RIP1-RIP3-DRP1 pathway regulates NLRP3 inflammasome activation following subarachnoid hemorrhage

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The NLRP3 inflammasome functions as a crucial component of the inflammatory response in early brain injury (EBI) after subarachnoid hemorrhage (SAH). However, the mechanisms underlying the activation of NLRP3 inflammasome has not been well elucidated. In this study, we hypothesized the RIP1-RIP3-DRP1 pathway was involved in the activation of the NLRP3 inflammasome following SAH. SAH was induced by endovascular perforation in rats. Necrostatin-1 (Nec-1) or mitochondrial division inhibitor (Mdivi-1) was administered 1 h after SAH by intraperitoneal injection. SAH grade, neurological function, brain water content, Western blot, ROS assay, immunofluorescence and transmission electron microscopy were performed. SAH led to the upregulation of RIP1, RIP3, phosphorylated DRP1 and NLRP3 inflammasome. Nec-1 treatment reduced RIP1, RIP3, phosphorylated DRP1 and NLRP3 inflammasome, subsequently alleviated brain edema and neurological deficits at 24 h following SAH. The treatment with Mdivi-1 inhibited the expression of DRP1 protein, attenuated mitochondria damage and the generation of ROS, inhibited NLRP3 inflammasome and ameliorated brain edema and neurological deficits at 24 h after SAH. The activation of the NLRP3 inflammasome in EBI after SAH was mediated by RIP1-RIP3-DRP1 pathway. Nec-1 and Mdivi-1 can inhibit inflammation and improve neurological function after SAH.

Graphical abstract

The RIP1-RIP3-DRP1 pathway in the activation of NLRP3 inflammasome after SAH. Following the stimulation of TNF, the RIP1-RIP3 complex is formed and initiates the activation of MLKL and PGAM5, which eventually result in necroptosis. While after SAH, the RIP1-RIP3 complex is able to trigger the inflammation by a distinct pathway. SAH induces formation of the RIP1-RIP3 complex, which phosphorylates DRP1. DRP1 then induces mitochondrial fission, which leads to increased level of ROS and activated NLRP3 inflammasome. Once activated, NLRP3 inflammasome causes the processing of pro-caspase-1 into its active form and subsequently contributes to the inflammation following SAH.

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