Nitric Oxide Alters Human Microvascular Endothelial Cell Response to Cyclic Strain

Abstract

BACKGROUND: Nitric oxide (NO), a potent vasodilator and inhibitor of platelet function, is elaborated constitutively by endothelial cells through the oxidation of l-arginine by endothelial NO synthase. Although several biochemical agonists, such as bradykinin, have been shown to stimulate NO production by the endothelium, the effects of physical factors have been less well characterized. We have previously examined the shear-stress-dependent induction of NO production by the endothelium, and others have examined the effects of transmural pressure on NO production. In the current study, we analyzed the effects of cyclic strain or load in the presence and absence of an NO agonist on endothelial cell proliferation. METHODS AND RESULTS: Subconfluent human microvascular endothelial cells were grown on deformable culture plates in media containing 10% fetal bovine serum and 1 mM l-arginine, and then subjects to either 0, 11, 18, or 27% cyclic strain at a frequency of 1 Hz. Nitrogen oxides (S-nitrosothiols and free NO) in media were measured by photolysis-chemiluminescence at the end of 24 hours, as were cell number, [(3)H]thymidine incorporation, and total cell protein. In the absence of an NO agonist, 11% cyclic strain produced a 73 +/- 17% increase in nitrogen oxides compared with control (P <.05), whereas 18 and 27 cyclic strain produced no significant increase in nitrogen oxides compared with control. However, cells subjected to 27% strain increased cell number (by 98 +/- 17%) and [(3)H]thymidine incorporation (by 16 +/- 4%, P <.05) compared with control. In an attempt to examine further the effects of endogenous NO on the cells' proliferation response to increasing levels of cyclic strain, we incubated human microvascular endothelial cells with 1 µM bradykinin and subjected them to 27% cyclic strain. In the presence of bradykinin and 27% cyclic strain, production of nitrogen oxides and endothelial NO synthase activity were increased by 110 +/- 37% and 135 +/- 7%, respectively (P <.05 compared with control); however, we observed no significant increase in cell number (5 +/- 5%), despite an 86 +/- 7% increase in [(3)H]thymidine incorporation (P <.05). CONCLUSION: These results suggest that endogenous NO production by human microvascular endothelial cells regulates their growth response to cyclic strain. Modulation of NO production in vivo in areas of the vasculature that are subjected to increased levels of strain may represent one potential mechanism by which to alter endothelial cell proliferation.

Angiogenic microenvironment augments impaired endothelial responses under diabetic conditions

“…The results also show that strain has a significant effect on NO concentration; namely that the NO concentration is higher under strained conditions compared with static conditions for WT, acute HG, and db groups. These findings are consistent with previous studies that have shown that NO levels and NOS activity increase with strain application in both bovine aortic endothelial cells and human microvascular endothelial cells (4,55). However, in our study, this effect is not seen in the chronic HG group.…”

Mechanical Strain Regulates Endothelial Cell PatterningIn Vitro

“…Previous reports have similarly reported that cyclic strain enhanced cell proliferation, 21,36 likely related to the regulation of cell cycle-related genes. 37 The experiments performed in this study revealed that the proliferating cells were initially observed only at the edges of the cell populations and that cells located in the interior regions proliferated subsequently.…”

“…[13][14][15][16][17] In addition, ECs are exposed to cyclic strain, resulting from blood flow and the circumferential deformation of the vessels, and cyclic strain induces EC cytoskeletal reorganization. 18,19 Cyclic strain also inhibits EC apoptosis, 20 increases the proliferation rate, 21 and enhances metalloproteinase-2, 22 and membrane-type metalloproteinase-1 23 expression. These results suggest that cyclic strain may alter vessel formation, because survival, alignment, and proliferation of ECs and degradation of basement membrane are essential for forming new vessels.…”

Three-dimensional 10% cyclic strain reduces bovine aortic endothelial cell angiogenic sprout length and augments tubulogenesis in tubular fibrin hydrogels

“…The time spent mechanically stimulating tissue may be another key feature in the differences displayed between the prior work and our results. Most studies describing EC responses to cyclic strain have been done in experiments that last 48 h or less (Joung et al , 2006; Von Offenberg Sweeney et al , 2005; Collins et al , 2006; Rosales and Sumpio, 1992; Sumpio et al , 1998; Upchurch et al , 1998). Although data from early time points is critical to an understanding of the initial influence of mechanical stimulation on engineered tissue, these early time points may not reflect what these cells experience in long‐term culture.…”