INFLUENCE OF ZINC ON SELECTED CELLULAR FUNCTIONS OF CULTURED HUMAN RETINAL-PIGMENT EPITHELIUM

Zinc is a necessary micronutrient, usually abundant in human RPE. Our study was undertaken to determine the effects of short-term, zinc defi ciency on human retinal pigment epithelium (RPE) using a culture model of fetal human RPE cells. Human fetal RPE cells were isolated and cul tured in Goon's modified Ham's F-12 medium. For zinc depletion studies , cells were cultured for 1 week in Chelex-treated Dulbecco's modified Eagle's medium containing low (0.25 mu M) or physiologic (11 mu M) to tal zinc concentrations as determined by flame atomic absorption spect roscopy. Protein synthesis was determined by incorporation of S-35-cys teine/methionine and labeled proteins analysed by polyacrylamide gel e lectrophoresis. Several cell parameters and enzymes were significantly reduced below control when cultured in low zinc: zinc content (40%), proliferation (63%), protein/well (50%), catalase activity (68%), alka line phosphatase activity (61%), a-mannosidase activity (68%), and met allothionein (82%). No statistically significant decline was seen in a cid phosphatase activity, superoxide dismutase activity, glutathione p eroxidase activity and dexamethasone induction of metallothionein. Zin c repletion (100 mu M, 1 h) increased catalase and a-mannosidase activ ities from 32% and 33% of control to 75% and 73%, respectively. Cycloh eximide did not inhibit this short-term zinc-induced repletion of cata lase or cx-mannosidase. Protein synthesis in low zinc medium was depre ssed, but not significantly, as shown by incorporation of radiolabeled S-35-cysteine/methionine into newly synthesized proteins. The effects of zinc deficiency in cultured human RPE are selective. Adequate intr acellular zinc was required for maximal activity of some enzymes. The dependence of catalase activity on zinc was not predicted and may help explain the observed decline in catalase activity seen with age in RP E. Our model of zinc deficiency should proveuseful in elucidating the complex effects of zinc deficiency and repletion in human RPE.