Ssu72 regulates alveolar macrophage development and allergic airway inflammation by fine-tuning of GM-CSF receptor signaling

Background: Fine-tuning of immune receptor signaling is critical for the development and functioning of immune cells. Moreover, GM-CSF receptor (GM-CSFR) signaling plays an essential role in the development of certain myeloid lineage cells, including alveolar macrophages (AMs). However, the significance of fine-tuning of GM-CSFR signaling in AMs and its relevance in allergic inflammation have not been reported. Objective: Our aim was to explore whether phosphatase Ssu72, originally identified as a regulator of RNA polymerase II activity, regulates AM development and allergic airway inflammation by regulating GM-CSF signaling. Methods: To address these issues, we generated LysM-CreSsu72^fl/fl and Cd11c-CreSsu72^fl/fl mice and used ovalbumin- or house dust mite–induced allergic asthma models. Results: Following GM-CSF stimulation, Ssu72 directly bound to the GM-CSFR β-chain in AMs, preventing phosphorylation. Consistently, mature Ssu72-deficient AMs showed higher phosphorylation of the GM-CSFR β-chain and downstream molecules, which resulted in greater dysregulation of cell cycle, cell death, cell turnover, mitochondria-related metabolism, and LPS responsiveness in AMs than in mature wild-type AMs. The dysregulation was restored by using a Janus kinase 2 inhibitor, which reduced GM-CSFR β-chain phosphorylation. LysM-CreSsu72^fl/fl mice exhibited deficits in development and maturation of AMs, which were also seen postnatally in Cd11c-CreSsu72^fl/fl mice. Furthermore, LysM-CreSsu72^fl/fl mice were less responsive to ovalbumin- or house dust mite–induced allergic asthma models than the control mice were; however, their responsiveness was restored by adoptive transfer of JAK2 inhibitor–pretreated mature Ssu72-deficient AMs. Conclusion: Our results demonstrate that Ssu72 fine-tunes GM-CSFR signaling by both binding to and reducing phosphorylation of GM-CSFR β-chain, thereby regulating the development, maturation, and mitochondrial functions of AMs and allergic airway inflammation.