The pivotal role of the NLRC4 inflammasome in neuroinflammation after intracerebral hemorrhage in rats

Brain hemorrhage: Reducing inflammation and brain damage Treatments that target the proteins responsible for inflammation might reduce brain damage after a hemorrhage. Sudden bleeding into the brain, known as intracerebral hemorrhage (ICH), is associated with strokes and head injuries. Inflammation exacerbates ICH-induced injury after an incident, and is activated by protein complexes called inflammasomes. Jing Zhao and co-workers at Chongqing Medical University in China induced ICH symptoms in rats by extracting arterial blood and injecting it into the basal ganglia of the brain. When they artificially blocked expression of the inflammasome NLRC4, they saw reductions in neuron death, brain edema and damage to the blood-brain barrier. The team also identified a protein critical for activating NLRC4 and another protein that suppresses NLRC4. These findings could aid the development of treatments to block NLRC4 in the days after an ICH. The NLRC4 inflammasome, a member of the nucleotide-binding and oligomerization domain-like receptor (NLR) family, amplifies inflammation by facilitating the processing of caspase-1, interleukin (IL)-1 beta, and IL-18. We explored whether NLRC4 knockdown alleviated inflammatory injury following intracerebral hemorrhage (ICH). Furthermore, we investigated whether NLRC4 inflammasome activation can be adjusted by the regulator of G protein signaling 2/leucine-rich repeat kinase-2 pathway. Fifty microliters of arterial blood was drawn and injected into the basal ganglion to simulate the ICH model. NLRC4 small interfering RNAs (siRNAs) were utilized to knockdown NLRC4. An LRRK2 inhibitor (GNE7915) was injected into the abdominal cavity. Short hairpin (sh) RNA lentiviruses and lentiviruses containing RGS2 were designed and applied to knockdown and promote RGS2 expression. Neurological functions, brain edema, Western blot, enzyme-linked immunosorbent, hematoxylin and eosin staining, Nissl staining, immunoprecipitation, immunofluorescence assay and Evans blue dye extravasation and autofluorescence assay were evaluated. It was shown that the NLRC4 inflammasome was activated following ICH injury. NLRC4 knockdown extenuated neuronal death, damage to the blood-brain barrier, brain edema and neurological deficiency 3 days after ICH. NLRC4 knockdown reduced myeloperoxidase (MPO) cells as well as tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-1 beta and IL-18 following ICH. GNE7915 reduced pNLRC4 and NLRC4 inflammasome activation. RGS2 suppressed the interaction of LRRK2 and NLRC4 and NLRC4 inflammasome activation by regulating pLRRK2. Our study demonstrated that the NLRC4 inflammasome may aggravate the inflammatory injury induced by ICH and that RGS2/LRRK2 may relieve inflammatory injury by restraining NLRC4 inflammasome activation.