Glucocorticoids Modulate Th1 and Th2 Responses in Asthmatic Mouse Models by Inhibition of Notch1 Signaling

Background: Notch1 has been linked to the pathogenesis of asthma due to its contribution on Th1/Th2 imbalance. γ-Secretase inhibitor (GSI) acts as an effective blocker of Notch1 signaling. Glucocorticoids (GCs) are the most effective anti-inflammatory drugs for asthma. The present study investigated the involvement of the Notch1 pathway in the anti-inflammatory effect of GCs and its association with Th1/Th2 balance. Methods: The asthma model was established in BALB/c mice by sensitization with ovalbumin (OVA). Dexamethasone (DEX; 1 mg/kg) and/or GSI (0.03 mg/kg) was orally or intranasally administrated. Results: Compared to the OVA-sensitized mice, the administration of DEX and/or GSI significantly ameliorated the airway inflammation infiltration, goblet cell metaplasia, and airway hyper-responsiveness. The expression of IL-4 and IL-13, as well as the ratios of eosinophils and lymphocytes, were significantly decreased, whereas IFN-γ and IL-2 levels were significantly increased in bronchoalveolar lavage fluid after the administration of DEX and GSI. The expressions of the Notch1/NICD1 pathway were decreased after DEX and/or GSI administration in lung tissues, especially in CD4+ T cells. Also, a reduction of GATA3 and elevation of T-bet levels were correlated with the upregulation of Th1/Th2 ratios in lung tissues. Conclusions: Through the inhibition of Notch1 signaling, both GSI and GCs could regulate Th1/Th2 balance involved in allergic airway inflammation in OVA-induced asthma.