FGF-induced lens cell proliferation and differentiation is dependent on MAPK (ERK1/2) signalling

Combinatorial genetic manipulation of Cx50, PI3K and PTEN alters postnatal mouse lens growth and homeostasis

Introduction

Phosphoinositide 3-kinase (PI3K), Phosphatase and tensin homolog (PTEN) and connexin50 (Cx50) have individually been shown to play critical roles in the growth, development and maintenance of the lens and to functionally interact in vitro. To elucidate how gap junctional coupling mediated by Cx50 and intracellular signaling mediated by PI3K and PTEN synergistically interact to regulate lens homeostasis in vivo, we generated and characterized double knockout animal models lacking the p110α subunit of PI3K and Cx50, or PTEN and Cx50.

Methods

We interbred lens specific p110α and PTEN conditional knockout animals with Cx50 deficient mice to generate double knockouts. Animals and eyes were weighed, lenses were dissected, photographed, measured, fixed and sectioned for histological analysis. Lens epithelial cell proliferation was determined using 5-ethynyl-2'-deoxyuridine (EdU) labeling.

Results

Double knockout of p110α and Cx50 led to a significant reduction in lens and eye size, and a high rate of lens rupture. The individual cell proliferation defects of the Cx50 and p110α single knockout lenses both persisted in the double KO. Double deletion of Cx50 and PTEN produced severe lens defects, including cataract, aberrant cell migration, altered cell proliferation, vacuole formation and lens rupture.

Conclusion

The severe phenotypes in p110α/Cx50 and PTEN/Cx50 double deficient lenses suggest that PI3K, PTEN and Cx50 participate in both distinct and common regulatory pathways that are necessary to maintain normal lens growth and homeostasis.

Reduction of ETV1 is Identified as a Prominent Feature of Age-Related Cataract

PURPOSE

To identify the inactive genes in cataract lenses and explore their function in lens epithelial cells (LECs).

METHODS

Lens epithelium samples obtained from both age-related cataract (ARC) patients and normal donors were subjected to two forms of histone H3 immunoprecipitation: H3K9ac and H3K27me3 chromatin immunoprecipitation (ChIP), followed by ChIP-seq. The intersection set of "active genes in normal controls" and "repressed genes in cataract lenses" was identified. To validate the role of a specific gene, ETV1, within this set, quantitative polymerase chain reaction (qPCR), western blot, and immunofluorescence were performed using clinical lens epithelium samples. Small interference RNA (siRNA) was utilized to reduce the mRNA level of ETV1 in cultured LECs. Following this, transwell assay and western blot was performed to examine the migration ability of the cells. Furthermore, RNA-seq analysis was conducted on both cell samples with ETV1 knockdown and control cells. Additionally, the expression level of ETV1 in LECs was examined using qPCR under H2O2 treatment.

RESULTS

Six genes were identified in the intersection set of "active genes in normal controls" and "repressed genes in ARC lenses". Among these genes, ETV1 showed the most significant fold-change decrease in the cataract samples compared to the control samples. After ETV1 knockdown by siRNA in cultured LECs, reduced cell migration was observed, along with a decrease in the expression of β-Catenin and Vimentin, two specific genes associated with cell migration. In addition, under the oxidative stress induced by H2O2 treatment, the expression level of ETV1 in LECs significantly decreased.

CONCLUSIONS

Based on the findings of this study, it can be concluded that ETV1 is significantly reduced in human ARC lenses. The repression of ETV1 in ARC lenses appears to contribute to the disrupted differentiation of lens epithelium, which is likely caused by the inhibition of both cell differentiation and migration processes.

Clearing the light path: proteoglycans and their important roles in the lens and cornea

Some of the earliest studies of glycans were performed on mammalian corneas and lenses with many of the key concepts we currently recognize as being fundamental to our understanding of basic cell biology arising from these studies. Proteoglycans and their GAG side chains are essential components of the ECM of the lens capsule. They also are present in the anterior corneal epithelial basement membrane and the posterior (Decemet's) basement membrane, and they organize collagen fiber diameters and spacing in the corneal stroma to maintain stromal clarity. Studies using genetically engineered mice and characterization of spontaneously arising mutations in genes controlling proteoglycan synthesis have generated new insight into the roles played by proteoglycans in signal transduction. We now know that proteoglycans and GAGs can regulate cell signaling and the maintenance of avascularity and immune privilege that are hallmarks of these tissues. In addition, proteoglycan-rich matrices provide the pathways for immune cells to populate the surface of the lens as a response to corneal wounding and in a model of Experimental Autoimmune Uveitis. Here we describe what is known about proteoglycans and GAGs in the cornea and lens. This knowledge has begun to provide promising leads into new proteoglycan-based treatments aimed at restoring and maintaining homeostasis in the cornea. Future studies are needed to determine how these new drugs impact the recruitment of immune cells to the lens for functions in restoring/maintaining homeostasis in the eye.

Tonic ErbB signaling underlies TGFβ-induced activation of ERK and is required for lens cell epithelial to myofibroblast transition

Fibrosis is a major, but incompletely understood, component of many diseases. The most common vision-disrupting complication of cataract surgery involves differentiation of residual lens cells into myofibroblasts. In serum-free primary cultures of lens epithelial cells (DCDMLs), inhibitors of either ERK or of ErbB signaling prevent TGFβ from upregulating both early (fibronectin) and late (αSMA) markers of myofibroblast differentiation. TGFβ stimulates ERK in DCDMLs within 1.5 h. Kinase inhibitors of ErbBs, but not of several other growth factor receptors in lens cells, reduce phospho ERK to below basal levels in the absence or presence of TGFβ. This effect is attributable to constitutive ErbB activity playing a major role in regulating the basal levels pERK. Additional studies support a model in which TGFβ-generated reactive oxygen species serve to indirectly amplify ERK signaling downstream of tonically active ErbBs to mediate myofibroblast differentiation. ERK activity is in turn essential for expression of ErbB1 and ErbB2, major inducers of ERK signaling. By mechanistically linking TGFβ, ErbB, and ERK signaling to myofibroblast differentiation, our data elucidate a new role for ErbBs in fibrosis and reveal a novel mode by which TGFβ directs lens cell fate.

Conditional Ablation of Spred1 and Spred2 in the Eye Lens Negatively Impacts Its Development and Growth

The development and growth of the eye depends on normal lens morphogenesis and its growth. This growth, in turn, is dependent on coordinated proliferation of the lens epithelial cells and their subsequent differentiation into fiber cells. These cellular processes are tightly regulated to maintain the precise cellular structure and size of the lens, critical for its transparency and refractive properties. Growth factor-mediated MAPK signaling driven by ERK1/2 has been reported as essential for regulating cellular processes of the lens, with ERK1/2 signaling tightly regulated by endogenous antagonists, including members of the Sprouty and related Spred families. Our previous studies have demonstrated the importance of both these inhibitory molecules in lens and eye development. In this study, we build on these findings to highlight the importance of Spreds in regulating early lens morphogenesis by modulating ERK1/2-mediated lens epithelial cell proliferation and fiber differentiation. Conditional loss of both Spred1 and Spred2 in early lens morphogenesis results in elevated ERK1/2 phosphorylation, hyperproliferation of lens epithelia, and an associated increase in the rate of fiber differentiation. This results in transient microphakia and microphthalmia, which disappears, owing potentially to compensatory Sprouty expression. Our data support an important temporal role for Spreds in the early stages of lens morphogenesis and highlight how negative regulation of ERK1/2 signaling is critical for maintaining lens proliferation and fiber differentiation in situ throughout life.

Fibroblast growth factor-induced lens fiber cell elongation is driven by the stepwise activity of Rho and Rac

The spheroidal shape of the eye lens is crucial for precise light focusing onto the retina. This shape is determined by concentrically aligned, convexly elongated lens fiber cells along the anterior and posterior axis of the lens. Upon differentiation at the lens equator, the fiber cells increase in height as their apical and basal tips migrate towards the anterior and posterior poles, respectively. The forces driving this elongation and migration remain unclear. We found that, in the mouse lens, membrane protrusions or lamellipodia are observed only in the maturing fibers undergoing cell curve conversion, indicating that lamellipodium formation is not the primary driver of earlier fiber migration. We demonstrated that elevated levels of fibroblast growth factor (FGF) suppressed the extension of Rac-dependent protrusions, suggesting changes in the activity of FGF controlling Rac activity, switching to lamellipodium-driven migration. Inhibitors of ROCK, myosin and actin reduced the height of both early and later fibers, indicating that elongation of these fibers relies on actomyosin contractility. Consistent with this, active RhoA was detected throughout these fibers. Given that FGF promotes fiber elongation, we propose that it does so through regulation of Rho activity.

FGF-independent MEK1/2 signalling in the developing foetal testis is essential for male germline differentiation in mice

BACKGROUND

Disrupted germline differentiation or compromised testis development can lead to subfertility or infertility and are strongly associated with testis cancer in humans. In mice, SRY and SOX9 induce expression of Fgf9, which promotes Sertoli cell differentiation and testis development. FGF9 is also thought to promote male germline differentiation but the mechanism is unknown. FGFs typically signal through mitogen-activated protein kinases (MAPKs) to phosphorylate ERK1/2 (pERK1/2). We explored whether FGF9 regulates male germline development through MAPK by inhibiting either FGF or MEK1/2 signalling in the foetal testis immediately after gonadal sex determination and testis cord formation, but prior to male germline commitment.

RESULTS

pERK1/2 was detected in Sertoli cells and inhibition of MEK1/2 reduced Sertoli cell proliferation and organisation and resulted in some germ cells localised outside of the testis cords. While pERK1/2 was not detected in germ cells, inhibition of MEK1/2 after somatic sex determination profoundly disrupted germ cell mitotic arrest, dysregulated a broad range of male germline development genes and prevented the upregulation of key male germline markers, DPPA4 and DNMT3L. In contrast, while FGF inhibition reduced Sertoli cell proliferation, expression of male germline markers was unaffected and germ cells entered mitotic arrest normally. While male germline differentiation was not disrupted by FGF inhibition, a range of stem cell and cancer-associated genes were commonly altered after 24 h of FGF or MEK1/2 inhibition, including genes involved in the maintenance of germline stem cells, Nodal signalling, proliferation, and germline cancer.

CONCLUSIONS

Together, these data demonstrate a novel role for MEK1/2 signalling during testis development that is essential for male germline differentiation, but indicate a more limited role for FGF signalling. Our data indicate that additional ligands are likely to act through MEK1/2 to promote male germline differentiation and highlight a need for further mechanistic understanding of male germline development.

Fibroblast Growth Factor-induced lens fiber cell elongation is driven by the stepwise activity of Rho and Rac

The spheroidal shape of the eye lens is critical for precise light focusing onto the retina. This shape is determined by concentrically aligned, convexly elongated lens fiber cells along the anterior and posterior axis of the lens. Upon differentiation at the lens equator, the fiber cells increase in height as their apical and basal tips migrate towards the anterior and posterior poles, respectively. The forces driving this elongation and migration remain unclear. We found that membrane protrusions or lamellipodia are observed only in the maturing fibers undergoing cell curve conversion, indicating lamellipodium is not the primary driver of earlier fiber migration. We demonstrated that elevated levels of fibroblast growth factor (FGF) suppressed the extension of Rac-dependent protrusions, suggesting changes in the activity of FGF controling Rac activity, switching to lamellipodium-driven migration. Inhibitors of ROCK, myosin, and actin reduced the height of both early and later fibers, indicating elongation of these fibers relies on actomyosin contractility. Consistently, active RhoA was detected throughout these fibers. Given that FGF promotes fiber elongation, we propose it to do so through regulation of Rho activity.

Self-formation of concentric zones of telencephalic and ocular tissues and directional retinal ganglion cell axons

The telencephalon and eye in mammals are originated from adjacent fields at the anterior neural plate. Morphogenesis of these fields generates telencephalon, optic-stalk, optic-disc, and neuroretina along a spatial axis. How these telencephalic and ocular tissues are specified coordinately to ensure directional retinal ganglion cell (RGC) axon growth is unclear. Here, we report self-formation of human telencephalon-eye organoids comprising concentric zones of telencephalic, optic-stalk, optic-disc, and neuroretinal tissues along the center-periphery axis. Initially-differentiated RGCs grew axons towards and then along a path defined by adjacent PAX2+ VSX2+ optic-disc cells. Single-cell RNA sequencing of these organoids not only confirmed telencephalic and ocular identities but also identified expression signatures of early optic-disc, optic-stalk, and RGCs. These signatures were similar to those in human fetal retinas. Optic-disc cells in these organoids differentially expressed FGF8 and FGF9; FGFR inhibitions drastically decreased early RGC differentiation and directional axon growth. Through the RGC-specific cell-surface marker CNTN2 identified here, electrophysiologically excitable RGCs were isolated under a native condition. Our findings provide insight into the coordinated specification of early telencephalic and ocular tissues in humans and establish resources for studying RGC-related diseases such as glaucoma.

Self-formation of concentric zones of telencephalic and ocular tissues and directional retinal ganglion cell axons

The telencephalon and eye in mammals are originated from adjacent fields at the anterior neural plate. Morphogenesis of these fields generates telencephalon, optic-stalk, optic-disc, and neuroretina along a spatial axis. How these telencephalic and ocular tissues are specified coordinately to ensure directional retinal ganglion cell (RGC) axon growth is unclear. Here, we report self-formation of human telencephalon-eye organoids comprising concentric zones of telencephalic, optic-stalk, optic-disc, and neuroretinal tissues along the center-periphery axis. Initially-differentiated RGCs grew axons towards and then along a path defined by adjacent PAX2+ VSX2+ optic-disc cells. Single-cell RNA sequencing of these organoids not only confirmed telencephalic and ocular identities but also identified expression signatures of early optic-disc, optic-stalk, and RGCs. These signatures were similar to those in human fetal retinas. Optic-disc cells in these organoids differentially expressed FGF8 and FGF9; FGFR inhibitions drastically decreased early RGC differentiation and directional axon growth. Through the RGC-specific cell-surface marker CNTN2 identified here, electrophysiologically excitable RGCs were isolated under a native condition. Our findings provide insight into the coordinated specification of early telencephalic and ocular tissues in humans and establish resources for studying RGC-related diseases such as glaucoma.

Self-formation of concentric zones of telencephalic and ocular tissues and directional retinal ganglion cell axons

The telencephalon and eye in mammals are originated from adjacent fields at the anterior neural plate. Morphogenesis of these fields generates telencephalon, optic-stalk, optic-disc, and neuroretina along a spatial axis. How these telencephalic and ocular tissues are specified coordinately to ensure directional retinal ganglion cell (RGC) axon growth is unclear. Here, we report the self-formation of human telencephalon-eye organoids comprising concentric zones of telencephalic, optic-stalk, optic-disc, and neuroretinal tissues along the center-periphery axis. Initially-differentiated RGCs grew axons towards and then along a path defined by adjacent PAX2+ optic-disc cells. Single-cell RNA sequencing of CONCEPT organoids not only confirmed telencephalic and ocular identities but also identified expression signatures of early optic-disc, optic-stalk, and RGCs. These signatures were similar to those in human fetal retinas. Optic-disc cells in CONCEPT organoids differentially expressed FGF8 and FGF9 ; FGFR inhibitions drastically decreased RGC differentiation and directional axon growth. Through the identified RGC-specific cell-surface marker CNTN2, electrophysiologically-excitable RGCs were isolated under a native condition. Our findings provide insight into the coordinated specification of early telencephalic and ocular tissues in humans and establish resources for studying RGC-related diseases such as glaucoma.

Impact statement

A human telencephalon-eye organoid model that exhibited axon growth and pathfinding from retinal ganglion cell (RGC) axons is reported; via cell surface marker CNTN2 identified using scRNA-seq, early RGCs were isolated under a native condition.

Spatiotemporal Localisation of Heparan Sulphate Proteoglycans throughout Mouse Lens Morphogenesis

Heparan sulphate proteoglycans (HSPGs) consist of a core protein decorated with sulphated HS-glycosaminoglycan (GAG) chains. These negatively charged HS-GAG chains rely on the activity of PAPSS synthesising enzymes for their sulfation, which allows them to bind to and regulate the activity of many positively charged HS-binding proteins. HSPGs are found on the surfaces of cells and in the pericellular matrix, where they interact with various components of the cell microenvironment, including growth factors. By binding to and regulating ocular morphogens and growth factors, HSPGs are positioned to orchestrate growth factor-mediated signalling events that are essential for lens epithelial cell proliferation, migration, and lens fibre differentiation. Previous studies have shown that HS sulfation is essential for lens development. Moreover, each of the full-time HSPGs, differentiated by thirteen different core proteins, are differentially localised in a cell-type specific manner with regional differences in the postnatal rat lens. Here, the same thirteen HSPG-associated GAGs and core proteins as well as PAPSS2, are shown to be differentially regulated throughout murine lens development in a spatiotemporal manner. These findings suggest that HS-GAG sulfation is essential for growth factor-induced cellular processes during embryogenesis, and the unique and divergent localisation of different lens HSPG core proteins indicates that different HSPGs likely play specialized roles during lens induction and morphogenesis.

Multiomics Analysis Reveals Novel Genetic Determinants for Lens Differentiation, Structure, and Transparency

Recent advances in next-generation sequencing and data analysis have provided new gateways for identification of novel genome-wide genetic determinants governing tissue development and disease. These advances have revolutionized our understanding of cellular differentiation, homeostasis, and specialized function in multiple tissues. Bioinformatic and functional analysis of these genetic determinants and the pathways they regulate have provided a novel basis for the design of functional experiments to answer a wide range of long-sought biological questions. A well-characterized model for the application of these emerging technologies is the development and differentiation of the ocular lens and how individual pathways regulate lens morphogenesis, gene expression, transparency, and refraction. Recent applications of next-generation sequencing analysis on well-characterized chicken and mouse lens differentiation models using a variety of omics techniques including RNA-seq, ATAC-seq, whole-genome bisulfite sequencing (WGBS), chip-seq, and CUT&RUN have revealed a wide range of essential biological pathways and chromatin features governing lens structure and function. Multiomics integration of these data has established new gene functions and cellular processes essential for lens formation, homeostasis, and transparency including the identification of novel transcription control pathways, autophagy remodeling pathways, and signal transduction pathways, among others. This review summarizes recent omics technologies applied to the lens, methods for integrating multiomics data, and how these recent technologies have advanced our understanding ocular biology and function. The approach and analysis are relevant to identifying the features and functional requirements of more complex tissues and disease states.

FGF-2 Differentially Regulates Lens Epithelial Cell Behaviour during TGF-β-Induced EMT

Fibroblast growth factor (FGF) and transforming growth factor-beta (TGF-β) can regulate and/or dysregulate lens epithelial cell (LEC) behaviour, including proliferation, fibre differentiation, and epithelial–mesenchymal transition (EMT). Earlier studies have investigated the crosstalk between FGF and TGF-β in dictating lens cell fate, that appears to be dose dependent. Here, we tested the hypothesis that a fibre-differentiating dose of FGF differentially regulates the behaviour of lens epithelial cells undergoing TGF-β-induced EMT. Postnatal 21-day-old rat lens epithelial explants were treated with a fibre-differentiating dose of FGF-2 (200 ng/mL) and/or TGF-β2 (50 pg/mL) over a 7-day culture period. We compared central LECs (CLECs) and peripheral LECs (PLECs) using immunolabelling for changes in markers for EMT (α-SMA), lens fibre differentiation (β-crystallin), epithelial cell adhesion (β-catenin), and the cytoskeleton (alpha-tropomyosin), as well as Smad2/3- and MAPK/ERK1/2-signalling. Lens epithelial explants cotreated with FGF-2 and TGF-β2 exhibited a differential response, with CLECs undergoing EMT while PLECs favoured more of a lens fibre differentiation response, compared to the TGF-β-only-treated explants where all cells in the explants underwent EMT. The CLECs cotreated with FGF and TGF-β immunolabelled for α-SMA, with minimal β-crystallin, whereas the PLECs demonstrated strong β-crystallin reactivity and little α-SMA. Interestingly, compared to the TGF-β-only-treated explants, α-SMA was significantly decreased in the CLECs cotreated with FGF/TGF-β. Smad-dependent and independent signalling was increased in the FGF-2/TGF-β2 co-treated CLECs, that had a heightened number of cells with nuclear localisation of Smad2/3 compared to the PLECs, that in contrast had more pronounced ERK1/2-signalling over Smad2/3 activation. The current study has confirmed that FGF-2 is influential in differentially regulating the behaviour of LECs during TGF-β-induced EMT, leading to a heterogenous cell population, typical of that observed in the development of post-surgical, posterior capsular opacification (PCO). This highlights the cooperative relationship between FGF and TGF-β leading to lens pathology, providing a different perspective when considering preventative measures for controlling PCO.

Heparan sulfate proteoglycans (HSPGs) of the ocular lens

Heparan sulfate proteoglycans (HSPGs) reside in most cells; on their surface, in the pericellular milieu and/or extracellular matrix. In the eye, HSPGs can orchestrate the activity of key signalling molecules found in the ocular environment that promote its development and homeostasis. To date, our understanding of the specific roles played by individual HSPG family members, and the heterogeneity of their associated sulfated HS chains, is in its infancy. The crystalline lens is a relatively simple and well characterised ocular tissue that provides an ideal stage to showcase and model the expression and unique roles of individual HSPGs. Individual HSPG core proteins are differentially localised to eye tissues in a temporal and spatial developmental- and cell-type specific manner, and their loss or functional disruption results in unique phenotypic outcomes for the lens, and other ocular tissues. More recent work has found that different HS sulfation enzymes are also presented in a cell- and tissue-specific manner, and that disruption of these different sulfation patterns affects specific HS-protein interactions. Not surprisingly, these sulfated HS chains have also been reported to be required for lens and eye development, with dysregulation of HS chain structure and function leading to pathogenesis and eye-related phenotypes. In the lens, HSPGs undergo significant and specific changes in expression and function that can drive pathology, or in some cases, promote tissue repair. As master signalling regulators, HSPGs may one day serve as valuable biomarkers, and even as putative targets for the development of novel therapeutics, not only for the eye but for many other systemic pathologies.

Mitogen-activated protein kinase inhibitor PD98059 improves neuroimmune dysfunction in experimental autoimmune encephalomyelitis in SJL/J mice through the inhibition of nuclear factor-kappa B signaling in B cells

Multiple sclerosis (MS) is a severe autoimmune disease leading to demyelination, followed by consequent axonal degeneration, causing sensory, motor, cognitive, and visual symptoms. Experimental autoimmune encephalomyelitis (EAE) is the most well-studied animal model of MS. Most current MS treatments are not completely effective, and severe side effects remain a great challenge. In this study, we report the therapeutic efficacy of PD98059, a potent mitogen-activated protein kinase inhibitor, on proteolipid protein (PLP)_139-151-induced EAE in SJL/J mice. Following the induction of EAE, mice were intraperitoneally treated with PD98059 (5 mg/kg for 14 days) daily from day 14 to day 28. This study investigated the effects of PD98059 on C-C motif chemokine receptor 6 (CCR6), CD14, NF-κB p65, IκBα, GM-CSF, iNOS, IL-6, TNF-α in CD45R⁺ B lymphocytes using flow cytometry. Furthermore, we analyzed the effect of PD98059 on CCR6, CD14, NF-κB p65, GM-CSF, iNOS, IL-6, and TNF-α mRNA and protein expression levels using qRT-PCR analysis in brain tissues. Mechanistic investigations revealed that PD98059-treated in mice with EAE had reduced CD45R⁺CCR6⁺, CD45R⁺CD14⁺, CD45R⁺NF-κB p65⁺, CD45R⁺GM-CSF⁺, CD45R⁺iNOS⁺, CD45R⁺IL-6⁺, and CD45R⁺TNF-α⁺ cells and increased CD45R⁺IκBα⁺ cells compared with vehicle-treated control mice in the spleen. Moreover, downregulation of CCR6, CD14, NF-κB p65, GM-CSF, iNOS, IL-6, and TNF-α mRNA expression level was observed in PD98059-treated mice with EAE compared with vehicle-treated control mice in the brain tissue. The results of this study demonstrate that PD98059 modulates inflammatory mediators through multiple cellular mechanisms. The results of this study suggest that PD98059 may be pursued as a therapeutic agent for the treatment of MS.

Lens Epithelial Explants Treated with Vitreous Humor Undergo Alterations in Chromatin Landscape with Concurrent Activation of Genes Associated with Fiber Cell Differentiation and Innate Immune Response

Lens epithelial explants are comprised of lens epithelial cells cultured in vitro on their native basement membrane, the lens capsule. Biologists have used lens epithelial explants to study many different cellular processes including lens fiber cell differentiation. In these studies, fiber differentiation is typically measured by cellular elongation and the expression of a few proteins characteristically expressed by lens fiber cells in situ. Chromatin and RNA was collected from lens epithelial explants cultured in either un-supplemented media or media containing 50% bovine vitreous humor for one or five days. Chromatin for ATAC-sequencing and RNA for RNA-sequencing was prepared from explants to assess regions of accessible chromatin and to quantitatively measure gene expression, respectively. Vitreous humor increased chromatin accessibility in promoter regions of genes associated with fiber differentiation and, surprisingly, an immune response, and this was associated with increased transcript levels for these genes. In contrast, vitreous had little effect on the accessibility of the genes highly expressed in the lens epithelium despite dramatic reductions in their mRNA transcripts. An unbiased analysis of differentially accessible regions revealed an enrichment of cis-regulatory motifs for RUNX, SOX and TEAD transcription factors that may drive differential gene expression in response to vitreous.

Autophagy Requirements for Eye Lens Differentiation and Transparency

Recent evidence points to autophagy as an essential cellular requirement for achieving the mature structure, homeostasis, and transparency of the lens. Collective evidence from multiple laboratories using chick, mouse, primate, and human model systems provides evidence that classic autophagy structures, ranging from double-membrane autophagosomes to single-membrane autolysosomes, are found throughout the lens in both undifferentiated lens epithelial cells and maturing lens fiber cells. Recently, key autophagy signaling pathways have been identified to initiate critical steps in the lens differentiation program, including the elimination of organelles to form the core lens organelle-free zone. Other recent studies using ex vivo lens culture demonstrate that the low oxygen environment of the lens drives HIF1a-induced autophagy via upregulation of essential mitophagy components to direct the specific elimination of the mitochondria, endoplasmic reticulum, and Golgi apparatus during lens fiber cell differentiation. Pioneering studies on the structural requirements for the elimination of nuclei during lens differentiation reveal the presence of an entirely novel structure associated with degrading lens nuclei termed the nuclear excisosome. Considerable evidence also indicates that autophagy is a requirement for lens homeostasis, differentiation, and transparency, since the mutation of key autophagy proteins results in human cataract formation.

Role of FGF10/FGFR2b Signaling in Homeostasis and Regeneration of Adult Lacrimal Gland and Corneal Epithelium Proliferation

Purpose

Fibroblast growth factor 10 (FGF10) is involved in eye, meibomian, and lacrimal gland (LG) development, but its function in adult eye structures remains unknown. This study aimed to characterize the role of FGF10 in homeostasis and regeneration of adult LG and corneal epithelium proliferation.

Methods

Quantitative reverse transcription PCR was used for analysis of FGF10 expression in both early postnatal and adult mouse LG, and RNA sequencing was used to analyze gene expression during LG inflammation. FGF10 was injected into the LG of two mouse models of Sjögren's syndrome and healthy controls. Flow cytometry, BrdU cell proliferation assay, immunostaining, and hematoxylin and eosin staining were used to evaluate the effects of FGF10 injection on inflammation and cell proliferation in vivo. Mouse and human epithelial cell cultures were treated with FGF10 in vitro, and cell viability was assessed using WST-8 and adenosine triphosphate (ATP) quantification assays.

Results

The level of Fgf10 mRNA expression was lower in adult LG compared to early postnatal LG and was downregulated in chronic inflammation. FGF10 injection into diseased LGs significantly increased cell proliferation and decreased the number of B cells. Mouse and human corneal epithelial cell cultures treated with FGF10 showed significantly higher cell viability and greater cell proliferation.

Conclusions

FGF10 appears to promote regeneration in damaged adult LGs. These findings have therapeutic potential for developing new treatments for dry eye disease targeting the ability of the cornea and LG to regenerate.

A possible connection between reactive oxygen species and the unfolded protein response in lens development: From insight to foresight

The lens is a relatively special and simple organ. It has become an ideal model to study the common developmental characteristics among different organic systems. Lens development is a complex process influenced by numerous factors, including signals from the intracellular and extracellular environment. Reactive oxygen species (ROS) are a group of highly reactive and oxygen-containing molecules that can cause endoplasmic reticulum stress in lens cells. As an adaptive response to ER stress, lens cells initiate the unfolded protein response (UPR) to maintain normal protein synthesis by selectively increasing/decreasing protein synthesis and increasing the degradation of misfolded proteins. Generally, the UPR signaling pathways have been well characterized in the context of many pathological conditions. However, recent studies have also confirmed that all three UPR signaling pathways participate in a variety of developmental processes, including those of the lens. In this review, we first briefly summarize the three stages of lens development and present the basic profiles of ROS and the UPR. We then discuss the interconnections between lens development and these two mechanisms. Additionally, the potential adoption of human pluripotent stem-cell-based lentoids in lens development research is proposed to provide a novel perspective on future developmental studies.

Double Deletion of PI3K and PTEN Modifies Lens Postnatal Growth and Homeostasis

We have previously shown that the conditional deletion of either the p110α catalytic subunit of phosphatidylinositol 3-kinase (PI3K), or its opposing phosphatase, phosphatase and tensin homolog (PTEN), had distinct effects on lens growth and homeostasis. The deletion of p110α reduced the levels of phosphorylated Akt and equatorial epithelial cell proliferation, and resulted in smaller transparent lenses in adult mice. The deletion of PTEN increased levels of phosphorylated Akt, altered lens sodium transport, and caused lens rupture and cataract. Here, we have generated conditional p110α/PTEN double-knockout mice, and evaluated epithelial cell proliferation and lens homeostasis. The double deletion of p110α and PTEN rescued the defect in lens size seen after the single knockout of p110α, but accelerated the lens rupture phenotype seen in PTEN single-knockout mice. Levels of phosphorylated Akt in double-knockout lenses were significantly higher than in wild-type lenses, but not as elevated as those reported for PTEN single-knockout lenses. These results showed that the double deletion of the p110α catalytic subunit of PI3K and its opposing phosphatase, PTEN, exacerbated the rupture defect seen in the single PTEN knockout and alleviated the growth defect observed in the single p110α knockout. Thus, the integrity of the PI3K signaling pathway was absolutely essential for proper lens homeostasis, but not for lens growth.

Radiation-Induced Alterations in Proliferation, Migration, and Adhesion in Lens Epithelial Cells and Implications for Cataract Development

The lens of the eye is one of the most radiosensitive tissues. Although the exact mechanism of radiation-induced cataract development remains unknown, altered proliferation, migration, and adhesion have been proposed as factors. Lens epithelial cells were exposed to X-rays (0.1-2 Gy) and radiation effects were examined after 12 h and 7 day. Proliferation was quantified using an MTT assay, migration was measured using a Boyden chamber and wound-healing assay, and adhesion was assessed on three extracellular matrices. Transcriptional changes were also examined using RT-qPCR for a panel of genes related to these processes. In general, a nonlinear radiation response was observed, with the greatest effects occurring at a dose of 0.25 Gy. At this dose, a reduction in proliferation occurred 12 h post irradiation (82.06 ± 2.66%), followed by an increase at 7 day (116.16 ± 3.64%). Cell migration was increased at 0.25 Gy, with rates 121.66 ± 6.49% and 232.78 ± 22.22% greater than controls at 12 h and 7 day respectively. Cell adhesion was consistently reduced above doses of 0.25 Gy. Transcriptional alterations were identified at these same doses in multiple genes related to proliferation, migration, and adhesion. Overall, this research began to elucidate the functional changes that occur in lens cells following radiation exposure, thereby providing a better mechanistic understanding of radiation-induced cataract development.

An Atlas of Heparan Sulfate Proteoglycans in the Postnatal Rat Lens

Purpose

The arrangement of lens cells is regulated by ocular growth factors. Although the effects of these inductive molecules on lens cell behavior (proliferation, survival, and fiber differentiation) are well-characterized, the precise mechanisms underlying the regulation of growth factor-mediated signaling in lens remains elusive. Increasing evidence highlights the importance of heparan sulfate proteoglycans (HSPGs) for the signaling regulation of growth factors; however, the identity of the different lens HSPGs and the specific roles they play in lens biology are still unknown.

Methods

Semiquantitative real-time (RT)‐PCR and immunolabeling were used to characterize the spatial distribution of all known HSPG core proteins and their associated glycosaminoglycans (heparan and chondroitin sulfate) in the postnatal rat lens. Fibroblast growth factor (FGF)-2-treated lens epithelial explants, cultured in the presence of Surfen (an inhibitor of heparan sulfate [HS]-growth factor binding interactions) were used to investigate the requirement for HS in FGF-2-induced proliferation, fiber differentiation, and ERK1/2-signaling.

Results

The lens expresses all HSPGs. These HSPGs are differentially localized to distinct functional regions of the lens. In vitro, inhibition of HS-sulfation with Surfen blocked FGF-2-mediated ERK1/2-signaling associated with lens epithelial cell proliferation and fiber differentiation, highlighting that these cellular processes are dependent on HS.

Conclusions

These findings support a requirement for HSPGs in FGF-2 driven lens cell proliferation and fiber differentiation. The identification of specific HSPG core proteins in key functional lens regions, and the divergent expression patterns of closely related HSPGs, suggests that different HSPGs may differentially regulate growth factor signaling networks leading to specific biological events involved in lens growth and maintenance.

Mycobacterium tuberculosis effector PPE36 attenuates host cytokine storm damage via inhibiting macrophage M1 polarization

Tuberculosis caused by Mycobacterium tuberculosis remains a serious global public health threat. Macrophage polarization is crucial for the innate immunity against M. tuberculosis. However, how M. tuberculosis interferes with macrophage polarization is elusive. We demonstrated here that M. tuberculosis PPE36 (Rv2108) blocked macrophage M1 polarization, preventing the cytokine storm, and alleviating inflammatory damage to mouse immune organs. PPE36 inhibited the polarization of THP-1 cell differentiation to M1 macrophages, reduced mitochondrial dehydrogenase activity, inhibited the expression of CD16, and repressed the expression of pro-inflammatory cytokines IL-6 and TNF-α, as well as chemokines CXCL9, CXCL10, CCL3, and CCL5. Intriguingly, in the mouse infection model, PPE36 significantly alleviated the inflammatory damage of immune organs caused by a cytokine storm. Furthermore, we found that PPE36 inhibited the polarization of macrophages into mature M1 macrophages by suppressing the ERK signaling. The study provided novel insights into the function and mechanism of action of M. tuberculosis effector PPE36 both at the cellular and animal level.

H3K4me2 Promotes the Activation of lncCPSET1 by Jun in the Chicken PGC Formation

Primordial germ cells are the ancestors of female and male cells. Current research has shown that long non-coding RNA (lncRNA) and Histone methylation are the pivotal epigenetic factors in the PGC formation. However, there are few studies on the regulatory mechanism of lncRNA in the formation of PGC. Here, we define the lncRNA highly expressed in chicken PGC, lncCPSET1 (chicken-PGC-specifically-expressed transcript 1) This study found that compared with the interference of lncCPSET1/histone methylase Mll2 alone, the PGC formation was severely inhibited with the interference of lncCPSET1 and histone methylase Mll2 jointly in vivo and in vitro. Studies on the transcription level of lncCPSET1 found that H3K4me2 and transcription factor Jun have a positive effect on the activation of lncCPSET1; while DNA hypomethylation inhibits the expression of lncCPSET1. In terms of mechanism, compared with DNA methylation, H3K4me2 dominates lncCPSET1 activation. H3K4me2 can be enriched in the lncCPSET1 promoter, change its chromosome conformation, recruit the transcription factor Jun, and activate the expression of lncCPSET1. Taken together, we confirmed the model that H3K4me2 rather than DNA hypomethylation mediates Jun to regulate lncCPSET1 transcription, which broadens the study of lncCPSET1 pre-transcriptional mechanism.

LncRNA TUG1 regulates FGF1 to enhance endothelial differentiation of adipose-derived stem cells by sponging miR-143

Adipose-derived stem cells (ADSCs) have emerged as a cell source for regeneration medicine. ADSCs possess the capacity to differentiate into endothelial cells and serve an essential role in vascular development and function. LncRNA taurine upregulated gene 1 (TUG1) has recently been linked with angiogenesis in hepatoblastoma. However, the roles of TUG1 in endothelial differentiation of ADSCs remain unidentified. Human adipose-derived stem cells (hADSCs) were obtained and characterized by flow cytometry, Oil red O and Alizarin Red staining. HADSCs were maintained in the endothelial differentiation medium and the expressions of TUG1, miR-143, and FGF1 were examined by qRT-PCR. To assess endothelial differentiation, the expressions of CD31, von Willebrand factor (vWF), VE-cadherin were examined by Western blot analysis, qRT-PCR, and immunofluorescence. Tube formation in Matrigel was examined. The interactions between TUG1 and miR-143, miR-143 and FGF1 were validated by luciferase assays. During the endothelial differentiation process, TUG1 and FGF1 were upregulated, whereas miR-143 was downregulated. TUG1 overexpression downregulated miR-143, upregulated FGF1, CD31, vWF, and VE-cadherin, and enhanced capillary tube formation. Luciferase assays showed that TUG1 interacted with miR-143, and FGF1 was a direct target of miR-143. Furthermore, the enhancement of endothelial differentiation induced by TUG1 overexpression was abolished by miR-143 overexpression. Our findings implicated that lncRNA TUG1 promoted endothelial differentiation of ADSCs by regulating the miR-143/FGF1 axis.

Differential effects of MEK inhibitors on rat neural stem cell differentiation: Repressive roles of MEK2 in neurogenesis and induction of astrocytogenesis by PD98059

Neural stem cells (NSCs) proliferate and differentiate into neurons and glia depending on the culture environment. However, the underlying mechanisms determining the fate of NSCs are not fully understood. Growth factors facilitate NSC proliferation through mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) and MAPK activation, and NSCs differentiate into neurons, astrocytes, or oligodendrocytes when mitogens are withdrawn from the culture media. Here, we aimed to identify the effects and roles of MEK signaling on the determination of NSC fate. MEK inhibitors, U0126, SL327, and PD98059, had differential effects on NSC differentiation. U0126 and SL327, which are known to inhibit MEK1 and MEK2, induced neuronal differentiation, whereas PD98059, which is reported to preferentially inhibit MEK1 at higher concentrations, increased astrocytogenesis. Knockdown of MEK2 using small interfering RNA increased neurogenesis and over-expression of wild type (WT) MEK2 inhibited neurogenesis, suggesting a repressive role of MEK2 in neuronal differentiation. The chemical structure of PD98059 appears to be important for induction of astrocytogenesis because not only PD98059 (2'-amino-3'-methoxyflavone) but also its chemical structural mimetic, 3'-methoxyflavone, enhanced astrocytogenesis. Therefore, in our study, we suggest that MEK inhibitors have distinct functions in determining NSC fate. Inhibition of MEK2 is important for induction of neurogenesis in NSCs. U0126 and SL327 increase neurogenesis through MEK2 inhibition, whereas PD98059 induced astrocytogenesis in NSCs, which is mediated by the chemical structure, particularly the 3'-methoxy group rather than its renowned MEK1 inhibition.

Ca2+-PKCα-ERK1/2 signaling pathway is involved in the suppressive effect of propofol on proliferation of neural stem cells from the neonatal rat hippocampus

Neonatal exposure to propofol induces persistent behavioral abnormalities in adulthood. In addition to triggering the apoptosis of neurons in the developing brain, anesthetics may contribute to the development of cognitive deficits by interfering neurogenesis. Given the importance of neural stem cell (NSC) proliferation in neurogenesis, the effect of propofol on NSC proliferation and the mechanisms underlying this effect were investigated. Hippocampal NSC proliferation from neonatal rats was examined using 5-bromo-2'-deoxyuridine incorporation assays in vitro. The [Ca²⁺]i was analyzed using flow cytometry. The activations of protein kinase C (PKC)-α and extracellular signal-regulated kinases 1/2 (ERK1/2) were measured by western blot. Our results showed that propofol significantly inhibited NSC proliferation in vitro. [Ca²⁺]i and activations of PKCα and ERK1/2 in NSCs were markedly suppressed by propofol (5, 10, 20, 40 and 80 μM). Ca²⁺ channel blocker verapamil, PKCα inhibitor chelerythrine and ERK1/2 kinase inhibitor PD98059 exerted their maximal effects on NSC function at concentrations of 20, 10 and 20 μM, respectively. Propofol (20 μM) could not produce further additional suppression effects when used in combination with verapamil (20 μM), chelerythrine (10 μM) or PD98059 (20 μM). In addition, phorbol-12-myristate-13-acetate (PMA, a activator of PKC) markedly attenuated the suppressive effects of propofol on ERK1/2 phosphorylation and NSC proliferation. The inhibition effects on PKCα activation, ERK1/2 phosphorylation and NSC proliferation induced by propofol were significantly improved by BayK8644 (a calcium channel agonist). These results indicate that propofol can inhibits hippocampal NSC proliferation by suppressing the Ca²⁺-PKCα-ERK1/2 signaling pathway.

Spred negatively regulates lens growth by modulating epithelial cell proliferation and fiber differentiation

Spred, like Sprouty (Spry) and also Sef proteins, have been identified as important regulators of receptor tyrosine kinase (RTK)-mediated MAPK/ERK-signaling in various developmental systems, controlling cellular processes such as proliferation, migration and differentiation. Spreds are widely expressed during early embryogenesis, and in the eye lens, become more localised in the lens epithelium with later development, overlapping with other antagonists including Spry. Given the synexpression of Spreds and Spry in lens, in order to gain a better understanding of their specific roles in regulating growth factor mediated-signaling and cell behavior, we established and characterised lines of transgenic mice overexpressing Spred1 or Spred2, specifically in the lens. This overexpression of Spreds resulted in a small lens phenotype during ocular morphogenesis, retarding its growth by compromising epithelial cell proliferation and fiber differentiation. These in situ findings were shown to be dependent on the ability of Spreds to suppress MAPK-signaling, in particular FGF-induced ERK1/2-signaling in lens cells. This was validated in vitro using lens epithelial explants, that highlighted the overlapping role of Spreds with Spry2, but not Spry1. This study provides insights into the putative function of Spreds and Spry in situ, some overlapping and some distinct, and their importance in regulating lens cell proliferation and fiber differentiation contributing to lens and eye growth.

A comprehensive spatial-temporal transcriptomic analysis of differentiating nascent mouse lens epithelial and fiber cells

Elucidation of both the molecular composition and organization of the ocular lens is a prerequisite to understand its development, function, pathology, regenerative capacity, as well as to model lens development and disease using in vitro differentiation of pluripotent stem cells. Lens is comprised of the anterior lens epithelium and posterior lens fibers, which form the bulk of the lens. Lens fibers differentiate from lens epithelial cells through cell cycle exit-coupled differentiation that includes cellular elongation, accumulation of crystallins, cytoskeleton and membrane remodeling, and degradation of organelles within the central region of the lens. Here, we profiled spatiotemporal expression dynamics of both mRNAs and non-coding RNAs from microdissected mouse nascent lens epithelium and lens fibers at four developmental time points (embryonic [E] day 14.5, E16.5, E18.5, and P0.5) by RNA-seq. During this critical time window, multiple complex biosynthetic and catabolic processes generate the molecular and structural foundation for lens transparency. Throughout this developmental window, 3544 and 3518 genes show consistently and significantly greater expression in the nascent lens epithelium and fibers, respectively. Comprehensive data analysis confirmed major roles of FGF-MAPK, Wnt/β-catenin, PI3K/AKT, TGF-β, and BMP signaling pathways and revealed significant novel contributions of mTOR, EIF2, EIF4, and p70S6K signaling in lens formation. Unbiased motif analysis within promoter regions of these genes with consistent expression changes between epithelium and fiber cells revealed an enrichment for both established (e.g. E2Fs, Etv5, Hsf4, c-Maf, MafG, MafK, N-Myc, and Pax6) transcription factors and a number of novel regulators of lens formation, such as Arntl2, Dmrta2, Stat5a, Stat5b, and Tulp3. In conclusion, the present RNA-seq data serves as a comprehensive reference resource for deciphering molecular principles of normal mammalian lens differentiation, mapping a full spectrum of signaling pathways and DNA-binding transcription factors operating in both lens compartments, and predicting novel pathways required to establish lens transparency.

ERK1/2 and JNK signaling synergistically modulate mitogenic effect of fibroblast growth factor 2 on liver cell

Proliferation of the adult hepatocyte population represents a central feature of tissue regeneration after liver injury and resection. This process could be driven by a diverse range of mitogens, such as hepatocyte growth factor (HGF) and fibroblast growth factor (FGF). Among FGF family, FGF2 is closely related to wound repair and cell proliferation. FGF2 does function in the process of angiogenesis in regenerating liver, while fewer reports are concerned with the impact and underlying mechanism of FGF2 on liver cell proliferation. To this end, an immortalized human normal hepatocyte L02 and mouse primary hepatocytes were exposed to FGF2 in this study. We demonstrate that FGF2 significantly enhances liver cell proliferation. Treatment with FGF2 obviously increases the phosphorylation level of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and c-Jun N-terminal kinase (JNK). Activity inhibition or expression down-regulation prove that both ERK1/2 and JNK signaling are required for FGF2-mediated effect on liver cell proliferation. Interestingly, interfering of ERK1/2 signaling results in marked decrease of JNK activation under FGF2 treatment, and JNK signaling is also involved in regulation of FGF2-induced ERK1/2 activation, suggesting that cross-talk between ERK1/2 and JNK signaling is important for FGF2 mitogenic activity. Both ERK1/2 and JNK signal via CREB to function in proliferation impact of FGF2 on liver cells. Taken together, this study reveals that ERK and JNK pathways synergistically regulate FGF2-induced liver cell proliferation via phosphorylating CREB, which will contribute to the understanding of FGF2 impact on liver cell proliferation and liver regeneration.

Negative regulation of lens fiber cell differentiation by RTK antagonists Spry and Spred

Sprouty (Spry) and Spred proteins have been identified as closely related negative regulators of the receptor tyrosine kinase (RTK)-mediated MAPK pathway, inhibiting cellular proliferation, migration and differentiation in many systems. As the different members of this antagonist family are strongly expressed in the lens epithelium in overlapping patterns, in this study we used lens epithelial explants to examine the impact of these different antagonists on the morphologic and molecular changes associated with fibroblast growth factor (FGF)-induced lens fiber differentiation. Cells in lens epithelial explants were transfected using different approaches to overexpress the different Spry (Spry1, Spry2) and Spred (Spred1, Spred2, Spred3) members, and we compared their ability to undergo FGF-induced fiber differentiation. In cells overexpressing any of the antagonists, the propensity for FGF-induced cell elongation was significantly reduced, indicative of a block to lens fiber differentiation. Of these antagonists, Spry1 and Spred2 appeared to be the most potent among their respective family members, demonstrating the greatest block in FGF-induced fiber differentiation based on the percentage of cells that failed to elongate. Consistent with the reported activity of Spry and Spred, we show that overexpression of Spry2 was able to suppress FGF-induced ERK1/2 phosphorylation in lens cells, as well as the ERK1/2-dependent fiber-specific marker Prox1, but not the accumulation of β-crystallins. Taken together, Spry and Spred proteins that are predominantly expressed in the lens epithelium in situ, appear to have overlapping effects on negatively regulating ERK1/2-signaling associated with FGF-induced lens epithelial cell elongation leading to fiber differentiation. This highlights the important regulatory role for these RTK antagonists in establishing and maintaining the distinct architecture and polarity of the lens.

ERK1/2-Dependent Gene Expression Contributing to TGFβ-Induced Lens EMT

PURPOSE

This study aims to highlight some of the genes that are differentially regulated by ERK1/2 signaling in TGFβ-induced EMT in lens, and their potential contribution to this pathological process.

MATERIALS AND METHODS

Rat lens epithelial explants were cultured with or without TGFβ over a 3-day-culture period to induce EMT, in the presence or absence of UO126 (ERK1/2 signaling inhibitor), both prior to TGFβ-treatment, or 24 or 48 hours after TGFβ treatment. Smad2/3-nuclear immunolabeling was used to indicate active TGFβ signaling, and quantitative RT-PCR was used to analyze changes in the different treatment groups in expression of the following representative genes: TGFβ signaling (Smad7, Smurf1, and Rnf111), epithelial markers (Pax6, Cdh1, Zeb1, and Zeb2), cell survival/death regulators (Bcl2, Bax, and Bad) and lens mesenchymal markers (Mmp9, Fn1, and Col1a1), over the 3 days of culture.

RESULTS

ERK1/2 was found to regulate the expression of Smurf1, Smad7, Rnf11, Cdh1, Pax6, Zeb1, Bcl2, Bax, and Bad genes in lens cells. TGFβ signaling was evident by nuclear localization of Smad2/3 and this was effectively blocked by pre-treatment with UO126, but not by post-treatment with this ERK1/2 signaling inhibitor. TGFβ induced the expression of its signaling partners (Smad7, Smurf1, and Rnf111), as well as lens mesenchymal genes (Mmp9, Fn1, and Col1a1), consistent with its role in inducing an EMT. These TGFβ-responsive signaling genes, as well as the mesenchymal markers, were all positively regulated by ERK1/2-activity. The expression levels of the lens epithelial genes we examined, and genes that were associated with cell death/survival, were not directly impacted by TGFβ.

CONCLUSIONS

TGFβ-mediated ERK1/2 signaling positively modulates the expression of mesenchymal genes in lens epithelial explants undergoing EMT, in addition to regulating TGFβ-mediated regulatory genes. Independent of TGFβ, ERK1/2 activity can also regulate the expression of endogenous lens epithelial genes, highlighting its potential key role in regulation of both normal and pathological lens cellular processes.

Role of Hippo Pathway Effector Tafazzin Protein in Maintaining Stemness of Umbilical Cord-Derived Mesenchymal Stem Cells (UC-MSC)

Tafazzin (TAZ) protein has been upregulated in various types of human cancers, although the basis for elevation is uncertain, it has been made definite that the effect of mutation in the hippo pathway, particularly when it is switched off, considerably activates tafazzin transcriptionally and thus this results in tissue or tumor overgrowth. Recent perceptions into the activity of tafazzin, have ascribed to it, a role as stem cell factor in mouse mesenchymal and as well as in neural stem cells. Being a downstream molecule in Hippo signalling, phosphorylation or dephosphorylation of tafazzin gene regulates its transcriptional activity and the stemness of mesenchymal stem cells. Commonly, extracellular matrix controls the stem cell fate commitment and perhaps tafazzin controls stemness through altering the extra cellular matrix. Extracellular matrix is generally made up of prime proteoglycans and the fate stabilization of the resulting lineages is surveilled by engineering these glycans. Tafazzin degradation and addition of proteoglycans affect physical attributes of the extracellular matrix that drives cell differentiation into various lineages. Thus, tafazzin along with major glycans present in the extracellular matrix is involved in imparting stemness. However, there are incoherent molecular events, wherein both tafazzin and the extracellular matrix components, together either activate or inhibit differentiation of stem cells. This review discusses about the role of tafazzin oncoprotein as a stemness factor.

A role for Hippo/YAP-signaling in FGF-induced lens epithelial cell proliferation and fibre differentiation

Recent studies indicate an important role for the transcriptional co-activator Yes-associated protein (YAP), and its regulatory pathway Hippo, in controlling cell growth and fate during lens development; however, the exogenous factors that promote this pathway are yet to be identified. Given that fibroblast growth factor (FGF)-signaling is an established regulator of lens cell behavior, the current study investigates the relationship between this pathway and Hippo/YAP-signaling during lens cell proliferation and fibre differentiation. Rat lens epithelial explants were cultured with FGF2 to induce epithelial cell proliferation or fibre differentiation. Immunolabeling methods were used to detect the expression of Hippo-signaling components, Total and Phosphorylated YAP, as well as fibre cell markers, Prox-1 and β-crystallin. FGF-induced lens cell proliferation was associated with a strong nuclear localisation of Total-YAP and low-level immuno-staining for phosphorylated-YAP. FGF-induced lens fibre differentiation was associated with a significant increase in cytoplasmic phosphorylated YAP (inactive state) and enhanced expression of core Hippo-signaling components. Inhibition of YAP with Verteporfin suppressed FGF-induced lens cell proliferation and ablated cell elongation during lens fibre differentiation. Inhibition of either FGFR- or MEK/ERK-signaling suppressed FGF-promoted YAP nuclear translocation. Here we propose that FGF promotes Hippo/YAP-signaling during lens cell proliferation and differentiation, with FGF-induced nuclear-YAP expression playing an essential role in promoting the proliferation of lens epithelial cells. An FGF-induced switch from proliferation to differentiation, hence regulation of lens growth, may play a key role in mediating Hippo suppression of YAP transcriptional activity.

Crk proteins transduce FGF signaling to promote lens fiber cell elongation

Specific cell shapes are fundamental to the organization and function of multicellular organisms. Fibroblast Growth Factor (FGF) signaling induces the elongation of lens fiber cells during vertebrate lens development. Nonetheless, exactly how this extracellular FGF signal is transmitted to the cytoskeletal network has previously not been determined. Here, we show that the Crk family of adaptor proteins, Crk and Crkl, are required for mouse lens morphogenesis but not differentiation. Genetic ablation and epistasis experiments demonstrated that Crk and Crkl play overlapping roles downstream of FGF signaling in order to regulate lens fiber cell elongation. Upon FGF stimulation, Crk proteins were found to interact with Frs2, Shp2 and Grb2. The loss of Crk proteins was partially compensated for by the activation of Ras and Rac signaling. These results reveal that Crk proteins are important partners of the Frs2/Shp2/Grb2 complex in mediating FGF signaling, specifically promoting cell shape changes.

As an embryo develops, its cells divide multiple times to transform into the specialized cell types that form our tissues and organs. To carry out specific roles, cells need to be of a certain shape. For example, in mammals, the cells that make up the main portion of the eye lens, develop into a fiber-like shape to be perfectly aligned with each other. This enables them to transmit light to the retina at the rear end of the eye. To do so, the lens cells increase over 1000 times in length with the help of a group of proteins called the Fibroblast Growth Factor, or FGF for short.

The FGF pathway includes a network of interacting proteins that transmit signals to molecules inside the lens cells to control how they specialize and grow. However, until now it was not clear how it does this. Here, Zhang et al. used mouse lens-cells grown in the laboratory to investigate how FGF signaling causes cells to change their structure. The experiments revealed two related proteins called Crk and Crkl that linked the FGF pathway with another signaling system. When these two proteins were removed from the lens cells, the lens cells were still able to specialize, but could no longer grow in length. This suggests that these two processes are independent of each other.

Moreover, Crk and Crkl helped the cells to change shape by increasing the amount of another group of proteins called Ras, which are known to both help cells to specialize and to regulate their shape. Zhang et al. discovered that the amount of Ras proteins determined whether cells specialized or modified their shape by changing the organization of proteins in the cell.

Millions of children are born with cataracts, a disease caused when lens cells fail to shape properly. A better knowledge of FGF signaling may help to understand how cataracts develop and inspire future treatments. Moreover, the pathways identified in this study could also apply to other organs and diseases in which FGF signaling is active.

Dose-dependent functions of fibroblast growth factor 9 regulate the fate of murine XY primordial germ cells

Male differentiation of primordial germ cells (PGCs) is initiated by the inhibition of entry into meiosis and exposure to male-inducing factor(s), which are regulated by somatic elements of the developing gonad. Fibroblast growth factor 9 (FGF9) produced by pre-Sertoli cells is essential for male gonadal differentiation and also contributes to survival and male differentiation of XY PGCs. However, it is not clear how FGF9 regulates PGC fate. Using a PGC culture system, we identified dose-dependent, fate-determining functions of FGF9 in XY PGCs. Treatment with low levels of FGF9 (0.2 ng/ml) increased expression of male-specific Dnmt3L and Nanos2 in XY PGCs. Conversely, treatment with high levels of FGF9 (25 ng/ml) suppressed male-specific gene expression and stimulated proliferation of XY PGCs. Western blotting showed that low FGF9 treatment enhanced p38 MAPK (mitogen-activated protein kinase) phosphorylation in the same cells. In contrast, high FGF9 treatment significantly stimulated the ERK (extracellular signal-regulated kinase)1/2 signaling pathway in XY PGCs. We investigated the relationship between the ERK1/2 signaling pathway stimulated by high FGF9 and regulation of PGC proliferation. An ERK1/2 inhibitor (U0126) suppressed the PGC proliferation that would otherwise be stimulated by high FGF9 treatment, and increased Nanos2 expression in XY PGCs. Conversely, a p38 MAPK inhibitor (SB202190) significantly suppressed Nanos2 expression that would otherwise be stimulated by low FGF9 in XY PGCs. Taken together, our results suggest that stage-specific expression of FGF9 in XY gonads regulates the balance between proliferation and differentiation of XY PGCs in a dose-dependent manner.

Aqueous humour-induced lens epithelial cell proliferation requires FGF-signalling

The eye lens grows by systematic proliferation of its epithelial cells and their differentiation into fibre cells. The anterior aqueous humour regulates lens epithelial cell proliferation whereas posteriorly, the vitreous stimulates lens fibre differentiation. Vitreous-derived members of the fibroblast growth factor (FGF) family induce fibre differentiation, with added support for FGFs as putative regulators of aqueous-induced lens cell proliferation. To further characterize this, given FGFs' known affinity for proteoglycans, we compared the effect of proteoglycan sulphation in growth factor- and aqueous-induced lens cell proliferation. Disruption of proteoglycan sulphation in lens cells specifically impacted on aqueous- and FGF-induced MAPK/ERK1/2-signalling, but not on that induced by other mitogens such as PDGF; however, cell proliferation was reduced in all treatment groups, regardless of the mitogen. Overall, by disrupting proteoglycan activity, we further highlight the significant role of FGFs in aqueous-induced ERK1/2 phosphorylation leading to lens cell proliferation.

Killing two birds with one stone: dual blockade of integrin and FGF signaling through targeting syndecan-4 in postoperative capsular opacification

The most common complication after cataract surgery is postoperative capsular opacification, which includes anterior capsular opacification (ACO) and posterior capsular opacification (PCO). Increased adhesion of lens epithelial cells (LECs) to the intraocular lens material surface promotes ACO formation, whereas proliferation and migration of LECs to the posterior capsule lead to the development of PCO. Cell adhesion is mainly mediated by the binding of integrin to extracellular matrix proteins, while cell proliferation and migration are regulated by fibroblast growth factor (FGF). Syndecan-4 (SDC-4) is a co-receptor for both integrin and FGF signaling pathways. Therefore, SDC-4 may be an ideal therapeutic target for the prevention and treatment of postoperative capsular opacification. However, how SDC-4 contributes to FGF-mediated proliferation, migration, and integrin-mediated adhesion of LECs is unclear. Here, we found that downregulation of SDC-4 inhibited FGF signaling through the blockade of ERK1/2 and PI3K/Akt/mTOR activation, thus suppressing cell proliferation and migration. In addition, downregulation of SDC-4 suppressed integrin-mediated cell adhesion through inhibiting focal adhesion kinase (FAK) phosphorylation. Moreover, SDC-4 knockout mice exhibited normal lens morphology, but had significantly reduced capsular opacification after injury. Finally, SDC-4 expression level was increased in the anterior capsule LECs of age-related cataract patients. Taken together, we for the first time characterized the key regulatory role of SDC-4 in FGF and integrin signaling in human LECs, and provided the basis for future pharmacological interventions of capsular opacification.

Dual function of TGFβ in lens epithelial cell fate: implications for secondary cataract

The most common vision-disrupting complication of cataract surgery is posterior capsule opacification (PCO; secondary cataract). PCO is caused by residual lens cells undergoing one of two very different cell fates: either transdifferentiating into myofibroblasts or maturing into lens fiber cells. Although TGFβ has been strongly implicated in lens cell fibrosis, the factors responsible for the latter process have not been identified. We show here for the first time that TGFβ can induce purified primary lens epithelial cells within the same culture to undergo differentiation into either lens fiber cells or myofibroblasts. Marker analysis confirmed that the two cell phenotypes were mutually exclusive. Blocking the p38 kinase pathway, either with direct inhibitors of the p38 MAP kinase or a small-molecule therapeutic that also inhibits the activation of p38, prevented TGFβ from inducing epithelial-myofibroblast transition and cell migration but did not prevent fiber cell differentiation. Rapamycin had the converse effect, linking MTOR signaling to induction of fiber cell differentiation by TGFβ. In addition to providing novel potential therapeutic strategies for PCO, our findings extend the so-called TGFβ paradox, in which TGFβ can induce two disparate cell fates, to a new epithelial disease state.

ERK1/2 signaling is required for the initiation but not progression of TGFβ-induced lens epithelial to mesenchymal transition (EMT)

Transforming Growth Factor Beta (TGFβ) potently induces lens epithelial to mesenchymal transition (EMT). The resultant mesenchymal cells resemble those found in plaques of human forms of subcapsular cataract. Smad signaling has long been implicated as the sole driving force of TGFβ-mediated activity. Rat lens epithelial explants were used to examine the role of the Smad-independent signaling, namely the MAPK/ERK1/2 signaling pathway, in the initiation and progression of TGFβ-induced EMT. Phase contrast microscopy was used to observe the morphological changes associated with TGFβ-induced EMT in this model, including cell elongation, cell membrane blebbing, cell loss as indicated by the area of bare capsule and capsular wrinkling. The levels of Smad2, Smad2/3 and ERK1/2 phosphorylation measured using western blotting confirmed that the addition of UO126 was sufficient in blocking all TGFβ-induced ERK1/2 activation, as well as reducing Smad signaling at 18 h. Immunofluorescent labeling and further western blotting confirmed that TGFβ-induced EMT was associated with an increase in α-smooth muscle actin (α-SMA) and a reduction of E-cadherin at cell borders. Pre-treatment with UO126 was effective at blocking the TGFβ-induced EMT, as evidenced by a reduction of α-SMA expression and protein labeling, E-cadherin labeling at cell borders, and a reduction of cell loss, cell elongation and capsular wrinkling. Post-treatment with UO126 at 2 and 6 h after TGFβ addition was also effective at blocking EMT while post-treatment with UO126 at 24 and 48 h was not sufficient in hampering TGFβ-induced EMT. Our data implicates ERK1/2 signaling in the initiation but not the progression of TGFβ-induced EMT in rat lens epithelial cells. The tight regulation of intracellular signaling pathways such as ERK1/2 are required for the maintenance of lens epithelial cell integrity and hence tissue transparency. A greater understanding of the molecular mechanisms that drive the induction and progression of EMT in the lens will provide the basis for potential therapeutics for human cataract.

Nuclear ERK5 inhibits progression of leukemic monocytes to macrophages by regulating the transcription factor PU.1 and heat shock protein HSP70

Differentiation therapy can supplement the therapy of APL, but other subtypes of AML are treated principally with cytotoxic agents, with few lasting remissions. While the induction of monocyte followed by macrophage differentiation by vitamin D derivatives (VDDs) is dramatic in cultured AML cells of all subtypes, attempts to translate this to the clinic have not been effective. Thus, better understanding of the mechanisms underlying VDD-induced differentiation may improve this approach. The key events in this form of differentiation include increased expression of CD11b, and the transcription factor PU.1 is known to be a part of this process. We show here that in the transition of monocytes to macrophages induced by a VDD, ERK5, a member of the MAPK family of signaling molecules, prevents PU.1 expression. However, upon ERK5 inhibition PU.1 protein is stabilized by HSP70.Thus, ERK5 may be a target for manipulation of the immunoregulatory actions of macrophages in cancer.

β1-integrin controls cell fate specification in early lens development

Integrins are heterodimeric cell surface molecules that mediate cell-extracellular matrix (ECM) adhesion, ECM assembly, and regulation of both ECM and growth factor induced signaling. However, the developmental context of these diverse functions is not clear. Loss of β1-integrin from the lens vesicle (mouse E10.5) results in abnormal exit of anterior lens epithelial cells (LECs) from the cell cycle and their aberrant elongation toward the presumptive cornea by E12.5. These cells lose expression of LEC markers and initiate expression of the Maf (also known as c-Maf) and Prox1 transcription factors as well as other lens fiber cell markers. β1-integrin null LECs also upregulate the ERK, AKT and Smad1/5/8 phosphorylation indicative of BMP and FGF signaling. By E14.5, β1-integrin null lenses have undergone a complete conversion of all lens epithelial cells into fiber cells. These data suggest that shortly after lens vesicle closure, β1-integrin blocks inappropriate differentiation of the lens epithelium into fibers, potentially by inhibiting BMP and/or FGF receptor activation. Thus, β1-integrin has an important role in fine-tuning the response of the early lens to the gradient of growth factors that regulate lens fiber cell differentiation.

FGFR and PTEN signaling interact during lens development to regulate cell survival

Lens epithelial cells express many receptor tyrosine kinases (RTKs) that stimulate PI3K-AKT and RAS-RAF-MEK-ERK intracellular signaling pathways. These pathways ultimately activate the phosphorylation of key cellular transcription factors and other proteins that control proliferation, survival, metabolism, and differentiation in virtually all cells. Among RTKs in the lens, only stimulation of fibroblast growth factor receptors (FGFRs) elicits a lens epithelial cell to fiber cell differentiation response in mammals. Moreover, although the lens expresses three different Fgfr genes, the isolated removal of Fgfr2 at the lens placode stage inhibits both lens cell survival and fiber cell differentiation. Phosphatase and tensin homolog (PTEN), commonly known as a tumor suppressor, inhibits ERK and AKT activation and initiates both apoptotic pathways, and cell cycle arrest. Here, we show that the combined deletion of Fgfr2 and Pten rescues the cell death phenotype associated with Fgfr2 loss alone. Additionally, Pten removal increased AKT and ERK activation, above the levels of controls, in the presence or absence of Fgfr2. However, isolated deletion of Pten failed to stimulate ectopic fiber cell differentiation, and the combined deletion of Pten and Fgfr2 failed to restore differentiation-specific Aquaporin0 and DnaseIIβ expression in the lens fiber cells.

Regulation of c-Maf and αA-Crystallin in Ocular Lens by Fibroblast Growth Factor Signaling

Fibroblast growth factor (FGF) signaling regulates a multitude of cellular processes, including cell proliferation, survival, migration, and differentiation. In the vertebrate lens, FGF signaling regulates fiber cell differentiation characterized by high expression of crystallin proteins. However, a direct link between FGF signaling and crystallin gene transcriptional machinery remains to be established. Previously, we have shown that the bZIP proto-oncogene c-Maf regulates expression of αA-crystallin (Cryaa) through binding to its promoter and distal enhancer, DCR1, both activated by FGF2 in cell culture. Herein, we identified and characterized a novel FGF2-responsive region in the c-Maf promoter (-272/-70, FRE). Both c-Maf and Cryaa regulatory regions contain arrays of AP-1 and Ets-binding sites. Chromatin immunoprecipitation (ChIP) assays established binding of c-Jun (an AP-1 factor) and Etv5/ERM (an Ets factor) to these regions in lens chromatin. Analysis of temporal and spatial expression of c-Jun, phospho-c-Jun, and Etv5/ERM in wild type and ERK1/2 deficient lenses supports their roles as nuclear effectors of FGF signaling in mouse embryonic lens. Collectively, these studies show that FGF signaling up-regulates expression of αA-crystallin both directly and indirectly via up-regulation of c-Maf. These molecular mechanisms are applicable for other crystallins and genes highly expressed in terminally differentiated lens fibers.

Hutterite-type cataract maps to chromosome 6p21.32-p21.31, cosegregates with a homozygous mutation in LEMD2, and is associated with sudden cardiac death

BACKGROUND

Juvenile-onset cataracts are known among the Hutterites of North America. Despite being identified over 30 years ago, this autosomal recessive condition has not been mapped, and the disease gene is unknown.

METHODS

We performed whole exome sequencing of three Hutterite-type cataract trios and follow-up genotyping and mapping in four extended kindreds.

RESULTS

Trio exomes enabled genome-wide autozygosity mapping, which localized the disease gene to a 9.5-Mb region on chromosome 6p. This region contained two candidate variants, LEMD2 c.T38G and MUC21 c.665delC. Extended pedigrees recruited for variant genotyping revealed multiple additional relatives with juvenile-onset cataract, as well as six deceased relatives with both cataracts and sudden cardiac death. The candidate variants were genotyped in 84 family members, including 17 with cataracts; only the variant in LEMD2 cosegregated with cataracts (LOD = 9.62). SNP-based fine mapping within the 9.5 Mb linked region supported this finding by refining the cataract locus to a 0.5- to 2.9-Mb subregion (6p21.32-p21.31) containing LEMD2 but not MUC21. LEMD2 is expressed in mouse and human lenses and encodes a LEM domain-containing protein; the c.T38G missense mutation is predicted to mutate a highly conserved residue within this domain (p.Leu13Arg).

CONCLUSION

We performed a genetic and genomic study of Hutterite-type cataract and found evidence for an association of this phenotype with sudden cardiac death. Using combined genetic and genomic approaches, we mapped cataracts to a small portion of chromosome 6 and propose that they result from a homozygous missense mutation in LEMD2.

Sprouty gain of function disrupts lens cellular processes and growth by restricting RTK signaling

Sprouty proteins function as negative regulators of the receptor tyrosine kinase (RTK)-mediated Ras/Raf/MAPK pathway in many varied physiological and developmental processes, inhibiting growth factor-induced cellular proliferation, migration and differentiation. Like other negative regulators, Sprouty proteins are expressed in various organs during development, including the eye; ubiquitously expressed in the optic vesicle, lens pit, optic cup and lens vesicle. Given the synexpression of different antagonists (e.g, Sprouty, Sef, Spred) in the developing lens, to gain a better understanding of their specific role, in particular, their ability to regulate ocular growth factor signaling in lens cells, we characterized transgenic mice overexpressing Sprouty1 or Sprouty2 in the eye. Overexpression of Sprouty in the lens resulted in reduced lens and eye size during ocular morphogenesis, influenced by changes to the lens epithelium, aberrant fiber cell differentiation and compromised de novo maintenance of the lens capsule. Here we demonstrate an important inhibitory role for Sprouty in the regulation of lens cell proliferation and fiber differentiation in situ, potentially through its ability to modulate FGF- (and even EGF-) mediated MAPK/ERK1/2 signaling in lens cells. Whilst growth factor regulation of lens cell proliferation and fiber differentiation are required for orchestrating lens morphogenesis and growth, in turn, antagonists such as Sprouty are just as important for regulating the intracellular signaling pathways driving lens cellular processes.

Synergistic interaction between the fibroblast growth factor and bone morphogenetic protein signaling pathways in lens cells

Relatively little is known about how receptor tyrosine kinase ligands can positively cooperate with BMP signaling. Primary cultures of lens cells were used to reveal an unprecedented type of cross-talk between the canonical FGF and BMP signaling pathways that regulates lens cell differentiation and intercellular coupling.

Fibroblast growth factors (FGFs) play a central role in two processes essential for lens transparency—fiber cell differentiation and gap junction–mediated intercellular communication (GJIC). Using serum-free primary cultures of chick lens epithelial cells (DCDMLs), we investigated how the FGF and bone morphogenetic protein (BMP) signaling pathways positively cooperate to regulate lens development and function. We found that culturing DCDMLs for 6 d with the BMP blocker noggin inhibits the canonical FGF-to-ERK pathway upstream of FRS2 activation and also prevents FGF from stimulating FRS2- and ERK-independent gene expression, indicating that BMP signaling is required at the level of FGF receptors. Other experiments revealed a second type of BMP/FGF interaction by which FGF promotes expression of BMP target genes as well as of BMP4. Together these studies reveal a novel mode of cooperation between the FGF and BMP pathways in which BMP keeps lens cells in an optimally FGF-responsive state and, reciprocally, FGF enhances BMP-mediated gene expression. This interaction provides a mechanistic explanation for why disruption of either FGF or BMP signaling in the lens leads to defects in lens development and function.