Decreased levels of CD95 and caspase-8 mRNA in multiple sclerosis patients with gadolinium-enhancing lesions on MRI

Caspase-8 in inflammatory diseases: a potential therapeutic target

Caspase-8, a renowned cysteine-aspartic protease within its enzyme family, initially garnered attention for its regulatory role in extrinsic apoptosis. With advancing research, a growing body of evidence has substantiated its involvement in other cell death processes, such as pyroptosis and necroptosis, as well as its modulatory effects on inflammasomes and proinflammatory cytokines. PANoptosis, an emerging concept of cell death, encompasses pyroptosis, apoptosis, and necroptosis, providing insight into the often overlapping cellular mortality observed during disease progression. The activation or deficiency of caspase-8 enzymatic activity is closely linked to PANoptosis, positioning caspase-8 as a key regulator of cell survival or death across various physiological and pathological processes. Aberrant expression of caspase-8 is closely associated with the development and progression of a range of inflammatory diseases, including immune system disorders, neurodegenerative diseases (NDDs), sepsis, and cancer. This paper delves into the regulatory role and impact of caspase-8 in these conditions, aiming to elucidate potential therapeutic strategies for the future intervention.

Myeloid caspase-8 restricts RIPK3-dependent proinflammatory IL-1β production and CD4 T cell activation in autoimmune demyelination

Caspase-8 functions at the crossroad of programmed cell death and inflammation. Here, using genetic approaches and the experimental autoimmune encephalomyelitis model of inflammatory demyelination, we identified a negative regulatory pathway for caspase-8 in infiltrated macrophages whereby it functions to restrain interleukin (IL)-1β-driven autoimmune inflammation. Caspase-8 is partially activated in macrophages/microglia in active lesions of multiple sclerosis. Selective ablation of Casp8 in myeloid cells, but not microglia, exacerbated autoimmune demyelination. Heightened IL-1β production by caspase-8-deficient macrophages underlies exacerbated activation of encephalitogenic T cells and production of GM-CSF and interferon-γ. Mechanistically, IL-1β overproduction by primed caspase-8-deficient macrophages was mediated by RIPK1/RIPK3 through the engagement of NLRP3 inflammasome and was independent of cell death. When instructed by autoreactive CD4 T cells in the presence of antigen, caspase-8-deficient macrophages, but not their wild-type counterparts, released significant amount of IL-1β that in turn acted through IL-1R to amplify T cell activation. Moreover, the worsened experimental autoimmune encephalomyelitis progression in myeloid Casp8 mutant mice was completely reversed when Ripk3 was simultaneously deleted. Together, these data reveal a functional link between T cell-driven autoimmunity and inflammatory IL-1β that is negatively regulated by caspase-8, and suggest that dysregulation of the pathway may contribute to inflammatory autoimmune diseases, such as multiple sclerosis.

Fas-Fas Ligand: Checkpoint of T Cell Functions in Multiple Sclerosis

Fas and Fas Ligand (FasL) are two molecules involved in the regulation of cell death. Their interaction leads to apoptosis of thymocytes that fail to rearrange correctly their T cell receptor (TCR) genes and of those that recognize self-antigens, a process called negative selection; moreover, Fas–FasL interaction leads to activation-induced cell death, a form of apoptosis induced by repeated TCR stimulation, responsible for the peripheral deletion of activated T cells. Both control mechanisms are particularly relevant in the context of autoimmune diseases, such as multiple sclerosis (MS), where T cells exert an immune response against self-antigens. This concept is well demonstrated by the development of autoimmune diseases in mice and humans with defects in Fas or FasL. In recent years, several new aspects of T cell functions in MS have been elucidated, such as the pathogenic role of T helper (Th) 17 cells and the protective role of T regulatory (Treg) cells. Thus, in this review, we summarize the role of the Fas–FasL pathway, with particular focus on its involvement in MS. We then discuss recent advances concerning the role of Fas–FasL in regulating Th17 and Treg cells’ functions, in the context of MS.

Similar sensitivity of regulatory T cells towards CD95L-mediated apoptosis in patients with multiple sclerosis and healthy individuals

Impaired suppressive function of CD4(+)CD25(high) regulatory T cells (T(reg)) has been reported as a novel pathogenetic mechanism in Multiple sclerosis (MS). We addressed if high apoptosis sensitivity of MS-T(reg) could explain this functional T(reg) defect. T(reg) from treatment-naïve MS patients showed high sensitivity towards CD95Ligand-mediated apoptosis and exhibited enhanced cell death to IL-2 and TCR-signal deprivation. Since susceptibility of T(reg) to cell death was similar in MS patients and healthy controls, this cannot explain the inhibitory dysfunction of T(reg) associated with MS. Furthermore, as cell death is not enhanced, therapeutic expansion of MS-T(reg)in vitro should be a reasonable and novel therapeutic option.

Apoptosis of T cells in peripheral blood and cerebrospinal fluid is associated with disease activity of multiple sclerosis

Apoptotic elimination of pathogenic T cells is considered to be one of regulatory mechanisms in multiple sclerosis (MS). To explore the potential relationship between Fas-mediated apoptosis and the disease course of MS, we examined apoptosis, defined by annexin V (AV) binding, and Fas (CD95) expression in CD4+ and in CD8+ T cells in MS patients by using five-color flow cytometry. The percentage of AV+CD4+CD3+ cells and CD95+AV+CD4+CD3+ cells in peripheral blood and cerebrospinal fluid (CSF) were significantly decreased in active MS patients compared with inactive MS patients. A significantly lower proportion of CD95+AV+CD8+CD3+ cells in CSF was observed in active MS patients compared with inactive MS patients, but not in peripheral blood. These results indicate that the resistance of T cells to Fas-mediated apoptosis is involved in exacerbation of MS and/or that Fas-mediated apoptosis of T cells is associated with remission of MS.

Progrès récents concernant les mécanismes immunitaires de la sclérose en plaques

INTRODUCTION

Multiple sclerosis (MS) is a heterogeneous disease. From an immunological point of view, it is considered an inflammatory TH1-mediated autoimmune disease of unknown origin, targeting myelin proteins.

STATE OF ART

Neuropathological analysis of MS lesions classified different clinical MS types according to the preponderance of different subsets of immune cells in the lesions (clinico-pathological correlation). Ex vivo analysis of various immunological parameters (like cytokines, antigenic targets) and MRI findings suggest a heterogeneous process leading to the autoimmune destruction of the myelin sheath. Clinical therapeutic trials, especially those using monoclonal antibodies, have recently improved our understanding of the immunology of MS, by focusing our interest on molecules modulating the reactivity of T or B cells, and on the influence of adhesion molecules on relapsing remititing MS. Finally, large scale transcriptional analysis of MS and EAE lesions gave a large amount of information about molecules that are up or down regulated during the disease process, and identified new candidates like osteopontin, which ended up being a key proinflammatory molecule influencing the course of the disease and a therapeutic target for EAE.

PERSPECTIVES

Investigating the numerous MS and EAE large scale transcriptional profiles will allow new hypotheses to arise, especially in the immunological field of MS. The relationship between inflammation and axonal loss is one of the key questions raised by researchers, and whether these two processes are directly related or not is still debated today.

CONCLUSION

A better understanding of the immunology of MS would lead to the discovery of new therapeutic and biological tools, allowing practical improvement of MS patient care.

Programmed cell death of myelin basic protein-specific T lymphocytes is reduced in patients with acute multiple sclerosis

We investigated the apoptosis of myelin basic protein (MBP)-specific T lymphocytes in multiple sclerosis (MS) patients with acute (AMS) or stable (SMS) MS by evaluating the expression of apoptosis markers on peripheral cells. Cells of healthy controls (HC) were evaluated as well. Results showed that mitogen-stimulated apoptosis was comparable among patients and controls, whereas MBP-stimulated CD4+ and CD8+ 7-AAD+ and 7-AAD+ Fas+ cell (apoptotic cells) were significantly reduced in AMS patients. A reduction of the apoptotic rate of myelin-specific CD4+ and CD8+ T lymphocytes could be involved in the immune-mediated destruction of the myelin sheath seen in AMS patients.

An update on neuroimaging of multiple sclerosis

PURPOSE OF REVIEW

The advent of magnetic resonance imaging provided a powerful tool for monitoring the dynamics of pathological changes in multiple sclerosis, but conventional approaches offer only limited information that is directly relevant to clinical progression. Continued developments of imaging methods and their use for diagnosis, monitoring pathology and understanding disease progression are reviewed here.

RECENT FINDINGS

Magnetic resonance imaging is now well established as a clinical test for multiple sclerosis, but the specific ways in which imaging information should best be incorporated into diagnostic criteria are still debated. New data defining the substantial pathology in grey matter, regional variation in the progression of pathology and the relationship between the spatial distribution of pathological changes and symptoms are providing an increasingly compelling description of changes relevant to disability. Molecular-imaging approaches promise much more detailed descriptions. Functional magnetic resonance imaging, which suggests that adaptive functional changes could limit clinical expression of pathology, are providing further clues to the link between measures of pathology and disability.

SUMMARY

New data further reinforce the view that pathology relevant to clinical progression of multiple sclerosis can be defined by imaging. A range of biologically more specific markers are becoming available using positron emission tomography, as well as magnetic resonance imaging.