The molecular chaperone alphaA-crystallin enhances lens epithelial cell growth and resistance to UVA stress

Molecular Chaperones as Therapeutic Target: Hallmark of Neurodegenerative Disorders

Misfolded and aggregated proteins build up in neurodegenerative illnesses, which causes neuronal dysfunction and ultimately neuronal death. In the last few years, there has been a significant upsurge in the level of interest towards the function of molecular chaperones in the control of misfolding and aggregation. The crucial molecular chaperones implicated in neurodegenerative illnesses are covered in this review article, along with a variety of their different methods of action. By aiding in protein folding, avoiding misfolding, and enabling protein breakdown, molecular chaperones serve critical roles in preserving protein homeostasis. By aiding in protein folding, avoiding misfolding, and enabling protein breakdown, molecular chaperones have integral roles in preserving regulation of protein balance. It has been demonstrated that aging, a significant risk factor for neurological disorders, affects how molecular chaperones function. The aggregation of misfolded proteins and the development of neurodegeneration may be facilitated by the aging-related reduction in chaperone activity. Molecular chaperones have also been linked to the pathophysiology of several instances of neuron withering illnesses, enumerating as Parkinson's disease, Huntington's disease, and Alzheimer's disease. Molecular chaperones have become potential therapy targets concerning with the prevention and therapeutic approach for brain disorders due to their crucial function in protein homeostasis and their connection to neurodegenerative illnesses. Protein homeostasis can be restored, and illness progression can be slowed down by methods that increase chaperone function or modify their expression. This review emphasizes the importance of molecular chaperones in the context of neuron withering disorders and their potential as therapeutic targets for brain disorders.

Self-reported cataract surgery and 10-year all-cause and cause-specific mortality: findings from the National Health and Nutrition Examination Survey

PURPOSE

To investigate the association of self-reported cataract surgery with all-cause and cause-specific mortality using a large-scale population-based sample.

METHODS

Data from the 1999-2008 cycles of the National Health and Nutrition Examination Survey were used. A self-reported history of cataract surgery was considered a surrogate for the presence of clinically significant cataract surgery. Mortality data were ascertained from National Death Index records. Hazard ratios (HRs) and 95% confidence intervals (CIs) for survival were estimated using Cox proportional hazards regression models.

RESULTS

A total of 14 918 participants were included in the analysis. During a median follow-up of 10.8 (Interquartile range, IQR, 8.25-13.7) years, 3966 (19.1%) participants died. Participants with self-reported cataract surgery were more likely to die from all causes and specific causes (vascular disease, cancer, accident, Alzheimer's disease, respiratory disease, renal disease and others) compared with those without (all Ps <0.05). The association between self-reported cataract surgery and all-cause mortality remained significant after multiple adjustments (HR=1.13; 95% CI 1.01 to 1.26). For cause-specific mortality, multivariable Cox models showed that self-reported cataract surgery predicted a 36% higher risk of vascular-related mortality (HR=1.36; 95% CI 1.01 to 1.82). The association with other specific causes of mortality did not reach statistical significance after multiple adjustments.

CONCLUSIONS

This study found significant associations of self-reported cataract surgery with all-cause and vascular mortalities. Our findings provide potential insights into the pathogenic pathways underlying cataract.

Environmentally relevant concentrations of F-53B induce eye development disorders-mediated locomotor behavior in zebrafish larvae

The perfluorooctane sulfonate alternative, F-53B, induces multiple physiological defects but whether it can disrupt eye development is unknown. We exposed zebrafish to F-53B at four different concentrations (0, 0.15, 1.5, and 15 μg/L) for 120 h post-fertilization (hpf). Locomotor behavior, neurotransmitters content, histopathological alterations, morphological changes, cell apoptosis, and retinoic acid signaling were studied. Histology and morphological analyses showed that F-53B induced pathological changes in lens and retina of larvae and eye size were significantly reduced as compared to control. Acridine orange (AO) staining revealed a dose-dependent increase in early apoptosis, accompanied by upregulation of p53, casp-9 and casp-3 genes. Genes related to retinoic acid signaling (aldh1a2), lens developmental (cryaa, crybb, crygn, and mipa) and retinal development (pax6, rx1, gant1, rho, opn1sw and opn1lw) were significantly downregulated. In addition, behavioral responses (swimming speed) were significantly increased, while no significant changes in the neurotransmitters (dopamine and acetylcholine) level were observed. Therefore, in this study we observed that exposure to F-53B inflicted histological and morphological changes in zebrafish larvae eye, induced visual motor dysfunctions, perturbed retinoid signaling and retinal development and ultimately triggering apoptosis.

The Role of Small Heat Shock Proteins in Protein Misfolding Associated Motoneuron Diseases

Motoneuron diseases (MNDs) are neurodegenerative conditions associated with death of upper and/or lower motoneurons (MNs). Proteostasis alteration is a pathogenic mechanism involved in many MNDs and is due to the excessive presence of misfolded and aggregated proteins. Protein misfolding may be the product of gene mutations, or due to defects in the translation process, or to stress agents; all these conditions may alter the native conformation of proteins making them prone to aggregate. Alternatively, mutations in members of the protein quality control (PQC) system may determine a loss of function of the proteostasis network. This causes an impairment in the capability to handle and remove aberrant or damaged proteins. The PQC system consists of the degradative pathways, which are the autophagy and the proteasome, and a network of chaperones and co-chaperones. Among these components, Heat Shock Protein 70 represents the main factor in substrate triage to folding, refolding, or degradation, and it is assisted in this task by a subclass of the chaperone network, the small heat shock protein (sHSPs/HSPBs) family. HSPBs take part in proteostasis by bridging misfolded and aggregated proteins to the HSP70 machinery and to the degradative pathways, facilitating refolding or clearance of the potentially toxic proteins. Because of its activity against proteostasis alteration, the chaperone system plays a relevant role in the protection against proteotoxicity in MNDs. Here, we discuss the role of HSPBs in MNDs and which HSPBs may represent a valid target for therapeutic purposes.

Methodologies to unlock the molecular expression and cellular structure of ocular lens epithelial cells

The transparent ocular lens in the anterior chamber of the eye is responsible for fine focusing of light onto the retina. The lens is entirely cellular with bulk of the tissue composed of fiber cells, and the anterior hemisphere of the lens is covered by a monolayer of epithelial cells. Lens epithelial cells are important for maintaining fiber cell homeostasis and for continual growth of the lens tissue throughout life. Cataracts, defined as any opacity in the lens, remain the leading cause of blindness in the world. Following cataract surgery, lens epithelial cells can undergo a process of epithelial-to-mesenchymal transition (EMT), leading to secondary cataracts due to posterior capsular opacification (PCO). Since the epithelial cells make up only a small fraction of the lens, specialized techniques are required to study lens epithelial cell biology and pathology. Studies using native lens epithelial cells often require pooling of samples to obtain enough cells to make sufficient samples for traditional molecular biology techniques. Here, we provide detailed protocols that enable the study of native mouse lens epithelial cells, including immunostaining of the native lens epithelium in flat mounts, extraction of RNA and proteins from pairs of lens epithelial monolayers, and isolation of lens epithelial cells for primary culture. These protocols will enable researchers to gain better insight on representative molecular expression and cellular structure of lens epithelial cells. We also provide comparative data between native, primary culture, and immortalized lens epithelial cells and discuss the advantages and disadvantages of each technique presented.

Proposed Role for Internal Lens Pressure as an Initiator of Age-Related Lens Protein Aggregation Diseases

The process that initiates lens stiffness evident in age-related lens protein aggregation diseases is thought to be mainly the result of oxidation. While oxidation is a major contributor, the exposure of lens proteins to physical stress over time increases susceptibility of lens proteins to oxidative damage, and this is believed to play a significant role in initiating these diseases. Accordingly, an overview of key physical stressors and molecular factors known to be implicated in the development of age-related lens protein aggregation diseases is presented, paying particular attention to the consequence of persistent increase in internal lens pressure.

Insights on Human Small Heat Shock Proteins and Their Alterations in Diseases

The family of the human small Heat Shock Proteins (HSPBs) consists of ten members of chaperones (HSPB1-HSPB10), characterized by a low molecular weight and capable of dimerization and oligomerization forming large homo- or hetero-complexes. All HSPBs possess a highly conserved centrally located α-crystallin domain and poorly conserved N- and C-terminal domains. The main feature of HSPBs is to exert cytoprotective functions by preserving proteostasis, assuring the structural maintenance of the cytoskeleton and acting in response to cellular stresses and apoptosis. HSPBs take part in cell homeostasis by acting as holdases, which is the ability to interact with a substrate preventing its aggregation. In addition, HSPBs cooperate in substrates refolding driven by other chaperones or, alternatively, promote substrate routing to degradation. Notably, while some HSPBs are ubiquitously expressed, others show peculiar tissue-specific expression. Cardiac muscle, skeletal muscle and neurons show high expression levels for a wide variety of HSPBs. Indeed, most of the mutations identified in HSPBs are associated to cardiomyopathies, myopathies, and motor neuropathies. Instead, mutations in HSPB4 and HSPB5, which are also expressed in lens, have been associated with cataract. Mutations of HSPBs family members encompass base substitutions, insertions, and deletions, resulting in single amino acid substitutions or in the generation of truncated or elongated proteins. This review will provide an updated overview of disease-related mutations in HSPBs focusing on the structural and biochemical effects of mutations and their functional consequences.

Synchrotron-based FTIR microspectroscopy of protein aggregation and lipids peroxidation changes in human cataractous lens epithelial cells

Cataract is the leading cause of blindness worldwide but the mechanisms involved in the process of cataractogenesis are not yet fully understood. Two most prevalent types of age-related cataracts are nuclear (N) and cortical (C) cataracts. A common environmental factor in most age-related cataracts is believed to be oxidative stress. The lens epithelium, the first physical and biological barrier in the lens, is build from lens epithelial cells (LECs). LECs are important for the maintenance of lens transparency as they control energy production, antioxidative mechanisms and biochemical transport for the whole lens. The purpose of this study is to characterize compounds in LECs originated from N and C cataracts, by using the synchrotron radiation-based Fourier Transform Infrared (SR-FTIR) microspectroscopy, in order to understand the functional importance of their different bio-macromolecules in cataractogenesis. We used the SR-FTIR microspectroscopy setup installed on the beamline MIRAS at the Spanish synchrotron light source ALBA, where measurements were set to achieve single cell resolution, with high spectral stability and high photon flux. The results showed that protein aggregation in form of fibrils was notably pronounced in LECs of N cataracts, while oxidative stress and the lipids peroxidation were more pronounced in LECs of C cataracts.

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.

The small heat shock proteins, especially HspB4 and HspB5 are promising protectants in neurodegenerative diseases

Small heat shock proteins (sHsps) are a group of proteins with molecular mass between 12 and 43 kDa. Currently, 11 members of this family have been classified, namely HspB1 to HspB11. HspB1, HspB2, HspB5, HspB6, HspB7, and HspB8, which are expressed in brain have been observed to be related to the pathology of neurodegenerative diseases, including Parkinson's, Alzheimer's, Alexander's disease, multiple sclerosis, and human immunodeficiency virus-associated dementia. Specifically, sHsps interact with misfolding and damaging protein aggregates, like Glial fibrillary acidic protein in AxD, β-amyloid peptides aggregates in Alzheimer's disease, Superoxide dismutase 1 in Amyotrophic lateral sclerosis and cytosine-adenine-guanine/polyglutamine (CAG/PolyQ) in Huntington's disease, Spinocerebellar ataxia type 3, Spinal-bulbar muscular atrophy, to reduce the toxicity or increase the clearance of these protein aggregates. The degree of HspB4 expression in brain is still debated. For neuroprotective mechanisms, sHsps attenuate mitochondrial dysfunctions, reduce accumulation of misfolded proteins, block oxidative/nitrosative stress, and minimize neuronal apoptosis and neuroinflammation, which are molecular mechanisms commonly accepted to mirror the progression and development of neurodegenerative diseases. The increasing incidence of the neurodegenerative diseases enhanced search for effective approaches to rescue neural tissue from degeneration with minimal side effects. sHsps have been found to exert neuroprotective functions. HspB5 has been emphasized to reduce the paralysis in a mouse model of experimental autoimmune encephalomyelitis, providing a therapeutic basis for the disease. In this review, we discuss the current understanding of the properties and the mechanisms of protection orchestrated by sHsps in the nervous system, highlighting the promising therapeutic role of sHsps in neurodegenerative diseases.

Probing the changes in gene expression due to α-crystallin mutations in mouse models of hereditary human cataract

The mammalian eye lens expresses a high concentration of crystallins (α, β and γ-crystallins) to maintain the refractive index essential for lens transparency. Crystallins are long-lived proteins that do not turnover throughout life. The structural destabilization of crystallins by UV exposure, glycation, oxidative stress and mutations in crystallin genes leads to protein aggregation and development of cataracts. Several destabilizing mutations in crystallin genes are linked with human autosomal dominant hereditary cataracts. To investigate the mechanism by which the α-crystallin mutations Cryaa-R49C and Cryab-R120G lead to cataract formation, we determined whether these mutations cause an altered expression of specific transcripts in the lens at an early postnatal age by RNA-seq analysis. Using knock-in mouse models previously generated in our laboratory, in the present work, we identified genes that exhibited altered abundance in the mutant lenses, including decreased transcripts for Clic5, an intracellular water channel in Cryaa-R49C heterozygous mutant lenses, and increased transcripts for Eno1b in Cryab-R120G heterozygous mutant lenses. In addition, RNA-seq analysis revealed increased histones H2B, H2A, and H4 gene expression in Cryaa-R49C mutant lenses, suggesting that the αA-crystallin mutation regulates histone expression via a transcriptional mechanism. Additionally, these studies confirmed the increased expression of histones H2B, H2A, and H4 by proteomic analysis of Cryaa-R49C knock-in and Cryaa;Cryab gene knockout lenses reported previously. Taken together, these findings offer additional insight into the early transcriptional changes caused by Cryaa and Cryab mutations associated with autosomal dominant human cataracts, and indicate that the transcript levels of certain genes are affected by the expression of mutant α-crystallin in vivo.

The Photobiology of Lutein and Zeaxanthin in the Eye

Lutein and zeaxanthin are antioxidants found in the human retina and macula. Recent clinical trials have determined that age- and diet-related loss of lutein and zeaxanthin enhances phototoxic damage to the human eye and that supplementation of these carotenoids has a protective effect against photoinduced damage to the lens and the retina. Two of the major mechanisms of protection offered by lutein and zeaxanthin against age-related blue light damage are the quenching of singlet oxygen and other reactive oxygen species and the absorption of blue light. Determining the specific reactive intermediate(s) produced by a particular phototoxic ocular chromophore not only defines the mechanism of toxicity but can also later be used as a tool to prevent damage.

A conserved role of αA-crystallin in the development of the zebrafish embryonic lens

αA- and αB-crystallins are small heat shock proteins that bind thermodynamically destabilized proteins thereby inhibiting their aggregation. Highly expressed in the mammalian lens, the α-crystallins have been postulated to play a critical role in the maintenance of lens optical properties by sequestering age-damaged proteins prone to aggregation as well as through a multitude of roles in lens epithelial cells. Here, we have examined the role of α-crystallins in the development of the vertebrate zebrafish lens. For this purpose, we have carried out morpholino-mediated knockdown of αA-, αBa- and αBb-crystallin and characterized the gross morphology of the lens. We observed lens abnormalities, including increased reflectance intensity, as a consequence of the interference with expression of these proteins. These abnormalities were less frequent in transgenic zebrafish embryos expressing rat αA-crystallin suggesting a specific role of α-crystallins in embryonic lens development. To extend and confirm these findings, we generated an αA-crystallin knockout zebrafish line. A more consistent and severe lens phenotype was evident in maternal/zygotic αA-crystallin mutants compared to those observed by morpholino knockdown. The penetrance of the lens phenotype was reduced by transgenic expression of rat αA-crystallin and its severity was attenuated by maternal αA-crystallin expression. These findings demonstrate that the role of α-crystallins in lens development is conserved from mammals to zebrafish and set the stage for using the embryonic lens as a model system to test mechanistic aspects of α-crystallin chaperone activity and to develop strategies to fine-tune protein-protein interactions in aging and cataracts.

The role of a lens survival pathway including sox2 and αA-crystallin in the evolution of cavefish eye degeneration

BACKGROUND

The teleost Astyanax mexicanus is a single species consisting of eyed surface-dwelling (surface fish) and blind cave-dwelling (cavefish) morphs. Cavefish eyes are lost through apoptosis of the lens, which in turn promotes the degeneration of other optic tissues. The αA-crystallin (αA-crys) gene is strongly downregulated in the cavefish lens and is located in a genomic region (QTL) responsible for eye loss. Therefore, αA-crys has been proposed as a candidate for regulating cavefish eye degeneration. The purpose of this study was to determine the mechanism of αA-crys downregulation and its role in cavefish eye degeneration.

RESULTS

The involvement of αA-crys in eye degeneration was confirmed by knocking down its expression in surface fish, which led to apoptosis of the lens. The underlying reason for αA-crys downregulation in cavefish was investigated by comparing genomic αA-crys DNA sequences in surface fish and cavefish, however, no obvious cis-regulatory factors were discovered. Furthermore, the cavefish αA-crys allele is expressed in surface fish x cavefish F1 hybrids, indicating that evolutionary changes in upstream genes are most likely responsible for αA-crys downregulation. In other species, Sox2 is one of the transcription factors that regulate lens crystallin genes during eye development. Determination of sox2 expression patterns during surface fish and cavefish development showed that sox2 is specifically downregulated in the cavefish lens. The upstream regulatory function of Sox2 was demonstrated by knockdown in surface fish, which abolished αA-crys expression and induced lens apoptosis.

CONCLUSIONS

The results suggest that αA-crys is required for normal eye development in cavefish via suppression of lens apoptosis. The regulatory changes involved in αA-crys downregulation in cavefish are in trans-acting factors rather than cis-acting mutations in the αA-crys gene. Therefore, αA-crys is unlikely to be the mutated gene(s) associated with an Astyanax eye QTL. The results reveal a genetic pathway leading from sox2 to αA-crys that is required for survival of the lens in Astyanax surface fish. Defects in this pathway may be involved in lens apoptosis and thus a cause of cavefish eye degeneration.

Molecular mechanism of formation of cortical opacity in CRYAAN101D transgenic mice

PURPOSE

The CRYAAN101D transgenic mouse model expressing deamidated αA-crystallin (deamidation at N101 position to D) develops cortical cataract at the age of 7 to 9 months. The present study was carried out to explore the molecular mechanism that leads to the development of cortical opacity in CRYAAN101D lenses.

METHODS

RNA sequence analysis was carried out on 2- and 4-month-old αA-N101D and wild type (WT) lenses. To understand the biologic relevance and function of significantly altered genes, Ingenuity Pathway Analysis (IPA) was done. To elucidate terminal differentiation defects, immunohistochemical, and Western blot analyses were carried out.

RESULTS

RNA sequence and IPA data suggested that the genes belonging to gene expression, cellular assembly and organization, and cell cycle and apoptosis networks were altered in N101D lenses. In addition, the tight junction signaling and Rho A signaling were among the top three canonical pathways that were affected in N101D mutant. Immunohistochemical analysis identified a series of terminal differentiation defects in N101D lenses, specifically, increased proliferation and decreased differentiation of lens epithelial cells (LEC) and decreased denucleation of lens fiber cells (LFC). The expression of Rho A was reduced in different-aged N101D lenses, and, conversely, Cdc42 and Rac1 expressions were increased in the N101D mutants. Moreover, earlier in development, the expression of major membrane-bound molecular transporter Na,K-ATPase was drastically reduced in N101D lenses.

CONCLUSIONS

The results suggest that the terminal differentiation defects, specifically, increased proliferation and decreased denucleation are responsible for the development of lens opacity in N101D lenses.

Cell biological roles of αB-crystallin

αB-crystallin, also called HspB5, is a molecular chaperone able to interact with unfolding proteins. By interacting, it inhibits further unfolding, thereby preventing protein aggregation and allowing ATP-dependent chaperones to refold the proteins. αB-crystallin belongs to the family of small heat-shock proteins (sHsps), which in humans consists of 10 different members. The protein forms large oligomeric complexes, containing up to 40 or more subunits, which in vivo consist of heterooligomeric complexes formed by a mixture of αB-crystallin and other sHsps. αB-crystallin is highly expressed in the lens and to a lesser extent in several other tissues, among which heart, skeletal muscle and brain. αB-crystallin plays a role in several cellular processes, such as signal transduction, protein degradation, stabilization of cytoskeletal structures and apoptosis. Mutations in the αB-crystallin gene can have detrimental effects, leading to pathologies such as cataract and cardiomyopathy. This review describes the biological roles of αB-crystallin, with a special focus on its function in the eye lens, heart muscle and brain. In addition its therapeutic potential is discussed.

Antiapoptotic properties of α-crystallin-derived peptide chaperones and characterization of their uptake transporters in human RPE cells

PURPOSE

The chaperone proteins, α-crystallins, also possess antiapoptotic properties. The purpose of the present study was to investigate whether 19 to 20-mer α-crystallin-derived mini-chaperone peptides (α-crystallin mini-chaperone) are antiapoptotic, and to identify their putative transporters in human fetal RPE (hfRPE) cells.

METHODS

Cell death and caspase-3 activation induced by oxidative stress were quantified in early passage hfRPE cells in the presence of 19 to 20-mer αA- or αB-crystallin-derived or scrambled peptides. Cellular uptake of fluorescein-labeled, α-crystallin-derived mini-peptides and recombinant full-length αB-crystallin was determined in confluent hfRPE. The entry mechanism in hfRPE cells for α-crystallin mini-peptides was investigated. The protective role of polycaprolactone (PCL) nanoparticle encapsulated αB-crystallin mini-chaperone peptides from H2O2-induced cell death was studied.

RESULTS

Primary hfRPE cells exposed to oxidative stress and either αA- or αB-crystallin mini-chaperones remained viable and showed marked inhibition of both cell death and activation of caspase-3. Uptake of full-length αB-crystallin was minimal while a time-dependent uptake of αB-crystallin-derived peptide was observed. The mini-peptides entered the hfRPE cells via the sodium-coupled oligopeptide transporters 1 and 2 (SOPT1, SOPT2). PCL nanoparticles containing αB-crystallin mini-chaperone were also taken up and protected hfRPE from H2O2-induced cell death at significantly lower concentrations than free αB-crystallin mini-chaperone peptide.

CONCLUSIONS

αA- and αB-crystallin mini-chaperones offer protection to hfRPE cells and inhibit caspase-3 activation. The oligopeptide transporters SOPT1 and SOPT2 mediate the uptake of these peptides in RPE cells. Nanodelivery of αB-crystallin-derived mini-chaperone peptide offers an alternative approach for protection of hfRPE cells from oxidant injury.

Comparative proteomic analysis identifies age-dependent increases in the abundance of specific proteins after deletion of the small heat shock proteins αA- and αB-crystallin

Mice with deletion of genes for small heat shock proteins αA- and αB-crystallin (αA/αB(-/-)) develop cataracts. We used proteomic analysis to identify lens proteins that change in abundance after deletion of these α-crystallin genes. Wild-type (WT) and αA/αB(-/-) knockout (DKO) mice were compared using two-dimensional difference gel electrophoresis and mass spectrometric analysis, and protein identifications were validated by Mascot proteomic software. The abundance of histones H2A, H4, and H2B fragment, and a low molecular weight β1-catenin increased 2-3-fold in postnatal day 2 lenses of DKO lenses compared with WT lenses. Additional major increases were observed in abundance of βB2-crystallin and vimentin in 30-day-old lenses of DKO animals compared with WT animals. Lenses of DKO mice were comprised of nine protein spots containing βB2-crystallin at 10-40-fold higher abundance and three protein spots containing vimentin at ≥2-fold higher abundance than in WT lenses. Gel permeation chromatography identified a unique 328 kDa protein in DKO lenses, containing β-crystallin, demonstrating aggregation of β-crystallin in the absence of α-crystallins. Together, these changes provide biochemical evidence for possible functions of specific cell adhesion proteins, cytoskeletal proteins, and crystallins in lens opacities caused by the absence of the major chaperones, αA- and αB-crystallins.

The eye as a model of ageing in translational research--molecular, epigenetic and clinical aspects

The eye and visual system are valuable in many areas of translational research such as stem cell therapy, transplantation research and gene therapy. Changes in many ocular tissues can be measured directly, easily and objectively in vivo (e.g. lens transparency; retinal blood vessel calibre; corneal endothelial cell counts) and so the eye may also be a uniquely useful site as a model of ageing. This review details cellular, molecular and epigenetic mechanisms related to ageing within the eye, and describes ocular parameters that can be directly measured clinically and which might be of value in ageing research as the translational "window to the rest of the body". The eye is likely to provide a valuable model for validating biomarkers of ageing at molecular, epigenetic, cellular and clinical levels. A research agenda to definitively establish the relationship between biomarkers of ageing and ocular parameters is proposed.

Analysis of the cytoprotective role of α-crystallins in cell survival and implication of the αA-crystallin C-terminal extension domain in preventing Bax-induced apoptosis

α-Crystallins, initially described as the major structural proteins of the lens, belong to the small heat shock protein family. Apart from their function as chaperones, α-crystallins are involved in the regulation of intracellular apoptotic signals. αA- and αB-crystallins have been shown to interfere with the mitochondrial apoptotic pathway triggering Bax pro-apoptotic activity and downstream activation of effector caspases. Differential regulation of α-crystallins has been observed in several eye diseases such as age-related macular degeneration and stress-induced and inherited retinal degenerations. Although the function of α-crystallins in healthy and diseased retina remains poorly understood, their altered expression in pathological conditions argue in favor of a role in cellular defensive response. In the Rpe65⁻/⁻ mouse model of Leber's congenital amaurosis, we previously observed decreased expression of αA- and αB-crystallins during disease progression, which was correlated with Bax pro-death activity and photoreceptor apoptosis. In the present study, we demonstrated that α-crystallins interacted with pro-apoptotic Bax and displayed cytoprotective action against Bax-triggered apoptosis, as assessed by TUNEL and caspase assays. We further observed in staurosporine-treated photoreceptor-like 661W cells stably overexpressing αA- or αB-crystallin that Bax-dependent apoptosis and caspase activation were inhibited. Finally, we reported that the C-terminal extension domain of αA-crystallin was sufficient to provide protection against Bax-triggered apoptosis. Altogether, these data suggest that α-crystallins interfere with Bax-induced apoptosis in several cell types, including the cone-derived 661W cells. They further suggest that αA-crystallin-derived peptides might be sufficient to promote cytoprotective action in response to apoptotic cell death.

Reduction of experimental diabetic vascular leakage and pericyte apoptosis in mice by delivery of αA-crystallin with a recombinant adenovirus

AIMS/HYPOTHESIS

The study aimed to evaluate the efficacy of recombinant adenovirus expressing αA-crystallin (Ad-αAc-Gfp) in reducing pericyte loss within retinal vasculature in early diabetes.

METHODS

Diabetes was induced by streptozotocin injection into C57BL/6 mice. Ad-αAc-Gfp was delivered by intravitreous injection to the right eyes of mice 2 weeks before induction of diabetes. Vascular leakage was determined by fluorescent angiography, Evans Blue leakage assay and leucocyte adhesion test. Production of αA-crystallin was analysed by immunoblotting and double immunostaining and pericyte loss was analysed by pericyte count.

RESULTS

Vessel leakage and pericyte loss were observed in the streptozotocin-induced diabetic retina. Decreased abundance of αA-crystallin in retinas 2 and 6 months after the induction of diabetes was confirmed by two-dimensional electrophoretic analysis, immunoblotting and RT-PCR. Double immunofluorescence staining for αA-crystallin and NG2 chondroitin sulphate proteoglycan revealed that αA-crystallin was predominantly produced in the retinal pericyte and that the number of αA-crystallin-producing pericytes decreased in the diabetic retina. Retinal infection with Ad-αAc-Gfp led to decreased pericyte loss and vascular leakage compared with control.

CONCLUSIONS/INTERPRETATION

Intravitreal delivery of Ad-αAc-Gfp protects against vascular leakage in the streptozotocin-induced model of diabetes. This effect is associated with the inhibition of diabetic retinal pericyte loss in early diabetes, suggesting that αA-crystallin has a role in preventing the pathogenesis of early diabetic retinopathy.

Molecular and functional characterization of HdHSP20: a biomarker of environmental stresses in disk abalone Haliotis discus discus

Heat shock proteins (HSPs) production in cell is inducible by many physical and chemical stressors, providing adaptive significance for organisms when faced with environmental changes. In this study, we characterized a novel small HSP gene from disk abalone, designated as HdHSP20, and investigated its temporal expression by different environmental stimuli. The full-length genome sequence of HdHSP20 is composed of three exons and two introns. The 5' flanking region contains multiple putative transcription factor binding sites related to stress response. The open reading frame of the HdHSP20 cDNA is 480 bp and encodes 160 amino acid residues with 18.76 kDa molecular mass. The deduced amino acid sequence shares highest similarity with HSP20 genes from other invertebrates. HdHSP20 also shows several structural signatures of small HSP, including the conserved α-crystallin domain, the absence of cysteine residues, a high number of Glx/Asx residues and the compact β-sandwich structure in the C-terminal region. Overexpression of recombinant HdHSP20 protein conveyed enhanced thermotolerance to Escherichia coli cells, suggesting its functional activity in the cellular chaperone network. qRT-PCR measurements of HdHSP20 mRNA level have shown rapid and drastic induction by extreme temperatures, extreme salinities, heavy metals and the microbial infections. Collectively, our results suggest that HdHSP20 gene is likely involved in the stress resistant mechanisms in disk abalone. Its expression may serve as a potential biomarker capable to indicate a stress state in abalone due to extreme environmental change and pathogen infection.

Novel roles for α-crystallins in retinal function and disease

α-Crystallins are key members of the superfamily of small heat shock proteins that have been studied in detail in the ocular lens. Recently, novel functions for α-crystallins have been identified in the retina and in the retinal pigmented epithelium (RPE). αB-Crystallin has been localized to multiple compartments and organelles including mitochondria, golgi apparatus, endoplasmic reticulum and nucleus. α-Crystallins are regulated by oxidative and endoplasmic reticulum stress, and inhibit apoptosis-induced cell death. α-Crystallins interact with a large number of proteins that include other crystallins, and apoptotic, cytoskeletal, inflammatory, signaling, angiogenic, and growth factor molecules. Studies with RPE from αB-crystallin deficient mice have shown that αB-crystallin supports retinal and choroidal angiogenesis through its interaction with vascular endothelial growth factor. αB-Crystallin has also been shown to have novel functions in the extracellular space. In RPE, αB-crystallin is released from the apical surface in exosomes where it accumulates in the interphotoreceptor matrix and may function to protect neighboring cells. In other systems administration of exogenous recombinant αB-crystallin has been shown to be anti-inflammatory. Another newly described function of αB-crystallin is its ability to inhibit β-amyloid fibril formation. α-Crystallin minichaperone peptides have been identified that elicit anti-apoptotic function in addition to being efficient chaperones. Generation of liposomal particles and other modes of nanoencapsulation of these minipeptides could offer great therapeutic advantage in ocular delivery for a wide variety of retinal degenerative, inflammatory and vascular diseases including age-related macular degeneration and diabetic retinopathy.

Specific phosphorylation of αA-crystallin is required for the αA-crystallin-induced protection of astrocytes against staurosporine and C2-ceramide toxicity

We previously reported that αA-crystallin and protease-activated receptor are involved in protection of astrocytes against C2-ceramide- and staurosporine-induced cell death (Li et al., 2009). Here, we investigated the molecular mechanism of αA-crystallin-mediated cytoprotection. We found that the expression of mutants mimicking specific phosphorylation of αA-crystallin increases the protection of astrocytes. However, the expression of mutants mimicking unphosphorylation of αA-crystallin results in loss of protection. These data revealed that the phosphorylation of αA-crystallin at Ser122 and Ser148 is required for protection. Furthermore, we explored the mechanism of cytoprotection of astrocytes by αA-crystallin. Application of specific inhibitors of p38 and ERK abrogates the protection of astrocytes by over-expression of αA-crystallin. Thus, p38 and ERK contribute to protective processes by αA-crystallin. This is comparable to our previous results which demonstrated that p38 and ERK regulated protease-activated receptor-2 (PAR-2)/αB-crystallin-mediated cytoprotection. Furthermore, we found that PAR-2 activation increases the expression of αA-crystallin. Thus, endogenous αA-crystallin protects astrocytes via mechanisms, which regulate the expression and/or phosphorylation status of αA-crystallin.

Inhibition of lens photodamage by UV-absorbing contact lenses

PURPOSE

To determine whether class 1 UV-blocking contact lenses protect against UVB radiation-induced damage in a human lens epithelial cell line (HLE B-3) and postmortem human lenses using a proteomics approach.

METHODS

HLE B-3 cells were exposed to 6.4 mW/cm(2) UVB radiation at 302 nm for 2 minutes (768 mJ/cm(2)) with or without covering by senofilcon A class 1 UV-blocking contact lenses or lotrafilcon A non-UV-blocking (lotrafilcon A has some UV-blocking ability, albeit minimal) contact lenses. Control cells were not exposed to UVB radiation. Four hours after treatment, cells were analyzed by two-dimensional difference gel electrophoresis and tandem mass spectrometry, and changes in protein abundance were quantified. F-actin and microtubule cytoskeletons were examined by fluorescence staining. In addition, human donor lenses were exposed to UVB radiation at 302 nm for 4 minutes (1536 mJ/cm(2)). Cortical and epithelial cell proteins were scraped from lens surfaces and subjected to the same protein analyses.

RESULTS

Senofilcon A lenses were beneficial for protecting HLE B-3 cells against UVB radiation-induced changes in caldesmon 1 isoform, lamin A/C transcript variant 1, DEAD (Asp-Glu-Ala-Asp) box polypeptide, β-actin, glyceraldehyde 3-phosphate dehydrogenase (G3PDH), annexin A2, triose phosphate isomerase, and ubiquitin B precursor. These contact lenses also prevented actin and microtubule cytoskeleton changes typically induced by UVB radiation. Conversely, non-UV-blocking contact lenses were not protective. UVB-irradiated human lenses showed marked reductions in αA-crystallin, αB-crystallin, aldehyde dehydrogenase 1, βS-crystallin, βB2-crystallin, and G3PDH, and UV-absorbing contact lenses significantly prevented these alterations.

CONCLUSIONS

Senofilcon A class 1 UV-blocking contact lenses largely prevented UVB-induced changes in protein abundance in lens epithelial cells and in human lenses.

Cloning of crystallin from orange-spotted grouper and characterization of its activity as potential protective agent

Oxidative stress associated with nodavirus infection is poorly understood, especially pertaining to infection-mediated brain injury. Indirect evidence indicates that infection increases cellular abundance of reactive oxygen species (ROS) with consequent increase in cellular dityrosine production. The detection of dityrosine in nodavirus-infected grouper was demonstrated using immunohistochemical (IHC) staining. Proteomic analyses with eye tissues of healthy grouper revealed more abundant expression of crystallin protein in the eye than in various tissues, which was confirmed by real-time polymerase chain reaction and IHC analyses. Grouper crystallin belongs to a small heat shock protein family with chaperone-like function that prevents heat-induced and oxidative stress-induced protein aggregation. Recombinant crystallin induced nitric oxide (NO) production in RAW 264.7 cells after treatment. The results provide new insight into the pathogenesis of nodavirus and demonstrate an experimental rationale for antioxidant therapy research.

Quantitative iTRAQ analysis of retinal ganglion cell degeneration after optic nerve crush

Retinal ganglion cells (RGCs) are central nervous system (CNS) neurons that transmit visual information from the retina to the brain. Apoptotic RGC degeneration causes visual impairment that can be modeled by optic nerve crush. Neuronal apoptosis is also a salient feature of CNS trauma, ischemia (stroke), and diseases of the CNS such as Alzheimer's, Parkinson's, multiple sclerosis, and amyotrophic lateral sclerosis. Optic nerve crush induces the apoptotic cell death of ∼ 70% of RGCs within the first 14 days after injury. This model is particularly attractive for studying adult neuron apoptosis because the time-course of RGC death is well established and axon regeneration within the myelinated optic nerve can be concurrently evaluated. Here, we performed a large scale iTRAQ proteomic study to identify and quantify proteins of the rat retina at 1, 3, 4, 7, 14, and 21 days after optic nerve crush. In total, 337 proteins were identified, and 110 were differentially regulated after injury. Of these, 58 proteins were upregulated (>1.3 ×), 46 were downregulated (<0.7 ×), and 6 showed both positive and negative regulation over 21 days, relative to normal retinas. Among the differentially expressed proteins, Thymosin-β4 showed an early upregulation at 3 days, the time-point that immediately precedes the induction of RGC apoptosis after injury. We examined the effect of exogenous Thymosin-β4 administration on RGC death after optic nerve injury. Intraocular injections of Thymosin-β4 significantly increased RGC survival by ∼ 3-fold compared to controls and enhanced axon regeneration after crush, demonstrating therapeutic potential for CNS insults. Overall, our study identified numerous proteins that are differentially regulated at key time-points after optic nerve crush, and how the temporal profiles of their expression parallel RGC death. This data will aid in the future development of novel therapeutics to promote neuronal survival and regeneration in the adult CNS.

Importance of eye lens α-crystallin heteropolymer with 3:1 αA to αB ratio: stability, aggregation, and modifications

Chaperone-like activity (CLA) of α-crystallin is essential not only for the maintenance of eye lens transparency but also in the biology of other tissues. Eye lens α-crystallin is a heteropolymer composed of two homologous subunits, αA and αB, and in most vertebrates they are present in a ratio of 3:1. The structural and functional significance of this specific ratio of α-crystallin subunits is of considerable interest in understanding its role in the eye lens transparency. Previously, we have shown that although at physiologically relevant conditions αB-crystallin has greater CLA, under stress conditions such as elevated temperatures α-crystallin heteropolymer with 3:1 αA to αB ratio displayed higher CLA (Srinivas et al., Biochem. J., 2008, 414, 453 - 460). Herein, we provide a rationale for the existence of α-crystallin heteropolymer with 3:1 αA to αB ratio in terms of structural stability, aggregation pattern, and susceptibility to posttranslational modifications that could explain the importance of the heteropolymer of α-crystallin in the eye lens. We demonstrate that αA-crystallin is not only more stable but also imparts stability to the heteropolymer by preventing the aggregation of αB-crystallin at higher temperatures by using differential scanning calorimetry, size-exclusion chromatography, and denaturant-induced unfolding methods. Further, the physiological significance of heteropolymer with higher proportion of αA subunit is substantiated by using a heteropolymer with mutant (F71L) αA-crystallin and the susceptibility of 3:1 heteropolymer to glycation-induced modifications. Thus, the existence of 3:1 heteropolymer might be vital for the eye lens transparency under diverse conditions to prevent cataract.

Activation of the unfolded protein response by a cataract-associated αA-crystallin mutation

αA-crystallin is a lens chaperone that plays an essential role in the transparency and refractive properties of the lens. Mutations in αA-crystallin have been associated with the development of hereditary cataracts. The R49C mutation of αA-crystallin (αA-R49C) was identified in a four-generation Caucasian family with hereditary cataracts. The αA-R49C protein forms larger-than-normal oligomers in the lens and has decreased solubility. This aberrant αA-R49C oligomerization suggests that protein folding is altered. However, whether activation of the unfolded protein response (UPR) occurs during crystallin mutation-induced cataract formation and whether the UPR causes cell death under these conditions is unclear. We investigated UPR activation in an in vivo mouse model of αA-R49C using immunoblot analysis of lens extracts. We found that expression of the endoplasmic reticulum (ER) chaperone, BiP, was 5-fold higher in homozygous αA-R49C lenses than in wild type lenses. Analysis of proteins typically expressed during the UPR revealed that ATF-4 and CHOP levels were also higher in homozygous lenses than in wild type lenses, while the opposite was true of ATF-6 and XBP-1. Taken together, these findings show that mutation of αA-crystallin induces activation of the UPR during cataract formation. They also suggest that the UPR is an important mediator of cell death observed in homozygous αA-R49C lenses.

αA-Crystallin associates with α6 integrin receptor complexes and regulates cellular signaling

α-Crystallins are small heat-shock proteins important to lens transparency that provide the lens with its refractive properties. In their role as molecular chaperones, these crystallins also prevent protein aggregation, affect cytoskeletal remodeling, enhance resistance to cell stress, and provide lens cells with protection against apoptosis. While many of the functions assigned to αA-crystallin are attributable to its presence in the cytoplasm of lens cells, αA-crystallin also has been detected at the lens plasma membrane. However, how αA-crystallin becomes linked to the plasma membrane or what its functions are at this site has remained unknown. In this study, we examined the mechanisms by which αA-crystallin becomes associated with the lens membrane, focusing specifically on its interaction with membrane receptors, and the differentiation-specificity of these interactions. We also determined how the long-term absence of αA-crystallin alters receptor-linked signaling pathways. αA-crystallin association with membrane receptors was determined by co-immunoprecipitation analysis; its membrane localization was examined by confocal imaging; and the effect of αA-crystallin loss-of-function on the activation state of signaling molecules in pathways linked to membrane receptors was determined by immunoblot analysis. The results show that, in lens epithelial cells, plasma membrane αA-crystallin was primarily localized to apicolateral borders, reflecting the association of αA-crystallin with E-cadherin complexes. These studies also provide the first evidence that αA-crystallin maintained its association with the plasma membrane in lens cortical fiber cells, where it was localized to lateral interfaces, and further show that this association was mediated, in part, by αA-crystallin interaction with α6 integrin receptor complexes. We report that the absence of αA-crystallin led to constitutive activation of the stress kinases p38 and JNK, classical inducers of apoptotic cell death, and the loss of the phospho-Bad pro-survival signal, effects that were greatest in differentiating lens fiber cells. Concurrent with this, activation of FAK and ERK kinases was increased, demonstrating that these receptor-linked pathways also were dysregulated in the absence of αA-crystallin. These data link αA-crystallin plasma membrane association to its differentiation-state-specific interaction with E-cadherin and α6 integrin receptor complexes. The changes in cell signaling in αA-crystallin-null lenses suggest that dysregulation of receptor-linked cell-signaling pathways that accompany the failure of αA-crystallin to associate with membrane receptors may be responsible for the induction of apoptosis. The observed changes in lens cell signaling likely reflect long-term functional adaptations to the absence of the αA-crystallin chaperone/small heat-shock protein.

The inhibition of CMV promoter by heat shock factor 4b is regulated by Daxx

Heat shock factor 4 (Hsf4b) has been identified as a novel cataractogenic protein whose mutation has been closely associated with hereditary cataracts in humans and animals. It acts both as a transcription activator and a transcription inhibitor in the regulation of its downstream targets during lens development. However, the signaling factors that regulate Hsf4b transcription activity are still not completely defined. Here, we found that Hsf4b, not Hsf4a (another isoform of Hsf4), acts as the inhibitor of CMV promoter as well as the activator of Hsp25 in the Hsf4-/- mouse lens epithelial cell line (mLEC/hsf4-/-). Hsf4b inhibits CMV-promoter activity by directly binding to TTCC (HSE motif) at 173-176bps in the CMV promoter. The phosphorylation of Hsf4b/S299 in the PDSM motif, which is absent in Hsf4a, participates in the negative regulation of the CMV promoter. The transcriptional inhibition of Hsf4b is associated with transcriptional inhibitor Daxx. Hsf4b can interact and co-localize with Daxx in the nucleus, and their association is regulated by the phosphorylation of Hsf4b/S299. In addition, we found that Hsf4a and Hsf1 were also associated with Daxx. However, in contrast to activating Hsf1, Daxx can repress Hsf4b-induced expression of Hsp25 in the mLEC/hsf4-/- cell line. Our results demonstrate that the transcription-inhibitory function of Hsf4b is regulated by the phosphorylation of Hsf4b/S299 and phosphorylation-dependent association with Daxx.

Detection and prevention of ocular phototoxicity of ciprofloxacin and other fluoroquinolone antibiotics

Fluoroquinolone (FLQ) drugs are a potent family of antibiotics used to treat infections including ocular infections. To determine if these antibiotics may be phototoxic to the eye, we exposed human lens epithelial cells to 0.125-1 mm FLQs (ciprofloxacin [Cipro], lomefloxacin [Lome], norfloxacin [Nor] and ofloxacin [Ofl]), the precursor quinolone nalidixic acid (Nalid) and UVA radiation (2.5 J cm(-2)). Based on fluorescence confocal microscopy, FLQs are diffused throughout the cytoplasm and preferentially located in the lysosomes of lens epithelial cells. Neither FLQ exposure alone nor UVA exposure alone reduced cell viability. However, with exposure to UVA radiation the FLQs studied (Cipro, Nor, Lome and Ofl) induced a phototoxic reaction that included necrosis, apoptosis, loss of cell viability as measured by MTS, and membrane damage as determined by the lactate dehydrogenase assay. Both Nalid and all FLQs studied (Cipro, Nor, Lome and Ofl) photopolymerized the lens protein alpha-crystallin. Phototoxic damage to lens epithelial cells and/or alpha-crystallin will lead to a loss of transparency of the human lens. However, if precautions are taken to filter all UV radiation from the eye while taking these antibiotics, eye damage may be prevented.

In vivo lens deficiency of the R49C alphaA-crystallin mutant

The R49C mutation of alphaA-crystallin (alphaA-R49C) causes hereditary cataracts in humans; patients in a four-generation Caucasian family were found be heterozygous for this autosomal dominant mutation. We previously generated knock-in mouse models of this mutation and found that by 2 months of age, heterozygous mutant mice exhibited minor lens defects including reduced protein solubility, altered signaling in epithelial and fiber cells, and aberrant interactions between alphaA-crystallin and other lens proteins. In contrast, homozygous mutant alphaA-R49C knock-in mice displayed earlier and more extensive lens defects including small eyes and small lenses at birth, death of epithelial and fiber cells, and the formation of posterior, nuclear, and cortical cataracts in the first month of life. We have extended this study to now show that in alphaA-R49C homozygous mutant mice, epithelial cells failed to form normal equatorial bow regions and fiber cells continued to die as the mice aged, resulting in a complete loss of lenses and overall eye structure in mice older than 4 months. These results demonstrate that expression of the hereditary R49C mutant of alphaA-crystallin in vivo is sufficient to adversely affect lens growth, lens cell morphology, and eye function. The death of fiber cells caused by this mutation may ultimately lead to loss of retinal integrity and blindness.

Changes in retinal alphaB-crystallin (cryab) RNA transcript levels during periods of altered ocular growth in chickens

Changes in retinal crystallin gene expression have been implicated in the development of myopia in animal models. We therefore investigated the expression of alphaB-crystallin (cryab) in the chicken retina during periods of increased ocular growth induced by form-deprivation and negative lens-wear, and during periods of decreased ocular growth induced by diffuser removal from previously form-deprived eyes, and plus lens-wear. Cryab RNA transcript levels in the chicken retina were measured using semi-quantitative real-time RT-PCR, at times between 1 h and 10 days after the fitting of diffusers or negative lenses, and at times between 1 h and 3 days following the removal of diffusers from previously form-deprived eyes, or the addition of plus lenses. Changes in expression for each condition at each time-point are analysed relative to expression in retinas from age-matched untreated control birds. No change in relative expression of cryab RNA transcript was detected 1 h after fitting diffusers to induce form-deprivation myopia. A transient increase in cryab RNA transcript expression was detected around 1 day later (p = 0.02), but expression returned to control levels after three days. After 7 (p = 0.005) and 10 (p = 0.001) days, retinal cryab RNA transcript expression progressively increased relative to controls. After removal of the diffusers, to initiate recovery, cryab RNA transcript expression remained elevated, with only a slight return to control levels. During the development of lens-induced myopia, no changes in cryab RNA transcript expression relative to controls were seen on day 1, but increases were seen at 10 days (p = 0.004). No significant changes in retinal cryab RNA transcript expression were seen in response to plus lenses compared to either contralateral control values (MANOVA; F = 0.60, p = 0.48) or age-matched untreated values (MANOVA; F = 4.10, p = 0.08). Changes in retinal cryab RNA transcript expression were not systematically related to changes in the rate of eye growth. The role of the transient increase in cryab expression observed after 1 day of form-deprivation, which was not seen after fitting negative lenses, is unclear. The later increases in relative cryab expression seen during the development of form-deprivation and lens-induced myopia occur too late to have a major role in the differential regulation of eye growth between experimental and control eyes. Given that cryab is a member of the small heat shock protein family, the later increases may reflect the emergence of cell damage related to high myopic pathology in the experimentally enlarged eyes and retina.

AlphaA-crystallin R49Cneo mutation influences the architecture of lens fiber cell membranes and causes posterior and nuclear cataracts in mice

Background

αA-crystallin (CRYAA/HSPB4), a major component of all vertebrate eye lenses, is a small heat shock protein responsible for maintaining lens transparency. The R49C mutation in the αA-crystallin protein is linked with non-syndromic, hereditary human cataracts in a four-generation Caucasian family.

Methods

This study describes a mouse cataract model generated by insertion of a neomycin-resistant (neo^r) gene into an intron of the gene encoding mutant R49C αA-crystallin. Mice carrying the neo^r gene and wild-type Cryaa were also generated as controls. Heterozygous knock-in mice containing one wild type gene and one mutated gene for αA-crystallin (WT/R49C^neo) and homozygous knock-in mice containing two mutated genes (R49C^neo/R49C^neo) were compared.

Results

By 3 weeks, WT/R49C^neo mice exhibited large vacuoles in the cortical region 100 μm from the lens surface, and by 3 months posterior and nuclear cataracts had developed. WT/R49C^neo mice demonstrated severe posterior cataracts at 9 months of age, with considerable posterior nuclear migration evident in histological sections. R49C^neo/R49C^neo mice demonstrated nearly complete lens opacities by 5 months of age. In contrast, R49C mice in which the neo^r gene was deleted by breeding with CreEIIa mice developed lens abnormalities at birth, suggesting that the neo^r gene may suppress expression of mutant R49C αA-crystallin protein.

Conclusion

It is apparent that modification of membrane and cell-cell interactions occurs in the presence of the αA-crystallin mutation and rapidly leads to lens cell pathology in vivo.

Alpha A-crystallin and alpha B-crystallin, newly identified interaction proteins of protease-activated receptor-2, rescue astrocytes from C2-ceramide- and staurosporine-induced cell death

Protease-activated receptor-2 (PAR-2) is a G protein-coupled receptor activated by trypsin and other trypsin-like serine proteases. The widely expressed PAR-2 is involved in inflammation response but the physiological/pathological roles of PAR-2 in the nervous system are still uncertain. In the present study, we report novel PAR-2 interaction proteins, alphaA-crystallin and alphaB-crystallin. These 20 kDa proteins have been implicated in neurodegenerative diseases like Alexander's disease, Creutzfeldt-Jacob disease, Alzheimer's disease, and Parkinson's disease. Results from yeast two-hybrid assay using the cytoplasmic C-tail of PAR-2 as bait suggested that alphaA-crystallin interacts with PAR-2. We further demonstrate the in vitro and cellular in vivo interaction of C-tail of PAR-2 as well as of full-length PAR-2 with alphaA(alphaB)-crystallins. We use pull-down, co-immunoprecipitation, and co-localization assays. Analysis of alphaA-crystallin deletion mutants showed that amino acids 120-130 and 136-154 of alphaA-crystallin are required for the interaction with PAR-2. Co-immunoprecipitation experiments ruled out an interaction of alphaA(alphaB)-crystallins with PAR-1, PAR-3, and PAR-4. This demonstrates that alphaA(alphaB)-crystallins are PAR-2-specific interaction proteins. Moreover, we investigated the functional role of PAR-2 and alpha-crystallins in astrocytes. Evidence is presented to show that PAR-2 activation and increased expression of alpha-crystallins reduced C2-ceramide- and staurosporine-induced cell death in astrocytes. Thus, both PAR-2 and alpha-crystallins are involved in cytoprotection in astrocytes.

HSPB7 is a SC35 speckle resident small heat shock protein

BACKGROUND

The HSPB family is one of the more diverse families within the group of HSP families. Some members have chaperone-like activities and/or play a role in cytoskeletal stabilization. Some members also show a dynamic, stress-induced translocation to SC35 splicing speckles. If and how these features are interrelated and if they are shared by all members are yet unknown.

METHODS

Tissue expression data and interaction and co-regulated gene expression data of the human HSPB members was analyzed using bioinformatics. Using a gene expression library, sub-cellular distribution of the diverse members was analyzed by confocal microscopy. Chaperone activity was measured using a cellular luciferase refolding assay.

RESULTS

Online databases did not accurately predict the sub-cellular distribution of all the HSPB members. A novel and non-predicted finding was that HSPB7 constitutively localized to SC35 splicing speckles, driven by its N-terminus. Unlike HSPB1 and HSPB5, that chaperoned heat unfolded substrates and kept them folding competent, HSPB7 did not support refolding.

CONCLUSION

Our data suggest a non-chaperone-like role of HSPB7 at SC35 speckles.

GENERAL SIGNIFICANCE

The functional divergence between HSPB members seems larger than previously expected and also includes non-canonical members lacking classical chaperone-like functions.

Attenuation of aldose reductase gene suppresses high-glucose-induced apoptosis and oxidative stress in rat lens epithelial cells

AIMS

A major contributory factor to diabetic cataract formation is increased aldose reductase (AR) activity in the polyol pathway. We investigated the effects of aldose reductase inhibition by RNA interference (RNAi) of the aldose reductase gene and administration of an aldose reductase inhibitor (ARI) on the changes induced by high glucose levels in rat lens epithelial cells (RLECs).

METHODS

Small interfering RNAs (siRNAs) were designed to target the coding sequence of rat AR-siRNA. RLECs were cultured in either normal or high d-glucose. Western analysis was performed to monitor AR expression. MTS (3-(4-5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt) and TUNEL assays were used to detect apoptotic cell death. Intracellular reactive oxygen species (ROS) were assessed by using DCFH-DA. Activation of nuclear factor-kappaB (NF-kappaB) was measured by an ELISA-based detection method.

RESULTS

Both siRNA and ARI suppressed increased levels of ROS, activation of NF-kappaB, and apoptotic cell death induced by high glucose levels. Inhibition of rAR expression by siRNA and inhibition of AR activity by ARI also suppressed sorbitol accumulation.

CONCLUSIONS

Both inhibition of rAR expression by rAR siRNA and inhibition of rAR activity by an ARI appeared effective in diminishing the changes of RLECs associated with high glucose levels.

Mechanism of insolubilization by a single-point mutation in alphaA-crystallin linked with hereditary human cataracts

AlphaA-crystallin is a small heat shock protein that functions as a molecular chaperone and a lens structural protein. The R49C single-point mutation in alphaA-crystallin causes hereditary human cataracts. We have previously investigated the in vivo properties of this mutant in a gene knock-in mouse model. Remarkably, homozygous mice carrying the alphaA-R49C mutant exhibit nearly complete lens opacity concurrent with small lenses and small eyes. Here we have investigated the 90 degrees light scattering, viscosity, refractive index, and bis-ANS fluorescence of lens proteins isolated from the alphaA-R49C mouse lenses and found that the concentration of total water-soluble proteins showed a pronounced decrease in alphaA-R49C homozygous lenses. Light scattering measurements on proteins separated by gel permeation chromatography showed a small amount of high-molecular mass aggregated material in the void volume which still remains soluble in alphaA-R49C homozygous lens homogenates. An increased level of binding of beta- and gamma-crystallin to the alpha-crystallin fraction was observed in alphaA-R49C heterozygous and homozygous lenses but not in wild-type lenses. Quantitative analysis with the hydrophobic fluorescence probe bis-ANS showed a pronounced increase in fluorescence yield upon binding to alpha-crystallin from mutant as compared with the wild-type lenses. These results suggest that the decrease in the solubility of the alphaA-R49C mutant protein was due to an increase in its hydrophobicity and supra-aggregation of alphaA-crystallin that leads to cataract formation. Our study further shows that analysis of mutant proteins from the mouse model is an effective way to understand the mechanism of protein insolubilization in hereditary cataracts.

Alpha-crystallin protected axons from optic nerve degeneration after crushing in rats

In mature mammals, optic nerve injury results in apoptosis of retinal ganglion cells. The literature confirms that lens injury enhances retinal ganglion cells survival, but the mechanism is not very clear. Using silver staining method and computer image analysis techniques, the effect of alpha-crystallin, a major component of the lens in the survival of retinal ganglion cell axons, was investigated in vivo after intravitreal injections. The results showed that enhanced survival of axotomized axons was observed beyond the crush site after a single intravitreal administration of alpha-crystallin at the time of axotomy. Axonal density of the retinal ganglion cell was significantly greater than in the untreated controls until 2 weeks after injection. This effect declined by 4 weeks after injection but survival of axons remained greater than controls. These findings indicate that alpha-crystallin plays a key role in protecting axons after optic nerve injury.

Phototoxicity and cytotoxicity of fullerol in human lens epithelial cells

The water-soluble, hydroxylated fullerene [fullerol, nano-C60(OH)22-26] has several clinical applications including use as a drug carrier to bypass the blood ocular barriers. We have assessed fullerol's potential ocular toxicity by measuring its cytotoxicity and phototoxicity induced by UVA and visible light in vitro with human lens epithelial cells (HLE B-3). Accumulation of nano-C60(OH)22-26 in the cells was confirmed spectrophotometrically at 405 nm and cell viability estimated using MTS and LDH assays. Fullerol was cytotoxic to HLE B-3 cells maintained in the dark at concentrations higher than 20 microM. Exposure to either UVA or visible light in the presence of >5 microM fullerol-induced phototoxic damage. When cells were pretreated with non-toxic antioxidants: 20 microM lutein, 1 mM N-acetyl cysteine, or 1 mM l-ascorbic acid prior to irradiation, only the singlet oxygen quencher-lutein significantly protected against fullerol photodamage. Apoptosis was observed in lens cells treated with fullerol whether or not the cells were irradiated, in the order UVA>visible light>dark. Dynamic light scattering (DLS) showed that in the presence of the endogenous lens protein alpha-crystallin, large aggregates of fullerol were reduced. In conclusion, fullerol is both cytotoxic and phototoxic to human lens epithelial cells. Although the acute toxicity of water-soluble nano-C60(OH)22-26 is low, these compounds are retained in the body for long periods, raising concern for their chronic toxic effect. Before fullerols are used to deliver drugs to the eye, they should be tested for photo- and cytotoxicity in vivo.

Mechanism of small heat shock protein function in vivo: a knock-in mouse model demonstrates that the R49C mutation in alpha A-crystallin enhances protein insolubility and cell death

alphaA-crystallin (Cryaa/HSPB4) is a small heat shock protein and molecular chaperone that prevents nonspecific aggregation of denaturing proteins. Several point mutations in the alphaA-crystallin gene cause congenital human cataracts by unknown mechanisms. We took a novel approach to investigate the molecular mechanism of cataract formation in vivo by creating gene knock-in mice expressing the arginine 49 to cysteine mutation (R49C) in alphaA-crystallin (alphaA-R49C). This mutation has been linked with autosomal dominant hereditary cataracts in a four-generation Caucasian family. Homologous recombination in embryonic stem cells was performed using a plasmid containing the C to T transition in exon 1 of the cryaa gene. alphaA-R49C heterozygosity led to early cataracts characterized by nuclear opacities. Unexpectedly, alphaA-R49C homozygosity led to small eye phenotype and severe cataracts at birth. Wild type littermates did not show these abnormalities. Lens fiber cells of alphaA-R49C homozygous mice displayed an increase in cell death by apoptosis mediated by a 5-fold decrease in phosphorylated Bad, an anti-apoptotic protein, but an increase in Bcl-2 expression. However, proliferation measured by in vivo bromodeoxyuridine labeling did not decline. The alphaA-R49C heterozygous and homozygous knock-in lenses demonstrated an increase in insoluble alphaA-crystallin and alphaB-crystallin and a surprising increase in expression of cytoplasmic gamma-crystallin, whereas no changes in beta-crystallin were observed. Co-immunoprecipitation analysis showed increased interaction between alphaA-crystallin and lens substrate proteins in the heterozygous knock-in lenses. To our knowledge this is the first knock-in mouse model for a crystallin mutation causing hereditary human cataract and establishes that alphaA-R49C promotes protein insolubility and cell death in vivo.

The lens epithelium: focus on the expression and function of the alpha-crystallin chaperones

Lens epithelial cells are the parental cells responsible for growth and development of the transparent ocular lens. Many elegant investigations into their biology have focused on the factors that initiate and regulate lens epithelial cell differentiation. Because they serve key transport and cell maintenance functions throughout life, and are the primary source of metabolic activity in the lens, mechanisms to maintain lens epithelial cell integrity and survival are critical for lens transparency. The molecular chaperones alpha-crystallins are abundant proteins synthesized in the differentiated lens fiber cell cytoplasm. However, their expression in lens epithelial cells has only been appreciated very recently. Besides their important roles in the refractive and light focusing properties of the lens, alpha-crystallins have been implicated in a number of non-refractive pathways including those involving stress response, apoptosis and cell survival. The most convincing evidence for their importance in the lens epithelium has been shown by studies on the properties of lens epithelial cells from alphaA and alphaB-crystallin gene knockout mice. Novel combination of genetics, cell and molecular biology should lead to a greater understanding of how lens epithelial cells proliferate, differentiate and survive.

Crystallins in the eye: Function and pathology

Crystallins are the predominant structural proteins in the lens that are evolutionarily related to stress proteins. They were first discovered outside the vertebrate eye lens by Bhat and colleagues in 1989 who found alphaB-crystallin expression in the retina, heart, skeletal muscles, skin, brain and other tissues. With the advent of microarray and proteome analysis, there is a clearer demonstration that crystallins are prominent proteins both in the normal retina and in retinal pathologies, emphasizing the importance of understanding crystallin functions outside of the lens. There are two main crystallin gene families: alpha-crystallins, and betagamma-crystallins. alpha-crystallins are molecular chaperones that prevent aberrant protein interactions. The chaperone properties of alpha-crystallin are thought to allow the lens to tolerate aging-induced deterioration of the lens proteins without showing signs of cataracts until older age. alpha-crystallins not only possess chaperone-like activity in vitro, but can also remodel and protect the cytoskeleton, inhibit apoptosis, and enhance the resistance of cells to stress. Recent advances in the field of structure-function relationships of alpha-crystallins have provided the first clues to their underlying roles in tissues outside the lens. Proteins of the betagamma-crystallin family have been suggested to affect lens development, and are also expressed in tissues outside the lens. The goal of this paper is to highlight recent work with lens epithelial cells from alphaA- and alphaB-crystallin knockout mice. The use of lens epithelial cells suggests that crystallins have important cellular functions in the lens epithelium and not just the lens fiber cells as previously thought. These studies may be directly relevant to understanding the general cellular functions of crystallins.

Scallop lens Ω-crystallin (ALDH1A9): A novel tetrameric aldehyde dehydrogenase

Scallop eye lens Omega-crystallin is an inactive aldehyde dehydrogenase (ALDH1A9) related to cytoplasmic ALDH1A1 and mitochondrial ALDH2 that migrates by gel filtration chromatography as a homodimer. Because mammalian ALDH1A1 and ALDH2 are homotetramers, we investigated the native molecular mass of scallop Omega-crystallin by multi-angle laser light scattering. The results indicate that the scallop Omega-crystallin is a tetrameric, not a dimeric protein. Moreover, phylogenetic tree analysis shows that scallop Omega-crystallin clusters with the mitochondrial ALDH2 and ALDH1B1 rather than the cytoplasmic ALDH1A, yet it lacks the mitochondrial N-terminal leader sequence characteristic of the mitochondrial ALDHs. The mitochondrial grouping, enzymatic inactivity, and anomalous gel filtration behavior make scallop cytoplasmic Omega-crystallin an interesting protein for structural studies of evolutionary adaptations to become an enzyme-crystallin.