Adenosine triggers early astrocyte reactivity that provokes microglial responses and drives the pathogenesis of sepsis-associated encephalopathy in mice

Transcranial direct current stimulation alleviates chronic pain in knee osteoarthritis by modulating microglial and astrocytic polarization and neuroinflammation

AIMS

Knee osteoarthritis (KOA) chronic pain is linked to neuroinflammation mediated by reactive astrocytes in the primary somatosensory cortex (S1). Reactive astrocytes are classified into neurotoxic A1 and neuroprotective A2 phenotypes, with activated microglia promoting A1 astrocyte formation during chronic pain progression. This study aimed to investigate whether transcranial direct current stimulation (tDCS) can alleviate KOA chronic pain by modulating glial phenotype conversion and neuroinflammatory processes.

MAIN METHODS

Rats received an intra-articular injection of monosodium iodoacetate (MIA) in the left knee to model KOA pain. Additionally, rats received intraperitoneal injections of the NF-κB inhibitor BAY 11-7082 and underwent tDCS. Pain thresholds were assessed using von Frey filaments and a hot plate. Changes in microglia, astrocytes, and inflammatory factor expression were analyzed with Western blotting, immunofluorescence, and reverse transcription-quantitative PCR.

KEY FINDINGS

At 4 and 7 days after MIA injection, microglia exhibited a proinflammatory M1 phenotype, accompanied by increased expression of IL-1α, TNF-α, and C1q. From day 7 to 21 post-injection, astrocytes displayed a neurotoxic A1 phenotype. The NF-κB/NLRP3/IL-18 signaling pathway was significantly upregulated in KOA rats. Treatment with BAY 11-7082 or tDCS significantly alleviated mechanical allodynia and thermal hyperalgesia, shifting microglia from M1 to M2 and astrocytes from A1 to A2 polarization, while suppressing the NF-κB/NLRP3/IL-18 pathway and reducing neuroinflammation.

SIGNIFICANCE

These findings suggest that tDCS may alleviate KOA chronic pain through modulation of glial activation states and suppression of central neuroinflammation, highlighting its potential as a non-invasive therapeutic approach.

A Chemistry-Informed Generative Deep Learning Approach for Enhancing Voltammetric Neurochemical Sensing in Living Mouse Brain

Exploring the time-resolved dynamics of neurochemicals is essential for deciphering neuronal functions, intercellular communication, and neurophysiological or pathological mechanisms. However, the complex interplay among neurochemicals between neurocytes, coupled with extensive chemical signal crosstalk, puts simultaneous sensing of multiple neurochemicals into a longstanding challenge. Herein, we report a chemistry-informed generative neural network (CIGNN) model to separate the Faradaic and the non-Faradaic components from voltammetric currents, minimizing their mutual interference and enhancing quantitative accuracy. With the assistance of generative deep learning, we successfully establish a new platform for in vivo neurochemical sensing, which is validated by simultaneously monitoring the dynamics of dopamine (DA), ascorbic acid (AA), and ionic strength in a neuroinflammation mouse model. We observe that the stimulation with KCl solution triggers a significant enhancement of AA efflux on the model mice (300 ± 50 μM) compared with that from the control mice (170 ± 20 μM), as well as a significant decrease of ion influx (55 ± 7 mM) compared with that from the control mice (120 ± 16 mM), while not evoking a significant change in the DA release from the model mice (2.8 ± 0.3 μM) versus that from the control mice (3.0 ± 0.5 μM). This work provides a robust tool for studying multineurochemical signaling and elucidating the molecular mechanisms underlying various brain activities.

Stress-Induced Sleep Dysregulation: The Roles of Astrocytes and Microglia in Neurodegenerative and Psychiatric Disorders

Stress and sleep share a reciprocal relationship, where chronic stress often leads to sleep disturbances that worsen neurodegenerative and psychiatric conditions. Non-neuronal cells, particularly astrocytes and microglia, play critical roles in the brain's response to stress and the regulation of sleep. Astrocytes influence sleep architecture by regulating adenosine signaling and glymphatic clearance, both of which can be disrupted by chronic stress, leading to reduced restorative sleep. Microglia, activated under stress conditions, drive neuroinflammatory processes that further impair sleep and exacerbate brain dysfunction. Additionally, the gut-brain axis mediates interactions between stress, sleep, and inflammation, with microbial metabolites influencing neural pathways. Many of these effects converge on the disruption of synaptic processes, such as neurotransmitter balance, synaptic plasticity, and pruning, which in turn contribute to the pathophysiology of neurodegenerative and psychiatric disorders. This review explores how these cellular and systemic mechanisms contribute to stress-induced sleep disturbances and their implications for neurodegenerative and psychiatric disorders, offering insights into potential therapeutic strategies targeting non-neuronal cells and the gut-brain axis.

Dysregulation of Astrocytic ATP/Adenosine Release in the Hippocampus Cause Cognitive and Affective Disorders: Molecular Mechanisms, Diagnosis, and Therapy

The gliotransmitter adenosine 5'-triphosphate (ATP) and its enzymatic degradation product adenosine play a major role in orchestrating in the hippocampus cognitive and affective functions via P2 purinoceptors (P2X, P2Y) and P1 adenosine receptors (A1, A2A). Although numerous reviews exist on purinoceptors that modulate these functions, there is an apparent gap relating to the involvement of astrocyte-derived extracellular ATP. Our review focuses on the following issues: An impeded release of ATP from hippocampal astrocytes through vesicular mechanisms or connexin hemichannels and pannexin channels interferes with spatial working memory in rodents. The pharmacological blockade of P2Y1 receptors (P2Y1Rs) reverses the deficits in learning/memory performance in mouse models of familial Alzheimer's disease (AD). Similarly, in mouse models of major depressive disorder (MDD), based on acute or chronic stress-induced development of depressive-like behavior, a reduced exocytotic/channel-mediated ATP release from hippocampal astrocytes results in the deterioration of these behavioral responses. However, on the opposite, the increased stimulation of the microglial/astrocytic P2X7R-channel by ATP causes neuroinflammation and in consequence depressive-like behavior. In conclusion, there is strong evidence for the assumption that gliotransmitter ATP is intimately involved in the pathophysiology of cognitive and affective neuron/astrocyte-based human illnesses opening new diagnostic and therapeutic vistas for AD and MDD.

Region-specific neuroprotective effects of meldonium pretreatment in two models of sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common yet poorly understood complication of sepsis, which poses a burden in clinical settings, as its management relies on supportive care without targeted pharmacological interventions. Meldonium is a drug approved for ischemic heart disease but has also gained attention for its neuroprotective effects. In animal models of sepsis, meldonium pretreatment exerted antioxidative, antiapoptotic, and anti-inflammatory effects, but its neurological effects have not been studied in SAE. In the present study, rats were pretreated with meldonium for 4 weeks, before sepsis was induced via a faecal intraperitoneal injection (FIP) or a lipopolysaccharide (LPS) injection. The cerebellum, medulla oblongata, and prefrontal cortex were examined due to their involvement in functions that are often impaired in sepsis. Eight hours post-sepsis induction, markers of brain injury were assessed, including reflexes scores, dry to wet brain mass ratio, prooxidant-antioxidant balance (PAB), advanced oxidation protein products (AOPP), lipid peroxidation (LPO), phosphatidylcholine (PC) to lysophosphatidylcholine (LPC) ratio, HMGB1 and haptoglobin protein expression, and CD73 activity. Meldonium-pretreated FIP-septic rats showed an earlier decline in reflex scores compared to the sepsis-only group, accompanied by a slight brain water accumulation. However, in both models of sepsis, meldonium pretreatment prevented alterations in the PAB, AOPP, and LPO in a region-specific manner. It also preserved the PC/LPC ratio in the prefrontal cortex of FIP-septic rats and in all regions of LPS-septic rats. Haptoglobin protein content was altered only in FIP-septic rats, and preserved by meldonium pretreatment in the cerebellum and medulla oblongata of these rats. Additionally, meldonium pretreatment preserved CD73 activity in the medulla oblongata and prefrontal cortex of FIP-septic rats and in the cerebellum and prefrontal cortex of LPS-septic rats. In conclusion, our study is the first to demonstrate that pretreatment with meldonium, a drug that has shown neuroprotective effects in other invasive models can also provide benefits in SAE, with the extent of protection depending on both the model of sepsis induction and the specific brain region investigated. Our findings support the discussion on the importance of selecting the right sepsis model and studying individual brain regions when investigating SAE and potential therapeutic approaches.

PD-L1/PD-1 checkpoint pathway regulates astrocyte morphogenesis and myelination during brain development

Programmed cell death protein 1 (PD-1) and its primary ligand PD-L1 are integral components of a significant immune checkpoint pathway, widely recognized for its central role in cancer immunotherapy. However, emerging evidence highlights their broader involvement in both the central and peripheral nervous systems. In this study, we demonstrate that PD-L1/PD-1 signaling in astrocytes during mouse brain development regulates astrocyte maturation and morphogenesis via the MEK/ERK pathway by targeting the downstream effector cysteine and glycine rich protein 1 (CSRP1). This enhanced astrocyte morphological complexity results in increased end-foot coverage of blood vessels. Additionally, aberrant secretion of CSRP1 by astrocytes interacts with oligodendrocyte precursor cells (OPCs) membrane proteins annexin A1 (ANXA1) and annexin A2 (ANXA2), leading to the exclusion of migrating OPCs from blood vessels. This disruption in OPC migration and differentiation results in abnormal myelination and is associated with cognitive deficits in the mice. Our results provide critical insights into the function of PD-L1/PD-1 signaling in astrocyte-OPC interactions and underscore its relevance to glial cell development and pathogenesis in neurodevelopmental disorders.

Glial vascular Unit as a bridge between Blood-Brain Barrier and glymphatic System: Roles in sepsis-associated encephalopathy

This article underscores the Glial Vascular Unit (GVU) 's possible role in bridging the Blood-Brain Barrier (BBB) and Glymphatic System in Sepsis-associated encephalopathy (SAE). Future studies should prioritize understanding the mechanistic underpinnings of GVU dysfunction in sepsis and explore interventions aimed at modulating BBB permeability, astrocytic function, and glymphatic clearance. Understanding these complex mechanisms is crucial for developing therapeutic strategies aimed at mitigating the neurological impact of sepsis and improving outcomes for patients with SAE.

Identification and Evaluation of Lipocalin-2 in Sepsis-Associated Encephalopathy via Machine Learning Approaches

Purpose

Sepsis-associated encephalopathy (SAE) critically contributes to poor prognosis in septic patients. Identifying and screening key genes responsible for SAE, as well as exploring potential targeted therapies, are vital for improving the management of sepsis and advancing precision medicine.

Patients and Methods

Single-cell RNA sequencing (scRNA-seq) was administrated to identify cell subpopulations related to poor prognosis in septic patients. Next, hierarchical dynamic weighted gene co-expression network analysis (hdWGCNA) was employed to identify genes associated with specific neutrophil subpopulations. Enrichment analysis revealed the biological functions of these genes. Subsequently, neuroinflammation-related genes were obtained to construct a neuroinflammation-related signature. The AddModuleScore algorithm was used to calculate neuroinflammation scores for each cell subpopulation, whereas the CellCall algorithm was used to assess the crosstalk between neutrophils and other cell subpopulations. To identify key genes accurately, four binary classification machine learning algorithms were utilized. Finally, Western blotting and behavioral tests were used to confirm the role of LCN2-related neuroinflammation in septic mice.

Results

This study utilized scRNA-seq to reveal the critical role of peripheral neutrophils during sepsis, identifying these neutrophils as contributors to poor prognosis and associated with neuroinflammation. On the basis of various machine learning algorithms, we discovered that Lipocalin-2 (LCN2) may be the key gene involved in neutrophil-induced SAE. To prove these findings, we conducted in vivo experiments and an animal model. Increased LCN2 expression and cognitive dysfunction occurred in septic mice. Additionally, the levels of markers of astrocytes and microglia and inflammatory factors such as TNF-α and IL-6 were significantly increased. All these phenomena were reversed by the downregulation of LCN2.

Conclusion

The upregulation of LCN2 expression on peripheral neutrophils is a critical step that triggers neuroinflammation in the central nervous system during SAE.

The Cholinergic Amelioration of Sepsis-Induced Baroreflex Dysfunction and Brainstem Inflammation Is Negated by Central Adenosine A3 Receptors

Background/Objectives: Sepsis has been shown to depress arterial baroreceptor function, and this effect is counterbalanced by the cholinergic anti-inflammatory pathway. Considering the importance of central adenosine receptors in baroreceptor function, this study tested whether central adenosine A3 receptors (A3ARs) modulate the cholinergic-baroreflex interaction in sepsis and whether this interaction is modulated by mitogen-activated protein kinases (MAPKs) and related proinflammatory cytokines. Methods: Sepsis was induced by cecal ligation and puncture (CLP) and rats were instrumented with femoral and intracisternal (i.c.) catheters. Baroreflex sensitivity (BRS) was measured 24 h later in conscious animals using the vasoactive method, which correlates changes in blood pressure caused by i.v. phenylephrine (PE) and sodium nitroprusside (SNP) to concomitant reciprocal changes in heart rate. Results: The reduction in reflex bradycardic (BRS-PE), but not tachycardic (BRS-SNP), responses elicited by CLP was reversed by i.v. nicotine in a dose-related manner. The BRS-PE effect of nicotine was blunted following intracisternal administration of IB-MECA (A3AR agonist, 4 µg/rat). The depressant action of IB-MECA on the BRS facilitatory action of nicotine was abrogated following central inhibition of MAPK-JNK (SP 600125), PI3K (wortmannin), and TNFα (infliximab), but not MAPK-ERK (PD 98059). Additionally, the nicotine suppression of sepsis-induced upregulation of NFκB and NOX2 expression in the nucleus tractus solitarius (NTS) was negated by A3AR activation. The molecular effect of IB-MECA on NFκB expression disappeared in the presence of SP 600125, wortmannin, or infliximab. Conclusions: The central PI3K/MAPK-JNK/TNFα pathway contributes to the restraining action of A3ARs on cholinergic amelioration of sepsis-induced central neuroinflammatory responses and impairment of the baroreceptor-mediated negative chronotropism.

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knockin mouse model of Alzheimer disease

The disease's trajectory of Alzheimer disease (AD) is associated with and negatively correlated to hippocampal hyperexcitability. Here, we show that during the asymptomatic stage in a knockin (KI) mouse model of Alzheimer disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma, and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer disease.

Acute hyperglycemia exacerbates neuroinflammation and cognitive impairment in sepsis-associated encephalopathy by mediating the ChREBP/HIF-1α pathway

OBJECTIVES

Delirium is a prominent symptom of sepsis-associated encephalopathy (SAE) and is highly prevalent in septic patients hospitalized in the intensive care unit, being closely connected with raised mortality rates. Acute hyperglycemia (AH) has been recognized as a separate risk factor for delirium and a worse prognosis in critically sick patients. Nevertheless, the exact contribution of AH to the advancement of SAE is still unknown.

METHODS

This research retrospectively evaluated the connection between blood glucose levels (BGLs) and the incidence of delirium and death rates in septic patients in the ICU of a tertiary comprehensive hospital. In addition, a septic rat model was induced through cecal ligation and puncture (CLP), after which continuous glucose infusion was promptly initiated via a central venous catheter post-surgery to evaluate the potential implications of AH on SAE. Next, septic rats were assigned to four groups based on target BGLs: high glucose group (HG, ≥ 300 mg/dL), moderate glucose group (MG, 200-300 mg/dL), normal glucose group (NG, < 200 mg/dL), and a high glucose insulin-treated group (HI, 200-300 mg/dL) receiving recombinant human insulin treatment (0.1 IU/kg/min). The sham group (SG) received an equivalent volume of saline infusion and denoted the NG group. The effects of AH on neuroinflammation and cognitive function in septic rats were evaluated using behavioral tests, histopathological examination, TUNEL staining, ELISA, and Western blot. The effects of glucose levels on microglial activation and glucose metabolism following lipopolysaccharide (LPS, 1 μg/mL) exposure were assessed using CCK8 assay, qRT-PCR, Western blot, and ELISA.

RESULTS

Our findings revealed that AH during sepsis was a separate risk factor for delirium and assisted in predicting delirium occurrence. AH raised the levels of systemic and central inflammatory cytokines in septic rats, promoting neuronal apoptosis, blood-brain barrier disruption, and cognitive impairment. In addition, both in vivo and in vitro, an elevated glucose challenge increased the ChREBP, HIF-1α, glycolytic enzymes, and inflammatory cytokines expressions in microglia after exposure to CLP or LPS.

CONCLUSIONS

These results collectively suggest that hyperglycemia can exacerbate neuroinflammation and delirium by enhancing microglial glycolysis under septic conditions, potentially mediated by upregulation of the ChREBP/HIF-1α signaling pathway.

Shenfu Injection Mediated NLRP3/Caspase 1 Through (R)-Norcoclaurinee Alleviates Sepsis-Induced Cognitive Dysfunction

Background

Shenfu injection (SF) has demonstrated its potential to enhance cellular immunity and induce clinical regression in patients suffering from sepsis or infectious shock. However, the therapeutic effect of SF on sepsis-induced cognitive dysfunction (SAE) and the mechanisms involved are still unclear. We aimed to investigate the mechanism of SF in mice with SAE.

Methods

Sepsis was constructed by caecal ligation and puncture. Mice were injected intraperitoneally with SF or NLRP3 inhibitor. The hippocampus injury of brain tissues was evaluated, and the levels of inflammatory cytokines (IL-1β, IL-18) and NLRP3 and Caspase 1 were measured. The active ingredients of SF were analyzed using network pharmacology, and molecular docking of the active ingredients of SF with NLRP3 and Caspase 1 was performed. BV-2 cells were treated with LPS or norcoclaurine. CCK-8 detected the cell viability, and the levels of inflammatory cytokines and NLRP3 and Caspase 1 were measured.

Results

SF and NLRP3 inhibitor increased survival rate and the number of crossing the platform and decreased the escape latency time of sepsis mice. Moreover, SF and NLRP3 inhibitor improved neuronal damage and apoptosis in hippocampus of sepsis mice. In addition, SF and NLRP3 inhibitor reduced the levels of inflammatory cytokines, as well as inflammasomes in sepsis mice. There were 43 active ingredients in SF. Among them, 22 were Renshen and 21 were Fuzi. Renshen and Fuzi, the main active components of SF, form a complex regulatory network with NLRP3 and Caspase 1. (R)-norcoclaurine was most closely bound to NLRP3 with binding energy of -7.2 kJ·mol-1, ignavine was most closely bound to Caspase 1 with binding energy of -8.3 kJ·mol-1. Norcoclaurine increased the cell viability and decreased inflammation and pyroptosis.

Conclusion

SF regulated NLRP3/Caspase 1 through (R)-norcoclaurinee to prevent SAE.