Investigation of the biophysical properties of a fluorescently modified ceramide-1-phosphate

Investigation of nano- and microdomains formed by ceramide 1 phosphate in lipid bilayers

Biological membranes are renowned for their intricate complexity, with the formation of membrane domains being pivotal to the successful execution of numerous cellular processes. However, due to their nanoscale characteristics, these domains are often understudied, as the experimental techniques required for quantitative investigation present significant challenges. In this study we employ spot-variation z-scan fluorescence correlation spectroscopy (svzFCS) tailored for artificial lipid vesicles of varying composition and combine this approach with high-resolution imaging. This method has been harnessed to examine the lipid-segregation behavior of distinct types of ceramide-1-phosphate (C1P), a crucial class of signaling molecules, within these membranes. Moreover, we provide a quantitative portrayal of the lipid membranes studied and the domains induced by C1P at both nano and microscales. Given the lack of definitive conclusions from the experimental data obtained, it was supplemented with comprehensive in silico studies-including the analysis of diffusion coefficient via molecular dynamics and domain populations via Monte Carlo simulations. This approach enhanced our insight into the dynamic behavior of these molecules within model lipid membranes, confirming that nano- and microdomains can co-exist in lipid vesicles.

Cysteine Mutations in the Ebolavirus Matrix Protein VP40 Promote Phosphatidylserine Binding by Increasing the Flexibility of a Lipid-Binding Loop

Ebolavirus (EBOV) is a negative-sense RNA virus that causes severe hemorrhagic fever in humans. The matrix protein VP40 facilitates viral budding by binding to lipids in the host cell plasma membrane and driving the formation of filamentous, pleomorphic virus particles. The C-terminal domain of VP40 contains two highly-conserved cysteine residues at positions 311 and 314, but their role in the viral life cycle is unknown. We therefore investigated the properties of VP40 mutants in which the conserved cysteine residues were replaced with alanine. The C311A mutation significantly increased the affinity of VP40 for membranes containing phosphatidylserine (PS), resulting in the assembly of longer virus-like particles (VLPs) compared to wild-type VP40. The C314A mutation also increased the affinity of VP40 for membranes containing PS, albeit to a lesser degree than C311A. The double mutant behaved in a similar manner to the individual mutants. Computer modeling revealed that both cysteine residues restrain a loop segment containing lysine residues that interact with the plasma membrane, but Cys311 has the dominant role. Accordingly, the C311A mutation increases the flexibility of this membrane-binding loop, changes the profile of hydrogen bonding within VP40 and therefore binds to PS with greater affinity. This is the first evidence that mutations in VP40 can increase its affinity for biological membranes and modify the length of Ebola VLPs. The Cys311 and Cys314 residues therefore play an important role in dynamic interactions at the plasma membrane by modulating the ability of VP40 to bind PS.

Excitation of Fluorescent Lipid Probes Accelerates Supported Lipid Bilayer Formation via Photosensitized Lipid Oxidation

Fluorescent lipid probes are commonly used to label membranes of cells and model membranes like giant vesicles, liposomes, and supported lipid bilayers (SLB). Here, we show that excitation of fluorescent lipid probes with BODIPY-like conjugates results in a significant acceleration of the rupture and SLB formation process for unsaturated phospholipid vesicles on SiO₂ surfaces. The resulting SLBs also have smaller measured masses, which is indicative of a reduction in membrane thickness and/or membrane density. The excitation of fluorescent probes with NBD and Texas Red conjugates does not accelerate the SLB formation process. In the absence of fluorescent probes or light, the inclusion of oxidized phospholipids also accelerates SLB formation. The excitation-induced acceleration caused by BODIPY-like probes is eliminated when the probes are present with saturated phospholipids not susceptible to oxidation, and it is attenuated when a lipophilic antioxidant (α-tocopherol) is present. These results suggest that BODIPY-phospholipid conjugates are photosensitizers, and their excitation causes oxidation of lipid membranes, which significantly alters membrane properties.

Crosslink between lipids and acute uveitis: a lipidomic analysis

AIM

To explore the roles of phospholipids and sphingolipids in the inflammatory process of uveitis.

METHODS

Aqueous humor (AH) and the retina were obtained from endotoxin-induced uveitis (EIU) rats during the acute inflammation stage (24h after endotoxin injection). Lipids were extracted using a modified Bligh and Dyer method and subjected to mass spectrometric identification using class-specific lipid standards and ratiometric quantification. Relative intensity analysis was performed to evaluate the amount change of common lipids between the EIU and control groups.

RESULTS

Unique lipid species encompassing all five phospholipid classes were found in both control and the EIU AH and retina. Commensurate with the significantly increased level of lysophospholipids in the EIU AH and retina, we found that the ratio of lysophospholipids to total phospholipids was significantly increased too. We also detected a significant increase in 18:0 lysophosphatidylcholine levels in the EIU group (fold change =6.4 in AH and 3.8 in retina). Cer240, Cer241, and SM240 levels remarkably increased in the EIU AH. Enhanced C12 ceramide-1-phosphate (C12 C-1-P), C16 C-1-P, C24 C-1-P, and upregulated Cer160, Cer240, SM120, and SM240 were found in EIU retina. C-1-P was believed to restore homeostasis by inhibiting nuclear factor kappa B (NF-κB) activation. However, we still found elevated NF-κB levels in the EIU retina.

CONCLUSION

A variety of lipids might have played a critical role in EIU inflammation. Exogenous topical application of these protective lipids or inhibition of these pro-inflammatory lipids may be useful therapeutic strategies for the resolution of EIU.