Heme Oxygenase-1 Exerts a Protective Role in Ovalbumin-induced Neutrophilic Airway Inflammation by Inhibiting Th17 Cell-mediated Immune Response

Background: Heme oxygenase-1 (HO-1) is an inducible enzyme that exerts multiple physiological functions. Results: Induction of HO-1 inhibits Th17-mediated neutrophilic airway inflammation in vivo and suppresses Th17 cell differentiation in vitro. Conclusion: HO-1 exhibits anti-inflammatory activity in non-eosinophilic asthma (NEA) by inhibiting Th17 responses. Significance: HO-1 may become a novel therapeutic target in NEA. Allergic asthma is conventionally considered as a Th2 immune response characterized by eosinophilic inflammation. Recent investigations revealed that Th17 cells play an important role in the pathogenesis of non-eosinophilic asthma (NEA), resulting in steroid-resistant neutrophilic airway inflammation. Heme oxygenase-1 (HO-1) has anti-inflammation, anti-oxidation, and anti-apoptosis functions. However, its role in NEA is still unclear. Here, we explore the role of HO-1 in a mouse model of NEA. HO-1 inducer hemin or HO-1 inhibitor tin protoporphyrin IX was injected intraperitoneally into ovalbumin-challenged DO11.10 mice. Small interfering RNA (siRNA) was delivered into mice to knock down HO-1 expression. The results show that induction of HO-1 by hemin attenuated airway inflammation and decreased neutrophil infiltration in bronchial alveolar lavage fluid and was accompanied by a lower proportion of Th17 cells in mediastinal lymph nodes and spleen. More importantly, induction of HO-1 down-regulated Th17-related transcription factor retinoic acid-related orphan receptor t (RORt) expression and decreased IL-17A levels, all of which correlated with a decrease in phosphorylated STAT3 (p-STAT3) level and inhibition of Th17 cell differentiation. Consistently, the above events could be reversed by tin protoporphyrin IX. Also, HO-1 siRNA transfection abolished the effect of hemin induced HO-1 in vivo. Meanwhile, the hemin treatment promoted the level of Foxp3 expression and enhanced the proportion of regulatory T cells (Tregs). Collectively, our findings indicate that HO-1 exhibits anti-inflammatory activity in the mouse model of NEA via inhibition of the p-STAT3-RORt pathway, regulating kinetics of RORt and Foxp3 expression, thus providing a possible novel therapeutic target in asthmatic patients.