In Vitro Generation of Brain Regulatory T Cells by Co-culturing With Astrocytes

Legius Syndrome mutations in the Ras-regulator SPRED1 abolish its membrane localization and potentially cause neurodegeneration

The SPRED family proteins act as negative regulators of the Ras-ERK pathway: the N-terminal EVH1 domain interacts with the Ras-GAP domain (GRD) of the NF1 protein, while the C-terminal Sprouty-related (SPR) domain promotes membrane localization of SPRED, thereby recruiting NF-1 to Ras. Loss-of-function mutations in the hSPRED1 cause Legius syndrome in an autosomal dominant manner. In this study, we investigated the effects of missense mutations in the SPR domain identified in patients with Legius syndrome. Among 18 mutations we examined, six (C368S, M369L, V408E, P415A, P415L and P422R) have defects in the palmitoylation of the SPRED1 protein, losing plasma membrane localization and forming cytoplasmic granular aggregates. To evaluate the in vivo effects of SPR mutations, knock-in (KI) mice with P415A and P415V substitutions or M417Afs*4, a C-terminal 28 amino acid deletion, were generated. All these KI mice exhibited cranial malformations, a characteristic feature of Legius syndrome. However, both P415A and P415V mutants formed granular aggregates, whereas M417Afs*4 showed a diffuse cytoplasmic distribution, and Spred1P415A and Spred1P415V mice, but not Spred1M417Afs∗4 mice, developed cerebellar ataxia and Purkinje cell loss with age. These data suggest that in addition to loss of palmitoylation, the C-terminal region is required for the granular aggregate formation and Purkinje cell loss. The autophagy inducer spermidine rescued the ataxia phenotypes and Purkinje cell loss in Spred1P415A mice. These results suggest that some, but not all, SPR mutations that lose lipid modification induce abnormal cytoplasmic aggregation, which could be a target for autophagic clearance, and potentially cause neurodegenerative diseases.

Brain regulatory T cells

The brain, long thought to be isolated from the peripheral immune system, is increasingly recognized to be integrated into a systemic immunological network. These conduits of immune-brain interaction and immunosurveillance processes necessitate the presence of complementary immunoregulatory mechanisms, of which brain regulatory T cells (Treg cells) are likely a key facet. Treg cells represent a dynamic population in the brain, with continual influx, specialization to a brain-residency phenotype and relatively rapid displacement by newly incoming cells. In addition to their functions in suppressing adaptive immunity, an emerging view is that Treg cells in the brain dampen down glial reactivity in response to a range of neurological insults, and directly assist in multiple regenerative and reparative processes during tissue pathology. The utility and malleability of the brain Treg cell population make it an attractive therapeutic target across the full spectrum of neurological conditions, ranging from neuroinflammatory to neurodegenerative and even psychiatric diseases. Therapeutic modalities currently under intense development include Treg cell therapy, IL-2 therapy to boost Treg cell numbers and multiple innovative approaches to couple these therapeutics to brain delivery mechanisms for enhanced potency. Here we review the state of the art of brain Treg cell knowledge together with the potential avenues for future integration into medical practice.

Experimental Models to Study Immune Dysfunction in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is a chronic, age-related, progressive multisystem disease associated with neuroinflammation and immune dysfunction. This review discusses the methodological approaches used to study the changes in central and peripheral immunity in PD, the advantages and limitations of the techniques, and their applicability to humans. Although a single animal model cannot replicate all pathological features of the human disease, neuroinflammation is present in most animal models of PD and plays a critical role in understanding the involvement of the immune system (IS) in the pathogenesis of PD. The IS and its interactions with different cell types in the central nervous system (CNS) play an important role in the pathogenesis of PD. Even though culture models do not fully reflect the complexity of disease progression, they are limited in their ability to mimic long-term effects and need validation through in vivo studies. They are an indispensable tool for understanding the interplay between the IS and the pathogenesis of this disease. Understanding the immune-mediated mechanisms may lead to potential therapeutic targets for the treatment of PD. We believe that the development of methodological guidelines for experiments with animal models and PD patients is crucial to ensure the validity and consistency of the results.

Sortilin Expression Levels and Peripheral Immunity: A Potential Biomarker for Segregation between Parkinson's Disease Patients and Healthy Controls

Parkinson's disease (PD) is characterized by substantial phenotypic heterogeneity that limits the disease prognosis and patient's counseling, and complicates the design of further clinical trials. There is an unmet need for the development and validation of biomarkers for the prediction of the disease course. In this study, we utilized flow cytometry and in vitro approaches on peripheral blood cells and isolated peripheral blood mononuclear cell (PBMC)-derived macrophages to characterize specific innate immune populations in PD patients versus healthy donors. We found a significantly lower percentage of B lymphocytes and monocyte populations in PD patients. Monocytes in PD patients were characterized by a higher CD40 expression and on-surface expression of the type I membrane glycoprotein sortilin, which showed a trend of negative correlation with the age of the patients. These results were further investigated in vitro on PBMC-derived macrophages, which, in PD patients, showed higher sortilin expression levels compared to cells from healthy donors. The treatment of PD-derived macrophages with oxLDL led to higher foam cell formation compared to healthy donors. In conclusion, our results support the hypothesis that surface sortilin expression levels on human peripheral monocytes may potentially be utilized as a marker of Parkinson's disease and may segregate the sporadic versus the genetically induced forms of the disease.

Modulation of Neuroinflammation: Advances in Roles and Mechanisms of the IL-33/ST2 Axis Involved in Ischemic Stroke

Interleukin (IL)-33 was initially recognized as a constituent of the IL-1 cytokine family in 2005. It exerts pleiotropic effects by regulating immune responses via its binding to the receptor ST2 (IL-33R). The IL-33/ST2 pathway has been linked to several inflammatory disorders. In human and rodents, the broad expression of IL-33 in spinal cord tissues and brain indicates its central nervous system-specific functions. Growing evidence supports the protective effects of the IL-33/ST2 pathway in ischemic stroke, along with a better understanding of the underlying mechanisms. IL-33 plays a crucial role in the regulation of the release of inflammatory molecules from glial cells in response to neuropathological lesions. Moreover, IL-33/ST2-mediated neuroprotection following cerebral ischemia may be linked to T-cell function, specifically regulatory T cells. Soluble ST2 (sST2) acts as a decoy receptor in the IL-33/ST2 axis, blocking IL-33 signaling through the membrane ST2 receptor. sST2 has also been identified as a potential inflammatory biomarker of ischemic stroke. Targeting sST2 specifically to eliminate its inhibition of the protective IL-33/ST2 pathway in ischemic brain tissues is a promising approach for the treatment of ischemic stroke.

Treg cell: Critical role of regulatory T-cells in depression

Depression is a highly prevalent disorder of the central nervous system. The neuropsychiatric symptoms of clinical depression are persistent and include fatigue, anorexia, weight loss, altered sleep patterns, hyperalgesia, melancholia, anxiety, and impaired social behaviours. Mounting evidences suggest that neuroinflammation triggers dysregulated cellular immunity and increases susceptibility to psychiatric diseases. Neuroimmune responses have transformed the clinical approach to depression because of their roles in its pathophysiology and their therapeutic potential. In particular, activated regulatory T (Treg) cells play an increasingly evident role in the inflammatory immune response. In this review, we summarized the available data and discussed in depth the fundamental roles of Tregs in the pathogenesis of depression, as well as the clinical therapeutic potential of Tregs. We aimed to provide recent information regarding the potential of Tregs as immune-modulating biologics for the treatment and prevention of long-term neuropsychiatric symptoms of depression.

Neuroinflammation in Acute Ischemic and Hemorrhagic Stroke

PURPOSE OF REVIEW

This review aims to provide an overview of neuroinflammation in ischemic and hemorrhagic stroke, including recent findings on the mechanisms and cellular players involved in the inflammatory response to brain injury.

RECENT FINDINGS

Neuroinflammation is a crucial process following acute ischemic stroke (AIS) and hemorrhagic stroke (HS). In AIS, neuroinflammation is initiated within minutes of the ischemia onset and continues for several days. In HS, neuroinflammation is initiated by blood byproducts in the subarachnoid space and/or brain parenchyma. In both cases, neuroinflammation is characterized by the activation of resident immune cells, such as microglia and astrocytes, and infiltration of peripheral immune cells, leading to the release of pro-inflammatory cytokines, chemokines, and reactive oxygen species. These inflammatory mediators contribute to blood-brain barrier disruption, neuronal damage, and cerebral edema, promoting neuronal apoptosis and impairing neuroplasticity, ultimately exacerbating the neurologic deficit. However, neuroinflammation can also have beneficial effects by clearing cellular debris and promoting tissue repair. The role of neuroinflammation in AIS and ICH is complex and multifaceted, and further research is necessary to develop effective therapies that target this process. Intracerebral hemorrhage (ICH) will be the HS subtype addressed in this review. Neuroinflammation is a significant contributor to brain tissue damage following AIS and HS. Understanding the mechanisms and cellular players involved in neuroinflammation is essential for developing effective therapies to reduce secondary injury and improve stroke outcomes. Recent findings have provided new insights into the pathophysiology of neuroinflammation, highlighting the potential for targeting specific cytokines, chemokines, and glial cells as therapeutic strategies.

iAstrocytes do not restrain T cell proliferation in vitro

The cross-talk between T cells and astrocytes occurring under physiological and, even more, neuroinflammatory conditions may profoundly impact the generation of adaptive immune responses in the nervous tissue. In this study, we used a standardized in vitro co-culture assay to investigate the immunomodulatory properties of astrocytes differing for age, sex, and species. Mouse neonatal astrocytes enhanced T cell vitality but suppressed T lymphocyte proliferation in response to mitogenic stimuli or myelin antigens, regardless of the Th1, Th2 or Th17 T cell phenotype. Studies comparing glia cells from adult and neonatal animals showed that adult astrocytes were more efficient in inhibiting T lymphocyte activation than neonatal astrocytes, regardless of their sex. Differently from primary cultures, mouse and human astrocytes derived from reprogrammed fibroblasts did not interfere with T cell proliferation. Overall, we describe a standardized astrocyte-T cell interaction in vitro assay and demonstrate that primary astrocytes and iAstrocytes may differ in modulating T cell function.

Regulatory T Cell Therapeutics for Neuroinflammatory Disorders

A delicate balance of immune regulation exists in the central nervous system (CNS) that is often dysreg-ulated in neurological diseases, making them complicated to treat. With altered immune surveillance in the diseased or injured CNS, signals that are beneficial in the homeostatic CNS can be disrupted and lead to neuroinflammation. Recent advances in niche immune cell subsets have provided insight into the complicated cross-talk between the nervous system and the immune system. Regulatory T cells (Tregs) are a subset of T cells that are capable of suppressing effector T-cell activation and regulating immune tolerance, and play an important role in neuroprotection. Tregs have been shown to be effective therapies in a variety of immune-related disorders including, graft-versus-host disease (GVHD), type 1 diabetes (T1D), and inflammatory bowel disease (IBD), as well as within the CNS. Recently, significant advancements in engineering T cells, such as chimeric antigen receptor (CAR) T cells, have led to several approved therapies suggesting the safety and efficacy for similar engineered Treg therapies. Further, as understanding of the immune system's role in neuroinflammation has progressed, Tregs have recently become a potential therapeutic in the neurology space. In this review, we discuss Tregs and their evolving role as therapies for neuroinflammatory related disorders.

T cells in the brain inflammation

The immune system is deeply involved in autoimmune diseases of the central nervous system (CNS), such as multiple sclerosis, N-methyl-d-aspartate (NMDA) receptor encephalitis, and narcolepsy. Additionally, the immune system is involved in various brain diseases including cerebral infarction and neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). In particular, reports related to T cells are increasing. T cells may also play important roles in brain deterioration and dementia that occur with aging. Our understanding of the role of immune cells in the context of the brain has been greatly improved by the use of acute ischemic brain injury models. Additionally, similar neural damage and repair events are shown to occur in more chronic brain neurodegenerative brain diseases. In this review, we focus on the role of T cells, including CD4⁺ T cells, CD8⁺ T cells and regulatory T cells (Tregs) in cerebral infarction and neurodegenerative diseases.