A tale of two cells: Regulatory T cell-microglia cross-talk in the ischemic brain

Temporal immune profiling in the cerebrospinal fluid and blood of patients with aneurysmal subarachnoid hemorrhage

Delayed cerebral ischemia (DCI) is a significant complication of aneurysmal subarachnoid hemorrhage (aSAH). This study profiled immune responses after aSAH and evaluated their association with DCI onset. Twelve aSAH patients were enrolled. Leukocyte populations and cytokine levels were analyzed in cerebrospinal fluid (CSF) and peripheral blood (PB) on days 3, 5, 7, 10, and 14 post-aSAH. PB mononuclear cells (PBMCs) were collected, and their cytokine production quantified following stimulation. Mixed-effects models reveal distinct immune cell dynamics in CSF compared with blood. Monocyte/macrophage numbers continue to increase in both CSF and PBMCs for days post-aSAH. CD4+ human leukocyte antigen II+ T cells and CD8+ CD154+ T cells increased in circulation over time. Unstimulated PBMCs showed increased interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha production, peaking at 7 d post-aSAH, coinciding with typical DCI onset. Ex vivo stimulation of PBMCs showed that only IL-6 significantly changed over time. In CSF, cytokines peaked 5 d postinjury, preceding immune cell profile alterations. Our findings reveal a time-dependent immune response following aSAH, with distinct within-patient patterns in CSF and PB. The early CSF cytokine peak preceding immune cell changes suggests a potential mechanistic link and identifies the cytokine response as a potential therapeutic target. This cytokine surge may drive immune cell expansion and prime PBMCs for increased inflammatory activity, potentially contributing to DCI risk. Future studies should explore the importance and sources of specific cytokines in driving immune activation. These insights may inform the development of targeted immunomodulatory strategies for preventing or managing DCI in aSAH patients.

The immunomodulatory effects of GLP-1 receptor agonists in neurogenerative diseases and ischemic stroke treatment

Glucagon-like peptide-1 (GLP-1) receptor is widely distributed in the digestive system, cardiovascular system, adipose tissue and central nervous system. Numerous GLP-1 receptor-targeting drugs have been investigated in clinical studies for various indications, including type 2 diabetes and obesity (accounts for 70% of the total studies), non-alcoholic steatohepatitis, Alzheimer's disease, and Parkinson's disease. This review presented fundamental information regarding two categories of GLP-1 receptor agonists (GLP-1RAs): peptide-based and small molecule compounds, and elaborated their potential neuroprotective effects by inhibiting neuroinflammation, reducing neuronal apoptosis, and ultimately improving cognitive function in various neurodegenerative diseases. As a new hypoglycemic drug, GLP-1RA has a unique role in reducing the concurrent risk of stroke in T2D patients. Given the infiltration of various peripheral immune cells into brain tissue, particularly in the areas surrounding the infarct lesion, we further investigated the potential immune regulatory mechanisms. GLP-1RA could not only facilitate the M2 polarization of microglia through both direct and indirect pathways, but also modulate the quantity and function of T cell subtypes, including CD4, CD8, and regulatory T cells, resulting into the inhibition of inflammatory responses and the promotion of neuronal regeneration through interleukin-10 secretion. Therefore, we believe that the "Tregs-microglia-neuron/neural precursor cells" axis is instrumental in mediating immune suppression and neuroprotection in the context of ischemic stroke. Given the benefits of rapid diffusion, favorable blood-brain barrier permeability and versatile administration routes, these small molecule compounds will be one of the important candidates of GLP-1RA. We look forward to the further clinical evidence of small molecule GLP-1RA intervention in ischemic stroke or T2D complicated by ischemic stroke.

Regulatory T Cells for Stroke Recovery: A Promising Immune Therapeutic Strategy

BACKGROUND

Stroke remains a leading cause of mortality and disability among adults. Given the restricted therapeutic window for intravascular interventions and neuroprotection during the acute phase, there has been a growing focus on tissue repair and functional recovery in the subacute and chronic phases after stroke. The pro-inflammatory microglial polarization occurs in subacute and chronic phases after stroke and may represent therapeutic targets for stroke recovery. CD4+ regulatory T cells (Tregs), a subtype of T cells with immunosuppressive effects, have been shown to be important in stroke. Tregs infiltrate into the brain primarily during the subacute and chronic phases following a stroke. Infiltrating Tregs play a critical role in mitigating pro-inflammatory microglial responses, modulating the immune microenvironment, and promoting the functional restoration of the damaged brain following a stroke.

METHODS

A systematic literature search was conducted in PubMed, Scopus, and Web of Science and then conduct a comprehensive analysis of the searched literature.

RESULTS

This review provides a comprehensive summary of recent preclinical research advances on the role of Tregs in stroke, with a particular focus on their reparative functions during the subacute and chronic phases. It discusses changes in peripheral and brain infiltrating Tregs post-stroke, their functions and underlying mechanisms, and therapeutic strategies involving Tregs. Additionally, this review explores the potential and challenges associated with the clinical application of Tregs in ischemic stroke.

CONCLUSION

Treg cell-related therapy represents a promising immune-therapeutic strategy for stroke recovery. However, there are several critical issues that must be resolved before its advancement to clinical application.

Update on the mechanism of microglia involvement in post-stroke cognitive impairment

Post-stroke cognitive impairment (PSCI) is a clinical syndrome characterized by cognitive deficits that manifest following a stroke and persist for up to 6 months post-event. This condition is grave, severely compromising patient quality of life and longevity, while also imposing substantial economic burdens on societies worldwide. Despite significant advancements in identifying risk factors for PSCI, research into its underlying mechanisms and therapeutic interventions remains inadequate. Microglia, the brain's primary immune effector cells, are pivotal in maintaining, nurturing, defending, and repairing neuronal function, a process intrinsically linked to PSCI's progression. Thus, investigating microglial activation and mechanisms in PSCI is crucial. This paper aims to foster new preventive and therapeutic approaches for PSCI by elucidating the roles, mechanisms, and characteristics of microglia in the condition.

Stroke in the Time of Circadian Medicine

Time-of-day significantly influences the severity and incidence of stroke. Evidence has emerged not only for circadian governance over stroke risk factors, but also for important determinants of clinical outcome. In this review, we provide a comprehensive overview of the interplay between chronobiology and cerebrovascular disease. We discuss circadian regulation of pathophysiological mechanisms underlying stroke onset or tolerance as well as in vascular dementia. This includes cell death mechanisms, metabolism, mitochondrial function, and inflammation/immunity. Furthermore, we present clinical evidence supporting the link between disrupted circadian rhythms and increased susceptibility to stroke and dementia. We propose that circadian regulation of biochemical and physiological pathways in the brain increase susceptibility to damage after stroke in sleep and attenuate treatment effectiveness during the active phase. This review underscores the importance of considering circadian biology for understanding the pathology and treatment choice for stroke and vascular dementia and speculates that considering a patient's chronotype may be an important factor in developing precision treatment following stroke.