75 research outputs found
Unravelling intermittent features in single particle trajectories by a local convex hull method
We propose a new model-free method to detect change points between distinct
phases in a single random trajectory of an intermittent stochastic process. The
local convex hull (LCH) is constructed for each trajectory point, while its
geometric properties (e.g., the diameter or the volume) are used as
discriminators between phases. The efficiency of the LCH method is validated
for six models of intermittent motion, including Brownian motion with different
diffusivities or drifts, fractional Brownian motion with different Hurst
exponents, and surface-mediated diffusion. We discuss potential applications of
the method for detection of active and passive phases in the intracellular
transport, temporal trapping or binding of diffusing molecules, alternating
bulk and surface diffusion, run and tumble (or search) phases in the motion of
bacteria and foraging animals, and instantaneous firing rates in neurons
Temperature and friction fluctuations inside a harmonic potential
In this article we study the trapped motion of a molecule undergoing diffusivity fluctuations inside a harmonic potential. For the same diffusing-diffusivity process, we investigate two possible interpretations. Depending on whether diffusivity fluctuations are interpreted as temperature or friction fluctuations, we show that they display drastically different statistical properties inside the harmonic potential. We compute the characteristic function of the process under both types of interpretations and analyze their limit behavior. Based on the integral representations of the processes we compute the mean-squared displacement and the normalized excess kurtosis. In the long-time limit, we show for friction fluctuations that the probability density function (PDF) always converges to a Gaussian whereas in the case of temperature fluctuations the stationary PDF can display either Gaussian distribution or generalized Laplace (Bessel) distribution depending on the ratio between diffusivity and positional correlation times
Selective and WashâResistant Fluorescent Dihydrocodeinone Derivatives Allow SingleâMolecule Imaging of ÎŒâOpioid Receptor Dimerization
ÎŒâOpioid receptors (ÎŒâORs) play a critical role in the modulation of pain and mediate the effects of the most powerful analgesic drugs. Despite extensive efforts, it remains insufficiently understood how ÎŒâORs produce specific effects in living cells. We developed new fluorescent ligands based on the ÎŒâOR antagonist Eâpânitrocinnamoylaminoâdihydrocodeinone (CACO), that display high affinity, long residence time and pronounced selectivity. Using these ligands, we achieved singleâmolecule imaging of ÎŒâORs on the surface of living cells at physiological expression levels. Our results reveal a high heterogeneity in the diffusion of ÎŒâORs, with a relevant immobile fraction. Using a pair of fluorescent ligands of different color, we provide evidence that ÎŒâORs interact with each other to form shortâlived homodimers on the plasma membrane. This approach provides a new strategy to investigate ÎŒâOR pharmacology at singleâmolecule level
Selective and washâresistant fluorescent dihydrocodeinone derivatives allow singleâmolecule imaging of ÎŒâopioid receptor dimerization
ÎŒâOpioid receptors (ÎŒâORs) play a critical role in the modulation of pain and mediate the effects of the most powerful analgesic drugs. Despite extensive efforts, it remains insufficiently understood how ÎŒâORs produce specific effects in living cells. We developed new fluorescent ligands based on the ÎŒâOR antagonist Eâpânitrocinnamoylaminoâdihydrocodeinone (CACO), that display high affinity, long residence time and pronounced selectivity. Using these ligands, we achieved singleâmolecule imaging of ÎŒâORs on the surface of living cells at physiological expression levels. Our results reveal a high heterogeneity in the diffusion of ÎŒâORs, with a relevant immobile fraction. Using a pair of fluorescent ligands of different color, we provide evidence that ÎŒâORs interact with each other to form shortâlived homodimers on the plasma membrane. This approach provides a new strategy to investigate ÎŒâOR pharmacology at singleâmolecule level
Filamin A organizes Îłâaminobutyric acid type B receptors at the plasma membrane
The γ-aminobutyric acid type B (GABA(B)) receptor is a prototypical family C G protein-coupled receptor (GPCR) that plays a key role in the regulation of synaptic transmission. Although growing evidence suggests that GPCR signaling in neurons might be highly organized in time and space, limited information is available about the mechanisms controlling the nanoscale organization of GABA(B) receptors and other GPCRs on the neuronal plasma membrane. Using a combination of biochemical assays in vitro, single-particle tracking, and super-resolution microscopy, we provide evidence that the spatial organization and diffusion of GABA(B) receptors on the plasma membrane are governed by dynamic interactions with filamin A, which tethers the receptors to sub-cortical actin filaments. We further show that GABA(B) receptors are located together with filamin A in small nanodomains in hippocampal neurons. These interactions are mediated by the first intracellular loop of the GABA(B1) subunit and modulate the kinetics of Gα(i) protein activation in response to GABA stimulation
Immunopathogenesis and proposed clinical score for identifying Kelch-like protein-11 encephalitis
In this study, we report the clinical features of Kelch-like protein 11 antibody-associated paraneoplastic neurological syndrome, design and validate a clinical score to facilitate the identification of patients that should be tested for Kelch-like protein 11 antibodies, and examine in detail the nature of the immune response in both the brain and the tumour samples for a better characterization of the immunopathogenesis of this condition. The presence of Kelch-like protein 11 antibodies was retrospectively assessed in patients referred to the French Reference Center for paraneoplastic neurological syndrome and autoimmune encephalitis with (i) antibody-negative paraneoplastic neurological syndrome [limbic encephalitis (n = 105), cerebellar degeneration (n = 33)] and (ii) antibody-positive paraneoplastic neurological syndrome [Ma2-Ab encephalitis (n = 34), antibodies targeting N-methyl-D-aspartate receptor encephalitis with teratoma (n = 49)]. Additionally, since 1 January 2020, patients were prospectively screened for Kelch-like protein 11 antibodies as new usual clinical practice. Overall, Kelch-like protein 11 antibodies were detected in 11 patients [11/11, 100% were male; their median (range) age was 44 (35-79) years], 9 of them from the antibody-negative paraneoplastic neurological syndrome cohort, 1 from the antibody-positive (Ma2-Ab) cohort and 1 additional prospectively detected patient. All patients manifested a cerebellar syndrome, either isolated (4/11, 36%) or part of a multi-system neurological disorder (7/11, 64%). Additional core syndromes were limbic encephalitis (5/11, 45%) and myelitis (2/11, 18%). Severe weight loss (7/11, 64%) and hearing loss/tinnitus (5/11, 45%) were common. Rarer neurologic manifestations included hypersomnia and seizures (2/11, 18%). Two patients presented phenotypes resembling primary neurodegenerative disorders (progressive supranuclear palsy and flail arm syndrome, respectively). An associated cancer was found in 9/11 (82%) patients; it was most commonly (7/9, 78%) a spontaneously regressed ('burned-out') testicular germ cell tumour. A newly designed clinical score (MATCH score: male, ataxia, testicular cancer, hearing alterations) with a cut-off â„4 successfully identified patients with Kelch-like protein 11 antibodies (sensitivity 78%, specificity 99%). Pathological findings (three testicular tumours, three lymph node metastases of testicular tumours, one brain biopsy) showed the presence of a T-cell inflammation with resulting anti-tumour immunity in the testis and one chronic, exhausted immune response - demonstrated by immune checkpoint expression - in the metastases and the brain. In conclusion, these findings suggest that Kelch-like protein 11 antibody paraneoplastic neurological syndrome is a homogeneous clinical syndrome and its detection can be facilitated using the MATCH score. The pathogenesis is probably T-cell mediated, but the stages of inflammation are different in the testis, metastases and the brain
How Carvedilol activates ÎČ<sub>2</sub>-adrenoceptors
Carvedilol is among the most effective ÎČ-blockers for improving survival after myocardial infarction. Yet the mechanisms by which carvedilol achieves this superior clinical profile are still unclear. Beyond blockade of ÎČ(1)-adrenoceptors, arrestin-biased signalling via ÎČ(2)-adrenoceptors is a molecular mechanism proposed to explain the survival benefits. Here, we offer an alternative mechanism to rationalize carvedilolâs cellular signalling. Using primary and immortalized cells genome-edited by CRISPR/Cas9 to lack either G proteins or arrestins; and combining biological, biochemical, and signalling assays with molecular dynamics simulations, we demonstrate that G proteins drive all detectable carvedilol signalling through ÎČ(2)ARs. Because a clear understanding of how drugs act is imperative to data interpretation in basic and clinical research, to the stratification of clinical trials or to the monitoring of drug effects on the target pathway, the mechanistic insight gained here provides a foundation for the rational development of signalling prototypes that target the ÎČ-adrenoceptor system
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