Spatial organization acts on cell signaling: how physical force contributes to the development of cancer

Neuromechanobiology: An Expanding Field Driven by the Force of Greater Focus

The brain processes information by transmitting signals through highly connected and dynamic networks of neurons. Neurons use specific cellular structures, including axons, dendrites and synapses, and specific molecules, including cell adhesion molecules, ion channels and chemical receptors to form, maintain and communicate among cells in the networks. These cellular and molecular processes take place in environments rich of mechanical cues, thus offering ample opportunities for mechanical regulation of neural development and function. Recent studies have suggested the importance of mechanical cues and their potential regulatory roles in the development and maintenance of these neuronal structures. Also suggested are the importance of mechanical cues and their potential regulatory roles in the interaction and function of molecules mediating the interneuronal communications. In this review, the current understanding is integrated and promising future directions of neuromechanobiology are suggested at the cellular and molecular levels. Several neuronal processes where mechanics likely plays a role are examined and how forces affect ligand binding, conformational change, and signal induction of molecules key to these neuronal processes are indicated, especially at the synapse. The disease relevance of neuromechanobiology as well as therapies and engineering solutions to neurological disorders stemmed from this emergent field of study are also discussed.

Organoids as a Model for Colorectal Cancer

Modelling human diseases in in vitro systems is undisputedly an invaluable research tool, yet there are many limitations. Some of those limitations have been overcome through the introduction of organoid culture systems, which have revolutionised colorectal cancer research and enabled an array of new experimental techniques. This 3D system models the physiology, shape, dynamics and cell make-up of the intestinal epithelium producing a relevant and highly adaptable model system. The increased functional relevance of this model compared to the use of 2D cancer cell lines makes it an invaluable tool for both basic and translational research. As the limitations of this system are being overcome to make high-throughput assays possible, it is clear that organoids are becoming a mainstay of colorectal cancer research. This review aims to explore the advantages and limitations of this system and discusses the future directions enabled by this model.

Molecular Mechanoneurobiology: An Emerging Angle to Explore Neural Synaptic Functions

Neural synapses are intercellular asymmetrical junctions that transmit biochemical and biophysical information between a neuron and a target cell. They are very tight, dynamic, and well organized by many synaptic adhesion molecules, signaling receptors, ion channels, and their associated cytoskeleton that bear forces. Mechanical forces have been an emerging factor in regulating axon guidance and growth, synapse formation and plasticity in physiological and pathological brain activity. Therefore, mechanical forces are undoubtedly exerted on those synaptic molecules and modulate their functions. Here we review current progress on how mechanical forces regulate receptor-ligand interactions, protein conformations, ion channels activation, and cytoskeleton dynamics and discuss how these regulations potentially affect synapse formation, stabilization, and plasticity.

Nanomechanical characterization of living mammary tissues by atomic force microscopy

The mechanical properties of living cells and tissues are important for a variety of functional processes in vivo, including cell adhesion, migration, proliferation and differentiation. Changes in mechano-cellular phenotype, for instance, are associated with cancer progression. Atomic force microscopy (AFM) is an enabling technique that topographically maps and quantifies the mechanical properties of complex biological matter in physiological aqueous environments at the nanometer length scale. Recently we applied AFM to spatially resolve the distribution of nanomechanical stiffness across human breast cancer biopsies in comparison to healthy tissue and benign tumors. This led to the finding that AFM provides quantitative mechano-markers that may have translational significance for the clinical diagnosis of cancer. Here, we provide a comprehensive description of sample preparation methodology, instrumentation, data acquisition and analysis that allows for the quantitative nanomechanical profiling of unadulterated tissue at submicron spatial resolution and nano-Newton (nN) force sensitivity in physiological conditions.

Fluorescence-based force/tension sensors: a novel tool to visualize mechanical forces in structural proteins in live cells

SIGNIFICANCE

Three signaling systems, chemical, electrical, and mechanical, ubiquitously contribute to cellular activities. There is limited information on the mechanical signaling system because of a lack of tools to measure stress in specific proteins. Although significant advances in methodologies such as atomic force microscopy and laser tweezers have achieved great success in single molecules and measuring the mean properties of cells and tissues, they cannot deal with specific proteins in live cells.

RECENT ADVANCES

To remedy the situation, we developed a family of genetically encoded optical force sensors to measure the stress in structural proteins in living cells. The sensors can be incorporated into specific proteins and are not harmful in transgenic animals. The chimeric proteins distribute and function as their wild-type counterparts, and local stress can be read out from changes in Förster resonance energy transfer (FRET).

CRITICAL ISSUES

Our original sensor used two mutant green fluorescence proteins linked by an alpha helix that served as a linking spring. Ever since, we have improved the probe design in a number of ways. For example, we replaced the helical linker with more common elastic protein domains to better match the compliance of the wild-type hosts. We greatly improved sensitivity by using the angular dependence of FRET rather than the distance dependence as the transduction mechanism, because that has nearly 100% efficiency at rest and nearly zero when stretched.

FUTURE DIRECTIONS

These probes enable researchers to investigate the roles of mechanical force in cellular activities at the level of single molecules, cells, tissues, and whole animals.

Genetically encoded force sensors for measuring mechanical forces in proteins

THERE ARE THREE SOURCES OF FREE ENERGY FOR CELLS: chemical potential, electrical potential and mechanical potential. There is little known about the last one since there have not been simple ways to measure stress in proteins in cells. we have now developed genetically encoded force sensors to assess the stress in fibrous proteins in living cells. These FReT based fluorescence sensors can be read out at video rates and provide real time maps of the stress distribution in cells, tissues and animals. The sensors can be inserted into specific proteins and in general do not disturb the normal function or anatomy. The original sensors used mutant GFPs linked by elastic linkers. These sensors provide a linear output with applied stress but the response is linear in strain. To improve contrast and dynamic range we have now developed a new class of sensors that are smaller making them less invasive, and have much higher intrinsic sensitivity since force modulates the angle between the donor and acceptor much more than the distance between them. Known as cpstFRET, the probe shows improved biocompatibility, wider dynamic range and higher sensitivity.