J Neuroinflammation︱Peng Ying's research group reveals the regulatory role of microglia mitophagy in morphine-induced central nervous system inflammatory inhibition

Written by ︱ Peng Jialing ︱ Wang Sizhen Morphine is one of the commonly used opioids for analgesia in clinical practice, but morphine dependence can appear from the beginning, resulting in widespread morphine dependence and abuse[1]
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In people who use morphine for a long time, it is often accompanied by the suppression of the immune system, which can be reflected in peripheral immunosuppression, such as the functional suppression of T lymphocytes [2], the dysfunction of antigen presentation [3], the inhibition of the activity of natural killer cells, Reduction in the number of circulating immune cells [4], atrophy of the spleen and thymus [5]
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In addition, in addition to the peripheral immune system, long-term morphine use will lead to a decrease in the clearance of the central immune response regulatory system against exogenous infection, and is prone to aggravation of central nervous system infection, which affects clinical prognosis such as surgical recovery, infection damage, tumor progression, etc.

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However, there are few studies on the mechanism of immunosuppression in the central nervous system caused by long-term morphine use
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Exploring the mechanism of central immunosuppression caused by long-term morphine use will improve the limitations of morphine clinical application and benefit more patients with advanced cancer pain
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 Mitochondria are involved in various cellular physiological processes, participate in various signaling pathways to regulate the function of the immune system, and are the intermediate hub and response platform of various inflammatory pathways [6]
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Mitophagy is an autophagy pathway that selectively removes damaged and aging mitochondria, and is an important pathway for mitochondrial quality control in the body
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Defective mitophagy is closely related to the release of inflammatory factors and the homeostasis of immune cells, which are involved in various inflammatory disorders and autoimmune diseases [7]
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In addition, the products of many pathogens can regulate the body's inflammatory response by regulating mitophagy
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Thus, mitophagy is inseparable from the host's anti-infection inflammatory response
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 NLRX1 (nucleotide binding domain and leucine rich repeat containing family member X1) is the only mitochondrial-localized NLR family member
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In April 2019, Chinese researchers discovered for the first time that the NACHT region of NLRX1 has a conserved LIR pattern recognition region [8], and proposed for the first time that NLRX1 has the function of regulating mitophagy and is a new type of mitophagy receptor protein
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The results of this study have gradually drawn researchers' attention to the mechanism by which NLRX1 regulates mitophagy.
However, more research is needed to clarify under what conditions NLRX1 dominates the regulation of mitophagy and how to regulate it
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 On April 12, 2022, Ying Peng's team from the Department of Neurology, Sun Yat-sen Memorial Hospital, Sun Yat-sen University published a research paper online entitled "Morphine‑induced microglial immunosuppression via activation of insufficient mitophagy regulated by NLRX1" in the Journal of Neuroinflammation
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This paper proposes that NLRX1 protein mediates the occurrence of incomplete mitophagy in microglia and participates in the regulation of chronic morphine exposure-induced inflammatory suppression in the central nervous system
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Peng Jialing and Pan Jingrui are the co-first authors of the paper, and Professor Peng Ying is the corresponding author of the paper
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The research team first detected mitochondrial proteins and LC3B (microtubule-as-sociated protein 1 light chain 3) autophagosomes by copy number detection of mitochondrial DNA and immunofluorescence staining, and found that 1.
0 μM morphine promotes mitophagy in microglia cells.
Shows concentration specificity
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The further research team used AD-mCherry-GFP-LC3B adenovirus infection technology to monitor the changes of autophagic flux in microglia treated with different concentrations of morphine, and found the intracytoplasmic accumulation of autophagosomes when treated with 1.
0 μM morphine, suggesting that the possible Degradation barriers
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At the same time, the expression of NLRX1 protein was significantly up-regulated in the 1.
0 μM morphine treatment group, and subsequent experimental techniques such as colocalization analysis, co-immunoprecipitation and RNAi confirmed that the activation of NLRX1 in microglia after morphine treatment and the direct interaction with LC3B Increased binding regulates the occurrence of mitophagy in microglia (Figure 1)
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Figure 1 NLRX1 mediates morphine-induced microglial mitophagy (Source: Peng J, et al.
, J Neuroinflammation, 2022) After damaged mitochondria are wrapped by autophagosomes, mitophagosomes can be formed, and mitochondrial Autophagosomes are formed by wrapping abnormal mitochondria in membrane-like structures that are isolated from the outside world
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The membrane structure then fuses with the lysosomal membrane to form mature mitolysosomes (mitolysosomes).
After the damaged mitochondria are completely degraded by lysosomal enzymes, it can be called complete mitophagy [9]
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However, when exploring where the mitophagy flux goes, the team found that NLRX1 mediates abnormal lysosomal function (Fig.
2), abnormal lysosome production, acidification, and morphine-treated microglia.
Inability to recognize and fuse with mitophagosomes, resulting in the inability to successfully complete the initiated mitophagy, that is, incomplete mitophagy, and the accumulation of mitophagosomes and immature phagolysosomes in the cytoplasm
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Figure 2 NLRX1 mediates morphine-induced lysosomal dysfunction, leading to incomplete mitophagy (Source: Peng J, et al.
, J Neuroinflammation, 2022) Most studies have confirmed that low concentrations of morphine (0.
1 μM to 10 μM) can cause decreased immune function of immune cells[10,11]
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This study further confirmed that 1.
0 μM morphine caused microglia to be in a state of inflammatory suppression, which was closely related to NLRX1-mediated incomplete mitophagy (Fig.
3A)
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When LPS mimics exogenous infection stimulation, the infection damage of microglia is aggravated (Figure 3B-C), and NLRX1 silencing by RNAi or shRNA lentivirus can effectively inhibit the inflammatory suppression state of microglia and LPS stimulation after injury (Fig.
3A,D)
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Figure 3 NLRX1-mediated incomplete mitophagy leads to microglial inflammatory inhibition and post-infection injury (Source: Peng J, et al.
, J Neuroinflammation, 2022) In a mouse model of immunosuppression, we found that the regulation of mitophagy by NLRX1 in brain tissue was spatially specific
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In this mouse model, the regulation of mitophagy by NLRX1 in brain tissue mainly occurs in microglia in the cortex, striatum, and cerebellum, which have been reported to play an immunoregulatory function [12,13] ]
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Under the stimulation of exogenous infection injury LPS, long-term morphine mice developed severe inflammatory factor storm, which is consistent with the previous study [14]
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The research team believes that during long-term morphine exposure, microglia cannot respond to exogenous infection stimuli in a timely manner, and the persistence of injury stimuli leads to immune depletion of microglia and accumulation of pathological microglia, resulting in severe inflammatory injury and inflammatory factor storm [15]
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When the expression of NLRX1 was down-regulated in the brain region, the immune response ability of microglia was alleviated, which could timely resist the invasion of exogenous infection in the central nervous system, and curb the occurrence of inflammatory storm
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Fig.
4 Spatial distribution of NLRX1-mediated mitophagy in the brain tissue of chronic morphine-exposed immunosuppressed mice (Source: Peng J, et al.
, J Neuroinflammation, 2022) Fig.
5 Work summary: Microglia mitochondrial autophagy The regulatory role of phagocytosis in morphine-induced central nervous system inflammatory inhibition (Source: Peng J, et al.
, J Neuroinflammation, 2022) Conclusions and discussions, inspiration and prospects The role of incomplete mitophagy in chronic morphine-exposed microglial inflammatory suppression (Fig.
5), this study proposes a regulatory role for the presence of NLRX1 on lysosomal function, extending NLRX1-mediated mitophagy possible way, which provides a bridge between mitochondria and lysosomes
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However, it needs to be clear that the regulation of mitophagy differs in different ways under different conditions.
This study proposes that the regulation of NLRX1 plays an important role in the morphine-induced microglial inflammatory inhibition model, but it is undeniable that it may be accompanied or preceded by Other control methods need more research to explore
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Link to the original text: https://doi.
org/10.
1186/s12974-022-02453-7 The corresponding author of the paper is Professor Peng Ying, Department of Neurology, Sun Yat-sen Memorial Hospital, and Dr.
Peng Jialing and Dr.
Pan Jingrui are the co-first authors of the paper
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This research was supported by the National Key R&D Program (2018YFC1314400 and 2018YFC1314401 to Y.
Peng), the Natural Science Foundation of Guangdong Province (2018A030313076 to J.
Pan), and the Fundamental Research Fund for Colleges and Universities Sun Yat-Sen University Young Teacher Cultivation Project (19ykpy101 to J.
Pan) funding
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Peng Jialing (first from the left in the second row), Pan Jingrui (third from the left in the first row), Professor Peng Ying (sixth from the left in the first row) (Photo courtesy of: Sun Yat-sen Memorial Hospital Neurology Peng Ying Research Group) Selected previous articles [1 ] Curr Biol︱ Novelty detection and the relationship between surprise and recency in the primate brain [2] Neurosci Bull︱ Qian Lingjia's research group reveals that homocysteine ​​modulates the effect of DNA methylation during chronic stress Cognitive function【3】Front Aging Neurosci︱Ma Tao’s team revealed the mechanism of Chinese medicine compound multi-pathway and multi-target to improve energy metabolism in Alzheimer’s disease【4】Aging Cell︱Gao Xu’s team found that good sleep quality can delay air pollution Acceleration of aging caused by [5] Autophagy︱ Shen Hanming's group reveals a new mechanism of autophagy-related protein WIPI2 regulating mitochondrial outer membrane protein degradation and mitophagy [6] Neuron's heavy review︱ Sheng Zuhang's team focuses on the maintenance and energy supply of axon mitochondria Important role in neurodegenerative diseases and repair after nerve injury【7】Cell Death Dis︱Kong Hui et al.
Reveal the role of P2X7/NLRP3 inflammasome pathway in early diabetic retinopathy【8】Sci Adv︱Xingguo Liu/ Tian Mei's team discovered a new mechanism of mitochondrial clearance in drug-induced Parkinson's syndrome【9】Front Aging Neurosci︱Gut preparation can affect postoperative delirium by changing the composition of flora【10】Mol Psychiatry︱C/EBPβ/AEP revealed by Ye Keqiang’s group Signaling pathways mediate atherosclerosis and its induced Alzheimer's disease.
Recommended for high-quality scientific research training courses [1] Symposium on Patch Clamp and Optogenetics and Calcium Imaging Technologies May 14-15 Tencent Conference [2] Scientific Research Skill︱The 4th Near Infrared Brain Function Data Analysis Class (Online: 2022.
4.
18~4.
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Edited by Wang Sizhen End of this paperJournal of Neuroinflammation, 12:120 (2015).
Plate making︱Sizhen Wang End of this articleJournal of Neuroinflammation, 12:120 (2015).
Plate making︱Sizhen Wang End of this article