Inhibition of the NLRP3 inflammasome reduces brain edema and regulates the distribution of aquaporin-4 after cerebral ischaemia-reperfusion
Introduction
Stroke is a serious illness that threatens human life. A total of 87% of all strokes are ischaemic strokes [1]. The consequence of ischaemic stroke is neurological dysfunction. Ischaemic nerve tissue becomes necrotic due to oxygen and glucose deprivation. The blood-brain barrier (BBB) is destroyed, immune cells infiltrate and post-ischaemic inflammation occurs. Inflammatory mediators from leukocytes and injured brain cells enhance the permeability of the vasculature and exacerbate cerebral edema [2]. Cerebral edema is a life-threatening complication of ischaemic brain injury. Surgical treatment and hyperosmolar agents may be the only effective options, and there is no effective pathogenic treatment for cerebral edema. Therefore, it is significant to explore therapies for brain edema in ischaemic stroke.
The NLRP3 inflammasome activates cleavage of pro-IL-1β and pro-IL-18 dependent on caspase-1 and triggers pyroptosis. Evidence has indicated that the NLRP3 inflammasome promotes inflammatory response and ischaemia injury after ischaemic stroke [3,4]. MCC950 is known as a selective molecular for the NLRP3 inflammasome inhibiting in inflammatory disease [5]. MCC950 attenuates brain injury and cerebral edema by suppressing the NLRP3 inflammasome in subarachnoid haemorrhage and intracerebral haemorrhage (ICH) [6,7]. In our previous study, we demonstrated that MCC950 alleviates injury after cerebral ischaemia-reperfusion, and it also inhibits the IL-23/IL-17 axis signaling [8]. The regulatory role of the NLRP3 inflammasome in brain edema is not fully known. Therefore, in this study, we aimed to observe the effect of MCC950 on brain edema in cerebral ischaemia-reperfusion.
Aquaporin-4 (AQP4) is a kind of the membrane transport proteins and mainly located in astrocytes in the central nervous system (CNS). AQP4 is involved in cerebral water balance, neuroexcitation and astrocyte migration [9]. AQP4 facilitates water movement into the brain tissue through the intact BBB in cytotoxic brain edema and facilitates the exit of excess water from the brain in vasogenic brain edema [10,11]. It has been demonstrated that AQP4 deficiency in mice and the inhibiting of AQP4 by TGN-020 both reduce brain edema and improve neurological outcomes in cerebral ischaemia [10,12]. AQP4 also plays an intrinsic proinflammatory role in the CNS. AQP4 deficiency in mice is correlated with reduced neuroinflammation and decreased severity of the symptoms of experimental autoimmune encephalomyelitis (EAE) [13]. Endothelin-1 (ET-1) is a vasoconstrictor and related to the inflammatory response in the brain under ischaemic conditions [14]. ET-1 contributes to ischaemic injury through increasing accumulation of water, inducing cerebral edema, and impairing the BBB [15]. These results suggest it is important of AQP4 and ET-1 for modulating brain water transport, and this process may be regulated by inflammation. We further explored the effects of the NLRP3 inflammasome on AQP4 and ET-1 to reveal the relationship between the inflammasome and BBB disorders in cerebral ischaemic injury.
Section snippets
Animals
Male C57BL/6 mice (weighing 23–27 g, Beijing Vital River Laboratory Animal Technology Co, Ltd., China) were housed in animal care facility under the laboratory conditions of 25 °C, 50–60% humidity, and a 12 h light/dark periods. The mice were given free access to water and food. All experiments were conducted in accordance with the National Institute of Health guidelines for the care and use of laboratory animals in research and were approved by the Laboratory Animals Ethics Committee of the
The mRNA levels of the NLRP3 inflammasome were elevated after tMCAO in mice
Our previous study reported that the protein expression of the NLRP3 inflammasome is elevated after tMCAO [8]. To investigate the change in the mRNA levels of molecules related to the NLRP3 inflammasome after tMCAO, RT-PCR was performed on brain tissue 6 h, 24 h, 72 h, 5 d and 7 d after tMCAO (Fig. 1C–E). Fig. 1C shows that the NLRP3 mRNA level was significantly increased 6 h (p < 0.001), 24 h (p < 0.001) and 72 h (p < 0.05) after tMCAO (n = 3/group). Fig. 1D shows that the IL-1β mRNA level was
Discussion
More and more evidence has shown the important roles that the NLRP3 inflammasome plays in mediating inflammation and affecting the progression of ischaemic stroke [20]. We demonstrated that the NLRP3 inflammasome is activated after tMCAO and facilitates ischaemia-reperfusion injury previously [8]. In this study, we confirmed that NLRP3 inflammasome inhibition by MCC950 alleviated brain edema and reduced the expression of molecules associated with brain edema after cerebral
Conclusion
In summary, our study provided evidence that the NLRP3 inflammasome is a vital therapeutic target for brain edema after tMCAO. The NLRP3 inflammasome inhibition reduced brain edema and BBB disruption. MCC950, a selective inhibitor of the NLRP3 inflammasome, suppressed the expression of AQP4 and ET-1 and regulated the distribution of AQP4 after cerebral ischaemia-reperfusion in mice. It might be crucial to choose the appropriate intervention time and characterize the type of brain edema.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (grant number 81873746).
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