Day 3 :
Teikyo University School of Medicine, Tokyo, Japan
Keynote: Electron Microscopic Visualization and Recording of Myosin Head Recovery and Power Strokes in Hydrated Myosin filaments Using the Gas Environmental Chamber
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Haruo Sugi graduated from post-graduated school in the University of Tokyo with the degree of PhD in 1962, and was appointed to be an Instructor in Physiology, in the University of Tokyo Medical School. From 1965 to 1967, he worked at Columbia University as research associate, and at the National Instututes of Health as a visiting scientist. Sugi was Professor and Chairman in Teikyo University Medical School from 1973 to 2004 when he became Emeritus Professor. He was Chairman of Muscle Commission in the International Union of Physiological Sciences from 1998 to 2008 (IUPS). He organized Symposia on molecular mechanism of muscle contraction six times, each followed by Proceeding published from University of Tokyo Press, Plenum, Kluwer and Springer and regarded as milestones of progress in this area of research work.
Although more than 50 years have passed since the monumental discovery of sliding filament mechanism in muscle contraction, the molecular mechanism of myosin head movement, coupled with ATP hydrolysis, is still a matter for debate and speculation. A most straightforward way to study myosin head movement, producing myofilament sliding, may be to directly record ATP-induced myosin head movement in hydrated, living myosin filaments using the gas environmental chamber (EC) attached to an electron microscope . While the EC has long been used by materials scientists for the in situ observation of chemical reaction of inorganic compounds, we are the only group successfully using the EC to record myosin head movement in living myosin filaments. We position-mark individual myosin heads by attaching gold particles (diameter, 20nm) via three different monoclonal antibodies, attaching to (1) at the distal region of myosin head catalytic domain (CAD), (2) at the myosin head converter domain(COD), and (3) at the myosin head lever arm domain(LD). First, we recoded ATP-induced myosin head movement in the absence of actin filaments, and found that myosin heads moved away from the central bare region of myosin filaments (Fig. 1). This finding constitutes the first direct electron microscopic recording of myosin head recovery stroke under a condition in which myosin heads almost freely with an average amplitude of ~7nm. After many efforts, we succeeded in recording ATP-induced myosin head power stroke in actin-myosin filament mixture in 2015. Since only a limited proportion of myosin eads can be activated by a limited amount of ATP applied, myosin heads only move by stretching adjacent sarcomere structures, i.e. nominally “isometric condition”. As shown in Fig.2, myosin head CAD did not move parallel to the filament axis in the standard ionic strength, while it moved parallel to the filament axis at low ionic strength, in accordance with our physiological experiments on single muscle fibers. These results indicate that myosin head movement does not necessarily obey predictions of the swinging lever arm hypothesis appearing in every textbooks.
University Grenoble Alpes,France
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Dr Julien Bras (H index: 32; 122 scientific papers, 11 patents) is Associate professor at Grenoble Institute of Technology (Grenoble INP Pagora). He is member of Institut Universitaire de France (IUF, 2016-2021). He is deputy director of LGP2 (Laboratory of Pulp & Paper Science) and head of the “Multiscale Biobased Material” group (ab. 40 pers.). He has directly supervised 23 PhD and 14 Post-doc focusing on research on Biomaterials, Nanocellulose & Specialty papers. After engineer diploma in Chemistry and a PhD on Renewable Materials in 2004, he worked in industry few years as Innovation Manager within Ahlstrom Specialty paper and then left industry to become associate professor since 2006.
Through his different experiences, he develops several competences. His expertise deals particularly with Nanocellulose, biobased and smart materials. More precisely, he proposed new way of production, characterization and functionalization of nanocellulose for several applications since more than 10 years. He has already coordinated or supervised several industrial and European projects in FP6, FP7 and Marie-Curie calls. He is involved in a Labex & Carnot institute organization as WP leader and is associate editor for an Elsevier Journal (Industrial Crops and products).
Studied since the 1950s, biocompatible materials, also called biomaterials, are now used in a variety of applications such as: artificial joint implants, tissue engineering, drug release monitoring, and cell therapy. One of the most common motifs to influence cell behavior in the presence of biomaterials is to change the mechanical properties of the biomaterial substrate. This oral presentation will propose an overview of a recent project focusing on designing cellulose nanomaterials. It was hypothesized that nanocellulose-based substrates could be fabricated with various elastic moduli to change the characteristics of MSCs. All stages of material development from creating high-value added nanocomposites and their effect on stem cell behavior in culture were performed during this research. First Cellulose nanofibril films were prepared and their mechanical properties in liquid were tuned by drying procedure. Cell growth was much higher with stiffer CNF films. Composites with alginate and cellulose nanocrystals were also prepared and different stiffness values were achieved with modifying the percentage of CNC and CaCl2 content but also by using stimuli responsive approaches. Such difference was then correlated to cell growth values. All these results will open new high value added application for nanocellulose based materials and favor cell differention but also 3D cell growth for tissue engineering or even 3D printing of bio-inks.