Stimulation of angiogenesis through collagen gel by applying shear stress and interstitial flow

Abstract

The induction of angiogenesis has been documented in many diseases such as cancer, arthritis, and diabetes. Angiogenesis can be stimulated by a variety of signals including a mechanical stress applied to the apical side of endothelial cells. To get a better understanding of this mechanical stimulus, a parallel plate flow chamber was designed and tested to elicit a constant laminar flow onto a monolayer of endothelial cells. The goal of this research was to develop a more physiologically similar in vitro system to study the effects of shear stress on endothelial cells. Unlike prior flow chamber apparatus, this chamber allows the cells to be seeded on collagen gel rather than a rigid substrate to more closely mimic in vivo environment. A shear stress of I Pa was applied to the endothelial cells for a duration of 36 hours. Results show that after flow was initiated for this duration, a change in shape of the endothelial cells can be seen when compared to the static condition. Elongation and alignment of cells plated on collagen gel can be seen in the direction of flow, though not at pronounced as the elongation typically seen from cells plated on rigid substrates. Nuclear and F-actin staining also revealed similar results.

(cont.) The nuclear staining revealed a confluent monolayer formation occurred prior to flow and was maintained throughout the experiment. A change in organization of the F-actin fibers, from radially protruding out from the nucleus during static condition to a more ordered arrangement after the flow was implemented could also be seen. The changes in cell appearance illustrates that the mechanical stimulus of a shear stress has an effect on endothelial cell arrangement and suggests that this effect depends to some degree on the cell adhesion substrate stiffness. Furthermore, new research in this area can look at both the signaling that leads to these morphological changes as well as the factors that control angiogenesis.