Background Microglia can not only detrimentally augment secondary injury but also potentially promote recovery. However, the mechanism underlying the regulation of microglial phenotypes after stroke remains unclear. Methods Mice were subjected to middle cerebral artery occlusion for 60 min. At 3 days after reperfusion, the effects of activation and suppression of triggering receptor expressed on myeloid cells 2 on immunocyte phenotypes (n = 5), neurobehavioral scores (n = 7), infarct volumes (n = 8), and neuronal apoptosis (n = 7) were analyzed. In vitro, cultured microglia were exposed to oxygen–glucose deprivation for 4 h. Inflammatory cytokines, cellular viability (n = 8), neuronal apoptosis (n = 7), and triggering receptor expressed on myeloid cells 2 expression (n = 5) were evaluated in the presence or absence of triggering receptor expressed on myeloid cell-specific small interfering RNA or triggering receptor expressed on myeloid cells 2 overexpression lentivirus. Results Triggering receptor expressed on myeloid cells 2 expression in the ischemic penumbra peaked at 3 days after ischemia–reperfusion injury (4.4 ± 0.1-fold, P = 0.0004) and was enhanced in interleukin-4/interleukin-13–treated microglia in vitro (1.7 ± 0.2-fold, P = 0.0119). After oxygen–glucose deprivation, triggering receptor expressed on myeloid cells 2 conferred neuroprotection by regulating the phenotypic conversion of microglia and inflammatory cytokine release. Intraperitoneal administration of triggering receptor expressed on myeloid cells 2 agonist heat shock protein 60 or unilateral delivery of a recombinant triggering receptor expressed on myeloid cells 2 lentivirus into the cerebral ventricle induced a significant neuroprotective effect in mice (apoptotic neurons decreased to 31.3 ± 7.6%; infarct volume decreased to 44.9 ± 5.3%). All values are presented as the mean ± SD. Conclusions Activation or up-regulation of triggering receptor expressed on myeloid cells 2 promoted the phenotypic conversion of microglia and decreased the number of apoptotic neurons. Our study suggests that triggering receptor expressed on myeloid cells 2 is a novel regulator of microglial phenotypes and may be a potential therapeutic target for stroke.

Tanshinone IIA (TSA), a principal component derived from the Traditional Chinese Medicine Danshen has been suggested to exert neuroprotective effect against experimental cerebral ischemic/reperfusion injury. But the associated underlying mechanisms still have not been understood. The current study characterized the role of nuclear factor erythroid two-related factor-induced antioxidant response in the neuroprotective efficacy of TSA treatment. The focal cerebral ischemia/reperfusion model was established by 60-minute middle cerebral artery occlusion. At the onset during reperfusion, mice were treated with 10 mg/kg TSA intraperitoneally. The mRNA and nuclear factor erythroid 2 (Nrf2) protein expression, the antioxidant enzymes, and oxidative production levels were measured. To further verify the role of Nrf2 in the neuroprotective effect induced by TSA, the Nrf2 small silenced RNA and Nrf2 knockout mice were used, the neurological function, brain infarct volume, and cellular apoptosis examination were assessed. TSA treatment improved neurological scores, reduced infarct volume, and attenuated the cellular apoptosis. TSA treatment upregulated the expression of Nrf2 mRNA and the contents of Nrf2 protein in nuclear extract. Nrf2 activation by TSA treatment increased the contents of antioxidant enzymes, and reduced the generation of oxidative productions. Either Nrf2 knockdown or Nrf2 knockout abolished the antioxidative and neuroprotective effect of TSA treatment. These results demonstrate that the Nrf2 activation contributes to TSA-induced neuroprotection from experimental ischemic stroke through maintaining antioxidant effect.

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