Cytometry of raft and caveola membrane microdomains: from flow and imaging techniques to high throughput screening assays

The Antipsychotic Risperidone Alters Dihydroceramide and Ceramide Composition and Plasma Membrane Function in Leukocytes In Vitro and In Vivo

Atypical or second-generation antipsychotics are used in the treatment of psychosis and behavioral problems in older persons with dementia. However, these pharmaceutical drugs are associated with an increased risk of stroke in such patients. In this study, we evaluated the effects of risperidone treatment on phospholipid and sphingolipid composition and lipid raft function in peripheral blood mononuclear cells (PBMCs) of older patients (mean age >88 years). The results showed that the levels of dihydroceramides, very-long-chain ceramides, and lysophosphatidylcholines decreased in PBMCs of the risperidone-treated group compared with untreated controls. These findings were confirmed by in vitro assays using human THP-1 monocytes. The reduction in the levels of very-long-chain ceramides and dihydroceramides could be due to the decrease in the expression of fatty acid elongase 3, as observed in THP-1 monocytes. Moreover, risperidone disrupted lipid raft domains in the plasma membrane of PBMCs. These results indicated that risperidone alters phospholipid and sphingolipid composition and lipid raft domains in PBMCs of older patients, potentially affecting multiple signaling pathways associated with these membrane domains.

Sex hormone-binding globulin provides a novel entry pathway for estradiol and influences subsequent signaling in lymphocytes via membrane receptor

The complex effects of estradiol on non-reproductive tissues/cells, including lymphoid tissues and immunocytes, have increasingly been explored. However, the role of sex hormone binding globulin (SHBG) in the regulation of these genomic and non-genomic actions of estradiol is controversial. Moreover, the expression of SHBG and its internalization by potential receptors, as well as the influence of SHBG on estradiol uptake and signaling in lymphocytes has remained unexplored. Here, we found that human and mouse T cells expressed SHBG intrinsically. In addition, B lymphoid cell lines as well as both primary B and T lymphocytes bound and internalized external SHBG, and the amount of plasma membrane-bound SHBG decreased in B cells of pregnant compared to non-pregnant women. As potential mediators of this process, SHBG receptor candidates expressed by lymphocytes were identified in silico, including estrogen receptor (ER) alpha. Furthermore, cell surface-bound SHBG was detected in close proximity to membrane ERs while highly colocalizing with lipid rafts. The SHBG-membrane ER interaction was found functional since SHBG promoted estradiol uptake by lymphocytes and subsequently influenced Erk1/2 phosphorylation. In conclusion, the SHBG-SHBG receptor-membrane ER complex participates in the rapid estradiol signaling in lymphocytes, and this pathway may be altered in B cells in pregnant women.

Using Zebrafish for High-Throughput Screening of Novel Cardiovascular Drugs

Cardiovascular diseases remain a major challenge for modern drug discovery. The diseases are chronic, complex, and the result of sophisticated interactions between genetics and environment involving multiple cell types and a host of systemic factors. The clinical events are often abrupt, and the diseases may be asymptomatic until a highly morbid event. Target selection is often based on limited information, and though highly specific agents are often identified in screening, their final efficacy is often compromised by unanticipated systemic responses, a narrow therapeutic index, or substantial toxicities. Our understanding of complexity of cardiovascular disease has grown dramatically over the past 2 decades, and the range of potential disease mechanisms now includes pathways previously thought only tangentially involved in cardiac or vascular disease. Despite these insights, the majority of active cardiovascular agents derive from a remarkably small number of classes of agents and target a very limited number of pathways. These agents have often been used initially for particular indications and then discovered serendipitously to have efficacy in other cardiac disorders or in a manner unrelated to their original mechanism of action. In this review, the rationale for in vivo screening is described, and the utility of the zebrafish for this approach and for complementary work in functional genomics is discussed. Current limitations of the model in this setting and the need for careful validation in new disease areas are also described. An overview is provided of the complex mechanisms underlying most clinical cardiovascular diseases, and insight is offered into the limits of single downstream pathways as drug targets. The zebrafish is introduced as a model organism, in particular for cardiovascular biology. Potential approaches to overcoming the hurdles to drug discovery in the face of complex biology are discussed, including in vivo screening of zebrafish genetic disease models.

A dynamic network of estrogen receptors in murine lymphocytes: fine-tuning the immune response

The actual level of circulating estrogen (17β-estradiol, E2) has a serious impact on regulation of diverse immune cell functions, where their classical cytoplasmic receptors, ERα and ERβ, act as nuclear transcriptional regulators of multiple target genes. There is growing evidence, however, for rapid, "non-nuclear" regulatory effects of E2 on lymphocytes. Such effects are likely mediated by putative membrane-associated receptor(s) (mER), but the mechanistic details and the involved signaling pathways still remained largely unknown because of their complexity. Here, we show that in lymphocytes, mERs can signalize themselves, and upon ligation, they are able to coordinate translocation of other E2Rs to the PM. Our data firmly imply existence of a complex, dynamic network of at least seven ER forms in murine lymphocytes: cytoplasmic and membrane-linked forms of ERα, ERβ, or GPR30 and a mER that can receive extracellular E2 signals. The latter mERs are likely palmitoylated, as they are enriched in lipid-raft microdomains, and their E2 binding is also cholesterol dependent. The data also support that ligation of mERs can induce rapid regulatory signals to lymphocytes and then internalize and let the E2 liberate in lysosomes. In addition, they can dynamically control the cell-surface linkage of other cytoplasmic ERs. As demonstrated by the differential effects of mER or cytoplasmic ER ligation on the proliferation of activated T and B lymphocytes, such a dynamic E2R network can be considered as a tool to manage accommodation/fine-tuning of lymphocytes to rapidly changing hormone levels.

Epigallocatechin 3-O-gallate induces 67 kDa laminin receptor-mediated cell death accompanied by downregulation of ErbB proteins and altered lipid raft clustering in mammary and epidermoid carcinoma cells

Since the administration of synthetic medicines is associated with drug resistance and undesired side effects, utilization of natural compounds could be an alternative and complementary modality to inhibit or prevent the development of tumors. Epigallocatechin 3-O-gallate (EGCG, 1), the major flavan component of green tea, and genistein (2), a soy isoflavonoid, are known to have chemopreventive and chemotherapeutic effects against cancer. This study demonstrated that both flavonoids inhibit cell proliferation, an effect enhanced under serum-free conditions. Compound 1, but not 2, induced downregulation of ErbB1 and ErbB2 in mammary and epidermoid carcinoma cells, and its inhibitory effect on cell viability was mediated by the 67 kDa laminin receptor (67LR). While 1 was superior in inducing cell death, 2 was more efficient in arresting the tumor cells in the G2/M phase. Furthermore, number and brightness analysis revealed that 1 decreased the homoclustering of a lipid raft marker, glycosylphosphatidylinositol-anchored GFP, and it also reduced the co-localization between lipid rafts and 67LR. The main conclusion made is that the primary target of 1 may be the lipid raft component of the plasma membrane followed by secondary changes in the expression of ErbB proteins. Compound 2, on the other hand, must have other unidentified targets.

The productive entry pathway of HIV-1 in macrophages is dependent on endocytosis through lipid rafts containing CD4

Macrophages constitute an important reservoir of HIV-1 infection, yet HIV-1 entry into these cells is poorly understood due to the difficulty in genetically manipulating primary macrophages. We developed an effective genetic approach to manipulate the sub-cellular distribution of CD4 in macrophages, and investigated how this affects the HIV-1 entry pathway. Pluripotent Stem Cells (PSC) were transduced with lentiviral vectors designed to manipulate CD4 location and were then differentiated into genetically modified macrophages. HIV-1 infection of these cells was assessed by performing assays that measure critical steps of the HIV-1 lifecycle (fusion, reverse transcription, and expression from HIV-1 integrants). Expression of LCK (which tethers CD4 to the surface of T cells, but is not normally expressed in macrophages) in PSC-macrophages effectively tethered CD4 at the cell surface, reducing its normal endocytic recycling route, and increasing surface CD4 expression 3-fold. This led to a significant increase in HIV-1 fusion and reverse transcription, but productive HIV-1 infection efficiency (as determined by reporter expression from DNA integrants) was unaffected. This implies that surface-tethering of CD4 sequesters HIV-1 into a pathway that is unproductive in macrophages. Secondly, to investigate the importance of lipid rafts (as detergent resistant membranes - DRM) in HIV-1 infection, we generated genetically modified PSC-macrophages that express CD4 mutants known to be excluded from DRM. These macrophages were significantly less able to support HIV-1 fusion, reverse-transcription and integration than engineered controls. Overall, these results support a model in which productive infection by HIV-1 in macrophages occurs via a CD4-raft-dependent endocytic uptake pathway.

Role of lipid rafts in liver health and disease

Liver diseases are an increasingly common cause of morbidity and mortality; new approaches for investigation of mechanisms of liver diseases and identification of therapeutic targets are emergent. Lipid rafts (LRs) are specialized domains of cellular membranes that are enriched in saturated lipids; they are small, mobile, and are key components of cellular architecture, protein partition to cellular membranes, and signaling events. LRs have been identified in the membranes of all liver cells, parenchymal and non-parenchymal; more importantly, LRs are active participants in multiple physiological and pathological conditions in individual types of liver cells. This article aims to review experimental-based evidence with regard to LRs in the liver, from the perspective of the liver as a whole organ composed of a multitude of cell types. We have gathered up-to-date information related to the role of LRs in individual types of liver cells, in liver health and diseases, and identified the possibilities of LR-dependent therapeutic targets in liver diseases.

Cardiac Arrhythmia: In vivo screening in the zebrafish to overcome complexity in drug discovery

IMPORTANCE OF THE FIELD: Cardiac arrhythmias remain a major challenge for modern drug discovery. Clinical events are paroxysmal, often rare and may be asymptomatic until a highly morbid complication. Target selection is often based on limited information and though highly specific agents are identified in screening, the final efficacy is often compromised by unanticipated systemic responses, a narrow therapeutic index and substantial toxicities. AREAS COVERED IN THIS REVIEW: Our understanding of complexity of arrhythmogenesis has grown dramatically over the last two decades, and the range of potential disease mechanisms now includes pathways previously thought only tangentially involved in arrhythmia. This review surveys the literature on arrhythmia mechanisms from 1965 to the present day, outlines the complex biology underlying potentially each and every rhythm disturbance, and highlights the problems for rational target identification. The rationale for in vivo screening is described and the utility of the zebrafish for this approach and for complementary work in functional genomics is discussed. Current limitations of the model in this setting and the need for careful validation in new disease areas are also described. WHAT THE READER WILL GAIN: An overview of the complex mechanisms underlying most clinical arrhythmias, and insight into the limits of ion channel conductances as drug targets. An introduction to the zebrafish as a model organism, in particular for cardiovascular biology. Potential approaches to overcoming the hurdles to drug discovery in the face of complex biology including in vivo screening of zebrafish genetic disease models. TAKE HOME MESSAGE: In vivo screening in faithful disease models allows the effects of drugs on integrative physiology and disease biology to be captured during the screening process, in a manner agnostic to potential drug target or targets. This systematic strategy bypasses current gaps in our understanding of disease biology, but emphasizes the importance of the rigor of the disease model.

Identifying the spatial distribution of vitamin E, pulmonary surfactant and membrane lipids in cells and tissue by confocal Raman microscopy

Every organ compromises of several different cell types. When studying the effects of a chosen compound within this organ or tissue uptake, localisation, metabolism, and the effect itself can be expected to differ between cells. Using the example of Vitamin E in pulmonary tissue we introduce confocal Raman Microscopy as a superior method to localise lipid-soluble compounds within tissues and cells. We describe the analyses of vitamin E, its oxidation products, and metabolites as well as pulmonary surfactant phospholipids in fixed lung tissue sections. Examples of main structural membrane lipids (PC, cholesterol) and an example of a lipid-signalling molecule (ceramide) are also included. Confocal Raman microscopy is a non-destructive optical method of analysing chemical and physical composition of solids, liquids, gases, gels, and solutions. The method is rich in information allowing discrimination of chemically similar molecules (including geometric isomers) and sensitive monitoring of subtle physical interactions. Additionally, Raman spectroscopy is relatively insensitive to water allowing the analysis of aqueous solutions and suspensions typical in biochemistry. In contrast, Raman spectroscopy is sensitive to non-polar molecules making it ideal for lipidomics research.

Disease-specific biomarker discovery by aptamers

RNA and DNA aptamers developed by an in vitro selection process, Systematic Evolution of Ligands by EXponential enrichment (SELEX), comprise a novel class of high-affinity and specific capture agents, which can be easily modified for cytometry and in vivo applications. A novel application of this technique (Cell SELEX) explores the expression of cell surface epitopes that differ between two given cell types or between healthy and diseased cells. Using whole cells as targets, aptamer libraries can be identified that bind to biomarkers expressed by target cells and not by any other cells. Aptamers have been developed that specifically interact with cell surface epitopes of trypanosomes or distinguish between the differences in molecular signature of somatic and cancer cells. Aside from its use for target cell identification by image and flow cytometry and laser-scanning microscopy, aptamers can be used for ligand-mediated purification and identification of their binding proteins in target cell membranes. In this review, we discuss an approach for the development of aptamers targeting parasite-derived surface proteins of Trypanosoma and Plasmodium.

The density of GM1-enriched lipid rafts correlates inversely with the efficiency of transfection mediated by cationic liposomes

Although cationic liposome-mediated transfection has become a standard procedure, the mechanistic details of the process are unknown. It has been suggested that endocytic uptake of lipoplexes is efficient, and transfectability is largely determined by later steps. In this article, we stained GM1-enriched membrane microdomains, a subclass of lipid rafts, with subunit B of cholera toxin and correlated transfection efficiency with their density by quantitatively evaluating microscopic images. We found a strong anticorrelation between the density of GM1-enriched membrane microdomains and the efficacy of transfection monitored by measuring the expression level of GFP in different cell lines transfected by lipofection using two different transfection agents. These findings imply that GM1-enriched membrane microdomains interfere with the process of lipofection. The blocked step must be endocytosis since the accumulation of fluorescently labeled plasmids was lower in cells with high content of GM1-enriched membrane microdomains. Such a correlation was not observed in cells transfected by electroporation. By comparing the efficiency of lipofection in several cell lines we found that those with a high density of GM1-enriched membrane microdomains were the most resistant to transfection. We conclude that the inhibition of lipofection by GM1-enriched membrane microdomains is a general rule, and that endocytosis of lipoplexes can be rate limiting in cells with high density of GM1-enriched membrane rafts.

Lipid rafts and caveolae and their role in compartmentation of redox signaling

Membrane (lipid) rafts and caveolae, a subset of rafts, are cellular domains that concentrate plasma membrane proteins and lipids involved in the regulation of cell function. In addition to providing signaling platforms for G-protein-coupled receptors and certain tyrosine kinase receptors, rafts/caveolae can influence redox signaling. This review discusses molecular characteristics of and methods to study rafts/caveolae, determinants that contribute to the localization of molecules in these entities, an overview of signaling molecules that show such localization, and the contribution of rafts/caveolae to redox signaling. Of particular note is the evidence that endothelial nitric oxide synthase (eNOS), NADPH oxygenase, and heme oxygenase, along with other less well-studied redox systems, localize in rafts and caveolae. The precise basis for this localization and the contribution of raft/caveolae-localized redox components to physiology and disease are important issues for future studies.