Impaired T cell immunity and response to infection and immunization is a common feature in the elderly. We have previously shown that Asparagine (N) - linked protein glycosylation serves as a critical negative regulator of T cell immunity in both mice and humans. Virtually all cell surface and secreted proteins in animal cells are modified by the addition of complex carbohydrates in the ER/Golgi secretory pathway, providing molecular information not encoded in the genome. The branching and number of N-glycans per protein molecule cooperate to regulate binding to galectins, forming a molecular lattice that controls the distribution, clustering and endocytosis of surface glycoproteins in a predictable manner to affect cell growth and differentiation. Genetic and metabolic control of N-glyan branching negatively regulates T cell receptor clustering/signaling, enhances surface retention of the anti-inflammatory receptors Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4) and Transforming Growth Factor - receptor (TR) and inhibits pro-inflammatory TH1 and TH17 while promoting anti-inflammatory TH2 and induced T regulatory cell (iTreg) differentiation. Increasing N-glycan branching in T cells in vitro and in vivo by metabolically increasing substrate supply to Golgi enzymes via supplementation with the simple sugar N-acetylglucosamine (GlcNAc) suppresses T cell growth, enhances CTLA-4 and TGF-RI/II surface expression, blocks TH1/TH17 differentiation and inhibits autoimmunity. Preliminary analysis suggests aging in humans and mice is associated with increases in serum GlcNAc levels and N-glycan branching in T cells, including nave, central and effector memory T cells. Indeed, hypo-proliferative in vitro responses in aged mouse and human T cells is rescued by down-regulating N-glycan branching using a small molecule Golgi inhibitor. We hypothesize that age-dependent increases in N-glycan branching significantly contributes to impaired T cell immunity and hypo-responsiveness to infection/immunization in the elderly. To confirm and expand on this hypothesis, the following aims are proposed.
Aim 1 will confirm increased N-glycan branching in human T cell subsets of the elderly.
Aim 2 will confirm that genetic and small molecule inhibition of N-glycan branching rejuvenates T cell responses in the elderly.
Aim 3 examines the mechanism for age dependent increases in N-glycan branching, examining both genetic and metabolic regulation. Positive results will suggest down-regulation of N-glycan branching as a therapeutic strategy to rejuvenate T cell responses in the elderly.

Public Health Relevance

Aging is accompanied by increased susceptibility to infection from defective immune responses. We have previously shown that the addition of specific sugars to proteins (i.e. protein glycosylation) suppresses immune function. Here we examine the possibility that age dependent increases in protein glycosylation contribute to immune dysfunction and infection risk in the elderly.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Special Emphasis Panel (ZAI1-LAR-I (S1))
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Prabhudas, Mercy R
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University of California Irvine
Schools of Medicine
United States
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Araujo, Lindsey; Khim, Phillip; Mkhikian, Haik et al. (2017) Glycolysis and glutaminolysis cooperatively control T cell function by limiting metabolite supply to N-glycosylation. Elife 6:
Mkhikian, Haik; Mortales, Christie-Lynn; Zhou, Raymond W et al. (2016) Golgi self-correction generates bioequivalent glycans to preserve cellular homeostasis. Elife 5: