Poroelastic osmoregulation of living cell volume

Abstract

Summary Cells maintain their volume through fine intracellular osmolarity regulation. Osmotic challenges drive fluid into or out of cells causing swelling or shrinkage, respectively. The dynamics of cell volume changes depending on the rheology of the cellular constituents and on how fast the fluid permeates through the membrane and cytoplasm. We investigated whether and how poroelasticity can describe volume dynamics in response to osmotic shocks. We exposed cells to osmotic perturbations and used defocusing epifluorescence microscopy on membrane-attached fluorescent nanospheres to track volume dynamics with high spatiotemporal resolution. We found that a poroelastic model that considers both geometrical and pressurization rates captures fluid-cytoskeleton interactions, which are rate-limiting factors in controlling volume changes at short timescales. Linking cellular responses to osmotic shocks and cell mechanics through poroelasticity can predict the cell state in health, disease, or in response to novel therapeutics.

The cytoplasm of living cells can sustain transient and steady intracellular pressure gradients

“…Together, these experiments show that pressure gradients lead to intracellular flows whose propagation follows Darcy’s law with a hydraulic permeability consistent with those derived by other experimental approaches 1,3,29 .…”

“…In Hela cells, previous work has reported ‫ܦ‬ ~40ߤ ݉ ଶ ‫ݏ/‬ 26 , leading to an estimate of the characteristic time of fluid efflux ‫ݐ‬ ~225 ‫.ݏ݉‬ As this is larger than the rise time, we expect poroelasticity to contribute to mechanical relaxation. To detect the global response of the cell surface to local force application with high spatial accuracy, we employed defocusing microscopy 3,25 . In this technique, collagen-coated fluorescent beads are tethered to the cell surface.…”

“…To detect the global response of the cell surface to local force application with high spatial accuracy, we employed defocusing microscopy 3,25 . In this technique, collagen-coated fluorescent beads are tethered to the cell surface.…”

“…To gain insights into the importance of the membrane-cortex layer, we varied its thickness and diffusion constant. While its thickness had little influence 3 , its diffusion constant strongly affected the length-scale of the gradient ( Fig 4j ), with high diffusion constants leading to gradients that reached the initial cell pressure over short length-scales. This is consistent with previous work that showed that localised exposure of cells to high osmolarity medium leads to localised dehydration with a sharp transition in pore size (and hence D р ) between the exposed and non-exposed region 29 .…”

Evaluating the Impact of a Biomimetic Mechanical Environment on Cancer Invasion and Matrix Remodeling

“…These results indicate that the changes in the stiffness of the cancer microenvironment originate from multi-facetted simultaneous processes including protein deposition, protein crosslinking, protein degradation, fiber alignment, compaction of matrix fibers, and pore size changes. [58,59] Furthermore, active contractile forces can also contribute to the stiffness of the tissue. Both HCT 116 and HT-29 tumoroids go through enzymatic degradation, however in the HT-29 tumoroid, the active cellgenerated forces out-balances the degradation leading to an overall stiffer tumoroid after 21 days.…”