Elsevier

Life Sciences

Volume 251, 15 June 2020, 117638
Life Sciences

Inhibition of the NLRP3 inflammasome reduces brain edema and regulates the distribution of aquaporin-4 after cerebral ischaemia-reperfusion

https://doi.org/10.1016/j.lfs.2020.117638Get rights and content

Highlights

  • MCC950 suppressed the NLRP3 and gasdermin D after tMCAO in mice.

  • MCC950 attenuated brain edema and BBB disruption after tMCAO in mice.

  • MCC950 reduced AQP4 expression and regulated its distribution after tMCAO in mice.

  • MCC950 reduced the level of ET-1 after tMCAO in mice.

Abstract

Aims

Brain edema is a common threat to life in ischaemic brain injury. The NLRP3 inflammasome promotes the inflammatory injury after ischaemic stroke. Previous studies have shown that aquaporin-4 (AQP4) modulates brain water transport and endothelin-1 (ET-1) induces cerebral edema. However, the contribution of the NLRP3 inflammasome to regulation of brain edema and blood-brain barrier (BBB) disruption in cerebral ischaemia-reperfusion is elusive. The aim of this study is to investigate the effect of inhibition of the NLRP3 inflammasome by MCC950 on regulation of cerebral edema, BBB disruption and the expression of AQP4 and ET-1 in cerebral ischaemia-reperfusion.

Main methods

The male C57BL/6 mice were used to establish the experimental transient middle cerebral artery occlusion (tMCAO) model. The mice were intraperitoneally injected with MCC950. Changes in NLRP3, IL-1β, IL-18, the pyroptosis protein gasdermin D (GSDMD), brain water content, AQP4 and ET-1 in brain tissue were detected.

Key findings

MCC950 inhibited NLRP3 and GSDMD after tMCAO. MCC950 improved cerebral edema and alleviated the damage of BBB after tMCAO. The levels of AQP4 and ET-1 were decreased by MCC950. In addition, MCC950 regulated the distribution of AQP4 after tMCAO in mice.

Significance

The NLRP3 inflammasome facilitated brain edema and BBB disruption after cerebral ischaemia-reperfusion in mice, and NLRP3 inflammasome inhibition with MCC950 regulated the expression and distribution of AQP4 in the infarct area. Hence, the NLRP3 inflammasome is considered to be an important target for the treatment of brain edema in cerebral ischaemia-reperfusion, and MCC950 has potential value for ischaemic stroke treatment.

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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