ADAM8 Activates NLRP3 Inflammasome to Promote Cerebral Ischemia-Reperfusion Injury

Stroke is the leading cause of death and disability in humans. Strokes are classified as either ischemic or hemorrhagic. Ischemic stroke accounts for 70–80% of the cases. Inflammation is a key factor in ischemic brain injury. Studies have shown that inflammatory response induced by NLRP3 inflammasome is one of the root causes of brain damage in mice with cerebral ischemia. However, its specific mechanism in cerebral ischemia is still unclear. ADAM8 (a disintegrin and metalloproteases 8) is a transmembrane protein with different functions. It plays an important role in tumors and neuroinflammation-related diseases. However, the role and molecular mechanism of ADAM8 in cerebral ischemia injury are still unclear. This study aims to evaluate the role of ADAM8 in cerebral ischemic injury and explore its signal transduction mechanism. This experiment shows that ADAM8 can significantly cause neurological deficits in MCAO mice and can substantially cause ipsilateral cerebral edema and cerebral infarction in MCAO mice. In addition, ADAM8 can significantly induce cortical cell apoptosis in MCAO mice, leading to the loss of neurons and the expression of proinflammatory factors COX2, iNOS, TNFα, and IL-6. Importantly, we confirmed that ADAM8 mediates the inflammatory response by promoting the activation of NLRP3 inflammasome, microglia, and astrocytes. These results indicate that ADAM8 may be a candidate drug target for the prevention and treatment of the cerebral ischemic injury.

N-Myc Downstream-Regulated Gene 2 (Ndrg2): A Critical Mediator of Estrogen-Induced Neuroprotection Against Cerebral Ischemic Injury

Growing evidence indicates that estrogen plays a pivotal role in neuroprotection against cerebral ischemia, but the molecular mechanism of this protection is still elusive. N-myc downstream‐regulated gene 2 (Ndrg2), an estrogen-targeted gene, has been shown to exert neuroprotective effects against cerebral ischemia in male mice. However, the role of Ndrg2 in the neuroprotective effect of estrogen remains unknown. In this study, we first detected NDRG2 expression levels in the cortex and striatum in both female and male mice with western blot analyses. We then detected cerebral ischemic injury by constructing middle cerebral artery occlusion and reperfusion (MCAO-R) models in Ndrg2 knockout or conditional knockdown female mice. We further implemented estrogen, ERα or ERβ agonist replacement in the ovariectomized (OVX) Ndrg2 knockouts or conditional knockdowns female mice, then tested for NDRG2 expression, glial fibrillary acidic protein (GFAP) expression, and extent of cerebral ischemic injury. We found that NDRG2 expression was significantly higher in female than in male mice in both the cortex and striatum. Ndrg2 knockouts and conditional knockdowns showed significantly aggravated cerebral ischemic injury in female mice. Estrogen and ERβ replacement treatment (DPN) led to NDRG2 upregulation in both the cortex and striatum of OVX mice. Estrogen and DPN also led to GFAP upregulation in OVX mice. However, the effect of estrogen and DPN in activating astrocytes was lost in Ndrg2 knockouts OVX mice and primary cultured astrocytes, but partially retained in conditional knockdowns OVX mice. Most importantly, we found that the neuroprotective effects of E2 and DPN against cerebral ischemic injury were lost in Ndrg2 knockouts OVX mice but partially retained in conditional knockdowns OVX mice. These findings demonstrate that estrogen alleviated cerebral ischemic injury via ERβ upregulation of Ndrg2, which could activate astrocytes, indicating that Ndrg2 is a critical mediator of E2-induced neuroprotection against cerebral ischemic injury.

Low-Dose Piperlongumine Rescues Impaired Function of Endothelial Progenitor Cells and Reduces Cerebral Ischemic Injury in High-Fat Diet-Fed Mice

It is of great clinical significance to develop potential novel strategies to prevent cardio-cerebrovascular complications in patients with hyperlipidemia. Vascular Endothelial integrity and function play a key role in the prevention of cardio-cerebrovascular diseases. Endothelial progenitor cells (EPCs) can home to sites of ischemic injury and promote endothelial regeneration and neovascularization. Hypercholesterolemia impairs the function of EPC. The present study attempted to identify the effect of piperlongumine on EPCs’ angiogenic potential and cerebral ischemic injury in high-fat diet-fed (HFD-fed) mice. Here, we showed that treatment with low-does piperlongumine (0.25 mg/kg/day) for 8 weeks significantly improved EPCs function and reduced the cerebral ischemic injury (both infarct volumes and neurobehavioral outcomes) in HFD-fed mice. In addition, low-dose piperlongumine administration increased intracellular NO level and reduced intracellular O2- level in EPCs of HFD-fed mice. Moreover, incubation with piperlongumine (1.0 μM, 24 h) reduced thrombospondin-1/2 (TSP-1/2, a potent angiogenesis inhibitor) expression levels in EPCs from HFD-fed mice, increased the therapeutic effect of EPC from HFD-fed mice on cerebral ischemic injury reduction and angiogenesis promotion in HFD-fed mice, and the donor derived EPCs homed to the recipient ischemic brain. In conclusion, low-dose piperlongumine can enhance EPCs’ angiogenic potential and protect against cerebral ischemic injury in HFD-fed mice. It is implied that treatment with low-dose piperlongumine might be a potential option to prevent ischemic diseases (including stroke) in patients with hyperlipidemia, and priming with piperlongumine might be a feasible way to improve the efficacy of EPC-based therapy for ischemic diseases.

Neuroprotective Effect of Quercetin during Cerebral Ischemic Injury Involves Regulation of Essential Elements, Transition Metals, Cu/Zn Ratio, and Antioxidant Activity

Cerebral ischemia results in increased oxidative stress in the affected brain. Accumulating evidence suggests that quercetin possesses anti-oxidant and anti-inflammatory properties. The essential elements magnesium (Mg), zinc (Zn), selenium (Se), and transition metal iron (Fe), copper (Cu), and antioxidants superoxide dismutase (SOD) and catalase (CAT) are required for brain functions. This study investigates whether the neuroprotective effects of quercetin on the ipsilateral brain cortex involve altered levels of essential trace metals, the Cu/Zn ratio, and antioxidant activity. Rats were intraperitoneally administered quercetin (20 mg/kg) once daily for 10 days before ischemic surgery. Cerebral ischemia was induced by ligation of the right middle cerebral artery and the right common carotid artery for 1 h. The ipsilateral brain cortex was homogenized and the supernatant was collected for biochemical analysis. Results show that rats pretreated with quercetin before ischemia significantly increased Mg, Zn, Se, SOD, and CAT levels, while the malondialdehyde, Fe, Cu, and the Cu/Zn ratio clearly decreased as compared to the untreated ligation subject. Taken together, our findings suggest that the mechanisms underlying the neuroprotective effects of quercetin during cerebral ischemic injury involve the modulation of essential elements, transition metals, Cu/Zn ratio, and antioxidant activity.