Age-associated declines in T cell function contribute to the higher incidences, longer recovery periods, and elevated morbidity and mortality from infectious and neoplastic diseases in the elderly. Impaired T cell function, as measured by IL-2 production and cell proliferation, contributes significantly to immune senescence. Age-related reductions in IL-2 production are associated with defects in the recruitment of signaling molecules to immune synapses, the adhesive junction that forms between a T cell and an antigen- presenting cell. This has been demonstrated by using immunofluorescence microscopy to monitor the translocation of individual proteins to the immune synapse. Accumulating evidence indicates that the plasma membrane is laterally compartmentalized into small lipid microdomains that coalesce around the activated T cell receptor (TCR), where they facilitate the recruitment of signaling proteins required for IL-2 production. The resulting structures incorporate both lipid rafts and protein scaffolds, and exist as small ~200nm 'signalosomes' within the immune synapse. Age-related differences in overall composition the immune synapse have not been evaluated in a systematic manner. Furthermore, the mechanisms responsible for the impaired recruitment of proteins to the immune synapse remain unknown. Changes affecting the composition of the plasma membrane, particularly changes affecting the sphigolipid metabolite ceramide, have significant impacts on lipid raft structure, and could influence the assembly of signalosomes. Age-related changes in the sphingolipid composition of the plasma membrane have not been examined. However, our preliminary data indicate that T cells from old mice have significantly higher levels of specific sphingolipids. These changes in cellular composition may contribute to the reduced ability of aged T cells to form effective immune synapse. We hypothesize that TCR-induced signalosomes exhibit age-related differences in their patterns of protein and lipid recruitment, and that changes in the sphingolipid composition of aged T cells impact the downstream signaling cascades that regulate IL-2 production. We will test this hypothesis using an enhanced magnetic immunoisolation procedure in conjunction with state-of-the-art proteomic and lipidomic methods. We will further test this hypothesis by inducing age-related changes in cellular sphingolipids and measuring immune synapse formation and T cell activation. These studies will provide the first comprehensive investigation of the protein and lipid content of the signaling complexes formed in response to antigenic stimulation. The information obtained from these proteomic and lipidomic analyses of the immune synapse will form the basis for constructing a 'map' of age-related changes in T cells. This map will enhance our understanding of the molecular bases of immune senescence, and will promote the development of strategies to reverse the detrimental changes associated with aging. The age related decline in T cell (immune cells important for fighting against pathogens and tumors) function is an important determinant of the health and quality of life in elderly. The underlying mechanisms of these defects are not completely known. This project will utilize state-of-the-art methods to construct a 'map' of the key age-related changes in lipids and proteins of T cells. This map will enhance our understanding of the molecular bases of immune senescence, and will promote the development of strategies to reverse the detrimental changes associated with aging. ? ? ?
| Molano, Alberto; Huang, Zhaofeng; Marko, Melissa G et al. (2012) Age-dependent changes in the sphingolipid composition of mouse CD4+ T cell membranes and immune synapses implicate glucosylceramides in age-related T cell dysfunction. PLoS One 7:e47650 |
