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

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.

We employed Th17-skewing differentiation and NEA mouse models to study the role of HO-1 in regulating IL-6-STAT3-RORγt/SOCS3 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 CD4⁺ IL-17A⁺ , CD4⁺ IL-6R⁺ , and CD4⁺ 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.

Here, we show that hemin-induced HO-1 overexpression is required to mediate this process. Specifically, HO-1 decreased STAT3 phosphorylation but not IL-6R/IL-23R expression or JAK1/JAK2 activation in CD4⁺ T cells. The effect was accompanied by co-inhibition of SOCS3, a negative feedback factor of STAT3 activation. HO-1 bound to three domains on STAT3 (DNA-binding, linker, and transactivation domains) to directly regulate STAT3 activation. Conversely, either forced expression of a constitutively active STAT3 mutant or application of small-interfering RNA (siRNA) for HO-1 reversed these effects.

Our data suggest that HO-1 exerts its inhibitory effect on Th17 cell differentiation by directly associating and blocking STAT3 phosphorylation. We speculate that hemin may be a potential therapeutic candidate for the treatment of other types of immune and pulmonary inflammatory-related diseases.