TREM-1-targeting LP17 attenuates cerebral ischemia-induced neuronal injury by inhibiting oxidative stress and pyroptosis

https://doi.org/10.1016/j.bbrc.2020.05.056Get rights and content

Highlights

  • TREM-1-targeting LP-17 alleviates ischemic neuronal damage and microglial activation in MCAO rats.

  • TREM-1-targeting LP-17 attenuates inflammation, oxidative stress and pyroptosis in MCAO rats.

  • Suppressing TREM-1 inhibits oxidative stress and pyroptosis in OGDR-treated co-culture cells.

Abstract

Stroke ranks as the second leading cause of disability and death globally. Trigger receptors expressed on myeloid cells (TREM) −1 are responsible for the activation of the innate immune response and also play a critical role in inflammation. In this study, we reported the contribution of TREM-1 after ischemic damage in a rat middle cerebral artery occlusion (MCAO) model. This study also demonstrated that TREM-1 expression was upregulated following cerebral infarction in rats. TREM-1 inhibition was determined using its selective inhibitor, LP17, which indicated a neuroprotective effect on cerebral infarction damage. The findings revealed that inhibition of TREM-1 by administering LP17 improved cerebral damage and decreased ischemic areas and brain water contents. Moreover, LP17 decreased MCAO-induced microglial activation and neurodegeneration, evidenced by a reduction in the expression of microglial Iba-1 and FJ-B positive cells, and reversed neuronal loss. Besides, the contribution of LP17 to ischemic neuronal damage may be associated with a decrease in the production of pro-inflammatory cytokines, and enhanced production of anti-inflammatory cytokine IL-10. Both in vivo and in vitro studies showed that inhibiting TREM-1 attenuated ROS accumulation, lipid per-oxidation (LPO) contents such as malondialdehyde (MDA) and enhanced the superoxide dismutase (SOD) activity after ischemia. Inhibiting TREM-1 alleviated inflammation and pyroptosis found in MCAO rats. This was achieved through the inhibition of the levels of NLRP3, caspase-1, ASC (an apoptosis-associated speck-like protein containing a CARD) and gasdermin D. These results confirmed that inhibiting TREM-1 protects against ischemia-induced neuronal damage and alleviates microglial mediated neuro-inflammation by reducing oxidative stress and pyroptosis. Therefore, blocking TREM-1 expression provides an effective intervention for improving ischemic stroke.

Introduction

Ischemic stroke is one of the most common cerebrovascular diseases and a leading cause of disability and mortality in adults worldwide [1]. Microglial are mononuclear phagocytic cells in the central nervous system. They are important cellular mediators of neuroinflammation after cerebral infarction [2]. Following ischemia damage, microglial are rapidly activated and undergo phenotypic and morphological changes [3]. Several studies focused on the basic regulation mechanism of microglial activation which results in the secretion of pro-inflammatory cytokines [4], and also promote protective microglial to secret anti-inflammatory cytokines, such as IL-10 [5]. However, anti-inflammatory treatments have been tested in clinical trials, but the expected outcomes in ischemic stroke have not yet been disclosed [6]. Therefore, there is a need to investigate the molecular mechanism of microglial activation in cerebral infarction.

Pyroptosis is a form of programmed necrosis triggered by caspase-1 activation in NLRP3 inflammasomes. It is distinct from other forms of cell death since it is associated with the activation of inflammasomes and mediated by gasdermin D (GSDMD) [7]. Pyroptosis also plays a critical role in the pathogenesis of cerebrovascular diseases, such as ischemia damage [8]. The NLRP3 inflammasomes are assembled and activated following cerebral ischemic/reperfusion (I/R) injury and results in activation of GSDMD [9]. Cerebral infarction is also associated with various complicated pathological processes, including oxidative stress and inflammation [10]. During ischemia, nitric oxide (NO) and hydroxyl free radicals are generated, which can cause ROS accumulation, inflammation, and pyroptosis [11,12]. The triggering receptor expressed on myeloid cells-1 (TREM-1) is a recently discovered cell surface receptor and a member of the extracellular immunoglobulin family. TREM-1 engagement triggers the synthesis and release of pro-inflammatory cytokines [13]. Previous studies have shown that TREM-1 plays a critical role in diseases, such as myocardial infarction and atherosclerosis [14,15]. Moreover, inhibiting TREM-1 reduces the pro-inflammatory cytokine release and activation of pyroptosis by decreasing ROS accumulation in acute lung injury [16]. However, the effect of TREM-1 and its downstream consequences on neuroinflammation following ischemic stroke needs further investigation.

In this study, we investigated whether microglial TREM-1 mediates neuroinflammation following ischemic damage and if the involvement is through interaction with oxidative stress and pyroptosis.

Section snippets

Animals models

All the animal studies were conducted according to the guidelines of the Animal Care and use Committee of Jinan University. Sprague Dawley rats aged 3 months old and weighing between 300 and 350 g were supplied by the Guangdong Medical Laboratory Animal Center. The rats were anesthetized with a 10% chloral hydrate (3 ml/kg, BBI, China) (i.p.) solution and MCAO model established as previously described [17]. TREM-1 inhibitory peptide LP17 (1 mg/kg, GenScript, China) was intranasally administered

TREM-1 expression is induced following MCAO in rats

Fluoro-Jade B (FJB) staining was significantly increased 12 h after operation, and the expression peaked at 3 d in the peri-infarct regions after MCAO. This revealed the degenerated neurons and activated microglial triggered by MCAO (Fig. 1A). TREM-1 mRNA and protein expression levels were progressively elevated in the peri-infarct regions, especially at 3 d after MCAO (Fig. 1C–E). Immunofluorescent results showed that the TREM-1 expression was higher compared with the sham rats after MCAO

Discussion

In this study, inhibition of TREM-1 ameliorated neurological deficit scores and reduced ischemic brain damage. Interestingly, TREM-1 was found to be a significant target molecule involved in neuronal damage caused by microglial activation in ischemia. This was associated with the inhibition of oxidative stress and pyroptosis. These findings strongly suggest that inhibiting TREM-1 may be used as a prospective neuroprotective mechanism and LP17 is a promising agent against cerebral I/R damage.

Declaration of competing interest

We declare that none of the work contained in this manuscript is published in any language or currently under consideration at any other journal, and there are no conflicts of interest to declare. All authors have contributed to, read, and approved this submitted manuscript in its current form.

Acknowledgements

This work was supported by the Natural Science Foundation of Guangdong Province (2020A1515011249), and the National Natural Science Foundation of China (81171084).

References (32)

  • D. Zhang et al.

    Gasdermin D serves as a key executioner of pyroptosis in experimental cerebral ischemia and reperfusion model both in vivo and in vitro

    J. Neurosci. Res.

    (2019)
  • L. Wu et al.

    Targeting oxidative stress and inflammation to prevent ischemia-reperfusion injury

    Front. Mol. Neurosci.

    (2020)
  • G. Cao et al.

    Ruscogenin attenuates cerebral ischemia-induced blood-brain barrier dysfunction by suppressing TXNIP/NLRP3 inflammasome activation and the MAPK pathway

    Int. J. Mol. Sci.

    (2016)
  • J. Klesney-Tait et al.

    The TREM receptor family and signal integration

    Nat. Immunol.

    (2006)
  • J. Lee et al.

    Monosodium urate crystal-induced triggering receptor expressed on myeloid cells 1 is associated with acute gouty inflammation

    Rheumatology

    (2016)
  • T. Liu et al.

    Blocking triggering receptor expressed on myeloid cells-1 attenuates lipopolysaccharide-induced acute lung injury via inhibiting NLRP3 inflammasome activation

    Sci. Rep.

    (2016)
  • Cited by (0)

    1

    These authors contributed equally to this work.

    View full text