Quantitative image analysis of F-actin in endothelial cells

Filamentous actin (F-actin) plays a central role in maintaining endothelial barrier function. Thrombin and histamine, two inflammatory mediators that increase endothelial permeability, can alter F-actin production and distribution. In this study, we use a newly developed image analysis technique to show that these two inflammatory mediators differentially alter F-actin structure.

Human umbilical vein endothelial cells were grown to confluence and treated with either histamine (1 microM), thrombin (1 microM) or the agonist's vehicle. The endothelium was stained with BODIPY-phallodin, and digitized images were taken of the treated cells. The digitized images of individual human umbilical vein endothelial cells (HUVEC) were imported into a F-actin image analysis program (FAAP) and converted to layers, each one pixel thick. The program then determined the mean gray level (which corresponded to the amount of F-actin) in each layer starting from the outside of the cell (layer 1) and progressing in one pixel layer increments towards the center of the cell (layer 32).

Both inflammatory mediators increased endothelial F-actin production, however, the distribution of the actin was different. Thrombin increased the presence of stress fibers, while also decreasing peripheral banding actin. In contrast, histamine had no effect on peripheral actin compared to control, but did increase the presence of F-actin stress fibers.

These results establish that thrombin and histamine alter endothelial F-actin production in different locations within the cell, which can be quantified using an image analysis program.