Limiting Autoimmune Neuroinflammation using Novel T Cell Suppressants & Investigating Overlapping Lysosomal Reductase Function in Macrophages and Osteoclasts
Date
2019-07-19
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Abstract
Aberrant activation of adaptive immune cells can culminate in autoimmune diseases such as multiple sclerosis (MS). Recently, potent anti-inflammatory properties for the cooling compound, icilin, and its receptor target, Transient Receptor Potential Melastatin-8 (TRPM8), were characterized in the context of inflammatory colitis—the first half of this dissertation describes an attempt to repurpose the anti-inflammatory qualities of icilin and TRPM8 for the treatment of lymphocyte-mediated neuroinflammation. We found icilin treatment strongly attenuated experimental autoimmune encephalomyelitis (EAE), a murine model of MS, via an unexpected TRPM8-independent mechanism. Icilin inhibited the proliferation, polarization and downstream effector function of CD4+ T cells, suggesting a promising drug for limiting neuroinflammation. Citing the advantageous pharmacodynamics of icilin, we additionally screened a library of icilin-related analogues for anti-proliferative character. We identified several lead compounds with improved anti-proliferative properties compared to icilin in vitro and preliminary efficacy in vivo limiting EAE severity. Collectively, this work characterizes a new class of T cell suppressants while emphasizing clear off-target effects for the cooling drug icilin beyond TRP channel activation. Antigen presenting cells such as macrophages process phagocytosed cargo within the highly degradative phagolysosome, facilitating antigenic stimulation of T cells and adaptive immunity. The redox microenvironment of the phagolysosomal lumen regulates several phagolysosomal biochemistries, including proteolysis and disulfide reduction. The lysosomal enzyme γ-interferon-inducible lysosomal thiol reductase (GILT) directly catalyzes disulfide reduction and enhances proteolysis by thiol-dependent cysteine cathepsins within the phagolysosome—while clearly implicated in antigen processing, secondary roles for GILT remain largely undefined. The second half of this dissertation establishes a role for GILT in osteoclasts, bone resorbing cells derived from macrophages. GILT expression was highly upregulated in osteoclasts in response to osteoclastogenic and inflammatory cytokines, and GILT-deficient mice were discovered to be osteopetrotic. In vitro, GILT-deficient osteoclasts demonstrated a reduced capacity to resorb bone. GILT not only directly reduced disulfides within bone matrix structural proteins, but also enhanced the activity of cathepsin K, the prototypical osteoclast collagenase. Thus, this work reveals a novel, non-immunological role for GILT in osteoclast function and bone turnover.
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Keywords
Icilin, TRPM8, Multiple Sclerosis, EAE, T Cell, GILT, Redox, Osteoclast, Macrophage, Lysosome, Cathepsin
Citation
Ewanchuk, B. W. (2019). Limiting Autoimmune Neuroinflammation using Novel T Cell Suppressants & Investigating Overlapping Lysosomal Reductase Function in Macrophages and Osteoclasts (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.