Date of Award

2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Cell and Molecular Biology

Abstract

Multiple Sclerosis (MS) is a demyelinating disorder of the central nervous system affecting 0.1% of the population in the Northern hemisphere. MS is a complex disease that depends on genetic and environmental factors and is controlled by multiple genes that exert a modest effect in the overall disease outcome. The complex nature of the disease complicates the study of individual genes and their contribution in the disease process. To investigate mechanisms underlying the development of diseases like MS and how disease course can be manipulated, animal models have been extensively used, with Experimental Allergic Encephalomyelitis (EAE) being the principle autoimmune model for MS. Even though EAE, like MS, is a complex disease and polygenic in nature, it can be reduced to monogenic intermediate or subphenotypes, which allows for identification of the causative gene and its mechanism. One such subphenotype of EAE in mice, Bordetella pertussis toxin-induced histamine sensitization (Bphs) is controlled by Hrh1, gene encoding mouse histamine receptor H1 (H1R), wherein sensitized animals of susceptible strains die upon histamine challenge and resistant strains do not. Moreover, mice deficient in H1R (H1RKO) show delayed onset and reduced severity in the clinical course of EAE. However, the mechanism by which H1R and its polymorphisms regulate EAE is unknown. As a disease susceptibility gene, Hrh1 could act in different cell types and at several checkpoints in the disease process. This includes endothelial cells that regulate blood-brain barrier, antigen presenting cells or T cells, which regulate the cytokine production. Using transgenic mice expressing H1R exclusively in T cells, this study shows that H1R expression in T cells is sufficient to restore the EAE severity and the disease associated cytokine production of H1RKO mice to wild type levels. H1R from susceptible and resistant strains of mice differ by three amino acids. The P-V-P haplotype (H1RS) is associated with disease susceptibility whereas the L-MS (H1RR) haplotype is associated with less severe disease. In this study, using transgenic mice, we show that reexpression of H1RS fully complements the clinical EAE and the disease-associated cytokine production of H1RKO mice to wild type levels, however, reexpression of H1RR fails to do so. These data suggest that H1RR is not functional relative to H1RS. Mechanistically, using 293T cells, we show that the two H1R alleles exhibit differential cell surface expression and altered intracellular trafficking, with the H1RR allele being retained within the endoplasmic reticulum (ER). Moreover, we show that all three residues (L-M-S) comprising the H1RR haplotype are required for altered expression. Thus, polymorphisms influencing cell surface expression of H1R regulate immune functions and autoimmune disease susceptibility.

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