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

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

Insights into the biochemical and biophysical mechanisms mediating the longevity of the transparent optics of the eye lens.

In the human eye, a transparent cornea and lens combine to form the "refracton" to focus images on the retina. This requires the refracton to have a high refractive index "n," mediated largely by extracellular collagen fibrils in the corneal stroma and the highly concentrated crystallin proteins in the cytoplasm of the lens fiber cells. Transparency is a result of short-range order in the spatial arrangement of corneal collagen fibrils and lens crystallins, generated in part by post-translational modifications (PTMs). However, while corneal collagen is remodeled continuously and replaced, lens crystallins are very long-lived and are not replaced and so accumulate PTMs over a lifetime. Eventually, a tipping point is reached when protein aggregation results in increased light scatter, inevitably leading to the iconic protein condensation-based disease, age-related cataract (ARC). Cataracts account for 50% of vision impairment worldwide, affecting far more people than other well-known protein aggregation-based diseases. However, because accumulation of crystallin PTMs begins before birth and long before ARC presents, we postulate that the lens protein PTMs contribute to a "cataractogenic load" that not only increases with age but also has protective effects on optical function by stabilizing lens crystallins until a tipping point is reached. In this review, we highlight decades of experimental findings that support the potential for PTMs to be protective during normal development. We hypothesize that ARC is preventable by protecting the biochemical and biophysical properties of lens proteins needed to maintain transparency, refraction, and optical function.

Alzheimer's disease amyloid-ß pathology in the lens of the eye.

Neuropathological hallmarks of Alzheimer's disease (AD) include pathogenic accumulation of amyloid-ß (Aß) peptides and age-dependent formation of amyloid plaques in the brain. AD-associated Aß neuropathology begins decades before onset of cognitive symptoms and slowly progresses over the course of the disease. We previously reported discovery of Aß deposition, ß-amyloidopathy, and co-localizing supranuclear cataracts (SNC) in lenses from people with AD, but not other neurodegenerative disorders or normal aging. We confirmed AD-associated Aß molecular pathology in the lens by immunohistopathology, amyloid histochemistry, immunoblot analysis, epitope mapping, immunogold electron microscopy, quantitative immunoassays, and tryptic digest mass spectrometry peptide sequencing. Ultrastructural analysis revealed that AD-associated Aß deposits in AD lenses localize as electron-dense microaggregates in the cytoplasm of supranuclear (deep cortex) fiber cells. These Aß microaggregates also contain αB-crystallin and scatter light, thus linking Aß pathology and SNC phenotype expression in the lenses of people with AD. Subsequent research identified Aß lens pathology as the molecular origin of the distinctive cataracts associated with Down syndrome (DS, trisomy 21), a chromosomal disorder invariantly associated with early-onset Aß accumulation and Aß amyloidopathy in the brain. Investigation of 1249 participants in the Framingham Eye Study found that AD-associated quantitative traits in brain and lens are co-heritable. Moreover, AD-associated lens traits preceded MRI brain traits and cognitive deficits by a decade or more and predicted future AD. A genome-wide association study of bivariate outcomes in the same subjects identified a new AD risk factor locus in the CTNND2 gene encoding δ-catenin, a protein that modulates Aß production in brain and lens. Here we report identification of AD-related human Aß (hAß) lens pathology and age-dependent SNC phenotype expression in the Tg2576 transgenic mouse model of AD. Tg2576 mice express Swedish mutant human amyloid precursor protein (APP-Swe), accumulate hAß peptides and amyloid pathology in the brain, and exhibit cognitive deficits that slowly progress with increasing age. We found that Tg2576 trangenic (Tg+) mice, but not non-transgenic (Tg-) control mice, also express human APP, accumulate hAß peptides, and develop hAß molecular and ultrastructural pathologies in the lens. Tg2576 Tg+ mice exhibit age-dependent Aß supranuclear lens opacification that recapitulates lens pathology and SNC phenotype expression in human AD. In addition, we detected hAß in conditioned medium from lens explant cultures prepared from Tg+ mice, but not Tg- control mice, a finding consistent with constitutive hAß generation in the lens. In vitro studies showed that hAß promoted mouse lens protein aggregation detected by quasi-elastic light scattering (QLS) spectroscopy. These results support mechanistic (genotype-phenotype) linkage between Aß pathology and AD-related phenotypes in lens and brain. Collectively, our findings identify Aß pathology as the shared molecular etiology of two age-dependent AD-related cataracts associated with two human diseases (AD, DS) and homologous murine cataracts in the Tg2576 transgenic mouse model of AD. These results represent the first evidence of AD-related Aß pathology outside the brain and point to lens Aß as an optically-accessible AD biomarker for early detection and longitudinal monitoring of this devastating neurodegenerative disease.

The occhiolino (occ) mutant Zebrafish, a model for development of the optical function in the biological lens.

BACKGROUND: Zebrafish visual function depends on quality optics. An F3 screen for developmental mutations in the Zebrafish nervous system was conducted in wild-type (wt) AB Zebrafish exposed to 3 mM of N-ethyl-N-nitrosourea (ENU). RESULTS: Mutant offspring, identified in an F3 screen, were characterized by a small pupil, resulting from retinal hypertrophy or hyperplasia and a small lens. Deficits in visual function made feeding difficult after hatching at approximately 5-6 days postfertilization (dpf). Special feeding conditions were necessary for survival of the occhiolino (occ) mutants after 6 dpf. Optokinetic response (OKR) tests measured defects in visual function in the occ mutant, although electroretinograms (ERGs) were normal in the mutant and wt. Consistent with the ERGs, histology found normal retinal structure in the occ mutant and wt Zebrafish. However, lens development was abnormal. Multiphoton imaging of the developmental stages of live embryos confirmed the formation of a secondary mass of lens cells in the developing eye of the mutant Zebrafish at 3-4 dpf, and laminin immunohistochemistry indicated the lens capsule was thin and disorganized in the mutant Zebrafish. CONCLUSIONS: The occ Zebrafish is a novel disease model for visual defects associated with abnormal lens development. Developmental Dynamics 246:915-924, 2017. © 2017 Wiley Periodicals, Inc.

Functional sequences in human alphaB crystallin.

BACKGROUND: Human alphaB crystallin (HspB5) contains the alpha crystallin core domain, a series of antiparallel beta-strands organized into the characteristic beta sandwich of small heat shock proteins (sHsps). The full 3-dimensional structure for alpha crystallin has not been determined and the mechanism for the biological activity remains elusive because sHsps participate in multiple interactions with a broad range of target proteins that favor self-assembly of polydisperse fibrils and complexes. We selected human alphaB crystallin to study interactive sequences because it is involved in many human condensation, amyloid, and aggregation diseases and it is very sensitive to the destabilization of unfolding proteins. Sophisticated methods are being used to analyze and complete the structure of alphaB crystallin with the expectation of understanding sHsp function. This review considers the identification of interactive sites on the surface of the alphaB crystallin, which may be the key to understanding the multifunctional activity of human alphaB crystallin. SCOPE OF REVIEW: This review summarizes the research on the identification of the bioactive interactive sequences responsible for the function of human alphaB crystallin, an sHsp with chaperone-like activity. MAJOR CONCLUSIONS: The multifunctional activity of human alphaB crystallin results from the interactive peptide sequences exposed on the surface of the molecule. The multiple, non-covalent, interactive sequences can account for the selectivity and sensitivity of alphaB crystallin to the initiation of protein unfolding. GENERAL SIGNIFICANCE: Human alphaB crystallin may be an important part of an endogenous protective mechanism in aging cells and tissues. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

A method to prevent protein delocalization in imaging mass spectrometry of non-adherent tissues: application to small vertebrate lens imaging.

MALDI imaging requires careful sample preparation to obtain reliable, high-quality images of small molecules, peptides, lipids, and proteins across tissue sections. Poor crystal formation, delocalization of analytes, and inadequate tissue adherence can affect the quality, reliability, and spatial resolution of MALDI images. We report a comparison of tissue mounting and washing methods that resulted in an optimized method using conductive carbon substrates that avoids thaw mounting or washing steps, minimizes protein delocalization, and prevents tissue detachment from the target surface. Application of this method to image ocular lens proteins of small vertebrate eyes demonstrates the improved methodology for imaging abundant crystallin protein products. This method was demonstrated for tissue sections from rat, mouse, and zebrafish lenses resulting in good-quality MALDI images with little to no delocalization. The images indicate, for the first time in mouse and zebrafish, discrete localization of crystallin protein degradation products resulting in concentric rings of distinct protein contents that may be responsible for the refractive index gradient of vertebrate lenses.

Evolution of the vertebrate beaded filament protein, Bfsp2; comparing the in vitro assembly properties of a "tailed" zebrafish Bfsp2 to its "tailless" human orthologue.

In bony fishes, Bfsp2 orthologues are predicted to possess a C-terminal tail domain, which is absent from avian, amphibian and mammalian Bfsp2 sequences. These sequences, are however, not conserved between fish species and therefore questions whether they have a functional role. For other intermediate filament proteins, the C-terminal tail domain is important for both filament assembly and regulating interactions between filaments. We confirm that zebrafish has a single Bfsp2 gene by radiation mapping. Two transcripts (bfsp2α and bfsp2ß) are produced by alternative splicing of the last exon. Using a polyclonal antibody specific to a tridecameric peptide in the C-terminal tail domain common to both zebrafish Bfsp2 splice variants, we have confirmed its expression in zebrafish lens fibre cells. We have also determined the in vitro assembly properties of zebrafish Bfsp2α and conclude that the C-terminal sequences are required to regulate not only the diameter and uniformity of the in vitro assembly filaments, but also their filament-filament associations in vitro. Therefore we conclude zebrafish Bfsp2α is a functional orthologue conforming more closely to the conventional domain structure of intermediate filament proteins. Data mining of the genome databases suggest that the loss of this tail domain could occur in several stages leading eventually to completely tailless orthologues, such as human BFSP2.

Age-related loss of auditory sensitivity in the zebrafish (Danio rerio).

Age-related hearing loss (ARHL), also known as presbycusis, is a widespread and debilitating condition impacting many older adults. Conventionally, researchers utilize mammalian model systems or human cadaveric tissue to study ARHL pathology. Recently, the zebrafish has become an effective and tractable model system for a wide variety of genetic and environmental auditory insults, but little is known about the incidence or extent of ARHL in zebrafish and other non-mammalian models. Here, we evaluated whether zebrafish exhibit age-related loss in auditory sensitivity. The auditory sensitivity of adult wild-type zebrafish (AB/WIK strain) from three adult age subgroups (13-month, 20-month, and 37-month) was characterized using the auditory evoked potential (AEP) recording technique. AEPs were elicited using pure tone stimuli (115-4500 Hz) presented via an underwater loudspeaker and recorded using shielded subdermal metal electrodes. Based on measures of sound pressure and particle acceleration, the mean AEP thresholds of 37-month-old fish [mean sound pressure level (SPL) = 122.2 dB ± 2.2 dB SE re: 1 µPa; mean particle acceleration level (PAL) = -27.5 ± 2.3 dB SE re: 1 ms-2] were approximately 9 dB higher than that of 20-month-old fish [(mean SPL = 113.1 ± 2.7 dB SE re: 1 µPa; mean PAL = -37.2 ± 2.8 dB re: 1 ms-2; p = 0.007)] and 6 dB higher than that of 13-month-old fish [(mean SPL = 116.3 ± 2.5 dB SE re: 1 µPa; mean PAL = -34.1 ± 2.6 dB SE re: 1 ms-2; p = 0.052)]. Lowest AEP thresholds for all three age groups were generally between 800 Hz and 1850 Hz, with no evidence for frequency-specific age-related loss. Our results suggest that zebrafish undergo age-related loss in auditory sensitivity, but the form and magnitude of loss is markedly different than in mammals, including humans. Future work is needed to further describe the incidence and extent of ARHL across vertebrate groups and to determine which, if any, ARHL mechanisms may be conserved across vertebrates to support meaningful comparative/translational studies.

Early lens development in the zebrafish: a three-dimensional time-lapse analysis.

In vivo, high-resolution, time-lapse imaging characterized lens development in the zebrafish from 16 to 96 hr postfertilization (hpf). In zebrafish, the lens placode appeared in the head ectoderm, similar to mammals. Delamination of the surface ectoderm resulted in the formation of the lens mass, which progressed to a solid sphere of cells separating from the developing cornea at approximately 24 hpf. A lens vesicle was not observed and apoptosis was not a major factor in separation of the lens from the future cornea. Differentiation of primary fibers began in the lens mass followed by formation of the anterior epithelium after delamination was complete. Secondary fibers differentiated from elongating epithelial cells near the posterior pole. Quantification characterized three stages of lens growth. The study confirmed the advantages of live-cell imaging for three-dimensional quantitative structural characterization of the mechanism(s) responsible for cell differentiation in formation of a transparent, symmetric, and refractile lens.

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

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

The zebrafish lens proteome during development and aging.

PURPOSE: Changes in lens protein expression during zebrafish development results in a smooth gradient of refractive index necessary for excellent optical function. Age-related changes in crystallin expression have been well documented in mammals but are poorly understood in the zebrafish. METHODS: In the zebrafish lens, a systematic analysis of protein content with age was performed using size exclusion chromatography (SEC) combined with linear trap quadrupole Fourier transform tandem mass spectrometry (LTQ-FT LC-MS/MS; rank-order shotgun) proteomics in lenses of larval, juvenile, and adult zebrafish. RESULTS: alpha-Crystallins, previously shown to have low abundance in the zebrafish lens, were found to increase dramatically with maturation and aging. SEC determined that beta-crystallin was predominant at 4.5 days. With age, the alpha- and gamma-crystallins increased, and a high molecular weight fraction appeared between six weeks and six months to become the dominant component by 2.5 years. Similarly, shotgun proteomics determined that beta-crystallins were the predominant proteins in the young lens. With age, the proportion of alpha- and gamma-crystallins increased dramatically. After crystallins, calpain 3, membrane, and cytoskeletal proteins were most abundant. Five new beta-crystallins and 13 new gamma-crystallins were identified. CONCLUSIONS: As expected, SEC and proteomics demonstrated changing levels of protein expression with age, especially among the crystallins. The results also confirmed the existence of novel crystallins in the zebrafish genome.

Absence of SPARC leads to impaired lens circulation.

SPARC is a matricellular glycoprotein involved in regulation of extracellular matrix, growth factors, adhesion, and migration. SPARC-null mice have altered basement membranes and develop posterior sub-capsular cataracts with cell swelling and equatorial vacuoles. Exchange of fluid, nutrients, and waste products in the avascular lens is driven by a unique circulating ion current. In the absence of SPARC, increased circulation of fluid, ions, and small molecules led to increased fluorescein distribution in vivo, loss of resting membrane polarization, and altered distribution of small molecules. Microarray analysis of SPARC-null lenses showed changes in gene expression of ion channels and receptors, matrix and adhesion genes, cytoskeleton, immune response genes, and cell signaling molecules. Our results confirm the hypothesis that the regulation of SPARC on cell-capsular matrix interactions can increase the circulation of fluid and ions in the lens, and the phenotype in the SPARC-null mouse lens is the result of multiple intersecting functional pathways.

Interactive sequences in the molecular chaperone, human alphaB crystallin modulate the fibrillation of amyloidogenic proteins.

Multiple interactive domains are involved in the activity of the stress protein, alphaB crystallin that protects against the unfolding, aggregation, and toxicity of amyloidogenic proteins. Six peptides corresponding to the interactive sequences 41STSLSPFYLRPPSFLRAP58, 73DRFSVNLDVKHFS85, 101HGKHEERQDE110, 113FISREFHR120, 131LTITSSLSSDGV142, and 156ERTIPITRE164 in human alphaB crystallin were synthesized and evaluated in Thioflavin T fluorescence assays for their effects on the modulation of fibrillation of four disease-related amyloidogenic proteins: amyloid-beta, alpha-synuclein, transthyretin, and beta2-microglobulin. The 73DRFSVNLDVKHFS85 and 101HGKHEERQDE110 peptides in the conserved alpha crystallin core domain of alphaB crystallin were the most effective fibril inhibitors. 73DRFSVNLDVKHFS85 completely inhibited alpha-synuclein fibrillation and reduced the fibrillation of amyloid-beta, transthyretin, and beta2-microglobulin by >50%. 101HGKHEERQDE110 completely inhibited amyloid-beta fibrillation and reduced the fibrillation of alpha-synuclein, transthyretin, and beta2-microglobulin by >50%. The peptides FSVN, NLDV, HGKH, and HEER, which are synthetic fragments of 73DRFSVNLDVKHFS85 and 101HGKHEERQDE110, inhibited fibrillation of all four amyloidogenic proteins by >75%. In contrast, the peptides FISREFHR, ERTIPITRE, DRFS, KHFS, and EERQ were the strongest promoters of fibrillation. Molecular modeling of the interactions between transthyretin and beta2-microglobulin and the synthetic bioactive peptides determined that residues Phe-75, Ser-76, Val-77, Asn-78, Leu-79, and Asp-80 in 73DRFSVNLDVKHFS85 and residues His-101, Lys-103, His-104, Glu-105, and Arg-107 in 101HGKHEERQDE110 interact with exposed residues in the beta strands, F and D of transthyretin and beta2-microglobulin, respectively, to modulate fibrillation. This is the first characterization of specific bioactive peptides synthesized on the basis of interactive domains in the small heat shock protein, alphaB crystallin that protect against the fibrillation of amyloidogenic proteins.

Interactive sequences in the stress protein and molecular chaperone human alphaB crystallin recognize and modulate the assembly of filaments.

Molecular chaperones including the small heat shock proteins, alphaB crystallin and sHSP27 participate in the assembly, disassembly, and reorganization of the cytoskeleton during cell development and differentiation. While alphaB crystallin and sHSP27 stabilize and modulate filament assembly and re-organization, the sequences and structural domains mediating interactions between these proteins and filaments are unknown. It is important to define these interactive domains in order to understand differential interactions between chaperones and stable or unfolding filaments and their function in the cellular stress response. Protein pin arrays identified sequences in human alphaB crystallin that selectively interacted with native or partially unfolded filament proteins desmin, glial-fibrillary acidic protein, and actin. Circular dichroism spectroscopy determined differences in the structure of these filaments at 23 and 45 degrees C. Seven alphaB crystallin sequences had stronger interactions with desmin and six sequences had stronger interactions with glial-fibrillary acidic protein at 23 degrees C than at 45 degrees C. The alphaB crystallin sequences (33)LESDLFPTSTSLSPFYLRPPSFLR(56) and (129)DPLTITSSLSSDGV(145) had the strongest interactions with actin at 23 degrees C, while (57)APSWFDTG(64), (111)HGFISREF(118), (145)VNGPRKQVSG(154), and (155)PERTIPITREEK(165) had the strongest interactions with actin at 45 degrees C. The actin interactive sequences of alphaB crystallin overlapped with previously identified alphaB crystallin chaperone sequences and were synthesized to evaluate their effect on the assembly and aggregation of actin. Full-length alphaB crystallin and the core domain chaperone sequence (131)LTITSSLSSDGV(143) promoted actin polymerization at 37 degrees C and inhibited depolymerization and aggregation at 50 degrees C. The results support the hypothesis that interactive domains in alphaB crystallin have multiple functions in stabilizing the cytoskeleton and protecting cytosolic proteins from unfolding.

The beta4-beta8 groove is an ATP-interactive site in the alpha crystallin core domain of the small heat shock protein, human alphaB crystallin.

The site for ATP interactions in human alphaB crystallin, the archetype of small heat-shock proteins, was identified and characterized to resolve the controversial role of ATP in the function of small heat-shock proteins. Comparative sequence alignments identified the alphaB crystallin sequence, (82)KHFSPEELKVKVLGD(96) as a Walker-B ATP-binding motif that is found in several ATP-binding proteins, including five molecular chaperones. Fluorescence resonance energy transfer and mass spectrometry using a novel fluorescent ATP analog, 8-azido-ATP-[gamma]-1-naphthalenesulfonic acid-5(2-aminoethylamide) (azido-ATP-EDANS) and a cysteine mutant of human alphaB crystallin (S135C) conjugated with a fluorescent acceptor, eosin-5-maleimide (EMA) identified the beta4-beta8 groove as the ATP interactive site in alphaB crystallin. A 44% decrease in the emitted fluorescence of azido-ATP-EDANS at the absorption maximum of S135C-EMA and a corresponding 50% increase in the fluorescence emission of S135C-EMA indicated a close spatial relationship between azido-ATP-EDANS and the center of the beta8 strand ((131)LTITSSLS(138)). Liquid chromatography, electrospray ionization mass spectrometry identified two peptide fragments of the alphaB crystallin Walker-B motif photo-affinity-labeled with azido-ATP-EDANS confirming the beta4-beta8 groove as an ATP interactive site. The results presented here clearly establish the beta4-beta8 groove as the ATP interactive region in alphaB crystallin, and are in contrast to the existing paradigm that classifies small heat-shock proteins as ATP-independent chaperones.

An in vitro model of posterior capsular opacity: SPARC and TGF-beta2 minimize epithelial-to-mesenchymal transition in lens epithelium.

PURPOSE: This report presents a novel model for studies of extracellular matrix (ECM) in posterior capsular opacification (PCO) in vitro. Lens epithelial cells (LEC) were cultured with an intraocular lens (IOL) on a surface of type IV collagen in an evaluation of the importance of the ECM-cell interaction in formation of PCO. Abnormal migration, proliferation, and expression of proteins associated with the epithelial-to-mesenchymal transition (EMT) that characterizes PCO were observed in the presence and absence of the matricellular protein SPARC (secreted protein, acidic and rich in cysteine), which regulates matrix-cell interactions. METHODS: The model for PCO in vitro consisted of an IOL placed on a membrane coated with collagen IV, a major constituent of the lens capsule. LECs from the lenses of wild-type (WT) and SPARC-null (SP-null) mice were cultured in the presence or absence of 10 ng/mL TGF-beta2 and 20 mug/mL recombinant human SPARC (rhSP) for up to 6 days. The migration of LECs was quantified. Labeling with BrdU and the measurement of DNA synthesis were assays for cell proliferation. Expression of the EMT markers, collagen type I, fibronectin, and alpha-smooth muscle actin were assessed using immunocytochemistry or Western immunoblots. RESULTS: LEC migration, proliferation, and the synthesis of EMT markers were enhanced in SP-null compared with WT LECs. TGF-beta2 inhibited the migration and proliferation of both WT and SP-null LECs in the presence of rhSP. TGF-beta2 increased the production of collagen type I, fibronectin, and alpha-SMA. The responses of SP-null LECs were rescued by the addition of recombinant human (rh)SP. CONCLUSIONS: A simple IOL culture system was useful for the evaluation of the effects of SPARC and TGF-beta2 on PCO in vitro. The action of TGF-beta2 on LEC migration and proliferation is influenced by SPARC, a regulator of matrix-cell interactions. The results indicate a functional intersection between pathways activated by TGF-beta2 and SPARC in the formation of PCO.

The function of the beta3 interactive domain in the small heat shock protein and molecular chaperone, human alphaB crystallin.

Knowledge of the interactive domains on the surface of small heat shock proteins (sHSPs) is necessary for understanding the assembly of complexes and the activity as molecular chaperones. The primary sequences of 26 sHSP molecular chaperones were aligned and compared. In the interactive beta3 sequence, 73DRFSVNLDVKHFS85 of human alphaB crystallin, Ser-76, Asn-78, Lys-82, and His-83 were identified as nonconserved residues on the exposed surface of the alpha crystallin core domain. Site-directed mutagenesis produced the mutant alphaB crystallins: S76E, N78G, K82Q, and H83F. Domain swapping with homologous beta3 sequences, 32EKFEVGLDVQFFT44 from Caenorhabditis elegans sHSP12.2 or 69DKFVIFLDVKHFS81 from alphaA crystallin, resulted in the mutant alphaB crystallins, CE1 and alphaA1, respectively. Decreased chaperone activity was observed with the point mutants N78G, K82Q, and H83F and with the mutant, CE1, in aggregation assays using betaL crystallin, alcohol dehydrogenase (ADH), or citrate synthase (CS). The S76E mutant had minimal effect on chaperone activity, and domain swapping with alphaA crystallin had no effect on chaperone activity. The mutations that resulted in altered chaperone activity, produced minimal modification to the secondary, tertiary, and quaternary structure of human alphaB crystallin as determined by ultraviolet circular dichroism spectroscopy, chymotrypsin proteolysis, and size exclusion chromatography. Chaperone activity was influenced by the amount of unfolding of the target proteins and independent of complex size. The results characterized the importance of the exposed side chains of Glu-78, Lys-82, and His-83 in the interactive beta3 sequence of the alpha crystallin core domain in alphaB crystallin for chaperone function.

Insights into the domains required for dimerization and assembly of human alphaB crystallin.

Protein pin array technology was used to identify subunit-subunit interaction sites in the small heat shock protein (sHSP) alphaB crystallin. Subunit-subunit interaction sites were defined as consensus sequences that interacted with both human alphaA crystallin and alphaB crystallin. The human alphaB crystallin protein pin array consisted of contiguous and overlapping peptides, eight amino acids in length, immobilized on pins that were in a 96-well ELISA plate format. The interaction of alphaB crystallin peptides with physiological partner proteins, alphaA crystallin and alphaB crystallin, was detected using antibodies and recorded using spectrophotometric absorbance. Five peptide sequences including 37LFPTSTSLSPFYLRPPSF54 in the N terminus, 75FSVNLDVK82)(beta3), 131LTITSSLS138 (beta8) and 141GVLTVNGP148 (beta9) that form beta strands in the conserved alpha crystallin core domain, and 155PERTIPITREEK166 in the C-terminal extension were identified as subunit-subunit interaction sites in human alphaB crystallin using the novel protein pin array assay. The subunit-subunit interaction sites were mapped to a three-dimensional (3D) homology model of wild-type human alphaB crystallin that was based on the crystal structure of wheat sHSP16.9 and Methanococcus jannaschi sHSP16.5 (Mj sHSP16.5). The subunit-subunit interaction sites identified and mapped onto the homology model were solvent-exposed and had variable secondary structures ranging from beta strands to random coils and short alpha helices. The subunit-subunit interaction sites formed a pattern of hydrophobic patches on the 3D surface of human alphaB crystallin.

The effects of drug delivery via hydrophilic acrylic (hydrogel) intraocular lens systems on the epithelial cells in culture.

BACKGROUND AND OBJECTIVE: Secondary posterior subcapsular opacification is still among the most important complications after phacoemulsification. MATERIALS AND METHODS: This study was designed to assess the inhibitory effects of drugs delivered via hydrophilic acrylic (hydrogel) intraocular lens (IOL) systems in vitro. Lens epithelial cells were collected from albino rabbits. The following seven groups of hydrogel IOLs were prepared: untreated IOLs and IOLs infiltrated with diclofenac sodium, tranilast, mitomycin C, colchicines, 5-fluorouracil, and ethylenediaminetetraacetic acid. The IOLs were fixed to a Cell Culture Insert; they were then bathed and incubated in minimum essential medium containing cultured lens epithelial cells. Subsequently, a comparative analysis of the cells adhering to the collagen membrane and the lens surfaces was conducted. RESULTS: Adhesion of lens epithelial cells to the lens surfaces and the collagen membrane was observed in the control group. However, only slight cellular adhesion was found on the surfaces of the IOLs and on the collagen membrane in the treated IOL groups. CONCLUSION: Use of hydrogel IOLs infiltrated with drugs was associated with inhibition of posterior subcapsular opacification in vitro.

Expression of the matricellular protein SPARC in murine lens: SPARC is necessary for the structural integrity of the capsular basement membrane.

SPARC (Secreted Protein, Acidic and Rich in Cysteine) is a matricellular glycoprotein that modulates cell proliferation, adhesion, migration, and extracellular matrix (ECM) production. Although SPARC is generally abundant in embryonic tissues and is diminished in adults, we have found that the expression of SPARC in murine lens persists throughout embryogenesis and adulthood. Our previous studies showed that targeted ablation of the SPARC gene in mice results in cataract formation, a pathology attributed partially to an abnormal lens capsule. Here we provide evidence that SPARC is not a structural component of the lens capsule. In contrast, SPARC is abundant in lens epithelial cells, and newly differentiated fiber cells, with stable expression in wild-type mice up to 2 years of age. Pertubation of the lens capsule in animals lacking SPARC appears to be a consequence of the invasion of the lens cells situated beneath the capsule. Immunoreactivity for SPARC in the lens cells was uneven, with minimal reactivity in the epithelial cells immediately anterior to the equator. These epithelial cells appeared essentially noninvasive in SPARC-null mice, in comparison to the centrally located anterior epithelial cells, in which strong labeling by anti-SPARC IgG was observed. The posterior lens fibers exhibited cytoplasmic extensions into the posterior lens capsule, which was severely damaged in SPARC-null lenses. The expression of SPARC in wild-type lens cells, together with the abnormal lens capsule in SPARC-null mice, indicated that the structural integrity of the lens capsule is dependent on the matricellular protein SPARC. The effects of SPARC in the lens appear to involve regulation of lens epithelial and fiber cell morphology and functions rather than deposition as a structural component of the lens capsule.