Estradiol and dihydrotestosterone regulate endothelial cell barrier function after hypergravity-induced alterations in MAPK activity

1 Department of Biochemistry and Molecular Biology and Center for Genetics and Molecular Medicine, School of Medicine, 2 Department of Physics, and 3 Department of Bioengineering, Speed School of Engineering, University of Louisville, Louisville, Kentucky Submitted 4 August 2006 ; accepted in final form 8 March 2007 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 17 -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. paracellular permeability; estrogen; androgen Address for reprint requests and other correspondence: C. M. Klinge, Dept. of Biochemistry and Molecular Biology and Center for Genetics and Molecular Medicine, School of Medicine, Univ. of Louisville, KY 40292 (e-mail: carolyn.klinge{at}louisville.edu )