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Diminished activation of the MAP kinase pathway in CD3-stimulated T lymphocytes from old mice
G Gorgas1, E R Butch, K L Guan
1Department of Pathology, University of Michigan, School of Medicine, Ann Arbor 48109, USA.
Abstract:
Stimulation of the ERK family of protein kinases ('extracellular signal regulated kinases', also known as MAP kinases) plays an important role in the activation of many cell types, including T lymphocytes. ERKs are activated when they are phosphorylated by an upstream activator, the dual-specific protein kinase MEK. To see if aging leads to an impairment of MEK activation in mouse T cells, we used a mobility shift assay in which activation of MEK leads to phosphorylation and altered mobility of ERK-2 kinase. Similarly, we monitored mobility of pp90rsk, a known ERK substrate, as an indication of ERK function. We found an age-related decline in the ability of mouse T cells to activate both MEK and ERK function in response to stimulation by antibodies to the CD3 chain of the T cell receptor. Aging did not alter the kinetics of enzyme activation, but did diminish (by about 2-fold) the maximal level of substrate converted into the slower migrating form. Naive and memory CD4 T cells from young mice were equally able to convert ERK2 to its slower migrating form, suggesting that the decline in MEK function is not likely to be attributable to the shift, with age, from naive to memory T cell predominance. Our data suggest that age-dependent declines in gene activation, including genes for key cytokines like IL-2, may be due to declines in the upstream signals that lead to activation of the MEK/ERK protein kinase cascade.
Insights
Aging impairs T cell activation by reducing MEK/ERK signaling. This age-related decline in extracellular signal-regulated kinases (ERK) function may explain reduced gene activation in older mice.
Area of Science:
- Immunology
- Cell Signaling
- Aging Research
Background:
- Extracellular signal-regulated kinases (ERK), also known as MAP kinases, are crucial for T lymphocyte activation.
- ERK activation is dependent on phosphorylation by the upstream kinase MEK.
- Age-related changes in immune function are well-documented, but the underlying molecular mechanisms are not fully understood.
Purpose of the Study:
- To investigate whether aging impairs MEK activation and subsequent ERK function in mouse T cells.
- To determine the impact of aging on the MEK/ERK signaling cascade in response to T cell receptor stimulation.
Main Methods:
- Mobility shift assays were used to monitor the phosphorylation and altered mobility of ERK-2 kinase, indicating MEK activation.
- Mobility of pp90rsk, an ERK substrate, was monitored to assess ERK function.
- T cells from young and aged mice were stimulated via antibodies to the CD3 chain of the T cell receptor.
Main Results:
- A significant age-related decline was observed in the ability of mouse T cells to activate both MEK and ERK.
- The maximal level of MEK/ERK substrate conversion decreased approximately twofold in aged T cells.
- Aging did not alter the kinetics of enzyme activation, and the decline was not attributable to a shift in T cell populations (naive vs. memory).
Conclusions:
- Aging leads to a functional decline in the MEK/ERK protein kinase cascade within T cells.
- This age-dependent impairment in MEK/ERK signaling may contribute to reduced gene activation, including key cytokines like IL-2, in older individuals.
- The findings highlight a potential molecular basis for age-related immunosenescence.