The immunometabolite S-2-hydroxyglutarate exacerbates perioperative ischemic brain injury and cognitive dysfunction by enhancing CD8+ T lymphocyte-mediated neurotoxicity

Tryptophan-rich diet and its effects on Htr7+ Tregs in alleviating neuroinflammation and cognitive impairment induced by lipopolysaccharide

BACKGROUND

Neuroinflammation is a vital pathogenic mechanism for neurodegenerative diseases such as Alzheimer's, schizophrenia, and age-related cognitive decline. Regulatory T cells (Tregs) exhibit potent anti-inflammatory properties and can modulate neurodegenerative diseases arising from central nervous system inflammatory responses. However, the role of Tregs in neuroinflammation-related cognitive dysfunction remains unclear. It is highly plausible that Htr7+ Tregs expressing unique genes associated with the nervous system, including the Htr7 gene encoding the serotonin receptor 5-HT7, play a pivotal role.

METHODS

Mice were given a tryptophan-rich diet (with a tryptophan content of 0.6%) or a normal diet (with a tryptophan content of 0.16%). The neuroinflammation-mediated cognitive dysfunction model was established by intracerebroventricular injection of lipopolysaccharide (LPS) in 8-week-old C57BL/6J mice. The activation and infiltration of Tregs were measured using flow cytometry. Primary Tregs were cocultured separately with primary CD8+ T cells and primary microglia for in vitro validation of the impact of 5-HT and 5-HT7 receptor on Tregs. Prior to their transfer into recombination activating gene 1 (Rag1-/-) mice, Tregs were ex vivo transfected with lentivirus to knock down the expression of Htr7.

RESULTS

In this study, the tryptophan-rich diet was found to reverse LPS-induced cognitive impairment and reduce the levels of 5-HT in peripheral blood. The tryptophan-rich diet led to increased levels of 5-HT in peripheral blood, which in turn promoted the proliferation and activation of Htr7+ Tregs. Additionally, the tryptophan-rich diet was also shown to attenuate LPS-mediated neuroinflammation by activating Htr7+ Tregs. Furthermore, 5-HT and 5-HT7 receptor were found to enhance the immunosuppressive effect of Tregs on CD8+ T cells and microglia. In Rag1-/- mice, Htr7+ Tregs were shown to alleviate LPS-induced neuroinflammation and cognitive impairment.

CONCLUSIONS

Our research revealed the ability of Htr7+ Tregs to mitigate neuroinflammation and prevent neuronal damage by suppressing the infiltration of CD8+ T cells into the brain and excessive activation of microglia, thereby ameliorating LPS-induced cognitive impairment. These insights may offer novel therapeutic targets involving Tregs for neuroinflammation and cognitive impairment.

Perioperative stroke deteriorates white matter integrity by enhancing cytotoxic CD8+ T-cell activation

AIM

To explore the regulatory mechanisms of microglia-mediated cytotoxic CD8+ T-cell infiltration in the white matter injury of perioperative stroke (PIS).

METHODS

Adult male C57BL/6 mice were subjected to ileocolic bowel resection (ICR) 24 h prior to permanent distant middle cerebral artery occlusion (dMCAO) to establish model PIS. White matter injury, functional outcomes, peripheral immune cell infiltration, and microglia phenotype were assessed up to 28 days after dMCAO using behavioral phenotyping, immunofluorescence staining, transmission electron microscopy, western blot, and FACS analysis.

RESULTS

We found surgery aggravated white matter injury and deteriorated sensorimotor deficits up to 28 days following PIS. The PIS mice exhibited significantly increased activation of peripheral and central CD8+ T cells, while significantly reduced numbers of mature oligodendrocytes compared to IS mice. Neutralizing CD8+ T cells partly reversed the aggravated demyelination following PIS. Pharmacological blockage or genetic deletion of receptor-interacting protein kinase 1 (RIPK1) activity could alleviate CD8+ T-cell infiltration and demyelination in PIS mice.

CONCLUSION

Surgery exacerbates demyelination and worsens neurological function by promoting infiltration of CD8+ T cells and microglia necroptosis, suggesting that modulating interactions of CD8+ T cells and microglia could be a novel therapeutic target of long-term neurological deficits of PIS.

Oncometabolite 2-hydroxyglutarate regulates anti-tumor immunity

"Oncometabolite" 2-hydroxyglutarate (2-HG) is an aberrant metabolite found in tumor cells, exerting a pivotal influence on tumor progression. Recent studies have unveiled its impact on the proliferation, activation, and differentiation of anti-tumor T cells. Moreover, 2-HG regulates the function of innate immune components, including macrophages, dendritic cells, natural killer cells, and the complement system. Elevated levels of 2-HG hinder α-KG-dependent dioxygenases (α-KGDDs), contributing to tumorigenesis by disrupting epigenetic regulation, genome integrity, hypoxia-inducible factors (HIF) signaling, and cellular metabolism. The chiral molecular structure of 2-HG produces two enantiomers: D-2-HG and L-2-HG, each with distinct origins and biological functions. Efforts to inhibit D-2-HG and leverage the potential of L-2-HG have demonstrated efficacy in cancer immunotherapy. This review delves into the metabolism, biological functions, and impacts on the tumor immune microenvironment (TIME) of 2-HG, providing a comprehensive exploration of the intricate relationship between 2-HG and antitumor immunity. Additionally, we examine the potential clinical applications of targeted therapy for 2-HG, highlighting recent breakthroughs as well as the existing challenges.

Multifunctional IrOx Neural Probe for In Situ Dynamic Brain Hypoxia Evaluation

Perioperative cerebral hypoxia and neonatal hypoxia-ischemic encephalopathy are the main triggers that lead to temporary or permanent brain dysfunction. The pathogenesis is intimately correlated to neural activities and the pH of the microenvironment, which calls for a high demand for in situ multitype physiological signal acquisition in the brain. However, conventional pH sensing neural interfaces cannot obtain the characteristics of multimodes, multichannels, and high spatial resolution of physiological signals simultaneously. Here, we report a multifunctional implantable iridium oxide (IrOx) neural probe (MIIONP) combined with electrophysiology recording, in situ pH sensing, and neural stimulation for real-time dynamic brain hypoxia evaluation. The neural probe modified with IrOx films exhibits outstanding electrophysiology recording and neural stimulation performance and long-term stable high spatial pH sensing resolution of about 100 μm, and the cytotoxicity of IrOx microelectrodes was investigated as well. In addition, 4 weeks' tracking of the same neuron firing and instantaneous population spike captured during electrical stimulation was achieved by MIIONP. Finally, in a mouse brain hypoxia model, the MIIONP has demonstrated the capability of synchronous in situ recording of the pH and neural firing changes in the brain, which has a valuable application in dynamic brain disease evaluation through real-time acquisition of multiple physiological signals.

CD8+ T cells in brain injury and neurodegeneration

The interaction between the peripheral immune system and the brain is increasingly being recognized as an important layer of neuroimmune regulation and plays vital roles in brain homeostasis as well as neurological disorders. As an important population of T-cell lymphocytes, the roles of CD8+ T cells in infectious diseases and tumor immunity have been well established. Recently, increasing number of complex functions of CD8+ T cells in brain disorders have been revealed. However, an advanced summary and discussion of the functions and mechanisms of CD8+ T cells in brain injury and neurodegeneration are still lacking. Here, we described the differentiation and function of CD8+ T cells, reviewed the involvement of CD8+ T cells in the regulation of brain injury including stroke and traumatic brain injury and neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), and discussed therapeutic prospects and future study goals. Understanding these processes will promote the investigation of T-cell immunity in brain disorders and provide new intervention strategies for the treatment of brain injury and neurodegeneration.

miR-26a Improves Microglial Activation and Neuronal Apoptosis in a Rat Model of Cerebral Infarction by Regulating the TREM1-TLR4/MyD88/NF-κB Axis

Emerging studies have indicated that abnormally expressed microRNAs (miRNAs) are related to the pathogenesis of cerebral ischemia. Nevertheless, the function of miR-26a in neuronal damage and microglial activation during cerebral infarction remains elusive. It was revealed that miR-26a was downregulated in oxygen-glucose deprivation (OGD)-treated microglia and neurons. Overexpressing miR-26a reduced the inflammatory reaction in BV2 cells and decreased neuronal apoptosis following OGD stimulation. miR-26a upregulation inactivated the TLR4/MyD88/NF-κB pathway and inhibited TREM1 expression. Repressing NF-κB phosphorylation inhibited the miR-26a level. As supported by the dual-luciferase reporter assay, TREM1 was directly targeted by miR-26a. Furthermore, a rat model of middle cerebral artery occlusion (MCAO) was built. We discovered that miR-26a improved cognitive, learning, and motor functions and reduced cerebral edema in MCAO rats. Mechanistically, upregulating miR-26a reduced inflammation and neuronal apoptosis by mitigating the TREM1-TLR4/MyD88/NF-κB pathway in the MCAO rat model. Collectively, this study verified that the miR-26a-TREM1-TLR4/MyD88/NF-κB axis contributes to modulating OGD-mediated microglial activation and neuronal injury.

Casein Reactivates Dopaminergic Nerve Injury and Intestinal Inflammation with Disturbing Intestinal Microflora and Fecal Metabolites in a Convalescent Parkinson's Disease Mouse Model

Parkinson's disease (PD) is the fastest-growing neurodegenerative disease, with pathogenic causes elusive and short of effective treatment options. Investigations have found that dairy products positively correlate with the onset of PD, but the mechanisms remain unexplored. As casein is an antigenic component in dairy products, this study assessed if casein could exacerbate PD-related symptoms by stimulating intestinal inflammation and unbalanced intestinal flora and be a risk factor for PD. Using a convalescent PD mouse model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), the results showed casein reduced motor coordination, caused gastrointestinal dysfunction, reduced dopamine content, and induced intestinal inflammation. Meanwhile, casein disturbed gut microbiota homeostasis by increasing the Firmicutes/Bacteroidetes ratio, decreasing α-diversity, and caused abnormal alterations in fecal metabolites. However, these adverse effects of casein attenuated much when it had hydrolyzed by acid or when antibiotics inhibited the intestinal microbiota of the mice. Therefore, our results suggested that casein could reactivate dopaminergic nerve injury and intestinal inflammation and exacerbate intestinal flora disorder and its metabolites in convalescent PD mice. These damaging effects might be related to disordered protein digestion and gut microbiota in these mice. These findings will provide new insights into the impact of milk/dairy products on PD progression and supply information on dietary options for PD patients.

T-cell receptor signaling modulated by the co-receptors: Potential targets for stroke treatment

Stroke is a severe and life-threatening disease, necessitating more research on new treatment strategies. Infiltrated T lymphocytes, an essential adaptive immune cell with extensive effector function, are crucially involved in post-stroke inflammation. Immediately after the initiation of the innate immune response triggered by microglia/macrophages, the adaptive immune response associated with T lymphocytes also participates in the complex pathophysiology of stroke and partially informs the outcome of stroke. Preclinical and clinical studies have revealed the conflicting roles of T cells in post-stroke inflammation and as potential therapeutic targets. Therefore, exploring the mechanisms that underlie the adaptive immune response associated with T lymphocytes in stroke is essential. The T-cell receptor (TCR) and its downstream signaling regulate T lymphocyte differentiation and activation. This review comprehensively summarizes the various molecules that regulate TCR signaling and the T-cell response. It covers both the co-stimulatory and co-inhibitory molecules and their roles in stroke. Because immunoregulatory therapies targeting TCR and its mediators have achieved great success in some proliferative diseases, this article also summarizes the advances in therapeutic strategies related to TCR signaling in lymphocytes after stroke, which can facilitate translation. DATA AVAILABILITY: No data was used for the research described in the article.

The role of T cells in acute ischemic stroke

Acute ischemic stroke (AIS) is associated with high rates of disability and mortality, exerting a substantial impact on overall survival and health-related quality of life. Treatment of AIS remains challenging given that the underlying pathologic mechanisms remain unclear. However, recent research has demonstrated that the immune system plays a key role in the development of AIS. Numerous studies have reported infiltration of T cells into ischemic brain tissue. While some types of T cells can promote the development of inflammatory responses and aggravate ischemic damage in patients with AIS, other T cells appear to exert neuroprotective effects via immunosuppression and other mechanisms. In this review, we discuss the recent findings regarding the infiltration of T cells into ischemic brain tissue, and the mechanisms governing how T cells can facilitate tissue injury or neuroprotection in AIS. Factors influencing the function of T cells, such as intestinal microflora and sex differences, are also discussed. We also explore the recent research on the effect of non-coding RNA on T cells after stroke, as well as the potential for specifically targeting T cells in the treatment of stroke patients.