Induction of stress proteins in cultured human RPE-derived cells

Oxidative stress regulates expression of claudin-1 in human RPE cells

Age-related macular degeneration (AMD) is a neurodegenerative disease associated with irreversible loss of central vision in the elderly. Disruption of the homeostatic function of the retinal pigment epithelium (RPE) is thought to be fundamental to AMD pathogenesis, and oxidative stress is implicated in the associated RPE damage. We examined the effects of oxidative stress on the expression of junctional proteins in cultured human retinal pigment epithelial (ARPE-19) cells. Reverse transcription-PCR and immunoblot analyses revealed that expression of the tight-junction protein claudin-1 was increased at both the mRNA and protein levels 8 to 12 h after exposure of ARPE-19 cells to H2O2, whereas that of the tight-junction protein ZO-1 or the adherens-junction protein N-cadherin was unaffected. Expression of both claudin-1 and N-cadherin was down-regulated by exposure of the cells to H2O2 for longer periods (24 to 48 h). Oxidative stress also induced the phosphorylation of p38 mitogen-activated protein kinase (MAPK) with a time course similar to that apparent for the up-regulation of claudin-1 expression. Furthermore, the increase in the abundance of claudin-1 induced by H2O2 was blocked by the p38 inhibitor SB203580. Phosphorylation of the MAPKs ERK and JNK was not affected by H2O2. Our results suggest that modulation of claudin-1 expression in the RPE by oxidative stress may contribute to the pathogenesis of AMD.

Effects of crystallin-β-b2 on stressed RPE in vitro and in vivo

BACKGROUND

Crystallins are thought to play a cytoprotective role in conditions of cellular stress. The aim of this study was to determine the effects of crystallin-β-b2 (cryβ-b2) and crystallin-β-b3 (cryβ-b3) on ARPE-19 cells in vitro and on the retinal pigment epithelium (RPE) in vivo.

METHODS

The influence of cryβ-b2 and cryβ-b3 on the viability, proliferation and dying of ARPE-19 was measured by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium assay, bromo-2-deoxyuridine assay and life/death assay. The expressions of cryβ-b2, cryβ-b3, glial-derived neurotrophic factor (GDNF), and galectin-3 (Gal-3) in ARPE-19 cells were evaluated using immunohistochemistry (IHC), Western blotting (WB) and real-time-quantitative-PCR (qRT-PCR). To evaluate the response of cryβ-b2 and cryβ-b3 to stressed ARPE-19 cells, the cells were exposed to UV-light. In a rat model, cryβ-b2-expressing neural progenitor cells (cryβ-b2-NPCs) were injected intravitreally after retinal stress induced by optic nerve axotomy to examine whether they influence the RPE. Protein expression was examined 2 and 4 weeks postsurgery using IHC and WB.

RESULTS

Detectable alterations of GDNF, and Gal-3 were found in ARPE-19 cells upon exposure to UV light. Adding the crystallins to the medium promoted proliferation and increased viability of ARPE-19 cells in vitro. The obtained data support the view that these crystallins possess epithelioprotective properties. Likewise, in vivo, intravitreally injected cryβ-b2 and transplanted cryβ-b2-NPCs protected RPE from indirectly induced stress.

CONCLUSIONS

The data suggest that the RPE response to retinal ganglion cell denegeration is mediated via crystallins, which may thus be used therapeutically.

Triamcinolone acetonide prevents oxidative stress-induced tight junction disruption of retinal pigment epithelial cells

PURPOSE

Oxidative stress is known to disrupt the integrity of retinal pigment epithelium (RPE) tight junctions. The goal of this study is to evaluate the effect of triamcinolone acetonide (TA) on the junctional integrity of RPE under oxidative stress and to identify the underlying mechanisms.

METHODS

Second passage porcine RPE cells were cultured on 6-well membrane inserts until 4 weeks after reaching confluence. Cells were incubated with TA (10(-5) M) for 30 min. FITC-containing medium was added to the upper chamber (cell's apical side). The cells were then challenged with 1 mM Hydrogen Peroxide (H(2)O(2)). After 5 h, the fluorescence intensity of the medium from lower chamber (cell's basolateral side) was measured using a fluorescence spectrofluorophotometer. This transepithelial flux of FITC-dextran was measured until the 21st day. The immunolocalization of occludin and F-actin was examined with fluorescence microscope. Reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio was determined by a colorimetric assay kit.

RESULTS

Non-lethal oxidative stress by H(2)O(2) increased transepithelial flux of FITC-dextran significantly. TA inhibited this increase and preserved the lower flux through the whole experimental period. This permeability change by H(2)O(2) was reversible and recovered to the normal level within 3 weeks. In immunohistological study, H(2)O(2) reduced linear occludin staining at the cell border and increased actin stress fibers. TA prevented H(2)O(2)-induced disruption of junctional assembly of occludin and F-actin. Glutathione assay demonstrated that intracellular GSH/GSSG ratio decreased significantly with H(2)O(2), while TA preserved this ratio by up-regulating GSH synthesis.

CONCLUSIONS

TA has a protective effect against oxidative stress-induced disruption of RPE tight junction by preserving cellular redox state.

Recent advances in gastrointestinal pathophysiology: role of heat shock proteins in mucosal defense and ulcer healing

The defense mechanism of the gastrointestinal mucosa against aggressive factors, such as hydrochloric acid, bile acid and non-steroidal anti-inflammatory drugs, mainly consists of functional, humoral and neuronal factors. Mucus-alkaline secretion, mucosal microcirculation, and motility act as functional factors, while prostaglandins and nitric oxide act as humoral factors, and capsaicin sensitive sensory neurons act as neuronal factors. All the above factors are known to contribute to mucosal protection. In recent years, heat shock proteins (HSPs), to include HSP70, have been implicated to be an additional factor utilized for the defense mechanisms of the gastrointestinal mucosa at the intracellular level. The expression of HSP70 and HSP47 markedly changes during the development and healing of chronic gastric ulcers in rats. It was revealed that HSC70 (a constitutive form of HSP70) is coprecipitated with cyclooxygenase-1 and the neuronal form of nitric oxide synthase after treatment with a mild irritant (20% ethanol). A positive relationship between enhanced interaction of HSC70 with either cyclooxygenase-1 or nitric oxide synthase and mucosal protection against a strong irritant (100% ethanol) was observed. It was concluded that HSPs might contribute to mucosal defense mechanisms and ulcer healing, most probably through protecting key enzymes related to cytoprotection.

Neurotrophic factors, cytokines and stress increase expression of basic fibroblast growth factor in retinal pigmented epithelial cells

Basic fibroblast growth factor (bFGF) and FGF receptors have been localized to photoreceptors and retinal pigmented epithelium (RPE), but the function of bFGF in adult retina and RPE is unknown. Exogenous bFGF has a neuroprotective effect in retina and brain and its expression is increased in some neurons in response to cytokines or stress. In this study, we investigated the effect of light, other types of stress, neurotrophic factors, and cytokines on bFGF levels in cultured human RPE. Some agents that protect photoreceptors from the damaging effects of constant light, including brainderived neurotrophic factor (BDNF), ciliary neurotrophic factor, and interleukin-1 beta, increase bFGF mRNA levels in RPE cells. Intense light and exposure to oxidizing agents also increase bFGF mRNA levels in RPE cells and cycloheximide blocks the increase. An increase in bFGF protein levels was demonstrated by ELISA in RPE cell supernatants after incubation with BDNF or exposure to intense light or oxidizing agents. These data indicate that bFGF is modulated in RPE cells by stress and by agents that provide protection from stress and support the hypothesis that bFGF functions as a survival factor in the outer retina.

Expression of interleukin-15 and its receptor by human fetal retinal pigment epithelial cells

PURPOSE

IL-15 and IL-15 receptor expression was measured in retinal pigment epithelial (RPE) cells to support a possible role of IL-15 in ocular inflammatory and immune responses.

METHODS

Reverse transcription-coupled polymerase chain reaction (RT-PCR) and Northern blot analysis of IL-15 mRNA in previously characterized non-transformed and simian virus (SV)-40 transformed human fetal RPE cells were carried out. Biological activities of IL-15 produced by the RPE cells were assayed by co-culture with IL-15 responsive cells. Expression of the IL-15 receptor (IL-15R) alpha, IL-2R beta and gamma chains were examined by RT-PCR.

RESULTS

Both non-transformed and SV-40 transformed human fetal RPE cells express IL-15, a T cell growth factor which has similar biological activities to IL-2, and the expression of IL-15 is enhanced by interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha) stimulation. In addition, transcripts for all three IL-15 receptor components (IL-15R alpha, IL-2R beta and IL-2R gamma) were detected in these cells.

CONCLUSIONS

RPE cells produce IL-15, which may play an important role in ocular immune and inflammatory responses by stimulating infiltrated T cells and RPE cells via paracrine and autocrine loops, respectively.

Chronic inhalation exposure to ozone and nitric acid elevates stress-inducible heat shock protein 70 in the rat lung

The ability of urban oxidant and acid air pollutants to induce heat shock proteins (HSPs) in the mammalian lung is not known. Such proteins are known to be correlated with environmental stress and pathophysiological conditions. In this study, stress-inducible HSP 70 was assessed by slot-blotting in rat lungs (N=10 per group) following inhalation exposures for 4 h per day, 3 days per week for 40 weeks to the following pollutants: (a) purified air;(b) 0.15 ppm ozone (O3);(c)50 micrograms/m3 nitric acid (HNO3); or(d) a combination of both 0.15 ppm O3 and 50 micrograms/m3 HNO3. At 24 h following the last exposure, samples from the right apical lobe of the lung were obtained for either slot-blotting or gel electrophoretic separation, subsequent protein immunoblotting, and chemiluminescence detection of HSP 70 levels. Experiments demonstrate that stress-inducible HSP 70 was present constitutively in the control lungs and was separable from the constitutive form of HSP 70. Slot-blotting analysis demonstrate that the O3 and HNO3 exposures alone produced significant elevations of HSP70. Specifically, either O3 or HNO3 alone significantly elevated lung stress-inducible HSP 70 levels by 277% and 221% respectively, above control levels. The group exposed to combined O3 and HNO3 showed a 177% elevation in lung stress-inducible HSP 70 that was significantly greater that the group inhaling purified air, but this effect was less than the effects of either pollutant component alone. Moreover, all exposure groups were significantly different from one another. These results indicate that stress-inducible HSP 70 in the rat lung is highly elevated after chronic inhalation exposures to both O3 and HNO3 when administered either alone or in combination within the range of urban ambient concentrations.

Induction of stress proteins in SV-40 transformed human RPE-derived cells by organic oxidants

The expression and induction of heat shock proteins (HSPs) were examined in cultured SV-40-transformed human retinal pigment epithelial (RPE)-derived cells following exposure to chemical oxidants. Concentrations of hydrogen peroxide and the organic oxidants tert-butyl hydroperoxide, cumene hydroperoxide and linoleic acid hydroperoxide were used under conditions where cell viability was between 75% and 90% as determined by the trypan blue exclusion tests. The types of HSPs that are either induced and/or elevated from constitutive levels in cultured transformed cells were separated both by SDS-PAGE and by two-dimensional gel electrophoresis. Subsequent immunoblotting was performed with both a monoclonal antibody (MAb C92) specific for only the stress-inducible form of HSP 70, namely HSP 72, and with a monoclonal antibody (MAb N27) specific for both the stress-inducible HSP 72 and its constitutive form, HSP 73. As positive controls for comparison, other types of stressing agents were used that included heat shock at 41 degrees C for various times and exposure to the proline analogue, azetidine-2-carboxylic acid (AzC). Protein immunoblotting analysis demonstrate that: (a) Stress-inducible HSP 72 is present at low levels in non-stressed cultured transformed RPE-derived cells and in fresh bovine retina and RPE, but is not detectable in non-stressed cultured lung fibroblasts until induction with heat shock; and (b) Stress-inducible HSP 72 is elevated from constitutive levels in RPE-derived cultured cells after exposure to various oxidants. After cellular exposure to both organic oxidants and to AzC in the presence of L-[35-S]-methionine, two-dimensional gel electrophoresis confirmed the elevation of newly synthesized HSP 72. Thus, these results indicate that cultured human SV-40-transformed RPE-derived cells are capable of elevated HSP 72 biosynthesis under conditions of oxidative stress produced by organic oxidants.