Changes in albumin precursor and heat shock protein 70 expression and their potential role in response to corneal epithelial wound repair

The Role of Heat Shock Protein 70 (HSP70) in the Pathogenesis of Ocular Diseases-Current Literature Review

Heat shock proteins (HSPs) have been attracting the attention of researchers for many years. HSPs are a family of ubiquitous, well-characterised proteins that are generally regarded as protective multifunctional molecules that are expressed in response to different types of cell stress. Their activity in many organs has been reported, including the heart, brain, and retina. By acting as chaperone proteins, HSPs help to refold denatured proteins. Moreover, HSPs elicit inhibitory activity in apoptotic pathways and inflammation. Heat shock proteins were originally classified into several subfamilies, including the HSP70 family. The aim of this paper is to systematise information from the available literature about the presence of HSP70 in the human eye and its role in the pathogenesis of ocular diseases. HSP70 has been identified in the cornea, lens, and retina of a normal eye. The increased expression and synthesis of HSP70 induced by cell stress has also been demonstrated in eyes with pathologies such as glaucoma, eye cancers, cataracts, scarring of the cornea, ocular toxpoplasmosis, PEX, AMD, RPE, and diabetic retinopathy. Most of the studies cited in this paper confirm the protective role of HSP70. However, little is known about these molecules in the human eye and their role in the pathogenesis of eye diseases. Therefore, understanding the role of HSP70 in the pathophysiology of injuries to the cornea, lens, and retina is essential for the development of new therapies aimed at limiting and/or reversing the processes that cause damage to the eye.

Evaluation of histologic, antiapoptotic and antioxidant effects of melatonin against the acute ocular toxicity of Cisplatin

This study aimed to investigate the protective effect of melatonin against the acute toxicity of cisplatin in ocular tissues. The eyes of 40 rats were divided into 4 groups: Control group (10 rats), Melatonin (Mel) group (10 rats), Cisplatin (Cis) group (10 rats), Melatonin (Mel) + Cisplatin (Cis) group (10 rats). Retina, cornea, and ciliary body tissues were examined after hematoxylin-eosin staining of sections obtained from the eyes and were scored for disorganization and degeneration. Apoptotic cells were counted for the retina, cornea, and ciliary body with the TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end labeling) method. The total antioxidant status (TAS) / total oxidant status (TOS) of homogenized eye tissues were measured. While apoptotic cells were found to increase in the cornea of the Cisplatin (Cis) group, no difference was found regarding the retina and ciliary body cell count. An increased number of apoptotic cells in the cornea of the Cis group was found while there was a decrease in the group where Cisplatin and Melatonin were administered together (Mel+Cis group). There was no statistically significant difference amongst groups for TOS or TAS. Melatonin had a partial protective effect against histological damage.

Association of Cyclin Dependent Kinase 10 and Transcription Factor 2 during Human Corneal Epithelial Wound Healing in vitro model

Proper wound healing is dynamic in order to maintain the corneal integrity and transparency. Impaired or delayed corneal epithelial wound healing is one of the most frequently observed ocular defect and difficult to treat. Cyclin dependen kinase (cdk), a known cell cycle regulator, required for proper proliferating and migration of cell. We therefore investigated the role of cell cycle regulator cdk10, member of cdk family and its functional association with transcriptional factor (ETS2) at active phase of corneal epithelial cell migration. Our data showed that cdk10 was associated with ETS2, while its expression was upregulated at the active phase (18 hours) of cell migration and gradually decrease as the wound was completely closed. Topical treatment with anti-cdk10 and ETS2 antibodies delayed the wound closure time at higest concentration (10 µg/ml) compared to control. Further, our results also showed increased mRNA expression of cdk10 and ETS2 at active phase of migration at approximately 2 fold. Collectively, our data reveals that cdk10 and ETS2 efficiently involved during corneal wound healing. Further studies are warranted to better understand the mechanism and safety of topical cdk10 and ETS2 proteins in corneal epithelial wound-healing and its potential role for human disease treatment.

Aspergillus flavus induced alterations in tear protein profile reveal pathogen-induced host response to fungal infection

Aspergillus flavus and Fusarium sp. are primary causative agents of keratitis that results in corneal tissue damage leading to vision loss particularly in individuals from the tropical parts of the world. Proteins in the tear film collected from control and keratitis patients was profiled and compared. A total of 1873 proteins from control and 1400 proteins from patient tear were identified by mass spectrometry. While 847 proteins were found to be glycosylated in the patient tear, only 726 were glycosylated in control tear. And, some of the tear proteins showed alterations in their glycosylation pattern after infection. Complement system proteins, proteins specific for neutrophil extracellular traps and proteins involved in would healing were found only in the patient tear. The presence of these innate immune system proteins in the tear film of patients supports the previous data indicating the involvement of neutrophil and complement pathways in antifungal defense. High levels of wound healing proteins in keratitis patient tear implied activation of tissue repair during infection. The early appearance of the host defense proteins and wound healing response indicates that tear proteins could be used as an early marker system for monitoring the progression of pathogenesis. Identification of negative regulators of the above defense pathways in keratitis tear indicates an intricate balance of pro and anti-defense mechanisms operating in fungal infection of the eye.

SIGNIFICANCE

Tear proteins from control and mycotic keratitis patients were separated into glycoproteins and non-glycosylated proteins and then identified by mass spectrometry. Tear proteins from keratitis patients showed alteration in the glycosylation pattern indicating the alteration of glycosylation machinery due to infection. Neutrophil extracellular traps specific proteins, complement pathway proteins, as well as wound healing proteins, were found only in patient tear showing the activation of antifungal defense in the patient tear. Negative regulators of these defense pathways were also found in patient tear indicating a fine balance between pathogen clearance and host tissue destruction during fungal infection depending upon the individual specific host - pathogen interaction. This understanding could be used to predict the progression and outcome of infection.

Proteomic Analysis of the Vitreous following Experimental Retinal Detachment in Rabbits

Purpose. The pathogenesis of rhegmatogenous retinal detachment (RRD) remains incompletely understood, with no clinically effective treatment for potentially severe complications such as photoreceptor cell death and proliferative vitreoretinopathy. Here we investigate the protein profile of the vitreous following experimental retinal detachment using a comparative proteomic based approach. Materials and Methods. Retinal detachment was created in the right eyes of six New Zealand red pigmented rabbits. Sham surgery was undertaken in five other rabbits that were used as controls. After seven days the eyes were enucleated and the vitreous was removed. The vitreous samples were evaluated with two-dimensional polyacrylamide gel electrophoresis and the differentially expressed proteins were identified with tandem mass spectrometry. Results. Ten protein spots were found to be at least twofold differentially expressed when comparing the vitreous samples of the sham and retinal detachment surgery groups. Protein spots that were upregulated in the vitreous following retinal detachment were identified as albumin fragments, and those downregulated were found to be peroxiredoxin 2, collagen-Iα1 fragment, and α-1-antiproteinase F. Conclusions. Proteomic investigation of the rabbit vitreous has identified a set of proteins that help further our understanding of the pathogenesis of rhegmatogenous retinal detachment and its complications.

Single cell gene expression analysis in injury-induced collective cell migration

Collective cell behavior in response to mechanical injury is central to various regenerative and pathological processes. Using a double-stranded locked nucleic acid probe for monitoring real-time intracellular gene expression, we examined the spatiotemporal response of epithelial cells during injury-induced collective migration and compared to the blocker assay with minimal injury as control. We showed that cells ∼150 μm from the wound edge exhibit a gradient in response to mechanical injury, expressing different genes depending on the wounding process. While release of contact inhibition is sufficient to trigger the migratory behavior, cell injury additionally induces reactive oxygen species, Nrf2 protein, and stress response genes, including heat shock protein 70 and heme oxygenase-1, in a spatiotemporal manner. Furthermore, we show that Nrf2 has an inhibitory role in injury-induced epithelial-mesenchymal transition, suggesting a potential autoregulatory mechanism in injury-induced response. Taken together, our single-cell gene expression analyses reveal modular cell responses to mechanical injury, manipulation of which may afford novel strategies for tissue repair and prevention of tumor invasion in the future.

Proteomic analysis of ophthalmic disease

Proteomics, a highly sophisticated way to study the protein profile of various biological tissues or fluids, has hitherto had a relatively limited role ophthalmic science. Of the few proteomic studies that have been performed, liquid chromatography, electrophoresis gel separation and mass spectrometry have been utilized to investigate the proteome of several different eye structures and fluids from both humans and animal models. Ophthalmic proteomic studies have so far attempted to identify proteins unique to the eye, to investigate protein changes due to the onset of various diseases and to identify proteins that could act as markers of disease. Proteomics has the potential to improve the way in which eye disease is diagnosed and potentially even treated by identifying novel pathogenic pathways that may be susceptible to therapeutic manipulation. The aim of this review is to give an overview the current and potential application of proteomic science to ophthalmic research.

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.

Albumin precursor and Hsp70 modulate corneal wound healing in an organ culture model

In order to investigate the role of albumin precursor and Hsp70 in corneal wound healing, we have analyzed the distribution of these proteins in wounded and non-wounded corneas of rabbits and the effects of topical applications of anti-albumin precursor and anti-Hsp70 antibodies on wound healing. Anti-albumin precursor and anti-Hsp70 antibodies were topically applied in healing corneal epithelium of rabbit eyes in organ culture. Corneas were allowed to heal in vitro for up to 120 h in serum-free medium with 5 and 10 μg/ml or without (migrating control) anti-albumin precursor/ or anti-Hsp70 antibodies. Fibronectin (Fb) (5 μg/ml) was used as a positive control. Immunofluorescence labelling was used to detect proteins in corneal epithelium at various time intervals following an epithelial defect. Delay in wound healing (p<0.005) was observed with 10 μg/ml anti-albumin antibody labelling. A similar pattern was observed when anti-fibronectin antibody (5 μg/ml) alone and in combination with anti-albumin (10 μg/ml) was ectopically added with wound closure occurring at 120 h. However with anti-Hsp70 antibody (5 μg/ml) slightly delayed (p<0.005) wound closure was observed at 96 h and considerable retardation >120 h with 10 μg/ml. Additionally, immunofluoresence showed a strong co-localization of Hsp70 and albumin precursor during the active phase of wound healing. The presence of albumin precursor and Hsp70 in the epithelial compartment of the cornea indicates a role for these proteins in modulating cell behavior such as epithelial growth, adhesion or regeneration, thus contributing to corneal epithelial wound healing.

Lung tissue regeneration after induced injury in Runx3 KO mice

Runx3 is essential for normal murine lung development, and Runx3 knockout (KO) mice, which die soon after birth, exhibit alveolar hyperplasia. Wound healing, tissue repair, and regeneration mechanisms are necessary in humans for proper early lung development. Previous studies have reported that various signaling molecules, such as pErk, Tgf-beta1, CCSP, pJnk, Smad3, and HSP70 are closely related to wound healing. In order to confirm the relationship between lung defects caused by the loss of function of Runx3 and wound healing, we have localized various wound-healing markers after laser irradiation in wild-type and in Runx3 KO mouse lungs at post-natal day 1. Our results indicate that pERK, Tgf-beta1, CCSP, pJnk, and HSP70 are dramatically down-regulated by loss of Runx3 during lung wound healing. However, Smad3 is up-regulated in the Runx3 KO laser-irradiated lung region. Therefore, the lung wound-healing mechanism is inhibited in the Runx3 KO mouse, which shows abnormal lung architecture, by reduced pErk, Tgf-beta1, CCSP, pJnk, and HSP70 and by induced Smad3.

Elevated albumin in retinas of monkeys with experimental glaucoma

PURPOSE

To establish the identity of a prominent protein, approximately 70 kDa, that is markedly increased in the retina of monkeys with experimental glaucoma compared with the fellow control retina, the relationship to glaucoma severity, and its localization in the retina.

METHODS

Retinal extracts were subjected to 2-D gel electrophoresis to identify differentially expressed proteins. Purified peptides from the abundant 70 kDa protein were analyzed and identified by liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) separation, and collision-induced dissociation sequencing. Protein identity was performed on MASCOT (Matrix Science, Boston, MA) and confirmed by Western blot. The relationship between the increase in this protein and glaucoma severity was investigated by regression analyses. Protein localization in retina was evaluated by immunohistochemistry with confocal imaging.

RESULTS

The abundant protein was identified as Macaca mulatta serum albumin precursor (67 kDa) from eight non-overlapping proteolytic fragments, and the identity was confirmed by Western blot. The average increase in retinal albumin content was 2.3 fold (P = 0.015). In glaucoma eyes, albumin was localized to some neurons of the inner nuclear layer, in the inner plexiform layer, and along the vitreal surface, but it was only found in blood vessels in control retinas.

CONCLUSIONS

Albumin is the abundant protein found in the glaucomatous monkey retinas. The increased albumin is primarily localized to the inner retina where oxidative damage associated with experimental glaucoma is known to be prominent. Since albumin is a major antioxidant, the increase of albumin in the retinas of eyes with experimental glaucoma may serve to protect the retina against oxidative damage.

Immunohistochemical markers for corneal stem cells in the early developing human eye

The corneal epithelium is continuously being renewed. Differentiated epithelial cells originate from limbal stem cells (LSCs) located in the periphery of the cornea, the corneoscleral limbus. We have recently identified superoxide dismutase 2 (SOD2) and cytokeratin (CK) 15 as limbal basal cell markers and potential markers for LSCs and early transient amplifying cells in human adults. In this study, we describe the development of the ectodermally derived LSCs and the mesodermally derived niche cells from the time at which the cornea is defined (week 6) until the formation of the early limbal niche (week 14) in human embryos and fetuses. The expression of SOD2 and CK15 was investigated together with other recently identified limbal proteins. Previously suggested LSC and differentiation markers (PAX6, aquaporin-1 and nestin) were also investigated. Both SOD2 and CK15 were present in the corneal epithelium from week 6. However, in week 14 they were predominantly expressed in the limbal epithelium. Both proteins were expressed already from week 7 in a stromal triangular region from which the early mesodermal limbal niche most likely originates. PAX6 was expressed in both ectodermally and mesodermally derived parts of the limbal niche, underscoring the importance of PAX6 in niche formation.

Differences in the protein expression in limbal versus central human corneal epithelium--a search for stem cell markers

In the search for potential limbal stem cell protein markers, the purpose of this study was to characterize differences in protein expression between human central and limbal corneal epithelium by a proteomic approach using two-dimensional polyacrylamide gel electrophoresis (2D PAGE) combined with mass spectrometry (LC-MS/MS). The results were subsequently confirmed by Western blotting and immunohistochemistry. We detected more than 1000 protein spots in each gel. Thirty-two spots were significantly over-expressed in the central part and 70 spots were significantly over-expressed in the limbal part. We identified 25 different proteins. Among these 11 proteins representing different cellular locations and functions were selected for further investigations. Most interestingly, superoxide dismutase 2 (SOD2), was expressed in clusters of cells in the basal limbal epithelium. Heat shock protein 70 protein 1 (HSP70.1) and annexin I were highly abundant in limbal epithelium, although they were also present in the central epithelium to a minor extent. Among the proteins primarily expressed in the limbal fraction we further identified cytokeratin (CK) 15, CK19 and alpha enolase, which have been reported previously to be related to the limbal basal epithelium. The basal limbal epithelium consists of clusters of slow cycling limbal stem cells and rapid cycling transient amplifying cells. Ideally, proteins exclusively expressed in the limbal part of the epithelium may serve as markers for the basal limbal cells. SOD2 and CK15 identify clusters of limbal basal cells and therefore they may serve as markers for limbal stem cells in conjunction with the earliest transient amplifying cells.