Maturation of Monocyte-Derived DCs Leads to Increased Cellular Stiffness, Higher Membrane Fluidity, and Changed Lipid Composition
Jennifer J. Lühr,
Nils Alex,
Lukas Amon,
Martin Kräter,
Markéta Kubánková,
Erdinc Sezgin,
Christian H. K. Lehmann,
Lukas Heger,
Gordon F. Heidkamp, et al.
Frontiers in Immunology
11
590121
(2020)
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Dendritic cells (DCs) are professional antigen-presenting cells of the immune system. Upon sensing pathogenic material in their environment, DCs start to mature, which includes cellular processes, such as antigen uptake, processing and presentation, as well as upregulation of costimulatory molecules and cytokine secretion. During maturation, DCs detach from peripheral tissues, migrate to the nearest lymph node, and find their way into the correct position in the net of the lymph node microenvironment to meet and interact with the respective T cells. We hypothesize that the maturation of DCs is well prepared and optimized leading to processes that alter various cellular characteristics from mechanics and metabolism to membrane properties. Here, we investigated the mechanical properties of monocyte-derived dendritic cells (moDCs) using real-time deformability cytometry to measure cytoskeletal changes and found that mature moDCs were stiffer compared to immature moDCs. These cellular changes likely play an important role in the processes of cell migration and T cell activation. As lipids constitute the building blocks of the plasma membrane, which, during maturation, need to adapt to the environment for migration and DC-T cell interaction, we performed an unbiased high-throughput lipidomics screening to identify the lipidome of moDCs. These analyses revealed that the overall lipid composition was significantly changed during moDC maturation, even implying an increase of storage lipids and differences of the relative abundance of membrane lipids upon maturation. Further, metadata analyses demonstrated that lipid changes were associated with the serum low-density lipoprotein (LDL) and cholesterol levels in the blood of the donors. Finally, using lipid packing imaging we found that the membrane of mature moDCs revealed a higher fluidity compared to immature moDCs. This comprehensive and quantitative characterization of maturation associated changes in moDCs sets the stage for improving their use in clinical application.
High-precision protein-tracking with interferometric scattering microscopy
Richard W. Taylor,
Cornelia Holler,
Reza Gholami Mahmoodabadi,
Michelle Küppers,
Houman Mirzaalian Dastjerdi,
Vasily Zaburdaev,
Alexandra Schambony,
Vahid Sandoghdar
Frontiers in Cell and Developmental Biology
8
590158
(2020)
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The mobility of proteins and lipids within the cell, sculpted oftentimes by the organisation of the membrane, reveals a great wealth of information on the function and interaction of these molecules as well as the membrane itself. Single particle tracking has proven to be a vital tool to study the mobility of individual molecules and unravel details of their behaviour. Interferometric scattering (iSCAT) microscopy is an emerging technique well suited for visualising the diffusion of gold nanoparticle-labelled membrane proteins to a spatial and temporal resolution beyond the means of traditional fluorescent labels. We discuss the applicability of interferometric single particle tracking (iSPT) microscopy to investigate the minutia in the motion of a protein through measurements visualising the mobility of the epidermal growth factor receptor in various biological scenarios on the live cell.
Exogenous ethanol induces a metabolic switch that prolongs the survival of Caenorhabditis elegansdauer larva and enhances its resistance to desiccation
Damla Kaptan,
Sider Penkov,
Xingyu Zhang,
Vamshidhar R. Gade,
Bharath Kumar Raghuraman,
Roberta Galli,
Julio L. Sampaio,
Robert Haase,
Edmund Koch, et al.
The dauer larva ofCaenorhabditis elegans, destined to survive long periods of food scarcity and harsh environment, does not feed and has a very limited exchange of matter with the exterior. It was assumed that the survival time is determined by internal energy stores. Here, we show that ethanol can provide a potentially unlimited energy source for dauers by inducing a controlled metabolic shift that allows it to be metabolized into carbohydrates, amino acids, and lipids. Dauer larvae provided with ethanol survive much longer and have greater desiccation tolerance. On the cellular level, ethanol prevents the deterioration of mitochondria caused by energy depletion. By modeling the metabolism of dauers of wild-type and mutant strains with and without ethanol, we suggest that the mitochondrial health and survival of an organism provided with an unlimited source of carbon depends on the balance between energy production and toxic product(s) of lipid metabolism.
Liquid Phase Separation Controlled by pH
Omar Adame-Arana,
Christoph A. Weber,
Vasily Zaburdaev,
Jacques Prost,
Frank Julicher
Biophysical Journal
119
(8)
1590-1605
(2020)
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We present a minimal model to study the effects of pH on liquid phase separation of macromolecules. Our model describes a mixture composed of water and macromolecules that exist in three different charge states and have a tendency to phase separate. This phase separation is affected by pH via a set of chemical reactions describing protonation and deprotonation of macromolecules, as well as self-ionization of water. We consider the simple case in which interactions are captured by Flory-Huggins interaction parameters corresponding to Debye screening lengths shorter than a nanometer, which is relevant to proteins inside biological cells under physiological conditions. We identify the conjugate thermodynamic variables at chemical equilibrium and discuss the effective free energy at fixed pH. First, we study phase diagrams as a function of macromolecule concentration and temperature at the isoelectric point of the macromolecules. We find a rich variety of phase diagram topologies, including multiple critical points, triple points, and first-order transition points. Second, we change the pH relative to the isoelectric point of the macromolecules and study how phase diagrams depend on pH. We find that these phase diagrams as a function of pH strongly depend on whether oppositely charged macromolecules or neutral macromolecules have a stronger tendency to phase separate. One key finding is that we predict the existence of a reentrant behavior as a function of pH. In addition, our model predicts that the region of phase separation is typically broader at the isoelectric point. This model could account for both in vitro phase separation of proteins as a function of pH and protein phase separation in yeast cells for pH values close to the isoelectric point of many cytosolic proteins.
Exogenous ethanol induces a metabolic switch that prolongs the survival of Caenorhabditis elegansdauer larva and enhances its resistance to desiccation
Damla Kaptan,
Sider Penkov,
Xingyu Zhang,
Vamshidhar R. Gade,
Bharath Kumar Raghuraman,
Roberta Galli,
Julio L. Sampaio,
Robert Haase,
Edmund Koch, et al.
The dauer larva ofCaenorhabditis elegans, destined to survive long periods of food scarcity and harsh environment, does not feed and has a very limited exchange of matter with the exterior. It was assumed that the survival time is determined by internal energy stores. Here, we show that ethanol can provide a potentially unlimited energy source for dauers by inducing a controlled metabolic shift that allows it to be metabolized into carbohydrates, amino acids, and lipids. Dauer larvae provided with ethanol survive much longer and have greater desiccation tolerance. On the cellular level, ethanol prevents the deterioration of mitochondria caused by energy depletion. By modeling the metabolism of dauers of wild-type and mutant strains with and without ethanol, we suggest that the mitochondrial health and survival of an organism provided with an unlimited source of carbon depends on the balance between energy production and toxic product(s) of lipid metabolism.
Ultrahigh-speed imaging of rotational diffusion on a lipid bilayer
Mahdi Mazaheri,
Jens Ehrig,
Alexey Shkarin,
Vasily Zaburdaev,
Vahid Sandoghdar
We studied the rotational and translational diffusion of a single gold nanorod linked to a supported lipid bilayer with ultrahigh temporal resolution of two microseconds. By using a home-built polarization-sensitive dark-field microscope, we recorded particle trajectories with lateral precision of three nanometers and rotational precision of four degrees. The large number of trajectory points in our measurements allows us to characterize the statistics of rotational diffusion with unprecedented detail. Our data show apparent signatures of anomalous diffusion such as sublinear scaling of the mean-squared angular displacement and negative values of angular correlation function at small lag times. However, a careful analysis reveals that these effect stem from the residual noise contributions and confirms normal diffusion. Our experimental approach and observations can be extended to investigate diffusive processes of anisotropic nanoparticles in other fundamental systems such as cellular membranes or other two-dimensional fluids.
Contact
Immunophysics Division Prof. Vasily Zaburdaev Principal Investigator
Max-Planck-Zentrum für Physik und Medizin Kussmaulallee 2 Room 02.116 91054 Erlangen, Germany +49 9131 8284 102
