Interleukin-7 (IL-7) signaling is essential for the development and peripheral maintenance of several blood cell types. Deficiencies in IL-7 or either component of its receptor result in major hematopoietic defects, causing T-cell-negative (T-), B-cell-negative (B-), natural killer cell-negative (NK-) severe combined immunodeficiency (SCID) in mice. In humans, mutations in the IL-7 receptor alpha (IL-7Ra) gene have been found to cause T-, B+, NK+ SCID, and more recently a single nucleotide polymorphism in the IL-7Ra gene has been associated with autoimmunity. In addition, IL-7 has been shown to be a critical mediator of peripheral T- cell homeostasis, survival, and function. Nevertheless, the molecular mechanism underlying the diverse functions of IL-7 remain poorly understood.
We aim to uncover a new mechanism by which IL-7 signaling may regulate both T-cell development and peripheral function, namely through regulation of N-glycosylation. Insight in these areas may lead to new therapeutic avenues for both autoimmunity and congenital, acquired and induced lymphopenias. The roles of IL-7 are intricately involved with T-cell receptor (TCR) signaling, such that many of the effects of IL-7 correlate with alterations in TCR signal strength. N-glycosylation is a co-translational modification that affects nearly all cell-surface and secreted proteins. Cell surface glycoproteins interact with galectins in proportion to the number and branching of attached N-glycans, forming a molecular lattice that globally regulates the concentration and signaling of surface receptors. In T-cells, N-glycan branching opposes TCR clustering and signaling to suppress T-cell growth and autoimmunity. Our preliminary data demonstrate that IL-7 signaling leads to dramatic changes in N-glycan branching in T-cells. IL-7Ra mutant mice display a two to three fold increase in T-cell N-glycan branching, among the largest changes observed outside of genetic manipulation of Golgi enzymes. This hyper-glycosylation is predicted to markedly inhibit TCR signal strength and thus TCR signal mediated development, survival, and proliferation. We hypothesize that IL-7 regulates T-cell development and growth by altering N-glycan branching. To examine this hypothesis we propose to "rescue" hyper-glycosylation in IL-7Ra deficient mice by additionally knocking Mgat1 and Mgat5, two key N-glycan branching enzymes. This will allow us to directly asses the role of N-glycosylation in IL-7 mediated hematopoietic development, peripheral function, and homeostasis by comparing these processes in IL-7Ra-/- mice to mice with additional defect in glycosylation enzymes. These studies will provide insights about the interaction of IL-7 and TCR signaling, leading to a greater understanding of the development and maintenance of the lymphoid compartment. Furthermore, discerning the role of N-glycosylation in IL-7 signaling may provide new therapeutic avenues for both immunodeficiencies and autoimmune disease.

Public Health Relevance

Defects in the development and growth of white blood cells impact many blood and immunological disorders. This proposal examines the signals that control the development and growth of white blood cells, which may lead to better therapies for disorders as diverse as infection, immunodeficiency and autoimmunity.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Individual Predoctoral NRSA for M.D./Ph.D. Fellowships (ADAMHA) (F30)
Project #
5F30HL108451-03
Application #
8445432
Study Section
Special Emphasis Panel (ZRG1-F07-E (20))
Program Officer
Chang, Henry
Project Start
2011-04-22
Project End
2016-04-21
Budget Start
2013-04-22
Budget End
2014-04-21
Support Year
3
Fiscal Year
2013
Total Cost
$35,671
Indirect Cost
Name
University of California Irvine
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
046705849
City
Irvine
State
CA
Country
United States
Zip Code
92697
Zhou, Raymond W; Mkhikian, Haik; Grigorian, Ani et al. (2014) N-glycosylation bidirectionally extends the boundaries of thymocyte positive selection by decoupling Lck from Ca²? signaling. Nat Immunol 15:1038-45
Li, Carey F; Zhou, Raymond W; Mkhikian, Haik et al. (2013) Hypomorphic MGAT5 polymorphisms promote multiple sclerosis cooperatively with MGAT1 and interleukin-2 and 7 receptor variants. J Neuroimmunol 256:71-6
Grigorian, Ani; Mkhikian, Haik; Demetriou, Michael (2012) Interleukin-2, Interleukin-7, T cell-mediated autoimmunity, and N-glycosylation. Ann N Y Acad Sci 1253:49-57