Abstract
Background and Purpose- Accumulated evidence suggests that hemin-a breakdown product of hemoglobin-plays a pivotal role in the inflammatory injuries that result after hemorrhagic stroke through the Toll Like Receptor 2-Toll Like Receptor 4 signal pathway. However, the mechanism of how hemin triggers neuronal necroptosis directly after intracranial hemorrhage (ICH) is still an area of active research. As animal model and preclinical studies have shown, the recombinant interleukin-1 receptor antagonist (IL-1RA) improves clinical outcomes after stroke. As such, we have chosen to investigate the mechanism of how IL-1RA exerts protective effect in hemin-induced neuronal necroptosis after ICH. Methods- Our ICH model was induced by hemin injection in C57BL/6 mice and IL-1R1-/- mice. In addition, we used primary cultured neurons to assess hemin-induced cell death. Co-immunoprecipitation, immunoblot, immunofluorescent staining, neurological deficit scores, and brain water content were used to study the mechanisms of IL-1R1 modulation in neuronal necroptosis both in vitro and in vivo. Results- Free hemin could mediate neuronal necroptosis directly by assembling necrosome complex and then to trigger cell death. This phenomenon was driven by IL-1R1 as IL-1R1 can form a complex with necrosome. After treatment with IL-1RA, both the expression and translocation of the necrosome decreased while disruption of the interaction between IL-1R1 and RIP1/RIP3 (receptor interacting protein 1/3) increased neuron survival. In addition, the IL-1R1-deficient mice demonstrated lower levels of necrosome components, including RIP1, RIP3, and MLKL (mixed lineage kinase domain-like protein), compared with control groups after hemin treatment. In addition, the neurological deficit scores, brain water content, and inflammatory response were all also reduced in the IL-1R1-deficient mice. Conclusions- Functional inhibition of the interaction between IL-1R1 and the necrosome complex improves neuron survival and promotes the recovery of neurological function in experimental ICH. Targeting IL-1R1/RIP1/RIP3 assembly could be a promising therapeutic strategy for patients with ICH.