Addition of lysophospholipids with large head groups to cells inhibits Shiga toxin binding

Dimethyl sulfoxide as a novel therapy in a murine model of acute lung injury

INTRODUCTION

The endothelial glycocalyx on the luminal surface of endothelial cells contributes to the permeability barrier of the pulmonary vasculature. Dimethyl sulfoxide (DMSO) has a disordering effect on plasma membranes, which prevents the formation of ordered membrane domains important in the shedding of the endothelial glycocalyx. We hypothesized that DMSO would protect against protein leak by preserving the endothelial glycocalyx in a murine model of acute respiratory distress syndrome (ARDS).

METHODS

C57BL/6 mice were given ARDS via intratracheally administered lipopolysaccharide (LPS). Dimethyl sulfoxide (220 mg/kg) was administered intravenously for 4 days. Animals were sacrificed postinjury day 4 after bronchoalveolar lavage (BAL). Bronchoalveolar lavage cell counts and protein content were quantified. Lung sections were stained with fluorescein isothiocyanate-labeled wheat germ agglutinin to quantify the endothelial glycocalyx. Human umbilical vein endothelial cells (HUVECs) were exposed to LPS. Endothelial glycocalyx was measured using fluorescein isothiocyanate-labeled wheat germ agglutinin, and co-immunoprecipitation was performed to measure interaction between sheddases and syndecan-1.

RESULTS

Dimethyl sulfoxide treatment resulted in greater endothelial glycocalyx staining intensity in the lung when compared with sham (9,641 vs. 36,659 arbitrary units, p < 0.001). Total BAL cell counts were less for animals receiving DMSO (6.93 × 10 6 vs. 2.49 × 10 6 cells, p = 0.04). The treated group had less BAL macrophages (189.2 vs. 76.9 cells, p = 0.02) and lymphocytes (527.7 vs. 200.0 cells, p = 0.02). Interleukin-6 levels were lower in DMSO treated. Animals that received DMSO had less protein leak in BAL (1.48 vs. 1.08 μg/μL, p = 0.02). Dimethyl sulfoxide prevented LPS-induced endothelial glycocalyx loss in HUVECs and reduced the interaction between matrix metalloproteinase 16 and syndecan-1.

CONCLUSION

Systemically administered DMSO protects the endothelial glycocalyx in the pulmonary vasculature, mitigating pulmonary capillary leak after acute lung injury. Dimethyl sulfoxide also results in decreased inflammatory response. Dimethyl sulfoxide reduced the interaction between matrix metalloproteinase 16 and syndecan-1 and prevented LPS-induced glycocalyx damage in HUVECs. Dimethyl sulfoxide may be a novel therapeutic for ARDS.

Succinate metabolism and membrane reorganization drives the endotheliopathy and coagulopathy of traumatic hemorrhage

Acute hemorrhage commonly leads to coagulopathy and organ dysfunction or failure. Recent evidence suggests that damage to the endothelial glycocalyx contributes to these adverse outcomes. The physiological events mediating acute glycocalyx shedding are undefined, however. Here, we show that succinate accumulation within endothelial cells drives glycocalyx degradation through a membrane reorganization-mediated mechanism. We investigated this mechanism in a cultured endothelial cell hypoxia-reoxygenation model, in a rat model of hemorrhage, and in trauma patient plasma samples. We found that succinate metabolism by succinate dehydrogenase mediates glycocalyx damage through lipid oxidation and phospholipase A2-mediated membrane reorganization, promoting the interaction of matrix metalloproteinase 24 (MMP24) and MMP25 with glycocalyx constituents. In a rat hemorrhage model, inhibiting succinate metabolism or membrane reorganization prevented glycocalyx damage and coagulopathy. In patients with trauma, succinate levels were associated with glycocalyx damage and the development of coagulopathy, and the interaction of MMP24 and syndecan-1 was elevated compared to healthy controls.

Biological functions of bacterial lysophospholipids

Lysophospholipids (LPLs) are lipid-derived metabolic intermediates in the cell membrane. The biological functions of LPLs are distinct from their corresponding phospholipids. In eukaryotic cells LPLs are important bioactive signaling molecules that regulate many important biological processes, but in bacteria the function of LPLs is still not fully defined. Bacterial LPLs are usually present in cells in very small amounts, but can strongly increase under certain environmental conditions. In addition to their basic function as precursors in membrane lipid metabolism, the formation of distinct LPLs contributes to the proliferation of bacteria under harsh circumstances or may act as signaling molecules in bacterial pathogenesis. This review provides an overview of the current knowledge of the biological functions of bacterial LPLs including lysoPE, lysoPA, lysoPC, lysoPG, lysoPS and lysoPI in bacterial adaptation, survival, and host-microbe interactions.

HPLC–(Q)-TOF-MS-Based Study of Plasma Metabolic Profile Differences Associated with Age in Pediatric Population Using an Animal Model

A deep knowledge about the biological development of children is essential for appropriate drug administration and dosage in pediatrics. In this sense, the best approximation to study organ maturation is the analysis of tissue samples, but it requires invasive methods. For this reason, surrogate matrices should be explored. Among them, plasma emerges as a potential alternative since it represents a snapshot of global organ metabolism. In this work, plasma metabolic profiles from piglets of different ages (newborns, infants, and children) obtained by HPLC–(Q)-TOF-MS at positive and negative ionization modes were studied. Improved clustering within groups was achieved using multiblock principal component analysis compared to classical principal component analysis. Furthermore, the separation observed among groups was better resolved by using partial least squares-discriminant analysis, which was validated by bootstrapping and permutation testing. Thanks to univariate analysis, 13 metabolites in positive and 21 in negative ionization modes were found to be significant to discriminate the three groups of piglets. From these features, an acylcarnitine and eight glycerophospholipids were annotated and identified as metabolites of interest. The findings indicate that there is a relevant change with age in lipid metabolism in which lysophosphatidylcholines and lysophoshatidylethanolamines play an important role.

The Protein Toxins Ricin and Shiga Toxin as Tools to Explore Cellular Mechanisms of Internalization and Intracellular Transport

Protein toxins secreted by bacteria and found in plants can be threats to human health. However, their extreme toxicity can also be exploited in different ways, e.g., to produce hybrid toxins directed against cancer cells and to study transport mechanisms in cells. Investigations during the last decades have shown how powerful these molecules are as tools in cell biological research. Here, we first present a partly historical overview, with emphasis on Shiga toxin and ricin, of how such toxins have been used to characterize processes and proteins of importance for their trafficking. In the second half of the article, we describe how one can now use toxins to investigate the role of lipid classes for intracellular transport. In recent years, it has become possible to quantify hundreds of lipid species using mass spectrometry analysis. Thus, it is also now possible to explore the importance of lipid species in intracellular transport. The detailed analyses of changes in lipids seen under conditions of inhibited toxin transport reveal previously unknown connections between syntheses of lipid classes and demonstrate the ability of cells to compensate under given conditions.

Therapeutic Strategies to Protect the Central Nervous System against Shiga Toxin from Enterohemorrhagic Escherichia coli

Infection with Shiga toxin-producing Escherichia coli (STEC) may cause hemorrhagic colitis, hemolytic uremic syndrome (HUS) and encephalopathy. The mortality rate derived from HUS adds up to 5% of the cases, and up to 40% when the central nervous system (CNS) is involved. In addition to the well-known deleterious effect of Stx, the gram-negative STEC releases lipopolysaccharides (LPS) and may induce a variety of inflammatory responses when released in the gut. Common clinical signs of severe CNS injury include sensorimotor, cognitive, emotional and/or autonomic alterations. In the last few years, a number of drugs have been experimentally employed to establish the pathogenesis of, prevent or treat CNS injury by STEC. The strategies in these approaches focus on: 1) inhibition of Stx production and release by STEC, 2) inhibition of Stx bloodstream transport, 3) inhibition of Stx entry into the CNS parenchyma, 4) blockade of deleterious Stx action in neural cells, and 5) inhibition of immune system activation and CNS inflammation. Fast diagnosis of STEC infection, as well as the establishment of early CNS biomarkers of damage, may be determinants of adequate neuropharmacological treatment in time.

Proteomics and Lipidomics Investigations to Decipher the Behavior of Willaertia magna C2c Maky According to Different Culture Modes

Willaertia magna C2c Maky is a free-living amoeba that has demonstrated its ability to inhibit the intracellular multiplication of some Legionella pneumophila strains, which are pathogenic bacteria inhabiting the aquatic environment. The Amoeba, an industry involved in the treatment of microbiological risk in the water and plant protection sectors, has developed a natural biocide based on the property of W. magna to manage the proliferation of the pathogen in cooling towers. In axenic liquid medium, amoebas are usually cultivated in adhesion on culture flask. However, we implemented a liquid culture in suspension using bioreactors in order to produce large quantities of W. magna. In order to investigate the culture condition effects on W. magna, we conducted a study based on microscopic, proteomics and lipidomics analyzes. According to the culture condition, amoeba exhibited two different phenotypes. The differential proteomics study showed that amoebas seemed to promote the lipid metabolism pathway in suspension culture, whereas we observed an upregulation of the carbohydrate pathway in adherent culture. Furthermore, we observed an over-regulation of proteins related to the cytoskeleton for W. magna cells grown in adhesion. Regarding the lipid analysis, suspension and adhesion cell growth showed comparable lipid class compositions. However, the differential lipid analysis revealed differences that confirmed cell phenotype differences observed by microscopy and predicted by proteomics. Overall, this study provides us with a better insight into the biology and molecular processes of W. magna in different culture lifestyles.

Diacylglycerol kinase and phospholipase D inhibitors alter the cellular lipidome and endosomal sorting towards the Golgi apparatus

The membrane lipids diacylglycerol (DAG) and phosphatidic acid (PA) are important second messengers that can regulate membrane transport by recruiting proteins to the membrane and by altering biophysical membrane properties. DAG and PA are involved in the transport from the Golgi apparatus to endosomes, and we have here investigated whether changes in these lipids might be important for regulation of transport to the Golgi using the protein toxin ricin. Modulation of DAG and PA levels using DAG kinase (DGK) and phospholipase D (PLD) inhibitors gave a strong increase in retrograde ricin transport, but had little impact on ricin recycling or degradation. Inhibitor treatment strongly affected the endosome morphology, increasing endosomal tubulation and size. Furthermore, ricin was present in these tubular structures together with proteins known to regulate retrograde transport. Using siRNA to knock down different isoforms of PLD and DGK, we found that several isoforms of PLD and DGK are involved in regulating ricin transport to the Golgi. Finally, by performing lipidomic analysis we found that the DGK inhibitor gave a weak, but expected, increase in DAG levels, while the PLD inhibitor gave a strong and unexpected increase in DAG levels, showing that it is important to perform lipidomic analysis when using inhibitors of lipid metabolism.

Verotoxin Receptor-Based Pathology and Therapies

Verotoxin, VT (aka Shiga toxin,Stx) is produced by enterohemorrhagic E. coli (EHEC) and is the key pathogenic factor in EHEC-induced hemolytic uremic syndrome (eHUS-hemolytic anemia/thrombocytopenia/glomerular infarct) which can follow gastrointestinal EHEC infection, particularly in children. This AB5 subunit toxin family bind target cell globotriaosyl ceramide (Gb₃), a glycosphingolipid (GSL) (aka CD77, pk blood group antigen) of the globoseries of neutral GSLs, initiating lipid raft-dependent plasma membrane Gb₃ clustering, membrane curvature, invagination, scission, endosomal trafficking, and retrograde traffic via the TGN to the Golgi, and ER. In the ER, A/B subunits separate and the A subunit hijacks the ER reverse translocon (dislocon-used to eliminate misfolded proteins-ER associated degradation-ERAD) for cytosolic access. This property has been used to devise toxoid-based therapy to temporarily block ERAD and rescue the mutant phenotype of several genetic protein misfolding diseases. The A subunit avoids cytosolic proteosomal degradation, to block protein synthesis via its RNA glycanase activity. In humans, Gb₃ is primarily expressed in the kidney, particularly in the glomerular endothelial cells. Here, Gb₃ is in lipid rafts (more ordered membrane domains which accumulate GSLs/cholesterol) whereas renal tubular Gb₃ is in the non-raft membrane fraction, explaining the basic pathology of eHUS (glomerular endothelial infarct). Females are more susceptible and this correlates with higher renal Gb₃ expression. HUS can be associated with encephalopathy, more commonly following verotoxin 2 exposure. Gb₃ is expressed in the microvasculature of the brain. All members of the VT family bind Gb₃, but with varying affinity. VT2e (pig edema toxin) binds Gb₄ preferentially. Verotoxin-specific therapeutics based on chemical analogs of Gb₃, though effective in vitro, have failed in vivo. While some analogs are effective in animal models, there are no good rodent models of eHUS since Gb₃ is not expressed in rodent glomeruli. However, the mouse mimics the neurological symptoms more closely and provides an excellent tool to assess therapeutics. In addition to direct cytotoxicity, other factors including VT–induced cytokine release and aberrant complement cascade, are now appreciated as important in eHUS. Based on atypical HUS therapy, treatment of eHUS patients with anticomplement antibodies has proven effective in some cases. A recent switch using stem cells to try to reverse, rather than prevent VT induced pathology may prove a more effective methodology.

Phospholipases in neuronal function: A role in learning and memory?

Despite the human brain being made of nearly 60% fat, the vast majority of studies on the mechanisms of neuronal communication which underpin cognition, memory and learning, primarily focus on proteins and/or (epi)genetic mechanisms. Phospholipids are the main component of all cellular membranes and function as substrates for numerous phospholipid-modifying enzymes, including phospholipases, which release free fatty acids (FFAs) and other lipid metabolites that can alter the intrinsic properties of the membranes, recruit and activate critical proteins, and act as lipid signalling molecules. Here, we will review brain specific phospholipases, their roles in membrane remodelling, neuronal function, learning and memory, as well as their disease implications. In particular, we will highlight key roles of unsaturated FFAs, particularly arachidonic acid, in neurotransmitter release, neuroinflammation and memory. In light of recent findings, we will also discuss the emerging role of phospholipase A₁ and the creation of saturated FFAs in the brain.

Lysophosphatidylinositols, from Cell Membrane Constituents to GPR55 Ligands

Lysophosphatidylinositols (LPIs) are membrane constituents that alter the properties of said membranes. However, recent data showing that the once orphan receptor, GPR55, can act as a receptor for LPIs has sparked a renewed interest in LPIs as bioactive lipids. As evidence supporting the importance of LPIs and/or GPR55 is continuously accumulating and because LPI levels are altered in a number of pathologies such as obesity and cancer, the coming years should bring new, exciting discoveries to this field. In this review, we discuss the recent work on LPIs and on their molecular target, the GPR55 receptor. First, we summarize the metabolism of LPIs before outlining the cellular pathways activated by GPR55. Then, we review the actions of LPIs and GPR55 that could have potential pharmacological or therapeutic applications in several pathophysiological settings, such as cancer, obesity, pain, and inflammation.

Exogenous lysophospholipids with large head groups perturb clathrin-mediated endocytosis

In this study, we have investigated how clathrin-dependent endocytosis is affected by exogenously added lysophospholipids (LPLs). Addition of LPLs with large head groups strongly inhibits transferrin (Tf) endocytosis in various cell lines, while LPLs with small head groups do not. Electron and total internal reflection fluorescence microscopy (EM and TIRF) reveal that treatment with lysophosphatidylinositol (LPI) with the fatty acyl group C18:0 leads to reduced numbers of invaginated clathrin-coated pits (CCPs) at the plasma membrane, fewer endocytic events per membrane area and increased lifetime of CCPs. Also, endocytosis of Tf becomes dependent on actin upon LPI treatment. Thus, our results demonstrate that one can regulate the kinetics and properties of clathrin-dependent endocytosis by addition of LPLs in a head group size- and fatty acyl-dependent manner. Furthermore, studies performed with optical tweezers show that less force is required to pull membrane tubules outwards from the plasma membrane when LPI is added to the cells. The results are in agreement with the notion that insertion of LPLs with large head groups creates a positive membrane curvature which might have a negative impact on events that require plasma membrane invagination, while it may facilitate membrane bending toward the cell exterior.