Nrf2 regulates microglia-mediated phagocytosis and neuroinflammation after intracerebral hemorrhage

Abstract

Activated microglia is essential for hematoma clearance and recovery after intracerebral hemorrhage (ICH). This study aims to evaluate the effect of microglial functional transformation in hematoma clearance after ICH. Through in vitro and in vivo experiments, we also investigate whether Nuclear factor erythroid 2-related factor 2 (Nrf2) -mediated microglial phagocytosis and inflammatory response plays a role in hematoma clearance and functional recovery after ICH. In vitro experiments, BV-2 cells were cultured and randomly divided into 4 groups, including normal control, microglia + Nrf2-siRNA (100 nmol/L), microglia + monascin (15 µM), and microglia + Xuezhikang (200 µg/mL) groups. In vivo experiments, 42 mice were divided into 2 groups, i.e., sham, ICH+vehicle, ICH+Nrf2-/-, ICH+monascin (10mg/kg/day, twice) and ICH+ Xuezhikang (0.2g/kg/day, twice) groups. Further, neurologic scores, hemoglobin levels, microglial phagocytosis, brain expression of CD80/Trem1/TNF-α (pro-inflammatory cytokines), and CD206/Trem2/ BDNF(anti-inflammatory cytokines) were analyzed 72 hours after surgery. The results showed that Nrf2 agonists improved neurological deficits and decreased hemoglobin levels after ICH through regulating microglial functional transformation. Administration of Nrf2 agonist- monascin/ Xuezhikang improved microglia-mediated phagocytosis of erythrocytes and bio-particles through Nrf2 upregulation. Alternatively, monascin/ Xuezhikang promoted the expression of Triggering receptor II expressed on myeloid cells(Trem2), CD206, and BDNF while inhibiting the expression of Trem1,CD80, and TNF-α in microglia. Conversely, Nrf2 inhibition (Nrf2 siRNA or Nrf2-/-) demonstrated conflicting results after ICH. Microglial functional transformations are implicated in hematoma clearance after ICH. Nrf2 activation leads to microglial functional transformation and phagocytic responses then exert its neuroprotection after ICH. Nrf2 activator (Monascin /Xuezhikang) improves hematoma clearance and alleviates neuroinflammation by regulating microglial functional alteration after ICH.