Age‐associated changes in mitogen‐induced protein phosphorylation in murine T lymphocytes

Publisher Website
Google Scholar
Abstract
Since T lymphocyte proliferation declines with age, and since activation of a still only partially defined set of protein kinases is thought to play a critical role in T cell activation, we have carried out a systematic survey of age‐related changes in protein phosphorylation in T lymphocytes. We used two‐dimensional electro‐phoretic analysis to examine lysates prepared from T cells after 10 min of exposure to mitogens [anti‐CD3, concanavalin A (Con A) and phorbol 12‐myristate 13‐acetate (PMA) plus ionomycin] and nonmitogenic activators (PMA or ionomycin used separately). Our results show a progressive, life‐long decline in the levels of anti‐CD3‐induced phosphorylation of all 16 phosphoproteins that respond vigorously in T cells of young mice. Mice 10‐18 months of age showed levels of response that were clearly below those induced in young mice, while responses of mice 22‐24 months of age were even more severely diminished. Responses to Con A, PMA, ionomycin and a combination of PMA plus ionomycin were equally blunted in old mice, except for 2 (of 12) phosphoproteins that continued to respond to PMA even in the old animals. None of the phosphoproteins which were ionomycin responsive in young mice continued to respond in old mice, although 1 (of 3) ionomycin‐inhibitable phosphoproteins remained inhibitable in old mice. We also found three phosphoproteins which became phosphorylated in response to anti‐CD3, PMA and Con A (but not ionomycin) only in old mice, and a pair of phosphoproteins which were unresponsive to all mitogens but showed a higher “baseline” phosphorylation in T cells from old mice. Comparing phosphoprotein patterns between CD8− and CD8−CD45RB− T cells from young mice allowed us to identify nine phosphoproteins that were strongly responsive to anti‐CD3 only when when CD45RB+ (i.e. virgin) cells were present. Although the immune system of old mice consists largely of memory T cells, the change in phosphoprotein phosphorylation patterns cannot simply be explained by the accumulation of this cell type. We conclude that aging leads to a global impairment of several distinct protein kinase pathways in both virgin and memory T cell sets.