Effects of Simulated Microgravity on Human Umbilical Vein Endothelial Cell Angiogenesis and Role of the PI3K-Akt-eNOS Signal Pathway

Abstract

Endothelial cells are very sensitive to microgravity and the morphological and functional changes in endothelial cells are believed to be at the basis of weightlessness-induced cardiovascular deconditioning. It has been shown that the proliferation, migration, and morphological differentiation of endothelial cells play critical roles in angiogenesis. However, the influence of microgravity on the ability of endothelial cells to foster angiogenesis remains to be explored in detail. In the present study, we used a clinostat to simulate microgravity, and we observed tube formation, migration, and expression of endothelial nitric oxide synthase (eNOS) in human umbilical vein endothelial cells (HUVEC-C). Specific inhibitors of eNOS and phosphoinositide 3-kinase (PI3K) were added to the culture medium and gravity-induced changes in the pathways that mediate angiogenesis were investigated. After 24 h of exposure to simulated microgravity, HUVEC-C tube formation and migration were significantly promoted.This was reversed by co-incubation with the specific inhibitor of N-nitro-L-arginine methyl ester hydrochloride (eNOS). Immunofluorescence assay, RT-PCR, and Western blot analysis demonstrated that eNOS expression in the HUVEC-C was significantly elevated after simulated microgravity exhibition. Ultrastructure observation via transmission electron microscope showed the number of caveolae organelles in the membrane of HUVEC-C to be significantly reduced. This was correlated with enhanced eNOS activity. Western blot analysis then showed that phosphorylation of eNOS and serine/threonine kinase (Akt) were both up-regulated after exposure to simulated microgravity. However, the specific inhibitor of PI3K not only significantly downregulated the expression of phosphorylated Akt, but also downregulated the phosphorylation of eNOS. This suggested that the PI3K-Akt signal pathway might participate in modulating the activity of eNOS. In conclusion, the present study indicates that 24 h of exposure to simulated microgravity promote angiogenesis among HUVEC-C and that this process is mediated through the PI3K-Akt-eNOS signal pathway.

Endothelial microparticles increase in mitral valve disease and impair mitral valve endothelial function

“…The expression and phosphorylation at the Ser 1177 site of eNOS are important to maintain the endothelial cell function (28,31). Protein kinase Akt can phosphorylate eNOS directly on serine 1179 (1177) and activate the enzyme, leading to NO production (15,21,40). The activity of the Akt/eNOS pathway represents the endothelial function.…”

Growing Tissues in Real and Simulated Microgravity: New Methods for Tissue Engineering

“…However, after 24 h of clinorotation, tube formation and migration as well as endothelial nitric oxide synthase (eNOS) activity of human umbilical vein endothelial cells were significantly increased, suggesting an s-mg-mediated promotion of angiogenesis via the PI3K-Akt-eNOS pathway. 93 In addition, Wang et al showed that clinorotation also upregulated inducible NOS (iNOS) in an AP-1-dependent manner and suggested a possible involvement of this pathway in the development of postflight orthostatic intolerance. 94 In parallel to observations in r-mg, the cytoskeleton of ECs grown on the clinostat was remodeled.…”

Effects of hypergravity on the angiogenic potential of endothelial cells

“…Results concerning the effects of mechanical stress on the assembly of ECs into capillary-like structures in vitro are still poorly understood. For instance, simulated microgravity conditions have been reported to enhance capillary-like structure formation by HUVECs cultured in matrigel [37]. Nonetheless, considering microgravity and hypergravity as having opposite effects is not a straightforward conclusion [8].…”