Abstract

Postflight orthostatic intolerance (POI) was reported to be higher in female than male astronauts and may result from sex-dependent differences in endothelial cell (EC) barrier permeability. Here the effect of 17beta-estradiol (E(2)) and dihydrotestosterone (DHT) on the expression of the tight junction protein occludin, EC barrier function, and MAPK activation over time was tested after subjecting human umbilical vein EC (HUVEC) to brief hypergravity identical to that experienced by astronauts during liftoff (LO) into space. After LO hypergravity, HUVEC showed a time-dependent decrease in occludin correlating with an increase in paracellular permeability and a decrease in transendothelial electrical resistance, indicating a decrease in EC barrier function. LO hypergravity inhibited MAPK activation, which remained suppressed 4 h after LO. Inhibition of MAPK activation correlated with decreased phosphotyrosine occludin, decreased cytochrome-c oxidase activity, and increased paracellular permeability, suggesting a mechanism by which LO hypergravity decreased EC barrier function. Time-dependent differences in MAPK activation, decreased occludin, and EC barrier function between HUVEC treated with E(2) vs. DHT were observed. HUVEC showed delayed activation of MAPK with DHT, i.e., 4 h rather than 2 h for E(2), which correlated with decreased paracellular permeability and the observed sex differences in POI in astronauts. These data temporally separate E(2) and DHT effects in HUVEC and provide evidence for the possible protective roles of sex steroids on EC function after brief exposure to low hypergravity.