Lanosterol reverses protein aggregation in cataracts

Metabolism and Biological Activities of 4-Methyl-Sterols

4,4-Dimethylsterols and 4-methylsterols are sterol biosynthetic intermediates (C4-SBIs) acting as precursors of cholesterol, ergosterol, and phytosterols. Their accumulation caused by genetic lesions or biochemical inhibition causes severe cellular and developmental phenotypes in all organisms. Functional evidence supports their role as meiosis activators or as signaling molecules in mammals or plants. Oxygenated C4-SBIs like 4-carboxysterols act in major biological processes like auxin signaling in plants and immune system development in mammals. It is the purpose of this article to point out important milestones and significant advances in the understanding of the biogenesis and biological activities of C4-SBIs.

A novel mutation of PANK4 causes autosomal dominant congenital posterior cataract

Though many mutations have been identified to be associated with the occurrence of congenital cataract, pathogenic loci in some affected families are still unknown. Clinical data and genomic DNA were collected from a four-generation Chinese family. Candidate mutations were independently verified for cosegregation in the whole pedigree. Linkage analysis showed that the disease-causing mutation was located between 1p36.21 and 1p36.33. Analysis of the whole-exome sequencing data combined with linkage analysis identified a novel pathogenic variant (g.2451906C>T) at intron 4 of Pantothenate kinase 4 (PANK4 protein, PANK4 gene) in 1p36.32|606162. This variant showed complete cosegregation with the phenotype in the pedigree. The mutation was not detected in 106 normal controls nor in 40 sporadic congenital cataract patients. The mutation was demonstrated to significantly reduce the expression of the PANK4 protein level in the blood of cataract patients than that in normal individuals by ELISA. Pank4^-/- mice showed a cataract phenotype with increased numbers of apoptotic lens epithelial cells, fiber cell aggregation, and significant mRNA variation of crystallin family members. Thus, the association of a new entity of an autosomal dominant cataract with mutations in PANK4, which influences cell proliferation, apoptosis of lens epithelial cells, crystallin abnormalities, and fiber cell derangement, subsequently induces cataract.

Express Screening of Tear Fluid for Evaluation of the Concentration of Lanomax Using Multisensory Stripping Voltammetry and Multivariate Statistics

The drug concentrations monitoring is very important for finding the right dosage. The developed method is based on the recognition of multidimensional images, which are produced by multisensory electrochemical systems that provide reliable information on objects being tested, using multidimensional statistics. The measurements were carried out using a planar solid-state electrode. The test solution was a 0.05 M KCl solution, which contained the $ {\rm{Z}}{{\rm{n}}_2}^ + ,{\rm{C}}{{\rm{d}}_2}^ + ,{\rm{P}}{{\rm{b}}_2}^ + ,{\rm{C}}{{\rm{o}}_2}^ + $ and $ {\rm{H}}{{\rm{g}}_2}^ + $ metal cations in the concentration of 5 • 10−5 M. The efficiency of this method in determining lanosterol with accounting for changes in its concentration with over time has been demonstrated. In order to determine concentrations of Lanomax in tear fluid, a procedure for multisensory stripping voltammetry has been developed and tested. It has been shown that the effect of lacrimal fluid on metal dissolution currents in the test system lasts 12 hours after the Lanomax instillation.

Nutritional effect on age-related cataract formation and progression

PURPOSE OF REVIEW

To provide a comprehensive summary of the latest evidence-based data on nutrients linked to the pathogenesis of cataract formation and progression.

RECENT FINDINGS

This summary of peer-reviewed publications emphasizes the ongoing effort to modulate the cataractogenous process through nutrition, and points at an only weak evidence for the contribution of a specific nutrient to this process. Although observational studies successfully demonstrated a positive correlation between specific nutrients intake and age-related cataract, such evidence was usually lacking in following interventional studies. Three metanalyses point towards a beneficial effect of high intake of vitamin C, vitamin E and vitamin A on the risk of age-related cataract. New studies point at a protective effect of a high intake of vitamin K1 and vitamin D but negate the influence of Mediterranean diet or an overall high dairy consumption on the progression of cataract in a subgroup of patients. Sterols are candidate nutrients for future investigation.

SUMMARY

Nutrition rich in fruits and vegetables, and a high dietary intake of vitamins A, C, D, E and K1 may be inversely associated with the risk of age-related cataract. More studies involving patients in a wide range of nutritional status are required to establish the long-term benefit of nutritional supplements.

Lanosterol and 25-hydroxycholesterol dissociate crystallin aggregates isolated from cataractous human lens via different mechanisms

Cataract, a crystallin aggregation disease, is the leading cause of human blindness worldwide. Surgery is the only established treatment of cataracts and no anti-cataract drugs are available thus far. Recently lanosterol and 25-hydroxycholesterol have been reported to redissolve crystallin aggregates and partially restore lens transparency in animals. However, the efficacies of these two compounds have not been quantitatively studied ex vivo using patient tissues. In this research, we developed a quantitative assay applicable to efficacy validations and mechanistic studies by a protocol to isolate protein aggregates from the surgically removed cataractous human lens. Our results showed that both compounds were effective for human cataractous samples with EC50 values at ten micromolar level. The efficacies of both compounds strongly depended on cataract severity. Lanosterol and 25-hydroxycholesterol were two mechanistically different lead compounds of anti-cataract drug design.

Bi-allelic Mutations in LSS, Encoding Lanosterol Synthase, Cause Autosomal-Recessive Hypotrichosis Simplex

Hypotrichosis simplex (HS) is a rare form of hereditary alopecia characterized by childhood onset of diffuse and progressive scalp and body hair loss. Although research has identified a number of causal genes, genetic etiology in about 50% of HS cases remains unknown. The present report describes the identification via whole-exome sequencing of five different mutations in the gene LSS in three unrelated families with unexplained, potentially autosomal-recessive HS. Affected individuals showed sparse to absent lanugo-like scalp hair, sparse and brittle eyebrows, and sparse eyelashes and body hair. LSS encodes lanosterol synthase (LSS), which is a key enzyme in the cholesterol biosynthetic pathway. This pathway plays an important role in hair follicle biology. After localizing LSS protein expression in the hair shaft and bulb of the hair follicle, the impact of the mutations on keratinocytes was analyzed using immunoblotting and immunofluorescence. Interestingly, wild-type LSS was localized in the endoplasmic reticulum (ER), whereas mutant LSS proteins were localized in part outside of the ER. A plausible hypothesis is that this mislocalization has potential deleterious implications for hair follicle cells. Immunoblotting revealed no differences in the overall level of wild-type and mutant protein. Analyses of blood cholesterol levels revealed no decrease in cholesterol or cholesterol intermediates, thus supporting the previously proposed hypothesis of an alternative cholesterol pathway. The identification of LSS as causal gene for autosomal-recessive HS highlights the importance of the cholesterol pathway in hair follicle biology and may facilitate novel therapeutic approaches for hair loss disorders in general.

Small heat shock proteins: Simplicity meets complexity

Small heat shock proteins (sHsps) are a ubiquitous and ancient family of ATP-independent molecular chaperones. A key characteristic of sHsps is that they exist in ensembles of iso-energetic oligomeric species differing in size. This property arises from a unique mode of assembly involving several parts of the subunits in a flexible manner. Current evidence suggests that smaller oligomers are more active chaperones. Thus, a shift in the equilibrium of the sHsp ensemble allows regulating the chaperone activity. Different mechanisms have been identified that reversibly change the oligomer equilibrium. The promiscuous interaction with non-native proteins generates complexes that can form aggregate-like structures from which native proteins are restored by ATP-dependent chaperones such as Hsp70 family members. In recent years, this basic paradigm has been expanded, and new roles and new cofactors, as well as variations in structure and regulation of sHsps, have emerged.

It takes a dimer to tango: Oligomeric small heat shock proteins dissociate to capture substrate

Small heat-shock proteins (sHsps) are ubiquitous molecular chaperones, and sHsp mutations or altered expression are linked to multiple human disease states. sHsp monomers assemble into large oligomers with dimeric substructure, and the dynamics of sHsp oligomers has led to major questions about the form that captures substrate, a critical aspect of their mechanism of action. We show here that substructural dimers of two plant dodecameric sHsps, Ta16.9 and homologous Ps18.1, are functional units in the initial encounter with unfolding substrate. We introduced inter-polypeptide disulfide bonds at the two dodecameric interfaces, dimeric and nondimeric, to restrict how their assemblies can dissociate. When disulfide-bonded at the nondimeric interface, mutants of Ta16.9 and Ps18.1 (Ta_CT-ACD and Ps_CT-ACD) were inactive but, when reduced, had WT-like chaperone activity, demonstrating that dissociation at nondimeric interfaces is essential for sHsp activity. Moreover, the size of the Ta_CT-ACD and Ps_CT-ACD covalent unit defined a new tetrahedral geometry for these sHsps, different from that observed in the Ta16.9 X-ray structure. Importantly, oxidized Ta_dimer (disulfide bonded at the dimeric interface) exhibited greatly enhanced ability to protect substrate, indicating that strengthening the dimeric interface increases chaperone efficiency. Temperature-induced size and secondary structure changes revealed that folded sHsp dimers interact with substrate and that dimer stability affects chaperone efficiency. These results yield a model in which sHsp dimers capture substrate before assembly into larger, heterogeneous sHsp-substrate complexes for substrate refolding or degradation, and suggest that tuning the strength of the dimer interface can be used to engineer sHsp chaperone efficiency.

A novel mutation in the CRYAA gene associated with congenital cataract and microphthalmia in a Chinese family

Background

Congenital cataract is the leading cause of blindness in children worldwide. Approximately half of all congenital cataracts have a genetic basis. Protein aggregation is the single most important factor in cataract formation.

Methods

A four-generation Chinese family diagnosed with autosomal dominant congenital cataracts and microphthalmia was recruited at the Shengjing Hospital of China Medical University. Genomic DNA was extracted from the peripheral blood of the participants. All coding exons and flanking regions of seven candidate genes (CRYAA, CRYBA4, CRYBB2, CRYGC, GJA8, MAF, and PITX3) were amplified and sequenced. Restriction fragment length polymorphism (RFLP) assays were performed to confirm the candidate causative variant, c.35G > T in the CRYAA gene. We constructed pcDNA3.1(+)-CRYAA expression plasmids containing either the wild-type or the R12L mutant alleles and respectively transfected them into HEK293T cells and into HeLa cells. Western blotting was performed to determine protein expression levels and protein solubility. Immunofluorescence was performed to determine protein sub-cellular localization.

Results

A heterozygous variant c.35G > T was identified in exon 1 of CRYAA, which resulted in a substitution of arginine to leucine at codon 12 (p.R12L). The nucleotide substitution c.35G > T was co-segregated with the disease phenotype in the family. The mutant R12L-CRYAA in HEK293T cells showed a significant increase in the expression level of the CRYAA protein compared with the wild-type cells. Moreover, a large amount of the mutant protein aggregated in the precipitate where the wild-type protein was not detected. Immunofluorescence studies showed that the overexpressed mutant CRYAA in HeLa cells formed large cytoplasmic aggregates and aggresomes.

Conclusions

In summary, we described a case of human congenital cataract and microphthalmia caused by a novel mutation in the CRYAA gene, which substituted an arginine at position 12 in the N-terminal region of αA-crystallin. The molecular mechanisms that underlie the pathogenesis of human congenital cataract may be characterized by the prominent effects of the p.R12L mutation on αA-crystallin aggregation and solubility. Our study also expands the spectrum of known CRYAA mutations.

Topical nanodelivery system of lutein for the prevention of selenite-induced cataract

Cataracts are responsible for half of the world blindness, surgery being the only viable treatment. Lutein, a naturally occurring carotenoid in the eye, has the potential to reduce cataract progression by protecting the eye from photo-oxidative stress. To restore the eye's natural line of defense against photo-oxidative stress, a formulation was developed using zein and poly(lactic-co-glycolic acid) nanoparticles (NPs) embedded in an optimized bioadhesive thermosensitive gel for the delivery of lutein via topical application. Cataracts were induced in Crl:WI rats via selenite injection at 13 days post-partum, followed by 7 days of treatment with free lutein or lutein-loaded NPs administered orally or topically. Cataract severity was significantly reduced in rats treated with topical applications of lutein-loaded NPs compared to the positive control, while no significant differences were observed in rats treated with other lutein formulations including oral and topically applied free lutein.

Synthesis, Evaluation, and Structure-Activity Relationship Study of Lanosterol Derivatives To Reverse Mutant-Crystallin-Induced Protein Aggregation

We describe here the development of potent synthetic analogues of the naturally occurring triterpenoid lanosterol to reverse protein aggregation in cataracts. Lanosterol showed superiority to other scaffolds in terms of efficacy and generality in previous studies. Various modified lanosterol derivatives were synthesized via modification of the side chain, ring A, ring B, and ring C. Evaluation of these synthetic analogues draws a clear picture for SAR. In particular, hydroxylation of the 25-position in the side chain profoundly improved the potency, and 2-fluorination further enhanced the biological activity. This work also revealed that synthetic lanosterol analogues could reverse multiple types of mutant-crystallin aggregates in cell models with excellent potency and efficacy. Notably, lanosterol analogues have no cytotoxicity but can improve the viability of the HLE-B3 cell line. Furthermore, representative compound 6 successfully redissolved the aggregated crystallin proteins from the amyloid-like fibrils in a concentration-dependent manner.

BLM can regulate cataract progression by influencing cell vitality and apoptosis

Age-related cataract (ARC) is the most common cause of severe visual impairment and blindness. The precise mechanisms of ARC are not completely understood, but it is well accepted that oxidative damage plays an important role in the disease pathogenesis. BLM, the key enzyme of the double-strand break repair (DSBR) pathway, is part of a family of DNA unwinding enzymes and has a crucial role in multiple steps of the DNA recombination, replication and repair processes. We have recently shown that BLM-rs1063147 is initially associated with nuclear ARC in a cross-section study. Therefore, we wanted to study the effects of BLM on ARC progression. In ARC patients, BLM transcription in lens capsules was decreased, so did the BLM protein, and after UVB irradiation, BLM mRNA and protein levels were increased in SRA01/04 cells. Upon silencing BLM in SRA01/04 cells and rat lens, cell vitality and apoptosis were altered, and the rat lens opacification was considerable. In conclusion, BLM can regulate cataract progression by influencing cell vitality and apoptosis.

Genetic landscape of isolated pediatric cataracts: extreme heterogeneity and variable inheritance patterns within genes

Pediatric cataract represents an important cause of pediatric visual impairment. While both genetic and environmental causes for pediatric cataract are known, a large proportion remains idiopathic. The purpose of this review is to discuss genes involved in isolated pediatric cataract, with a focus on variable inheritance patterns within genes. Mutations in over 52 genes are known to cause isolated pediatric cataract, with a major contribution from genes encoding for crystallins, transcription factors, membrane proteins, and cytoskeletal proteins. Interestingly, both dominant and recessive inheritance patterns have been reported for mutations in 13 different cataract genes. For some genes, dominant and recessive alleles represent distinct types of mutations, but for many, especially missense variants, there are no clear patterns to distinguish between dominant and recessive alleles. Further research into the functional effects of these mutations, as well as additional data on the frequency of the identified variants, is needed to clarify variant pathogenicity. Exome sequencing continues to be successful in identifying novel genes associated with congenital cataract but is hindered by the extreme genetic heterogeneity of this condition. The large number of idiopathic cases suggests that more genes and potentially novel mechanisms of gene disruption remain to be identified.

Mechanistic insights into the switch of αB-crystallin chaperone activity and self-multimerization

αB-Crystallin (αBc) is a small heat shock protein that protects cells against abnormal protein aggregation and disease-related degeneration. αBc is also a major structural protein that forms polydisperse multimers that maintain the liquid-like property of the eye lens. However, the relationship and regulation of the two functions have yet to be explored. Here, by combining NMR spectroscopy and multiple biophysical approaches, we found that αBc uses a conserved β4/β8 surface of the central α-crystallin domain to bind α-synuclein and Tau proteins and prevent them from aggregating into pathological amyloids. We noted that this amyloid-binding surface can also bind the C-terminal IPI motif of αBc, which mediates αBc multimerization and weakens its chaperone activity. We further show that disruption of the IPI binding impairs αBc self-multimerization but enhances its chaperone activity. Our work discloses the structural mechanism underlying the regulation of αBc chaperone activity and self-multimerization and sheds light on the different functions of αBc in antagonizing neurodegeneration and maintaining eye lens liquidity.

Use of Lipid-Lowering Drugs and the Risk of Cataract: A Population-Based Nested Case-Control Study

Eye lens membrane cells require high cholesterol concentrations that might be counteracted by lipid-lowering drugs. Using a nationwide database, we conducted a nested case-control study to evaluate the risk of cataract development associated with the use of lipid-lowering drugs. Patients aged 45 years and over with first cataract surgery in 2014 (cases) and up to four controls matched on age, gender, diabetes, hypothyroidism, glucocorticoid use, cardiovascular risk, and area of residence were included in the study. Among the 2,811 cases and 11,106 matched controls included, analyses showed a significantly increased risk of cataract surgery for a cumulative exposure to fibrates exceeding 5 years (adjusted odds ratio (aOR) 1.58; 95% confidence interval (CI): 1.17-2.15), unlike cumulative exposure to statins, whatever the dose or duration of treatment (aORs from 1.00-1.08, none being significant). This study highlighted an increased risk of cataract surgery with prolonged use of fibrates but not of statins.

Lanosterol Synthase Pathway Alleviates Lens Opacity in Age-Related Cortical Cataract

Purpose

Lanosterol synthase (LSS) abnormity contributes to lens opacity in rats, mice, dogs, and human congenital cataract development. This study examined whether LSS pathway has a role in different subtypes of age-related cataract (ARC).

Methods

A total of 390 patients with ARC and 88 age-matched non-ARC patients were enrolled in this study. LSS expression was analyzed by western blot and enzyme-linked immunosorbent assay (ELISA). To further examine the function of LSS, we used U18666A, an LSS inhibitor in rat lens culture system.

Results

In lens epithelial cells (LECs), LSS expression in LECs increased with opaque degree C II, while it decreased with opaque degree C IV and C V. While in the cortex of age-related cortical cataract (ARCC), LSS expression was negatively related to opaque degree, while lanosterol level was positively correlated to opaque degree. No obvious change in both LSS and lanosterol level was found in either LECs or the cortex of age-related nuclear cataract (ARNC) and age-related posterior subcapsular cataract (ARPSC). In vitro, inhibiting LSS activity induced rat lens opacity and lanosterol effectively delayed the occurrence of lens opacity.

Conclusions

This study indicated that LSS and lanosterol were localized in the lens of human ARC, including ARCC, ARNC, and ARPSC. LSS and lanosterol level are only correlated with opaque degree of ARCC. Furthermore, activated LSS pathway in lens is protective for lens transparency in cortical cataract.

Protein aggregation in cell biology: An aggregomics perspective of health and disease

Maintaining protein homeostasis (proteostasis) is essential for cellular health and is governed by a network of quality control machinery comprising over 800 genes. When proteostasis becomes imbalanced, proteins can abnormally aggregate or become mislocalized. Inappropriate protein aggregation and proteostasis imbalance are two of the central pathological features of common neurodegenerative diseases including Alzheimer, Parkinson, Huntington, and motor neuron diseases. How aggregation contributes to the pathogenic mechanisms of disease remains incompletely understood. Here, we integrate some of the key and emerging ideas as to how protein aggregation relates to imbalanced proteostasis with an emphasis on Huntington disease as our area of main expertise. We propose the term "aggregomics" be coined in reference to how aggregation of particular proteins concomitantly influences the spatial organization and protein-protein interactions of the surrounding proteome. Meta-analysis of aggregated interactomes from various published datasets reveals chaperones and RNA-binding proteins are common components across various disease contexts. We conclude with an examination of therapeutic avenues targeting proteostasis mechanisms.

Rosmarinic Acid Restores Complete Transparency of Sonicated Human Cataract Ex Vivo and Delays Cataract Formation In Vivo

Cataract, the leading cause of vision impairment worldwide, arises from abnormal aggregation of crystallin lens proteins. Presently, surgical removal is the only therapeutic approach. Recent findings have triggered renewed interest in development of non-surgical treatment alternatives. However, emerging treatments are yet to achieve full and consistent lens clearance. Here, the first ex vivo assay to screen for drug candidates that reduce human lenticular protein aggregation was developed. This assay allowed the identification of two leading compounds as facilitating the restoration of nearly-complete transparency of phacoemulsified cataractous preparation ex vivo. Mechanistic studies demonstrated that both compounds reduce cataract microparticle size and modify their amyloid-like features. In vivo studies confirmed that the lead compound, rosmarinic acid, delays cataract formation and reduces the severity of lens opacification in model rats. Thus, the ex vivo assay may provide an initial platform for broad screening of potential novel therapeutic agents towards pharmacological treatment of cataract.

Chemical chaperone treatment improves levels and distributions of connexins in Cx50D47A mouse lenses

Mouse Cx50D47A and human Cx50D47N are non-functional connexin mutants that cause dominantly-inherited cataracts. In tissue culture expression experiments, they both exhibit impaired cellular trafficking and gap junction plaque formation. Lenses of mice expressing Cx50D47A have cataracts, reduced size, drastically decreased levels of connexin50, and less severely reduced levels of connexin46. The PERK-dependent pathway of the ER response to misfolded proteins is activated, and they have impaired differentiation with retained cellular organelles. Since treatments that enhance protein folding improve trafficking and plaque formation by Cx50D47N and other mutant connexins in vitro, and they are successful therapeutics for some other diseases caused by misfolded proteins, we tested the efficacy of the chemical chaperone, 4-phenylbutyrate (4-PBA) in cultured cells and mice expressing Cx50D47A. 4-PBA treatment increased the formation of Cx50D47A-containing plaques at appositional membranes of transiently transfected HeLa cells. Heterozygous Cx50D47A mice were treated with 4-PBA by addition to the drinking water and parenteral injection of pregnant mice (starting 10 days after pairing of males and females) and their pups. Lenses from 1-month-old mice were examined by darkfield illumination and immunofluorescence microscopy. Protein levels were determined by immunoblotting. Cataract size and density were not detectably different between the control and the 4-PBA-treated groups. Lens size was not increased following treatment. Levels of connexin46 and connexin50 were significantly increased in lenses of 4-PBA-treated mice compared with saline-treated animals. Immunofluorescence showed an increased abundance of connexin46 immunoreactivity and puncta. The ratio of phosphorylated to total EIF2α was not altered, and levels of organellar proteins were not significantly reduced, suggesting that the ER response to misfolded proteins and differentiation were not changed. Thus, treatment with 4-PBA improved critical pathological issues in these mice (low connexin and gap junction abundance), but the magnitude of this recovery (especially for Cx50) was inadequate to impact the reduced size or the opacification of Cx50D47A lenses.

NMR Biochemical Assay for Oxidosqualene Cyclase: Evaluation of Inhibitor Activities on Trypanosoma cruzi and Human Enzymes

Oxidosqualene cyclase (OSC), a membrane-associated protein, is a key enzyme of sterol biosynthesis. Here we report a novel assay for OSC, involving reaction in aqueous solution, NMR quantification in organic solvent, and factor analysis of spectra. We evaluated one known and three novel inhibitors on OSC of Trypanosoma cruzi, a parasite causative of Chagas disease, and compared their effects on human OSC for selectivity. Among them, one novel inhibitor showed a significant parasiticidal activity.

Research in Rare Disease: From Genomics to Proteomics

Jessica Lacoste from the Donnelly Centre at the University of Toronto was awarded best poster at the annual Society of Biomolecular Imaging and Informatics meeting held in San Diego, September 2017. Her work focuses on characterizing the protein localization of variants involved in rare disease. The current works and future directions of research in rare disease are summarized in the following overview.

Light-focusing human micro-lenses generated from pluripotent stem cells model lens development and drug-induced cataract in vitro

Cataracts cause vision loss and blindness by impairing the ability of the ocular lens to focus light onto the retina. Various cataract risk factors have been identified, including drug treatments, age, smoking and diabetes. However, the molecular events responsible for these different forms of cataract are ill-defined, and the advent of modern cataract surgery in the 1960s virtually eliminated access to human lenses for research. Here, we demonstrate large-scale production of light-focusing human micro-lenses from spheroidal masses of human lens epithelial cells purified from differentiating pluripotent stem cells. The purified lens cells and micro-lenses display similar morphology, cellular arrangement, mRNA expression and protein expression to human lens cells and lenses. Exposing the micro-lenses to the emergent cystic fibrosis drug Vx-770 reduces micro-lens transparency and focusing ability. These human micro-lenses provide a powerful and large-scale platform for defining molecular disease mechanisms caused by cataract risk factors, for anti-cataract drug screening and for clinically relevant toxicity assays.

Sterol Metabolism and Transport in Atherosclerosis and Cancer

Cholesterol is a vital lipid molecule for mammalian cells, regulating fluidity of biological membranes, and serving as an essential constituent of lipid rafts. Mammalian cells acquire cholesterol from extracellular lipoproteins and from de novo synthesis. Cholesterol biosynthesis generates various precursor sterols. Cholesterol undergoes metabolic conversion into oxygenated sterols (oxysterols), bile acids, and steroid hormones. Cholesterol intermediates and metabolites have diverse and important cellular functions. A network of molecular machineries including transcription factors, protein modifiers, sterol transporters/carriers, and sterol sensors regulate sterol homeostasis in mammalian cells and tissues. Dysfunction in metabolism and transport of cholesterol, sterol intermediates, and oxysterols occurs in various pathophysiological settings such as atherosclerosis, cancers, and neurodegenerative diseases. Here we review the cholesterol, intermediate sterol, and oxysterol regulatory mechanisms and intracellular transport machineries, and discuss the roles of sterols and sterol metabolism in human diseases.

Investigation of the radiotherapy-related changes in the eye lens using computed tomography entropy analysis

OBJECTIVE

The aim of this study was to apply texture analysis to investigate whether there was a change in the lens following radiotherapy.

PATIENTS AND METHOD

Patients who received radiotherapy (RT) for head and neck cancer or brain tumor were enrolled. Computed tomography (CT) images taken in the last month before RT and the most recent images after RT were compared. Entropy values were calculated using lens attenuation values. The lens doses were obtained from the dose-volume histogram data.

RESULTS

A total of 55 lenses were evaluated. The mean Hounsfield Unit value of the lenses was 66.14±12.16 before RT and 72.02±9.12 after RT (p = 0.007). The mean entropy value was 1.87±0.31 before RT and this reduced to 1.31±0.34 after RT (p < 0.001), respectively. As time increased, the difference in entropy also increased (p = 0.007). A correlation close to statistical significance was determined between the entropy difference and minimum, maximum and mean lens radiation dose (p = 0.052, p = 0.052, p = 0.063, respectively). The entropy difference was significantly reduced in the >4 Gy group (p = 0.046).

CONCLUSION

Study results indicated that the entropy values in the lens were signifcantly changed after radiotherapy and the degree of the change associated with dose and time.

Congenital cataract with LSS gene mutations: a new case report

BACKGROUND

Congenital cataract is one of the major causes of blindness and amblyopia in children. About one-third of the cases are inherited.

CASE PRESENTATION

We applied whole exome sequencing for a pediatric patient with congenital cataract, small penis, baldness and absence of eyebrows and detected a compound heterozygous mutation in the lanosterol synthase (LSS) gene. These two mutations were inherited from the patient's parents. Both mutations altered the amino acid coding, at highly conserved amino acid residues.

CONCLUSIONS

We concluded that the mutations affect the structural stability of the protein to some extent.

The 100 most influential papers about cataract surgery: a bibliometric analysis

AIM

To identify the 100 most cited papers in cataract surgery, we performed a comprehensive bibliometric analysis basing on the literature search on the Thomson Reuters Web of Knowledge.

METHODS

The number of citations, including the total citations, latest 5y citations and average citation number per year (ACY), authorship, year of publication, major topics, journal of publication, country and institution of origin of each paper were recorded and then analyzed. Pearson's correlation analysis was conducted to evaluate the correlation between the published year and the number of citations. The correlation between journal's impact factor (IF) and number of citations was assessed as well.

RESULTS

The most cited paper was the classic paper done by the European Society of Cataract & Refractive Surgeons (ESCRS) group. This paper focused on the topic of endophthalmitis. Not only the most cited papers originated from the USA, but also some American institutions like Johns Hopkins University, Harvard Medical School, etc. had the most citations. Pearson's correlation analysis indicated that the latest 5y citations and ACY were significantly related with the published year (5y citations: r=0.615, P<0.001; ACY: r=0.657, P<0.001), whereas no association between the total number of citations and published year was found (r=0.045). Moreover, the IFs of journals were found to have no significant effect on the number of total citations.

CONCLUSION

To our knowledge, this is the first study on the most influential papers in cataract surgery after a comprehensive research of relevant literatures. The present work may provide us concise information concerning the development history of cataract surgery over the past 66y.

Whales, lifespan, phospholipids, and cataracts

This study addresses the question: why do rats get cataracts at 2 years, dogs at 8 years, and whales do not develop cataracts for 200 years? Whale lens lipid phase transitions were compared with the phase transitions of other species that were recalculated. The major phospholipids of the whale lens were sphingolipids, mostly dihydrosphingomyelins with an average molar cholesterol/phospholipid ratio of 10. There was a linear correlation between the percentage of lens sphingolipid and lens lipid hydrocarbon chain order until about 60% sphingolipid. The percentage of lens sphingolipid correlated with the lens lipid phase transition temperature. The lifespan of the bowhead whale was the longest of the species measured and the percentage of whale lens sphingolipid fit well in the correlation between the percentage of lens sphingolipid and lifespan for many species. In conclusion, bowhead whale lens membranes have a high sphingolipid content that confers resistance to oxidation, allowing these lenses to stay clear relatively longer than many other species. The strong correlation between sphingolipid and lifespan may form a basis for future studies, which are needed because correlations do not infer cause. One could hope that if human lenses could be made to have a lipid composition similar to whales, like the bowhead, humans would not develop age-related cataracts for over 100 years.

Quantitation of lanosterol in the vitreous humor of rabbits after ocular administration of lanosterol/thermogel formulation by ultra high performance liquid chromatography-tandem mass spectrometry with the electrospray ionization mode

Cataracts are the most common cause of blindness worldwide affecting tens of millions of people. Here, we report a simple, rapid, sensitive and specific method by ultra performance liquid chromatography-tandem mass spectrometry with the electrospray ionization mode (UPLC-ESI-MS/MS) for quantitation of lanosterol, a possible effective drug for cataracts, in the vitreous humor of rabbits after ocular administration. The injected lanosterol was prepared by dispersing lanosterol molecules into the poly-(dl-lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly-(dl-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) thermogel solution. The analyte and internal standard (IS, panaxadiol) were extracted by the simple protein precipitation with methanol. The chromatographic separation used an Agilent RRHD SB-C₁₈ column with a methanol mobile phase containing 50mM of ammonium acetate aqueous solution (with 0.1% formic acid) (95:5, v/v). The protonated analyte was quantitated in positive ionization by multiple reaction monitoring (MRM) with a mass spectrometer. The mass transitions m/z 443.5→235 and m/z 461→127 were used to measure the analyte and IS, respectively. The assay exhibited a linear dynamic range of 1-1250ngmL^-1 for lanosterol in vitreous samples. The lower limit of quantitation (LLOQ) was 1ngmL^-1 with a relative standard deviation (RSD) of less than 15%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 5min per sample offered a throughput of more than 200 samples per day. This validated method was used to analyze vitreous samples of New Zealand white rabbits for pharmacokinetic studies. The results provided useful information on pharmacological action mechanism of lanosterol and were meaningful for cataract treatment among the elderly population.

Non-invasive tryptophan fluorescence measurements as a novel method of grading cataract

Development of non-invasive treatments for cataract calls for a sensitive diagnostic assay. We conducted a study to test whether the ratio of folded tryptophan to non-tryptophan fluorescence emission (F-factor) may be used for grading cataracts in human lenses. The F-factor was measured on aspirated lens material from eyes undergoing femtosecond laser assisted cataract surgery (FLACS) and was compared to a preoperative optical grading of cataract using Scheimpflug imaging. The preoperative optical grading allocated the cataracts to 1 of 4 categories according to the density of the cataract. All cataracts were age-related. Lens material from 16 eyes of 14 patients was included in the study. Cataracts were preoperatively graded in categories 1, 2 and 3. No lenses were category 4. For nuclear cataracts mean values of F-factor were 52.9 (SD 12.2), 61.7 (SD 5.3) and 75.7 (SD 8.9) for categories 1, 2 and 3 respectively. Linear regression on F-factor as a function of preoperative grading category showed increasing values of F-factor with increasing preoperative grading category, R² = 0.515. Our experiment showed that preoperative optical grading of cataracts by Scheimpflug imaging may correlate to measures of tryptophan and non-tryptophan fluorescence in human lenses. Based on our results we find that measuring the ratio between tryptophan- and non-tryptophan fluorescence may be a future tool for grading cataracts, but further research is needed.

Identification of a novel GJA3 mutation in a large Chinese family with congenital cataract using targeted exome sequencing

Autosomal dominant congenital cataract (ADCC) is a clinically and genetically heterogeneous ocular disease in children that results in serious visual impairments or even blindness. Targeted exome sequencing (TES) is an efficient method used for genetic diagnoses of inherited diseases. In the present study, we used a custom-made TES panel to identify the genetic defect of a four-generation Chinese family with bilateral pulverulent nuclear cataracts. A novel heterozygous missense mutation c.443C>T (p. T148I) in GJA3 was identified. The results of the bioinformatic analysis showed that the mutation was deleterious to the structure and hemichannel function of Cx46 encoded by GJA3. Plasmids expressing wild-type and mutant human Cx46 were constructed and ectopically expressed in human lens epithelial cells (HLECs) or human embryonic kidney (HEK-293) cells. Fluorescent images indicated aggregated signals of mutant protein in the cytoplasm, and a higher protein level was also detected in T148I stable cell lines. In summary, we identified a novel mutation in GJA3 for ADCC, which provided molecular insights into the pathogenic mechanism of ADCC.

Cataracts

An estimated 95 million people worldwide are affected by cataract. Cataract still remains the leading cause of blindness in middle-income and low-income countries. With the advancement of surgical technology and techniques, cataract surgery has evolved to small-incisional surgery with rapid visual recovery, good visual outcomes, and minimal complications in most patients. With the development of advanced technology in intraocular lenses, the combined treatment of cataract and astigmatism or presbyopia, or both, is possible. Paediatric cataracts have a different pathogenesis, surgical concerns, and postoperative clinical course from those of age-related cataracts, and the visual outcome is multifactorial and dependent on postoperative visual rehabilitation. New developments in cataract surgery will continue to improve the visual, anatomical, and patient-reported outcomes. Future work should focus on promoting the accessibility and quality of cataract surgery in developing countries.

Paradigm shifts, peregrinations and pixies in ophthalmology

Human ingenuity is challenged by defending vision, our highest bandwidth sense. Special challenges are presented by the replacement or repair of highly specialized but scarce tissue within the constraints of transparency, tissue shape and alignment, tissue borders and pressure maintenance. Many, mostly destructive, surgical procedures were developed prior to an understanding of underlying pathophysiology. For a number of conditions, both reconstructive and destructive procedures co-exist, yet there are few guidelines as to the better approach. Because the consequences of these procedures may take many years to surface (consistent with a stem cell role in long-term tissue maintenance), guidance may be provided by the elucidation of underlying principles from these approaches. Illustrative examples from clinical, basic research and biotechnology, particularly relating to pterygium, ocular surface squamous neoplasia, dry-eye syndrome, corneal rehabilitation and replacement, cataract surgery, strabismus surgery and bionic eye research, are described. An unexpected consequence of bionic device development has been an appreciation of the sophistication of tissues being replaced, given the limitations of available biomaterials. Examples of how this has provided insights into ocular disease will be illustrated. Stem cell and biomaterial technologies are starting to impact at a time when cost-effectiveness is under scrutiny. Both efficacy and cost will need to be considered as these interventions are introduced. It appears that the paradigm shift rate is accelerating and there is evidence of this in ophthalmology. Lessons learned from the areas of destructive versus reconstructive surgery and the limitations of development of bionic replacements will be used to illustrate how new procedures and technologies can be developed.

Transcriptome of the GSH-Depleted Lens Reveals Changes in Detoxification and EMT Signaling Genes, Transport Systems, and Lipid Homeostasis

Purpose

To understand the effects of glutathione (GSH)-deficiency on genetic processes that regulate lens homeostasis and prevent cataractogenesis.

Methods

The transcriptome of lens epithelia and fiber cells was obtained from C57BL/6 LEGSKO (lens GSH-synthesis knockout) and buthionine sulfoximine (BSO)-treated LEGSKO mice and compared to C57BL/6 wild-type mice using RNA-Seq. Transcriptomic data were confirmed by qPCR and Western blot/ELISA on a subset of genes.

Results

RNA-Seq results were in excellent agreement with qPCR (correlation coefficients 0.87-0.94 and P < 5E-6 for a subset of 36 mRNAs). Of 24,415 transcripts mapped to the mouse genome, 441 genes showed significantly modulated expression. Pathway analysis indicated major changes in epithelial-mesenchymal transition (EMT) signaling, visual cycle, small molecule biochemistry, and lipid metabolism. GSH-deficient lenses showed upregulation of detoxification genes, including Aldh1a1, Aldh3a1 (aldehyde dehydrogenases), Mt1, Mt2 (metallothioneins), Ces1g (carboxylesterase), and Slc14a1 (urea transporter UT-B). Genes in canonical EMT pathways, including Wnt10a, showed upregulation in lens epithelia samples. Severely GSH-deficient lens epithelia showed downregulation of vision-related genes (including crystallins). The BSO-treated LEGSKO lens epithelia transcriptome has significant correlation (r = 0.63, P < 0.005) to that of lens epithelia undergoing EMT. Protein expression data correlated with transcriptomic data and confirmed EMT signaling activation.

Conclusions

These results show that GSH-deficiency in the lens leads to expression of detoxifying genes and activation of EMT signaling, in addition to changes in transport systems and lipid homeostasis. These data provide insight into the adaptation and consequences of GSH-deficiency in the lens and suggest that GSH plays an important role in lenticular EMT pathology.

Amyloid β-Sheet Secondary Structure Identified in UV-Induced Cataracts of Porcine Lenses using 2D IR Spectroscopy

Cataracts are formed by the aggregation of crystallin proteins in the eye lens. Many in vitro studies have established that crystallin proteins precipitate into aggregates that contain amyloid fibers when denatured, but there is little evidence that ex vivo cataracts contain amyloid. In this study, we collect two-dimensional infrared (2D IR) spectra on tissue slices of porcine eye lenses. As shown in control experiments on in vitro αB- and γD-crystallin, 2D IR spectroscopy can identify the highly ordered β-sheets typical of amyloid secondary structure even if the fibers themselves are too short to be resolved with TEM. In ex vivo experiments of acid-treated tissues, characteristic 2D IR features are observed and fibers >50nm in length are resolved by transmission electron microscopy (TEM), consistent with amyloid fibers. In UV-irradiated lens tissues, fibers are not observed with TEM, but highly ordered β-sheets of amyloid secondary structure is identified from the 2D IR spectra. The characteristic 2D IR features of amyloid β-sheet secondary structure are created by as few as four or five strands and so identify amyloid secondary structure even if the aggregates themselves are too small to be resolved with TEM. We discuss these findings in the context of the chaperone system of the lens, which we hypothesize sequesters small aggregates, thereby preventing long fibers from forming. This study expands the scope of heterodyned 2D IR spectroscopy to tissues. The results provide a link between in vitro and ex vivo studies and support the hypothesis that cataracts are an amyloid disease.

Cataract-associated P23T γD-crystallin retains a native-like fold in amorphous-looking aggregates formed at physiological pH

Cataracts cause vision loss through the large-scale aggregation of eye lens proteins as a result of ageing or congenital mutations. The development of new treatments is hindered by uncertainty about the nature of the aggregates and their mechanism of formation. We describe the structure and morphology of aggregates formed by the P23T human γD-crystallin mutant associated with congenital cataracts. At physiological pH, the protein forms aggregates that look amorphous and disordered by electron microscopy, reminiscent of the reported formation of amorphous deposits by other crystallin mutants. Surprisingly, solid-state NMR reveals that these amorphous deposits have a high degree of structural homogeneity at the atomic level and that the aggregated protein retains a native-like conformation, with no evidence for large-scale misfolding. Non-physiological destabilizing conditions used in many in vitro aggregation studies are shown to yield qualitatively different, highly misfolded amyloid-like fibrils.

Aggregation of eye lens proteins leads to cataracts, a major cause of blindness. Here the authors use solid state NMR to probe the structure of γD-crystallin eye lens proteins aggregates, which are found to retain a native-like conformation.

Self-renewing Monolayer of Primary Colonic or Rectal Epithelial Cells

BACKGROUND & AIMS

Three-dimensional organoid culture has fundamentally changed the in vitro study of intestinal biology enabling novel assays; however, its use is limited because of an inaccessible luminal compartment and challenges to data gathering in a three-dimensional hydrogel matrix. Long-lived, self-renewing 2-dimensional (2-D) tissue cultured from primary colon cells has not been accomplished.

METHODS

The surface matrix and chemical factors that sustain 2-D mouse colonic and human rectal epithelial cell monolayers with cell repertoires comparable to that in vivo were identified.

RESULTS

The monolayers formed organoids or colonoids when placed in standard Matrigel culture. As with the colonoids, the monolayers exhibited compartmentalization of proliferative and differentiated cells, with proliferative cells located near the peripheral edges of growing monolayers and differentiated cells predominated in the central regions. Screening of 77 dietary compounds and metabolites revealed altered proliferation or differentiation of the murine colonic epithelium. When exposed to a subset of the compound library, murine organoids exhibited similar responses to that of the monolayer but with differences that were likely attributable to the inaccessible organoid lumen. The response of the human primary epithelium to a compound subset was distinct from that of both the murine primary epithelium and human tumor cells.

CONCLUSIONS

This study demonstrates that a self-renewing 2-D murine and human monolayer derived from primary cells can serve as a physiologically relevant assay system for study of stem cell renewal and differentiation and for compound screening. The platform holds transformative potential for personalized and precision medicine and can be applied to emerging areas of disease modeling and microbiome studies.

Mutations and mechanisms in congenital and age-related cataracts

The crystalline lens plays an important role in the refractive vision of vertebrates by facilitating variable fine focusing of light onto the retina. Loss of lens transparency, or cataract, is a frequently acquired cause of visual impairment in adults and may also present during childhood. Genetic studies have identified mutations in over 30 causative genes for congenital or other early-onset forms of cataract as well as several gene variants associated with age-related cataract. However, the pathogenic mechanisms resulting from genetic determinants of cataract are only just beginning to be understood. Here, we briefly summarize current concepts pointing to differences in the molecular mechanisms underlying congenital and age-related forms of cataract.