The analysis of F-actin structure of mesenchymal stem cells by quantification of fractal dimension

Abstract

The actin cytoskeleton is indispensable for the motility and migration of all types of cells; therefore, it plays a crucial role in the ability of the tissues to repair. Mesenchymal stem cells are intensively used in regenerative medicine, but usually relatively low percent of transplanted cells reaches the injury. To overcome this evident limitation, researchers try to enhance the motility and migration rate of the cells. As one of the approaches, co-cultivation and preconditioning of stem cells with biologically active compounds, which can cause actin cytoskeleton rearrangements followed by an increase of migratory properties of the cells, could be applied. The observed changes in F-actin structure induced by the compounds require quantitative estimation, and measurement of fluorescence intensity of the F-actin image captured by various microscopic techniques is commonly used nowadays. However, this approach could not always accurately detect the observed changes in the shape and structure of actin cytoskeleton. At this time, the image of F-actin has an irregular geometric pattern, and thus could be considered and characterized as a fractal object. To quantify the re-organization of cellular F-actin in terms of fractal geometry Minkovsky’s box-counting method is suitable, but it is not widely used nowadays. We modified and improved the previously described method for fractal dimension measurement, and successfully applied it for the quantification of the F-actin structures of human mesenchymal stem cells.

Facilitation of Cell Cycle and Cellular Migration of Rat Schwann Cells by O‐Carboxymethyl Chitosan to Support Peripheral Nerve Regeneration

“…[ 50 ] Filamentous actin (F‐actin) plays a critical role in myelination, glial membrane protein linkage, and tissue repair ability. [ 51 ] The organization of F‐actin was examined in rat Schwann RSC96 cells, following co‐culture with CM‐chitosan for 48 h. Phalloidin green staining, associated proportionally with F‐actin distribution, showed a greater intensity in RSC96 cells treated with CM‐chitosan (50–800 µg mL −1 ) than in control cells ( Figure 7 A,B). F‐actin organization significantly increased in Schwann cells cultured with CM‐chitosan ( p < 0.05).…”

Piperazine Derivative Stabilizes Actin Filaments in Primary Fibroblasts and Binds G-Actin In Silico

“…To visualize the reorganization of F-actin microfilaments, cells were stained with rhodamine-conjugated phalloidin. We used two methods to quantify the organization of F-actin microfilaments: (1) quantification of the change in the mean grey value of rhodamine-phalloidin fluorescence [ 43 ], which allowed us to evaluate the changes in the mass of F-actin; and (2) measuring the fractal dimension change by the box-counting method [ 19 , 21 , 44 , 45 ]. The measurement of the fractal dimension allowed us to quantify the structural changes in F-actin organization.…”

“…Fractal dimension analysis was performed with the box-counting method as previously described [ 19 , 20 , 21 ]. To calculate the fractal dimension, an image must be split into foursquare boxes with a side length of e, and then the number of boxes N ( e ) covering any part of the object is calculated.…”

Viscoelastic relaxation of fibroblasts over stiff polyacrylamide gels by atomic force microscopy

“…The box-counting method was applied to the binarized images to calculate the fractal dimension D f of the cells. To avoid interference of the image orientation, the cell images were rotated 360 o by increments of 15 o , and the final D f of each cell is the average of such rotations [37]. The cell area is also determined from the analysis of the binarized images.…”