MEK1/2 Signalling establishes an alloreactive effector T cell program through SMAD4 during cardiac allograft rejection
Jiulu Zhao, Shuan Ran, Sijie Zhou, Yuan Li, Wang Zhan, Longyong Lai, Jikai Cui, Jiahong Xia, Jie WuAbstract
Background
Acute allograft rejection is largely dependent on T cell‐driven immune responses; however, the molecular programs that establish and maintain effector T cell states during rejection remain incompletely defined.
Methods
Single‐cell transcriptomic analysis was conducted to characterize the activation of signalling pathways in T cells during acute allograft rejection. The function of MEK1/2 signalling was evaluated both in vitro and in vivo using mice with targeted deletion of Mek1/2 in T cells and pharmacological inhibition. Phosphoproteomic analysis, immunofluorescence staining, and western blotting were conducted to investigate downstream signalling mechanisms, particularly those involving SMAD4.
Results
Effector CD4 and CD8 T cells exhibited enhanced MEK/ERK pathway activation throughout the rejection process. MEK1/2 inhibition, either via genetic deletion or pharmacological blockade, attenuated T cell activation and effector activity, leading to reduced rejection and prolonged graft survival. Phosphoproteomic analysis identified SMAD4 as a key downstream effector of MEK1/2 signalling. Mechanistically, MEK1/2 deficiency reduced SMAD4 nuclear translocation in activated T cells, accompanied by diminished effector T cell responses.
Conclusions
MEK1/2 signalling regulates T cell activation and effector phenotypes via SMAD4 nuclear translocation in heart transplant rejection. Therapeutic intervention targeting this pathway may contribute to alloimmune response regulation and improve transplant outcomes.