The Stability of Lipid Rafts-Like Micro-Domains Is Dependent on the Available Amount of Cholesterol

Lipid rafts are sterol and sphingolipid rich membrane domains that possibly may play roles in multiple cellular processes. These domains are still the matter of debate and it is still unknown by which mechanism if any and organisms promote their formation. This study centers on the ease of in vitro formation of lipid rafts-like structures as it relates to the relative availability of sphingolipids, phospholipids, cholesterol, and membrane proteins. Following a 12 h incubation period, isolation and extraction of the lipid rafts-like assemblies, the composition of the structures was evaluated using HPLC. Cholesterol and sphingomyelin were detected at 206 nm and phosphatidylcholine was detected at 254 nm. Identification of lactose permease, a typical membrane protein, was done using FTIR. The thermal stability of the produced structures was also determined. Results show that the addition of cholesterol significantly increased both the amount of insoluble lipid rafts-like structures and their stability, and that the availability of a minimum amount of sphingolipid was necessary to produce larger amounts of more stable structures. However, the addition of phospholipids hindered the formation of lipid rafts-like assemblies and those formed were generally less stable.

Emodin suppresses LPS-induced proinflammatory responses and nuclear factor-B activation by disruption of lipid rafts and TLR-4 recruitment in endothelial cells

Emodin [1,3,8-Trihydroxy-6-methylanthraquinone] has been reported to exhibit vascular anti-inflammatory properties.However,the relevant anti-inflammatory mechanisms are not well understood.The present study was design to explore the molecular target(s) of emodin

Toy model that explains the regulation of cholesterol on lipid rafts

Cholesterol,as a common lipid on mammalian cell membranes,plays an important role in the formation of lipid rafts.Recent experiments suggest that the strength of cholesterol's regulation on lipid rafts can be affected by the length of the unsaturated phospholipid acyl chain on the membrane.In order to understand this observation,a simplified toy model containing three different molecules is proposed in this paper,where the tail length of phospholipids is considered.This model shows the regulation of membrane cholesterol on the phase separation of the lipid mixture and the formation of nano-domains,and also suggests that the configuration entropy of phospholipid tails is an essential factor.

Single virus tracking of Ebola virus entry through lipid rafts in living host cells

Ebola virus(EBOV)is one of the most pathogenic viruses in humans which can cause a lethal hemorrhagic fever.Understanding the cellular entry mechanisms of EBOV can promote the development of new therapeutic strategies to control virus replication and spread.It has been known that EBOV virions bind to factors expressed at the host cell surface.Subsequently,the virions are internalized by a macropinocytosis-like process,followed by being trafficked through early and late endosomes.Recent researches indicate that the entry of EBOV into cells requires integrated and functional lipid rafts.Whilst lipid rafts have been hypothesized to play a role in virus entry,there is a current lack of supporting data.One major technical hurdle is the lack of effective approaches for observing viral entry.To provide evidence on the involvement of lipid rafts in the entry process of EBOV,we generated the fluorescently labeled Ebola virus like particles(VLPs),and utilized single-particle tracking(SPT)to visualize the entry of fluorescent Ebola VLPs in live cells and the interaction of Ebola VLPs with lipid rafts.In this study,we demonstrate the compartmentalization of Ebola VLPs in lipid rafts during entry process,and inform the essential function of lipid rafts for the entry of Ebola virus.As such,our study provides evidence to show that the raft integrity is critical for Ebola virus pathogenesis and that lipid rafts can serve as potential targets for the development of novel therapeutic strategies.

Linking Lipid Metabolism with Cell Transformation and Tumor Progression

Carbohydrates,lipids,and proteins are the three major nutrients required by the human body.The lipids,comprising triglycerides,phospholipids,and sterols,provide energy and essential fatty acids for the body,and are required for the growth and maintenance of human cells and tissues.A variety of lipid molecules and their intermediates are involved in cell signaling and inflammation,and have been reported to promote tumor transformation and progression.Fatty acid biosynthetic enzymes are also involved in the lipid metabolism of tumors.Dyslipidemia is closely related to many solid tumors,and may both play a role in both tumorigenesis and be a consequence of tumor development.Therefore,abnormal lipid metabolism is strongly associated with tumor transformation and progression.This review discusses the signaling pathways,related genes,enzymes,and inflammatory cell factors involved in tumor lipid metabolism,as well as the roles of dyslipidemia in tumor transformation and progression.We believe the information provided will serve as valuable reference highlighting molecules that can be targeted to improve the treatment of tumors.

Membrane lipid raft organization during cotton fiber development

Background:Cotton fiber is a single-celled seed trichome that originates from the ovule epidermis.It is an excellent model for studying cell elongation.Along with the elongation of cotton fiber cell,the plasma membrane is also extremely expanded.Despite progress in understanding cotton fiber cell elongation,knowledge regarding the relationship of plasma membrane in cotton fiber cell development remains elusive.Methods:The plasma membrane of cotton fiber cells was marked with a low toxic fluorescent dye,di-4-ANEPPDHQ,at different stages of development.Fluorescence images were obtained using a confocal laser scanning microscopy.Subsequently,we investigated the relationship between lipid raft activity and cotton fiber development by calculating generalized polarization(GP values)and dual-channel ratio imaging.Results:We demonstrated that the optimum dyeing conditions were treatment with 3μmol·L-1 di-4-ANEPPDHQ for 5 min at room temperature,and the optimal fluorescence images were obtained with 488 nm excitation and500–580 nm and 620–720 nm dual channel emission.First,we examined lipid raft organization in the course of fiber development.The GP values were high in the fiber elongation stage(5–10 DPA,days past anthesis)and relatively low in the initial(0 DPA),secondary cell wall synthesis(20 DPA),and stable synthesis(30 DPA)stages.The GP value peaked in the 10 DPA fiber,and the value in 30 DPA fiber was the lowest.Furthermore,we examined the differences in lipid raft activity in fiber cells between the short fiber cotton mutant,Li-1,and its wild-type.The GP values of the Li-1 mutant fiber were lower than those of the wild type fiber at the elongation stage,and the GP values of 10 DPA fibers were lower than those of 5 DPA fibers in the Li-1 mutant.Conclusions:We established a system for examining membrane lipid raft activity in cotton fiber cells.We verified that lipid raft activity exhibited a low-high-low change regularity during the development of cotton fiber cell,and the pattern was disrupted in the short lint fiber Li-1 mutant,suggesting that membrane lipid order and lipid raft activity are closely linked to fiber cell development.

Real-time detection of LMP1/LMP1 interaction in MβCD-induced apoptosis of nasopharyngeal carcinoma cells using FRET method

Latent mermbrane protein 1(LMP1)is known as an oncoprotein in nasopharyngeal carcinoma(NPC)cells,which is considered to have a strong association with growth,invasion and metastasis of NPC cells through lipid rafts.Met hy-A-cyclodextrin(M3CD)can disrupt lipid rafts through cholesterol depletion.In this study,we revealed that MICD induced apoptosis in two kinds of NPC cells including CNE1 cells,a LMP1 negative nasopharyngeal squamous carcinoma cell line,and CNE1-LMP1 cells,a LMP1-positive nasopharyngeal squamous carcinoma cell line.Furthermore,the impact of MBCD on LMP1 was investigated by fuorescence resonance energy transfer(FRET)method in NPC cells.Synchronized tempo spatial and spectral detection of LMP1/LMP1 interaction were performed using fluorescence microscope and spectrograph.FRET efficiency indicated that LMP1/LMP1 interaction gradully enhanced after M9CD treatment.MTT assays showed that M8CD caused strong cytotoxicity in CNE1 cells,but cauused relatively weaker cytotoxicity in CNE1-LMP1 cells,which indicated that LMP1 may regulate sensitivity of NPC cells to MBCD.Then,detection of cleaved caspase-3 in two kinds of NPC cells indicated that LMP1 may inhibit activation of caspase 3.These results strongly suggested that MBCD can induce apoptosis of NPC cells,but enhancing of LMP1/LMP1 interaction may likely resist apoptosis through inhibiting cleavage of caspase-3.

Cholesterol synthesis inhibition or depletion in axon regeneration

Cholesterol is biosynthesized by all animal cells. Beyond its metabolic role in steroidogenesis, it is enriched in the plasma membrane where it has key structural and regulatory functions. Cholesterol is thus presumably important for post-injury axon regrowth, and this notion is supported by studies showing that impairment of local cholesterol reutilization impeded regeneration. However, several studies have also shown that statins, inhibitors of 3-hydroxy-3-methylglutaryl-Co A reductase, are enhancers of axon regeneration, presumably acting through an attenuation of the mevalonate isoprenoid pathway and consequent reduction in protein prenylation. Several recent reports have now shown that cholesterol depletion, as well as inhibition of cholesterol synthesis per se, enhances axon regeneration. Here, I discussed these findings and propose some possible underlying mechanisms. The latter would include possible disruptions to axon growth inhibitor signaling by lipid raft-localized receptors, as well as other yet unclear neuronal survival signaling process enhanced by cholesterol lowering or depletion.

New insight into the oncogenic mechanism of the retroviral oncoprotein Tax

Human T cell leukemia virus type 1(HTLV-1),an etio-logical factor that causes adult T cell leukemia and lym-phoma(ATL),infects over 20 million people worldwide.About 1 million of HTLV-1-infected patients develop ATL,a highly aggressive non-Hodgkin's lymphoma without an effective therapy.The pX region of the HTLV-1 viral genome encodes an oncogenic protein,Tax,which plays a central role in transforming CD4+ T lymphocytes by deregulating oncogenic signaling pathways and promoting cell cycle progression.Expression of Tax following viral entry is critical for promoting survival and proliferation of human T cells and is required for initiation of oncogenesis.Tax exhibits diverse functions in host cells,and this oncoprotein primarily targets IκB kinase complex in the cytoplasm,resulting in persistent activation of NF-κB and upregulation of its responsive gene expressions that are crucial for T cell survival and cell cycle progression.We here review recent advances for the pathological roles of Tax in modulating IκB kinase activity.We also discuss our recent observation that Tax connects the IκB kinase complex to autophagy pathways.Understanding Tax-mediated pathogenesis will provide insights into development of new therapeutics in controlling HTLV-1-associated diseases.

Multi-functional vesicles improve Helicobacter pylori eradication by a comprehensive strategy based on complex pathological microenvironment

Helicobacter pylori(H.pylori),creating a global infection rate over 50%,presents great challenges in clinical therapies due to its complex pathological microenvironment in vivo.To improve the eradication efficacy,herein we fabricated a pharmaceutical vesicle RHL/Cl-Ch-cal where cholesterol-PEG,calcitriol and first-line antibiotic clarithromycin were co-loaded in the rhamnolipid-composed outer lipid layer.RHL/Cl-Ch-cal could quickly penetrate through gastric mucus layer to reach H.pylori infection sites,and then effectively destroyed the architecture of H.pylori biofilms,killed dispersed H.pylori and inhibited the re-adhesion of residual bacteria(called biofilms eradication tetralogy).Moreover,RHL/Cl-Ch-cal activated the host immune response to H.pylori by replenishing cholesterol to repair lipid raft on the cell membrane of host epithelial cells.Finally,RHL/Cl-Ch-cal killed the intracellular H.pylori through recovering the lysosomal acidification and assisting degradation.In experiments,RHL/Cl-Ch-cal demonstrated prominent anti-H.pylori efficacy in the classical H.pylori-infected mice model.Therefore,the study provides a“comprehensive attack”strategy for anti-H.pylori therapies including biofilms eradication tetralogy,immune activation and intracellular bacteria killing.

Overexpression of sigma-1 receptor inhibits ADAM10 and ADAM17 mediated shedding in vitro

The sigma-1 receptor is a molecular chaperone protein highly enriched in the brain.Recent studies linked it to many diseases,such as drug addition,Alzheimer’s disease,stroke,depression,and even cancer.Sigma-1 receptor is enriched in lipid rafts,which are membrane microdomains essential in signaling processes.One of those signaling processes is ADAM17-and ADAM10-dependent ectodomain shedding.By using an alkaline phosphatase tagged substrate reporter system,we have shown that ADAM10-dependent BTC shedding was very sensitive to both membrane lipid component change and sigma-1 receptor agonist DHEAS treatment while ADAM17-dependent HB-EGF shedding was not;and overexpression of sigma-1 receptor diminished ADAM17-and ADAM10-dependent shedding.Our results indicate that sigma-1 receptor plays an important role in modifying the function of transmembrane proteases.

Plasma membrane calcium ATPase 4b inhibits nitric oxide generation through calcium-induced dynamic interaction with neuronal nitric oxide synthase

The activation and deactivation of Ca^(2+)- and calmodulindependent neuronal nitric oxide synthase (nNOS) in the central nervous system must be tightly controlled to prevent excessive nitric oxide (NO) generation. Considering plasma membrane calcium ATPase (PMCA) is a key deactivator of nNOS, the present investigation aims to determine the key events involved in nNOS deactivation of by PMCA in living cells to maintain its cellular context. Using time-resolved Förster resonance energy transfer (FRET), we determined the occurrence of Ca^(2+)-induced protein-protein interactions between plasma membrane calcium ATPase 4b (PMCA4b) and nNOS in living cells. PMCA activation significantly decreased the intracellular Ca 2+ concentrations ([Ca^(2+)]_(i)), which deactivates nNOS and slowdowns NO synthesis. Under the basal [Ca^(2+)]_(i) caused by PMCA activation, no protein-protein interactions were observed between PMCA4b and nNOS. Furthermore, both the PDZ domain of nNOS and the PDZ-binding motif of PMCA4b were essential for the protein-protein interaction. The involvement of lipid raft microdomains on the activity of PMCA4b and nNOS was also investigated. Unlike other PMCA isoforms, PMCA4 was relatively more concentrated in the raft fractions. Disruption of lipid rafts altered the intracellular localization of PMCA4b and affected the interaction between PMCA4b and nNOS, which suggest that the unique lipid raft distribution of PMCA4 may be responsible for its regulation of nNOS activity. In summary, lipid rafts may act as platforms for the PMCA4b regulation of nNOS activity and the transient tethering of nNOS to PMCA4b is responsible for rapid nNOS deactivation.