Acid Sphingomyelinase is a critical regulator in cytotoxic granule secretion of primary T lymphocytes

The acid sphingomyelinase (ASMase) hydrolyses the membrane lipid sphingomyelin into ceramide and phosporylcholine. ASMase localises to phagosomes, endosomes, lysosomes and the plasma membrane, i.e. those subcellular sites which are at the crossroads of many immunological processes. One of these is granule-mediated cytotoxicity as the major effector mechanism of CD8+ cytotoxic T lymphocytes (CTL). Cytotoxic granules have been characterized previously as secretory lysosomes. This raised the question, whether ASMase contributes to granule-mediated cytotoxicity of CD8+ T cells. In my diploma project, I have already shown that ASMase is required for the effective control of the acute infection with the Lymphocytic Choriomeningitis Virus (LCMV) in mice. More specifically, ASMase-deficient (ASMase-/-) CTL were shown to be severely impaired in their virus-specific cytotoxicity. This project aimed at elucidating the ASMase-dependent mechanism contributing to effective cytotoxicity of CD8+ CTL. Analysis of ASMase-/- CD8+ T cells revealed that the transcription, translation, intracellular storage and processing of cytotoxic effector molecules proceed without defects. Moreover, in ASMase-/- CD8+ T cells no hints for the accumulation of sphingomyelin were detected. These findings excluded excessive sphingomyelin as the cause for impaired cytotoxicity. The specificity of the ASMase-dependent mechanism was shown by a strongly reduced T cell receptor-triggered release of cytotoxic effector molecules while secretion of the chemokine RANTES was not impaired in ASMase-/- CTL. In ASMase-/- T cells, cytotoxic granules were shown to fuse properly with the plasma membrane at the immunological synapse. The very last step of granule exocytosis, i.e. the extrusion of granular contents, is impaired by deficiency in ASMase. Even in CTL unable to generate high molecular weight granule matrix, the secretion of low molecular weight granule contents was strongly impaired by ASMase-deficiency. Biomorphometry revealed that cytotoxic granules are of identical size in wt and ASMase-/- CTL prior to fusion with the plasma membrane. However, after fusion with the plasma membrane, in ASMase-/- CD8+ T cells the granules remain significantly larger than in wt cells. This phenomenon can be explained by the biophysical consequences of ASMase activity: Generation of ceramide in wt cells increases the surface tension within the inner leaflet of cytotoxic granules. According to Laplace�s law this facilitates the collapse of the fused granule, thus leading to effective extrusion of the granules contents

Aging-associated deficit in CCR7 is linked to worsened glymphatic function, cognition, neuroinflammation, and β-amyloid pathology

Aging leads to a progressive deterioration of meningeal lymphatics and peripheral immunity, which may accelerate cognitive decline. We hypothesized that an age-related reduction in C-C chemokine receptor type 7 (CCR7)-dependent egress of immune cells through the lymphatic vasculature mediates some aspects of brain aging and potentially exacerbates cognitive decline and Alzheimer\u27s disease-like brain β-amyloid (Aβ) pathology. We report a reduction in CCR7 expression by meningeal T cells in old mice that is linked to increased effector and regulatory T cells. Hematopoietic CCR7 deficiency mimicked the aging-associated changes in meningeal T cells and led to reduced glymphatic influx and cognitive impairment. Deletion of CCR7 in 5xFAD transgenic mice resulted in deleterious neurovascular and microglial activation, along with increased Aβ deposition in the brain. Treating old mice with anti-CD25 antibodies alleviated the exacerbated meningeal regulatory T cell response and improved cognitive function, highlighting the therapeutic potential of modulating meningeal immunity to fine-tune brain function in aging and in neurodegenerative diseases

Migration of cytotoxic lymphocytes in cell cycle permits local MHC I–dependent control of division at sites of viral infection

Virus-specific cytotoxic CD8+ T cells are in cell cycle as they transit from lymphoid tissues to sites of infection

Image segmentation for neuroscience: Lymphatics

A recent discovery in neuroscience prompts the need for innovation in image analysis. Neuroscientists have discovered the existence of meningeal lymphatic vessels in the brain and have shown their importance in preventing cognitive decline in mouse models of Alzheimer s disease. With age, lymphatic vessels narrow and poorly drain cerebrospinal fluid, leading to plaque accumulation, a marker for Alzheimer s disease. The detection of vessel boundaries and width are performed by hand in current practice and thereby suffer from high error rates and potential observer bias. The existing vessel segmentation methods are dependent on user-defined initialization, which is time-consuming and difficult to achieve in practice due to high amounts of background clutter and noise. This work proposes a level set segmentation method featuring hierarchical matting, LyMPhi, to predetermine foreground and background regions. The level set force field is modulated by the foreground information computed by matting, while also constraining the segmentation contour to be smooth. Segmentation output from this method has a higher overall Dice coefficient and boundary F1-score compared to that of competing algorithms. The algorithms are tested on real and synthetic data generated by our novel shape deformation based approach. LyMPhi is also shown to be more stable under different initial conditions as compared to existing level set segmentation methods. Finally, statistical analysis on manual segmentation is performed to prove the variation and disagreement between three annotators

Parenchymal border macrophages regulate tau pathology and tau-mediated neurodegeneration

International audienceParenchymal border macrophages (PBMs) reside close to the central nervous system parenchyma and regulate CSF flow dynamics. We recently demonstrated that PBMs provide a clearance pathway for amyloid-β peptide, which accumulates in the brain in Alzheimer’s disease (AD). Given the emerging role for PBMs in AD, we explored how tau pathology affects the CSF flow and the PBM populations in the PS19 mouse model of tau pathology. We demonstrated a reduction of CSF flow, and an increase in an MHCII + PBM subpopulation in PS19 mice compared with WT littermates. Consequently, we asked whether PBM dysfunction could exacerbate tau pathology and tau-mediated neurodegeneration. Pharmacological depletion of PBMs in PS19 mice led to an increase in tau pathology and tau-dependent neurodegeneration, which was independent of gliosis or aquaporin-4 depolarization, essential for the CSF-ISF exchange. Together, our results identify PBMs as novel cellular regulators of tau pathology and tau-mediated neurodegeneration