integrative-toolkit-to-analyze-cellular-signals-forces-motion

Integrative Toolkit to Analyze Cellular Signals: Forces, Motion, Morphology, and Fluorescence

Quantitative assessment of cellular forces and motion advanced considerably over the last four decades. These advancements provided the framework to ...

University of South Alabama

The mechanical microenvironment of an endothelial cell includes a stable protein scaffold on the basal side, flowing blood on the apical side and contractile cells on the lateral sides. Interaction with the protein scaffold and flowing blood modulates the ability of endothelial cells to migrate, align and maintain barrier function. Interaction with neighbors provides the endothelial monolayer unique "collective" properties. However, the nature of local mechanical signaling - i.e., the local functional consequence of a cell interacting with its contractile neighbors - remains unclear. Using an advancing sheet of pulmonary microvascular endothelial cells, here we examine the mechanical properties of an individual cell and its neighboring region. By combining Monolayer Stress Microscopy (MSM) with a novel analysis, we assessed several mechanical properties of an individual cell and its neighboring region. Across the monolayer, mechanical properties of the neighboring region defined multicellular "subdivisions" wherein constituent cells were exposed to a similar mechanical microenvironment. Adjacent subdivisions were separated by a narrow interface where adjoining cells were exposed to remarkably different mechanical microenvironments. Comparison of temporal fluctuations in mechanical properties of individual cells and those of their neighboring regions suggested three distinct intercellular mechanical signaling processes. These processes indicated that change in size, shape and speed of individual cells is associated with change in contractile forces in their neighboring regions. In summary, we present a novel approach to assess the mechanical interactions of individual cells with their contractile neighbors and identify potential functional consequences of such interactions.

Mechanical signaling in a pulmonary microvascular endothelial cell monolayer.

In the field of endothelial biology, the term "shear forces" is tied to the forces exerted by the flowing blood on the quiescent cells. But endothelial cells themselves also exert physical forces on their immediate and distant neighbors. Specific factors of such intrinsic mechanical signals most relevant to immediate neighbors include normal (F) and shear (F) components of intercellular tractions, and those factors most relevant to distant neighbors include contractile or dilatational (M) and shear (M) components of the moments of cytoskeletal forces. However, for cells within a monolayer, F, F, M, and M remain inaccessible to experimental evaluation. Here, we present an approach that enables quantitative assessment of these properties. Remarkably, across a collectively migrating sheet of pulmonary microvascular endothelial cells, F was of the same order of magnitude as F. Moreover, compared to the normal components (F, M) of the mechanical signals, the shear components (F, M) were more distinctive in the cells closer to the migration front. Individual cells had an innately collective tendency to migrate along the axis of maximum contractile moment - a collective migratory process we referred to as cellular plithotaxis. Notably, larger F and M were associated with stronger plithotaxis, but dilatational moment appeared to disengage plithotactic guidance. Overall, cellular plithotaxis was more strongly associated with the "shear forces" (F, M) than with the "normal forces" (F, M). Finally, the mechanical state of the cells with fast migration speed and those with highly circular shape were reminiscent of fluid-like and solid-like matter, respectively. The results repeatedly pointed to neighbors imposing shear forces on a cell as a highly significant event, and hence, the term "shear forces" must include not just the forces from flowing fluid but also the forces from the substrate and neighbors. Collectively, these advances set the stage for deeper understanding of mechanical signaling in cellular monolayers.

Article	Year
Mechanical signaling in a pulmonary microvascular endothelial cell monolayer. Biochemical and biophysical research communications\| PubMed ID: 31514994	2019
Unleashing shear: Role of intercellular traction and cellular moments in collective cell migration. Biochemical and biophysical research communications\| PubMed ID: 31879014	2020

Alyson Nguyen

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