Polyglutamine aggregates impair lipid membrane integrity and enhance lipid membrane rigidity

Polyanionic lipopolysaccharides (LPS) play an important role in regulating the permeability of the outer membrane (OM) of Gram-negative bacteria. Impairment of the LPS-enriched OM is essential in initiating the bactericidal activity of polymyxins. We are interested in how colistin (polymyxin E) affects the membrane permeability of LPS/phospholipid bilayers. Our vesicle leakage experiment showed that colistin binding enhanced bilayer permeability; the maximum increase in the bilayer permeability was positively correlated with the LPS fraction. Addition of magnesium ions abolished the effect of LPS in enhancing bilayer permeabilization. To describe the vesicle leakage behavior from a structural perspective, we performed liquid atomic force microscopy (AFM) measurements on planar lipid bilayers. We found that colistin caused the formation of nano- and macroclusters that protruded from the bilayer by ∼2 nm. Moreover, cluster development was promoted by increasing the fraction of LPS or colistin concentration but inhibited by magnesium ions. To explain our experimental data, we proposed a lipid clustering model where colistin binds to LPS to form large-scale complexes segregated from zwitterionic phospholipids. The discontinuity (and thickness mismatch) at the edge of LPS–colistin clusters will create a passage that allows solutes to permeate through. The proposed model is consistent with all data obtained from our leakage and AFM experiments. Our results of LPS-dependent membrane restructuring provided useful insights into the mechanism that could be used by polymyxins in impairing the permeability barrier of the OM of Gram-negative bacteria.

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“…We have previously used this method to evaluate changes in bilayer permeability caused by different compounds. 38−40…”

Section: Resultsmentioning

confidence: 99%

Lipopolysaccharide-Dependent Membrane Permeation and Lipid Clustering Caused by Cyclic Lipopeptide Colistin

2018

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“…But the exact mechanism of hIAPP-induced membrane disruption is far from clear. And numerous models have been described during recent years [ 38 – 41 ]. A report concluded that soluble oligomers from several types of amyloids, including hIAPP, specifically increase lipid bilayer conductance, while the soluble low molecular weight species have no effect, suggesting that this may represent the common primary mechanism of pathogenesis in amyloid-related diseases, such as AD, PD and diabetes [ 42 ].…”

Section: Discussionmentioning

confidence: 99%

Lipid accelerating the fibril of islet amyloid polypeptide aggravated the pancreatic islet injury in vitro and in vivo

Gao

Wang

et al. 2018

Lipids Health Dis

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BackgroundThe fibrillation of islet amyloid polypeptide (IAPP) triggered the amyloid deposition, then enhanced the loss of the pancreatic islet mass. However, it is not clear what factor is the determinant in development of the fibril formation. The aim of this study is to investigate the effects of lipid on IAPP fibril and its injury on pancreatic islet.MethodsThe fibril form of human IAPP (hIAPP) was tested using thioflavin-T fluorescence assay and transmission electron microscope technology after incubated with palmitate for 5 h at 25 °C. The cytotoxicity of fibril hIAPP was evaluated in INS-1 cells through analyzing the leakage of cell membrane and cell apoptosis. Type 2 diabetes mellitus (T2DM) animal model was induced with low dose streptozotocin combined the high-fat diet feeding for two months in rats. Plasma biochemistry parameters were measured before sacrificed. Pancreatic islet was isolated to evaluate their function.ResultsThe results showed that co-incubation of hIAPP and palmitate induced more fibril form. Fibril hIAPP induced cell lesions including cell membrane leakage and cell apoptosis accompanied insulin mRNA decrease in INS-1 cell lines. In vivo, Plasma glucose, triglyceride, rIAPP and insulin increased in T2DM rats compared with the control group. In addition, IAPP and insulin mRNA increased in pancreatic islet of T2DM rats. Furthermore, T2DM induced the reduction of insulin receptor expression and cleaved caspase-3 overexpression in pancreatic islet.ConclusionsResults in vivo and in vitro suggested that lipid and IAPP plays a synergistic effect on pancreatic islet cell damage, which implicated in enhancing the IAPP expression and accelerating the fibril formation of IAPP.

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“…Experimental procedure has been described elsewhere. 21–23 Briefly, mica supported planar bilayers are formed by injecting SUVs into the AFM liquid cell using a syringe pump. Once a complete bilayer is formed (~20 min), 10 mM HEPES at pH 7.0 is injected to remove excess SUVs.…”

Section: Methodsmentioning

confidence: 99%

Kinetic Defects Induced by Melittin in Model Lipid Membranes: A Solution Atomic Force Microscopy Study

Pan

Khadka

2016

J. Phys. Chem. B

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Quantitative characterization of membrane defects (pores) is important for elucidating molecular basis of many membrane active peptides. We study kinetic defects induced by melittin in vesicular and planar lipid bilayers. Fluorescence spectroscopy measurements indicate that melittin induces time-dependent calcein leakage. Solution atomic force microscopy (AFM) is used to visualize melittin induced membrane defects. After initial equilibration, the most probable defect radius is ~3.8 nm in 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) bilayers. Unexpectedly, defects become larger with longer incubation, accompanied by substantial shape transformation. The initial defect radius is ~4.7 nm in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers. Addition of 30mol% cholesterol to DOPC bilayers suppresses defect kinetics, although the inhibitory impact is negated by longer incubation. Overall, the kinetic rate of defect development follows DLPC > DOPC > DOPC/cholesterol. Kinetic defects are also observed when anionic lipids are present. Based on the observation that defects can occupy as large as 40% of the bilayer surface, we propose a kinetic defect growth model. We also study the effect of melittin on the phase behavior of DOPC/egg-sphingomyelin/cholesterol bilayers. We find that melittin initially suppresses or eliminates liquid-ordered (Lo) domains; Lo domains gradually emerge and become the dominant species with longer incubation. Defects in phase coexisting bilayers have a most probable radius of ~5 nm, and are exclusively localized in the liquid-disordered (Ld) phase. Our experimental data highlight that melittin induced membrane defects are not static; conversely, spontaneous defect growth is intrinsically associated with membrane permeabilization exerted by melittin.

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Polyglutamine aggregates impair lipid membrane integrity and enhance lipid membrane rigidity

Cited by 19 publications

References 63 publications

Lipopolysaccharide-Dependent Membrane Permeation and Lipid Clustering Caused by Cyclic Lipopeptide Colistin

Lipopolysaccharide-Dependent Membrane Permeation and Lipid Clustering Caused by Cyclic Lipopeptide Colistin

Lipid accelerating the fibril of islet amyloid polypeptide aggravated the pancreatic islet injury in vitro and in vivo

Kinetic Defects Induced by Melittin in Model Lipid Membranes: A Solution Atomic Force Microscopy Study

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