Macrophage-specific deletion of HO-1 aggravates radiation-induced lung injury through an PP2A-dependent manner

Radiation-induced lung injury (RILI) is a common complication associated with radiotherapy for thoracic malignancies, and its etiology and pathogenesis remain poorly understood. This study aims to elucidate the role and its underling mechanism of heme oxygenase-1 (HO-1) in the progression of RILI. Our findings revealed that HO-1 levels were significantly elevated in the serum of RILI patients, as well as in lung tissues and macrophages of RILI mice. Meanwhile, by deleting lung macrophages with chlodronate liposomes, we demonstrated the critical involvement of macrophages in RILI development. Through the generation of macrophage-specific HO-1 knockout (HO-1^fl/flLysM^cre) and HO-1^flox/flox (HO-1^fl/fl) mice, we establish a RILI mouse model and showed that macrophage-specific HO-1 depletion exacerbated RILI, as evidenced by increased pathological damage, oxidative stress, and inflammatory responses. Additionally, HO-1 deficiency or pharmacological inhibition HO-1 by ZnPP significantly exacerbated X-ray-induced reactive oxygen species (ROS) generation and pro-inflammatory cytokine production in bone marrow-derived macrophage (BMDMs). In contrast, treatment with the HO-1 inducer Hemin mitigated irradiation-induced oxidative stress and inflammation, thereby alleviating RILI. Further mechanistic study revealed that HO-1 deficiency enhanced X-ray-induced phosphorylation of FoxO3a and NF-κB p65 (p65), inhibited the co-location of FoxO3a and p65 in the cytoplasm, and promoted the nuclear translocation of p65, while suppressing the expression of protein phosphatase 2A (PP2A). Importantly, PP2A siRNA interference attenuated the effects of HO-1 deficiency on the phosphorylation of FoxO3a and p65, as well as inflammation induced by X-ray. Moreover, Hemin exerted protective effects against inflammation and RILI by promoting PP2A-mediated suppression of FoxO3a/NF-κB signaling pathway. In conclusion, our findings suggest that macrophage-specific deletion of HO-1 exacerbates X-ray-induced inflammation and RILI, potentially through the inhibition of PP2A-mediated suppression of the FoxO3a/NF-κB pathway. These results provide novel insights into the pathogenesis of RILI and identify potential therapeutic targets and agents for the treatment of RILI.