UVB Irradiation-Induced Changes in the 27-kd Heat Shock Protein (HSP27) in Human Corneal Epithelial Cells

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 Therapeutic Roles of Recombinant Hsp90α on Cornea Epithelial Injury

Purpose

The purpose of this study was to explore the therapeutic role of heat shock protein 90 (Hsp90) in wound healing of injury cornea epithelium.

Methods

The right eye of C57BL/6N male mice were performed the debridement wounds in the center of the cornea using an algerbrush II blade. The injured area was determined by staining the cornea with fluorescein sodium and measured with image-J. Immunoblotting, ELISA and immunochemistry were used for determining protein expression. The quantitation PCR was performed to measure mRNA expression.

Results

Hsp90α is upregulated at both the mRNA and protein levels, and is secreted extracellularly into the corneal stroma and tear film during the healing process after corneal injury in mice. This upregulation is associated with activation of HSF1. Administration of recombinant exogenous Hsp90α (eHsp90α) speeds up wound healing of injured corneal epithelium. The eHsp90α binds to low-density lipoprotein (LDL)-related protein-1 (LRP-1) on the corneal epithelial cells and increases phosphorylation of AKT at S473, which is associated with proliferation and migration corneal epithelial cells in vitro or vivo. Inhibition of AKT by its inhibitor LY294002 abolishes eHsp90α-induced migration and proliferation of corneal epithelial cells.

Conclusions

Hsp90α is upregulated and secreted after corneal injury and acts to promote the healing process. Recombinant Hsp90α may be a promising therapeutic drug candidate for corneal injury.

What Makes Cornea Immunologically Unique and Privileged? Mechanistic Clues from a High-Resolution Proteomic Landscape of the Human Cornea

Success rates of corneal transplantation are particularly high owing to its unique, innate immune privilege derived from a phenomenon known as Anterior Chamber-Associated Immune Deviation (ACAID). Of note, cornea is a transparent, avascular structure that acts as a barrier along with sclera to protect the eye and contributes to optical power. Molecular and systems biology mechanisms underlying ACAID and the immunologically unique and privileged status of cornea are not well known. We report here a global unbiased proteomic profiling of the human cornea and the identification of 4824 proteins, the largest catalog of human corneal proteins identified to date. Moreover, signaling pathway analysis revealed enrichment of spliceosome, phagosome, lysosome, and focal adhesion pathways, thereby demonstrating the protective functions of corneal proteins. We observed an enrichment of neutrophil-mediated immune response processes in the cornea as well as proteins belonging to the complement and ER-Phagosome pathways that are suggestive of active immune and inflammatory surveillance response. This study provides a key expression map of the corneal proteome repertoire that should enable future translational medicine studies on the pathological conditions of the cornea and the mechanisms by which cornea immunology are governed. Molecular mechanisms of corneal immune privilege have broad relevance to understand and anticipate graft rejection in the field of organ transplantation.

Development of an in vitro model to study the biological effects of blinking

PURPOSE

To develop a mechanical model in which a contact lens is swept over ocular surface cells under conditions that mimic the force and speed of the blink, and to investigate the resulting biological changes.

METHODS

A computer controlled mechanical instrument was developed to hold a dish containing 3D cultured stratified human ocular surface epithelial cells, across which an arm bearing a contact lens was swept back and forth repeatedly at a speed and force mimicking the human blink. Cells were subjected to repeated sweep cycles for up to 1 h at a speed of 120 mm/s with or without an applied force of 19.6 mN (to mimic pressure exerted by upper eyelid), after which the cell layer thickness was measured, the cell layer integrity was investigated using fluorescent quantum dots (6 and 13 nm) and the phosphorylation levels of various protein kinases were analyzed by human phospho-kinase arrays. Data for selected kinases were further quantitated by enzyme immunoassays.

RESULTS

The thickness of the cell layers did not change after exposure to sweep cycles with or without applied force. Quantum dots (6 and 13 nm) were able to penetrate the layers of cells exposed to sweep cycles but not layers of untreated control cells. The phosphorylation levels of HSP27 and JNK1/2/3 increased for cells exposed to sweep cycles with applied force compared to untreated control cells.

CONCLUSIONS

The in vitro mechanical instrument is a useful tool to investigate the effects of blinking on the ocular surface.

mTOR Inhibition Mitigates Molecular and Biochemical Alterations of Vigabatrin-Induced Visual Field Toxicity in Mice

BACKGROUND

Gamma-vinyl-γ-aminobutyric acid (GABA) (vigabatrin) is an antiepileptic drug and irreversible GABA transaminase inhibitor associated with visual field impairment, which limits its clinical utility. We sought to relate altered visual evoked potentials associated with vigabatrin intake to transcriptional changes in the mechanistic target of rapamycin (mTOR) pathway and GABA receptors to expose further mechanisms of vigabatrin-induced visual field loss.

METHODS

Vigabatrin was administered to mice via an osmotic pump for two weeks to increase GABA levels. Visual evoked potentials were examined, eye samples were collected, and gene expression was measured by quantitative reverse transcription-polymerase chain reaction. Similarly, human retinal pigment epithelial cells (ARPE19) were exposed to vigabatrin and treated with mTOR inhibitors for mTOR pathway analysis and to assess alterations in organelle accumulation by microscopy.

RESULTS

Dysregulated expression of transcripts in the mTOR pathway, GABA_A/B receptors, metabotropic glutamate (Glu) receptors 1/6, and GABA/glutamate transporters in the eye were found in association with visual evoked potential changes during vigabatrin administration. Rrag genes were upregulated in both mouse eye and ARPE19 cells. Immunoblot of whole eye revealed greater than three fold upregulation of a 200 kDa band when immunoblotted for ras-related guanosine triphosphate binding D. Microscopy of ARPE19 cells revealed selective reversal of vigabatrin-induced organelle accumulation by autophagy-inducing drugs, notably Torin 2. Changes in the mTOR pathway gene expression, including Rrag genes, were corrected by Torin 2 in ARPE19 cells.

CONCLUSIONS

Our studies, indicating GABA-associated augmentation of RRAG and mTOR signaling, support further preclinical evaluation of mTOR inhibitors as a therapeutic strategy to potentially mitigate vigabatrin-induced ocular toxicity.

Heat-shock protein expression in canine corneal wound healing

OBJECTIVE

Heat-shock proteins, particularly the 70-kDa member (Hsp70), have been implicated in facilitating wound healing in multiple tissues. Expression and localization of three HSPs were assessed in normal and wounded canine corneas to elucidate a role in epithelial healing.

METHODS

Paraffin-embedded normal corneas, acute and repeatedly abraded corneas, and keratectomies of spontaneous chronic corneal epithelial defects (SCCEDs) were subjected to routine immunohistochemistry for Hsp27, 47, and 70 expression. Ex vivo corneal defects were created and treated with anti-HSPs or IgG controls, and wound healing was monitored. Primary cultures of canine corneal stromal fibroblasts and corneal epithelial cells were treated with exogenous Hsp70, and an artificial wound was created in vitro to monitor restoration of the monolayer.

RESULTS

Normal canine corneas exhibited constitutive expression of all HSPs evaluated. Inducible expression was demonstrated in acutely wounded tissues, and expression in the chronically abraded corneas was relocalized. All HSP expression was below the limits of detection in the epithelium of SCCED samples. Inhibition of HSPs in culture resulted in delayed wound healing when compared to controls. Hsp70-treated fibroblasts demonstrated significantly (P < 0.001) increased migration and proliferation compared to the vehicle control; however, there was no significant effect of exogenous Hsp70 on corneal epithelial cells.

CONCLUSIONS

These findings suggest that HSPs are induced in the normal canine cornea during re-epithelialization. Hsp70 expression is likely important for inducing the cytoarchitectural remodeling, migration, and proliferation necessary early in the canine corneal healing response, and suppressed expression may contribute to the pathophysiology of nonhealing defects.

Hyaluronic acid-dependent protection against UVB-damaged human corneal cells

Within ultraviolet radiation, ultraviolet B (UVB) is the most energetic and damaging to humans. At the protein level, UVB irradiation downregulates the expression of antioxidant enzymes leading to the accumulation of reactive oxygen species (ROS). Due to lacking of a global analysis of UVB-modulated corneal proteome, we investigate in vitro the mechanism of UVB-induced corneal damage to determine whether hyaluronic acid (HA) is able to reduce UVB irradiation-induced injury in human corneal epithelial cells. Accordingly, human corneal epithelial cell lines (HCE-2) were irradiated with UVB, followed by incubation with low molecular weight HA (LMW-HA, 100 kDa) or high molecular weight HA (HMW-HA, 1,000 kDa) to investigate the physiologic protection of HMW-HA in UVB-induced corneal injury, and to perform a global proteomic analysis. The data demonstrated that HA treatment protects corneal epithelial cells in the UVB-induced wound model, and that the molecular weight of HA is a crucial factor. Only HMW-HA significantly reduces the UVB-induced cytotoxic effects in corneal cells and increases cell migration and wound-healing ability. In addition, proteomic analysis showed that HMW-HA might modulate cytoskeleton regulation, signal transduction, biosynthesis, redox regulation, and protein folding to stimulate wound healing and to prevent these UVB-damaged cells from cell death. Further studies evidenced membrane-associated progesterone receptor component 1 (mPR) and malate dehydrogenase (MDH2) play essential roles in protecting corneal cells from UVB irradiation. This study reports on UVB-modulated cellular proteins that might play an important role in UVB-induced corneal cell injury and show HMW-HA to be a potential substance for protecting corneal cells from UVB-induced injury.

Phenotypic alteration of limbal niche-associated limbal epithelial stem cell deficiency by ultraviolet-B exposure-induced phototoxicity in mice

Good vision requires a healthy cornea, and a healthy cornea needs healthy stem cells. Limbal epithelial stem cells (LESCs) are a traditional source of corneal epithelial cells and are recruited for the continuous production of epithelium without seizing throughout an animal's life, which maintains corneal transparency. Like the maintenance of other adult somatic stem cells, the maintenance of LESCs depends on the specific microenvironmental niche in which they reside. The purpose of this study was to determine the microenvironmental damage associated with LESCs fate due to ultraviolet (UV)-B exposure in a mouse model. Structural alteration and deregulation of the stem cell and its neighboring niche components were observed by using clinical, morphological, explant culture study, and flowcytometric analysis, which demonstrated that the limbal microenvironment plays an important role in cornea-related disease development. In UV-exposed mice, overexpression of vascular endothelial growth factor receptor 2 indicated neovascularization, decreased CD38 expression signified the alteration of limbal epithelial superficial cells, and the loss of limbal stem cell marker p63 indicated limbal stem cell deficiency in the limbal vicinity. We concluded that LESC deficiency diseases (LESCDDs) are associated with pathophysiological changes in the LESC niche, with some inhibitory interception such as UV-B irradiation, which results in corneal defects.

Expression of phosphorylated heat shock protein 27 during corneal epithelial wound healing

PURPOSE

The 27-kDa heat shock protein (HSP27) has been implicated in wound healing in multiple tissues. We investigated the expression and localization of phosphorylated HSP27 during epithelial wound healing in the murine cornea.

METHODS

Corneas of 8- to 10-week-old C57BL6 mice were wounded by epithelial debridement (n = 40). Unwounded corneas served as controls (n = 3). After 3, 7, and 14 days, phosphorylated HSP27 localization in wounded corneas was observed by confocal immunohistochemistry and double immunogold labeling transmission immunoelectron microscopy. Western blot analysis was performed to determine expression levels of phosphorylated HSP27 in scraped epithelia. Phosphorylated HSP27 localization was also separately performed with confocal immunohistochemistry 8 hours after epithelial debridement to investigate the early epithelial wound-healing process.

RESULTS

In unwounded corneas, phosphorylated HSP27 was localized only to the superficial epithelium. In contrast, phosphorylated HSP27 was localized in the basal and superficial epithelia 3 days after corneal epithelial wounding. After 7 and 14 days, HSP27 localization was similar to that in unwounded controls. Expression levels of phosphorylated HSP27 were greater in wounded corneal epithelia on day 3 than in unwounded controls and on day 14. After 8 hours, phosphorylated HSP27 expression was prominent in the leading edge of migrating corneal epithelium.

CONCLUSIONS

Constitutive expression of phosphorylated HSP27 is limited to the superficial corneal epithelium in unwounded murine corneas. Changes in HSP27 epithelial distribution and expression levels after corneal epithelial wounding suggest that phosphorylated HSP27 plays a role in early phase of corneal epithelial wound healing.

Heat shock proteins in the human eye

Heat shock proteins (Hsps) are believed to primarily protect and maintain cell viability under stressful conditions such as those occurring during thermal and oxidative challenges chiefly by refolding and stabilizing proteins. Hsps are found throughout the various tissues of the eye where they are thought to confer protection from disease states such as cataract, glaucoma, and cancer. This minireview summarizes the placement, properties, and roles of Hsps in the eye and aims to provide a better comprehension of their function and involvement in ocular disease pathogenesis.

Cigarette smoke-related hydroquinone induces filamentous actin reorganization and heat shock protein 27 phosphorylation through p38 and extracellular signal-regulated kinase 1/2 in retinal pigment epithelium: implications for age-related macular degeneration

Retinal pigment epithelium (RPE)-derived membranous debris named blebs, may accumulate and contribute to sub-RPE deposit formation, which is the earliest sign of age-related macular degeneration (AMD). Oxidative injury to the RPE might play a significant role in AMD. However, the underlying mechanisms are unknown. We previously reported that hydroquinone (HQ), a major pro-oxidant in cigarette smoke, foodstuff, and atmospheric pollutants, induces actin rearrangement and membrane blebbing in RPE cells as well as sub-RPE deposits in mice. Here, we show for the first time that phosphorylated Heat shock protein 27 (Hsp27), a key regulator of actin filaments dynamics, is up-regulated in RPE from patients with AMD. Also, HQ-induced nonlethal oxidative injury led to Hsp27mRNA up-regulation, dimer formation, and Hsp27 phosphorylation in ARPE-19 cells. Furthermore, we found that a cross talk between p38 and extracellular signal-regulated kinase (ERK) mediates HQ-induced Hsp27 phosphorylation and actin aggregate formation, revealing ERK as a novel upstream mediator of Hsp27 phosphorylation. Finally, we demonstrated that Hsp25, p38, and ERK phosphorylation are increased in aging C57BL/6 mice chronically exposed to HQ, whereas Hsp25 expression is decreased. Our data suggest that phosphorylated Hsp27 might be a key mediator in AMD and HQ-induced oxidative injury to the RPE, which may provide helpful insights into the early cellular events associated with actin reorganization and bleb formation involved in sub-RPE deposits formation relevant to the pathogenesis of AMD.

Differential expression of small heat shock protein 27 (Hsp27) in Ataxia telangiectasia brains

Ataxia telangiectasia (A-T) is a progressive neurodegenerative disorder caused by disruption of the gene, ataxia telangiectasia mutated (ATM). Present study was aimed at identifying proteins that are present in abnormal levels in A-T brain that may identify alternative targets for therapeutic interventions. Proteomic and Western blot analysis have shown massive expression of the small heat shock protein 27 (Hsp27) in frontal cortices of A-T brains compared to negligible levels in controls. The expression of other stress proteins, Hsp70, alphaB-crystallin, and prohibitin remained unchanged in the A-T and control brains. Significant decreases in reactive oxygen species, protein carbonyl groups and lipid peroxidation products were observed in the A-T brains. There is no evidence of caspase 3 activation or DAXX mediated apoptosis. We propose that neurons in the frontal lobe are protected by the expression of Hsp27, which scavenges the oxidative stress molecules formed consequent to the primary loss of ATM function.