γ-Secretase Inhibitor Reduces Allergic Pulmonary Inflammation by Modulating Th1 and Th2 Responses

Rationale: gamma-Secretase inhibitor (GSI) has been used to effectively block Notch signaling, which is implicated in the differentiation and functional regulation of T helper (Th) effector cells. In asthma, a subset of CD4(+) T cells is believed to initiate and perpetuate the disease. Objectives: The aim of this study was to evaluate the therapeutic potential of GSI against allergic asthma. Methods: GSI was administered to an ovalbumin-sensitized mouse via an intranasal route at the time of ovalbumin challenge. Measurements and Main Results: The administration of GSI inhibits asthma phenotypes, including eosinophilic airway inflammation, goblet cell metaplasia, methacholine-induced airway hyperresponsiveness, and serum IgE production. GSI treatment of bronchoalveolar lavage cells stimulated via TCR or non-TCR pathways led to a decrease in Th2 cytokine production with a concomitant increase in Th1 cytokine secretion. Expression of Hes-1, a target of Notch signaling, was down-regulated in conjunction with a reduction of Notch intracellular domain and GATA-3 levels after GSI treatment of bronchoalveolar lavage cells. GSI treatment resulted in an inhibition of NF-kappa B activation, and combined treatment with GSI and an NF-kappa B inhibitor augmented IFN-gamma production in a synergistic manner. Conclusions: These data suggest that GSI directly regulates Th1 and Th2 responses in allergic pulmonary inflammation through a Notch signaling-dependent pathway and that GSI is of high therapeutic value for treating asthma by inhibiting airway inflammatory responses.