The Role of Sulfatides in Axon–Glia Interactions

Improvement of Lipid Detection in Mouse Brain and Human Uterine Tissue Sections Using In Situ Matrix Enhanced Secondary Ion Mass Spectrometry

The potential of mass spectrometry imaging, and especially ToF-SIMS 2D and 3D imaging, for submicrometer-scale, label-free molecular localization in biological tissues is undisputable. Nevertheless, sensitivity issues remain, especially when one wants to achieve the best lateral and vertical (nanometer-scale) resolution. In this study, the interest of in situ matrix transfer for tissue analysis with cluster ion beams (Bin+, Arn+) is explored in detail, using a series of six low molecular weight acidic (MALDI) matrices. After estimating the sensitivity enhancements for phosphatidylcholine (PC), an abundant lipid type present in almost any kind of cell membrane, the most promising matrices were softly transferred in situ on mouse brain and human uterine tissue samples using a 10 keV Ar3000+ cluster beam. Signal enhancements up to 1 order of magnitude for intact lipid signals were observed in both tissues under Bi5+ and Ar3000+ bombardment. The main findings of this study lie in the in-depth characterization of uterine tissue samples, the demonstration that the transferred matrices also improve signal efficiency in the negative ion polarity and that they perform as well when using Bin+ and Arn+ primary ions for analysis and imaging.

Fatty Acid 2-Hydroxylase and 2-Hydroxylated Sphingolipids: Metabolism and Function in Health and Diseases

Sphingolipids containing acyl residues that are hydroxylated at C-2 are found in most, if not all, eukaryotes and certain bacteria. 2-hydroxylated sphingolipids are present in many organs and cell types, though they are especially abundant in myelin and skin. The enzyme fatty acid 2-hydroxylase (FA2H) is involved in the synthesis of many but not all 2-hydroxylated sphingolipids. Deficiency in FA2H causes a neurodegenerative disease known as hereditary spastic paraplegia 35 (HSP35/SPG35) or fatty acid hydroxylase-associated neurodegeneration (FAHN). FA2H likely also plays a role in other diseases. A low expression level of FA2H correlates with a poor prognosis in many cancers. This review presents an updated overview of the metabolism and function of 2-hydroxylated sphingolipids and the FA2H enzyme under physiological conditions and in diseases.

Sulfatide Deficiency, an Early Alzheimer's Lipidomic Signature, Causes Brain Ventricular Enlargement in the Absence of Classical Neuropathological Hallmarks

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive memory loss and a decline in activities of daily life. Ventricular enlargement has been associated with worse performance on global cognitive tests and AD. Our previous studies demonstrated that brain sulfatides, myelin-enriched lipids, are dramatically reduced in subjects at the earliest clinically recognizable AD stages via an apolipoprotein E (APOE)-dependent and isoform-specific process. Herein, we provided pre-clinical evidence that sulfatide deficiency is causally associated with brain ventricular enlargement. Specifically, taking advantage of genetic mouse models of global and adult-onset sulfatide deficiency, we demonstrated that sulfatide losses cause ventricular enlargement without significantly affecting hippocampal or whole brain volumes using histological and magnetic resonance imaging approaches. Mild decreases in sulfatide content and mild increases in ventricular areas were also observed in human APOE4 compared to APOE2 knock-in mice. Finally, we provided Western blot and immunofluorescence evidence that aquaporin-4, the most prevalent aquaporin channel in the central nervous system (CNS) that provides fast water transportation and regulates cerebrospinal fluid in the ventricles, is significantly increased under sulfatide-deficient conditions, while other major brain aquaporins (e.g., aquaporin-1) are not altered. In short, we unraveled a novel and causal association between sulfatide deficiency and ventricular enlargement. Finally, we propose putative mechanisms by which sulfatide deficiency may induce ventricular enlargement.

[Introduction to Myelin Research]

Myelin is a multilamellar membrane structure formed by oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS). It has been recognized as an insulator that is essential for the rapid and efficient propagation of action potentials by saltatory conduction. However, recently many studies have shown that myelin and myelin-forming cells interact with axons and regulate the nervous system far more actively than previously thought. For example, myelination changes axons dynamically and divides them into four distinct functional domains: node of Ranvier, paranode, juxtaparanode, and internode. Voltage-gated Na⁺ channels are clustered at the node, while K⁺ channels are at the juxtaparanode, and segregation of these channels by paranodal axoglial junction is necessary for proper axonal function. My research experience began at the neurology ward of the Niigata University Medical Hospital, where I saw a patient with peripheral neuropathy of unknown etiology more than 37 years ago. In the patient's serum, we found an autoantibody against a glycolipid enriched in the PNS. Since then, I have been interested in myelin because of its beautiful structure and unique roles in the nervous system. In this review, our recent studies related to CNS and PNS myelin are presented.

New developments in RiPP discovery, enzymology and engineering

Covering: up to June 2020Ribosomally-synthesized and post-translationally modified peptides (RiPPs) are a large group of natural products. A community-driven review in 2013 described the emerging commonalities in the biosynthesis of RiPPs and the opportunities they offered for bioengineering and genome mining. Since then, the field has seen tremendous advances in understanding of the mechanisms by which nature assembles these compounds, in engineering their biosynthetic machinery for a wide range of applications, and in the discovery of entirely new RiPP families using bioinformatic tools developed specifically for this compound class. The First International Conference on RiPPs was held in 2019, and the meeting participants assembled the current review describing new developments since 2013. The review discusses the new classes of RiPPs that have been discovered, the advances in our understanding of the installation of both primary and secondary post-translational modifications, and the mechanisms by which the enzymes recognize the leader peptides in their substrates. In addition, genome mining tools used for RiPP discovery are discussed as well as various strategies for RiPP engineering. An outlook section presents directions for future research.

Decreased turnover of the CNS myelin protein Opalin in a mouse model of hereditary spastic paraplegia 35

Spastic paraplegia 35 (SPG35) (OMIM: 612319) or fatty acid hydroxylase-associated neurodegeneration (FAHN) is caused by deficiency of fatty acid 2-hydroxylase (FA2H). This enzyme synthesizes sphingolipids containing 2-hydroxylated fatty acids, which are particularly abundant in myelin. Fa2h-deficient (Fa2h-/-) mice develop symptoms reminiscent of the human disease and therefore serve as animal model of SPG35. In order to understand further the pathogenesis of SPG35, we compared the proteome of purified CNS myelin isolated from wild type and Fa2h-/- mice at different time points of disease progression using tandem mass tag labeling. Data analysis with a focus on myelin membrane proteins revealed a significant increase of the oligodendrocytic myelin paranodal and inner loop protein (Opalin) in Fa2h-/- mice, whereas the concentration of other major myelin proteins was not significantly changed. Western blot analysis revealed an almost 6-fold increase of Opalin in myelin of Fa2h-/- mice aged 21-23 months. A concurrent unaltered Opalin gene expression suggested a decreased turnover of the Opalin protein in Fa2h-/- mice. Supporting this hypothesis, Opalin protein half-life was reduced significantly when expressed in CHO cells synthesizing 2-hydroxylated sulfatide, compared to cells synthesizing only non-hydroxylated sulfatide. Degradation of Opalin was inhibited by inhibitors of lysosomal degradation but unaffected by proteasome inhibitors. Taken together, these results reveal a new function of 2-hydroxylated sphingolipids namely affecting the turnover of a myelin membrane protein. This may play a role in the pathogenesis of SPG35.