Frequency Response of a Viscoelastic Tensegrity Model: Structural Rearrangement Contribution to Cell Dynamics

2005 ◽  
Vol 128 (4) ◽  
pp. 487-495 ◽  
Author(s):  
Patrick Cañadas ◽  
Sylvie Wendling-Mansuy ◽  
Daniel Isabey
Keyword(s):  
Frequency Response ◽  
Essential Feature ◽  
Structural Rearrangement ◽  
Contact Dynamics ◽  
Specific Power ◽  
Viscous Effects ◽  
Cell Dynamics ◽  
Frequency Dependent ◽  
Tensegrity Structure

In an attempt to understand the role of structural rearrangement onto the cell response during imposed cyclic stresses, we simulated numerically the frequency-dependent behavior of a viscoelastic tensegrity structure (VTS model) made of 24 elastic cables and 6 rigid bars. The VTS computational model was based on the nonsmooth contact dynamics (NSCD) method in which the constitutive elements of the tensegrity structure are considered as a set of material points that mutually interact. Low amplitude oscillatory loading conditions were applied and the frequency response of the overall structure was studied in terms of frequency dependence of mechanical properties. The latter were normalized by the homogeneous properties of constitutive elements in order to capture the essential feature of spatial rearrangement. The results reveal a specific frequency-dependent contribution of elastic and viscous effects which is responsible for significant changes in the VTS model dynamical properties. The mechanism behind is related to the variable contribution of spatial rearrangement of VTS elements which is decreased from low to high frequency as dominant effects are transferred from mainly elastic to mainly viscous. More precisely, the elasticity modulus increases with frequency while the viscosity modulus decreases, each evolution corresponding to a specific power-law dependency. The satisfactorily agreement found between present numerical results and the literature data issued from in vitro cell experiments suggests that the frequency-dependent mechanism of spatial rearrangement presently described could play a significant and predictable role during oscillatory cell dynamics.

scholarly journals An antisense noncoding RNA enhances translation via localised structural rearrangements of its cognate mRNA

2021 ◽  
Author(s):  
Rodrigo S Reis ◽  
Jules Deforges ◽  
Romy R Schmidt ◽  
Jos H M Schippers ◽  
Yves Poirier
Keyword(s):  
Antisense Rna ◽  
Noncoding Rna ◽  
Regulatory Region ◽  
Structural Rearrangement ◽  
Start Codon ◽  
Structural Rearrangements ◽  
Eukaryotic Genes ◽  
Inhibitory Region ◽  
Rna Interaction

Abstract A large portion of eukaryotic genes are associated with noncoding, natural antisense transcripts (NATs). Despite sharing extensive sequence complementarity with their sense mRNAs, mRNA-NAT pairs elusively often evade dsRNA-cleavage and siRNA-triggered silencing. More surprisingly, some NATs enhance translation of their sense mRNAs by yet unknown mechanism(s). Here we show that translation enhancement of the rice (Oryza sativa) PHOSPHATE1.2 (PHO1.2) mRNA is enabled by specific structural rearrangements guided by its noncoding antisense RNA (cis-NATpho1.2). Their interaction in vitro revealed no evidence of widespread intermolecular dsRNA formation, but rather specific local changes in nucleotide base-pairing, leading to higher flexibility of PHO1.2 mRNA at a key high GC regulatory region inhibiting translation, approximately 350 nucleotides downstream of the start codon. Sense-antisense RNA interaction increased formation of the 80S complex in PHO1.2, possibly by inducing structural rearrangement within this inhibitory region, thus making this mRNA more accessible to 60S. This work presents a framework for nucleotide-resolution studies of functional mRNA-antisense pairs. One-sentence summary: Interaction between PHO1.2 mRNA and its cis-natural antisense transcript enhances translation via a mechanism involving a local conformational shift and disruption of a key inhibitory region.

Abstract 17071: Cell Communication Inference in Macrophages

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Nika Taghdiri ◽  
Kevin R King ◽  
David Calcagno ◽  
Zhenxing Fu ◽  
Kenneth Huang ◽  
...  
Keyword(s):  
Image Analysis ◽  
Analytical Methods ◽  
Cell Injury ◽  
Diffusion Mechanism ◽  
Cell Communication ◽  
In Vivo Studies ◽  
Cell Dynamics ◽  
Calcium Indicator

Introduction: Tissue macrophages play diverse roles in the cardiovascular system during health and disease. They have diverse functions within tissues, but our understanding of their dynamics is limited because most macrophage characterization assays are destructive and have low temporal resolution. We asked whether these cells are dynamic and interconnected. Methods: Here, we describe experimental and analytical methods for measuring cell dynamics and inferring communication between cells in vitro and in vivo. We created a mouse (Csf1r-Cre x GCaMP5) expressing the Cre-inducible genetically encoded calcium indicator GCaMP5 under the regulation of the innate immune promoter, Csf1r, to non-destructively quantify high-frequency cell dynamics and differentiated them in culture using m-CSF. We developed custom image analysis routines and parameterization strategies for classifying calcium responses. Results: Our studies revealed that calcium reporter BMDMs display minimal fluctuations at baseline but exhibit a dynamic response to immunogenic DNA sensing. DNA-induced isolated cell injury and death, which precipitated cell communication that spread with a velocity of [9μm/s], consistent with an extracellular diffusion mechanism. We developed quantitative image analysis methods that corrected for random calcium fluctuations and identified statistically significant areas of correlated calcium changes suggestive of communication. An analytical pipeline enabled quantification of calcium spike dynamics and correlations of dynamic calcium profiles of single cell sharing a local microenvironment. This resulted in an “improbable synchrony” metric that allowed localization of communication in time and space. We adapted the pipeline for in vivo studies and tested them in a dorsal window chamber model using intravital microscopy. At 2Hz sampling frequency, we identified 27 potential communication events as they responded to complex microenvironmental cues in vivo. Conclusion: The experimental and analytical methods for inferring cell communication provide a new quantitative toolkit for investigating known as-yet undiscovered cell communication pathways.

Characteristics of Electrically Evoked Somatodendritic Dopamine Release in Substantia Nigra and Ventral Tegmental Area In Vitro

1997 ◽  
Vol 77 (2) ◽  
pp. 853-862 ◽  
Author(s):  
M. E. Rice ◽  
S. J. Cragg ◽  
S. A. Greenfield
Keyword(s):  
Electrical Stimulation ◽  
Substantia Nigra ◽  
Ventral Tegmental Area ◽  
Dopamine Release ◽  
Substantia Nigra Pars Compacta ◽  
Frequency Dependent ◽  
Body Regions ◽  
Ventral Tegmental ◽  
Da Release

Rice, M. E., S. J. Cragg, and S. A. Greenfield. Characteristics of electrically evoked somatodendritic dopamine release in substantia nigra and ventral tegmental area in vitro. J. Neurophysiol. 77: 853–862, 1997. Somatodendritic dopamine (DA) release from neurons of the midbrain represents a nonclassical form of neuronal signaling. We assessed characteristics of DA release during electrical stimulation of the substantia nigra pars compacta (SNc) in guinea pig midbrain slices. With the use of parameters optimized for this region, we compared stimulus-induced increases in extracellular DA concentration ([DA]o) in medial and lateral SNc, ventral tegmental area (VTA), and dorsal striatum in vitro. DA release was monitored directly with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Detection of DA in SNc was confirmed by electrochemical, pharmacological, and anatomic criteria. Voltammograms of the released substance had the same peak potentials as those of DA obtained during in vitro calibration, but different from those of the indoleamine 5-hydroxytryptamine. Similar voltammograms were also obtained in the DA-rich striatum during local electrical stimulation. Contribution from the DA metabolite 3,4-dihydroxyphenylacetic acid to somatodendritic release was negligible, as indicated by the lack of effect of the monoamine oxidase inhibitor pargyline (20 μM) on the signal. Lastly, DA voltammograms could only be elicited in regions that were subsequently determined to be positive for tyrosine hydroxylase immunoreactivity (TH-ir). The frequency dependence of stimulated DA release in SNc was determined over a range of 1–50 Hz, with a constant duration of 10 s. Release was frequency dependent up to 10 Hz, with no further increase at higher frequencies. Stimulation at 10 Hz was used in all subsequent experiments. With this paradigm, DA release in SNc was tetrodotoxin insensitive, but strongly Ca2+ dependent. Stimulated [DA]o in the midbrain was also site specific. At the midcaudal level examined, DA efflux was significantly greater in VTA (1.04 ± 0.05 μM, mean ± SE) than in medial SNc (0.52 ± 0.05 μM), which in turn was higher than in lateral SNc (0.35 ± 0.03 μM). This pattern followed the apparent density of TH-ir, which was also VTA > medial SNc > lateral SNc. This report has introduced a new paradigm for the study of somatodendritic DA release. Voltammetric recording with electrodes of 2–4 μm tip diameter permitted highly localized, direct detection of endogenous DA. The Ca2+ dependence of stimulated release indicated that the process was physiologically relevant. Moreover, the findings that somatodendritic release was frequency dependent across a range characteristic of DA cell firing rates and that stimulated [DA]o varied markedly among DA cell body regions have important implications for how dendritically released DA may function in the physiology and pathophysiology of substantia nigra and VTA.

Quantitative Action Spectroscopy Reveals ARPE-19 Sensitivity to Long-Wave Ultraviolet Radiation at 350 nm and 380 nm

2021 ◽  
Author(s):  
Graham Anderson ◽  
Andrew McLeod ◽  
Pierre Bagnaninchi ◽  
Baljean Dhillon
Keyword(s):  
Ultraviolet Radiation ◽  
Cell Viability ◽  
Age Related Macular Degeneration ◽  
Cell Dynamics ◽  
Cell Viability Assay ◽  
Cell Parameters ◽  
Viability Analysis ◽  
Age Related

The role of ultraviolet radiation (UVR) exposure in the pathology of age-related macular degeneration (AMD) has been debated for decades with epidemiological evidence failing to find a clear consensus for or against it playing a role. A key reason for this is a lack of foundational research into the response of living retinal tissue to UVR in regard to AMD-specific parameters of tissue function. We, therefore, explored the response of cultured retinal pigmented epithelium (RPE), the loss of which heralds advanced AMD, to specific wavelengths of UVR across the UV-B and UV-A bands found in natural sunlight. Using a bespoke in vitro UVR exposure apparatus coupled with bandpass filters we exposed the immortalised RPE cell line, ARPE-19, to 10nm bands of UVR between 290 and 405nm. Physical cell dynamics were assessed during exposure in cells cultured upon specialist electrode culture plates which allow for continuous, non-invasive electrostatic interrogation of key cell parameters during exposure such as monolayer coverage and tight-junction integrity. UVR exposures were also utilised to quantify wavelength-specific effects using a rapid cell viability assay and a phenotypic profiling assay which was leveraged to simultaneously quantify intracellular reactive oxygen species (ROS), nuclear morphology, mitochondrial stress, epithelial integrity and cell viability as part of a phenotypic profiling approach to quantifying the effects of UVR. Electrical impedance assessment revealed unforeseen detrimental effects of UV-A, beginning at 350nm, alongside previously demonstrated UV-B impacts. Cell viability analysis also highlighted increased effects at 350nm as well as 380nm. Effects at 350nm were further substantiated by high content image analysis which highlighted increased mitochondrial dysfunction and oxidative stress. We conclude that ARPE-19 cells exhibit a previously uncharacterised sensitivity to UV-A radiation, specifically at 350nm and somewhat less at 380nm. If upheld in vivo, such sensitivity will have impacts upon geoepidemiological risk scoring of AMD.

The Frequency Response of Electrochemical Wall Shear Probes in Pulsatile Flow

1987 ◽  
Vol 109 (1) ◽  
pp. 60-64 ◽  
Author(s):  
L. Talbot ◽  
J. J. Steinert
Keyword(s):  
Mass Transfer ◽  
Frequency Response ◽  
Pulsatile Flow ◽  
Straight Tube ◽  
Asymptotic Results ◽  
Frequency Dependent ◽  
Shear Rates ◽  
Pulsatile Flows ◽  
Wall Shear ◽  
Good Agreement

The frequency response of surface-mounted electrochemical mass transfer probes used to deduce wall shear rates has been investigated experimentally for the case of fully developed laminar pulsatile flow in a straight tube. Generally good agreement is found with the asymptotic results obtained by Lighthill’s methods. The significance of the results with regard to the investigation of models of pulsatile flows of physiological interest is discussed. It is concluded that the frequency-dependent phase and amplitude corrections required to obtain accurate wall shear measurements are of such magnitudes as to render impractical the use of electrochemical probes to determine wall shear rates in these flows.

scholarly journals In vitro analysis of multiple blood flow determinants using red blood cell dynamics under oscillatory flow

The Analyst ◽  
2020 ◽  
Vol 145 (18) ◽  
pp. 5996-6005
Author(s):  
Ziya Isiksacan ◽  
Murat Serhatlioglu ◽  
Caglar Elbuken
Keyword(s):  
Blood Flow ◽  
Blood Cell ◽  
Measurement Method ◽  
Oscillatory Flow ◽  
Optical Analysis ◽  
Cell Dynamics ◽  
Multiple Blood ◽  
Vitro Analysis ◽  
In Vitro Analysis

A handheld platform and measurement method for optical analysis of hemorheological parameters from 50 μl undiluted blood inside a miniaturized channel.

scholarly journals The scaffold-protein IQGAP1 enhances and spatially restricts the actin-nucleating activity of Diaphanous-related formin 1 (DIAPH1)

2020 ◽  
Vol 295 (10) ◽  
pp. 3134-3147 ◽  
Author(s):  
Anan Chen ◽  
Pam D. Arora ◽  
Christine C. Lai ◽  
John W. Copeland ◽  
Trevor F. Moraes ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Actin Filament ◽  
Intramolecular Interaction ◽  
Essential Feature ◽  
Temporal Regulation ◽  
Iq Motif ◽  
Sequential Binding ◽  
Spatio Temporal

The actin cytoskeleton is a dynamic array of filaments that undergoes rapid remodeling to drive many cellular processes. An essential feature of filament remodeling is the spatio-temporal regulation of actin filament nucleation. One family of actin filament nucleators, the Diaphanous-related formins, is activated by the binding of small G-proteins such as RhoA. However, RhoA only partially activates formins, suggesting that additional factors are required to fully activate the formin. Here we identify one such factor, IQ motif containing GTPase activating protein-1 (IQGAP1), which enhances RhoA-mediated activation of the Diaphanous-related formin (DIAPH1) and targets DIAPH1 to the plasma membrane. We find that the inhibitory intramolecular interaction within DIAPH1 is disrupted by the sequential binding of RhoA and IQGAP1. Binding of RhoA and IQGAP1 robustly stimulates DIAPH1-mediated actin filament nucleation in vitro. In contrast, the actin capping protein Flightless-I, in conjunction with RhoA, only weakly stimulates DIAPH1 activity. IQGAP1, but not Flightless-I, is required to recruit DIAPH1 to the plasma membrane where actin filaments are generated. These results indicate that IQGAP1 enhances RhoA-mediated activation of DIAPH1 in vivo. Collectively these data support a model where the combined action of RhoA and an enhancer ensures the spatio-temporal regulation of actin nucleation to stimulate robust and localized actin filament production in vivo.

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