Sestrin 2 attenuates sepsis-associated encephalopathy through the promotion of autophagy in hippocampal neurons

Targeting novel regulated cell death：Ferroptosis, pyroptosis, and autophagy in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE), a common neurological complication of sepsis, is a heterogenous complex clinical syndrome caused by the dysfunctional response of a host to infection. This dysfunctional response leads to excess mortality and morbidity worldwide. Despite clinical relevance with high incidence, there is a lack of understanding for its both its acute/chronic pathogenesis and therapeutic management. A better understanding of the molecular mechanisms behind SAE may provide tools to better enhance therapeutic efficacy. Mounting evidence indicates that some types of non-apoptotic regulated cell death (RCD), such as ferroptosis, pyroptosis, and autophagy, contribute to SAE. Targeting these types of RCD may provide meaningful targets for future treatments against SAE. This review summarizes the core mechanism by which non-apoptotic RCD leads to the pathogenesis of SAE. We focus on the emerging types of therapeutic compounds that can inhibit RCD and delineate their beneficial pharmacological effects against SAE. Within this review we suggest that pharmacological inhibition of non-apoptotic RCD may serve as a potential therapeutic strategy against SAE.

Mechanism and role of mitophagy in the development of severe infection

Mitochondria produce adenosine triphosphate and potentially contribute to proinflammatory responses and cell death. Mitophagy, as a conservative phenomenon, scavenges waste mitochondria and their components in the cell. Recent studies suggest that severe infections develop alongside mitochondrial dysfunction and mitophagy abnormalities. Restoring mitophagy protects against excessive inflammation and multiple organ failure in sepsis. Here, we review the normal mitophagy process, its interaction with invading microorganisms and the immune system, and summarize the mechanism of mitophagy dysfunction during severe infection. We highlight critical role of normal mitophagy in preventing severe infection.

Sestrin2 attenuates depressive-like behaviors and neuroinflammation in CUMS mice through inhibiting ferroptosis

Sestrin2 (SESN2) is a stress-inducible protein and acts as a neuroprotective regulator. The present study aimed to explore the antidepressant activity of SESN2 and its relevant mechanism. Depression mouse model was established by chronic unpredictable mild stress (CUMS) for a successive 5 weeks. Behaviors tests were conducted to examine depressive-like behaviors including sugar preference test, tail suspension test and open field test. The expression of SESN2 and ferroptosis-related proteins was examined by western blot. The production of cytokines was measured by ELISA. Iron deposition was assessed using Prussian blue staining and Fe 2+ content was measured using commercial kits. Lipid peroxidation was evaluated by thiobarbituric acid reactive substances assay. BV-2 cells were treated with LPS to induce microglial activation, which was evaluated by the iba-1 level adopting immunofluorescence assay. The ferroptosis inducer Erastin was adopted for the pretreatment in BV-2 cells to conduct a rescue experiment. SESN2 was downregulated in CUMS-induced mice, and SESN2 overexpression dramatically ameliorated CUMS-induced depression-like behaviors. Meanwhile, SESN2 reduced the production of pro-inflammatory cytokines and iba-1 level in hippocampus of CUMS mice, as well as reducing iron deposition and lipid peroxidation, demonstrating that SESN2 reduced microglial activation, neuroinflammation and ferroptosis in CUMS mice. Similarly, SESN2 also restricted iba-1 level, pro-inflammatory cytokines production, and ferroptosis in LPS-induced BV-2 cells, which was partly reversed by additional treatment of Erastin. These findings suggest that SESN2 possesses potent antidepressant property through inhibiting ferroptosis and neuroinflammation.

SESN2 attenuates sevoflurane-induced cognitive impairment and neuroinflammation in rats

Long-term use of sevoflurane, an inhalation anesthetic, could negatively impact cognitive function. Current studies have suggested that cognitive impairment induced by sevoflurane may be associated with neuroinflammation. Sestrin2 (SESN2), which belongs to a family of stress-inducible genes, has been reported to exert neuroprotective effects against brain injury. However, its role and underlying mechanisms in sevoflurane-induced cognitive dysfunction in aged rats remain unknown. A sevoflurane-induced aging rat injury model with or without SESN2 overexpression was constructed. The learning and memory abilities of rats were evaluated by the MWM test. ELISA assay and qRT-PCR were conducted to analyze the level of pro-inflammatory factors in the hippocampus. Levels of oxidative stress markers were measured by DHE staining or kit methods. Neuronal apoptosis in the hippocampus was detected using TUNEL assay. Expression of proteins were analyzed by western blot. Sevoflurane exposure caused elevated protein level of SESN2 in hippocampus and cognitive impairment of aged rats. Importantly, overexpression of SESN2 alleviated sevoflurane-induced cognitive dysfunction and inhibited the production of pro-inflammatory factors, oxidative stress, and neuronal apoptosis in the hippocampus. Furthermore, SESN2 overexpression suppressed NLRP3 inflammasome activation induced by sevoflurane. These findings suggested that SESN2 could exert neuroprotective against sevoflurane-induced nerve injury of aged rats through anti-oxidant and anti-inflammatory effects.

Deciphering the molecular classification of pediatric sepsis: integrating WGCNA and machine learning-based classification with immune signatures for the development of an advanced diagnostic model

Introduction: Pediatric sepsis (PS) is a life-threatening infection associated with high mortality rates, necessitating a deeper understanding of its underlying pathological mechanisms. Recently discovered programmed cell death induced by copper has been implicated in various medical conditions, but its potential involvement in PS remains largely unexplored. Methods: We first analyzed the expression patterns of cuproptosis-related genes (CRGs) and assessed the immune landscape of PS using the GSE66099 dataset. Subsequently, PS samples were isolated from the same dataset, and consensus clustering was performed based on differentially expressed CRGs. We applied weighted gene co-expression network analysis to identify hub genes associated with PS and cuproptosis. Results: We observed aberrant expression of 27 CRGs and a specific immune landscape in PS samples. Our findings revealed that patients in the GSE66099 dataset could be categorized into two cuproptosis clusters, each characterized by unique immune landscapes and varying functional classifications or enriched pathways. Among the machine learning approaches, Extreme Gradient Boosting demonstrated optimal performance as a diagnostic model for PS. Discussion: Our study provides valuable insights into the molecular mechanisms underlying PS, highlighting the involvement of cuproptosis-related genes and immune cell infiltration.

Resistance exercise alleviates the prefrontal lobe injury and dysfunction by activating SESN2/AMPK/PGC-1α signaling pathway and inhibiting oxidative stress and inflammation in mice with myocardial infarction

OBJECTIVES

Myocardial infarction (MI) induces inflammatory response and oxidative stress in the brain, which would be one of the causes of cardiac dysfunction. Exercise training is viewed as a feasible strategy to improve cardiac function of the infarcted heart. The aim of this study was to investigate whether exercise training could alleviate MI-induced prefrontal lobe injury via activating Sestrin2 (SESN2) signaling and inhibiting oxidative stress and inflammation.

METHODS

Male C57BL/6 mice were divided into five groups: control group (CON), aerobic exercise group (AE), resistance exercise group (RE), whole-body vibration group (WBV) and electrical stimulation group (ES); and three groups: sham-operated group (S), sedentary MI group (MI) and MI with resistance exercise group (MRE). After four weeks of training, sensorimotor function, spatial learning, long-term and spatial memory, and cardiac function were detected. Then, mice were euthanized, and the prefrontal areas were separated for HE, Nissl, SESN2, microtubule-associated protein 2 (MAP2), neuron-specific nucleoprotein (NeuN), and TUNEL staining. Activation of SESN2/adenosine monophosphate-activated protein kinase (AMPK)/peroxisome proliferator activated receptor γ coactivator-1α (PGC-1α) signaling pathway and expression of proteins related to oxidative stress, inflammation and apoptosis in the prefrontal lobe were detected by western blotting.

RESULTS

Different types of exercise training all activated the SESN2/AMPK/PGC-1α signaling pathway, and the effect of RE is the best. RE improved sensorimotor, learning, and memory impairments, increased the expressions of antioxidant, anti-inflammatory and anti-apoptotic proteins, reduced oxidative stress, inflammation and apoptosis, ultimately alleviated the prefrontal lobe injury and dysfunction in mice with MI.

CONCLUSION

RE alleviates MI-indued prefrontal lobe injury and dysfunction by inhibiting the levels of oxidative stress, inflammation and apoptosis, partially via activating SESN2/AMPK/PGC-1α signaling pathway.

The pathogenesis and potential therapeutic targets in sepsis

Sepsis is defined as "a life-threatening organ dysfunction caused by dysregulated host systemic inflammatory and immune response to infection." At present, sepsis continues to pose a grave healthcare concern worldwide. Despite the use of supportive measures in treating traditional sepsis, such as intravenous fluids, vasoactive substances, and oxygen plus antibiotics to eradicate harmful pathogens, there is an ongoing increase in both the morbidity and mortality associated with sepsis during clinical interventions. Therefore, it is urgent to design specific pharmacologic agents for the treatment of sepsis and convert them into a novel targeted treatment strategy. Herein, we provide an overview of the molecular mechanisms that may be involved in sepsis, such as the inflammatory response, immune dysfunction, complement deactivation, mitochondrial damage, and endoplasmic reticulum stress. Additionally, we highlight important targets involved in sepsis-related regulatory mechanisms, including GSDMD, HMGB1, STING, and SQSTM1, among others. We summarize the latest advancements in potential therapeutic drugs that specifically target these signaling pathways and paramount targets, covering both preclinical studies and clinical trials. In addition, this review provides a detailed description of the crosstalk and function between signaling pathways and vital targets, which provides more opportunities for the clinical development of new treatments for sepsis.

Mitophagy-related genes could facilitate the development of septic shock during immune infiltration

Septic shock often occurs following critically low blood pressure in patients with sepsis, and is accompanied by a high death rate. Although mitophagy is associated with infection and immune responses, its role in septic shock remains unknown. This study screened effective mitophagy-related genes (MRGs) for medical practice and depicted immune infiltration situations in patients with septic shock. Gene expression profiles of GSE131761 from the Gene Expression Omnibus database were compiled for differential analysis, weighted gene co-expression network analysis, and immune infiltration analysis, while other GSE series were used as validation datasets. A series of validation methods were used to verify the robustness of hub genes, while a nomogram and prognosis model were established for medical practice. Six genes were screened via combinations of differentially expressed genes, weighted gene co-expression network analysis, and MRGs. From this, 3 hub genes (MAP1LC3B, ULK1, and CDC37) were chosen for subsequent analysis based on different validation methods. Gene set enrichment analysis showed that leukocyte trans-endothelial migration and the p53 signaling pathway were abnormally activated during septic shock. Immune infiltration analysis indicated that the imbalance of neutrophils and CD4 naive T cells was significantly correlated with septic shock progression. A nomogram was generated based on MAP1LC3B, ULK1, and CDC37, as well as age. The stability of our model was confirmed using a calibration plot. Importantly, patients with septic shock with the 3 highly expressed hub genes displayed worse prognosis than did patients without septic shock. MAP1LC3B, ULK1, and CDC37 are considered hub MRGs in the development of septic shock and could represent promising diagnostic and prognostic biomarkers in blood tissue. The validated hub genes and immune infiltration pattern expand our knowledge on MRG functional mechanisms, which provides guidance and direction for the development of septic shock diagnostic and therapeutic markers.

Autophagy Suppresses Ferroptosis by Degrading TFR1 to Alleviate Cognitive Dysfunction in Mice with SAE

Sepsis-associated encephalopathy (SAE) is a serious complication of sepsis that is characterized by long-term cognitive impairment, which imposes a heavy burden on families and society. However, its pathological mechanism has not been elucidated. Ferroptosis is a novel form of programmed cell death that is involved in multiple neurodegenerative diseases. In the current study, we found that ferroptosis also participated in the pathological process of cognitive dysfunction in SAE, while Liproxstatin-1 (Lip-1) effectively inhibited ferroptosis and alleviated cognitive impairment. Additionally, since an increasing number of studies have suggested the crosstalk between autophagy and ferroptosis, we further proved the essential role of autophagy in this process and demonstrated the key molecular mechanism of the autophagy-ferroptosis interaction. Currently, we showed that autophagy in the hippocampus was downregulated within 3 days of lipopolysaccharide injection into the lateral ventricle. Moreover, enhancing autophagy ameliorated cognitive dysfunction. Importantly, we found that autophagy suppressed ferroptosis by downregulating transferrin receptor 1 (TFR1) in the hippocampus, thereby alleviating cognitive impairment in mice with SAE. In conclusion, our findings indicated that hippocampal neuronal ferroptosis is associated with cognitive impairment. In addition, enhancing autophagy can inhibit ferroptosis via degradation of TFR1 to ameliorate cognitive impairment in SAE, which shed new light on the prevention and therapy for SAE.

Sestrin2 suppresses ferroptosis to alleviate septic intestinal inflammation and barrier dysfunction

OBJECTIVE

Alterations in intestinal function play a crucial role in the pathogenesis of sepsis, and the repair of the intestinal barrier is a potential strategy for the treatment of sepsis. Sestrin2 (SESN2), a highly conserved stress-responsive protein, can be induced in response to stress.

AIM

This paper aimed to explore the role and mechanism of SESN2 in septic intestinal dysfunction. Methods: Blood samples were collected from patients with septic intestinal dysfunction, and Caco-2 cells were subjected to lipopolysaccharide (LPS) to construct in vitro models. The expression level of SESN2 was determined in the blood samples and cells. The impacts of SESN2 overexpression on cell inflammation, oxidative stress, barrier integrity, and MAPK/Nrf2 signaling were evaluated. To determine the mediated role of MAPK signaling and ferroptosis, AMPK inhibitor (Compound C) and ferroptosis inducer (erastin) were separately used to treat cells, and the influences on the above aspects in cells were assessed.

RESULTS

The expression level of SESN2 was down-regulated in patients with septic intestinal dysfunction and LPS-induced cells. SESN2 overexpression was found to suppress cell inflammation and oxidative stress, maintain barrier integrity and activate AMPK/Nrf2 signaling. Following the AMPK signaling was inhibited or the ferroptosis was triggered, the effects of SESN2 overexpression on the cells were both reversed.

CONCLUSION

Reduced SESN2 contributed to inflammatory response and barrier dysfunction in septic intestinal dysfunction by promoting ferroptosis via activating the AMPK/Nrf2 signaling pathway.

Function and regulation of ULK1: From physiology to pathology

The expression of ULK1, a core protein of autophagy, is closely related to autophagic activity. Numerous studies have shown that pathological abnormal expression of ULK1 is associated with various human diseases such as neurological disorders, infections, cardiovascular diseases, liver diseases and cancers. In addition, new advances in the regulation of ULK1 have been identified. Furthermore, targeting ULK1 as a therapeutic strategy for diseases is gaining attention as new corresponding activators or inhibitors are being developed. In this review, we describe the structure and regulation of ULK1 as well as the current targeted activators and inhibitors. Moreover, we highlight the pathological disorders of ULK1 expression and its critical role in human diseases.

(-)-Epicatechin Reduces Neuroinflammation, Protects Mitochondria Function, and Prevents Cognitive Impairment in Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy is a common neurological complication of sepsis. Despite advances in pathological and diagnostic investigations, its treatment remains a major challenge. In sepsis-associated encephalopathy, neuroinflammatory overactivation and mitochondrial damage are thought to contribute to cognitive and behavioral impairments. In this study, we found that administration of (−)-Epicatechin, a dietary flavonoid of the flavan-3-ol subgroup, improves memory deficits and behavior performance by ameliorating neuroinflammation, regulating mitochondria function, enhancing synaptic plasticity, and reducing neuronal loss in a mouse model of lipopolysaccharide-induced sepsis. We further show that the AMPK signaling pathway might be among the mechanisms involved in the beneficial memory effects. Our data demonstrated the potential of (−)-Epicatechin as a new drug candidate for the treatment of sepsis-associated cognitive impairment by targeting AMPK.

VIP alleviates sepsis-induced cognitive dysfunction as the TLR-4/NF-κB signaling pathway is inhibited in the hippocampus of rats

Cognitive dysfunction caused by sepsis-associated encephalopathy (SAE) is still poorly understood. It is reported that vasoactive intestinal peptide (VIP) exerts its anti-inflammatory effects in multiple diseases, while its biological function in SAE remains unclear. We aimed to figure out whether VIP has influence on sepsis-induced neuroinflammation and cognitive dysfunction. To induce sepsis, rats were subjected to cecal ligation and puncture (CLP) operation. Morris water maze test and fear conditioning test were conducted to reveal cognitive dysfunctions. TUNEL assay was performed to evaluate apoptosis. We found out that the expression of VIP was downregulated in the hippocampus of septic rats. VIP was verified to attenuate sepsis-induced memory impairment following CLP. Additionally, we examined apoptosis and inflammation in rats' hippocampus. It is worth noting that VIP inhibited the apoptosis in the hippocampus and reduced the productions of proinflammatory cytokines TNF-α, IL-6 and IL-1β. Furthermore, our data confirmed that VIP was involved in regulating the TLR-4/NF-κB signaling. In conclusion, VIP inhibited neuroinflammation and cognitive impairment in hippocampus of septic rats through the TLR-4/NF-κB signaling pathway.

Target Sestrin2 to Rescue the Damaged Organ: Mechanistic Insight into Its Function

Sestrin2 is a stress-inducible metabolic regulator and a conserved antioxidant protein which has been implicated in the pathogenesis of several diseases. Sestrin2 can protect against atherosclerosis, heart failure, hypertension, myocardial infarction, stroke, spinal cord injury neurodegeneration, nonalcoholic fatty liver disease (NAFLD), liver fibrosis, acute kidney injury (AKI), chronic kidney disease (CKD), and pulmonary inflammation. Oxidative stress and cellular damage signals can alter the expression of Sestrin2 to compensate for organ damage. Different stress signals such as those mediated by P53, Nrf2/ARE, HIF-1α, NF-κB, JNK/c-Jun, and TGF-β/Smad signaling pathways can induce Sestrin2 expression. Subsequently, Sestrin2 activates Nrf2 and AMPK. Furthermore, Sestrin2 is a major negative regulator of mTORC1. Sestrin2 indirectly regulates the expression of several genes and reprograms intracellular signaling pathways to attenuate oxidative stress and modulate a large number of cellular events such as protein synthesis, cell energy homeostasis, mitochondrial biogenesis, autophagy, mitophagy, endoplasmic reticulum (ER) stress, apoptosis, fibrogenesis, and lipogenesis. Sestrin2 vigorously enhances M2 macrophage polarization, attenuates inflammation, and prevents cell death. These alterations in molecular and cellular levels improve the clinical presentation of several diseases. This review will shed light on the beneficial effects of Sestrin2 on several diseases with an emphasis on underlying pathophysiological effects.

Sestrin2 in atherosclerosis

Atherosclerosis (AS) is the pathological basis of numerous lethal diseases, such as myocardial infarction, heart failure, and stroke. As we know, almost twenty million people worldwide die of the arterial diseases annually. Sestrin2 is a stress-inducing protein, which serves as a guardian by activating AMPK, inhibiting mTOR, and maintaining redox balance beneath various stress environments. A large number of studies show that Sestrin2 would shield the body from injury by stress. Moreover, it has been demonstrated that Sestrin2 is closely connected with AS. Here, this article reviewed the involvement of Sestrin2 in the pathogenesis of AS from four aspects: cellular mechanism, oxidative stress, inflammation, and lipid metabolism. Current evidence reveals that Sestrin2 is a novel target for the prevention and treatment of AS.

Artemisinin improves neurocognitive deficits associated with sepsis by activating the AMPK axis in microglia

Sepsis is life-threatening organ dysfunction due to dysregulated systemic inflammatory and immune response to infection, often leading to cognitive impairments. Growing evidence shows that artemisinin, an antimalarial drug, possesses potent anti-inflammatory and immunoregulatory activities. In this study we investigated whether artemisinin exerted protective effect against neurocognitive deficits associated with sepsis and explored the underlying mechanisms. Mice were injected with LPS (750 μg · kg-1 · d-1, ip, for 7 days) to establish an animal model of sepsis. Artemisinin (30 mg · kg-1 · d-1, ip) was administered starting 4 days prior LPS injection and lasting to the end of LPS injection. We showed that artemisinin administration significantly improved LPS-induced cognitive impairments assessed in Morris water maze and Y maze tests, attenuated neuronal damage and microglial activation in the hippocampus. In BV2 microglial cells treated with LPS (100 ng/mL), pre-application of artemisinin (40 μΜ) significantly reduced the production of proinflammatory cytokines (i.e., TNF-α, IL-6) and suppressed microglial migration. Furthermore, we revealed that artemisinin significantly suppressed the nuclear translocation of NF-κB and the expression of proinflammatory cytokines by activating the AMPKα1 pathway; knockdown of AMPKα1 markedly abolished the anti-inflammatory effects of artemisinin in BV2 microglial cells. In conclusion, atemisinin is a potential therapeutic agent for sepsis-associated neuroinflammation and cognitive impairment, and its effect is probably mediated by activation of the AMPKα1 signaling pathway in microglia.

SESTRINs: Emerging Dynamic Stress-Sensors in Metabolic and Environmental Health

Proper timely management of various external and internal stresses is critical for metabolic and redox homeostasis in mammals. In particular, dysregulation of mechanistic target of rapamycin complex (mTORC) triggered from metabolic stress and accumulation of reactive oxygen species (ROS) generated from environmental and genotoxic stress are well-known culprits leading to chronic metabolic disease conditions in humans. Sestrins are one of the metabolic and environmental stress-responsive groups of proteins, which solely have the ability to regulate both mTORC activity and ROS levels in cells, tissues and organs. While Sestrins are originally reported as one of several p53 target genes, recent studies have further delineated the roles of this group of stress-sensing proteins in the regulation of insulin sensitivity, glucose and fat metabolism, and redox-function in metabolic disease and aging. In this review, we discuss recent studies that investigated and manipulated Sestrins-mediated stress signaling pathways in metabolic and environmental health. Sestrins as an emerging dynamic group of stress-sensor proteins are drawing a spotlight as a preventive or therapeutic mechanism in both metabolic stress-associated pathologies and aging processes at the same time.

Sestrin 2 attenuates sepsis-associated encephalopathy through the promotion of autophagy in hippocampal neurons

Sepsis‐associated encephalopathy (SAE) has typically been associated with a poor prognosis. Although sestrin 2 (SESN2) plays a crucial role in metabolic regulation and the stress response, its expression and functional roles in SAE are still unclear. In the present study, SAE was established in mice through caecal ligation and puncture (CLP). The adeno‐associated virus 2 (AAV2)‐mediated SESN2 expression (ie overexpression and knockdown) system was injected into the hippocampi of mice with SAE, and subsequently followed by electron microscopic analysis, the Morris water maze task and pathological examination. Our results demonstrated an increase of SESN2 in the hippocampal neurons of mice with SAE, 2‐16 hours following CLP. AAV2‐mediated ectopic expression of SESN2 attenuated brain damage and loss of learning and memory functions in mice with SAE, and these effects were associated with lower pro‐inflammatory cytokines in the hippocampus. Mechanistically, SESN2 promoted unc‐51‐like kinase 1 (ULK1)‐dependent autophagy in hippocampal neurons through the activation of the AMPK/mTOR signalling pathway. Finally, AMPK inhibition by SBI‐0206965 blocked SESN2‐mediated attenuation of SAE in mice. In conclusion, our findings demonstrated that SESN2 might be a novel pharmacological intervention strategy for SAE treatment through promotion of ULK1‐dependent autophagy in hippocampal neurons.