Murugesan Raju

αA-Crystallin Peptide 66SDRDKFVIFLDVKHF80 Accumulating in Aging Lens Impairs the Function of α-Crystallin and Induces Lens Protein Aggregation

Background The eye lens is composed of fiber cells that are filled with α-, β- and γ-crystallins. The primary function of crystallins is to maintain the clarity of the lens through ordered interactions as well as through the chaperone-like function of α-crystallin. With aging, the chaperone function of α-crystallin decreases, with the concomitant accumulation of water-insoluble, light-scattering oligomers and crystallin-derived peptides. The role of crystallin-derived peptides in age-related lens protein aggregation and insolubilization is not understood. Methodology/Principal Findings We found that αA-crystallin-derived peptide, 66 SDRDKFVIFLDVKHF 80, which accumulates in the aging lens, can inhibit the chaperone activity of α-crystallin and cause aggregation and precipitation of lens crystallins. Age-related change in the concentration of αA-(66-80) peptide was estimated by mass spectrometry. The interaction of the peptide with native crystallin was studied by multi-angle light scattering and fluorescence methods. High molar ratios of peptide-to-crystallin were favourable for aggregation and precipitation. Time-lapse recordings showed that, in the presence of αA-(66-80) peptide, α-crystallin aggregates and functions as a nucleus for protein aggregation, attracting aggregation of additional α-, β- and γ-crystallins. Additionally, the αA-(66-80) peptide shares the principal properties of amyloid peptides, such as β-sheet structure and fibril formation. Conclusions/Significance These results suggest that crystallin-derived peptides such as αA-(66-80), generated in vivo, can induce age-related lens changes by disrupting the structure and organization of crystallins, leading to their insolubilization. The accumulation of such peptides in aging lenses may explain a novel mechanism for age-related crystallin aggregation and cataractogenesis.

αA-Crystallin–Derived Mini-Chaperone Modulates Stability and Function of Cataract Causing αAG98R-Crystallin

Background A substitution mutation in human αA-crystallin (αAG98R) is associated with autosomal dominant cataract. The recombinant mutant αAG98R protein exhibits altered structure, substrate-dependent chaperone activity, impaired oligomer stability and aggregation on prolonged incubation at 37°C. Our previous studies have shown that αA-crystallin–derived mini-chaperone (DFVIFLDVKHFSPEDLTVK) functions like a molecular chaperone by suppressing the aggregation of denaturing proteins. The present study was undertaken to determine the effect of αA-crystallin–derived mini-chaperone on the stability and chaperone activity of αAG98R-crystallin. Methodology/Principal Findings Recombinant αAG98R was incubated in presence and absence of mini-chaperone and analyzed by chromatographic and spectrometric methods. Transmission electron microscope was used to examine the effect of mini-chaperone on the aggregation propensity of mutant protein. Mini-chaperone containing photoactive benzoylphenylalanine was used to confirm the interaction of mini-chaperone with αAG98R. The rescuing of chaperone activity in mutantα-crystallin (αAG98R) by mini-chaperone was confirmed by chaperone assays. We found that the addition of the mini-chaperone during incubation of αAG98R protected the mutant crystallin from forming larger aggregates that precipitate with time. The mini-chaperone-stabilized αAG98R displayed chaperone activity comparable to that of wild-type αA-crystallin. The complexes formed between mini-αA–αAG98R complex and ADH were more stable than the complexes formed between αAG98R and ADH. Western-blotting and mass spectrometry confirmed the binding of mini-chaperone to mutant crystallin. Conclusion/Significance These results demonstrate that mini-chaperone stabilizes the mutant αA-crystallin and modulates the chaperone activity of αAG98R. These findings aid in our understanding of how to design peptide chaperones that can be used to stabilize mutant αA-crystallins and preserve the chaperone function.

Alpha-crystallin-derived peptides as therapeutic chaperones☆

BACKGROUND The demonstration of chaperone-like activity in peptides (mini-chaperones) derived from α-crystallins chaperone region has generated significant interest in exploring the therapeutic potential of peptide chaperones in diseases of protein aggregation. Recent studies in experimental animals show that mini-chaperones could reach intended targets and alter the disease phenotype. Although mini-chaperones show potential benefits against protein aggregation diseases, they do tend to form aggregates on storage. There is thus a need to fine-tune peptide chaperones to increase their solubility, pharmacokinetics, and biological efficacy. SCOPE OF REVIEW This review summarizes the properties and the potential therapeutic roles of mini-chaperones in protein aggregation diseases and highlights some of the refinements needed to increase the stability and biological efficacy of mini-chaperones while maintaining or enhancing their chaperone-like activity against precipitation of unfolding proteins. MAJOR CONCLUSIONS Mini-chaperones suppress the aggregation of proteins, block amyloid fibril formation, stabilize mutant proteins, sequester metal ions, and exhibit antiapoptotic properties. Much work must be done to fine-tune mini-chaperones and increase their stability and biological efficacy. Peptide chaperones could have a great therapeutic value in diseases associated with protein aggregation and apoptosis. GENERAL SIGNIFICANCE Accumulation of misfolded proteins is a primary cause for many age-related diseases, including cataract, macular degeneration, and various neurological diseases. Stabilization of native proteins is a logical therapeutic approach for such diseases. Mini-chaperones, with their inherent antiaggregation and antiapoptotic properties, may represent an effective therapeutic molecule to prevent the cascade of protein conformational disorders. Future studies will further uncover the therapeutic potential of mini-chaperones. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Addition of αA-crystallin sequence 164-173 to a mini-chaperone DFVIFLDVKHFSPEDLT alters the conformation but not the chaperone-like activity.

It has been shown that αA-mini-chaperone, a peptide representing the chaperone binding site in αA-crystallin, prevents destabilized protein aggregation. αA-Mini-chaperone has been shown to form amyloid fibrils. This study was undertaken to improve the stability of αA-mini-chaperone while preserving its anti-aggregation activity by fusing the flexible and solvent-exposed C-terminal 164–173 region of αA-crystallin to the mini-chaperone sequence DFVIFLDVKHFSPEDLT. The resulting chimeric chaperone peptide, DFVIFLDVKHFSPEDLTEEKPTSAPSS (designated CP1), was characterized. Circular dichroism studies showed that unlike αA-mini-chaperone with its β-sheet structure, the CP1 peptide exhibited a random structure. Transmission electron microscopy (TEM) examination of the CP1 peptide incubated in a shaker at 37 °C for 72 h did not reveal amyloid fibrils, whereas αA-mini-chaperone showed distinct fibrils. Consistent with TEM observation, the thioflavin T binding assay showed an increased level of dye binding in the mini-chaperone incubated at 37 °C and subjected to shaking but not of the CP1 peptide incubated under similar conditions. The chaperone activity of the CP1 peptide was comparable to that of αA-mini-chaperone against denaturing alcohol dehydrogenase, citrate synthase, and α-lactalbumin. Transduction of both peptide chaperones to COS-7 cells showed no cytotoxic effects. The antioxidation assay involving the H2O2 treatment of COS-7 cells revealed that αA-mini-chaperone and the CP1 peptide have comparable cytoprotective properties against H2O2-induced oxidative damage in COS-7 cells. This study therefore shows that the addition of C-terminal sequence 164–173 of αA-crystallin to αA-mini-chaperone influences the conformation of αA-mini-chaperone without affecting its chaperone function or cytoprotective activity.

The critical role of the central hydrophobic core (residues 71–77) of amyloid-forming αA66-80 peptide in α-crystallin aggregation: a systematic proline replacement study

Abstract Age-related cataract formation is marked by the progressive aggregation of lens proteins. The formation of protein aggregates in the aging lens has been shown to correlate with the progressive accumulation of a range of post-translational crystallin modifications, including oxidation, deamidation, racemization, methylation, acetylation, N- and C-terminal truncations and low molecular weight (LMW) crystallin fragments. We found that an αA-crystallin-derived peptide, αA66-80 (1.8 kDa), is a prominent LMW peptide concentrated in water-insoluble fractions of the aging lens. The peptide has amyloid-like properties and preferentially insolubilizes α-crystallin from lens-soluble fractions. It binds at multiple sites and forms a hydrophobically driven non-covalent complex with α-crystallin to induce α-crystallin aggregation. To define the specific role of the αA66-80 peptide in age-related protein aggregation and cataract formation, it is important to understand the mechanisms by which this peptide acts. We used scanning proline mutagenesis to identify which particular sequences of the peptide drive it to form amyloid-like fibrils and induce α-crystallin aggregation. The secondary structure and the aggregate morphology of the peptides were determined using circular dichroism and transmission electron microscopy, respectively. Peptides were also tested for their ability to induce α-crystallin aggregation. We found that proline replacement of any residue in the sequence FVIFLDV, which corresponds to residues 71–77, led to an absence of both fibril formation and α-crystallin aggregation. The apparently critical role of 71–77 residues in αA66-80 explains their significance in the self-assembly processes of the peptide and further provide insights into the mechanism of peptide-induced aggregation. Our findings may have applications in the design of peptide aggregation inhibitors.

Glia Maturation Factor Dependent Inhibition of Mitochondrial PGC-1α Triggers Oxidative Stress-Mediated Apoptosis in N27 Rat Dopaminergic Neuronal Cells

Parkinson’s disease (PD) is a progressive neurodegenerative disease affecting over five million individuals worldwide. The exact molecular events underlying PD pathogenesis are still not clearly known. Glia maturation factor (GMF), a neuroinflammatory protein in the brain plays an important role in the pathogenesis of PD. Mitochondrial dysfunctions and oxidative stress trigger apoptosis leading to dopaminergic neuronal degeneration in PD. Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α or PPARGC-α) acts as a transcriptional co-regulator of mitochondrial biogenesis and energy metabolism by controlling oxidative phosphorylation, antioxidant activity, and autophagy. In this study, we found that incubation of immortalized rat dopaminergic (N27) neurons with GMF influences the expression of peroxisome PGC-1α and increases oxidative stress, mitochondrial dysfunction, and apoptotic cell death. We show that incubation with GMF reduces the expression of PGC-1α with concomitant decreases in the mitochondrial complexes. Besides, there is increased oxidative stress and depolarization of mitochondrial membrane potential (MMP) in these cells. Further, GMF reduces tyrosine hydroxylase (TH) expression and shifts Bax/Bcl-2 expression resulting in release of cytochrome-c and increased activations of effector caspase expressions. Transmission electron microscopy analyses revealed alteration in the mitochondrial architecture. Our results show that GMF acts as an important upstream regulator of PGC-1α in promoting dopaminergic neuronal death through its effect on oxidative stress-mediated apoptosis. Our current data suggest that GMF is a critical risk factor for PD and suggest that it could be explored as a potential therapeutic target to inhibit PD progression.

Lens Crystallin Modifications and Cataract in Transgenic Mice Overexpressing Acylpeptide Hydrolase

Background: Acylpeptide hydrolase (APH) in the lens may have an integral role in cataract formation. Results: Transgenic overexpression of APH results in crystallin cleavage, impaired lens development, and cataract. Conclusion: APH may be involved in the generation of peptides that have the potential to induce protein aggregation. Significance: The transgenic APH mouse model could help us understand the role of crystallin fragments in cataractogenesis. The accumulation of crystallin fragments in vivo and their subsequent interaction with crystallins are responsible, in part, for protein aggregation in cataracts. Transgenic mice overexpressing acylpeptide hydrolase (APH) specifically in the lens were prepared to test the role of protease in the generation and accumulation of peptides. Cataract development was seen at various postnatal days in the majority of mice expressing active APH (wt-APH). Cataract onset and severity of the cataracts correlated with the APH protein levels. Lens opacity occurred when APH protein levels were >2.6% of the total lens protein and the specific activity, assayed using Ac-Ala-p-nitroanilide substrate, was >1 unit. Transgenic mice carrying inactive APH (mt-APH) did not develop cataract. Cataract development also correlated with N-terminal cleavage of the APH to generate a 57-kDa protein, along with an increased accumulation of low molecular weight (LMW) peptides, similar to those found in aging human and cataract lenses. Nontransgenic mouse lens proteins incubated with purified wt-APH in vitro resulted in a >20% increase in LMW peptides. Crystallin modifications and cleavage were quite dramatic in transgenic mouse lenses with mature cataract. Affected lenses showed capsule rupture at the posterior pole, with expulsion of the lens nucleus and degenerating fiber cells. Our study suggests that the cleaved APH fragment might exert catalytic activity against crystallins, resulting in the accumulation of distinct LMW peptides that promote protein aggregation in lenses expressing wt-APH. The APH transgenic model we developed will enable in vivo testing of the roles of crystallin fragments in protein aggregation.

Investigating Risk Factors for Cataract Using the Cerner Health Facts® Database

Title: Investigating Risk Factors for Cataract Using the Cerner Health Facts® Database Background: A retrospective study was performed using the Cerner Health Facts® database, a HIPAA compliant and deidentified database, to evaluate risk factors associated with cataract. Methods and Findings: Using ICD-9 codes, a study group population was determined by selecting all patients in the database who visited the eye clinic. A data-driven approach was used to select multiple variables and odds ratio analysis was performed to determine the association of the risk factors with cataract formation. Odds ratio analysis indicated that 7 variables out of 18 were at a 20% or higher odds for developing of cataract. These include gentamicin, hypertension, lipid metabolism disorder, obesity, steroids and type-two diabetes and lacrimal disorder. Conclusion: This is the first study to show a link between lacrimal disorders and the development of cataract.

Cell‐Penetrating Chaperone Peptide Prevents Protein Aggregation and Protects against Cell Apoptosis

Many of the newly discovered therapeutic peptides and molecules are limited by their inability to cross the cell membrane. In the present study, a cell‐penetrating peptide (CPP), VPTLK, derived from Ku70 protein, is employed to facilitate the entry of a minichaperone across the cell membrane. Previous studies suggest that the minichaperone peptide representing the chaperone site in αA‐crystallin, which can inhibit protein aggregation associated with proteopathies, has therapeutic potential. A synthetic minichaperone is prepared by fusing the VPTLK sequence to N‐terminus of minichaperone (FVIFLDVKHFSPEDLTVKGRD) to get VPTLKFVIFLDVKHFSPEDLTVKGRD peptide, which is called “CPPGRD.” The amino acids, glycine–arginine–aspartic acid (GRD), are added to increase the solubility of the peptide. The chaperone‐like function of CPPGRD is measured using unfolding conditions for alcohol dehydrogenase and α‐lactalbumin. The antiapoptotic action of the peptide chaperone is evaluated using H2O2‐induced Cos‐7 and ARPE‐19 cell apoptosis assays. The results show that the CPPGRD has both chaperone function and antiapoptotic activity. Additionally, the CPPGRD is found to prevent β‐amyloid fibril formation and suppress β‐amyloid toxicity. The present study demonstrates that the CPPGRD protects unfolding proteins from aggregation and prevents cellular apoptosis. Therefore, the CPPGRD is a minichaperone with potential to become a therapeutic agent for protein aggregation diseases.

Corneal transplant failure associated with smoking

This retrospective study was conducted in the University of Missouri’s cornea transplant service from January 1, 2010 to September 30, 2015 to determine whether smoking increases the risk of corneal transplant failure. Cornea transplant patient’s records were identified via the Informatics for Integrity Biology and the Bedside data query portal using the ICD-9 codes for penetrating keratoplasty (11.64), endothelial keratoplasty (11.62, 11.63 and 11.69) and 996.51 for corneal transplant failures. A total of 257 patients were identified. The study sample was 52% female and 48% male. A total of 151 patients had penetrating keratoplasty, while 106 had endothelial keratoplasty. Penetrating keratoplasty patients with a history of smoking had a significantly higher rate of transplant failure (73%) versus those with no history of smoking (53%). Endothelial keratoplasty patients with a smoking history had a slightly higher rate of transplant failure (33.3%) versus those with no history of smoking (30%). Glaucoma patients with smoking habits also had a higher transplant failure rate (70%) compared to glaucoma patients without a smoking history (52%). Further, the study showed that female smokers and younger smokers (<54) have higher transplant failure rates. Overall the study found that patients with a history of smoking have higher rates of corneal transplant failure than non-smokers. Correspondence to: Frederick W. Fraunfelder, department of Ophthalmology, Mason Eye Institute, One Hospital Drive, Columbia, Missouri 65212, USA, Tel: 573-882-1029; Fax: 573-882-8474; E-mail: fraunfelderf@health.missouri.edu.