Lipid Rafts in Signalling, Diseases, and Infections: What Can Be Learned from Fluorescence Techniques?

Abstract

Lipid rafts are dynamic microdomains in the membrane, rich in cholesterol and sphingolipids, that are critical for biological processes like cell signalling, membrane trafficking, and protein organization. Their essential role is claimed in both physiological and pathological conditions, including cancer, neurodegenerative diseases, and viral infections, making them a key area of research. Fluorescence-based approaches, including super-resolution fluorescence microscopy techniques, enable precise analysis of the organization, dynamics, and interactions of these microdomains, thanks also to the innovative design of appropriate fluorescent probes. Moreover, these non-invasive approaches allow for the study of live cells, facilitating the collection of quantitative data under physiologically relevant conditions. This review synthesizes the latest insights into the role of lipid rafts in biological and pathological processes and underscores how fluorescence techniques have advanced our understanding of these critical microdomains. The findings emphasize the pivotal role of lipid rafts in health and disease, providing a foundation for future research and potential therapeutic interventions.

Keywords: fluorescent probes; infections; lipid rafts; liquid-ordered phase; neurodegenerative disease; super resolution.

Figure 5

(A) Super-resolution 2D STED microscopy of cholesterol-rich nanodomains in the plasma membranes of living SH-SY5Y cells. (B) Super-imposed images of living cells visualized by both conventional deconvolved confocal (LSCM) and STED nanoscopy. (C) Magnified square insets (i–iii) in (B). Solid white line 1 in (A) has been used to show STED resolution improvement with nanodomains in the original paper. Adapted from Ref. [151] 2021 Copyright’s Wiley. (D) Single-molecule imaging of mXFP-TpoR diffusion (yellow) and the cortical actin cytoskeleton (cyan) of a representative cell analysed in Winkelmann et al. [161]. Magenta dots: single localization; yellow lines: trajectories faded in time. Scale bar: 2 µm. Adapted from Ref. [161] 2024 Copyright’s Nature.

Figure 1

Schematic representation of lipid raft regions and their involvement in both cellular functions and diseases. Created with BioRender.com.

Figure 2

Representative confocal fluorescence image of giant unilamellar vesicle formed from native pulmonary surfactant membranes, labelled with the lipophilic fluorescent probes DiIC18 (red) and Bodipy-PC (green). Adapted from Ref. [44] 2004. The green areas correspond to the liquid-disordered regions and the red background corresponds to the liquid-ordered phase. The scale bar corresponds to 20 μm.

Figure 3

Schematic representation of the lipid bilayer, illustrating the distinction between the liquid-disordered (Ld) and liquid-ordered (Lo) phases. The Lo phase is enriched in cholesterol, sphingolipids, and gangliosides, which are key components of lipid rafts. Responses of fluorescent probes: the spectral parameters change depending on the stiffness, polarity, and viscosity of the membrane.

Figure 4

Schematic representation of the principles of widefield, confocal, and two-photon microscopies, together with fluorescence recovery after photobleaching (FRAP) and Förster resonance energy transfer (FRET) techniques.