Ageing and vision: structure, stability and function of lens crystallins

Systemically administered mini α-crystallin peptide delays cataract progression in streptozotocin-induced diabetic rats

α-Crystallin in the mammalian eye lens composed of αA-Crystallin (αAC) and αB-Crystallin (αBC) subunits present in a 3:1 ratio. These proteins exhibit chaperone-like activity, helping to protect cells from various forms of stress. Specific sequences within αAC (70KFVIFLDVKHFSPEDLTVK88) and αBC (73DRFSVNLDVKHFSPEELKVK92) have been shown to possess effective chaperone and anti-apoptotic properties. However, their protective effects in diabetic cataract (DC) have not been explored. The current study explored the protective effects of systemically administered mini-αA and αBC peptides, both individually and in combination (3:1 ratio) against streptozotocin (STZ)-induced DC in rats. Hyperglycemia was induced in Sprague-Dawley rats through intraperitoneal (I.P.) injection of STZ, while control rats received PBS. Starting from the onset of cataract development, a group of diabetic rats was treated with mini-αA, or mini-αB, or their combination for four months via IP administration. Cataract progression and maturation were monitored using a slit lamp biomicroscope. To understand the underlying biochemical and molecular processes, we assessed changes in protein content, protein insolubilization, oxidative stress, endoplasmic reticulum (ER) stress, apoptotic cell death, and caspase-3 activity. Although the mini peptides did not prevent STZ-induced hyperglycemia, they delayed cataract progression in diabetic rats. Furthermore, mini peptides reduced protein aggregation and insolubilization, alleviated oxidative and ER stress, and mitigated hyperglycemia-induced apoptosis by lowering caspase-3 activity and Bax levels. This study demonstrates that systemic administration of mini α-crystallin peptides can delay DC progression by mitigating protein aggregation, oxidative stress, ER stress, and apoptosis. These findings suggest potential therapeutic applications for mini α-crystallin peptides in treating DC.

Activation mechanism of small heat shock protein HSPB5 revealed by disease-associated mutants

Found from bacteria to humans, small heat shock proteins (sHSPs) are the least understood protein chaperones. HSPB5 (or αB-crystallin) is among the most widely expressed of the 10 human sHSPs, including in muscle, brain, and eye lens where it is constitutively present at high levels. A high content of disorder in HSPB5 has stymied efforts to uncover how its structure gives rise to function. To uncover its mechanisms of action, we compared human HSPB5 and two disease-associated mutants, R120G and D109H. Expecting to learn how the mutations lead to loss of function, we found instead that the mutants are constitutively activated chaperones while wild-type HSPB5 can transition reversibly between nonactivated (low activity) and activated (high activity) states in response to changing conditions. Techniques that provide information regarding interactions and accessibility of disordered regions revealed that the disordered N-terminal regions (NTR) that are required for chaperone activity exist in a complicated interaction network within HSPB5 oligomers and are sequestered from solvent in nonactivated states. Either mutation or an activating pH change causes rearrangements in the network that expose parts of the NTR, making them more available to bind an aggregating client. Although beneficial in the short-term, failure of the mutants to adopt a state with lower activity and lower NTR accessibility leads to increased coaggregation propensity and, presumably, early cataract. The results support a model where chaperone activity and solubility are modulated through the quasi-ordered NTR and its multiple competing interactions.

Glipizide inhibits the glycation of alpha-crystallin: A combined in vitro and in silico approach in retinopathy management

In human eye, structural proteins, known as crystallins, play a crucial role in maintaining the eye's refractive index. These crystallins constitute majority of the total soluble proteins found in the eye lens. Among them, α-crystallins (α-CR) is one of the major components. Under hyperglycaemic conditions, crystallins become susceptible to glycation that ultimately leads to advanced glycation endproducts (AGEs) formation. Glipizide is a well-known oral medication used in controlling levels of blood sugar, this drug stimulates the insulin release from pancreas. However, this drug has not been thoroughly investigated for its impact on α-CR glycation. In this study, we explored glipizide's protective role against glucose-induced α-CR glycation. Remarkably, glipizide effectively inhibited the formation of early glycation products, ultimately reducing AGEs formation. Additionally, glipizide provides protection against modifications of free lysine residues and lowered the carbonyl content. To gain deeper insights into mechanism of inhibition, we turn to binding studies and bioinformatics. Glipizide formed stable complex with α-CR with values of Gibbs energy ranging from -5.848 to -6.695 kcal/mol. Molecular docking revealed the binding energy as -6.5 kcal/mol and lysine residues emerged as a prominent among the key interacting residues. Notably, glipizide appears to mask lysine residues, thereby contributing to the inhibition of α-CR glycation. Furthermore, analysis of molecular simulation data reinforces the stability of this complex. Consequently, the stable α-CR-glipizide complex may prevent glucose from binding to α-CR. Overall, glipizide holds promise as a preventive measure against glycation of eye lens proteins, potentially benefiting in diabetic retinopathy.

Deep Characterization of Isomerization in the Human Eye Lens Proteome by Crystallin-Depleted Data-Independent Acquisition

The eye lens is a unique tissue optimized for light transmission and refraction, necessitating dissolution of all organelles in mature fiber cells. This absence of organelles prevents protein turnover and leads to the accumulation of many spontaneous modifications over time. One modification that is oft overlooked is isomerization, despite its known impact on protein structure, interference with enzymatic activity, and association with disease. Prior analysis of isomerization in the lens has been limited to a small number of targets, consisting primarily of the highly abundant crystallin proteins. Proteomic coverage can be greatly increased by first depleting the crystallins and then employing state-of-the-art data-independent acquisition (DIA) mass spectrometry (MS). However, this approach has not been combined with data analysis methods capable of identifying isomers. By so doing, we identified hundreds of previously unreported, noncrystallin Asp isomer sites. To a lesser extent, isomerization was also detected at serine and glutamic acid, consistent with previous reports of relative isomerization propensities. Interestingly, we also identify histidine isomerization sites in a select number of peptides associated with metal adduction. We further analyzed our results according to primary sequence and secondary structure to explore factors potentially influencing isomerization. Finally, we found that while isomerization percents for individual proteins are modestly accurate predictor of age, inclusion of multiple isomerized sites affords a more accurate prediction of age, which may be useful for applications in forensics.

Impact of crowding on aggregation of UV-irradiated βL-crystallin and chaperone like activity of α-crystallin depends of the nature of a crowding agent

The effect of crowding on the aggregation of UV irradiated βL-crystallin and the chaperone-like activity of α-crystallin has been studied. PEG-20000, BSA and γ-crystallin were used as crowders. It was shown that the initial rate of aggregation of UV irradiated βL-crystallin depended on the type of crowder: the rate did not change in the presence of BSA, doubled when the concentration of γ-crystallin reached 30 mg/ml, and increased linearly with increasing PEG concentration. It was found that PEG is not an inert compound, but causes additional destabilization and denaturation of UV irradiated βL-crystallin. The nucleation time of UV irradiated βL-crystallin aggregation in the presence of BSA and γ-crystallin decreased linearly with an increase in the excluded volume up to 5 %, then remained constant. It was found that BSA and γ-crystallin reduced the initial adsorption capacity of α-crystallin, which was used to quantify chaperone-like activity, in a concentration-dependent manner. g-crystallin demonstrated a greater ability to suppress chaperone-like activity compared to BSA. This difference is due to γ-crystallin ability to interact with α-crystallin. The obtained results indicate the importance of using the exact same crowders that in vivo create the environment of the biochemical process for study in vitro.

Role of human γD-crystallin tryptophans in the ultraviolet radiation response

Cataracts are the leading cause of reversible blindness worldwide, primarily associated with the aggregation of proteins such as γ-crystallins, which are essential for maintaining lens transparency. Among these, human γD-crystallin (HγD) contains four conserved tryptophans, hypothesized to act as a protective mechanism against ultraviolet (UV) radiation. This study investigated the effects of low-dose UV-B radiation on HγD and its variants, in which each tryptophan was replaced by phenylalanine. The substitutions did not significantly affect the protein's secondary or tertiary structure but markedly reduced thermal stability, particularly in the W42F mutant. Aggregation kinetics were accelerated in all variants, with pronounced increases observed in the W130F and W156F mutants. Molecular dynamics simulations revealed that these substitutions disrupt hydrophobic interactions in both the N- and C-terminal domains, promoting instability and enhancing aggregation propensity. UV radiation induced chemical modifications, where Trp42 and Trp130 were the most affected, further driving aggregation. Changes in fluorescence spectra after UV exposure indicated the breakdown of the tryptophan indole ring and the formation of degradation products. These results confirm that tryptophans in HγD serve a crucial protective role against UV-induced damage by preserving structural stability and minimizing aggregation.

Aggregation inhibitory effect of vitamin C on cataract-associated P23T γD-crystallin

Cataract is a progressive loss of eye lens transparency, as a result of age-related chemical modifications or due to congenital mutations in crystallins. A vital antioxidant in the aqueous humor, the vitamin C, has been suggested to hold potential for the prophylaxis of age-related cataract. However, the effect of vitamin C on congenital cataract has not yet been investigated. Here, we explored the aggregation inhibitory effect of vitamin C on the P23T human γD-crystallin mutant, associated with congenital cataract. The effect of vitamin C on the aggregation propensity of P23T human γD-crystallin was investigated by solution NMR, atomic force microscopy (AFM), and other biophysical techniques. We found that vitamin C is able to prevent and reverse P23T human γD-crystallin aggregation in a dose-dependent manner. In particular, NMR data suggest that the inhibitory effect of vitamin C on P23T human γD-crystallin phase-separation is probably mediated by interacting with aggregation prone regions. AFM images of P23T human γD-crystallin under native aggregating conditions revealed the appearance of amorphous aggregates, that disassemble into monomers in the presence of vitamin C. The current study highlights and confirms the possibility that vitamin C is able to dissolve crystallin aggregates, potentially slowing the onset or reversing cataract.

Effect of lens crystallins aggregation on cataract formation

Cataracts represent one of the leading causes of blindness globally. The World Health Organization's 2019World Report on Vision indicates that approximately 65.2 million individuals worldwide experience varying degrees of visual impairment or blindness attributable to cataracts. The prevalence of this condition is significantly increasing, largely due to the accelerated aging of the global population. The lens of the eye is primarily composed of crystallins, which are categorized into three families: α-, β-, and γ-crystallins. The highly ordered structure and interactions among these crystallins are crucial for maintaining lens transparency. Disruptions in the interactions within or between crystallins can compromise this delicate architecture, exposing hydrophobic surfaces that lead to crystallin aggregation and subsequent cataract formation. Currently, surgical intervention is the sole treatment for cataracts, and the cataract surgery rate in China remains considerably lower than that of developed nations. Investigating the mechanisms of crystallins interaction and aggregation is essential for understanding the molecular pathogenesis of cataract formation, which may inform the development of targeted therapies and preventative strategies. This paper reviews recent scientific advancements in the research field of lens crystallins aggregation and cataract formation.

Localization of fluorescent gold nanoparticles throughout the eye after topical administration

The human eye is a highly intricate sensory organ. When a condition requiring treatment occurs, eyedrops, which represent 90% of all ophthalmic treatments, are most frequently used. However, eyedrops are associated with low bioavailability, with less than 0.02% of therapeutic molecules reaching the anterior chamber. Thus, new delivery systems are required to ensure sufficient drug concentration over time at the target site. Gold nanoparticles are a promising avenue for drug delivery; however, they can be difficult to track in biological systems. Fluorescent gold nanoparticles, which have the same ultrastability and biocompatibility as their nonfluorescent counterpart, could act as an effective imaging tool to study their localization throughout the eye after administration. Thus, this study (1) synthesized and characterized fluorescent gold nanoparticles, (2) validated similar properties between nonfluorescent and fluorescent gold nanoparticles, and (3) determined their localization in the eye after topical application on ex vivo rabbit eyes. The fluorescent gold nanoparticles were synthesized, characterized, and identified in the cornea, iris, lens, and posterior segment of rabbit eyeballs, demonstrating tremendous potential for future drug delivery research.

Cataractous Eye Protein Isolate Stabilized Gold Nanoparticles Prevent Their Ethanol-Induced Aggregation

Due to their distinctive optical, electrical, and catalytic characteristics, gold nanoparticles (AuNPs) have found increasing use for a wide range of applications, including biomedicine and catalysis. Inherent agglomeration propensities impair their functional qualities, stability, and biocompatibility. This work investigates the potential applications of the cataractous eye protein isolate (CEPI), a waste product rich in proteins from cataract surgery, as a novel AuNP stabilizing agent. It was found that CEPI can successfully stabilize AuNPs under a variety of situations, preventing ethanol-induced aggregation and preserving their structural integrity. Using spectroscopic and analytical techniques, including UV-Vis spectroscopy, dynamic light scattering (DLS), circular dichroism (CD) spectroscopy, and fluorescence quenching studies, we confirmed the successful binding of CEPI to AuNPs and the enhanced stability of the conjugates. A shift in the localized surface plasmon resonance (LSPR) peak and modifications to the secondary structure of the CEPI were indicative of strong binding and protective effects between CEPI and AuNPs. These findings suggest that CEPI, an underutilized biomaterial, can serve as an effective and biocompatible stabilizer for AuNPs, with potential applications in biomedical and therapeutic fields.

Determination of Trends Underlying Aspartic Acid Isomerization in Intact Proteins Reveals Unusually Rapid Isomerization of Tau

Spontaneous chemical modifications in long-lived proteins can potentially change protein structure in ways that impact proteostasis and cellular health. For example, isomerization of aspartic acid interferes with protein turnover and is anticorrelated with cognitive acuity in Alzheimer's disease. However, few isomerization rates have been determined for Asp residues in intact proteins. To remedy this deficiency, we used protein extracts from SH-SY5Y neuroblastoma cells as a source of a complex, brain-relevant proteome with no baseline isomerization. Cell lysates were aged in vitro to generate isomers, and extracted proteins were analyzed by data-independent acquisition (DIA) liquid chromatography-mass spectrometry (LC-MS). Although no Asp isomers were detected at day 0, isomerization increased over time and was quantifiable for 105 proteins by day 50. Data analysis revealed that the isomerization rate is influenced by both primary sequence and secondary structure, suggesting that steric hindrance and backbone rigidity modulate isomerization. Additionally, we examined lysates extracted under gentle conditions to preserve protein complexes and found that protein-protein interactions often slow isomerization. Base catalysis was explored as a means to accelerate Asp isomerization due to findings of accelerated asparagine deamidation. However, no substantial rate enhancement was found for isomerization, suggesting fundamental differences in acid-base chemistry. With an enhanced understanding of Asp isomerization in proteins in general, we next sought to better understand Asp isomerization in tau. In vitro aging of monomeric and aggregated recombinant tau revealed that tau isomerizes significantly faster than any similar protein within our data set, which is likely related to its correlation with cognition in Alzheimer's disease.

Cataract-prone variants of γD-crystallin populate a conformation with a partially unfolded N-terminal domain under native conditions

Human γD-crystallin, a monomeric protein abundant in the eye lens nucleus, must remain stably folded for an individual's entire lifetime to avoid aggregation and protein deposition-associated cataract formation. γD-crystallin contains two homologous domains, an N-terminal domain (NTD) and a C-terminal domain (CTD), which interact via a hydrophobic interface. Several familial mutations in the gamma crystallin gene are linked to congenital early-onset cataract, most of which affect the NTD. Some of these, including V75D and W42R, are known to populate intermediates under partially denaturing conditions possessing a natively folded CTD and a completely unfolded NTD. We employed hydrogen-deuterium exchange mass spectrometry to probe the structural and energetic features of variants of γD-crystallin under both native and partially denaturing conditions. For V75D and W42R, we identify a species under native conditions that retains partial structure in the NTD and is structurally and energetically distinct from the intermediate populated under partially denaturing conditions. Residues at the NTD-CTD interface play crucial roles in stabilizing this intermediate, and disruption of interface contacts either by amino acid substitution or partial denaturation permits direct observation of two intermediates simultaneously. These data suggest that the intermediate identified under native conditions is accessed from the native state and not on the folding pathway. The intermediate we have identified here exposes hydrophobic amino acids that are buried in both the folded full-length protein and in the protein's stable isolated domains. Such nonnative exposure of a hydrophobic patch may play an important role in cataract formation.

Amino acid δ15N in eye lens laminae reveals life-time ontogenetic trophic shifts of a highly migratory species

Investigating the feeding ecology through the ontogenesis of highly migratory species such as the Pacific Bluefin tuna (PBFT; Thunnus orientalis) is difficult due to its extensive home range and cross-oceanic migration. Here, we show the potential of conducting nitrogen stable isotope (δ15N) analyses in bulk tissue and amino acids (AAs) in consecutive eye lens laminae of PBFT to reconstruct the trophic life history for an individual tuna. The δ15Nbulk profiles between individuals caught in the wild and pen-raised were compared. For all individuals, δ15Nbulk values increased with increasing eye lens diameter or fork length, and exhibited low variation among individual profiles despite tuna being captured in different months. Large δ15Nbulk shifts (6.8‰-8.5‰) were quantified between the first and last deposited laminae for each individual, suggesting major ontogenetic changes in either foraging areas or trophic position. AA δ15N values indicate that this highly migratory schooling predator switches feeding areas from lower to higher δ15N baseline values, reflecting feeding on both sides of the north Pacific, and tends to feed on prey of higher trophic position as it grows. Together, stable isotope analysis in bulk tissue and individual AAs in eye lens laminae could be a powerful approach to investigate changes in the foraging habitat and trophic status of highly migratory species.

The more smoking the more cataract: A study on smoking, snus use and cataract in a Swedish population

PURPOSE

To examine the prevalence of self-reported cataract and cataract surgery, and the incidence of cataract surgery, in relation to smoking and use of the moist smokeless tobacco product snus.

METHODS

In 2014/2015, individuals born in 1951 (n = 18 055) in the Västra Götaland County, Sweden, were invited to participate. Of these, 9743 (54%) accepted participation and 9316 (52%) remained after exclusion criteria were applied. Participants answered a questionnaire with items about eye conditions, smoking, snus, gender, education, asthma, chronic obstructive pulmonary disease, corticosteroid use, diabetes mellitus, weight and height. Prevalence ratios (PRs) for self-reported cataract and cataract surgery were calculated. The incidence of cataract surgery was assessed, and hazard ratios (HRs) were presented.

RESULTS

Having ever smoked was associated with a higher prevalence ratio of self-reported cataract (PR 1.19, 95% confidence interval [CI] 1.04-1.35) and cataract surgery (PR 1.27, 95% CI 1.06-1.53), compared to those who had never been daily smokers. Currently, a smoker was associated with a higher HR of cataract surgery (HR 1.34, 95% CI 1.04-1.74), as well as having been a former smoker (HR 1.27, 95% CI 1.03-1.56). Total years of smoking were associated with an increased risk for cataract surgery (HR 1.05, 95% CI 1.02-1.08 for 5 years of smoking). Snus use was not associated with an increased prevalence of cataract or incidence of cataract surgery, except among women who were current snus users (HR for cataract surgery 2.04, 95% CI 1.16-3.60 n = 108).

CONCLUSION

Smoking is associated with a higher prevalence of cataracts, and a higher incidence of cataract surgery, indicating a dose-response relationship. However, there was no firm association between snus use and cataract.

Analysis of mouse lens morphological and proteomic abnormalities following depletion of βB3-crystallin

Crystallin proteins serve as both essential structural and as well as protective components of the ocular lens and are required for the transparency and light refraction properties of the organ. The mouse lens crystallin proteome is represented by αA-, αB-, βA1-, βA2-, βA3-, βA4-, βB1-, βB2-, βB3-, γA-, γB-, γC-, γD-, γE, γF-, γN-, and γS-crystallin proteins encoded by 16 genes. Their mutations are responsible for lens opacification and early onset cataract formation. While many cataract-causing missense and nonsense mutations are known for these proteins, including the human CRYBB3 gene, the mammalian loss-of function model of the Crybb3 gene remains to be established. Herein, we generated the first mouse model via deletion of the Crybb3 promoter that abolished expression of the βB3-crystallin. Histological analysis of lens morphology using newborn βB3-crystallin-deficient lenses revealed disrupted lens morphology with early-onset phenotypic variability. In-depth lens proteomics at four time points (newborn, 3-weeks, 6-weeks, and 3-months) showed both down- and up-regulation of various proteins, with the highest divergence from control mice observed in 3-months lenses. Apart from the βB3-crystallin, another protein Smarcc1/Baf155 was down-regulated in all four samples. In addition, downregulation of Hspe1, Pdlim1, Ast/Got, Lsm7, Ddx23, and Acad11 was found in three time points. Finally, we show that the βB3-crystallin promoter region, which contains multiple binding sites for the transcription factors AP-2α, c-Jun, c-Maf, Etv5, and Pax6 is activated by FGF2 in primary lens cell culture experiments. Together, these studies establish the mouse Crybb3 loss-of-function model and its disrupted crystallin and non-crystallin proteomes.

Characterization of the Interaction of Human γS Crystallin with Metal Ions and Its Effect on Protein Aggregation

Cataracts are diseases characterized by the opacity of the ocular lens and the subsequent deterioration of vision. Metal ions are one of the factors that have been reported to induce crystallin aggregation. For HγS crystallin, several equivalent ratios of Cu(II) promote protein aggregation. However, reports on zinc are contradictory. To characterize the process of metal ion binding and subsequent HγS crystallin aggregation, we performed dynamic light scattering, turbidimetry, isothermal titration calorimetry, fluorescence, and nuclear magnetic resonance experiments. The data show that both metal ions have multiple binding sites and promote aggregation. Zinc interacts mainly with the N-terminal domain, inducing small conformational changes, while copper interacts with both domains and induces unfolding, exposing the tryptophan residues to the solvent. Our work provides insight into the mechanisms of metal-induced aggregation at one of the lowest doses that appreciably promote aggregation over time.

A novel cataract-related mutation R10P in γA-crystallin increases susceptibility to thermal shock and ultraviolet radiation of γA-crystallin

Congenital cataract is one of the most common causes of childhood blindness, typically resulting from genetic mutations. Over a hundred gene mutations associated with congenital cataract have been identified, with approximately half occurring in the Crystallin genes. In this study, we identified a novel γA-crystallin pathogenic mutation (c. 29G > C, p. Arg10Pro (R10P)), from a four-generation Chinese family with congenital cataract, and investigated its potential molecular mechanisms underlying congenital cataracts. We compared the protein structure and stability of purified the wild type (WT) and R10P under physiological conditions and environmental stresses (UV irradiation, pH imbalance, heat shock, and chemical denaturation) using spectroscopic experiments, SEC analysis, and the UNcle protein analysis system. The results demonstrate that γA-R10P has no significant impact on the structure of γA-crystallin on normal condition. However, it is more sensitive to UV irradiation at high concentrations and prone to aggregation at high temperatures. Therefore, our study reveals the crucial role of the conserved site mutation R10P in maintaining protein structure and stability, providing new insights into the mechanisms of cataract formation.

Unusually Rapid Isomerization of Aspartic Acid in Tau

Spontaneous chemical modifications in long-lived proteins can potentially change protein structure in ways that impact proteostasis and cellular health. For example, isomerization of aspartic acid interferes with protein turnover and is anticorrelated with cognitive acuity in Alzheimer's disease. However, few isomerization rates have been determined for Asp residues in intact proteins. To remedy this deficiency, we used protein extracts from SH-SY5Y neuroblastoma cells as a source of a complex, brain-relevant proteome with no baseline isomerization. Cell lysates were aged in vitro to generate isomers, and extracted proteins were analyzed by data-independent acquisition (DIA) liquid chromatography-mass spectrometry (LC-MS). Although no Asp isomers were detected at Day 0, isomerization increased across time and was quantifiable for 105 proteins by Day 50. Data analysis revealed that isomerization rate is influenced by both primary sequence and secondary structure, suggesting that steric hindrance and backbone rigidity modulate isomerization. Additionally, we examined lysates extracted under gentle conditions to preserve protein complexes and found that protein-protein interactions often slow isomerization. Base catalysis was explored as a means to accelerate Asp isomerization due to findings of accelerated asparagine deamidation. However, no substantial rate enhancement was found for isomerization, suggesting fundamental differences in acid-base chemistry. With an enhanced understanding of Asp isomerization in proteins in general, we next sought to better understand Asp isomerization in tau. In vitro aging of monomeric and aggregated recombinant tau revealed that tau isomerizes significantly faster than any similar protein within our dataset, which is likely related to its correlation with cognition in Alzheimer's disease.

Influence of Cataract Causing Mutations on αA-Crystallin: A Computational Approach

The αA-crystallin protein plays a vital role in maintaining the refractive index and transparency of the eye lens. Significant clinical studies have emerged as the αA-crystallin is prone to aggregation, resulting in the formation of cataracts with varied etiologies due to mutations. This work aims to comprehend the structural and functional role of cataract-causing mutations in αA-crystallin, particularly at N-Terminal and α-Crystallin Domains, using in-silico approaches including molecular dynamics simulation. About 19 mutants of αA-crystallin along with native structure were simulated for 100 ns and the post-simulations analyses reveal pronounced dynamics of αA-crystallin due to the enhanced structure flexibility as its native compactness was lost and is witnessed mainly by the mutants R12L, R21L, R21Q, R54L, R65Q, R116C and R116H. It is observed that αA-crystallin discloses the NTD motions as the dominant one and the same was endorsed by the linear variation between Rg and the center-of-mass of αA-crystallin. Interestingly, such enhanced dynamics of αA-crystallin mutants associated with the structure flexibility is internally modulated by the dynamic exchange of secondary structure elements β-sheets and coils (R2 = 0.619) during simulation. Besides, the observed pronounced dynamics of dimer interface region (β3-L6-β4 segment) of ACD along with CTD dynamics also gains importance. Particularly, the highly dynamic mutants are also characterized by enhanced non-covalent and hydrophobic interactions which renders detrimental effects towards its stability, and favours possible protein unfolding mechanisms. Overall, this study highlights the mutation-mediated structural distortions in αA-crystallin and demands the need for further potential development of inhibitors against cataract formation.

Measurement of absolute abundance of crystallins in human and αA N101D transgenic mouse lenses using 15N-labeled crystallin standards

Stable isotope labeled standards of all major human lens crystallins were created to measure the abundance of lens endogenous crystallins from birth to adulthood. All major human crystallins (αA, αB, βA2, βA3/A1, βA4, βB1, βB2, βB3, γA, γB, γC, γD, γS) were cloned with N-terminal 6 x His tagged SUMO for ease of purification and the ability to generate natural N-termini by SUMO protease cleavage when producing crystallins for structure/function studies. They were then expressed in 15N-enriched media, quantified by mass spectrometry, and mixed in proportions found in young human lens to act as an artificial lens standard. The absolute quantification method was tested using soluble protein from 5-day, 23-day, 18-month, and 18-year-old human lenses spiked with the 15N artificial lens standard. Proteins were trypsinized, relative ratios of light and heavy labeled peptides determined using high-resolution precursor and data independent MS2 scans, and data analysis performed using Skyline software. Crystallin abundances were measured in both human donor lenses and in transgenic mouse αA N101D cataract lenses. Technical replicates of human crystallin abundance measurements were performed with average coefficients of variation of approximately 2% across all 13 crystallins. αA crystallin comprised 27% of the soluble protein of 5-day-old lens and decreased to 16% by 18-years of age. Over this time period αB increased from 6% to 9% and the αA/αB ratio decreased from 4.5/1 to 2/1. γS-crystallin also increased nearly 2-fold from 7% to 12%, becoming the 3rd most abundant protein in adult lens, while βB1 increased from 14% to 20%, becoming the most abundant crystallin of adult lens. Minor crystallins βA2, βB3, and γA comprised only about 1% each of the newborn lens soluble protein, and their abundance dropped precipitously by adulthood. While 9 of the SUMO tagged crystallins were useful for purification of crystallins for structural studies, γA, γB, γC, and γD were resistant to cleavage by SUMO protease. The abundance of WT and N101D human αA in transgenic mouse lenses was approximately 40-fold lower than endogenous mouse αA, but the deamidation mimic human αA N101D was less soluble than human WT αA. The high content of αA and the transient abundance of βA2, βB3, and γA in young lens suggest these crystallins play a role in early lens development and growth. βB1 becoming the most abundant crystallin may result from its role in promoting higher order β-crystallin oligomerization in mature lens. The full set of human crystallin expression vectors in the Addgene repository should be a useful resource for future crystallin studies. 15N labeling of these crystallins will be useful to accurately quantify crystallins in lens anatomic regions, as well as measure the composition of insoluble light scattering crystallin aggregates. The standards will also be useful to measure the abundance of crystallins expressed in transgenic animal models.

Effect of osmolytes and posttranslational modifications on modulating the chaperone function of α-crystallin

Proteins are responsible for a vast majority of various cellular effector processes. α-crystallin is one of the most important proteins in the lens of the eye, which acts as a molecular chaperone that keeps the lens transparent and refractive. α-crystallin is categorized as an intrinsically disordered protein (IDP), devoid of a stable three-dimensional structure, in contrast to conventional globular proteins. Because of its structural flexibility, it can stop denatured proteins from aggregating and building up within the lens over time. α-crystallin's dynamic quaternary structure, which allows it to exist in a variety of oligomeric forms, from dimers to massive assemblies, improves its chaperone function and flexibility. Its intrinsically disordered nature enables it to interact with a variety of client proteins due to its large non-polar and polar residue content and lack of a hydrophobic core. Furthermore, under physiological stress, osmolytes like sorbitol, TMAO, and urea are essential in regulating the stability and function of α-crystallin. Post-translational modifications (PTMs) such as glycation, in which reducing sugars combine with amino groups on the protein to generate advanced glycation end-products, impair α-crystallin's ability to function. These AGEs can cross-link α-crystallin molecules to prevent protein aggregation, changing their structure and decreasing their chaperone action. Because of their raised blood glucose levels, diabetics have an increased chance of developing cataracts as a result of this process. Comprehending how glycation and other PTMs affect α-crystallin is crucial for formulating treatment plans to maintain lens transparency and fight cataracts linked to aging and metabolic disorders.

Metabolomic Disparities in Intraocular Fluid Across Varied Stages of Cataract Progression: Implications for the Analysis of Cataract Development

Introduction: The lens's metabolic demands are met through a continuous circulation of aqueous humor, encompassing a spectrum of components such as organic and inorganic ions, carbohydrates, glutathione, urea, amino acids, proteins, oxygen, carbon dioxide, and water. Metabolomics is a pivotal tool, offering an initial insight into the complexities of integrated metabolism. In this investigative study, we systematically scrutinize the composition of intraocular fluid in individuals afflicted with cataracts. Methods: The investigation involved a comprehensive analysis of aqueous humor samples from a cohort comprising 192 patients. These individuals were stratified by utilizing the SPONCS classification system, delineating distinct groups characterized by the hardness of cataracts. The analytical approach employed targeted quantitative metabolite analysis using HILIC-based liquid chromatography coupled with high-resolution mass spectrometric detection. The metabolomics data analysis was performed with MetaboAnalyst 5.0. Results: The results of the enrichment analysis have facilitated the inference that the discerned disparities among groups arise from disruptions in taurine and hypotaurine metabolism, variations in tryptophan metabolism, and modifications in mitochondrial beta-oxidation of short-chain saturated fatty acids and pyrimidine metabolism. Conclusion: A decline in taurine concentration precipitates diminished glutathione activity, prompting an elevated requirement for NAD+ and instigating tryptophan metabolism along the kynurenine pathway. Activation of this pathway is additionally prompted by interferon-gamma and UV radiation, leading to the induction of IDO. Concurrently, heightened mitochondrial beta-oxidation signifies a distinctive scenario in translocating fatty acids into the mitochondria, enhancing energy production.

Truncation mutations of CRYGD gene in congenital cataracts cause protein aggregation by disrupting the structural stability of γD-crystallin

Congenital cataracts, a prevalent cause of blindness in children, are associated with protein aggregation. γD-crystallin, essential for sustaining lens transparency, exists as a monomer and exhibits excellent structural stability. In our cohort, we identified a nonsense mutation (c.451_452insGACT, p.Y151X) in the CRYGD gene. To explore the effect of truncation mutations on the structure of γD-crystallin, we examined the Y151X and T160RfsX8 mutations, both located in the Greek key motif 4 at the cellular and protein level in this study. Both truncation mutations induced protein misfolding and resulted in the formation of insoluble aggregates when overexpressed in HLE B3 and HEK 293T cells. Moreover, heat, UV irradiation, and oxidative stress increased the proportion of aggregates of mutants in the cells. We next purified γD-crystallin to estimate its structural changes. Truncation mutations led to conformational disruption and a concomitant decrease in protein solubility. Molecular dynamics simulations further demonstrated that partial deletion of the conserved domain within the Greek key motif 4 markedly compromised the overall stability of the protein structure. Finally, co-expression of α-crystallins facilitated the proper folding of truncated mutants and mitigated protein aggregation. In summary, the structural integrity of the Greek key motif 4 in γD-crystallin is crucial for overall structural stability.

A lipidomic study on the lens epithelial cells of patients with age related cataracts

Age related cataracts (ARC) represent the main reason for blindness globally. The lens epithelial cells (LECs) participate not only in the metabolism of many substances in the lens but also in maintaining lens transparency. This study used lipidomics to investigate the metabolic differences in LECs of ARC patients with different severity, aiming at identifying potential metabolic biomarkers of ARC. Patients diagnosed with ARC and underwent cataract surgery at Shanghai Tongren Hospital were selected to participate in this study, which were classified as mild ARC group and severe ARC group. During their cataract surgery, anterior lens capsules(LCs) containing LECs were obtained. The lipidomics of LECs were analyzed using the liquid chromatography‑mass spectrometry (LC-MS). Potential pathways of lipids were searched for using databases such as the Kyoto Encyclopedia of Genes and Genomes (KEGG) and MetaboAnalyst platform. In LEC lipids, 26 lipids have been identified as potential biomarkers between mild ARC and severe ARC, with AUC values of 0.67-0.94. The pathway analysis results revealed that the Glycerophospholipid (GPL) metabolism was significantly influenced, indicating that these metabolic markers contribute significantly to regulating this pathway. The LEC metabolic spectrum demonstrates a proficient ability to differentiate between patients with varying levels of cataracts. Herein, we have successfully identified potential metabolic biomarkers and pathways that have proven to be valuable in enhancing our understanding of ARC pathogenesis. The finding has translational value for developing new cataract treatment methods in the future.

UV light and the ocular lens: a review of exposure models and resulting biomolecular changes

UV light is known to cause damage to biomolecules in living tissue. Tissues of the eye that play highly specialised roles in forming our sense of sight are uniquely exposed to light of all wavelengths. While these tissues have evolved protective mechanisms to resist damage from UV wavelengths, prolonged exposure is thought to lead to pathological changes. In the lens, UV light exposure is a risk factor for the development of cataract, which is a condition that is characterised by opacity that impairs its function as a focusing element in the eye. Cataract can affect spatially distinct regions of the lens. Age-related nuclear cataract is the most prevalent form of cataract and is strongly associated with oxidative stress and a decrease in the antioxidant capacity of the central lens region. Since UV light can generate reactive oxygen species to induce oxidative stress, its effects on lens structure, transparency, and biochemistry have been extensively investigated in animal models in order to better understand human cataract aetiology. A review of the different light exposure models and the advances in mechanistic understanding gained from these models is presented.

Anti-Cataract Effect of the Traditional Aqueous Extract of Yerba Mate (Ilex paraguariensis A. St.-Hil.): An In Ovo Perspective

INTRODUCTION

The therapeutic effect of different doses of the traditional aqueous extract of dried leaves of yerba mate (Ilex paraguariensis A. St.-Hil.) was investigated in an experimental cataract model in chicken embryos.

METHODS AND RESULTS

LC-MS/MS analysis allowed the identification and quantification of 53 metabolites. In the hydrocortisone-induced cataract model, lenses were examined morphologically after treatment and parameters related to oxidative stress (total antioxidant/oxidant status (TAS/TOS), glutathione (GSH), and malondialdehyde (MDA)) were evaluated. Antiproliferative cell nuclear antigen (PCNA) and caspase-3 H-scores were determined and crystallin alpha A (CRYAA) gene expression in the lenses was measured by RT-PCR. The degree of cataract decreased in all treatment groups. While there was no significant difference in TAS levels compared to the negative control, TOS, GSH, and MDA levels were dose-dependently regulated. Treatment groups other than the high-dose group regulated the decrease in PCNA and the increase in caspase-3. CRYAA gene expression increased significantly only at the lowest dose.

CONCLUSION

YM, which is becoming increasingly popular as a traditional tea, showed a therapeutic effect on hydrocortisone-induced cataracts in chicken embryos at relatively low doses.

Tissue, cellular, and molecular level determinants for eye lens stiffness and elasticity

The eye lens is a transparent, ellipsoid tissue in the anterior chamber that is required for the fine focusing of light onto the retina to transmit a clear image. The focusing function of the lens is tied to tissue transparency, refractive index, and biomechanical properties. The stiffness and elasticity or resilience of the human lens allows for shape changes during accommodation to focus light from objects near and far. It has long been hypothesized that changes in lens biomechanical properties with age lead to the loss of accommodative ability and the need for reading glasses with age. However, the cellular and molecular mechanisms that influence lens biomechanical properties and/or change with age remain unclear. Studies of lens stiffness and resilience in mouse models with genetic defects or at advanced age inform us of the cytoskeletal, structural, and morphometric parameters that are important for biomechanical stability. In this review, we will explore whether: 1) tissue level changes, including the capsule, lens volume, and nucleus volume, 2) cellular level alterations, including cell packing, suture organization, and complex membrane interdigitations, and 3) molecular scale modifications, including the F-actin and intermediate filament networks, protein modifications, lipids in the cell membrane, and hydrostatic pressure, influence overall lens biomechanical properties.

Aging of the eye: Lessons from cataracts and age-related macular degeneration

Aging is the greatest risk factor for chronic human diseases, including many eye diseases. Geroscience aims to understand the effects of the aging process on these diseases, including the genetic, molecular, and cellular mechanisms that underlie the increased risk of disease over the lifetime. Understanding of the aging eye increases general knowledge of the cellular physiology impacted by aging processes at various biological extremes. Two major diseases, age-related cataract and age-related macular degeneration (AMD) are caused by dysfunction of the lens and retina, respectively. Lens transparency and light refraction are mediated by lens fiber cells lacking nuclei and other organelles, which provides a unique opportunity to study a single aging hallmark, i.e., loss of proteostasis, within an environment of limited metabolism. In AMD, local dysfunction of the photoreceptors/retinal pigmented epithelium/Bruch's membrane/choriocapillaris complex in the macula leads to the loss of photoreceptors and eventually loss of central vision, and is driven by nearly all the hallmarks of aging and shares features with Alzheimer's disease, Parkinson's disease, cardiovascular disease, and diabetes. The aging eye can function as a model for studying basic mechanisms of aging and, vice versa, well-defined hallmarks of aging can be used as tools to understand age-related eye disease.

Cumulative asparagine to aspartate deamidation fails to perturb γD-crystallin structure and stability

Deamidation frequently is invoked as an important driver of crystallin aggregation and cataract formation. Here, we characterized the structural and biophysical consequences of cumulative Asn to Asp changes in γD-crystallin. Using NMR spectroscopy, we demonstrate that N- or C-terminal domain-confined or fully Asn to Asp changed γD-crystallin exhibits essentially the same 1H-15N HSQC spectrum as the wild-type protein, implying that the overall structure is retained. Only a very small thermodynamic destabilization for the overall Asn to Asp γD-crystallin variants was noted by chaotropic unfolding, and assessment of the colloidal stability, by measuring diffusion interaction parameters, yielded no substantive differences in association propensities. Furthermore, using molecular dynamics simulations, no significant changes in dynamics for proteins with Asn to Asp or iso-Asp changes were detected. Our combined results demonstrate that substitution of all Asn by Asp residues, reflecting an extreme case of deamidation, did not affect the structure and biophysical properties of γD-crystallin. This suggests that these changes alone cannot be the major determinant in driving cataract formation.

Characterization of different-sized human αA-crystallin homomers and implications to Asp151 isomerization

Site-specific modifications of aspartate residues spontaneously occur in crystallin, the major protein in the lens. One of the primary modification sites is Asp151 in αA-crystallin. Isomerization and racemization alter the crystallin backbone structure, reducing its stability by inducing abnormal crystallin-crystallin interactions and ultimately leading to the insolubilization of crystallin complexes. These changes are considered significant factors in the formation of senile cataracts. However, the mechanisms driving spontaneous isomerization and racemization have not been experimentally demonstrated. In this study, we generated αA-crystallins with different homo-oligomeric sizes and/or containing an asparagine residue at position 151, which is more prone to isomerization and racemization. We characterized their structure, hydrophobicity, chaperone-like function, and heat stability, and examined their propensity for isomerization and racemization. The results show that the two differently sized αA-crystallin variants possessed similar secondary structures but exhibited different chaperone-like functions depending on their oligomeric sizes. The rate of isomerization and racemization of Asp151, as assessed by the deamidation of Asn151, was also found to depend on the oligomeric sizes of αA-crystallin. The predominant isomerization product via deamidation of Asn151 in the different-sized αA-crystallin variants was L-β-Asp in vitro, while various modifications occurred around Asp151 in vivo. The disparity between the findings of this in vitro study and in vivo studies suggests that the isomerization of Asp151 in vivo may be more complex than what occurs in vitro.

Characterization of βB2-crystallin tryptophan mutants reveals two different folding states in solution

Conserved tryptophan residues are critical for the structure and the stability of β/γ-crystallin in the lenses of vertebrates. During aging, in which the lenses are continuously exposed to ultraviolet irradiation and other environmental stresses, oxidation of tryptophan residues in β/γ-crystallin is triggered and impacts the lens proteins to varying degrees. Kynurenine derivatives, formed by oxidation of tryptophan, accumulate, resulting in destabilization and insolubilization of β/γ-crystallin, which correlates with age-related cataract formation. To understand the contribution of tryptophan modification on the structure and stability of human βB2-crystallin, five tryptophan residues were mutated to phenylalanine considering its similarity in structure and hydrophilicity to kynurenine. Among all mutants, W59F and W151F altered the stability and homo-oligomerization of βB2-crystallin-W59F promoted tetramerization whereas W151F blocked oligomerization. Most W59F dimers transformed into tetramer in a month, and the separated dimer and tetramer of W59F demonstrated different structures and hydrophobicity, implying that the biochemical properties of βB2-crystallin vary over time. By using SAXS, we found that the dimer of βB2-crystallin in solution resembled the lattice βB1-crystallin dimer (face-en-face), whereas the tetramer of βB2-crystallin in solution resembled its lattice tetramer (domain-swapped). Our results suggest that homo-oligomerization of βB2-crystallin includes potential inter-subunit reactions, such as dissociation, unfolding, and re-formation of the dimers into a tetramer in solution. The W>F mutants are useful in studying different folding states of βB2-crystallin in lens.

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.

Loss of αBa-crystallin, but not αA-crystallin, increases age-related cataract in the zebrafish lens

The vertebrate eye lens is an unusual organ in that most of its cells lack nuclei and the ability to replace aging protein. The small heat shock protein α-crystallins evolved to become key components of this lens, possibly because of their ability to prevent aggregation of aging protein that would otherwise lead to lens opacity. Most vertebrates express two α-crystallins, αA- and αB-crystallin, and mutations in each are linked to human cataract. In a mouse knockout model only the loss of αA-crystallin led to early-stage lens cataract. We have used the zebrafish as a model system to investigate the role of α-crystallins during lens development. Interestingly, while zebrafish express one lens-specific αA-crystallin gene (cryaa), they express two αB-crystallin genes, with one evolving lens specificity (cryaba) and the other retaining the broad expression of its mammalian ortholog (cryabb). In this study we used individual mutant zebrafish lines for all three α-crystallin genes to determine the impact of their loss on age-related cataract. Surprisingly, unlike mouse knockout models, we found that the loss of the αBa-crystallin gene cryaba led to an increase in lens opacity compared to cryaa null fish at 24 months of age. Loss of αA-crystallin did not increase the prevalence of cataract. We also used single cell RNA-Seq and RT-qPCR data to show a shift in the lens expression of zebrafish α-crystallins between 5 and 10 days post fertilization (dpf), with 5 and 6 dpf lenses expressing cryaa almost exclusively, and expression of cryaba and cryabb becoming more prominent after 10 dpf. These data show that cryaa is the primary α-crystallin during early lens development, while the protective role for cryaba becomes more important during lens aging. This study is the first to quantify cataract prevalence in wild-type aging zebrafish, showing that lens opacities develop in approximately 25% of fish by 18 months of age. None of the three α-crystallin mutants showed a compensatory increase in the expression of the remaining two crystallins, or in the abundant βB1-crystallin. Overall, these findings indicate an ontogenetic shift in the functional importance of individual α-crystallins during zebrafish lens development. Our finding that the lens-specific zebrafish αBa-crystallin plays the leading role in preventing age-related cataract adds a new twist to our understanding of vertebrate lens evolution.

Testing mixing rules for structural and dynamical quantities in multi-component crowded protein solutions

Crowding effects significantly influence the phase behavior and the structural and dynamic properties of the concentrated protein mixtures present in the cytoplasm of cells or in the blood serum. This poses enormous difficulties for our theoretical understanding and our ability to predict the behavior of these systems. While the use of course grained colloid-inspired models allows us to reproduce the key physical solution properties of concentrated monodisperse solutions of individual proteins, we lack corresponding theories for complex polydisperse mixtures. Here, we test the applicability of simple mixing rules in order to predict solution properties of protein mixtures. We use binary mixtures of the well-characterized bovine eye lens proteins α and γB crystallin as model systems. Combining microrheology with static and dynamic scattering techniques and observations of the phase diagram for liquid-liquid phase separation, we show that reasonably accurate descriptions are possible for macroscopic and mesoscopic signatures, while information on the length scale of the individual protein size requires more information on cross-component interaction.

Seeing further into the early steps of the endangered atlantic goliath grouper (Epinephelus itajara): Eye lenses high resolution isotopic profiles reveal ontogenetic trophic and habitat shifts

Estuarine mangroves are often considered nurseries for the Atlantic Goliath grouper juveniles. Yet, the contributions of different estuarine primary producers and habitats as sources of organic matter during early ontogenetic development remain unclear. Given the species' critically endangered status and protection in Brazil, obtaining biological samples from recently settled recruits in estuaries is challenging. In this study, we leveraged a local partnership with fishers and used stable isotope (C and N) profiles from the eye lenses of stranded individuals or incidentally caught by fishery to reconstruct the trophic and habitat changes of small juveniles. The eye lens grows by the apposition of protein-rich layers. Once these layers are formed, they become inert, allowing to make inferences on the trophic ecology and habitat use along the development of the individual until its capture. We used correlations between fish size and the entire eye lens size, along with estuarine baselines, to reconstruct the fish size and trophic positions for each of the lens layers obtained. We then used dominant primary producers and basal sources from mangrove sheltered, exposed estuarine and marine habitats to construct an ontogenetic model of trophic and habitat support changes since maternal origins. Our model revealed marine support before the juveniles reached 25 mm (standard length), followed by a rapid increase in reliance on mangrove sheltered sources, coinciding with the expected size at settlement. After reaching 60 mm, individuals began to show variability. Some remained primarily supported by the mangrove sheltered area, while others shifted to rely more on the exposed estuarine area around 150 mm. Our findings indicate that while mangroves are critical for settlement, as Goliath grouper juveniles grow, they can utilize organic matter produced throughout the estuary. This underscores the need for conservation strategies that focus on seascape connectivity, as protecting just one discrete habitat may not be sufficient to preserve this endangered species and safeguard its ecosystem functions.

Effect of Pressure on the Conformational Landscape of Human γD-Crystallin from Replica Exchange Molecular Dynamics Simulations

Human γD-crystallin belongs to a crucial family of proteins known as crystallins located in the fiber cells of the human lens. Since crystallins do not undergo any turnover after birth, they need to possess remarkable thermodynamic stability. However, their sporadic misfolding and aggregation, triggered by environmental perturbations or genetic mutations, constitute the molecular basis of cataracts, which is the primary cause of blindness in the globe according to the World Health Organization. Here, we investigate the impact of high pressure on the conformational landscape of wild-type HγD-crystallin using replica exchange molecular dynamics simulations augmented with principal component analysis. We find pressure to have a modest impact on global measures of protein stability, such as root-mean-square displacement and radius of gyration. Upon projecting our trajectories along the first two principal components from principal component analysis, however, we observe the emergence of distinct free energy basins at high pressures. By screening local order parameters previously shown or hypothesized as markers of HγD-crystallin stability, we establish correlations between a tyrosine-tyrosine aromatic contact within the N-terminal domain and the protein's end-to-end distance with projections along the first and second principal components, respectively. Furthermore, we observe the simultaneous contraction of the hydrophobic core and its intrusion by water molecules. This exploration sheds light on the intricate responses of HγD-crystallin to elevated pressures, offering insights into potential mechanisms underlying its stability and susceptibility to environmental perturbations, crucial for understanding cataract formation.

The Functional Significance of High Cysteine Content in Eye Lens γ-Crystallins

Cataract disease is strongly associated with progressively accumulating oxidative damage to the extremely long-lived crystallin proteins of the lens. Cysteine oxidation affects crystallin folding, interactions, and light-scattering aggregation especially strongly due to the formation of disulfide bridges. Minimizing crystallin aggregation is crucial for lifelong lens transparency, so one might expect the ubiquitous lens crystallin superfamilies (α and βγ) to contain little cysteine. Yet, the Cys content of γ-crystallins is well above the average for human proteins. We review literature relevant to this longstanding puzzle and take advantage of expanding genomic databases and improved machine learning tools for protein structure prediction to investigate it further. We observe remarkably low Cys conservation in the βγ-crystallin superfamily; however, in γ-crystallin, the spatial positioning of Cys residues is clearly fine-tuned by evolution. We propose that the requirements of long-term lens transparency and high lens optical power impose competing evolutionary pressures on lens βγ-crystallins, leading to distinct adaptations: high Cys content in γ-crystallins but low in βB-crystallins. Aquatic species need more powerful lenses than terrestrial ones, which explains the high methionine content of many fish γ- (and even β-) crystallins. Finally, we discuss synergies between sulfur-containing and aromatic residues in crystallins and suggest future experimental directions.

Proteostatic Remodeling of Small Heat Shock Chaperones─Crystallins by Ran-Binding Protein 2─and the Peptidyl-Prolyl cis-trans Isomerase and Chaperone Activities of Its Cyclophilin Domain

Disturbances in protein phase transitions promote protein aggregation─a neurodegeneration hallmark. The modular Ran-binding protein 2 (Ranbp2) is a cytosolic molecular hub for rate-limiting steps of phase transitions of Ran-GTP-bound protein ensembles exiting nuclear pores. Chaperones also regulate phase transitions and proteostasis by suppressing protein aggregation. Ranbp2 haploinsufficiency promotes the age-dependent neuroprotection of the chorioretina against phototoxicity by proteostatic regulations of neuroprotective substrates of Ranbp2 and by suppressing the buildup of polyubiquitylated substrates. Losses of peptidyl-prolyl cis-trans isomerase (PPIase) and chaperone activities of the cyclophilin domain (CY) of Ranbp2 recapitulate molecular effects of Ranbp2 haploinsufficiency. These CY impairments also stimulate deubiquitylation activities and phase transitions of 19S cap subunits of the 26S proteasome that associates with Ranbp2. However, links between CY moonlighting activity, substrate ubiquitylation, and proteostasis remain incomplete. Here, we reveal the Ranbp2 regulation of small heat shock chaperones─crystallins in the chorioretina by proteomics of mice with total or selective modular deficits of Ranbp2. Specifically, loss of CY PPIase of Ranbp2 upregulates αA-Crystallin, which is repressed in adult nonlenticular tissues. Conversely, impairment of CY's chaperone activity opposite to the PPIase pocket downregulates a subset of αA-Crystallin's substrates, γ-crystallins. These CY-dependent effects cause age-dependent and chorioretinal-selective declines of ubiquitylated substrates without affecting the chorioretinal morphology. A model emerges whereby inhibition of Ranbp2's CY PPIase remodels crystallins' expressions, subdues molecular aging, and preordains the chorioretina to neuroprotection by augmenting the chaperone capacity and the degradation of polyubiquitylated substrates against proteostatic impairments. Further, the druggable Ranbp2 CY holds pan-therapeutic potential against proteotoxicity and neurodegeneration.

Evaluation of a retinal oximetry image quality indicator in patients with cataract

PURPOSE

To evaluate a new automated retinal oximetry image quality indicator with cataract as a clinical model.

METHODS

Sixty-one eyes in 61 patients were imaged by the Oxymap T1 Retinal Oximeter at baseline and 25 eyes were also examined 3 weeks after cataract surgery. Image quality (0-10 on a continuous scale) was compared with standardized AREDS cataract grading and Pentacam lens densitometry. Associations with retinal oximetry measurements and visual acuity were examined.

RESULTS

Image quality correlated with total, nuclear and posterior subcapsular cataract grades (ANOVA, p < 0.05), tended to be associated with lens densitometry and it improved from 4.3 ± 1.4 to 5.7 ± 1.0 (p < 0.05) after cataract surgery. Very low image quality, below 3, led to vessel detection failure in retinal oximetry images. Higher image qualities were linearly associated with higher measured retinal oxygen saturations (r = 0.52 in arteries and r = 0.46 in veins; p < 0.001).

CONCLUSION

Retinal oximetry image quality deteriorated with increasing cataract density and improved after cataract surgery, supporting its use as a measure of optical clarity. The numerical quality indicator demonstrated a threshold below which images of poor optical quality should be discarded. Image quality affects the estimates of retinal oximetry parameters and should therefore be included in future analyses.

Biodegradable Solid Polymer Electrolytes from the Discarded Cataractous Eye Protein Isolate

The protein extracted from the discarded eye lenses postcataract surgery, referred to as the cataractous eye protein isolate (CEPI), is employed as a polymer matrix for the construction of solid polymer electrolyte species (SPEs). SPEs are expected to be inexpensive, conductive, and mechanically stable in order to be economically and commercially viable. Environmentally, these materials should be biodegradable and nontoxic. Taking these factors into account, we investigated the possibility of using a discarded protein as a polymer matrix for SPEs. Natural compounds sorbitol and sinapic acid (SA) are used as the plasticizer and cross-linker, respectively, to tune the mechanical as well as electrochemical properties. The specific material formed is demonstrated to have high ionic conductivity ranging from ∼2 × 10-2 to ∼8 × 10-2 S cm-1. Without the addition of any salt, the ionic conductivity of sorbitol-plasticized non-cross-linked CEPI is ∼7.5 × 10-2 S cm-1. Upon the addition of NaCl, the conductivity is enhanced to ∼8 × 10-1 S cm-1. This study shows the possibility of utilizing a discarded protein CEPI as an alternative polymer matrix with further potential for the construction of tunable, flexible, recyclable, biocompatible, and biodegradable SPEs for flexible green electronics and biological devices.

The α-crystallin Chaperones Undergo a Quasi-ordered Co-aggregation Process in Response to Saturating Client Interaction

Small heat shock proteins (sHSPs) are ATP-independent chaperones vital to cellular proteostasis, preventing protein aggregation events linked to various human diseases including cataract. The α-crystallins, αA-crystallin (αAc) and αB-crystallin (αBc), represent archetypal sHSPs that exhibit complex polydispersed oligomeric assemblies and rapid subunit exchange dynamics. Yet, our understanding of how this plasticity contributes to chaperone function remains poorly understood. Using biochemical and biophysical analyses combined with single-particle electron microscopy (EM), we examined structural changes in αAc, αBc and native heteromeric lens α-crystallins (αLc) in their apo-states and at varying degree of chaperone saturation leading to co-aggregation, using lysozyme and insulin as model clients. Quantitative single-particle analysis unveiled a continuous spectrum of oligomeric states formed during the co-aggregation process, marked by significant client-triggered expansion and quasi-ordered elongation of the sHSP oligomeric scaffold, whereby the native cage-like sHSP assembly displays a directional growth to accommodate saturating conditions of client sequestration. These structural modifications culminated in an apparent amorphous collapse of chaperone-client complexes, resulting in the creation of co-aggregates capable of scattering visible light. Intriguingly, these co-aggregates maintain internal morphological features of highly elongated sHSP oligomers with striking resemblance to polymeric α-crystallin species isolated from aged lens tissue. This mechanism appears consistent across αAc, αBc and αLc, albeit with varying degrees of susceptibility to client-induced co-aggregation. Importantly, our findings suggest that client-induced co-aggregation follows a distinctive mechanistic and quasi-ordered trajectory, distinct from a purely amorphous process. These insights reshape our understanding of the physiological and pathophysiological co-aggregation processes of α-crystallins, carrying potential implications for a pathway toward cataract formation.

Cell Penetrability of a γ-Crystallin Peptide Fragment from the Discarded Cataractous Eye Emulsion

The efficiency of the intracellular transport of medication and target specificity is frequently hampered by biological obstacles. The potential for therapeutic use of peptide fragments from naturally occurring proteins is promising, as peptides exhibit high selectivity due to several possibilities of interaction with their target. Certain peptide sequences, often referred to as cell-penetrating peptides (CPPs), are those that can penetrate cell membranes. Our goal is to find these sequences in the discarded postcataractery surgery emulsion known as the cataractous eye protein isolate (CEPI). One peptide fragment from this discarded protein has been identified to be a potential CPP based on the similarities with other well-known CPPs. Cell membrane penetrability and cytotoxicity of the peptide have been investigated. Fibroblast cells were incubated with the fluorescently labeled peptide and were observed under fluorescence as well as under confocal microscopy. It was found that the peptide possesses a cell-penetrating ability.

In vivo quasi-elastic light scattering detects molecular changes in the lenses of adolescents with Down syndrome

Down syndrome (DS) is the most common chromosomal disorder in humans. DS is associated with increased prevalence of several ocular sequelae, including characteristic blue-dot cerulean cataract. DS is accompanied by age-dependent accumulation of Alzheimer's disease (AD) amyloid-β (Aβ) peptides and amyloid pathology in the brain and comorbid early-onset Aβ amyloidopathy and colocalizing cataracts in the lens. Quasi-elastic light scattering (QLS) is an established optical technique that noninvasively measures changes in protein size distributions in the human lens in vivo. In this cross-sectional study, lenticular QLS correlation time was decreased in adolescent subjects with DS compared to age-matched control subjects. Clinical QLS was consistent with alterations in relative particle hydrodynamic radius in lenses of adolescents with DS. These correlative results suggest that noninvasive QLS can be used to evaluate molecular changes in the lenses of individuals with DS.

Natural Product Isolation of the Extract of Cleome rupicola Fruits Exhibiting Antioxidant Activity

Cataracts are the leading cause of blindness worldwide, however, there is currently no drug-based treatment. Plants that exhibit antioxidant properties have shown promising anticataract effects, likely because they supplement the activity of glutathione, the major antioxidant in lens cells. An extract of Cleome rupicola, a desert plant found in the United Arab Emirates, has traditionally been used to treat cataracts. Phytochemical screening of the aqueous extract established the presence of flavonoids, tannins, steroid derivatives, and reducing sugars. Fractioning of extracts from the fruits using high-performance liquid chromatography (HPLC) yielded the isolation of the anthelmintic compound cleomin, and its structure was confirmed using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy.

Exploring the significance of potassium homeostasis in copper ion binding to human αB-Crystallin

αB-Crystallin (αB-Cry) is a small heat shock protein known for its protective role, with an adaptable structure that responds to environmental changes through oligomeric dynamics. Cu(II) ions are crucial for cellular processes but excessive amounts are linked to diseases like cataracts and neurodegeneration. This study investigated how optimal and detrimental Cu(II) concentrations affect αB-Cry oligomers and their chaperone activity, within the potassium-regulated ionic-strength environment. Techniques including isothermal titration calorimetry, differential scanning calorimetry, fluorescence spectroscopy, inductively coupled plasma atomic emission spectroscopy, cyclic voltammetry, dynamic light scattering, circular dichroism, and MTT assay were employed and complemented by computational methods. Results showed that potassium ions affected αB-Cry's structure, promoting Cu(II) binding at multiple sites and scavenging ability, and inhibiting ion redox reactions. Low concentrations of Cu(II), through modifications of oligomeric interfaces, induce regulation of surface charge and hydrophobicity, resulting in an increase in chaperone activity. Subunit dynamics were regulated, maintaining stable interfaces, thereby inhibiting further aggregation and allowing the functional reversion to oligomers after stress. High Cu(II) disrupted charge/hydrophobicity balance, sewing sizable oligomers together through subunit-subunit interactions, suppressing oligomer dissociation, and reducing chaperone efficiency. This study offers insights into how Cu(II) and potassium ions influence αB-Cry, advancing our understanding of Cu(II)-related diseases.

CRYAB stop-loss variant causes rare syndromic dilated cardiomyopathy with congenital cataract: expanding the phenotypic and mutational spectrum of alpha-B crystallinopathy

Missense mutations in the alpha-B crystallin gene (CRYAB) have been reported in desmin-related myopathies with or without cardiomyopathy and have also been reported in families with only a cataract phenotype. Dilated cardiomyopathy (DCM) is a disorder with a highly heterogeneous genetic etiology involving more than 60 causative genes, hindering genetic diagnosis. In this study, we performed whole genome sequencing on 159 unrelated patients with DCM and identified an unusual stop-loss pathogenic variant in NM_001289808.2:c.527A>G of CRYAB in one patient. The mutant alpha-B crystallin protein is predicted to have an extended strand with addition of 19 amino acid residues, p.(Ter176TrpextTer19), which may contribute to aggregation and increased hydrophobicity of alpha-B crystallin. The proband, diagnosed with DCM at age 32, had a history of bilateral congenital cataracts but had no evidence of myopathy or associated symptoms. He also has a 10-year-old child diagnosed with bilateral congenital cataracts with the same CRYAB variant. This study expands the mutational spectrum of CRYAB and deepens our understanding of the complex phenotypes of alpha-B crystallinopathies.

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.

Surface modification of polydimethylsiloxane by the cataractous eye protein isolate

Polydimethylsiloxane (PDMS), even though widely used in microfluidic applications, its hydrophobic nature restricts its utility in some cases. To address this, PDMS may be used in conjunction with a hydrophilic material. Herein, the PDMS surface is modified by plasma treatment followed by cross-linking with the cataractous eye protein isolate (CEPI). CEPI-PDMS composites are prepared at three pH and the effects of CEPI on the chemical, physical, and electrical properties of PDMS are extensively investigated. The cross-linking between PDMS and the protein are confirmed by FTIR, and the contact angle measurements indicate the improved hydrophilic nature of the composite films as compared to PDMS. Atomic Force Microscopy results demonstrate that the surface roughness is enhanced by the incorporation of the protein and is a function of the pH. The effective elastic modulus of the composites is improved by the incorporation of protein into the PDMS matrix. Measurements of the dielectric properties of these composites indicate that they behave as capacitors at lower frequency range while demonstrating resistive characteristics at higher frequency. These composites provide preliminary ideas in developing flexible devices for potential applications in diverse areas such as energy storage materials, and thermo-elective wireless switching devices.

Senile Cataract Formation Does Not Affect Crystalline Lens Thickness

INTRODUCTION

Characterizing lens thickness (LT) in patients with cataracts is important for better understanding the lens aging process and for designing new intraocular lens power formulas. This study aimed to analyze the influence of common senile cataract formation on the LT, anterior (ACS) and posterior (PCS) cortex space, and nuclear thickness (NT), controlling for sex, age, and axial length.

METHODS

A cross-sectional study was performed. A consecutive sample of 603 volunteers (403 women, 200 men) aged 59.1 ± 18.8 years was recruited. The standardized Lens Opacification Classification System (LOCS)-III was used to classify eyes (randomly selected) into cataractous and non-cataractous groups. Also, they were classified according to the cataract location (presence or absence of cortical, nuclear, or posterior subcapsular cataract). Optical biometry was performed to measure LT, ACS, NT, and PCS. Propensity score was used to match participants one-to-one for sex, age, and axial length. Groups were compared using the Student's t test or Yuen's test.

RESULTS

The four classifications divided unmatched eyes into: 361 cataractous lenses and 242 non-cataractous, 226 cortical and 377 non-cortical cataractous, 313 nuclear and 290 non-nuclear cataractous and 242 subcapsular and 361 non-subcapsular cataractous. Before matching, cataractous eyes showed significantly higher LT (4.52 ± 0.39 vs. 3.94 ± 0.46 mm, p < 0.001), ACS (0.75 ± 0.20 vs. 0.58 ± 0.23 mm, p < 0.001), NT (3.34 ± 0.23 vs. 3.18 ± 0.25 mm, p < 0.001) and PCS (0.42 ± 0.19 vs. 0.37 ± 0.19 mm, p = 0.003). Matched lens, cortical, nuclear, and subcapsular cataract samples comprised 146, 258, 182, and 226 eyes, respectively. After matching, no significant differences were observed in LT (4.34 ± 0.37 vs. 4.33 ± 0.36 mm, p = 0.94), ACS (0.72 ± 0.20 vs. 0.76 ± 0.19 mm, p = 0.08), NT (3.31 ± 0.22 vs. 3.30 ± 0.23 mm, p = 0.24) and PCS (0.42 ± 0.19 vs. 0.43 ± 0.16 mm, p = 0.79).

CONCLUSIONS

The presence of senile cortical, nuclear, and posterior subcapsular cataract have no effect on LT, ACS, NT, and PCS. Confounding factors should be controlled for when measuring LT and its main components.

Celastrol regulates the oligomeric state and chaperone activity of αB-crystallin linked with protein homeostasis in the lens

Protein misfolding and aggregation are crucial pathogenic factors for cataracts, which are the leading cause of visual impairment worldwide. α-crystallin, as a small molecular chaperone, is involved in preventing protein misfolding and maintaining lens transparency. The chaperone activity of α-crystallin depends on its oligomeric state. Our previous work identified a natural compound, celastrol, which could regulate the oligomeric state of αB-crystallin. In this work, based on the UNcle and SEC analysis, we found that celastrol induced αB-crystallin to form large oligomers. Large oligomer formation enhanced the chaperone activity of αB-crystallin and prevented aggregation of the cataract-causing mutant βA3-G91del. The interactions between αB-crystallin and celastrol were detected by the FRET (Fluorescence Resonance Energy Transfer) technique, and verified by molecular docking. At least 9 binding patterns were recognized, and some binding sites covered the groove structure of αB-crystallin. Interestingly, αB-R120G, a cataract-causing mutation located at the groove structure, and celastrol can decrease the aggregates of αB-R120G. Overall, our results suggested celastrol not only promoted the formation of large αB-crystallin oligomers, which enhanced its chaperone activity, but also bound to the groove structure of its α-crystallin domain to maintain its structural stability. Celastrol might serve as a chemical and pharmacological chaperone for cataract treatment.