Biology subjects

Ge, L.

Publications and source records attributed to Ge, L..

41 records · Page 3Linked to original sources

bioRxiv2019

Super-resolution microscopy unveils FIP200-scaffolded, cup-shaped organization of mammalian autophagic initiation machinery

Autophagy is an essential physiological process by which eukaryotic cells degrade and recycle cellular materials. Although the biochemical hierarchies of the mammalian autophagy pathway have been identified, questions remain regarding the sequence, subcellular location, and structural requirements of autophagosome formation. Here, we characterize the structural organization of key components of the mammalian autophagic initiation machinery at [~]20 nm spatial resolution via three-color, three-dimensional super-resolution fluorescence microscopy. We thus show that upon cell starvation, FIP200, a large structural protein of the ULK1 complex with no direct yeast homolog, scaffolds the formation of cup-like structures located at SEC12-enriched remodeled ER-exit sites prior to LC3 lipidation. This cup scaffold, then, provides a structural asymmetry to enforce the directional recruitment of downstream components, including the Atg12-Atg5-Atg16 complex, WIPI2, and LC3, to the cup inside. Moreover, we provide evidence that the early autophagic machinery is recruited in its entirety to these cup structures prior to LC3 lipidation, and gradually disperses and dissociates on the outer face of the phagophore membrane during elongation. We thus shed new light on the physical process of mammalian autophagic initiation and development at the nanometer-scale.

cell biology↗

bioRxiv2019

Mechanical effects of MitraClip on leaflet stress and myocardial strain in functional mitral regurgitation: A finite element modeling study.

PurposeMitraClip is the sole percutaneous device approved for functional mitral regurgitation (MR; FMR) but MR recurs in over one third of patients. As device-induced mechanical effects are a potential cause for MR recurrence, we tested the hypothesis that MitraClip increases leaflet stress and procedure-related strain in sub-valvular left ventricular (LV) myocardium in FMR associated with coronary disease (FMR-CAD).\n\nMethodsSimulations were performed using finite element models of the LV + mitral valve based on MRI of 5 sheep with FMR-CAD. Models were modified to have a 20% increase in LV volume ({uparrow}LV_VOLUME) and MitraClip was simulated with contracting beam elements (virtual sutures) placed between nodes in the center edge of the anterior (AL) and posterior (PL) mitral leaflets. Effects of MitraClip on leaflet stress in the peri-MitraClip region of AL and PL, septo-lateral annular diameter (SLAD), and procedure-related radial strain (Err) in the sub-valvular myocardium were calculated.\n\nResultsMitraClip increased peri-MitraClip leaflet stress at end-diastole (ED) by 22.3{+/-}7.1 kPa (p<0.0001) in AL and 14.8{+/-}1.2 kPa (p<0.0001) in PL. MitraClip decreased SLAD by 6.1{+/-}2.2 mm (p<0.0001) and increased Err in the sub-valvular lateral LV myocardium at ED by 0.09{+/-}0.04 (p<0.0001)). Furthermore, MitraClip in {uparrow}LV_VOLUME was associated with persistent effects at ED but also at end-systole where peri-MitraClip leaflet stress was increased in AL by 31.9{+/-}14.4 kPa (p=0.0268) and in PL by 22.5{+/-}23.7 kPa (p=0.0101).\n\nConclusionsMitraClip for FMR-CAD increases mitral leaflet stress and radial strain in LV sub-valvular myocardium. Mechanical effects of MitraClip are augmented by LV enlargement.

bioengineering↗

bioRxiv2019

The mineralization characteristics of organic carbon and particle composition analysis in reconstructed soil with different proportions of soft rock and sand

The organic carbon mineralization process can reflect the release intensity of soil CO2. Therefore, the study of organic carbon mineralization and particle composition analysis of soft rock and sand compound soil can provide technical support and theoretical basis for the theory of soil organic reconstruction. Based on the previous research, this paper mainly selected four typical treatments of 0:1 (CK), 1:5 (C1), 1:2 (C2) and 1:1 (C3), respectively, and analyzed the soil organic carbon mineralization process and particle composition by lye absorption method, laser particle size meter and scanning electron microscope. The results showed that there was no significant difference in organic carbon content between C1, C2 and C3 treatments, but they were significantly higher than CK treatment (P < 0.05). The organic carbon mineralization rate of each treatment accords with a logarithmic function throughout the culture period (P < 0.01), which can be divided into a rapid decline phase of 1-11 days and a steady decline phase of 11-30 days. The cumulative mineralization amount on the 11th day reached 54.96%-74.44% of the total mineralization amount. At the end of the culture, the cumulative mineralization and potential mineralizable organic carbon content of C1 and C2 treatments were significantly higher than those of CK treatment, and the cumulative mineralization rate was also the lowest with C1 and C2 treatment. The turnover rate constant of soil organic carbon in each treatment was significantly lower than that of CK treatment, and the residence time increased. With the increase of volume fraction of soft rock, the content of silt and clay particles increases gradually, the texture of soil changes from sandy soil to sandy loam, loam and silty loam, and because of the increase of small particles, the structure of soil appears to collapse when the volume ratio of soft rock was 50%. In summary, the ratio of soft rock to sand volume was 1:5-1: 2, which can effectively increased the accumulation of soil organic carbon. At this time, the distribution of soil particles was more uniform, the soil structure was stable, and the mineralization level of unit organic carbon was lower. The research results have practical significance for the large area popularization of soft rock and sand compound technology.

ecology↗

bioRxiv2019

Left Ventricular Chamber Shape During Vena Caval Occlusion: Improved MRI-based Measurement of the End-Systolic Pressure-Volume Relationship in Normal Sheep

The left ventricular (LV) end-systolic pressure volume relationship (ES; ESPVR) is the cornerstone of systolic LV function analysis. Recently, it became possible to measure 2D LV chamber shape during vena cava occlusion (VCO) with MRI. We used an improved level-set semi-automatic segmentation method (LSSM) to determine the effect of VCO on LV geometry, ES pressure area (PA) and ESPVR. 10 healthy adult sheep were anesthetized. LV pressure transducer and inferior vena cava (IVC) balloon catheter were percutaneously inserted. Ferumoxytol (0.125 ml/kg iv; AMAG Pharmaceuticals, Waltham, MA) was given to enhance blood pool contrast. LV pressure and 2D retrospectively-gated cine MRI of LV cross sections 25 (Apex), 50 (Mid) and 75% (Base) of the distance from the apex to the base of the LV were obtained during separate IVC balloon inflations (VCO). LV pressure was digitally filtered and LV chamber segmented with the LSSM. Cross sectional area, major and minor axes, major axis orientation, ESPAR and ESPVR were calculated. The LSSM had excellent reliability. All cross sections became more elliptical during VCO. The orientation (angle) of each major axis relative to the anterior RV insertion shifted during VCO. However, the orientation remained toward the septum. There was chamber collapse (LV area < 0.25 cm2) at the apical level during VCO (7 cases). ESPAR was non-linear at all levels. ESPVR was non-linear because of apical collapse. In conclusion, MRI-based measurement of LV geometry, ESPAR and ESPVR during VCO is a valuable method that may lead to improved understanding of systolic LV function. New and NoteworthyReal-time MRI was used to continuously measure the LV PA relationship as loading conditions were transiently varied in anesthetized sheep. All three examined cross-sections became more elliptical during VCO. The ESPAR were non-linear at all three cross-sections. Chamber collapse at the apical level during VCO resulted in a non-linear ESPVR. The heart contracted in a non-concentric manner during VCO which could inform modeling studies and elucidate mechanisms underlying LV adaptations to sudden load changes.

bioengineering↗

bioRxiv2017

Remodeling of ER-exit sites initiates a membrane supply pathway forautophagosome biogenesis

Autophagosomes are double-membrane vesicles generated during autophagy. Biogenesis of the autophagosome requires membrane acquisition from intracellular compartments, the mechanisms of which are unclear. We previously found that a relocation of COPII machinery to the ER-Golgi intermediate compartment (ERGIC) generates ERGIC-derived COPII vesicles which serve as a membrane precursor for the lipidation of LC3, a key membrane component of the autophagosome. Here we employed super-resolution microscopy to show that starvation induces the enlargement of ER-exit sites (ERES) positive for the COPII activator, SEC12, and the remodeled ERES patches along the ERGIC. A SEC12 binding protein, CTAGE5, is required for the enlargement of ERES, SEC12 relocation to the ERGIC, and modulates autophagosome biogenesis. Moreover, FIP200, a subunit of the ULK protein kinase complex, facilitates the starvation-induced enlargement of ERES independent of the other subunits of this complex and associates via its C-terminal domain with SEC12. Our data indicate a pathway wherein FIP200 and CTAGE5 facilitate starvation-induced remodeling of the ERES, a prerequisite for the production of COPII vesicles budded from the ERGIC that contribute to autophagosome formation.

cell biology↗