Analysis of long-range chromatin contacts, compartments and looping between mouse embryonic stem cells, lens epithelium and lens fibers

BACKGROUND

Nuclear organization of interphase chromosomes involves individual chromosome territories, "open" and "closed" chromatin compartments, topologically associated domains (TADs) and chromatin loops. The DNA- and RNA-binding transcription factor CTCF together with the cohesin complex serve as major organizers of chromatin architecture. Cellular differentiation is driven by temporally and spatially coordinated gene expression that requires chromatin changes of individual loci of various complexities. Lens differentiation represents an advantageous system to probe transcriptional mechanisms underlying tissue-specific gene expression including high transcriptional outputs of individual crystallin genes until the mature lens fiber cells degrade their nuclei.

RESULTS

Chromatin organization between mouse embryonic stem (ES) cells, newborn (P0.5) lens epithelium and fiber cells were analyzed using Hi-C. Localization of CTCF in both lens chromatins was determined by ChIP-seq and compared with ES cells. Quantitative analyses show major differences between number and size of TADs and chromatin loop size between these three cell types. In depth analyses show similarities between lens samples exemplified by overlaps between compartments A and B. Lens epithelium-specific CTCF peaks are found in mostly methylated genomic regions while lens fiber-specific and shared peaks occur mostly within unmethylated DNA regions. Major differences in TADs and loops are illustrated at the ~ 500 kb Pax6 locus, encoding the critical lens regulatory transcription factor and within a larger ~ 15 Mb WAGR locus, containing Pax6 and other loci linked to human congenital diseases. Lens and ES cell Hi-C data (TADs and loops) together with ATAC-seq, CTCF, H3K27ac, H3K27me3 and ENCODE cis-regulatory sites are shown in detail for the Pax6, Sox1 and Hif1a loci, multiple crystallin genes and other important loci required for lens morphogenesis. The majority of crystallin loci are marked by unexpectedly high CTCF-binding across their transcribed regions.

CONCLUSIONS

Our study has generated the first data on 3-dimensional (3D) nuclear organization in lens epithelium and lens fibers and directly compared these data with ES cells. These findings generate novel insights into lens-specific transcriptional gene control, open new research avenues to study transcriptional condensates in lens fiber cells, and enable studies of non-coding genetic variants linked to cataract and other lens and ocular abnormalities.

Insights into the dual nature of αB-crystallin chaperone activity from the p.P39L mutant at the N-terminal region

The substitution of leucine to proline at position 39 (p.P39L) in human αB-crystallin (αB-Cry) has been associated with conflicting interpretations of pathogenicity in cataracts and cardiomyopathy. This study aimed to investigate the effects of the p.P39L mutation on the structural and functional features of human αB-Cry. The mutant protein was expressed in Escherichia coli (E. coli) and purified using anion exchange chromatography. We employed a wide range of spectroscopic analyses, gel electrophoresis, transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques to investigate the structure, function, stability, and fibrillation propensity of the mutant protein. The p.P39L mutation caused significant changes in the secondary, tertiary, and quaternary structures of human αB-Cry and increased the thermal stability of the protein. The mutant αB-Cry exhibited an increased chaperone activity and an altered oligomeric size distribution, along with an increased propensity to form amyloid aggregates. It is worth mentioning, increased chaperone activity has important positive and negative effects on damaged cells related to cataracts and cardiomyopathy, particularly by interfering in the process of apoptosis. Despite the apparent positive nature of the increased chaperone activity, it is also linked to adverse consequences. This study provides important insights into the effect of proline substitution by leucine at the N-terminal region on the dual nature of chaperone activity in human αB-Cry, which can act as a double-edged sword.

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.

Transcriptome alterations in sf3b4-depleted zebrafish: Insights into cataract formation in retinitis pigmentosa model

Posterior subcapsular cataract (PSC) frequently develops as a complication in patients with retinitis pigmentosa (RP). Despite numerous scientific investigations, the intricate pathomechanisms underlying cataract formation in individuals affected by RP remain elusive. Therefore, our study aims to elucidate the potential pathogenesis of cataracts in an RP model using splicing factor subunit 3b (sf3b4) mutant zebrafish. By analyzing our previously published transcriptome dataset, we identified that, in addition to RP, cataract was listed as the second condition in our transcriptomic analysis. Furthermore, we confirmed the presence of nucleus retention in the lens fiber cells, along with abnormal cytoskeleton expression in both the lens fiber cells and lens epithelial cells in sf3b4-depleted fish. Upon closer examination, we identified 20 differentially expressed genes (DEGs) that played a role in cataract formation, with 95 % of them related to the downregulation of structural lens proteins. Additionally, we also identified that among all the DEGs, 13 % were associated with fibrotic processes. It seems that the significant upregulation of inflammatory mediators, in conjunction with TGF-β signaling, plays a central role in the cellular biology of PSC and posterior capsular opacification (PCO) in sf3b4 mutant fish. In summary, our study provides valuable insights into cataract formation in the RP model of sf3b4 mutants, highlighting its complexity driven by changes in structural lens proteins and increased cytokines/growth factors.

Mutations in alpha-B-crystallin cause autosomal dominant axonal Charcot-Marie-Tooth disease with congenital cataracts

BACKGROUND AND PURPOSE

Mutations in the alpha-B-crystallin (CRYAB) gene have initially been associated with myofibrillar myopathy, dilated cardiomyopathy and cataracts. For the first time, peripheral neuropathy is reported here as a novel phenotype associated with CRYAB.

METHODS

Whole-exome sequencing was performed in two unrelated families with genetically unsolved axonal Charcot-Marie-Tooth disease (CMT2), assessing clinical, neurophysiological and radiological features.

RESULTS

The pathogenic CRYAB variant c.358A>G;p.Arg120Gly was segregated in all affected patients from two unrelated families. The disease presented as late onset CMT2 (onset over 40 years) with distal sensory and motor impairment and congenital cataracts. Muscle involvement was probably associated in cases showing mild axial and diaphragmatic weakness. In all cases, nerve conduction studies demonstrated the presence of an axonal sensorimotor neuropathy along with chronic neurogenic changes on needle examination.

DISCUSSION

In cases with late onset autosomal dominant CMT2 and congenital cataracts, it is recommended that CRYAB is considered for genetic testing. The identification of CRYAB mutations causing CMT2 further supports a continuous spectrum of expressivity, from myopathic to neuropathic and mixed forms, of a growing number of genes involved in protein degradation and chaperone-assisted autophagy.

Indications for Systemic and Genetic Testing in Patients with Congenital Cataracts

Congenital cataracts account for a significant proportion of blindness in children worldwide. They affect approximately 12-136 per 100,000 births worldwide. A genetic etiology is present in a large proportion of patients and can lead to isolated cataracts or those in the context of genetic multisystem disorders. We present two examples of genetically determined childhood cataracts and briefly review the work-up of such patients. Mutations in numerous genes have been identified that cause congenital cataracts, such as those encoding for crystallins, connexins and aquaporins, as well as some developmental regulatory proteins. Identifying the genetic or molecular etiology of congenital cataract is essential for identifying and better understanding the pathways leading to this disease, and for providing individualized genetic counseling and guiding treatment for possible associated systemic problems.

Mutational analysis of CRYAA gene of cataract and investigating risk assessment factors responsible for eye diseases in district buner, KPK, Pakistan

This research has been designed to analyze the risk factors of major eye diseases and the genetic alterations contributing to the manifestation of such disease. For this purpose, data was collected from 256 patients diagnosed by an ophthalmologist by using a specialized questionnaire. Blood samples were collected from 100 patients to perform a genetic investigation of cataracts. Whole genomic DNA was extracted from blood samples via the phenol-chloroform method. The purified DNA was used as the template for the amplification of about 400 bp fragments amplifying exons 1 and 2 of the CRYAA gene. The statistical analysis showed that 68% of individuals were blind due to cataracts. During molecular analysis, nucleotide sequences obtained have resulted in one silent mutation that occured at 20 positions in exon 2. It was replacing A>G which in turn substitutes the Lysine at position 70 for Arginine. It was interpreted by statistical analysis that this mutation did not result in a significant change in the CRYAA gene. In addition, protein analysis showed no significant changes in the structure of normal and mutated genes. At last, it is concluded that environmental risk factors play a major role in the studied diseases as compared to genetic factors. It is recommended to extend the study to a larger population to study all exons of the CRYAA gene as well as develop better estimates of the magnitude of the problems of visual loss and eye diseases in the Pakistani population.

A crystallin mutant cataract with mineral deposits

Connexin mutant mice develop cataracts containing calcium precipitates. To test whether pathologic mineralization is a general mechanism contributing to the disease, we characterized the lenses from a nonconnexin mutant mouse cataract model. By cosegregation of the phenotype with a satellite marker and genomic sequencing, we identified the mutant as a 5-bp duplication in the γC-crystallin gene (Crygcdup). Homozygous mice developed severe cataracts early, and heterozygous animals developed small cataracts later in life. Immunoblotting studies showed that the mutant lenses contained decreased levels of crystallins, connexin46, and connexin50 but increased levels of resident proteins of the nucleus, endoplasmic reticulum, and mitochondria. The reductions in fiber cell connexins were associated with a scarcity of gap junction punctae as detected by immunofluorescence and significant reductions in gap junction-mediated coupling between fiber cells in Crygcdup lenses. Particles that stained with the calcium deposit dye, Alizarin red, were abundant in the insoluble fraction from homozygous lenses but nearly absent in wild-type and heterozygous lens preparations. Whole-mount homozygous lenses were stained with Alizarin red in the cataract region. Mineralized material with a regional distribution similar to the cataract was detected in homozygous lenses (but not wild-type lenses) by micro-computed tomography. Attenuated total internal reflection Fourier-transform infrared microspectroscopy identified the mineral as apatite. These results are consistent with previous findings that loss of lens fiber cell gap junctional coupling leads to the formation of calcium precipitates. They also support the hypothesis that pathologic mineralization contributes to the formation of cataracts of different etiologies.

Cataract-causing Y204X mutation of crystallin protein CRYβB1 promotes its C-terminal degradation and higher-order oligomerization

Crystallin proteins are a class of main structural proteins of the vertebrate eye lens, and their solubility and stability directly determine transparency and refractive power of the lens. Mutation in genes that encode these crystallin proteins is the most common cause for congenital cataracts. Despite extensive studies, the pathogenic and molecular mechanisms that effect congenital cataracts remain unclear. In this study, we identified a novel mutation in CRYBB1 from a congenital cataract family, and demonstrated that this mutation led to an early termination of mRNA translation, resulting in a 49-residue C-terminally truncated CRYβB1 protein. We show this mutant is susceptible to proteolysis, which allowed us to determine a 1.2-Å resolution crystal structure of CRYβB1 without the entire C-terminal domain. In this crystal lattice, we observed that two N-terminal domain monomers form a dimer that structurally resembles the WT monomer, but with different surface characteristics. Biochemical analyses and cell-based data also suggested that this mutant is significantly more liable to aggregate and degrade compared to WT CRYβB1. Taken together, our results provide an insight into the mechanism regarding how a mutant crystalin contributes to the development of congenital cataract possibly through alteration of inter-protein interactions that result in protein aggregation.

Human Mutated MYOT and CRYAB Genes Cause a Myopathic Phenotype in Zebrafish

Myofibrillar myopathies (MFMs) are a group of hereditary neuromuscular disorders sharing common histological features, such as myofibrillar derangement, Z-disk disintegration, and the accumulation of degradation products into protein aggregates. They are caused by mutations in several genes that encode either structural proteins or molecular chaperones. Nevertheless, the mechanisms by which mutated genes result in protein aggregation are still unknown. To unveil the role of myotilin and αB-crystallin in the pathogenesis of MFM, we injected zebrafish fertilized eggs at the one-cell stage with expression plasmids harboring cDNA sequences of human wildtype or mutated MYOT (p.Ser95Ile) and human wildtype or mutated CRYAB (p.Gly154Ser). We evaluated the effects on fish survival, motor behavior, muscle structure and development. We found that transgenic zebrafish showed morphological defects that were more severe in those overexpressing mutant genes. which developed a myopathic phenotype consistent with that of human myofibrillar myopathy, including the formation of protein aggregates. Results indicate that pathogenic mutations in myotilin and αB-crystallin genes associated with MFM cause a structural and functional impairment of the skeletal muscle in zebrafish, thereby making this non-mammalian organism a powerful model to dissect disease pathogenesis and find possible druggable targets.

Impact of α-crystallin protein loss on zebrafish lens development

The α-crystallin small heat shock proteins contribute to the transparency and refractive properties of the vertebrate eye lens and prevent the protein aggregation that would otherwise produce lens cataracts, the leading cause of human blindness. There are conflicting data in the literature as to what role the α-crystallins may play in early lens development. In this study, we used CRISPR gene editing to produce zebrafish lines with mutations in each of the three α-crystallin genes (cryaa, cryaba and cryabb) to prevent protein production. The absence of each α-crystallin protein was analyzed by mass spectrometry, and lens phenotypes were assessed with differential interference contrast microscopy and histology. Loss of αA-crystallin produced a variety of lens defects with varying severity in larvae at 3 and 4 dpf but little substantial change in normal fiber cell denucleation. Loss of αBa-crystallin produced no substantial lens defects. Our cryabb mutant produced a truncated αBb-crystallin protein and showed no substantial change in lens development. Mutation of each α-crystallin gene did not alter the mRNA levels of the remaining two, suggesting a lack of genetic compensation. These data suggest that αA-crystallin plays some role in lens development, but the range of phenotype severity in null mutants indicates its loss simply increases the chance for defects and that the protein is not essential. Our finding that cryaba and cryabb mutants lack noticeable lens defects is congruent with insubstantial transcript levels for these genes in lens epithelial and fiber cells through five days of development. Future experiments can explore the molecular mechanisms leading to lens defects in cryaa null mutants and the impact of αA-crystallin loss during zebrafish lens aging.

Blood transcriptome of Rasa Aragonesa rams with different sexual behavior phenotype reveals CRYL1 and SORCS2 as genes associated with this trait

Reproductive fitness of rams is seasonal, showing the highest libido during short days coinciding with the ovarian cyclicity resumption in the ewe. However, the remarkable variation in sexual behavior between rams impair farm efficiency and profitability. Intending to identify in vivo sexual behavior biomarkers that may aid farmers to select active rams, transcriptome profiling of blood was carried out by analyzing samples from 6 sexually active (A) and 6 nonactive (NA) Rasa Aragonesa rams using RNA-Seq technique. A total of 14,078 genes were expressed in blood but only four genes were differentially expressed (FDR < 0.10) in the A vs. NA rams comparison. The genes, acrosin inhibitor 1 (ENSOARG00020023278) and SORCS2, were upregulated (log2FC > 1) in active rams, whereas the CRYL1 and immunoglobulin lambda-1 light chain isoform X47 (ENSOARG00020025518) genes were downregulated (log2FC < -1) in this same group. Gene set Enrichment Analysis (GSEA) identified 428 signaling pathways, predominantly related to biological processes. The lysosome pathway (GO:0005764) was the most enriched, and may affect fertility and sexual behavior, given the crucial role played by lysosomes in steroidogenesis, being the SORCS2 gene related to this signaling pathway. Furthermore, the enriched positive regulation of ERK1 and ERK2 cascade (GO:0070374) pathway is associated with reproductive phenotypes such as fertility via modulation of hypothalamic regulation and GnRH-mediated production of pituitary gonadotropins. Furthermore, external side of plasma membrane (GO:0009897), fibrillar center (GO:0001650), focal adhesion (GO:0005925), and lamellipodium (GO:0030027) pathways were also enriched, suggesting that some molecules of these pathways might also be involved in rams' sexual behavior. These results provide new clues for understanding the molecular regulation of sexual behavior in rams. Further investigations will be needed to confirm the functions of SORCS2 and CRYL1 in relation to sexual behavior.

Expression of oxysterols in human lenses: Implications of the sterol pathway in age-related cataracts

Lanosterol, an oxysterol molecule, has been proposed to help maintain lens transparency by inhibiting the formation of protein aggregates. This sterol is produced by the enzyme lanosterol synthase and is part of a metabolic pathway that forms cholesterol as a final step. Abnormalities in lanosterol synthase are responsible for congenital cataracts. The αA-crystallin protein, which acts as a molecular chaperone to lanosterol synthase, has been reported to have anti-protein aggregation, anti-inflammatory and anti-apoptotic properties. In this work, we evaluated the correlation of lanosterol synthase and αA-crystallin in human cataractous lenses with the grade of opacity, as well as the expression of lanosterol synthase, farnesyl DPP, geranyl synthase and squalene epoxidase genes. Lanosterol synthase and αA-crystallin were overexpressed in cataractous lenses as well as farnesyl-DP synthase, squalene epoxidase, lanosterol synthase and geranyl synthase genes in cataratous lenses in comparison with normal lenses. Our data confirm that lanosterol synthase and the sterol pathway are upregulated in cataractous lenses. This argues for a functional role of the oxysterol pathway and its products as an important mediator in the pathogenesis of human cataracts.

Generation of Lens Progenitor Cells and Lentoid Bodies from Pluripotent Stem Cells: Novel Tools for Human Lens Development and Ocular Disease Etiology

In vitro differentiation of human pluripotent stem cells (hPSCs) into specialized tissues and organs represents a powerful approach to gain insight into those cellular and molecular mechanisms regulating human development. Although normal embryonic eye development is a complex process, generation of ocular organoids and specific ocular tissues from pluripotent stem cells has provided invaluable insights into the formation of lineage-committed progenitor cell populations, signal transduction pathways, and self-organization principles. This review provides a comprehensive summary of recent advances in generation of adenohypophyseal, olfactory, and lens placodes, lens progenitor cells and three-dimensional (3D) primitive lenses, "lentoid bodies", and "micro-lenses". These cells are produced alone or "community-grown" with other ocular tissues. Lentoid bodies/micro-lenses generated from human patients carrying mutations in crystallin genes demonstrate proof-of-principle that these cells are suitable for mechanistic studies of cataractogenesis. Taken together, current and emerging advanced in vitro differentiation methods pave the road to understand molecular mechanisms of cataract formation caused by the entire spectrum of mutations in DNA-binding regulatory genes, such as PAX6, SOX2, FOXE3, MAF, PITX3, and HSF4, individual crystallins, and other genes such as BFSP1, BFSP2, EPHA2, GJA3, GJA8, LIM2, MIP, and TDRD7 represented in human cataract patients.

Oxysterol Compounds in Mouse Mutant αA- and αB-Crystallin Lenses Can Improve the Optical Properties of the Lens

Purpose

To investigate how cataract-linked mutations affect the gradient refractive index (GRIN) and lens opacification in mouse lenses and whether there is any effect on the optics of the lens from treatment with an oxysterol compound.

Methods

A total of 35 mice including wild-type and knock-in mutants (Cryaa-R49C and Cryab-R120G) were used in these experiments: 26 mice were treated with topical VP1-001, an oxysterol, in one eye and vehicle in the other, and nine mice were untreated controls. Slit lamp biomicroscopy was used to analyze the lens in live animals and to provide apparent cataract grades. Refractive index in the lenses of 64 unfixed whole mouse eyes was calculated from measurements with X-ray phase tomography based on X-ray Talbot interferometry with a synchrotron radiation source.

Results

Heterozygous Cryaa-R49C lenses had slightly irregularly shaped contours in the center of the GRIN and distinct disturbances of the gradient index at the anterior and posterior poles. Contours near the lens surface were denser in homozygous Cryab-R120G lenses. Treatment with topical VP1-001, an oxysterol, showed an improvement in refractive index profiles in 61% of lenses and this was supported by a reduction in apparent lens opacity grade by 1.0 in 46% of live mice.

Conclusions

These results indicate that α-crystallin mutations alter the refractive index gradient of mouse lenses in distinct ways and suggest that topical treatment with VP1-001 may improve lens transparency and refractive index contours in some lenses with mutations.

Crystallins as Important Pathogenic Targets for Accumulation of Structural Damages Resulting in Protein Aggregation and Cataract Development: Introduction to This Special Issue of Biochemistry (Moscow)

This issue of Biochemistry (Moscow) is dedicated to the role of protein misfolding and aggregation in cataract development. In fact, many genetic mutations or chemical and physical deleterious factors can initiate alterations in the macrostructural order and proper folding of eye lens proteins, which in some cases result in the formation of large light-scattering aggregates, affecting the quality of vision and making lens more prone to cataract development. Diabetes mellitus, which is associated with oxidative stress and mass production of highly reactive compounds, can accelerate unfolding and aggregation of eye lens proteins. This journal issue contains reviews and research articles that describe the destructive effects of mutations and highly reactive metabolites on the structure and function of lens crystallin proteins, as well important molecules in the lens's natural defense system involved in protection against deleterious effects of the physical and chemical factors.

Absent in melanoma 1-like (AIM1L) serves as a novel candidate for overall survival in hepatocellular carcinoma

Identifying biomarkers for hepatocellular carcinoma (HCC) survival is of great importance for the early detection, monitoring, and predicting for prognosis. This study aimed to investigate the candidate biomarkers for predicting overall survival (OS) in HCC patients. Using RTCGAToolbox, top 50 upregulated differential expressed genes (DEGs) were identified. The least absolute shrinkage and selection operator (LASSO) and Cox models were used to select powerful candidate genes, and log rank method was used to address the survivor functions of potential biomarkers. Selected by LASSO model, ANLN, TTK, AIM1L and person neoplasm cancer status might be candidate parameters associated with OS in HCC patients. After adjusting person neoplasm cancer status, ANLN and TTK levels in Cox model, AIM1L was identified as a risk factor for predicting OS in HCC patients (HR = 1.5, P = 0.037). Validated in The Cancer Genome Atlas (TCGA), International Cancer Genome Consortium (ICGC) and Gene Expression Omnibus (GEO) series, AIM1L was significantly overexpressed in tumor tissues compared to nontumor tissues (all P < 0.0001). HCC patients with high AIM1L in tumor tissues had significantly unfavorable OS compared to those with low AIM1L in TCGA, ICGC, Gene Expression Profiling Interactive Analysis (GEPIA) and Kaplan-Meier Plotter datasets (all P < 0.05). Conclusively, AIM1L is upregulated in tumor samples and serves as a novel candidate for predicting unfavorable OS in HCC patients.

Deciphering the association of intronic single nucleotide polymorphisms of crystallin gene family with congenital cataract

Purpose

Introns play an important role in gene regulation and expression. Single nucleotide polymorphisms (SNPs) in introns have the potential to cause disease and alter the genotype-phenotype association. Hence, this study aimed to decipher the association of SNPs in the introns of the crystallin gene in congenital cataracts.

Methods

SNPs in the introns of crystallin gene family - CRYAA (rs3788059), CRYAB (rs2070894), CRYBA4 (rs2071861), and CRYBB2 (rs5752083, rs5996863) - were genotyped in 248 participants consisting of 141 congenital cataracts and 107 healthy controls by allele-specific oligonucleotide polymerase chain reaction method. Around 10% of samples for each SNPs were sequenced to confirm the genotypes. The allele, genotype, and haplotype frequency were evaluated by the SHEsis online tool.

Results

Using dominant model, the "A" allele of rs3788059 was found to have an increased risk toward congenital cataract development whereas the "G" allele was found to be protective (AA + AG vs. GG; odds ratio [OR] 95% confidence interval [CI] = 3.73 [1.71, 8.15], P = 0.0009). The "A" allele of both rs2070894 (AA + AG vs. GG; OR [95% CI] = 0.49 [0.29, 0.84], P = 0.012) and rs5752083 (AA + AC vs. CC; OR [95% CI] = 0.25 [0.08, 0.76], P = 0.016) were suggested to have a protective role by the dominant model. The A-C-T haplotype (rs2071861, rs5752083, and rs5996863) was found to be a significant risk factor for the development of congenital cataract.

Conclusion

Intronic SNPs in crystallin genes may play a role in the predisposition toward congenital cataract. However, the present findings need to be replicated in a large cohort with more number of samples.

Inherited cataracts: Genetic mechanisms and pathways new and old

Cataract(s) is the clinical equivalent of lens opacity and is caused by light scattering either by high molecular weight protein aggregates in lens cells or disruption of the lens microarchitecture itself. Genetic mutations underlying inherited cataract can provide insight into the biological processes and pathways critical for lens homeostasis and transparency, classically including the lens crystallins, connexins, membrane proteins or components, and intermediate filament proteins. More recently, cataract genes have been expanded to include newly identified biological processes such as chaperone or protein degradation components, transcription or growth factors, channels active in the lens circulation, and collagen and extracellular matrix components. Cataracts can be classified by age, and in general congenital cataracts are caused by severe mutations resulting in major damage to lens proteins, while age related cataracts are associated with variants that merely destabilize proteins thereby increasing susceptibility to environmental insults over time. Thus there might be separate pathways to opacity for congenital and age-related cataracts whereby congenital cataracts induce the unfolded protein response (UPR) and apoptosis to destroy the lens microarchitecture, while in age related cataract high molecular weight (HMW) aggregates formed by denatured crystallins bound by α-crystallin result in light scattering without severe damage to the lens microarchitecture.

Novel Mutation in CRYBB3 Causing Pediatric Cataract and Microphthalmia

Up to 25% of pediatric cataract cases are inherited, with half of the known mutant genes belonging to the crystallin family. Within these, crystallin beta B3 (CRYBB3) has the smallest number of reported variants. Clinical ophthalmological and genetic-dysmorphological evaluation were performed in three autosomal dominant family members with pediatric cataract and microphthalmia, as well as one unaffected family member. Peripheral blood was collected from all participating family members and next-generation sequencing was performed. Bioinformatics analysis revealed a novel missense variant c.467G>A/p.Gly156Glu in CRYBB3 in all family members with childhood cataract. This variant is classified as likely pathogenic by ACMG, and no previous descriptions of it were found in ClinVar, HGMD or Cat-Map. The only other mutation previously described in the fifth exon of CRYBB3 is a missense variant that causes a change in amino acid from the same 156th amino acid to arginine and has been associated with pediatric cataract and microphthalmia. To the best of our knowledge, this is the first time the c.467G>A/p.Gly156Glu variant is reported and the second time a mutation in CRYBB3 has been associated with microphthalmia.

µ-Crystallin: A thyroid hormone binding protein

µ-Crystallin is a NADPH-regulated thyroid hormone binding protein encoded by the CRYM gene in humans. It is primarily expressed in the brain, muscle, prostate, and kidney, where it binds thyroid hormones, which regulate metabolism and thermogenesis. It also acts as a ketimine reductase in the lysine degradation pathway when it is not bound to thyroid hormone. Mutations in CRYM can result in non-syndromic deafness, while its aberrant expression, predominantly in the brain but also in other tissues, has been associated with psychiatric, neuromuscular, and inflammatory diseases. CRYM expression is highly variable in human skeletal muscle, with 15% of individuals expressing ≥13 fold more CRYM mRNA than the median level. Ablation of the Crym gene in murine models results in the hypertrophy of fast twitch muscle fibers and an increase in fat mass of mice fed a high fat diet. Overexpression of Crym in mice causes a shift in energy utilization away from glycolysis towards an increase in the catabolism of fat via β-oxidation, with commensurate changes of metabolically involved transcripts and proteins. The history, attributes, functions, and diseases associated with CRYM, an important modulator of metabolism, are reviewed.

Small Hsps as Therapeutic Targets of Cystic Fibrosis Transmembrane Conductance Regulator Protein

Human small heat shock proteins are molecular chaperones that regulate fundamental cellular processes in normal and pathological cells. Here, we have reviewed the role played by HspB1, HspB4 and HspB5 in the context of Cystic Fibrosis (CF), a severe monogenic autosomal recessive disease linked to mutations in Cystic Fibrosis Transmembrane conductance Regulator protein (CFTR) some of which trigger its misfolding and rapid degradation, particularly the most frequent one, F508del-CFTR. While HspB1 and HspB4 favor the degradation of CFTR mutants, HspB5 and particularly one of its phosphorylated forms positively enhance the transport at the plasma membrane, stability and function of the CFTR mutant. Moreover, HspB5 molecules stimulate the cellular efficiency of currently used CF therapeutic molecules. Different strategies are suggested to modulate the level of expression or the activity of these small heat shock proteins in view of potential in vivo therapeutic approaches. We then conclude with other small heat shock proteins that should be tested or further studied to improve our knowledge of CFTR processing.

Long Non-Coding RNA CRYBG3 Promotes Lung Cancer Metastasis via Activating the eEF1A1/MDM2/MTBP Axis

The occurrence of distant tumor metastases is a major barrier in non-small cell lung cancer (NSCLC) therapy, and seriously affects clinical treatment and patient prognosis. Recently, long non-coding RNAs (lncRNAs) have been demonstrated to be crucial regulators of metastasis in lung cancer. The aim of this study was to reveal the underlying mechanisms of a novel lncRNA LNC CRYBG3 in regulating NSCLC metastasis. Experimental results showed that LNC CRYBG3 was upregulated in NSCLC cells compared with normal tissue cells, and its level was involved in these cells' metastatic ability. Exogenously overexpressed LNC CRYBG3 increased the metastatic ability and the protein expression level of the metastasis-associated proteins Snail and Vimentin in low metastatic lung cancer HCC827 cell line. In addition, LNC CRYBG3 contributed to HCC827 cell metastasis in vivo. Mechanistically, LNC CRYBG3 could directly combine with eEF1A1 and promote it to move into the nucleus to enhance the transcription of MDM2. Overexpressed MDM2 combined with MDM2 binding protein (MTBP) to reduce the binding of MTBP with ACTN4 and consequently increased cell migration mediated by ACTN4. In conclusion, the LNC CRYBG3/eEF1A1/MDM2/MTBP axis is a novel signaling pathway regulating tumor metastasis and may be a potential therapeutic target for NSCLC treatment.

βA1-crystallin regulates glucose metabolism and mitochondrial function in mouse retinal astrocytes by modulating PTP1B activity

βA3/A1-crystallin, a lens protein that is also expressed in astrocytes, is produced as βA3 and βA1-crystallin isoforms by leaky ribosomal scanning. In a previous human proteome high-throughput array, we found that βA3/A1-crystallin interacts with protein tyrosine phosphatase 1B (PTP1B), a key regulator of glucose metabolism. This prompted us to explore possible roles of βA3/A1-crystallin in metabolism of retinal astrocytes. We found that βA1-crystallin acts as an uncompetitive inhibitor of PTP1B, but βA3-crystallin does not. Loss of βA1-crystallin in astrocytes triggers metabolic abnormalities and inflammation. In CRISPR/cas9 gene-edited βA1-knockdown (KD) mice, but not in βA3-knockout (KO) mice, the streptozotocin (STZ)-induced diabetic retinopathy (DR)-like phenotype is exacerbated. Here, we have identified βA1-crystallin as a regulator of PTP1B; loss of this regulation may be a new mechanism by which astrocytes contribute to DR. Interestingly, proliferative diabetic retinopathy (PDR) patients showed reduced βA1-crystallin and higher levels of PTP1B in the vitreous humor.

Effect of a Lens Protein in Low-Temperature Culture of Novel Immortalized Human Lens Epithelial Cells (iHLEC-NY2)

The prevalence of nuclear cataracts was observed to be significantly higher among residents of tropical and subtropical regions compared to those of temperate and subarctic regions. We hypothesized that elevated environmental temperatures may pose a risk of nuclear cataract development. The results of our in silico simulation revealed that in temperate and tropical regions, the human lens temperature ranges from 35.0 °C to 37.5 °C depending on the environmental temperature. The medium temperature changes during the replacement regularly in the cell culture experiment were carefully monitored using a sensor connected to a thermometer and showed a decrease of 1.9 °C, 3.0 °C, 1.7 °C, and 0.1 °C, after 5 min when setting the temperature of the heat plate device at 35.0 °C, 37.5 °C, 40.0 °C, and 42.5 °C, respectively. In the newly created immortalized human lens epithelial cell line clone NY2 (iHLEC-NY2), the amounts of RNA synthesis of αA crystallin, protein expression, and amyloid β (Aβ)1-40 secreted into the medium were increased at the culture temperature of 37.5 °C compared to 35.0 °C. In short-term culture experiments, the secretion of Aβ1-40 observed in cataracts was increased at 37.5 °C compared to 35.0 °C, suggesting that the long-term exposure to a high-temperature environment may increase the risk of cataracts.

Human cataractous lenses contain cross-links produced by crystallin-derived tryptophanyl and tyrosyl radicals

Protein insolubilization, cross-linking and aggregation are considered critical to the development of lens opacity in cataract. However, the information about the presence of cross-links other than disulfides in cataractous lenses is limited. A potential role for cross-links produced from tryptophanyl radicals in cataract development is suggested by the abundance of the UV light-sensitive Trp residues in crystallin proteins. Here we developed a LC-MS/MS approach to examine the presence of Trp-Trp, Trp-Tyr and Tyr-Tyr cross-links and of peptides containing Trp-2H (-2.0156 Da) in the lens of three patients diagnosed with advanced nuclear cataract. In the proteins of two of the lenses, we characterized intermolecular cross-links between βB2-Tyr¹⁵³-Tyr¹⁰⁴-βA3 and βB2-Trp¹⁵⁰-Tyr¹³⁹-βS. An additional intermolecular cross-link (βB2-Tyr⁶¹-Trp²⁰⁰-βB3) was present in the lens of the oldest patient. In the proteins of all three lenses, we characterized two intramolecular Trp-Trp cross-links (Trp¹²³-Trp¹²⁶ in βB1 and Trp⁸¹-Trp⁸⁴ in βB2) and six peptides containing Trp -2H residues, which indicate the presence of additional Trp-Trp cross-links. Relevantly, we showed that similar cross-links and peptides with modified Trp-2H residues are produced in a time-dependent manner in bovine β-crystallin irradiated with a solar simulator. Therefore, different crystallin proteins cross-linked by crystalline-derived tryptophanyl and tyrosyl radicals are present in advanced nuclear cataract lenses and similar protein modifications can be promoted by solar irradiation even in the absence of photosensitizers. Overall, the results indicate that a role for Trp-Tyr and Trp-Trp cross-links in the development of human cataract is possible and deserves further investigation.

The transcription factor CREB acts as an important regulator mediating oxidative stress-induced apoptosis by suppressing αB-crystallin expression

The general transcription factor, CREB has been shown to play an essential role in promoting cell proliferation, neuronal survival and synaptic plasticity in the nervous system. However, its function in stress response remains to be elusive. In the present study, we demonstrated that CREB plays a major role in mediating stress response. In both rat lens organ culture and mouse lens epithelial cells (MLECs), CREB promotes oxidative stress-induced apoptosis. To confirm that CREB is a major player mediating the above stress response, we established stable lines of MLECs stably expressing CREB and found that they are also very sensitive to oxidative stress-induced apoptosis. To define the underlying mechanism, RNAseq analysis was conducted. It was found that CREB significantly suppressed expression of the αB-crystallin gene to sensitize CREB-expressing cells undergoing oxidative stress-induced apoptosis. CREB knockdown via CRISPR/CAS9 technology led to upregulation of αB-crystallin and enhanced resistance against oxidative stress-induced apoptosis. Moreover, overexpression of exogenous human αB-crystallin can restore the resistance against oxidative stress-induced apoptosis. Finally, we provided first evidence that CREB directly regulates αB-crystallin gene. Together, our results demonstrate that CREB is an important transcription factor mediating stress response, and it promotes oxidative stress-induced apoptosis by suppressing αB-crystallin expression.

Qishen Granule alleviates endoplasmic reticulum stress-induced myocardial apoptosis through IRE-1-CRYAB pathway in myocardial ischemia

ETHNOPHARMACOLOGICAL RELEVANCE

Qishen Granule (QSG) is a prevailing traditional Chinese medicine formula that displays impressive cardiovascular protection in clinical. However, underlying mechanisms by which QSG alleviates endoplasmic reticulum (ER) stress-induced apoptosis in myocardial ischemia still remain unknown.

AIM OF THE STUDY

This study aims to elucidate whether QSG ameliorates ER stress-induced myocardial apoptosis to protect against myocardial ischemia via inositol requiring enzyme 1 (IRE-1)-αBcrystallin (CRYAB) signaling pathway.

MATERIALS AND METHODS

Left anterior descending (LAD) ligation induced-ischemic heart model and oxygen-glucose deprivation-reperfusion (OGD/R)-induced H9C2 cells injury model were established to clarify the effects and potential mechanism of QSG. Ethanol extracts of QSG (2.352 g/kg) were orally administered for four weeks and Ginaton Tablets (100 mg/kg) was selected as a positive group in vivo. In vitro, QSG (800 μg/ml) or STF080310 (an inhibitor of IRE-1, 10 μM) was co-cultured under OGD/R in H9C2 cells. Inhibition of IRE-1 was conducted in H9C2 cells to further confirm the exact mechanism. Finally, to define the active components of anti-cardiomyocyte apoptosis in QSG which absorbed into the blood, we furtherly used the OGD/R-induced cardiomyocyte apoptosis model to evaluate the effects.

RESULTS

QSG treatment improved cardiac function, ameliorated inflammatory cell infiltration and myocardial apoptosis. Similar effects were revalidated in OGD/R-induced H9C2 injury model. Western blots demonstrated QSG exerted anti-apoptotic effects by regulating apoptosis-related proteins, including increasing Bcl-2 and caspase 3/12, reducing the expressions of Bax and cleaved-caspase 3/12. Mechanistically, the IRE-1-CRYAB signaling pathway was significantly activated by QSG. Co-treatment with STF080310, the IRE-1 specific inhibitor significantly compromised the protective effects of QSG in vitro. Especially, the active components of QSG including Formononetin, Tanshinone IIA, Tanshinone I, Cryptotanshinon and Harpagoside showed significantly anti-apoptosis effects.

CONCLUSION

QSG protected against ER stress-induced myocardial apoptosis via the IRE-1-CRYAB pathway, which is proposed as a promising therapeutic target for myocardial ischemia.

Biology of Inherited Cataracts and Opportunities for Treatment

Cataract, the clinical correlate of opacity or light scattering in the eye lens, is usually caused by the presence of high-molecular-weight (HMW) protein aggregates or disruption of the lens microarchitecture. In general, genes involved in inherited cataracts reflect important processes and pathways in the lens including lens crystallins, connexins, growth factors, membrane proteins, intermediate filament proteins, and chaperones. Usually, mutations causing severe damage to proteins cause congenital cataracts, while milder variants increasing susceptibility to environmental insults are associated with age-related cataracts. These may have different pathogenic mechanisms: Congenital cataracts induce the unfolded protein response and apoptosis. By contrast, denatured crystallins in age-related cataracts are bound by α-crystallin and form light-scattering HMW aggregates. New therapeutic approaches to age-related cataracts use chemical chaperones to solubilize HMW aggregates, while attempts are being made to regenerate lenses using endogenous stem cells to treat congenital cataracts.

Transcriptional profiling of single fiber cells in a transgenic paradigm of an inherited childhood cataract reveals absence of molecular heterogeneity

Our recent single-cell transcriptomic analysis has demonstrated that heterogeneous transcriptional activity attends molecular transition from the nascent to terminally differentiated fiber cells in the developing mouse lens. To understand the role of transcriptional heterogeneity in terminal differentiation and the functional phenotype (transparency) of this tissue, here we present a single-cell analysis of the developing lens, in a transgenic paradigm of an inherited pathology, known as the lamellar cataract. Cataracts hinder transmission of light into the eye. Lamellar cataract is the most prevalent bilateral childhood cataract. In this disease of early infancy, initially, the opacities remain confined to a few fiber cells, thus presenting an opportunity to investigate early molecular events that lead to cataractogenesis. We used a previously established paradigm that faithfully recapitulates this disease in transgenic mice. About 500 single fiber cells, manually isolated from a 2-day-old transgenic lens were interrogated individually for the expression of all known 17 crystallins and 78 other relevant genes using a Biomark HD (Fluidigm). We find that fiber cells from spatially and developmentally discrete regions of the transgenic (cataract) lens show remarkable absence of the heterogeneity of gene expression. Importantly, the molecular variability of cortical fiber cells, the hallmark of the WT lens, is absent in the transgenic cataract, suggesting absence of specific cell-type(s). Interestingly, we find a repetitive pattern of gene activity in progressive states of differentiation in the transgenic lens. This molecular dysfunction portends pathology much before the physical manifestations of the disease.

CRYAB protects cardiomyocytes against heat stress by preventing caspase-mediated apoptosis and reducing F-actin aggregation

CRYAB is a small heat shock protein (sHSP) that has previously been shown to protect the heart against various cellular stresses; however, its precise function in myocardial cell injury caused by heat stress remains unclear. This study aimed to investigate the molecular mechanism by which CRYAB protects cardiomyocytes against heat stress. We constructed two H9C2 cell lines that stably express CRYAB protein to differing degrees: CRYAB-5 and CRYAB-7. Both CRYAB-5 and CRYAB-7 showed significantly reduced granular degeneration and vacuolar degeneration following heat stress compared to control cells. In addition, CRYAB overexpression in H9C2 cells relieved cell cycle proportion at the G0/G1 phase following heat stress compared to control cells. These protective effects were associated with the level of CRYAB protein expression. Our immunofluorescence analysis showed CRYAB could translocate from the cytoplasm to the nucleus under heat stress conditions, but that CRYAB co-localized with F-actin (which accumulates under stress conditions). Indeed, overexpression of CRYAB significantly reduced the aggregation of F-actin in H9C2 cells caused by heat stress. Furthermore, overexpressing CRYAB protein significantly reduced the apoptosis of cardiomyocytes induced by heat stress, likely by reducing the expression of cleaved-caspase 3. Collectively, our results show overexpression of CRYAB significantly increases the heat resistance of H9C2 cardiomyocytes, likely by reducing F-actin aggregation (thus stabilizing the cytoskeleton), regulating the cell cycle, and preventing caspase-mediated apoptosis.

The p75NTR-mediated effect of nerve growth factor in L6C5 myogenic cells

OBJECTIVE

During muscle development or regeneration, myocytes produce nerve growth factor (NGF) as well as its tyrosine-kinase and p75-neurotrophin (p75NTR) receptors. It has been published that the p75NTR receptor could represent a key regulator of NGF-mediated myoprotective effect on satellite cells, but the precise function of NGF/p75 signaling pathway on myogenic cell proliferation, survival and differentiation remains fragmented and controversial. Here, we verified the role of NGF in the growth, survival and differentiation of p75NTR-expressing L6C5 myogenic cells, specifically inquiring for the putative involvement of the nuclear factor κB (NFκB) and the small heat shock proteins (sHSPs) αB-crystallin and Hsp27 in these processes.

RESULTS

Although NGF was not effective in modulating myogenic cell growth or survival in both standard or stress conditions, we demonstrated for the first time that, under serum deprivation, NGF sustained the activity of some key enzymes involved in energy metabolism. Moreover, we confirmed that NGF promotes myogenic fusion and expression of the structural protein myosin heavy chain while modulating NFκB activation and the content of sHSPs correlated with the differentiation process. We conclude that p75NTR is sufficient to mediate the modulation of L6C5 myogenic differentiation by NGF in term of structural, metabolic and functional changes.

High-Throughput Genetic Screening of 51 Pediatric Cataract Genes Identifies Causative Mutations in Inherited Pediatric Cataract in South Eastern Australia

Pediatric cataract is a leading cause of childhood blindness. This study aimed to determine the genetic cause of pediatric cataract in Australian families by screening known disease-associated genes using massively parallel sequencing technology. We sequenced 51 previously reported pediatric cataract genes in 33 affected individuals with a family history (cases with previously known or published mutations were excluded) using the Ion Torrent Personal Genome Machine. Variants were prioritized for validation if they were predicted to alter the protein sequence and were absent or rare with minor allele frequency <1% in public databases. Confirmed mutations were assessed for segregation with the phenotype in all available family members. All identified novel or previously reported cataract-causing mutations were screened in 326 unrelated Australian controls. We detected 11 novel mutations in GJA3, GJA8, CRYAA, CRYBB2, CRYGS, CRYGA, GCNT2, CRYGA, and MIP; and three previously reported cataract-causing mutations in GJA8, CRYAA, and CRYBB2 The most commonly mutated genes were those coding for gap junctions and crystallin proteins. Including previous reports of pediatric cataract-associated mutations in our Australian cohort, known genes account for >60% of familial pediatric cataract in Australia, indicating that still more causative genes remain to be identified.

Upregulation and phosphorylation of HspB1/Hsp25 and HspB5/αB-crystallin after transient middle cerebral artery occlusion in rats

Ischemic stroke leads to cellular dysfunction, cell death, and devastating clinical outcomes. The cells of the brain react to such a cellular stress by a stress response with an upregulation of heat shock proteins resulting in activation of endogenous neuroprotective capacities. Several members of the family of small heat shock proteins (HspBs) have been shown to be neuroprotective. However, yet no systematic study examined all HspBs during cerebral ischemia. Here, we performed a comprehensive comparative study comprising all HspBs in an animal model of stroke, i.e., 1 h transient middle cerebral artery occlusion followed by 23 h of reperfusion. On the mRNA level out of the 11 HspBs investigated, HspB1/Hsp25, HspB3, HspB4/αA-crystallin, HspB5/αB-crystallin, HspB7/cvHsp, and HspB8/Hsp22 were significantly upregulated in the peri-infarct region of the cerebral cortex of infarcted hemispheres. HspB1 and HspB5 reached the highest mRNA levels and were also upregulated at the protein level, suggesting that these HspBs might be functionally most relevant. Interestingly, in the infarcted cortex, both HspB1 and HspB5 were mainly allocated to neurons and to a lesser extent to glial cells. Additionally, both proteins were found to be phosphorylated in response to ischemia. Our data suggest that among all HspBs, HspB1 and HspB5 might be most important in the neuronal stress response to ischemia/reperfusion injury in the brain and might be involved in neuroprotection.

Correlations of single nucleotide polymorphisms of CRYAA and CRYAB genes with the risk and clinicopathological features of children suffering from congenital cataract

BACKGROUND

The study aims to explore the correlations of the single nucleotide polymorphisms (SNPs) of CRYAA and CRYAB with the risk and clinicopathological features of children with congenital cataract.

METHODS

The study enrolled 168 children diagnosed as congenital cataract (case group) and 172 normal children (control group) from May 2015 to May 2016. Genomic DNA extraction was performed using a QIAamp DNA blood mini kit. Polymerase chain reaction (PCR) products were genotyped using an ABI direct sequencer. Haplotype, allele, and genotype frequencies of CRYAA and CRYAB gene polymorphisms analyses were carried out using the SHEsis software. Logistic regression analysis was performed in order to analyze the risk factors for children suffering from congenital cataract.

RESULTS

Presence of significant differences between the case and control groups' genotype and allele frequencies of CRYAA rs7278468 and CRYAB rs370803064/rs387907338. TA of CRYAB gene might increase congenital cataract risk in children, while GCG of CRYAA gene and GC of CRYAB gene might decrease congenital cataract risk in children. CRYAA rs7278468, CRYAB rs370803064/rs387907338 polymorphisms were significantly correlated to uncorrected visual acuity, best-corrected visual acuity, nystagmus, visual axis opacification, microcornea, lens opacity, posterior capsular thickening, and degrees of posterior capsule opacification after operation in children with congenital cataract. Logistic regression analysis revealed that the T allele of CRYAA rs7278468, A allele of CRYAB rs370803064, T allele of CRYAB rs387907338, family history, and TA haplotype of CRYAB gene were risk factors for children with congenital cataract.

CONCLUSION

Our findings demonstrated that CRYAA rs7278468 and CRYAB rs370803064/rs387907338 are correlated with the risk and clinicopathological features of children suffering from congenital cataract.

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.

Tryptophan and Non-Tryptophan Fluorescence of the Eye Lens Proteins Provides Diagnostics of Cataract at the Molecular Level

The chemical nature of the non-tryptophan (non-Trp) fluorescence of porcine and human eye lens proteins was identified by Mass Spectrometry (MS) and Fluorescence Steady-State and Lifetime spectroscopy as post-translational modifications (PTM) of Trp and Arg amino acid residues. Fluorescence intensity profiles measured along the optical axis of human eye lenses with age-related nuclear cataract showed increasing concentration of fluorescent PTM towards the lens centre in accord with the increased optical density in the lens nucleolus. Significant differences between fluorescence lifetimes of "free" Trp derivatives hydroxytryptophan (OH-Trp), N-formylkynurenine (NFK), kynurenine (Kyn), hydroxykynurenine (OH-Kyn) and their residues were observed. Notably, the lifetime constants of these residues in a model peptide were considerably greater than those of their "free" counterparts. Fluorescence of Trp, its derivatives and argpyrimidine (ArgP) can be excited at the red edge of the Trp absorption band which allows normalisation of the emission spectra of these PTMs to the fluorescence intensity of Trp, to determine semi-quantitatively their concentration. We show that the cumulative fraction of OH-Trp, NFK and ArgP emission dominates the total fluorescence spectrum in both emulsified post-surgical human cataract protein samples, as well as in whole lenses and that this correlates strongly with cataract grade and age.

Structural and functional consequences of chaperone site deletion in αA-crystallin

The chaperone-like activity of αA-crystallin has an important role in maintaining lens transparency. Previously we identified residues 70-88 as a chaperone site in αA-crystallin. In this study, we deleted the chaperone site residues to generate αAΔ70-76 and αAΔ70-88 mutants and investigated if there are additional substrate-binding sites in αA-crystallin. Both mutant proteins when expressed in E. coli formed inclusion bodies, and on solubilizing and refolding, they exhibited similar structural properties, with a 2- to 3-fold increase in molar mass compared to the molar mass of wild-type protein. The deletion mutants were less stable than the wild-type αA-crystallin. Functionally αAΔ70-88 was completely inactive as a chaperone, while αAΔ70-76 demonstrated a 40-50% reduction in anti-aggregation activity against alcohol dehydrogenase (ADH). Deletion of residues 70-88 abolished the ADH binding sites in αA-crystallin at physiological temperature. At 45°C, cryptic ADH binding site(s) became exposed, which contributed subtly to the chaperone-like activity of αAΔ70-88. Both of the deletion mutants were completely inactive in suppressing aggregation of βL-crystallin at 53°C. The mutants completely lost the anti-apoptotic property that αA-crystallin exhibits while they protected ARPE-19 (a human retinal pigment epithelial cell line) and primary human primary lens epithelial (HLE) cells from oxidative stress. Our studies demonstrate that residues 70-88 in αA-crystallin act as a primary substrate binding site and account for the bulk of the total chaperone activity. The β3 and β4 strands in αA-crystallin comprising 70-88 residues play an important role in maintenance of the structure and in preventing aggregation of denaturing proteins.

Sporadic and Familial Congenital Cataracts: Mutational Spectrum and New Diagnoses Using Next-Generation Sequencing

Congenital cataracts are a significant cause of lifelong visual loss. They may be isolated or associated with microcornea, microphthalmia, anterior segment dysgenesis (ASD) and glaucoma, and there can be syndromic associations. Genetic diagnosis is challenging due to marked genetic heterogeneity. In this study, next-generation sequencing (NGS) of 32 cataract-associated genes was undertaken in 46 apparently nonsyndromic congenital cataract probands, around half sporadic and half familial cases. We identified pathogenic variants in 70% of cases, and over 68% of these were novel. In almost two-thirds (20/33) of these cases, this resulted in new information about the diagnosis and/or inheritance pattern. This included identification of: new syndromic diagnoses due to NHS or BCOR mutations; complex ocular phenotypes due to PAX6 mutations; de novo autosomal-dominant or X-linked mutations in sporadic cases; and mutations in two separate cataract genes in one family. Variants were found in the crystallin and gap junction genes, including the first report of severe microphthalmia and sclerocornea associated with a novel GJA8 mutation. Mutations were also found in rarely reported genes including MAF, VIM, MIP, and BFSP1. Targeted NGS in presumed nonsyndromic congenital cataract patients provided significant diagnostic information in both familial and sporadic cases.

CRYβA3/A1-Crystallin Knockout Develops Nuclear Cataract and Causes Impaired Lysosomal Cargo Clearance and Calpain Activation

βA3/A1-crystallin is an abundant structural protein of the lens that is very critical for lens function. Many different genetic mutations have been shown to associate with different types of cataracts in humans and in animal models. βA3/A1-crystallin has four Greek key-motifs that organize into two crystallin domains. It shown to bind calcium with moderate affinity and has putative calcium-binding site. Other than in the lens, βA3/A1 is also expressed in retinal astrocytes, retinal pigment epithelial (RPE) cells, and retinal ganglion cells. The function of βA3/A1-crystallin in the retinal cell types is well studied; however, a clear understanding of the function of this protein in the lens has not yet been established. In the current study, we generated the βA3/A1-crystallin knockout (KO) mouse and explored the function of βA3/A1-crystallin in lens development. Our results showed that βA3-KO mice develop congenital nuclear cataract and exhibit persistent fetal vasculature condition. At the cellular level KO lenses show defective lysosomal clearance and accumulation of nuclei, mitochondria, and autophagic cargo in the outer cortical region of the lens. In addition, the calcium level and the expression and activity of calpain-3 were increased in KO lenses. Taken together, these results suggest the lack of βA3-crystallin function in lenses, alters calcium homeostasis which in turn causes lysosomal defects and calpain activation. These defects are responsible for the development of nuclear cataract in KO lenses.

Interaction of βA3-Crystallin with Deamidated Mutants of αA- and αB-Crystallins

Interaction among crystallins is required for the maintenance of lens transparency. Deamidation is one of the most common post-translational modifications in crystallins, which results in incorrect interaction and leads to aggregate formation. Various studies have established interaction among the α- and β-crystallins. Here, we investigated the effects of the deamidation of αA- and αB-crystallins on their interaction with βA3-crystallin using surface plasmon resonance (SPR) and fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET) methods. SPR analysis confirmed adherence of WT αA- and WT αB-crystallins and their deamidated mutants with βA3-crystallin. The deamidated mutants of αA–crystallin (αA N101D and αA N123D) displayed lower adherence propensity for βA3-crystallin relative to the binding affinity shown by WT αA-crystallin. Among αB-crystallin mutants, αB N78D displayed higher adherence propensity whereas αB N146D mutant showed slightly lower binding affinity for βA3-crystallin relative to that shown by WT αB-crystallin. Under the in vivo condition (FLIM-FRET), both αA-deamidated mutants (αA N101D and αA N123D) exhibited strong interaction with βA3-crystallin (32±4% and 36±4% FRET efficiencies, respectively) compared to WT αA-crystallin (18±4%). Similarly, the αB N78D and αB N146D mutants showed strong interaction (36±4% and 22±4% FRET efficiencies, respectively) with βA3-crystallin compared to 18±4% FRET efficiency of WT αB-crystallin. Further, FLIM-FRET analysis of the C-terminal domain (CTE), N-terminal domain (NTD), and core domain (CD) of αA- and αB-crystallins with βA3-crystallin suggested that interaction sites most likely reside in the αA CTE and αB NTD regions, respectively, as these domains showed the highest FRET efficiencies. Overall, results suggest that similar to WT αA- and WTαB-crystallins, the deamidated mutants showed strong interactionfor βA3-crystallin. Variable in vitro and in vivo interactions are most likely due to the mutant’s large size oligomers, reduced hydrophobicity, and altered structures. Together, the results suggest that deamidation of α-crystallin may facilitate greater interaction and the formation of large oligomers with other crystallins, and this may contribute to the cataractogenic mechanism.

The impact of Hydrogen peroxide on structure, stability and functional properties of Human R12C mutant αA-crystallin: The imperative insights into pathomechanism of the associated congenital cataract incidence

The oxidative stress in eye lens which occurs during inflammation and under chronic hyperglycemia has been already indicated in the pathogenesis of cataract disorders. The aim of this study was to examine structural and functional properties of R12C mutant αA-Crystallin (αA-Cry) in the presence of hydrogen peroxide. The study was done using different spectroscopic techniques and gel mobility shift assay. According to results of our study, H2O2 oxidation strongly compromises the chaperone function of the R12C mutant but not of wild-type αA-Cry. Also, it affects the structural properties of both wild-type and mutant proteins, albeit to different degree. The H2O2 exposure promotes extensive disulfide mediated oligomerization of the R12C mutant but not of the wild-type as revealed by gel mobility shift assay and dynamic light scattering. Moreover, in the presence of hydrogen peroxide, the mutant protein demonstrates severe conformational and protease instability and increased amyloidogenic propensity. The obtained results suggest that incubation of R12C mutant recombinant αA-Cry with hydrogen peroxide accelerates the molecular events which have been already implicated in the pathomechanism of cataract development. Taken together these results suggest that individuals carrying the R12C mutation are at an increased risk to develop early-onset cataract under condition of oxidative stress.

Rescue of αB Crystallin (HSPB5) Mutants Associated Protein Aggregation by Co-Expression of HSPB5 Partners

HSPB5 (also called αB-crystallin) is a ubiquitously expressed small heat shock protein. Mutations in HSPB5 have been found to cause cataract, but are also associated with a subgroup of myofibrillar myopathies. Cells expressing each of these HSPB5 mutants are characterized by the appearance of protein aggregates of primarily the mutant HSPB5. Like several members of the HSPB family, HSPB5 can form both homo-oligomeric and hetero-oligomeric complexes. Previous studies showed that co-expression of HSPB1 and HSPB8 can prevent the aggregation associated with the HSPB5 (R120G) mutant in cardiomyocytes and in transgenic mice. In this study, we systematically compared the effect of co-expression of each of the members of the human HSPB family (HSPB1-10) on the aggregation of three different HSPB5 mutants (R120G, 450 Δ A, 464 Δ CT). Of all members, co-expression of HSPB1, HSPB4 and HSPB5 itself, most effectively prevent the aggregation of these 3 HSPB5 mutants. HSPB6 and HSPB8 were also active but less, whilst the other 5 HSPB members were ineffective. Co-expression of Hsp70 did not reduce the aggregation of the HSPB5 mutants, suggesting that aggregate formation is most likely not related to a toxic gain of function of the mutants per se, but rather related to a loss of chaperone function of the oligomeric complexes containing the HSPB5 mutants (dominant negative effects). Our data suggest that the rescue of aggregation associated with the HSPB5 mutants is due to competitive incorporation of its partners into hetero-oligomers hereby negating the dominant negative effects of the mutant on the functioning of the hetero-oligomer.

Follicular thyroglobulin enhances gene expression necessary for thyroid hormone secretion

We have previously shown that follicular thyroglobulin (Tg) has an unexpected function as an autocrine negative-feedback regulator of thyroid hormone (TH) biosynthesis. Tg significantly suppressed the expression of genes necessary for iodide transport and TH synthesis by counteracting stimulation by TSH. However, whether follicular Tg also regulates intracellular TH transport and its secretion from thyrocytes is not known. In the present study, we examined the potential effect of follicular Tg on TH transport and secretion by quantifying the expression of two TH transporters: monocarboxylate transporter 8 (MCT8) and μ-crystallin (CRYM). Our results showed that follicular Tg at physiologic concentrations enhanced both the mRNA and protein expression levels of MCT8 and CRYM in a time- and dose-dependent manner in rat thyroid FRTL-5 cells. Although both the sodium/iodide symporter (NIS), an essential transporter of iodide from blood into the thyroid, and MCT8, a transporter of synthesized TH from the gland, were co-localized on the basolateral membrane of rat thyrocytes in vivo, Tg decreased NIS expression and increased the expression of MCT8 by counteracting TSH action. Thus, the effect of Tg on TH secretion opposed its previously described negative-feedback suppression of TH synthesis. Our results indicate that Tg mediates a complex intrinsic regulation of gene expression that is necessary to balance two opposing vectorial transport systems: the inflow of newly synthesized TH and the outflow of TH by external secretion.

Expression of truncated PITX3 in the developing lens leads to microphthalmia and aphakia in mice

Microphthalmia is a severe ocular disorder, and this condition is typically caused by mutations in transcription factors that are involved in eye development. Mice carrying mutations in these transcription factors would be useful tools for defining the mechanisms underlying developmental eye disorders. We discovered a new spontaneous recessive microphthalmos mouse mutant in the Japanese wild-derived inbred strain KOR1/Stm. The homozygous mutant mice were histologically characterized as microphthalmic by the absence of crystallin in the lens, a condition referred to as aphakia. By positional cloning, we identified the nonsense mutation c.444C>A outside the genomic region that encodes the homeodomain of the paired-like homeodomain transcription factor 3 gene (Pitx3) as the mutation responsible for the microphthalmia and aphakia. We examined Pitx3 mRNA expression of mutant mice during embryonic stages using RT-PCR and found that the expression levels are higher than in wild-type mice. Pitx3 over-expression in the lens during developmental stages was also confirmed at the protein level in the microphthalmos mutants via immunohistochemical analyses. Although lens fiber differentiation was not observed in the mutants, strong PITX3 protein signals were observed in the lens vesicles of the mutant lens. Thus, we speculated that abnormal PITX3, which lacks the C-terminus (including the OAR domain) as a result of the nonsense mutation, is expressed in mutant lenses. We showed that the expression of the downstream genes Foxe3, Prox1, and Mip was altered because of the Pitx3 mutation, with large reductions in the lens vesicles in the mutants. Similar profiles were observed by immunohistochemical analysis of these proteins. The expression profiles of crystallins were also altered in the mutants. Therefore, we speculated that the microphthalmos/aphakia in this mutant is caused by the expression of truncated PITX3, resulting in the abnormal expression of downstream targets and lens fiber proteins.

In vivo substrates of the lens molecular chaperones αA-crystallin and αB-crystallin

αA-crystallin and αB-crystallin are members of the small heat shock protein family and function as molecular chaperones and major lens structural proteins. Although numerous studies have examined their chaperone-like activities in vitro, little is known about the proteins they protect in vivo. To elucidate the relationships between chaperone function, substrate binding, and human cataract formation, we used proteomic and mass spectrometric methods to analyze the effect of mutations associated with hereditary human cataract formation on protein abundance in αA-R49C and αB-R120G knock-in mutant lenses. Compared with age-matched wild type lenses, 2-day-old αA-R49C heterozygous lenses demonstrated the following: increased crosslinking (15-fold) and degradation (2.6-fold) of αA-crystallin; increased association between αA-crystallin and filensin, actin, or creatine kinase B; increased acidification of βB1-crystallin; increased levels of grifin; and an association between βA3/A1-crystallin and αA-crystallin. Homozygous αA-R49C mutant lenses exhibited increased associations between αA-crystallin and βB3-, βA4-, βA2-crystallins, and grifin, whereas levels of βB1-crystallin, gelsolin, and calpain 3 decreased. The amount of degraded glutamate dehydrogenase, α-enolase, and cytochrome c increased more than 50-fold in homozygous αA-R49C mutant lenses. In αB-R120G mouse lenses, our analyses identified decreased abundance of phosphoglycerate mutase, several β- and γ-crystallins, and degradation of αA- and αB-crystallin early in cataract development. Changes in the abundance of hemoglobin and histones with the loss of normal α-crystallin chaperone function suggest that these proteins also play important roles in the biochemical mechanisms of hereditary cataracts. Together, these studies offer a novel insight into the putative in vivo substrates of αA- and αB-crystallin.

Strain-independent increases of crystallin proteins in the retina of type 1 diabetic rats

Diabetic retinopathy is the leading cause of vision loss in working-age individuals in the United States and is expected to continue growing with the increased prevalence of diabetes. Streptozotocin-induced hyperglycemia in rats is the most commonly used model for diabetic retinopathy. Previous studies have shown that this model can lead to different inflammatory changes in the retina depending on the strain of rat. Our previous work has shown that crystallin proteins, including members of the alpha- and beta/gamma-crystallin subfamilies, are upregulated in the STZ rat retina. Crystallin proteins have been implicated in a number of cellular processes, such as neuroprotection, non-native protein folding and vascular remodeling. In this current study, we have demonstrated that unlike other strain-dependent changes, such as inflammatory cytokines and growth factor levels, in the STZ rat, the protein upregulation of crystallins is consistent across the Brown Norway, Long-Evans and Sprague-Dawley rat strains in the context of diabetes. Taken together, these data illustrate the potential critical role played by crystallins, and especially alpha-crystallins, in the retina in the context of diabetes.

Molecular and structural analysis of genetic variations in congenital cataract

OBJECTIVE

To determine the relative contributions of mutations in congenital cataract cases in an Indian population by systematic screening of genes associated with cataract.

METHODS

We enrolled 100 congenital cataract cases presenting at the Dr. R. P. Centre for Ophthalmic Sciences, a tertiary research and referral hospital (AIIMS, New Delhi, India). Crystallin, alpha A (CRYAA), CRYAB, CRYGs, CRYBA1, CRYBA4, CRYBB1, CRYBB2, CRYBB3, beaded filament structural protein 1 (BFSP1), gap function protein, alpha 3 (GJA3), GJA8, and heat shock transcription factor 4 gene genes were amplified. Protein structure differences analysis was performed using Discovery Studio (DS) 2.0.

RESULTS

The mean age of the patients was 17.45±16.51 months, and the age of onset was 1.618±0.7181 months. Sequencing analysis of 14 genes identified 18 nucleotide variations. Fourteen variations were found in the crystallin genes, one in Cx-46 (GJA3), and three in BFSP1.

CONCLUSIONS

Congenital cataract shows marked clinical and genetic heterogeneity. Five nucleotide variations (CRYBA4:p.Y67N, CRYBB1:p.D85N, CRYBB1:p.E75K, CRYBB1:p.E155K, and GJA3:p.M1V) were predicted to be pathogenic. Variants in other genes might also be involved in maintaining lens development, growth, and transparency. The study confirms that the crystallin beta cluster on chromosome 22, Cx-46, and BFSP1 plays a major role in maintaining lens transparency. This study also expands the mutation spectrum of the genes associated with congenital cataract.

Ectopic activation of Wnt/β-catenin signaling in lens fiber cells results in cataract formation and aberrant fiber cell differentiation

The Wnt/β-catenin signaling pathway controls many processes during development, including cell proliferation, cell differentiation and tissue homeostasis, and its aberrant regulation has been linked to various pathologies. In this study we investigated the effect of ectopic activation of Wnt/β-catenin signaling during lens fiber cell differentiation. To activate Wnt/β-catenin signaling in lens fiber cells, the transgenic mouse referred to as αA-CLEF was generated, in which the transactivation domain of β-catenin was fused to the DNA-binding protein LEF1, and expression of the transgene was controlled by αA-crystallin promoter. Constitutive activation of Wnt/β-catenin signaling in lens fiber cells of αA-CLEF mice resulted in abnormal and delayed fiber cell differentiation. Moreover, adult αA-CLEF mice developed cataract, microphthalmia and manifested downregulated levels of γ-crystallins in lenses. We provide evidence of aberrant expression of cell cycle regulators in embryonic lenses of αA-CLEF transgenic mice resulting in the delay in cell cycle exit and in the shift of fiber cell differentiation to the central fiber cell compartment. Our results indicate that precise regulation of the Wnt/β-catenin signaling activity during later stages of lens development is essential for proper lens fiber cell differentiation and lens transparency.