Taylor A, Berger J J, Reddan J, Zuliani A
Laboratory for Nutrition and Cataract Research, USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111.
In Vitro Cell Dev Biol. 1991 Apr;27A(4):287-92. doi: 10.1007/BF02630905.
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 greater than 125) passage. Long-lived (t1/2 greater than 10 h) and short-lived (t1/2 less than 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 amount 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.
蛋白水解能力的改变与老年眼晶状体的异常有关，但该假说的体内试验一直难以进行。为了模拟衰老过程，我们将8岁兔子的细胞培养至早期（群体倍增水平为20至30）和晚期（群体倍增水平大于125）传代。用[³H]亮氨酸标记长寿命（半衰期大于10小时）和短寿命（半衰期小于10小时）的细胞内蛋白质，并测定细胞对血清去除应激产生蛋白水解反应的能力。对于早期传代细胞，在有血清和无血清情况下长寿命蛋白质的平均半衰期分别为62小时和39小时。对于晚期传代细胞，在有血清和无血清情况下长寿命蛋白质的平均半衰期分别为58小时和43小时。无血清时早期和晚期传代细胞内蛋白水解的净增加分别为59%和35%。因此，体外老化的兔晶状体上皮细胞对血清去除的蛋白水解反应仅为“年轻”细胞的60%。早期传代细胞对血清去除反应增强的能力似乎涉及在有血清时较低的蛋白水解稳态水平以及在无血清时更大程度的蛋白水解增强。不到2%的蛋白质存在于短寿命蛋白质池中。在有血清和无血清情况下短寿命蛋白质的蛋白水解速率没有差异。就有血清时的基础蛋白水解速率和血清去除时产生蛋白水解反应的能力而言，这些兔晶状体上皮细胞与牛晶状体上皮细胞和成纤维细胞相似。
