NLRP3 inflammasome contributes to inflammation after intracerebral hemorrhage

Abstract

Objective The NLRP3 (NALP3, cryopyrin) inflammasome, a key component of the innate immune system, facilitates caspase-1 and interleukin (IL)–1β processing, which amplifies the inflammatory response. Here, we investigated whether NLRP3 knockdown decreases neutrophil infiltration, reduces brain edema, and improves neurological function in an intracerebral hemorrhage (ICH) mouse model. We also determined whether mitochondrial reactive oxygen species (ROS) governed by mitochondrial permeability transition pores (mPTPs) would trigger NLRP3 inflammasome activation following ICH. Methods ICH was induced by injecting autologous arterial blood (30μl) into a mouse brain. NLRP3 small interfering RNAs were administered 24 hours before ICH. A mPTP inhibitor (TRO-19622) or a specific mitochondria ROS scavenger (Mito-TEMPO) was coinjected with the blood. In naive animals, rotenone, which is a respiration chain complex I inhibitor, was applied to induce mitochondrial ROS production, and followed by TRO-19622 or Mito-TEMPO treatment. Neurological deficits, brain edema, enzyme-linked immunosorbent assay, Western blot, in vivo chemical cross-linking, ROS assay, and immunofluorescence were evaluated. Results ICH activated the NLRP3 inflammasome. NLRP3 knockdown reduced brain edema and decreased myeloper-oxidase (MPO) levels at 24 hours, and improved neurological functions from 24 to 72 hours following ICH. TRO-19622 or Mito-TEMPO reduced ROS, NLRP3 inflammasome components, and MPO levels following ICH. In naive animals, rotenone administration induced mPTP formation, ROS generation, and NLRP3 inflammasome activation, which were then reduced by TRO-19622 or Mito-TEMPO. Interpretation The NLRP3 inflammasome amplified the inflammatory response by releasing IL-1β and promoting neutrophil infiltration following ICH. Mitochondria ROS may be a major trigger of NLRP3 inflammasome activation. The results of our study suggest that the inhibition of the NLRP3 inflammasome may effectively reduce the inflammatory response following ICH.

Poststroke Inflammasome Expression and Regulation in the Peri-Infarct Area by Gonadal Steroids after Transient Focal Ischemia in the Rat Brain

“…This is consistent with observations reported after spinal cord injury [47]. After intracerebral hemorrhage, NLRP3 inhibition reduced the inflammatory response, suggesting also an important function for this type of inflammasome [48]. …”

AIM2 and NLRC4 inflammasomes contribute with ASC to acute brain injury independently of NLRP3

“…The types of inflammasome activated in the brain may also depend upon the nature of the injury. For example, in a mouse model of intracerebral hemorrhage the NLRP3 inflammasome is reported to drive brain edema and behavioral deficits (52). It was reported recently that heme, a breakdown product of blood, activates the NLRP3 inflammasome (53).…”

Hemolysis-induced lethality involves inflammasome activation by heme

“…In a model of unilateral uretral obstruction, heme and the active forms of caspase-1 and IL-1β are increased (63). It has been demonstrated that inflammation, renal dysfunction, and death triggered by transient renal artery occlusion, a model of tubular necrosis induced by ischemiareperfusion, was dependent on NLRP3 (53), and intracerebral hemorrhage also activates the NLRP3 inflammasome in a mechanism dependent on mtROS (65). We observed that the pathogenesis of hemolysis was dependent on inflammasome components, demonstrated by the high resistance of mice lacking Nlrp3, Asc, or Caspase-1.…”