International Journal of Molecular Sciences Review Multiplicity of Glycosphingolipid-Enriched Microdomain-Driven Immune Signaling Noriko Yokoyama 1,† , Kei Hanafusa 1,†, Tomomi Hotta 1, Eriko Oshima 1, Kazuhisa Iwabuchi 1,2,3 and Hitoshi Nakayama 1,2,3,* 1 Institute for Environmental and Gender-Specific Medicine, Juntendo University, Graduate School of Medicine, Urayasu, Chiba 279-0021, Japan; [email protected] (N.Y.); [email protected] (K.H.); [email protected] (T.H.); [email protected] (E.O.); [email protected] (K.I.) 2 Laboratory of Biochemistry, Juntendo University Faculty of Health Care and Nursing, Urayasu, Chiba 279-0023, Japan 3 Infection Control Nursing, Juntendo University Graduate School of Health Care and Nursing, Urayasu, Chiba 279-0023, Japan * Correspondence: [email protected]; Tel.: +81-47-353-3171; Fax: +81-47-353-3178 † These authors contributed equally to this work. Abstract: Glycosphingolipids (GSLs), together with cholesterol, sphingomyelin (SM), and glyco- sylphosphatidylinositol (GPI)-anchored and membrane-associated signal transduction molecules, form GSL-enriched microdomains. These specialized microdomains interact in a cis manner with various immune receptors, affecting immune receptor-mediated signaling. This, in turn, results in the regulation of a broad range of immunological functions, including phagocytosis, cytokine production, antigen presentation and apoptosis. In addition, GSLs alone can regulate immunological functions Citation: Yokoyama, N.; Hanafusa, by acting as ligands for immune receptors, and exogenous GSLs can alter the organization of mi- K.; Hotta, T.; Oshima, E.; Iwabuchi, crodomains and microdomain-associated signaling. Many pathogens, including viruses, bacteria and K.; Nakayama, H. Multiplicity of fungi, enter host cells by binding to GSL-enriched microdomains. Intracellular pathogens survive Glycosphingolipid-Enriched inside phagocytes by manipulating intracellular microdomain-driven signaling and/or sphingolipid Microdomain-Driven Immune metabolism pathways. This review describes the mechanisms by which GSL-enriched microdomains Signaling. Int. J. Mol. Sci. 2021, 22, regulate immune signaling. 9565. https://doi.org/10.3390/ ijms22179565 Keywords: glycosphingolipids; microdomain; immune signaling Academic Editor: Jean-Pierre Jaffrézou Received: 30 July 2021 1. Introduction Accepted: 1 September 2021 Membrane microdomains, also called lipid rafts, consist of glycosphingolipids (GSLs), Published: 3 September 2021 cholesterol, sphingomyelin (SM), glycosylphosphatidylinositol (GPI)-anchored proteins and membrane-associated signal transduction molecules [1,2]. GSLs, a predominant com- Publisher’s Note: MDPI stays neutral ponent of microdomains, are characterized structurally by their hydrophobic ceramide with regard to jurisdictional claims in and hydrophilic glycan moieties. The ceramide moiety contains fatty acid chains that vary published maps and institutional affil- widely in length [3]. More than 400 types of GSLs have been identified based on differences iations. in their glycan structures [4]. Cell surface receptors bind ligands expressed on other cells (in trans) to communicate with neighboring cells, whereas a large number of cell surface receptors interact with ligands expressed on the same cell (in cis)[5]. The hydrophobic ceramide moiety enables GSLs to interact with the steroid ring system of cholesterol via van Copyright: © 2021 by the authors. der Waals forces and hydrogen bonds [6,7]. In addition, the hydrophilic glycan moieties of Licensee MDPI, Basel, Switzerland. GSLs interact in cis with each other, promoting the lateral interaction of GSLs with other This article is an open access article components of cellular membranes. These interactions result in the phase separation of distributed under the terms and GSL-enriched membrane microdomains. GSL-enriched microdomains in the outer surfaces conditions of the Creative Commons of membranes are able to associate with membrane proteins and lipid-anchored signal Attribution (CC BY) license (https:// transduction molecules, which are localized in the inner surfaces of membranes [8–10]. creativecommons.org/licenses/by/ These supramolecular complexes provide signaling platforms for cellular functions. The 4.0/). Int. J. Mol. Sci. 2021, 22, 9565. https://doi.org/10.3390/ijms22179565 https://www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 2 of 24 Int. J. Mol. Sci. 2021, 22, 9565 and lipid-anchored signal transduction molecules, which are localized in the inner2 of 24 sur- faces of membranes [8–10]. These supramolecular complexes provide signaling platforms for cellular functions. The types of GSLs and their metabolism are not only cell type spe- cific but also depend on whether the cells are proliferating or differentiating [4,11]. GSL- types of GSLs and their metabolism are not only cell type specific but also depend on enriched microdomains are therefore thought to be involved in a large number of biolog- whether the cells are proliferating or differentiating [4,11]. GSL-enriched microdomains ical functions, including immunological functions (Figures 1 and 2). This review describes are therefore thought to be involved in a large number of biological functions, including immunologicalthe mechanisms functions by which (Figures GSL-enriched1 and2). micr Thisodomains review describes modulate the receptor mechanisms functions by and whichsignal GSL-enrichedtransductions microdomains in immune signaling, modulate receptorfocusing functions generally and on signal findings transductions in our labora- intory. immune signaling, focusing generally on findings in our laboratory. FigureFigure 1.1.Schematic Schematic pathway pathway of of GSL GSL biosynthesis. biosynthesis. GSLs GSLs and an thed the related related molecules molecules referred referred to in thisto in this reviewreview are are shown. shown. Int. J. Mol. Sci. 2021, 22, x 9565 FOR PEER REVIEW 3 of 24 Figure 2. Multiplicity of GSL-enriched microdomain-driven immune signaling. ( A) Schematic image showing multiplicity of GSL-enriched microdomain-driven signaling in immune cells.cells. In both innate and adaptiveadaptive immunity, GSL-enrichedGSL-enriched microdomains affect immune signaling by themselves or by cis-interactioninteraction withwith variousvarious immuneimmune receptors.receptors. This results in various immune responses, suchsuch asas cytokinecytokine production,production, phagocytosis/phagosomephagocytosis/phagosome maturati maturation,on, antigen presentation and apoptosis. GSL-enriched microdomains are present not only in plasma membranes but also in membranes of intracellular apoptosis. GSL-enriched microdomains are present not only in plasma membranes but also in membranes of intracellular organelles, such as lysosomes and phagosomes. LacCer forms membrane microdomains on intracellular granules, includ- organelles, such as lysosomes and phagosomes. LacCer forms membrane microdomains on intracellular granules, including ing lysosomes, in human neutrophils, and these LacCer-enriched microdomains on phagosomes act as a platform of in- lysosomes,tracellular signaling in human required neutrophils, for phagosome and these LacCer-enriched maturation (fusi microdomainson of lysosomes on phagosomesto pathogen-containing act as a platform phagosomes). of intracellular GD3 signalingforms membrane required microdomains for phagosome on maturationmitochondria-associated (fusion of lysosomes membranes to pathogen-containing (MAMs) and contributes phagosomes). to autophagosome GD3 forms as- membranesembly. ER, microdomains endoplasmic reticulum. on mitochondria-associated Golgi, Golgi apparatus. membranes (B) Schematic (MAMs) image and contributes showing cis to-interactions autophagosome between assembly. GSL- ER,enriched endoplasmic microdomains reticulum. and Golgi,immune Golgi recept apparatus.ors. The (transferB) Schematic of signals image induced showing bycis ligand-interactions binding between into cells GSL-enriched involves the microdomainsdirect binding of and these immune ligands receptors. to GSL-enriched The transfer microdomains of signals in induced plasma bymembranes, ligand binding followed into by cells the involvestransduction the directof the bindingsignals through of these membrane-associated ligands to GSL-enriched signal microdomains transduction in plasmamolecules. membranes, In addition, followed signaling by the molecule-associated transduction of the GSL-en- signals throughriched microdomains membrane-associated interact in signal cis with transduction various receptor molecules. proteins, In addition, leading to signaling a variety molecule-associated of immune responses. GSL-enriched Thus, GSL- enriched microdomains provide signaling platforms for ligand binding to the plasma membranes of immune cells. Intra- microdomains interact in cis with various receptor proteins, leading to a variety of immune responses. Thus, GSL-enriched cellular GSL-enriched microdomains may provide platforms for cross-talk among several types of proteins, such as mem- microdomains provide signaling platforms for ligand binding to the plasma membranes of immune cells. Intracellular GSL- brane-associated and signaling proteins and sphingolipid metabolites. enriched microdomains may provide platforms for cross-talk among several types of proteins, such as membrane-associated and signaling proteins and sphingolipid2. Physicochemical metabolites. Properties of GSL-Enriched Microdomains 2.