Effects of aging in vitro on intracellular proteolysis in cultured rabbit lens epithelial cells in the presence and absence of serum |
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Authors: | Allen Taylor Joseph J Berger John Reddan Antoinette Zuliani |
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Institution: | (1) Laboratory for Nutrition and Cataract Research, USDA Human Nutrition Research Center on Aging at Tufts University, 711 Washington Street, 02111 Boston, Massachusetts;(2) Biological Sciences, Oakland University, 48063 Rochester, Michigan |
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Abstract: | Summary Alterations in proteolytic capabilities have been associated with abnormalities in the aged eye lens, but in vivo tests of
this hypothesis have been difficult to pursue. To simulate aging, we cultured cells from an 8-yr-old rabbit to early (population-doubling
level 20 to 30) and late (population-doubling level > 125) passage. Long-lived (t1/2>10 h) and short-lived (t1/2<10 h) intracellular proteins were labeled with 3H]leucine, and the ability of the cells to mount a proteolytic response to the stress of serum withdrawal was determined.
For early passage cells, the average t1/2 of long-lived proteins in the presence and absence of serum was 62 and 39 h, respectively. For late-passage cells, the average
t1/2 of long-lived proteins in the presence and absence of serum was 58 and 43 h, respectively. The net increase in intracellular
proteolysis in the absence of serum was 59 and 35% for early and late-passage cells, respectively. Thus, in vitro-aged rabbit
lens epithelial cells mount only 60% the proteolytic response to serum removal shown in “younger” cells. The enhanced ability
of early passage cells to respond to serum removal seems to involve lower homeostatic levels of proteolysis in the presence
of serum and greater enhancement of proteolysis in the absence of serum. Less than 2% of the protein is in the pool of short-lived
proteins. Rates of proteolysis of short-lived proteins in the presence and absence of serum were indistinguishable. With respect
to basal proteolytic rates in the presence of serum and ability to mount a proteolytic response upon serum withdrawal, these
rabbit lens epithelial cells are similar to bovine lens epithelial cells and fibroblasts.
This work was supported in part by contract 53-3K06-5-10 U.S. Department of Agriculture, Washington, DC, Massachusetts Lions
Eye Research FUnd, Inc., the Daniel and Florence Guggenheim Foundation, and a grant EY00362 from the National Eye Institute,
Bethesda, MD. |
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Keywords: | eye lens aging stress proteolysis epithelial cells |
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