Article

Reactive oxygen species mediates the apoptosis induced by transforming growth factor beta(2) in human lens epithelial cells.

Eye Center, Affiliated Second Hospital, School of Medicine, Zhejiang University, Hangzhou 310009, China.
Biochemical and Biophysical Research Communications (impact factor: 2.48). 04/2007; 354(1):278-83. DOI:10.1016/j.bbrc.2006.12.198 pp.278-83
Source: PubMed

ABSTRACT Transforming growth factor beta(2) (TGF-beta(2)), a growth regulator of human lens epithelial cells (HLECs), also regulates the death of these cells. Dose-response analysis showed that the TGF-beta(2) concentration needed to induce HLECs death (100 pg/ml) was 10 times that needed to inhibit growth in these cells (10 pg/ml). TGF-beta(2)-induced apoptosis in HLECs was preceded by an induction of reactive oxygen species (ROS) and a decrease in glutathione in the intracellular content, indicating that this factor induces oxidative stress in HLECs. Studies performed to analyze the levels of c-fos mRNA, a gene whose expression is modulated by the redox state, demonstrated that only high, apoptotic concentrations of TGF-beta(2) (100 pg/ml) produced an increase in the mRNA levels of this gene, the level of induction being similar to that found when cells were incubated in the presence of hydrogen peroxide. Finally, the cell death induced by TGF-beta(2) in HLECs was partially blocked by radical scavengers, which decreased the percentage of apoptotic cells, whereas these agents did not modify the growth-inhibitory effect elicited by TGF-beta(2) in these cells. The results presented in this paper provide evidence for the involvement of an oxidative process in the apoptosis elicited by TGF-beta(2) in HLECs.

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    Ke Yao, Panpan Ye, Li Zhang, Jian Tan, Xiajing Tang, Yidong Zhang
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    ABSTRACT: Oxidative stress has long been recognized as an important mediator of apoptosis in lens epithelial cells and also plays an important role in the pathogenesis of cataracts. (-)-Epigallocatechin gallate (EGCG), the most abundant component in green tea, has potent antioxidant activity. The goals of this study were to determine the protective effect of EGCG against H(2)O(2)-induced apoptotic death and the possible mechanisms involved in human lens epithelial (HLE) cells. HLEB-3, a human lens epithelial cell line, was exposed to various concentrations of H(2)O(2) and EGCG and subsequently monitored for cell death by the MTT assay and flow cytometric analysis using Annexin V and PI. The effect of EGCG in protecting HLE cells from cell death was determined by various assays after the cells were exposed to H(2)O(2). The ability of EGCG to block the accumulation of intracellular reactive oxygen species and the loss of mitochondrial membrane potential (Deltapsim) induced by H(2)O(2) was examined with dichlorofluorescein (DCF) fluorescence and 5,5',6,6'-tetrachloro-1,1',3,3'-tetrathylbenzimidazol carbocyanine iodide (JC-1). The expression of cytochrome c, caspase-9, caspase-3, and Bcl-2 family proteins was measured by western blotting. The changed expression of the mitogen activated protein kinase (MAPK) and Akt pathways was also detected by western blot. In the present study, EGCG protected against cell death caused by H(2)O(2) in HLEB-3 cells. EGCG reduced the H(2)O(2)-induced generation of reactive oxygen species (ROS), the loss of mitochondrial membrane potential (Deltapsim), and the release of cytochrome c from the mitochondria into the cytosol. EGCG inhibited the H(2)O(2)-stimulated increase of caspase-9 and caspase-3 expression and the decrease of the Bcl-2/Bax ratio. Moreover, EGCG attenuated the reduced activation and expression of ERK, p38 MAPK, and Akt induced by H(2)O(2). These findings suggest that EGCG protects HLE cells from the mitochondria-mediated apoptosis induced by H(2)O(2) through the modulation of caspases, the Bcl-2 family, and the MAPK and Akt pathways.
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    Article: Glutathione and catalase suppress TGFß-induced cataract-related changes in cultured rat lenses and lens epithelial explants
    Coral G Chamberlain, Kylie J Mansfield, Anna Cerra
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    ABSTRACT: Purpose: The damaging effects of oxidative stress and transforming growth factor-β (TGFβ)-induced transdifferentiation of lens epithelial cells have both been implicated independently in the etiology of cataract. The aim of this study was to investigate whether the presence of antioxidant systems in the lens influences the ability of lens epithelial cells to respond to TGFβ. Methods: Whole lenses from young rats were cultured with or without TGFβ in the presence or absence of reduced glutathione (GSH). Lens epithelial explants from weanling rats were used to investigate the effects of GSH and catalase on TGFβ-induced cataract-related changes. Lenses were monitored for opacification for three to four days, photographed, and then processed for routine histology. Explants were assessed by phase contrast microscopy, enzyme-linked immunosorbent assay (ELISA) of α-smooth muscle actin (αSMA), and/or immunolocalization of αSMA and Pax6, markers for transdifferentiation and normal lens epithelial phenotype, respectively. Results: In cultured lenses, GSH strongly suppressed TGFβ-induced opacification and subcapsular plaque formation. In explants, both GSH and catalase suppressed changes typically associated with TGFβ-induced transdifferentiation including wrinkling of the lens capsule, cell-surface blebbing, apoptotic cell loss, induction of αSMA, and loss of Pax6 expression. Conclusions: This study suggests that antioxidant systems present in the normal lens, which protect the epithelium against the damaging effects of reactive oxygen species, may also serve to protect it against the potentially cataractogenic effects of TGFβ. Taken together with other recent studies, it also raises the possibility that TGFβ may induce cataract-related changes in lens epithelial cells via release of hydrogen peroxide.
    Graduate School of Medicine - Papers.
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Keywords

agents
 
apoptotic cells
 
apoptotic concentrations
 
c-fos mRNA
 
cell death induced
 
decrease
 
Dose-response analysis
 
factor induces oxidative stress
 
growth regulator
 
growth-inhibitory effect elicited
 
HLECs
 
human lens epithelial cells
 
hydrogen peroxide
 
induce HLECs death
 
induction
 
intracellular content
 
mRNA levels
 
reactive oxygen species
 
TGF-beta(2)-induced apoptosis
 
Transforming growth factor beta(2)
 

Ke Yao