Supplementary Material for: The Role of Proteasome Inhibitor MG132 in 2,4-Dinitrofluorobenzene-Induced Atopic Dermatitis in NC/Nga Mice

Background: Although immunosuppressants for therapy of atopic dermatitis (AD) are still being sought, proteasome inhibitors are also potential candidates for the treatment of AD. Proteasome inhibitors exert various effects by blocking proteasomal degradation and help regulate processes such as apoptosis induction via caspase-9, cell cycle progression via cyclins, NF-κB inactivation via IκB, and downregulation of antigen cross-presentation. The cells targeted by proteasome inhibitors are therefore activated cells undergoing proliferation or differentiation, and antigen-presenting cells carrying out protein degradation. Objectives: This study investigated the therapeutic effects and side effects of a proteasome inhibitor, MG132, on the treatment of AD. Methods: AD-like disease in NC/Nga mice housed under specific pathogen-free conditions was induced by repeated application of 2,4-dinitrofluorobenzene (DNFB). Disease progression was evaluated by inflammation score, histopathology, and serum IgE level, and the effects of systemic MG132 administration were investigated. The percentages and absolute numbers for each population of Th1, Th2, and Th17 cells in the axillary lymph nodes were analyzed by flow cytometry. Results: DNFB application increased the expression of a unique major histocompatibility complex class I mutant molecule D/L^dm7 in dendritic cells (DCs), and increased Th1 and Th17 cells in NC/Nga mice. In vivo MG132 administration to NC/Nga mice with DNFB-induced dermatitis reduced Th17 cells but maintained the level of Th1 cells, resulting in the alleviation of dermatitis lesions by decreasing both serum IgE hyperproduction and mast cell migration. To understand the mechanisms maintaining Th1 cell levels following in vivo MG132-administration, we focused on the role of proteasomes regulating D/L^dm7 expression. Interestingly, 20S proteasome activity was higher in NC/Nga DCs than in BALB/c DCs. In vitro MG132 administration partially increased D/L^dm7 expression in a dose-dependent manner during DC maturation, and induced IFN-γ production from autoreactive CD8+ T cells but not from CD4+ T cells following coculturing with D/L^dm7-upregulated DCs. Conclusion: Although MG132 administration temporarily alleviated AD pathogenesis in NC/Nga mice, prolonged MG132 treatment may result in immunopathogenesis leading to chronic AD due to its side effect of maintaining Th1 levels via autoreactive CD8+ T cells.