Identification of proteins that modify cataract of mouse eye lens

The protective role of HSP27 in ocular diseases

Heat shock proteins (HSPs) are stress-induced proteins that are important constituents of the cell's defense system. The activity of HSPs enhances when the cell undergoes undesirable environmental conditions like stress. The protective roles of HSPs are due to their molecular chaperone and anti-apoptotic functions. HSPs have a central role in the eye, and their malfunction has been associated with the manifestation of ocular diseases. Heat shock protein 27 (HSP27, HSPB1) is present in various ocular tissues, and it has been found to protect the eye from disease states such as retinoblastoma, uveal melanoma, glaucoma, and cataract. But some recent studies have shown the destructive role of HSP27 on retinal ganglionic cells. Thus, this article summarizes the role of heat shock protein 27 in eye and ocular diseases and will focus on the expression, regulation, and function of HSP27 in ocular complications.

The Contribution of Fluoride to the Pathogenesis of Eye Diseases: Molecular Mechanisms and Implications for Public Health

This study provides diverse lines of evidence demonstrating that fluoride (F) exposure contributes to degenerative eye diseases by stimulating or inhibiting biological pathways associated with the pathogenesis of cataract, age-related macular degeneration and glaucoma. As elucidated in this study, F exerts this effect by inhibiting enolase, τ-crystallin, Hsp40, Na⁺, K⁺-ATPase, Nrf2, γ -GCS, HO-1 Bcl-2, FoxO1, SOD, PON-1 and glutathione activity, and upregulating NF-κB, IL-6, AGEs, HsP27 and Hsp70 expression. Moreover, F exposure leads to enhanced oxidative stress and impaired antioxidant activity. Based on the evidence presented in this study, it can be concluded that F exposure may be added to the list of identifiable risk factors associated with pathogenesis of degenerative eye diseases. The broader impact of these findings suggests that reducing F intake may lead to an overall reduction in the modifiable risk factors associated with degenerative eye diseases. Further studies are required to examine this association and determine differences in prevalence rates amongst fluoridated and non-fluoridated communities, taking into consideration other dietary sources of F such as tea. Finally, the findings of this study elucidate molecular pathways associated with F exposure that may suggest a possible association between F exposure and other inflammatory diseases. Further studies are also warranted to examine these associations.

Annexin A12-26 Treatment Improves Skin Heterologous Transplantation by Modulating Inflammation and Angiogenesis Processes

Skin graft successful depends on reduction of local inflammation evoked by the surgical lesion and efficient neovascularization to nutrition the graft. It has been shown that N-terminal portion of the Annexin A1 protein (AnxA1) with its anti-inflammatory properties induces epithelial mucosa repair and presents potential therapeutic approaches. The role of AnxA1 on wound healing has not been explored and we investigated in this study the effect of the peptide Ac2-26 (N-terminal AnxA1 peptide Ac2-26; AnxA1_2-26) on heterologous skin scaffolds transplantation in BALB/c mice, focusing on inflammation and angiogenesis. Treatment with AnxA1_2-26, once a day, from day 3-60 after scaffold implantation improved the take of the implant, induced vessels formation, enhanced gene and protein levels of the vascular growth factor-A (VEGF-A) and fibroblast influx into allograft tissue. It also decreased pro- while increasing anti-inflammatory cytokines. The pro-angiogenic activity of AnxA1_2-26 was corroborated by topical application of AnxA1_2-26 on the subcutaneous tissue of mice. Moreover, treatment of human umbilical endothelial cells (HUVECs) with AnxA1_2-26 improved proliferation, shortened cycle, increased migration and actin polymerization similarly to those evoked by VEGF-A. The peptide treatment instead only potentiated the tube formation induced by VEGF-A. Collectively, our data showed that AnxA1_2-26 treatment favors the tissue regeneration after skin grafting by avoiding exacerbated inflammation and improving the angiogenesis process.

Small heat shock protein speciation: novel non-canonical 44 kDa HspB5-related protein species in rat and human tissues

When analyzing small stress proteins of rat and human tissues by electrophoretic methods followed by western blotting, and using the anti-HspB1/anti-HspB5 antibody clone 8A7, we unexpectedly found a protein with a molecular mass of ~44 kDa. On two-dimensional gels, this protein resolved into four distinct species. Electrophoretic and immunological evidence suggests that this 44 kDa protein is a derivative of HspB5, most likely a covalently linked HspB5 dimer. This HspB5-like 44 kDa protein (HspB5L-P44) is particularly abundant in rat heart, brain, and renal cortex and glomeruli. HspB5L-P44 was also found in human brains, including those from patients with Alexander disease, a condition distinguished by cerebral accumulation of HspB5. Gray matter of such a patient contained an elevated amount of HspB5L-P44. A spatial model of structurally ordered dimeric HspB5 α-crystallin domains reveals the exposed and adjacent position of the two peptide segments homologous to the HspB1-derived 8A7 antigen determinant peptide (epitope). This explains the observed extraordinary high avidity of the 8A7 antibody towards HspB5L-P44, as opposed to commonly used HspB5-specific antibodies which recognize other epitopes. This scenario also explains the remarkable fact that no previous study reported the existence of HspB5L-P44 species. Exposure of rat endothelial cells to UV light, an oxidative stress condition, temporarily increased HspB5L-P44, suggesting physiological regulation of the dimerization. The existence of HspB5L-P44 supports the protein speciation discourse and fits to the concept of the protein code, according to which the expression of a given gene is reflected only by the complete set of the derived protein species.

Proteomic analysis of the glutathione-deficient LEGSKO mouse lens reveals activation of EMT signaling, loss of lens specific markers, and changes in stress response proteins

PURPOSE

To determine global protein expression changes in the lens of the GSH-deficient LEGSKO mouse model of age-related cataract for comparison with recently published gene expression data obtained by RNA-Seq transcriptome analysis.

METHODS

Lenses were separated into epithelial and cortical fiber sections, digested with trypsin, and labeled with isobaric tags (10-plex TMT^TM). Peptides were analyzed by LC-MS/MS (Orbitrap Fusion) and mapped to the mouse proteome for relative protein quantification.

RESULTS

1871 proteins in lens epithelia and 870 proteins in lens fiber cells were quantified. 40 proteins in LEGSKO epithelia, 14 proteins in LEGSKO fiber cells, 22 proteins in buthionine sulfoximine (BSO)-treated LEGSKO epithelia, and 55 proteins in BSO-treated LEGSKO fiber cells had significantly (p<0.05, FDR<0.1) altered protein expression compared to WT controls. HSF4 and MAF transcription factors were the most common upstream regulators of the response to GSH-deficiency. Many detoxification proteins, including aldehyde dehydrogenases, peroxiredoxins, and quinone oxidoreductase, were upregulated but several glutathione S-transferases were downregulated. Several cellular stress response proteins showed regulation changes, including an upregulation of HERPUD1, downregulation of heme oxygenase, and mixed changes in heat shock proteins. NRF2-regulated proteins showed broad upregulation in BSO-treated LEGSKO fiber cells, but not in other groups. Strong trends were seen in downregulation of lens specific proteins, including β- and γ-crystallins, lengsin, and phakinin, and in epithelial-mesenchymal transition (EMT)-related changes. Western blot analysis of LEGSKO lens epithelia confirmed expression changes in several proteins.

CONCLUSIONS

This dataset confirms at the proteomic level many findings from the recently determined GSH-deficient lens transcriptome and provides new insight into the roles of GSH in the lens, how the lens adapts to oxidative stress, and how GSH affects EMT in the lens.

[Expression of heat shock protein 27 in cigarette smoke extract-induced injury of human gingival fibroblasts]

OBJECTIVE

This research aimed to observe the expression of heat shock protein 27 (HSP27) in human gingival fibroblasts (HGFs) cell injury induced by different concentrations of cigarette smoke extract (CSE).

METHODS

The third to eighth generations of cultured HGFs were treated with serially diluted CSE of different concentrations (0, 2.5%, 5.0%, 12.5%, 25.0%, 50.0%). Wound-healing assay was performed to determine the migration of HGFs, and Western blot was used to determine the expression of HSP27.

RESULTS

The migration capability of HGFs weakened with the increase of CSE concentration. HSP27 expression was negative in normal HGFs but positive in CSE-intervened HGFs in a concentration-dependent manner.

CONCLUSION

HSP27 concentration increased in the CSE-induced injury of HGFs. This finding suggests that HSP27 plays an important role in CSE-induced epithelial injury.

[Expression of heat shock protein 27 in cigarette smoke extract-induced injury of human gingival fibroblasts]

OBJECTIVE

This research aimed to observe the expression of heat shock protein 27 (HSP27) in human gingival fibroblasts (HGFs) cell injury induced by different concentrations of cigarette smoke extract (CSE).

METHODS

The third to eighth generations of cultured HGFs were treated with serially diluted CSE of different concentrations (0, 2.5%, 5.0%, 12.5%, 25.0%, 50.0%). Wound-healing assay was performed to determine the migration of HGFs, and Western blot was used to determine the expression of HSP27.

RESULTS

The migration capability of HGFs weakened with the increase of CSE concentration. HSP27 expression was negative in normal HGFs but positive in CSE-intervened HGFs in a concentration-dependent manner.

CONCLUSION

HSP27 concentration increased in the CSE-induced injury of HGFs. This finding suggests that HSP27 plays an important role in CSE-induced epithelial injury.

Group II archaeal chaperonin recognition of partially folded human γD-crystallin mutants

The features in partially folded intermediates that allow the group II chaperonins to distinguish partially folded from native states remain unclear. The archaeal group II chaperonin from Methanococcus Mauripaludis (Mm-Cpn) assists the in vitro refolding of the well-characterized β-sheet lens protein human γD-crystallin (HγD-Crys). The domain interface and buried cores of this Greek key conformation include side chains, which might be exposed in partially folded intermediates. We sought to assess whether particular features buried in the native state, but absent from the native protein surface, might serve as recognition signals. The features tested were (a) paired aromatic side chains, (b) side chains in the interface between the duplicated domains of HγD-Crys, and (c) side chains in the buried core which result in congenital cataract when substituted. We tested the Mm-Cpn suppression of aggregation of these HγD-Crys mutants upon dilution out of denaturant. Mm-Cpn was capable of suppressing the off-pathway aggregation of the three classes of mutants indicating that the buried residues were not recognition signals. In fact, Mm-Cpn recognized the HγD-Crys mutants better than (wild-type) WT and refolded most mutant HγD-Crys to levels twice that of WT HγD-Crys. This presumably represents the increased population or longer lifetimes of the partially folded intermediates of the mutant proteins. The results suggest that Mm-Cpn does not recognize the features of HγD-Crys tested-paired aromatics, exposed domain interface, or destabilized core-but rather recognizes other features of the partially folded β-sheet conformation that are absent or inaccessible in the native state of HγD-Crys.

Connexin mutants and cataracts

The lens is a multicellular, but avascular tissue that must stay transparent to allow normal transmission of light and focusing of it on the retina. Damage to lens cells and/or proteins can cause cataracts, opacities that disrupt these processes. The normal survival of the lens is facilitated by an extensive network of gap junctions formed predominantly of connexin46 and connexin50. Mutations of the genes that encode these connexins (GJA3 and GJA8) have been identified and linked to inheritance of cataracts in human families and mouse lines. In vitro expression studies of several of these mutants have shown that they exhibit abnormalities that may lead to disease. Many of the mutants reduce or modify intercellular communication due to channel alterations (including loss of function or altered gating) or due to impaired cellular trafficking which reduces the number of gap junction channels within the plasma membrane. However, the abnormalities detected in studies of other mutants suggest that they cause cataracts through other mechanisms including gain of hemichannel function (leading to cell injury and death) and formation of cytoplasmic accumulations (that may act as light scattering particles). These observations and the anticipated results of ongoing studies should elucidate the mechanisms of cataract development due to mutations of lens connexins and abnormalities of other lens proteins. They may also contribute to our understanding of the mechanisms of disease due to connexin mutations in other tissues.

Human TRiC complex purified from HeLa cells contains all eight CCT subunits and is active in vitro

Archaeal and eukaryotic cytosols contain group II chaperonins, which have a double-barrel structure and fold proteins inside a cavity in an ATP-dependent manner. The most complex of the chaperonins, the eukaryotic TCP-1 ring complex (TRiC), has eight different subunits, chaperone containing TCP-1 (CCT1-8), that are arranged so that there is one of each subunit per ring. Aspects of the structure and function of the bovine and yeast TRiC have been characterized, but studies of human TRiC have been limited. We have isolated and purified endogenous human TRiC from HeLa suspension cells. This purified human TRiC contained all eight CCT subunits organized into double-barrel rings, consistent with what has been found for bovine and yeast TRiC. The purified human TRiC is active as demonstrated by the luciferase refolding assay. As a more stringent test, the ability of human TRiC to suppress the aggregation of human γD-crystallin was examined. In addition to suppressing off-pathway aggregation, TRiC was able to assist the refolding of the crystallin molecules, an activity not found with the lens chaperone, α-crystallin. Additionally, we show that human TRiC from HeLa cell lysate is associated with the heat shock protein 70 and heat shock protein 90 chaperones. Purification of human endogenous TRiC from HeLa cells will enable further characterization of this key chaperonin, required for the reproduction of all human cells.

Crystallin distribution patterns in Litoria infrafrenata and Phyllomedusa sauvagei lenses

The eye lens remains transparent because of soluble lens proteins known as crystallins. For years γ-crystallins have been known as the main lens proteins in lower vertebrates such as fish and amphibians. The unique growth features of the lens render it an ideal structure to study ageing; few studies have examined such changes in anuran lenses. This study aimed to investigate protein distribution patterns in Litoria infrafrenata and Phyllomedusa sauvagei species. Lenses were fractionated into concentric layers by controlled dissolution. Water-soluble proteins were separated into high (HMW), middle (MMW) and low molecular weight (LMW) fractions by size-exclusion HPLC and constituents of each protein class revealed by 1DE and 2DE. Spots were selected from 2DE gels on the basis of known ranges of subunit molecular weights and pH ranges and were identified by MALDI-TOF/TOF MS following trypsin digestion. Comparable lens distribution patterns were found for each species studied. Common crystallins were detected in both species; the most prominent of these was γ-crystallin. Towards the lens centre, there was a decrease in α- and β-crystallin proportions and an increase in γ-crystallins. Subunits representing taxon-specific crystallins demonstrating strong sequence homology with ζ-crystallin/quinone oxidoreductase were found in both L. infrafrenata and P. sauvagei lenses. Further work is needed to determine which amphibians have taxon-specific crystallins, their evolutionary origins, and their function.

Cytoplasmic amino acids within the membrane interface region influence connexin oligomerization

Gap junction channels composed of connexins connect cells, allowing intercellular communication. Their cellular assembly involves a unique quality-control pathway. Some connexins [including connexin43 (Cx43) and Cx46] oligomerize in the trans-Golgi network following export of stabilized monomers from the endoplasmic reticulum (ER). In contrast, other connexins (e.g., Cx32) oligomerize early in the secretory pathway. Amino acids near the cytoplasmic aspect of the third transmembrane domain have previously been shown to determine this difference in assembly sites. Here, we characterized the oligomerization of two connexins expressed prominently in the vasculature, Cx37 and Cx40, using constructs containing a C-terminal dilysine-based ER retention/retrieval signal (HKKSL) or treatment with brefeldin A to block ER vesicle trafficking. Both methods led to intracellular retention of connexins, since the cells lacked gap junction plaques. Retention of Cx40 in the ER prevented it from oligomerizing, comparable to Cx43. By contrast, ER-retained Cx37 was partially oligomerized. Replacement of two amino acids near the third transmembrane domain of Cx43 (L152 and R153) with the corresponding amino acids from Cx37 (M152 and G153) resulted in early oligomerization in the ER. Thus, residues that allow Cx37 to oligomerize early in the secretory pathway could restrict its interactions with coexpressed Cx40 or Cx43 by favoring homomeric oligomerization, providing a structural basis for cells to produce gap junction channels with different connexin composition.

The endoplasmic reticulum protein folding factory and its chaperones: new targets for drug discovery?

Cytosolic heat shock proteins have received significant attention as emerging therapeutic targets. Much of this excitement has been triggered by the discovery that HSP90 plays a central role in the maintenance and stability of multifarious oncogenic membrane receptors and their resultant tyrosine kinase activity. Numerous studies have dealt with the effects of small molecules on chaperone- and stress-related pathways of the endoplasmic reticulum (ER). However, unlike cytosolic chaperones, relatively little emphasis has been placed upon translational avenues towards targeting of the ER for inhibition of folding/secretion of disease-promoting proteins. Here, we summarise existing small molecule inhibitors and potential future targets of ER chaperone-mediated inhibition. Client proteins of translational relevance in disease treatment are outlined, alongside putative future disease treatment modalities based on ER-centric targeted therapies. Particular attention is paid to cancer and autoimmune disorders via the effects of the GRP94 inhibitor geldanamycin and its population of client proteins, overloading of the unfolded protein response, and inhibition of members of the IL-12 family of cytokines by celecoxib and non-coxib analogues.

Alterations to proteins in the lens of hereditary Crygs-mutated cataractous mice

PURPOSE

To investigate the altered expression of proteins in the lens of mice with inherited cataracts.

METHODS

Mice with inherited cataracts caused by a spontaneous mutation of the gene gamma S-crystallin (Crygs) were used as the subjects. Lens proteins were extracted and separated by two-dimensional electrophoresis (2-DE). The spots representing differential proteins were first identified by image analysis, and then further analyzed by matrix assisted laser desorption/ionization-time of flight-tandem mass spectrometry (MALDI-TOF-MS/MS).

RESULTS

2-DE were conducted under high (882 microg) and low dosage (190 microg) of sample. Under each condition, the numbers of protein spots found in cataract lenses were similar to those in normal lenses (p>0.05). Seventeen proteins were identified in normal lenses, including alphaA- to alphaB-, betaA1- to betaA4-, betaB1- to betaB3-, gammaA- to gammaF-, and gammaS-crystallin, and bead-filament structure protein (BFSP/filensin). Seven differential ones were consistently identified. In the cataract lenses BFSP and gammaS-crystallin were absent; gammaF-crystallin was downregulated; and betaA1-, betaB1-, betaB2-, and alphaB-crystallin were upregulated. Those abnormally upregulated crystallins, when compared to normal ones, had smaller molecular weight, suggesting possible truncation.

CONCLUSIONS

The mutant Crygs gene can lead to changes of BFSP/filensin and other crystallins. The changes to these crystallins, together, may secondarily lead to cataract formation.

Global gene expression analysis of lenses from different mouse strains and in the alpha3Cx46 knockout mouse

PURPOSE

Disruption of the mouse gene encoding the gap junction subunit alpha3 connexin 46 (alpha3Cx46) results in the formation of lens cataracts that have a severity affected by the genetic background of the mouse strain. To identify the genes that influence the severity of the nuclear opacity, global gene expression was analyzed in lenses from the 129SvJae strain and compared to the C57BL/6J strain.

METHODS

Lens transcripts were subjected to cDNA microarray analysis. Results on selected genes were confirmed by real-time PCR.

RESULTS

GENES THAT WERE DETERMINED TO BE ALTERED IN EXPRESSION LEVELS AS A RESULT OF STRAIN DIFFERENCES COULD BE CLUSTERED INTO THREE GROUPS: energy metabolism, stress response, and cell growth.

CONCLUSIONS

There were no observed changes in gene expression as a result of the lack of alpha3Cx46 in the different mouse strains, suggesting that the pathways mediated by this connexin do not influence gene transcription in the lens. Analysis of the transcript changes due to strain differences provides new insights into potential genetic modifiers of cataractogenesis. More detailed experimentation will be needed to determine if these observed changes do indeed affect cataractogenesis.

Characteristics of ethylnitrosourea-induced cataracts

PURPOSE

This study analyzed genes associated with the morphology and regulation of ethylnitrosourea (ENU)-induced cataract mouse.

MATERIALS AND METHODS

Immunohistochemistry analysis using anti-crystallins and PCNA antibody revealed that the localization pattern of these specific markers differed between the cataractous and wild-type lens epithelium. Two-dimensional electrophoresis and microarray techniques were used to identify the proteins and genes related to ENU-induced cataract.

RESULTS

A novel ENU-induced mutation in the mouse led to nuclear and cortical opacity of the eye lens at 5 weeks postnatal. This cataract phenotype was similar to that of the zonular-pulverulent type of human cataract. Crystallin proteins and gap-junction genes have relations to the formation of cataract.

CONCLUSIONS

Together, the results suggest that various proteins affect the formation and specific phenotypes of ENU-induced cataract mouse.

ERp29 restricts Connexin43 oligomerization in the endoplasmic reticulum

Connexin43 (Cx43) is a gap junction protein that forms multimeric channels that enable intercellular communication through the direct transfer of signals and metabolites. Although most multimeric protein complexes form in the endoplasmic reticulum (ER), Cx43 seems to exit from the ER as monomers and subsequently oligomerizes in the Golgi complex. This suggests that one or more protein chaperones inhibit premature Cx43 oligomerization in the ER. Here, we provide evidence that an ER-localized, 29-kDa thioredoxin-family protein (ERp29) regulates Cx43 trafficking and function. Interfering with ERp29 function destabilized monomeric Cx43 oligomerization in the ER, caused increased Cx43 accumulation in the Golgi apparatus, reduced transport of Cx43 to the plasma membrane, and inhibited gap junctional communication. ERp29 also formed a specific complex with monomeric Cx43. Together, this supports a new role for ERp29 as a chaperone that helps stabilize monomeric Cx43 to enable oligomerization to occur in the Golgi apparatus.