Membrane cholesterol removal changes mechanical properties of cells and induces secretion of a specific pool of lysosomes

Microfluidic Electroporation Arrays for Investigating Electroporation-Induced Cellular Rupture Dynamics

Electroporation is pivotal in bioelectrochemistry for cellular manipulation, with prominent applications in drug delivery and cell membrane studies. A comprehensive understanding of pore generation requires an in-depth analysis of the critical pore size and the corresponding energy barrier at the onset of cell rupture. However, many studies have been limited to basic models such as artificial membranes or theoretical simulations. Challenging this paradigm, our study pioneers using a microfluidic electroporation chip array. This tool subjects live breast cancer cell species to a diverse spectrum of alternating current electric field conditions, driving electroporation-induced cell rupture. We conclusively determined the rupture voltages across varying applied voltage loading rates, enabling an unprecedented characterization of electric cell rupture dynamics encompassing critical pore radius and energy barrier. Further bolstering our investigation, we probed cells subjected to cholesterol depletion via methyl-β-cyclodextrin and revealed a strong correlation with electroporation. This work not only elucidates the dynamics of electric rupture in live cell membranes but also sets a robust foundation for future explorations into the mechanisms and energetics of live cell electroporation.

Effect of LDL Extracted from Human Plasma on Membrane Stiffness in Living Endothelial Cells and Macrophages via Scanning Ion Conductance Microscopy

Mechanical properties of living cells play a crucial role in a wide range of biological functions and pathologies, including atherosclerosis. We used low-stress Scanning Ion-Conductance Microscopy (SICM) correlated with confocal imaging and demonstrated the topographical changes and mechanical properties alterations in EA.hy926 and THP-1 exposed to LDL extracted from CVD patients' blood samples. We show that the cells stiffened in the presence of LDL, which also triggered caveolae formation. Endothelial cells accumulated less cholesterol in the form of lipid droplets in comparison to THP-1 cells based on fluorescence intensity data and biochemical analysis; however, the effect on Young's modulus is higher. The cell stiffness is closely connected to the distribution of lipid droplets along the z-axis. In conclusion, we show that the sensitivity of endothelial cells to LDL is higher compared to that of THP-1, triggering changes in the cytoskeleton and membrane stiffness which may result in the increased permeability of the intima layer due to loss of intercellular connections and adhesion.

OxLDL induces membrane structure rearrangement leading to biomechanics alteration and migration deficiency in macrophage

Cholesterol sequestration from plasma membrane has been shown to induce lipid packing disruption, causing actin cytoskeleton reorganization and polymerization, increasing cell stiffness and inducing lysosomal exocytosis in non-professional phagocytes. Similarly, oxidized form of low-density lipoprotein (oxLDL) has also been shown to disrupt lipid organization and packing in endothelial cells, leading to biomechanics alterations that interfere with membrane injury and repair. For macrophages, much is known about oxLDL effects in cell activation, cytokine production and foam cell formation. However, little is known about its impact in the organization of macrophage membrane structured domains and cellular mechanics, the focus of the present study. Treatment of bone marrow-derived macrophages (BMDM) with oxLDL not only altered membrane structure, and potentially the distribution of raft domains, but also induced actin rearrangement, diffuse integrin distribution and cell shrinkage, similarly to observed upon treatment of these cells with MβCD. Those alterations led to decreased migration efficiency. For both treatments, higher co-localization of actin cytoskeleton and GM1 was observed, indicating a similar mechanism of action involving raft-like domain dynamics. Lastly, like MβCD treatment, oxLDL also induced lysosomal spreading in BMDM. We propose that OxLDL induced re-organization of membrane/cytoskeleton complex in macrophages can be attributed to the insertion of oxysterols into the membrane, which lead to changes in lipid organization and disruption of membrane structure, similar to the effect of cholesterol depletion by MβCD treatment. These results indicate that oxLDL can induce physical alterations in the complex membrane/cytoskeleton of macrophages, leading to significant biomechanical changes that compromise cell behavior.

Child type 1 diabetes associated with mother vaginal bacteriome and mycobiome

Mother vaginal microbes contribute to microbiome of vaginally delivered neonates. Child microbiome can be associated with autoimmune diseases, such as type 1 diabetes (T1D). We collected vaginal DNA samples from 25 mothers with a vaginally delivered child diagnosed with T1D and samples from 24 control mothers who had vaginally delivered a healthy child and analyzed bacteriome and mycobiome of the samples. The total DNA of the samples was extracted, and ribosomal DNA regions (16S for bacteria, ITS2 for fungi) were amplified, followed by next-generation sequencing and machine learning. We found that alpha-diversity of bacteriome was increased (P < 0.002), whereas alpha-diversity of mycobiome was decreased (P < 0.001) in mothers with a diabetic child compared to the control mothers. Beta-diversity analysis suggested differences in mycobiomes between the mother groups (P = 0.001). Random forest models were able to effectively predict diabetes and control status of unknown samples (bacteria: 0.86 AUC, fungi: 0.96 AUC). Our data indicate several fungal genera and bacterial metabolic pathways of mother vaginal microbiome to be associated with child T1D. We suggest that early onset of T1D in a child has a relationship with altered mother vaginal microbiome and that both bacteriome and mycobiome contribute to this shift.

Cancer cells resist antibody-mediated destruction by neutrophils through activation of the exocyst complex

BACKGROUND

Neutrophils kill antibody-opsonized tumor cells using trogocytosis, a unique mechanism of destruction of the target plasma. This previously unknown cytotoxic process of neutrophils is dependent on antibody opsonization, Fcγ receptors and CD11b/CD18 integrins. Here, we demonstrate that tumor cells can escape neutrophil-mediated cytotoxicity by calcium (Ca2+)-dependent and exocyst complex-dependent plasma membrane repair.

METHODS

We knocked down EXOC7 or EXOC4, two exocyst components, to evaluate their involvement in tumor cell membrane repair after neutrophil-induced trogocytosis. We used live cell microscopy and flow cytometry for visualization of the host and tumor cell interaction and tumor cell membrane repair. Last, we reported the mRNA levels of exocyst in breast cancer tumors in correlation to the response in trastuzumab-treated patients.

RESULTS

We found that tumor cells can evade neutrophil antibody-dependent cellular cytotoxicity (ADCC) by Ca2+-dependent cell membrane repair, a process induced upon neutrophil trogocytosis. Absence of exocyst components EXOC7 or EXOC4 rendered tumor cells vulnerable to neutrophil-mediated ADCC (but not natural killer cell-mediated killing), while neutrophil trogocytosis remained unaltered. Finally, mRNA levels of exocyst components in trastuzumab-treated patients were inversely correlated to complete response to therapy.

CONCLUSIONS

Our results support that neutrophil attack towards antibody-opsonized cancer cells by trogocytosis induces an active repair process by the exocyst complex in vitro. Our findings provide insight to the possible contribution of neutrophils in current antibody therapies and the tolerance mechanism of tumor cells and support further studies for potential use of the exocyst components as clinical biomarkers.

Experimental Investigations on the Conductance of Lipid Membranes under Differential Hydrostatic Pressure

The unassisted transport of inorganic ions through lipid membranes has become increasingly relevant to an expansive range of biological phenomena. Recent simulations indicate a strong influence of a lipid membrane's curvature on its permeability, which may be part of the overall cell sensitivity to mechanical stimulation. However, most ionic permeability experiments employ a flat, uncurved lipid membrane, which disregards the physiological relevance of curvature on such investigations. To fill this gap in our knowledge, we adapted a traditional experimental system consisting of a planar lipid membrane, which we exposed to a controlled, differential hydrostatic pressure. Our electrophysiology experiments indicate a strong correlation between the changes in membrane geometry elicited by the application of pressure, as inferred from capacitance measurements, and the resulting conductance. Our experiments also confirmed the well-established influence of cholesterol addition to lipid membranes in adjusting their mechanical properties and overall permeability. Therefore, the proposed experimental system may prove useful for a better understanding of the intricate connections between membrane mechanics and adjustments of cellular functionalities upon mechanical stimulation, as well as for confirmation of predictions made by simulations and theoretical modeling.

Synthesis of plant-derived cholesterol from bisnoralcohol

Currently, the market demand of the non-animal-derived cholesterol is increasing. A novel synthetic route of producing cholesterol was developed through multiple reactions from plant-sourced and commercially available bisnoralcohol (BA). The key reaction conditions, including solvents, reaction temperatures, bases and reducing agents of the route were investigated and optimized. In this straightforward synthetic pathway of cholesterol, most of the reaction steps possess high conversions with average yields of 94%, and the overall yield is up to 74% (5 steps) from the BA. The epicholesterol and were also synthesized. This promising route offers economical and efficient strategies for potential large-scale production of plant-derived cholesterol.

Phospholipid exchange shows insulin receptor activity is supported by both the propensity to form wide bilayers and ordered raft domains

Insulin receptor (IR) is a membrane tyrosine kinase that mediates the response of cells to insulin. IR activity has been shown to be modulated by changes in plasma membrane lipid composition, but the properties and structural determinants of lipids mediating IR activity are poorly understood. Here, using efficient methyl-alpha-cyclodextrin mediated lipid exchange, we studied the effect of altering plasma membrane outer leaflet phospholipid composition upon the activity of IR in mammalian cells. After substitution of endogenous lipids with lipids having an ability to form liquid ordered (Lo) domains (sphingomyelins) or liquid disordered (Ld) domains (unsaturated phosphatidylcholines (PCs)), we found that the propensity of lipids to form ordered domains is required for high IR activity. Additional substitution experiments using a series of saturated PCs showed that IR activity increased substantially with increasing acyl chain length, which increases both bilayer width and the propensity to form ordered domains. Incorporating purified IR into alkyl maltoside micelles with increasing hydrocarbon lengths also increased IR activity, but more modestly than by increasing lipid acyl chain length in cells. These results suggest that the ability to form Lo domains as well as wide bilayer width contributes to increased IR activity. Inhibition of phosphatases showed that some of the lipid dependence of IR activity upon lipid structure reflected protection from phosphatases by lipids that support Lo domain formation. These results are consistent with a model in which a combination of bilayer width and ordered domain formation modulates IR activity via IR conformation and accessibility to phosphatases.

Effect of cell geometry in the evaluation of erythrocyte viscoelastic properties

The red blood cell membrane-cytoskeleton is a complex structure mainly responsible for giving the cell rigidity and shape. It also provides the erythrocyte with the ability to pass through narrow capillaries of the vertebrate blood circulatory system. Although the red blood cell viscoelastic properties have been extensively studied, reported experimental data differ by up to three orders of magnitude. This could be attributed to the natural cell variability, to the different techniques employed, and also to the models used for the cell response, which are highly dependent on cell geometry. Here, we use two methodologies based on optical tweezers to investigate the viscoelastic behavior of healthy human red blood cells, one applying small cell deformations (microrheology) and another imposing large deformations (tether extraction). We also establish a defocusing microscopy-based method to characterize the cell geometry and thus the erythrocyte form factor, an essential parameter that allows comparisons among the viscoelastic properties at different conditions. Moreover, for small deformations, a soft glassy rheology model is used to discuss the results, while for large deformations two surface shear moduli and one surface viscosity are determined, together with the surface tension and bending modulus of the erythrocyte membrane lipid component. We also show that F-actin is not detected in tethers, although the erythrocyte membrane has physical properties like those of other adherent cells, known to have tethers containing F-actin inside. Altogether, our results show good agreement with the reported literature and we argue that, to properly compare the viscoelastic properties of red blood cells in different situations, the task of cell geometry characterization must be accomplished. This may be especially important when the influence of agents, like the malaria parasite, induces changes in both the geometry and chemical constituents of the erythrocyte membrane. Together, the new methodologies and procedures used in this study would allow the erythrocyte community to better explore the mechanical behavior of red blood cells and may be useful to characterize erythrocyte viscoelasticity changes in several blood diseases.

Protocol to measure the membrane tension and bending modulus of cells using optical tweezers and scanning electron microscopy

The elastic properties of cell membranes, particularly the membrane tension and bending modulus, are known to be key regulators of cellular functions. Here, we present a correlative and integrated tool based on optical tweezers and scanning electron microscopy to accurately determine these properties in a variety of cell types. Although there are intrinsic difficulties associated with correlative experiments, we believe that the methods presented can be considered a suitable protocol for determining the elastic properties of cell membranes.

For complete details on the use and execution of this protocol, please refer to Soares et al. (2020).

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Protocol to obtain the membrane tension and bending modulus of cells

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Detailed procedures to measure the membrane tether force with optical tweezers

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Correlative optical tweezers-scanning electron microscopy to measure the tether radius

Measuring Intracellular Vesicle Density and Dispersion Using Fluorescence Microscopy and ImageJ/FIJI

Cell signalling, cell secretion, and plasma membrane repair are processes that critically rely on intracellular vesicles, important components of the endocytic and secretory pathways. More specifically, the strategic distribution of intracellular vesicles is important for diverse cellular processes. The method presented here is a simple, affordable, and efficient tool to analyze the distribution of intracellular vesicles such as lysosomes, endosomes, Golgi vesicles or secretory granules under different experimental conditions. The method is an accessible way to analyze the density and dispersion of intracellular vesicles by combining immunofluorescence with pixel-based quantification software (e.g., ImageJ/FIJI). This protocol can be used widely within the scientific community because it utilizes ImageJ/FIJI, an open source software that is free. By tracking fluorescent vesicles based on their position relative to cell nuclei we are able to quantify and analyze their distribution throughout the cell.

Membrane Elastic Properties During Neural Precursor Cell Differentiation

Neural precursor cells differentiate into several cell types that display distinct functions. However, little is known about how cell surface mechanics vary during the differentiation process. Here, by precisely measuring membrane tension and bending modulus, we map their variations and correlate them with changes in neural precursor cell morphology along their distinct differentiation fates. Both cells maintained in culture as neural precursors as well as those plated in neurobasal medium reveal a decrease in membrane tension over the first hours of culture followed by stabilization, with no change in bending modulus. During astrocyte differentiation, membrane tension initially decreases and then increases after 72 h, accompanied by consolidation of glial fibrillary acidic protein expression and striking actin reorganization, while bending modulus increases following observed alterations. For oligodendrocytes, the changes in membrane tension are less abrupt over the first hours, but their values subsequently decrease, correlating with a shift from oligodendrocyte marker O4 to myelin basic protein expressions and a remarkable actin reorganization, while bending modulus remains constant. Oligodendrocytes at later differentiation stages show membrane vesicles with similar membrane tension but higher bending modulus as compared to the cell surface. Altogether, our results display an entire spectrum of how membrane elastic properties are varying, thus contributing to a better understanding of neural differentiation from a mechanobiological perspective.

Kinetoplastid Membrane Protein-11 Induces Pores in Anionic Phospholipid Membranes: Effect of Cholesterol

Kinetoplastid membrane protein-11 (KMP-11), expressed in all stages of leishmanial life cycle, is considered a potential candidate for leishmaniasis vaccine. KMP-11 is found on the membrane surface of the parasite. Although the biological function of KMP-11 is unknown, we hypothesize from its sequence analysis that it may interact with the macrophage membrane and may influence the entry process of the parasite into the host cell. To validate this hypothesis, we have investigated the interaction of KMP-11 with unilamellar anionic phospholipid vesicles and explored its pore-forming activity. The decrease in negative ζ-potential of the vesicles and reduction in the fluorescence intensity of membrane-bound dye DiI C-18 suggest a strong association of KMP-11 with the membrane. The fluorescence leakage experiment as well as phase contrast microscopy shows direct evidence of KMP-11-induced pore formation in an anionic membrane. Incorporation of cholesterol into the membrane has been found to inhibit pore formation induced by KMP-11, suggesting an important role of cholesterol in leishmaniasis. Interestingly, vesicles containing only neutral phospholipid do not exhibit any tendency toward pore formation.

Direct monitoring of drug-induced mechanical response of individual cells by atomic force microscopy

Mechanical characteristics of individual cells play a vital role in many biological processes and are considered as indicators of the cells' states. Disturbances including methyl-β-cyclodextrin (MβCD) and cytochalasin D (cytoD) are known to significantly affect the state of cells, but little is known about the real-time response of single cells to these drugs in their physiological condition. Here, nanoindentation-based atomic force microscopy (AFM) was used to measure the elasticity of human embryonic kidney cells in the presence and absence of these pharmaceuticals. The results showed that depletion of cholesterol in the plasma membrane with MβCD resulted in cell stiffening whereas depolymerization of the actin cytoskeleton by cytoD resulted in cell softening. Using AFM for real-time measurements, we observed that cells mechanically responded right after these drugs were added. In more detail, the cell´s elasticity suddenly increased with increasing instability upon cholesterol extraction while it is rapidly decreased without changing cellular stability upon depolymerizing actin cytoskeleton. These results demonstrated that actin cytoskeleton and cholesterol contributed differently to the cell mechanical characteristics.

OxLDL alterations in endothelial cell membrane dynamics leads to changes in vesicle trafficking and increases cell susceptibility to injury

Plasma membrane repair (PMR) is an important process for cell homeostasis, especially for cells under constant physical stress. Repair involves a sequence of Ca²⁺-dependent events, including lysosomal exocytosis and subsequent compensatory endocytosis. Cholesterol sequestration from plasma membrane causes actin cytoskeleton reorganization and polymerization, increasing cell stiffness, which leads to exocytosis and reduction of a peripheral pool of lysosomes involved in PMR. These changes in mechanical properties are similar to those observed in cells exposed to oxidized Low Density Lipoprotein (oxLDL), a key molecule during atherosclerosis development. Using a human umbilical vein endothelial cell line (EAhY926) we evaluated the influence of mechanical modulation induced by oxLDL in PMR and its effect in endothelial fragility. Similar to MβCD (a drug capable of sequestering cholesterol) treatment, oxLDL exposure led to actin reorganization and de novo polymerization, as well as an increase in cell rigidity and lysosomal exocytosis. Additionally, for both MβCD and oxLDL treated cells, there was an initial increase in endocytic events, likely triggered by the peak of exocytosis induced by both treatments. However, no further endocytic events were observed, suggesting that constitutive endocytosis is blocked upon treatment and that the reorganized cytoskeleton function as a mechanical barrier to membrane traffic. Finally, the increase in cell rigidity renders cells more prone to mechanical injury. Together, these data show that mechanical modulation induced by oxLDL exposure not only alters membrane traffic in cells, but also makes them more susceptible to mechanical injury, which may likely contribute to the initial steps of atherosclerosis development.

Cyclodextrin triggers MCOLN1-dependent endo-lysosome secretion in Niemann-Pick type C cells

In specialized cell types, lysosome-related organelles support regulated secretory pathways, whereas in nonspecialized cells, lysosomes can undergo fusion with the plasma membrane in response to a transient rise in cytosolic calcium. Recent evidence also indicates that lysosome secretion can be controlled transcriptionally and promote clearance in lysosome storage diseases. In addition, evidence is also accumulating that low concentrations of cyclodextrins reduce the cholesterol-storage phenotype in cells and animals with the cholesterol storage disease Niemann-Pick type C, via an unknown mechanism. Here, we report that cyclodextrin triggers the secretion of the endo/lysosomal content in nonspecialized cells and that this mechanism is responsible for the decreased cholesterol overload in Niemann-Pick type C cells. We also find that the secretion of the endo/lysosome content occurs via a mechanism dependent on the endosomal calcium channel mucolipin-1, as well as FYCO1, the AP1 adaptor, and its partner Gadkin. We conclude that endo-lysosomes in nonspecialized cells can acquire secretory functions elicited by cyclodextrin and that this pathway is responsible for the decrease in cholesterol storage in Niemann-Pick C cells.

Leishmania amazonensis hijacks host cell lysosomes involved in plasma membrane repair to induce invasion in fibroblasts

Intracellular parasites of the genus Leishmania are the causative agents of leishmaniasis. The disease is transmitted by the bite of a sand fly vector which inoculates the parasite into the skin of mammalian hosts, including humans. During chronic infection the parasite lives and replicates inside phagocytic cells, notably the macrophages. An interesting but overlooked finding is that other cell types and even non-phagocytic cells have been found infected by Leishmania spp. Nevertheless, the mechanisms by which Leishmania invades such cells were not studied to date. Here we show that L. amazonensis can actively induce their own entry into fibroblasts independently of actin cytoskeleton activity, thus by a mechanism that is distinct from phagocytosis. Invasion involves subversion of host cell functions such as calcium signaling and recruitment and exocytosis of host cell lysosomes involved in plasma membrane repair.

Membrane Destabilization Induced by Lipid Species Increases Activity of Phosphorothioate-Antisense Oligonucleotides

Chemically modified antisense oligonucleotides with phosphorothioate linkages (PS-ASOs) mediate site-specific cleavage of RNA by RNase H1 and are broadly used as research and therapeutic tools. PS-ASOs can enter cells via endocytic pathways and escape from membrane-enclosed endocytic organelles to reach target RNAs. We recently found that lysobisphosphatidic acid is required for release of PS-ASOs from late endosomes. Here, we evaluated the effects of other lipids on PS-ASO intracellular trafficking and activities. We show that free fatty acids, ceramide, and cholesterol increase PS-ASO activities. Free fatty acids induced formation of lipid droplets without changing the intracellular localization of PS-ASOs in early or late endosomes. Ceramide and cholesterol did not obviously induce the formation of lipid droplets, but cholesterol caused enlargement of endosome size and volume. Although none of those lipids appeared to influence PS-ASO internalization or intracellular trafficking processes, all led to an increase in leakiness of late endosomes. Thus, the membrane destabilization induced by these lipids likely contributes to PS-ASO release from late endosomes, which, in turn, increases PS-ASO activity.

Membrane tension: A challenging but universal physical parameter in cell biology

The plasma membrane separates the interior of cells from the outside environment. The membrane tension, defined as the force per unit length acting on a cross-section of membrane, regulates many vital biological processes. In this review, we summarize the first historical findings and the latest advances, showing membrane tension as an important physical parameter in cell biology. We also discuss how this parameter must be better integrated and we propose experimental approaches for key unanswered questions.

Membrane Mechanics of Primary Afferent Neurons in the Dorsal Root Ganglia of Rats

Membrane mechanics is an important biological factor regulating many cellular functions including cell motility, intercellular and intracellular signaling, gene expression, and membrane ion channel activity. Primary afferent neurons transduce sensory information about temperature, touch, and pain. These sensory functions may be profoundly affected by the states of primary afferent neuron mechanics. However, membrane mechanics of primary afferent neurons is largely unknown. In this study, we established the optical trapping technique for determining membrane mechanics of cultured primary afferent neurons of the dorsal root ganglia (DRG). We further determined the roles of cytoskeleton and membrane lipids in DRG neuron mechanics. We found that DRG neurons had a plasma membrane tension of ∼54 pN/μm, and the tension was significantly decreased to ∼29 pN/μm by cytochalasin D treatment to disrupt actin cytoskeleton and increased to ∼79 pN/μm by methyl-β-cyclodextrin treatment to sequester membrane cholesterol. DRG neuron membrane stiffness was not significantly affected by the cytoskeleton disruption but was significantly increased after cholesterol sequestration. Our findings elucidate membrane mechanical properties of primary afferent neurons, which provide, to our knowledge, a new perspective on their sensory functions.

LAMP-2 absence interferes with plasma membrane repair and decreases T. cruzi host cell invasion

Trypanosoma cruzi enters host cells by subverting the mechanism of cell membrane repair. In this process, the parasite induces small injuries in the host cell membrane leading to calcium entry and lysosomal exocytosis, which are followed by compensatory endocytosis events that drive parasites into host cells. We have previously shown that absence of both LAMP-1 and 2, major components of lysosomal membranes, decreases invasion of T. cruzi into host cells, but the mechanism by which they interfere with parasite invasion has not been described. Here we investigated the role of these proteins in parasitophorous vacuole morphology, host cell lysosomal exocytosis, and membrane repair ability. First, we showed that cells lacking only LAMP-2 present the same invasion phenotype as LAMP1/2-/- cells, indicating that LAMP-2 is an important player during T. cruzi invasion process. Second, neither vacuole morphology nor lysosomal exocytosis was altered in LAMP-2 lacking cells (LAMP2-/- and LAMP1/2-/- cells). We then investigated the ability of LAMP-2 deficient cells to perform compensatory endocytosis upon lysosomal secretion, the mechanism by which cells repair their membrane and T. cruzi ultimately enters cells. We observed that these cells perform less endocytosis upon injury when compared to WT cells. This was a consequence of impaired cholesterol traffic in cells lacking LAMP-2 and its influence in the distribution of caveolin-1 at the cell plasma membrane, which is crucial for plasma membrane repair. The results presented here show the major role of LAMP-2 in caveolin traffic and membrane repair and consequently in T. cruzi invasion.

Inositol 1, 4, 5-trisphosphate-dependent nuclear calcium signals regulate angiogenesis and cell motility in triple negative breast cancer

Increases in nuclear calcium concentration generate specific biological outcomes that differ from those resulting from increased cytoplasmic calcium. Nuclear calcium effects on tumor cell proliferation are widely appreciated; nevertheless, its involvement in other steps of tumor progression is not well understood. Therefore, we evaluated whether nuclear calcium is essential in other additional stages of tumor progression, including key steps associated with the formation of the primary tumor or with the metastatic cascade. We found that nuclear calcium buffering impaired 4T1 triple negative breast cancer growth not just by decreasing tumor cell proliferation, but also by enhancing tumor necrosis. Moreover, nuclear calcium regulates tumor angiogenesis through a mechanism that involves the upregulation of the anti-angiogenic C-X-C motif chemokine 10 (CXCL10-IP10). In addition, nuclear calcium buffering regulates breast tumor cell motility, culminating in less cell invasion, likely due to enhanced vinculin expression, a focal adhesion structural protein. Together, our results show that nuclear calcium is essential for triple breast cancer angiogenesis and cell migration and can be considered as a promising strategic target for triple negative breast cancer therapy.

Cholesterol depletion impairs contractile machinery in neonatal rat cardiomyocytes

Cholesterol regulates numerous cellular processes. Depleting its synthesis in skeletal myofibers induces vacuolization and contraction impairment. However, little is known about how cholesterol reduction affects cardiomyocyte behavior. Here, we deplete cholesterol by incubating neonatal cardiomyocytes with methyl-beta-cyclodextrin. Traction force microscopy shows that lowering cholesterol increases the rate of cell contraction and generates defects in cell relaxation. Cholesterol depletion also increases membrane tension, Ca2+ spikes frequency and intracellular Ca2+ concentration. These changes can be correlated with modifications in caveolin-3 and L-Type Ca2+ channel distributions across the sarcolemma. Channel regulation is also compromised since cAMP-dependent PKA activity is enhanced, increasing the probability of L-Type Ca2+ channel opening events. Immunofluorescence reveals that cholesterol depletion abrogates sarcomeric organization, changing spacing and alignment of α-actinin bands due to increase in proteolytic activity of calpain. We propose a mechanism in which cholesterol depletion triggers a signaling cascade, culminating with contraction impairment and myofibril disruption in cardiomyocytes.

Influence of Membrane Receptor Lateral Diffusion on the Short-Term Depression of Acetylcholine-Induced Current in Helix Neurons

We have studied how various drugs increasing the rate of nicotinic acetylcholine receptors (nAChRs) lateral diffusion affect the depression of ACh-induced current in land snail Helix lucorum neurons responsible for defensive behavior. The acetylcholine (ACh) iontophoretic application protocol imitated the behavioral habituation protocol for the intact animal. We found that the drugs decreasing cholesterol level in cell membranes as methyl-β-cyclodextrin 1 mM and Ro 48-8071 2 µM, and polyclonal antibodies to actin-binding proteins as spectrin 5 µg/ml and merlin 2.5 µg/ml have changed the dynamic of ACh-current depression. The nAChRs lateral diffusion coefficient was obtained by fluorescence recovery after photobleaching. A curve fitting model specially created for analysis of short-term choline sensitivity depression in snail neurons helped us evaluate separately the contribution of nAChRs lateral diffusion, their endocytosis and exocytosis to observed effects during electrophysiological experiments. Taken together, we hypothesize that nAChRs lateral diffusion plays an important role in the cellular correlate of habituation in land snail Helix lucorum neurons.

Studying the effects of asymmetry on the bending rigidity of lipid membranes formed by microfluidics

In this article we detail a robust high-throughput microfluidic platform capable of fabricating either symmetric or asymmetric giant unilamellar vesicles (GUVs) and characterise the mechanical properties of their membranes.

Cholesterol Alters the Dynamics of Release in Protein Independent Cell Models for Exocytosis

Neurons communicate via an essential process called exocytosis. Cholesterol, an abundant lipid in both secretory vesicles and cell plasma membrane can affect this process. In this study, amperometric recordings of vesicular dopamine release from two different artificial cell models created from a giant unilamellar liposome and a bleb cell plasma membrane, show that with higher membrane cholesterol the kinetics for vesicular release are decelerated in a concentration dependent manner. This reduction in exocytotic speed was consistent for two observed modes of exocytosis, full and partial release. Partial release events, which only occurred in the bleb cell model due to the higher tension in the system, exhibited amperometric spikes with three distinct shapes. In addition to the classic transient, some spikes displayed a current ramp or plateau following the maximum peak current. These post spike features represent neurotransmitter release from a dilated pore before constriction and show that enhancing membrane rigidity via cholesterol adds resistance to a dilated pore to re-close. This implies that the cholesterol dependent biophysical properties of the membrane directly affect the exocytosis kinetics and that membrane tension along with membrane rigidity can influence the fusion pore dynamics and stabilization which is central to regulation of neurochemical release.

Profiling of individual human red blood cells under osmotic stress using defocusing microscopy

We use a quantitative phase imaging technique, defocusing microscopy (DM), to measure morphological, chemical, and mechanical parameters of individual red blood cells (RBCs) immersed in solutions with different osmolalities. We monitor the RBCs’ radius, volume, surface area, sphericity index, and hemoglobin content and concentration. The complete shape of cells is recovered and the effects of their adhesion to the glass substrate are observed. Finally, membrane fluctuation measurements give us information about the cells deformability.

Anti-erythrocyte antibodies may contribute to anaemia in Plasmodium vivax malaria by decreasing red blood cell deformability and increasing erythrophagocytosis

Background

Plasmodium vivax accounts for the majority of human malaria infections outside Africa and is being increasingly associated in fatal outcomes with anaemia as one of the major complications. One of the causes of malarial anaemia is the augmented removal of circulating non-infected red blood cells (nRBCs), an issue not yet fully understood. High levels of auto-antibodies against RBCs have been associated with severe anaemia and reduced survival of nRBCs in patients with falciparum malaria. Since there are no substantial data about the role of those antibodies in vivax malaria, this study was designed to determine whether or not auto-antibodies against erythrocytes are involved in nRBC clearance. Moreover, the possible immune mechanisms elicited by them that may be associated to induce anaemia in P. vivax infection was investigated.

Methods

Concentrations of total IgG were determined by sandwich ELISA in sera from clinically well-defined groups of P. vivax-infected patients with or without anaemia and in healthy controls never exposed to malaria, whereas the levels of specific IgG to nRBCs were determined by cell-ELISA. Erythrophagocytosis assay was used to investigate the ability of IgGs purified from each studied pooled sera in enhancing nRBC in vitro clearance by THP-1 macrophages. Defocusing microscopy was employed to measure the biomechanical modifications of individual nRBCs opsonized by IgGs purified from each group.

Results

Anaemic patients had higher levels of total and specific anti-RBC antibodies in comparison to the non-anaemic ones. Opsonization with purified IgG from anaemic patients significantly enhanced RBCs in vitro phagocytosis by THP-1 macrophages. Auto-antibodies purified from anaemic patients decreased the nRBC dynamic membrane fluctuations suggesting a possible participation of such antibodies in the perturbation of erythrocyte flexibility and morphology integrity maintenance.

Conclusions

These findings revealed that vivax-infected patients with anaemia have increased levels of IgG auto-antibodies against nRBCs and that their deposition on the surface of non-infected erythrocytes decreases their deformability, which, in turn, may enhance nRBC clearance by phagocytes, contributing to the anaemic outcome. These data provide insights into the immune mechanisms associated with vivax malaria anaemia and may be important to the development of new therapy and vaccine strategies.

Rab27b is Involved in Lysosomal Exocytosis and Proteolipid Protein Trafficking in Oligodendrocytes

Myelination by oligodendrocytes in the central nervous system requires coordinated exocytosis and endocytosis of the major myelin protein, proteolipid protein (PLP). Here, we demonstrated that a small GTPase, Rab27b, is involved in PLP trafficking in oligodendrocytes. We showed that PLP co-localized with Rab27b in late endosomes/lysosomes in oligodendrocytes. Short hairpin-mediated knockdown of Rab27b not only reduced lysosomal exocytosis but also greatly diminished the surface expression of PLP in oligodendrocytes. In addition, knockdown of Rab27b reduced the myelin-like membranes induced by co-culture of oligodendrocytes and neurons. Our data suggest that Rab27b is involved in myelin biogenesis by regulating PLP transport from late endosomes/lysosomes to the cell membrane in oligodendrocytes.

Cholesterol Extraction from Cell Membrane by Graphene Nanosheets: A Computational Study

The health risk associated with high cholesterol levels in the human body has motivated intensive efforts to lower them by using specialized drugs. However, little research has been reported on utilizing nanomaterials to extract extra cholesterol from living tissues. Graphene possesses great potential for cholesterol extraction from cell membranes due to its distinct porous structure and outstanding surface adhesion. Here we employ dissipative dynamic simulations to explore pathways for cholesterol extraction from a cell membrane by a sheet of graphene using a coarse-grained graphene nanosheets (CGGN) model. We first demonstrate that the self-assembly process among a single layer of graphene and a group of randomly distributed cholesterol molecules in the aqueous environment, which provides a firm foundation for graphene-cholesterol interactions and the dynamic cholesterol extraction process from the cell membrane. Simulations results show that graphene is capable of removing cholesterol molecules from the bilayer membrane. The interaction between graphene and cholesterol molecules plays an important role in determining the amount of extracted cholesterol molecules from the cell membrane. Our findings open up a promising avenue to exploit the capability of graphene for biomedical applications.

Pathogenesis, Epidemiology, Diagnosis and Clinical Aspects of Smith-Lemli-Opitz Syndrome

INTRODUCTION

Smith-Lemli-Opitz Syndrome (SLOS) is a malformation syndrome inherited in an autosomal recessive fashion. It is due to a metabolic defect in the conversion of 7-dehydrocholesterol to cholesterol, which leads to an accumulation of 7-dehydrocholesterol and frequently a deficiency of cholesterol. The syndrome is characterized by typical dysmorphic facial features, multiple malformations, and intellectual disability.

AREAS COVERED

In this paper we provide an overview of the clinical phenotype and discuss how the manifestations of the syndrome vary depending on the age of the patients. We then explore the underlying biochemical defect and pathophysiological alterations that may contribute to the many disease manifestations. Subsequently we explore the epidemiology and succinctly discuss population genetics as they relate to SLOS. The next section presents the diagnostic possibilities. Thereafter, the treatment and management as is standard of care are presented.

EXPERT OPINION

Even though the knowledge of the underlying molecular mutations and the biochemical alterations is being rapidly accumulated, there is currently no efficacious therapy addressing neurological dysfunction. We discuss the difficulty of treating this disorder, which manifests as a combination of a malformation syndrome and an inborn error of metabolism. A very important factor in developing new therapies is the need to rigorously establish efficacy in controlled trials.

Mechanisms of graphyne-enabled cholesterol extraction from protein clusters

Functionalized graphyne provides a novel vehicle for cholesterol removal from protein clusters by molecular dynamics simulations.

Trypasonoma cruzi uses a specific subset of host cell lysosomes for cell invasion

Trypanosoma cruzi is an intracellular parasite that depends on host cell lysosome recruitment and fusion for cell infection. Recently, we have shown that host cells present two differentially regulated lysosome pools. Treatment with methyl-beta cyclodextrin, a drug able to sequester cholesterol from plasma membrane, triggers the exocytosis of peripheral lysosomes, while treatment with Latrunculin-A, an actin depolymerizing drug, recruits a more internal pool. In this work we aimed to study which pool is used by the T. cruzi during invasion. We have shown that invasion is impaired when cells are previously treated with methyl-beta cyclodextrin, but not with Latrunculin-A, indicating that T. cruzi uses the cortical pool for invasion.