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- Barakovic, M, et al.
(författare)
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Bundle-Specific Axon Diameter Index as a New Contrast to Differentiate White Matter Tracts
- 2021
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Ingår i: Frontiers in neuroscience. - : Frontiers Media SA. - 1662-4548 .- 1662-453X. ; 15, s. 646034-
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Tidskriftsartikel (refereegranskat)abstract
- In the central nervous system of primates, several pathways are characterized by different spectra of axon diameters. In vivo methods, based on diffusion-weighted magnetic resonance imaging, can provide axon diameter index estimates non-invasively. However, such methods report voxel-wise estimates, which vary from voxel-to-voxel for the same white matter bundle due to partial volume contributions from other pathways having different microstructure properties. Here, we propose a novel microstructure-informed tractography approach, COMMITAxSize, to resolve axon diameter index estimates at the streamline level, thus making the estimates invariant along trajectories. Compared to previously proposed voxel-wise methods, our formulation allows the estimation of a distinct axon diameter index value for each streamline, directly, furnishing a complementary measure to the existing calculation of the mean value along the bundle. We demonstrate the favourable performance of our approach comparing our estimates with existing histologically-derived measurements performed in the corpus callosum and the posterior limb of the internal capsule. Overall, our method provides a more robust estimation of the axon diameter index of pathways by jointly estimating the microstructure properties of the tissue and the macroscopic organisation of the white matter connectivity.
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- Holm, Åsa, et al.
(författare)
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Lipid rafts are required for the effects of Leishmania donovani lipophosphoglycan on periphagosomal F-actin and phagosomal maturation
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Lipophosphoglycan (LPG) is the major surface glycoconjugate on Leishmania donovani promastigotes, and is cmcial for pro mastigote survival following phagocytosis by macrophages. LPG consists of a chain of repeating phosphodisaccharides anchored to the parasite membrane by a lysophosphatidylinositol lipid anchor with an unusually long saturated fatty acid residue. During phagocytosis, LPG transfers from the parasite surface to the plasma membrane of the host macrophage. The presence of LPG alters the biophysical properties of the host cell membrane and the signaling capacity of the macrophage. LPG induces accumulation ofF-actin around the phagosome, and inhibits phagosome maturation. The effects of LPG on the host ce!l include inhibition of PKCα, a PKC isoenzyme involved in F-actin tumover.The biophysical properties of the LPG lipid anchor suggest that it partitions into caveolae or lipid rafts, which are cholesterol-rich plasma membrane microdomains central for signal transduction. Since PKCa is enriched in caveolae/lipid rafts in other cell types, we investigated if lipid rafts constitute a platform for the interaction of LPG and PKCα. We found that the plasma membrane of human monocyte-derived macrophages were rich in lipid rafts, but did not contain caveolae. LPG colocalized with lipid raft markers after interaction with WT L. donovani promastigotes. The presence of LPG inhibited the translocation of PKCα to the plasma membrane. Destruction of lipid rafts by cholesterol depletion lead to a complete eradication of LPG's effects on periphagosomal F-actin and phagosomal maturation. We also found that cholesterol depletion reduced uptake of WT L. donovani promastigotes, while uptake of an LPG-defective mutant was not affected.We conclude that LPG partitions to lipid rafts in the plasma membrane of human macrophages and inhibits the translocation of PKCα to the membrane. The presence of lipid rafts is a prerequisite for LPG to exert its effects on host cell actin and phagosomal maturation.
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