Fluid-flow induced wall shear stress and epithelial ovarian cancer peritoneal spreading

Abstract

Epithelial ovarian cancer (EOC) is usually discovered after extensive metastasis have developed in the peritoneal cavity. The ovarian surface is exposed to peritoneal fluid pressures and shear forces due to the continuous peristaltic motions of the gastro-intestinal system, creating a mechanical micro-environment for the cells. An in vitro experimental model was developed to expose EOC cells to steady fluid flow induced wall shear stresses (WSS). The EOC cells were cultured from OVCAR-3 cell line on denuded amniotic membranes in special wells. Wall shear stresses of 0.5, 1.0 and 1.5 dyne/cm(2) were applied on the surface of the cells under conditions that mimic the physiological environment, followed by fluorescent stains of actin and β-tubulin fibers. The cytoskeleton response to WSS included cell elongation, stress fibers formation and generation of microtubules. More cytoskeletal components were produced by the cells and arranged in a denser and more organized structure within the cytoplasm. This suggests that WSS may have a significant role in the mechanical regulation of EOC peritoneal spreading.

Figure 1. OVCAR-3 Cell culture.

(A) In a plastic flask, 3 days after seeding. (B) On an amniotic membrane in special wells, 4 days after seeding (50 K cells per well). Phase contrast light microscope. Magnification: x10.

Figure 2. (A) Scheme of the experimental system and for application of WSS on cultured cells.

The flow chamber can hold 3 well bottoms. (B) Drawing of the components of the flow chamber and the well bottoms.

Figure 3. An example for the measurements of long and short diameters, corresponding to the major and minor axes of an ellipse, marked on the confocal images of the cells using designated image processing software.

Figure 4. (A) Three different levels of stress fibers formation.

(a) Low level, mostly cortical actin and almost no stress fibers, (b) Intermediate level, some fibers are formed, mostly in cell protrusions, and (c) High level, most of the cell’s central area is abundant with stress fibers. (B) Three different levels of microtubules formation: (a) Low level, mostly β-tubulin fragments and almost no cytoplasmic microtubules, (b) Intermediate level, some microtubules were formed inside the cell, and (c) High level, a dense network of microtubules was generated inside the cells.

Figure 5. (A) Elongation of the cells, defined by the aspect ratio of the ellipsoid diameters.

The arrows are pointing at representing cells. (a) Control culture, (b) 0.5 dyne/cm² culture, (c) 1.0 dyne/cm² culture, and (d) 1.5 dyne/cm² cultures. (B) Variation of the logarithmic value of the aspect ratio that define the level of cell elongation with the level of the applied shear stress (±standard deviation).

Figure 6. (A) Actin staining in cultures of EOC cells.

(a) Control culture (no WSS), (b) cells exposed to WSS of 0.5 dyne/cm², (c) cells exposed to WSS of 1.0 dyne/cm², and (d) cells exposed to WSS of 1.5 dyne/cm². (B) The percentage of cells in each of three levels of stress fibers formation, for different levels of shear stress. (C) The logarithmic mean aspect ratio of cell elongation for every level of stress fibers formation (±2·standard error).

Figure 7. (A) β-tubulin staining in cultures of EOC cells.

(a) Control culture (no WSS), (b) cells exposed to WSS of 0.5 dyne/cm², (c) cells exposed to WSS of 1.0 dyne/cm², and (d) cells exposed to WSS of 1.5 dyne/cm². (B) the percentage of cells in each of three levels of microtubules formation, for different levels of shear stress. (C) The logarithmic mean aspect ratio of cell elongation for every level of microtubules formation (±2·standard error).