Paclitaxel suppresses Tau-mediated microtubule bundling in a concentration-dependent manner

Choi, Myung Chul,Chung, Peter J.,Song, Chaeyeon,Miller, Herbert P.,Kiris, E.,Li, Youli,Wilson, Leslie,Feinstein, Stuart C.,Safinya, Cyrus R. Elsevier 2017 Biochimica et biophysica acta, General subjects Vol.1861 No.1

<P><B>Abstract</B></P> <P><B>Background</B></P> <P>Microtubules (MTs) are protein nanotubes comprised of straight protofilaments (PFs), head to tail assemblies of αβ-tubulin heterodimers. Previously, it was shown that Tau, a microtubule-associated protein (MAP) localized to neuronal axons, regulates the average number of PFs in microtubules with increasing inner radius <<I> R</I> <SUB>in</SUB> <SUP>MT</SUP> > observed for increasing Tau/tubulin-dimer molar ratio Φ<SUB>Tau</SUB> at paclitaxel/tubulin-dimer molar ratio Λ<SUB>Ptxl</SUB> =1/1.</P> <P><B>Methods</B></P> <P>We report a synchrotron SAXS and TEM study of the phase behavior of microtubules as a function of varying concentrations of paclitaxel (1/32≤Λ<SUB>Ptxl</SUB> ≤1/4) and Tau (human isoform 3RS, 0≤Φ<SUB>3RS</SUB> ≤1/2) at room temperature.</P> <P><B>Results</B></P> <P>Tau and paclitaxel have opposing regulatory effects on microtubule bundling architectures and microtubule diameter. Surprisingly and in contrast to previous results at Λ<SUB>Ptxl</SUB> =1/1 where microtubule bundles are absent, in the lower paclitaxel concentration regime (Λ<SUB>Ptxl</SUB> ≤1/4), we observe both microtubule doublets and triplets with increasing Tau. Furthermore, increasing paclitaxel concentration (up to Λ<SUB>Ptxl</SUB> =1/1) slightly decreased the average microtubule diameter (by ~1 PF) while increasing Tau concentration (up to Φ<SUB>3RS</SUB> =1/2) significantly increased the diameter (by ~2–3 PFs).</P> <P><B>Conclusions</B></P> <P>The suppression of Tau-mediated microtubule bundling with increasing paclitaxel is consistent with paclitaxel seeding more, but shorter, microtubules by rapidly exhausting tubulin available for polymerization. Microtubule bundles require the aggregate Tau-Tau attractions along the microtubule length to overcome individual microtubule thermal energies disrupting bundles.</P> <P><B>General significance</B></P> <P>Investigating MAP-mediated interactions between microtubules (as it relates to <I>in vivo</I> behavior) requires the elimination or minimization of paclitaxel.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Increasing paclitaxel suppresses Tau-mediated microtubule bundling. </LI> <LI> A length-dependent mechanism for Tau-mediated microtubule bundling is proposed. </LI> <LI> Understanding MAP/microtubule behavior requires elimination of paclitaxel use. </LI> </UL> </P>

뉴질랜드 양록업의 현황과 전망

Wilson Peter R.,Barry Tom N. 한국양록협회 1991 양록회보 Vol.14 No.-

뉴질랜드 양록업의 현황과 전망(下)

Wilson Peter R. 한국양록협회 1992 양록회보 Vol.15 No.-

Direct force measurements reveal that protein Tau confers short-range attractions and isoform-dependent steric stabilization to microtubules

Chung, Peter J.,Choi, Myung Chul,Miller, Herbert P.,Feinstein, H. Eric,Raviv, Uri,Li, Youli,Wilson, Leslie,Feinstein, Stuart C.,Safinya, Cyrus R. National Academy of Sciences 2015 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.112 No.47

<P><B>Significance</B></P><P>The microtubule-associated protein Tau is known to stabilize microtubules against depolymerization in neuronal axons, ensuring proper trafficking of organelles along microtubules in long axons. Abnormal interactions between Tau and microtubules are implicated in Alzheimer’s disease and other neurodegenerative disorders. We directly measured forces between microtubules coated with Tau isoforms by synchrotron small-angle X-ray scattering of reconstituted Tau–microtubule mixtures under osmotic pressure (mimicking molecular crowding in cells). We found that select Tau isoforms fundamentally alter forces between microtubules by undergoing a conformational change on microtubule surfaces at a coverage indicative of an unusually extended Tau state. This gain of function by longer isoforms in imparting steric stabilization to microtubules is essential in preventing microtubule aggregation and loss of function in organelle trafficking.</P><P>Microtubules (MTs) are hollow cytoskeletal filaments assembled from αβ-tubulin heterodimers. Tau, an unstructured protein found in neuronal axons, binds to MTs and regulates their dynamics. Aberrant Tau behavior is associated with neurodegenerative dementias, including Alzheimer’s. Here, we report on a direct force measurement between paclitaxel-stabilized MTs coated with distinct Tau isoforms by synchrotron small-angle X-ray scattering (SAXS) of MT-Tau mixtures under osmotic pressure (<I>P</I>). In going from bare MTs to MTs with Tau coverage near the physiological submonolayer regime (Tau/tubulin-dimer molar ratio; Φ<SUB>Tau</SUB> = 1/10), isoforms with longer N-terminal tails (NTTs) sterically stabilized MTs, preventing bundling up to <I>P</I><SUB>B</SUB> ∼ 10,000–20,000 Pa, an order of magnitude larger than bare MTs. Tau with short NTTs showed little additional effect in suppressing the bundling pressure (<I>P</I><SUB>B</SUB> ∼ 1,000–2,000 Pa) over the same range. Remarkably, the abrupt increase in <I>P</I><SUB>B</SUB> observed for longer isoforms suggests a mushroom to brush transition occurring at 1/13 < Φ<SUB>Tau</SUB> < 1/10, which corresponds to MT-bound Tau with NTTs that are considerably more extended than SAXS data for Tau in solution indicate. Modeling of Tau-mediated MT–MT interactions supports the hypothesis that longer NTTs transition to a polyelectrolyte brush at higher coverages. Higher pressures resulted in isoform-independent irreversible bundling because the polyampholytic nature of Tau leads to short-range attractions. These findings suggest an isoform-dependent biological role for regulation by Tau, with longer isoforms conferring MT steric stabilization against aggregation either with other biomacromolecules or into tight bundles, preventing loss of function in the crowded axon environment.</P>

Contrast-enhanced ultrasound approach to the diagnosis of focal liver lesions: the importance of washout

양현경,김태경,Peter N. Burns,장현정,Yuko Kono,Korosh Khalili,Stephanie R. Wilson 대한초음파의학회 2019 ULTRASONOGRAPHY Vol.38 No.4

Contrast-enhanced ultrasound (CEUS) is a powerful technique for differentiating focal liver lesions (FLLs) without the risks of potential nephrotoxicity or ionizing radiation. In the diagnostic algorithm for FLLs on CEUS, washout is an important feature, as its presence is highly suggestive of malignancy and its characteristics are useful in distinguishing hepatocellular from nonhepatocellular malignancies. Interpreting washout on CEUS requires an understanding that microbubble contrast agents are strictly intravascular, unlike computed tomography or magnetic resonance imaging contrast agents. This review explains the definition and types of washout on CEUS in accordance with the 2017 version of the CEUS Liver Imaging Reporting and Data System and presents their applications to differential diagnosis with illustrative examples. Additionally, we propose potential mechanisms of rapid washout and describe the washout phenomenon in benign entities.

Minireview - Microtubules and Tubulin Oligomers: Shape Transitions and Assembly by Intrinsically Disordered Protein Tau and Cationic Biomolecules

Safinya, Cyrus R.,Chung, Peter J.,Song, Chaeyeon,Li, Youli,Miller, Herbert P.,Choi, Myung Chul,Raviv, Uri,Ewert, Kai K.,Wilson, Leslie,Feinstein, Stuart C. American Chemical Society 2019 Langmuir Vol.35 No.48

<P>In this minireview, which is part of a special issue in honor of Jacob N. Israelachvili’s remarkable research career on intermolecular forces and interfacial science, we present studies of structures, phase behavior, and forces in reaction mixtures of microtubules (MTs) and tubulin oligomers with either intrinsically disordered protein (IDP) Tau, cationic vesicles, or the polyamine spermine (4+). Bare MTs consist of 13 protofilaments (PFs), on average, where each PF is made of a linear stack of αβ-tubulin dimers (i.e., tubulin oligomers). We begin with a series of experiments which demonstrate the flexibility of PFs toward shape changes in response to local environmental cues. First, studies show that MT-associated protein (MAP) Tau controls the diameter of microtubules upon binding to the outer surface, implying a shape change in the cross-sectional area of PFs forming the MT perimeter. The diameter of a MT may also be controlled by the charge density of a lipid bilayer membrane that coats the outer surface. We further describe an experimental study where it is unexpectedly found that the biologically relevant polyamine spermine (+4e) is able to depolymerize <I>taxol-stabilized</I> microtubules with efficiency that increases with decreasing temperature. This MT destabilization drives a dynamical structural transition where inside-out curving of PFs, during the depolymerization peeling process, is followed by reassembly of ring-like curved PF building blocks into an array of helical inverted tubulin tubules. We finally turn to a very recent study on pressure-distance measurements in bundles of MTs employing the small-angle X-ray scattering (SAXS)-osmotic pressure technique, which complements the surface-forces-apparatus technique developed by Jacob N. Israelachvili. These latter studies are among the very few which are beginning to shed light on the precise nature of the interactions between MTs mediated by MAP Tau in 37 °C reaction mixtures containing GTP and lacking taxol.</P> [FIG OMISSION]</BR>

Performance Accuracy of Wrist-Worn Oximetry and Its Automated Output Parameters for Screening Obstructive Sleep Apnea in Children

Mon Ohn,Kathleen J Maddison,Julie Nguyen,Daisy Evans,Natasha Bear,R. Nazim Khan,Peter R Eastwood,Britta S. von Ungern-Sternberg,Andrew C Wilson,Jennifer H Walsh 대한수면연구학회 2023 Journal of sleep medicine Vol.20 No.2

Objectives: Obstructive sleep apnea (OSA) increases the risk of perioperative adverse events in children. While polysomnography (PSG) remains the reference standard for OSA diagnosis, oximetry is a valuable screening tool. The traditional practice is the manual analysis of desaturation clusters derived from a tabletop device using the McGill oximetry score. However, automated analysis of wearable oximetry data can be an alternative. This study investigated the accuracy of wrist-worn oximetry with automated analysis as a preoperative OSA screening tool. Methods: Healthy children scheduled for adenotonsillectomy underwent concurrent overnight PSG and wrist-worn oximetry. PSG determined the obstructive apnea-hypopnea index (OAHI). Oximetry data were auto-analyzed to determine 3% oxygen desaturation index (ODI3) and visually scored as per McGill criteria. The logistic regression model assessed the predictive performance of ODI3 for detecting the presence and severity of OSA after adjusting for covariates. Results: Seventy-six children (34 females), aged (mean±standard deviation) 5.7±1.6 years were classified, based on PSG-derived OAHI, as no OSA (n=31), mild (n=31), and moderate-severe OSA (n=14). Oximetric ODI3 was identified as the sole predictor of moderate-severe OSA (OAHI≥5 events/h) (odds ratio 1.38, 95% confidence interval 1.15, 1.65, <i>p</i>=0.001). The best diagnostic performance was at ODI3=5 events/h (78.6% sensitivity, 75.8% specificity [receiver operating characteristic-area under the curve {ROC-AUC}=0.857]). ODI3 was also more sensitive than the McGill oximetry score in diagnosing moderate-severe OSA (78.6% by ODI3 vs. 33.0% by McGill). The performance was suboptimal for any level of OSA (OAHI≥1 event/h) (75.6% sensitivity, 61.3% specificity [ROC-AUC=0.709]). Conclusions: Wrist-worn oximetry-derived automated ODI3 can reliably identify moderate-severe OSA in children undergoing adenotonsillectomy, making it a potentially useful preoperative OSA screening tool.