The role of metallothionein IIa in defending lens epithelialcells against cadmium and TBHP induced oxidative stress

[摘要] Purpose: Heavy metals and other forms of oxidative stress have beenimplicated as key factors in the formation of age-related cataract inhumans. Metallothioneins are a group of proteins known to play importantroles in defending cells against the cytotoxic effects of heavy metals.However, little is known about their involvement in defending againstother forms of oxidative stress. Here, we examined the ability ofmetallothionein IIa (MTIIa) to protect human lens epithelial cellsagainst cadmium and tertiary butyl hydroperoxide (TBHP)-inducedoxidative stress.Methods: MTIIa over-expressing human lens epithelial cells(SRA01/04) were created by retroviral mediated gene transfer. Normal andMTIIa over-expressing cells were exposed to various concentrations ofcadmium and TBHP and subsequently monitored for cell death, changes incell phenotype and differences in growth rate. In addition, expressionlevels of three other important antioxidant genes, heme oxygenase-1,thioredoxin reductase-1, and manganese superoxide dismutase weremonitored by real-time RT-PCR following exposure to TBHP.Results: Analysis of the over expressing cell lines revealed anapproximate 3-4 fold increase in MTIIa expression relative to controlcells, resulting in as much as 20% protection against cadmium-inducedoxidative stress (p<0.001). The MTIIa over expressing cells were alsosignificantly more resistant to TBHP treatment while control cellsexhibited significant shrinking and rounding-up following 3-6 h TBHPtreatment, no changes were observed in TBHP-treated over expressingcells. When control cells were treated for 3 h or overnight with TBHP,40-45% cell death occurred by day three. However, no cell death wasobserved at this time for the treated MTIIa over-expressing cell line.In addition, TBHP induced the expression of MTIIa, heme oxygenase-1,thioredoxin reductase-1, and MnSOD in both normal and MTIIaover-expressed cell lines. Interestingly the latter three genes wereinduced at 2-3 fold higher levels in TBHP-treated MTIIa over-expressingcells, compared to treated control cells (p=0.001, p=0.02, and p=0.01,respectively).Conclusions: These data indicate that over-expression of MTIIa inhuman lens epithelial cells results in protection against cadmium andTBHP-induced oxidative stress. In addition, the results suggest thatMTIIa, and/or its ability to chelate metals, may play a role inregulating expression of other important antioxidant genes in responseto oxidative stress.

[学科分类] 生物化学/生物物理