the complexity of pigmentation patterns. While certain individuals are characterized by more uniform 'integrated' colour patterns, others exhibit many more degrees of freedom with respect to the distribution of colour 'modules' across the fins and flank. Our data reveal, for the first time, a genetic basis for this difference. Finally, we implicate pax3a as a mediator of continuous variation in the levels of xanthophore-based colour along the cichlid flank.

A novel hypoxia-associated subset of FN1 high MITF low melanoma cells: identification, characterization, and prognostic value

In many human cancers, the epithelial-to-mesenchymal transition has an important role in the induction of cancer stem-like cells, and hence, in the causation of intratumoral heterogeneity. This process, also referred to as mesenchymal mimicry, is, however, only poorly understood in melanoma and histological correlation is still lacking. In an immunohistochemical analysis of a large prospective series of 220 primary and metastatic melanomas for the well-known epithelial-to-mesenchymal transition marker FN1, we observed melanoma cells with high FN1 expression in metastases with ischemic necrosis, but rarely or not at all in samples lacking evidence of hypoxia. In a blinded, retrospective series of 82 melanoma metastases with 10-year follow-up, the presence of clusters of these FN1(high) melanoma cells correlated significantly with shortened melanoma-specific survival, highlighting the prognostic value of their presence. We describe in detail the unique light- and electron-microscopic features of these FN1(high) melanoma cells, enabling their identification in routinely hematoxylin-and-eosin-stained sections. In addition, by laser microdissection and subsequent gene expression analysis and immunohistochemistry, we highlight their distinctive, molecular phenotype that includes expression of various markers of the epithelial-to-mesenchymal transition (eg, ZEB1) and of melanoma stem-like cells (eg, NGFR), and lack of immunoreactivity for the melanocytic marker MITF. This phenotype could be reproduced in vitro by culturing melanoma cells under hypoxic conditions. Functionally, the hypoxic microenvironment was shown to induce a more migratory and invasive cell type. In conclusion, we identified a novel clinically relevant FN1(high)MITF(low) cell type in melanoma associated with ischemic necrosis, and propose that these cells reside at the crossroad of the epithelial-to-mesenchymal transition and stem-like cell induction, plausibly triggered by the hypoxic environment.

Oncogenic roles of EMT-inducing transcription factors

The plasticity of cancer cells underlies their capacity to adapt to the selective pressures they encounter during tumour development. Aberrant reactivation of epithelial-mesenchymal transition (EMT), an essential embryonic process, can promote cancer cell plasticity and fuel both tumour initiation and metastatic spread. Here we discuss the roles of EMT-inducing transcription factors in creating a pro-tumorigenic setting characterized by an intrinsic ability to withstand oncogenic insults through the mitigation of p53-dependent oncosuppressive functions and the gain of stemness-related properties.

Phenanthrene causes ocular developmental toxicity in zebrafish embryos and the possible mechanisms involved

Recent studies show that polycyclic aromatic hydrocarbons (PAHs) may be a candidate cause of developmental defects of the retina, but the mechanism is still unclear. We evaluated the mechanism(s) underlying PAH-induced retinal development defects due to exposure to environmental concentrations of Phenanthrene (Phe) in zebrafish. We found that exposure to environmental concentrations of Phe caused obvious morphological changes, developmental retardation, apoptosis, and reduction of cell proliferation in the retina. Our results indicated that Phe could cause visual system developmental defects. Phe exposure up-regulated aryl hydrocarbon receptor (AhR) and microphthalmia-associated transcription factor (Mtif) expression, and down-regulated zinc finger E-box binding homeobox 1 (Zeb1) and paired box 6 (Pax6). Moreover, we demonstrated that AhR was a repressor of Zeb1. We propose that Phe's ocular toxicity is mediated by up-regulating AhR, which then down-regulates Zeb1, in turn inducing Mitf expression while inhibiting Pax6 expression.

A switch in the expression of embryonic EMT-inducers drives the development of malignant melanoma

Aberrant expression of embryonic epithelial-mesenchymal transition-inducing transcription factors (EMT-TFs) in epithelial cells triggers EMT, neoplastic transformation, stemness, and metastatic dissemination. We found that regulation and functions of EMT-TFs are different in malignant melanoma. SNAIL2 and ZEB2 transcription factors are expressed in normal melanocytes and behave as tumor-suppressor proteins by activating an MITF-dependent melanocyte differentiation program. In response to NRAS/BRAF activation, EMT-TF network undergoes a profound reorganization in favor of TWIST1 and ZEB1. This reversible switch cooperates with BRAF in promoting dedifferentiation and neoplastic transformation of melanocytes. We detected EMT-TF reprogramming in late-stage melanoma in association with enhanced phospho-ERK levels. This switch results in E-cadherin loss, enhanced invasion, and constitutes an independent factor of poor prognosis in melanoma patients.

Development of human embryonic stem cell therapies for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of vision loss in older adults and ultimately leads to the death of photoreceptor cells in the macular area of the neural retina. Currently, treatments are only available for patients with the wet form of AMD. In this review, we describe recent approaches to develop cell-based therapies for the treatment of AMD. Recent research has focused on replacing the retinal pigment epithelium (RPE), a monolayer of cells vital to photoreceptor cell health. We discuss the various methods used to differentiate and purify RPE from human embryonic stem cells (HESC), and describe the surgical approaches being used to transplant these cells in existing and forthcoming clinical trials.

The culture and maintenance of functional retinal pigment epithelial monolayers from adult human eye

The retinal pigment epithelium (RPE) is implicated in many eye diseases, including age-related macular degeneration, and therefore isolating and culturing these cells from recently deceased adult human donors is the ideal source for disease studies. Adult RPE could also be used as a cell source for transplantation therapy for RPE degenerative disease, likely requiring first in vitro expansion of the cells obtained from a patient. Previous protocols have successfully extracted RPE from adult donors; however improvements in yield, cell survival, and functionality are needed. We describe here a protocol optimized for adult human tissue that yields expanded cultures of RPE with morphological, phenotypic, and functional characteristics similar to freshly isolated RPE. These cells can be expanded and cultured for several months without senescence, gross cell death, or undergoing morphological changes. The protocol takes around a month to obtain functional RPE monolayers with accurate morphological characteristics and normal protein expression, as shown through immunohistochemistry analysis, RNA expression profiles via quantitative PCR (qPCR), and transepithelial resistance (TER) measurements. Included in this chapter are steps used to extract RPE from human adult globes, cell culture, cell splitting, cell bleaching, immunohistochemistry, and qPCR for RPE markers, and TER measurements as functional test.

Silencing of GPNMB by siRNA inhibits the formation of melanosomes in melanocytes in a MITF-independent fashion

Background

Melanosomes are specialized membrane-surrounded organelles, which are involved in the synthesis, storage and transport of melanin. Glycoprotein (transmembrane) non-metastatic melanoma protein b (GPNMB), a melanosome-specific structural protein, shares significant amino acid sequence homology with Pmel-17. Proteomic analysis demonstrated that GPNMB is present in all stages (I-IV) of melanosomes. However, little is known about the role of GPNMB in melanosomes.

Methodology/Principal Findings

Using real-time quantitative PCR, Western blotting and immunofluorescence analysis, we demonstrated that the expression of GPNMB in PIG1 melanocytes was up-regulated by ultraviolet B (UVB) radiation. Transmission electron microscopy analysis showed that the total number of melanosomes in PIG1 melanocytes was sharply reduced by GPNMB-siRNA transfection. Simultaneously, the expression levels of tyrosinase (Tyr), tyrosinase related protein 1 (Trp1), Pmel17/gp100 and ocular albinism type 1 protein (OA1) were all significantly attenuated. But the expression of microphthalmia-associated transcription factor (MITF) was up-regulated. Intriguingly, in GPNMB silenced PIG1 melanocytes, UVB radiation sharply reduced MITF expression.

Conclusion

Our present work revealed that the GPNMB was critical for the formation of melanosomes. And GPNMB expression down-regulation attenuated melanosome formation in a MITF-independent fashion.

MEK-ERK and heparin-susceptible signaling pathways are involved in cell-cycle entry of the wound edge retinal pigment epithelium cells in the adult newt

The onset mechanism of proliferation in mitotically quiescent retinal pigment epithelium (RPE) cells is still obscure in humans and newts, although it can be a clinical target for manipulating both retinal diseases and regeneration. To address this issue, we investigated factors or signaling pathways involved in the first cell-cycle entry of RPE cells upon retinal injury using a newt retina-less eye-cup culture system in which the cells around the wound edge of the RPE exclusively enter the cell cycle. We found that MEK-ERK signaling is necessary for their cell-cycle entry, and signaling pathways whose activities can be modulated by heparin, such as Wnt-, Shh-, and thrombin-mediated pathways, are capable of regulating the cell-cycle entry. Furthermore, we found that the cells inside the RPE have low proliferation competence even in the presence of serum, suggesting inversely that a loss of cell-to-cell contact would allow the cells to enter the cell cycle.

Comparison of FRPE and human embryonic stem cell-derived RPE behavior on aged human Bruch's membrane

PURPOSE

To compare RPE derived from human embryonic stem cells (hES-RPE) and fetal RPE (fRPE) behavior on human Bruch's membrane (BM) from aged and AMD donors.

METHODS

hES-RPE of 3 degrees of pigmentation and fRPE were cultured on BM explants. Explants were assessed by light, confocal, and scanning electron microscopy. Integrin mRNA levels were determined by real-time polymerase chain reaction studies. Secreted proteins in media were analyzed by multiplex protein analysis after 48-hour exposure at culture day 21.

RESULTS

hES-RPE showed impaired initial attachment compared to fRPE; pigmented hES-RPE showed nuclear densities similar to fRPE at day 21. At days 3 and 7, hES-RPE resurfaced BM to a limited degree, showed little proliferation (Ki-67), and partial retention of RPE markers (MITF, cytokeratin, and CRALBP). TUNEL-positive nuclei were abundant at day 3. fRPE exhibited substantial BM resurfacing at day 3 with decreased resurfacing at later times. Most fRPE retained RPE markers. Ki-67-positive nuclei decreased with time in culture. TUNEL staining was variable. Increased integrin mRNA expression did not appear to affect cell survival at day 21. hES-RPE and fRPE protein secretion was similar on equatorial BM except for higher levels of nerve growth factor and thrombospondin-2 (TSP2) by hES-RPE. On submacular BM, fRPE secreted more vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor, and platelet-derived growth factor; hES-RPE secreted more TSP2.

CONCLUSIONS

Although pigmented hES-RPE and fRPE resurfaced aged and AMD BM to a similar, limited degree at day 21, cell behavior at earlier times was markedly dissimilar. Differences in protein secretion may indicate that hES-RPE may not function identically to native RPE after seeding on aged or AMD BM.

Snail2 controls mesodermal BMP/Wnt induction of neural crest

The neural crest is an induced tissue that is unique to vertebrates. In the clawed frog Xenopus laevis, neural crest induction depends on signals secreted from the prospective dorsolateral mesodermal zone during gastrulation. The transcription factors Snail2 (Slug), Snail1 and Twist1 are expressed in this region. It is known that Snail2 and Twist1 are required for both mesoderm formation and neural crest induction. Using targeted blastomere injection, morpholino-based loss of function and explant studies, we show that: (1) Snail1 is also required for mesoderm and neural crest formation; (2) loss of snail1, snail2 or twist1 function in the C2/C3 lineage of 32-cell embryos blocks mesoderm formation, but neural crest is lost only in the case of snail2 loss of function; (3) snail2 mutant loss of neural crest involves mesoderm-derived secreted factors and can be rescued synergistically by bmp4 and wnt8 RNAs; and (4) loss of snail2 activity leads to changes in the RNA levels of a number of BMP and Wnt agonists and antagonists. Taken together, these results identify Snail2 as a key regulator of the signals involved in mesodermal induction of neural crest.

Taz-tead1 links cell-cell contact to zeb1 expression, proliferation, and dedifferentiation in retinal pigment epithelial cells

PURPOSE. The Hippo signaling pathway imposes the cell contact inhibition that establishes organ size and tissue topology from Drosophila to mammals. This pathway regulates activity of the Yap and Taz transcription factors, which link epithelial-mesenchymal transition (EMT) to cell proliferation. Here, the authors provide evidence that Taz and its coactivator, Tead1, regulate expression of the EMT transcription factor Zeb1 to control RPE cell proliferation and differentiation. METHODS. Real-time PCR was used to examine mRNA expression during RPE dedifferentiation in primary cultures of RPE cells and after knockdown of Yap and Taz by lentivirus shRNA. Immunofluorescence was used to follow subcellular localization of proteins in cells. Chromatin immunoprecipitation was used to detect Taz at the Zeb1 promoter in vivo. RESULTS. Zeb1 is overexpressed during RPE dedifferentiation, leading to cell proliferation, EMT, and repression of the RPE specification transcription factor gene Mitf. Taz-TEAD1 translocation to the nucleus coincides with loss of cell-cell contact and with onset of Zeb1 expression in the nucleus. shRNA knockdown of Taz prevented the overexpression of Zeb1 and, in turn, prevented proliferation, repression of Mitf and Mitf target genes, and EMT when RPE cells were placed in primary culture. Taz binds to the Zeb1 promoter in vivo, suggesting that it directly induces Zeb1 transcription. CONCLUSIONS. These results provide evidence of a molecular mechanism linking cell-cell contact to cell proliferation and dedifferentiation in RPE cells.

Protective effects of human iPS-derived retinal pigment epithelium cell transplantation in the retinal dystrophic rat

Transformation of somatic cells with a set of embryonic transcription factors produces cells with the pluripotent properties of embryonic stem cells (ESCs). These induced pluripotent stem (iPS) cells have the potential to differentiate into any cell type, making them a potential source from which to produce cells as a therapeutic platform for the treatment of a wide range of diseases. In many forms of human retinal disease, including age-related macular degeneration (AMD), the underlying pathogenesis resides within the support cells of the retina, the retinal pigment epithelium (RPE). As a monolayer of cells critical to photoreceptor function and survival, the RPE is an ideally accessible target for cellular therapy. Here we report the differentiation of human iPS cells into RPE. We found that differentiated iPS-RPE cells were morphologically similar to, and expressed numerous markers of developing and mature RPE cells. iPS-RPE are capable of phagocytosing photoreceptor material, in vitro and in vivo following transplantation into the Royal College of Surgeons (RCS) dystrophic rat. Our results demonstrate that iPS cells can be differentiated into functional iPS-RPE and that transplantation of these cells can facilitate the short-term maintenance of photoreceptors through phagocytosis of photoreceptor outer segments. Long-term visual function is maintained in this model of retinal disease even though the xenografted cells are eventually lost, suggesting a secondary protective host cellular response. These findings have identified an alternative source of replacement tissue for use in human retinal cellular therapies, and provide a new in vitro cellular model system in which to study RPE diseases affecting human patients.