Measurement of orientation and distribution of cellular alignment and cytoskeletal organization

Endothelial cells elongate and align with the direction of applied fluid sh ear stress. Previously, automated methods for analysis of cell orientation distribution have used Fourier- or fractal-based methods. We used intensity gradients in images of control and sheared endothelial cells to measure or ientation distributions. Automated measurements of mean orientation and ang ular deviation compared favorably with manual measurements, There was a sig nificantly greater angular deviation in images of control cells compared wi th sheared cells. Automated methods were also used to quantify organization of cytoskeletal fibers using the local angular deviation and a measure of the local coalignment of fibers called the coalignment ratio. The local ang ular deviation of microtubules and microfilaments was significantly smaller in sheared cells compared with control. The coalignment of cytoskeletal fi bers was significantly greater in sheared cells. We conclude that image Int ensity gradients can be used rapidly, accurately, and objectively to measur e cell orientation distributions and cytoskeletal filament organization. (C ) 1999 Biomedical Engineering: Society. [S0090-6964(99)00506-8].