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Matthias Weiss - One of the best experts on this subject based on the ideXlab platform.
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Anisotropic and Anomalous Diffusion in Mitotic Cells
Biophysical Journal, 2016Co-Authors: Matthias WeissAbstract:Protein diffusion in crowded Intracellular Fluids is a crucial determinant of many vital biochemical pathways.Frequently an anomalous diffusion of macromolecules in the cytoplasm and nucleoplasm of eukaryotic cells has been reported, and associated changes in biochemical reactions have been discussed in some detail [1].Here we show that different degrees of crowding combined with an obstructed and anomalous diffusion are key determinants of protein exchange between cytoplasm and nucleoplasm during nuclear envelope breakdown (NEB) at the onset of mitosis [2]. After NEB, a contiguous nucleo-cytoplasmic fluid is established that features an anisotropically varying anomalous diffusion of macromolecules during metaphase [3]: Diffusion appears less anomalous along the mitotic spindle axis as compared to perpendicular directions. As a consequence, the long-time diffusion of macromolecules preferentially points along the spindle axis, leading to a prolonged residence of macromolecules in the spindle region. The observed anisotropic diffusion is proposed to support the dynamic formation of a dynamic spindle matrix that controls and guides later steps in mitosis.[1] Weiss, Int. Rev. Cell Mol. Biol., 307, 383-417 (2014).[2] Schweizer, Pawar, Weiss & Maiato, J. Cell Biol. 210, 695 (2015).[3] Pawar, Donth & Weiss, Curr. Biol. 24, 1905 (2014).
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Anisotropic Diffusion of Macromolecules in the Contiguous Nucleocytoplasmic Fluid during Eukaryotic Cell Division
Current Biology, 2014Co-Authors: Nisha Pawar, Claudia Donth, Matthias WeissAbstract:Summary Character and rapidity of protein diffusion in Intracellular Fluids are key determinants of the dynamics and steady state of a plethora of biochemical reactions [1, 2]. So far, an anomalous diffusion in cytoplasmic Fluids with viscoelastic and even glassy characteristics has been reported in a variety of organisms on several length scales and timescales [3–6]. Here, we show that the contiguous fluid of former cytoplasm and nucleoplasm features an anisotropically varying diffusion of macromolecules during eukaryotic cell division. In metaphase, diffusion in the contiguous nucleocytoplasmic fluid appears less anomalous along the spindle axis as compared to perpendicular directions. As a consequence, the long-time diffusion of macromolecules preferentially points along the spindle axis, leading to prolonged residence of macromolecules in the spindle region. Based on our experimental data, we suggest that anisotropic diffusion facilitates the encounter and interaction of spindle-associated proteins, e.g., during the formation of a dynamic spindle matrix [7].
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Insights Into The Microscopic Origin Of Anomalous Diffusion From Crowded Solutions
Biophysical Journal, 2009Co-Authors: Jedrzej Szymanski, Matthias WeissAbstract:Subdiffusive motion of tracer molecules has been observed in many crowded environments, ranging from polymer and protein solutions to Intracellular Fluids. Yet, a clear understanding of the microscopic origins of subdiffusive motion and the variation of the anomaly in crowded media is still missing. To address this point, we have studied the diffusion of tracer molecules in crowded solutions with varying composition using fluorescenc correlation spectroscopy (FCS). Aiming at capturing the essential processes that lead to anomalous diffusion, we observed that none of the artificial mixtures yielded the degree of subdiffusion that has been observed for Intracellular Fluids, i.e. artificially crowded solutions appear too simple to account for the high degree of anomaly observed in cells. Comparing time and ensemble averages of the tracers' mean square displacement furthermore indicated that ergodicity is unbroken. Hence, the monitored diffusive process cannot be described properly by a (non-stationary) continuous time random walk.
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Probing the nanoscale viscoelasticity of Intracellular Fluids in living cells
Biophysical journal, 2007Co-Authors: Gernot Guigas, Claudia Kalla, Matthias WeissAbstract:We have used fluorescence correlation spectroscopy to determine the anomalous diffusion properties of fluorescently tagged gold beads in the cytoplasm and the nucleus of living cells. From the extracted mean-square displacement v(τ) ∼ τα, we have determined the complex shear modulus G(ω) ∼ ωα for both compartments. Without treatment, all tested cell lines showed a strong viscoelastic behavior of the cytoplasm and the nucleoplasm, highlighting the crowdedness of these Intracellular Fluids. We also found a similar viscoelastic response in frog egg extract, which tended toward a solely viscous behavior upon dilution. When cells were osmotically stressed, the diffusion became less anomalous and the viscoelastic response changed. In particular, the anomality changed from α ≈ 0.55 to α ≈ 0.66, which indicates that the Zimm model for polymer solutions under varying solvent conditions is a good empirical description of the material properties of the cytoplasm and the nucleoplasm. Since osmotic stress may eventually trigger cell death, we propose, on the basis of our observations, that Intracellular Fluids are maintained in a state similar to crowded polymer solutions under good solvent conditions to keep the cell viable.
Ruth E. Blake - One of the best experts on this subject based on the ideXlab platform.
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probing the metabolic water contribution to Intracellular water using oxygen isotope ratios of po4
Proceedings of the National Academy of Sciences of the United States of America, 2016Co-Authors: Hui Li, Sae Jung Chang, Chan Yu, Ruth E. Blake, Fei WangAbstract:Knowledge of the relative contributions of different water sources to Intracellular Fluids and body water is important for many fields of study, ranging from animal physiology to paleoclimate. The Intracellular fluid environment of cells is challenging to study due to the difficulties of accessing and sampling the contents of intact cells. Previous studies of multicelled organisms, mostly mammals, have estimated body water composition—including metabolic water produced as a byproduct of metabolism—based on indirect measurements of Fluids averaged over the whole organism (e.g., blood) combined with modeling calculations. In microbial cells and aquatic organisms, metabolic water is not generally considered to be a significant component of Intracellular water, due to the assumed unimpeded diffusion of water across cell membranes. Here we show that the 18O/16O ratio of PO4 in Intracellular biomolecules (e.g., DNA) directly reflects the O isotopic composition of Intracellular water and thus may serve as a probe allowing direct sampling of the Intracellular environment. We present two independent lines of evidence showing a significant contribution of metabolic water to the Intracellular water of three environmentally diverse strains of bacteria. Our results indicate that ∼30–40% of O in PO4 comprising DNA/biomass in early stationary phase cells is derived from metabolic water, which bolsters previous results and also further suggests a constant metabolic water value for cells grown under similar conditions. These results suggest that previous studies assuming identical isotopic compositions for Intracellular/extracellular water may need to be reconsidered.
Jeanpaul Rieu - One of the best experts on this subject based on the ideXlab platform.
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high frequency mechanical properties of tumors measured by brillouin light scattering
Physical Review Letters, 2019Co-Authors: Jeremie Margueritat, Angelique Virgonecarlotta, Sylvain Monnier, Helene Delanoeayari, Hichem C Mertani, Alice Berthelot, Quentin Martinet, Xavier Dagany, Charlotte Riviere, Jeanpaul RieuAbstract:The structure of tumors can be recapitulated as an elastic frame formed by the connected cytoskeletons of the cells invaded by interstitial and Intracellular Fluids. The low-frequency mechanics of this poroelastic system, dictated by the elastic skeleton only, control tumor growth, penetration of therapeutic agents, and invasiveness. The high-frequency mechanical properties containing the additional contribution of the internal Fluids have also been posited to participate in tumor progression and drug resistance, but they remain largely unexplored. Here we use Brillouin light scattering to produce label-free images of tumor microtissues based on the high-frequency viscoelastic modulus as a contrast mechanism. In this regime, we demonstrate that the modulus discriminates between tissues with altered tumorigenic properties. Our micrometric maps also reveal that the modulus is heterogeneously altered across the tissue by drug therapy, revealing a lag of efficacy in the core of the tumor. Exploiting high-frequency poromechanics should advance present theories based on viscoelasticity and lead to integrated descriptions of tumor response to drugs.
Margareta Hammarlund-udenaes - One of the best experts on this subject based on the ideXlab platform.
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Effect of transporter inhibition on the distribution of cefadroxil in rat brain
Fluids and Barriers of the CNS, 2014Co-Authors: Xiaomei Chen, Irena Loryan, Maryam Payan, Richard F Keep, David E Smith, Margareta Hammarlund-udenaesAbstract:Background Cefadroxil, a cephalosporin antibiotic, is a substrate for several membrane transporters including peptide transporter 2 (PEPT2), organic anion transporters (OATs), multidrug resistance-associated proteins (MRPs), and organic anion transporting polypeptides (OATPs). These transporters are expressed at the blood–brain barrier (BBB), blood-cerebrospinal fluid barrier (BCSFB), and/or brain cells. The effect of these transporters on cefadroxil distribution in brain is unknown, especially in the extracellular and Intracellular Fluids within brain. Methods Intracerebral microdialysis was used to measure unbound concentrations of cefadroxil in rat blood, striatum extracellular fluid (ECF) and lateral ventricle cerebrospinal fluid (CSF). The distribution of cefadroxil in brain was compared in the absence and presence of probenecid, an inhibitor of OATs, MRPs and OATPs, where both drugs were administered intravenously. The effect of PEPT2 inhibition by intracerebroventricular ( icv ) infusion of Ala-Ala, a substrate of PEPT2, on cefadroxil levels in brain was also evaluated. In addition, using an in vitro brain slice method, the distribution of cefadroxil in brain Intracellular fluid (ICF) was studied in the absence and presence of transport inhibitors (probenecid for OATs, MRPs and OATPs; Ala-Ala and glycylsarcosine for PEPT2). Results The ratio of unbound cefadroxil AUC in brain ECF to blood (K_p,uu,ECF) was ~2.5-fold greater during probenecid treatment. In contrast, the ratio of cefadroxil AUC in CSF to blood (K_p,uu,CSF) did not change significantly during probenecid infusion. Icv infusion of Ala-Ala did not change cefadroxil levels in brain ECF, CSF or blood. In the brain slice study, Ala-Ala and glycylsarcosine decreased the unbound volume of distribution of cefadroxil in brain (V_u,brain), indicating a reduction in cefadroxil accumulation in brain cells. In contrast, probenecid increased cefadroxil accumulation in brain cells, as indicated by a greater value for V_u,brain. Conclusions Transporters (OATs, MRPs, and perhaps OATPs) that can be inhibited by probenecid play an important role in mediating the brain-to-blood efflux of cefadroxil at the BBB. The uptake of cefadroxil in brain cells involves both the influx transporter PEPT2 and efflux transporters (probenecid-inhibitable). These findings demonstrate that drug-drug interactions via relevant transporters may affect the distribution of cephalosporins in both brain ECF and ICF.
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In vitro methods for estimating unbound drug concentrations in the brain interstitial and Intracellular Fluids.
Drug metabolism and disposition: the biological fate of chemicals, 2007Co-Authors: Markus Fridén, Anubha Gupta, Madeleine Antonsson, Ulf Bredberg, Margareta Hammarlund-udenaesAbstract:Concentrations of unbound drug in the interstitial fluid of the brain are not rapidly measured in vivo. Therefore, measurement of total drug levels, i.e., the amount of drug per gram of brain, has been a common but unhelpful practice in drug discovery programs relating to central drug effects. This study was designed to evaluate in vitro techniques for faster estimation of unbound drug concentrations. The parameter that relates the total drug level and the unbound interstitial fluid concentration is the unbound volume of distribution in the brain (V(u,brain)). It was measured in vitro for 15 drugs using brain slice uptake and brain homogenate binding methods. The results were validated in vivo by comparison with V(u,brain) microdialysis results. The slice method results were within a 3-fold range of the in vivo results for all but one compound, suggesting that this method could be used in combination with total drug levels to estimate unbound interstitial fluid concentrations within reasonable limits. Although successful in 10 of 15 cases, the brain homogenate binding method failed to estimate the V(u,brain) of drugs that reside predominantly in the interstitial space or compounds that are accumulated Intracellularly. Use of the simple methods described in this article will 1) allow quantification of active transport at the blood-brain barrier in vivo, 2) facilitate the establishment of a relationship between in vitro potency and in vivo activity for compounds acting on central nervous system targets, and 3) provide information on Intracellular concentrations of unbound drug.
Gernot Guigas - One of the best experts on this subject based on the ideXlab platform.
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Probing the nanoscale viscoelasticity of Intracellular Fluids in living cells
Biophysical journal, 2007Co-Authors: Gernot Guigas, Claudia Kalla, Matthias WeissAbstract:We have used fluorescence correlation spectroscopy to determine the anomalous diffusion properties of fluorescently tagged gold beads in the cytoplasm and the nucleus of living cells. From the extracted mean-square displacement v(τ) ∼ τα, we have determined the complex shear modulus G(ω) ∼ ωα for both compartments. Without treatment, all tested cell lines showed a strong viscoelastic behavior of the cytoplasm and the nucleoplasm, highlighting the crowdedness of these Intracellular Fluids. We also found a similar viscoelastic response in frog egg extract, which tended toward a solely viscous behavior upon dilution. When cells were osmotically stressed, the diffusion became less anomalous and the viscoelastic response changed. In particular, the anomality changed from α ≈ 0.55 to α ≈ 0.66, which indicates that the Zimm model for polymer solutions under varying solvent conditions is a good empirical description of the material properties of the cytoplasm and the nucleoplasm. Since osmotic stress may eventually trigger cell death, we propose, on the basis of our observations, that Intracellular Fluids are maintained in a state similar to crowded polymer solutions under good solvent conditions to keep the cell viable.
