Lens development

Effect of compound treatments on mouse lens viscoelasticity

Previous studies have shown that pharmaceutical agents such as lipoic acid have the ability to soften the lens, presenting a promising avenue for treating presbyopia. One obstacle encountered in the preclinical stage of such agents is the need for precise measurements of lens elasticity in experimental models. This study aimed to evaluate the effects of 25-hydroxycholesterol, lipoic acid, and obeticholic acid on the viscoelastic properties of mouse lenses using a custom-built elastometer system. Data were acquired on lenses from C57BL/6J female mice from two age groups: young (age: 8-10 weeks) and old (age: 32-43 weeks). OD lenses were used as the control and OS lenses were treated. Control lenses were immersed in Dulbecco's Modified Eagle Medium (DMEM) and treatment lenses were immersed in a compound solution containing 25-hydroxycholesterol (5 young and 5 old), lipoic acid at 2.35 mM (5 young and 5 old), lipoic acid at 0.66 mM (5 old), or obeticholic acid (5 old) at 37 °C for 18 h. After treatment, the mouse lenses were placed in a DMEM-filled chamber within a custom-built elastometer system that recorded the load and lens shape as the lens was compressed by 600 μm at a speed of 50 μm/s. The load was continuously recorded during compression and during stress-relaxation. The compression phase was fit with a linear function to quantify lens stiffness. The stress-relaxation phase was fit with a 3-term exponential relaxation model providing relaxation time constants (t1, t2, t3), and equilibrium load. The lens stiffness, time constants and equilibrium load were compared for the control and treated groups. Results revealed an increase in stiffness with age for the control group (young: 1.16 ± 0.11 g/mm, old: 1.29 ± 0.14 g/mm) and relaxation time constants decreased with age (young: t1 = 221.9 ± 29.0 s, t2 = 24.7 ± 3.8 s, t3 = 3.12 ± 0.87 s, old: t1 = 183.0 ± 22.0 s, t2 = 20.6 ± 2.6 s and t3 = 2.24 ± 0.43 s). Among the compounds tested, only 25-hydroxycholesterol produced statistically significant changes in the lens stiffness, relaxation time constants, and equilibrium load. In conclusion, older mouse lenses are stiffer and less viscous than young mouse lenses. Notably, no significant change in lens stiffness was observed following treatment with lipoic acid, contrary to previous findings.

Regulation of water flow in the ocular lens: new roles for aquaporins

The ocular lens is an important determinant of overall vision quality whose refractive and transparent properties change throughout life. The lens operates an internal microcirculation system that generates circulating fluxes of ions, water and nutrients that maintain the transparency and refractive properties of the lens. This flow of water generates a substantial hydrostatic pressure gradient which is regulated by a dual feedback system that uses the mechanosensitive channels TRPV1 and TRPV4 to sense decreases and increases, respectively, in the pressure gradient. This regulation of water flow (pressure) and hence overall lens water content, sets the two key parameters, lens geometry and the gradient of refractive index, which determine the refractive properties of the lens. Here we focus on the roles played by the aquaporin family of water channels in mediating lens water fluxes, with a specific focus on AQP5 as a regulated water channel in the lens. We show that in addition to regulating the activity of ion transporters, which generate local osmotic gradients that drive lens water flow, the TRPV1/4-mediated dual feedback system also modulates the membrane trafficking of AQP5 in the anterior influx pathway and equatorial efflux zone of the lens. Since both lens pressure and AQP5-mediated water permeability (P H 2 O ${P_{{{\mathrm{H}}_{\mathrm{2}}}{\mathrm{O}}}}$ ) can be altered by changes in the tension applied to the lens surface via modulating ciliary muscle contraction we propose extrinsic modulation of lens water flow as a potential mechanism to alter the refractive properties of the lens to ensure light remains focused on the retina throughout life.

One-step biofabrication of liquid core-GelMa shell microbeads for in situ hollow cell ball self-assembly

There are many instances of hollow-structure morphogenesis in the development of tissues. Thus, the fabrication of hollow structures in a simple, high-throughput and homogeneous manner with proper natural biomaterial combination is valuable for developmental studies and tissue engineering, while it is a significant challenge in biofabrication field. We present a novel method for the fabrication of a hollow cell module using a coaxial co-flow capillary microfluidic device. Sacrificial gelatin laden with cells in the inner layer and GelMa in the outer layer are used via a coaxial co-flow capillary microfluidic device to produce homogenous micro-beads. The overall and core sizes of core-shell microbeads were well controlled. When using human vein vascular endothelial cells to demonstrate how cells line the inner surface of core-shell beads, as the core liquifies, a hollow cell ball with asymmetric features is fabricated. After release from the GelMa shell, individual cell balls are obtained and deformed cell balls can self-recover. This platform paves way for complex hollow tissue modeling in vitro, and further modulation of matrix stiffness, curvature and biochemical composition to mimic in vivo microenvironments.

Cataract-related variant R114C increases βA3-crystallin susceptibility to environmental stresses by disrupting the protein senior structure

Congenital cataract is a major cause of childhood blindness worldwide, with crystallin mutations accounting for over 40 % of gene-mutation-related cases. Our research focused on a novel R114C mutation in a Chinese family, resulting in bilateral coronary cataract with blue punctate opacity. Spectroscopic experiments revealed that βA3-R114C significantly altered the senior structure, exhibiting aggregation, and reduced solubility at physiological temperature. The mutant also displayed decreased resistance and stability under environmental stresses such as UV irradiation, oxidative stress, and heat. Further, cellular models confirmed its heightened sensitivity to environmental stresses. These data suggest that the R114C mutation impairs the hydrogen bond network and structural stability of βA3-crystallin, particularly at the boundary of the second Greek-key motif. This study revealed the pathological mechanism of βA3-R114C and may help in the development of potential treatment strategies for related cataracts.

Supercontinuum intrinsic fluorescence imaging heralds free view of living systems

Optimal imaging strategies remain underdeveloped to maximize information for fluorescence microscopy while minimizing the harm to fragile living systems. Taking hint from the supercontinuum generation in ultrafast laser physics, we generated supercontinuum fluorescence from untreated unlabeled live samples before nonlinear photodamage onset. Our imaging achieved high-content cell phenotyping and tissue histology, identified bovine embryo polarization, quantified aging-related stress across cell types and species, demystified embryogenesis before and after implantation, sensed drug cytotoxicity in real-time, scanned brain area for targeted patching, optimized machine learning to track small moving organisms, induced two-photon phototropism of leaf chloroplasts under two-photon photosynthesis, unraveled microscopic origin of autumn colors, and interrogated intestinal microbiome. The results enable a facility-type microscope to freely explore vital molecular biology across life sciences.

Prdx6 Regulates Nlrp3 Inflammasome Activation-Driven Inflammatory Response in Lens Epithelial Cells

The continuum of antioxidant response dysregulation in aging/oxidative stress-driven Nlrp3 inflammasome activation-mediated inflammatory response is associated with age-related diseases. Peroxiredoxin (Prdx) 6 is a key antioxidant that provides cytoprotection by regulating redox homeostasis. Herein, using lens epithelial cells (LECs) derived from the targeted inactivation of Prdx6 gene and aging lenses, we present molecular evidence that Prdx6-deficiency causes oxidative-driven Nlrp3 inflammasome activation, resulting in pyroptosis in aging/redox active cells wherein Prdx6 availability offsets the inflammatory process. We observed that Prdx6-/- and aging LECs harboring accumulated reactive oxygen species (ROS) showed augmented activation of Nlrp3 and bioactive inflammatory components, like Caspase-1, IL-1β, ASC and Gasdermin-D. Similar to lipopolysaccharide treatment, oxidative exposure led to further ROS amplification with increased activation of the Nlrp3 inflammasome pathway. Mechanistically, we found that oxidative stress enhanced Kruppel-like factor 9 (Klf9) expression in aging/Prdx6-/- mLECs, leading to a Klf9-dependent increase in Nlrp3 transcription, while the elimination of ROS by the delivery of Prdx6 or by silencing Klf9 prevented the inflammatory response. Altogether, our data identify the biological significance of Prdx6 as an intrinsic checkpoint for regulating the cellular health of aging or redox active LECs and provide opportunities to develop antioxidant-based therapeutic(s) to prevent oxidative/aging-related diseases linked to aberrant Nlrp3 inflammasome activation.

Single-Cell RNA Sequencing Analysis of the Early Postnatal Mouse Lens Epithelium

Purpose

The lens epithelium maintains the overall health of the organ. We used single-cell RNA sequencing (scRNA-seq) technology to assess transcriptional heterogeneity between cells in the postnatal day 2 (P2) epithelium and identify distinct epithelial cell subtypes. Analysis of these data was used to better understand lens growth, differentiation, and homeostasis on P2.

Methods

scRNA-seq on P2 mouse lenses was performed using the 10x Genomics Chromium Single Cell 3' Kit (v3.1) and short-read Illumina sequencing. Sequence alignment and preprocessing of data were conducted using 10x Genomics Cell Ranger software. Seurat was employed for preprocessing, quality control, dimensionality reduction, and cell clustering, and Monocle was utilized for trajectory analysis to understand the developmental progression of the lens cells. CellChat and GO analyses were used to explore cell-cell communication networks and signaling interactions.

Results

Lens epithelial cells (LECs) were divided into seven subclusters, classified by specific gene markers. The expression of crystallin, cell-cycle, and metabolic genes was not uniform, indicating distinct functional roles of LECs. Trajectory analysis predicted a bifurcation of differentiating and cycling cells from an Igfbp5+ progenitor pool. We also identified heterogeneity in signaling molecules and pathways, suggesting that cycling and progenitor subclusters have prominent roles in coordinating crosstalk.

Conclusions

scRNA-seq corroborated many known markers of epithelial differentiation and proliferation while providing further insight into the pathways and genes directing these processes. Interestingly, we demonstrated that the developing epithelium can be divided into distinct subpopulations. These clusters reflect the transcriptionally diverse roles of the epithelium in proliferation, signaling, and maintenance.

Ocular development after highly effective modulator treatment early in life

Highly effective cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulator therapies (HEMT), including elexacaftor-tezacaftor-ivacaftor, correct the underlying molecular defect causing CF. HEMT decreases general symptom burden by improving clinical metrics and quality of life for most people with CF (PwCF) with eligible CFTR variants. This has resulted in more pregnancies in women living with CF. All HEMT are known to be able pass through the placenta and into breast milk in mothers who continue on this therapy while pregnant and breast feeding. Toxicity studies of HEMT in young rats demonstrated infant cataracts, and case reports have reported the presence of congenital cataracts in early life exposure to HEMT. This article reviews the evidence for how HEMT influences the dynamic and interdependent processes of healthy and abnormal lens development in the context of HEMT exposure during pregnancy and breastfeeding, and raises questions that remain unanswered.

Aquaporin water channels: roles beyond renal water handling

Aquaporin (AQP) water channels are pivotal to renal water handling and therefore in the regulation of body water homeostasis. However, beyond the kidney, AQPs facilitate water reabsorption and secretion in other cells and tissues, including sweat and salivary glands and the gastrointestinal tract. A growing body of evidence has also revealed that AQPs not only facilitate the transport of water but also the transport of several small molecules and gases such as glycerol, H2O2, ions and CO2. Moreover, AQPs are increasingly understood to contribute to various cellular processes, including cellular migration, adhesion and polarity, and to act upstream of several intracellular and intercellular signalling pathways to regulate processes such as cell proliferation, apoptosis and cell invasiveness. Of note, several AQPs are highly expressed in multiple cancers, where their expression can correlate with the spread of cancerous cells to lymph nodes and alter the response of cancers to conventional chemotherapeutics. These data suggest that AQPs have diverse roles in various homeostatic and physiological systems and may be exploited for prognostics and therapeutic interventions.

Non-canonical Wnt signaling in the eye

Wnt signaling comprises a group of complex signal transduction pathways that play critical roles in cell proliferation, differentiation, and apoptosis during development, as well as in stem cell maintenance and adult tissue homeostasis. Wnt pathways are classified into two major groups, canonical (β-catenin-dependent) or non-canonical (β-catenin-independent). Most previous studies in the eye have focused on canonical Wnt signaling, and the role of non-canonical signaling remains poorly understood. Additionally, the crosstalk between canonical and non-canonical Wnt signaling in the eye has hardly been explored. In this review, we present an overview of available data on ocular non-canonical Wnt signaling, including developmental and functional aspects in different eye compartments. We also discuss important changes of this signaling in various ocular conditions, such as keratoconus, aniridia-related keratopathy, diabetes, age-related macular degeneration, optic nerve damage, pathological angiogenesis, and abnormalities in the trabecular meshwork and conjunctival cells, and limbal stem cell deficiency.

Modulation of Membrane Trafficking of AQP5 in the Lens in Response to Changes in Zonular Tension Is Mediated by the Mechanosensitive Channel TRPV1

In mice, the contraction of the ciliary muscle via the administration of pilocarpine reduces the zonular tension applied to the lens and activates the TRPV1-mediated arm of a dual feedback system that regulates the lens' hydrostatic pressure gradient. In the rat lens, this pilocarpine-induced reduction in zonular tension also causes the water channel AQP5 to be removed from the membranes of fiber cells located in the anterior influx and equatorial efflux zones. Here, we determined whether this pilocarpine-induced membrane trafficking of AQP5 is also regulated by the activation of TRPV1. Using microelectrode-based methods to measure surface pressure, we found that pilocarpine also increased pressure in the rat lenses via the activation of TRPV1, while pilocarpine-induced removal of AQP5 from the membrane observed using immunolabelling was abolished by pre-incubation of the lenses with a TRPV1 inhibitor. In contrast, mimicking the actions of pilocarpine by blocking TRPV4 and then activating TRPV1 resulted in sustained increase in pressure and the removal of AQP5 from the anterior influx and equatorial efflux zones. These results show that the removal of AQP5 in response to a decrease in zonular tension is mediated by TRPV1 and suggest that regional changes to PH2O contribute to lens hydrostatic pressure gradient regulation.

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.

Aquaporin 5 maintains lens transparency by regulating the lysosomal pathway using circRNA

The lens is transparent, non-vascular, elastic and wrapped in a transparent capsule. The lens oppacity of AQP5^-/- mice was increased more than that of wild-type (AQP5^+/+ ) mice. In this study, we explored the potential functional role of circular RNAs (circRNAs) and transcription factor HSF4 in lens opacity in aquaporin 5 (AQP5) knockout (AQP5^-/- ) mice. Autophagy was impaired in the lens tissues of AQP5^-/- mice. Autophagic lysosomes in lens epithelial cells of AQP5^-/- mice were increased compared with AQP5^+/+ mice, based on analysis by transmission electron microscopy. The genetic information of the mice lens was obtained by high-throughput sequencing, and then the downstream genes were analysed. A circRNA-miRNA-mRNA network related to lysosomal pathway was constructed by the bioinformatics analysis of the differentially expressed circRNAs. Based on the prediction of the TargetScan website and the validation by dual luciferase reporter assay and RNA immunoprecipitation-qPCR, we found that circRNA (Chr16: 33421321-33468183+) inhibited the function of HSF4 by sponging microRNA (miR-149-5p), and it downregulated the normal expression of lysosome-related mRNAs. The accumulation of autophagic lysosome may be one of the reasons for the abnormal development of the lens in AQP5^-/- mice.

Hydralazine Revives Cellular and Ocular Lens Health-Span by Ameliorating the Aging and Oxidative-Dependent Loss of the Nrf2-Activated Cellular Stress Response

A major hallmark of aging-associated diseases is the inability to evoke cellular defense responses. Transcriptional protein Nrf2 (nuclear factor erythroid-derived 2-related factor) plays a pivotal role in the oxidative stress response, cellular homeostasis, and health span. Nrf2's activation has been identified as a therapeutic target to restore antioxidant defense in aging. Here, we demonstrated that FDA-approved drug, hydralazine (Hyd), was a reactivator of the Nrf2/ARE (antioxidant response element) pathway in various ages and types of mouse (m) or human (h) lens epithelial cells (LECs) and mice lenses in-vitro/in-vivo. This led to Hyd-driven abatement of carbonyls, reduced reactive oxygen species (ROS), and reduced 4-HNE/MDA-adducts with cytoprotection, and extended lens healthspan by delaying/preventing lens opacity against aging/oxidative stress. We elucidated that Hyd activated the protective signaling by inducing Nrf2 to traverse from the cytoplasm to the nucleus and potentiated the ARE response by direct interaction of Nrf2 and ARE sequences of the promoter. Loss-of-function study and cotreatment of Hyd and antioxidant, N-acetyl cysteine (NAC) or Peroxiredoxin (Prdx)6, specified that Nrf2/ARE-driven increase in the promoter activity was Hyd-dependent. Our study provides proof-of concept evidence and, thereby, paves the way to repurposing Hyd as a therapeutic agent to delay/prevent aging and oxidative-related disorders.

A tamoxifen-inducible Cre knock-in mouse for lens-specific gene manipulation

Mouse models are valuable tools in studying lens biology and biochemistry, and the Cre-loxP system is the most used technology for gene targeting in the lens. However, numerous genes are indispensable in lens development. The conventional knockout method either prevents lens formation or causes simultaneous cataract formation, hindering the studies of their roles in lens structure, growth, metabolism, and cataractogenesis during lens aging. An inducible Cre-loxP mouse line is an excellent way to achieve such a purpose. We established a lens-specific Cre ERT2 knock-in mouse (LCEK), an inducible mouse model for lens-specific gene targeting in a spatiotemporal manner. LCEK mice were created by in-frame infusion of a P2A-CreERT2 at the C-terminus of the last coding exon of the gene alpha A crystallin (Cryaa). LCEK mice express tamoxifen-inducible Cre recombinase uniquely in the lens. Through ROSAmT/mG and two endogenous genes (Gclc and Rbpj) targeting, we found no Cre recombinase leakage in the lens epithelium, but 50-80% leakage was observed in the lens cortex and nucleus. Administration of tamoxifen almost completely abolished target gene expression in both lens epithelium and cortex but only mildly enhanced gene deletion in the lens nucleus. Notably, no overt leakage of Cre activity was detected in developing LCEK lens when bred with mice carrying loxP floxed genes that are essential for lens development. This newly generated LCEK line will be a powerful tool to target genes in the lens for gene functions study in lens aging, posterior capsule opacification (PCO), and other areas requiring precision gene targeting.

Obligatory Role of AMPK Activation and Antioxidant Defense Pathway in the Regulatory Effects of Metformin on Cellular Protection and Prevention of Lens Opacity

Increasing levels of oxidative-stress due to deterioration of the Nrf2 (NFE2-related factor)/ARE (antioxidant response element) pathway is found to be a primary cause of aging pathobiology. Metformin having anti-aging effects can delay/halt aging-related diseases. Herein, using lens epithelial cell lines (LECs) of human (h) or mouse (m) and aging h/m primary LECs along with lenses as model systems, we demonstrated that Metformin could correct deteriorated Bmal1/Nrf2/ARE pathway by reviving AMPK-activation, and transcriptional activities of Bmal1/Nrf2, resulting in increased antioxidants enzymatic activity and expression of Phase II enzymes. This ensued reactive oxygen species (ROS) mitigation with cytoprotection and prevention of lens opacity in response to aging/oxidative stress. It was intriguing to observe that Metformin internalized lens/LECs and upregulated OCTs (Organic Cation Transporters). Mechanistically, we found that Metformin evoked AMPK activation-dependent increase of Bmal1, Nrf2, and antioxidants transcription by promoting direct E-Box and ARE binding of Bmal1 and Nrf2 to the promoters. Loss-of-function and disruption of E-Box/ARE identified that Metformin acted by increasing Bmal1/Nrf2-mediated antioxidant expression. Data showed that AMPK-activation was a requisite for Bmal1/Nrf2-antioxidants-mediated defense, as pharmacologically inactivating AMPK impeded the Metformin's effect. Collectively, the results for the first-time shed light on the hitherto incompletely uncovered crosstalk between the AMPK and Bmal1/Nrf2/antioxidants mediated by Metformin for blunting oxidative/aging-linked pathobiology.

The role of FYCO1-dependent autophagy in lens fiber cell differentiation

FYCO1 (FYVE and coiled-coil domain containing 1) is an adaptor protein, expressed ubiquitously and required for microtubule-dependent, plus-end-directed transport of macroautophagic/autophagic vesicles. We have previously shown that loss-of-function mutations in FYCO1 cause cataracts with no other ocular and/or extra-ocular phenotype. Here, we show fyco1 homozygous knockout (fyco1-/-) mice recapitulate the cataract phenotype consistent with a critical role of FYCO1 and autophagy in lens morphogenesis. Transcriptome coupled with proteome and metabolome profiling identified many autophagy-associated genes, proteins, and lipids respectively perturbed in fyco1-/- mice lenses. Flow cytometry of FYCO1 (c.2206C>T) knock-in (KI) human lens epithelial cells revealed a decrease in autophagic flux and autophagic vesicles resulting from the loss of FYCO1. Transmission electron microscopy showed cellular organelles accumulated in FYCO1 (c.2206C>T) KI lens-like organoid structures and in fyco1-/- mice lenses. In summary, our data confirm the loss of FYCO1 function results in a diminished autophagic flux, impaired organelle removal, and cataractogenesis.Abbreviations: CC: congenital cataracts; DE: differentially expressed; ER: endoplasmic reticulum; FYCO1: FYVE and coiled-coil domain containing 1; hESC: human embryonic stem cell; KI: knock-in; OFZ: organelle-free zone; qRT-PCR: quantitative real-time PCR; PE: phosphatidylethanolamine; RNA-Seq: RNA sequencing; SD: standard deviation; sgRNA: single guide RNA; shRNA: shorthairpin RNA; TEM: transmission electron microscopy; WT: wild type.

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.

Redox Homeostasis in Ocular Tissues: Circadian Regulation of Glutathione in the Lens?

Accumulating evidence in tissues suggests an interconnection between circadian clocks and redox regulation. Diurnal variations in antioxidant levels, circadian rhythms of antioxidant enzyme activity, and differences in oxidative stress markers at different times of the day all indicate that oxidative stress responses follow a circadian rhythm. Disruptions of circadian rhythms are linked to a number of age-related diseases, including those in the eye. Typically, ocular tissues contain a robust antioxidant defence system to maintain redox balance and minimise oxidative stress and damage. The lens, in particular, contains remarkably high levels of the antioxidant glutathione (GSH). However, with advancing age, GSH levels deplete, initiating a chain of biochemical events that ultimately result in protein aggregation, light scattering, and age-related cataracts. While there is evidence that the lens exhibits circadian rhythms in the synthesis and release of melatonin, little is known about the regulation or function of timekeeping mechanisms in the lens. Since circadian rhythms are disrupted with age, and the depletion of GSH in the lens is a known initiating factor in the development of age-related cataracts, understanding the mechanisms involved in regulating GSH levels may lead to the future development of approaches to manipulate the clock to restore GSH levels and redox balance in the lens, and protect the lens from cataracts.

Mapping Glucose Uptake, Transport and Metabolism in the Bovine Lens Cortex

Purpose: To spatially correlate the pattern of glucose uptake to glucose transporter distributions in cultured lenses and map glucose metabolism in different lens regions. Methods: Ex vivo bovine lenses were incubated in artificial aqueous humour containing normoglycaemic stable isotopically-labelled (SIL) glucose (5 mM) for 5 min-20 h. Following incubations, lenses were frozen for subsequent matrix-assisted laser desorption/ionisation (MALDI) imaging mass spectrometry (IMS) analysis using high resolution mass spectrometry. Manually dissected, SIL-incubated lenses were subjected to gas chromatography-mass spectrometry (GC-MS) to verify the identity of metabolites detected by MALDI-IMS. Normal, unincubated lenses were manually dissected into epithelium flat mounts and fibre cell fractions and then subjected to either gel-based proteomic analysis (Gel-LC/MS) to detect facilitative glucose transporters (GLUTs) by liquid chromatography tandem mass spectrometry (LC-MS/MS). Indirect immunofluorescence and confocal microscopy of axial lens sections from unincubated fixed lenses labelled with primary antibodies specific for GLUT 1 or GLUT 3 were utilised for protein localisation. Results: SIL glucose uptake at 5 min was concentrated in the equatorial region of the lens. At later timepoints, glucose gradually distributed throughout the epithelium and the cortical lens fibres, and eventually the deeper lens nucleus. SIL glucose metabolites found in glycolysis, the sorbitol pathway, the pentose phosphate pathway, and UDP-glucose formation were mapped to specific lens regions, with distinct regional signal changes up to 20 h of incubation. Spatial proteomic analysis of the lens epithelium detected GLUT1 and GLUT3. GLUT3 was in higher abundance than GLUT1 throughout the epithelium, while GLUT1 was more abundant in lens fibre cells. Immunohistochemical mapping localised GLUT1 to epithelial and cortical fibre cell membranes. Conclusion: The major uptake site of glucose in the bovine lens has been mapped to the lens equator. SIL glucose is rapidly metabolised in epithelial and fibre cells to many metabolites, which are most abundant in the metabolically more active cortical fibre cells in comparison to central fibres, with low levels of metabolic activity observed in the nucleus.

Markers of Hypoxia and Metabolism Correlate With Cell Differentiation in Retina and Lens Development

Recent studies have provided novel insights of co-development of the neural and vascular elements of the retina. Knowledge of these relationships are crucial to understand the impact of therapeutic measures in Retinopathy of Prematurity (ROP). ROP is imposed by therapeutic oxygen upon immature retinal blood vessels and neural cells causing delayed development and vascular regression. However, the impact of hyperoxia on developing retinal neurons is less understood because some aspects of normal development remain unknown. The metabolic changes during differentiation of retinal progenitor cells to functional neurons is one such aspect. We correlated immunomarkers of hypoxia with markers of metabolic change in developing retinal neurons during the early postnatal period in mice. The same marker proteins were studied in secondary lens fiber differentiation at postnatal day-3 (P3). Nuclear localization of the oxygen-sensitive subunits of hypoxia inducible factor, HIF-1α and HIF-2α was correlated with increasing mitochondrial content in differentiating neurons. Nuclear HIF was also correlated with AMP-dependent protein kinase (AMPK), and the AMPK phosphorylation target PPAR-gamma coactivator-1alpha (PGC-1α), the principal regulator of mitochondrial biogenesis. Expression of AMPK, PGC1α and HIF-2α in secondary fiber differentiation was visible in each profile of the lens equator. Strong nuclear localization for all markers was present at the onset of secondary fiber differentiation, and reflected changes in size, mitochondrial content, and metabolism. We speculate that the 'physiological hypoxia' that drives retinal vascular development is cell-specific and reliant upon neuronal differentiation and mitochondrial biogenesis. We suggest that the onset of differentiation increases energy consumption that is detected by AMPK. In turn AMPK increases mitochondrial biogenesis via PGC-1α. Mitochondrial oxygen consumption may then create intracellular hypoxia that activates HIF. This progression is congruent with the expression of these markers in secondary lens fiber differentiation and nuclear localization of HIF-2α. Nuclear localization of HIF-1α and HIF-2α in the postnatal retina is less defined than in the lens as it may involve the remnant of HIF expression from the embryonic period that is sustained and increased by intracellular hypoxia caused by increasing mitochondrial oxygen consumption. This the first report of the involvement of HIF-2α, AMPK and PGC-1α in lens development.

Switching of Redox Signaling by Prdx6 Expression Decides Cellular Fate by Hormetic Phenomena Involving Nrf2 and Reactive Oxygen Species

Changes in intracellular reactive oxygen species (ROS) levels due to remodeling of antioxidant defense can affect the status of biological homeostasis in aging/oxidative stress. Peroxiredoxin 6 (Prdx6), an antioxidant gene downstream target for the Nrf2 pathway, plays a role in regulating ROS homeostasis. Using aging human (h) lens epithelial cells (LECs) or Prdx6-deficient (Prdx6^-/-) mouse (m) LECs, here we showed that dichlorofluorescein (DCF) oxidation or H₂O₂ were strictly controlled by Prdx6. We observed that a moderate degree of oxidative stress augmented Nrf2-mediated Prdx6 expression, while higher doses of H₂O₂ (≥100 µM) caused a dramatic loss of Prdx6 expression, resulting in increased DCF oxidation and H₂O₂ amplification and cell death. Mechanistically, at increased oxidative stress, Nrf2 upregulated transcriptional factor Klf9, and that Klf9 bound to the promoter and repressed the Prdx6 gene. Similarly, cells overexpressing Klf9 displayed Klf9-dependent Prdx6 suppression and DCF oxidation with H₂O₂ amplification, while ShKlf9 reversed the process. Our data revealed that H₂O₂ and DCF oxidation levels play a hormetical role, and the Nrf2-Klf9-Prdx6 pathway is pivotal for the phenomena under the conditions of oxidative load/aging. On the whole, the results demonstrate that oxidative hormetical response is essentially based on levels of oxidative triggering and the status of Klf9-Prdx6 pathway activation; thus, Klf9 can be considered as a therapeutic target for hormetic shifting of cellular defense to improve protective resilience to oxidative stress.

Programmable Electrodeposition of Janus Alginate/Poly-L-Lysine/Alginate (APA) Microcapsules for High-Resolution Cell Patterning and Compartmentalization

Encapsulation of live cells in protective, semipermeable microcapsules is one of the kernel techniques for in vitro tissue regeneration, cell therapies, and pharmaceutical screening. Advanced fabrication techniques for cell encapsulation have been developed to meet different requirements. Existing cell encapsulation techniques place substantial constraints on the spatial patterning of live cells as well as on the compartmentalization of heterotypic cells. Alginate-Poly-L-lysine-alginate (APA) microcapsules that use sodium alginate as the polyanion and poly-L-lysine (PLL) as the polycation have been extensively employed for cell microencapsulation due to their excellent biocompatibility and biodegradability. This study proposes a novel method for developing programmable Janus APA microcapsules with variable shapes and sizes by using electrodeposition. By the versatile design of the microelectrode device, sequential electrodeposition is triggered to electro-address the cells at specific locations immobilized within a Janus APA microcapsule. The osteogenesis is evaluated by resembling cell compartmentalized and vascularized osteoblast-laden constructs. This technique allows precise spatial patterning of heterotypic cells inside the APA microcapsule, enabling the observation of cellular growth, interactions, and differentiation in a well-controlled chemical and mechanical microenvironment.

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.

Physiological Mechanisms Regulating Lens Transport

The transparency and refractive properties of the lens are maintained by the cellular physiology provided by an internal microcirculation system that utilizes spatial differences in ion channels, transporters and gap junctions to establish standing electrochemical and hydrostatic pressure gradients that drive the transport of ions, water and nutrients through this avascular tissue. Aging has negative effects on lens transport, degrading ion and water homeostasis, and producing changes in lens water content. This alters the properties of the lens, causing changes in optical quality and accommodative amplitude that initially result in presbyopia in middle age and ultimately manifest as cataract in the elderly. Recent advances have highlighted that the lens hydrostatic pressure gradient responds to tension transmitted to the lens through the Zonules of Zinn through a mechanism utilizing mechanosensitive channels, multiple sodium transporters respond to changes in hydrostatic pressure to restore equilibrium, and that connexin hemichannels and diverse intracellular signaling cascades play a critical role in these responses. The mechanistic insight gained from these studies has advanced our understanding of lens transport and how it responds and adapts to different inputs both from within the lens, and from surrounding ocular structures.

Defect of LSS Disrupts Lens Development in Cataractogenesis

Congenital cataract is one of the leading causes of blindness in children worldwide. About one-third of congenital cataracts are caused by genetic defects. LSS, which encodes lanosterol synthase, is a causal gene for congenital cataracts. LSS is critical in preventing abnormal protein aggregation of various cataract-causing mutant crystallins; however, its roles in lens development remain largely unknown. In our study, we generated a mouse model harboring Lss G589S mutation, which is homologous to cataract-causing G588S mutation in human LSS. Lss^G589S/G589S mice exhibited neonatal lethality at postal day 0 (P0), whereas these mice showed severe opacity in eye lens. Also, we found that cataract was formed at E17.5 after we examined the opacity of embryonic lens from E13.5 to E18.5. Moreover, disrupted lens differentiation occurred at E14.5 prior to formation of the opacity of eye lens, shown as delayed differentiation of lens secondary fiber and disordered lens fiber organization. In addition, RNA-seq analysis indicated that cholesterol synthesis signaling pathways were significantly downregulated. Overall, our findings provide clear evidence that a mouse model harboring a homozygous Lss G589S mutation can recapitulate human congenital cataract. Our study points out that LSS functions as a critical determinant of lens development, which will contribute to better understanding LSS defects in cataractogenesis and developing therapies for cataracts.

Human brain organoids assemble functionally integrated bilateral optic vesicles

During embryogenesis, optic vesicles develop from the diencephalon via a multistep process of organogenesis. Using induced pluripotent stem cell (iPSC)-derived human brain organoids, we attempted to simplify the complexities and demonstrate formation of forebrain-associated bilateral optic vesicles, cellular diversity, and functionality. Around day 30, brain organoids attempt to assemble optic vesicles, which develop progressively as visible structures within 60 days. These optic vesicle-containing brain organoids (OVB-organoids) constitute a developing optic vesicle's cellular components, including primitive corneal epithelial and lens-like cells, retinal pigment epithelia, retinal progenitor cells, axon-like projections, and electrically active neuronal networks. OVB-organoids also display synapsin-1, CTIP-positive myelinated cortical neurons, and microglia. Interestingly, various light intensities could trigger photosensitive activity of OVB-organoids, and light sensitivities could be reset after transient photobleaching. Thus, brain organoids have the intrinsic ability to self-organize forebrain-associated primitive sensory structures in a topographically restricted manner and can allow interorgan interaction studies within a single organoid.

Exacerbation of Background Nuclear Cataracts in Sprague-Dawley Rats in Embryo-Fetal Development Studies With JNJ-42165279, a Fatty Acid Amide Hydrolase Inhibitor

Fetal examinations in embryo-fetal developmental (EFD) studies are based on macroscopic and dissecting microscopic evaluations, and histopathology is rarely performed other than to confirm macroscopic findings. Fetal lens examination is therefore generally limited to the presence, size, shape, and color of any abnormality. In a Sprague-Dawley rat EFD study with the fatty acid amide hydrolase (FAAH) inhibitor JNJ-42165279, an unusually high incidence of macroscopic granular foci was noted within the lens of gestation day 21 fetuses across all groups including controls, with higher incidence in the high-dose group. On histological evaluation of the lenses from fetuses with/without gross findings, primary lens fiber hypertrophy (swelling) and degeneration were observed across vehicle- and JNJ-42165279-exposed fetuses. In a follow-up study to investigate the progression or resolution of the fetal lens changes, animals exposed to suprapharmacological doses of JNJ-42165279 in utero had higher incidence of nuclear cataracts as detected via slit-lamp ophthalmic examinations on postnatal days 18 to 21 and 35 to 41. No histologic correlates for these cataracts were identified. We conclude that fetal primary lens fiber hypertrophy and nuclear cataracts at ophthalmology, are common background changes in this rat strain that are exacerbated by in utero exposure to the FAAH inhibitor JNJ-42165279.

Cellular FLICE-like inhibitory protein (cFLIP) critically maintains apoptotic resistance in human lens epithelial cells

The present study aims to understand the mechanism of the lens epithelial cell's strong anti-apoptotic capacity and survival in the mature human lens that, on the one hand, maintains lens transparency over several decades, while on the other hand, increases the risk of posterior capsule opacification (PCO). Here we compared FHL124 cells and HeLa cells, spontaneously immortalized epithelial cell lines derived from the human lens and cervical cancer cells, respectively, of their resistance to TNFα-mediated cell death. TNFα plus cycloheximide (CHX) triggered almost all of HeLa cell death. FHL124 cells, however, were unaffected and able to block caspase-8 activation as well as prevent caspase-3 and PARP-1 cleavage. Interestingly, despite spontaneous NFκB and AP-1 activation and upregulation of multiple cell survival/anti-apoptotic genes in both cell types, only FHL124 cells were able to survive the TNFα challenge. After screening and comparing the cell survival genes, cFLIP was found to be highly expressed in FHL124 cells and substantially upregulated by TNFα stimulation. FHL124 cells with a mild cFLIP knockdown manifested a profound apoptotic response to TNFα stimulus similar to HeLa cells. Most importantly, we confirmed these findings in an ex vivo lens capsular bag culture system. In conclusion, our results show that cFLIP is a critical gene that is regulating lens epithelial cell survival.

In Vivo Quasi-Elastic Light Scattering Eye Scanner Detects Molecular Aging in Humans

The absence of clinical tools to evaluate individual variation in the pace of aging represents a major impediment to understanding aging and maximizing health throughout life. The human lens is an ideal tissue for quantitative assessment of molecular aging in vivo. Long-lived proteins in lens fiber cells are expressed during fetal life, do not undergo turnover, accumulate molecular alterations throughout life, and are optically accessible in vivo. We used quasi-elastic light scattering (QLS) to measure age-dependent signals in lenses of healthy human subjects. Age-dependent QLS signal changes detected in vivo recapitulated time-dependent changes in hydrodynamic radius, protein polydispersity, and supramolecular order of human lens proteins during long-term incubation (~1 year) and in response to sustained oxidation (~2.5 months) in vitro. Our findings demonstrate that QLS analysis of human lens proteins provides a practical technique for noninvasive assessment of molecular aging in vivo.

Glycation-mediated protein crosslinking and stiffening in mouse lenses are inhibited by carboxitin in vitro

Proteins in the eye lens have negligible turnover and therefore progressively accumulate chemical modifications during aging. Carbonyls and oxidative stresses, which are intricately linked to one another, predominantly drive such modifications. Oxidative stress leads to the loss of glutathione (GSH) and ascorbate degradation; this in turn leads to the formation of highly reactive dicarbonyl compounds that react with proteins to form advanced glycation end products (AGEs). The formation of AGEs leads to the crosslinking and aggregation of proteins contributing to lens aging and cataract formation. To inhibit AGE formation, we developed a disulfide compound linking GSH diester and mercaptoethylguanidine, and we named it carboxitin. Bovine lens organ cultured with carboxitin showed higher levels of GSH and mercaptoethylguanidine in the lens nucleus. Carboxitin inhibited erythrulose-mediated mouse lens protein crosslinking, AGE formation and the formation of 3-deoxythreosone, a major ascorbate-derived AGE precursor in the human lens. Carboxitin inhibited the glycation-mediated increase in stiffness in organ-cultured mouse lenses measured using compressive mechanical strain. Delivery of carboxitin into the lens increases GSH levels, traps dicarbonyl compounds and inhibits AGE formation. These properties of carboxitin could be exploited to develop a therapy against the formation of AGEs and the increase in stiffness that causes presbyopia in aging lenses.

Metabolome profiling of the developing murine lens

Metabolomics is a study of the entire repertoire of metabolites in a cell at a particular time point. Here, we investigate the mouse lens at multiple embryonic and postnatal time points to establish the metabolome profile during early lens development. The lenses were isolated at six time points including embryonic day 15 (E15) and E18 and postnatal day 0 (P0), P3, P6, and P9. A total of four biological replicates of each time point, each consisting of 25 mg of lens tissue were preserved. Sample preparation was performed by protein precipitation followed by centrifugation to remove proteins and recover metabolites. The resulting extract was subjected to reverse phase/ultra-performance liquid chromatography-tandem mass spectrometry. Metabolome profiling identified a total of 353 metabolites in mouse lens, marked with an abundance of collagen, antioxidant, glycosaminoglycans, lipid, amino acid, and energy-related metabolites. A comparative metabolome analysis identified >200 metabolites exhibiting increased levels (p < 0.05) at latter time points relative to E15. Principal component analysis revealed distinct metabolomic signatures running from E15 to P9 while random forest analysis categorized lipid-, amino acid-, and nucleotide-related metabolites contributing significantly to the separation of the time points. To the best of our knowledge, this is the first report investigating the mouse lens metabolome at multiple embryonic and postnatal time points.

Clock Protein Bmal1 and Nrf2 Cooperatively Control Aging or Oxidative Response and Redox Homeostasis by Regulating Rhythmic Expression of Prdx6

Many disorders of aging, including blinding-diseases, are associated with deficiency of brain and muscle arnt-like protein 1 (Bmal1) and, thereby, dysregulation of antioxidant-defense pathway. However, knowledge is limited regarding the role of Bmal1 regulation of antioxidant-pathway in the eye lens/lens epithelial cells (LECs) at the molecular level. We found that, in aging human (h)LECs, a progressive decline of nuclear factor erythroid 2-related factor 2 (Nrf2)/ARE (antioxidant response element)-mediated antioxidant genes was connected to Bmal1-deficiency, leading to accumulation of reactive oxygen species (ROS) and cell-death. Bmal1-depletion disrupted Nrf2 and expression of its target antioxidant genes, like Peroxiredoxin 6 (Prdx6). DNA binding and transcription assays showed that Bmal1 controlled expression by direct binding to E-Box in Prdx6 promoter to regulate its transcription. Mutation at E-Box or ARE reduced promoter activity, while disruption of both sites diminished the activity, suggesting that both sites were required for peak Prdx6-transcription. As in aging hLECs, ROS accumulation was increased in Bmal1-deficient cells and the cells were vulnerable to death. Intriguingly, Bmal1/Nrf2/Prdx6 and PhaseII antioxidants showed rhythmic expression in mouse lenses in vivo and were reciprocally linked to ROS levels. We propose that Bmal1 is pivotal for regulating oxidative responses. Findings also reveal a circadian control of antioxidant-pathway, which is important in combating lens/LECs damage induced by aging or oxidative stress.

Connexin43 and connexin50 channels exhibit different permeability to the second messenger inositol triphosphate

Gap junction channels made of different connexins have distinct permeability to second messengers, which could affect many cell processes, including lens epithelial cell division. Here, we have compared the permeability of IP₃ and Ca²⁺ through channels made from two connexins, Cx43 and Cx50, that are highly expressed in vertebrate lens epithelial cells. Solute transfer was measured while simultaneously monitoring junctional conductance via dual whole-cell/perforated patch clamp. HeLa cells expressing Cx43 or Cx50 were loaded with Fluo-8, and IP₃ or Ca²⁺ were delivered via patch pipette to one cell of a pair, or to a monolayer while fluorescence intensity changes were recorded. Cx43 channels were permeable to IP₃ and Ca²⁺. Conversely, Cx50 channels were impermeable to IP₃, while exhibiting high permeation of Ca²⁺. Reduced Cx50 permeability to IP₃ could play a role in regulating cell division and homeostasis in the lens.

Generation and proteome profiling of PBMC-originated, iPSC-derived lentoid bodies

Here, we report proteome profiling of peripheral blood mononuclear cell (PBMC)-originated, induced pluripotent stem cell (iPSC)-derived, lens-like organoids termed lentoid bodies at two differentiation time points. A small aliquot of the blood sample was ascertained to collect PBMCs that were reprogrammed to iPSCs. The PBMC-originated, iPSCs were differentiated to lentoid bodies employing the "fried egg" method. Quantitative real-time PCR (qRT-PCR) analysis revealed increased expression levels of lens-associated markers in lentoid bodies while transmission electron microscopy identified closely packed lens epithelial- and differentiating fiber-like cells in lentoid bodies. Total cellular protein was extracted from lentoid bodies at differentiation day 25 and mass spectrometry identified a total of 9,473 proteins. The low counts of crystallin proteins at differentiation day 25 prompted us to re-examine the proteome at differentiation day 35 as we reasoned that 10 additional days of differentiation will increase the crystallin count. However, we did not detect any substantial increase in crystallin protein counts at differentiation day 35. In conclusion, we report generation and proteome profiles of PBMC-originated, iPSC-derived lentoid bodies at multiple differentiation time points.

Calponin-3 deficiency augments contractile activity, plasticity, fibrogenic response and Yap/Taz transcriptional activation in lens epithelial cells and explants

The transparent ocular lens plays a crucial role in vision by focusing light on to the retina with loss of lens transparency leading to impairment of vision. While maintenance of epithelial phenotype is recognized to be essential for lens development and function, knowledge of the identity of different molecular mechanisms regulating lens epithelial characteristics remains incomplete. This study reports that CNN-3, the acidic isoform of calponin, an actin binding contractile protein, is expressed preferentially and abundantly relative to the basic and neutral isoforms of calponin in the ocular lens, and distributes predominantly to the epithelium in both mouse and human lenses. Expression and MEKK1-mediated threonine 288 phosphorylation of CNN-3 is induced by extracellular cues including TGF-β2 and lysophosphatidic acid. Importantly, siRNA-induced deficiency of CNN3 in lens epithelial cell cultures and explants results in actin stress fiber reorganization, stimulation of focal adhesion formation, Yap activation, increases in the levels of α-smooth muscle actin, connective tissue growth factor and fibronectin, and decreases in E-cadherin expression. These results reveal that CNN3 plays a crucial role in regulating lens epithelial contractile activity and provide supporting evidence that CNN-3 deficiency is associated with the induction of epithelial plasticity, fibrogenic activity and mechanosensitive Yap/Taz transcriptional activation.

The negative regulatory Spred1 and Spred2 proteins are required for lens and eye morphogenesis

The transparent and refractive properties of the ocular lens are dependent on its precise cellular structure, supported by the regulation of lens cellular processes of proliferation and differentiation that are essential throughout life. The ERK/MAPK-signalling pathway plays a crucial role in regulating lens cell proliferation and differentiation, and in turn is regulated by inhibitory molecules including the Spred family of proteins to modulate and attenuate the impact of growth factor stimulation. Given Spreds are strongly and distinctly expressed in lens, along with their established inhibitory role in a range of different tissues, we investigated the role these antagonists play in regulating lens cell proliferation and differentiation, and their contribution to lens structure and growth. Using established mice lines deficient for either or both Spred 1 and Spred 2, we demonstrate their role in regulating lens development by negatively regulating ERK1/2 activity. Mice deficient for both Spred 1 and Spred 2 have impaired lens and eye development, displaying irregular lens epithelial and fibre cell activity as a result of increased levels of phosphorylated ERK1/2. While Spred 1 and Spred 2 do not appear to be necessary for induction and early stages of lens morphogenesis (prior to E11.5), nor for the formation of the primary fibre cells, they are required for the continuous embryonic growth and differentiation of the lens.

Comparative transcriptome analysis of hESC- and iPSC-derived lentoid bodies

The ocular lens serves as an excellent system to investigate the intricate details of development and differentiation. Generation of lentoid bodies or lens-like structures using pluripotent stem cells is important for understanding the processes critical for lens morphogenesis and the mechanism of cataractogenesis. We previously reported the generation of peripheral blood mononuclear cell (PBMC)-originated, induced pluripotent stem cells (iPSCs). Here, we report generation of lentoid bodies from human embryonic stem cells (hESCs) and (PBMC)-originated, iPSCs employing the “fried egg” method with brief modifications. The ultrastructure analysis of hESC- and iPSC-derived lentoid bodies identified closely packed lens epithelial- and differentiating fiber-like cells. In addition, we performed RNA sequencing (RNA-Seq) based transcriptome profiling of hESC- and iPSC-derived lentoid bodies at differentiation day 25. Next-generation RNA sequencing (RNA-Seq) of hESC- and iPSC-derived lentoid bodies detected expression (≥0.659 RPKM) of 13,975 and 14,003 genes, respectively. Comparative transcriptome analysis of hESC- and iPSC-derived lentoid bodies revealed 13,563 (>96%) genes common in both datasets. Among the genes common in both transcriptome datasets, 12,856 (~95%) exhibited a quantitatively similar expression profile. Next, we compared the mouse lens epithelial and fiber cell transcriptomes with hESC- and iPSC-derived lentoid bodies transcriptomes and identified > 96% overlap with lentoid body transcriptomes. In conclusion, we report first-time comparative transcriptome analysis of hESC- and iPSC-derived lentoid bodies at differentiation day 25.

Lens Connexin Channels Have Differential Permeability to the Second Messenger cAMP

Purpose

Gap junction channels exhibit connexin specific biophysical properties, including the selective intercellular passage of larger solutes, such as second messengers. Here, we have examined the cyclic nucleotide permeability of the lens connexins, which could influence events like epithelial cell division and differentiation.

Methods

We compared the cAMP permeability through channels composed of Cx43, Cx46, or Cx50 using simultaneous measurements of junctional conductance and intercellular transfer. For cAMP detection, the recipient cells were transfected with a cAMP sensor gene, the cyclic nucleotide-modulated channel from sea urchin sperm (SpIH). cAMP was introduced via patch pipette into the cell of the pair that did not express SpIH. SpIH-derived currents were recorded from the other cell of a pair that expressed SpIH. cAMP permeability was also directly visualized in transfected cells using a chemically modified fluorescent form of the molecule.

Results

cAMP transfer was observed for homotypic Cx43 channels over a wide range of junctional conductance. Homotypic Cx46 channels also transferred cAMP, but permeability was reduced compared with Cx43. In contrast, homotypic Cx50 channels exhibited extremely low permeability to cAMP, when compared with either Cx43, or Cx46.

Conclusions

These data show that channels made from Cx43 and Cx46 result in the intercellular delivery of cAMP in sufficient quantity to activate cyclic nucleotide-modulated channels. The data also suggest that the greatly reduced cAMP permeability of Cx50 channels could play a role in the regulation of cell division in the lens.

Verification and spatial mapping of TRPV1 and TRPV4 expression in the embryonic and adult mouse lens

The transient receptor protein vanilloid channels, TRPV1 and TRPV4, have recently been shown to be mechanosensors in the ocular lens that act to transduce physical changes in lens volume and internal hydrostatic pressure into the activation of signalling pathways in lens epithelial cells. These pathways in turn regulate ion and water transport to ensure that the optical properties of the lens remain constant. Despite the functional evidence that implicate the roles of TRPV1 and TRPV4 in the lens, their respective cellular expression patterns in the different regions of the lens has to date not been fully characterised. Using Western blotting we have confirmed that TRPV1 and TRPV4 are expressed throughout all regions (epithelium, outer cortex, inner cortex/core) of the adult mouse lens. Subsequent immunolabeling of lens cryosections confirmed that TRPV1 and TRPV4 are expressed throughout all regions of the lens, but revealed differentiation-dependent differences in the subcellular expression of the two channels in the different regions. In the epithelium and outer cortex, intense TRPV1 and TRPV4 labeling was predominately associated with the cytoplasm. In a discrete zone in the inner cortex, labeling for both proteins was greatly diminished, but could be enhanced by incubating sections with the detergent Triton X-100 to reveal TRPV1 and TRPV4 labelling that was associated with the membrane. This suggests that in this region of the lens there is a potential interacting protein that masks the binding of the TRPV1 and TRPV4 antibodies to their respective epitopes in the lens inner cortex. In the core of the lens, which contains the embryonic nucleus, TRPV1 and TRPV4 labelling was associated exclusively with fibre cell membranes. This labelling in the lens core of the adult mouse lens appeared to originate in early development as a similar membrane labelling was observed at embryonic day 10 (E10) of the cells in the lens vesicle that subsequently forms the embryonic nucleus in the adult lens. During subsequent stages of embryonic development TRPV1 and TRPV4 remained membranous in the inner cortex and core, while showing labelling that was associated with the cytoplasm in the superficial outer cortical region. The extent of cytoplasmic labelling for TRPV4, but not TRPV1, in this cortical region could however be dynamically regulated by cutting the zonules that normally attach the lens to the ciliary body. We have shown an early onset and continuous expression of TRPV1 and TRPV4 across all lens regions, and that TRPV4 can be dynamically trafficked into the membranes of differentiating fibre cells, results that suggests that these mechanosensitive channels may also be functionally active in lens fibre cells.

Jagged1 protein processing in the developing mammalian lens

Notch signaling regulates a multitude of cellular processes. During ocular lens development this pathway is required for lens progenitor growth, differentiation and maintenance of the transition zone. After ligand-receptor binding, the receptor proteins are processed, first by ADAM proteases, then by γ-secretase cleavage. This results in the release of a Notch intracellular domain (N-ICD), which is recruited into a nuclear transcription factor complex that activates Notch target genes. Previous in vitro studies showed that the Delta-like and Jagged ligand proteins can also be cleaved by the γ-secretase complex, but it remains unknown whether such processing occurs during in vivo vertebrate development. Here we show that mouse and human lens progenitor cells endogenously express multiple Jagged1 protein isoforms, including a Jagged1 intracellular domain. We also found that pharmacologic blockage of γ-secretase activity in vitro resulted in an accumulation of Jagged1 polypeptide intermediates. Finally, overexpression of an epitope-tagged Jagged1 intracellular domain displayed nuclear localization and induced the upregulation of endogenous JAG1 mRNA expression. These findings support the idea that along with its classical role as a Notch pathway ligand, Jagged1 is regulated post-translationally, to produce multiple active protein isoforms.

Summary: The Notch pathway ligand protein Jagged1 undergoes multiple catalytic cleavages, regulated by Adam proteases and the gamma-secretase complex, during mammalian lens development, similar to Notch receptor proteins.

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.

Sumoylation-deficient Prdx6 repairs aberrant Sumoylation-mediated Sp1 dysregulation-dependent Prdx6 repression and cell injury in aging and oxidative stress

Progressive deterioration of antioxidant response in aging is a major culprit in the initiation of age-related pathobiology induced by oxidative stress. We previously reported that oxidative stress leads to a marked reduction in transcription factor Sp1 and its mediated Prdx6 expression in lens epithelial cells (LECs) leading to cell death. Herein, we examined how Sp1 activity goes awry during oxidative stress/aging, and whether it is remediable. We found that Sp1 is hyper-Sumoylated at lysine (K) 16 residue in aging LECs. DNA binding and promoter assays revealed, in aging and oxidative stress, a significant reduction in Sp1 overall binding, and specifically to Prdx6 promoter. Expression/overexpression assay revealed that the observed reduction in Sp1-DNA binding activity was connected to its hyper-Sumoylation due to increased reactive oxygen species (ROS) and Sumo1 levels, and reduced levels of Senp1, Prdx6 and Sp1. Mutagenesis of Sp1 at K16R (arginine) residue restored steady-state, and improved Sp1-DNA binding activity and transactivation potential. Extrinsic expression of Sp1K16R increased cell survival and reduced ROS levels by upregulating Prdx6 expression in LECs under aging/oxidative stress, demonstrating that Sp1K16R escapes the aberrant Sumoylation processes. Intriguingly, the deleterious processes are reversible by the delivery of Sumoylation-deficient Prdx6, an antioxidant, which would be a candidate molecule to restrict aging pathobiology.

Proteome Profiling of Developing Murine Lens Through Mass Spectrometry

Purpose

We previously completed a comprehensive profile of the mouse lens transcriptome. Here, we investigate the proteome of the mouse lens through mass spectrometry–based protein sequencing at the same embryonic and postnatal time points.

Methods

We extracted mouse lenses at embryonic day 15 (E15) and 18 (E18) and postnatal day 0 (P0), 3 (P3), 6 (P6), and 9 (P9). The lenses from each time point were preserved in three distinct pools to serve as biological replicates for each developmental stage. The total cellular protein was extracted from the lens, digested with trypsin, and labeled with isobaric tandem mass tags (TMT) for three independent TMT experiments.

Results

A total of 5404 proteins were identified in the mouse ocular lens in at least one TMT set, 4244 in two, and 3155 were present in all three TMT sets. The majority of the proteins exhibited steady expression at all six developmental time points; nevertheless, we identified 39 proteins that exhibited an 8-fold differential (higher or lower) expression during the developmental time course compared to their respective levels at E15. The lens proteome is composed of diverse proteins that have distinct biological properties and functional characteristics, including proteins associated with cataractogenesis and autophagy.

Conclusions

We have established a comprehensive profile of the developing murine lens proteome. This repository will be helpful in identifying critical components of lens development and processes essential for the maintenance of its transparency.

Presenilin gene function and Notch signaling feedback regulation in the developing mouse lens

Presenilins (Psen1 and Psen2 in mice) are polytopic transmembrane proteins that act in the γ-secretase complex to make intra-membrane cleavages of their substrates, including the well-studied Notch receptors. Such processing releases the Notch intracellular domain, allowing it to physically relocate from the cell membrane to the nucleus where it acts in a transcriptional activating complex to regulate downstream genes in the signal-receiving cell. Previous studies of Notch pathway mutants for Jagged1, Notch2, and Rbpj demonstrated that canonical signaling is a necessary component of normal mouse lens development. However, the central role of Psens within the γ-secretase complex has never been explored in any developing eye tissue or cell type. By directly comparing Psen single and double mutant phenotypes during mouse lens development, we found a stronger requirement for Psen1, although both genes are needed for progenitor cell growth and to prevent apoptosis. We also uncovered a novel genetic interaction between Psen1 and Jagged1. By quantifying protein and mRNA levels of key Notch pathway genes in Psen1/2 or Jagged1 mutant lenses, we identified multiple points in the overall signaling cascade where feedback regulation can occur. Our data are consistent with the loss of particular genes indirectly influencing the transcription level of another. However, we conclude that regulating Notch2 protein levels is particularly important during normal signaling, supporting the importance of post-translational regulatory mechanisms in this tissue.

The klotho-related protein KLPH (lctl) has preferred expression in lens and is essential for expression of clic5 and normal lens suture formation

KLPH/lctl belongs to the Klotho family of proteins. Expressed sequence tag analyses unexpectedly revealed that KLPH is highly expressed in the eye lens while northern blots showed that expression is much higher in the eye than in other tissues. In situ hybridization in mouse localized mRNA to the lens, particularly in the equatorial epithelium. Immunofluorescence detected KLPH in lens epithelial cells with highest levels in the germinative/differentiation zone. The gene for KLPH in mouse was deleted by homologous recombination. Littermate knockout (KO) and wild type (WT) mice were compared in a wide panel of pathology examinations and were all grossly normal, showing no systemic effects of the deletion. However, the lens, while superficially normal at young ages, had focusing defects and exhibited age-related cortical cataract by slit lamp examination. Whole-lens imaging showed that KO mice had disorganized lens sutures, forming a loose double-y or x instead of the tight y formation of WT. RNA-seq profiles for KO and WT littermates confirmed the absence of KLPH mRNA in KO lens and also showed complete absence of transcripts for Clic5, a protein associated with cilium/basal body related auditory defects in a mouse model. Immunofluorescence of lens epithelial flat mounts showed that Clic5 localized to cilia/centrosomes. Mice mutant for Clic5 (jitterbug) also had defective sutures. These results suggest that KLPH is required for lens-specific expression of Clic5 and that Clic5 has an important role in the machinery that controls lens fiber cell extension and organization.

Crim1 is required for maintenance of the ocular lens epithelium

The development and growth of the vertebrate ocular lens is dependent on the regulated proliferation of an anterior monolayer of epithelial cells, and their subsequent differentiation into elongate fiber cells. The growth factor rich ocular media that bathes the lens mediates these cellular processes, and their respective intracellular signaling pathways are in turn regulated to ensure that the proper lens architecture is maintained. Recent studies have proposed that Cysteine Rich Motor Neuron 1 (Crim1), a transmembrane protein involved in organogenesis of many tissues, might influence cell adhesion, polarity and proliferation in the lens by regulating integrin-signaling. Here, we characterise the lens and eyes of the Crim1^KST264 mutant mice, and show that the loss of Crim1 function in the ocular tissues results in inappropriate differentiation of the lens epithelium into fiber cells. Furthermore, restoration of Crim1 levels in just the lens tissue of Crim1^KST264 mice is sufficient to ameliorate most of the dysgenesis observed in the mutant animals. Based on our findings, we propose that tight regulation of Crim1 activity is required for maintenance of the lens epithelium, and its depletion leads to ectopic differentiation into fiber cells, dramatically altering lens structure and ultimately leading to microphthalmia and aphakia.

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.