In Vitro Shear Stress Responses of Endothelin-1 in African American and Caucasian HUVECs

Abstract

Higher levels of plasma Endothelin-1 (ET1), a potent vasoconstrictor, have been reported in African Americans (AA) when compared to Caucasians (CA). However, this racial difference has never been considered when investigating the endothelin system at the cell level. PURPOSE: To determine the effects of laminar shear stress (LSS), which mimics the exercise shear stress on the endothelium, in vitro and the effects of aerobic exercise training on the endothelin system in vivo. METHODS: AA (n=2) and CA (n=2) human umbilical vein endothelial cells (HUVECs) were cultured and underwent LSS using a cone and plate system at both 5 dyne/cm2 and 20 dyne/cm2 for 24 hours. Western Blots were performed to determine Endothelin Converting Enzyme 1 (ECE1) expression. Cell media ET1 content was measured using an ELISA Assay (Assay Designs Inc.). AA subjects (n=15) ages 41-62, who were sedentary, non-diabetic, non-smoking, and free of cardiovascular disease underwent 6 months of aerobic exercise training (3days/week, 65% of VO2max, 40 minutes/day). Plasma ET1 levels were determined before and after exercise training via ELISA assay (Assay Designs Inc.). RESULTS: AA HUVECs had higher amounts of secreted ET1 (267.9±53.6 vs. 132.5±13.0 pg/μg, p=.133) and higher ECE1 expression (0.812±0.065 vs. 0.638±0.02 relative density, p=.127) than Caucasian HUVECs at LSS levels of 5 dyne/cm2. After high physiological LSS (20 dyne/cm2) ET1 was reduced in both African American (267.9±53.5 vs. 120.0±18.2 pg/μg, p=.149) and Caucasian (132.5±13.0 vs. 94.1±30.1 pg/μg, p=.537) HUVECs. ECE1 expression was increased in African American HUVECs (0.812±0.065 vs. 1.085±0.295 relative density, p=.587) and unchanged in Caucasian HUVECs (0.638±0.02 vs. 0.695±0.093 relative density, p=.578) after high LSS (20 dyne/cm2). Additionally, aerobic exercise training significantly (p≤0.05) lowered plasma ET1 levels in African Americans (2.78 pg/ml vs. 0.565 pg/ml, p=.024). CONCLUSION: African American HUVECs present higher levels of ECE1 expression and higher amounts of secreted ET1 than Caucasian HUVECs at resting levels of LSS. Both shear stress and aerobic exercise can lower levels of ET1 in vitro and in vivo respectively. Further research with a larger sample size will be needed to confirm these findings.