The dynamic adaptation of primary human endothelial cells to simulated microgravity.

Culture of human endothelial cells for 10 d in real microgravity onboard the International Space Station modulated more than 1000 genes, some of which are involved in stress response. On Earth, 24 h after exposure to simulated microgravity, endothelial cells up-regulate heat shock protein (HSP) 70. To capture a broad view of endothelial stress response to gravitational unloading, we cultured primary human endothelial cells for 4 and 10 d in the rotating wall vessel, a U.S. National Aeronautics and Space Administration-developed surrogate system for benchtop microgravity research on Earth. We highlight the crucial role of the early increase of HSP70 because its silencing markedly impairs cell survival. Once HSP70 up-regulation fades away after 4 d of simulated microgravity, a complex and articulated increase of various stress proteins (sirtuin 2, paraoxonase 2, superoxide dismutase 2, p21, HSP27, and phosphorylated HSP27, all endowed with cytoprotective properties) occurs and counterbalances the up-regulation of the pro-oxidant thioredoxin interacting protein (TXNIP). Interestingly, TXNIP was the most overexpressed transcript in endothelial cells after spaceflight. We conclude that HSP70 up-regulation sustains the initial adaptive response of endothelial cells to mechanical unloading and drives them toward the acquisition of a novel phenotype that maintains cell viability and function through the sequential involvement of different stress proteins.-Cazzaniga, A., Locatelli, L., Castiglioni, S., Maier, J. A. M. The dynamic adaptation of primary human endothelial cells to simulated microgravity.