CELL GEOMETRIC CONSTRAINTS REGULATE NUCLEAR AND CHROMATIN PLASTICITY VIA ACTOMYOSIN CONTRACTILITY

Ph.DPH.D. IN MECHANOBIOLOGY (FOS

Mechanical Strain Promotes Oligodendrocyte Differentiation by Global Changes of Gene Expression.

Differentiation of oligodendrocyte progenitor cells (OPC) to oligodendrocytes and subsequent axon myelination are critical steps in vertebrate central nervous system (CNS) development and regeneration. Growing evidence supports the significance of mechanical factors in oligodendrocyte biology. Here, we explore the effect of mechanical strains within physiological range on OPC proliferation and differentiation, and strain-associated changes in chromatin structure, epigenetics, and gene expression. Sustained tensile strain of 10-15% inhibited OPC proliferation and promoted differentiation into oligodendrocytes. This response to strain required specific interactions of OPCs with extracellular matrix ligands. Applied strain induced changes in nuclear shape, chromatin organization, and resulted in enhanced histone deacetylation, consistent with increased oligodendrocyte differentiation. This response was concurrent with increased mRNA levels of the epigenetic modifier histone deacetylase Hdac11. Inhibition of HDAC proteins eliminated the strain-mediated increase of OPC differentiation, demonstrating a role of HDACs in mechanotransduction of strain to chromatin. RNA sequencing revealed global changes in gene expression associated with strain. Specifically, expression of multiple genes associated with oligodendrocyte differentiation and axon-oligodendrocyte interactions was increased, including cell surface ligands (Ncam, ephrins), cyto- and nucleo-skeleton genes (Fyn, actinins, myosin, nesprin, Sun1), transcription factors (Sox10, Zfp191, Nkx2.2), and myelin genes (Cnp, Plp, Mag). These findings show how mechanical strain can be transmitted to the nucleus to promote oligodendrocyte differentiation, and identify the global landscape of signaling pathways involved in mechanotransduction. These data provide a source of potential new therapeutic avenues to enhance OPC differentiation in vivo.We gratefully acknowledge funding from the National Multiple Sclerosis Society (RG4855A1/1), the Human Frontiers Science Program (RGP0015/2009-C), and the National Research Foundation of Singapore through the Singapore-MIT Alliance for Research and Technology (SMART), BioSystems and Micromechanics (BioSyM) interdisciplinary research group

Hunting for pentaquarks

According to a news release dated 16 April 2005, recent experimental data from JLAB, the Thomas Jefferson National Accelerator facility in Newport News, Virginia, USA point to the absence of the pentaquark called Q+, at the place where it was expected. This surprising result due to the CLAS collaboration (where CLAS stands for the CEBAF Large Acceptance Spectrometer; CEBAF stands for the Continuous Electron Beam Accelerator Facility, which was the name of JLAB) contradicts the findings of several prior experiments, including some of its own, which indicated that at least one kind of pentaquark exists in the mass range 1525-1555 MeV/c2 (for a review, see Hicks1), while none of the experiments could definitively prove its existence. This recent experiment was based on a high energy photon beam on a liquid hydrogen target. It had considerably greater statistics; in fact, two orders of magnitude greater than a similar experiment in Germany carried out by the SAPHIR collaboration at the ELSA (Electron Stretcher Accelerator) in Bonn2, which had seen evidence for the existence of pentaquarks. At JLAB, work is continuing in the hunt for pentaquarks with even higher statistics, and the data are being analysed with the possibility of publication of results later this year. The CLAS collaboration is likely to gather more data in 2006 by searching for other pentaquark candidates

High-resolution Imaging of Nuclear Dynamics in Live Cells under Uniaxial Tensile Strain

© 2019 Journal of Visualized Experiments. Extracellular mechanical strain is known to elicit cell phenotypic responses and has physiological relevance in several tissue systems. To capture the effect of applied extracellular tensile strain on cell populations in vitro via biochemical assays, a device has previously been designed which can be fabricated simply and is small enough to fit inside tissue culture incubators, as well as on top of microscope stages. However, the previous design of the polydimethylsiloxane substratum did not allow high-resolution subcellular imaging via oil-immersion objectives. This work describes a redesigned geometry of the polydimethylsiloxane substratum and a customized imaging setup that together can facilitate high-resolution subcellular imaging of live cells while under applied strain. This substratum can be used with the same, earlier designed device and, hence, has the same advantages as listed above, in addition to allowing high-resolution optical imaging. The design of the polydimethylsiloxane substratum can be improved by incorporating a grid which will facilitate tracking the same cell before and after the application of strain. Representative results demonstrate high-resolution time-lapse imaging of fluorescently labeled nuclei within strained cells captured using the method described here. These nuclear dynamics data give insights into the mechanism by which applied tensile strain promotes differentiation of oligodendrocyte progenitor cells

Micropillar displacements by cell traction forces are mechanically correlated with nuclear dynamics

10.1016/j.bbrc.2015.04.041Biochemical and Biophysical Research Communications4612372-37

Mechanical Strain Alters Cellular and Nuclear Dynamics at Early Stages of Oligodendrocyte Differentiation

Mechanical and physical stimuli including material stiffness and topography or applied mechanical strain have been demonstrated to modulate differentiation of glial progenitor and neural stem cells. Recent studies probing such mechanotransduction in oligodendrocytes have focused chiefly on the biomolecular components. However, the cell-level biophysical changes associated with such responses remain largely unknown. Here, we explored mechanotransduction in oligodendrocyte progenitor cells (OPCs) during the first 48h of differentiation induction by quantifying the biophysical state in terms of nuclear dynamics, cytoskeleton organization, and cell migration. We compared these mechanophenotypic changes in OPCs exposed to both chemical cues (differentiation factors) and mechanical cues (static tensile strain of 10%) with those exposed to only those chemical cues. We observed that mechanical strain significantly hastened the dampening of nuclear fluctuations and decreased OPC migration, consistent with the progression of differentiation. Those biophysical changes were accompanied by increased production of the intracellular microtubule network. These observations provide insights into mechanisms by which mechanical strain of physiological magnitude could promote differentiation of progenitor cells to oligodendrocytes via inducing intracellular biophysical responses over hours to days post induction.Singapore. National Research Foundation (Singapore-MIT Alliance for Research and Technology (SMART))Saks-Kavanaugh Foundatio

How cells respond to environmental cues - insights from bio-functionalized substrates

Biomimetic materials have long been the (he)art of bioengineering. They usually aim at mimicking in vivo conditions to allow in vitro culture, differentiation and expansion of cells. The past decade has witnessed a considerable amount of progress in soft lithography, bio-inspired micro-fabrication and biochemistry, allowing the design of sophisticated and physiologically relevant micro- and nano-environments. These systems now provide an exquisite toolbox with which we can control a large set of physicochemical environmental parameters that determine cell behavior. Bio-functionalized surfaces have evolved from simple protein-coated solid surfaces or cellular extracts into nano-textured 3D surfaces with controlled rheological and topographical properties. The mechanobiological molecular processes by which cells interact and sense their environment can now be unambiguously understood down to the single-molecule level. This Commentary highlights recent successful examples where bio-functionalized substrates have contributed in raising and answering new questions in the area of extracellular matrix sensing by cells, cell-cell adhesion and cell migration. The use, the availability, the impact and the challenges of such approaches in the field of biology are discussed