University of California, Irvine
Sprague Hall, Rm 208
839 Medical Sciences Court
949-824-9775
mdemetri@uci.edu

The molecular biology and glycobiology of T cell dysfunction in organ specific autoimmunity.

Our laboratory focuses on the molecular biology and glycobiology of T cell function in relation to autoimmune diseases such as Multiple Sclerosis. Autoimmune diseases result from immune mediated damage to specific target tissue(s). For example, in Multiple Sclerosis, the myelin sheath that surrounds axons is destroyed; blocking the conduction of the action potential and producing neurological symptoms such as loss of vision, incoordination, weakness and numbness. While the cause of Multiple Sclerosis and other autoimmune diseases is unknown, complex genetic inheritance plays an important role in the development of disease. Multiple genetic loci have been associated with autoimmune disease susceptibility, but for the most part these genes have yet to be identified

The animal model for MS, Experimental Autoimmune Encephalomyelitis (EAE), is a T cell mediated disease. We have recently identified b1,6 N-acetylglucosaminyltransferase V (Mgat5), an enzyme in the Asn (N)-linked protein glycosylation pathway (Fig 1), as a potent negative regulator of T cell activation and autoimmunity in mice (Demetriou et al (2001) Nature 409 733).

The activation of naive T cells requires the recognition of peptide/MHC by the T cell receptor coupled to other co-signaling events, such as T cell associated CD28 binding its ligand B7-1 & 2 on antigen presenting cells (APC). This initiates a signaling cascade that results in actin cytoskeleton re-organization and the formation a specialized contact area between the T cell and the APC termed the immune synapse. This contact site is characterized by a central area of clustered TCR and the adhesion molecule CD2 (the c-SMAC: central-supramolecular activation complex) that is surrounded by clustered LFA-1 integrin (the p-SMAC: peripheral-supramolecular activation complex). The formation and integrity of the immune synapse is believed to be central to the activation and proliferation of T cells.

By using microsphere beads coated with anti-CD3ε antibody, we have demonstrated that Mgat5 deficiency markedly enhances TCR clustering at the immune synapse (Fig 2), leading to augmented downstream signaling, actin microfilament re-organization and T cell activation. The reduced activation thresholds present in Mgat5^-/- T cells is associated with increased susceptibility to EAE and the spontaneous development of kidney autoimmune disease in Mgat5^-/- mice. Mutation or dysregulation of Mgat5 in humans may be a contributing factor in the pathogenesis of autoimmune diseases such as MS.

Cell surface proteins in mammalian cells are modified with complex-type Asn (N) -linked carbohydrates of variable chain lengths and composition. Mgat5 modified glycans are preferentially extended by two or more N-acetyllactosamine units, forming poly-N-acetyllactosamine chains. Poly-N-acetyllactosamine is a preferred ligand for galectins, a family of carbohydrate binding proteins that modulate T cell signaling, proliferation and apoptosis. Our data indicates that Mgat5 modified glycans associated with the TCR complex bind galectin-3, sequestering the TCR complex within a multivalent cell surface galectin-glycoprotein lattice that restricts ligand dependant TCR clustering at the immune synapse (Fig 3; for review see Lowe (2001) Cell 104 809-812). The absence of Mgat5 glycans disrupts this lattice, thereby enhancing agonist induced TCR clustering, downstream signaling and T cell activation.

The current focus of our laboratory is to further define the structure and function of the T cell galectin-glycoprotein lattice and its role in regulating T cell homeostasis and autoimmunity.

Selected Publications

Demetriou, M., Granovsky, M, Quaggin, S, and Dennis, J.W. (2001). Negative Regulation of T-cell Activation and Autoimmunity by Mgat5 N-Glycosylation. Nature 409, 733-738.

Minireview: Lowe, J.B. Glycosylation, Immunity and Autoimmunity. Cell 104, 809-812.

Dennis, J.W., Warren, C.E., Granovsky, M, Demetriou, M. (2001). Genetic defects in N-glycosylation and cellular diversity in mammals. Current Opinion in Structural Biology 11(5), 601-607.

Binkert, C., Demetriou, M, Sukhu, B., Szweras, M, Tenenbaum, H.C., and Dennis, J.W. (1999). Regulation of Osteogenesis by Fetuin. Journal of Biological Chemistry. 274 (40), 28514-20.

Demetriou, M., Binkert, C., Sukhu, B., Tenenbaum, H.C., and Dennis, J.W. (1996). Fetuin/alpha2-HS glycoprotein is a transforming growth factor-beta type II receptor mimic and cytokine antagonist. Journal of Biological Chemistry. 271 (22), 12755-61.

Demetriou, M., Nabi, I.R., Coppolino, M., Dedhar, S., and Dennis, J.W. (1995). Reduced contact-inhibition and substratum adhesion in epithelial cells expressing GlcNAc-transferase V. Journal of Cell Biology. 130(2), 383-92.

Fernandes, B., Sagman, U., Auger, M., Demetriou, M., and Dennis, J.W. (1991). Beta 1-6 branched oligosaccharides as a marker of tumor progression in human breast and colon neoplasia. Cancer Research. 51. 718-23.

List of Publications via PubMed (NIH National Library of Medicine)