Heme oxygenase‐1 directly binds STAT3 to control the generation of pathogenic Th17 cells during neutrophilic airway inflammation

Abstract Background Specific JAK / STAT pathways play a critical role in the functional differentiation of distinct Th subsets. Previously, we showed that HO ‐1, a stress‐inducible protein, inhibits Th17 cell differentiation and alleviates neutrophilic airway inflammation, but the responsible molecular basis remains unclear. Methods We employed Th17‐skewing differentiation and NEA mouse models to study the role of HO ‐1 in regulating IL ‐6‐ STAT 3‐ ROR γt/ SOCS 3 signaling pathway to control Th17 cell‐mediated neutrophilic airway inflammation. The levels of cytokines and expressions of relative signaling molecules were measured by ELISA , western blot, and qPCR , respectively. Frequency of CD 4 + IL ‐17A + , CD 4 + IL ‐6R + , and CD 4 + IL ‐23R + cells was analyzed by FCM . The interaction between HO ‐1 and signaling pathway‐related proteins was determined by co‐immunoprecipitation and western blot. Results Here, we show that hemin‐induced HO ‐1 overexpression is required to mediate this process. Specifically, HO ‐1 decreased STAT 3 phosphorylation but not IL ‐6R/ IL ‐23R expression or JAK 1/ JAK 2 activation in CD 4 + T cells. The effect was accompanied by co‐inhibition of SOCS 3, a negative feedback factor of STAT 3 activation. HO ‐1 bound to three domains on STAT 3 ( DNA ‐binding, linker, and transactivation domains) to directly regulate STAT 3 activation. Conversely, either forced expression of a constitutively active STAT 3 mutant or application of small‐interfering RNA (si RNA ) for HO ‐1 reversed these effects. Conclusions Our data suggest that HO ‐1 exerts its inhibitory effect on Th17 cell differentiation by directly associating and blocking STAT 3 phosphorylation. We speculate that hemin may be a potential therapeutic candidate for the treatment of other types of immune and pulmonary inflammatory‐related diseases.